i^tatt College of ^Qtimltmt Sit Cornell WlnitittSit^ attjaca. J%. @. Htfirarj CORNELL UNIVERSITY LIBRARY 3 1924 050 716 707 Cornell University Library The original of tliis book is in tlie Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924050716707 GRAY'S BOTANICAL TEXT-BOOK. Volume II. PHYSIOLOGICAL BOTANY. GRAY'S BOTANICAL TEXT-BOOK CONSISTS OF Vol. I. Steuctueal Botany. Bj- Asa Gray. II. Physiological Botany. By George L. Goodale. III. Introduction to Ceyptogamic Botany, both Structural and Systematic. By William G. Farlow. {In preparation.) rV. Sketch of the Natural Orders of PniENOGAMOus Plants ; their Special Morphologj', Useful Pro- ducts, &c. (In preparation.) GRAY'S BOTANICAL TEXT-BOOK. (SIXTH EDITION.) Vol. II. PHYSIOLOGICAL BOTANY. I. OUTLINES OF THE HISTOLOGY OF PH^NOQ-AMOUS PLANTS. . II. VEGETABLE PHYSIOLOGY. BY GEORGE LINCOLN GOOD ALB, A. M., M. D., PROFE980I! OF BOTANY IN HARVAKD UNIVERSITY. NEW YORK ■ : • CINCINNATI • : • CHICAGO AMERICAN BOOK COMPANY ^/ ■^A/J f 1» CxU Copyright, 1885, By Geokqk Lincoln Goodalb. .f iprlnteS bs TOlUlam Hvlsoii 1fiew jgoil!, TH. S. H. PEEFACE TO THE SEEIES. The first edition of the Botanical Text-Book was pub- lished in the year 1842, the fifth in 1857. Each edition has been in good part rewritten, — the present one entirely so, — and the compass of the work is now extended. More elementary works than this, such as the writer's Lessons in Botany (which contains all that is necessary to the prac- tical study of systematic Phsenogamous Botany by means of Manuals and local Floras), are best adapted to the needs of the young beginner, and of those who do not intend to study Botany comprehensively and thoroughly. The present treatise is intended to serve as a text-book for the higher and completer instruction. To secure the requisite fulness of treatment of the whole range of sub- jects, it has been decided to divide the work into distinct volumes, each a treatise by itself, which may be indepen- dently used, while the whole will compose a comprehen- sive botanical course. The volume on the Structural and Morphological Botany of Phsenogamous Plants properly comes first. It should thoroughly equip a botanist for the scientific prosecution of Systematic Botany, and furnish needful preparation to those who proceed to the study of Vegetable Physiology and Anatomy, and to the wide and varied department of Cryptogamic Botany. vi PREFACE. The volume upon Physiological Botany (Vegetable His- tology and Physiology) has been prepared by the writer's colleague, Professor Goodale. The Introduction to Cryptbgamous Botany, both struc- tural and systematic, is assigned to the writer's colleague. Professor Faelow. A fourth volume, a sketch of the Natural Orders of Phsenogamous Plants, and of their special Morphology, Classification, Distribution, Products, etc., wiU be needed to complete the series : this the writer may rather hope than expect himself to draw up. ASA GRAY Hereakidm op Hakvard University, Camgridgx. PKEFACE TO VOLUME 11. The present volume is devoted to a consideration of the microscopic structure, the development, and the func- tions of flowering plants ; that is, to their Vegetable His- tolog}', Organogeny, and Physiology. In the first volume of the Botanical Text-Book these topics were treated only incidentally, or in an elementary manner, as an introduc- tion to Morphology. Cryptogams, or flowerless plants, are treated in this ^rolume only so far as their study may throw light on certain features of the anatomy and physiology of Phseno- gams. The simple structure of many of the flowerless plants, especially of those of the lower grades, makes them suitable objects in which to investigate numerous phe- nomena of vegetable nutrition, growth, and reproduction, and they have been extensively employed as convenient material for this purpose. Reference must therefore be made in the present treatise to some of the more important results. Vegetable Histology treats of the minute anatomy of plants. A knowledge of its leading facts is indispensable to a clear understanding of Vegetable Physiology, and their presentation must needs precede any satisfactory examination of the latter. The technique of Vegetable Histology requires special treatment, and therefore cori- via PREFACE. sideiable space has been devoted to its appliances and methods. This special treatment has been supplemented by a series of practical exercises which the student is urged to perform in the order designated. It will be seen that in some cases several examples are suggested : the beginner is advised to examine thoroughly at least one of the examples under each head. Organogeny, the study of nascent organs, occupies much of the middle ground between Histology, Morphology, and Physiology. The means by which it is investigated are those of Histology, but its answers are given to Mor- phology. For convenience, the study of the development of each organ of the plant is made to precede the examina- tion of its mature state. Vegetable Physiology concerns itself with the life of plants. The appliances of which it makes use are taken chiefly from Physics and Chemistry, and facility in their employment demands some practical acquaintance with those departments. To one who has worked systemati- cally in a physical and chemical laboratory, experimental vegetable physiology presents little difficulty. To aid the work of students whose opportunities for experimenting in Physics and Chemistry have been slight, a series of practical exercises in Experimental Physiology has been added. The appliances selected for these examples are not complicated or expensive, and it is hoped that teachers and students alike may find their employment practica- ble. The Praxis embodies in compendious and conven- ient form the directions which have been employed by the author in his classes. The illustrations of tissues and of apparatus have been taken from many sources. They have been selected with PREFACE. IX reference to the special needs of those students to whom the larger works and the current journals are not easily accessible. The same rule has been largely followed in the treatment of citations from authorities. Where it has been possible to do so without too great sacrifice of space, the phraseology of the original reference has been given. In the preparation of this volume the author has had at many steps the wise counsel of his teacher and associate, Professor AsA Geay, to whom he wishes to make Lis grateful acknowledgments. In the proof-reading, verification of references, and In- dex, Mr. W. W. NoLBN, Assistant in Biology, has rendered aid of great value. His painstaking and good judgment have lightened in every way a formidable and burdensome task. GEORGE LINCOLN GOODALE. Botanic Garden op Harvard University, Cambridge, Mass., August, 1885. CONTENTS. PART I. INTRODUCTION. HISTOLOGICAL APPLIANCES. p^^^ Microscopes .... 1 Dissecting Instruments 2 Media and Reagents 4 Staining Agents ... 15 Mounting-media . . ... 20 CHAPTER I. THE VEGETABLE CELL IN GENERAL: ITS STETJCTURE, COMPOSITION, AND PRINCIPAL CONTENTS. Protoplasm 26 The Cell-waU 29 Cellulose 31 Modifications of the Cell-wall 34 Plastids 40 Protein Granules 44 Starch 47 Inulin 50 Cell-sap 61 Crystals 52 CHAPTER II. CELLS IN THEIR MODIFICATIONS AND KINDS, AND THE TISSUES THEY COMPOSE. Typical and Transformed Cells . 56 Parenchyma 60 Parenchyma proper 60 Epidermis 64 Epidermal Cells 65 Trichomes 68 Stomata 70 Cork 74 Xll CONTENTS. Page Pkosenchtma 76 Prosenchyrna proper T7 Woody JTibres 80 Tracheids . . 82 Tracheae, or Ducts 84 Liber-fibres 87 Ckierose-cells 91 Latex-cells 94 Receptacles for Secretions 97 Intercellular Spaces 99 CHAPTER III. MINUTE STRUCTURE AND DEVELOPMENT OF THE ROOT, STEM, AND LEAF OF PH^^NOGAMOUS PLANTS. The Systems of Tissues 102 Structure of a Fibro-vascular Bundle 103 The Root 106 Primary Structure 106 The Root-cap 107 The Piliferous Layer 108 The Central Cylinder . . , 110 Secondary Structure 112 The Stem 118 Primary Structure 119 The Epidermis 119 Primary Cortex 119 Primary Bundles 120 Pith 124 Medullary Rays 124 Course of the Bundles 125 Secondary Structure . . 135 Of Monocotyledons 135 Of Dicotyledons 136 Changes by Growth 137 Anomalous Stems 138 Spring and Autumn Wood 138 Annual Layers 139 Color of Wood 141 Preservation of Wood .... 142 Density 144 Bark 147 Secondary Liber 147 Cork 148 Injuries of the Stem 149 Lenticels 151 Grafting 152 CONTENTS. Xlli Page Rudimentary and Transformed Branches 153 Stems of Vascular Cryptogams 154 Stems of Mosses 154 The Lbaj? 156 Development 155 Bundles 156 Parenchyma 158 Epidermis 161 Fall of the Leaf 162 Leaves of Cryptogams 164 CHAPTER IV. MINUTE STRUCTURE AND DEVELOPMENT OF THE FLOWER, FRUIT, AND SEED. The Flower 166 Preparation of Material for the Study of its Development .... 166 Stages in its Formation . . 168 Tissue Systems of the Flower . . 170 Development of the Stamens . . 171 Style, Stigma, and Ovary ... .... 172 Distribution of Fibro-vascular Bundles in Simple Pistils 173 Distribution of Fibro-vascular Bundles in Compound Pistils . . . 173 Formation of the Ovule ... . 175 The Fkuit . 176 Its Structure 176 Its Coloring-matters 177 The Seed 178 Structure of the Seed-coat and its Appendages 178 Nucleus of the Seed 181 Food Materials and Protein Granules in Seeds 182 CHAPTER V. PHYSIOLOGICAL CLASSIFICATION OF TISSUES. Division of Labor in the Plant 185 Work of the Plant Organism . 185 Organs and their Classification 186 Haberlandt's Classification of Organs 187 Mechanics of Tissues 188 Strength of Tissues o 190 Stereom and Mestom 192 Siv CONTENTS. PART II. CHAPTER VI. PROTOPLASM AND ITS RELATIONS TO ITS SURROUNDINGS. PAGE Occurrence of Protoplasm 1"^ Chemical and Physical Properties of Protoplasm 197 Protoplasmic Movements '^^ Relations of Protoplasm to Heat 201 To Light 206 To Electricity 207 To Mechanical Irritation . 208 To Gravitation 209 To Moisture 209 To Various Gases . . 210 Structure of Protoplasm 211 Continuity of Protoplasm 214 Relations of the Cell-wall to Protoplasm 218 Historical Note regarding Protoplasm 219 CHAPTER VII. DIFFUSION, OSMOSIS, AND ABSORPTION OF LIQUIDS. Diffusion and Osmosis 221 Diffusion of Liquids 221 Rate of Diffusion 222 Osmosis 224 Precipitation-membranes 225 Traube's Cell . . 226 Pfeffer's Apparatus for Osmosis ... . . 226 Absorption of Liquids through Roots 230 Root-hairs 231 Extent of Root-systems 282 Adhesion of Soil to Roots 2.33 Do Roots go in Search of Food ? 235 CHAPTER VIII. SOILS, ASH CONSTITUENTS, AND WATER-CULTURE Amount of Water and of Ash in Plants 236 Soils 237 Formation of Soils 237 CONTENTS. XV PAGE Classification of Soils 238 Absorption and Retention of Moisture by Soils 239 Chemical Absorption by Soils 243 Condensation of Gases by Soils 244 Root-absorption of Saline Matters from Soils 244 Temperature of Soils . 245 Effects of Roots upon Soils 246 Ash CoNSTiTDiSNTS of Plants 246 Amount and Distribution 246 Composition 247 Water-cultdre 248 Apparatus . 249 Nutrient Solutions . 250 Method of Practice 251 OrFioE OF THE Different Ash Constituents 252 Potassium 252 Calcium and Magnesium 253 Phosphorus 253 Iron 254 Chlorine 254 Sulphur 255 Sodium ... 255 Rarer Constituents 255 CHAPTER IX. TRANSFER OF WATER THROUGH THE PLANT. The Relations of Watek to Tissues 257 Transfer of Water in Woody Plants • 258 Determination of the Path and Rate of Transfer 259 Rate of Ascent of Water in Stems 261 Effect, upon Transfer of Water, of Exposing a Cut Surface to the Air 263 Pressure and Bleeding 264 Exudation of Water from Uninjured Parts of Plants 267 Teanspikation 2^° Stomata 268 Mechanism -^o" Relations to External Influences 270 Amount of Water given off in Transpiration 271 Transpiration compared with Evaporation proper 275 Effect of Moisture in the Air upon Transpiration 275 Effect of the Soil upon Transpiration 276 Relations of Temperature to Transpiration 277 Effect upon Transpiration of Light 277 Of different Rays of the Spectrum 278 Of Mechanical Shook 278 BelatioL of Age of Leaves to Transpiration 279 XVI CONTENTS. PAGE Relation of Transpiration to Absorption 279 Adaptations of Plants to Dry Climates 280 Chief Effects of Transpiration upon the Plant 281 Influence of Transpiration upon Amount of Moisture in the Air . . 281 Effect of Transpiration upon the Soil 283 Do Leaves absorb Aqueous Vapor? 283 CHAPTER X. ASSIMILATION. Appropeiation of Caebon, oe Assimilation peopeb 285 Conditions of Assimilation 285 Assimilating System of the Plant 285 Chlorophyll 286 Origin of the Granules 287 Occurrence of the Granules 288 Structure of the Granules vs'59 The Chlorophyll Pigment, and its Extraction nyO Spectrum of Chlorophyll 292 Fluorescence of Chlorophyll 294 Plants devoid of Chlorophyll 294 " Colored " Plants 294 Etiolation 295 Chlorosis 297 Autumnal Changes of Color 297 Chlorophyll in Evergreen Leaves . , 298 The Raw Materials required for Assimilation, and their Reception by the Assimilating Organs 299 Absorption of Carbonic Acid by Water Plants 299 Absorption of Carbonic Acid by Land Plants 300 Diffusion of Gases 301 Passage of Gases through Epidermis free from Stomata 302 Passage of Gases through Stomata . . 303 Composition of the Atmosphere 303 Practical Study of Assimilation . 305 Energy 307 Classification of the Rays of the Spectrum . 308 The Depth to which Light can penetrate Green Tissues 309 Quality of Light which penetrates the Tissues of a Leaf .... 309 Effect of Colored Light upon Assimilation 310 Measurement of the Amount of Assimilation 312 Engelmann's Method 314 Effect of Artificial Light upon Assimilation .... . 316 Relations of Temperature to Assimilation . 316 Effect upon Assimilation of Variations in the Amount of Carbonic Acid furnished the Plant 318 CONTENTS. XVn PAGE Balio of the Oxygen evolved by Plants to tliat of tlie Carbonic Acid decomposed . . . 319 What are the Products of Assimilation proper ■? 320 First Visible Product of Assimilation 321 Formic Aldehyde Hypothesis ... . . 322 Pringsheim's Views in regard to the First Product of Assimilation . 322 Early History of Assimilation . . . . .... . 323 Appropriation op Nituogen . . . 325 Amount of Nitrogen in Plants . . 325 Sources of Nitrogen furnished to Plants . .... 327 Nitrogen Compounds in the Atmospliere . . . 331 Nitrogen Compounds in Rain-water . . . . . . . 331 Office of the Atmosphere in the Formation and Distribution of Nitro- gen Compounds . ... ... . . 332 Products of the Decomposition of Animal and Vegetable Matter . . 333 Natural and Artificial Fertilizers . . . . . 334 Synthesis of Albuminous Matters in the Plant . . 335 Appropriation op Sulphur ... . . .... . 336 -Appropriation of Okganic Matters . . ... ... 337 Humus-plants, or Saprophytes . ... 337 Parasites . . .... 338 Insectivorous or Carnivorous Plants . 338 Drosera rotundifolia 339 Dionsea muscipula 842 Aldrovanda ... 344 Drosophyllum 345 Roridula 345 Bvblis .346 Pinguicula . 345 Utrioularia 346 Genlisea 346 Sarracenia 347 Darlingtonia . 349 Nepenthes 349 Dipsacus, or Teasel 350 Epiphytes, or Air-plants 352 CHAPTER XI. CHANGES OF OKGANIC MATTER IN THE PLANT. Transmutation, or Metastasis ... 354 Utilization of Food 354 For Supply of Energy for Work . . 355 For Repair of Waste . . . 355 For Construction of New Parts .... . 355 Assimilation proper compared with Respiration . 356 Course of Transfer of the Assimilated Matters in the Plant .... 356 KVIU CONTENTS. PAGE Classification of the Principal Organic Products 367 Products free from Nitrogen ... 357 Carboliydrates . 357 Vegetable Acids. 360 Pats, or Glycerides 360 Certain Astringents 361 Glucosides 362 Etiiereal Oils 362 Resins and Balsams . . 363 Products containing Nitrogen 363 Albumin-like Matters 363 Asparagin . . . 364 Alkaloids 365 Unorganized Ferments 365 Respiration .... ... .... 367 Measurement of Respiration . .... 367 Plants in Dwelling-houses 868 Relations of the Carbonic Acid given off in Respiration to the Oxy- gen absorbed . 368 Influence of Temperature and Light upon Respiration .... o6i) Resting State 369 Respiration accompanied by an Evolution of Heat 370 Intramolecular Respiration . . ... 3^0 CHAPTER XII. VEGETABLE GROWTH. Nature of Growth 373 Cell-division 374 In the Development of Stomata 376 In Cambium . . 377 In the Development of Pollen-grains 379 In Plant-hairs 380 Directions in whicli the new Cell-wall may be laid down .... 380 Growth of the Cell-wall 382 Measurement of Growth 383 Conditions necessary for Growth 384 Relations of Growth to Temperature 385 To Light 387 To Supply of Oxygen 388 Periodical Changes in the Rate of Growth 389 Properties of New Cells and Tissues 389 Tensions in the Cell-wall 390 Tension of Tissues 390 Geotropism 392 Heliotropism 892 Hydrotropism 398 CONTENTS. XIX PAGE Thermotropism 394 Assumption of Definite Form during Growtli 394 Amount of Force exerted during Growth 395 CHAPTER XIII. MOVEMENTS. Locomotion . 397 Movements of Chlorophyll Granules in Leaves 398 Hygroscopic Movements 399 Movements due to Changes in Structure during Ripening of Fruits . 400 Revolving Movements, or Cireumnutation . , . 400 Methods of Observation 401 In Seedlings 403 Of the Young Parts of Mature Plants 405 In Twining Plants 405 Modified Cireumnutation 407 iNvctitropic or Sleep Movements ... . 409 Of Cotyledons 411 Of Floral Organs 412 Times of Opening and Closing of Flowers . 412 Spontaneous or Autonomic Movements 413 Telegraph Plant 413 Cause of Autonomic Movements not fully known . 414 Sensitiveness Of Roots *1^ Of Stems and Branches ^^^ Of Tendrils ^^'^ OfPetioles *^^ Of Leaf-blades ^^^ Of Sensitive Plant *20 Of Stamens *^^ Effects of Anaesthetics upon Sensitiveness 424 CHAPTER XrV. REPRODUCTION. Individuality in Plants . . Methods of Reproduction . . . . Fertilization in Angiosperms The Pistil The Stigmatic Secretion . . , The Pollen-grain Structure 425 426 426 427 427 427 428 Contents ^^ XX CONTENTS. PAGE Emission of tlie Pollen-tube 429 Time required for tlie Descent of tlie Pollen-tube 431 The Ovule 432 Structure and Development 432 Changes following Fertilization 435 FERTILIZATION IN Gtmnospeems 437 Tlie Pollen-grain 437 The Ovule 43? Contact of the Pollen with the Ovule 438 Contrast between the Results of Sexuai and Non-sexual Reproduction 443 Bud-propagation . . 444 Apogamy . . 446 Parthenogenesis . . 446 Polyembryony ... . 446 Close and Cross Fertilization . . . 447 Nectar . . . . . .... . 4S1 Secreting glands . .... 451 Specific Gravity . 452 Period of most Copious Secretion . 452 Colors of Flowers , . . .... 452 Odors of Flowers 454 Hybridization 455 CHAPTER XV. THE SEED AND ITS GERMINATION. Nature of the Life of the Embryo 459 Ripening of Fruits and Seeds 460 Dissemination of Seeds 460 Vitality of Seeds 461 Germination . . 462 Conditions of Germination 462 Moisture 462 Access of Free Oxygen 464 Temperature , . 464 Phenomena of Germination ... 466 Fire-weeds 469 CHAPTER XVI. RESISTANCE OF PLANTS TO UNTOWARD INFLUENCES. Extremes of Heat and Cold ... 470 Winterkilling . 472 Intense Light 473 Improper Food 473 COilTENTS. XSl PAGE toisons 473 Noxious Gases . 473 Liquids and Solids . . 476 Meclianiual Injuries 476 LivDEX 178 PHYSIOLOGICAL BOTANY. INTRODUCTION. HISTOLOGICAL APPLIANCES. The instruments and other appliances used in the exami- nation of minute vegetable structure are, with the exception of a few special ones to be considered later, the following : — 1. Simple microscope. For the preliminary preparation ot many objects, a simple stage-microscope is indispensable. It should be furnished with only the best lenses, preferablj- doub- lets or triplets, magnifying from ten to at least twenty diameters. The glass portion of the stage should be not less than an inch and a half in diameter ; supports at the sides of the stage, on which the wrists raa^' rest during dissections, are of considerable use. If the compound microscope described below is provided also with an inverting eye-piece and with an objective of long focus, it can be made to serve for most dissections ; otherwise a simple microscope should always be at hand. 2. Compound microscope. When reduced to its simplest terms, this consists of a stage, or flat support for the objec^t to be ex- amined, an adjustable tube carrying two combinations of lenses, the objective and the eye-piece, and flnallj- some means of illu- minating the object. The desiderata to be borne in mind in the selection of a compound microscope for use in Vegetable His- tology, are : excellence in the optical parts, ease and steadiness in their adjustment, and simplicit}' of construction. Other things being equal, a microscope with a short tube and with a low stand will be most convenient, on account of the large number of cases in which reagents must be employed, their application requiring a horizontal stage. S INTRODtJCTIOi^. 3. Three objectives and two eye-pieces, from combinations of whicli magnifying powers of fort^' to eiglit hundred diameters can be obtained, will suflice for nearlj' all the histological work described in this volume. Two objectives and a single eye- piece furnishing powers of sixtj" to five hundred diameters are enough for all ordinary investigations of minute structure. Ade- quate and convenient illumination is secured by a plane and a concave mirror under the stage. If this is supplemented by an achromatic condenser, so much the better. The stage, prefer- ably thin, should be provided with a perforated revolving disc, or other suitable sj-stem of diaphragms, by which its centi-al aperture can be made larger or smaller. 4. The student ought, at the outset of his work, to make himself familiar with the principal effects which are produced in the appearance of the object in the field of the microscope, by changes in the amount and direction of the light thrown by the mirror. Details can sometimes be brought out clearly by oblique illumination, which are onl}' faintly, if at all, seen in direct light. 5. In general, low magnifying powers are to be preferred to higher ones ; and combinations of high objectives with low eye- pieces, securing a given magnifying power, are always better than those in which low objectives and high eye-pieces are used to obtain the same enlargement. 6. The slips of glass, or "slides," upon which microscopic objects are commonl3- prepared and preserved, are three inches (76 mm.) long b}' one inch (25 mm.) wide. This is for most cases a more convenient size than that frequently employed in Germany ; namely, 48 X 28 millimeters. The glass should be free from color and from imperfections. The preparation to be examined under the microscope should be covered with a disc of thin glass before it is brought under the objective. Perfect cleanliness of sUde and cover-glass is absolutel}' necessarj- in all examinations, and must be secured by the exercise of scrupulous care.^ 7. Dissecting instrumentr.. Sharp delicate needles, by whicli 1 For cleaning glass perfectly, the following preparation may be used : — A strong solution of potassic bichromate to which about half as much con- centrated sulphuric acid is cautiously added. To this mixture add an equal volume of water. The glass slips, or covers, are to be kept in this solution for a short time, and then thoroughly rinsed in pure water, after which they may be dried with cloth or wash-leather. For ordinary use alcohol of usual strength answers the purpose very well. INTRODUCTION. 3 tlie parts can be separated bj- teasing, are often better than an}' cutting instruments. Tlie}- are indispensable in tiie ex- amination of very young flower-buds, and of great use in the isolation of tissues under the dissecting microscope. 8. Sufficiently thin sections of soft parts ma}- be made by any keen-edged Itnife. A razor of good quality is generally to be preferred to the ordinary dissecting scalpel, since its wide and stiff blade can be held with greater steadiness, and its steel admits of as sharp an edge. As a rule, the razor should be dipped in water before using, as this permits the steel to pass more easily through tissues.^ If the parts from which sections are to be made are too small to be held in the fingers, they can be firmlj' seized between slices of pith. It is often convenient to imbed the object in paraffin or in an alcoiiolic solution of soap.^ These melt below the temperature of boihng water, but are solid at ordinary temperatures, and the latter, if properly made, is transparent. A little of the molted imbedding sub- stance is poured into a small cone of glazed paper, and when it begins to cool, the object is placed in the middle of the mass. Upon complete cooling it is firmh- hold therein. Before putting the object into paraffin it should first be satu- rated with alcohol, and this replac;ed bj- benzol or oil of cloves, in order to enable the paraffin to hold the specimen firmly. The paraffin may be dissolved away from the sections by application of benzol, oil of cloves, or turpentine (see also 110). 9. Thin sections are best removed from the knife by a camel's-hair pencil, and are to be placed at once in water or some other liquid. Except in certain cases, water may be used as a medium for the preliminarj' examination of sections. 10. Microtome. Any of the simpler microtomes, or section- cutters, will bo convenient in much histological work, and of great use in the preparation of a series of sections from any very minute object, since this permits them all to be of exactly the same thickness. 11. Measurements. Microscopic objects are measured by micrometers. Tlie eje-pieco micrometer can be more rapidly used than one on the stage of the instrument; and if its value 1 Advantage is freiiiieiitly gaineJ by moistening the edge of the knife with dilute potassic hydrate before dipping It in water, thus removmg traces of oil which may have adhered to it during sliarpening. fjut potassic hydrate should not be used in this way if reagents are to be subsequently employed. 2 Made by dissolving enough of any good transparent soap in hot alcohol, to form, upon cooling, a firm, clear mass. 4 INTKODUCTIOX. for the rlifferent objectives and for the length of ticbe has been determined accurately, it is usual]3' preferable. Tlie values of the spaces in the cj-e-piece micrometer are ascertained by comparison with known values of the spaces on a standard stage micrometer ; for example, i( one space in the eye-piece micrometer corresponds to five spaces of the stage micrometer, and the latter has a value of one thousandth of a mfllimeter, each space of the former equals five thousandths of a millimeter. The unit of microscopic measurement is the " micro-milli- meter,"' one thousandth of a millimeter. It is expressed b3- the Greek iu. 12. Drawing. An image of the object under the microscope may be cast bj- reflection upon paper at the side of the micio- scope, by means of a Camera lucida. Several forms of the Camera lucida are adapted to use with the tube of the micro- scope in a vertical position, and are more convenient for the majoritj' of eases coming within the scope of the present work. Oberhauser's, IMilne Edwards's, and Abbe's are of this kind. 13. Polarizing' apparatus. This is of great use in the exami- nation of certain contents of cells. It consists of two Nicol prisms, one below the stage of the microscope and receiving the light which is reflected from the mirror, the other in tlie eye-piece. Upon turning one of the prisms, distinctive op- tical characters, not otherwise seen, are presented by grains of starch, etc. 14. Media and reagents. The fluid in which a microscopic specimen is submitted to examination is technicall}' known as its medium. Chemical agents subsequently added for the purpose of producing changes by which the chemical character of the objects may be recognized, s,re termed reagents. Some of the media, however, in common use produce characteristic changes in certain cases, and might be as trul^- referred to the latter class as several of the reagents themsehes. The substances in ' For convenience of refei-ence, ments is given : — the following table of comparative measure- /x, INXBES. 1 000039 2 000079 3 000118 i 000157 6 000197 6 ... 7 ... 8 .... 9 .... 10 .... Inches. 000236 000276 000315 000354 000394 Inches. (j. TTrW= 2.5399 TTsVt = 25.3997 tAtv =253.9972 One meter = 39.370432 inches. INTKOUUCTION. 5 which microscopic specimens are preserved are termed mounting- media. 15. Media. In all ordinary- cases pure water is the best medium in which to place the object for examination. If dis- tilled water cannot be procured, filtered rainwater or melted ice will answer perfectlj'. In some instances water produces an immediate change eitlier in the cell-wfU or in the contents of the cells. For instance, the superficial cells of the coats of many seeds swell up at once when they are placed in water, and lose their former shape ; on the other hand, important contents in the seeds of man^- plants are dissolved immediately when the sections are moistened. Hence, other media must bo sometimes substituted for water. Absolute akoliol (see 40) is the most useful for meeting the cases above referred to. Thus, if a sec- tion of a seed-coat be first examined in absolute alcohol, and the alcohol be gradually' replaced by water as directed in 17, the changes due to water will take place slowly, and can be watched throughout. For the cases in which the cell contents are sus- pected of undergoing change from water, castor-oil is a useful mediiuB. If thought best, this can be removed subsequently from the specimen by alcohol or ether, and the latter in turn may be made to gi\e place to water, and the changes can be followed with certainty. 16. Gl3cerin (see 60), either concentrated or somewhat diluted with water, is a highly useful medium, imparting a good degree of transparenc}' to most specimens. It withdraws a part of the water of the cell-sap, and in the case of thin-walled cells this is followed b}' some change of form. The remarkable effects produced upon some of the contents of cells by the action of glycerin and similar agents will be referred to under Protoplasm. 17. One medium may be replaced by another by the careful use of bibulous paper. Good filtering paper is the best for this purpose. If a little of the liquid which it is desired to place under the cover-glass be put at the edge of the cover, and the opposite edge be then touched lightl}' with the paper, the liquid will be at once drawn through. By successive applications of the same liquid, tiie specimen can be thoroughly washed without removal of the cover-glass. 18. Reagents. F<}ur reagents are in very common use in nearly all histological examinations ; namelj', caustic potash, a solution of iodine, an acid, and a staining agent. Even in ordi- nary cases, however, it is desirable to have a somewhat wider choice than this, and therefore the following brief hints are 6 INTKODUUTION. given as to the preparation and employment of some of the most useful reagents. More detailed directions must be sought in special treatises upon micro-chemistry.^ The list and the general rules here given will serve for most investigations. 19. It is best to try first a very small amount of the reagent, and carefully note its effect before adding more. If it is neces- sary to increase the amount, draw a little through b}- means of bibulous paper, as previously directed. Many reagents are slow in producing their elfects. Hence some time must be allowed to elapse before one reagent is replaced by another, and it is well in some cases to apply slight heat to accelerate or increase the action ; but this must be very cautiously done. 20. If one reagent is to be followed by another, attention must be gi\en to the effects whieJi the reagents have upon each other, or upon the medium, as well as upon the specimen. For instance, small dai-k crystals of iodine separate from an alcoholic solution when this is brought into contact with water. Remo\al of the cover-glass is advised in all cases where one reagent is to be washed out before the application of a second, or where one is to be immediatelj- followed by another, provided the specimen is not so delicate as to be disturbed by it. Some parts of the specimen are apt to escape action, if the washing or the intro- duction of several reagents in these operations is conducted without lifting the cover; but b^- the exercise of great care both these operations may be carried on successfully by the use of bibulous paper without removing the cover-glass. 21. Owing to their importance, potash and iodine are de- scribed first. The other reagents are given in alphabetical order, for convenience of reference. 22. Potash^ Potassic Jiydrale, Caustic potnssa, are names interchangeably given to white solid potassa and to its solutions. This substance absorbs carbonic acid so eagerly from the air, that it must be kept in glass-stoppered bottles. To prevent the stoppers from becoming fastened b}- the action of the alkali on the glass, it is well to smear them with vaseline or paraflfin. 23. Solutions of two strengths are used. I. Concentrated. Solid potassa is dissolved in the smallest amount of water (not far from half its own weight) b^- which it will become liquid. This dense sj'rupj- liquid is too strong for ordinary use. II. A common solution made with one part of solid potassa in three, 1 Consult the following : Botanical Micro-Chemistvy, by Poulsen, translated by Trelease (Cassino, Boston), 1884. Hilfsbueh by Behrens (Schwetsobke, Braunschweig), 1884. INTRODUCTION. 7 five, or ten parts of water, depending upon the particular case in which it is to be used. 24. For use as a macerating agent in separating cells, a strong solution is preferable, and is more efficient when it is slightly warmed. For dissolving or rendering transparent most of the contents of cells, more dilute solutions are better. Owing to the prompt effect produced on tlie cell-wall, and upon the contents of cells, especially- of 3'oung ones, a moderately strong solution of potassa is the most useful clearing agent that we have. After a mass of tissue, for instance an embryo, has been acted on by a solution of potassa until it has become translucent, it is to be cautiously subjected to the action of an acid, preferably acetic or hydrochloric, and then washed. A second treatment, or even a third, may be necessarj- to make the object sufficiently clear. Sometimes, however, the potassa renders the tissues too nearly transparent, in which case they may be slightl}' clouded by a little alum-water. This process of clearing tissues was first used by Hanstein in the examination of tlie tissues at points of growth, and it is of very wide applicabilit}'. 25. Some structures are darkened at first by the use of potassa, but cautious treatment afterwards with a dilute acid and a second application of potassa will generally produce a good degree of transparency. 26. Potassa is a solvent for many of the substances which incrust the cell-wall, but in most cases the solutions must be used warm ; in a few instances heated even to boiling. The cell-wall, washed after such treatment, will give the cellulose reactions (see 145). Suberin can thus be removed from the cell-walls of cork, forming Tvith the potassa 3-ellowi3li drops. 27. As the aqueous solution of potassa causes considerable swelling of the cell-wall, it is desirable to have also at hand an alcoholic solution. This is best made by mixing 95 per cent alcohol with a strong aqueous solution of potassa until a cloudiness appears. The mixture is then to be shaken fre- quentlj', and, after a day or so, the clear liquid above is to be carefully poured off. This solution, may be diluted with alcohol if necessarj-.^ 28. Solutions of caustic soda can replace potassa in most of the foregoing reactions. The special cases in which these alkalies are employed for the identification of certain contents of cells will be described later. 1 Eiissow's Potash-alcohol. 8 INTRODUCTION. 29. Iodine. This element is only ^'ery slightly soluble in pure water. Upon exposure to strong light, however, a some- what larger amount of iodine passes into solution after a while, owing probably to formation of hydriodic acid. If it is neces- sary to examine the effect of iodine alone, as in certain parts of Lichens, a fresh solution should be used. In fact, it is recom- mended that in such cases a minute fragment of solid iodine be placed in pure water under the cover-glass at the mom.ent of examination. 30. But for all ordinary examinations, a solution of iodine in water which contains iodide of potassium is used. The propor- tions employed vary widely. A convenient strength is obtained hy dissolving one gram of iodine and five grams of potassic iodide in enough water to make one hundred cubic centimeters. Even this solution is too strong for some purposes. In a few cases a different solution is advised, made hy dissolving five centigrams of iodine and twentj* centigrams of potassic iodide in fifteen grams of water.^ But, in general, dilute solutions are preferable. 31. A solution of iodine and iodide of potassium in glyce- rin is employed by some. An alcoholic solution is sometimes useful. 32. Iodine is a characteristic test for starch, to which it imparts a blue color, depending for its depth ehiefl_v upon the strength of tlie solution. Iodine in absolute alcohol gives with Ayy starch a brownish color ; if the alcohol is not absolute, that is, anhjdrous, a blue color is given as with ordinary aqueous solutions. 33. In most cases cellulose is colored pale jellow to deep brown by iodine. If the specimen is acted on by concentrated sulphuric acid, either just before or just after the application of the iodine, a blue color appears. This reaction for cellulose is disguised by various incrusting matters, which can be removed by strong acids or alkalies ; after their j'emoval the washed specimen will give the characteristic cellulose reaction (see also 143). 34. Iodine and a metallic iodide in a strong solution of chlo- ride of zinc form a very useful reagent for cellulose, to which a blue color is given. The reagent is easily made bj- dissolving pure zinc in concentrated hjdrochloric acid until there is no further action of the acid. The solution, with a little metallic 1 Poulseii. INTKODUOTION. » zinc still undissolved, is to be evaporated to a syrupy consist- ence, saturated with potassic iodide, an'TK0DUCTI0N. specimen is affected b^' water, as is the case with mucilagi- nous tissues, crystalloifls, etc. As a reagent for use under the cover-glass it is more satisfactory tiian common alcohol, but in keeping it the greatest care must be exercised to exclude ' moisture. 41. Alum. Either potash- or ammonia-alum may be used to diminish the transparency of cells which have been acted on by potassa (see 24). Alum is a mordant in some of the processes for staining (see 98). 42. Ammoriia. Aqueous ammonia may replace the fixed allvalies, potassa and soda, but possesses no advantage over them except in its somewhat slower and less violent action. For its use in the examination of albuminoids, see 125. Its principal use in microscopj' is in tlie preparation of certain staining agents (see 77) and cuprammonia. 43. Anilin chloride. Dissolved in alcohol, this reagent im- parts a pale yellow color to lignified cell-walls. Upon addition of hydrochloric acid, the color is mnch deepened. This is Hohnel's test for lignin. 44. Anilin sulphate. This substance in aqueous or alcoholic solution gives to lignified cell-walls a pale yellow color, which is much deeper when the reagent is followed by sulphuric acid, — Wiesner's test for lignin. 45. Argentic nitrate, or nitrate of silver, in extremely dilute alkaline solution freshlj- made, has been recommended for dis- criminating between living and dead protoplasm, the former turning dark, the latter remaining unchanged (see details in Part II.). 46. Asparagin. A concentrated solution of asparagin is suggested b^' Borodin for the recognition of asparagin itself when its crystals have been formed in tissues blanched by dark ness. 47. Auric chloride, long used for staining preparations in animal histology, has been somewhat employed for coloring the cells of certain lower plants, and in the same manner as argentic nitrate, for detecting the condition of protoplasm. 48. Jienzol is a powerful solvent for various vegetable fats and resins. It is also used for the preparation of benzol-balsam (see 112), and in dissolving paraffin (see 8). 49. Calcic chloride. Treub employs tliis for clearing tis- sues. Tiie fresh section, after having been moistened bv a little water, is covered with dry powdered chloride, warmed until it is about dry, and afterwards placed in a little water. INTRODUCTION. 11 From this it is to be transferred to glycerin, where it soon becomes clear. ^ 50. Calcic hypochlorite in aqneous solution bleaches many tissues without the use of an acid, but, in general, specimens which ha^'e been subjected to its action are more thoroughly de- colorized if they are subsequently placed in dilute hydi'ochloric acid, washed in pure water, and finally transferred to glycerin. Preparations which have been bleached by this method are easily colored by some of the staining agents described on page 15. Sodic hypochlorite may replace it in all cases. 51. Carbon disulpliide is used as a solvent for fats. 52. Carbolic acid, or phenol, dissolved in the least quantity of concentrated hydrochloric acid which will take it up, gives a green color with lignified cells. It is better to add to a few drops of the strongest hydrochloric acid a small quantity of crystallized phenol, warm the mixture slightly, and upon its cooling add enough acid to remove anj- cloudiness. 53. Chloral hydrate in aqueous solution is recommended by Arthur Meyer- as a clearing agent. Two parts of water are added to five parts of cliloral, and used somewhat above the temperature of 15° C. 54. Chromic acid. The pure acid, in strong solution, acts promptly on cell- walls, dissolving all except those which are silicified and those which are cutinized. Even the latter j'iekl to prolonged action. If the solution is more dilute, the action goes on only so far as to cause swelling of the cell-wall, bring- ing out, in special cases, a ver3' distinct stratification. Solutions which are so dilute as to be merely pale yellow cause hardening of soft tissues, and this acid therefore forms an excellent adju- vant to alcohol for this purpose (see Part II.). 55. Cuprammonia. To a solution of cupric sulphate add enough soda (or potassa) to produce a precipitate. After removal of the excess of liquid by filtration, place the precipitate in a flask, wash once with water which has been freed from air by boiling, and then dissolve the mass in the least quantitj' of con- centrated ammonia which will take it up. The freshly prepared solution should act promptl}' on delicate fibres of cellulose, cotton for example, causing them to swell and apparent! 3- pass into solution. Lignified and cutinized cell-walls are not acted 1 Flahault: Accroissement terminal de la racine. Ann. des So. nat., 187 vi. p. 24. 2 Das Chlorophyllkom, Leipzig, 1883. 12 INTRODUCTION. upon until the foreign matter has been removed by the agenta previouslj- spoken of (see 26). This reagent, known as Schweizer's,^ possesses its chief in- terest from the fact that it is the only liquid known in which cellulose appears to dissolve without essential change of compo- sition. It has a limited application in the discrimination of fibres used in the arts. 56. Gupric acetate in aqueous solution is used as a preparatory liquid for the examination of resins. The part to be examined js liept in a concentrated solution for some dajs, and sections are then made from it. If certain resins are present, they will appear of a green color. The above is Franchimont's test based on a reaction discovered b} Unverdorben.^ 67. Ciqoric sulphate in saturated aqueous solution is used for the detection of certain carbohydrates (see 184) and albumi- noidal matters (sec 124). Commercial blue vitriol, recrystallized two or three times, will answer for all ordinarj- cases. 58. Ether is used as a solvent for fats, etc. 59. Ferric chloride in aqueous solution was formerly recom- mended as a test for the tannins;^ the tannin of oak-bark be- coming bluish-black ; that in the leaves of the sumach, greenish- black. But the distinctions are not constant. Ferric acetate and sulphate are now more generally' used than the chloride as a test, and are better. 60. Glycerin. Onl^- the purest glycerin sliould ever be em- ployed in microscopic examinations. The following are among the most important of its many applications: 1. In clearing specimens. It is used not only as an adjuvant in tlie Hanstein and other methods of clearing, but, in man3- cases, it serves well without any other reagent. 2. To cause withdrawal of water from fresh cells, the degree of effect depending on the strength of the glj'ceriu. 3. In the examination of protein grannies (see 175). 4. As a test for inulin; this substance separates sooner or later in the form of sphajrocrystals. 5. As a solvent for iodine (see 31). 61 . Hydrochloric acid. Pure concentrated add is one of tlie most satisfactory agents for the maceration of woody tissues. When dilute, it serves for the discrimination between carbonates and oxalates, the former dissolving with effervescence, the latter - Sohweizer: Vierteljahraschrift natur. Ges., Ziuich, 1857. ' BehrensrHilfsbuch, p. 377. " Watts's edition of Fownes's Chem., p. 672. IJSITBODUCTION. 13 without. It must be ictnembei-ed that acetic acid dissolves carbonates, but not oxalates (see 36). This acid has been used b}- Pringsheim ' in the study of chloroplijll grains ; fresh sections of tissues containing cliloro- phj'll being exposed to the action of tlie acid for some hours. From the grains, minute spheres of a brownisli color become nearlj' detached, and these afterwards appear as clusters of acicular crj-stals (see Part II.). Hydrochloric acid is also of use in tlie examination of some protein matters (see 124). 62. Iiulol (Niggl's test'^ for lignin) is used in an aqueous so- lution. The specimen, subjected to the action of the solution for a few minutes, is transferred to sulphuric acid of specific gravity 1.2 (made by adding one part of concentrated acid to four parts of water). Lignified structures become red. 63. Mercuric cMoricle, or corrosive sublimate, dissolved in fiftj- parts of absolute alcohol renders protein grains insoluble in water. Pfeffer' recommends that the specimen should remain in this reagent at least twelve hours. Dippel* uses a dilute aqueous solution (1 in 600) to render visible the currents in the most delicate threads of protoplasm (and for the demonstration of the nucleus without affecting the other contents of the cell). 64. MilloTbS reagent^ commonl3- called acid nitrate of mercury, is best prepared, according to its discoverer, by pouring upon pure mercury- its own weight of concentrated nitric acid. For a short time the action is violent ; when it subsides a little, gently warm the liquid until the metal is completely dissoh'cd. The solution is immediately diluted by twice its volume of pure water. After a few hours the liquid is to be decanted from the crystalline mass which has formed, and it is then readj* for use.' This reagent is more efficient when freshly made. Albuminoid substances are colored red by this reagent even in the cold, but much more readily upon the application of heat. According to Millon, the reaction is due to the presence in the liquid of both mercuric nitrate and nitrite. This reagent has been employed for the demonstration of the stratification and spiral striation of certain cell-walls. 65. Nitric acid gives to protein matters a yellow color, which is intensified upon the subsequent use of ammonia. The ^ Pringsheim's Jahrbiicher, Bd. xii. p. 294, et seq. 2 Flora, 1881, p. 645, et seq. 3 Pringsheim's Jahvbuchor, viii. p. 441. ' Dippel; Das Mikroskop, i. p. 281. ' Quoted from Behrens : Hilfsb. p. 247. 14 INTKODUCTION. same treatment, especiallj- if the slide is slightly warmed, colors the so-called intercellular substance yellow. The acid is also used as a test for suberin (see 158). 66. Osmic acid (perosmic acid) is very volatile, and there- fore is best preserved in sealed glass tubes until wanted for use, when the tube can be broken under water. Even from the aque- ous solution the irritating acid escapes in small amount, render- ing it a disagreeable reagent to work with. The solutions are usually of one per cent strength. Oils are colored biown by the reduction of the acid to me- tallic osmium on the surface of the drops. Living protoplasm is killed at once by even dilute solutions of this acid, and there is usuallj- more or less discoloration of the different parts. Hence it is a useful agent for arresting the processes of cell- division and growth at any desired stage. Advantage is some- times gained, according to Poulsen,^ by the combination with it of chromic acid. 67. Phenol (see carbolic acid, 52). 68. Phloraglucin^ used bj' Wiesner as a test for lignin.' The specimen is first acted on by hydrochloric acid, and then moistened by a solution of phloroglucin in water or alcohol. If the cell-walls are lignified, the}' will at once assume a red color. HiJhnel'' suggests the employment of a strong decoction of cherry wood instead of the phloroglucin. Used in the same way, it im- parts a violet color to lignified cells. This test is hardly so satisfactorj- as the other. 69. Potassic bichromate in aqueous solution is used to harden tissues, and is about as good as chromic acid. It has been also emploj-ed by Sanio* for the detection of tannin. 70. Potassic chlorate, used with nitric acid, is the most con- venient maceiating agent. If a few small crystals of this salt are added to a little concentrated nitric acid in a test-tube con- taining a fragment of wood, and liie liquid is carefully warmed, violent action begins somewhat below the point of boiling, and the wood is speedily disintegrated. By selecting acid of the right strength, and by careful regulation of the heat applied, the action of the liquid can be kept well under control, so that almost any degree of action can be obtained. It is not safe to use this reagent in the room where delicate apparatus is kept, ^ Miliroohemie, p. 19. 2 Sitziingsber. Akad. Wien, 1878, p. 60. 8 H). 1877, p. 685. 1 Bot. Zeitnng, 1863, p. 17. INTRODUCTION. lO since the gases evolved act upon metals. This is Schulze's macerating process. 71. Potassic nitrate,^ used in the examination of proto- plasm (see Part II.). 72. Rosolic acid, or corallin, dissolved in water containing a trace of sodic carbonate, forms a purple fluid which colors ^ege- table mucus red. It is used also to demonstrate the structure of cribrose-tissue.^ 73. Schweizer's reagent (see cuprammonia). 74. Sodic chloride (common salt), used in aqueous solution in the examination of protoplasm (see 120). 75. Sugar. Cane sugar dissolved in water to form a thick sjTup is allowed to act for some time on tissues containing pro- toplasm : a drop of concentrated sulphuric acid is then placed on the object, when the protoplasm will talic on a faint rose-red color. The reaction is uncertain. 76. Sulphuric acid. Pure concentrated acid is used as an adjuvant in man^' tests, e. in.* Carmin is dissolved in a solution of potash-alum or ammonia-alum until the required color is obtained. This has been modified by Tangl as follows : To a saturated solution of alum, enough carmin is added to give a deep color (1 grm. in 100 c.c. of solution), the whole boiled for ten minutes, and filtered upon cooling. 88. WoodwarcV s carmin. " Pulverized carmin 7^ grains, water of ammonia 20 drops, absolute alcohol half an ounce, glycerin 1 ounce, distilled water 1 ounce. Put the pulverized carmin in a test-tube and add the ammonia. Boil slowh' for a few seconds, and set aside uncorked for a da^', to get rid of the excess of ammonia. Add the mixed water and glycerin, and next the alcohol, and filter." 89. Carmin with picric acid. This agent, known as Rau- vier's picrocarmin, is made by cautious)}- adding to a concentrated solution of picric acid enough ammonia-carmin solution (81) to saturate it, and then evaporating to one-fifth the volume. 1 Beale : How to Work with the Microscope, p. 125. ■' Behrens: Hilfsbuch, p. 258. 3 Behrens: Hilfsbuch, p. 257. In Dippel(Das Mikroskop),p. 285, the pro- portions are somewhat different. •• Archiv. fiir Mikrosk. Anat., 1879, p. 465. Tangl, in Pringsh. Jahrb., B(l. xii., 1880, p. 170. 2 18 INTRODUCTION. Upon cooling, a slight sediment is deposited. After filtration from this sediment the liquid is evaporated to dr}-ness, and afterwards dissolved in water in the proportion of 1 : 100. Another formula is: 1 gram of carmin and 4 c. c. of concen- trated ammonia are mixed with 200 c. c. of water, and 5 grams of picric acid then added. After nearlj' complete solution the clear liquid is poured off, and exposed to the air for some weeks. The red powder left after this slow evaporation is to be dis- solved when required in water in the proportion of 2 :100, and the solution filtered through two thicknesses of filter-paper. Cochineal, the substance from which carmin is prepared, may be used in aqueous extract, or with alum. The formula for the preparation with ahnn is given as follows : Rub to a fine powder one gram of cochineal with one gram of burnt alum ; mix with 100 c.c. of water, and boil down to 60 c. c. Wlien cold, filter the solution several times, and add a few drops of carbolic acid. 90. Ilmmatoxylin (a dj-e obtained from logwood) is used dis- solved in alcohol, or alum-water, according to circumstances. Fre}- gives the formula: 1 gram of haimatoxylin is dissolved in absolute alcohol. This solution is added, drop b}' drop, to a three per cent aqueous solution of alum, until it becomes deep violet in color. After exposure to the air for a few days, it is to be filtered, and is then ready for use ; but a fresh filtration will be found necessarj- after a time. Poulsen advises that a few drops of a ten per cent solution of alum be added to an aqueous solution of hsematoxylin (.3.5 gram in 10 c.c. water). Aqueous extracts of several other d3-e-woods can replace htematoxylin in some cases, but they have no advantage over it. 91. Picric acid (trinitropheuic acid) in aqueous solution is valuable for staining and hardening protoplasm. It may be used alone, combined with carmin (see 89), or with nigrosin. 92. Alkanet-root (alkanna) in alcoholic solution tinges resin- ous globules and serves to prepare for cutting specimens which contain them. The method of use is described under " Resins." 93. The coal-tar colors. Under this name are comprised the anilin derivatives and a few others of a slightlj- different origin. The following table will indicate to some extent the changes of color which may be expected when these dyes are used with tissues Avhich have a marked acid or alkaline reaction. But it should be observed that the names of several of the dj-es are loosely applied, and that the dyes made by different manufac- turers are not always of the same character or strength. All of the dyes mentioned below are soluble in water and alcohol. INTRODUCTIOX. 19 Ntime. Effect ofdilute 11 CI. Effect cf dilute Ammouia. Ihd (lyes. Magenta. Color fades to brown or 1 purple. gilt Fades completely. Safranin. Color changes to purple, and Little change. a brown precipitate occurs. Kel anilin. Deep orange-brown color. Reddish precipitate. Arid iizo-rubiu. Slight change of lint. Little change. Eosin Orange precipitate. No uiarked i-hange. I'ouceau. No change of color Yellow and Orange (lyes No change. Pnlid vellnw. Purple precipitate. Little change. Orange "R.'* Unchanged. Unchanged. GolJ orauge. Little change. Green dyes. Color deepens to red. Methj l-green. The bluish tint becomes deep Fades out. green. Brilliant (^reen, Fades .''omewhat. Whitish precipitate. Kmerald green. Fades out. nine and Violet dyes. Whitish precipitate. Cotton-blue "B '' Unchang-d. Fades somewhat. Methyl-violet " BBBBBB." Greenisli precipitate. Purple pi-ccipitate. Nigrosin. Little change. Little change. 94. A solution of any of the above dj'es consisting of one gram witli enough water to make one hundred cubic centimeters, although too strong for most cases, is ver^- convenient, since it can easilj- be diluted at will. From even ver^- dilute solutions parts of a specimen, for instance, a cross-section of a stem, will take up some of the color with more or less change. If the staining is too dee[), a part of the color can be removed by careful washing in alcohol, or in a very dilute acid or alkali (see above table for each case). 95. Double-staining . It is sometimes possible to color dif- ferent parts of a specimen with more than one dye ; for instance, staining Ihe fibres of the baik green, and the wood of the same specimen red. The best results are obtained by the use of an alcoholic solution of one of the dyes and an aqueous solution of the other. Tl.e following method proposed by Rothrock ' gives excellent results, The dyes are Woodward's carmin (see 88) and anilin green (or "iodine green"). The specimen (whether bleached by sodic hypochlorite or left unbleached) is first thoroughly saturated by alcohol, which hardens it, and causes contraction of the contents ; it is then kept for a daj- in a dilute ' Botanical Gazette, September, 1879. 20 INTRODUCTION. alcoholic solution of anilin green. In a, row of watch-cr3-stals the following hquids are placed: (1) water, (2) Woodward's carmiu, (3, 4, 5) alcohol, (G) absolute alcohol, (7) oil of cloves. Tlie specimen, taken from the green, is dipped for a moment in water, tlien for about a minute in the carmin, then successively through the alcohols, in each of wiiich it remains ten to twenty minutes, except in the first, where it remains only long enough to have the unfixed carmin washed awa3\ From the last alcohol it goes into oil of cloves (or benzol), where it should remain long enough to become perfectly transparent. It is then to be mounted in balsam. 96. Double-staining can also be effected bj- the successive use of haematox3'lin and an anihn color. Bj- the use of two or more anilin dyes different parts of a specimen may be colored differ- ently ; but as a rule all these effects are uncertain, and cannot be relied upon for the positive identification of tissues. In general, however, long bast fibi-es take characteristic colors. 97. Tlie following combinations for double-staining are rec- ommended bj- Dr. Stirling,' and though originallj- designed only for animal tissues, serve well with sections of plants : — 1. Osmic acid and picrocarmin. 2. Picric acid and picro- carmin. 3. Picrocarmin and logwood (hsematoxylin). 4. Pi- crocarmin and an anilin dj-e. 5. Logwood and iodine green. 6. Elosin and iodine green. 7. Eosin and logwood. 8. Gold chloride and an anilin dye. 98. In the cases which require special treatment, for instance, the staining of the nucleus, the precautions laid down must be attended to in order to insure success. But in the ordinary instances where it is desirable to stain a specimen merely to bring some part into prominence for purposes of demonstration, the widest choice in d3-es and their use is advised. A few mor- dants liave been tried in order to fix the colors, but with little success. The best are tannin in solution, and aqueous solutions of an3' of the alums. A little practice will show which mordant is best for each case. 99. Specimens stained 1)3' nearly all of the above d\'es can be mounted securely in balsam, as directed in section 110 ; but glycerin and glycerin-jelly mounts are apt to become faded or discolored after a time. 100. Mounting-media. Pollen and other dr3' specimens are preserved in shallow cells formed by a thin ring of asphalt- 1 Journ. Anat. and Phys., 1881, p, 349. INTRODUCTION. 21 cement, varnish, or white lead, allowed to dr}- nearl_y to hardness, upon which a cover-glass fits firmly-, and is retained by a second ring of the same cement. If the precaution is talien to have the cover-glass fit evenly- to the first laj-er of cement, tliere is little danger that the subsequent layer, which is to hold the cover in place, will creep under it and into the cell. 101. Glycerin, pure water, calcic chloride solution, potassic acetate, and like liquids may be used as mounting-media in cells prepared iu the manner just mentioned, but made of greater thickness. Care must be observed to avoid touching the upper edge of the cement ring with the liquid ; and yet the cell must be completel}- filled, in order to exclude air. 102. If a specimen has been prei)ared in glycerin, and it is not considered well to disturb the cover-glass, a cement ring or square can be built up around the cover at a little distance from it, provided the glass slide is thoroughly cleaned at the place where the cement is to be put. After the requisite number of laj-ers have hardened sufficiently, a ring of the same or, better, of a more quicklj- drjMng cement may be placed across from the edge of the cell to the cover-glass, to hold it in place. As this, in dr3"ing, will contract somewhat, it is a good plan to place two or three fragments of thin glnss under the cover, that these may receive the pressure and prevent crushing the specimen. 103. Of the mounting-media, one of the best is glj'cerin and acetic acid in equal parts, boiled and filtered. It serves well for thin-walled specimens (especiall3- in the lower plants). 104. Specimens of fresh cells or of juicy tissues which are to be mounted in gl3'cerin are best treated in the manner recom- mended In- Beale.' " The specimen is first immersed in weak glycerin, and the density of the fluid is gradually- increased, either by adding from time to time a few drops of strong gly- cerin, until it bears the strongest, or bj- allowing the original weak solution to become gradually' concentrated by slow evapo- ration. In this way, in the course of two or three da3-s the softest and most delicate tissues may be made to swell out almost to their original volume in the densest glycerin or sj-rup. They become more transparent, but no chemical alteration is produced, and the addition of water will at any time cause the specimen to assume its ordinary' characters." 105. It is plain that mounts in anj' liquid must be liable to injur}' from displacement of the cover-glass ; but this can be 1 How to Work with the Microscope, p. 360. 22 INTRODUCTION. partially guarded against by fastening to the upper surface of the slide, near its two ends, square pieces of pasteboard a little thicker than the cell itself. 106. Glycerin-jelly, a mixture of glycerin with pure gelatin, is liquid at the temperature of boiling water, and solidifies again on cooling. Any specimen which is not injured by being slightly heated can be mounted satisfactorily in the jellj', provided it is first thoroughly- saturated with gl^xerin. But this precaution is by no means necessar}' in all cases. 107. A drop of the melted jell3-, fi'ee from air-bubbles, is placed on the slide (a fragment of the solid jellj- can be melted on the slide if preferred), the specimen placed therein, and the cover-glass, previously moistened slightl_y on the under side with glycerin, is carefullj- laid on, and the preparation now allowed to cool. When the jelly is again hard, a varnish or cement ring may be placed around the edge of the cover to hold it in place. Asphalt-cement is apt to impart to the jell}- a dark tinge, which may sooner or later spoil the mount, and hence the colorless varnishes are better. 108. The edge of the jelly may be lightly touched with a strong solution of a chromate, for instance, bichromate of potas- sium, and exposed for a while to light. This renders the jelly insoluble, and firmly sets it. 109. The following are among the best formulas for making this useful mounting-medium : — One part of pure gelatin, three parts of water, and four of glycerin (Schacht, quoted by Dippel). Nordstedt uses the same proportions, and advises the addition of a small piece of cam- phor or a drop of carbolic acid, to prevent moulding. One part of gelatin is soaked in six parts of water for two hours, seven parts of glycerin are added, and one per cent of carbolic acid is added to the whole. The mass is heated for fifteen minutes, with constant stii-ring, and then filtered through glass-wool. All the ingredients must be absolutely pure (Kaiser, Bot. Centrbl., 1880, p. ih). The proportions employed in the second formula, but without the addition of the carbolic acid, give a clearer jell3' ; and it has not been apt to mould, especially if the cork of the bottle con- taining it be wrapped in a thin piece of linen, which has been dipped in dilute carbolic acid. 110. Canada halsam. This is used either (1) alone, or (2) in solution. In either case the specimen must be free from water, and permeated by some liquid easily miscible with the balsam. TNTEODUCTION. ■L6 This is easily effected b^' first saturating the object with alcohol (beginning preferably with dilute, and then using stronger), in order to expel all water ; next placing the alcoholic specimen in oil of cloves, turpentine, or benzol, until the alcohol is in turn expelled. The specimen thus permeated is transferred to balsam which has been previously placed on the slide. Care must always be taken to have the balsam perfectly free from air-bubbles. 111. When used alone, the balsam on the slide maj- be heated, to drive off a part of its more volatile constituents, and the specimen can then be placed in the warm liquid. But this method is not applicable when the specimen is affected by slight beating ; it is best adapted to hard tissues, like woods and fibres. Balsam which has thus been heated hardens on cooling to a good degree of firmness. This firmness is secured with balsam used without heat only after a longer lapse of time, during which the more volatile matters have escaped. 112. If pure balsam is caiUiously heated in a capsule until it no longer gives ofl' ^apoi-s, the melted mass will cool into a pale amber-colored solid. This solid dissolved in a small quantity of benzol forms a liquid of the consistence of syrup, which is useful for all mounting where heat is injurious. The specimens must be treated successivelj' with alcohol and benzol, and thej' are then readj- to be immersed in the benzol-balsam on the slide. An equally' serviceable solution is made by dissolving the mass in chloroform. Chloroform-balsam requires the specimen to be saturated with chloroform before immersion. 113. In all the above cases two precautions will save disap- pointment : 1st. the slides and cover-glasses should be heated slightl}^ to drive ofl' any moisture on the surfaces which are to come in contact with the mounting-medium ; 2d. the covers should be held in place by means of a slight weight, or by the pressure of a spring clip, until the balsam or its solution has become tolerably firm. A little experience will show that speci- mens mounted in balsam may require a somewhat different management of the mirror under the stage from those which are mounted in a medium with a different refractive power. Daraar may replace balsam when the latter, wliich is the better, is not to be had. 114. Hoi/el's mounting-media are highly recommended by Strasburger. ' The one which is preferred for anilin preparations ' Das botan. Practicum, 1884, p. 40. 24 INTRODUCTION. is made bj' adding colorless pieces of gum-arabic to a solution of potassic acetate or ammonic acetate, until the liquid becomes of the density of thick syrup, while in that intended for carmin preparations the gum is dissolved in a five to ten per cent aqueous solution of chloral hydrate, and about ten per cent of glycerin added. Either of these media, or a plain solution of pure gum-arabic, will be found to answer admirably for all prepa- rations of woods which are to be photographed. 115. The edges of the cover-glass are usually painted with some varnish of good qualitj-. Those in best repute are : — 1. Asphalt-varnish, to be thinned with turpentine when too thick. 2. Maskenlack, a German ])reparation, thinned witli alcohol. 3. Mikroskopirlack, also thinned with absolute alcohol. 4. Shell- lac in alcohol, tinged with some anilin color. If a few drops of castor-oil are added to the solution, it dries into a less brittle finish. 5. Gold-size. 6. White lead (with oil). It is a good plan to revai'nish slides whenever the varnish first shows any indication of breaking away. A few works in regard to microscopic manipulation and micro-chemistry which ma3- be advantageously' consulted bj' the student are the following : — Beale. How to Work with the Microscope (London). This is a large octavo volume, with very minute desciiptions of microscopical appliances and manipulation. Several editions have been )irinted. Cakpentbr. The Microscope (London). A small octavo of about 900 pp. This work deals at some length with the structure of animals and plants. Behkens. Hilfsbuch zur Ausfiihrung Mikroskopischer Untersuchungen im Botanischen Laboratorium (Braunschweig, 1883). This is specially de- voted to microscopic manipulation and micro-chemistry. An English trans- lation has appeared. PouLSEN. Botanical Micro -Chemistry. Translated and enlarged by Pro- fessor Wm. Trelease (Boston, 1884). An excellent account of the chemicals used in the examination of vegetable structures, together with some directions for their employment. Strasediigeu. Das botanische Practicum. See an account of this work on page 165. Bower and Vine.s. A Course of Practical Instruction in Botany (London, 1885). A most useful and couvenient guide to the study of the histology of fiowering plants, ferns, and their allies. PART I. CHAPTER I. TnE VEGETABLE CELL IN GENERAL : ITS STUCTUEE, COM- POSITION, AND PKINCIPAL CONTENTS. lie. The unit in Vegetable Anatomy, the fundamental compo- nent of which the fabric of plants is constructed, and from which all the diverse histological elements are derived, is the cell. Even the elements which are the least cellular in appearance, and wliich have names of their own (as fibres, ducts, etc.), are onl}' transformed cells, or simple combinations of tliem ; so that the cell is the t3pe as well as the unit of vegetable structure, as indeed it is of animal structure also. The name cell is one which would not be given to it if the nomenclature were to be founded upon our present knowledge. Cells were original!)' taken to be onl}' closed cavities in a vegetable mass.' We now 1 The earliest recognition of ceUuIar strncture in plants appears in Robert Hooke's MIcrograplila (1665), p. 113. "Our microscope informs us that the substance of cork is altogether fiU'd with air, and that that air is perfectly enclosed in little boxes or cells distinct from one another." Nehemiah Grew, of London (The Anatomy of Plants, book i. p. 4), under date of 1671, says of the mass through which the framework of a young plant is distributed, "It is a Body very curiously organiz'd, consisting of an iniinite number of extreme small bladders," etc. Malpighi, of Bologna, in a work presented to the Eoyal Society in the same year, uses nearly the same language: "Exterior etenini cuticula utriculis, seu sacculis horizontali ordine locatis, ita ut annulus effornietur, componitur, etc." (Anatomes Plautarura Idea, p. 2). As a preliminary study, a beginner .should prepare and examine a few sec- tions like the following : — (1) From the tip of the root of a bean (which has germinated on wet sponge or paper) cut a thin section lengthwise, and carefully examine it under a power of 200-400 diameters. If the section is thin enough, the contents of the cells can be made out, and will be seen to consist of a colorless lining (proto- jilasm), in which one part (ttc nucleus) appears denser than the rest. Next, treat the section with a solution of iodine, and notice what parts are colored, — the protoplasm and nucleus are yellow and brown, but the cells on the looser part of the tip contain bluish granules {starch). This starch can best be shown by first dissolving out the prgtoplasm with dilute potash. 26 THE VEGETABLE CELL ]N GENERAL. know them to be organs and even organisms. Histology therC' fore begins with the coll in its independent condition. 117. A complete and living vegetable cell consists of a cell- wall enclosing certain essential contents. 118. In their earliest state some of the lower plants exist as a mass of motile living matter, not bounded by anj- envelope. But in all plants of the higher grades the living matter of the cell is from the verj- first protected by a cell- wall. 119. That which is essential to the vital activity of a cell is an apparently half-solid sul)Stance, — -protoplasm. With the prop- erties of protoplasm as a living thing. Physiology and not His- tology" is immediatel3' concerned. But it is necessary throughout the stud}' of Histology to make a distinction between the cells which are vitally acti\e and those which serve chiefly or wholly- some mechanical end ; and hence attention mnst be called at the outset to the means b}' which the lixing matter of the cell can be identified. 120. Protoplasm exists in all j'oung cells — for instance, in the soft cone of tissue in buds, in root-tips, and other i)oints of growth — as a nearly transparent or finely granular substance.' It completely fills the interior of very young cells, but with increase of the cells in size there arise cavities (vacuoles) con- tainuig sap, and these bj' their enlargement and confluence may appear to occup}' the entire space within the cell. If, however, such a cell be acted upon by anything which causes contraction (2) Make a tlnii section through the petiole of a begonia or some common house-plant, and observe the granules iinbedded in the protoplasm (clilorophyll- gramdes); notice also crystals, either in masses or single. (3) Examine a thin section through dry pine wood, test with iodine, and observe the absence of protoplasmic matters. Examiuc in the same way any hard wood. (4) Make a section through any starchy seed, for instance a common bean, and treat it with a solution of iodine ; notice the distribution of protoplasmic matters in the form of thin irregular films throughout the cells. Examine a similar section in oil, and see what differences, if any, can be detected. Prob- ably the jiresence of protein granules will be made! out. From these jireliminary examinations a beginner will have demonstrated the protoplasmic matter in its active, resting, and reserve states ; he will have seen chlorophyll, the nucleus, and starch, the chief form in wliich food is stored in plants. He will also have seen a few of the more common crystals. After such a study the student is urged to examine practically the charac- teristics of the cell-wall and the cell-contents as they are presented in this chapter-. 1 By the use of staining agents, especially haamatoxylin, protoplasm can in many cases be shown to possess a complicated mesh of very delicate fibre.'-. PROTOPLASM. 27 of the protoplasm,' as, for instance, a solution of common salt, the protoplasm separates from the cell-wall, and b^' its con- traction shows clearly that it is a closed sac. At a later stage in some cells even this thin protoplasmic sac wholly dis- appears. 121. Protoplasm Itself must be regarded as essentially transparent and colorless, but it is seldom found without some admixture of other mat- l^r^h ters, which give it a granul-ar appearance. The granules are generallj" very small, and f '^_ as a rule are not found at the periphery of the mass. The limiting surface of the proto- plasmic mass is further dis- tinguished by being somewhat denser and firmer than the sub- stance it encloses ; and although it cannot be separated from the latter M'^ mechanical means, it is often spoken of as a film ['^ which take up the coloring matter readily, le;iving the remainder of the mass unstained. It is believed by Schmitz that the unstained mass is a homoge- neous liquid filling the meshes (Sitzungsber. der niederrhein. Gesellschaft in Bonn, 1880). 1 Such substances ai'e termed plasmolytic agents. 2 Of the appearance of- protoplasm, the following remarks by Mohl, who first gave it the name iu 1846, are of interest. " If a tissue composed of young cells be left some time in alcohol, or treated with nitric or muriatic acid, a very thin, finely granular membraue becomes detached from the inside of the wall of the cell in the form of a closed vesicle, which becomes more or less con- tracted, and consequently removes all the contents of the cell, which are enclosed in this vesicle, from the wall of the cell. Reasons hereafter to be discussed have led me to call this inner cell the primordial utricle. ... In the centre of the young cell, with rare exceptions, lies the so-called nucleus celltilce of Eobert Brown. . . . The remainder of the cell is more or less densely filled with an opai|ue, viscid fluid of a white colour, having granules intermingled in it, which fluid I call protoplasm " (Mohl; The Vegetable Cell, Henfrey's Translation, 1852, pp. 36, 37). Fio. 1. From developing anther of Orchis maciilata, showing young cells com- pletely filled with protoplasm. Observe also the nucleus with its nucleolus, in each cell. (Guignard. ) Fig. 2. A hair from the stamen of Tradescantia pilosa, showing the protoplasm in the form of granular threads running from side to side of the cell-cavity. The white spaces between these threads are vacuoles. The nucleus can also be seen in each of the four cells. (Jacobs.) 28 THE VEGETABLE CELL IN GENERAL. and where there is any break in the continuity of the mass, for instance in the case of sap-cavities, a similar limiting film may be supposed to exist. 122. The consistence of protoplasm depends on the amount of water which it contains. Thus in drj- seeds it is nearly' as tough as horn, while in the same seeds during germination it becomes like softened gelatin. It absorbs water readilj- and be- comes permeated by it, thereby increasing its apparent fluidit}-, but it never becomes a true fluid. Moreover, there is a limit to the amount of water which it takes up. 123. Chemically considered, protoplasm is a very complex substance. It belongs to a group of bodies of which the albumin of egg may be conveniently taken as the type. They undergo many slight but sometimes remarkable changes, and have been collectively termed proteids. The terms albuminoids and pro- teids may be used interchangeably (see 857). 124. The albuminoids, or proteids, which form with water the bulk of protoplasm proper, are of course associated with the matters which this living substance makes, uses, and discards. But these matters exist in the protoplasm in ver3- different pro- portions at different times, though never in such amount as to obscure the peculiar reactions of the albuminoids. These are the following: 1. The yellow or brownish color imparted by solutions of iodine. 2. The purple color produced when the specimen first saturated with a solution of cupric sulphate is acted on by potassic h3drate. 3. The rose color, often faint, which follows the successive action of a solution of sugar and strong sulphuric acid. 4. The red color given by Millon's reagent. This test generallj' requires the cautious application of heat. 5. The yellow or orange color following the application, in succession, of strong nitric acid and amnionic hydrate. 125. Dilute solutions of the caustic alkalies dissolve proto- plasm ; concentrated solutions do not. If a young cell is acted on b^' concentrated potash, its protoplasm is not essentially affected ; but if water is now added, the protoplasm dissolves at once. 126. The spherical or ellipsoidal mass found in the protoplasm of active cells, and difiering from the rest of the protoplasm in its greater density, is the nucleus. The sharply defined point often seen in the nucleus is the nucleolus. 127. The nucleus undergoes remarkable changes during the earliest stages of the cell, which will be described in the chapter on "Growth." The relations which exist between the proto- THE CELL-WALL. 29 plasm in one cell with that in contiguous cells will be considered in Chapter VI. 128. The cell-wail. The cell-wall is produced from materials contained in protoplasm, ' and is laid down in intimate contact with it, as an even homogeneous film which exhibits at first no obvious structure, but with increase in size generally' becomes modified in appearance, consistence, and composition. 129. Its evenness of surface is in most cases early lost by addition of new matter, giving rise to protuberances or marliings of diflTerent sorts. Though at first possessing no evident struc- ture, it may become clearlj' difll'erentiated into laj-ers, and thus become stratified, or striations maj- ajipear. Its consistence, at the outset that of the most delicate bleached linen fibre, maj' soon become changed, on the one hand to that of soft gelatin, or on the other to that of the densest wood. Moreover, although devoid of color when first produced, it maj' acquire distinct color- ation ; and, lastlj-, its chemical character nia3' undergo such im- portant changes that its normal reactions are no longer given. 130. The marking's of tiie cell-wall. Uniform thickening of the whole cell-wall is extremely rare ; even in the examples which are commonly given to illustrate it, pores or channels, more or less distinctly visible, interrupt its continuitj'. 131. The thickenings may possess great irregularity, or thej' may be so strictly localized and regular as to form characteristic features of the widest use in diagnosis. They ma}' pi'oject out- wardlj', forming ridges, spines, and other sculpturings ; or, as is most com- monlj' the case, inwardlj', giving rise to rings, spirals, etc. 132. If tlie wall is thickened through- out, except at well-defined points, de- pressions or pits are produced, varying considerably in outline, but occurring generall}' as simple dots or lines. In some cases it is not difficult to see that these dots or lines are true pores or fissures running from one cell to the next. ' Accoi'ding to Schinitz, the cell-wall is produced by the conversion of the, limiting film of protoplasm into cellulose. That the cell-wall is formed at the limiting film admits of no question. Fig. 3. Pitted duct; from stem of Ciohorium Intybus. (Jacobs.) \ 30 THE VEGETABLE CELL IN GENERAL. 133. Bordered pits are a very common modification of the last. A comparatively large spot remains unthickened, but becomes covered b}' a low dome whicii has at its top a small aperture ; at a corresponding point of the wall of the neighbor- ing cell another thickening produces a similar dome, so that the two domes constitute a double convex body which appears as a disc with a central perforation. These bodies are known as discoid markings. 134. Sometimes the spot covered by the arched projection or dome is elliptical instead of round. When this kind of marking becomes linear, or nearly so, it is termed scalariform. 135. When annular and spiral thickenings occur the cell-wall lying between them remains so thin tliat a slight strain suf- fices to break it, releasing the rings and coils. The number, the direc- tion, and the stee[)ness of the spi- rals furnish in some cases diagnostic features. 136. Besides spirals and rings, there are intermediate forms, which pass easily over into netted or reticu- lated thickenings. It happens some- times that the reticulated markings are so regular that their interspaces appear as regular polj-gons. 137. Tlie external sculpturing of the cell-wall can be seen in many pollen-grains, and in the hairs of many plants, though in the latter case the projections ma}' be partly due to irregularities in the form of the cell. 13.8. Stratiflcation and striation. The cell-wall, even at an early stage, frequently exhibits a distinctly stratified structure. In some cases, at least, removal of all the water whicli forms a constituent of the wall obhterates every trace of sta'atification, and this fact supports the hypothesis that the appearance of lamination is caused by differences in tlie amount of water con- tained in alternating layers of the wall. The less strongly refractive la3-ers are supposed to contain more water than those which are highly refractive. But there are cases of stratification in Fig. 4. Annular and spiral markings; vertical section through stem of Tradescantia pilosa. (Jacobs.) CELLULOSE. 31 which cannot be satisfactoril}' explained by this hj-pothesis. There are, besides, numerous instances in which tlie stratified appearance is not clearlj' shown until the cell has been acted on by an acid or an alkali ; a good example of this is afforded b}' the firm cells of the albumen of the vegetable ivory (Phy- telephas) .* 139. An appearance of spiral striation,'' ascribed also to the unequal distribution of water, is often seen, especially in the cells of the liber of Apocynaceas and allied orders, and in many wood-cells. The striations are not constant as regards the steepness of the spiral ; in fact, in a few instances rings instead of spirals are present. A striated appearance is sometimes pre- sented in walls which have been deprived of all their water. 140. Chemically considered, the young cell-wall consists essen- tially of cellulose, a substance which has the same percentage composition as starch, namely, C|.H,|,05. Even in its purest state it is associated with a trace of mineral matters which remain behind as asli when it is burned, and in the living cell it is always permeated by water. 141. Cellulose is not soluble in an}' of the following hquids commonly used in microscopic manipulations, — water, alcohol, glj'cerin, dilute alkalies, and dilute acids. It is, however, more or less strongly acted on by hot concentrated alkalies, without passing into true solution, and it is apparent!}' dissolved by strong sulphuric acid. Whether cellulose becomes truly dis- solved by concentrated sulphuric acid, or mere!}' forms some other carbohydrate under its action, is of little consequence, so far as the destruction of cell-walls is concerned. In nearly all cases its action is so energetic that the wall of a cell can be ' As shown by Molil, the action of a mineral acid of proper degree of con- centration causes the wall to swell up, and the lamellar structure becomes very distinct. " By this means the lamellar structure may be demonstrated even in those cases in which the unaltered membrane appeared completely homogeneous" (Mold; Vegetable Cell, p. 10). " " The stratification is visible on the transverse and longitudinal sections of the cell-wall, the striation on the surface as well ; it is usually most evident there, but is in general less easily seen than the stratification ; it depends on the presence of alternately more or less dense layers in the cell-wall, meeting its surface at an angle. Generally two such -systems of layers may be recog- nized mutually intersecting one another. There are thus all together three systems of layers present in cell-wall ; one concentric with the surface, and two vertical or oblique to it mutually intersecting, like the cleavage planes of a crystal splitting in three directions (Niigeli) ; and just as this cleavage is some- times more evident in one direction, sometimes in another, so it is also with the stratification and striation " (Sachs: Text-book, 2d Eng. ed., p. 20). 32 THE VEGETABLE CELL IN GENERAL. ■wlioll}- removed b}- this acid, even without destroying the proto- plasmic contents ; and this fact has been extensive]}' en)plo3ed in the examination of tlie continuity of the protoplasm in con- tiguous cells.^ 142. The only known solvent from which cellulose can be re- covered without change of composition is Schweizer's reagent, ammoniacal solution of cupric oxide. In this liquid, cellu- lose swells considerably, and slowly disappears. It is thought bj' some chemists that it does not truly dissolve. From its apparent solution, it can be precipitated in the form of a floccu- lent mass b^' acids, salts of many kinds, and even by the addi- tion of a large amount of water (sec 55) . 143. Freshlj- prepared aqueous and alcoholic solutions of iodine do not color pure cellulose beyond giving a faint j-ellow- ish tint ; but if the reagents have been kept for some time, par- ticularly in the light, they may impart a blue color.^ The latter 1 Unsized, well-bleached linen paper is nearly pure cellulose. If it is dipped in a cold mixture of one volume of water and two volumes of strong sulphuric acid, withdrawn after ten to twenty seconds, and washed thoroughly in water, and finally in dilute ammoniacal water, it becomes much like parchment. This " vegetable parchment " is a suitable membrane for certain experiments in absorption. The acid in this experiment is supposed to convert at least a portion of the cellulose into a substance which closely resembles starch in its chemical reactions, termed ainyloid. Parchment paper can be made also by concenti'ated zinc chloride, and by a few other agents. ^ Mohl (The Vegetable Cell, p. 24, Eng. Trans.) says: "When imbued with iodine, it becomes indigo-blue if wetted with water.'' In a note on pages 28 and 29, he further says : " My researches shewed me that the in- fluence of sulphuric acid was by no means necessary for tlie production of the blue colour in membranes which are not strongly incrusted, as in the paren- chymatous cells of succulent organs, but that iodine and water alone are suffi- cient ; while in full-grown and hardened cells sometimes the primary membrane alone, sometimes even a greater or smaller portion of the secondary layers had through the deposition of foreigii substances, altogether lost the property of becoming blue on the application of sul[)hurio acid and iodine, altliough they were still composed of cellulose, and iodine alone would very readily jiroduee a blue colour in all their membranes after the infiltrated matters had been removed. The means I employed to remove the infiltrated substances were caustic potash and nitric acid. . . . After this treatment, the wliole of the layers of all elen)entary organs are coloured a beautiful blue by iodine even when they offer so great a resistance to the action of sulphuric acid before the treatment with nitric, as is the case in the outer membrane of wood-cells and of vessels, and in the brown cells at the circumference of the vascular bundles in Fems." It is plain that, in the latter cases, the cell-wall had been very powerfully acted on before the application of the iodine, and to this severe preliminary ti-eatment may be ascribed the efficiency of the latter in producing the blue color. EEACTIONS OF CELLULOSE. S3 color, however, is given even bj' fresh solutions of iodine to cellulose which has been previously treated with certain cherri- cal agents, for instance, strong sulphuric acid. A convenient method of employing this reaction as a test for cellulose is to thoroughly moisten the object with a dilute so^.utiou of iodine, and then to apph* strong sulphuric acid, upon which the cellulose immediately' turns bright blue. It is sometimes advantageous to dilute the sulphuric acid employed, either with water or with glj-cerin ; but for most cases the concentrated acid is the best. Schulze's solution of iodine, better known as chloroiodide of zinc, used alone, gives with pure cellulose a blue color inclining to purple. This reaction, though not alwa3-s so prompt as the other, is generalU^ more manageable, and, on the whole, more satisfactory-. In a few instances the cell-membrane becomes j'ellowish- brown throughout, upon the application of an iodine solution, a reaction which might be easily mistaken for that which albn- minoids give ; that the color, however, is not here due to their presence, appears on subjecting the tissue to the action of Millon's reagent. Vertical sections of the stem of Begonia, as noticed by Nageli, afford an instructive example of this.^ ' That the yellow color imparted by iodine has been otherwise inter^rezbC, will appear from the following : — Harting(Ann. des So. uat., ser. 3, tome v. p. 328) states, that "all ligni£e\d those which have undergone the mucilaginous ma|i|||^Q, absorb water freely. On the other hand, the walls of ^^^^HKlS found chiefly on the exterior of organs are repellentl^HP^Lstance which imparts the repellent character to the cel^Kl^is .nJ*^°o^° as cutin ; when restricted to cork it is called sub^t -■ 157. Cutin and suberin have been described a^ifferen t sub- stances ; but although the former is more generalh/associat'sd wWii*. waxy matters, its reactions are essentiallj- the same as' yhose of suberin. The water-prooflng of the cell-wall maj^ be superficial, as in most joung epidermal cells, or it may afl"ect the whole structure of the wall, as in the case of cork. If a distinction is made between the two states, the first maj- be termed cutiniza- tion, the second, suberification. 158. Cutin can be removed from the walls with which it is associated, by the use of Schulze's macerating liquid, subsequent treatment with potassa, and careful washing. It is sometimes necessary- to heat the section in potassa before the cellulose can be completely freed from the other matters. 159. Hohnel' has shown that the wall of a cork-cell, with the exception of the 3'ouDg cork-cells in Coniferse, is composed of five plates: (1) a middle plate, common to the tvro contiguous cells; (2) two plates, one on each side of the latter, consisting of cellulose which is both cutinized and lignifled ; (3) two plates of cellulose forming the inner lining of the respective cells. The latter plates may be more or less lignifled. Differences in the relative proportions of these constituent plates give rise to dif- ferences in the character of different kinds of cork. 160. As in the case of lignin, the diflflculty of extracting cutin renders its chemical composition doubtful. It is usually given as follows : — Carbon 73-74 per cent. Hydrogen 10 " Oxygen 17-16 " But there is also a trace of nitrogenous matter demonstrable ; this probably belongs to residual protein matters which are in 1 Sitzungsber. d. k. Akad. Wien, Bd. lx.xvi. 1 Abth. MINERALIZATION. 39 the cell-cavitj', ancl not in the cell-wall. Sulphuric acid and chromic acid, even when concentrated, produce little effect on cutinized membranes, bejond removing traces of cellulose pres- ent in the cell- wall. The latter acid, however, increases the transparency of cutinized membranes, especially after prolonged action. 161. Potassic h3-drate softens such membranes and colors them yellow ; when heated it breaks them into a granular mass which may be removed bj' careful washing. Cautiouslj- heated with Schulze's macerating liquid, they disintegrate into granules of eerie acid, — a substance which dissolves in alcohol, ether, and benzol. Several of the coal-tar colors stain the cutinized por- tions of cell-walls very deeply ; if the specimen thus colored is placed in absolute alcohol, the cutinized parts alone remain colored.' Two points relative to the cutinization of epidermal cells may be noted : (1) the cutin may take on the form of lay- ers, often numerous and conspicuous ; (2) there may be a con- siderable irregularit\' in the outline of the deposits, sometimes as folds, hooks, and the like, which do not strictly conform to the cellulose wall on which they arise. 162. Mineralization of the cell- wall. Although all cell- walls, even the most delicate, can be shown to contain traces of inor- ganic matter, it is only in a few special cases that such substances appear in a form to be noticed under the microscope. Minerali- zation of the wall may be general or local, ma}- depend upon the presence of cr3-stals or of amorphous deposits, and these may consist of silicic acid or of calcium salts. 163. General mineralization of the wall depends most fre- qnentlj' on silicic acid, and ma}' be best demonstrated bj- first boiling the specimen in nitric acid, drying, heating to redness on platinum-foil, and, lastly, treating again with nitric acid. The silicic acid remains behind as a delicate skeleton which copies in all particulars the contour of the wall of which it formed a part. Fine examples are afforded by the harder grasses.^ Calcium salts ma}' exist in crystalline or amorphous form, and ma}- be distinguished by the tests to be given for them under the section on " Crystals." That in some cases they constitute an integrant part of the wall itself admits of no question. 164. In the cells of many plants, especially Urticacese, pedi- cellated concretions occur, which, on superficial examination, 1 Olivier: Bull. Soo. bot. de Fr., 1880, p. 234. 2 Tabasheer consists of tlie siliceous substances which occur in the joints of bamboo in large ijuantities. 40 THE VEGETABLE CELL IN GEMEKAL. appear to be much like the sphere-crjstals described in 18G. But if they are carefull}- treated with dilute lydrochloric acid, the chief part of the concretion disappears, leaving behind a delicate trace of cellulose which was intermingled with it. That this cellulose was an in- trusive growth into the cell from the wall, is shown bj- a studj' of its develop- ment. In most cases such concretions (C.vstoliths) are plainly- stalked, but in some instances thej' are onl}- obscurely stalked, and are with difflcultj- distin- guished from the ordinary cell concre- tions. In the leaf of Ficus elastica (see Fig. 6) the}- are more completely devel- oped than in any other common plant. 165. Otiier changes, chiefly those of degradation, maj- take place in the cell- viall, giving rise to products varfously known as gums, resins, &c. ; but in all these cases there is such a commingling of the cellulose derivatives with those formed from the contents of the cell, that they cannot be readily dis- tinguished. 166. Protoplasm, as was shown in the previous sections, gives rise upon its exterior to the cell-wall. Inside the cell, likewise, it produces, either directly or indirectlj-, various substances. In the present chapter these substances are to be considered onlj- so far as relates to their detection and identification. Most of them are to be examined later, with reference to their office in the life of plants. 167. Plastids. In the protoplasm of active cells certain gran- ules having substantially the same chemical and, with the excep- tion of their color, the same physical properties as protoplasm, are clearly differentiated. They are imbedded in the general protoplasmic mass, and are not separable from it b^- mechanical means. 168. Such grannies may be convenientlj' referred to three tj'pes,' depending upon the color : (1) those which are green, — 1 Recent investigations render It probable that these three kinds of granules are derived fi'om a common source, and although hardly distinguishable from Fio. 6. Cystolitli from the upper part of a leaf of Ficns elastica. e, epidermis; /i, liypoderma; cCy cystolitli; ch, ch, cells containing cMorophyll. It will be observed that the pedicel of the cystolith appears to be attached to the lower wall of the upper epidermal cells. CHLOROPHYLL GRANULES. 41 Chloroplastids, or chlorophyll granules, also called chloroleu- cites ; (2) those which have some color other than green, — Chromoplastids, or chromoleucites ; (3) those which are devoid of color, — Leucoplastids, or leucites. 169. Chlorophyll Granides^ or Chloroplastids, are met with in the green parts of all plants ; in fact, to them the green color is due. But they are some- times masked by the presence of color in the cell-sap. Their shape is spherical or spheroidal, and somewhat flattened. They have an average diameter of 2 to 5 fj., but many granules are con- siderably larger than this. It frequently happens that they be- come of great size, owing to the presence of solid contents, — for instance, starch, — which may accumulate in large amount. 170. If the granules are sub- jected to the action of alcohol, their coloring matter is wholly removed ; but the}' retain their former volume and shape, ap- pearing faintl}- outlined in the protoplasmic mass in which they are imbedded. Hence it is proper to distinguish be- tween the chlorophj-ll body of the chloroplastid and the chloro- phyll pigment which imparts to 7 it its characteristic color. The chloropluU bod}- may be sliown, b}' the process described in 61, to be somewhat spongy in structure, and to have on its each other at the outset, become chloi'oplastids, chromoplastids, or leucoplas- tids, according to the part which each is to play. Moreover, one kind of granule can, under certain conditions, perform work which properly belongs to another, and hence it is not always easy to identify the different kinds. In most cases, however, their discrimination is very simple. They are also called, collectively, Cbromatopbores. Fio. 7. Chloropliyll granules in tbe leaf of Vallisneria spiralis. ^5=. (Weiss.) 42 THE VEGETABLE CELL IN GENERAL. exterior a delicate film. Mej-er believes that the coloring matter takes the form of grains of extreme minuteness which are inter- spersed through the whole substance, wliile Tschireli holds that the pigment, dissolved in a liquid similar to the ethereal oils, is diffused through the mass. 171. If starch is present in large amount in chloroplastids, iodine causes at once a deep bluish-brown color ; but if the starch is not very abundant, the characteristic blue reaction is concealed by the yellow produced by the protein reaction of the protoplasm. Hence it is well, after having removed the chlorophyll pigment by alcohol and subsequent washing with water, to treat the speci- men with moderately strong potassic hydrate in order to dissolve the protein matters. If this has been well done, and the speci- men carefully freed from the potash, the protoplasmic mass and its imbedded granules will seem to have completely disappeared ; but the skilful use of oblique illumination will show that an un- dissolved trace of something having the former contours remains behind. Application of iodine brings out minute blue points where the grannies were. Chloral hjdrate of the strength recommended in 53 may replace potassic hydrate in this examination. 172. The starch in chlorophyll granules is sometimes wholly within the granule ; but it is occa- sionally — especiallj' in the case of flattened granules — found on their exterior, forming a noticeable pro- tuberance. 173. When a plant containing g chlorophyll gi-anules is kept for a time in darkness, the production of starch is arrested ; and if other forms of activity continue, even that starch which has already accumulated in the granules soon disappears. Furthermore, the color of the grannies is changed fi-om green to yellow ; and if the change is not arrested at this point by bringing the plant again into the light, all the granules will break up and be- come apparently merged in the 9a Fm. 8. Chloropliyll granules wilh protrurling starch-grains. From the cortex of Philodenilron granrtifolium. »f°. (Schimper.) Fig. 9 (i. From tlie epiflermis of Pliilodeiidron grandifollam. Young cell with amylc genie bodies newly formed. >{". (Schimper.) LEUCOPLASTIDS. 43 general protoplasmic mass of the cells, being no longer l^acog- nizable. Those, however, which have been changed no further than by loss of color, closely resemble another kind of granule ; namely, leueoplastids. (For exceptions see Chapter X) . 174. Leueoplastids. These are found in parts which are normally devoid of chlorophyll, such as tubers, rhizomes, etc. They may be wholly colorless, or faintly tinged with yellow, and hence are apt to escape detection. They may be considered as the points around which starch accumulates when stored for tlie future needs of the plant. Schimper,' who first accurately de- scribed them in all their relations, terms them " starch genera- tors ; " they are also known as amylogenic bodies, which of course means the same thing. They are seen to the best advan- 1 ScMmper: Bot. Zeit., 1880, 1881, 1883. Fig 9 &. Same, more advanced: a, tlie amylogenic bodies are covered with starch- grains; 6, two nuclei on a cell-wall, each surrounded by amylogenic bodies covered by starch. ';». (Schimpev.) Fig. 10. a. Young amylogenic bodies surrounding the nucleus of a cell in the root of Phajus grandifolius; b, same, with starch-grahis developing; c, same, more advanced, ej". (Schimper.) 44 THE VEGETABT,E CELL IN GENERAL. tage in thin sections of manj- starchy tissues, by the use of dilute tincture of iodine, which colors them more or less deeplj' yellow. Millon's reagent colors them red. Owing to the minuteness of the leucoplastids, the following explicit directions by Strasburger will aid in their detection : Make thin longitudinal sections through the upper part of a 30ung pseudobulb of Phajus grandifolius, taking care that the cut extends to its green surface. Immediately place the sections in an alcoholic solution of iodine diluted with one half its volume of water. (Picric acid may be advantageously used instead of the iodine solution.) In good preparations the leucoplastids will be seen in the inner part of the section as small staff-shaped bodies which, at the first glance, appear to be homogeneous, but are afterwards recognized as somewhat granular in structure. The section is next to be examined nearer its outer part, and it will then be seen that the bodies there possess a green color, are larger, and lenticnlar in form. They are also plainly- porous, their increase in size being apparently associated with a spongi- ness of their substance. Their size diminishes towards the outer cellular layers, they become somewhat rounded, and finallj- take the familiar form of chlorophj-ll granules. Prismatic colorless protein crystals are frequent!}- associated with these bodies. In sections which are placed in water, the leucoplastids disap- pear almost instantaneously, and even the chlorophyll granules soon begin to disorganize, while the swollen protein crystals then appear as colorless parts of the latter. In the rhizome of Iris Germanica the sections for examination must be taken parallel to the surface. In uninjured cells the leucoplastids appear as collections of protoplasm at the end of each starch-granule. If the section is in water, the leucoplastids become granular and finally break up into minute granules which show the Brownian or molecular movement.^ Chromoplastids, or the color-granules which occur abundantly in flowei's and fruits, will be specially treated later. 175. Protein granules. The protein matters in plants have been divided into two classes: (1) the active, such as active protoplasm, the nucleus, etc. ; (2) the reserve, which can change their dormant condition and become active when occasion de- mands. Inacti^'e, amorphous protoplasm, as it sometimes exists in certain cells, where it is simplj- a tough shapeless mass, does not need further consideration at present ; the reserve matters 1 Strasburger: Das botan. Practicinn, 1884, pp. 67, 68. PROTEIN GRANULES. 45 now to be examined being those wliicli take the form of more or less regular grains. These which are known as 176. Protein granules may be either independent, or asso- ciated with other substances. In nearly all cases thej- are more or less soluble in water, and hence require special treatment for their satisfactorj- examination. Colls supposed to contain them may be placed for examination in any fixed oil, and the granules will remain unchanged. A more practicable method of treatment is suggested by Pfeffer ; namely, to subject the grannies to the action of an alco- holic solution of mercuric chloride, b3- which they are rendered insolubte (see 63). The solution is made bj' dissolving one part of mercuric chloride (corrosive sublimate) in fifty parts of absolute alcohol ; in this solution the thin sections of seeds, etc., suspected of containing pro- tein granules, must be kept for at least twelve hours. Upon removal to water, after tliis period, tliej- remain substantially unchanged. The precaution must be taken not to touch with au}' metal the sections after they have been placed in the mercuric chloride solution. They must be removed bj- a eamel's-hair brush. 177. The protein matter of which protein granules consist ma}- be wholly with- out definite shape, or a por- tion may assume somewhat the form of crystals. The latter have been called pro- tein crystals or crystalloids, and they are generally associated, in the granules of which they form a part, with inorganic matters either amorphous or ci-ystalline. H,ence in some protein gran- ules we have to distinguish between the inorganic contents, the Fig. U. Cells from cotyledons of Vicia sativa, showing protein matters in a finely divided state, intermingled with starch-granules. (Schmidt.) Fin. 12. Protein granules from the endosperm of liiciiius communis. The specimen is in oil. H". (Pfetfer. ) Fig. 13. Protein granules from the endosperm of Ricinus communis. The specimen, first treated with mercuric chloride in absolute alcohol, is now in water. *^^. (Pfeffer.) 46 THE VEGETABLE CELL IN GENERAL. protein crj-stal-like bodies, and the protein basis or stroma in ■which all of these are held. The protein basis sometimes, if not alwaj's, appears to consist of two substances, differing in their solubility in water, and com- mingled as granulose and cellulose are in starch- granules. While the pro- tein basis is generallj' verj' soluble in water (not per se, but owing to the pres- ence of potassic phos- phate), the protein crj'stals are insoluble, or onlj- slightly affected by it, usually becoming more or less swollen. After solution of the protein basis has taken place, a delicate membrane is left behind, and through this transparent film tlie protein crystals are clearly seen. The relatiA'e amounts of protein basis and protein crystals varj- wideh' ; in some cases the former appears to be wanting, Ihe latter whollj" filling the interior of the mem- brane. Such crystals appear in potato-tubers in the form of small cubes. Protein crystals of great beauty are easily dem- onstrated in the endosperm of the common Brazil-nut (Ber- tholletia). Very instructive phenomena are presented when different sections of the seed are subjected to the following reagents; (1) osmic acid (one per cent solution) ; (2) heematoxylin Pig. 14. Single iirotein grnnnles treated as in Pig. 12. '{o. (Pfeffer.) Fig. 15. Protein granules tVnm Silybum marifinum. In the cell on the left they have crystalline contents; in that on the right, globoids This section was taken from the cotyledons of a dormant seed, and after treatment with mercuric chloride in alcohol was placed in water, ^nfl, (PfefTer.) Fig. 16. The mesh of the ground mass of the cell has been cleared by dilute potassic hydrate and hydrochloric acid, n = nucleus. ^\'^. (Pfeffer.) Fig 17. Cells from the cotyledons of a germinating seed which has just ruptured the seed-coat. The protein granules have disappeared, but their contents are recognizable, 'p. (Pfeffer.) Fig. 18. Silybum marianum. Cell from the cotyledon of a nearly ripe seed in which the formation of protein granules has just begun. ^5". (Pfeffer.) STAKCH. 47 in concentrated glycerin; (3) concentrated potassic hj-drate, water being added afterwards. Permanent preparations of pro- tein crystals can be made by first acting on the section with mercuric chloride for a day or more, washing in water, staining with eosin, and finally mounting in potassic acetate (101). The inorganic matters associated with the protein crj'Stals in protein granules are either (1) amorphous or globular con- cretions of a double phosphate of calcium and magnesium, known as globoids^ or (2) cr3-stalline clusters of calcic oxalate. The protein granules, espe- ciallj- those which are most com- plex in their composition, are also known as Aleurone grains. The protein crystals are generallj' termed crystalloids} For an analytical classification of protein granules in seeds, see pages 182 and 183. 178. Starch, the principal form in which the elaborated food of plants is held in reserve, occurs as minute spheroidal or pol^-Jiedral granules. Under a suf- ficiently- high power, and witii proper management of the miri'or of the microscope, the single gran- ules exhibit an appearance of stratification which is sometimes very distinct, but more commonly obscure ; in the latter case dilute chromic acid can be used to ren- der the stratification plainer. The laj-ers of stratification are ar- - often very eccentrically, as in potato 1 Tlie fact that protein crystals have, as a rule, less constancy in their angles than inorganic crystals, taken together with the fact of their swelling when immersed in water, has led authors to speak of them as crystalloids rather than as ciystals. Bat Famintzin has recently shown that certain ciystalline forms artificially produced obscure these distinctions, since they agree more closely in some of their physical characters with organic structures than with ordinary inorganic crystals (Ber. der deutsch. hot. Gesellsch., 1884, p. 32). Fio. 19. A cell from nutmeg lying in oil. In the ground mass are very numerous crystals of fat. Some of the granules are compound starch-granules, but others are protein granules with crystalloids. The rhombic granule has hardly any envelope. *^. (Pfeffer.) Pig. 20. Globoids of Vitis vinifera. ^'^. (Pfeffer.) Fig. 21. Large protein granules from Vitis vinifera. =?». (Pfeffer.) Fig. 22 Whcat-graiu, showing cells containing starch-granules. (Schinidt.) ranged around a point, ■ 48 THE VEGETABLE' CELL IN GENERAL. starch, or with great regular- ity, as in wlieat. This point is known as the nucleus, or hilum. If two or more nuclei are dis- cernible, the granule is said to be compound. 23 Occasionally manj' small sin- gle granules cohere slightly to form an aggregate which can be easily- broken. According to Wiesner, there may be as many as 30,000 granules in a single aggregate of this kind. Both simple and compound granules may occur in the same cell, but some plants have only simple, and others only com- pound granules. Canna and Curcuma may be cited as exam- 'S^J^^kf^.iSMt^i ~C^ pies of the former; Jatropha, of ^ *V;*i«^^ li the latter. Since starch occurs in every plant in all stages of development, the size of the granules must be extremely variable. Nevertheless, a statement of the more common limits may aid in their identification. Wiesner gives the following limits of size for some of the more common sorts of starch, first grouping them into small, medium, and large grannies. Small granules (from 0.002 to 0.015 mm.) : as the simple granules of rice, oats, buck- wheat ; also the smaller granules of wheat, rye, barley, etc. Medium granules (from 0.02 to 0.05 mm.) : as the compound granules of rice and oats, the larger ones of wheat, rye, and barley, the simple granules of Indian corn, and of the common leguminous plants. Large granules (distinguishable as granules to the naked eye) : as the simple granules of Curcuma leucorrhiza, Canna edulis, potato, etc. Fig. 23. Starch-granules from the bnlb of Phajus grandifoliiis, showing the nu- cleus at the upper part and the starch generator or amylogcnic body below, 'f. (Scliiuiper. ) Fro. 24. Cells from potato-tuber, showing starch-granules (Schmidt ) Fio. 25. Starch-granules from sarsapariUa. (Berg and Schmidt.) STARCH. 49 °° /^ "o * -to 27 Starch is insoluble in cold water, but forms with boiling water a paste in whicli all traces of structure are lost. If a specimen of starch be gently heated with water upon a glass slide, the granules will be seen to swell at a temperature of Q^CX^ (S»% 33 40°-50° C, and the appearance of stratification will often be- come plainer. The alkalies and mineral acids generally hasten the Fis. 26. Starcli-granulcsofwlieat. Fio. 29. Sfarcli-granules of oats. Fig. 27. Starcli-gramiles of Indian corn. Fig. 30. Starch-granules of rice. Fig 28. Staroli-granules of barley. Fig. 31. Starch-granules of potato. Fig. 32 Starch-granules of Maranta (arrow-root) Fig. 33. Starcb-grauules of Bomarla (Chili arrow-root). Fig. 34. Starch-granules of Vicia sativa, var. leucosperma. All the figures of starch are from Berg and Schmidt. 4 60 THE VEGETABLE CELL IN GENERAL. formation of starch-paste, and bring about some other changes, such as its conversion into soUible matters. 179. Starch is usually said to have the following composition, C„H|„Oj, and these proportions are doubtless correctly stated ; but it is probable that the molecular constitution is more com- plex than this formula would indicate.^ 180. When starch is acted on by saliva or pepsin, it is slowlj' separated into two substances, one of which passes into solution, while the other remains as a skeleton, and with little change of form. This delicate framework, which remains after the soluble matter is removed, is closely related to cellulose, as shown by its behavior with reagents, and has received the uame of starch cellulose. The substance which is removed by the action of saliva is termed granidose. 181. When starch is not associated with too large a propor- tion of protein matters, it can always be detected by the blue color which it takes with iodine in solution ; but if protein sub- stances are present in considerable amount, they maj- obscure the reaction by the yellowish or brown color which iodine im- parts to them. Iodine does not, however, always produce a blue color with starch ; the shade may vary towai-ds red, fcjrming a purple which may be almost black. Furthermore, as the tran- sient color given hy this reagent fades, it may pass through various tints of orange and j-ellow. Protein matters which mask the starch reaction maj- be re- moved by careful treatment of the specimen ■« ith potassic hy- drate (not too concentrated), and subsequent washing with pure water. After such treatment it sometimes happens that the starch appears as a diffused mass instead of in minute dots. 182. When starch-granules are seen in polarized light they generally exhibit two crossed lines which appear to turn as the Nicol prism is revolved. Many kinds of starch give under the polarizer characteristic figures, many of them of great beautj'. 183. Inuliu, although occurring in solution in cells, is never- theless thrown down in characteristic forms by means of the preservative media alcohol and glycerin, and can be examined as a solid. If the root of Dahlia, Ilelianthus, or anj- of the com- mon Compositse which store up their food in fleshy underground parts, be subjected to the action of alcohol for a few daj-s, thin sections will exhibit in the cells peculiar masses of a spheroidal Beitr. z. nalieren Keiintniss der Starkegruppe, 1874. INULIN. 61 form wliich are distinctly radiating in structure. Occasionally tliese masses have large rifts which run across the surface of the sphere. In composition, inulin closely resembles starch, but does not give any color with iodine. To de- tect it when in solution, a thin sec- tion of the plant containing it is moistened on the glass slide with absolute alcohol, when a cloudj- pre- cipitate will at once appear ; in a short time (the supply of alcohol having been replenished as it evap- orates) the specimen grows clearer, and small sphserocrj'stals of inulin are seen. If now the specimen is carefully washed with water, the smaller granules disappear and the well-defined remain. 184. The carbohydrates dissolred in the cell-sap maj- be grouped in two classes : (1) those whicli are isomers of cellulose (i. e., have the same per- centage composition, CuHi.iO^), and (2) the sugars. 1. The isomers of cellulose are mucilage, gums, and dextrin, all of which are probably derivatives of starch. Various sub- stances intermediate between them have been described, but the above are all that need now be taken into account. («) Mucilage, when not plainly resulting from the breaking up of the cell- wall, is colored red by rosolic acid, and the color is not readil}' removed by alcohol, {b) The gums, of which cherry gum may be taken as an example, are not tinged by rosolic acid, (c) Dextrin can be detected by Trommer's test, which Sachs ap- plies as follows : a section which is at least a few cells in thick- ness is placed in a porcelain capsule with a strong solution of cupric sulphate, and the liquid is heated to boiling ; the specimen is then washed in water, and dipped at once in hot potassa. If the cells contain either dextrin or grape-sugar, there will immediately appear a reddish precipitate. To discriminate be- tween dextrin and grape-sugar, it is merely necessary' to keep portions of the plant to be examined in 90 or 95 per cent alcohol, which will dissolve out the sugar and leave the dextrin, if any Fig. 35. Spliaerocrystals of inulin from root of Cicliory treated with alcoliol. *p. (Javobs. ) 52 THE VEGETABLE CELL IN GENERAL. is present. Usually all the grape-sugar is extracted in a day or two. 2. The sugars. Grape-sugar has been just referred to as giving the same reaction as dextrin with Trommer's test. Its formula is G^^f)^. Cane-sugar, which has the formula CjjH^jO,,, gives no red precipitate with the same test, but the liquid in the cells becomes bright blue, and quickly diffuses into the potassa.* 185. Crystals are of such general occui'rence in widely differ- ent orders of the higher plants, that there are perhaps none in which the}' ma}' not be detected. The}' have been found in nearly all parts of the vegetable structure, more commonly in the interior of parenchyma cells, sometimes in specialized crys- tal-receptacles, occasionally in the very substance of the cell- wall. They occur either singly or in groups ; either separate or barely coherent, or in various degi-ees of combination. When solitary and simple the}- are usually octabedra or prisms, and their aggregations are combinations of these. Good octahedral crystals are afforded by the petioles of Begonia ; examples of the prismatic form are found in the outer scales of onions, in-orange leaves, in the inner bark of maples and apple- trees, and in most of the tissues of Iris and its allies. When the prisms are very long and slender their angles and faces are seldom well defined.^ Indeed, the most attenuated forms are usually terete, or slightly flattened, and taper gradually to a point at both ends. To these De CandoUe long ago gave the name Maphides, — that is, needles.^ These are generally massed in a compact bundle, like a wheat-sheaf, occupying a large part of the interior of the containing cell. Raphides are by no means of such general occurrence as are ordinary crystals, but (as Gulliver has pointed out) are seemingly restricted to certain orders.* The}- are universal in Araceae and Onagracese. In the common Arums and Callas, raphides-bearing cells may readily be found in the parenchyma 1 Pringsheim's Jahrb., iil. p. 187. In the Sitzungsber. d. k. Akad. Wien, foi' 1859, Sachs has given colored figures illustrative of these reactions. 2 When the longer prisms are clearly defined, they are referable to the mono- elinie system. Measurements of angles are given by Holzner, in Flora, 1864, p. 292. A paper by Bailey (Am. Journ. of So. and Arts, vol. xlviii., 1846, p. 17) also contains determinations. ' Organographie, 1827, p. 125. * Gulliver has examined representative plants of all the more important orders of the British Flora, with respect to the occurrence of diagnostic crys- tals (Annals and Magazine of Natural History, 1863 to 1867). CRYSTALS. 53 of the leaves, and detached entire ; on becoming turgid when wetted, they will usually discharge their raphides one by one from one or both ends of the cell until the bundle is almost exhausted.^ 186. When the ordinary' octahedral or prismatic crystals are aggregated or combined, they generally compose a spherical mass. Such aggrega- tions are of two principal types : ( 1 ) those made up of many small crystals irregular- ly grouped, and usually- presenting sharp points over the surface, as in Fig. 36 a; (2) those with a distinctly radiated structure (Fig. 36 1). Good examples of the former are abundant in the foliage of Chenopo- diaceas and the stems of Cactaceffi. Clusters belonging to the latter, or stellate, t3'pe are not uncommon in Malvaceae. Both forms have been termed SphcBraphides ^ and Sphere-crystals. The term cystolith, sometimes improperly applied to them, should be whollj- restricted to the peculiar bodies described on page 40. 187. Owing to the mechanical difficulty of isolating plant- 1 Turpin (Annales des Sc. nat., ser. 2, tome v., 1836) described the raphldes- beaving cells of Caladium, in which tliis discharge takes place, under the name of Mforines. 2 " They are most irregularly scattered through the tissues of the plant. ... I have never failed to find them in a single species of the order Caryo- phyllacese, Geraniaceae, Lythi'acese, Saxifragaceae, and Urticaceas, and believe that few if any orders could be named in which sphseraphides do not exist as part and parcel of the healthy and growing structure of the plant " (Gulliver, in Annals and Magazine of Natural History, vol. xii., 1863, p. 227). Fig. 36. The more important forms of crystals of calcic oxalate: a, three cells from" the petiole of Begoni.i maiiicata ; 6, from the leaf of Tradescantia discolor ; c and d, from the leaf of Allium Cepa; e, from the inner bark of .iEsculus Hippocastamim ; /, from the leaf of Cycas revoluta; g, a cell containing raphides, from the frond of Lemna trisiilca; A, a single crystal from the same, more highly magnified ; i, sphjero- crystal from Phallus caninus. (Kny, ) 54 THE VEGETABLE CELL IN GENERAL. crystals for examination, tlieir chemical composition has not jet been determined with certainty in all cases. Tliat a protoplas- mic film usually envelops both solitary and aggregated crystals, can be shown by the method pointed out hj Pa3-en ; ' namely, 1)3' dissolving tlie crystal slowly in very dilute nitric acid, and testing with iodine, when the film will become yellowish-brown. It has also been made out be3ond question that some crystals have a considerable admixture of cellulosic matter, and that a few others are covered by a membrane of cellulose.'' But these two substances do not obscure the chemical reactions in ordinary- cases, by which it has been shown that the larger number of crys- tals consist of calcic oxalate, after which, in frequency of occur- rence, comes the carbonate of the same metal. These two salts can be easily distinguished from each other by the following simple tests : — Reagent. Calcic Oxalate. Calcic Carbonate. Acetic acid. Hydrocliloric acid. No effect. Dis.solve.s without ef- fervescence. Dissolves witli effer. veseence. Dissolves with effer- vescence. Since those two salts may occur in the same specimen, it is best to use acetic acid first ; by this agent all traces of the carbonate are removed, and hydrochloric acid can then be applied in order to detect the presence of oxalates. Sanio ' and Holzner have shown conclusively that many crystals which have been supposed to be calcic carbonate consist merely' of the oxalate. Crystals of calcic sulphate have been repoi'ted as occurring in certain Musacea?,' in the bark of the willow, in the roots of aconite, bryony', and rhubarb ; and also in the root of a 3'oung bean.^ Calcic phosphate is said to have been detected in the 1 Payen : Mem. des savants Strangers, ix., 1846, p. 91. 2 Eosanoff (Bot. Zeit., 1865, 1867), Crystals in pith of Ricinus and Kerria. Pfitzer (Flora, 1872), crystals in the leaves of orange and the bark of many trees. Hilgers has investigated the occurrence of crystals at different periods of growth of different oi-gans. From his results it appears, (1) that in the veiy youngest parts no crystals are to be found ; (2) they appear, however, very early in most parts, and (3) speedily attain their maximum size, after which they undergo no change (Pringsheim's Jahrb., vi., 1867, p. 285). s Sanio : Monatsber. Berliner Akad., 1857. * Van Tieghem ; Traite de Botaniqup, p. 526. * Sitzungsberichte der Wiener Akad., xxxvii., 1859, p. 106. CRYSTALS. 55 wood of Tectona grandis (Indian Teak).^ Holznei ' uses the following reaction to detect calcic sulphate : a solution of baric chloride (not too concentrated) is brought into contact with the crystal under examination ; calcic sulphate soon becomes covered with a whitish deposit of baric sulphate. This test failed to show the presence of calcic sulphate in the plant- crj-stals hitherto referred to this salt ; thej- all gave, however, the reaction for the oxalate. 188. Crystals closely resembling in most respects those which are found in cells can be produced by Vesqne's method.'' Three test-tubes are placed side bj' side : in the first is a moderately' strong solution of calcic chloride ; in the middle one, a five per cent solution of sugar; and in the third, a solution of potassic oxalate. From the liquid in the first to that in the second a short strip of filtering-paper runs, and a similar strip passes from the second to the third test-tuhe ; and thus the liquids in the three tubes are brought into indirect contact. Ciystals will be formed in the middle tube, their character depending upon the nature of the liquid there. In a solution of sugar, raphides are produced ; in pure water, prisms of small size, but with sharpl}- defined faces and angles. 189. According to Souchay and Lenssen,^ monoclinic (" Clino- rhombic ") crystals of calcic oxalate containing two equivalents of water are produced upon quick precipitation, while bj' very- slow action right octahedra with six equivalents of water are formed. A few works of reference are the following : — MoHL. Principles of the Anatomy and Physiology of the Vegetable Cell. Translated by Henfrey (London, 1852). An octavo of 158 pages. This is an excellent translation of a classical work. HoFMEiSTEB. Die Lehre von der Pilanzenzelle (Leipzig, 1867). An octavo of 397 pages. The volume treats very fully of the physical properties of pro- toplasm. Ebermayek. Physiologische Chemie der Pflanzen (Berlin, 1882). This is the first volume of an expensive work which deals with the relations of plants to soil and climate. HusEMANN und HiLGEK. Die Pflanzenstoffe (Berlin, 1882). Two large volumes. It has very extensive references to the literature of the subject, and most of its abstracts are excellent. 1 Pies : Faturkundig Tijdschrift voor Nedrlandsch-Indie, 1858, p. 345. Quoted from Holzner. ^ Flora, 1864, p. 283. This communication contains a good abstract of the literature of plant-crystals up to 1862. ' Ann. des Sc. nat, ser. 5, tome xix., 1874, p. 300. * Annalen der Chemie und Phai-macie, c, 1856, p. 311. CHAPTER II. CELLS IN THEIR MODIFICATIONS AND KINDS, AND THE TISSUES THEY COMPOSE. 190. "While ciyptogamous plants of the lower grade may consist of single colls, or of a series or stratum of simple and undifferentiated cells, pliiBnogaraous plants, although equallj' simple and homogeneous at the initiation of each individual, develop into a more complex organization, at an earl^' period differentiate some of their cells into peculiar kinds, multiply the kinds into tissues or fabric, and of these build np the organs and parts which are familiar in ordinarj- vegetation. 191. The inicroscropical studj- of the parts even of a single herb or tree, and much more that of a variety of plants, reveals numerous forms or kinds of cells, and also (as might be expected from their common origin) brings to view series of gi'adations between the kinds, sometimes even between those which are, upon the whole, widely differentiated from each other. While, therefore, a general classification of the cells of any ordinary plant into kinds is easj-, any classification which shall satis- factorilj- exhibit our present knowledge of the histological ele- ments, and discriminate their varieties, is very difficult, if not at this time practically impossible. At least, it must be said that the most recent classifications are based upon considerations of a character too recondite and special to be mastered at the beginning by an ordinarj- student. 192. The most general and obvious division of the histological components of a stem, root, or leaf would be into, (1) funda- mental or typical cells, and (2) transformed cells. The first are those in which the normal cellular character persists without pro- found, if an^-, alteration or disguise ; as in the pulp of leaves, the pith of stems, and in a portion of the bark. The second are those which assume or affect lengthened or fibrous forms and a longi- tudinal development (at least in all axes, and commonly in leaves and other expanded organs), and, combined into threads, fasci- cles, bundles, or more massive structures, constitute the frame- work, which imparts solidity and strength throughout. Some TYPICAL CELLS. 57 of these cells are so long in proportion to their breadth, and of such diminished calibre, that they have naturally been called fibres, although all gradations between them and tj-pical cells maj' be demonstrated. All these cells are interchangeably called woody fibres or w^ood-cells, and one kind of them takes the name of bast-cells. 193. Others are of larger calibre, are peculiarly' marked by thickenings on certain lines or in certain patterns, incline to be developed end to end in a chain or row, and to become confluent at the junctions, so as to form conduits of considerable length ; these are called vessels, or ducts. Vessels and fibres are associated in the plant ; almost ever^- separate thread of frame- woi'k consists of both, and so is called a fibro-vascular bundle or fascicle. Moreover, the known gradations between the two arc such as to render a complete distinction between them near!}' im- practicable ; so that thej' form tlie fibro-vascular, or, when a single word is used, the vascular sjstem. To this system, also, pertain specially diffferentiated cells, such as cribrose-cells, in the bark, etc. 194. All these are developed in or among the fundamental or untransformed cells, and originate from the differentiation of some of them. 195. The fundamental or tj-pical cells may therefore be said to constitute the fundamental sj-stem ; whicli maj- also be con- veniently called the cellular system, in contradistinction to the vascular. 196. In an ordinar\' leaf it forais all but the framework of ribs and veins ; in the stem of a dicotj-ledon, the outer bark, the pith, and the rays wliich traverse the wood ; in that of a mono- cotj-ledon, which generally has a looser texture than the last, it is the common mass through which the definite bundles of the vascular s^'stem are distributed. Of the fundamental system, the most typical or unmodified cells are such as the chlorophyll- bearing cells of leaves and of the gi'een bark of stems, as well as those with uneolored contents forming the pith, etc. Borrowing a word from the old anatomists, the early investigators of vege- table structure called tissues composed of such cells Parenchy- ma, perhaps taking the idea of the name from leaves in which the veins are distributed througli the softer parts as blood-vessels through the parenchj-ma of the glands. 197. Parenchyma, therefore, is tiie name of cellular tissue In contradistinction to fibro-vascular tissue. In its primary sense, only comparatively- soft and thin-walled cellular tissue 58 MORPHOLOGY OF THE CELL. took this name, and this is indeed typical parenchyma; but the name rightly includes, :is species or varieties, thicker-walled and even solidified tissues composed of cells similar in other respects to the type, as those in the hard endosperm of seeds. 198. A counterpart mime, Prosenchyma, was emploj-ed to designate tissues formed of elongated cells, such especially as wood-cells and bast-cells. These being usually thick-walled, and those of t3-pical parenchj-ma thin-walled, this character was brought into the definition ; that is, cells of prosenchj-ma were said to be thick-walled as well as long and narrow, those of parenchyma thin-walled as well as isodiametric. But this dis- tinction does not hold out well. All fibro-vascular tissues are thlu-walled at first, and some remain so ; while portions of pure parenchyma ma3- become thick-walled, firm and hard, or take on every intermediate condition. So that prosench3-ma ma}- be best held to denote tissue of the fibro-vascular system, and typically that formed of wood-cells.^ 199. An explanation of the mode of production, multiplica- tion, and ti-ansformation of cells is deferred to a later stage. Suffice it here to advert to the fact that every phsEuogamous plant, originating in the seed, begins as an isolated cell, which develops into a globular cluster of parenchyma cells, and grows into the embryo or rudimentary plantlet, taking on the shape and degree of development characteristic of its kind. In embryos which are considerablj' developed in the seed, tiie axis and be- ginnings of tlie leaves are already outlined or rudimentarily indicated there ; in otliers the indication takes place in the early stages of germination. 200. From this if not from an earlier period development is no longer homogeneous. A superficial layer of the common parenchj ina becomes distinguishable as the epidermis ; while in an inner zone, or at special points, certain cells develop into ducts and wood-cells (prosenchyma), and thus are initially delineated the outlines of the systems or regions which are to characterize the whole growth; namely, — taking a dicotyledonous embryo for the type, — an epidermal layer, a cortical layer, a fibro-vascu- lar zone, and a medullary- portion. As stem and root develop, these primordial tissues complete themselves and have only to go on growing, each after its kind ; but at the developing points (aijex of the stem and of the root), as also in special portions or 1 " Zu dem Prosencliym ini ■neitern Siinie konnen wir auch die Gefasse ziihlen " (Niigeli : Beitrage, i. p. 2). CLASSIFICATION OF CELLS. 59 zones, initial differentiation continues. Here the nascent tissue, consisting of parenclij'ma cells, multipl3-ing by successive divi- sions, and also tlie nascent proseuch^-nia as it forms and while still capable of further division, has been named Meristem. 201. Meristem, therefore, is not a kind of tissue, but the nascent state or earlj' condition of any tissue. It is developing parcuchj-ma, either multiplying as such, or differentiating into elongated forms, as for instance, in cambium. Leaving the processes of cell-development to be considered under the head of "Growth," and tlic disposition of cells and tissues in the fabric to be described under the several organs (root, stem, leaf, etc.) which they compose, the kinds of cells are here to be indicated, without particular reference to their arrangement in the plant. In all classifications of objects which are understood to have been developed from one type, interme- diate forms of almost ever}- gradation are to be expected. It is specially so witli plant-cells ; and of them it should be said, once for all, that the kinds which have received distinct names, with or without sufficient reason, are only t3pes, or leading modiSca- tions, — some of a very marked, some of a quite subordinate character.' 202. Plant-cells are to be described in this chapter under the following classification : — I. Cells of the fundamental system, or parenchyma cells, — permanent t3-pical cells. 1. Parench3ma cells, strictl}' so called, including as modi- fications collench3-ma cells and sclerotic parench3-ma cells, or grit-cells, such as the lignified cells of seed- coats and drupes, etc. 2. Epidermal cells, and their modifications; e. g., Tri- chomes. 3. Cork-cells, forming suborous parenchyma, or cork. II. Cells and modified cells of the fibro-vascular system, — pros- ench3-ma in the widest sense. 1. Cells of prosenclyma proper. a. Typical wood-cells and wood3' fibres, including libri- form cells (Sanio), and the secondar}' wood-cells (De Bary). b. Vasiform wood-cells, or Trachcids. J Sometimes a single cell in a uniform tissue may develop nnlike its neigh- bors as regards one or more of the following characters : form, size, nature of cell-wall or cell-conteiits. Such cells are termed by Sachs, idioblasts. 60 MOEPHOLOGY OF THE CEIii. 2. Vessels, or ducts. a. Dotted. b. Spirally marked. c. Annular. d. Reticulated. e. Trabecular. 3. Bast-cells, Bast-fibres, or Liber-fibres. III. Sieve-cells, or Cribrose-cells. IV. Latex-cells. Intercellular spaces and canals are neither cells nor tissues, but they require consideration in connection with them. I Cells of the Fundamental System, — Parenchyma in the widest sense, including Modifications for Protective Surfaces. PARENCHYMA. 203. This term is applied at present to all typical cellular tissue except that which belongs to the epidermal system. It therefore constitutes the mass which sur- rounds fibro-vascu- lar bundles, forming pith, medullary rays, the pulp of leaves and fruits, etc. It occurs in nearly all parts of all plants. The elements of parenchyma are sim- ple cells more or less separable from each other, in some cases bj- slight pressure, and iu others by the cautious use of a macerating solution. The cells vary greatly in form, but usually are polyhedral or spheroidal. Extended classifications of the cells themselves, based upon form, have been made, but they arc of no utility and of small historical interest. Yet three principal shapes ma^' well be distinguished ; namely, short or isodiametric, elongated, and flattened. Fig. 37. Parencliyma from stem of Marrubiuiu. i}», (Jacobs.) PARENCHYMA. 61 204. In the j-oungest state of organs short parenchj-ma cells form the whole mass ; here they are relatively small, filled with protoplasm, and have no intercellular spaces. Later they are changed in shape and size, may have conspicuous in- tercellular spaces, and the protoplasm may be replaced, at least in part, by other matters. 205. If the cells are loosely aggregated and have conspicuous in- tercellular spaces, the tissue is called spongy parenchyma. The cells in such cases are apt to be more or less branched, and in some plants assume regular stellate forms. 206. Elongated parenchyma cells are generally more com- pactly combined than the short ones. They are well seen in the upper part of most leaves, whore they have received the significant name palisade^cdls. 207. Flattened parenchj-ma cells are the common form in the vertical plates (medullarj- ra3"s) which radiate from the pith to the bark in woody plants. 208. The walls of t3-pical pa- renchj-ma cells are thin, and may be variously marked with pits, especially at the points of con- tact with other cells. Thicken- ing threads forming reticulations and spirals are not uncommon ; the latter occur in the aerial roots of OrchidaceiB. A crum- pling or folding-in of the wall is seen in some of the cells of pine leaves. Fig. 38. Forms of parencbyma in leaf of Pyrus communis. (Jacobs.) Fio. 39. From pitli of Sambucus uigra, showing pitted walls. (Oris. ) 62 MOBPHOLOGY OF THE CELL. 209. Thin-walled parenchyma cells play an important part in assimilating and storing, and special names are given to cells which have these offices, such as clilorophyll parenchyma, starch parench^'ma, etc. In the tissues of most succulents, and in the leaves of a few plants, some of tlie parenchyma cells are filled witli clear sap and more or less mucilaginous matter, and con- stitute the so-called water tissue. 210. The walls of typical parenchyma cells consist of ordinary cellulose ; but even slight deviations from the tj'pe furnish good illustrations of lignified and of cutinized membranes. 211. Ligniflcation may increase the thiclcness of the cell-wall, greatly reducing the cell-cavity, or it may merely- harden the membrane without much thickening. The parenchj-ma cells found associated witli other elements in. woody tissues liave walls of the latter character ; the grit-cells in pears and many other fruits show good examples of the former. Such hai'dened cells are called sclerotic parenchyma cells. FiO. 40. Sclerotic parenchyma cells from fruit of the pear. (Weiss.* ENDODERMIS. 63 In many cases it can be shown thickened walls, as shown in Fig. 41.1 212. Certain modified pa- renchyma cells are often united to form sheaths around flbro- vascnlav bundles. These cells are prismatic, and in close apposition. Their walls are thin, except at their faces of mutual contact, where they are conspicuously thickened, and often plicate, and nearly all parts of the membrane are more or less cutinized. that canals run thronwh these 213. These cells con- stitute the endodermis. The}- generally contain a large amount of starch. 214. Parenchyma cells may undergo the mu- cilaginous modification (see 147), as in the con- ductive tissue of the stjle of man}' flowers and the albumen of many seeds. This change is common also in the lower plants. 215. An appearance closely resembling in some points that pro- duced by the mucilagi- nous modification is pre- 1 A second kind of sclerotic iiavenchyma sometimes accompanies the longer sclerotic cells in a few •ferns and son)e monocotyledons. Its cells appear as if segments of a jointed fibre, somewhat flattened on the side next the long cells, and decidedly convex on the other. Such flattened cells are unequally thick- eiied on the two sides, and the walls are somewhat siliciHcd. But the most striking feature in many cases is the deposition within the cavity of the cell of a mass of silicic acid ; this is well seen in the hard cells which accompany the fihro-vascular threads in the leaves of some palms. Fig. 41. A sclerotic cell from the nutshell of Juglans regia. (Reinke.) Fig. 42. Section tlirough the central cylimier of a binary root of a vascular crypto- gam (Cyathea meUullaris). p, r, r = endodermis. (Van Tiegliem.) 64 MOEPHOLOGY OF THE CELL. sentecl by the parenchyma cells just under the epidermis, or outer layers of cells, in many plants. The cell-wall is thickened a b very considerably at the angles, and upon the application of dilute acids swells greatlj-, but without becoming clearly muci- laginous. When moist, such cells have a bluish- 0?^ 44 white color and a marked lustre. They are known as 216. Collenchyma cells. They are generally some- what elongated, and so united as to form threads which possess great strength, and are believed to serve an important me- chanical office in the plant. Good examples of these are afforded by the stems of manj' Umbelliferae. EPIDERMIS. 217. This is the outermost layer of cells covering the sur- face of the plant. In some of the higher plants it persists with little change throughout the life of the organism ; in others it is Fig. 43. Pavencliyma with wnlls which have undergone the gelatinous modification: a, from tlie centre of the style of Salvia scabiosaefolia ; b, from the stigma of Gesneria elongata. (Capus.) Fio. 44, Transverse section of root-stock of Smilaclna bifolia, showing collenchyma cells just under the epidermis, ep. Note also the ordinary parenchyma atpc, and the endodermis at ap. (Van Tieghem.) EPIDERMIS. 65 sooner or later thrown off, and replaced by a subjacent protective tissue, — cork. 218. Except at peculiar openings (stomata, etc.), the epider- mal cells are in close apposition. Upon their exposed surface the}' are cutinized, and thus a continuous hyaline film is formed, known as the Cuticle?- 219. Sometimes the epidermis may be torn off without much disturbing the underlying tissues. 220. Besides the cells which compose the proper tissue of the epidermis, there are certain ap- pendages or accessory structures, mainlj' hairs or analogous pro- ductions (together called tri- chomes) , and peculiar cells which constitute the stomata. 221. Epidermal cells proper are in uninterrupted contact. They are usuallj' of a tabular or pris- matic form. The lines which mark their outlines as viewed from above are sometimes straight, but oftener sinuous, at least on the longer sides of the cell, which here as elsewhere correspond with the direction of growth. Near stomata and trichomes the cells frequently assume very irregular forms. 222. Their upper or free surface is generally slighth" convex, and often has minute outgrowths, for instance, in velvety petals ; when these arc larger and longer, thej' constitute the simplest form of plant hairs. 223. Delicate epidermis possesses thin walls ; but in a large number of fleshy and tough plants the walls have considerable thickening, j'et not always on the same part. Thus in the leaves of Cycads the upper wall is the thicker ; in many Bromeliaceae, the lower and side walls. In a few cases the cell-cavit}' is nearly filled by the thickening material. Stratification, striation, and pitting of the cell-wall may also occur, great diversity existing in all these respects. 224. When tlie epidermis is ver}' delicate, the demonstration of the thiu film of cuticle requires great care in the emploj^ment 1 By De CandoUe the tei"in cuticle was applied to the layers of epidermal cells, and not restricted to the cutinized film (Physiologie, 1832, p. 109). Fig . 45. Stoma of Sambucus nigra surrounded by epidermis. 5 66 MOKPHOLOGY OF THE CELL. of the reagents. According to de Barj-,' the cuticle merely covers the pure soft cellulose membrane of the epidermal cells when these are thin-walled ; but when the walls are thicker, especially in epidermis which is long-lived, that part of the cell- wall which borders on the cuticle becomes infiltrated with cutin, and thus there arise one or more layers of modified cellulose, each of which exhibits the reac- tions of cutin. When such cells are treated with warm potassic hydrate (a ten per cent solution is, on the whole, strong enough), the cutin is slowlj- removed, and the cellulose wall remains, although with con- siderable loss of substance. Walls which are thus impregnated with cutin in strata form cuticularized layers? The management of a warm solution of potassic hydrate, in order to obtain satisfactorj' re- sults in the demonstration of the fine stratification, demands much care. It is advisable to appl^- very gradual increments of heat to the glass slide in the case of the more delicate specimens. 225. Waxy and resinous matters are frequently associated with the cuticle. In some cases the amount of such substances is large, and assumes commercial importance. The young leaves of the wax palm (Ceroxylon andicola) are said 1 Vergleichende Anatomie, p. 80. 2 This division into apparent lamellse can lie easily demonstrated in some cases by the application of cliloroiodide of zinc, which imparts a yellowish color to the thick film, except at its outer surface. Mohl explained the struc- ture of the exposed cell-wall in Viscuni album, where the film is very thick, as follows : "The epidermis cells consist here of two or three generations enclosed one within another, of which all the thickened walls on the outer side have become blended together into a membrane composing the cuticle. These layers are to be called the outicular layers of the epidermis, to dis- tinguish them from the mass secreted on the outside of the cells, the true Fig 46. Transverse section of the leaf of Aloe verrucosa: a, section in water, — the' non-cuticularized parts of tlie membranes shaded; above these are the cuticular layers covered by the cuticle proper ; 6, section heated in potassic hydrate ; the cuticle proper has been raised from the cuticularized layers; c. section boiled in potassic hy- drate; cuticle proper removed, epidermal cells separated, outicular layers distinguished by finer stratlllcatian. EPIDERMIS. 67 to yield twenty-five pounds of wax to each tree. Bayberiy wax is a more familiar example. 226. To such waxy coatings is due the glaucous appearance of the lea\'es and fruits ol' many plants. The coatings are chiefl3' of the following kinds (de Bary ') : — 1. Coherent laj'ers or incrustations upon the epidefmis. 2. Crowded vertical rods of considerable length, as, for instance, those on tlie internodes of Saccharum offlcinarum, from ten to fifteen hundredths of a millimeter in height. 3. Very short rods or rounded grains. These, on the leaves of Tropoeolum, are not very near together, but on those of the cabbage, tulip, etc., are more crowded. 4. When the grains are more minute, and have the shape of needles irregularly massed together, they constitute the peculiar bloom of the leaves of Eucalyptus, Eicinus, etc. 227. Between the above kinds there are many intermediate ones, Agave Americana, for instance, furnishing forms between the two last named. 228. Epidermal cells proper have a delicate lining of proto- plasm and a distinct nucleus. The cell-sap is generally colorless and transparent, allowing light to pass with very little obstruc- tion to the layers beneath the epidermis ; but in some cases it is so colored as to impart a conspicuous hue to the plant. In manj' water-plants there is no well-marked distinction be- tween epidermis and the subjacent tissue, even the cells of the upper layer containing chlorophyll, but epidermal cells are mostly free from either chlorophyll or starch. Brongniart has shown that some amphibious plants have chlorophyll in the epidermal cells of the aquatic but not of the terrestrial form. That the rule is not universal is shown by Callitriche, which, according to Hegelmaier, has epidermis without chlorophyll in both forms. 229. Epidermis usually consists of only one stratum of cells, but it may be made up of two, three, or even more layers. Division of the original epidermal cells by one or more partitions parallel to the surface of the leaf gives rise to superposed cells ; and thus multiple epidermis results, as in the upper surface of cuticle, which is soluble in caustic potash, and in most cases forms but a very thin coating over the epidermal cells" (Veg. Cell, Henfrey's trans., p. 35). Good examples for study of the different kinds of cuticular infiltrations are afforded by the following, — leaves of Dianthuscaryophyllus, Galanthus nivalis, Ilex, Finns, Hoya, Sassafras, and Taxus, and twigs of Viscura and of Oleander. 1 Botanische Zeitung, 1871. 68 MORPHOLOGY OF THE CELL. the leaves of man}- species of Peperomia, Ficus, and Begonia. Multiple epidermis is not alwa3S of even thickness throughoiit ; sometimes a portion may be oiih' one or two cells thick, while adjacent portions are composed of man}- lajers. Such differ- ences are generall}- associated with the occurrence of stomata, hairs, etc. The subjacent cells in some forms of multiple epi- dermis are smaller than those above them, and in tliese eases the arrangement of the cells in the successi\-e laj-ers presents striking inequalities. 230. Trichonies. Under this term are included the multifarious forms of hairs, scales, bristles, and prickles. Hairs are sometimes of diverse forms on the same plant, and even on the same part, but sometimes so pecu- liar and uniform throughout large genera, or even orders, that they aid in their iden- tification ; as, for instance, in MaipighiacesE, Loasacese, and Elseagnaceae. 231. Simple hairs, whether branched or unbranched, are formed by the prolongation of a single epidermal cell, either slight, forming a mere papilla, or to a great length, as in the so-called fibres of cotton. Simple hairs are abundant upon the rootlety of most plants at a little distance behind the ad- vancing tip, where they play an important part. 232. Compound hairs are of all degrees of com- plexity. They may start from a single cell, or from a group of cells, and may have the derivative cells arranged in many waj-s. The cells at or near the 47(1 Fro. 47 a. Upper portion of a glandular hair of Mart^niiaproboscldea. if. (Martinet.) Pig. 47 6. View from above, of the upper portion of the same. i}". (Martinet) Fig. 48. Cynoglospum officinale. Longitudinal section through a young angular bristle at the beginnitig of the thickening. ={'. (Strasburger.) TRICHOMES. foot of the hair may differ somewhat in shape, size, and arrange- ment from the other epidermal cells. The}- ma}' form an emi- nence upon which the foot rests, or they may be somewhat sunken so that the body of the hair hardly reaches the general surface of the epidermis ; but usually the hair projects for a considerable distance above the border of the depression. Both simple and compound hairs may be variously curved and branched, giving rise to stellate and many other forms. 233. Scales are trichoraes which are mostly compound, and consist of discs borne hy their edges or cen- tres, either with or without a short foot or stalk. If the disc is com- posed of radiating cells, the scale becomes stellate, a form which re- sembles or passes into the stellate and tufted hairs common in Mal- vace£E, etc. Well-marked stellate scales are met with in Oleaceoe and Elaeagnacese. 234. JBristles, pricMes and epidermal spines are firmer or stouter outgrowths. When such outgrowths are trulj' epidermal, the}- come off with the epidermis. Hairs, scales, and prickles differ very greatly as to their per- sistence, some being exceedingly short-lived, as, for instance, the hairs which occur on roots ; while others, for instance the prickles on the rose, last for long periods. 235. In certain outgrowths from the edges of leaves or else- where the structure is complicated by the presence of a portion of the underlining framework. This is notabl}- the case in the fringe upon the leaves of Droserace£e. There are all degrees of variation between such trichomatous outgrowths and spinulose teeth, or lobes. 236. The consistence of the cell-wall in trichomes varies widely, from extreme tenuity to the densitj- of a silicifled wall. The more delicate hairs are transparent, so that the contents Fio. 49. Branching unicellular hairs: a, from Hamulus (the hop); b, stellate hair of Deutzia. (Van Tieghem.) 70 MORPHOLOGY OF THE CELL. 238. Stomata. can be plainly seen, thus affording opportunity for examining the movements of ])roloplasn;i, and for the study of the effects of reagents upon the contents of cells. Young hairs contain miich protoplasmic matter; at a later stage they have a large proportion of cell-sap ; still later many are filled only with air. 237. At first tlie epidermis is always completely continu- ous, the cells being in close contact with each other; but soon there appear, especially in leaves, guarded openings through which the interior of the plant is brought into com- munication with the surrounding atmosphere. Tliese apertures are of two principal kinds, the most important and widely dis- tributed being These are combinations of epidermal cells of a peculiar character, between which a narrow slit extends directly through the epidermis to an intercellular space be- low. The cells bordering the slit are well termed guardian cells, on account of their opening and closing under certain circumstances. The neighboring epidermal cells are frequently arranged in a definite order ; and the po- sition of the stoma has in many cases a plain relation to the underlying framework. Stomata belong especially to green organs exposed to the air t but they have been detected on all superficial parts of the plant, with the exception of roots.* 239. Viewed from above, stomata appear generally as elliptical bodies through which runs a narrow slit in the direction of the longer diameter. Each guardian cell is therefore half the ellipse. The cleft varies in width according to certain external condi- 1 The following cases are cited ty de Bary (Vergl. Anat., p. 49) : On rhizo- inata and tubers (young potatoes), on tbe perianth, the anther (in Lilium bulbiferum), on the pistil, on the seed-coat (Canna). Plants destitute of chloro- phyll may also be destitute of stomata, as in Monotropa Hypopitys ; or have them only on the pistil, as in Lathraia. Pio. 60. Arlult stoma of Hyacinthus orientalls, seen from above. (Strasbnrger.> Fig. 51. The same, seen from below. STOMATA. 71 tions hereafter to be described, the stoma being in fact a deh- catel}- balanced valve. A vertical section shows that the outer part of the opening is wider than the narrow passage farther down, and that the space below this widens somewhat towards the intercellular cavity.^ 1 The following table, compiled from figures given by Weiss, gives the num- ber of storaata on the upper and under sides of the leaves of various plants for the most part readily pi-ocurable by students. To sliow the wide differences in size, the longer and shorter diameters have been added, and, finally, the frac- tion of a square millimeter covered by a single stoma. Name of plant. Abies balsamea Abies nigra Acer Pseudoplatanus, L. . . Amarantus cauilatus, L. , . Anemone iiemorosa, L. . . . Asclepias incaruata, L. , . . Aveiia sativa, L Berberis vulgaris, L Betula alba, L • Brassiua cileracea, L Buxus serapervirens .... Caltlia palustris, Ij Euphorbia Cyparissias, L. . Ficus elasticti Galantlius nivalis, L . . . . Geranium Robertianum . . . Heliantbus annuus, L. . . , Hydrangea quercifolia, Bertr. Ilex Cassine Juglans nifira, L, . . . Lilium bulbiferum, L. ... Madura aurantiaoa, Nutt. , . Mim.osa pudica, L Morus alba, L NyrapliiBa alba, L Piiius Strobus, L Piuus sylvestris, L. .... PisuiQ sativum, L Pittosporam Tobira, Alt. . . Populus dilatata, Ait. . . . Ribea aureura, Pursli .... Secale cereale, L Sequoia gigantea (young plants) Sileiie inflata, Sm. Solanum Dulcamara .... Stellaria media, Sm Syriuga vulgaris, L Vinca minor, L Vinca minor, var. variegata . Zea Mais, L Number in sq. mm. 31 171 67 219 30 176 460 142 BO 101 55 71 60 128 91 228 82 400 67 191 27 229 237 301 208 43 259 145 55 297 325 330 213 461 62 251 71 2r6 145 25 82 166 263 477 4(15 158 0.047 0.042 0.024 I 0.012 j 0.020 045 0.026 1 0.051 i O.OGO 0.033 0.029 032 042 0.027 0.028 0.034 045 0.034 0.020 0.029 0.024 0.071 0.022 (0.017 I 0.026 I 0.018 I 0.029 0.026 0.051 0.034 0.024 031 ; 035 0.0:J3 0.036 0.051 0.053 0.033 0.021 029 O.OiS 0.029 0.024 0.037 0.031 0.027 017 I 0.012 j 0.017 040 018 I 035 i 0.050 0.022 0.018 0.031 0,03* 0.018 019 0.022 0.032 0.023 0.019 0.025 018 0,050 0.016 I 0.009 I 0.015 I 0,008 1 0.021 0.022 0.032 0.023 0.017 0.027 ( 0.024 1 0.021 025 029 0.033 0.021 0.014 0.036 018 0.018 0.016 0.029 The space in a sq. mm covered by a stoma. 0.0270 0247 0.0706 0.1137 0.0176 0.1074 0.0104 2070 0.1945 O.O307 0.0323 0.0303 0.0386 0.0139 0.0758 0.0792 0.2B60 11.0731 0.1280 0.0947 0703 0.0554 0,1305 0,0972 0.0942 0.0482 0.0989 0.1187 0.0323 0.3356 0.1995 0.1015 0.1206 0.1503 0.1751 0.0695 0.0927 0.0547 0.04.36 0.0091 0.2494 0.1471 0.1025 0269 0.1434 0905 0.0607 0.1162 0.1961 0.1223 0,1332 72 MORPHOLOGY OF THE CELL. The cells thus slightl3f separated at by subsequent growth bring about changes in the relations of the neighboring cells. In Sedum, as shown by Strasburger, there are preparatory divi- sions in different di- rections, 'wliile in some monocotj-ledons there are simultaneous divisions in contigu- ous epidermal cells. 241 . Stomata are not present, at least in a perfect form, in any submerged 240. As appears from the following figures, the first stage in the devel- opment of an ordinary stoma is the separation of a part of an epider- mal cell by means of a vertical partition, thus forming the mother-cell of the stoma. This next divides by a verti- cal plane •which soon exhibits a narrow chink, their common wall may plant. In aquatics with 63 6 63 s Fig. 52. Vertical section of stoma of Hyacintlius orlentalis. (Strasburger. ) Pig. 53 a, b, c. Three stages in the development of the stomata of Sedum spurlum. mg. 63c shows the narrow slit maJe by the neighboring epidermal cells. (Strasburger.) STOMATA. 73 floating leaves they are confined to the upper surface of the leaf. The leaves of certain plants, as those of monocotj-ledons and those which take a vertical po- sition, have tliem in nearly equal numbers on the two sides ; but in most cases the number on the under exceeds that on the upper surface, as will be seen from the table on page 71. As regards the approxi- mate number on leaves of average size in some of our common plants, the following figures may be of interest : '■ — Nymphsea 7,650,000 Bra.ssica oleracea, 11,540,000 Helianthus annuus 13,000,000 242. Water-pores. Directly over the extremities of the fibres of the framework of many green leaves are found apertures in the epidermis which have no true guardian cells,* but which closely resemble ordinary stomata in most other respects. •Owing ^ That is, the bordering cells do not close under external influences. Fig. 54. Vertical section of stoma of Scdum apurium. (Strasburger. ) Fig. 55. Water-pores in leaf of Bocbea cocciiiea. The left-baud figure shows both an ordinary stoma (the lower one) and a water-pore (the upper), as seen on upper surface of leaf Tbe rigbt-hand figure sbows tbe structure displayed by a vertical section. (Van Tiegliim.) 74 MORPHOLOGY OF THE CELL. to the fact that their cavit}- answering to the intercellular space of a stoma is often filled with water instead of air, these have been called water-pores. At certain times liquid water passes through these pores, collecting at the opening and sometimes leaving there, upon evaporation, slight incrustations of calcic carbonate. Water-pores assume different forms and vary much in size. Good examples are afforded by many Aroideae, by the teeth of the leaves in some species of Fuchsia, the leaf-margins in Tropseolum, etc.^ Small rifts of nearlj- the same shape can be found in certain grasses ; but in these the aperture comes from a mechanical rup- ture,^ and the underlying structure is very simple.* CORK. 243. This protective tissue is formed beneath and replaces epidermis in the older superficial parts of plants ; it also con- stitutes the films by which wounds are healed. Onlj- the inner layers of cork-tissue possess cellular activity, those which lie outside of them having perished : tlie former contain protoplasm and are capable of cell-division; the latter contain air, and occasionally small clusters of crystals. The inner, active, and growing lasers are known as cork meristem, cork cambium, or P hello g en ; the outer, [jroduced from this and no longer living, make up the bulk of the outer bark, and are ordinaril3' called cork. Although the older cork-tissues must be further described in Chapter III., under "Bark," their elements may be conven- iently treated of now in connection with the cells which produce them. 244. Origin. Cork may arise from several different sources, the principal of which are the following: (1) from division of cells in the epidermis (e. (7., species of Pyrus, Salix, Viburnum, etc.) ; (2) more commonly from underlying parenchyma, In a few cases even from that which occurs in the inner bark (the bast parenchyma), as in Vitis and Spiraea; (3) from parenclyma at injured surfaces, as in the healing of wounds. 245. It is normally produced upon the stems and roots of flowerihg plants, especially dicotyledons. Its cells are generally ^ For a full account of water-pores, see de Bary's Anatomic, p. 54, and Jahrb. konigl. botan. Garten, Berlin, 1883. ^ De Baiy ; Anatomic, p. 57. ' Gardiner: Proceedings Camb. Pliil. Soc, 1883. CORK. 75 formed by the division of tlie mother-cell into two tabular cells, by ii jjartitioii parallel to the surface of the organ, in most eases the outer cell becomes cork, while the inner re- tains its power of division and in turn produces new cells. But with the first appearance of the cork- layer a change takes place in all layers lying to the outside of it : they are cut off' from nutritive supplies and soon die. The con- tinuous layers of cork are called, collectivel}', Peri- derm, a name restricted by Mohl to tough cork in distinction from soft cork, but now employed with a wider signification. 246. Cork meristem gives rise to successive layers of cork-cells : if the new layers differ much from the preceding in the shape and size of their cells, an appearance of stratification naturally results. Cork meristem ma}', in exceptional instances, produce on its inner side permanent parencli^-ma, the cells of which contain chlorophyll ; these green layers are called Phel- loderm, and are observed well in the beech, willow, etc. (see Chapter 111.). 247. Cork-cells are tabular, or sometimes cubical, and witli few exceptions have no intercellular spaces. In the case of very flat cells which cohere more firml}' lateiall}' than in the line of the radius, the cork-tissue may be readily separated in films or sheets. 248. The walls of older cork-cells are cutinized or suberized throughout. The demonstration of cellulose in cork-cells is not possible unless the cells have been first acted on by solvents, Fig. 56 Formation of cork in a brancli of liibes nigrum, one year old ; part of trans- verse section; A, hair; e, epiilerniis; pry cortical [larencliynia, somewhat distorted; K, tlie total product of the phellogen c; k, cork-cells; pd, phelloderm j b, bast-cells. ISachs.) 76 MORPHOLOGY OF THE CELL. such as caustic potash, and the like. But sometimes the cell- ■wall seems to be completelj- changed into covk-substance. 249. Cork-substance behaves towards reagents in nearly- all respects as culin does (see 157). ^m^ onooooii- 57 250. Cells which have been completel3' snherized can be sepa- rated from each other b}- the gradual action of Schulze's macer- ating solution.* 2.51. The color of cork-cells is not dependent npon the amount of the change of the wall into cork-substance. The walls of the cells in some species of willow are colorless, while those in other species are distinctly yellow ; and yet the former have been as thoroughly changed into cork-substance as the latter. II. Cells of the Fibro-vasoular System, — Prosenchyma in the widest seuse. 252. The cells and modified cells of this S3-stem constitute the framework of a plant. In a few of the higher and in many of the lower plants it is barely if at all developed, the entire structure consisting, in such cases, of a mass of parenchyma covered by epidermis. But in most plants it exists as a skeleton 1 This fact has led to the belief that there exists in such cases .in interme- diate plate which differs in its character fi-om the rest of the cell-wall ; but prolonged action of the same reagent, especially with warming, causes the cells to break down and ultimately form a disorganized mass. Pig. 57. Formation of cork and seconilary cortex in Betulaverrucosa. A, B, C, D, snccessiTO stages; 1, first layer of seconilary cortex; 2, layer which divides in B, to give outside the first layer of curk (shown in C), and a layer, 3, within, which again divides ill I). (Sauio.) WOOD-PARENCHYMA. ( 7 bringing all parts into closer relations, and strengthening the whole. 253. The cells are normally of considerable length in pro- portion to the transverse diameter, and are generally' more or less sharpl}- pointed (prosench^ma proper). The most impor- tant of the modifled cells belonging to this S3-stem unite to form long rows in which the terminal partitions are nearly or quite obliterated, throwing the cavities into one, and thus forming a cylinder, termed a duct. Between proper prosench3-ma cells and ducts there are numerous connecting forms which render impossible anj' attempt at classifying them exactly.' Associated with these cells, but differing in some important particulars, are cribrose and latex cells, which for convenience are here to receive separate treatment. 254. Before developing the provisional classification given on page 59, attention must first be directed to the peculiar transitional forms constantly met with, which belong as much to parenchyma as to prosenchj^ma, but are more conveniently examined in connection with the associated wood-elements. Chief among these intermediate forms must be mentioned those of which Fig. 58, No. 9, nmy be taken as a represen- tative. Here the whole structural element is isolated as an elongated combination of three cells, one of which has flattened ends, while the other two, attached to these ends, have their free extremities pointed. In spite of their form, such cells are usuallj' described as wood-parench3-ma cells. When their walls are thicker, they are not easily distinguishable from septate libriform cells (see 263) . 255. The forms shown in Fig. 59, No. 19, are common in the wood of many plants, notably the oaks. They are rela- tively small, have rather blunt extremities and thin walls. They occur with these characters especially in the autumnal wood of the oaks (see 395), while in the spring wood they are apt to 1 For the satisfactory study of the relations of the elements of prosenchyma, very thin sections are necessary; hut for the examination of the elements them- selves, recourse to some process of maceration, by which they can be isolated, Is always desirable. In general, there is nothing preferable to Schulze's solu- tion in any strength adapted to the special case; it must be remembered that the slow action of a dilute solution gives better results than the more rapid action of a concentrated one. If the section to be examined is first subjected to the action of the macerating solution of proper strength and then thoroughly washed, it can be dissected at pleasure under a high power of a simple lens. This method is always to be prefen-ed to the ordinary one of disintegrating the whole specimen and obtaining a confused mass of separated cells. 78 MORPHOLOGY OF THE CELL. pass over into the variety shown in Fig. 59, No. 18. The latter are known as " conjugate cells." PROSENCHYMA PROPER. 256. Typical wood-cells. These are best illustrated bj- elon- gated, often pointed cells, of which good examples are found in the cambium layer (that is, the layer of merismatic or formative 10 Fig 58. Drawings of wood-elements. 1-7. Avicennia sp. 1. "Wood-parenchyma cells united with eauli other; tangential section. 2, 3, 4. Conjugate wood-parenchyma cells isolated hy Schulze's solution. 5, 6. Portions of spirally striated llbriform fibres isolated by Schulze's sclutioii. 7. The septum of a duct. 8-12. Tectona grandis; the elements separated by maceration. 8. Conjugate wood-parenchyma cells. 9, Ordinary wood-parenchyma fibre 10. Substitute fibre. 11. Simple librifonn fibre. 12. Sep- tate librifnrm fibre. 15. Porlieria hygrometrica; conjugate substitute fibres seen in radial section. The wood-cells are omitted in order not to confuse the diagram. 37. Radial aecfion through the wood of Jatroplia Manihot. 38. Tangential section through a libriform fibre and two cells from a medullary ray. of the same plant. 39-42. Bast-cells of Cytisus Lnburnum. 39. Cross-section through a part of a young' bast-bundle acted on by cblnroiodide of zinc. 40. 41, 42 Cross-sections through young bast-cells, acted on by chloroiodlde of zinc. (Sanio.) "WOOD-ELEMENTS . 79 tissue just under the bark of dicotyledonous plants). Their walls are thin, and at first nearly or quite free from pits or other markings. They grade into tliree constantly recurring forms ; namely, (I) parenchyma (see 254) ; (2) attenuated forms, often so slen- der as to deserve the name of fibres ; (3) forms with peculiar markings at most points of contact, and thus much resembling ducts or vessels. Fig. 59. Drawings of wood-elements. 13. Trartiei'd from Tectona grandis. 14-18. Porlieria hygrometrica. 14. Conjugate substitute fibres seen in transverse section. 16. Ordinary substitute fibre after maceration. 17, 18. Conjugate substitute fibres after maceration. 19-22. Cytisus Laburnum ; the elements separated by maceration. 19. Wood-parenchyma fibre. 20. Substitute fibre. 21. Simple libriform fibre. 22. Tra.- clieid. 23. Cross-section througli tlie cambium and youngest wood of Cytisus Labur- num. 24-2~>. Ducts from MaliouiaAqnifolium. 24. After maceration. 25. Longitudinal section. 26-31. Ducts from Hieracium, separated by maceration ; showing the ex- tremity only. 32-34. Ducts from Onorpordon acantliium, separated by maceration. 35. Spirally marlted duct from Vitis vinifera, after macerntion. 36. Libriform fibre from Jatropha Manihot. (Sanio.) 80 MOUPHOLOGV OF THE CELL. 257. The drawings of ■wood-elements represented in Figs. 58 and 59 are from Sanio's worls, and are given witti his nomen- clature. The cells figured in Nos. 10 and 16, termed by Sanio substitute fibres (German, Ersatzfasern), answer well to the t3-pe of prosenchj-ma. When tliese cells are much reduced in calibre, thej- are known as libriform fibres. 258. Ordinarj- prosenclyma cells usually have simple pits, but no true spirals. The pits may be round, and of the same size as those on the ducts with wliicli thej- maj' be in contact, but some- times they are elongated slits, and run obliquel}-, as shown in Fig. 59. If two of these cells are in contact, processes may extend from one cell to corresponding protrusions in the other, and thus one cell is united with the next. Hy careful raacera- cion such cells can be sepai'ated, and then each appears to have one or more rows of squai-e teeth or short tubes. It sometimes happens that the wall at the end of these intrusive tubes is broken down, thus allowing free communication between the cells. Good examples of substitution cells are to be found in the wood of Magnolia, Liriodendron, man}' Leguminosa;, etc. They are not so common, iiowever, as conjugate parenchyma cells (see Fig. 58). 259. Woody fibres are of two chief classes : (1) those in which the narrowed cavity is continuous throughout the whole length, and (2) those which have partitions dividing it (sep- tate fibres). The flist class has been again divided into two groups depend- ing upon the presence of starch, but the division is not wholly satisfiictory. The first group comprises all those fibres which have a trace of protoplasm, wiiile those of the second have also more or less starch, and generally- some tannin. All of these woody fibres resemble the bast-fibres of the inner bark ot dicotyledons so closely that they have been well called libriform. Tliey are described by Sanio, from whose paper on the subject most of these names arc taken, as being always spindle or fibre-form, relatively strongly thickened, and occa- sionally furnished with bordered pits which somewliat resemble those of vasiform elements (264), but are smaller and less clearly defined. Thej- never have true spiral markings, and very seldom any spiral striation. They contain during the periods of rest of vegetation in winter more or less starch, and perhaps some chlorophyll and tannin, but at other times only air. LIBRIFORM CELLS. 81 260. The nnseptato fibres, tlie true libriform cells, are only sparingly pitted, except in a few species like Oleander, where the}- are pitted on both the radial and tangential walls. The pits are generally elongated and oblique, and according to Sauio always running from left to right. 261. The cell-wall of these fibres is always lignified, and pre- sents three layers ; and in some instances there is also a layer which is plainly- gelatinous, e. 2 & 1 1 1 1 B 3 8 c la? c « o to ® 03 y il ^ ^ o O 1^ 11 ■3f^5 fii ■g c« f5g£ o t C c8 B c c u oj3 II s S 1 11. 1 1 il 1 o . 11 . 2 S & o O cs*^ S: ■^ Sf-a " rt'S £ s i .a !■ O = >^ « 1 P5 i I o O CSC qj © rt 60 mi .Q CC w rO W >.o.!S 1» c S s 5 a- i'i^ -,'= CO bov S .2 •g o . II 1 il o c ■3 i 11 •i Bi- gg's i2 = =^ gas ^i « ■§ §2 i 1 i 1" S o 1 09 It ^3 11 II ins lit (ill II II. ^1 tog .:3 o 0-3 « cs i d s S n , endodermis; m, peripheral layer of the cylinder; I, Uber fascicles; 7-, woody fascicle; c, conjunctive parenchyma (pith and medullary raj s). (Van Tieghcm.) 112 MINUTE STRUCTURE OF THE HOOT. duccd to a single duct, as iu some Carices, or there maj- be a large duct surrounded by smaller ones with or without inter- vening cells, or many large and small ducts variously conjoined. Moreover, there are all degrees of compactness in the union of the different bundles of woody tissue with each other. 339. The cribrose part of the bundle may be reduced to a single cribrose tube (e.g., Anacharis), or two or three (e. ff., Pon- tederia) ; but usually there are mauj-, which maj' be variously disposed. 340. Bast-fibres may be associated with the cribrose-oells in the primary structure of the root, and they may be scattered (and occasionallj- with some sclerotic parenchjma) in the cortex. In Philodeudrcm these scattered groups of bast-Iibres frequently contain oleo-resin canals. Secondary Structure. 341. The older parts of roots, even the recently formed por- tions lying just back of the root-hairs, may undergo changes either b}' the alteration of their existing tissue elements or by the in- troduction of new ele- ments. Some roots, however, do not suffer much change fiom first to last. Their cells may become more strongly cutinized or lignified as the case maj' be, but no new elements are brought in. This is true of the i-oots of man3- monocotyledons, but in dicotyledons the secondarj- changes are generall}' verj' marked. The changes maj- af- fect either the I'ortex or the central cylinder ; in some cases the former more than the latter. Fio.93. Soctioii Hirougli tlioceiUralcyliri'lerofabinary root of avascular cryptogam (Cyatbea meilullaris): :cept in the matter of trichomes, throughout the life of the plant ; but in most ligneous plants it is replaced, often early, by other pro- tective tissues. Persistent epidermis is found in many woody and half- woody plants ; for instance, Russelia juncea, Lej-ces- teria formosa, and Ptelea trifoliata. In Palms ^ " the epidermis exists in old age only in the cane- like and calamoid stems ; in the rest it is more or less destroyed by the action of the weather. In Calamus it consists of a simple layer of minute cells elongated in the direction from without inward, and forms a ston}', brittle, shining layer." 3G1. The primary cortex' consists essentiail}' of parenchj-ma in which isolated cells of a peculiar character maj- often be found, such, for instance, as crj'stal cells, laticiferous cells, tannin cells, and the like (see 292) ; and its intercellular spaces sometimes serve as receptacles for the various exudations. The paren- chyma cells generally contain more or less chlorophyll, and some starch. 3G2. Immediatelj' beneath the epidermis, and not easilj- dis- tinguished from multiple epidermis, is a portion of the cortex known as Hypoderma.* It is rarely sclerotic parenchyma, more ' In the plumule and other buds all these parts exist potentially ; and the sequence of their development can be successfully followed out by the enii>loy- mcnt of seeds in different stages of germination, or buds collected on succes- sive days in spring and preserved at once in alcohol. In all cases care must be taken to have the date of collection of each specimen recorded in such a manner that no confusion can afterwards arise. 2 Mohl : Ray Society, Eeports and Papers iu Botany. The Palm-stem, Heufrey's Translation, 18-19, p. 14. ■^ Vesque (iu Ann. des Sc. nat., sdr. C, tome ii., 1875, p. 82) gives a very full treatment of the subject. * The word Hypoderma was introduced by Kraus (Pringsheim's Jahrb., 1865-66, p. 321), to designate the layer of colorless cells under the epidermis of leaves, "das Analogon des Uindencollenchyms." It has since been ex- tended to apply to the external cortex just under the epidermis of stems. 120 MINTTTE STRUCT DEE OF THE STEM. frequently it is coUenchj-ma. Excellent illustrations of the latter kind of hypoclerma are furnished by most Malvaceae and LabiatiB. 363. Sclileiden'' distinguished four types of external cortical layers in dicotyledonous stems : 1. That existing as a perfectly closed layer (penetrated in some eases only hj- small canals opening into stomata) ; as in most of the Cactacse, Rosa, Begonia, etc. 2. That divided into many bundles, so that the green cor- tical parench^una reaches tlie epidermis ; e. g., in Malvaceae, Sola- nacese, etc. 3. That which may be quite distinctlj' recognized as a special laj'er, but still grading into parenchyma at the borders ; e. g., in Pyrus Mains, Hedera, Ficus, etc. 4. That more completely merging into cortical parenchyma, and therefore less distinct; e. ™> tbe fascicles from the second pair of leaves ; g, /■, s, —p, n, J' Both lateral strands of a leaf in such a case as this run down through one internode, bend outwards at the node below, and attach themselves to the lateral strands belonging there. Suppose, now, that a cross-section of the stem of Clematis is made at the lowest node represented in Fig. 102 ; all the fibro- vascular bundles at that point will be seen in their relative posi- tions, some of them cut squarely off, others obliquely, according to curves which they make. A cross-section in the internode above would show slen- derer bundles, but all arranged in much the same manner as in the thicker inter- node below ; that is, in a circle.* The circle is made up of flbro-vas- cular bundles which have an inner por- tion of wood ; within the circle is paren- chyma (the pith) , and outside of it more parenchyma (the cortex) , which can be stripped off with the bast-portion of the central cylinder as bark. Compare Fig. 102 with Fig. 103. In the latter, the stem does not exhibit in cross-section the flbro-vascular bundles arranged in a circle : they are more or less scattered ; there is no clearly de- fined central portion nor well-marked outer portion free from them. Hence it cannot be said that such a stem has any distinction of pith, wood, and bark. A further distinction may be here noted ; namely, that the bundles in Fig. 102 have the power of increasing in '^"'' tliickness, adding new wood and new bast to the primary struc- 1 Another feature must be attentively studied ; namely, the relation of the forming bundles to the young leaves at the upper part of the stem. One may say the bundles descend from the leaf to the stem, or ascend from the stem to the leaf. But since the development of the leaf part and the steni part of a bundle goes on together, these terms, ascend and descend, should be under- stood to refer to our method of tracing the bundles out, and not to the method of their development. fascicles from the third pair of leaves ; x, i, fascicles of tlie fourtli pair of leaves ; ^, a^ — 7, S, pairs of undeveloped leaves not as yet having fascicles. The diagram illustrates both Clematis Viticella and C. Vitalba. (Nageli.) Fig. 103. Longitudinal section through the stem of Aspidistra elatior, showing the curved course of the fibro-vascular bundles in the simplest palm-type. (Falkenberg.) 128 MINUTE STRUCTUKE OF THE STEM. ture (see 390) ; but in Fig. 103 the bundles are closed (see 315), and incapable of r f f ?'-. ^ further increase in /» 7 \ Yl * tliickness. Hence ^ ^ ^ /\ A, anyfurthergrowth x> I I 1 in thickness of the "T ^/T ^A "^ \ '^ V- --TV stem shown in N \ 1 Fig. 103 must be by the intercala- V l tion of new bun- l1l ~1 * NT i^Aj dies. f\ I fi 379. It was held by Desfontaines ^ that the new vas- j cular bundles in 1/ \ 1 Palms originate in Im n ' "' ^X'INN \ 1 1 Quoted by Mohl, 1 1 in The Structure of the Palm-Stem (The Ray Society, Reports and Papers ou Bot- any; London, 1849). Another illustration of the arrangement of fibro-vasrular bundles is here given : — i \ The stem of the Vi- 'mH\\i \ ^ tis vinifera is usually \ t c f' \'j regarded as sympo- / s \ dial; that is, it is com- 1 ' posed of internodes 1 belonging to different ; axes (see vol. i. pp. 54 and 154). In this species of grapevine two leaves in sncces- i sion have a tendril on 1 the opposite side, then 1 follows a leaf without " " any tendril, next the ^"^ sec^uence of two with Fifl. 101. Diagrammatio projection, showing the disposition of the fibro- vascular bun- dles in ;i leafy shoot ()i' Vil is vinifera. Each leaf has five fascicles, which are unsymme trically arranged : Cud J2 Botanical name. Common name. Region. <^ Sequoia gigantea. Big Tree. California. 0.2882 18.20 Films Strobus. Wliite Pine. North Atlantic. 0.3854 24.02 Tsuga Canadensis. Hemlock. North Atlantic. 0.4239 26 42 Liviodendron Tulipi- Wliite wood. Atlantic, 0.4230 26.36 fera. Taxodium distichura. Cypress. South Atlantic. 0.4643 27.65 Castanea vulgaris, var. Chestnut. Atlantic. 0.4504 28 07 Americana. Abioa nigra. Black Spruce. North Atlantic. 0.4584 28 57 Populua grandidentata Poplar. North Atlantic. 0.4632 28.87 Pinus resinosa. Norway Pine, North Atlantic. 0.4854 30.25 Pinus rigida. Pitch Pine. Atlantic Coast. 0.5151 32.10 Acer dasycarpura. Silver Maple. Atlantic. 0.5269 32>4 Pyrus Americana Mountain-Ash. Atlantic. 0.5451 33 97 Betula nigra. Red Birch. Atlantic. 0..W62 35 91 Platauus occidentalis. Sycamore, Button wood Atlantic. 0.5678 35.38 Juglaiis nigra. Black Walnut. Atlantic. 0.6115 38.11 Larix Americana. Larcli. North Atlantic. 0.6236 38.80 Ulmus Americana. White Elm. Atlantic. 0.6506 40 54 Fraxiiius Americana White Ash. Atlantic. 0.6543 40 77 Quercus rubra. Red Oak. Atlantic. 0.6540 40 75 Acer saecharinum. Sugar Maple. Atlantic. 0.6912 43.08 Fagus ferruginea. Beech. Atlantic. 0.6883 42 89 Quercus alba. Wliite Oak. Atlantic. 0.7470 46 35 Betula lenta. Cherry-Birch. Atlantic. 0.7617 47.47 Quercus virens. Live Oak. South Atlantic. 0.9501 69.21 Guaiacum sanctum. Lignum Vitae. Semi-tropical Florida. 1,1432 71.24 The specimens used in the above determinations hy Mr. S. P. Sharpies were dried at a temperatui-e of 100° C. until they ceased to lose weight, when the specific gravities were obtained hy measurement with micrometer calipers and calculation from the weights of the specimens. For the purpose of utilizing histological features in the identification of woods, classificatory tables have been prepared by many autliors. One of the most useful of these is given in Schacht's work, Die PHanzenzclle, in which the different wood-cells of Conilerje are described, in order to aid in the recog- nition of the genera. .Another is de Bary's (Vergleichende Anatomie. p. .609, 10 146 MINUTE STRUCT0KB OF THE STEM. from each other bj- mechanical or chemical means for use in the manufacture of paper-pulp. The woods which appear to have translated in Saolis's Text-book, 2d Eug. ed., p. 651), in which the structural characters of many kinds of wood are given. The table will be found con- venient for i-eference. 1. Wood consisting only of tracheids with bordered pits : — Winterere ( Drimys Winteri, Tasmannia aromatica ; also Trochodendron aralioides) : (Conifers). 2. Wood consisting of vessels, tracheids, parenchyma, and intermediate cells ; that is, substitute or replacing cells or fibres (ersatzfasern) : — a. With no intermediate cells ; Ilex aquifolium, Staphylea pinnata, Rosa canina, Crataegus raonogyna, Pyrus communis. Spiraea opulifolia. Camellia, etc. i. With no jiarenchyma ; Porlieria. c. With both parenchyma and intermediate cells ; Jasminum revolutum, Kerria, Potentilla fruticosa, Casuarina equisetifolia and torulosa, Aristolochia Sipho, etc. 3. Wood consisting of vessels, tracheids, fibres, parenchyma, and intermediate cells : — a. With no intermediate cells ; fibres unseptate ; e. g., Sambncus nigra and racemosa, Acer platanoides, Pseudoplatanus, and campestris. 6. With both parenchyma and intermediate cells ; fibres unseptate ; Ber- beris vulgaris, Mahonia ; (Ephedra). c. With no intermediate cells; fibres septate and unseptate; Punica, Euonymus latifolius and Europaeus, Celastrus scandens, Vitis vini- fera. Fuchsia globosa, Centradenia grandifolia, Hedera Helix, etc. d. With all four kinds of cells ; Miihlenbeckia coinplexa, Fious. 4. Wood consisting of vessels, tracheids, fibres, parenchyma, and intermediate cells. This is the most common, and may be taken as the typical structtire : a. With no intermediate cells ; Sparmanuia Africana, Calycanthus, Rham- nus catharticus, Eibes rubrum, Quercus, Castanea, Carplnus sp., Amygdaleaj, Melaleuca, Callistemon sp., etc. i. With no parenchyma ; Caragana arhorescens. c. With both kinds of cells ; most foliage-trees and shrubs; e. g., Salix, Populus sp., Liriodendron, Magnolia acuminata, Alnus glutinosa, Betula alba, Juglaus regia, Nerium, Tilia, Hakea suaveolens, Ailan- thus, Robinia, Gleditschia sp., Ulex Europgeus, etc. 5. Wood consisting of vessels, fibres, parenchyma, and intermediate cells : — a. With no parenchyma ; Viscum album. b. With no intermediate cells ; Avicemiia. c. With both kinds of cells ; Fraxinus excelsior, Ornus, Citrus medica, Platanns, etc. 6. Wood consisting of vessels, fibres, and parenchyma : — Cheiranthus Cheiri, Begonia. Also many Crassulacese and Caryophyl- lacese. 7. Wood consisting of vessels, fibres, parenchyma, and true woody-fibres : — Colens Macraei, FAigenia australis, Hydrangea hortensis. 8. Wood consisting of vessels, tracheids, woody fibres, septate fibres, paren- chyma, and intermediate cells : — Ceratonia siliqua, Biguonia capreolata ; it is, however, still doubtful if true woody-fibres are present. SECONDARY LIBER. 147 been most extensively employed up to the present time are some of the species of Abies, Betula, Populus, Tilia, and Liriodendron Tulipifera (bi the United States sometimes called "Poplar"). The chemical processes depend (1) upon the solvent power of caustic soda under pressure, and with heat, upon the so-c;vIled intercellular substance which unites the cells, or (2) upon the similar power of a gulphite, preferably maguesic, also under pressure and with heat. 413. Bark. A, Secondary liber. Each yearly addition to the bluer surface of the bark is seldom plainly distinguishable from those which have preceded it, and hence we cannot determine positively the age of an old tree by the layers of its inner bark. The bast-fibres of a single year often cling together in a strik- ing manner, forming bands or strips of considerable strength, and in a few cases, notably that of Daphne Lagetta, there are fine meshes between the fibres, so that the inner bark seems to be composed of layers of delicate lace. A piece of thick bark of linden macerated for a while in water becomes so softened that the younger portion of the inner bark can be easily separated into the annual layers. Strips of the coherent fibres form the Russia matting of commerce. The strips often measure 2-3 meters in length, 2-5 cm. in width, and .04- .08 mm. in thickness. Scattered among the individual bard-bast fibres there are many parenchyma cells, some of which plainly belong to the medullary rays, and others to the fibro- vascular bundles. 414. The bast-fibres, in a few instances, instead of being re- tained upon the stem for an indefinite period, are separated early, leaving the newer bast exposed. This is the case with some of our species of Vitis, in which the bast becomes detached in the form of long, loose shreds after the first year. 415. The crystals found in bast are very abundant. They are chiefly monoclinic, and occur both singl3' — arranged in rows — and in clusters. i 416. The appearance and distribution of the fibres of bast ?■ De Bary gives the following list, taken chiefly from Sanio : — Clusters of crystals in bast of Juglans regia, Rhus typhina, Viburnum Oxy- coccus, V. Lantana, Prunus Padus, Punica Granatum, Ptelea trifoliata, Eibes nigrum, Lonicera 'Ritarica. Single monoclinic crystals in bast of species of Acer, and the Pomacese, Robinia, Cladrastis, lllmus campestris, Berberis, etc. Single monoclinic crystals and clusters in bast of Quercus, Celtis, Jisculus Hippoeastanum, Hamamelis Virginica, Morus, Salix, Fagus, Populus, Car- pinus, Betula, Tilia, etc. 148 MllJUTE STEUOTUEE OF THEl STEM. are so characteristic in certain kinds of barli tiiat tlie^' maj' be used for identification. An example is given below. ^ 417. B, Cork, which has alreadj' been described in part in Chapter 11 , plaj's a ver^- important part in the structure of older Ijark. Its relations to the cells which produce it, and to the epidermis which it displaces at an early period of its growth, will be plain from an examination of Fig. 117. In its production there are periodic arrests of activity just as in the case of wood, and hence in cork-tissue of firm texture it is possible to detect the lines of annual demarcation. When the cork of the cork- oak has reached a merchantable thickness (usuall}' in ten to fifteen years), it is removed down to the phellogen, or cork cambium, and from this tissue new growths begin. ^ ' ' ' The libel' is traversed by medullary rays, whieli in cinchona are mostly very obvious, and j>roject more or less distinctly into the middle cortical tissue. The liber is separated hy the medullary rays into wedges, which are constituted of a parenchymatous part, and of yellow or orange fibres. The number, color, shape, and size, but chiefly the arrangement of these fibres, confer a certain character common to all the barks of the group under consideration. " The liber-fibres are elongated and bluntly pointed at their ends, but never branched, mostly spindle-shaped, straight, or slightly curved, and not exceed- ing in length 3 mm. They are consequently of a simpler structure than the analogous cells of most other oflicinal barks. They are about J to J mm. thick, their transverse section exhibiting a quadrangular rather than a circu- lar outline. Their walls are strongly thickened by numerous secondaiy depos- its, the cavity being reduced to a narrow cleft, a structure which explains the brittleness of the fibres. The liber-fibres are either irregularly scattered in the liber-rays, or they form radial lines transversely intersected by narrow strips of parenchyma, or they are densely packed in short bundles. It is a peculiarity of cinchona barks that these bundles consist always of a few fibres (three to five or seven), whereas in many other barks (as cinnamon) analogous bundles are made up of a large number of fibres. Barks provided with long bundles of the latter kind acquire therefrom a very fibrous fracture, whilst cinchona barks, from their short and simple fibres, exhibit a short fracture. It is rather granular in Calisaya bark, in which the fibres are almost isolated by parenchymatous tissue. In the bark of G. scrobicnlata a somewhat short fibrous fracture is due to the arrangement of the fibres in radial rows. In C. pubescens the fibres are in short bundles, and produce a rather woody frac- ture" (Fliickiger and Hanbury, Pharmacographia, p. 317). 2 As noticed in 246, the inner layer of cork-meristem may give rise to paren- chyma cells containing chlorophyll. Of these cells Sanio says : "They never become cork-cells, but are truly parenchymatous ; they are filled with chloro- phyll, starch, and sometimes with crystals. They never become lignified, but the wall reiriains as unchanged cellulose, and, in short, tliey are true cortical cells. Since, then, they owe their origin to the activity of the cork-meristem, but behave throughout their whole subsequent development precisely like the cells of the cortex, they may be called cork-cortex cells. When they foi-m a distinctly defined layer, the term Phelloderm is appropriate" (Pringsheim's Jahrb., 1860, p. 47).' BARK. 149 418. In some plants, notably the birch, papery layers exfo- liate from time to time, while in some otlier plants, e.g.^ the shag-bark hickory, large strips of irregular form and thickness are detached. Owing to the mode of their formation, such sepa- rated pieces may contain very heterogeneous elements. Of them Sachs says:' "Not un- frequently the formation of cork penetrates much deeper [than the peri- derm] : lamellae of cork arise deep within the stem as it increases in thick- ness ; parts of the funda- mental tissue and of the fibro-vascular bundles, or of the tissue which after- wards proceeds from them, become, as it were, cut out by lamellae of cork. Since everything which lies outside such a struc- ture dies and dries up, a peripheral layer of dried tissue collects, which is very various in its form and origin. This struc- tui'e, abundant in Conif- erse and in many dicotj'- ledonous trees, is the hark, the most complicated epidermal structure in the vegetable kingdom." 419. iDJnries of the stem. The stem, especiall3' in the case of plants living many years, is particularly liable to injuries, the most frequent of which are of course the wounds left b}' the fall- ing of the lower limbs. It is proper to treat here of the natural repair of sucli injuries. 420. When any part of a plant suffers serious mechanical injury by which the deeper tissues are exposed, the surface of 1 Text-book, 2d Eng. ed., 1882, p. 95. Fig. 117. Formation of cork in a branch of Eibes nigrum, one year old; part of a transverse section ; e, epidermis ; A, hair ; b, bast-cells ; pr, cortical parenchyma dis- torted by the increase in the thicltness of the branch ; K, total product of the phellogen c ; It, the cork-cells radially in rows, formed from c in centrifugal order ; pd, phelloderm (parenchyma containing chlorophyll formed centripetally from c). (Sachs.) 150 MINUTE STRUCTtTEE Ol' THE STEM. the wound exhales moisture very rapidly, and under ordinary circumstances, except in spring, soon becomes dry. As Hartig^ has shown, the drjing of the exposed tissues is fatal to their component cells, and the organic contents speedily undergo eliemical decomposition. The products of this decomposition have been further shown by him to be fatal to neighboring cells, and under certain conditions the mischief may progress to an irreparable extent. But usually there is an arrest of the de- structive action either from lack of the free oxygen necessary for the putrefactive process, or by the protection afforded by tissues for repair. Wounds in resinous trees a,re measurabl3- hindered from effecting much damage, owing to the exudation of liquid resins which exclude air. 421. The smaller wounds of a plant are generally healed by cork or by callus. 1. By cork. The superficial layer of cells at the surface of the wound is destroyed by the injury, and dries at once. In soft tissues the layer just below this immediatelj' becomes merismatic, and behaves precisely like normal cork- meristem, covering the entire wound with a grayish or brownish film, which is in unbroken connection with the edges of the wound. Extreme dryness of the air, or, on the other hand, ex- treme humiditj-, hinders repair bj' cork. 2. Hy callus. This is best studied in leaves and in -'cuttings.'' When a young, juicy leaf is wounded by an incision, some of the cells at the exposed surface may give rise to elongated sac-like bodies, which fill up the greater part of the injured cavity, and, according to Frank, ^ serve as a new epidermis. Or small cells in close apposition may be at once formed, and completely protect the tissue below. In " cuttings" the callus immediately forms a swelling near the wound. A portion of the callus maj' by continued cell-division extend over the cut end, everywhere bounded on its exposed surface by a cork laj-er. Activity of the cells in the callus and around the fibro-vascular bundles soon gives rise to new parts, for instance, roots. 422. It often happens under favorable conditions that a large mass" of tissue is graduallj' formed around, and finally over, a large injured surface. 1 Zersetzungserscheinungen des Holzes, Berlin, 1878. (Quoted bj' Fi"ank. ) 2 Die Pflanzenkrankheiten, 1879. i" Usually when a branch dies it remains attached for a while to the stem ; and no wound is in fact caused until the slow desiccation of the deeper tissues has gone on to a considerable extent, and without exposui-e to atmospheric air or outside moisture. When the branch at last falls off, the tissues around LENTICELS. 151 423. Lenticels are peculiar breaks in the continuity of the periderm of dicotyledons. In some cases they can be detected under minute elevations of the epidermis of the first year, which split open either at the end of that season or during the next, forming a rift running lengthwise of the stem, through this cleft underlying tissues appear, protruding in an irregular manner, the whole structure constituting a lenticel. According to Stahl,'' there are two types of lenticels : 1. Those with loose cells in the rift, alternating with denser lines of cells. This is the most common type, good examples being afforded by Alnus, Prunus, ^sculus, etc. 2. Those with closely united cells and with no alternating denser lines. Illustrations can be found in Sam- bucus (see Fig. 118), Salix, Cornus, etc. The same authority states that in winter both of these kinds form an impervious periderm-like layer. It appears from Stahl's examination that in their complete and open state they aid in the exchange of gases between the interior and exterior of the stem. Klebahn ^ its base are in a healthy condition, while the internal shaft of wood is dry, and not liable to undergo rapid decay. The formation of a separative mass over the wood can therefore go on to completion. 1 Bot. Zeit., 1873. Compare Haberlandt : Sitz. d. k. Akad. Wien, Band Ixxii. Abth. i., 1876. 2 Berichte der deutschen botanischen Gesellschaft, 1883, p. 119. Fig. 118. Section througli a lenticel in tbe periderm of Sambncus nigra : 1c, peri- derm; r, primary cortex; v, meristem, above which are the cells therefrom produced; 6, liber. (Stahl.) 152 MINUTE STEUCTUKE OP THE STEM. has lately shown that even in stems with the periderm free from lenticels, provision for exchange of gases is secured b}' certain intercellular spaces at or near the points where the medullary rays come to the periphery of the stem. 424. Grafting. If the cambium tissue of a young shoot is retained for a time in close apposition with that of a nearly related plant, union of the two parts may take, place, and the wound may heal by the natural process before described. Suc- cess in this operation depends upon selection of suitable stock and scion, choice of the proper season, freshness of the cut sur- faces, and, generallj', exclusion of air from the wound. The methods of bringing the surfaces of the stock and scion together in this operation of grafting are innumerable, but for the pres- ent purpose may be referred to two principal types : (1) that in which the scion, wholly separated from the plant on which it grew as a branch, is placed in some sort of a cleft of the plant which is thenceforth to furnish it with nourishment ; (2) that in which the scion is still retained in its connection with the parent plant, but is bent over and a freshly cut surface kept in contact with a cut surface of another plant, until the scion has fairly become attached by organic union. When this is accomplished, it is cut off from the parent plant. This type of grafting, in its many varieties, is known as " approach grafting." It takes place in nature, as shown in the following paragraph. -^ 425. Two branches of one plant may become united when, after removal of a section of bark from each, the two denuded surfaces are kept in apposition for a time. Such unions of axial organs are not rare. Occasionalh* they may take place between two shoots at a point near the root, so that the trunk will ulti- mately consist of a single deeply grooved stem. The union may be between two plants of the same species, or even between plants of different species. The attrition of two branches which have grown against one another may suffice to wear off the bark on both down to the cambium, and then, if their exposed surfaces are held together for a while, union will follow. Such natural grafts are met with frequently' at the borders of forests. 426. In the kindred operation of budding, a bud with a little of the tissue behind it is placed in a cleft in the bark of the stock, so that the cambium layer of the two maj' come into close contact. 427. The stem may be invaded by parasitic roots at any part, and its subsequent development seriouslj' affected therebj'. Such invasions often give rise to swellings, distortions, etc., by which RUDIMENTAllY AND TKANSFOEMED BKANUHES. 153 the structure of the stem becomes much disguised. In the case of parasites like Phoradendron, which hve for sevei'al years, a vertical section through the stem of the host-plant shows how complete the union is between the host and parasite. The junc- tion has been well compared to that which takes place between a scion and its stock, since the newer-formed tissues of both plants become perfectly united, and their subsequent growth goes on together. 428. The relations of the root to the stem are not complicated, except as regards the bundles at the " crown" of the root, or the point where it meets the stem. When the primary structure of dicotyledons in which the liber of the root is arranged in one way and that of the stem in another, as shown in Figs. 92 and 112, pages 111 and 137, is followed by the formation of a true cambium ring, tlie subsequent growth of root and stem is alike. Yearl3' additions are made in the root in the same way as in the stem ; but owing to the unequal resistance exerted by the soil, such increments are often very irregular. Roots may be produced at any part of a stem where adequate moisture and warmth are furnished ; but they strike off chiefly at nodes, and, in the case of cuttings, also at the seat of injury where the callus is formed. Such secondary roots form on stems in much the same manner as root-branches do upon roots. 429. Bndimentary and transformed branches present few ana- tomical difficulties. In the structure of a branch tendril, or runner, it is generally easy to recognize the degree of reduction which the normal flbro-vascular system has undergone. In the case of underground stems and branches there are often puzzling anomalies, but they can mostly be explained by the following facts brought out by Costantin,-' who has made a special stud3- of a large number of rhizomes: 1. The epidermis, if present, is modified by becoming cutiuized first on its outer walls, where it may acquire considerable thickness, and later on its lateral and internal walls. 2. The cortex increases either b}' enlargement of its cells or bj- their multiplication, the coUenchj-ma diminish- ing or completely disappearing. 3. A cork-layer is sometimes produced at an early period, from different points in the epi- dermis, in the cortical parenchyma, in the endodermis, in the peripheral layer of the bundles, or, lastly, in the liber. This replaces to a great extent the fibrous layer which is so com- mon in aerial, but never much developed in underground stems. ' 4-nii. des So. pat., ser 6, tome xvi., 1883, p. 164. 154 MINUTE STRUCTURE OK THE STEM. 4. The cortex is developed largelj' at the expense of the pith. 5. There is only slight lignificatioii of the elements. 6. There is a great accumulation of reserve materials. 430. The relations of a branch to the main axis of the stem seldom present any histological difficulties, the tissues of the former being continuous with those of the latter. When a branch breaks off close to the stem, and the portion remaining becomes buried by stem-tissues which are subsequentl}' produced, a knot is formed. 431. Steins of rascnlar cryptogams.'' The following outline indicates the principal points of difference between the stems of Phsenogams and those of Ferns, Equisetacese, and their allies. I. In vascular crj-ptogams the fibro-vascular bundles are closed and as a rule are concentric. 1. In Equisetnm they are slender and are arranged in a circle. From the median line of each tooth of the " sheath" (see Gray's Manual) a fascicle de- scends perpendicularly through one internode and divides at the one below into two branches, which unite with the lateral ones next to them. 2. In Osmundaceas the arrangement of the con- stituent parts of the central cylinder is not unlike that in certain ConiferiB. 3. Lycopodiacese have the bundles largely dependent upon the arrangement of the leaves, but the axial cylinder is essentially cauline. 4. Ferns proper maj- have (a) an axial cylin- der, or (/;) several concentricallj^ curved bundles. In either case there may also be isolated and rather slender bundles. In both cases above mentioned the bundles coalesce to form a \ery com- plicated network, which apparently is not dependent for its char- acter upon the distribution of the leaves upon the stem. II. In vascular cryptogams the parenchyma in certain places may become largel}- sclerotic, forming dense and often brown masses, the constituent cells of which are sometimes considerably elongated. III. The epidermis in Equisetacese is strongly silicifled. The stomata in these plants are in the grooves ; their development is peculiar in that from one epidermal cell four guardian cells are formed in one plane ; but soon the two outer cells grow more rapidly and crowd down the two inner ones, so that the latter afterwards become distinctly below them. The epidermal cells of Ferns frequently contain chlorophyll granules. 432. Stems of mosses. Here no true fibro-vascular bundles are met with, but elongated cells fill their place, forming what 1 Pe Bary : Vergleichend? Anatomie, p. 289 ct seq. DEVELOPMENT OV THE LEAP. 155 has been termed a fascicle. Comparison of these threads — if such they can indeed be called — with the rudimentary flbro- vascular bundles of some water-plants suggests that the former are bundles of the simplest possible kind. The parenchyma cells are bounded in true mosses by smaller, thicker- walled cells, which do not contain chlorophyll. THE LEAF. 433. It was shown in 322 that roots are formed under the superficial tissues of the stem, and have these outer layers, or derivatives from them, as coverings during at least a portion of their growth. But leaves are never thus covered by layers of stem-tissue ; hence they are termed exogenous productions, while the term endogenous is applied to the manner in which roots are formed. 434. Development. In the earliest stage of its development the leaf is a mere papilla consisting of nascent cortex (periblem) and nascent epidermis (dermatogen). As soon as the papilla elongates, or becomes flattened, some of its interior cells, making up procambium tissue (see 315), difllerentiate into fibro-vascular bundles. But the procambium of the nascent leaf and that of the cone of soft tissue constituting the growing-point of the stem are in unbroken connection with each other ; in like man- ner the bundles which are derived therefrom are continuous, and it is not possible to detect anj' line of demarcation between them. In fact, the newly formed bundles in a young leaf appear as if they are merely the slender prolongations and terminations of those in the young stem.^ 435. With the transverse and longitudinal enlargement of the nascent leaf there is generally more or less curvature, so that the outer, lower, and earlier leaves infold the upper leaves and the growing-point of the cone. In most cases, some of the lower leaves which thus envelop the growing-point become modi- fied to form protecting scales ; such is the ordinary structure of buds (see " Structural Botany," page 42, fig. 83). ^ It should be rememljered, however, that some of the bundles in the stem (see 365) may be derived from procambium peculiar to the stem, and which does not extend into the leaf. .Hence it is necessary to distinguish between stem-bundles, common bundles, and leaf-traces. The former belong to the stem alone ; the comihon bundles are common to stem and leaf; the leaf-traces are leaf-bundles which are in the stem and which at some point unite with other bundles of the same kind to form common bundles. 156 MINUTE STRUCTURE OF THE LEAP. 436. The growth of the j'oung leaf is plainlj' terminal at first, — that is, new cells are added just in front of the older ones; but it soon becomes intercalary as weU, new cells being introduced between those previously existing. According to the seat of activitj', this growth may be basipetal (the zone of growth being near the base of the leaf-blade) or basifugal (the zone nearer the apex of the leaf). In most cases the base of the leaf-blade and the stipules early attain a good degree of development, after which the petiole appears. For the purpose of noting the peculiar mode in which the leaf- blade expands, the simple device suggested by Hales '■ is perhaps as good as any. Through a piece of stiff pasteboard sharp pins are thrust, and fastened at equal distances from each other ; for instance, so as to form little squares of J inch side. By this sim- ple instrument a young leaf is pierced through with holes at equal distances ; then if the leaf elon- gates more than it widens in the space thus covered, the holes will separate in the direction of the length of the leaf more than in that of its width. The injury done to the leaf by these small perforations does not appear to check or other- wise much modify its growth. 437. Fibro-yascular bnndles. The distribution of fibro-vascular bundles in leaves has been con- sidered in Vol. I., under "Vena- tion." The two principal tj^pes of distribution of the bundles, there spoken of as "veins " or "nerves," were shown to be (1) parallel, (2) reticulated. Parallel venation (see Fig. 119) is characterized by having large "veins " or " nerves " running free through the leaf (that is, not connecting with each other), or without any obvious anastomo- sis ; while in reticulated venation the veins form a more or less com- plicated network. 1 Statical Essays, vol. i., 1731, p. 344. Fia. 119. Venationof theleaf ofOonvallarlalatifoUa. (Ettingshausen. ) VENATION OF LEAVES. 157 120 438. Parallel venation is of two principal kinds : (1) that in wliich. large nerves run in long curves from the base to the apex of the leaf; (2) that in which smaller nerves run generally at right an- gles from a main nerve (or midrib) to the edges of the leaf. In both these kinds of parallel venation the veins are more or less con- nected bj' means of inconspicuous cross-veinlets and b^- the anasto- mosing extremities, but some of the veins may be free. 439. Eeticulated venation is likewise of two principal kinds : (1) palmate (Fig. 120), in which relatively large veins diverge from each other at the base of the leaf ; (2) pinnate (Fig. 121), in which Fig. 120. Venation of the le^f of Asarum Europseum. (Ettingshansen.) Fig. 121. Venation of the leaf of Salix graiidifolia. (EttinesliauBcn.) 158 MINUTE STBUCTDEE OF THE LEAF. side veins strike off through the whole length of a strong midrib. In both these cases the veins divide and subdivide and have numerous cross-connections both large and small, until the ulti- mate ramifications are in great part free. 440. Thus it appears that in both types there is abundant communication between the veins of leaves ; but in some cases, especially in rudimentary and submerged leaves, in the leaves of Coniferee, etc., the veins are verj- generally free, and few if any cross-veinlets are met with. 441. The flbro-vascular bundles of leaves are essentially like those of stems (see 365), and need no special description here. Their extremities are for the most part tracheids, often arranged in double rows, but their diversities of structure and arrange- ment are innumerable. One of the more striking special cases of these has been already shown in the illustration of a water-pore («, Fig. 55) ; others will be considered later (see " Insectivorous Plants"). The tracheids which terminate the final ramifications of the veins in leaves are in close contact with parenchyma cells. 442. According to Casimir De CandoUe, the leaf maj' be re- garded histologically as a branch with its upper, that is its posterior, side atrophied.^ 443. The stipules have the same arrangement of elements in their fibro-vascular bundles as the blade, — that is, liber below (outside), wood above (inside). But in ligules (organs which are formed by radial deduplication) the arrangement is just the reverse of this, — the liber is above, the wood below. 444. Parenchyma. The forms of the parenchjma cells which constitute the pulp of leaves are: (1) spherical or nearlj' so; (2) ellipsoidal, sometimes much elongated ; (3) branched, some- times stellate. Examples of these three are often met with in the structure of a single leaf; the upper laj'ers generally being composed of ellipsoidal cells, the lower laj-ers of more nearly spherical ones, intermingled with some which are branched. 44.5. The arrangement of the parench^'ma of the leaf-blade is referred bj' de Bary^to two chief tj'pes : (1) the centric^ in whicli the chlorophyll parenchj'ma is uniformly disposed through- out the whole organ ; (2) the bifacial., in which there is a de- cided difference between the compact tissue of the upper and the spongy tissue of the lower side of the leaf. ' Arcliives des sciences de la Biblioth^ue unlverselle, 1868, tome xxxii. p. 32, "iin rameaii Ji face postevieuve atrophiee." ' Vergk'ichende Anatomie, p. 423. PARENCHYMA OF THE LEAF-BLADE. 159 446. The centric arrangement has two modifleations : (1) that in whicli the whole pulp is composed of chlorophyll parenchyma, but towards its mid- dle plane has larger cells with less chlo- rophyll, aud some- times has conspicu- ous lacunte (many grasses. Yucca flla- uieutosa, Crassula, etc.) ; (2) that in which it is composed of la3-ers which are uniformly distrib- uted above and be- low a middle laj'er of colorless cells free from chloroplyll, but, in succulents, ver}' rich in sap (Aloe, IMesembryanthemum, etc.). In both the foregoing modifica- tions the upper layer of the parenchyma may be composed of somewhat longer cells than those below, and to them can be applied the term more gener- ally given to those in the next type, namely, palisade-cells. 447. The bifacial arrangement has the (jlenser tissue in that part of tlio leaf which is exposed to the light. This usually consists of several layers of palisade paren- FlG. ]22. Leaf of Piiius Laricio. Cross-section of a part of the ]eaf, Blmwing the stoniata, hypnderraa, ami parenchyma. The fnldeil walls of the parenchvma-oells (see 208) are plainly shown in the cells below the resin-passage {TIC), where they have been emptied of their contents. (Kny.) Fig. 123. Transverse section of a leaf of Ilex Aquifolium, showing arrangement of the parenchyma: 2^p^ palisade parenchyma; pr, spongy parenchyma; /i, hypoderma; la, fibro-vascular bundle. Stomata are found only upon the lower surface of the leaf. (Areschoug. ) 160 MINUTE STRUCTURE OP THE LEAP. ch3-ma ; but the aggregate thickness of these may not be so great as that of the spongy parenchyma on the other side of the leaf (see 205). 448. In some plants the palisade parenchyma is found almost as abundantly in the under as in the upper portions of the leaves. Bessey ^ has shown that this is the case in the leaf of the Compass plant (Silphium laciuiatum) : " Its chlorophyll-bearing parenchyma is almost entirely- arranged as palisade tissue, so that the upper and lower portions are almost exactly identical in structure." Another plant possessing substantially the same leaf-structure is Lactuca Scariola. When its leaves are grown in the light, they take a vertical position (and generally stand north and south) ; but if grown in the shade, thej' are horizontal. The leaves which are developed in the light have palisade paren- chyma on both the upper and under portions ; •' but those which are developed in the shade have ordinary- parenchyma above and more or less stellate parenchyma below. 449. According to Stahl,' exposure of a leaf to light or shade during development has very much to do — in the plants thus far examined -r- with the fonn and arrangement of its paren- ch3ma. The leaves of the common beech afford good material for the studj- of the subject. In some cases, at least, those which are grown in the deep shade of a grove are different in texture from those which are formed in bright sunlight. 460. The parenchyma of the petiole is generally much Uke that of the stem to which it is attached ; layers or lines of thin- walled eollenchyma sometimes extending without interruption from the stem into the petiole. In the petioles of Cycads scle- rotic elements like those of the stem are often abundant, and ai-e continuous with them.^ 451. In some leaves which have the power of movement the petiole is much enlarged at its base, forming what is known as the pulvinus. The parenchyma of this structure is sometimes peculiar in being thick-walled on the upper side of the petiole and thin-walled on the under. Other peculiarities will be de- scribed under " Movements.'' 1 See also American Naturalist, 1877. 2 Pick : Botanisches Centralblatt, 1882, vol. xi. p. 441. 3 Stall! : Ucber den Einfluss des sonnigen oder scliattigen Standortes auf die Aiisbildung der Laubblattev, Jena, 1883. Haberlandt, on the other hand, does not think the elfect of light in con- trolling the character of leaf-.structure is well marked. * Kraus ; Pringsheim's Jahrb., 1865, vol. iv. p. 305. EPIDERMIS OP THK LEAF. 161 452. The epidermis of the leaf is continuous with that of the stem. Its principal features have been described in Chapter II., and only the following need now be recalled. 1. It may be simple, that is, composed of one layer of cells ; or multiple, — of more than one. 2. Immediately below it may be found in some cases one or more la3-ers of cells known as the hypodermu. 3. The epidermal cells are in un- broken contact with each other except at (1) rifts, (2) water-pores, (3) stomata. 4. Their surfaces may exhibit nearlj'. every form of trichome. 453. Glands secreting nectar are found on different portions of the leaves of various plants ; for example, at the junction of the petiole with the blade (Poplar), at the base of the petiole (Cassia occidentalis) , on the lower side of the midrib of the leaf (cotton- plant) , or scattered over the lamina (turban squash) . Such glands are particularly noticeable in insec- tivorous plants, as Sarracenia and Nepenthes (see Part II.). On making a section of one of the nectar-glands found on a young poplar leaf, the epidermis will be seen to be transformed into a double layer of thin- walled, elongated cells forming the secreting surface, which is charged, together with the parenchyma lying below it, with a syrup de- rived from the transformation of starch. At times the secretion from a gland is so abundant that drops of considerable size collect upon the surface of the leaf, and if rapid evaporation takes place, crystals of sugar are deposited at the gland.' 454. The leaves of submerged phsenogams, for example those of Potamogeton and Myriophyllum, possess no true epidermis ; the parenchyma is therefore in direct contact with the surround- 1 Trelease : Nectar and its Uses, in Report on Cotton Insects (United States Department of Agriculture, 1879), and Nectar-Glands of Popuhis, Botanical Gazette, vol. vi. p. 284. Fig. 124. Transverse section through leaf of Camellia (Thea) viridis, showing : a epidermis ; 6, branched liber-cell ; d, oil-drop ; e, crystals. (Mirbel.) 11 162 MINUTE STEUCTDEE OF THE LEAF. ing water. On the external surface its thin-walled cells are in close contact (there being nothing answering to stomata) ; but in the interior of the leaf there are often lacunae filled with air. These were thought bj- Brongniart to be essentially the same as those cavities found in the parenchyma of msnay marsh plants. The veins of submerged leaves have no true ducts ; the elon- gated fascicles generally consisting merely of rows of elongated cells. ^ 455. Roots may be produced from leaves in much the same way as they are from stems ; that is, some of the cells at the liber maj- divide in such a manner as to form a protuberance which pushes before it a part of the endodermis. As the root thus formed emerges, the tissues are speedily produced, the wood being continuous with the wood of the leaf, the liber with its liber. Eoots maj' arise naturallj' in some leaves by simplj- plac- ing them in contact with moist earth, or they may be produced artificially by mutilation of the petiole or lamina. Bryophyllum cal^cinum affords a good example of the former ; Begonia, Peperomia, etc., of the latter mode of origin. 456. Buds may form spontaneously on the margin of leaves, especially those in contact with a moist surface, or they may grow from the cells under the scar where a mutilated leaf has healed. 457. In some of these cases only the epidermal cells take part in producing the meristcm from which the bud is developed : in others the parenchj'ma just below the epidermis also divides, or the cells under the scar may produce all the axial tissue ele- ments. Begonia is an example of the first method of production. Bryophyllum of the second, Peperomia of the third. It is interesting to observe that in all these cases the bud forms without the intervention of tlie fibro-vascular bundles of the leaf. Tlie newly formed axis has flbro-\'ascular bundles, which may anastomose with those pre-existent in the leaf, but usually they are entirely distinct. The axis is, however, provided with its own rootsystem, and after a time it becomes severed by a plane of cork from the leaf which produced it. 458. Fall of the leaf. In deciduous plants the leaf separates from the stem or twig by the formation of a plane of cells '' cutting sharply through the petiole at or A^ery near its base. The dividing plane may be partially formed early in the growing 1 Brongniart : Ann. des Sc. nat., tome xxi., 1830, p. 442. 2 Called by Mohl the separative layer (Botaiiische Zeitung, 1860, p. 1). FALL OF THE LEAF. 163 season, but generally it is not far advanced in development until near tlie end of summer. Tlie leaflets of the larger compound leaves — for instance, those of Ailanthus, Gj-mnocladus, Ju- glans, etc. — afford excellent material for examining the process of defoliation. Strong leaves of iniy of the plants mentioned are to be kept between damp (not wet) paper in a warm place for a number of hours, when the formation of the dividing plane can be observed. The plane is so far completed by the end of the second or third day that the leaflets fall with the slightest touch. 459. The strong leaves of horse-chestnut are emplo3'ed bj' Strasburger as material for demonstrating the process of defolia- tion. He says that alcoholic material answers ver^- well for the purpose, but that it happens occasionally that the distinctive brown color of the cells adjoining the cutting plane is nearly or quite lost. The petiole is to be cut through in its median line, and then several verj' thin longitudinal sections parallel to this are to be carefully made and placed at once in water. In a good preparation the cells making up the cutting plane should be clearlj' seen extending from the epidermis of the petiole to the fibro-vascular bundles. If the leaf was taken at just the right time, the preparation should show also that the cutting plane has invaded even the tissue of the fibro-vascular bundles. The plane consists of one to several layers of cells, some of which are plainh' cutinized ; thus, as a rule, the place of separation is a scar healed before the leaf falls. It happens frequently that changes take place at the middle portion of the cutting plane, by which its la3ers near the leaf are forcibly separated from those nearer the stem ; in such cases the leaf falls because it is forced off.^ 460. The excision of the leaf usually takes place at the base of the petiole, so that the surface of the scar is even with the 1 "The provision for the separation being once complete, it requires little to effect it ; a desiccation of one side of the leaf-stalk, by causing an effort of torsion, will readily break through the small remains of the fibro-vascular bun- dles ; or the increased size of the coming leaf-bud will snap them ; or, if these causes are not in operation, a gust of wind, a heavy shower, or even the simple weight of the lamina, will be enough to disrupt the small connections and send the suicidal member to its grave. Such is the history of the fall of the leaf. "We have found that it is not an accidental occurrence, ari.sing simply from the vicissitudes of temperature and the like, but a regular and vital pro- cess which commences with the first formation of the organ, and is completed only when that, is no longer useful" (Dr. Inman, in Henfiey's Botanical Gazette, vol. i. p. 61). 164 MINUTE STETICTXJKE OP THE LEAF. surface of the stem ; but it may occur a little higher up, so that some of the petiole remains attached to the stem '■ (Rubus, Oxalis, etc.). 461. Evergreen leaves are those which remain upon the stem without much apparent cliange during at least one period of suspension of vegetation. The leaves of some evergreens per- sist through only one year, falling off as soon as those of the succeeding year have fully expanded. It is not unusual in warm temperate climates to have trees and shrubs which are normally deciduous in colder regions retain their leaves until new ones are produced. Pines and spruces lose some of their oldest leaves every j'ear, but new ones are as regularly formed. Their branches are never completely defoliated, but may bear at one time the leaves which have been formed during several 3ears. 462. The colors assumed by leaves before they fall can be better examined after the subject of the pigment of chlorophyll- granules has been treated in Part II. 463. The fronds of ferns and the leaves of their allies present few peculiarities, and do not need to be here examined. The formation in ferns of the sori, or spore-dots, the sporangia, or spore-cases, and the spores themselves falls properly within the province of Volume III. 464 . The leaves of mosses are characterized bj' great sim- plicity of structure. For their study any of the species of Poly- trichum, or Hair-cap Moss, will answer. In these there is no true fibro-vascnlar bundle ; a series of somewhat elongated and rather firm cells, known as the conducting thread, takes its place. Upon this conducting thread the parenchyma cells are distributed more or less regularly, on one side forming slender elevations four or five cells in height. The cells contain chlorophj'li, and generallj' much starch. " 465. In the thallophytes there is no clear distinction of leaf and axis ; the tissue consists throughout of parenclyma more or less modified. In some algae there is often a lateral parting of the frond into segments resembling leaves ; but as they are not leaves morphologicall}', they need no further consideration here. 1 For full and interesting accounts of the changes which cause the fall ot the leaf, see Mohl's paper in Botan. Zeitung, I860, p. 1, and also Van Tieghem and Guignard in Bull. Soc. bot. de France, 1882. ^ In Strashurger's Botanische Practicura, p. 304-, the student will find a full anil interesting account of the structure of the leaves of Polytrichum and Mnium. WORKS OF EEFEEENCE. 165 In the examination of the tissues of the organs of vegetation the student is referred to the following works : — De Bakt. Vergleichende Anatomie (Leipzig, 18V7). An octavo voluiue of about 660 pages, of which an excellent English translation is newly pub- lished under the title, " Comparative Anatomy of the Vegetative Organs of Phanerogams and Ferns," liy A. De Bary. Translated by F. 0. Bower and D. H. Scott, 1884. This exhaustive treatise gives all needful references to the literature of the subject up to 1876. MoHL. Vermischte Schrif'teu. This is a collection of Hugo von Mohl's most important works, which have appeared from time to time in various journals. Steasburger. Das botanische Practioum (Jena, 1884). This work, of which an English translation is promised, is of very great use both to beginners and advanced students of Histology. The directions for procuring, preserving, and using material are explicit, and for the most part are conveniently ar- ranged. The volume, of more than 600 pages, is divided into separate studies, such as the structure of the bast and wood of the pine, the anatomy of a few common leaves, etc. Oliver. Bibliography of the Stems of Dicotyledons (Natural History Re- view, 1862 and 1863). A citation of the more important works on the stems of different dicotyledons, arranged according to the natural families. For a treatment of the anatomy of the organs of aquatics and parasites, the fully illustrated work of Chatin may be consulted. Those curious to examine the diverse and now mostly abandoned views regarding the growth and structure of the stem, will find much of interest in the works of Du Petit Thouars and of Gaudichaud. An account of these and other views will be found in Schleiden's " Principles of Botany" (1849). CHAPTER IV. MINUTE STRUCTURE AND DEVELOPMENT OF THE FLOWER, FRUIT, AND SEED. THE FLOWER. 466. In Volume I. Chapter VI., it has been shown that a flower is to be regarded as a modified branch with ver}' short internodes and with the fohar expansions assuming forms unlike those of ordinary leaves. In the outer circle — the calj'x — the parts have frequently the texture and color of foliage ; but in all the other circles of the flower they are notablj' metamorphosed. Notwithstanding their disguises, the parts of the flower arc iden- tifiable as leafy structures arranged upon an axis. On the care- ful examination of flower-buds the homology between all their parts and those of a leaf-bud becomes evident. In fact, in their earliest state it is impossible to discriminate between these two kinds of buds. Each has a rounded or cone-like extremitj-, upon which are disposed at definite points the papillee which are to develop into foliar organs. In one, these papillae become green leaves ; in the other, the parts of a flower. 467. Two features in the development of flowers require special attention ; namely, the sequence in which the organs are produced, and the order in which the histological elements make their appearance. But it is not well in an^' given case to under- take the examination of the development either of the organs or of the tissues which compose them, until the student has made himself familiar with the characters of the full-grown flower. 468. Undeveloped racemes afford the beat material for the studj- of the developing organs of the flower, and it is generally possible to flnd in a single young cluster flowers in all the earlier stages of development. There are two good methods of pre- paring the material for the compound microscope : (1) the whole raceme, first decolorized by absolute alcohol and then softened by glycerin, is to be dissected under a simple lens, and the sepa- rate flowers are to be bleached with sodic hypochlorite ; or (2) the DEVELOPMENT OP TUIO FLOW Kit 167 very tip of the raceme is to b(; cut sqiiareh- across ;nid pltu'cd with a drop of water under a cover glass, when some of tlie joung- est flowers can be seen either standing \'ertically or slightlj- in- clined. The air can be drawn out from the specimen by placing the slide for a min- ute under the air-pnmp ; the outlines of the floral organs will then be distinct. 469. A still better method is to make tolerably thick vertical sections of separate flowers, one of whicli in each flower must be through the median line ; and tben, arranging the sections ^ in their proper sequence, clear them for examination either by the use of potassic hydrate (as directed in 24), or by the following method, recommended by Stras- burger as applicable to manj' cases of thick masses of soft tissues : Treat the part first with absolute alcohol for a daj- or two, and then place it in concentrated carbolic acid, after which it becomes clear. For the carbolic acid either of the 126 following may be substituted, — (1) three parts of oil of turpen- tine and one part of creosote, or (2) equal parts of alcohol and creosote. B}' any one of these methods it is generally possible to obtain preparations of sufficient clearness to exhibit in optical section all the internal tissues. $t,n 1 Pfefl'er advises that the young flowers should first be tinged with aniUii blue, and then imbedded in a strong solution of gum-arabic (to which a littli! glycerin has been added to prevent brittleness of the mass on drying). Then, when the gum is dry, sections can be easily cut in any direction. Fig. 125. Lysimachia quadrifolia. Flower seen from the side, and somewhat ob- liquely, the calyx being removed. At this period the parts of the corolla have not coalesced : sp, place where the excised sepals were ; p, petal ; st, stamen. (Pfeffer.) Fig. 126. Lysimachia quadrifolia. Thin longitudinal section throngh the median line of a flower, in which the organs are beginning to form. Before the sinuses of the- calyx, as well as before its lobes, cell-division has taken place on all sides ; for instance, at si, )i, and a;. (Pfeffer.) 168 MINUTE STRTJCTtJftE OF THE fLOWER. 470. The fully grown flower of Lysimaehia quadrifolia is thus characterized : Calyx hypogynons, deeply 5-parted, the lobes valvate or very slightly imbricated in the bud ; corolla l^'pogj-- nous, wheel-shaped, and deeply 5-parted with hardly any tube, its lobes convolute in the bud ; no teeth between the lobes of the corolla ; lobes of the corolla longer than the narrow lanceolate lobes of the calj'x ; stamens of unequal length, plainlj- united at the base, inserted opposite the lobes of the corolla, glandular ; anthers barely oblong ; ovary one-celled, surmounted bj' an un- divided style and stigma, and containing 10-15 ovules on a central placenta. Fig. 126 shows the appearance of a very young flower of this species ; on the rounded or somewhat flattened apex of the axis minute elevations are seen, the outer being the nascent sepals. Fig. 127 shows the flower in a more ad- vanced stage. Fig. 128 represents a portion only, the right, in a still more advanced condition. Fig. 129 exhibits all the organs of the flower, so far as they can be shown sp.u Fig. 127. Lysimaehia quadrifolia. A longitudinal section tlirough a flower some- wliat more advanced than in Fig. 126; the letters are the same as in Fig. 128. (PfeiFer.) Fig. 128. Lysimaehia quadrifolia. Longitudinal section through an elevation which is considerably advanced before the appearance of the petals: si, stamen; n, cells where the petals will appear. (Pfeffer.) Fig. 129. Lysimaehia quadrifolia. A longitudinal section through a flower in which all the organs are well developed, and even the parts of the ring by which the corolla- lobes are to coalesce have begun to grow : sv, sepal ; p, petal, or corolla-lobe ; st, stamen ; .9, ovary'; c, placenta ; sp. u, and p. u, the tissue uniting the i)art8 of the calyx and corolla respectively. (Pfeffer.) ORDER OP APPEARANCfi OP FLORAL ORGANS. 169 in a single longitudinal section. Comparison of tlie.su figures gives a clear idea of the sequence in which the organs make their appearance ; namely, in acropetal succession, — that is, the younger or newer are always nearest the extremitj*. 471. According to Paj'er, the sepals alwaj's precede the petals, the petals the stamens, and the stamens the pistils, in time of appearance. But in a few cases, of which Lysimachia is one, it may happen that a given circle of organs is somewhat de- la3'cd in forming ; for instance, in the figures the stamens are seen as considerable protuberances before the petals are clearly outlined. This fact has been considered by some to indicate that the corolla in such cases consists of an intercalated whorl between two other whorls already somewhat developed. But a careful examination of Lysimachia and most other cases shows rather that the petals or the corolla-lobes are laid down in their proper sequence, but that they are temporarily outstripped by the sepals and the stamens. The appearance of the forming flower when seen in vertical section is shown in Fig. 130, and a perspective view is given in Fig. 125, exhibiting the late-appearing petals and the much larger stamens. 472. Since the several organs of the flower are modified leaves symmetrically arranged on an axis, the histological con- stituents of a leafy branch will be found in the flower, albeit much modified in some of their characters. These constituents are, (1) a framework of flbro-vascular tissue, upon which is extended (2) parenchyma, covered by (3) epidermis. Fig. 130. Lysimachia quadrifolia. Longitudinal section through a flower in which the corolla is just appearing. The elevation on the right has been cut tljrough exactly in the median line, while that on the left has been cut on its edge. Letters the same as in Fig. 129. (Pfeffer.) 170 MINUTE STRtTCrUKE OF THE FLOW-EB. 473. The ilijro-vasculiir bundles of the flower are esseutiiilly the same as the collateral buiKlles found in ordinary green leaves, except that their elements are usually' more dehcate in texture, and in the inner whorls of organs very much reduced. 474. The parenchyma calls for no special remark beyond allu- sion to the fact that some one of the difierent kinds of internal glands is frequently associated with it. 475. The epidermis has stomata, — which are generally rudi- mentary, — and most of the forms of trichomes. One of the most interesting peculiarities of structure presented by the parts of the flower is found in the papillar outgrowths alluded to in 222. These are of course minute and short hairs, which, owing to their abundance, impart a velvety appearance to the part on which they occur. This appearance is well shown by the petals of a vorj' large number of the flowers most common in cultiva- tion. 476. The cuticle of the epidermal cells of the more delicate petals is sometimes ver}- distinctly striated in an irregular man- ner. The walls of the cells generally' have a sinuous outline. 477. The colors of petals and other colored parts of the flower are dependent either on the presence of corpuscles (the colored i)lastids) or of matters dissolved in the cell-sap. The following account of the coloring-matters in the very com- mon Viola tricolor is condensed from Strasburger. A vertical section through a petal exhibits the epidermis of the upper side as consisting of elongated papilte, while that of the lower side has onlj' slightly rounded ones. Just below the epi- dermis of the upper side there is a layer of compact cells, under which are several rows of smaller cells with conspicuous inter- cellular spaces. The cells of the epidermis of both sides contain violet sap and yellow granules ; the layer of compact cells under the epidermis of the upper side contains only _yellow granules. The striking diversities in color presented b}' different pai-ts of a given petal depend wholly upon combinations of these two ele- ments of color ; namely, violet sap and yellow granules. In some places which are devoid of either of these elements there are white spots ; at these places the light is refracted and re- flected by the intercellular spaces which contain air. If the air is removed bj- pressure, the spots will become transparent. 478. The cell-sap in the parts of the flower may have almost any color, especially shades of red and blue ; from this sap the coloring-matter sometimes crystallizes in the form of short and slender needles ; for instance, in Delphinium Consolida. BKVELOPMeNI' Oi? STAMENS. 171 1 2' 3' ep cm 479. Developmeut of the stamens. The following outline may serve as an iutroduution to the stud}- of the development of the stamens. At first, the stamen exists as a mass of homogeneous parench3-nia ; later, a del- icate fascicle, continuous with one in the filament, becomes differentiated in one part of the stamen, the connective. Four longitudinal ridges appear on the an- ther, which coincide with four lines of large cells within. These cells give rise to the mother-cells of the pollen and to the very dehcate pollen-sac.^ 480. The mother-cells of the pollen have at first thin walls, but later these become irregularly thickened. In a large number of cases — many mono- cotyledons, and most if not all dicoty- ledons — the nucleus of a mother-cell divides into two nuclei, which themselves divide -S ij at right angles to the -tdv5fe^^^^s^v rp>.-^^^-n-r^ plane of the first division, thus producing four nuclei forming a tetrahedron. Cell-walls are n ext form ed, and four cells are pro- duced, which are called the tetrad. After the mother-cells of the pollen have been changed into tetrads, the mass of pro- toplasm in each of the cells of a tetrad becomes covered, as Strasburger has shown, with a new 1 The cells which muke up the layer Ibrming the pollen-sac are known, collectively, as the Archcsporiuin. The epithelium which lines the pollen-sac has been termed the Tapetum. Fig. 131. Orchis inacnlata. A pollen-mass in process of enlargement, with the anther- wall on the outside: ep, epidermis; 1, layer of cells under the epidermis remaining un- divided ; 2' and 3', layers arising from division ; 3', the endothecium. The little mass cm, formed by the mother-cells, is surrounded by a thickened wall. 3^^. (Guignard ) Fig. 132. A, transverse section of a young anther of Mentha aquatica ; B, a fourth of this magnified; f, section through a young anther of Symphytum orientale; B, a fourth of this niagniiied. The clotted lines in A and C show the part taken for exami- nation. E, section of a young anther of Leucanthemnm vulgare ( W.-irraing.) 172 MlNU'M STHtJCTUEE OF THE FLUWfiK. cell-wall, the proper cell-wall of the pollen-grains. This wall ma}' be variously marked, sculptured, and cuticularized, giving rise to the characteristic forms and features of the grains as thej' are met with in the mature flower. In g3-mnosperras, the development of pollen-grains differs from that described in some particulars which are interesting chiefly from their resemblance t(j what occurs in the higher cryptogams. 481. The stigma is a surface fornied of peculiar cells which secrete a viscid, saccharine matter, slightly acid in reaction. In some cases the walls of the stigmatic cells undergo the mucilagi- nous modification (Solanum, etc.). The wide differences which exist in the character of the cells of the stigma are illustrated by the following examples : (1) cells with no marked papillie, as in Umbelliferse ; (2) papillose, as in Salvia, Convolvulus, Spiraea; (3) hairj-, as in Hypericum, Geranium ; (4) with compound hairs, as in Reseda. In some of the above the cells are rather loosely aggregated, while in others thej" are much more compactl}- com- bined. Bt'lovv the stigma the style often has collecting hairs, as in Compositse, Campanulacese, etc. (see Volume I. page 222). 482. The style is a prolongation of the ovarj-, and shares with it its fascicular system. In the interior there is a slender thread of loose tissue made up of thin-walled cells containing consider- able food-material, starch or oil, etc. The cell-walls often pass into the mucilaginous condition. The style is sometimes tubular, and lined with the tissue just described. 483. The simple ovary is a modified leaf-blade provided with epidermis, parenchyma, and a fascicular system. The epidermis of the outside of the ovary, and that which lines its cavity, may have all the characters of ordinary epidermis ; stomata and hairs maj' be present, the latter often being mere papillae, which upon the ripening of the ovary into the fruit become long hairs. 484. In the interior of the ovary there is frequently a pecul- iar modification, either of the epidermis itself or of the sub- jacent parenchyma as well. In such cases verj' loose tissue, sometimes appearing as if composed of felted hairs, lines the cavitj' of the ovary (or is found at some one portion of it). The walls of this tissue maj' undergo the mucilaginous modiflcation either in whole or in part. Its cells contain a considerable amount of food-materials (oil and starch). This loose tissue, together with that of the same character found in the style, is known as conductive tissue, and serves as a path of least resist- ance for the penetrating pollen-tube (see Part II.). 485. The distribution of the fibro-vascular bundles in ovaries FIBEO-VASCtTLAR BUNDLES OF THE OVAKY. 173 IS of much interest, and can best be examined under the two heads of " Simple Pistils" and " Compound Pistils." 486. Simple Pistils. The libro-vascular bundle consists of wood and liber running through the median line of the carpellarj^ leaf, — that is, through the dorsal suture. Two branches are given off by this bundle not far from the base of the leaf, near its two united margins, — that is, at the ventral suture. 487. The folded carpellary leaf has incurved margins ; so that whatever the arrangement of the wood and liber may be in the median line of the leaf, the reverse will be found at the margins. Thus in each of the three carpels shown in Fig. 133 a, the flbro- vaseular bundle running through the dorsal suture has liber on its outside (the unshaded portion) and wood on its inside (the dark portion). But in each of its branches at or near the ventral suture liber occurs on the inside (that is, nearest the centre of the flower) and wood on the outside. 488. Compound Pistils. If several carpels unite to form a compound ovary, the same inversion of the order of the parts of the bundles (as shown in Fig. 133 a) will be seen when the bundles at the centre of such an ovarj? are compared with those at its periphery (see diagrams b to/, Fig. 133). Fig. 133. Transverse section of superior ovaries, sliowing the arrangement of the flbro-vascular bundles of carpels: a, Eranthis hyemalis; b, Hyacinthus orientalis; c, Tulipa Gesneriana ; d, Impatiens tricornis ; e, Anagallis arvensis ; /, Lychnis dioica. (Van Tieghem.) 174 MINUTE STRtrCTtJRE O** THE FLOWEE. 489. But if the ovaries, instead of being superior, as those in Fig. 133, are inferior, as tliose in Fig. 134, furtlier complications are caused. The fibro-vaseular bundles of the several floral whorls united with the pistil are distributed in cu-cles in the parencliynia tissue of the ovary. Thus in Fig. 134 a, we find Ave such circles, corresponding to the calyx, corolla, stamens, and dorsal and ventral sutures of the carpel. The bundles in Fig. 134 a are arranged in radial lines from the centre outwards ; the six bundles nearest the centre of the ovary are those of the ventral sutures, and have wood outside and liber inside ; in the next circle the three with reverse arrangement of elements are those of the dorsal sutures from which the bundles just spoken of branched. In Fig. 134 b, all the fibro-vascular bundles save those of the carpels 'e \ u ^ are united to form a single circle, thus giv- ing rise to the three circles of bundles seen in the cross- section, and at the base of the ovary even these did not exist separate. In Fig. 134 c, the bun- dles of all the floral whorls are blended for a considerable height in the ovary ; finally, the bundles of the ventral sutures become separated from the rest, which continue united throughout, formmg the large buurlles seen on the periphery of the ovary in Fig. 134 c. The arrangement of the bundles in this figure should be compared with that in Fig. 133. 490. The structure of the peduncle and the pedicels is sub- stantially the same as that of the stem, and the structure of Fig. 134 Transverse section of the inferior ovary, allowing tlie arrangement of libro- vascular bundles both in the carpels and the external parts of the flower: a, AlstrcB- meria versicolor, the fascicles of the whorls independent; 6, Galanthus nivalis, the fascicles no longer so distinctly radial; c. Campanula Medium, the fascicles of the whorls blended. (Van Tiegbem.) DEVELOPMENT OF THE OVULE. 175 the bracts is much like that of the leaf ; therefore these need not be specially considered here. 491. Ovules are normally formed at deiinite points or lines upon the ovarian wall, which answer to the edges of the carpel- lary leaves. The funiculus arises as a slight elevation produced by the multiplication of a cell or a group of cells under the epidermis; in the centre of this elevation, and also under the epidermis, further development produces a spheroidal or cone- like mass, — the nucleus. Then, a little later, cells at the base of the nucleus begin to produce a cylinder (the inner integu- ment), and shortly after, a second one is formed below and outside this (the outer Integument). Subsequent development carries the outer integument quite up and around the inner one, and the nucleus; leaving a small opening (the foramen). For peculiarities in the morphology of the ovule, and for cases in which one or both integuments may be wanting, see Volume I. page 278. 492. The funiculus has a collateral flbro-vascular bundle, having its median plane coincident with that of the ovule. The bundle is surrounded by parenchyma and epidermis. It is fre- quently prolonged into the integuments, being there more or less branched. Fig. 135. Development of the ovule of Aristolochia Clematitls. A, young ovule in vertical section; B, same, more aUvaDced; ti, internal integument forming; C, a later stage of same; ti, internal integument; te, external integument forming; D and £, later stages of nucleus, to be described in Part II. (Warming.) 176 MINUTE STKUCTUEE OP THE PRTTIT. THE FRUIT. 493. The fruit is the ripened pistil. But, as shown in Vol- ume I., " it is a loose and multifarious term, applicable alike to a matured ovary, to a cluster of such ovaries, at least when somewhat coherent, to a ripeued ovary with cal^-x and other, floral parts adnate to it, and even to a ripened inflorescence when the parts are consolidated or compacted." 494. Histologically considered, fruits present few difliculties, although the changes in form which a pistil undergoes as it ripens are not greater than the changes which it maj' suffer in minute structure. These histological changes are referable to a few simple kinds : (1) a great development of sclerotic elements, seen in the harder dry-fruits and in the putamen of all stone-fruits ; (2) a large increase in the amount of soft-walled parenchyma, containing sap, as in the pulp of all fleshy fruits ; (3) a consid- erable development of color, especially in the superficial parts. 495. Sections to exhibit the structure of the verj- hard parts of fruits are made most easily hy carefull3- grinding the parts on a fine oil-stone. First, a fragment of the hard shell of a nut or of the putamen of a drupe is obtained by means of any strong cutting instrument, and a flat surface parallel to the plane of the section desired made by a clean file. On a glass slide a drop of Canada balsam is .placed, and heated until the more volatile portion is expelled (see 111). Then the flat side of the object just prepared is held upon this balsam until the latter becomes cool and hard ; and when thus securely fastened, the specimen is rubbed down on an oil-stone to any required de- gree of thinness. It is removable from the slide hy oil of turpentine, aud can afterwards be mounted in a fresh portion of balsam or of benzol-balsam (see 112). 496. The contents of the parenchyma cells of fruits depend very largely on the degree of maturity of the fruit. Changes in the contents go on from the formation of the fruit until it is fully ripe. In some of the more common cases these consist largely in the production of various sugars, especiall}' that which is known as fruit-sugar ; and organic acids, for instance, citric, tartaric, and malic acids. A consideration of these changes belongs to Part II. 497. The coloring-matters in fruits, like those in flowers, are either color-corpuscles (ehromoplastids), or substances dissolved in the cell-sap. In a few cases the walls of the cells them- selves have more or less color. COLORING-MATTERS OF FRUITS. 177 498. The berries of a common house-plant, Solanuni Pseuilu- capsieum, furnish excelleut material for the examination of the coloring-matters of fruits. The following account, condensed from Kraus,^ will show the essential characters of the color- granules in this case, and it siiould be compared with what has been alread\' said about the structure of chlorophyll granules and leucoplastids (168 et seq.), as well as with the account of the chromoplastids in the parts of flowers (477). A section through the ripe pericarp shows that it consists ol' twentj' to thirty or more layers of cells, in most of which color- granules occur. In the outermost cells the granules closely resemble both in form and structure ordinarj' granules of chloro- phyll. In some of the granules the coloring-matter is evenly' diffused through the whole mass, while in others it is confined to some one part, the rest of the granule remaining without color of any kind. In these cases the colored and the uncolored parts are not ver3' sharply' divided from each other. 499. Other granules less like chlorophyll-granules occur, in which there is a sharp demarcation between the colored and uncolored parts ; such have been shown to be vacuolar, the vacuoles assuming widely different shapes. These are abundant in the cells which lie five to eight laj-ers, or rather more, from the outside. In some of these the colored portion appears spindle-form or sickle-form, in others curved twice, like the letter S. It fre- quently happens that several of these long granules are placed end to end, forming an irregular chain. 500. In the part of the berry which envelops the seeds the color-granules are extremely slender, and needle-shaped.^ All of the granules lie in the protoplasm ; usually in greatest number in that lining the walls, and immediately around the nucleus. 501. Occasionally in the larger pericarp-cells roundisli col- ored objects are met with, which close examination shows are nothing but vacuoles in the protoplasm of the cell filled with colored sap ; sometimes these have been mistaken for the granules themselves, but they can usually be distinguished from them without difflcultj% on account of the distortion which they undergo upon slight pressure. 1 Kraus ; Pringsheim's Jahrti., 1872, p. 131. 2 Trecul: Ann. des Sc. nat., ser. 4, tome x, 1858, p. 154. Weiss: Sitz. d. k. JVkad. "Wien, 1864 (Band 1.), and 1866 (Band liv.). 12 178 MINUTE STliUCTURE OF THE SEED. THE SEED. 502. The ripened ovnle is the seed. In ripening, the ovule undergoes changes in the structure both of the integuments and the nucleus. The integuments of the seed answer morpliologi- call}' to the primine and secundine of the ovule ; the outer being the testa, or seed-shell, — also called spermoderm or episperm, — the inner the tegmen, or endopleura. The nucleus of tlie seed also answers to the nucleus of the ovule. The morpho- logical relations of the different parts of the seed have been sufficiently treated in the first volume, "Structural Botany," and therefore only the histological features will now be presented. 503. Considered as a whole, the testa varies greatly in con- sistence ; it is in some cases as dense as any sclerotic tissue, while in others it is pulpy, and in others still, membranaceous. But it is usually divisible under tlie microscope into two or more layers, which are not constant in their characters. 504. The ordinary la3'ers met witii in the seeds of most agricultural plants have been described T)y Nobbe '■ in the follow- ing terms: 1. The hard laj'er, composed generally of palisade or staff-like cells of considerable firmness. In Leguminosae it is the external layer, and its exposed surface is cuticularized. In flax and species of Brassica, it is the second, in cabbage and mustard, the third layer. In a few cases the cells of this layer are tabular instead of staff-shaped. 2. The mucilaginous layer, not present in all the common agricultural seeds, is com- posed of cells whose walls have the power of swelling greatly when they are placed in water. This layer is sometimes found in the outer part of the testa, sometimes in the inner. 3. The pigment layer, which imparts characteristic colors to the coats of the seeds of many plants, is not constant in the form of the cells. The color may reside in the cell-wall, or in the dried contents of the cell. Sometimes a few pigment-cells are scattered among others of a neutral tint, and even among those which cannot be said to have any proper color at all. In some cases one of the other layers may contain more or lesg color. In a few other instances the color is not dependent on a pigment layer ; for, as Frank '^ has shown, in the steel-blue seeds of species of Pseonia the color is purely a result of reflected light, and is in no wise due to the presence of any true coloring-matter. The dried seeds are dark red or dark brown ; but when thoroughly nioist- 1 Handbiich (lev SameiikunJe, p. 73. ^ Botanisclie Zeitiing, 1867. HAIKS. 179 ened with water (or better still in a freth state) , they are dis- tinctly blue. 4. The protein layer, the cells of which contain granular albuminoid matters. The layers just described are different in different seeds, and sometimes different in different parts of the same seed-coat, so that the division has really little utility. 505. The external in- tegument or testa may have well-developed hairs, as has been shown in Vol- ume I. p. 306. Only one of these cases of hairs can be here described; namely, those which form the felted covering of cot- ton-seeds, and which are the "cotton" of commerce. These are slender cells with col- lapsed walls. As they ap- proach maturity, the cells become more or less twisted ; the resulting spiral is that which imparts to cotton its value as a material for spin- ning. Some other seeds, notably those of species of Asclepias, have long and strong hairs, but none of these have any spiral twist which fits them for textile purposes. Regarding the size of cot- ton "fibres" (hairs of the seed), the following meas- urements by Ordway are of interest : Maximum length in the "sea-island" variety, about two inches (five centimeters); in Pig. 136. Cross-sections of cotton -fibres. A A, unraature fibres; B B, half-mature fibres; CO, fuliy mature fibres; Z>, section of fibre, sliowing laminated cell-walls. (Bowman.) Fig 137. ..4, Glassy, structureless fibre; 5, thin, pellucid, iuiraature fibre; C, half mature fibre, with thin cell-wall ; I> and E, fully mature fibre, with full twist and well- defined cell-wall. (Bowman.) 180 MINUTE STET7CTURE OF THE SEED. upland or "short-staple" cotton, a little over one inch and a half (three and three-fourths centimeters). The greatest width of fibre was found to be .0013 inch. A single fibre sustained without breaking a weight of 150 grains.-' 606. It has been shown in Volume I. that the seed-coats of many Polemoniaceje, etc., are furnished with microscopic hairs, " which come usefully into play in arresting farther dispersion at a propitious time or place. . . . The testa is coated with short hairs, which when wetted burst, or otherwise open and discharge along with mucilage one or more very attenuated long threads (spii'icles) which were coiled within. These protruding in all directions, and in immense numbers, form a limb.us of considera- ble size around the seed, and evidently must serve a useful en(l in fixing these small and light seeds to the soil in time of rain, or to moist ground, favorable to germination, to which thej- maj' be carried by the wind." The best example of this structure is afforded bj' the genus Collomia ; in this the spiricles are long and verv numerous. 507. The nervation of the seed-coats furnishes in many cases excellent diagnostic characters, but they need no special remark histologically. The forms of branching of the fibro- vasciilar bundle of the funiculus indicate that the ovule and seed are of the nature of leaflets on the margin of the carpellary leaf.2 ' The above measurements are approximate ; those which follow are the exact determinations as they are given by Professor Ordway in the Tenth Census of the United States. Length of fibre. Maximum length found in the "sea-island" variety of South Carolina, where it was 1.996 inches. The maximum length of the upland or "short-staple" cotton was 1.669 inches. The minimum of length (0.695 inch) was found in North Carolina cotton, grown on a light, sandy loam soil. Width of fibre. The widest (is'sififini inch wide) was quite short (0.945 inch). By far the largest number of wide fibres come from uplands. The "sea-island" variety had a width of rd^hs inch. Strength of fibre. The strongest specimen examined had a brealjlng weight of 149. 4 grains. Professor Ordway mentions some instances which lead him to think that the strength of the fibre may hold some relation to the amount of phosphoric acid in the soil where it is grown. Weight of seeds and lint. ( Maximum weight for five seeds with lint at- tached, 22.14 grains.) Light-weight seeds appear to come from sandy soils, heavy-weight seeds from heavy and productive soils. 2 The reader is referred to a memoir by Le Monnier, in Ann. des Sc. uat., sir. 5, tome xvi., 1872, p. 233, and one by Van Tieghem in same Journal, 1872. ALBUMINOUS AND EXALBUMINOUS SEEDS. 181 508. The so-called "grains" of the cereals are fruits instead of seeds ; the accompanying figures exhibit, therefore, not onlj* the a b c d, strnctur ovarian 509. nucleus ab c e of the integuments of the seeds, but also of the ripened wall. As shown in the " Structural Botany," page 309, the of the seed consists of the embryo and its supply of food. If the store of food is wholly within the tissues of the embryo, the 140 seed is said to be exalbuminous ; if partly outside of the embryo, as, for instance, in the cereals here figured, it is said to be albuminous. The albumen is the supply of food in the nucleus of the seed which is not stored v\ the embryo itself. Pig. 138. Cross-section from tlie periphery of tlie fruit of Zea Mais, liighly raagni- fled: a, fruit-capsule; b, seed-coat; c, adlierent cellular layer; d, starch containirg albumen of seed. (Berg and Schmidt.) Fig. 139. A cross-section from tlie periphery of the fruit of Avena sativa, highly magnified : a, chaff; b, fruit-capsule with the seod-coat ; r. adherent cellular layer ; rf, starch containing albuminoid parenchyma. (Berg and Schmidt. ) Fig. 140, Cross-section from the periphery of the fruit of Oryza sativa, highly mag- nified; a, chaff"; b, fruit-capsule with seed-coat; c, adherent cellular layer; d, starch containing albuminoid parenchyma. (Berg and Schmidt.) Fig. 141. Cross-section from the periphery of the fruit of Hordeum vulgare, highly magnified: a, chaft'; 6, fruit-capsule with the seed-coat; c, adherent cellular layer; rf, starch containing albuminoid parenchyma (Berg and Schmidt. ) 182 MINUTE STRUCTURE OF THE SEED. 510. The embryo may exist as a cluster of ijarenchyma cells without any clear distinction of parts, or it maj- possess a defi- nitely forrued axis and leaves (see "Structural Botany," p. 811). The microscopic structure of the nucleus has been illustrated in part b^' the figures of the grains of cereals (see also Fig. 22, on page 47), and it lias been considered also to some extent in the descriptions of the nascent root and the nascent stem in the embryo. The studj' of the development of the embryo within the seed belongs to a special subject, which will be treated in Part II. under " Reproduction." It therefore will suffice here to state that the parench3'ma cells of which the nucleus is composed contain food materials and protein matters in large amount. 511. The proper food materials in seeds are chieflj' oils and starches. The seeds of a large number of plants have been ex- amined by Niigeli^ with reference to the occurrence of starch, and the following facts are taken from his extensive treatise : — Gynmo- Monocoty- Dicotyle- Total, Phasnogams containing / f In all species sperms, Families ledons. Familits dons, Families. Familits 3 20 190 213 No starcl, in the seed i Jjl ^^'11."^""^ 10 1(1 10 10 1 In a small number 1 2 3 Starch in the albumen, not in the embryo In all species In a majority . ( In half. i 17 1 lli 1 3 34 2 3 Starch in the embryo. In all species 2 2 not in the albumen In all species 4 11 15 Starch in the albumi- In a majority 1 1 nous embryo 'In half. . . , 5 5 In a small number 13 13 Starch in the embryo In all species i 1 2 ami albumen In a majority 1 I In all species 2 21 30 £3 Starch in the seeil throughout In a majority 1 3 4 In half. . . 8 8 In a small number 13 13 i 512. The protein granules in seeds are classified by Vines''' as follows : — 1 Die Starkekbnier, 18S8, p. 387. - Proceeciings of the Boyal Society, vols, xxviii., xxx., and xxxi. On page 62 of the volume last mentioned the following table, of seeds and their aleiirone gi-ains Is given : — I, Soluble in water ,; Paeonia officinalis (type), Eanunculus acris, Aconitum Napellus, NigcUa daniasccna, Hellebonis foetidus, Amygdalus com- munis, Prnnus cerasus, Pyius nialus, Leontodon Taraxacum, Dipsa- ous FuUonum, Ipomcea purpurea, Phlox Drummondi, Vitis vinifera. II. Completely, and more or less readily, soluble in ten per cent NaCl solution. PROTEIN GRANULES IN SEEDS. 183 I. Soluble ia water; e. g., Pseonia officinalis. II. Completely, and more or less readily, soluble in ten per cent NaCl (sodio chloride) solution. a. Grains witliout crj'stalloids. (a.) Soluble in saturated NaCl solution after treatment with alcohol or ether ; e. g., Pisum sativum. (;8.) Soluble in saturated NaCl solution after treatment with alcohol, but not after ether; e.g., Helianthus annuus. b. Grains with crj'stalloids. (a.) Crystalloids soluble in saturated NaCl solution after treatment with alcohol or ether; e. g., Bertholletia excelsa. (/?.) Crj-stalloids soluble in saturated NaCl solution after alcohol but not after etlier ; e. g., Ricinus connnunis. a. Grains without crystalloids. (a.) Soluble in saturated NaCl solution after treatment with alcohol or ether : Lupiuus hirsutus (type), Vicia Faha, Pisum sativum, Phase- olus raultiflorus. Allium C'epa, Iris pumila (var. atroccerulea), Colchi- cum autumnale, Berberis vulgaris. Althaea rosea, Tropteoluni majus, Mercurialis annua, Empetrum nigrum. Primula officinalis. (|8. ) Soluble in saturated NaCl solution after alcohol, but not after ether : Helianthus annuus (type), Platycodon (Wahlenbergia) grandi- flora, Sabal Adansoni, Delphinium cardiopetalum, Trollius Europieus, Actea spicata, Caltha palustris, Aquilegia vulgaris, Dianthus Caryo- phyllus, Brassica rapa, Lepidiurn sativum, Medicago sativa, Larix europiea, Cynoglossum officinale, Spinaoia oleracea. b. Grains with crystalloids. (a.) Crystalloids soluble in saturated NaCl solution after treatment with alcohol or ether : Beitholletia excelsa (type), Adonis autuinna- lis, jEthusa Cynapium, Digitalis purpurea, Cucurbita Pepo. (|S. ) Crystalloids soluble in .saturated NaCl solution after alcohol, hut not after ether : Eicinus communis (type). Datura Stramonium, Atropa Belladonna, Elais Guineensis, Salvia officinales, Taxus bac- cata, Pinus Pinea, Cannabis sativa, Linum usitatissimum, Viola elatior, Ruta graveolens, Juglans regia. III. Partially soluble in ten per cent NaCl solution. a. Entirely soluble in one per cent sodic carbonate solution : Pulmonaria mollis, Omphalodes longiHora, Borago caucasica, Myosotis palustris, Clarkia pulchella. 6. Entirely soluble in dilute potassic hydrate. (a.) Grains without crystalloids : Anchusa officinalis, Lithospermum officinale, Echium vulgare, Heliotropium Peruvianum, Lythrum Salicaria. (/3. ) Grains without crystalloids: Cupressus Lawsoniana, Juniperus "ommunis, Euphorbia Lathyris. by which a 184 MINUTE STRUCTURE OF THE SEED. III. Partially soluble in ten per cent sodic chloride solution. a. Entirely soluble in one per cent sodic carbonate solu- tion ; e. g., Clarkia pulchella. b. Entirely soluble in dilute potassic hj^drate. (a.) Grains without crystalloids ; e. ^r., Lythrum Salicaria. (ft.) Grains with crystalloids ; e.;/., Juniperus communis. 513. The appendages of the seed known as the strophiole (at the base of the seed), the caruncle (at the micropyle or orifice), and the membranaceous and pulpy forms of arillus (see Vol- ume I. pages 308, 309) do not call for further remark. The separation of the fruit at maturit}-, and the separation of the ripened seed as well, are due to changes analogous to those described in 458, under the " Fall of the Leaf." Some of the special forms of mechanisms bj' wliich the detachment occurs may be examined in Part II., under " Dissemination." CHAPTER V. PHYSIOLOGICAL CLASSIFICATION OP TISSUES. DIVISION OF LABOR IN THE PLANT. 514. The simplest plant, a green cell living in water, pos- sesses all the appliances needful for the work of vegetation ; namelj', a protoplasmic bodj' containing chlorophyll, and a cell- wall protecting it. It finds in the water in which it floats, and in the sunlight to which it is exposed, everything requisite for its full activity. 515. Its work is twofold : First, that which it does not share ■with the animal, and which may therefore be called the proper office of the plant, — the production of organic matter out of inorganic materials, under the agency of light. This work is dependent upon the presence of chlorophyll in the cell, and is known as Assimilation. Second, that which the animal like- wise can perform, — the conversion into various forms of ac- tivity of the energy stored up in food. This takes place in the protoplasm, whether chlorophyll be present or absent. 516. In a spherical cell isolated from others and leading an independent existence, floating free in the water, and therefore presenting no one part exclusively to the light, there is very slight if indeed any division of labor. One part of its cellulose, protoplasm, or chloroph3'll has the same work to perform and is substantially under the same conditions as any other part. But if the cell becomes one of many aggregated to form a mass of tissue, its relations to its surroundings are not the same as be- fore, for its exterior is no longer equall}' exposed either to water or to light. The cells in the interior of such a mass must derive their supply of material from without through the agencj' of the neighboring cells ; hence division of labor begins. Inspection of the mass shows that some of its cells have the office of ab- sorption, others that of assimilation, others that of treasui-ing up the products of manufacture, etc. With this incipient divi- sion of labor there are also notable changes in the form of cells, by which a more complete adaptation to a particular kind of 186 PHYSIOLOGICAL CLASSIFICATION OF TISSUES. work is secured. These adaptations are as marked in the inter- nal anatomy as in the external configuration. 517. The parts of a living being which have definite kinds of work to do are known as organs^ (cf. epyov, work). Since they 1 The organs of the higher plants are reducible to three members ; that is, three types of structure, which bear to each otiier definite relations of position and seciuence of appearaufc. These members are the root, stem, and leaf, — to which some add also the plant-hair. In Sachs's Vorleaungeii, the number of members is given as two ; namely, root and shoot. In their very youngest state all the modified leaves upon a given jilant are indistinguishable from each other ; the leaves which are to become petals, stamens, leaf-traps, or tendrils, are like those which are to lie ordinary foliage. The same is true of modified stems and modified roots ; however diverse in shape and function the modified steins or branches of a plant may finally be, they are at their very beginning precisely alike. In the determination of the rank of an oi'gan, that is, its reference to one of the three plant-members already enumerated, the following criteria are em- ployed : (1) its position with respect to other parts ; (2) its nascent condi- tion ; (3) its presence or absence in organisms obviously allied to the one in which it occurs, its rank in these not being obscure. So far as the organs seen by the naked eye are concerned, it is seldom that any serious difficulty exists in the application of at least one of these criteria to the detennination of their rank, and it is generally possible to use more than one. But it is different in the case of the histological organs, for (1) the position can be made out only in sections of the given part ; (2) their early nascent condition is the simple cell, common to all tissues : (3) it is not easy to determine whether an organ exists in a rudimentary form in allied organisms or is wholly absent from them. It is so difficult to apply these criteria to the study of tissues, and the results obtained are so contradictory, that there is no complete agreement among botanists as to what constitutes a histological member except the sim- ple cell itself. In fact, as stated in 191, it is doubtful whether with the material now at hand it would be possible to construct a satisfactory system of tissue elements or histological organs upon a purely morphological basis. Even in the systems which most nearly approach this there are some physio- logical notions which have affected a few of the minor divisions. A classification of tissues upon the basis of physiology alone is open to serious objections ; one kind of work in the plant can be performedjjy diverse tissues, and on the other hand one kind of tissue can perform more than one liind of work. This is illustrated by the structural elements through which mecheinical ends are reached ; the long bast-fibres, woody fibres, coUenchyma, and short sclerotic parenchyma, — very diverse elements, but accomplishing the same result. Yet one of these, namely, the woody fibres, is among the most important of the elements by which crude li(|uids are carried through the plant. Moreover, in the examination of the minute structure of a part it is not easy to discriminate between the different offices which one of its given ele- ments may fill, because the element is associated with so many others in the formation of a complex organ. DIVISION OF LABOR IX THE PLANT. 187 are parts of a whole, — the organism, — they must have definite relations to each other as regards position and office. 518. The relations of origin and position, so far as the organs of the plant are concerned, are discussed in the first volume ; the relations of origin and position of the component parts of their structure have occupied the earlier portion of the present \oluinc. From a review of the facts there presented, it appears that anj' given part may subserve different ends ; for instance, a leaf may carry on its proper work, namely, that of assimilation, and at the same time may aid as a tendril, and, in the case of Nepenthes, as a stomach for digestion. On the other hand, it is equally clear that the same kind of work maj' frequently be performed by different parts. For instance, the proper woi'k of the leaf can be carried on by any green tissue ; not merely in propel- leaves, but in the cortex of young stems, and even in the outer tissues of young roots of certain aerial plants. It is there- fore sometimes advantageous in Vegetable Physiology to distin- guish between systems of tissues having different offices, rather than between organs which are often masses of heterogeneous tissues. 519. Among the systems of classifications of tissues chiefly upon a physiological basis is that of Haberlandt, which is as follows ; — A. The Protective System. 1. Of the surface (Epidermis, cork, and bark). 2. Of the skeleton (Bast-fibres, libriform cells, collenchyma, and sclerotic parenchyma) . £. The Nutritive System. 1. Absorbing system (Epithelium of roots and the root- hairs ; absorbing tissue of haustoria, etc.). 2. Assimilating system (Chlorophyll parenchj-ma, both pah- sade and spongy). 3. Conducting system (Conducting parenchyma, vascular bundles, latex cells and tubes). 4. Storing system (Reserve-tissues of seeds, bulbs, and tubers; water-tissue, etc.). 5. Aerating system (Aeriferous intercellular spaces, together with their external openings, stomata and lenticels). 6. Receptacles for secretions and excretions (Glands, oil, resin, and mucus canals, crystal-sacs, etc.). To these might be added the groups of tissues concerned in reproduction. 188 PHYSIOLOGICAL CLASSIFICATION OF TISSUES. MECHANICS OF TISSUES. 520. In Haberlandt's classification ^ the tissues having a me- chanical oflice to fill are brought into one group, which is then subdivided into (1) those tissues which protect the softer tissues of the interior from the harm which would result from exposure, and (2) those which hold the soft tissues in place. An exami- nation of the work performed by tissues maj' accompany- an in- vestigation of the work by organs themselves ; in the examina- tion of the work of organs in Part II. the necessary facts relative to their structure will be presented. 521. Those tissues which serve simplj' to impart strength to the plant belong almost as much to lifeless as to living parts, and can best be examined before the subjects of physiolog3' are taken lip. The present division has for its object the consideration of that which in Haberlandt's classification is called the skeleton, and which is known to serve chieflj- mechanical ends. 522. In the case of a water-plant, for instance an alga, which has about the same specific gravitj' as the water in which it is borne, no special mechanical support is demanded. Its own buoyancy suffices to keep the structure as a whole in place ; while the different parts of the simple organism have a degree of stability which enables them to resist the action of the waves. As might be expected, such an organism can attain a very great size ; for instance, Macrocystis pyrifera of the Southern Pacific Ocean has been known to measure nearly one thousand feet, and less trustworthy measurements have been recorded which far exceed this. In this and other water-plants the medium which buoys the plant up takes the place practicalh' of any internal framework. 523. A land-plant, existing in a far lighter medium than the water-plant, must have a definite mechanical support. Those species of Calamus which furnish the " rattan" of commerce pos- sess a terminal shoot from which are unfolded in rapid succession strong leaves armed with recurved hooks. Having reached the thickly clustering tops of a tropical forest, the terminal bud de- velops its leaves, and these cling with tenacitj' to the branches upon which they rest, so that the mechanical support is afforded in this case by the vegetation beneath. Thus supported, the ex- tension of the shoot is indefinite, so that examples of Calamus Physiologisclie Pflanzenauatomie (Leipzig, 1884). MECHANICAL ELEMENTS UE PLANTS. 189 with a length of 300 feet are not uncoiiimou, and some figures much higher than this are noted. 524. In both the above cases the extraordinarj- size has been attained with verj' little expenditure of material for mere me- chanical support. The same is true, although in a less striking because a more familiar manner, in our ordinary twining and climbing plants ; other plants or outside supports of some kind being necessary to bring their stems and leaves into the best relations to their surroundings. But what tissues serve to keep erect or in position the larger plants which are not water-plants or climbers ? What tissues serve mainly mechanical ends ? 525. The subject was extensively investigated, so far as monocotyledonous plants are concerned, by Schweudener,^ in 1874, since which time some important additions have been made. According to Schwendener, the mechanical elements in the plant are (1) bast-fibres, (2) libriform cells and fibres, (3) collench3'ma cells. That these are the chief elements of strength, especially in monocotj'ledonous plants, appears from his instructive experiments, which have been repeated bj' others. Strips, 150 to 400 mm. in length and about 2 to 5 mm. wide, were carefully taken from stems or leaves and immediately fastened in a vise at one end, the other end being firml}' grasped by strong pincers to which weights could be attached at will. Behind a strip, vertically suspended from the vise, a measuring-bar was placed, so that any elongation of the strip under tension could be accurately measured. After the apparatus was properly adjusted, a small weight was attached to the pincers, the elongation of tiie strip observed, and the weight then removed in order to see whether the strip recovered its original length. Up to a certain point the recovery was found to be complete ; bej'ond this point the elasticity was lost, and not again regained. 526. Strips from the middle part of the leaf of Phormium tenax, 390 mm. long and 1.5 to 2 mrn. wide, were placed in the apparatus and subjected to the action of a weight of 10 kilograms. They became 5 mm. longer, but on removal of the weight were found to recover their original length ; in other words, they re- mained perfectly elastic under this weight. A weight of 15 kilograms broke the strips into two parts. These strips con- tained only five flbro-vascnlar bundles, with an amount of bast which was believed to be about half a square millimeter in cross- 1 Das meohanische Princip im anatomlsohen Blate . .80 14.6 Hammered German steel 1.20 24.6 82. Brass . . . . . .75 4.85 Brass wire . . 135 13.3 Cast zinc . .24 2.3 Copper wire 1.00 12.1 Silver 11. 29 StiSKEUM AJtD MESTOM. 19l 528. The strength of other tissues besides bast has been meas- ured ; thus Ambronu assigns to eollenchyma a breaking- weight ol' 12 kilograms per square millimeter, and these cells become per- manentlj' elongated under a weight of from 1.5 to 2 kilograms. Ilaberlandt found that the breaking-weight of the internal " thread" of the common graj'beard lichen, Usnea barbata, is 1.7 kilograms per square millimeter, but that this thread could be stretched to double its length before breaking. The breaking- weight of cotton fibre is calculated to be between 18 and 20 kilograms per square millimeter, and that of the seed-hair of Asclepias Sjriaca not far from 40 kilograms. 529. Examination of anj' of the figures of flbro-vascular bundles given in Part I. shows how well their elements are dis- tributed in order to secure the greatest strength with econom}- of material. To the elements which impart strength to a bundle Schwendener has gi\'en the name stereom ; to the other parts of the bundle, mestom ; thus the fibres are stereom elements, the ducts are mestom elements. 530. The striking adaptations-' of the fibro-vascular bundles to serve as light and ver3' strong building materials in the plant ^ The following table from Schwendener, with a few illustrative examples, is given to serve as a guide to the student in tracing out a few of these adapta- tions : — DiSTRIDUTION OF MECHANICAL ELEMENTS IN MONOCOTYLEDONS. I. In cylindrical organs. 1. System of subepidermal nerves of bast. Simple fascicles of bast lie under the epidermis. First type. Arum, Arisaima. Second type. Petioles of Colocasia and Alocasia. 2. System of compound peripheral girders. Subepidermal fascicles of bast unite with those which lie more deeply to form girders in which the "web" or binding-tissue is partly mestom, partly parenchyma. Third type. Stems of Scirpus cfespitosus and Eriophomm alpinum. Fourth type. Stems (above ground) of Cyperus alternifolius. Fifth type. Stems of Schoenus nigricans. Sixth type. Stems of Juncus effusus. Seventh type. Carex lupulina. Eighth type. Scirpus lacustris. Ninth type. Isolepis paucifiora. Tenth type. Cladium Mariscus. 3. System characterized by a nerved hollow cylinder, the nerves of which are united with those at the epidermis. Eleventh type. Many grasses ; c. 01 Sarkin ) Ammonic carbonate 10 Asparagin and other amides 1.00 Pepton and Peptonoid ■ 4.00 Lecithin 20 Glycogen 4.73 iEthalium sugar 3.00 Calcic compounds of higher fatty acids ... 5.33 Calcic formate ) .2 Calcic acetate i ' ' ' Calcic carbonate 27.70 Sodic chloride 10 Hydropotassic phosphate (PO4K2H) .... 1.21 Iron phosphate (POjFe ?) 07 1 98 PROTOPLASM. 543. One hundred and seventy-nine grams of fresh proto- plasm of a soft consistence were placed in closeh' woven linen cloth and subjected to pressure by the hand ; 68 grams of a turbid fluid were expressed ; the mass was then placed under a pressure of 4,000 kilograms, by which 62 grams more were forced out, leaving a dry cake behind. Thus 66.7 per cent of the mass was pressed out. The fluid thus expressed has a specific gravity- of 1.209. That this fluid is intimatelj- incorpo- rated with the more solid portion of the protoplasm, appears from the fact that it cannot be forced from the protoplasm by cen- trifugal force alone. To it the name enchylenia Las been given ; to the solid matter, the name stroma is applicable. The amount of water contained in fresh protoplasm of ^thalium septicum is approximately 71.6 per cent. The reaction of protoplasm is alkaline. 544. In young cells the protoplasm exhibits essentially the same characteristics as those presented by the naked protoplasm of the Myxomycetes alreadj- alluded to. The phenomena in cells can be most satisfactoril3' seen in thin-walled plant-hairs. These should be transferred to a glass sHde with as little injury- as pos- sible, covered immediately' with pure water, and examined undeir a cover-glass which is prevented by bits of wax or thin glass from pressing on the delicate object. The stamen-hairs of Trad: escantia Virginica, pilosa, or zebrina are the best, for in thes6 the cells are sufficiently large to be managed without difficulty, and the walls are perfectly transparent. The cells in the thin leaves of many water-plants answer very well, but they generally contain so much chlorophyll that the protoplasm is obscured. The hairs of the flowers and of the young leaves of plants of the Gourd family and those of the nettle' are also excellent objects for the study of protoplasm ; and in general it may be said that almost any plant-hair, if it is young enough and has a thin wall, will serve very well (see Fig. 175). 545. Protoplasm in cells exists as a nearly colorless mass #- Ammonio-magnesic phosphate 1.44 Tricalcic phosphate 91 Calcic oxalate 10 Chlolesterin 1.40 Fatty acids extracted by ether 4.00 Eesinous matter 1.00 Glycerin, coloriug-mattei-, etc 18 Undetemiined matters 5.00 1 Huxley: Protoplasm (Half Hours with Modern Scientists) 1871). MOVEMENTS. 199 lining tlie walls and extending iiTegularlj- from side to side in slender threads. At some one part the mass appears a little denser than at others, and if the outline of this firmer mass is at all well defined it is easily recognized as the nucleus (see Fig. 2). 546. Circnlation of protoplasm in cells. Under a power of SOO diameters the delicate threads of protoplasm can be clearly' seen to have imbedded in them minute granules which are slowly moving. It happens sometimes that a slight warming is re- quired before any motion is apparent. When the current is fully established, its different changes can be watched for a long time without other disturbance of the specimen than that resulting from the addition of water to replace that lost by evaporation. Two features of the motion require special notice: (1) the granules do not pass from one cell to the contiguous one, but remain confined in one ; (2) the threads in which the granules move gradually change their shape and direction, growing wider in one place and becoming narrower in another, while at the points of contact with the lining of the wall the threads seem to slip or glide very slowly, and accumulations of the protoplasm here and there take place. The movement of the granules from place to place in a steady current is called the circulation of protoplasm ; the sluggish changes of the threads as they alter- nately increase and diminish in size resemble the amceboid movements (see 555 and Fig. 175). 547. In some examinations it is instructive to add a very little glycerin or sugar to the water on the slide, in order to cause a slight contraction of the protoplasm ; its whole mass then appears as a shrunken sac, in the interior of which the circulation can be detected. 548. In a good specimen of the stamen-hair of Tradescantia the protoplasmic currents are seen to course in slender threads with a considerable degree of regularity*. In some of the thi'eada or bands the currents go in one direction, in others in another ; and it occasionallj' happens, as Hofmeister has pointed out, that two opposite currents may pass in a single narrow channel. 549. There is more or less accumulation of protoplasmic matter in the immediate vicinity of the nucleus, and there are generally some slight projections into the interior of the cell. The rate of circulation appears to be greater at the middle of the threads than at the sides or ends of the cell. 550. If these movements in a cell are compared with the 200 PROTOPLASM. movements exhibited by naked protoplasm, no substantial dif- feience can be seen bej'ond that whicli depends upon the con- finement of the mass in one case within practically rigid walls. The naked protoplasm moves slowly from place to place, by thrusting out an irregular projection which soon enlarges, and in its turn gives out new projections, while the mass behind is slowlj' moving up. This movement is identical with that observed in tlie amoeba. In the substance of a mass of naked proto- plasm granules can be seen to move in varying channels ; and this corresponds strictlj' to the movement known as the cii'cu- lation. Moreover, in the naked protoplasm larger or smaller vacuoles (see 120) are observed to increase and diminish in size, their limiting walls answering essentially to the threads before described. 651. Kotation of protoplasm in cells. The film of protoplasm in contact with the cell-wall does not generally share in the movement of the softer part which it encloses, but usually- re- mains entirely stationarj-, or else verj- slowly shifts its posi- tion on the wall. In some cases, however, the whole mass of protoplasm slowly revolves on its own axis, carrying with it all imbedded matters. Tliis movement should be called rotation ; but the term is often employed interchangeably with circulation. 652. Eate of protoplasmic movements. In the cells of the shaft of an3' Chara which has transparent walls — for instance, Nitella — the rapid movement can be very clearly seen to be confined to the interior of the protoplasm, the outer part in which chlorophyll-granules are imbedded not moving to anj- great ex- tent, if indeed at all. At its interior the protoplasm moves with what seems under the microscope to be a ver3' rapid rate ; it is, however, absolutely very slow ; being only about one and a half millimeters per minute, at a temperature of 15° C. 553. The rate differs considerably in different plants ; for instance, according to several observers, the distance traversed in one minute at a temperature of 15° C. is as follows : — Name of plant. Potamogeton crispus, leaf-cell . . Cevatophyllum demersum, leaf-cell Tiadescantia Virginica, stamen-hair Sagittaria sagitttefolia .... Vallisneria spiralis Hydrocharis Morsus-rarse, root-hair Nitella flexilis, cells of the shaft . mm. Observer. .009 . . . Hofmeister. .094 . . . Mohl. .137 .174 . . . Mohl. .225-1.086 . , Mohl. .543 1.500-1.600 . Niigeli. AMCEBOID MOVEMENT. 201 In the naked protoplasm of M^-xomj-cetes the rates of move- ment of the currents are much greater, as Hofmeister shows by the following examples : — mm. per minute. Dijymium Serpula 10. Physarum .species 5.4 554. The above rates are not constant even in the same speci- men ; after having been uniform for a few minutes, the rate maj- slowly diminish for a time, the temperature and other con- ditions remaining apparently unchanged, and then as slowly increase until the maxinuim is again reached. Again, the rate is subject to sudden clianges. In general, however, it is nearly the same for the same part of a given plant. 555. The amoeboid moTement in naited protoplasm is rather more sluggish than the circulation, as the following figures from Hofmeister show : — mm. per mlnate. Didyinium Serpula 0.4 Physaruni sp 0.29 Stemonitis fusca . 0.15 The far more rapid movement of ciliated protoplasmic bodies will be described under "Movements." 556. The effects upon protoplasm of various agents — for in- stance, heat, light, electricity, etc. — can be studied in the same cells in which the movements are observed ; in fact, their effects upon the movements themselves are among the most striking phenomena noticed. It must be remembered, however, that in experimenting upon the protoplasm in cells which arc furnished with a cell-wall and provided with cell-sap, other factors are present than those which must be taken into account in deal- ing with the naked protoplasm of plasmodia. And hence it is proper in most cases, in interpreting the results obtained in experiments upon the protoplasm of cells, to speak of the effects of the agents upon the cells themselves. 557. Relations of protoplasm to heat. In experimenting upon the effect of heat on protoplasm, the apparatus generallj' em- ployed is the so-called warm chamber. In its simplest form this consists of a hollow-walled box, having a slit in which a slide can be placed, and at the centre of the upper and lower walls holes of the same size as the largest diaphragm of the micro- scope, so as to allow light to pass from the mirror directly through tiie slide and thence to the objective. Connected with the box are two tubes to which pieces of rubber tubing maj' 202 PKOTOPIiASM. be attacbed ; these pieces run to a small reservoir of water ■which can be heated at pleasure by means of a spirit-lamp, as shown in the figure. Suppose a slide to have upon it a gopd specim«n of a stamen-hair of Tradescantia, furnished with sufficient water and properly covered. It is placed in the aperture / of the hollow box, and the rest of the apparatus is tlien arranged as shown in the cut. The rate of circulation of the protoplasm is now carefully- observed, and the temperature shown by the thermometer t is also noted. With increments of heat from the upv current of yvater through the tube through the box the rale of the protoplasmic cii'culation is in- creased. The amount of heat applied can be easil}' regulated by the height of the reservoir. If it is desirable to observe the effects of cold, the resei'voir can be placed in a vessel of ice and raised above the stage of the microscope, so that a current of colli water can flow down through the box. 558. Experiments upon tiie effect of heat can also be con- veniently' conducted by means of a less expensive apparatus which consists of a double-walled box of zinc placed on firm supports at the height of a few inches above the table, and large RELATIONS OP PROTOPLASM TO HEAT. 203 enough to receive the body of the microscope. Through a hole in the top of the box the tube of the microscope projects for a short distance, and the front of the box is furnished with a glass window, which affords enough light for the mirror. The space between the walls of the box having been filled with water, and the object placed on the stage of the microscope, a lamp under the box is lighted, and the effects of the increase of temperature noted. It is best in this case to have the thermometer in the closest proximity to the slide. It is essential in the use of both these instruments to note the temperature at short intervals, and it is only by the greatest care in the use of the thermometer that an3' trustworthj- results can be obtained (see Fig. 170). 559. As might be expected from the nature of heat as a mode of molecular motion, the rate of protoplasmic movement is accelerated hy increase of temperature up to a given point (the optimum) ; with increase beyond this point the movement may continue, but with diminished rapiditj', until an upper limit of temperature (the maximum) is reached, above which no move- ment is observable. At or verj' near this limit structural changes take place, and death of the protoplasm speedilj' ensues. 560. The optimum temperature for protoplasmic movement is different for different plants, but is not far from 37°. 5 C. Name of plant. Optimum temperature. Observer. jSfitella syncarpa 37° Nageli.i Chara foetida 38°. 1 Velten.^ Vallisueria spiralis 38°. 75 "2 " " 40° Sachs.''! Anacharis Canadensis . . . 36°. 25 ... . Velten.^ 561. The maximum temperature beyond which no movement is seen, is also different for different plants, but may be given as not higlier than 50° C. Name of plant. Maximum. Observer. Chara fcetlda 42°. 81 Velten.''' Vallisneria spiralis 45° "2 " 60° Sachs.s Sachs * states that when the hairs of Cucurbita Pepo are im- mersed in water of 46° or 47° C. the protoplasmic movements are arrested within two minutes ; but that the hairs can bear 1 Beitrage z. wiss. Botanik, 1860, ii. p. 77. 2 Flora, 1876, p. 177 et seg. s Flora, 1864, p. 5 et scq. * Lehrbuch der Botanik, 1874, p. 700. 204 PROTOPLASM. exposure for ten minutes to a temperature of 49° - 50° in the air before arrest of movement takes place. In Tradescantia hairs the current stops within three minutes upon exposure in air of a temperature of 49°, beginning again when the temperature falls. 562. The lower limit (minimum) of temperature at which motion taltes place maj' be stated at 0° C, although — 2° has been observed '■ in a single plant, — Nitella sj-ncarpa. Until a temperature of at least 15° C. is attained, the move- ment is sluggish. 563. Sudden changes of temperature have been said by some writers to cause a temporary arrest of the protoplasmic move- ment. Thus de Vries ■' observed that in the root-hairs of Hydro- charis Morsus-ranse tlie protoplasmic current at 21°. 7 C. was so rapid that it passed through one millimeter in 205 seconds ; but upon sudden elevation of temperature to 33° C, 240 seconds were required for it to traverse the same distance. And Hof- meister' found that tlie rapid movement in Nitella flexilis was arrested in two minutes when the specimen was taken from a room at 18°.5 to one at 5°. But, on the other hand, Velten ^ failed to detect such an effect. 564. At or near the maximum temperature remarkable changes take place in the form of the protoplasmic threads and films. The}' become more or less rounded, although very irregularl}-, and may be completely disintegrated. Such changes have been noted by Max Sehultze ^ at a temperature of about 40° C. in the hairs of Urtica, the stamen-hairs of Tradescantia, and the leaf-cells of Vallisneria. According to Kuhne,° such changes take place within two minutes in the plasmodium of -^thalium septicum (see 540) at a temperature of 39° C. ; the plasmodium of Didymium serpula was affected in the same way at a con- siderably lower point, namelj', 30° C. 565. When subjected to a temperature lower than the mini- mum for movement, the protoplasmic mass may become disin- tegrated, the solid part separating from a watery portion, which latter may freeze.' If, now, very gradual increments of heat 1 Botan. Zeitiuig, 1871, p. 723 (Cohn). 2 Avohiv. Nterlanilaises, v., 1870, p. 385. " Die Lelire von der Pflaiizenzelle, 1867, p. 53. * Flora, 1876, p. 213. ' Das Protoplasma d. Rliizopoden iind Pflanzenzellen, 1863, p. 48. " tTntersnohungeii iiber das Protoplasma, 1864, p. 87. ' Untersucliungen liber das Protoplasma, 1864, p. 101.- KELATIONS OF PROTOPLASM TO HEAT. 205 are applied, the disorganized parts maj' become reunited, and after a while the movement may begin again. No such recovery, however, is possible when the protoplasmic mass has become disintegrated b3- a high temperature ; the change thus produced is practically coagulation.^ 566. The temperature of certain hot springs in which living algiE have been found shows that protoplasm can bear without injury a greater degree of heat than is indicated b}' the figures in 661. Thus algse have been seen in the following thermal waters : — Temperatare. Observer. Carlstad 53°. 7 C Cohn.^ Lip Islands .... 63° Hoppe-Seyler.' Dax 57° Sevres.* California Geysers . . 93° .... Brewer.^ Hoppe-Seyler found algae growing on the edge of a fumarole where they were subjected to a temperature (from the escaping vapor) of" 60°.° 567. That the protoplasm of manj' kinds of seeds and spores can preserve its vitalit}' during exposure to dry air at a tem- perature above that of boiling water has been shown by many experimenters ; ' but unless the precaution is taken to remove all water from the seeds by very careful and slow drying, any temperature above 100° C. is injurious. Seeds thus cautiouslj' freed from moisture have been heated to 110°, and even for a short time to 120°, without losing their povver of germination (see also "Germination"). Nor does there seem to be any es- sential difference between the seeds which contain oils and those which contain starch in their capacit}- to endure high tempera- tures. Hoffmann" and Pasteur^ have shown that the vitality of perfectly dry seeds and spores may in some cases be retained until a temperature of 130° C. is reached. 1 PfefFer : Pflanzenphysiologie, 1881, ii. p. 386. 2 Flora, 1862, p. 538. 8 Pfltiger's Arehiv., 1875, p. 118. ♦ Botan. Centvalblatt, 1880. p. 257. ' Am. Journ. So. and Arts, 2d series, xli. 391. 6 Pfliiger's Arcliiv., 1875, p. 118. A much higher temperature is noted hy Humboldt ; namely, 85° C. for the hot spring of Trinchera, Caraccas, in which he found the roots of certain plants growing. ' Milne Edwards and Colin : Ann. desSe. nat., s^r. 2, tome i., 1834, p. 264; Sachs's Handbuch der Experimental-Physiologie, 1865, p. 65 et seq. ; Just, in Cohn's Beitrage zur Biologie der Pfianzen, 1877, p. 311. 8 Pringsheim's Jahrb., 1860, p. 324. Ann. d. Chimie et de Physique, 1862, p. 90. 206 PKOTOPLASM. 568. On the other hand, the protoplasm of dry seeds can be subjected to extremely low temperatures without suffering anj' injury (see "Germination"). 569. Tlie relations of protoplasm to light are best examined in the Plasmodia of the mj^xomycetes and the hairs of Tradescantia, for here they are not complicated by the presence of chlorophyll (which, as will be seen later, exerts a marked influence). Ac- cording to Hofmeister, plasmodia thrust forth longer and more numerous processes in darkness than in light. In ^thaliiim sep- ticum the processes developed in light are short and compressed, while those grown in darkness are long, slender, and thin.^ This is especially noticeable when the light falls only on one side of the mass. In some of Baranetzky's experiments,^ in which the incident rays of light were parallel to the substratum (wet filtering-paper) on which the Plasmodium was placed, the change of form resulting from diminished extension on the lighted side and increased extension on the other was very marked after fifteen minutes' exposure to bright sunlight, while in diffused light half an hour was required for a similar change. These results should be compared with those obtained by Schleicher,' who observed that young plasmodia move towards light of low intensity, and that older plasmodia ma}' move even towards strong light. The movement into bright light appears to just precede the formation of the spores. 570. The more refrangible rays of light — that is, the violet and indigo — appear to be more efficient in influencing move- ment than are the less refrangible, — the red and j-ellow. 571. The " circulation" of protoplasm in plant-hairs goes on not only in darkness, but even when the hairs are developed on plants blanched by absence of light.^ No marked effect upon the rate of such movement appears to be caused by presence or absence of light, except so far as the concomitant action of heat comes into play. Hofmeister states that he saw the protoplasmic 1 Die Lelire von der Pflanzenzelle, 1867, p. 21. 2 Memoires de la soc. des sciences nat. de Clierbourg, 1875, p. 340. It is, however, well known that plasmodia often emerge slowly from their sub- stratum ; for instance, tan, if the surface is only very faintly lighted. 3 Jenaisehe Zeltschrift, 1878, p. 620. * Sachs : Botan. Zeit., 1863, Supplement. Eeinke : ibid., 1871, p. 797. Kraus : ibid., 1876, p. 504. Few observations have been recorded upon the effect upon protoplasmic movements of sudden changes of illumination. In the case of an amceba (Pelomyxa palustris) Engelraann found that light, and not its sudden withdrawal, appeared to exert a stimulant effect (Pfeffer : Pflanzenphysiologie, ii. p. 387). EELATIONS OP PROTOPLASM TO ELECTRICITY. 207 movement as distinctly in Iiairs -whicli had been developed in darkness, and had remained without light for thirty hours, as in any which had grown in the open daylight. According to Dii- trochet, it requires a withdrawal of the light for about twenty daj'S to cause an entire cessation of the movement in Chara. The effect of very intense light, and the influence exerted by it upon protoplasm containing chlorophyll, will be examined under " Assimilation." 572. Relations of protoplasm to electricity. Chemical changes within the plant result in the production of electrical currents in protoplasm ; at this point it is proper to examine briefl3' the eflfect produced upon protoplasm by continued and induced currents. When the Plasmodium of a myxomj'cete is placed between platinum electrodes on a glass slide under the microscope, and a current sent through the mass from one small Grove element, very little if any effect is observable ; but if the current from a few elements is emploj-ed, there is at once more or less rounding of the branched mass, and there may also be a reversal of the course of the circulation. When more elements are used, the protoplasm may be killed. If the protoplasm in cells be experi- mented upon, nearly similar phenomena are noticed. Protoplasm is not a good conductor of electricitj'. Jiirgensen made some experiments on the action of a current from small Grove ele- ments upon the leaf-cells of Vallisneria spiralis. A continued current from one element did not cause any appreciable change in the protoplasmic movement ; but when two, three, or four were emploj'ed, the current retarded the movement, and after a while completely arrested it. In those cases where the move- ment had been simplj' checked, it was re-established in full in- tensit}- shortly after cutting ofi' the current of electricity ; but in those where it had been entirely stopped, it did not begin again. .573. The effect of an intei-rupted current of electricity is essentially the same as that produced bj- mechanical shock. The protoplasm generally contracts at certain points forming small roundish masses in the lines of the slender threads, and the movements are arrested. 574. Hofmeister states that a constant current is practically without any influence upon the circulatory movement in the cells of . Chara,_ but that the interruption of tlie current produces nearly the same effect as a sudden mechanical shock or a sharp change of temperature. He observed essentially the same phe- nomena in the hairs of the nettle, although in these there was 208 PROTOPLASM. also more or less of the aggregation into rounded masses alluded to in 564. 575. The effect of mechanical irritation upon protoplasm in plants can be easily examined in cells or in plasmodia. Wiien a cell of Niteila wliich exhibits rapid circulation of protoplasm is held somewhat firnil}' by pressure on the cover-glass, the movement is arrested instantly, but after a shoi't time it is resumed. Even in those cases where the pressure has been sufficient to disturb the ari-angement of the chlorophyll granules, the arrested motions are soon to be seen again. For experi- ments upon the effect of pressure and shock, the stamen-hairs of Tradeseantia are oven better than cells of Niteila or Chara, for pressure brings about an apparent disintegration of the threads, and all motion is suspended for several minutes ; but if the injur}- has not been too severe, it soon begins again. How- far such injuries can be carried without affecting the vitality of the protoplasm, niaj- be seen from the following observations. According to Gozzi,^ if a cell of Chara is ligated firmly, the circulation is checked for a short time, and then begins in each half of the cell. It is stated by Hofmeister that when a root- hair of Hjdrocharis Morsus-ranse is severed, the protoplasm in the cell remains motionless for a short time, during which the cut surface of the cell is being closed b}- a portion of the proto- plasmic mass. When the surface is completely closed, the cir- culation begins again within the healed cell. 576. KosanofTs observation,'^ which has been repeated many times, is of much interest in connection with this subject. When a cell from the endosperm of Ceratophyllum demersum, haA ing rapid circulation of protoplasm, is placed under the mi- croscope, and a slight pressure is exerted on the cover-glass for a moment, the circulation stops at once, the thick axile threads of protoplasm begin to round at one or more places, and from the aggregations slight processes, somewhat like tenta- cles, appear. After a while these are retracted, and the normal circulation is resumed. But sometimes it happens that these tentacles become separated from the threads to which they be- long, for a time lie without movement near them, and then become again confluent with them. Mechanical shock ° causes the active plasmodia of the myxo- 1 Quoted by Hofmeister in Die Lelire von der Pflanzenzelle, 1867, p. 50. 2 Die Lehre von der Pflanzenzelle, p. 51. ^ Hofmeister : Pflanzenzelle, p. 26. RELATIONS OF PKOTOPLASM TO GRAVITATION. 209 nij-eetes to become rounded into the form of somewhat flattened drops, from which slender branches protrude after a short time. If pressure is novv made upon those portions of tlie branched Plasmodium in which circulation is to be seen, the movement stops at onoe, and is not resumed for two or three minutes ; but after that period of rest it goes on as before. When a Plasmodium is cut in halves, tlie circulation is to be seen after a while in the separated portions.^ 577. Eelations of protoplasm to gravitation. Concerning the influence of gravitation on the form assumed by protoplasm, it need only be said here that the less dense plasraodia appear some- times to yield to this force. But Pfeff'er ^ found that in a saturated atmosphere the plasmodium of -32thalium moved in the dark with equal freedom whether the moist bibulous paper on which it rested was held horizontally' or verticall}- ; Sti-asburger ' also has noted the same fact. If one part of the paper is more moist than an- other, it is to the very wet spot that the plasmodium wanders. 578. Belafcions of protoplasm to moisture. The relations of water to the activity of protoplasm are not j'et thoroughly under- stood. It has been seen (577) that there is a tendency of Plas- modia to move to the points where there is the most moisture ; and in general it may be said that a large amount of water is favorable to all protoplasmic movements. Thus Dehneeke ' found that the protoplasm in the cells of the collenchj-ma of Balsamina exhibited no circulation until the section had been placed in water ; and the same phenomena can be shown in sections of many active plants. On the other hand, Velten has shown that in some cases the protoplasmic movement stops when a plant-hair is placed or kept for a time in water, but is resumed if it is transferred to a dilute solution of gum-arabic, although the protoplasm was furnished with a greater supply of water in the former than in the latter case. 579. Some harmless plasmolytic agents (see p. 27), for in- stance a dilute solution of sugar, added to the water in which the 1 Pfeffer : Pflanzenphysiologie, 11. 390. 2 Pfeffer : Pflanzenphysiologie, ii. 388. 5 Wirkung des Liclites auf Schwarmsporen, 1878, p. 71. Dehneeke (Uebev nicht assimilirende Chlorophyllkbrper, 1880) has shown that the various bodies which occur in protoplasm of cells — for instance, chlorophyll granules, starch-grains, and the like — have a marked tendency to sink to that part of the cellulose wall which is lowest. The change of position takes place some- times in a few minutes, sometimes only after several hours. * Flora. 1881, p. 8. 14 210 PROTOPLASM. jjrotoplasm of the cells of Tradescantia stamen-hairs is exhibit- ing rapid circulation, cause an increase in the rate of movement. This fact has been considered to show, in connection with the eases mentioned, that for the most rapid circulation of proto- plasm there must be a definite amount of water, — the optimum. 580. When any of these plasmolytic agents are used in too concentrated a solution they may exert a much more marked effect upon the protoplasmic contents of a cell ; not only does all movement cease, but the mass shrinks into small bulk, and does not afterwards recover its former shape and size. As a result of their action, two other phenomena are presented : (1) the protoplasm of one cell can be seen in some cases to be connected through the cell-wall with the protoplasm in the adjoining cell ; (2) a change takes place in the firmness or turgor of the cell- wall. Both of these phenomena must receive attention at a later stage. When a cell containing living protoplasm is placed in a harmless and dilute solution of an^- coloring-matter, for instance logwood, its wall becomes more or less tinged by the dj-e, but the protoplasm retains for a while at least its power of move- ment, and does not take up any of the dye. If, however, the protoplasmic mass is injured or dead, it absorbs the coloring- matter with great avidity. 581. Belations of protoplasm to various gases. Experiments upon the effects of gases on the behavior of protoplasm can be best conducted by means of the simple gas-chamber shown in Fig. 195. A current of the gas employed is drawn through the tube a by means of anj- simple aspirator ; and in a few seconds the specimen previously placed upon the glass at 5, and protected by a cover-glass, is thoroughly surrounded by it. By the use of this apparatus it has been found that the presence of free oxygen is essential to protoplasmic movements. Hofmeister and Kiihne have shown that when this gas is no longer supplied to the protoplasmic mass or to the cells in which the protoplasm is contained, all movements cease. Thus Hofmeister' found that the circulation of Nitella was completely arrested in thirteen minutes after the air was wholly removed. Kuhne^ replaced by hjdrogen the air in which the hairs of Tradescantia had shown rapid movement, and after several hours all motion was arrested. 582. Corti," the discoverer of the circulation in Nitella, placed 1 Die Lehre von der Pflanzenzelle, p. 49. ^ Untersucluingen liber das Protoplasma, 1864, p. 107. ' Meyen : Pfliinzenpliysiologie, ii. 224. STRUCTURE OP PROTOPLASM. 211 cells in which the movements were plainlj- seen, in olive-oil, in order to exclude the air. A short time after this was done the movement stopped. In Hofmeister's ^ repetition of Corti's ex- periment the arrest of the protoplasmic movement occurred in five minntes in olive-oil ; after the oil had been carefully- poured off, the movements recommenced in thirt}- minutes. 583. Kiihne experimented also upon the replacement of the ox3-gen needful for protoplasmic movements bj- carbonic acid, and found this gas much better than oil for excluding air. Upon removal of the plant-hairs from oil, it is difficult to take away the last trace of adherent oil. 584. The ordinary auiesthetics, chloroform and ether, arrest the movements of protoplasm.^ 585. The strnctnre of protoplasm. Having thus briefl\- ex- amined some of the more striking phenomena of protoplasmic movement, the question must now be asked. What is the struc- ture of a substance which exhibits these phenomena? B^^ the highest power of the microscope it appears as a homo- geneous lyaline mass holding in its substance, but apparently as foreign bodies, ver}- minute granules. But when the proto- plasmic matter is stained bj- the skilful use of pigments, its homogeneous cliaracter disappears. 586. Schmitz has confirmed and extended the observations of Frommann, which show that in some cases at least the pro- toplasmic bodj' is a reticulated framework of extremely delicate fibrils, between the meshes of which is a homogeneous liquid. There is unobstructed communication between the different meshes, so that the whole of the liquid may be regarded as practically one mass. The network of fibrils does not possess any rigidity, bat is constantly mobile under favorable condi- tions, and undergoes manifold changes of form. The reticulated structure is most clearly- seen in the parietal protoplasm, and the larger bands of cells which contain relativel3' considerable sap. When, after hardening, protoplasm is carefully stained with haematoxylin, the whole mass appears to be equally and evenly colored ; but it is in reality- only the network which takes up the color, the liquid in the meshes remaining uncolored. Imbedded in the protoplasm, especially in the inner portions, there are generally minute granules which have a high degree of refringency, and which stain ver^- deeply with the dye ; these are the microsomata of Hanstein. 1 Die Lehre von der Pflanzenzelle, p. 49. 2 Claude Bernard : LcQons sur les Phenomeiies de la Vie, 1879. 212 PROTOPLASM. 587. Up to the present time the microscope has not revealed more than these facts respecting the intimate structure of proto- plasm, and from these alone no clear conception can be formed of the mechanics ' of protoplasmic movements. 588. It is just at this stage of the inquirj- respecting the structure of protoplasm that many have sought to apply an hypothesis known as Ntigeli's ; namely-, that all organized bodies consist of structural particles (termed micellce), each of whieli is individually enveloped bj- a film of water holding vari- ous substances in solution. According to Nageli's view, as origi- nally given, tlie micellae are never spherical, but possess a true crystalline character, as shown bj- the relations of organized bodies to polarized light.^ These micellae are believed to obey 1 Hofmeister regarded protoplasmic movements as directly dependent upou changes in the capacity of living jirotoplasm for absorbing water, shown by pulsating vacuoles (see 120). In the mass of a plasmodium, or in the free spores of some algse, there are generally to be detected easily under the micro- scope minute spherical cavities filled with watery sap which are constantly changing in size. Tlieir rhythm of change, or pulsation, as it is called, is differ- ent for different plants, varying from a few seconds to as many hours. Their increase iu size is usually gradual until the maximum is reached, when sud- denly the cavity or vacuole contracts even to the point of vanishing, and then it slowly begins to form again at the same place iu the mass. The rhythm of the pulsations can be made to vary with changes in the surround- ings ; for instance, with changes of temperature, or by the application of dilute solutions, or by any agent which modifies the absorptive power of proto- plasm for water. But these agents are also efficient in controlling the rate of protoplasmic movement. The spontaneously pulsating vacuoles appear to indicate that the absoi-ptive power of protoplasm changes spontaneously, and is different successively in different parts of the mass, thus disturbing the equilibrium of the soft mass sufficiently to force some portions from place to place. Bnt Hofmeister gave no explanation of the cause of variations in the imbibition power of proto[ilasm. 2 In his earliest work on the subject (Die Stiirkekorner, 1858) Nageli applied the word molecule (which had not then obtained such general acceptance in chemistry and physics, with a different signification) to what he now calls the micella. His hypothesis has undergone sundry changes from time to time, one of his last important publications (Theorie der Garung, 1879) containing some modifications. The terminology now proposed by Nageli applies the word p^eon to those aggregates of molecules which cannot be increased or diminished without changing their chemical nature ; for instance, crystals which contain water of crystallization would be called pleons, for the molecule HjO has a definite numerical relation to the molecules of the salts, and examples of similar pleons are afforded by such compound .salts as the alums. Compare with this the following statement : — " It has also been a question among chemists whether molecular combination was possible ; in other words, whether it is possible for molecules of different If NAEQELl'S HYPOTHESIS. 213 the followiag attractions : (1) that of cohesion, by which each individual micella is an aggregate of molecules ; (2) that which tends to bring adjacent micellae together ; (3) that of adhe- sion, by which the surfaces of the micellae retain their films of water. kinds to combine chemically, each preserving its integrity in the compound. . . . Any antecedent improbability on theoretical grounds is far more than out- weighed by the evidence of a large number of compounds whose constitution is most simply explained on the hypothesis of molecular combination. For example, in the crystalline salts it is impossible to doubt that the water exists as such, not as a pait of the salt molecule, but combined with it as a whole. So also there are a number of double salts whose constitution is most simply explained on a similar hypothesis " (Cooke's Chemical Philosophy, 18S2, p. 137). The word micella is applied by Nageli to those aggregates of molecules which (like crystals) can increase or diminish in size without changing their chemical nature. The micella is a-ssumed to be much larger than the pleon. "The internal structure of the micella is crystalline, while the exterior may assume any shape. " The micellae unite to form micellar aggregates ; of such the crystalline protein granules afford a good example. Thus, according to Nageli, five terms must be recognized, — the atom, the molecule, the pleon, the micella, and the micellar aggregate. Pfeffer applies a general term, Tagma, to all aggregates of molecules, thus bringing under one head the pleon, micella, and micellar aggregate ; and he applies the name Syntagma to all bodies made up of tagmata. The subject will be again referred to under " Osmosis." To make clearer the conception of a micella, it may be well to examine briefly two terms in common use ; namely, atom and molecule. When a solid body, for instance a crystal of sndic chloride (common salt), is mechanically separated into the smallest possible fragments, each particle still possesses all the properties of salt. Beyond this mechanical limit of sepa- ration the process of subdivision may be carried still further by solution : the minutest fragments of the salt can be broken up and diffused through the solvent, and yet not lose their essential character as salt ; in fact, they can be again recovered without change from the solution. But it is impossible to go beyond this latter limit of separation without altering the essential properties of the substance. In other words, by this subdivision the physical limit has been reached ; namely, the molecule. A molecule is understood to be the smallest amount of any substance which can exist as such in the free state. Hence the molecule is the physical unit. If, however, the salt is subdivided by chemical meanfi, — for instance, by the action of strong sulphuric acid, — its iilentity is destroyed, and its component parts enter into new relations, and cannot be restored to their original relations except by an exceedingly complicated process. In other words, the physical limit has been overpassed and the chemical limit reached ; namely, the atom. Atom is generally defined as "the smallest amount of a given substance which can exist in combination," or "the smallest mass of an element that exists in any molecule." The atom is the chemical unit. Atoms are variously combined to form molecules : molecules are variously aggregated to form masses. 214: PEOTOPLASM. Contiguous micellae in any organized substance, for instance cell-wall or starch, frequently possess different chemical charac- ters, as is shown by the fact that from such a substance one por- tion can be taken without materially disturbing the external form. 689. By means of the changes which go on in the formation of new micellae, and in their reconstruction, it is sought to account for the nutrition, growth, and movements of organized substances. This is essentially the basis on which Engelmann^ founds his explanation of the movements of protoplasm.'^ 590. Continuity of protoplasm. It was supposed until recently that the protoplasm in one young cell is completely shut off from that in contiguous cells by an imperforate cell-wall, and that even in the cases where the wall is perforate there is no communi- cation of protoplasm through the pores. There is abundant evidence to show the incorrectness of this view. In some cases the protoplasm in one cell is practically continuous with that in 1 Hermann's Handbuch der Physiologie, i. 1879, p. 374. 2 The application of this hypothesis by Sachs is given somewhat fully in the following extract (Text-book of Botany, 2d Eng. ed., 1882, p. 666) : "Chemical compounds of the most various kinds meet between the micellae of an organized body, so that they act upon and decompose one another. It is certain that all growth continues only so long as the growing parts of the cell are exposed to atmospheric air ; the oxygen of the air has an oxidizing effect on the chemical compounds contained in the organized stracture ; with every act of growth carbon dioxide is produceil and evolved. The equilibrium of the chemical forces is also continually disturbed by the necessary production of heat ; and this may also be accompanied by electrical action. The move- ments of the atoms and molecules within a growing organized body represent p definite amount of work, and the equivalent forces are set free by chemical changes. The essence of organization and life lies in this : — that organized structures are capable of a constant internal change ; and that, as long as. they are in contact with water and with oxygenated air, only a portion of their forces remains in equilibrium even in their interior, and determines the form or frame- work of the whole ; while new forces are constantly being set free by chemical changes between and in the molecules, which forces in their turn occasion further changes. This depends essentially on the peculiarity of mioellar struc- ture, which permits dissolved and gaseous (absorbed) substances to penetrate from without into every point of the interior, and to be again conveyed out- wards. Neither the chemical nor the molecular forces are ever in equilibrium in the protoplasm ; the most various elementary substances are present in it in the most various combinations ; fresh impulses to the disturbance of the Internal equilibrium are constantly being given by the chemical action of the oxygen pf the air ; and energy is continually being set free at the expense of the proto- plasm itself, which must lead to the most complex actions in a substance of so complicated a structure. Every impulse from without, even when impercep- tible, must call forth a complicated play of internal movements, of which we are able to perceive only the ultimate effect in an external change of form." CONTINUITY OF PEOTOPLASM IN CELLS. 215 the next, bj' means of delicate threads wliich pass through pores in the intervening cell-wall. Doubtful instances afforded by the cribrose-cells have been alreadj- alluded to (see 279). The endosperm cells of seeds of Str3-chnos Nux-vomiua afford a well-marked example of the cases of communication between cells of seeds. TangP advises that very thin sections jjarallel to the flat surface of the seed be shaken with dilute tincture of iodine or with a solution of iodine in iodide of potassium for about five minutes, and then thoroughly washed with pure water. The protoplasmic and other contents of the uninjured cells will then appear as a contracted ball having somewhat the shape of the cell. From the mass in one cell minute threads run through pores or canals in the wall to the masses in the adjoining cells, and there is no break in their continuit}'. In the endosperm of the allied species, Strychnos potatorum, Tangl did not detect canals of the character found in S. Nux-vomica. Gardiner'-* has demonstrated the existence of communication between the protoplasmic masses in contiguous cells of the pul- vini of the leaves of some plants having the power of motion. When sections of these lea^■es are placed in a solution of a salt which causes contraction of tiie protoplasm, the shrunken mass is seen to be connected with the cell-wall by extremely delicate threads of protoplasm. The threads can be traced to pits in the wall, and there it can be seen that the}- are exactly opposite the threads on the other side of the wall. If the solution of the salt used is too strong, some of the threads may be ruptured, and then one free end of each thread will retract to the main mass while its other part goes to the cell- wall. If fresh sections are treated with strong picric acid, and then, after washing in alco- hol, are stained with anilin blue, the continuity of the proto- plasm in uninjured cells becomes apparent. Mimosa affords excellent material for this purpose. Hillhouse' reports similar continuitj- of protoplasm in the cortex of the stem of Laburnum, and in the petiole of several leaves. The fresh material is to be placed for a few days in absolute alcohol, and the thin sections made from it are to be treated with dilute alcohol. The sections are then to be placed in concentrated sulphuric acid, and after the acid has removed the cell-wall, its excess is to be withdrawn by means of a pipette, ^ Pi'ingsheim's Jahrbiiolier, 1880, p. 170. ' Philosophical Transactions Royal Society, 1883, clxxiv. 817. s Botanisches Ceiitralblatt, 1-883, -xiv. 8&, -121. - - -, 216 PEOTOPLASM. and the preparation verj' carefully washed. The application of strong glj'cerin completes the treatment. The specimen must uot be removed from the slide during the whole series of opera- tions. If the manipulation has been careful throughout, the minute threads can be seen passing from one mass of protoplasm to the next. 591. The directions given by Strasburger for demonstrating the continuitj' of protoplasm are as follows : From the stem of a dicotyledonous shrub or tree (the diameter of which should be at least a centimeter) the periderm is removed by a knife, and ver3- thin tangential longitudinal sections are then made through the soft green bark. The parenchyma cells which are inter- mingled willi the liber contain more or less chlorophyll, and may have pits, the very smallest of which are not bordered (see 268). If the first sections have shown in any case that these cells are furnished with pits, others are then prepared and placed at once in a drop of a solution of iodine (that of iodine in an aqueous solution of potassic iodide is best). The excess of the solution is at once removed and the preparation covered with a glass cover. At the edge of the cover-glass there is placed a di-op of concentrated sulphuric acid, and by the side of this a couple of drops of dilute sulphuric acid ; when these ai-e mingled the mixture is allowed to flow under the cover-glass, while a bit of filtering-paper on the other edge of the glass draws it through. The specimen becomes dark blue. If the color is deep, the cover- glass is cautiously lifted and the preparation is tlien thoroughly but carefully washed in water. After this wasiiing, a drop of a solution of anilin blue is added, wherebj- the object becomes stained ; then, after washing again, a little glycerin ' is added, and the cover-glass is fastened down with some cement. For the examination of the specimen the strongest objectives — pref- erably the so-called "homogeneous immersion," employed with cedar-oil — are indispensaljle. Under a sufficiently high power the middle lamella of the wall is seen to be somewhat swollen, while the contents of the cells are contracted and colored. The periphery of the individual protoplasmic masses in the cells of the cortical parenchyma is smooth on that face which was in contact with the cell-wall hav- ing very small pits ; but it has minute protrusions on that face which was next the bordered pits. Moreover, the protrusions in contiguous cells are exactly opposite each other. Between • Strasbui'gev advises the addition of a little anilin blue to the glyoenn. CONTINUITY OF PKOTOPLASM IN CELLS. 217 the protrusions at the bordered pits there extend extremelj* deli- cate threads of protoplasm which have a granular character. The threads are somewhat curved (especially the outer ones), and are slightlj' swollen in the middle. In peculiarly good preparations it has been shown that there is an apparent inter- ruption at the middle of their course, but that at this break there are still minute filaments which serve to connect them. From these and kindred observations Strasburger and some others have adopted the view that there is sucli a degree of continuitj- between the protoplasmic masses in the cells that thej' form throughout the plant an unbroken whole.^ 592. That protoplasm maj- perhaps occur in intercellular spaces appears from the observations of Russow ^ and of Berthold.^ To demonstrate this, one-j-ear-old twigs of Ligustrum vulgare are hardened for a few daj-s in absolute alcohol, longitudinal sections of the primarj' cortex placed in dilute iodine solution (see 30), the excess of iodine removed, and dilute sulphuric acid added. The contents of the cells and of the intercellular spaces will then appear as yellowish-brown masses. 593. That protoplasm can in some cases pass through an im- perforate cell- wall appears from the observation of Cornu,* that in the formation of the macroconidia of a certain Nectria all the protoplasm of the five or six cells of the spore emerges to form the macroconidium, which arises as an outgrowth of one of the cells of the spore. The four or five partition-walls through which the protoplasm must pass are, however, neither dissolved nor perforated. It is probable that a striking phenomenon of fertilization in phsenogams, namely, the complete emptying of the pollen-tube of its protoplasm (see "Fertilization") without apparent break in the continuity of the wall, must be referred to the same pene- trative power of protoplasm. The withdrawal of the principal part of the protoplasmic matters from deciduous leaves before the fall of the leaf may be perhaps explained in the same way. Strasburger cites as an illustration of this penetrative power the well-known case of the removal of protoplasmic matters 1 Das botanisohB Practiomn, 1884, p. 617. Strasburger : Bau und Wachs- thum del- Zellhaiite, 1882, p. 246. Frommann ; Beobachtungeu iibev Structui des Protoplasma der Pflaiizenzellen, 1880. 2 Sitz. der Dorpater Naturforscher-Gesellschaft, 1882, p. 19. ' Berichte der deutschen botauisclien Gesellschaft, ii. 20. ^ Oomptes Eendus, 1877, tome Ixxxir. p. 133. 218 PROTOPLASM. from the cells around the buds which form on the incised leaves of Begonia.^ 594. The relations of the cell-wall to protoplasm are not 3-et full}- understood ; and in regard to some of them there exists among botanists considerable diversity of opinion. The two principal views are the following: 1. The cell-wall is formed bj- the solidification upon the exterior of a protoplasmic mass, of matters previously dissolved in it. The pellicle thus pro- duced is regarded as a sort of excretion (since in most cases it is not again to be dissolved and emploj'ed b}' the organism) or as a secretion (because in a few instances it can be dissolved and utilized a second time by the plant). The substance capa- ble of thus solidifying upon the surface of protoplasm consists of cellulose combined with water and a small amount of incombus- tible matters, but it is not positively known in what condition these were previousl}' combined in the protoplasm. 2. The cell-wall may be regarded as directly produced bj- a conversion of the outer film of protoplasm into cellulose with which some other matters are intermingled.^ 595. The young cell-wall ' is practically a homogeneous film of cellulose, which speedily undergoes changes both in its chemical and physical character. In man}- of the lower plants the wall differs in some particulars from that found in the higher plants (see p. 29), but the differences need not enter into the present description. 596. Two views are held respecting the mode of growth of the cell-wall. The first may be regarded as based upon the h^'pothesis of Nageli spoken of in 588. From some of the mate- rials held dissolved in the adherent film of water around each micella new micellae of cellulose are supposed to be produced, ' "That protoplasm can pass through closed cell-walls is beyond doubt" (Vines, note to second edition of Sachs's Text-book, p. 946). ^ The view that cellulose is a kind of secretion is stated at great length in flofraeister's PHanzenzelle, and in several communications by Sachs in Bota- nische Zeitung. The second view is given by Sehmitz, Sitz. der niederrhei- uischen Gesellschaft fiir Natur- und Heilkunde, Bonn, 1880. He bases his opinion largely upon the fact that in some cases the cells gradually become emptied of protoplasm as the amount of cell-wall increases, and upon the phe- nomena which attend the increase of the cell-wall in thickness. ' It was believed by some of the earlier phytotomists that the cell-wall was a close, firm network of extremely fine fibres, while others held it to be com- posed of minute granules. In these explanations of structure it was confessed that the ultimate fibres, or ultimate granules, lie quite beyond the reach of the highest powers of the microscope. GROWTH OF THE CELL-WALL. 219 which are interpolated between the old. This is the intuseus- ception theory. It has gradually displaced an older theor3-, nainelj-, that of growth by apposition. As llie older theory was usually held, it presented two niodificatious/ — one that the growth of a cell-wall in thickness taltes place on the exterior of the wall, so that in a stratified wall all tiie outermost portions are the newer ; the other, that all the new matter is laid down upon the interior of the old. The apposition theory- has recently attra<;ted much attention from the studies of Schmitz, and from its adoption and advocacy bj' Strasburger.^ As now held by these authois, the ^•iew is this : stratified and other cell-walls grow in thickness b^' the deposi- tion of new particles upon the inner face of the cell, much as a crj-stal adds new particles to itself; growth in surface is the result of a simple stretching of the wall by the pressure of the con- tents upon it. An}' solution which causes a shrinking of the contents of the cell, and thus diminishes the pressure on the wall, may cause a diminution of the size of the cell itself. The bearing of this upon the turgescence of the cell will be again adverted to under " Properties of New Cells and Tissues." To the physical characters of cellulose already mentioned (see 129), maj- now be added that property' wliich is possessed also by man}' other organized substances ; nameh", that of swell- ing greatlj' when placed in water. The wall of a living and active cell is of course moist, and its increase in size on tlic addition of more water is seldom marked ; but under certain circumstances the amount of water in the cell-wall even of an active cell may fall below its usual amount, and then tiie apphcation of water will cause an appreciable change of bulk. Such change in the amount of water may take place with great rapidit}' upon slight external disturbances, such as shock : in these cases, the amount of water in the protoplasm in contact is correspondingly modified. 597. Historical note regarding protoplasm. The word proto- plasm appears first in a memoir by Mohl, in 1846, "On the Movement of Sap in the Interior of Cells," which deals, however, 1 For an account of the two modifications of the apposition theory, the student is referred to Harting's paper, translated in Linnsea, 1846, and Mohl's, in Botanische Zeitung, 1846. A fair statement of the first modification is presented in Mulder's Physiological Chemistry. 2 Strasburger : Ban und Waehsthum der Zellhaiite, 1882. 220 PROTOPLASM. not SO much with the movement of what would to-da}- be called cell-sap, as with the general behavior of all the motile contents of active vegetable cells. After showing that his predecessors had not clearly understood the important part plaj-ed in the liffe of the cell by the viscous matter known vaguely up to that time as schleim, or mucus, Mohl points out the essential identitj- of the nucleus, primordial utricle, and the basic substance filling all but the sap-cavities of the cell. For the substance which is essential to the formation of every new cell and to the develop- ment of newly formed cells he proposed, upon phj-siological grounds, the significant name protoplasma. For convenience of reference, the paragraph in which the word is first employed is here given : — "Dawie schon bemerkt diese zahe Fliissigbeit iiberall, wo. Zellen .entstehen sollen, den ersten, die kunftigen Zellen andeutenden festen Bildungen vorausgeht, da wir ferner annehmeu miisseu, dass dieselbe das Material fiir dieBildung des Nucleus uiid des Primordialsclilauehes liefert, indem diese nicht nur in der niiohsten raumlichen Verbinduiig mit derselben stehen, sondern auch auf Jod auf analoge Weise reagiren, dass also ihre Oi'ganisation der Process ist, welclier die Entstehung der neuen Zelle eiiileitet, so mag es wolil gerechtfertigt sein, weun ich zur Bezeiclmung dieser Substanz eine auf diese pliysiologische Function sich beziehende Benennung in dem Worte Protoplasma vorschlage." i In 1835 Dujardin described a contractile substance capable of spontaneous movement in certaiu of the lower animals, to whicli he gave the name Sarcode. The identit3- of sarcode with that substance which forms the essential body of animal cells and Vith the protoplasm of vegetable cells was suggested by several investigators and finally demonstrated by Max Schultze in 1861.^ Schwann, even as early as 1839, pointed out various analogies and homologies between animal and vegetable cells, and enun- ciated the following proposition : animal cells are completely analogous to vegetable cells, and are quite as independent in their mode of growth. The bearing of Schultze's demonstra- tion upon the foregoing proposition is obvious. Schwann instituted also certain comparisons between the mode of forma- tion of cells and that of crystals ("Microscopical Researches into the Accordance in the Structure and Growth of Animals and Plants." translated b}- Henry Smith for the Sydenham Society, 1847). 1 Botanisclie Zeitung, 1846, p. 75. " Arohiv fiir Anatomie, Physiologie, und wiss. Medicln, 1861, pp. 1-27, and Das Protoplasma der Rhizopoden und der Pflanzenzellen, Leipzig, 1863. CHAPTER VII. DIFFUSION, OSMOSIS, AND ABSORPTION OF LIQUIDS. DIFFUSION AND OSMOSIS. 598. "When two liquids which are not miscible — for instance, oil and water — are shaken togetlier, and then left at rest, they will separate sooner or later, according to their specific gravity. But if two miscible liquids are shaken together, they remain as a homogeneous mixture no matter what their specific gravity may be. Also when two miscible liquids are left in contact, without any agitation they become thoroughly commingled, and constitute a uniform mixture ; this uniform commingling of two or more miscible fluids is termed diffusion} 599. Furthermore, if two miscible liquids are separated by a membrane which can be moistened by them, they will diffuse through it and make a uniform mixture. This latter kind of diffusion, in which the contact between the two liquids is not direct, but takes place through a septum of some substance, is known as osmosis. In the plant and in its surroundings the two kinds of diffusion play such an important part that they must receive special attention. 600. Diffusion of liqnids. The rate of diffusion varies with the nature of the liquids and the temperature. The statements in the following paragraphs are substantially as given by Graham.'' 1 Pfaundler applies this term to the commingling whether it is or is not hrought about by agitation (Miiller's Lehrbuch, 1877, i. 162). 2 They are based upon two series of experiments conducted with very sim- ple apparatus. In the first series a small, wide-mouthed vial containing one liquid was placed in a jar holding the other liqnid, allowed to stand a few days, withdrawn, and the amount of diffusion noted. In the second series Graham pursued the plan of placing in a cylindrical glass jar, 152 mm. high and 87 mm. wide, seven tenths of a liter of pure water, and then carefully car- rying to the bottom of the jar, by means of a iine pipette, one tenth of a liter of the liquid to be diffused. The jar was then left at rest in an apartment where the temperature was nearly constant, and after a certain time its contents were drawn off carefully in portions of fifty cubic centimeters, each portion evaporated separately, and the residue remaining after evaporation weighed. 990 DIFFUSION AND OSMOSIS. 601. Different salts in solutions of equal strength diffuse in unequal times. Thus potassic lydrate difi'uses with double the rate of potassic sulphate, and the latter with double the rate of crj'stallized sugar. But these substances have a compara- tively higli rate of diffusion. A solution of caramel (sugar heated till it becomes brown) diffuses very slowly ; the sugar in this case has been so changed in its character tliat its rate of diffusion has been reduced from a high to a verj- low one. Gela- tin maj- be taken as the representative of the almost " fixed" or slowly diffusible class of substances ; most crystalline substances, as lepresentatives of the highly diffusible class. The former are collectively' known as colloids (KoXXa, glue), the latter as crystal- loids. It must be noted that Graham's use of this word " crys- talloid " is different from that in which it has been employed in speaking of the protein bodies (177). 602. With each salt the rate of diffusion increases at a slightly higher rate than the temperature of the solution. 603. Tlie members of certain chemical groups are equallj' dif- fusible. Thus hydrochloric, hydrobromic, and hydriodic acids ; the chlorides, bromides, and iodides of the alkaline metals, etc., have equal rates of diffusion into pure water. 604. The diffusion of a solution of a salt into the dilute solution of another salt takes place nearly' as rapidlj- as into pure water ; The difference in the rates of diffusion of ten per cent solutions of different substances experimented upon in the manner described on the preceding page is clearly shown by the auuexed table. Number of stratum from above downwards. Sodic CUoride. Sugar. Gum. Tannin. 1 2 3 4 6 .104 .129 .162 .198 .267 .340 .429 .535 .654 .706 .881 .991 1.090 1.187 2,266 .005 .008 .012 .016 .030 .059 .102 .180 .305 .495 .740 1.075 1.435 1.75S 3.783 .003 .003 .003 .004 .003 .004 .006 .031 .097 .215 407 .734 1.167 1.731 5.601 .003 .003 .004 .003 .005 .007 .017 .031 .069 .145 .288 .556 1.060 1.719 6.097 6 7 . 8 9 10 11 12 13 14 15,16 9.999 10.003 9.999 9.997 The first series of experiments are described in Philosophical Transactions, 1850 ; the second, in 1861. RATES OP DIFFUSION. 223 but if the second solution contains some of the salt, like that in the first solution, the rate of diffusion is retarded. 605. The rate with which a salt passes from a stronger into a more dilute solution is nearly proportional to the degree of concentration. The approximate times required for the diffu- sion of equal weights of various substances into watef are given in the following table : — Hydrochloric acid 1. Sodic chloride 2.33 Magnesic sulphate 7. Cane-sugar 7. Albumin 49. Caramel ... 98. 606. Of the colloids, Graham sa3-s:^ "Low diffusibility is not the only property which the bodies last enumerated possess in common. . . . Although often largely soluble in water, they ' Philosophical Transactions, 1861. Graham says further : "Although chemically inert in the ordinary sense, colloids possess a compensating activity of their own arising out of their physical properties. While the rigidity of the crystalline structure shuts out external impressions, the softness of the gelatinous colloid partakes of fluidity, and enables the colloid to become a medium for liquid diS'usion, like water itself. The same penetrability appears to take the form of cementation in such colloids as can exist at a high temperature. Hence a wide sensibility on the part of colloids to external agents. Another and eminently characteristic qual- ity of colloids is their mutability. Their existence is a continued metastasis. A colloid may be compared in this respect to water while existing liquid at a temperature under its usual freezing point, or to a supersaturated saline solu- tion. Fluid colloids appear to have always a pectous modification {tttiktSs, curdled), as fibrin, casein, albumin. But certain liquid colloid substances are capable of forming a jelly, and yet still remain liquefiable by heat and soluble in water. Such is gelatin itself, which is not pectous in the condition of ani- mal jelly, but may be so as it exists in the gelatiferous tissues. Colloids often pass under the slightest influences from the first into the second condi- tion. The solution of hydrated silicic acid, for instance, is easily obtained in a state of purity, but it cannot be preserved. It may remain fluid for davs or weeks in a sealed tube, but is sure to gelatinize and become insoluble at last. Nor does the change of this colloid appear to stop at that point. For the mineral forms of silicic acid, deposited from water, such as flint, are often found to have passed during the geological ages of their existence, from the vitreous or colloidal into the crystalline condition (H. Eose). The colloidal is, in fact, a dynamical state of matter ; the cvystalloidal being the statical condition. The colloid possesses energia. It may be looked upon as the probable primaiy source of the force a[ipearing in the phenomena of vitality. To the gradual manner in which colloidal changes take place (for they always demand time as an element), may the characteristic protraction of chemico- crganic changes also be referred. " 224 DIFFUSION AND OSMOSIS. are held in solution by a most feeble force. The}' appear singu- larlj- inert in the capacitj- of acids and bases, and in all the ordi- nary chemical relations. But, on the other hand, their peculiar physical aggregation with the chemical indifference referred to, appears to be required in substances that can intervene in the organic processes of life. The plastic elements of the animal bodj- are found in this class." 607. Osmose, or Osmosis. Diffusion of liquids through mem- branes. The interposition of a permeable septum between mis- cible liquids does not prevent diffusion. Thus if a solution of sodic chloride is sepai'ated from pure water by an Intervening membrane, as one of bladder or of vegetable parchment (see page 32), diffusion takes place in about the same time as if no membrane were present. 608. For most experiments in osmosis the simple apparatus known as an osmometer answers very well. It consists of a small reservoir furnished with a membrane bottom, and a gradu- ated tube at its upper part. A very good osmometer can be prepared from a, short-necked bottle from which the bottom has been carefully removed. After the edges at the bottom have been made smooth, a piece of wet parchment paper is tightly fastened on bj' waxed thread. Great care must be taken to select parchment or parchment paper which is free from perfora- tions,^ and the tube at the neck must be well fitted to a velvet cork, so that no escape of liquid can take place in anj- waj'. A film of ordinary unsized paper evenl}- covered with a solution of warm gelatin, which cools to form a firm mass upon its surface, makes a good substitute for parchment in this apparatus. A thin film of white of egg coagulated hj- heat will also serve well for a covering. 609. The osmometer, filled to a certain point on the tube with the Hquid to be experimented upon, is suspended in pure water so that the liquid in the apparatus is on exactly the same level as the water. It will be seen bj- the experiment that not only does diffusion take place, but that there is a change in the level of the liquid in the tube. 610. When any of the more diffusible substances are placed in a state of solution in the reservoir, a small amount of the crj-stalloid passes outwards, while a much larger amount of 1 The existence of actual perforations in good parchment can be demon- strated by subjecting the apparatus to pressure, or even by repeatedly wiping the exposed surface of the parchment with filtering-paper. / rKECIPITATION-MEMBRANES. 225 water passes inwards. The change of level caused is of course accompanied b}- an immediate change iu the hj-drostatic pres- sure, and hence water should be added to or removed from the outer vessel, to balance iucqualities of height as fast as they occur. 611. The proportional amounts of the substances inter- changed have been determined by various observers. Joll3',* by au ingenious modification of the osmometer, obtained the following results ; the figures representing the weight of water which replaced in osmosis one part by weight of the substance : Sodic chloride ... 4.3 Sugar 7.1 Sodio sulphate 11.6 Magnesic sulphate 11.6 Potassic sulphate 12. Potassic hydrate 215.7 612. These figures are known as the osmotic equivalents of the respective substances, I)ut they are hy no means constant ; since, as Ludwig-" has shown, thej' depend partly on the de- gree of concentration of the solution used, the duration of the experiment, and the character of the membrane. 613. If, however, a colloidal hody is placed in the reseiToir, very little comparatively passes outwards, and in the case of some colloids nothing. " Indeed, an insoluble colloid, such as gum-tragacanth, placed in powder within the osmometer, was found to indicate the rapid entrance of water, to convert the gum into a bulky gelatinous hydrate. Here, no outward or double movement is possible."^ This verj' important fact must be borne in mind in the application of the phenomena of os- mose to those of absorption of liquids by the colloids in active vegetable cells. 614. Precipitation-membranes. Traube' (in 1867) discovered that when a drop of a solution of copper-sulphate is placed iu a solution of potassic ferroc3-anide, there is produced over its whole surface a coherent membrane (of precipitated cupric ferro- C3anide), known as a " precipitation-membraue." This at once begins to increase in size, but somewhat irregularh', as if breaks occurred at the upper part through which a portion of the liquid 1 Zeitschrift fur rationelle Medicin, 1849, vii. p. 83. " Poggendorff : Aiinalen der Physik und Chemie, Ixxviii. p. 307. 3 Graham : Journ. Chein. Soc, 1862, p. 269. * Archiv fiir Anat. u. Physiol, du Bois-Reymond u. Reichert, 1867, p. 87. 15 226 DIFFUSION AND OSMOSIS. ■within flowed out onlj' to meet the exterior liquid, and there formed instantlv a precipitate cohering with the edges of the rupture. If a fragment of chloride of copper is placed in a test- tube containing a strong solution of potassic ferroe3anide, the action is more rapid than with copper-sulphate. The fragment dissolves at once, and forms a green globule at the bottom of the tube. If it now be carefully watched, it will be seen that a delicate transparent film (the precipitate of cupric ferroC3-anide, ■which in a flocculent state is brown) is produced over the glob- ule, and the sphere begins at once to grow into a cylindrical body. The liquid in the upper jjart of the closed cylinder is almost colorless ; that at the bottom is deep greeu. The inter- mittent growth in height appears to admit of only one explana- tion ; namely, that the membrane is torn by the great pressure ■within, and the solution of copper chloride which flows through is immediatel}- covered bj' a newly formed film. By careful management, such growths of C3-Iindrical form can be produced several inches long. Traube also discovered that v/hen a drop of yS gelatin (gelatin which has been boiled contiuuousl3- for about three days, there- by losing its power of coagulation) is placed in a solution of tannin, a film forms at once, which begins to grow into a spheri- cal cell, but without the appearance of irregular and intermit- tent rupture. Such an artiflcial cell is best prepared b}- placing a glass tube having a drop of yS gelatin on the tip into a solution of tannin. Its growth is even and uninterrupted, and unless the apparatus is disturbed, no appearance of rupture is observed. A further discovery was made by Traube ; nanieh', that a co- herent film ma}- be formed even by the contact of pure water. The coagulum produced when gelatin is acted on by tannin (the so-called tannate of gelatin) is soluble in a concentrated solution of tannin, but is insoluble in a dilute solution. If a drop of a solution of tannate of gelatin thus prepared is placed in pure water, a coherent film forms at the surface which can increase up to a certain size.^ 615. Pfeffer has employed the precipitation-membranes dis- covered by Traube, in an ingenious apparatus bj' which the pressure developed in the so-called artificial cell can be accu- rately measured. The apparatus consists of a porous porcelain ' At this point should be mentioned the observation of Nageli, tliat when- ever cell-contents rich in protein matters come in contact with watery media, a membranous film is fovmed over the surface (Pflanzenphysiologische Unter- suchungen, 1855, pp. 9, 10). EXPERIMENTS OF PPEFJTBR. 227 or clay cell, like those which are used in tlie Buusen battery, connected bj' means of a glass collar with a suitable manometer. Within the cla^- cell a precipitation film is formed ; '■ the cell is ' The following account of details essential to success in these experiments of Prof. Pfeffer has been prepared by one of his students, Dr. W. P. Wilson. The principal portion of the apparatus is a porous porcelain cell, z, 46 mm. high and 16 mm. in diameter, with walls 1^ mm. in thickness. This cell is cemented on to a piece of glass tubing, v. A second piece of tubing, t, with lateral tube, is cemented into the tirst piece. The lateral opening is for the manometer m, the one at g is for the convenience of tilling and sealing the cell. One of the two fluids used in forming the membrane for experimentation is allowed to penetrate the porous cell from without. When this has thoroughly taken place, the second fluid is poured into the interior. The contact of the two fluids takes place, there- fore, on the inner surface of the porous cell, and here the precipitate is formed which is termed the pellicle-vutnbrane or precipita- tion-membrane. Substances which by their mutual contact give rise to such precipitation- membranes are termed membranogenic. It will readily be seen that during any internal pressure the porous porcelain cell acts as a support for the membrane. If the exterior solution is copper-sulphate, the interior solu- tion potassic ferrocyanide, then the precipi- tated membrane will be cuprio ferrocyanide. After the membrane has been fonned, then any solution not chemically incompatible with it may be employed in the cell ; namely, syrup from cane-sugar, a solution of saltpetre, or a still stronger solution of potassic ferro- cyanide than was used in the preparation of the cell. 143 As the successful working of the apparatus depends upon the exact carrying out of quite a number of minor details, the following description of the methods of putting the parts together may be found useful : — In order to insure absolute freedom from any foreign substance, the porcelain cell must be successively washed in dilute solutions of potassic hydrate and hydrochloric acid, and then thoroughly dried. Warm a piece of sealing-wax in the spirit-lamp and draw it to a point. Slowly heat the open end of the cell in the alcoholic flame. When hot enough to very readily melt the wax, apply the point; and while the cell is continually rotating, cover evenly a space to the depth of 15 mm. with wax in the interior. It should be about 2 mm. in thickness. Pick up the short piece of tubing, u, which has been previously waxed on one end, and rotate it over the flame. When both porcelain cell and glass tube are as warm as they can be made and yet the wax kept smooth 228 DIFFUSION AND OSMOSIS. then filled with any diffusible liquid, — for Instance, a dilute solu- tion of sugar, — the manometer is attached, and the whole appa- ratus is placed in pure water or an^- aqueous solution. and oven on all siJes, place them quickly together, lapping about 15 mm., and continue the rotary motion until cool. Take a scalpel with a point bent at right angles to the blade, heat it, and, inserting it in the glass tube, cut away the wax at its inner end, thus exposing a shoulder of the thickness of the glass. Roll out in the form of a pencil about 2 mm. in diameter a piece of sealing-wax which has been made a little soft by the addition of a drop or two of turpentine. A piece of this, equal in length to the inner circumference of the glass tube, in a long coil, should be placed on the point of the scalpel, carried in to the shoulder and pressed into it. A little heat very cautiously applied fi'om without, with projier turning of the cell, will easily cause this softer wax to flow and fill the shoulder with perfect smoothness. The use of the softer sealing-wax makes a joint wliich will not crack under strong pres- sure. Now cement the tube t very firmly into v, with the same precautions as above. Unless a pressure of more than three atmospheres is desired, the soft wax need not here be u.sed. The cell is now ready to be prepared for filling. In order to saturate the porous porcelain with any given solution, the air must first he wholly removed. Place the apparatus in a beaker of water which has been freed from air by boil- ing, and set the whole under the bell-jar of an air-pump. Exhaust and admit the air into the bell-jar repeatedly until bubbles can no longer be seen to rise from the porcelain. Transfer the cell to a three per cent solution of copper- suli>hate, and exhaust the air again. Four or five hours will be required for this .solution to thoroughly penetrate the porous cell. At the end of this time remove it from the copper-sulphate, empty it, and with some long twisted strips of bibulous paper quickly diy up all moisture from its inner surface. If at any time the exterior surface of the cell begins to appear dry before the moisture from within has been wholly removed, dip it at once in the solution from whence it came. At the moment when the moisture is properly removed, fill the cell to the second joint with a three per cent solution of potassic ferro- cyanide and replace it in the copper-sulphate, taking care that the surfaces of the two fluids are in the same plane. An interim of at least twelve hours must now elapse in order that the membrane may be properly formed. At the end of this time the cell is ready to be used, either with the solution which it already contains or with some other. If some other solution is to be employed, then carefully empty out the potassic ferrocyanide, and after washing the cell with a little distilled water, fill it with the fluid to be used. The cell must be so filled and sealed as to leave absolutely no air within, otherwise the pressure cannot be accurately measured. Insert a perforated rubber cork at g. Fill the manometer from the quicksilver to the extremity of the tube with potassic ferrocyanide, or whatever other solution is to be used in its place, and push it into position in the cork. Fill the cell com- pletely full, and press firmly into place the second perforated cork, taking great care, first, that no bubble of air remains at its base ; and second, that not a particle of potassic feiTocyanide comes in contact with the outside of the cell. A bent glass tube, drawn to a capillary point at one end, should now be filled with potassic fen-ocyanide and slowly pushed into the cork. If this is THE CELL AN OSMOTIC APPARATUS. 229 In certain experiments by Pfeffer, made vvitli a single cell, in whicli was a solution of cane-sugar containing a trace of one of tlie membrauogenic substances, wliile tlie water outside contained a trace of the other, the following pressures were indicated : — Percentage of sngar in the solution, by weight. Temperature. Mercurial pressure. 1 1 2 i 6 1 13°. 7 C. 13.6 14. 13.8 14.7 14.6 53.8 cm. 53.2 " 101.6 " 208.2 " 307.5 " 53.5 " With a 3.3 per cent solution of potassic nitrate in the cell, Pfeffer obtained a mercurial pressure of 436.8 era. 616. An active vegetable cell is an osmotic apparatus. The chief agent in its work of absorption is the peripheral film of the colloidal protoplasmic mass, and this receives mechanical support from the wall of cellulo.se in which it is lield. It was formerlj' believed that in osmosis there is always an exchange of materials, one current passing inwards (endosmose), the other outwards (exosmose) ; and there are numerous cases in which this is true, and in which the osmotic equivalent can be calculated (see 612). But Pfeffer's experiments show how great a force maj' be exerted by osmosis in cases in which tliere is little or no substance passing out to replace the liquid ab- sorbed. In the series of experiments in which a solution of sugar was employed in his osmotic apparatus, no trace of this properly done, any small quantity of air which may be in the upper part of the cork will rise during insertion to the capillary point. Gradually and cautiously warm the tube, beginning close to the cork. This will expand the fluid and drive the air wholly out. At the moment when the solution completely fills the tube, fuse the capillary point in the spirit-lamp. The cell is now entirely free from air and hermetically sealed. During the time of inserting the ma- nometer, corking, and sealing, the porcelain part of the cell must not be allowed to become dry, but must be frequently dipped into the solution from which it was taken. With unannealed brass wire secure both corks after the fashion of champagne-bottles. Now suspend the cell in the solution of copper sulphate so that the porce- lain shall be wholly submerged but shall not touch the sides of the vessel containing the solution. Note the position of the mercury in the manometer, and see that the temperature remains constant in the room. If the cell is perfect, a certain degree of pressure will be indicated in less than an hour. j ■ 230 ABSORPTION OP LIQUIDS THROUGH ROOTS. substance could afterwards be discovered in the water on the outside. Tlie apparatus lined witli its colloidal film, containing a small amount of saccharine solution, and surrounded by a very dilute aqueous solution of mineral matters, is an instructive imitation of a vegetable cell. ABSORPTION OF LIQUIDS THROUGH ROOTS. 617. Submerged aquatics may absorb with their whole surface. They are bathed in dilute saline solutions containing the gases essential to vegetati\'e activity, and the materials for their food can be taken from the medium surrounding them, perhaps quite as well by one of their parts as by another. This fact is well illus- trated bj' the larger algae, in which the organs populai-ly called roots are merelj' mechanical hold-fasts, and the work of absorp- tion can proceed at any part of the frond. The simplest diflfer- entiation of organs for absorption is met with in the rhizoids or complex root-hairs of mosses, and in the iilaments of fungi which bury themselves in a nutrient substratum. Above the mosses the differentiation of organs into roots for absorption, and stems for the support of the assimilative tissue, is very plain. For our present purpose it is best to begin an examination of the absorp- tion of liquids by plants with a study of the structure and the office of tlie root. 618. It has been shown in Part I. that the younger parts of the root are clothed with extremely- delicate epidermal cells, which, with the slender trichoraes associated with them, con- stitute the absorbing apparatus of tbe plant. (These epider- mal cells of the root, taken coUectivelj', have been called the Epiblema.^) 619. The root-tip with its protective cap does not share to anj'' great extent, if indeed at all, in the work of absorption ; and yet to the soft, spongj', rounded mass of tissue forming tbe root-tip was formerly given the name of spongiole, on account of its spongy nature, and its supposed office of sucking up nu- trient matters from the soil.^ 1 This term, early introduced, was retained by Schleiden : Principles of Scientific Botany, 1849, pp. 68, 218. 2 Thns De Candolle, in his Physiologic Vegetale, 1832, p. 41, says: "La succion des racines s'execute par des points speciaux qu'on nomme spongioles, qui sont composes d'un tissu cellulaire tres-fin et tonjours nouvcau, puis()ue les racines s'alongent sans cesse par leur extremite. Le hquide de la terre tend k entrer dans les meats de ce tissu : I. par la force de capillarite ; II. par EOOT-HAIES. 231 620. Koot-hairs. It was shown experimentally by Oiilert i in 1837, that the tip of the root is not the absorbing pait. By careful excision of the tip, and the use of a harmless water- proof varnish to cover the wound caused, he obtained full absorp- tion of liquids through the sides, and not the end of a young root. lie further demonstrated the very general occuri'ence of delicate hairs upon the sides of young roots, and expressed the opinion that these were the efficient agents in root absorption. 621. That the abundance of the hairs on new roots is depend- ent largelj' on the amount of moisture to which thej- are ex- posed, appears from experiments on the roots of some of the more common cultivated plants, — Allium Cepa, Cucurbita Pepo, Zea Mais, etc. In all these cases the plant can almost be said to regulate the amount of its absorbing surface by the amount of moisture within its reach, and it is thought b3- some that all the epidermal cells of a .young and developing root have the power of extending into hairs. The number of hairs to the square millimeter on a root of Zea Mais grown in a moist place was found by Schwarz to be 425 ; and on a root of Pisum sativum, 232. 622. Root-hairs are, as has been shown in Part I., cylindrical protuberances from the external wall of the epidermal cells. They varj' in length from .1 mm. to 8 mm. The former length occurs in a few gi'asses, the latter in some water plants. Schwarz gives the following measurements of length : root-hairs of Pota- mogeton, 5 mm. ; of Anacharis, 4 mm. ; of Brassiea Napus in moist air, 8 mm. ; of Pisum sativum and Avena sativa, 2.5 mm. ; of Vicia Faba, 8 mm. 623. When root-hairs are developed in contact with soil, they become much distorted (see Fig. 89), and generally dwarfed; they curve more or less irregularly around the particles of soil, and frequently are enlarged at the immediate place of contact. Moreover, the character of the cell-wall is somewhat changed at the place of contact with the particles ; in many instances the wall undergoes a sort of mucilaginous modification, and becomes so firmly united to the particles that these cannot be removed riiygroscopicite. Ces deux proprictes de tissu peuvent bieii expliquer I'enorme quaritite d'eau ijiii penetre dans la plante vivante, les variations de cette quan- tite selon les esp^ces, les saisons, etc. II souffit d'adniettre que les cellules des spongioles donees de contractions alternatives, augmenteut et diminuent alter- nativement les meats intercellulaires, et tendent ainsi h absorber de I'eau en quantite proportionnee Ji la force et h. la rapidite de leurs contractions vitales. " 1 Liniiaea, 1837. 232 ABSORPTION OF LIQUIDS THROUGH EOOTS. without laceration of the delicate cells. Notwithstanding the extreme tenuitj' of the cell-wall, it is thought by some to plaj' an important mechanical part in fastening the roots in the soil.'- 624. That the hairs upon the root vastly increase its absorb- ing surface is self-evident. Schwarz has shown that in Indian corn grown in moist air the surface presented by the velyety hairs which cover the joung roots is 5.5 times greater than that of the part of the root on which the hairs occur ; while the ratio of these surfaces in the roots of peas is as 12.4 to 1 ; and in the aerial roots of Scindapsus pinnatus, as 18.7 to 1. But all these figures, which are at best only approximate, appear to be verj' low. 625. Extent of Root-systems. In extending, the root, by- growth at its protected extremitj-, can insinuate itself between particles of soil which could not be easily displaced by simple thrust. The branches from the main root extend exactly as does the main root itself, — by continual additions just behind the tip, — and the area covered 1)\' a root-S3stem finally' becomes very large. One of the earliest recorded measurements is that by Hales, ^ who estimated that the roots of a sunflower (3 J ft. high), taken together, were no less than 1,448 feet in length. The plant had "eight main roots reaching fifteen inches deep, and side- ways from the stem ; it had, besides, a very thick busii of lateral roots, which extended every way in a hemisphere about nine inches from the stem and main roots." 62G. Nobbe has shown that in year-old plants of certain closelj' allied gymnosperms the root-systems differ remarkablj' in the number of the rootlets and the total length of the roots. ^ In three species the determinations of the total length were as follows : — 1 Haterlandt : Physiologische Pflanzenanatomie, 1884, p. 162. 2 Hales gives as the entire surface of these roots 2,286 .square inches, or 15.8 square feet (Vegetable Statics, 1731, p. 6). 8 The plants exauiined were grown from May to October. Two of Nobbe'a tables (Die landwu-thschaftlichen Versuchs-Stationen, xviii., 1875, p. 279) are here given : — a. Number of Rootlets. Norway Spruce. Silver Fir. Scotch Pine. Boots of the 1st order. " " 2(1 " " " 3d " " 4tli " " " 5tli " 1 85 162 5 1 48 85 1 404 1,935 749 26 EXTENT OF KOOT-SYSTEMS. 233 Silver Fir 1 meter. Norway Spruce 2 meters. Scotch Pine 12 meters. All the plants upon which these averages are based were grown under the same conditions. 627. When an}- plant is lifted, even with great care, from the soil in which it has grown, man}- of its more delicate root- lets are torn off and left behind. Hence it is difficult to ascertain the total amount of roots belonging to a plant. Even the best plan yet devised for cleaning the root previous to measur- ing it — that of allow- ing a stream of water to wash away all the earth which it will detach — usually causes a few of the finer rootlets to be carried off. It has been shown, however, that the roots of peas, beans, and the common cereals are abundantly branched to a depth of more than a meter, and that manj- of them penetrate considerably further. Schubart states that the amount, by weight, of roots in peas and wheat, compared with that b. Length in Millimeters. Norway Spruce Silver Fir. Scotch Pine. Eoots of the 1st orrter. " 2d " " " 3U " " " 4tb " " " 6th " 290 1,333 312 5 300 636 66 873 4,438 6,491 1,143 41 Fio. 144. Eoots of seedlings of Triticiim vulgare. B, plant four weeks older than A. The soil clings in "sach case to the ijomiger parts. (Sachs.) 234 ABSORPTION OF LIQUIDS THROUGH ROOTS. of the whole plant (all being dried), is less than fifty yer cent.' By comparison of the weights and lengths of average pieces of the roots of barley, it has been found that the whole root-system in a vigorous plant is not far from thirty-seven meters in length ; and that all this could be packed in a small volume of fine soil (about jij of a cubic foot).^ 628. The nature of the soil, and especially the amount of moisture and of nutritive matters which it contains, have a marked influence upon the development of the root-system of a plant. Other things being equal, fertility of the soil favors compact branching, as is siiown by experiments by Nobbe.' Indian corn was grown for a time in several cylinders con- taining clay soil ; then the earth was carefully washed awaj' and the roots were compared. In the first cylinder the soil had 1 Amounts as given iu Chemische Ackersmann, i. p. 193. Roots of winter wheat (in April) 40 per cent. " peas ( four weeks after planting) . . . ii " " " (at flowering) 2i " 2 Hellriegel : Hoffmann's Jalivesbericbt, 1864. Nobbe (Versachs-Stationen, 1875, p. 279) has given some instructive figures, showing the ratio of the surface above ground to that below in yearling plants of some common species of Conifers gi-own under similar conditions. Some of his figures are here given. a. SniiFACE OF Rootlets. Square millimeters. Silver Fir 2,452. Norway Spruce 4,139. Scotch Pine 20,515. b. SUKFACE OF THE GrEEN PaRTS OF THE PLANTS. Square millimeters. Silver Fir 1,451. Norway Spruce . 1,551. Scotch Pine 4,304. a. Ratio of Parts in the Plants examined. Silver Fir. Norway Spruce. Scotch Pine Parts above ground ... 100 : 107 : 297 Parts below gi-ound ... 100 : 168 : 837 d. Ratio of the Parts above ground to those below. Silver Fir 100 : 169 Norway Spruce 100 : 267 Scotch Pine 100 : 477 8 Versuchs-Statiouen, iv., 1862, pp. 220, 221. DEVELOPMENT OF KOOT-SYSTEMS. 235 been nniformlj' mixed with a fertilizing substance, and in this soil the roots had developed in a normal manner. In the sec- ond cj'linder a layer of the fertilizing material bad been [jlaced three to four centimeters below the surface, and in the soil at this plane the roots had branched verj' abundantly'. In the third cylinder a similar layer of the fertilizing matter had been placed half-way down the cylinder, and here the root-branches were far more numerous than elsewhere. In other cases the fertilizing substance had been placed at the bottom, around the sides, or in the middle of the cylinder, and in these places respec- tively the root-branches were most abundant. Substantially the same thing is observed in earth where the roots of plants meet with buried bones : the finer root-branches are developed around and afterwards in the substance of the decomposing animal matter, often forming dense mats.^ 629. In some cases roots extend to verj- great distances ; thus those of an elm have been known to fill up drains fifty yards distant from the tree.^ It may be said, in general, that the roots of the common forest and shade trees reach to and be- yond the eaves of the roof made bj- the leafy branches. "There is a constant relation between the horizontal extension of the branches and the lateral spreading of the roots. It is not by watering a tree close to the trunk that it will be kept in vigor, but by applying the water on the soil at the part correspond- ing to the ends of the branches. The rain which falls on a tree drops from the branches on that part of the soil which is situ- ated immediately al)ove the absorbing fibrils of the roots." ^ 630. The root-system of a plant, ever extending bj' its in- numerable subdivisions into new soil, and clothed near the extremities of the rootlets with delicate epidermal cells, is a complex apparatus for osmosis placed under the most favorable conditions for absorption. 631. The course of the water after it has found its way into a plant through the epidermal cells of the newer portions of the roots, and the pressure which at times the watery liquids in roots exert, can be more convenientlj' examined at a later stage (see Chapter IX., " Transfer of Water through the Plant "). 1 See also a i)aper by Detmcr : Versuchs-Stationen, 1872, p. 107. 2 Journal Eoyal Agricultural Society, vol. i. p. 364, contains some interest- ing cases of great length of roots. 8 Balfour : Class Book of Botany, 1854, p. 427. CHAPTER VIII. SOILS, ASH CONSTITUENTS, AND "WATER-CULTURE. 632. When a plant is carefullj- dried at a temperature slightly exceeding that of boiling water until it ceases to lose weight, there remains behind a brittle combustible residue. The dif- ference between the weight of the plant and that of the resi- due represents the amount of water previously contained in the plant. This differs widely, according to the kind of plant and its age. The following table gives the proportion of water contained in a few of the most common plants : — • Eed Clover, tefore flowering 83 per cent. " " in full flower 78 " Oats, before flowering 82 " " in flower 77 " Turnip (root) 91 " Beech (leaves), in summer 75 " " " in autumn 55 " Dry grains 14 to 15 " Dry woods 15 " 633. If the brittle residue left after complete expulsion of the water is burned in the open air, there remains beliind a small amount of gray ash ; all the rest is wholly consumed. The amount of ash also varies widely-, according to the kind of plant and its age. In the following table ' are given the proportions for a few common plants : — Per cent of ash in Per cent of aMi in fresli material. dry material. Red Clover 1.5 6.6 Sugar Beet (root) .8 4.3 Indian Corn 1.1 5.5 " (grain) 2.1 1.5 Beech (leaves), in summer ... 1.3 — " " in autumn ... 3. — 634. In a general way it maj' be said that the combustible matters are derived chieflj' from the atmosphere, while all the 1 The student is referred, for detailed accounts of analyses from which these figures have been chiefly taken, to Johnson's "How Crops Grow," 1868. FOKMATION OF SOILS. 237 water aud the Incombustible ash come from the soil. In the case of aquatics this general statement would not appear to hold, for thejr obtain all their substance from the water in which they live ; but, as will be seen later, this source is essentiallj' the same. We have examined in the previous chapter one of the means b}- which plants obtain their supplj' of water and ash materials, and it will be best to consider now the source from which this supply comes, before approaching the studj' of the combustible substance of plants. SOILS. 635. Formation of soils. Soils are produced bj' the disinte- gration of rocks. This may be mechanical, as that caused by crushing, attrition, and the action of frost; or it may be and generally is associated with more or less chemical change. In soils, some of the products of the decomposition of organic sub- stances are usually intermingled with purely mineral matters aggregated in various degrees of fineness. Soils exposed to atmospheric influences constantly change both in their ph^ysical properties and chemical composition, the changes being brought about chiefly by the combined action of moisture, carbonic acid, and oxygen. 636. Water not only wears awaj- solid rocks by its mechanical action, but after it has insinuated itself into the crevices of rooks it accomplishes the work of disintegration far more rapidly bj- its expansion during freezing.^ When rocks become loosened by running water, or by the slow movement of glaciers, the crushing and grinding of the pieces which come into contact are sufficient to pulverize the hardest of the more common ones. Water, especiall3' when it holds carbonic acid in solution, is a very important agent in ciianging the characters of rocks ; sometimes it does this by dissolving out portions of the rocks, sometimes by bringing about new combinations of their con- stituents. Moreover, rain-water contains a minute quantity of other matters besides carbonic acid, and these exert a powerful eflec!t in disintegrating and dissolving certain rocks. 637. The free oxygen of the atmosphere is also an efficient agent in the changes by which rocks are broken down to form 1 The amount of expansion ia usually given as approximately one fifteenth of the volume. 238 SOILS. soils. Manj- rocks contain fen-ous oxide, which readily under- goes farther oxidation ; certain sulphides in rocks are oxidizable under tlie ordinary conditions found in a moist atmosphere, and in such cases the chemical action results in rendering the rocks brittle. 638. Water can easily transport the finer particles of soil from where they were formed by disintegration of the rocks to points at distances from their source, varying with their weight. For this reason the particles accumulate in different degrees of fineness at different points along water-courses. 639. It is believed that during the Glacial period, when large portions of the northern hemisphere were covered deeph- with sheets of moving ice, immense amounts of coarse and fine soils were carried far from the places where they were formed, and were heaped up more or less irregularly in the masses which now form gravoll}- hills and ridges. The glacial action now going on in the Alps shows how vast must have been the soil- making and soil-carrying power of the glaciers which once cov- ered so much of our continent. 640. Soils which have not been carried by water or ice from the place where they were formed by some of tlie agencies men- tioned above are not generallj- of great depth, and their nature can usually be made out bj' examination of the contiguous rocks. 641. Classification of soils. For our present purpose soils may be classified as gravelh", sandj-, clayey, calcareous, loamy, and peaty. Gravelly soils difier widely in their chemical char- acter, since the pebbles which compose them may be either chiefly quartz and fragments of rocks in which quartz predominates, or there may be also a good proportion of limestone, or of feld- spathic rocks. With the coarse pebbles is intermingled a certain proportion of finer soil. Sandy soils are usually made up of fine quartz with which some otiier matters are asso- ciated, such as some compound of iron, grains of feldspathic minei-als, micaceous particles-, etc. In a few cases, however, the sandy soils differ widely from this composition ; for in- stance, the green sand of New Jerse3- contains a large proportion (more than flftj- per cent) of green grains of a silicate of iron and potassium. Clayey soils are generally derived from the dis- integration of various feldspathic rocks, and are mixtures of hydrated aluminic silicate with manj- other matters. Such soils are generally adhesive, are retentive of water, and dry into a hard mass ; these characters which belong to true clay are PHYSICAL PROPERTIES OF SOILS. 239 found also in some soils winch are not claj's, and hence the term clayey is sometimes loosely applied. Calcareous or lime soils contain calcic carbonate in large amount. To calcareous clay, when the ingredients are in a state of rather fine subdi- vision, the name marl is frequently applied. Peaty or humus soils are those which contain a considerable proportion of par- tially decaj-ed vegetable matter ; when such matter decaj-s under water it becomes peat, or muck ; when it decays without much water it is generally known as mould. 642. By mechanical analysis, as b}' simple washing and sift- ing, it is possible to separate a soil into its mechanical ingre- dients, which are : (1) Gravel ; (2) coarse sand ; (3) fine sand ; (4) clayej- sand ; (5) clayey substance, or fine claj'. The mechanical subdivision of soils has an important bearing upon their physical properties and upon tlieir adaptability' to the growth of roots and the sustenance of plants.^ From interesting studies hy Darwin,^ it is plain that in some localities earth-worms have exerted, by their burrowing and tunnelling, a vast influence in changing the phj'sical character of the soils in which they thrive. 643. Physical properties of soils. Of these, the most important to be considered here are those which affect the relations of soils to liqliids, to gases, and to heat ; for all of these dh'ectlj- aflTect the growth and indirectly- the nutrition of plants. 644. Absorption and retention of moisture by soils. It is con- venient to examine the relations of soils both to liquid water and to aqueous vapor. Soils can absorb from the atmosphere and condense upon the surface of their particles, or in their inter- stices, a certain amount of the vapor of water. This property of absorption, known as that of hygroscopicity, is different in different soils, as shown b}- the following table from Schubeler.' Five hundred centigrams of each soil carefullj- dried were spread over a surface of thirtj'-six thousand square millimeters, and exposed for varj-ing periods to an atmosphere saturated with water}- vapor ; the amounts of waters absorbed (in centi- grams) were as follows : — ^ The reader should examine a paper by J. D. Whitney (Plain, Prairie, and Forest), in which is discussed the probable influence of the extreme fineness of prairie soils upon the absence of forests. Sec American Naturalist, October and November, 1876. ^ Darwin : The Formation of Vegetable Mould through the Action of Worms. 3 Knop's Lehrbuch der Agricultur-Chemie, 1868, vol. ii. pp. 13, 14. 240 SOILS. 12 hours. 24 hours. 48 hours. 72 hours. Quartz sand . . 0.0 0.0 0.0 0.0 Calcareous sand 1.0 1.5 1.5 1.5 Clayey soils . . 10.5 to 15. 13 to 18. 14 to 20. 14 to 20.5 Clay .... 18.5 21.0 24.0 24.5 Garden earth . 17.5 22.5 25.0 26.0 Humus . . . 40.0 48.5 55.0 60.0 From these figures it appears (1) that the greater part of the vapor is condensed before the expiration of a single day, (2) that humus is b}' far the most hygroscopic, but (3) that clay can ab- sorb a large quantity of vapor. Temperature exerts a marked influence upon the capacity of soils to absorb aqueous vapor, as is shown by Knop's exami- nation ^ of a sand3' and of a lich earth ; the amount of vapor absorbed diminishes with elevation of temperature. 645. The amount of liquid water which soils can absorb and re- tain is ver}- different I'or different kinds of earth. In the follow- ing determinations by Schiibeler drj- soils were saturated with ■water upon a funnel, and the increase of weight was noted after all the excess of water had dripped awaj-. The first column gives the percentage of increase in weight of soil ; the second, the num- ber of volumes of water that one hundred volumes of soil can take up ; the third, the percentage of this water which evaporates from the soil in four hours when it is spread over a given surface.^ 1. 2. 3. Quartz sand Calcareous sand . . . Clay soil (60% clay) . . Clay soil (76% clay) . . Heavy clay (89% clay) . . Pure clay Humus ' 25 29 40 50 61 70 190 37.9 44.1 .51.4 57.3 62.9 66.2 69.2 88.4 75.9 62 34.9 31.9 25.5 646. The degree of fineness exerts also some Influence upon the absorptive power ; but while pulverization increases that ^ Versuclis-Stationen, vi., 1864, p. 281, where are found also some interesting results recorded by Knop, in regard to the absorption of aqueous vapor by various organic substances. ^ Knop's Lehrhuch, 1868, vol. ii. p. 26. The third column is cited from Johnson's "How Crops Feed," 1870, p. 180. s Samples of peat have been known to absorb from 300 to more than 600 per cent of water. ABSORPTION OF MOISTURE BY SOILS. 241 power in some kinds of soil it diminishes it in oliiers. Tlius Zenger has sliovvn tiiat fine quartz sand absorbs about twice as niuuh water as tliat wbicli is coarse ; on tbe otlier hand, fine bricli-clay is not so absorbent as coarse. 647. Admixture of heterogeneous matters with soil generally lowers the absorptive and retentive power both of the soil and of the added substances. Treutler examined certain soil mixtures in the following manner : fifty grams of the soil were placed in one hundred cubic centimeters of water for twent^'-four hours, the excess of water was allowed to drip away, and the amount then retained noted. The following are among his results : — SoOs. is .5 =8 Mixtures. o c a |S2 Fine earth 34.2 40 grm. fine earth and 10 grm. caustic lime 44. Quartz sand 14. 40 grm. quartz sand and 10 gnn. caustic lime 19. Caustic lime 61. 40 grm. quartz sand and 10 grm. bone-dust 16.5 Bone-dust 46. 30 grm. quartz sand and 20 gi-m. hone-dust 9. From Treutler's tables it appears that the absorptive and retentive capacit}' of a mixture of two substances tnaij equal that of the constituents, but that generall}' it becomes lower. G48. A soil ma}- be so fine and compact that rain will not readily penetrate it ; or on the other hand it may be so porous as to allow the water which falls on it to pass rapidl}' down through it. A soil of proper texture will receive the rains, and, as has been shown bj- the foregoing paragraphs, retain a certain amount in its pores, the excess draining awaj'. 649. Evaporation of water goes on continually from the sur- face of moist soil, unless the atmosphere is saturated, and the amount of evaporation depends largelj- upon the amount of moisture present in the state of vapor in the atmosphere at any given time. But the retentive power spoken of above (which is plainly opposed to evaporation) is very different in different soils ; for this reason about three times as much water evaporates from quartz sand as from the same amount of humus equally exposed for a given time. When b}' evaporation the soil be- comes dry at the surface, a draft is made upon the supply of •water retained in it at a greater depth, and this water then rises by capillarity to the drier layers. It is therefore said that there is a constant movement of. water in the soil. 6 242 SOILS. 650. A distinction may be properlj* made between (1) that water which remains as a copious suppli' beneath the surface of the ground, existing there plainlj' as a liquid, (2) that which ad- heres to the particles of soil imparting to them a moist appear- ance, (3) that wliich adheres to the particles of an air-drj- soil and which does not affect at all the appearance of the particles. The first has been called hydrostatic^ the second, capillary, the third, hygroscopic water. It is from the two latter that the roots of plants other than aquatics usually- obtain their supply of moisture.^ 651. The relations which evaporation and drainage bear to the total rain-fall upon the soil have been examined during a series of nineteen years at Eothamsted, in England. The fol- lowing figures are based on the results during ten j-ears (Sep- tember, 1870, to August, 1880). Eain-fall 30.68 iuchea. Drainage from soil at 20 inches depth 13.21 " at 40 " " 13.94 " ateO " " 12.17 " Amount of water retained by soil, or evaporated at 20 inches depth 17.47 " at 40 " " 16.74 " at 60 " " 18.51 " Percentage of rain-fall lo.st by drainage at 20 inches depth 43.1 " at 40 " " 45.4 " at 60 " " 39.7 Percentage of rain-fall retained by soil, or lost by evaporation at 20 inches depth 56.9 at 40 " " 54.6 at 60 " " 60.3 " 652. Soils are not only acted upon bj- the solvent power of water, as shown in 636, but manj- soils possess the remarkable propertj- of removing saline matters from aqueous solutions. The interesting fact that impure water can be freed from some of its foreign matter by being filtered through earth has long been known, but its significance in the nutrition of plants does not appear to have received attention until 1819. Gazzeri^at 1 For a full discussion of this subject, which is most important in its bear- ings upon the cultivation of plants, the student should study Johnson's ^' How Crops Feed," p. 199. 2 From a note by Orth: Versuchs-Stationen.xvi., 1873, p. 57. The discovery is generally ascribed to Bronner, 1836. The fullest treatment was by Way : Journal Eoyal Agricultural Society, 1850, and later. CHKMICAL ABSORPTIOX BY SOILS. 243 that date says : " Earth, especially claj-, seizes upon the sol- uble matters intrusted to it, and holds them back, in order that it nia3- gradually furnish them to plants according to their needs." 653. When dilute solutions of a salt are slowly- filtered through sand which contains a good admixture of clay, the water passes out for a time without more than a trace of the salt, and in some cases all the salt is retained bj' the soil. Even sewage liquids can b\' this method be freed from their offensive ingre- dients. This, phenomenon of fdtration is due to adhesion (that is, the attraction which the surface of one kind of matter has for another kind of matter). The sul)stances which are removed by the particles of soil are so fastened to them that even when the soil is washed iu pure water onlv traces of them are removed. 654. Chemical absorption by soils. Besides this physical ad- hesion, there are exhibited by many soils certain chemical phe- nomena also, which have been collectively termed chemical absorption. If a solution of potassic nitrate is filtered through a w-ell-pulverized cla}' soil containing an admixture of insoluble compounds of magnesium and caLuim, such as are met with in almost any ordinary soil, the water which drains off will con- tain ver}- little if indeed any potassium ; but it will have, in- stead, magnesium and calcic nitrate in appreciable amount. But this absorptive power of a soil is soon satisfied ; for after a certain amount of potassium has been removed no more is taken up. The strength of the saline solution affects the amount of absorption, more of the base being absorbed from strong solu- tions. Different substances are absorbed by the soil in different amounts ; thus in the experiments by Peters the bases were absorbed in the following order: (1) Potassa, (2) Ammonia, (3) Soda, (4) Magnesia, (5) Lime. Different soils absorb the same substance in different amounts, depending upon the plysi- cal condition of the soil, but chiefly, it is believed, upon the mode in which the substance is combined ; thus, more potassa is absorbed from the phosi)hate than from the carbonate, and more from the latter than from the sulphate. In general it may be said that the salts of the alkalies and the alkaline earths are so absorbed by rich soils that the bases are retained in new combinations, while the acids pass off, having also, of course, formed new combinations. The phos- phates and silicates are retained undecomposed. The case of 244 SOILS. the latter compounds ma}- be regarded as the ordinary phj-si- cul absorption, that of the former as the so-called chemical absorption. Goo. The matters absorbed by the soil may be released after a time and pass into solution again, or they maj' be displaced fi-om the soil-pai-ticles by the filtration of new solutions. When it is remembered that rain-water exerts a powerful solvent action upon some portions of the soil, and that, on the other hand, the soil can remove from aqueous solutions some of the matters therein dissolved, the complicated nature of the problem which presents itself is at once apparent. Examination of the waters which di-ain through soil, and -which may fairly represent the resultant of the solvent action of the water and the absorptive power of the soil, shows that from thirteen to fifty parts of solid matters may remain dissolved in 100,000 parts of water. (The question of nitrogen compounds in drainage-water will be ex- amined in a subsequent chapter.) 656. Condensation of gases by soils. Soils have the power of condensing in their pores certain amounts of different gases. These condensed gases arc released when the soils are subjected to a high temperature, saj- 140° C, and their amounts can then be measured. The figures below give the results of the meas- urements in several instances, 100 grams of soil being taken in each case. Soil. Cubic centimeters of gas yielded. Peat 162 Clay 30 Moist garden soil 14 It is found that in the soil there is present a smaller amount of oxj-gen and a lai'ger amount of nitrogen than in the atmos- lyhere. The percentage of carbonic acid in the soil is also some- what larger than that in the atmosphere ; especiall3' in soils which contain much organic matter. 657. Root-absorption of saline matters from soils. Having seen that the soil, the principal medium in which roots extend, pos- sesses the power of absorbing and retaining water, saline mat- ters, and gases, attention must next be directed to the conditions under which the root-hairs can abstract from it the matters requisite for the plant. These conditions are (1) presence of free oxjgen, (2) a certain temperature, (3) the presence of saline matters in an available form in the soil. 658. Free oxygen is necessary to all protoplasmic activity, SOIL TEMPERATURES. 245 and the plant will speedilj- show when the amount required for the absorptive activitj- of its roots is not furnislied. Different plants, however, require different amounts : thus aquatics and marsh-plants do not need so much oxygen for their roots as do plants which ordinarily grow in a porous soil. Partial ex- clusion of oxj-gen from the roots of the latter b}- keeping the soil saturated with water usuallj' injures the plants in a short time. It has been shown by Sachs and others that seedhngs of many plants normally growing in dryish soil will develop if treated as aquatics ; better results are obtained, however, if air is occasion- ally passed through the water. G59. The temperature needed for the absorptive activit}' of roots varies with different plants. It may be said, however, that for any given plant the absorptive power increases with increase of temperature. 6G0. Different soils have very different relations to temper- ature. Leaving out of account the small amount of warmth derived from the chemical changes going on in the soil bj^ which heat is evolved, it may be said that the heat of the soil is derived from the sun's rays. The angle at which these rays strike the soil must have a great influence upon its temperature. Again, there are various local causes, such as protecting or reflecting walls, which maj' considerablj- modifj- the temperature in any given case. The soil itself exerts a marked influence upon the amount of heat which it can receive and retain. Dark soils ab- sorb heat most readily ; but it has been shown that black soils are less absorbent of heat-rays than are those which are dark gray. The radiating power of a soil depends upon the character of its surface, being much greater in the case of fine mould than in that of coarse, gravelly soils. 661. It must be noted, however, that the heat-rays which fall upon a given soil may have different degrees of intensitj-. Some bodies (e. g. lampblack), can absorb and give off by radiation heat of high as well as that of low intensit3' ; while other bodies (e. g. snow), absorb heat of low intensitj' only. Heat of high intensity is converted into that of low intensity bj- the interpo- sition of a black covering of any kind which can absorb it and give it out below as heat of low intensity. 662. At the depth of fifty feet the temperature of the soil in the temperate zone varies within the limits of one degree, and at a depth somewhat below this it is constant. The stationaiy temperature at such a depth is the same as that of the mean 246 ASK CONSTITUENTS OF PLANTS. annual temperature of the atmosphere in temperate regions.* Moisture exerts a very great effect in equalizing the capacities of different soils for absorbing and retaining heat. 663. That the saline matters in the soil must be in a form in which the plant can make use of them, appears from what has been said about osmosis. It should be specially noticed, how- ever, that jounger roots may exert a solvent action upon soil- particles. Root-hairs, as Sachs ^ has shown, evolve small amounts of acid, which exert a distinctly corrosive effect upon certain min- eral matters with which they come in contact. Hence tliere is a continual unlocking of tlie nutritive mineral materials fastened in the soil ; the release being at the very points where the root-hairs are present to absorb them. ASH CONSTITUENTS OF PLANTS. 664. These occur in all parts of plants. It has been shown (p. 39) how frequently- cell-walls are impregnated or incrusted b3' mineral matters, which after careful calcination ma^- be left as a distinct skeleton of tlie tissues of which they formed a part. But the matters within cells, both the protoplasmic substance and the cell-sap, also contain a certain amount of incombustible ma- terial. The total amount of ash constituents varies greatly in different plants, in different parts of the same plant, and also 1 Penhallow, Soil Temperatures (Hougliton Farm Experiment Department),: 1884. See also Knop, Agricultur-Cliemie, i., 1868, p. 469. 2 Moldenhawer (Beytrage), in 1812, expressed the view that roots probably set free certain matters which can unloose nutritive materials. De Candolle (Physiologic, 1832) described the corrosive action of lichens on underlying rocks ; and Liebig, in 1839, studied the action of roots on the color of litmus solutions. Sachs's experiment (1860) is well adapted to class demonstration. A pol- ished plate of marble is covered with moist saw-dust, and in this a few seeds are- planted. After the seedlings have grown for a time the saw-dust is removed,- when the marks left upon the stone by tlie corroding rootlets can be plainly seen. If the corroded marble is rubbed slightly with a little vermilion, the traces made by the root-hairs will be very distinct. In the early publication of Sachs, the secretion by which the corrosion is effected was said to be car- bonic acid ; but he does not,appear to hold this view now. Whether the action is due to acetic acid, as Oudemann and Kanwenhoff suggest, or to different- acids varying with plants or times, as intimated by Pfeffer, it is certainly highly corrosive in some cases. In an experiment by Schulz, the rootlets of germinating Leguiiiinosse and Gramineie exhibited a faint alkaline reaction; (Journal fiir Praktische Chemie, Ixxxvii., 1862, p. 135). ; COMPOSITION OP THE ASH. 247 in many cases with the age of the plant. The following table * indicates the per cent of ash in a few instances : — Turnip (fi'csh) 7 Sugar beet (fresli) 8 Potatoes (fresb) 9 Red clover (fresh) ... ......... 1.3 Red clover (dry) 5.6 Birch-wood (dry) 2 Apple-tree wood (dry) 1.1 Walimt-wood (dry) 2.5 Birch-bark .... 1.1 Miilberi'y leaves (fresh) . 1.1 Horse-chestnut leaves (spring) 2.1 Horse-chestnut leaves (antumn) 3.0 Apples (fresh) .... .3 Pears (fresh) ... . . .4 Flax-seed ... . 3.2 Clover-seed ... 3.6 Hemp-seed 4.8 Beech-nuts .2.7 Wheat-grains ... . . . .1.7 Hemp (entire plant) . . 2.8 665. Composition of the ash of plants. Examination of trust- wortlij- analyses of the ash of flowering plants shows that certain elements are alwajs present in it. These are potassium, calcium, magnesium, and phosphorus. Besides these, which always ap-. pear in appreciable amount, there are others which are nearly or quite as constant in occurrence, although in some reports of analyses thej' are not given, because existing in such small pro- portion. Thej' are iron, chlorine, sulphur, and sodiicm. The elements mentioned are usually recorded in analyses in the fol- lowing combinations : potassa, phosphoric acid, lime, magnesia, sulphuric acid, soda, and ferric oxide. But it is to be observed that the combinations stated in tlie tabulation of analj'ses are by no means designed to exhibit all those in which the elements occur in the plant ; for instance, the sodium and potassium are presumabl}- combined with the chlorine. Again, it must be no- ticed that upon combustion the mineral matters in the plant are commingled with a larger or smaller amount of carbonates, the 1 E. Wolff, Die Mittlere Zusammensetzung dec Asche, 1865, p. 77 et seq. See also an excellent revised tran.slation of Wolffs tables in the Appendix of Johnson's "How Crops Grow" (1868). For the percentage of ash in trees ^nd woody plants, as well as the amounts of phosphoric acid and potash found- in such ash, see a very valuable table by Storer (Bulletin Bussey Institution, 1874, pp. 207-245). 248 WATER-CULTURE. amount depending somewhat "upon the temperature at which the ash is prepared." In the following short table a few of the manj- analyses collated by Johnson ^ have been brought together to exhibit the proportions of the ash constituents. Name of plant. 3 h 6 a ee g3 s s I-) i 02 " •a to g Eoot of sugar beet . 48. 14.4 6.4 9.5 4.7 10.4 1. 3.8 2.3 Potato tubers . . 60.9 18.3 2.4 4.6 7. 1.7 .9 1.9 2.7 Stalks of Indian corn 36.3 8.3 10.8 5.7 5.2 1.25 2.4 28.8 Wheat-grain . . 31.3 46.1 3.2 12.3 3.2 1.9 6G6. The foregoing table indicates that wide divei-sity exists in the amounts of the ordinary ash constituents of common plants. But comparison of a lai'ge number of analyses shows that the following general statements may be made : — 1. Plants which closel3' resemble each other in structural characters have substantially the same proportions of ash con- stituents. 2. The proportions of the ash constituents in anj- part of a plant may var^' within certain limits ; and these limits ma}- differ at different periods of growth. 3. The proportions may var^' widely for differeut parts of the same plant. 667. Not onl}' are the elements enumerated in the first list in 665 always present in the ash of flowering plants, but they are shown by experiment to be indispensable to their full develop- ment ; and there is a reasonable certainty that iron, sulphur, and probablj' chlorine, should be placed in the same category of indispensable elements. According to Nageli,^ some of the flowerless plants, notably the moulds and the schizomycetes, can attain full development with fewer elements. WATER-CULTURE. 668. Apparatus. While chemical analysis of the ash of plants reveals the character of the mineral matters which they absorb from water and soil, it cannot materially aid the investigator in ■■ How Crops Grow, 1868, p. 150. ^ Sitzungsb. d. bayer. Akad., 1879, p. 340. APPARATUS. 249 learning the office of each constituent. This is more satisfac- torily accomplished by water-culture, which, reduced to its sim- plest terms, consists in furnishing to the plant under proper conditions different mineral matters in aqueous solution, and noting their effects upon it. It has been long known that plants can be grown to a considerable size in ordinary river-water, or water holding in solution certain mineral salts. ^ But it was not until 1858 that the method of water-culture was sjstematically applied by Sachs, Knop, and Nohbe to the investigation of the relative value and the office of the different mineral constituents in the nutrition of plants. It has since been widely emploj'ed in the examination both of flowering and flowerless plants. 665. The method ado[)ted for ordinary flowering plants is es- sentially as follows : seeds are made to germinate upon some clean support, for instance moist sponge or cotton, horse-haircloth, or perforated parchraent-papor, and when the root of the seedling is a few centimeters long and the plumule is somewhat developed, the plantlet is secured to a firm support at the surface of a cy- lindrical glass vessel, in such a man- ner as to allow the roots to dip into the nutrient liquid which it contains, while the body of the seed is not im- mersed. One of the simplest sup- ports for the plantlet is shown in Fig. 145. A perforated cork is cut in halves, and the two parts are held together by a spring. The pressure exerted by the spring is sufficient to keep the plantlet in place, and not enough to injure it in any way. When the plant has attained the height of a few inches, it is well to provide a firm rod at the side of the cork, so that the stem can be held in place. Certain precautious have been found advantageous : (1) the roots in the liquid should be kept darkened ; (2) the solution should be fre- quently renewed. When skilfully managed, this method of culture gives very 1 Woodward (Philosophical Transactions, 1699) and Duhamel (Traite des Arbres, 1765) have given accounts of their cultivation of various plants in this way. 250 "WATEK-CTJLTUKE. satisfactoiy results ; in many cases plants have been carried safely throughout their whole development from seed to seed. The principal difficulties arise from the invasion of moulds, and from the continual changes which the nutrient solution under- goes. 670. In Tharandt,* where the method has been verj- success- fuUj- applied in numerous series of cultures, the following out- fit suffices: (1) small glass vessels covered with gauze, upon which the seeds swollen by twelve hours' immersion in water, and subsequenth- sprouted on filtering-paper, are placed for further development ; (2) wide-mouthed vessels of the capacity, respectively, of one, two, and three liters, each of which is pro- Tided with the spi'ing and cork alreadj' described. 671. By the careful use of these simple appliances the r61e which each of the ash constituents plays in the life and growth of plants has been ascertained. But although there is a sub- stantial agreement among experimenters as to the more impor- tant points, there are a few unsettled questions.'' 672. Normal nntrient solntion. It is plain that an aqueous solution of the salts necessary for the most active and complete development of the plant should have tlicse salts in tlie right proportion. The solution advised for ordinary- use in the above experiments is generally- known as the Tharandt normal-culture solution. Nobbe ^ gives the proportions as follows : — 1 Success in watev-cultnre demands the closest attention to all the external conditions of the plant. The amount of light and heat must be carefully regu- lated, and the plants must be kept free from any insects and parasitic fungi. The latter is one of the most difficult and discouraging tasks connected with the method of experimenting. In order to secure the best suiToundings for the cultivation of plants in water, a. heavy table moving with wheels on rails has been employed at the experiment-station at Tharandt ; upon this the glass vessels can be cariied with the least liability to jarring, from the open air in the daytime to a suitable protection at night or during wet weather. ^ Moreover it is to be borne in mind that the conditions of water-culture are very unlike those of ordinary culture in respect to the surroundings of the roots themselves, and it is believed that to this difference of conditions may be ascribed some of the unsettled questions. The root-hairs developed in contact with moiht particles of soil are not the same as those grown in water alone. To avoid this possible source of en-or, various finely divided substances have been suggested as a proper support for the roots and rootlets ; for instance, the charcoal from sugar, powdered quartz, etc. When these are employed, the roots of the plant are made to grow directly in the artificial soil which is watered with the experimental solutions. ' By the use of this solution buckwheat plants can be carried through their entire development, as is shown by Nobbe, in Versuchs-Stationen, 1868, p. 4. He arranged nine plants in five vessels, each of three litres capacity, in such NUTRIENT SOLUTIONS. 251 4 Equivalents of Potassic chloride 4 Equivalents of . . Calcic nitrate 1 Equivalent of . . Magnesic sulphate (oiystallized) One part of the mixture of these salts is to be dissolved in one thousand parts pure water, and then a trace of ferric phos- phate is to be added, and at times during any culture a trace also of potassic phosphate. The proportions of the above salts to a liter of water are given as follows by Bretfeld : ^ — Gram. Potassic chlorieytag ^ found that all plants experi- mented upon were able to absorb more or less zinc when it 1 Bretfeld : Das Versuchswesen, 1884, p. 134. ^ Holzner: Flora, 1867. Au interesthig paper by Hllgers (Pringsh. Jahrb., vi., 1867, p. 285) gives an aocomit of the formation of crystals of calcic oxalate in various parts of plants, and presents certain speculations as to their origin. ' Flora, 1862, p. 53. Further experiments are recorded by ICnop (Ver- suchs-Statioueu, iv., 1862, p. 176), Eautenberg and.Kiihn (Versuchs-Stationen, vi., 1864, p. 359), Birner and Lucanus ( Versuchs-Stationen, viii., 1866, p. 141). ■• Sachs : Handbuch der Experimental-physiologie, 1865, p. 153. ' Chemisches Central-blatt, 1870, p. 517. 256 WATER-CULTUKE. was offered in large amount; nevertheless, Gorup-Besanez' could detect none in peas and buckwheat cultivated in a soil containing a fair amount of zinc carbonate. It is sometimes said that Viola tricolor and Silene inflata grown on zinc soil talie up an appreciable amount of this element ; and further, that certain plants are directl}' affected in shape bj' the presence of zinc in the soil ; in fact, varieties based upon this supposed relation have been described. The experiments of Hoffmann, ■■* however, throw much doubt upon the relation of the zinc to a change of form, except in the single case of Viola lutea. Aluminium' occurs in traces in many plants, while in species of Lyeopodiura (e. g, coniplanatum) it is present in large amount. Manganese ■* is abundant in the ash of Trapa natans, Quercus Robur, and Castanea vesca. CiJesium and Rubidium ^ have been detected by tlie spectro- scope in minute amounts in many plants. Fluorine" has been found in the ash of L}'copodinm clava- tnm, and traces of it in other plants. Iodine and Bromine ' are found in marine algae, in much smaller proportions in aquatics growing in estuaries (for example, Zostera), and in minute amount in some plants grown far from the sea. Barium, Strontium, and Silver have been found in the ash of Fucus. Mercury, Lead, Copper, Cobalt, Nickel, Tin, Thallium, Selenium, Titanium, and Boron have all been found In' analysts in the ash of certain plants, but always in the merest traces. Arsenic^ has also been detected in a few instances. 1 Annalen der Chemie untl Phannaoie, cxxvii., 1863, p. 243. This yiaper contains an account of the relations of agricultural plants to raetaUio poisons. 2 Botanische Zeitung, 1875, p. 628. 3 Knop; Lehrbuch, p. 263 ; Eochleder: Phytochemie, 1854, p. 237. * Wolff's Die Mittlere Zusammensetzung der Asche. ^ Laspeyres : Annalen der Chemie und Pharaiacie, cxxxviii., 1866, p. 126. ^ Salm-Horstmar : Annalen der Physik und Chemie, cxi., 1860, p. 339. ' Chatin, in Comptes Eendus, Ixxxii., 1876, p. 128. 8 Numerous references to the literature of this subject will be found in Sachs's Experimental-physiologie, and in Mayer's Lehrbuch der Agrikultur- chemie. CHAPTER IX. TEANSFBR OF "WATER THROUGH THE PLANT. 686. Water is a constituent of all active cells. Tlie proto- plasmic body of the cell possesses a inarkerl affinity for it, and lip to a given point can abstract it fiom the ordinary surround- ings, but under certain conditions releases it again. If a water- plant in full activity is removed from water and exposed to the air, it speedily loses b}- evapoi'ation a considerable part of its constituent water, and shows the etfect of this loss by a col- lapsing of its cell-walls and by a withering of all its parts. But if only a small portion of the plant is lifted above the surface of the water, the loss which takes place will be partiall}- sup- plied by transfer through the cells remaining submerged. Two points are made clear b^' this simple experiment : (1) evapora- tion goes on with great rapidity from the exposed surface of the plant ; (2) only a part of the loss of water can be made good by transference from submerged portions. 687. Comparison of the structure of a water-plant with that of an ordinal'}- plant adapted to growth in the air shows that the surface of tlie latter is sucii as to prevent vevy rapid evapo- ration, and also that the loss caused liy the evaporation can be made good if the lower part of the plant remains in contact with water. In other words, the plant (1) has a surface which protects it against too great loss of water; and (2) is provided witli a system by which the needed supply of water can be replenished. 688. But it is not alone by evaporation from the surface that water is consumed by the plant. Wherever growth goes on or work is done, water is consumed, and a fresh supply is required. The question of the transfer of water is therefore a general one. SOME OF THE RELATIONS OF WATER TO TISSUES. 689. The cell-wall whic;h separates the cavity of one cell from that of its neighbor is a permeable membrane. According to the hypothesis of Niigeli (see 588), it is composed of solid par- ticles (micellae), each of which is enveloped in an adherent film 17 258 TRANSFER OF WATER THROUGH THE PLANT. of water, and thus prevented from coming in contact with those around it. According to this hypothesis, all the water in a cell- wall is practically continuous, and can flow freely between the micellae; therefore, if a cell contains its maximum amount of water, and the cell-wall is tense, the water is in a state of equi- librium. Likewise in a tissue containing its maximum amount of water this is in equililirium. But the balance can be easily dis- turbed in a plant b\' evaporation from the surface, or bj- other causes before mentioned. If, however, a sufficient part of the absorbing surface of the plant is in contact with water, the bal- ance can bo restored, since the water in the cell-walls is practi- cally continuous with that in the surroundings. The equilibrium is restored bj' the transfer of the water outside the cell-wall to the cell-wall itself, and thence to the parts within. The tendency to the restoration of the equilibrium of water in a plant is so great that root-hairs can abstract even the firmly adherent hj-gro- scopic water from particles of soil (see 644) . From the roots or other absorbing organs the water passes sooner or later to the place of consumption. 690. In most cellular plants and in masses of cellular tissue all the cell-walls have substantially the same capacity for transfer of water ; but in all plants which possess a fibro-vascular sj'stem the transfer takes place chiefly b^' means of the lignified cell- walls ; aud even in cellular plants like mosses, it is in tliose cells which are elongated and otherwise differentiated to form an im- perfectly developed framework that the rapid transfer is made. 691. Transfer of water in woody plants. In ligneous plants the water is transferred most rapidlj- through the woody tissues. This is experimentally proved by "girdling" their stems; that is, removing a ring of bark without injuring the wood. For a time the leaves remain fresli, and the plants appear to suffer only slightly, if indeed at all. An early experiment in regard to the transfer of water is that by Hales (in 1731), who says:^ "I cut ofl" the bark, for one inch length, quite round a like branch of the same oak ; eighteen days after the leaves were as green as any on tiie same tree." Further experiments have shown that the rapid transfer is made chiefly in the younger wood of the stem, and not in the heart-wood ; and, also, that the water is transferred most rapidlj' in the portions of new wood having the coarser texture known as spring wood ^ (see 395). 1 Statical Essays, 1., 1731, p. 130. ^ Saclis : Vorlesungen liber Pflanzenphysiologie, 1882, p. 275. PATH AND KATE OF TEANSFEK. 251) 692. The converse of Ilales's experiment is eqnallj- conclu- sive. If the continuity of the wood of a stem is interrupted b^' the removal of a short truncheon without at the same time much injuring the bark, the leaves wither in a siiort time. Cotta* asserts that upon a shoot of willow which still maintains its connection with the plant through the bark, but lias had a sec- tion of wood removed, the leaves will wither as quickly as they would upon a shoot wlioli}' severed from the parent plant. G93. That water can be conveyed through the stem in a direction opposite to its normal course is shown in an experi- ment by Hales : "I took a large branch of an apple-tree, and cemented up the transverse cut at the gi-eat end, and tied a wet bladder over it ; I then cut oft" the main top branch where it was f inch diameter, and set it thus inverted into a bottle of water. In three days and two nights it imbibed and perspired four pounds two ounces and one half of water, and the leaves con- tinued green ; the leaves of a bough cut oft" the same ti'ee at the same time with this, and not set in water, had been withered forty hours before."^ 894. Determination of path and rate of transfer. Two modes of experimenting have been employed in order to ascertain ex- actly the path and the rate b}' which water is transferred through ligneous plants. The first of these consists in using a colored solution, which, when taken into the plant, tinges all the tissues with which it comes directl3' in contact. The stem or branch used in the experiment is cut sharpl}- off and its end is plunged at once into a colored solution, for instance, of some aniline dye or some colored vegetable juice. As the liquid ascends the stem, certain portions of the tissues become more or less deeply- tinged, and its course and rate of ascent can he traced by sec- tions made at an^- given time, at different distances above the cut end. A similar method has been also employed by plunging in colored water the uninjured roots of the plant to be examined.' 1 Quoted by Pfelfer: Pflanzenphysiologie, i. 123. 2 Statical Essays, i., 1731, p. 131. 2 " Quel que soit le liquide employe et les variations de I'experience, les resultats generaux out peu varie, savoir : que I'eau coloree ne penetre ni par I'ecorce ni par la moelle, mais toujours au tiaveis du corps lignenx, tantot dans toute son etendue, quelquefois dans sa partie la plus jeune, savoir, I'ex- terieur du corps ligneux des exogenes, et I'interieur des endogfenes. On obtient ce meme vesultat general, soit qu'on plonge les plantes munies de toutes leurs racines, soit qu'on emploie des branches coupees " (De CandoUe's Physiologic vegetale, p. 83). 260 TEANSFEK OF WATER THROUGH THE PLANT. 695. The two objections to the first method are : (1) that the protoplasmic body of the cell resists the entrance of nearly all coloring-matters, therefore with many dyes it is necessary to experiment with cut stems and branches, allowing the dye to enter at the cut surface ; but, as will be shown later, a cut sur- face which has been exposed to the air, even for an instant, loses part of its power of absorbing water ; (2) it is by no means certain that tlie dye passes through the stem as I'apidl^' as the water in which it is dissolved. That it does not, seems more than probable from the simple experiment of suspending one end of a strip of filtei'-paper in a solution of any dye ; the water will rise faster than the d^-e, and form a moist space above that part of the paper which becomes colored. 696. The second method of experimenting is based upon the ease with which certain chemical substances foreign to the plant can be detected in it if once tiie}' can be introduced into and carried through its tissues. Dilute solutions of salts of lithium, for instance the citrate, serve best for this method, and Pfitzer suggests that they be applied to the roots of a plant which has been allowed to wilt somewhat from drought. 697. The two objections which maybe urged against the second method, are : (1) the chemical used may cause more or less dis- turbance in the plant, and may even excite disordered processes, and it is plain that no correct conclusions relative to the rapid- ity of transfer in a healthy plant can be drawn from one which is in a state of disease ; (2) the presence of a diffusible salt, for instance one of lithium, may change the osmotic relations of the tissues with which the salt comes in contact. But in spite of these serious difficulties, these methods are of considerable use when cautiously emploj-ed. 698. The above methods indicate that the most rapid transfer of water is through the lignified cell-walls of the framework of the plant. 'I'he source of supi)ly at the root furnishes the need- ful amount of water to the ligneous tissues of the fibrils, and these convey it to the converging bundles which constitute the framewoi-k of the plant. In the leaves the framework divides and subdivides to form the network of the leaf blade, and here the ligneous cells and ducts arc in intimate contact with the paren- chj'ma cells which make up the pulp of the leaf. That water finds its way by preference through the fibro-vascular bundles even in the more delicate parts, is shown by placing the cut peduncle of a white tulip, or other large white flower, in a harm- less dye, and then again cutting off its end in order to bring a RATE OF ASCENT IN THE STEM. 261 fresh surface in contact with the solution, wlien after a short time the dye will mount through the flower-stalk and tinge the parts of the perianth according to the course of the bundles. 699. Rate of ascent. The following are some of the discor- dant results obtained by the methods mentioned in C94 : — Name of plant Rate of a.scent per hour. Observer. Priinus Laiiroeerasus . . 42-100 em MoNab. Salix fragilis 85 " Sachs. Vitis vinifera 98 " Nicotiana Tabacum . . . 118 " " Heliantliiia .... 2200 " Pfitzer. 700. But little is known as to the reason of the high conduct- ing power of ligneous tissues. That it is not wholl}* due to capillaritj' (as lias been suggested on account of the abundance of ducts of small calibre in most wood), is shown by the struc- ture of the wood of coniferous plants in which no ducts are present. Again, at the very time when the evaporation from leaves of plants is most rapid, and the transfer of water to sup- ply the loss must be greatest, the cavities of the ducts are not wholly filled with liquid, but contain a considerable amount of air ; whereas according to the theor\' of capillarity they should contain only liquid. By a very ingenious series of experiments Sachs has determined the relative amount of space occupied by the cell-walls, water, and cavities in several fresh woods. In the case of fresh coniferous wood he found the following ratios in 100 cubic centimeters of wood: — Cell-wall, reckoned as dry 24.81 Water, in the cell-wall and in the cavities 58.63 Air-sjiaces ... 16.56 But, as Sachs says, since neither intercellular spaces nor ducts are present in this wood, the 16.56 per cent of air must be con- tained in the cavities of the wood-cells ; and further, since the cell-walls can take up only about half their volume of water (saj- 12.4 cubic centimeters), the remainder (46.23 c.c.) must exist in the cell-cavities. 701. The method of determining the amount of water held by the cell-walls of dry wood is t he following : — A thin cross-section of fresh wood is hung up in dry air until it ceases to lose weight. During drying a crack appears, run- ning from the centre to the circumference. After ascertaining the weight of the disc thoroughly dried (at 100° C), the wood is suspended in a saturated atmosphere until enough water is 262 TRANSFER OF WATER THROUGH THE PLANT. absorbed to cause a swelling of the tissues and a closing of th« crack. In this condition it is safe to assume tliat the cell-walls tliemselves are saturated, but that there is no liquid water in the cavity of the cells. Tlie difference between the weight of the dr3- and that of the saturated disc gives the weight of the water taken up and held ; tliis, converted into volume, is found to be approximately one half tiiat of tlie space occupied by the cell- wall itself. 702. The water which is taken up in relatively small amount and held in the micellar interstices of lignified cell-wall is in the state of equilibrium previously described. When, however, this equilibrium is disturbed by evaporation at aiij- point, there is an immediate transfer of the imbibed water to that point, and the loss from this transfer must be made good at once by the recep- tion of more water. This interstitial transfer may take place through any length of woody tissue, provided there is a con- sumption of the water at one extremity and an adequate supply at the other. When the consumption of water is only that which is due to the opening of growing buds, or to some chemical pro- cess, a slow transfer of water to the point of consumption ' must take place. When, however, it is duo to evaporation from the leaves, the transfer is exceedingly rapid. 703. Boehm''' considers the ascent of water in ligneous tissue ' to be "a phenomenon of filtration caused by differences in pres- 1 A similar transfer can be ilernonstrated to take place in porous inorganic matter, for instance powdered hydrated gypsum. If a long tube be filled with this material and well saturated with water, one end being placed in water and the other exposed to a dry atmosphere, the continual loss by evaporation above will be made good by water brought up from below. Jamin's apparatus for demonstrating the pressure exerted by the imbibition of water by a porous substance consists of a cj'linder, in the mouth of which can be placed a tightly fitting plug of wood, through which passes a ma- nometer tube. The pulverulent substance, for instance zinc oxide, is closely packed in the interior of the cylinder, around the open end of the manometer, and the whole apparatus is then placed in water. With zinc oxide the ma- nometer shows a jiressure of five atmospheres ; with powdered starch, more than six atmospheres. If a manometer is similarly placed in a block of dry chalk, and the chalk is then submerged, a pressure of three to four atmos- pheres is indicated (Le9ons ])rofessees devant la Society chimique, S&nce du 8 mars, 1861, quoted by Deheiain: Cours de Chimie Agricole, 1873, p. 165). 2 Ann. des So. nat., ser. 6, tome vi., 1878, p. 236. 3 As might be expected, woody tissues never conduct water so readily in a transverse as in a longitudinal direction. Experiments with regard to this have been conducted by Wiesner (Sitzungsb. d. Wien Akad., Bd. Ixxii. 1 Abth., 1875) upon cubes of wood. Four sides of these were protected by varnish KATK OF ASCKNT IN THE STEM. 263 sul-e in contiguous cells. ... In parencliyuiatous tissues filled with sap the movement of water caused by evapoi-ation is a function of the elasticitj- of the cell-walls and of atmosi)henc pressure." Herbert Spencer has shown that when a cut stem is quickly bent backwards and forwards tiiei-e is a marked increase iu tlie rapidity- with which colored fluids ascend through it. " To ascertain the amount of this propulsive action, I took from the same tree, a Laurel, two equal shoots, and, placing tbem in the same dye, subjected them to conditions that were alike in all respects save that of motion : while one remained at rest, the othrr was bent backwards and forwards, now by switching and now by straining with the fingers. After the lapse of an hour I found that the dye had ascended the oscillating shoot three times as far as it had ascended the stationary shoot, this re- sult being an average from several trials. Similar trials brought out similar effects in other structures."^ 704. Effect upon transfer of exposing a cut surface to the air. One of the most interesting characteristics of the wood^' tissues in relation to the transfer of water is the immediate change which the cut surface of a stem undergoes upon exposure to air, unfitting it for its full conductive woi-k. De Vries -^ has shown that when a shoot of a vigorous plant, for instance a Hehanthus, is bent down under water, care being taken not to break it even in the slightest degree, a clean sharp cut will give a surface which will retain the power of absorbing water for a long time ; while a similar shoot cut in the open air, even if the end is in- stantly plunged under water, will wither much sooner than the first. Shoots cut in the manner first described remain turgescent for several daj-s. If a cut shoot placed in water has begun to against the entrance and exit of water, and one of the two surfaces remaining uncovered was placed in water, the other exposed to air, when the transfer of water through the wood was found to be more rapid in a longitudinal tlian in a transverse, and in a radial than in a tangential direction. Another method of experimenting was also employed by him : five sides of a cube of wood were surrounded by separated portions of dry calcic chloride, and the remaining side was placed in contact with water ; the difference in rate of transfer ascertained by comparing the weights of the portions of calcic chloride after a fixed time was found to be essentially that given by the other method. Experiments by Sachs (Arbeiten des botan. lustituts in Wiirzhurg, 1879, p. 298), in whichwater was forced in different directions through the wood of coniferous stems, showed, however, that under pressure water passes through •wood more readily in a tangential than in a radial direction. ^ Transactions of Linnfean Society, xxv., 1866, p. 405. 2 Arbeiten des botan. Inst, in Wtirzburg, i., 1874, p. 292. 26J: TRANSFER OF WATER THROUGH THE PLANT. wilt, cutting off the stem a little higher up will cause it to regain in part the power of absorption which it lost upon exposure. 705. Although osmosis can have very little to do directlj'' with the rapid transfer of water through the stem, branches, and leaves, it plays, as has been seen, a very important part in the introduction of water into the plant, and in supplying the requi- site amount of it to cells which lie, so to speak, away from the main channel of transfer. 706. Pressure and " bleeding." If, before its leaves unfold, a grape-vine be cut off near the root, or a little higher up on the stem, the cut surfaces will bleed copiously. The part connected with the roots will continue to yield a supply of watery sap for a considerable time. The flow is plainly regulated to a very great degree by the stirromidings of the plant, being accelerated by heat and checked by cold. It is not merely passive ; the application of a suitable pressure-gauge shows that the escaping liquid exerts mnch force. One of the earl^' experiments on this subject was made by Hales, ^ who found the pressure in the case of the grape-vine to be equal to thirtj-eight inches (105 cm.) of mercury, or more than forty-three feet of water. Other experimenters have repoi'ted higher figures ; for example, Clark ^ found in Betula lenta a pressure of eighty -five feet of water. 707. Pitra ° has sliown that a certain amount of pressure is exerted by sap, even in stems which have been severed from the parent plant, the lower extremity being placsed in water. In some of his experiments lie found that it was not exerted at once, but only after the lapse of a considerable time. He further shows that a considerable pressure is exerted by the sap which flows out of a cut stem the leaves and twigs of which are submerged. 708. There are considerable individual differences in plants as to the foi-ce with which the sap flows from wounds. Wilson found that while one specimen of Ampelopsis quinquefolia gave ' Statical Essays, i., 1731, p. 114. " The apparatus for demonstrating the pressure can be easily used. Reduced to its simplest terms, it consists of a mercurial pressure-gauge, which can be securely attached to the wounded part of the plant. To the stump of the plant the gauge must be fastened by means of stout rubber tubing, which has been made to tit tightly around both plant and tube, and then wired lirmly to prevent the escape of any liquid. Dahlia variabilis, Vitis vinifera, and Helianthus annuus are good plants for purposes of demonstration. * Pringsheim's Jahrb., xi., 1878, p. 437. PRESSUEE OF THE SAP. 265 no pressure for the root-s3stera, another showed a pressure of twenty centimeters of mercury. 709. Bleeding is not by any means of universal occurrence in ■wounded plants. Horvath found none in tlie following cases: Humulus Lupulus, Hedera Helix, Syringa vulgaris, and Sam- bucus nigra. In some cases there appears to be bleeding only from the cut root, none occurring from the stem. 710. The bleeding from a plant may be greatest immediately after the wound is made, or it may in a few cases not reach a maximum for some hours or even days, after which it gradually- declines until it ceases. It ma^- recommence after the wound is reoi^ened. According to Hartig,' bleeding may continue in some cases for a month. 711. The amount of sap which escapes during bleeding is variable even in the same species. The following cases show that the loss is ver^' large : — Betula pai)yracea, 24 hours, 63 J lbs. (Clark). Agave Americana, 24 hours, 375 cubic inches (Humboldt). 712. Hofmeister lias given the following example, to show how large is the relative amount of sap which can flow from cer- tain plants. From a specimen of Urtica urens (stinging nettle), whose root-system bad a volume of 1,450 cubic centimeters, there escaped in 2^ days 11,260 cubic centimeters of sap. 713. The pressure at the cut surface of a plant varies widel^- in any given ease, according to the surroundings. The following details of an experiment b\' Clark- will indicate the variations in pressure noted during a comparative!}- short time. "A gauge was attached to a sugar-maple March 31st, three daj's after the maximum flow of sap for this species. . . . The mercury [in the gauge] was subject to constant and singular oscillations, standing nsuallj' in the morning below [its] zero, so that there was indicated a powerful suction into the tree, and rising rapidh' witii the sun until the force indicated was sufficient to sustain a column of water manj' feet in height. Thus at 6 A. M., April 21st, there was a suction into the tree sufficient to raise a column of water 25. 9.3 feet. As soon as the morning sun shone upon the tree the mercury- suddenly began to rise, so that at 8.15 a. m. the pressure outward was enough to 1 Botanische Zeitung, 1862, p. 89. '' Report of the Secretary of the Massachusetts Board of Agiiculture foi 1873, p. 187. 266 TRANSFER OF WATER THROUGH THE PLANT. sustain a column of water 18.47 feet in lieiglit, a change repre- sented by more tliau 44 feet of water." 714. The pressure of the sap rises and falls with the tempera- ture. The greatest pressure in ligneous plants is found when a cold night is followed by a warm morning. This has been ex- plained by the expansion of the air contained in the wood-cells and ducts. Detmer observed the greatest outtlow of sap in the case of the herbaceous plants Begonia and Cucurbita to be at a temperature of from 25° to 27" C, and that the outflow ceased at 32° for Begonia, at 43° for Cucurbita.' * 715. Besides the variations both in bleeding and in pressure of sap due to external influences there are some periodical changes which are not yet satisfactorilj- explained. Baranetzk}' found that the greatest extravasation of sap from the crown of the root took place in Ricinus between 8 and 10 o'clock a. m., in Helianthus annuus between 12 m. and 2 i>. m., and in Helianthus tuberosus between 4 and 6 p.m., tiie plants being under essen- tially the same conditions. 71G. The great pressure exerted by sap under certain condi- tions is thus explained by Sachs. From the root-hairs, into ■which the water comes by osmosis, it passes by osmosis into the parenchymatous cells of the cortex. " But a difficult^' occurs in answering the question why the tnrgescent cortical cells of the root expel their water onlj- inwards into the woodj' tissues, and not also through their outer walls. We may, however, here be helped by the supposition that the micellai- structure of the cell-walls is different on the outer and inner sides of the cells, and that those fac^ing the exterior of the root are best adapted for permitting filtration under higii endosmotio pressure." " Among the recorded experiments which sliow a great root- pressure is one by Clark, described by him thus : " A gauge was attached to tlie root of a black bircii-tree as follows. The tree stood in moist ground at the foot of a south slo[)e of a ravine, in such a situation that the earth around it was shaded by the 1 A full ami satisfactory treatme.nt of tliis subject in detail will he found in the following works : — Schroder : Beitrag zur Kenntniss der Friihjahrsperiode des Ahorn (Pringsh. Jahrb., vii., 1869). In this, the spring phenomena of the maple are clearly- given. Baranetzky : Untersuchungen iiber die Periodicitat des Blutens (Ahhandl. des naturforschende Graellschaft zu Halle, 1873). In this memoir the experiments cover a wide range. 2 Text-book of Botany, 2il English edition, 1882, p. 688. EXUDATION or WATER FROM UNlNJL'llKD PAUTS. 267 overhanging bank ffom the sun. The root was then followed I'loin the trunk to the distance of ten feet, wheie it was carefully cut off one foot below the surface, and a piece removed fioiu between the cut and the tree. The end of the root was en- tirely detached from the tree and l3ing in an horizontal position at the depth of one foot in the cold, damp earth, unreached by the sunshine, and for the most part unaffected by the temper- ature of the atmosphere, measured about one inch in diameter. To this was carefully adjusted a mercurial gauge April 26th. The pressure at once became evident, and rose constantly with very slight fluctuations, until at noon on the 30th of April it had attained the unequalled height of 85.80 feet of water." ^ 717. Pfefi"er'^ attributes the tendency of water to pass only inwards into the woody tissues wholly to the fact that upon that side of the cells whicli faces the interior of the root the osmotic capacity is greater. Within the plant the cell-walls are never saturated with pure water ; but the imbibed liquid is different on different sides, and hence the plasma membrane in contact with the sides must have different capacities for osmosis. 718. In midwinter or in earliest spring some of the tissues of ligneous plants are stored to a large extent with starch and other solid products manufactured during the previous season. At the coming of warmer weather chemical changes take place, largely following the absorption of water, by which these solid substances are transformed into a liquid state, occupy a gi-eater space than before, and of course exert much greater pressure. The saccharine sap of the maple represents that which dur- ing the early winter existed in the tissues as starchy matter. This conversion of material will be further discussed under '■ Metastasis." 719. Exudation of water from uninjiired parts of plants. Un- der certain circumstances water can exude in a liquid form from uninjured i)arts ; for instance, through chinks or rifts in the leaf- tips of many monocotyledonous plants, and through water-pores of dicotyledons, especialh' when these are j'oung. Musset ' reports eighty- five drops of liquid falling in one minute from the tip of a leaf of Colocasia esculenta. Duchartre* gives the following figures : Twent^'-five drops fell in one minute from 1 Ksport of the Secretary of the Mass. Board of Agriculture for 1873, p. 189. 2 Paanzeuphysiologie, i., 1881, p. 170. 8 Comptes Reiidus, Ixi., 1865, p. 683. * Ann. des Se. nat. hot., s^r. 4, tome xii., pp. 247, 250. 268 TKANSFER OF WATER THROUGH THE PLANT. the tip of a leaf of Colocasia antiquoriim, and 22.6 grams of liquid were collected in one night. From the j'oung leaves of certain Aroids water is sometimes ejected in a fine jet to a distance of a few inches.* In these and the previous cases the liquid escapes through rifts. TRANSPIRATION. 720. The evaporation of water from the surface of the younger parts of plants exposed to the air makes, as has now been seen, a continual draught upon the sources of -water-supply. But •while evaporation from the free surface of water or from any dead membrane ceases in an atmosphere satuiated with moisture, there is some experimental evidence to sliow that, under certain conditions of radiation, evaporation from tlie living plant may continue to take place even when the atmosphere is completely saturated. This difference between evaporation from a free sur- face and that from a plant, although not full}- established, ren- ders it advisable to emploj- for the latter plienomenon the terra transpiration. This term is sometimes employed in Physics with another signification ; but its prior use in Vegetable Tliysi- ology should prevent any confusion. 721. Stomata. Neither through the cutinized cell-walls of the- epidermis, nor tlirougli the suberized cell-walls of cork, can tianspi ration take place to any extent; ^ but at myriads of points in the epidermis of leaves and young stems there are minute orifices which permit tlio air outside the plant to come into communication with the air within. It has been shown in Part I. that these openings, the stomata, possess definite rela- tions as regards position to the intercellular spaces below them, ' Musset : Comptes Eendus, 1865. Muntingh(1672), according to a reference in Flora (1837, p. 717), noted the projection of a small jet of water from the leaf of an Aroid, as from a fountain. '■^ "It is of the liighest significance that those plants wlduh are sulmierged, or those pai-ts of |ilants which grow in the ground and therefore cannot Icse ■water by transpiration, possess a cuticle which permits water and dissolved matters to pass through with comparative facility ; while the parts growing in the air have a cuticle of a different quality, through which water passes cn'y ■with difficulty, and tlius tlicy are protected from too great a loss of water " (Pfpffef: PHanzenphysiologie, i., 1881, p. 139). The amount of a(jueons vapor which can escape through cuticle is very small. According to Bonssingault, .005 gram of water may evaporate in one hoar from one square centimeter of the rind of an apple, ■while from the surface of a peeled apple fifty-five times as much is lost (Agronomie, vi., 1878, Ji. 349). MECHANISM OF STOMATA. 269 SO that they maj' be fairly regarded as a part of the sj'stem for aerating the plant. 722. By reference to the structure of the more common kinds of leaves (see Chapter III.) , it will be seen that the terminations of the delicate fibrils of the framework approach very closely to the aeriferous spaces, and thus by the uninterrupted coiu- municalion between the minute fibrils in the root-system, the stem-sj'stem, and the leaf-system of the plant, water which has been absorbed bj- the roots is brought finally to tlic parenchyma cells which surround the spaces under the stomata. If it evaporates from the outer side of the wall of these cells into the intercellular spaces, the water maj' make its escape through the stomata. 723. Stomata are not mere ei)idermal rifts having an aper- tift-e of unvarying widtli. The guardian cells of a stoma are so arranged with respect to each other and the proper epidermal cells contiguous to them, that the width of tlie opening between them can be increased or diminished upon certain changes in the surrounding conditions. 724. Mechanism of Stomata. In examining the mechanism of stomata it is necessary to distinguish between their three parts which are shown in a vertical section ; namely, (1) the anterior groove, (2) the cleft, and (3) tlie posterior groove, which is usually continuous with an intercellular space. It is plain that a stoma is most widely open when the edges of the cleft are farthest apart and the rim of the cup not closed. Hence an inspection of the anterior face of a stoma is not sufllcient to show whether the stoma is most widely- open ; the width of the cleft itself must be ascertained. 725. In distinction from proper epidermal cells, the guardian cells contain chlorophyll, and hence under the influence of light can produce earbohj-drates (see "Assimilation"). As might be expected, the osmotic tension is different in these two groups of cells. 726. The following account, condensed from Strasburger, shows the relations which the guardian cells sustain to those around the stoma as regards the tliickness of the walls. The guardian cells are strongly thickened on the upper and under angles of the walls of tlieir opposed faces, while elsewhere their walls are relatively thin. At the cleft there are opposing projections forming its edges. The opening and closing of a stoma depend upon the difference in the thickness of the parts of the walls. When the turgesceuoe of the guardian cells 270 TRANSFER OF WATER THROUGH THE PLAKT. increases, they curve more strongly, and the cleft widens ; but when their turgesceuce dinaiuishes, the cleft becomes straighter and narrower, it being clear that with increasing turgesceuce the guardian cells must become more convex on the side of least resistance, and more concave upon the side of greatest resistance. 727. Relations of stomata to external influences. In a classical series of experiments upon the relations of stomata to their sur- roundings, Mohl^ has shown that when the uninjured leaves of certain oichids, lilies, etc., are wet with water, the clefts of the stomata open ; but these plants form exceptions to the general rule, for it was found that in the greater number of cases studied the cleft closes when the stoma is brought in contact with water. In Amaryllis and the grasses, this closing takes place with great rapidity-. • 728. Wlien a thin film of epidermis with its stomata is de- tached, and examined under the microscope, the behiivior is the reverse of that above. In a detached film the guardian cells of the stoma are partially freed from the action of the contiguous proper epidermal cells, and as a result the cleft widens when water is applied, the turgescence being increased ; but if a solu- tion of sugar in water is employed, the cleft grows narrower, since the turgescence of the cells is at once diminished by osmosis. According to Mold, in a wilted leaf the clefts of the stomata are partiality or wholly closed, but the ai)plication of water causes them to open. If kept wet, they soon close again. 729. The cleft of a stoma opens more widely in the light than in darkness ; tims leaves of Lilium which have been kept in the dark in a saturated atmosphere for some days have the stomata closed, and when wet the cleft opens only slightly. Upon exposure to sunlight, the cleft gradually opens. 730. According to Van Tieghem,^ stomata are always open in sunlight and closed in darkness. In order to cause open stomata to close, it is merely necessary to suddenly change the amount of light. This closing of the stomata takes place in half an hour when a bright light is replaced by diffused light. It has been found that heat has no marked effect upon the opening and closing of stomata ; thus when a plant is kept in darkness at a temperature of from 15° to 17° C, they are closed, ^ Botanische Zeitung, 1856. 2 Traits Je Botanique, 1884, p. 636. AMOUNT OF TRANSPERATION. 271 anrl will not open when the plant, still kept in darkness, is subjected to a higher temperature, say from 27° to 30° C. 731. From the foregoing, it appears (1) that stomata are delicately balanced valves, which are exceedingly sensitive to external influences; (2) that in wilted leaves the}- are partially closed ; (3) that in most eases, on the application of liquid water, stomata which are open close ; (4) that strong light causes stomata to open widely ; (5) that a sudden shock causes them to close. 732. Amount of water given off in transpiration.' This is determined chiefly by the balance. In the oft-cited experiment of Hales,'^ in 1724, the amount ' The earliest expeviiuents upon this subject appear to have been those by Woodward in 1699 (Philosophical Transactions). They were made from July to October, and gave the following results (here reduced for convenience to grams) : — Name of plant and kind of water furnished. First weight of the plant. Final weight of the plant. Total amount of waterevaporated. Mint in rain water . Mint in spring water . . Mint in Tliames water Pea in spring water . 1.79 172 1.79 6.27 2.88 2G8 3.45 6.46 192.3 163.6 159.6 160. Woodward's most interesting observations relate to the ratio of growth to evaporation when plants are cultivated in different kinds of water. Thus when mint was grown in water mixed with garden earth, the ratio of growth to evaporation was 1:52; but when it was grown in di.stilled water, 1:214. 2 "July .3, 1724, in order to find out the quantity imbibed and perspired by the Snn-Flower, I took a garden-pot with a large Sun-Flnwcr, 3 feet + J high, which was purposely planted in it when young ; it was of the large annual kind. " r covered the pot with a plate of thin milleil lead, and cemented all the joints fast, so as no vapour could pass, but only air, thro' a small glass tube nine inches long, which was fixed purposely near the stem of the plant, to make a free communication with the outward air, and that under the leaden plate. " I cemented also another short glass tube into the plate, two inches long and one inch in diameter. Thro' this tube I watered the plant, and then stopped it up with a cork ; I stopjied up also tlie holes at the bottom of the pot with corks. " I weighed this pot and plant morning and evening, for fifteen several days, from July 3, to Aug. 8, after which I cut off the plant close to the leaden plate, and then covered the stump well with cement ; and upon weighing found there perspired thro' the unglazed porous pot two ounces every twelve 272 TRANSFER OF WATER THROUGH THE PLANT. transpired from a vigorous sunflower, tliree feet and a lialf iiigh, during twelve hours of a very warm da^-, was one pound four- teen ounces, and, on an average, one pound four ounces was transpired every twelve hours. Anj' evaporation from the sur- face of the soil in the flower-pot in which the plant was growing was prevented by a lead cover. A still simpler method of preventing evaporation is to en- velop the flower-pot with a thin rubber meml»rane, and tie this tightly around the stem of the plant. A fresh supply of water can be given to the plant at any time by means of a tube close to the stem. In expeiiments upon transpiration the plant should be weighed frequentlj-, care being taken to note all the external conditions, such as light, moisture of the atmosphere, etc. For weighing, an open balance with large pans should be used. The form known as the box scale will answer all ordinary purposes ; but for delicate weighings one of special construction, having a long beam, is preferable. hours day, which heing allowed in the daily weighing of the plant and pot, I found the greatest perspiration of twelve hours in a very warm dry day, to he one pound fourteen ounces ; the middle i-ate of perspiration one pound four ounces. The perspiration of a dry warm night, without any sensihle dew, was about three ounces ; but when any sensible, tho' small dew, then the per- spiration was nothing ; and when a large dew, or some little rain in the night, the plant and pot was increased in weight two or three ounces. N. B. T?ie weights I made use of were Avoirdupoise weiyhts. " I cut off all the leaves of this plant, and laid them in five several parcels, according to their several sizes, and then measured the surface of a leaf of each- parcel, by laying over it a large lattice made with threads, in which the little sq^uares were J of an inch each ; by numbering of which 1 had the surface of the leaves in square inches, which multiplied by the number of the leaves in the corresponding parcels, gave me the area of all the leaves ; by which means I found the surface of the whole plant, above ground, to be equal to 5616 square inches, or 39 square feet. " I dug up another Sun-Flower, nearly of the same size, which had eight main roots, reaching fifteen inches deep and sideways from the stem : It had besides a very thick bush of lateral roots, from the eight main roots, which ex- tended every way in a Hemisphere, about nine inches from the stem and main roots. " In order to get an estimate of the length of all the roots, I took one of the main roots, with its laterals, and measured nnd wei",'bed them, and then weighed the other seven roots, with their laterals, by which means I found the sum of the length of all the roots to be no less than 1448 feet. " And supposing the periphery of these roots at a medium, to be ?8 "f "" inch, then their surface will be 2286 S(juare inches, or 15.8 square feet ; that is, equal to § of the surface of the plant above ground " (Vegetable Staticks, 2d 9d., 1731, vol. i. p. 4). KBUTIZKi S APPARATUS. 273 733. Vesque has devised an automatic api)aratus'' hy whieh the disturbance of the equilibrium of the balance as tlie water evaporates can be recorded upon a revolving drum. In this apparatus, as soon as the needle records tlic moment of descent of the beam, an electrical current releases a valve so as to per- mit the passage of a sufficient quantity of mercury to the losing side of the balance to restore the equilibrium. 731. The registering apparatus of Krutizky^ is simple, but unfortunately can be used only with cut stems or branches. It consists of a U-tnbe filled with water, in one end of which a leaf or stem (cut off under water) is inserted, through a tightly fitting cork. Tiirough a cork in the other end extends the short leg of a siphon. In a jar of water there floats a tube balanced to keep it erect. 'J'his is somewhat like an hj'drometer (but open at the top), and contains a certain amount of water into which comes the long leg of the siphon. When by evapora- tion from the plant water is drawn up through the siphon out of the floating tube, the tube (called a "swimmer") of course becomes j^g lighter and rises in the jar. If an index is attached to the swimmer, as in the figure, it can be used to record upon a revolving drum the rise of the swimmer as the plant transpires. To prevent evaporation from the water in the jar and in the swimmer, its surface is covered by a film of oil.' 735. When a transpiring plant is placed under a bell-jar, a certain amount of the transpired water will collect upon tiie inside of the jar, — often a sufl[icient quantitj' to appear as large 1 For a full account of its construction see Annales des So. nat., ser. 6, tome vi., 1878, p. 186. - Botanische Zeitung, 1878, p. 161. 3 A simpler piece of apparatus arranged by Pfeffer answers well for class demonstration. It is easily understood from Fig. 147. The fall of water in tho small lateral tube is very marked, but attention should be called to the varying pressure caused by the constantly changing level of the water in the tube. Fio. 116. Krutizky's apparatus. 18 274 TRANSFER OF WATEE THROUGH THE PLANT, Ueheraln.^ drops. This metliod of demonstrating transpiration has been used, when somewhat modified, l)y many investigators, notably ' It is well adapted to class experiments, since very simple appliances'^ can be nsed : for instance, a leafy stem can be inserted in a piece of pasteboard, and the cut end of the stem placed in a tumbler of water; another tum- bler, inverted over the stem, rests on the pasteboard. The water in the lower tnmbler is prevented from evaporating into the upper one. The amount of water which collects on the inside of the upper tumbler comes wliollj- from the transpiration of the plant, and will be found to vary according to the surroundings (see page 275 et seq). 736. If a weighed amount of calcic chlo- ride is placed with a transpiring plant in a confined atmosphere, the salt will readilj' take up the aqueons vapor, and its increase in weight gives the amount of water exhaled by the plant. This method of measuring the amoiuit of transpiration has been em- ploj-ed by several experimenters, who have obtained resnlts sub- stantiality in accord. It must be noted, however, that in this method the air to which the plant is exposed is rendered ab- normally drj- bj- the presence of the salt, and tlie plant is there- fore subjected to an unusual draft upon its water-supply. 737. Garreau's method of comparing the relative amounts of transpiration on opposite sides of a leaf is based on that last 147 ' Conrs lie Cliimie Agdcole, 1873, p. 180 et seq. '■' Henslow. See Oliver's Botany (1864), \i. 15. Fig. 147. Apparatus for demonstration of transplnitioii. ViQ. 148. Garreau's apparatus. TRANSPIRATION AND EVAPORATION COMPARED. 275 mentioned, and is of easy application. Two tubulated bell-jars, each furnished with a mercurj- trap (mand m'), are secured lirmly ■with soft wax to opposite sides of any largo leaf. In each bell- jar is a small capsule (c and c') containing dry calcic chloride of known weight. After a given time the salt placed in each bell- jar is weighed, and the excess over its original weight shows the amount of water transpired. The following are some of Gar- reau's results : — ■ (1) The quantity of water exhaled by the upper face of a leaf is to that exhaled by the lower as 1:1, 1:3, or some- times as 1 : 5. (2) There are marked but not exact relations between the quantity of water exhaled and the number of stomata.^ 738. Transpiration compared with evaporation proper. Tlie evaporation from a given surface of water is between three and six times as great as that from an equal surface of green leaves similarly exposed. Uuger^ found'that leaves of Digitalis pur- purea with a surface of five thousand square millimeters tran- spired from 3.232 to 1.232 grams in a given time ; while from an equal surface of water from 4.532 to 8.459 grams evaporated. Sachs* found that from a surface of sunflower stem and leaf meas- uring 4,920 centimeters enough water transpired to form a layer 2.23 mm. thick over the same surface ; while from an equal sur- face of water enough evaporated to lower the level 5.3 mm. Sachs also found that tlie evaporation from an animal ijaem- brane is greater than that from an equal surface of free water. When a surface of water is covered b^' a moist lawyer of vegetable parchment, evaporation is spmewhat retarded ;*■ but even then it is greater than that from an equal surface of leaves. But the area of a leaf does not express its evaporating sur- face, since the latter consists of intercellular spaces which have been estimated to bear tlie ratio of ten to one to the cuticularized exterior. In the intercellular spaces the air is saturated with moisture, hence the slowness of the rate of transpiration.' 739. Effect of moisture in the air upon transpiration. All ex- periments show that with increase in the amount of aqueous vapor contained in the air the amount of water transpired from 1 Aim. des. Sc. nat., ser. 3, tome xiii., 1849, p. 321. Bonnet's early ex- pei'iments are interesting. 2 Sitzungsb. d. Wiener Akad., Bd. xliv., Abth. 2, 1861, p. 206. ' Handbuch der Experiraental-physiologie, 1865, p. 231. '' Baranetzky : Botanische Zeitung, 1872, p. 65. ' American Naturalist, 1881, p. 385. 276 TRANSFER OF WATER THROUGH THE PLANT. a plant exposed to it dimiuishes.^ When the air is completely saturated, a slight amount of transpiration can take place,^ wiiich, as Sachs has pointed out,' is probably due to the fact that the temperature of the plant is higher than that of the surrounding air. 740. Instructive experiments upon the exhalation of moisture by some of the more common desert plants in the dry air of the Western plains have been made by Sereno Watson,* from which it appears that in about four hours young shoots furnished with about fifty per cent of leaves lost, when severed from the stem, water amounting to nearly half their weight. 741. Effect of the soil upon transpiration. The physical prop- erties of the soil have an influence upon transpiration. Sachs ^ cultivated [ilants of tobacco in clay and in sandy soil, and ob- served the amount of water transpired by them under like con- ditions. Although his experiments are not conclusive, they indicate that transpiration is more uniform from the foliage of the plants grown in «lay-thaii from the plants grown in sand ; the former soil is much more retentive of moisture, and tlius the suppl}' of hygroscoi)ic water is given up more gradually to the roots of the plant. The chemical properties of soils affect transpiration to a cer- tain extent. Senebier, in 1800, stated that acids increase the rate of transpiration, and he ascribed the same effect also to. 1 The relations between humidity of the air and transpiration are shown by tlie results obtained by Unger with two plants of Ricinus, one of which was in the open air, the other under a bell-jar. (The leaf surface of one jilant was X90, and that of the other 160 square centimeters ; but in the table a cor- rection has been made so that equal surfaces are compared). Duration of the Experiment. Loss of water, open air. Loss of water, bell-jar. Temperature of the air in C. July 19 to 20 " 20 to 21 " 21 to 22 Total ... 11.60 CO. 17.05 " 16.77 " 1.60 cc. 1.14 " 16. 13.6 15.4 45.42 cc. 4.35 cc. The total losses bear a ratio of 10.44 : 1. 2 Handbuch der Experimental-physiologie, 1865, p. 227. Deherain in Comptes Eendus, l.xix. p. 381. 3 Sitzungsber. d. Wiener Akad., Bd. xxvi., 1857, p. 326. * Report of the Geological Exploration of the Fortieth Parallel, Botany (1871), p. 1. ^ Versuchs-Stationen, 1859, p. 232. EFFECT OF HEAT UPON TRANSPIRATION. 277 alkalies. Bat as Sachs ■" showed in 1859, even a very little free acid in water hastens, while an alkali retards, transpiration. Burgerstein^ in a long series of experiments showed that while a single salt added to water in less amount than .5 per cent hastens transpiration, any per cent above this produces a marked retardation. When a solution of nutrient salts is used, even if its concentration is as low as .05 of solid matter, there is a retardation, and tliis is greater when tlie solution is more concentrated. In the experiments, the results of which are given below, four plants of Indian corn were employed. The temperature varied between 1G.7°, and 18° C, and the observations con- tinued through one hundred and tliree hours. The amounts transpired are given in percentages of the weiglit of the fresh plants. Nutrient solution 247.4 Distilled water 264.17 Potassic nitrate 283.2 Amnionic nitrate . . . . 334.2 742. Temperature and transpiration. Rise of temperature in- creases the rate of transpiration not only by affecting evaporation in general, but indirectly also by augmenting the absoi'ption of water and heightening the turgescence of the cells. Burger- stein shows that leafy twigs of yew can transpire even at a tempei-ature of — 10.7° C, while the leafless shoots of horse- ciiestnut are said by Wiesner to transpire at — 13° C.'' Sudden changes of temperature greatly influence tj'anspiration, since the " atmosphere and the plant cannot follow the course of temperature witti equal rapidit}', and a rareiioation of the air saturated with moisture within the plant must favor its release." * 743. Effect of light upon transpiration. Transpiration goes on more rapidh* in light than in darkness, even when the tempera- ture in darkness is somewhat higher. But differences in the intensity of diffused light do not produce very marked differences in the amount of transpiration. When, however, diffused light 1 Versuelis-Stationen, i., 1859, p. 223. Sachs met witli some anomalies in his experiments, in one case finding a noticeable retardation of transpiration upon the addition of an acid. 2 Sitzungsb. d. Wiener Akad., 1876 and 1878. ° Quoted by Pfeffer: Pflnnzen physiologic, i., 1881, p. 148. * Pfeffer ; Pflanzenphysiologie, i., 1881, p. 148. 278 TRANSFER OF "WATER THROUGH THE PLANT. is replaced by direct sunlight, the increase in transpiration is striking.^ 744. Effects of different rays upon ti'anspiration. Wiesner's conclusions,^ based on a study of transpiration in different raj-s of the spectrum, are as follows : (1) the presence of chlorophyll appreciably increases the action of light upon transpiration ; (2) it is the rays corresponding to the absorption-bands of chlorophj-11, and not the most luminous rays, which cause trans- piration ; (3) rays which have passed through a solution of chlorophyll have only a feeble effect upon the process ; (4) the non-luminous heat-rays act as do the luminous rays, but in a less marked manner, the ultra-violet chemical rays have sub- stantially no effect; (5) whatever the rays are, they always act b}' elevating the tempei-ature of the tissues. 745. Effect of sliock upon transpiration." According to Bara- netzk}-,* shaking a plant for a short time increases transpiration 1 As shown b}' the following experiments hy Wiesner : — Name of pi.*;nt. Iq darkness. In diffused tlay- liglit. In Bunliglit. Zea Mais, etiolated . . . Zea Mais, green Sparlinni J-.ncenm (flowers) Malva arborea (flowers) . . 106 Ti;^. 23 ■■ L 112 ing. 114 " 69 " 28 " 290 ing. 786 " 174 " 70 " The amounts of water are calculateii-for a surface of 100 square centimeters, and for one hour. But it is not Yierfeotly clear to what the special aetionof light ca7i be due. Theinp»»Se3 size of the cleft of stomata under liglit cannot account for all oases^^or according to Wiesner young maize plants, in which the transpiratii^rts large, have their stomata closed. 2 AnnaliHdes Sc. nat., ser 6, tome iv., 1877, in which may be found also a note ui^5h the same subject by Deherain. 5 See also Herbei-t Spencer's Experiments, on page 263. * Botanische Zeitung, 1872, p. 89. The following example will show the results of Baranetzky's experiment upon a leafy stem of Inula Helenium. Time (morning) State of plant. Transpiration in grams. Air temperature C°. Atmosplieric moisture. 7.40 quiet. _ _ 8.10 i( .50 22.1 76 per cent. 8.40 shaken. .62 22.2- 76 " 9.10 quiet. .68 22.4 76 " 9.40 " .47 22.6 76 " 10.10 " .m 22.7 77 " 10.40 tt .54 22.9 76 ' 11.10 sli.aken. .59 231 76 " 11.40 quiet. .4i 23.3 76 '• 12.10 <( .52 23.4 76 " RELATION OF TRANSPIKATION TO ABSORPTION. 279 appreciably ; if llie plant is then kept at rest, the rate falls be- low that previous to the shaking, after which it gradually rises to its normal point. Even a sharp single shock is enough to produce some effect upon transpiration, but the shaking must continue at least a second in order to change the rate ver3' much. If, however, the shaking is long continued, or short shakings are often repeated, there is a noticeable diminution in the rate. Baranetzk^' attributes the heightening of the rate b}- a sudden shock to the correspondingly sudden compression of the inter- cellular spaces and the consequent renewal of the air therein contained ; while the diminished rate which follows continued shaking is due to a partial closing of the storaata (see also 731). 746. Relation of age of leaves to traiispinitioii. According to Deherain'and Hohnel,'* young leaves exhale more water than older leaves. Experiments were made by the former upon the upper, middle, and lower leaves of rye. From the newly devel- oped leaves more water was exhaled than from the middle, and more from the latter than from those farther down the stem. Sachs' states that young leaves exhale less than those which are fully developed, but that there is some diminution in the case of oliXkov, leaf). The term chlorophyll, originally applied to the pigment rather than to the substance which contains it, is now used indifferently to denote the coloiing-matter and the portions of protoplasmic mass which are tinged by it. It is better, however, to designate the former chlorophyll pigment, the latter, chlorophyll granules, or grains. 766. in regard to the genesis of the chlorophyll granules which are the essential constituent of the assimilative cells, the 1 " Nous n'avons aucun droit pour nommer une substimre connue depuis longtennps, et k I'histoire de laquelle nous n'avons ajoute que quelques faits ; cependant nous proposerons, sans y mettre aucune importance, le nom de chlorophyle, de chloros, couleur, et tfiiXKov, feuille; ce nom indiquerait le r61e qu'elle joue dans la nature" (Pelletier and Caventou: Journ. de Pharmaeie, iii., 1817, 490). ORIGIN OF CHLOROPHYLL GRANULES. 287 following view' appears to bj most in consonance with recent investigations. Imbedded in the protoplasm at ever}- growing point there are pecnliar bodies (plastids) which have substan- tially the same characters and structure as the protoplasm, and are more or less clearly differentiated from it even at an eai'l}' period. As the cells which develop from the growing point assume the different characters which lit them for special ser- vice, for example, those in certain tubers and roots for store- houses, those in leaves for assimilation, and those in some flowers and fruits for color, their plastids maj- likewise assume special characters. Those which are destined' for the store- houses become leucoplastids, or starcii-formers ; those in green tissue, chloroplastids or ciilorophyll granules ; and those in col- ored flowers and fruits, chroraoplastids. As might be expected from their common origin, the plastids which under one set of conditions might become leucoplastids, may, under another set, become chloroplastids, etc. 767. The recognition of this view regarding the origin of chlorophyll grains, etc., although it is as yet partly- h^-potheti- cal, will enable the student to explain some of the extraordi- nary intermediate forms met with ; for instance, those where the 1 Meyei- (DaaCliliiropliyllkorn, 1883, and Botaiiisclies Central blatt, 1882) has readied substantially the same results as those obtained by Schimjier, which in the account above given have been presented with Scbiniper's nomenclature. Meyer employs, however, the somewhat differen t terminology given below. Older Nomenclature. Schimper. Meyer. Van Tieghem. General term. Special terms. Colorless protoplasmic granule. Ciilorophyll granule. Color-granule. Plattid. Leucoplastid, Cbloroplastid. Cliromoplastid. Trophoplast. Anaplast. Autoplast. Chromoplast. Leucite. Leucite proper. Oliloroleucite. Chromoleucite For a fuller account of the views of Meyer and Schimper, the student must consult the original memoirs in Botanische Zeitung, 1883, or an excellent abstract by Bower (Quarterly Journal of Microscopical Science, 1R84). Schmitz (Die Chromatophoren der Algen, 1882) has described at great length certain structures analogous to chlorophyll, occurring in some of the lower plants. These granular bodies, called chromatophores, possess consider- able diversity of form, but all agree in consisting of a matrix or basis permeated by cohn-ing-niatter. In most green algae there are also found one or more minute, rounded, granular, colorless bodies embedded in the chromatophore, known as pyrenoids. These are frequently associated with granules of starch. Chromatophores are believed by Schmitz to increase only by the process of division, but the pyrenoids either by division or by fresh formation/ ZSS ASSIMILATION. plastids of one sort can for a time undertake the office of the plastids of another sort. It explains, partial!}' at least, the in- trusion of chlorophjll grains into parts of the plant where thej- do not seem to propei'ly belong, and accounts for some of the apparent changes which the}- ma}' subsequently undergo. 768. According to the early investigations of the subject, the chlorophyll granules were regarded as differentiations, at an early stage in the embryo and seedling, from a mass of homo- geneous protoplasm : according to the present ^iew the}' are derivati\es by division from pre-existing plastids.^ When devel- oped in darkness, they are pale yellowish, or even devoid of color. Plants grown iu the dark (compare 788) become green upon ex()osure to the light, ijrovided they are not at the same time kept too cold. The minimum temperature at which they turn green is different for different plants, but may be said to be in general not far from 6° to 10° C. Certain Gymnosperms, notably seedlings of Abies and Finns, develop a bright green color in the deepest darkness, provided, as before stated, the temperature is not below a certain point. 769. Occurrence of the chlorophyll granules. The granules are found only very sparingly in epidermis, being chiefly confined to the guardian cells of stomata. They occur principally in paren- chyma cells, immediately below the epidermis, and seldom out of reach of the light. But they occur also in a few deep-seated structures, for instance, in the thick cortex of some ligneous plants, and in the tissues of not a few embryos. 770. That chlorophyll granules are found in the interior of some of the lower animals appears reasonably certain, but the green matter does not always present the same characters. Ac- cording to recent authorities, it assumes in most cases, for in- stance in Spongilla and Hydra, the form of minute granules. The pigment agrees in some of its essential properties with that of ordinary chloropliyll.^ In some cases it must still be considered an open question whether the granules may not be (or at least represent) independent organisms dwelling in certain cavities of 1 The views of Gris (Ann. des So. nat. bot., 1857) may be summarized as follows : The granules arise by differentiation of tlie protoplasm in certain yonng cells into two portions ; one of these assumes the form of roundisli or lenticular bodies (tlie proper granules), which under the influonce of liglit become colored green, while tlie other remains as a matrix in which they are embedded. ^ For an interesting treatment of this subject, consult Geddes : Nature, 1882, and LankeSter, Journal of the Royal Microscopical Society, 1882, p. 241. STKUCTUHE OP CHLOROPHYLL GHANULES. 2«9 these lower animals. These cases of possible symbiosis deserve and are receiving careful investigation. 771. Many species of plants derive all or a part of tlie organic matter required for llieir grovvtli and proper activities either from other plants (when they are called parasites), or fi-om decaying organic matters, such as vegetable mould (when tjjey are called sapropliytes). In tlie tissues of a few such plants minute traces of chlorophyll may sometimes be detected. 772. Strncture of cliloropliyll granules. Under a moderately high power of the microscope the granules appear as spheroidal ' or polyhedral bodies, apparently homogeneous in structure, hav- ing neither vacuoles nor granular matter. By the action of cer- tain solvents it is possible to remove from the granule the pigment which has imparted to it its characteristic color, when tlie mass remains without an}' change of form. Hence it is proper to distinguish between the cliloropliyll pig- ment and the chloro- phyll granule, each of whicli will now be considered. A method recently dis- covered makes it pos- sible to demonstrate the peculiar structure of the granules with- out complete removal of the pigment. This method, known as Pringsheim's,^ depends upon the action of dilute hydrochloric acid on the green parts of plants. When a thin green tissue, 149 1 In some of the Thallophytes, the whole or nearly the whole of the pvoto- jilasraic mass seems to he evenly colored, presenting the appearance of coloi'ed spirals, laniellffi, stellate fonns, etc.; anil snch colored masses are strictly chloro- phyll bodies (Die Chromatophoren der Algen. Fr. Schmitz. Bonn, 1882). 2 Pringsheim's Jahrli., xii., 1S79, p. 289. Fig. 149. Hypochlorii. ^, a cell of CEiogonium treated witli hyflrocliloric acid for a few honrs; Ji, the paTie after some days: C, J>, E, needle-like forms; F, two cells nf PrapernaVlia kept in liydrochlnric acid one month; G, cell of Anacharis in hydrochloric acid after five montts' treatment, (Pringsheim.) 19 290 ASSIMILATION. for instance a leaf of Vallisneria or of Anacharis, is treated witii a solution of one pai't of concentrated li^-drochlorie acid in four parts of water, tlie first cliange observed is merely a fading of ihe green color of tlie granules to a yellowish or brown. After a few hours, however, npon the periphery- of each granule tliere appears a small rounded mass of a deep brown color, generally keeping much the shape of the granule from which it has been extruded. Often more than one of these masses can be detected, and they sometimes assume needle-like or staff-like shapes. But, whatever their form may be, they carrj- out of the granule all of the coloring-matter, and lea\e it as a hone}' combed mass of its original shape. Similar extrusion of a colored mass can be effected bj' the action of the vapor of boiling water, or even b}' immersion in boiling water; but here the change is produced in a single hoin-, or even less (in some cases, in Ave minutes). When much starch is present in the chlorophyll granules there is generally considerable change of outline of the whole mass, and more or less breaking down of their internal structure. The nature of the vehicle which, under the action of hydrochloric acid or moist heat, carries out of the granule all of the coloring-matter, will be referred to later, under the name given it by Pringsheim, namely, Sypochlorin. 773. The mass of the granule is left by this removal of its coloring-matter, as a spong}- bod}- of about the original shape of the granule. This spongy stroma, or " trabecular mass," is plainl}' different from the granule which is decolorized by the action of solvents, for example, alcohol, ether, etc. ; for in the latter case the mass appears to be with an unbroken contour, and has a solid structure. 774. The chlorophyll pigment can be extracted, although with various associated waxy and fatty matters, by alcohol and other solvents. To prepare a solution of the pigment for a study of its most striking properties, fresh leaves should be bruised, acted on for a few hours in the dark by warm, strong alcohol, and then, without exposure to bright light, the liquid should be carefully decanted. It is not difficult to separate the dark green solution into two distinct colors by means of the following methods : — (1) Fremy's process. One volume of the alcoholic solution is shaken with a mixture of two volumes of ether and one of concentrated hydrochloric acid ; after standing for a time, its ujjper, or ether layer., is yellow (phylloxanthin or xanthophyll), while its lower, or acid layer, is blue or greenish blue (phyllo- THE CHLOfeOPHYLL tIGMBNT. 291 cyaniu). If considerable alcohol is now added, and the mixture shaken, the liquid again becomes thoroughly mixed and of a clear green color. Fremy's later researches have led him to re- gard the so-called phyllocyanin as really an acid (phyllocyanic), which is probably combined with potassium, and the salt thus formed mixed with phylloxanthin to form the green coloring- matter of chlorophyll. (2) Kraics's process. This method of separating the two coloring-matters is based on the action of benzol. The alcoholic solution prepared as directed on page 290, or, much better, with alcohol of 65 %, is shaken with about twice its volume of benzol, or, according to R. Sachsse, with benzin (sp. gr. .714). After a while the turbid liquid separates into a benzol layer above, having a bluish-green color, and an alcohol layer below, tinged yellow. The yellowish pigment is called by Kraus, xanthophyll, the bluish-green, kyanophyll. According to Wiesner, kyanophyll is nearly pure chlorophyll freed from its associated yellow pig- ment xanthophj-11. It is believed by manj' that the yellow pig- ment separated bj' this process is identical with that found in plants blanched (etiolated) in darkness, and which has been called etiolin. Diflerent methods (some of which are noticed briefly in the foot-notes ^ ) have been employed for the isolation of the pure ' (1 ) Berzelius evaporates the alooholio extract to dryness, andaf'ter treatment with hydrochloric acid (sp. gr. 1.14), again dissolves it in alcohol. He then precipitates vpith water, redissolves 'the precipitate after filtration, and lastly, by acetic acid, precipitates the nearly pure pigment (Annalen der Chemie und Pharmacie, xxi., 1837, p. 257 ; xxvii., 1838, p. 296.) (2) Fremy throws down from its alcoholic solution, by use of eitlier alumiiiic or magnesic Iiydrate, all coloring-matter ; and after thoroughly wasliiug the precipitate dissolves it in alcohol (Comptes Rendus, 1., 1860, p. 405 ; Ixi., 1865, p. 188). (3) Hopjie-Seyler first extracts all waxy matters from green leaves by repeatedly washing them with cold ether, and then treats the leaves with boiling absolute alcohol. After the alcoholic solution has been cooled, again heated, and allowed to stand, red- dish crystals (erythrophyll) separate from it. These are red in transmitted, but green or whitish in reflected light. After their separation the residue of the solution is evaporated to dryness and again dissolved in ether; from the ether ' solution, upon slow evaporation, granules are thrown down, which are brown in transmitted and green in reflected light. These granules may be obtained, by repeated solution and by spontaneous evaporation of the solution, in the form of crystals of a high degree of purity, which are called by Hoppe-Seyler chlorophyllan (Zeitschr. phys. Chera., iii. 1879, p. 339). (4) In Gautier's pro- cess, bruised leaves are mixed with sodic hydrate and pressed. After this the residue of the leaves is treated with alcohol at 55° C. , again pressed, and then treated with cold 83 per cent alcohol, all waxy matters being left by the pro- cess undissolved. The alcoholic solution is mixed with animal charcoal and 292 ASSIMILATION. coloring-matters of leaves : crystalline substances have been ob- tained, one of wliich, marked by its blue or bluish-green color, contains about five per cent of nitrogen.^ 775. Spectrum of chlorophyll. When a ray of white light which has passed through a coloring-matter, for instance, a solu- tion of one of the coal-tar dyes, red wine, or a solution of chlo- roph3-ll, is examined by means of a spectroscope, certain dark bands, known as the absori)tion-bauds, are observed at definite places in its spectrum. 77G. For convenience in examining the spectra of small amountsof coloring-matters, a direct-vision spectroscope attached to the tube of a microscope is employed, and the coloring-matter in question is placed in a flat-walled bottle or a glass cell on the stage of the microscope. The ray of light which is reflected from the mirror under the stage passes first through the colored matter, next through the objective, and lastlj- through the prisms which compose the microspectroscopic attachment to the tube. 777. In order to compare the spectra of different substances, a second prism or set of prisms is often used, by which the spec- trum of a second liquid can be projected by the side of that of allowed to stand for five days ; all the chloroiihyll pigment is thus removed by the cliarcoal. Alcohol of 65 per cent strength extracts from the coal a yellow crystallizable substance, while ether or benzine dissolves out matter which, upon evaporation of the solution, yields pure chlorophyll pigment (Comptes Rendus, Ixxxix., 1879, ji. 861). By the action of sodium on a benzine solution of the coloring-matter of Primula or of Allium, R. Sachsse has obtained two colored masses. One of these is green, solid at ordinary temperatures, in- soluble in pure water, soluble in a dilute alkali, and also in alcohol and ether; the other, yellow, brittle, crumbling into an orange mass, soluble in the same liquids as the first. Besides these two coloring substances he found also a glucoside (that is, a body which under certain conditions can be .split into some one of the sugars and another substance which is ca]iable of further changes). Both of the colored masses can be readily broken up into several different coloring-matters. The matters obtained by this process from the green mass differ from those obtained from the yellow, in containing about three to five per cent of nitrogen, while those from the yellow contain none at all. 1 The green crystals obtained by the evaporation of a purified solution of chloroi)hyll in alcohol are called chlorophyllan by Hoppe-Seyler, and chloro- phyll by Gautier. Their analysis reveals the following composition: — Hoppe-Soyler. Gautier. C. . . 73.345 73.97 H. 9.725 . . , 9.80 O. . . 9.525 . 10.33 N. . 5.C85 . 4.15 Ash . ... 1.73 . ... 1.75 SPECTRtJM OP CHLOROPHYLL. 293 the first. The spectra of chlorophyll solutions from two different sources can thus be at once compared. One of the combinations can also be employed to project the solar spectrum (unchanged by passing through any color whatever), and its constant lines (Fraunhofer's lines) can be used for the determination of posi- tion of the bands seen in the spectrum of the liquid by its side. 778. The spectra of many substances, among which chloro- phj'll occupies a prominent place, have absorption-bands of such constancy in position and appearance that they are justly regarded as characteristic. 779. The spectrum of an alcoholic solution of chlorophyll has been shown to be essentiallj' the same as that of the chlorophj'U granule itself. In order, however, to obtain all the absorption- bands characteristic of chlorophyll, it is necessary to examine successively solutions of different degrees of strengtli, some of the bands appearing only in dilute and others only in strong solutions. For comparison, absorption spectra obtained from different sources are here given. Fio. 150. Spectra of chlorophyll. The upper figure shows the spectrum of an alco- holic solution of medium concentration, while the middle figure gives all the absorption- bands of chlorophyll; those on the right as shown only in dilute solutions. The lowest figure exhibits the spectrum of a living leaf of Deutzla scabra. (Kraus.) 294 ASStMILAtlOi*. 780. The fluorescence of chlorophyll pigment is best shown by allowing rays of light, made convergent by passing through a double convex lens, to fall upon the surface or side of a strong alcoholic solution of chlorophyll. The color at the focus of the lens will then appear blood-red, but by transmitted light the same solution will appear dark green. By fluorescence is meant the property possessed by certain substances of diminishing tlie re- frangibility of some rays of light ; in the case of chloroph^'ll all the raj's towards the violet end of the spectrum are made to conform in refrangibility to those near the red. A bright solar spectrum '■ cast upon the side of a flat vessel containing a solu- tion of chlorophyll appears much like a stripe of dull red : in this red stripe are bands corresponding in their position to the absorption-bands of chlorophyll. If the blood-red color produced b3' a strong light falling on the surface of a concentrated solu- tion of chlorophyll is examined through a spectroscope, only red rays having the same degree of refrangibilitj' as those of the deep absorption-band of the chlorophyll spectrum come to the ej'e. 781. Plants without chlorophyll. If whole plants (certain parasites and saprophytes, for example, Monotropa) are either white or slightly tawny throughout, it is owing to a complete or partial absence of chlorophyll ; but in some instances such plants may impart to alcohol, in which they are immersed, a decided tinge, frequently blue. 782. "Colored" plants. When leaves or stems have some color other than green, they are said to be colored ; if two or more different colors are intermingled the parts are variegated. 783. In the case of healthy leaves exposed to light, white spots, streaks, etc., are generally, if not alwaj's, characterized by an absence of chlorophyll. Such spots have relations to their surroundings which are different from those of the contiguous green parts ; they do not have the power of assimilating in- organic matters. 784. In plants, the paleness of colors verging upon green or blue (for example, those in many kinds of cabbage) sometimes depends wholly on the existence upon the surface of the part, of a great amount of the waxy matters known eollectivel3' as bloom (see 226). The tissues beneath the surface may be vivid green. 785. Red and j-ellow colors of healthy and vigorous leaves are usually due to the presence in the cells (often merely those of 1 Hagenbach: Annalen der Physik und Chemie, cxli., 1870, p. 245. ETIOLATION. 295 the epidermis) of colored cell-sap. This is sometimes in such large amount as to mask completely the green granules which are contained in the same cells. 786. In the Floridea; (rose-red marine algse) the chlorophyll is masked bj' the presence of a reddish coloring-matter which is easily extracted b}- pure water. This reddish pigment is called phj-coerythrine. In solution it is carmine-red by transmitted, and orange by reflected light. Analogous pigments extracted by water from algae of colors other than red have received the following names, — phycopheeine (brownish), phj'cocyanine (bluish), phycoxanthine (yellowish-brown). "When these coloring-matters have been extracted by cold water, the chlorophyll is left unchanged in the plant, and it then imparts to the thallus its characteristic green color. Owing to the nearly complete insolubility of these reddish pigments in alcohol, and the complete solubility of the chlorophyll pigment in that liquid, a green color is given at once to alcohol when an alga is immersed therein. 787. Colored bodies, not readily, if indeed at all, distinguish- able from ordinarj' crj'stalloids (see 177), are found in many algse. In some cases these colored granules of cr3-stalline form occur normallj- in the living plant ; in others they arise from changes produced by the action of reagents upon the matters of the cells. The name rhodospermin, given by Cramer to the granules having the latter origin, has been adopted hy Klein in an extended memoir. 788. Etiolation. Green plants placed in darkness soon turn pale and become blanched or etiolated. The chlorophyll gran- ules change their color, and finally appear to become merged, with more or less change of form, in the protoplasmic mass, from which they are then no longer easil}' distinguishable. Etio- lated plauts when exposed to light recover their color only when the temperature is above a certain point. The action of light in restoring color is, moreover, local, being confined to the part of the plant which is exposed to its influence. It maj' be here noted that some plants are not etiolated until after long expos- ure to darkness ; thus the older parts of Cactus speciosus, kept in the dark, remained green for three months, but the new shoots were etiolated. Selaginella remained green from four to five months. 1 1 Sachs : Haiidbnch der Experimental-physiologie, 1865; also Botanische Zeitiing, 1864, and Flora, 1863. 296 ASSIMILATION. The instructive similarity between the spectrum of the yellow coloring-matter of chlorophyll and that of the so-called etiolin, or yellow coloring-matter which can be extracted from blanched leaves, is shown in the two figures here given. BOP B 1 T .4011 \wi> SCO I iilililiilm illllllniilmiliiii'hl ^om B C ill D ll'lllllMl'lllll [illliiiilii iiliiii'iiiii|iiiim 300 \liM SO' iulll 789. An alcoholic solution of chlorophyll undergoes very little if any change when kept in the dark ; but even a short exposure to strong light destroys its green color, and leaves the liquid pale brown, or nearly colorless. When, however, strong sun- light passes through a solution of chlorophyll before it reaches a second receptacle filled with the same liquid, the first solution protects the second for a considerable time ; and only after the first has lost a portion of its green color can the second be also acted upon. 790. Sachs ^ has pointed out the interesting fact that green leaves, especially those of delicate texture, become paler when exposed to a very bright light, and resume their deep green color when again subjected to a less intense light. If one leaf is partially' shaded by another, the shaded leaf preserves its nor- mal deep green color, while the leaf exposed to the light grows distinctly paler. This effect, due probably to a change of posi- tion of the chlorophyll grains, can be shown experimentally in the following manner : Fasten closelj- to a green leaf, still ^ Ber. iiber die Verhandlungen (Math. Phys. Classe) der Siichsischen Ge- sellsch. xi., 1859, 226 ; and also in Experimcntal-physiologie, 1865. Fig. 151. The upper spectrum is that of the yellow constituent of chlorophyll ftom Deutzia scabra; the lower, that of the coloring-matter of etiolated barley, in dilute solution. (Kraiis) COLOKS OF AUTUMN LEAVES. 297 connected to its plant, a narrow strip of ilexible lead or tin foil, and expose tiie leaf to bright sunlight. After a quarter or Imlf an hour remove the strip, and the spot which has been kept shaded by it will be seen to be distinctly deeper in color than the part wiiich has been exposed to the sun's rays. 791. Chlorosis, or blanching of plants from lack of iron. Although iron has not been detected as a constant component of the pure pigment of chlorophyll, this element has been siiown in many ways, especially by water-culture, to be essential to the green color and even to the normal formation of the granules. When a seedling of Indian corn is grown with its roots abundantly' supplied with a nutrient solution from which all salts of iron are absent, and it has all other condi- tions favorable to rapid and healthy development, the leaves are pale yellow, or even whitish, and the whole plant sooner or later appears sickly and ill-nourished. When, however, a salt of iron is supplied to the nutrient liquid, a normal green ■ coloi' is at once imparted to the leaves and the plant becomes healthy and vigorous. The effect of the local application of a salt of iron is thus described : When a weak solution of ferric chloride, fei'ric nitrate, or ferrous sulphate is applied to a leaf blanched by want of iron, the part moistened assumes a nor- mal green color in a few days, and sometimes in a much shorter period. Neither cobalt nor nickel salts have similar relations to chlorophyll.-^ 792. Autumnal changes in color. The leaves of many decidu- ous plants undergo changes of color at some period before they fall. In not a few instances these changes occur earl3' in tlie season after full development of the leaf; for example, during the first days of summer it is not unusual to find on the swami) maple bright red and yellow leaves. The colors, howe^'er, be- come most striking in temperate climates at the approach of autumn. The change of color in autumn leaves is due to changes which take place in the chlorophyll pigment. This breaks up into various matters of unknown composition, but classed in a gen- eral way with the erythrophyll (the reddish coloring-matter) and xanthophj'll (the j-eilowish), obtainable artificially from chloro- ph3'll. Comparison of the spectra of these substances exhibits certain very striking features of similarity'. 1 Eiisebe Gris, 1844, and Arthur Gris, in Ann, 4es Sl'. nat., tome vii., 1857, j). 179. 298 ASSIMILATION. 793. These autumnal changes have been compared, not in- aptly-, to those belonging to the ripening process in colored fruits ; but this general statement of similarity must not disguise the fact that in the ripening of fruits special chromoplastids play the chief part, whereas in the leaf before its fall there is a breaking up of the protoplasmic basis of the granules of chlorophyll,^ pre- paratory to the withdrawal from the leaves into the plant of the useful products of disintegration. The changes during disintegration may involve (1) both color and form of the gi-anules at one and the same time, or (2) the change in color may precede that in form, or (3) the latter mav occur first. 794. In general, the reddish coloring-matters are found in the cell-sap of the colored leaves, the yellow in the substance of the disintegrating grain, and, finally-, the brown in the modified character of the cell-wall itself. 795. That frost is not essential to the production of the leaf- colors of autumn is plain from the widely known fact that many leaves undergo precisely these changes of color long before any frosts appear. It is generally believed, however, that freezing ma^- somewhat hasten the process of chlorophjU disintegration •which underlies all the changes. The fact is generally recognized that the autumnal colors, crimson and scarlet, are more brilliant in the cooler portions of Amei'ica than those which characterize the foliage in Europe, and it has even been remarked that the leaves of American ti-ees cultivated in Europe do not undergo such marked changes of color as individuals of the same species do in their native habitat. This has been accounted for on the ground that there is less humidity in the atmosphere of eastern America ; but this explanation is not satisfactory, and exact observations regarding the relative brilliancy of color are wholly wanting. 796. Chlorophyll in evergreen leaves. At the approach of cold weather the leaves of evergreens undergo, according to Mohl,^ certain changes of color. Kraus ' recognizes two types of change: (1) the leaves become greenish brown, as in most Conifers, or (2) thej- take on a red color on the upper side, as in Mahonia and some species of Sedum. According to him, in leaves of the first type the chlorophyll granules become disinte- ' Sachs : Die Entleeiung der Blatter im Herbst, Flora, 1863, p. 200. ^ Vermisohte Schriften, 1845. ^ Sitzung.sb. der phys.-med. Societat zu Erlangen, 1871, 1872, AUTUMNAL CHANGES IN LEAVES OP BVBEGEBENS. 299 grated and impart a brown color to the [jrotoplasmic mass of the cells ; but in the leaves of the second tj'pe the color is due to a highl}- refractive reddish or yellow mass (supposed to be tan^ nin), concealing from a surface view the clustered chlorophyll granules within, which retain their vivid hue. In aU cases of evergreen leaves the granules of chlorophyll, at the beginning of the cold season, pass from the walls to the centre of the cells, and are there' aggregated in compact clusters. Their normal condition is restored in the warm days of early spring. 797. Kraus has examined the changes in autumn in the chloro- phyll of Rnscus aculeatus. He finds that in this plant some of the more superficial cells under the epidermis contain minute granular masses of a brownish color, but no chlorophyll granules are to be distinctly seen, and that the subjacent cells have more or less broken-down granules which are yellowish or brownish green. In the cells making up the more spongy tissues there are a few chlorophyll granules quite intact, but there are indications that some others have been completely destroyed and their coloring- matter taken up by the surrounding protoplasm, apparently in a state of solution. 798. It was thought bj' Kraus that the winter change in the character of the chloroph}!! was due to the lower temperature. He based his views largely upon experiments with a branch of Buxus (Box) ; but it has been shown by Batalin^ and Askenasy ^ that light has a more important influence upon the chlorophj'll than changes of temperature. 799. The raw materials required for assimilation, and their reception by the assimilating organs. These are (1) water and (2) carbonic acid. In earlier chapters it has been shown in what manner and to what extent water and small traces of min- eral matters are brought from the soil into the plant. It is now necessarj' to ascertain in what way carbonic acid enters the organism and is appropriated by it. 800. Absorption of carbonic acid by water plants. These can absorb carbonic acid substantially as they absorb mineral salts, directly from the water in which they live. The amount of car- bonic acid found in rain and other waters is variable, ranging, according to the best authorities, from about one per cent to considerablj' less than one tenth of one per cent. The amount existing in the free state in natural waters in which plants thrive 1 Botanische Zeitung, 1874. 2 Botanische Zeituns, 1875. 300 ASSIMILATION. is shown in the following table (taken from the comprehensive synopsis iu Watts's dictionary) : — Cubic centimeters in each liter of water. Loch Katrine (Scotland) . .3 Bala Lake (Wales) . l.X Ehine at Strasbiirg . . . . • . . 7.6 Ehone at Geneva . . . . . . . . g4 Thames at Kew . . 50.3 All the free carbonic acid dissolved in water can be expelled by boiling. •■ 801. Absorption of carbonic acid by land plants. These, with their foliage exposed to the air, obtain from that source all their supply of carbonic acid. No carbonic acid is taken up by their roots : ' the supply enters the plant through the younger epider- mal tissues, chiefly, of course, that of the leaves. By the process of respiration within the plant (see Chapter XI.) a small but ap- preciable amount of carbonic acid is produced, and a part of this is doubtless appropriated directly by the plant for the process of assimilation. 802. Carbonic acid and other gases found in the atmosphere sustain to vegetable membranes certain relations which must ^ According to Bunsen (Jahresb. der Chemie, 1853, p. 317), one volume of water absorbs at 760 mm. barometric pressure, and at the temperatures noted, the following amounts of various gases : — 3°2C. 19f.6C. Nitrogen 02189 vol 01515 vol. Oxygen 04553 " 03253 " Carbonic acid . . 1.5184 "... .8545 " According to the same authority, these gases occur in rain-water in the fol- lowing relative proportions : — 0" C. 10° C. 20° 0, Nitrogen ... 63.20 ... 63.49 .. . 63.69 Oxygen .... 33.88 . . 34.05 . . . 34.17 Carbonic acid . . 2.92 . . . 2.46 . . . 2.14 2 This appears to be settled by the results of experiments made by Moll: ( 1 ) when carbonic acid is afforded, even in excess, to shoots, whose leaves are kept in an atmosphere free from carbonic acid, no formation of starch takes place ; (2) if such leaves are in the open air, the formation of starch is not increased above its normal rate; (3) when carbonic acid is supplied to roots of plants wrhose leaves and shoots are kept in an atmosphere free from carbonic acid, no formation of starch takes place. If the leaves and shoots of such plants are in the open air, there is no increase of starch above the normal amount (Arbeiten des bot. Inst, in Wiirzburg, 1878, p. 113). DIFFUSION OP GASES. 301 now be presented in a general manner ; and some introductory reference must be here m.ade to the well-known physical proper- ties of gases.' 803. Diffusion of gases. When two or more gases are brought into contact, spontaneous intermixture takes place. This pro- cess of diffusion, as it is called, goes on even when the gases are verj' different in specific gravity, and when they are kept externally at perfect rest. Thus if a jar of carbonic acid be placed in connection with a jar of oxygen, the two gases, after a while, will become uniformly commingled. Similar commingling of gases also takes place through per- meable substances, such as thin plates of unglazed porcelain, graphite, films of membrane, etc. 804. Different gases difl'use through a given membrane in different times. The rates of diffusion of different gases at the same temperature and barometric pressure have been shown bj- Graham to differ nearly in the inverse ratio of the square roots of their densities, thus : — Rate of ditf usion t Name of gas. (air being taken as unity). r Density. Hydrogen . . . 3.83 3.78 nearly Carbonic oxide . . . 1.01 nearly . . . 1.01 " Nitrogen 1.01 " ... 1.01 " Oxygen . ... .95 " ... .95 " Carbonic acid 81 " . . .81 " 1 Graliam, who made a careful study of the laws which govern gaseous dif- fusion, has given the following clear account of the physical hypothesis, which is now generally received : " A gas is represented as consisting of solid and perfectly elastic spherical particles which move in all directions, and are ani- mated with different degrees of velocity in different gases. Confined in a vessel, the moving particles are constantly impinging against its sides and oc- casionally against each other, and this contact takes place without any loss of motion owing to the perfect elasticity of the particles. If the containing vessel be porous, then gas Is projected through the open channels, by the motion described, and escapes. Simultaneously the external air is carried inwards in the same manner and takes the place of the gas which leaves the vessel. To this molecular movement is due the elastic force, with the power to resist compression, possessed by gases. The molecular movement is acceler- ated by heat and retarded by cold, the tension of the gas being increased in the first instance and diminished in the second. Even when the same gas is present both without and within the vessel, or is in contact with both sides of our porous plate, the movement Is sustained without abatement — molecules continuing to enter and leave the vessel in equal number, although nothing of the kind is indicated by change of volume or otherwise. If the gases in communication be different, but possess sensibly the same specific gravity and molecular velocity as nitrogen and carbonic oxide do, an interchange of 302 ASSIMILATION. 805. The movements of gases within the plant are of two kinds, (1) molecular (see note on the previous page), and (2) "the movement of the whole mass depending exclusively- on expansive force." These are generally conjoined in the passage of gases through the plant. 806. Passage of gases through epidermis free from stoinata. The assimilating apparatus in ordinary land plants consists of parenchj'ma cells frequently so loosely conjoined as to liave very conspicuous intercellular passages, which communicate with sto- mata either directly or indirectly. All of these parenchyma cells, have walls of cellulose generally without any impregnation of foreign matter. But the peripheral cells which bound the whole as epidermis proper are cutinized on their exteinal aspect, and must possess relations to gases different from those presented by common parenchyma with uninfiltrated walls. 807. Through ordinary cell-walls, that is, those which are com- posed of nearly pure cellulose, water passes and gases diffuse with facility. But as cutinized cell-walls, like those of the epi- dermis of leaves, are nearl3' impervious to water and to aqueous vapor, it would at first sight appear unlikely that gases could make their way through them ; such, however, is not the case. Experiments upon epidermal tissues free from stomata show that under ordinary circumstances gases can diffuse through cutinized walls. Thus N. J. C. Miiller* used the epidermis of the leaves of Heemanthus puniceus in three series of experiments upon the diffusion of different gases. The membrane employed was, in the first series, two films of epidermis with a layer of water be- tween them ; in the second, two moist films without any layer of water ; in the third, two films joined together and then care- fully dried in an exsiccator at 40° C. The method used by Miiller is open in some of its details to criticism, but in a general way the results are instructive. The following are the mean ratios indicating the rate of diff'usion obtained : — Series I. Series 11. Series 111. Hydrogen Oxygen Nitrogen Carbonic acid 100 502 471 687 100 S5 73 48 100 37 30 45 molecules also takes place without any change in volume. With gases opposed of unequal density and molecular velocity, the permeation ceases, of course, to be equal in both directions " (Philosophical Transactions, 1863). 1 Pringsheim's Jahrb., 1869, p. 169. PASSAGE OF GASES THROUGH STOMATA. 303 808. Experiments by a wholly different method were con- ducted by Boussingault,^ upon leaves of Oleander. By a leaf having an upper surface of 37.2 square centimeters free from stomata, and completely closed on the under side by tallow, 17.5 cubic centimeters of carbonic acid were absorbed in a given time. In another series of experiments Boussingault fastened the under surfaces of two leaves closely together by means of paste, so that only the upper surfaces (free from stomata) were exposed to the air ; with these leaves nearly the same results were ob- tained as in the first series. 809. Passage of gases through stomata. Stomata (see Figs. 52 and 54) are practically minute apertures in thin plates, and under ordinarj' circumstances there is no obstruction to the readj' passage of gases through them from the surroundings into the interior of the plant. The changing pressure caused by agi- tation of the foliage exerts, as it does in aqueous transpiration, an important influence in facilitating this passage. 810. Merget '' holds that it is chiefly through stomata that the interchange of gases with the outer air takes place in the plant ; but, on tlie other hand, it is claimed by Barthelemy ^ that they play only a very subordinate part. There can be little doubt that the earlier view advanced and illustrated by Du- trochet,* and further by Garreau,^ is substantially correct ; namely, that gases enter and escape from the plant freelj' both by diff'u- sion through the cuticularized cell-walls of the epidermis and by passage through the stomata. 811. Atmospheric air is chiefly amixture of two gases, oxygen and nitrogen. The proportions in which these substances and others, occurring in much smaller amounts, are found in drj' air are usually stated as follows : — Proportions by volume. Proportions by weight. 2Sritrogen . 79.01984 76.8399 Oxygen 20.94000 23.1000 Carbonic acid 04000 .0600 Ammonia 00016 .0001 100. 100. 1 Agronomie, iv., 1868, p. 374. 2 Comptes Rendus, Ixxxiv., 1877, p. 376. Ann. des Sc. nat. hot., ser. 5, tome xix., 1874, p. 131. - Ann. des Sc. nat., tome xxv., 1832, p. 242. ^ Ann. des Sc. nat. bot., ser. 3, tomes xv., xvi. 304 ASSIMILATION. The first two substances occur in verj' nearly tlie same pro- portions in free atmospheric air wherever found, ^ but the amounts of the last two var^- within narrow limits. Besides the foregoing substances, the following are also men- tioned as having been found in dry air in minute traces : Nitric acid, nitrous acid, ozone, marsh gas, carbonic oxide, sulphurous, sulphjdric, and hj'drochloric acids, and hydrogen. 812. Under ordinary circumstances the proportion of car- bonic acid in the atmosphere does not increase much beyond the amount stated above, namely, four one-hundredths, or one twenty- fifth of one per cent.^ Petteukofer assigns one twentieth of one per cent as the amount in the air of Munich (1,690 feet above the level of the sea) . In confined spaces, however, the accumulation of carbonic acid (once known bj' the significant term fixed air) may be- come so gi'eat as to render the air irrespirable. It was the con- sideration of the question how such air could be again rendered lit for respiration that led to the first successful* investigation of the action of plants upon the atmosphere. 813. The amount of carbonic acid found in ordinary- water which has been exposed for a time to the air is sufficient for the supply' of this gas to water plants. The percentage of the gas in the atmosphere under ordinary conditions is ample for all the needs of land plants. The consideration of the effect of supplj- ing a larger amount than usual of this gas to water and land plants, in order thereby to influence the activity' of the assimila- tive process, must be deferred until all the conditions essential to assimilation have been considered ; but it may be said, in passing, that any large excess of carbonic acid over the supply furnished to plants in nature diminishes assimilative activity. ^ For a very Instructive summary of results of the examination of the air in different localities, the reader should consult "Air and Rain, the Begin- nings of a Chemical Climatology," by R. Angus Smith (London, 1872). ^ Angus Smith gives the foUowhig results of his examination in 1864 of the air of Manchester, England ; — Per cent of COa in atmosphere. In the streets, usual weather . . 0403 During fogs . ... . ... . .0679 Where the fields begin . . . . . .0369 In close buildings ... 1604 Minimum amount found in suburbs .... . . .0291 See also Ann. de Chimie et de Physique, 1883, for reports on the amount of COj in the atmosphere of different localities. * See the historical sketch, pp. 323, 324. PKACTICAL STUDY. 305 814. Practical study of iissimilatiou. Before examining the remaining conditions of assimilation, a simple experiment is liere described b3' which the reader can study in their proper relations all the essential conditions of the process, and thus obtain a clearer idea of the means by which the activit}' of assimilation is measured and the indispensable character of the conditions established. Fill a flve-inoh test-tube, provided with a foot, with fresh drinlc- ing water. In this place a sprig of one of the following water plants, — Anacharis Canadensis, Mj-riophyllum spicatum, M. verticillatum, or any leaf}' Myriophyllum (in fact, any small- leaved water plant with rather crowded foliage). This sprig should be prepared as follows : Cut the stem squarely off, four inches or so from the tip, dr^- the cut surface quickly with blotting-paper, then cover the end of the stem with a quickly drying varnish, for instance asphalt-varnish (see 115), and let it dry perfectly, keeping the rest of the stem if possible moist by means of a wet cloth. When the varnish is drj-, puncture it by a needle, and immerse the stem in the water in the test-tube, keeping the varnished larger end uppermost. If the submerged plant be now exposed to the strong rays of the sun, bubbles of oxygen gas will begin to pass off at an even and rapid rate, but not too fast to be easily counted. If the simple apparatus has begun to give off a regular succession of small bubbles, the fol- lowing experiments can be at once conducted. (1) Substitute for the fresh water some which has been boiled a few minutes before, and then allowed to completely cool : by the boiling, all the carbonic acid has been expelled. If the plant is immersed in this water and exposed to the sun's raj's, no bub- bles will be evolved ; there is no carbonic acid within reach of the plant for the assimilative process. But, (2) If breath from the lungs be passed by means of a slender glass tube through the water, a part of the carbonic acid exhaled from the lungs will be dissolved in it, and with this supply of the gas the plant begins the work of assimilation immediatch'. (3) If the light be shut off, the evolution of bubbles will pres- ently cease, being resumed soon after light again has access to the plant. (4) If glass of different colors be interposed in the path of the sun's rays, it will be shortly seen that orange light differs from violet light in its effects upon the rate of the evolution of the bubbles. (5) Place around the base of the test-tube a few fragments of 20 306 ASSIMILATION. ice, in order to appreciabty lower the temperature of the water. At a certain point it will be observed that uo bubbles are given off, and their evolution does not begin again until the water be- comes warm. (6) Examine, at the close of the series of simple experiments, some of the leaves with iodine solution, for the detection of starch. Even with no precaution the chlorophyll granules will reveal the presence of a considerable amount of the first visible product of assimilation, namel}-, starch. Lastlj-, keep a second uninjured spray of the same plant in the light for a time, and then in darkness for a day or two, after which examine it for starch ; probably after this lapse of time no starch can be de- tected, for although it has been made in the light, in darkness it has been consumed in the various activities of the plant. 815. According to the accepted theory, light consists of waves which are set in motion in a tenuous elastic medium termed the ether. The existence of this medium is made known to us only by the phenomena which light itself presents ; but, having as- sumed its existence, the phenomena of light can be explained. The tenuitj' of this medium, which fills all space, far exceeds that of any known gas, and its elasticit}' is far higher than that of an^' known elastic solid. In it a luminous body sets in mo- tion undulations which produce upon the retina the sensation of light ; upon differences in the amplitude and the duration ' of these undulations depend differences in the intensitj^ and the color of the light which reaches the eye.'' 1 The terms just employed, namely, amplitude and duration, seem hardly applicable to waves of such incredible minuteness and velocity as those named in the following table : — Color of Number of waves of light in one Length of each wave. light. second of time. Eed . 477 millions of millions. 650 millionths of a millimeter Orange . . . .506 " " " 609 Yellow . . 535 " " " 576 Green 577 " " " 536 Blue . . . 622 " " " 498 Indigo . 630 f( ti ti 470 Violet . . 699 " " 442 '^ "The intensity of the luminous impression must depend upon the force of the atomic blows which are transmitted to the optic nerves, and it is also evident that this force must be proportional to the square of the velocity of the oscillating atoms, or, what amounts to the same thing, to the square of the amplitude of the oscillation ; assuming, of course, that the oscillations are isochronous. The connection of color with the time of oscillation is not so TYPES OF ENERGY. 307 816. Light and assimilation proper. Energy has been defined as the power of doing work. Of this there are two tj-pes : the cnergj- of actual motion (sometimes termed kinetic), and the energj' of position (known as potential). The illustration of their difference is usually given as follows : A ball thrown up- wards has the power of overcoming the force of gravity tending to pvdl it down, and possesses energy of motion ; suppose the ball at the end of its course is lodged upon some projecting shelf, then its energy of motion disappears, and it now pos- sesses energj' of position. Whenever it is dislodged, it will fall with the same power which was required for its ascent. From this and similar examples it is plain that one form of energy can be changed into another ; when one seems to disappear, it has in fact merely been converted into some other. 817. These types of energy are to be found in molecules as well as in masses of matter. It is held that all molecules of all matter are in a state of motion, invisible, but none tlie less real. One form of sucih invisible kinetic energy is heat, and another is radiant light, where the energy of motion is embodied in the vibrations or undulations of the ethereal medium. A third form is that of electrical separation ; and still another, with which Physiologj' deals especially, is known as chemical separation, of which a familiar illustration may be given : An atom of oxj'gen has so strong an attraction for one of carbon, that if the two are united, it is difficult to separate them, the force required to do this being comparable to that demanded to raise a weight to a certain height. As in the latter case the weight held in its raised position represents by that position tlie force which was employed to raise it, so the separated atoms represent energy of position ready to be again converted into energj- of motion.'' obvious ; and why it is that the waves of ether heating with greater or less rapid- ity on the retina should produce such sensations as ,those of violet, blue, yellow, or red, the physiologist is wholly unable to explain. We have, however, an analogous phenomenon in sound, for musical notes are simply the effects of waves of air beating in a similar way ou the auditory nerves ; and, as is well known, the greater the freijuency of the beats, or, in other words, the more rapid the oscillations of the aerial molecules, the higher is the pitch of the note. Red color corresponds to low, and violet to high notes of music, and the gra- dations of color between these extremes, passing through various shades of yellow, green, blue, and indigo, correspond to the well-known gradations of nmsical pitch " (Cooke; Chemical Philosophy, 1882, p. 189). 1 It is seldom that one of these forms of molecular energy when exhibited in the phenomena of living beings is not associated with some other forrn, Thus 308 ASSIMILATION. 818. The conversion of the energy' of the motion of the ethe- real medium (in radiant light) into chemical separation of oxj-- gen from the carbon of carbonic acid, and the production of this treasured energy- under other forms, is the chief office of the plant. 819. Attention has alreadj' been called (see page 306) to the well-known fact that a beam of suuhght is composed of rays or lines of undulations differing both in respect to their amplitude and \'elocity. Hence it is to be expected that in their action on the plant these raj's, which are iu fact vehicles of kinetic energy, must have diverse effects. 820. Classiflcation of the rays of the spectrum. When a beam of sunlight is transmitted through a triangular prism, it is broken up into its constituent rays, which, falling upon a screen, form what is known as a spectrum. The colors of the spectrum grade from red at one end, through orange, yellow, green, blue, and indigo, to \iolet. The violet rajs are bent further from their course by the prism than any of the others above spoken of, and hence are termed the most refrangible ; experi- ment has also shown that these highly refrangible rays are most efficient in producing the chemical changes long known to be attributable to light : for this reason they have been denomi- nated chemical (or sometimes actinic) rays. The red rays are bent far less from their course than anj^ of the others above men- tioned, and hence they are termed the least refrangible. It is at the red end of the ^-isible spectrum that the greatest amount of heat is found. The rays which constitute .yellow and orange light are of medium refrangibility ; they arc the most distinctly luminous. It is proper, therefore, for convenience, to distin- guish rays of the solar spectrum as chemical, luminous, and heat rays, according to the dominant eflfect which thej' produce. But it should be stated that each of these three groups may share some of the work specially belonging to the others ; and further, that bej^ond the visible spectrum are rays which are efficient in accomplishing certain kinds of work. These latter are known respectivel}' as the ultra-violet and the ultra-red rays. Before examining the action of these different rays of light upon the assimilative activity of chlorophyll granules, inquiry must be made as to absorption, wliicli is essentially a process of moleciilai' adhrsion, is accompanied, as is capillary attraction, by electrical disturbances. In no case is energy lost . one form disappears only to reappear in some other, PASSAGE OF LIGHT THROUGH LEAVES. 309 821. The depth to which light can penetrate green tissues. This can be ascertained approximately by a simple apparatus sug- gested bj- Sachs. ■" A pasteboard tube, a foot or so in length and about an inch in diameter, is cut at oue end so as to fit around the ej-e verj' closely and allow no rays to enter except through the other end of the tube. If a thin leaf be placed over the distal end of the tube, and it be held towards a bright light, a large portion of the light will be received by the ej-e. If leaf after leaf be placed over the first, the green color soon gives way to a dull red, and finally is excluded altogether. The same apparatus shows to what depth light can penetrate superposed laj-ers of green cells taken from a stem or from thick leaves.^ 822. The quality of the light which penetrates a leaf, or which has passed through' one layer of cells containing chlorophyll, is shown by means of the spectroscope. From what has been shown (p. 296), it is clear that the light which acts on the cells below the first layer exposed to the sun's raj's must be different from the incident rays themselves. The light which reaches the deeper tissues of a leaf has passed througli more than one film of green tissue. 823. Tiie degree of intensity of white (that is, uncolored) light most favorable to assimilation has not been determined with certaintj-. The lowest limit at which an}' assimilation has been observed is considerably above that at which etiolated chloro- phj'U turns green. ^ 824. It has been shown * that very intense white light, even after it has been deprived of nearl}- all of its heat raj'S, can destroj' the vitality of vegetable cells. Considerabl}- before the death of the cells from this cause, the chlorophyll granules in them lose all their coloring-matter, even when thej' preserve their general form, and having once lost their green color, do not afterwards regain it. 1 Handbucli der Experimental-physiologie, 1865, p. 5. 2 But it has been shown by Hankel that the angle at which a beam of light strikes a plate of glass makes a noticeable difference in the amount of the chemi- cal rays which can pass through it ; thus while at a vertical angle 81 per cent of the ra,ys are transmitted, the rest being absorbed, at an angle of 60° the amount transmitted is reduced to 71 per cent, and at 80° to 33 per cent. The subject as relating to plants has not received the attention it deserves (Berichte iiber die Verhandhmgen der Siichsischen Gesellschaft der Wissenschaften). 3 Sachs ; Experimental-physiologie, 1865, p. 8. * Pringsheim : Monatsberichte der Berlin Akademie, 1879, 310 ASSIMILATION. 825. Colored light and assimilation. Daubeny, in 1835, was the first ^ to experiment systematically upon this subject. His method ^ of investigation was as follows: "A certain number of fresh leaves, which presented in each case an extent of surface as nearl}' as possible equal, and had been previously ascertained to give out equal quantities of oxygen, were introduced severally into jars filled with water impregnated with carbonic acid gas, placed on the surface of a pneumatic trough, and exposed for a certain time to the influence of the solar i-ays. The jars in which the leaves thus selected stood, were severally covered over by a wooden screen which intercepted all light from the in- cluded jar," excepting in front, where a frame was fitted, into which (1) colored glass or (2) flat bottles filled with differently colored liquids could be fastened, so that the light reaching the leaves could be variously modified. The amount and character of the gas escaping into the upper part of each jar were carefully determined. The leaves used were those of Brassica oleracea, Salicornia, Fucus, Tussilago, Cochlearia Armoracia, and Mentha viridis. Besides plain glass, the following colored varieties were employed : orange, red, blue, purple, green ; while the liquids used were, for blue, ammonio-sulphate of copper, and for red, port wine. In all cases Daubeny determined the amount of gas given off by the leaves, and afterwards analyzed it in order to ascertain the percentage of oxygen. He concluded from his experi- ments,^ "that the effect of light upon plants corresponds with its illuminating rather than with its chemical, or its calorific influence." 826. J. W. Draper, in 1844, published an account of his ex- periments upon the relations of green plants to light, as regards the amount of assimilative activity indicated bj- the oxj-gen given 1 Senebier and others had already conducted some inconclusive experiments iu nearly the same field. 2 On the Action of Light upon Plants, and of Plants upon the Atmosphere (Philosophical Transactions, 1836, p. 149). The activity of assimilation proper, as will he seen later, can he measured with a very close approximation to accuracy, by the amount of oxygen gas which is set free from the assimilating tissues, or, what amounts to substan- tially the same thing, by the amount of carbonic acid decomposed by them. For the sake of uniformity, the word assimilation is to be used in the follow- ipg paragraphs, even where the authorities cited refer to the process under f\e terms decomposition of carbonic acid, evolution of oxygen, etc. The term ) (similation, in its restricted sense, was adopted by Sachs (1863). ^ Philosophical Transactions, 1836, p. 151. DfeAPEil's EXPERIMENTS. 3ll off duj'ing exposure to different raj's of the solar spectrum. From his results it appears that "the rays which cause the decomposi- tion of carbonic acid gas have the same place in the spectrum as the orange, the 3'ellow, and the green ; the extreme red, the blue, the indigo, and the violet exerting no perceptible effect."^ Draper lays great stress upon the interesting fact previously noticed by Dauben}-, that the chemical rays appear to have no effect upon the work of assimilation. He does not, however, offer any explanation of the curious fact that the chemical activ- ity of the plant is dependent upon other rays than the chemical for its excitation. 827. The principal results obtained with submerged water plants bj' Cloez and Gratiolet,^ who exposed Potamogeton and 1 A Treatise on the Forces which produce the Organization of Plants, 1844, p. 177. The method of experimenting is detailed by Draper as follows : "Having, by long boiling and subsequent cooling, obtained water free from dissolved air, I saturated it with carbonic acid gas. Some grass leaves, the surfaces of which were carefully freed from any adherent bubbles or films of air by having been kept beneath carbonated water for three or four days, were provided. Seven glass tubes, each half an inch in diameter and si.^ inches long, were filled with carbonated water, and into the upper part of each the same number of blades of grass were placed, care being taken to have all as near as could be alike. The tubes were inserted side by side in a small pneumatic trough of porcelain. It is to be particularly remarked that the blades were of a pure green aspect, as seen in the water ; no glistening air- film, such as is always on freshly gathered leaves, nor any air bubbles, were attached to them. Great care was taken to secure this perfect freedom from air at the outset of the experiments. "The little trough was now placed in such a position that a solar spectrum, kept motionless by a heliostat and dispersed by a flint-glass prism in a hori- zontal direction, fell upon the tubes. By bringing the trough nearer to the prism or moving it farther off, the different colored spaces could be made to fall at pleasure on the inverted tubes. The beam of light was about three fourths of an inch in diameter. In a few minutes after the commencement of the experiment the tubes on which the orange, yellow, and green light fell commenced giving off minute gas bubbles ; and in about an hour and a half a quantity was collected sufficient for accurate measurement. "The gas thus collected in each tube having been transferred to another vessel and its quantity determined, the little trough, with all its tubes, was freely exposed to the sunshine. All the tubes now commenced actively evolv- ing gas, which, when collected and measured, served to show the capacity of each tube for carrying on the process. If the leaves in one were more sluggish, or exposed a smaller surface than the others, the quantity of gas evolved in that tube was correspondingly less. As may be readily supposed, I never could "et tubes so arranged as to act precisely alike ; but after a little practice I brought them sufficiently near .to equality. And in no instance was this testing-process of the power of each tube for evolving gas omitted after the experiment in the spectrum was over. " 2 Annales de Chimie et de Physique, ser. 3, tome xxxii., 1851, p. 67. 312 ASSlMlLAfrOU. IMyviophjlluiii to the action of light colored by passing through glass, may be stated as follows : The activity of the plant in decomposing carbonic acid diminishes with glasses used in the order given : (1) uncolored " ground" glass, (2) yellow, (3) un- colored transparent glass, (4) red, (5) green, (6) blue. By all the experimenters now referred to, the evolved gas was collected and examined. 828. Measurement of the anionnt of assimilation. Sachs, in 1864, appears to have been the first to employ the now well- known method of measuring the activity of the assimilative process by counting the bubbles of gas which are given off bj" a submerged water plant (see 814). Since the gas given off by the plant is not pure oxygen, but is variable in compo- sition,' the method cannot be regarded as sufficiently precise for verjr accurate experiment ; but as it admits of such rapid change in all external conditions, it answers for all practical purposes. 829. The effect of colored light upon the assimilative activity of plants not submerged, as in the above experiments, but in the air, was first examined by Cailletet,^ in 1867. lie placed the plant under bell-jars containing air with eighteen, twenty- 1 For remarks iipon the possible errors wliiuli may attend the nse of this method, consult Miiller (Prlngsheim's Jahrb. vi., 1868, p. 478). 2 L. Cailletet placed leaves in jars filled with air containing from 18 to 30 per cent of carbonic acid, and then exposed these to light which had passed through colored glass. In one case the light was transmitted through a solu- tion of iodine in carbon bisulphide. After an exposure of from eight to ten hourb, the amount of carbonic acid remaining undecomposed by the action of the leaves was found to be as follows : — Medium. Per cent of carbonic acid in the air. liemarlis as to cliemical activity ofUght. 18 p. li. 21 p. c. 30 p. c. Iodine in CS2 Green glass Violet glass Blue glass Eed glass Yellow glass Ground glass 18 20 18 17 7 5 21 30 19 16.50 5.50 1 30 37 28 27 23 18 2 Photographic paper not blackened. Argentic cbloride slowly discolored. Sensitive paper blackened rapidly. No blackening of argentic chloride or sensitized paper. Paper not blackened. Paper discolored rapidly. Two points must be specially noticed : (1) the striking effect of the large amount of carbonic acid in the third scries ; (2) the anomaly presented by the green glass, which is quite unexplained. It is to be regretted that no fuller account of the character of the gla.sses used is given (Comptes Rendus, Ixv., 1867, p. 322). timiriazeff's researches. 313 one, or thifty per eont oC earlioiiic iicid, and made of red, j-ellow, green, bluL', violet, and colorless glass. His results agree in general with tliose obtained by tlie other methods. 830. In 1870 further investigations in tlie same subject were made by Pfeffer.^ The following is a resume of the results of his experiments witli the leaves of five different plants exposed to colored liglit : Only the visible rays of the spectrum cause decomposition of carbonic acid ; and in this process the brightest, that is, the yellow rays, are as effleicnt as all the others taken to- gether, while the most refrangible rays, those which act most en- ergetically upon chloride of silver, have ouh' very slight influence upon the work of assimilation. Every color of the spectrum may be said to possess a s|iecific quantitative influence upon assimilation. This influence remains unchanged whether the color is isolated, combined with one, or with all the other coloi-s of the spectrum when it acts upon a part of a plant containing chlorophyll. 831. pjxaraination of the spectrum of chlorophyll (779) shows that the part of the spectrum which absorbs most of the rays is that which is pre-eminently its chemical end ; but by all the ob- servers whose results have been cited in the text, it is held that the chemical end is that which is least efficient in assimilation. With the exception of the narrow tliough strong absorption-band in the red, all the deep absorption-liands of chlorophyll and its solntions belong at the violet or chemical end of the spectrum. Mijller and Timiriazeff, cited in the notes, have endeavored to investigate this anomaly. 832. Timiriazeff,^ in a series of researches in 1877, experi- mented upon the slender leaves of Bamboo, which he placed in tubes of small calibre containing air of known composition, 1 Arbeiten des botun. Inst, in Wiirzburg, 1871, p. 1. The following works may also be cited : — A. von AVolkoff, Einige Untersiichungen libei' die Wlrkung des Liohtes von verschledener Intensitat auf die Ausscheidiing der Gase durch Wasserpflanzen. Pringsh. Jalirb., v., 1866, p. 1. Adolf Mayer, Production von organischer Pflanzen-Substanz bei Ausscliluss der chcmisclien Lichtstrahlen, Versuchs-Stationen, ix., ]867, p. 396. N. J. C. Miiller, Untersuchungen iiber die Diffusion der atmospharischen Gase in der Pflanze nnd die Gasausscheidung untev vevschiedenen Beleucht- ungsbedingungen, Pringsh. Jalirb., vi., 1867, 478 ; and vii., 1869, 145. Timiriazeff, Botaniache Zeitung, 1869, p. 169. Prillieux, Ann. des So. nat., ser. 5, tome x., 1869, p. 305. Baranetzky, Botanische Zeitung, 1871, p. 193. 2 Annales de Chimie et de Physique, ser. 5, tome xii., 1877, p. 355. S14 ASSIMlLAttON. and exposed to different parts of a large spectrum formed bj' a hollow pnsm filled with carbon bisulphide. By employing a nar- rower slit for the light than that used by previous exjierimeuters, he obtained an exposure of the leaves to a very limited portion of the spectrum : and to this difference in his apparatus he chieflj- attributes his results, which are at variance with those of his predecessors. Assuming that the results of his analysis of the evolved gas ai'e accurate, thej' indicate that the amount of car- bonic acid decomposed by leaves is proportional to the distri- bution of effective calorific energy in the spectrum. Timiriazeff'^ in his earlier paper did not himself attempt to apply his results to an explanation of the pecuhar relations of the rays of the spectrum to assimilation ; but Van Tieghem, who sub- stantially adopts the results of Timiriazeff, gives the following application of them to the associated phenomena. He calls atten- tion to the fact that the maximum of decomposition of carbonic acid, under the conditions of Timiriazeff's experiments, takes place at the deep absorption-band of chlorophyll, between 15 and C ; and therefore concludes that the decomposition of car- bonic acid by leaves exposed to solar radiation depends on two elements: (1) the elective absorption of the chlorophyll, and (2) the calorific energj- of the absorbed radiations. According to this view, the most efficient radiations must be those which, being best absorbed by the chlorophjU, possess at the same time the gi'eatest calorific energy. Hence, (1) the extreme red and the dark heat-rays, in spite of their extraordinary calorific energy, have no effect, because they pass through chlorophyll without \isible absorption ; and (2) the blue rays, which are very strongly absorbed, exert scarcely any effect, owing to their feeble calorific energj-.^ 833. Timiriazeffs results should be compared with those of Engelmann, who finds that for green cells the absolute maximum of assimilative activitj- lies in the red, between the lines B and C, at the point of the first and most pronounced absorption-band of chlorophyll, and that there is also more or less activity in the blue at F. If the cells are not of a green color, the maximum of activitj- is in some other point ; thus in the case of bluish-green cells it is in the yellow, and in that of red cells in the green. Engelmann's method is based upon the extraordinary sensi- 1 Ann. de Chimie et de Physiciue, ser. 5, tome xii., 1877, p. 394, and Ann. des Sc. nat., si5r. 7, tome ii., p. 99. '^ Traite de Botanique, 1884, p. 149. engelmann's researches. 315 tiveness' of certain bacteria to tlie presence of free oxj-gen. By an ingenious device, simple in its application, it is possible to determine the parts of tiie spectrum in which an assimilating cell or filament gives off oxygen most copiouslj-. Under the stage of the microscope is placed a microspectroscopc, which throws a clear spectrum upon an}- object on the glass slide in its place on the stage, for instance a filament of an alga. The alga is placed upon the slide in water which contains numbers of the common Bacterium (B. Termo), easily procured from putrescent matters. If it is kept from the light, or is exposed to only very faint light, all assimilative activity is suspended, and the bacteria after a time are quiescent. But when light in sufficient amount is permitted to pass through the specimen, assimilative activity is at once manifested, and the evolution of oxygen from the filament brings the bacteria into rapid movement. If, instead of white light, the rays from the spectroscope are passed through the specimen, the activity of the bacteria is equally manifest, but it is confined to a comparatively small part of the spectrum ; the bacteria collecting chiefly at the points whicli are known to coin- cide with the absorption-bands of chlorophyll.^ When a some- what thick cell is employed, there is a noticeable difference between the amount of activity' on its upper and under side. The figures show the ratio of activitj- of assimilation between tiie under side first exposed, and the upper side which receives light that has first passed through a green film. B-C. D. DJE. E-b, P. FJG. Lower . . . . 100. 48.5 37. 24. 36.5 10. Upper . . . . 36.5 94. 100. 52. 22. 12. It is to be noted tliat Engelmann did not in any case find any assimilation in uncolored chlorophyll, even when the light was tempered by the interposition of a colored medium (compare 850).' He has proved that assimilation proper takes place onlj' in ^ AccoriUng to Engelmann, the sensitiveness of bacteria is so great that by their reaction the trllUonth part of a milligram of oxygen can he detected (Botanische Zeltung, 1883, p. 4). Clerk Maxwell's estimate of the weight of a molecule of oxygen was one thirteen trillionth of a milligram (Philoso])hical Magazine, 1873, p. 453). 2 It is interesting to compare these determinations of the point of greatest assimilative efficiency in the spectrum with the results of Langley's researches upon the distribution of energy in the spectrum (American Journal of Science, XXV., 1883, p. 169). 3 Botanische Zeitung, 1882, p. 419; 1883, p. 17. 316 ASSIMILATION. protoplasm which contains coloring-mater, as for instance the chlorophyll granules, the colored granules in algae, etc. 834. Artificial light and assimilation. De CandoUe ^ exposed the submerged leaves of several species of plants to the light emitted by six Argand lamps, and failed to obtain thereby any evolution of gas. He estimated that the lamps had about five sixths of the intensity of sunlight. In this experiment the light, though insufficient to cause the evolution of gas, restored etiolated plants to their original green color. 835. When, however, a submerged water plant is exposed to the j-ays from a calcium light '^ (as that of an ordinary projecting lantern), there is a copious evolution of gas from its leaves. The light from burning magnesium wire is also sufficient to cause the decomposition of carbonic acid and the evolution of oxygen.^ 836. The influence of the electi-ic light upon assimilation has been investigated by numerous observers. Deherain, who ex- perimented in the Palais de ITndustrie, in Paris, found that the total assimilation produced in tlie leaves of Anacharis Canaden- sis, during an exposure for five da^'s, was not equal to that which followed exposure to sunhght for a single hour.* Siemens has shown that (1) many plants do not require any period of rest during the day, but thrive under continued illumination by elec- tric light and sun-light ; (2) electric light, properl3- regulated, accelerates growth, and produces upon plants eflects comparable to those produced hy sun-light.° 837. Temperature and assimilation proper. In certain cases the minimum temperature at which assimilation can take place is only slightly above the freezing-point of water. Boussingault ^ found that the leaves of the larch decompose carbonic acid at a temperature of from 0°.5-2°.5 C. ; while Kraus' gives the 1 Mem. pres. par divers Savans, h, I'Institut des Sciences, tome i., 1806, p. 333, and Physiologie vegetale, 1832, p. 131. Biot, in 1840 (Froriep's Notizen, xiii. 10), when measuring, in Spain, the length of a degree of latitude, found that the light from the powerful signal- ling apparatus used was not sufficient to cause any evolution of gas from sub- merged plants of Agave Americana. ^ Prillieux ; Comptes Eendns, Ixix., 1869, p. 408. * Heinrich : Versuchs-Stationen, xiii., 1871, p. 153. * Annales Agronomiques, tome vii., 1881, p. 385. 5 Proceedings of the Royal Society, xxx., pp. 210, 295, and Report of tlie British Association fur tlie Advancement of Science, 1881, p. 474. 6 Ann. des Sc. nat., ser. 5, tome x., 1868, p. 336. ' Kraus (Pringsh. Jalirb., ^■ii., p. 522) placed seedlings of Lepidium sativum in the dim light of the back of a room, wliere after six days the cotyledons ASSIMILATION AND TEMPERATUKE. 317 minimum temperature for assimilation b}- Anacliaris, Lepidium, and Betula as 3°-5° C. ; and Heinrich^ gives it as 2°. 5-4°. 5 C. for Hottonia. Tlie maximum temperature at which assimilation can occur in Anacharis ^ is between 4u° and 50° C. ; in Hottonia,'^ just be- low 56° C. The optimum'^ temperature for Hottonia appears to be not far from 31° C. showed no trace of starch. The plants were then distributed in three rooms of the temperatures mentioned in the annexed table, and with the results there detailed : — After 12o.8-13°,7 C. 5° 9-6°.5 C. 0^.3-0°.5 C. 2 hours. The first starch granules appear in the chlorophyll cells on the margin of tlie leaves. No starch. No starch 3 hours. Starch in the whole tip, margins, Some traces of starch at (( and petiole. margins of the leaves. 5 hours. Starch in the whole upper half of Tip and narrow edge with (( the leaf. starch. 13 hours. The whole leaf contained starch. Margin with much, sur- face with little starch. ^ Versuchs-Stationen, xiii., 1871, p. 136. ^ Schutzenberger and Quinquaud ; Comptea Eendus, Ixxvii., 1873, p. 272. 8 Heinrich ; Versuchs-Stationen, xiii., 1871, p. 136. * Heinrich's figures are .so instructive that they are here presented in the following table, which gives the number of bubbles of gas passing off from the cut surface of single leaves of Hottonia during the space of five minutes : Temp. C.° No. of babbles. 11 145-160 12 180-190 13 215- 15 245-255 17 255-265 21 325-360 22 375- 25 390-450 31 547-580 37 420-517 43 . . 225-255 50 110-220 56 The student must be reminded that the amount of gas which comes off in this experiment with submerged plants is not an exact measure of the assimilation. 318 ASSIMILATION. 838. The amount of carbonic acid unfavorable to assimilation. Experiments made by Saussure '■ at the beginning of tliis cen- tury- proved beyond question that plants are not tolerant of an atmosphere containing a large proi:jprtion of carbonic acid. In carbonic acid alone, or even in an atmosphere containing 66 per cent of this gas, vegetation was speedily destroyed. It was sliown, however, that if the plants were exposed to full liglit, they could sustain 8 per cent of carbonic acid without injury-. Saussure tliought that the presence of free ox^-gen is necessary to the assimilative work of the leaf. 839. In 1849, Daubenj'^ carried on an extensive series of re- searches, chief!}' upon plants allied to the dominant vegetation of the Carboniferous period, namelj', ferns and their allies, from which it appeared that even for these plants an amount of car- bonic acid above 10 per cent is injurious. Five species were placed in a receptacle containing about 46 liters of air, and to this air was added one per cent of carbonic acid, and also one per cent daily thereafter, until the amount present reached 20 per cent. This proportion was kept for twenty days, small amounts being added, as occasion required, to make up for loss bj' leakage. On the thirteenth day a sensible impairment of the plants was noticed ; and at the end of thirty dajs all of them had been more or less damaged, most having lost their fronds. 840. Boussingault,' in 1864, conducted a series of experi- ments in order to ascertain whether the presence of free oxygen in an 'atmosphere containing carbonic acid is necessary to the work of assimilation. The results of his researches are given as follows : — (1) Leaves exposed to sunlight, in pure carbonic acid, do not decompose this gas, or if at all, very slowlj'. (2) Leaves exposed to sunlight in an atmosphere containing a mixture of common air and carbonic acid decompose the latter gas rapidly ; but the oxygen of the air has no part in this operation, since, (3) Leaves exposed to sunlight rapidly decompose carbonic acid gas when this gas is mixed with nitrogen, hydrogen, car- bonic oxide, or carburetted hydrogen. 1 Saussure: Recherohes ohimiques sur la vegetation (Paris, 1804), p. 29. An earlier experiment was made by Percival. ^ Report of British Association, 1849, p. 56 ; and 1850, p. 159. » Agronomie, iv., 1868, p. 301. EELATIONS OF CARBONIC ACID TO ASSIMILATION. 319 841. The amount of carbonic acid most favorable to assimilation. The results of the most exhaustive study of the amount of car- bonic acid most favorable to assimilation have been given by their recorder as follows : — (1) Increase in the amount of carbonic acid in the air, up to a certain limit (the optimum), favors the evolution of oxygen by plants ; beyond this it is more or less injurious. (2) The optimum of carbonic acid is different for different plants : for GljTeria spectabilis on clear da3-s it is between 8 and 10 per cent ; for Tj-pha latifolia, between 5 and 7 per cent ; for Oleander, soraewliat less. (3) An}- given increase in the amount of carbonic acid below the optimum favors the evolution of ox3"gen far more than a similar increase above the optim.um hinders it. (4) The stronger the intensity of the light the more the evolu- tion of oxygen is favored by increase in the amount of carbonic acid up to the optimum ; and when this limit is passed the evolution is cheeked so much the less. (5) From (4) it follows that the influence of the intensity of the light on the evolution of ox3-gen is greater in proportion to the amount of carbonic acid in the air. 842. Batio of the oxygen evolved by plants to the carbonic acid decomposed. The volume of 0X3-gen evolved b}- plants during assimilation proper is very nearly that of tlie carbonic acid decomposed.^ Numerous experiments by Boussingault exhibit this relation in a \ery striking manner. In fort}--one experiments the volume of carbonic acid was to that of the oxj-gen set free as 100 : 98.7. 1 Saussure (Ri'clierches chiniiqnes sur la vegetation, 1804, pp. 40, 59) is regarded as the first to indicate this. He arrived at this conclusion by experi- menting upon a nnmber of plants under different conditions. His first recorded experiment consisted in surrounding seven plants of Vinca (Periwinkle) with an atmosphere containing a known quantity of carbonic acid gas. The plants were exposed to sunlight from five to eleven o'clock in the morning for six days, after which the air in the bell-jar was examined. Air in tlie jar Air in the jar before tlie experiment. after tlie experiment. Nitrogen . . . . . 4199 cubic cent. . 43-38 cubic cent. Oxygen . . . . 1116 . . 1408 " Carbonic acid . 431 " Total volume . 5746 " . . 5746 Saussure's conclusion is that plants, in decomposing carbonic acid, assimi- late a part of the oxygen gas therein contained, and, further, that the amount of carbon retained by the plant bears a definite relation to the amount of COj taken up by it. 320 ASSIMILATION. The following table bj- Boussingault ^ is very instructive, as it shows the relation of volume between the amount of carbonic acid consumed and the oxj-gen evolved in assimilation ; and also the decomposing power of various kinds of plants under different conditions.^ CO, (lisap- Oxygen Time of Surface CO, decomposed Constitu- Plants. appear- exposure of per square deci- tion of at- ing. to light. leaves. meter each hour. mosphere. c. c. c. c. b. m. cm. sq. c. c. Clierry laurel 52 5.9 4 134 .8 CO2 " 23.2 22.9 4 124 4.7 CO^-l-air. " 4, 4.5 4 90 10 CO2 " 19.6 19 9 4 90 6.5 COj-l-air. Pine 13.0 13.0 7 204 .9 COj " 18.1 17.8 7 204 1.3 CO^-f air. Oak 4.9 4.0 4 224 .5 COj " 25. 24.7 4 224 2.8 COj-l-air. Holly 5.1 4.9 6 30 52 1.8 (( Mistletoe 9.9 99 5 100 2. " 843. The gas emitted during the process of assimilation proper is not pure oxygen. Both Daubenj-' and Draper* found varia- ble amounts of nitrogen in all the cases examined b3' them. 844. What are the products of assimilation proper? It has now been shown under what conditions the green tissues of a plant decompose carljonic acid and evolve oxygen.^ As the chief result of this decomposition and its associated processes, there is formed witliiu the cells which contain chlorophyll a carbo- hydrate of some kind. This carboh3drate contains the same elements as the carbonic acid and the water fi-om which it was produced, but it contains less oxygen than the total amount found in those substances taken together. Hence the process of assimilation is essentiall}- one of reduction. There is, how- ever, no substantial agreement as to the nature or constitution of the primary carbohydrate formed by it. The difficulty wliich attends the investigation of assimilation 1 Agronomie, iv., 1868, p. 286. 2 A well-known relation of volume between oxygen and carbonic acid may here be pointed out ; namely, that "free oxygen occupies the same bulk as the carbonic acid produced by uniting it with carbon." * Philosophical Transactions, 1836. * " In every instance which I have examined, the gas evolved from leaves is not pure oxygen, but a variable mixture of oxygen and nitrogen. This result is of uniform occurrence" (Chemistry of Plants, 1844, p. 182). 5 For an account of the transient evolution of oxygen under exceptional circumstances where carbonic acid is not present, see Mtiller's Handbuch der Botanik, 1880. THE FIKST VISIBLE PRODUCT. 321 is apparent at a glance. The raw materials, the apparatus, and the ultimate products of manufacture are known ; but the intermediate processes b}- which chloroph} 11 granules under the influence of certain rays of light can cause the dissociation of carbon from the oxj-gen with wliicli it is combined in carbonic acid, and bring about the sj'nthcsis of an organic substance from materials wholly inorganic, are not at present known. 845. The wide field which the synthesis of organic from inor- ganic matter opens to conjecture has not been left unoccupied. It is generally admitted that in assimilation there is first formed some ternary substance, namely, one which contains the three elements, carbon, h3'drogen, and oxjgen ; and further, that this contains less ox^-gen than the two inorganic matters, car- bonic acid and water, from whicli it is produced, taken to- gether. Exactly what the ternary substance is, or how the dissociation or reduction is carried on in the chloroph3ll granule, is still left in doubt. 846. Starch (CjII^O^) is the first visible product of assimila- tion, as was first pointed out by Sachs in 1862.* Although Sachs appears to have held at one time that it is the first pro- duct, his later expressions are more guarded, and simply state the fact universally admitted, namel3-, that starch is the first product which the microscope can detect. When a seedling has been kept for a time in a diml^- lighted room, its cotyledons and other leaves grow pale or etiolated, and if they are examined for starch, no trace of it will be found. But upon a very short exposure of the plant to the direct raj-s of the sun, provided the other conditions are favorable, a certain amount of starch will appear in the chlorophj-U granules of the cells at the margin of the leaves. If the plant is again withdrawn from the light, its scant}' store of starch is speedily consumed, but on renewed in- solation the loss is made good ; this process can be repeated many times. From the constant appearance of starch in the chlorophj'U granules under the above circumstances it has been generally recognized as the first visible product of assimilation proper. But it has obviously such a complex molecular struc- ture that chemists are unwilling to believe that its formation in the plant is not preceded b}- the production of some simpler substance. Furthermore, there are a few cases in which oil replaces starch as the first visible product, thus indicating that there may be some earlier product possibly' common to both. 1 Botanische Zeitung, 1862 ; Flora, 1862. 21 322 ASSIMILATION. 847. Glucose. It is held by some that this product is glucose (C^H,jO|;) or some substance having the same atomic propor- tions of these elements. Early and not well-defined views in regard to glucose may be replaced b}- the following statement of a theory widelj- taught. 848. Formic aldehyde hypothesis. According to Gautier,^ chlorophyll exists in two conditions, white chJorophyll, rich in h^-drogen, and green cMorophyll^ poorer in this element. By his h3-pothesis the yellow ra}- absorbed b}' the assimilating tissues furnishes a certain amount of energ3- which is partiallj- con- verted into heat, and promotes evaporation of water (transpira- tion) ; and at the same time it permits the chlorophj-ll granule to decompose the water with which the protoplasmic mass is satu- rated. In the presence of CO^ and H^O the reducing process ■-gives rise to formic acid (CHgO^), which in its turn is reduced to formic (or methylie) aldelyde, CII^O. Tlie latter has the same atomic proportions as glucose (C^Hj^Oy). 849. Whether, in assimilation, the ternarj- substance be for- mic aldehyde, or glucose, or starch, it is certainly a substance capable of undergoing further oxidation, and hence, chemically speaking, an unsaturated comijound. When this unsaturated compound is oxidized,'^ a definite amount of energ}- of motion is set free, and this is manifested to us under one of its many phases, namely : (1) movements of the whole plant, as in some of the lowest organisms ; (2) movements of liquids within the plant, as in the transfer of matter to points of consumption ; (3) heat ; (4) electrical disturbances, and all the proper vital activities correlated with these. Tlie energy of motion in solar radiance is treasured for a time in the ternarj- and derivative products, thence to be released as occasion requires. 850. It is proper to refer at this point to a novel view in regard to the product of assimilation which has received much adverse criticism ; namely, that of Pringsheim.' Attention has already been called to the interesting observations bj' this bota- nist on the constitution of chlorophyll granules. In jjrosecuting his investigations he became convinced that the peculiar colored substance which is extruded from the granules under the influ- ence of certain agents is a product of assimilation. To this product he gave the name hypochlorin. According to him, when 1 La Chimie des Plantes. Revue Scientifique, Feb. 10, 1877, p. 767. ^ Compare Claude Bernard, IjeQons sur les Plienomfcnes de la Vie, 1878. 3 Jahrb., xu., 1879-1881, p. 288. EARLY HISTOKY. 323 anj' active cells containing clilorophyll granules are subjected to conditions favorable to assimilation, liypochlorin is formed in considerable amount ; but when tlie conditions for assimi- lation are not present, only traces of it are jiroduced. Prings- Leira used an entirely novel metliod of experimenting; namely", tliat of subjecting tlie chloroplyll granules to tlie action of intense light from which the heat rays had been extracted as perfectly as possible ; and under these conditions he failed to detect any hypochlorin, but observed a marlied increase in the amount of COj given off as in ordinary respiration (see Chapter XI.). Hence he arrived at tlie conclusion that assimilation proper is the cliaracteristic office of chlorophj'll granules solely on account of their pigment, which tempers the light reaching them. According to him, the pigment, by its absorption of the so-called chemical rajs, serves as a regulatory screen gov- erning the amount of light, and so controlling the amount of respiration and assimilation proper. 851. Ontline of the early history of assimilation. The follow- ing extracts from the works of early experimenters upon the relations of green leaves to the atmosphere show the manner in which the problem of assimilation was first attaclced. 852. Priestlej- ' discovered in 1771^ that air in which candles can no longer burn, and which is irrespirable, can be restored to its original condition by the presence in it, for a time, of vig- orous plants. The account below is given in, his own words : " Finding that candles would burn very well in air in which plants had grown a long time, and having had some reason to think, that there was sometliiug attending vegetation which restored air that had been injured by respiration, I thought it was possible that the same 1 Experiments and Observations on Diflerent Kinds of Air (3d edition, 1781), p. 51. ^ In 1754 Bonnet published his observations upon the behavior of leaves in water. It is well known that when green leaves are immersed in water and exposed to sunlight for a time, bubbles of air appear on their surface. Bonnet believed that the leaves drew common air from the water and this swelled into conspicuous bubbles under the heat of the sun. He was confirmed in this belief upon ascertaining that bubbles did not appear on green leaves ex- posed in water which has been boiled to expel the air (Recherches snr I'usage des Feuilles dans les Plantes, p. 26). If we consider the state of chemical science at the time of Bonnet's researches, his error is in no wise surprising. It is now known that the bubbles which Bonnet took to be air are nearly pure oxygen which escapes as a by-product of assimilation. But from water which has been boiled, all the carbonic acid essential to assimilation has been expelled. 824 ASSIMILATION. process might also restore the air that had been injured by the burning of caudles. "Accordingly on the 17th of August, 1771, 1 put a sprig of mint into a quantity of air, in which a wax candle had burned out, and found that, on the 27th of the same mouth, another candle burned perfectly well in it. This experiment I repeated, without the least variation in the event, not less than eight or ten times in the remainder of the summer. 1 " Several times I divided the quantity of air in which the candle had burned out, into two parts, and putting the plant into one of them, left the other in the same exposure, contained also in a glass vessel immersed in water, but without any plant; and never failed to find that a caudle would burn in the former, but not in the latter. I gen- erally found that five or six days were sufficient to restore this air, when the plant was in its vigour; whereas I have kept this kind of air in glass vessels immersed in water many months without being able to perceive that the least alteration had been made in it." 853. Ingenhousz in 1779 showed that light is necessarj' to assimilation. He proved experimentally that the purification of air does not go on in darkness, but that light is essential. His statements are here given : — " Plants not only have a faculty to correct bad air in six or ten days, by growing in it, as the experiments of Dr. Priestley indicate, but they perform this important office in a complete manner in a few hours. This wonderful operation is by no means owing to the vegetation of the plant, but to the influence of the light of the sun upon the plant. . . . This operation of plants diminishes towards the close of the day, and ceases entirely at sunset, except in a few plants which continue this duty somewhat longer than others. This office is not performed by the whole plant, but only by the leaves and the green stalks that support them. Acrid, ill-scented, and even the most poisonous plants perform this office in common with the mildest and the most salutary." ^ 1 Priestley thought that this effect upon the air is due to the growth of the plant, an idea which will be shown in Chapter XII. to be wholly erroneous. On pages 50 and 52 of the volume quoted above are the following statements : " One might have imagined that since common air is necessary to vegetable, as well as to animal life, both plants and animals had affected it in the same man- ner ; and I own 1 had that expectation when I first put a sprig of mint into a glass jar standing inverted in a vessel of water : but when it had continued growing there for some months 1 found that the air would neither extinguish a candle nor was it at all inconvenient to a mouse which I put into it. . . . This restoration of the air, I found, depended upon the vegetating state of the plant ; for though I kejit a great number of the fresh leaves of mint in a small quan- tity of air in which candles had burned out, and changed them frequently, for a long space of time, I could perceive no melioration in the state of the air." 2 Experiments upon Vegetables, discovering their great Power of purifying the Common Air in the Sun-shine, 1779, p. xxxiii. APPEOPRIATION OF NITEOGEIf. 325 854. Senebier ^ first demonstrated that plants obtain all their carbon from carbonic acid gas. 855. That definite quantitative relations exist between the amounts of carbonic acid decomposed, carbon retained, and oxy- gen evolved by the plant, was first pointed out by Saussure.^ APPROPRTATION" OF NITROGEN. 856. It has been shown that all land and man3' water plants contain a variable amount of air in their tissues, chiefly in the intercellular spaces and older modified cells (tracheids, trachese, etc.). When there is an active interchange of gases by any plant, a portion of the nitrogen contained in its included air is very likely to be eliminated. A trace of nitrogen is so generally found witii the oxygen evolved during assimilation proper, that this has been regarded by some as a constant accompaniment of the assimilative process. 857. Amount of nitrogen in the plant. Besides the free nitro- gen which constitutes a part of the included air of the plant, there is a certain amount of combined nitrogen alwaj's present in active cells as an essential component of tlieir living matter. The protoplasmic matters in plants contain about 15 per cent of nitrogen in combination. For all practical purposes they ma\'' be regarded as having chemically a common albuminous^ basis (roughly comparable to the white of egg), with which (as has 1 Memoires Physico-chymiijues, 1782. Many of Senehier's observations are almost identical with those of Ingen- honsz (as given in his "Nutrition of Plants"), and it has been thought by some that the priority of the above discovery belongs rightfully to the latter. It is to be remembered that at the date at which both of these experimenters were working, chemists were just beginning to acquire, through the studies of Lavoisier, clear notions in regard to the important part which oxygen plays, and that in the early part of this transition period an obscure nomen- clature renders it difficult to apportion to each of these observers his proper share of credit. 2 Recherehes ohimiques sur la vegetation, 1804. Some of the relations of light to the process of decomposition of carbonic acid by green parts of plants were first indicated by Daubeny, and further ex- amined by Draper. The subsequent history of assimilation, to which Sachs, Pfeffer, Engelniann, and many others have contributed, has been referred to in the text r-nd in citations in the notes. ^ Attention may again be called to the vaiious expressions employed to designate the compounds in the plant which resemble albumin, and which have been collectively termed albuminoids. Authors have made a distinction 326 ASSIMILATION. been seen on page 197) there is always intermingled an incon- stant aniouut of carbohydrates, or proper food-materials, etc. At different stages in the life of a cell its protoplasmic matters ma}' pass through considerable changes of form and structure, as indicated in an examination of a i-ipening seed ; but under all these varying conditions nitrogen in combination is never absent from the living substance of the plant. 858. For the formation of new protoplasmic matters in the plant, supplies of nitrogen in an available form must be fur- nished ; for healthful growth, these supplies must be adequate in amount. 859. Dissolved albuminous matters of various kinds are met with in the sap of some cells. Tliis in manj- cases appears to be, as will be shown later, a form in which their transport from one part of the plant to another is secured. A small number of these albuminous substances have been shown to be ferments, which plaj' a verj- impoitant part in the nutrition of the plant. 860. Although by far the greater part of the combined nitro- gen of the plant exists in one or more of the combinations men- tioned in Chapter XI., there is often to be detected a small and variable amount as a nitrate ' (generally potassic) , and even as a salt of ammonia. between certain groups of these bodies as tliey are represented in tlie animal kingdom, dividing them into (1) albuminoiia matters and (2) their derivatives or albuminoids (see Gorup-Besanez, Lehrbuch der Chemie, iii., 1874, p. 115). Although the latter term, without the re.striction here noted, is in commou use in vegetable physiology to designate these bodies, an objection can justly be urged against its employment, on account of the more common use iu botany of the word alhimen with an entirely different signification (see Volume I. p. 14). In 1838 Mulder published the theory that all these bodies are practically derivatives from one substance, termed by him proteine (from Trpwreiim, to be first) ; but it was soon shown that this theory was erroneous, and it has been generally abandoned. The term introduced by Mulder to designate the hypo- thetical compound common to all these bodies has, however, been since em- ployed to conveniently denote the whole class. In using the convenient term protein bodies, or proteids, to designate the members of this group, it must not be understood that the abandoned theory of Mulder is taken into account at all. ' For the detection of nitrates the following test may be employed : To a drop of tlie sap under examiniition add a drop of a solution of brucine, mix, and tlien add a few drops of concentrated sulphuric acid, when, if a nitrate is present, a red color will appear. Sprengel's reaction may also be used : One part of phenol is dissolved in four parts of concentrated sulphuric acid, and two parts of water are added. If a drop of this solution is added to a solid nitiate, a reddish color is produced. On adding strong ammouia, the color turns green and afterwards yellow. SOURCES OF NITROGEN FOR THE PLANT. S27 861. There can be found in a large number of plants a small amount of certain matters termed alkaloids, which contain a defi- nite percentage of nitrogen. Snch are morphia in the poppy, quinia in Peruvian bark, caffeine in coffee, etc. (see 961). 862. In most analyses tlie combined nitrogen of the plant is usually' rendered as "albuminoid." The percentages in a few cases are here given : ' — Red clover, full blossom . 3.7 Siigiir beets 8 to 1.0 CaiTot root ... 1.5 Carrot leaves 3.2 Cabbage .... 1.5 ■Winter wheat 13.0 Beans (field) 23.5 Apples . .22 to .52 Of these amounts about 16 per cent may be roughly estimated as the content of nitrogen. Therefore in such a case as the carrot root above mentioned, the total amount of nitrogen is really very small (0.24 per cent) ; but the presence of this small percentage is absolutely essential to the life as well as to the health of the plant. 863. Reserving for a later chapter all consideration of the numerous chemical transformations which nitrogenous matters may undergo in the plant, it is necessary to ask now, (1) whence can the plant obtain adequate supplies of available nitrogen, and (2) how can the plant appropriate, or, to use an equivalent term, assimilate them. 864. Sources of nitrogen for tlie plant. It must first be shown whence nitrogen is not sui)plied. Tlie free nitrogen of the at- mosphere does not appear to be directly- available for plants. Although most of the higher plants possess an aerating sj-stem (see p. 300), through wliich atmospheric air can easily enter and traverse the plant and be brought into contact witli the tissues, the nitrogen which forms so large a part of the atmosphere is not utilized. This is the interpretation of experiments in cul- ture in which e\ery kind of combined nitrogen is carefully ex- cluded from the plants while they have, at the same time the free nitrogen of the atmosphere in an unlimited supply. 865. The earliest^ systematic investigations relative to the 1 For other cases the student should consult the tables in the Appendix to Johnson's " How Crops Grow," ]868, pp. 385-392. 2 The following citations refer to earlier observations, none of which, how- ever, can be considered as having fixed any important points relative to the use of atmosi)herio nitrogen by plants : — 328 ASSIMILATION. above subject were made by Boussingault iu 1837/ who em- ployed the following method : In calcined soil, supplied with dis- tilled water, and having free access of air, clover was cultivated for two and for three months, and at the end of that time it was found that there was a very slight gain in nitrogen over the amount which had been present in the seed sown. In two parallel experiments with wheat no gain was observed. One j-ear later, peas, clover, and oats were experimented on ; botli tlie peas and clover gained a little nitrogen, but there was no gain whatever in the case of the oats. Boussinganlt's conclu- sions from this series have l)een stated as follows : Under several conditions certain plants seemed adapted to talie up the nitrogen in the atmosphere, but it is still a question under what circum- stances and in what state the nitrogen is fixed in the plants. 866. It was not, however, until 1851 that the subject received anj- further attention from Boussingault. In tliat and the two subsequent years his experiments were conducted with certain precautions, by wliich the plants were confined in limited vol- umes of air ; and in no case was an unequivocal gain in nitrogen to be detected. In 1854 he placed plants in a suitable recep- tacle where they could be supplied with a current of air washed to free it from all traces of combined nitrogen. The atmosphere within the receptacle was fiu'nished with from two to tliree per cent of carbonic acid. In all of the experiments, part of which were upon leguminous plants, there was a slight loss of nitrogen. 867. During the progress of the experiments now alluded to others were conducted in the following manner : Plants were placed iu a case from which nearly all dust could be excluded, but which would allow of a free circulation of the external air ; and under these circnmstances tliere was the verj' slight gain in nitrogen equal to about one twelfth of that contained in the seed sown. Boussingault attributed this almost inappreciable gain Priestley : Expei-iments and Observations on Different Kinds of Airs, ill., 1772. Sanssure ; Recherclies chimiques sur la vegetation, 1804, p. 205. In this will be found a short account of the results of the previous observers and also of Saussure's own conclusions, which are, — that plants do not appropriate any appreciable amount of nitrogen furnished to them as it exists in the atmosphere in the free state. ' For a short but excellent abstract in English of Boussinganlt's researches, referred to in the text, the student may consult Philosophical Transactions of the Royal Society for 1861, p. 447. The original communications are in Annales de Chimie et de Physit^ue, ser. 2, tomes Ixvii. and Ixix., 1838. ville's experiments. 329 to the awmonia in the atmosphere, and also to organic matters in small amount which rna}- have entered the case in the form of very fine dust ; but, taking into consideration all the conditions of the experiment, he was not inclined to the belief that anj- nitrogen had been received by the plants from the free nitrogen of the atmosphere. 868. In 1855 and 1858 the same chemist experimented npon certain plants which were supplied with a known amount of com- bined nitrogen in some available form. The results of his ex- periments have been formulated as follows : (1) There was no appropriation of free nitrogen ; (2) There was a slight loss of the nitrogen which had been supplied to the plant ; (3) The amount of assimilation of carbon bore a close relation to the amount of nitrogen taken up b}- the plant. 869. From 1849 to 1854 Georges Ville, of Paris, conducted experiments which were interpreted as showing that plants can take from the nitrogen of the atmosphere a certain part of that which they require. In the autumn of 1854 he carried on a series of researches at the Jardin des Plantes, under tlie super- vision of a committee appointed bj- the French Academ}'. To- wards the close of the work an element of error crept into it which could not then be eliminated ; but as to the result of the investigation the committee reported,^ — that the experi- ment made at the Museum d'Histoire Naturelle by M. Ville is consistent with the conclusions which he has drawn from his previous labors. 870. In 1861 Lawes, Gilbert, and Pugh,'^ of England, pub- ■^ The report by Chevreul will be fo\ind in Comptes Kendus, xli. p. 757. Eesults so directly in conflict as those of the two experimenters referred to in the text led others to investigate this subject, and in 1857-1859 an exhaustive series of investigations was carried on at Eotharasted, England, by Lawes, Gilbert, and Pugh. M&ne, in 1851, concluded from his experiments that plants do not appro- priate the free nitrogen of the air. Roy interpreted the results of his own experiments as showing that free nitrogen dissolved in water can be taken up by plants. Luea (1856) suggested that the air surrounding plants maybe ozonized, and thus the nitrogen in it converted into nitric acid and made available for the plants. Harting (1855) concluded that the free nitrogen of the air is not proved to serve directly for the nutrition of the plant. 2 Philosophical Transactions, 1861, p. 431. For an excellent description and drawing of the complicated apjiaratus employed in this capital investiga- tion the student may consult Johnson's "How Crops Feed," p. 30. 330 ASSIMILATION. lished the results of a series of experiments upon tlie suiiject of tlie appropriation of nitrogen bj- plants. These experiments were designed to settle the disputed question. Every conceivable pre- caution was taken to avoid any error, and the plants were grown under conditions as little unlike their ordinary surroundings as possible. Under these conditions to insure healthy growth, they were deprived of all access to nitrogen except as it existed in the free state in the atmosphere or dissolved in the water sup- plied to them. It was found that no plants appeared to make use of the free nitrogen of the atmosphere or of the nitrogen dissolved in water supplied to their roots. But in certain cases, especially of leguminous plants cultivated in the open air, there is an apparent gain in the amount of nitrogenous products in the plant over and above that which is directly attributable to the combined nitrogen furnished to it.' 1 The following extracts from the papei' by Lawes, Gilbert, and Pugh will convey a. clear idea of the cautious manner in which their important results are reported : — "The results obtained with Graminacese in 1858 . . . point without excep- tion to the fact that under the circumstances of growth to which the plants were subjected, no assimilation of free nitrogen has taken place. The regular pro- cess of cull-formation has gone on ; carbonic acid has been decomposed, and carbon and the elements of water have been transformed into cellulose ; the plants have drawn the nitrogenous compounds from the older cells to perfonn the mysterious office of the formation of new cells ; those parts have been de- veloped wliich required the smallest amount of nitrogen, and all the .stages of growth have been passed through to the forniation of glumes, pales, and awns for the seed. In fact, the plants have performed all the functions that it is possitjle for a plant to perform when deprived of a sufficient supply of com- bined nitrogen. They have gone on thus increasing their organic constituents with one constant amount of combined nitrogen until the percentage of that element in the vegetable matter is far below the ordinary amount of it, — that is, until the composition indicates that further development had ceased for want of a supply of available nitrogen. Throughout all these phases, water saturated with free nitrogen has been passing through the jilant ; nitrogen dis- solved in the finid of the cells has constantly been in the most intimate contact with the contents of the cells and with the cell-walls " (p. 523). Of leguminous plants the investigators say, "In those cases in which we have succeeded in getting leguminous plants to gi-ow pretty healthily for a considerable length of time, the results, so far as they go, confirm those ob- tained with Graminacese, not showing in their case, any more than with the latter, an assimilation of fi'ce nitrogen " (p. 526). Further, they say, " From the results of various investigations, as well as from other considerations, we think it may be concluded that under the cir- cumstances of our experiments, on the question of the assimilation of free nitrogen by plants, there would not be any supply to them of an unaccounted quantity of combined nitrogen due either to the formation of oxygen com- NITROGEN COMPOUNDS IN KAIN- WATER. 331 871. Nitrogen compounds in the atmosphere. The atmosphere contains minute amounts' of combined nitrogen in the form of ammonia, nitric acid, and nitrous acid. The ammonia is be- lieved to exist (except where from local causes there is an escape of free ammonia from some source) combined with either carbonic or nitric acid. 872. Nitrog'en in rain-water. The nitrogen compounds are more or less perfectly removable from the air bj' rain, and in solution can be made available to plants through the soil. It is now necessary to examine the results of analyses of rain- water in order to ascertain the amount of nitrogen contained in it. The following data are taken from the careful experiments at Rothamsted, under the direction of Lawes, Gilbert, and War- ington. The nitrogen existing as nitric acid and ammonia in the rainfall of one j-ear is not far from 3.3 pounds per acre. The proportion of this calculated as ammonia is between 2.3 and 2.6 pounds per acre, the residue being given as nitric acid. Be- sides the foregoing substances, there is also a small amount of nitrogenous oi'ganic matter in the air which appears in the analj'ses of rain-water, and amounts, according to Frankland, to .19 parts per million parts of water. Taking a somewhat lower estimate than this, Lawes, Gilbert, and Warington give the quantity of nitrogen in the form of organic matter annually pounds of it under the influence of ozone, or to that of ammonia under the influence of nascent hydrogen " (p. 540). But, as shown by Lawes, Gilbert, and Pugh, as well as by many other ex- perimenters, leguminous crops appropriate from some source considerably more nitrogen than do grasses; for instance, under apparently similar circumstances of supply of combined nitrogen. For an excellent treatment of the whole matter of appropriation of nitrogen, the student should consultmemoirsbjAtwater, "On the Acquisition of Atmos- pheric Nitrogen by Plants" (American Cliem. Journ., vol. vi., 1885, no. 6). 1 The following figures serve simply to indicate the wide range in results obtained by different observers who have investigated the amount of ammonia in the atmosphere. The data are from Proceedings of Am. As.soc. for Ad- vancement of Science, 1857, p. 152. Observer Sf t* AmonTit of ammoni.i in one million '°"" cubic meters atmosphere. Fresenius . Wiesbaden (during the day) .... 127.27 gr. " . " (at night) 219.47 " Kemp . . Ireland 4423.00 " Ville . . Paris 27.39 " Horsford . Boston (in July) 640.70 " 832 ASSIMILATION. contributed in the rain as 1.08 pounds per acre. "We may probabl}- take 4.5 pounds per acre as tlie best estimate we can at present give of tlie total combined nitrogen annuall}- su[)plied in the Rothamsted rainfall. This is only about two thirds as much as the earlier results indicated as due to ammonia and nitric acid alone. ... In addition to the combined nitrogen carried down from the atmosphere in rain, we have to consider any gain to the soil or to tlie croi) b3' direct absorption of am- monia or nitric acid from the air. As far as any gain from the atmosphere to tlie plant itself is concerned, there is very little direct experimental evidence on the point, but such as is avail- able would lead to the conclusion that its amount is practically immaterial. As to the amount of gain by absorption by the soil, there is unfortunately no direct or satisfactorj- evidence at command. P>om such evidence as does exist, we are disposed to conclude that with some soils the amount will probably be greater and with others less than that supplied by the rainfall." ' 873. Direct absorption of ammonia by leaves. Under certain circumstances ammonia can be absorbed directly by leaves. This will be further adverted to under "Appropriation of Organic Matters." 874. How the nitrogen compounds of the atmosphere are formed. It is a familiar fact that under certain circumstances the free nitro- gen of the atmosphere can be made to unite with ox^-gen for the production of nitric acid ; for instance, by the passage of a spark of electricity through a confined atmosphere a small amount of combined nitric acid raaj- be formed. The bearing of this fact upon the existence of nitrogen compounds in the atmosphere is very obvious. vSchlcesing,'' in an interesting study of the nitro- gen compounds of the air and soil, attributes to the atmosphere a verj' important ofHce in forming and distributing nitrogen com- pounds. According to him, the nitric acid contained in rain- waters on escaping from the soil, where it is onl}- lightly held, finds its waj- to the sea, where under various agencies (notably that of vegetable organisms of the lowest grade) it becomes, sooner or later, changed into ammonia. This readily escapes into the air, and is carried in the atmospheric currents to all parts of the world, becoming therebj- available to land plants. ^ Journal Royal Agricultural Society, vol. six., part 2, 1883. 2 Oomptes Renilus, tome Ixxxi., 1875. The same idea has been more or less treated by others. AVAILABLE NITROGEN IN THE SOIL. 333 875. Available nitrogen in the soil. "When animal matters ricli in nitrogen undergo rapid putrefaction,^ they give rise to numer- ous compounds, prominent among which are tliose of ammonia. Under certain conditions, notably tlie presence (1) of free 0x3'- gen in large amount, or (2) of an alkali, or an alkaline carbonate, such animal matters are also slowly broken up, and nitrates are formed. The process b3" which various compounds of nitrogen are converted into nitrates is termed nitrification. '-^ 876. Vegetable matters which contain nitrogenous substance in the usual amount may likewise undergo decomposition ; but owing to the presence in such matters of a large proportion of carbohydrates, for instance tlie cellulose of the cell-walls, the process of decomposition is more complex than in animal matters and its products more diverse. Some of the products are proba- bly- identical with those formed from the decomposition of albu- minous matters of animal origin ; namely, ammonia,^ or ammonia compounds, and nitrates ; but the larger number of them are compounds which are nearl}' or quite insoluble and have been thought to be inert.* But experiments have shown that under certain conditions these less available compounds of nitrogen 1 For a discussion of the various phases and conditions of decomposition the student is refei-red to the tliird volume of this series, in which the different forms of fcrmpntation and putrefaction are to be treated. It is enough now to note that these processes are essentially due to tlie presence and activity of minute organisms, — the lowest fungi. '■' The student will find in Johnson's "How Crops Feed," p. 289, an ex- cellent account of this most important topic. He is referred also to Bonssin- gault's " Agronomie," 1860, and various articles in Versuchs-Stationen. * The following data indicate the amounts of nitrogen in certain soils, as determined by Boussingault (Agronomie, ii., 1861, pp. 14, 18). The reduc- tions to pounds per acre are from Johnson's "How Crops Feed," p. 276. Source of the Soil. Ammonia. Nitrogen in organic conibinatiori. per cent. lbs per acre. per cent. lbs. per acre. Liebfrauenberg (light garden soil) Beclielbronn (wlieat-fleld clay) Argentan (ricli pasture) Eio Cupari, S. A. (rich leaf-mould) 0.0020 0.0009 0.0060 0525 100 45 300 2,875 .259 .139 .513 .685 12,970 6,985 25,650 31,250 * Experiments by Boussingault (Agronomie, i. 1860) can hardly be in- terpreted in any other way. One reason for his results has been sought in the fact that he employed only very small amounts of vegetable matter in his ad- mixtures of soil ; but all of his expeiiments are regarded as models of accui-acy 334 ASSIMILATION. in the soil can be turned to a very important account bj- the plant. 877. Nitrogen used by wild and cultivated plants. From the sources described, wild plants obtain a sufBeient supply of available nitrogen. In some localities, notabl}- in portions of the tropics and along the rich alluvial deposits of rivers, the stores of available nitrogen are so abundant that all vegetation flourishes with great vigor, and even cultivated plants, which ap- pear to be more exacting than wild plants in their demands for nitrogen, can obtain an adequate suppl3-. Further, it has been abundantlj- shown bj- the long-continued expei-iments at Eotham- sted, that the same soil, unenriched bj- additions of manures, can yield even after twentj-five jears ei5ough nitrogen for the needs of fair or moderate crops. 878. In the ordinarj- cultivation of plants it is profitable to augment in some waj" the supply of nitrogen in most soils. Under some circumstances this augmentation can be accom- plished to a certain extent by mere tillage or bj- the exposure of fresh portions of soil to the action of the atmosphere. But it is usually effected bj- the emploj'ment of natural or artificial manures. The former consist of the excrementitious matters of animals or of the waste products from plants. These ex- crementitious matters represent a large part of what the ani- mals have consumed, and must have come either directlj' or indirectlj- from the vegetable kingdom ; hence they only re- store to the soil that which plants had at some time removed therefrom. In the preparation of artificial fertilizers an effort is made to. provide for the plant the mineral and nitrogenous matters which it requires. A large proportion of these fertilizers are composed throughout, and can leave no doubt that, under the conditions of his trials, there was pvKCtically no iitilization of the soil nitrogen by the plants. On the other hand, experiments by Wolif (Chemisch.-Phavmaceut. Central- Bktt, 1852, p. 657), Johnson (Peat and its Uses, 1S66, p. 79), and Storer show that under certain conditions the plant can avail itself of the nitrogen organically combined in the soil. The works of the above authors, which are only a few of those bearing on this important matter, will place the student in possession of the methods of experimenting. Storer's interesting comniut:ication in the Bulletin of the Bussey Institu- tion (vol. i., 1874, p. 252), " On the Importance as Plant-food of the Nitrogen in Vegetable Mould," gives not only an account of his experiments but also a forcible presentation of the principal arguments in favor of the belief that the "soil-nitrogen " (that is, the nitrogen in vegetable mould) is by no means inert. SYNTHESIS OF ALBUMINOUS MATTERS 335 of a certain amount of available calcic phosphate together with. a salt of potassa and some available nitrogenous matter.^ It has been shown (p. 248) tliat some plants require more of one kind of food than others ; and hence the attempt has been often made to prepare exactly the special fertilizer which a given crop ma^' require. 879. Nitric acid and the nitrates. Experiments with water- culture have shown that plants can derive all the combined nitro- gen needed for their growth from nitric acid and the nitrates. But it has also been clearly shown that there are striking differ- ences in the capacitj^ which plants possess for appropriating nitrogen from these compounds. Even in the common agricul- tural plants there are some differences in this respect. 880. A large number of nitrogen compounds, such as as- paragin, urea, albumin, etc., have been employed in experiments upon plants, but most of the results possess little interest. It may be said, in general, that the so-called alkaloids (which con- tain nitrogen) cannot be utilized even by the very plants from which they were made.^ 881. Synthesis of albuininoas matters in the plant. A distinc- tion is made between the newl}- formed or first-formed albumi- nous substances in the plant and those which have undergone chemical changes in the organism, as for instance the changes in germination. Two views have been held respecting the place where the formation of the new pi'otein matters occurs in the 1 The following analyses, taken from the Kepovt of the Connecticut Agri- cultural Experiment Station for 1883, indicate tlie composition of a few such substances : — oi ^ Cm serve sur des feuilles de rican Naturalist, vii. relative to feeding of the glands of Drosera" eizbarkeit def Blatter von Aldrovanda" (Ver- 1 die Prov. Brandenbiwg). ^_'"enus's Fly-Trap" (IJatuve, x. p. lOS). Plants " (Kation, xviii. pp. 216, 232). tunicated by Darwin, and a short resumJ (British Association Reports, 1873. Stein: " Ueber dij handhmgen des bot. Vere 1874. Burdon Sander 1874. Asa Gray : An account of the observ of the subject up to that rWa 1874. JIe'l"'''".'^L^^gj^?clies on the pitchers of Sarracenia variokris, and the way iV)^;*(!WMiS!re caiig)it in them " (Nature, x. p. 253). 1874. HoaJSTT: Address before (lie Ui-itish A.ssociation for the Advance- ment of Science, puWished in full i„ t),e Repo,.t for 1874. This address gives „„ .vcellent nccoiint of the diffestiv.. «„ , j-ui^. = ^fllly Ni^penthes. powers of vaiions carnivorous plants, ^^'^la'rS- J- '^- Clai-k : "On the ab leavesof some insectivorous plants." Thif"'"" °^ nutrient material hy ths ments on the absorptive capacity of Drosera"!,"; r?''"'' *''" '-"suits of experi- the aid of the spectroscope. "nd Pi„g„i,„,^ couduoted with EPIPHYTES. 353 which they incorporate come to them in the forui of dust, which subsequently dissolves and is absorbed. The sources of their carbon and nitrogen have already been sufficiently explained. 1875. Darwin: " Insectivorous Plants." A work of 462 pages, more than half of wliich is devoted to Drosera. At tlie close of his exhaustive discussion of his experiments upon this plant, Mr. Darwin says : " I have now given a brief recapitulation of the chief points observed by me with respect to the structure, movements, constitution, and habits of Drosera rotundifolia ; and we see how little has been made out in comparison with what remains unexplained and unknown." 1875. Reess and Will . " Einige Bemerkungen iiber fleischessende Pflan- zen " (Botanische Zeitung, p. 713). 1875. Caiiby : " Uarlingtonia Californica" (Proceedings American Asso- ciation, p. 64). 1875. Cohn : " Ueber die Function der Blasen von Aldrovanda und Utricularia" (Beitrage zur Biologic der Pflanzen). 1875-6. Morren published in the Bulletin of the Royal Academy of Bel- gium the results of experiments wdiich may be interpreted as showing that the plants derive no benefit from their insects. 1875-6. Gorup-Besanez and Will published some observations regarding a pepton-forming ferment in plants, in Sitzungsberiuhte der physikalisch- mediciuisches Societat zu Erlangen. 1876. Francis Darwin : " The process of aggregation in the tentacles of Drosera rotundifolia " (Quarterly Journal of Microscopical Science, xvi. p. 309). 1876. Sydney H. Vines: "On the digestive ferment of Nepenthes" (Journal of Anatomy and Physiology, xi. p. 124). 1876. Faivre : " Recherches sur la structure, le mode de formation, et quelques points relatifs aux fonctions des urnes ehez le Nepenthes" (Comptes Rendu.?, Ixxxiii. p. 1155). 1876. Munk : " Die elektrischen und Bewegungsercheinungen am Blatter der Dionoja mu.scipula." 1877. Cramer : " Ueber die insectenfrcssenden Pflanzen." 1877. Aschman : " Les plantes insectivores," Luxemburg. 1877. Pfeffer : " Ueber fleischfressende PHanzen und iiber die Ernahrung durch Aufnahme organischer Stoffe uberhaupt " (Landwirthsch. Jahrb. v. Nathusius, p. 969). An excellent account of the mechanism and absorptive properties of carnivorous plants. 1879. Drude : " Die insektenfressenden Pflanzen." A full and interesting examination of the subject in Schenk's Handbuch der Botanik. 1882. Schimper : " Notizen iiber inseotenfressenden Pflanzen " ( Botanische Zeitung, xl. p. 225). Several jeux d' esprit have been published, in which the remarkable proper- ties of a few humble plants have been exaggerated into accounts of man- catching and man-eating trees of large size. •23 CHAPTER XI. CHANGES OF ORGANIC MATTER IN THE PLANT. 922. It has now been shown that under the influence of sun- light green plants produce organic matter out of inorganic materials. This organic matter is conveyed to points where it is to be used, or to tcmporarj- reservoirs where it is stored for future use. It undergoes manifold changes in the plant, until in the ordinary course of nature it is resolved at last into the verj- materials from which it originallj' came ; namely, carbonic acid and water. 923. Bnt as the organic matter of the plant represents in its construction a definite amount of energy of motion derived from solar radiance transformed into tlie enei'gy of position, in its apparent destruction is involved the reconversion of this energy of position into energy of motion. Between the first and last terms of these constructive and destructive processes very differ- ent periods of time may elapse in different cases, according to the changes which the organic matter undergoes. 924. That portion of the organic matter which is built into the fabric of the plant in the form of cellulose more or less modi- fled is not often broken down into its original components while the organism is living; but, by decay and bj- combustion, even this relatively permanent substance is decomposed, and its ele- ments are finally given back to the air and soil. A certain por- tion of the organic matter, however, undergoes speedy and striking changes, and all of these are now to be examined from another point of view. TRANSMUTATIOX, OR METASTASIS. 925. The phj-siological expression for the substance formed by chlorophyll in the sunlight is food. This substance is util- ized by the organism in many waj-s ; but of these only the fol- lowing need now be noticed: (I) for the supply of energy for movements and other work ; (2) for the repair of waste ; (3) for TRANSMUTATION. 355 the construction of new parts. The changes hy which these processes are performed take place in the protoplasm which recei\es and in some way disposes of the newl}- formed food. 926. Supply of energy for work. This is furnished by the process of oxidation. It will be remembered that the inorganic materials concerned in the production of the food of the plant, namely, carbonic acid and water, are highly oxidized compounds. By assimilation a part of the oxygen is liberated, and tiie or- ganic matter formed is some carbohydrate capable of oxidation. The reception of oxygen, the oxidation of the oxidizable matter, and the release of the products of oxidation by the plant are collective!}' termed resjnration. 927. Repair of waste. The living matter of plants, like the living matter of animals, being the seat of all the activities manifested by the organism, is constantly undergoing waste and demanding repair. The repair of waste is proper nutri- tion. 928. The construction of new parts. It has been shown (Chap- ter X.) that b}' the appropriation of nitrogen bj- the plant proteids are formed, and these are in great part utilized in the produc- tion of new protoplasmic matter. So far as the latter is an actual increase in snbstance, and not a mere repair of waste, it represents ti'ue growth. The growth of any root, stem, or leaf consists in the formation of new cells and the increase of these in size. In this process the production of new cell- wall is of course the most conspicuous phenomenon. The per- manent increase in size of the cell-walls of a plant disposes of a large part of the organic matter wiiich is prepared by assimila- tion, and this phase of growth is apt to divert attention from that which really underlies it ; nameh', growth of the protoplasm itself. 929. For convenience, the various chemical elianges which go on within the plant may be divided into two groups ; namely, transmutation and complete oxidation. In tlie former, the or- ganic matter elianges its properties in some way, either bj' the addition of new materials or by the reconstruction of its existing molecules, but, notwithstanding the change, still re- mains organic matter ; while in the latter it is resolved into its original inorganic components. The change of one kind of food into another, the transformation of starch into cellulose, and the formation of proteids, are good examples of transmutation : the consumption of food for the release of energy, an example of complete oxidation. The first of these groups of changes cor- 356 CHANGES OF ORGANIC MATTER IN THE PLANT. responds nearly to what has been called metastasis,^ the second to respiration. But it must be remembered that the distinction between the two groups is not absolute. 930. The contrast between assimilation and respiration is very marked : one is substantially the opposite of the other. The following tabular view displays the essential differences between them. Assimilation proper Respiration Takes place only in cells containing Takes place in all active cells. chlorophyll. Eequires light. Can proceed in darkness. Carbonic acid absorbe.d,oxygen set free. O-xygen absorbed, carbonic acid set free. Carbohydrates formed. Carbohydrates consumed. Energy of motion becomes energy of Energy of position becomes energy of position. motion. The plant gains in dry-weight. The plant loses dry-weight. Some of the changes which are grouped under transmutation, or metastasis, present almost as great a contrast to assimilation proper as that shown in the above table. 931. Course of transfer of assimilated matters. In the present state of knowledge it is impossible to trace all the chemical changes which assimilated matters undergo in the plant, or even the course which such matters take ; onl}- a few of the more ob- vious modifications have been investigated. Before proceeding to describe the important forms of organic substance in the plant, the following general considerations should be presented. The carbohydrates are believed to be transferred fiom one part to another, in the higher plants, through the thin-walled parenchyma. The reaction of these cells is almost uniformly' acid. The transfer takes place only when the carbohydrates are in solution. The albuminoids are probabh' carried chief!}' by means of the soft bast of the fibro-vascular bundles ; the cells of this bast have a slightly alkaline reaction. But that these are not the only paths of transfer, appears from the frequent occurrence of minute starch-grains in the sieve- cells, and, on the other hand, of dissolved albuminoids in paren- chyma cells. 1 The German word Stoffwechsel is usually translated metastasis, — a word long known in medicine with a totally different siguifiration from that above. Schwann's term, metabolism, much used in human physiology, expresses its idea better, but for some reasons the term transmutation appears preferable. CARBOHYDRATES. 35'< The direction of transfer of the above compounrls is towards the point of use, or of storing ; there is never anj' approach to a true circulation througliout the plant, corresponding, as was for- merly taught, to the circulation in animals. 932. Classification of the principal organic prodacts. For the present purpose these may be conveniently grouped into (1) those which are free from nitrogen, and (2) those which con- tain nitrogen. Some have been already treated of in earlier pages of this volume ; of the rest, little more than a mere enumeration can here be given. 933. Products free from nitrogen. I. Carbohydrates. In general these are solid bodies manj' of which are soluble in water. They are conveniently divided into the cellulose group, having the empirical formula, Cul-I,„Oj, and the sugars, — grape-sugar, fruit- sugar, and cane-sugar. The cellulose group comprises the following isomeric bodies : — 934. Cellulose. This substance (see page 31) is regarded as a product of the direct transformation of starch or its equivalent. When once separated from the protoplasm as cell-wall, cellulose is not again dissolved save in the exceptional cases of germi- nation where it serves as a food. Sachs has shown that in the germination of the date, the pitted tliickening masses of the cell-walls of the endosperm are dissolved and utihzed by the embryo. 935. Starch (see pages 47-50). The occurrence of this sub- stance in the chlorophyll granules under certain conditions has already been described. Its occurrence in reservoirs of food, and the relation of this to the starch-generators, have been dis- cussed in 174. The following table gi^'es some idea of the amount of starch found in the ordinary commercial sources : — Source. Amount of starcli present. Grains of wheat 64 per cent. Grains of corn 65 " " Grains of rice 76 " << Potato tubers 15-29 " " When starch is to be transferred from the places where it is held in reserve to the points where it is to be consumed, it is converted into a form of sugar by some one or more of the unorganized ferments occurring in plants. Although the sugar thus formed passes at once into soliition, it is a curious fact 368 CHANGES OF OEGANIC MATTER IN THE PLANT. that at certain points during its course this solution may tran- siently exhibit more or less fine-grained starch. The tendency of starch to form in this way is "\-ery remarkable in the process of germination. 930. Inulin. This substance is dissolved in cell-sap (see 183), but is easily separated from it upon immersion of the plant sec- tions in alcohol. It replaces starch in the roots and root-like stems of many perennials belonging to the following orders, — Liguliflorse (Compositae), Campanulaceae, and Lobeliaceee. 937. Ziicheiiin is abundant in certain lichens, amounting in Cetraria Islandica to more than 40 per cent. 938. Dextrin. Under tliis name are comprised at least two sulistances^ wliich are produced during the transformation of starch into sugar. Dextrin occurs in the .young sprouts of potato, in most bulbs as they are starting, and in the spring sap of many trees. 939. The Gums. These are amorphous substances which either dissolve in water or merely swell in it to form soft masses or thick viscous liquids. An example is Arabin (2C„H„,0j-|-H^0), the chief constituent of Gum Arabic, obtained from a species of Acacia. It is found associated with arabio acid, which is supposed to be combined with calcium. It occurs in cheriy-tree gum, and to a slight amount in the gum of manj- other plants. Of those gums which do not trul^- dissolve, must be mentioned Cerasin, abounding in cherry-tree gum ; Bassorin, or the essen- tial constituent of gum-tragacanth ; and Vegetable Mucus, which occurs in the seed-coats of flax, the pseudo-bulbs of many or- chids, and the leaves of some mallows. 940. The I'ectin Bodies. According to Freinj- these are derivatives from pectose, a neutral insoluble substance found in unripe fruits and in some flesli^' roots. Pectose undergoes various changes not yet understood. Vegetable jelly, obtained by boiling subacid fruits, is a familiar example of one of the products of such changes. 941. The sugar group. The more common members of this group are grape-sugar, fruit-sugar, and cane-sugar. The em- pirical formulas of these substances have simple relations, ex- hibited in the following table, in which the}' are compared with that of starch : — 1 For an account of the allied substances, amylodextrin and achroodextrin, see W. Nageli, Beltrage zur uaheren Kenntniss dev Starkegruppe, 1874. Thus, THE SUGARS. 359 Starch, C,U,fi^ Cane-sugar, CijHjjOu Grape-sugar and fruit-sugar, CuHijOg 2C,H,„0, + H,0 = C,,H^O,, Starch. Water. Cane-sugar. Cane-sugar. Water. Grape-sugar. Fruit-sugar. The three following classes of sugars, based upon their rela- tions to fermentation, have been made : (1) directly fermenta- ble, (2) indirectlj' lermentable, (3) non-fermentable sugars. To the third class belong Arabiuose, Sorbit, etc., which need no further notice here. The dii'ectlj' fermentable sugars are grape-sugar, fruit-sugar, and inverted sugar. 942. Grajje-sugar, otherwise termed glucose (or, on account of its turning tlie plane of polarization to the right, dextrose), is, as its name indicates, abundant in the grape, where it may form from 10 to 30 per cent of the juice. Figs contain, on an aver- age, 12 per cent ; sweet cherries, 9 to 10 per cent ; apples and pears, 7 to 10 per cent; plums, 2 to 5 per cent; and peaches less than 2 per cent of this sugar. 943. Fruit-sugar, sometimes known as Isevulose, is uncr3S- tallizable. It is associated in most ripe fruits with dextrose. 944. Inverted sugar occurs iu some ripe fruits, where, as Buignet has shown, it is formed from cane-sugar by the action of a ferment and not of a fruit-acid. It is also found iu the so-called honey-dew of the leaves of the Linden.^ 945. The indirectly fermentable sugars, of which common cane-sugar may be taken as the best example, ferment under the influence of yeast only when Ihey have first undergone a change by which they are converted into other sugars. 946. Cane-sugar occurs in the cell-sap of man}' plants, often in large amount. The following percentages are regarded as average ones : — 1 According to Boussingault, 120 square metres of linden leaves yield in a single warm July day between two and three kilograms of honey-dew. As to whether this substance is a product of an insect, or an exudation from leaves under peculiar conditions, is not yet settled (Ebermayer : Chemie der Pflanzen, 18S2, p. 255). 360 CHANGES OF ORGANIC MATTER IN THE PLANT. Sugar-cane stem 16-18 per cent. Sugar-beet 10-U " Sorghum 10-11 " Indian corn ... 5-7 " Sugar maple 8 " 947. Products free from nitrogen. II. Vegetable acids. Of these the most -widely distributed are oxalic, tartaric, citric, and malic acids. 948. Oxalic acid {G^f)^) occurs in almost ever}- plant, the amount in some reaching as high as 4 per cent. Most of it is combined with calcium or with potassium, a part remaining lui- combined. According to Miiller,' tlie fresh leaves of sugar-beet contain 4 per cent of this acid, of which one third is in solution. 949. Tartaric acid (C^H„Og) occurs free, and also combined ■with potassium in the juice of the grape and many other fruits. 950. Citric acid (CgHjOj) occurs in the amount of 6 to 9 per cent in the juice of lemons and allied fruits, and is asso- ciated with other acids in most of our subacid fruits, such as currants, cherries, etc. 951. Malic acid (C^II^Oj) occurs free, or combined with cal- cium, in the juices of many fruits and in the sap of manj- plants. It imparts the sour taste to our most common fruits. 952. Products free from nitrogen. III. Fats, or Glycerides. According to Ebermayer most of the fats which occur in plants are mixtures (not compounds) of the following three kinds of fats in different proportions : Tristearin or stearin, tripalmatin or palmatin, triolein or olein. The oils in most seeds, however, are free, fatty acids ; namelj', stearic, palmitic, and oleic. The fats are regarded as compound ethers formed from the triatomic alcohol glycerin, whence they have been sometimes termed Glycerin ethers. The following formulas exhibit one view as to their constitution : — Tristearin (tJisHasOJa | Qj Tripalmatin **^i^,^i°'' | O3 Triolein <'^%%°''' 'f Og Stearic acid C1JH30O2 Palmitic acid CJ5H32O.2 Oleic acid ^181184*^2 (Glycerin CaH^fOHJa) 1 Quoted by Ebermayer, Cliemie der Pflaiizen, p. 320. TANNIN AND ALLIED SUBSTANCES. 361 The oils form very intimate mixtures with the albuminoids in many cases, especially in seeds of such plants as Eieinus, etc. According to Sachs, *•' in the germination of all oih' seeds, sugar and starch are produced in the parenchyma of every growing part, disappearing from them only when the growth of the masses of tissue concerned has been completed. Since, in the case of Eieinus, the endosperm grows also independently, starch and sugar are, in accordance with the general rule, temporarily pro- duced in it. The cotyledons apparent!}' absorb the oil as such out of the endosperm, whence it is distributed into the paren- chyma of the hj-pocot^'ledonary stem and of the root, serving in the growing tissues as material for the formation of starch and sugar, which on their part are only precursors in the production of cellulose. In these processes tannin is also formed, which is of no further use, but remains in isolated cells, where it collects apparently unchanged until germination is completed. It can scarcely be doubted that the material for the formation of this tannin is also derived from the endosperm, although perhaps only after a series of metamorphoses. The absorption of oxygen, which is an essential accompaniment of everj' process of growth and especially of germination, has in this case, as in that of all oih' seeds, an additional significance, inasmuch as the formation of carbohydrates at the expense of the oil involves the appro- priation of oxygen." ' Vegetable wax is closely allied to the fats. 953. Products free from nitrogen. IV. Certain astringents. This indefinite group comprises various matters differing slightly from one another in some particulars, but agreeing in possessing a faint acid character, in changing color with salts of iron, and in combining with certain protein matters. Tannin is sometimes placed in the next category, namelj', among the glucosides ; but according to Schiff it is digallic acid. The most important mem- bers of this group are Ihnnin (the so-called tannic acid), Gallic acid, and the astringent principle in Cinchona, Catechu, and Kino. According to Niigeli, these matters are to be found in buds, in unripe fruits, and in those petals which become red or blue, dissolved in the cell-sap and diffusing through cell-walls. Tannin sometimes exists in little globules of solution, enveloped bj' a delicate film of albuminous matter ; for example, in the cells of the pulvinus of Mimosa and in the bark of many ligneous plants (Birch, Poplar, etc.). The following views are held as to 1 Text-book, 2d English ed., p. 716. 362 CHANGES OF ORGANIC MATTER IN THE PLANT. the formation of this substaDce : Many authors regard it as a product of tlie retrograde metamorphosis of certain carboh}-- drates ; Sachsse thinlis that it alvva\-s attends the formation of cellulose from starch, and that there is a slight evolution of carbonic acid ; Wiesner regards it as intermediate in the series which begins with the carboh3-drates and ends with the resins. This last view is also held by Hlasiwetz, who has ob- tained the same products from tanniu as from the resins, when each was fused with potassic hydrate. It is a significant fact that all the barks which are rich in tannin are also rich in starch. Nothing is positively known as to the function of tannin and its associated bodies in the plant. B}' Hartig they have been looked upon as reserve materials ; but Schroeder was not able to verify Hartig's observations. Bj' most observers these sub- stances are regarded as waste products, having no further nutri- tive function, but possibly playing some part in the formation of colors. The following table ^ shows their amount in some of the barks and other parts used in tanning : — Galls 30-77 per cent. Catechu 40-50 Divi-Divi 30-40 " Sumach 12-18 Oak bark 7-20 Willow bark 8-12 Hemlock bark 13-16 954. Products free from nitrogen. V. Most GIncosides. These are substances which under certain conditions, especially by the action of unorganized ferments, are broken up into glucose or some allied sugar, and at the same time some other body capable of further decomposition. Most of them are soluble in water. The following are among some of the best known : salicin, coni- ferin, aesculin, quercitrin. Tannin is often placed among the Glucosides. 955. Products free from nitrogen. VI. Ethereal oils. These are volatile liquids generally approaching Terpene (CuiH,,,) in chemical composition. Nothing is certainly known as to their formation in the plant. Thej' are not again taken up as plastic matter, but simply serve some function, often that of attraction 1 For other determinations see Ebermayer's Chemie der Pflanzen, p. 452, from which most of the above are taken ; also see the excellent table in the Tenth Census, vol. ix., p. 265. ALUUMlN-LlItE MATTERS. 363 or of protection. To their presence is due the fragrance of man}' fruits ;ind flowers, notabl}' those of orange, bergamot, and the mints. Associated with the ethereal oils, the camphors occupy a prominent place. They are generallj- regarded as the products of the slight oxidation of some ethereal oils. The following is the best known, C,|,H](.0 (Laurel-camphor). 956. Products free from nitrogen. VII. Resins and Balsams. These substances, whicli differ much in consistence, color, and other physical properties, contain comparative!}' little oxygen, are mostly amorphous, insoluble in water, and sometimes pos- sess a slight acid reaction. Balsams are defined as " mixtures of resins with volatile oils, the resins being produced from the oils b}- oxidation, so that a balsam ma}' be regarded as an intermediate product between a volatile oil and a perfect resin." ' The Balsams are generally divided into two groups : (1) those containing much cinnamic acid, as Balsam of Tolu, Peru, etc. ; and (2) those which are purely oleo-resinous, as Balsam Copaiba, Fir, etc.'^ Certain resins and caoutchouc-like matters are found in large amount in the latex. 957. Products containing nitrogen. I. The albnmin-Iike mat- ters. Ritthausen classifies these substances iuto (1) Albumin of plants ; (2) Casein of plants ; (3) Gelatin of plants. Albumin of plants is the term applied to the protein mat- ters which readily coagulate from their aqueous solutions upon the action of heat or acids. The coagula dissolve more or less readily in potassic hj'drate, exhibiting considerable differences in respect to solubilit}'. They contain from 2.6 to 4.6 per cent of ash, and have the following elementary composition : — Carbon 52.31-.'54.33 per cent. Hydrogen 7.13- 7.73 " Nitrogen 15.49-17.60 Sulphur 76- 1.55 " Oxygen 20.5,5-22.98 " Oasein of pla7its comprises the following substances : legu- min, gluten-casein, eonglutin. Solutions of these are precipi- tated by dilute acids and by rennet. The precipitates are readily 1 Watts: Dictionary of Chemistry, i., 1863, p. 491. 2 A solution of the coloring-matter of alkanet root in dilute alcohol applied to a thin section of a plant containing resins colors the resins red after a few minutes, but does not serve to distinguish one from another. 364 CHANGES OF OEGANIC MATTER IN THE PLANT. soluble in a solution of basic potassic phosphate. Their ultimate composition is nearlj- tlie same as that of the group just men- tioned. Gelatin of plants. The associated matters are (1) Gliadin, (2) Muccdiu, (3) Gluten-fibrin. These bodies are soluble in alcohol, and in water containing a small amount of acid or alkali. In their fresh state they are tough, viscid masses, only slightly soluble in water.' 958. Weyl does not accept Ritthausen's classification, but holds that legumin is a mixture of vegetable vitellin and casein ; and further, that there is no true casein in seeds, — the sub- stance called by this name being a product of secondary changes in the laboratory. 959. Products containing nitrogen. II. Asparagin {Cfl^fi^. This substance occurs in the shoots of Asparagus officinalis and many other plants, from which it can be obtained in the form of transparent crystals of the orthorhombic system. It is merely necessary to evaporate the juice of the plants to the consist- ence of a thin syrup, and after allowing it to stand for a time the crj'stals will separate, and may be purified by recrj'stalliza- tion. Pfeffer describes the following useful method of preparing them upon the slide of the microscope : A moderately thick sec- tion of the tissue suspected of containing asparagin is placed on a slide, covered with a bit of glass, and treated with absolute alcohol, when the crj'stals will be thrown down in the cells, or will form in the alcohol outside of the specimen. The character of the crystals can be known certainly by their insolubility in a concentrated aqueous solution of the same substance (see 46). The amount of asparagin in certain plants has been given as follows : — Name of Plant. Per cent of Asparagin. Observer. Roots of A-ltlisea .... 2. ... Plisson and Henry. Vetch genns . ... 1.5 .. . Piria. Radicles of a germinating plant dried at 100 C. . . 10.5 . . . Beyer. 960. Asparagin possesses its chief interest from the part which it probablj' plays in the transfer of nitrogenous matters through the plant. According to Pfeffer, althougii it cannot be detected with certainty in the seeds of the vetch and pea, it appears in the young parts, especiallj' in the lines of transfer (for 1 Hunt has called attention to a cnrious relation between the composition of animal gelatin and that of starch to which ammonia is added. ASPAEAGIN. 365 example, the petioles of the cotyledons). That the source of the asparagin must be the re.serve albuminous matters in tlie seed, appears from the following consideration : " The absolute amouut of nitrogen remains the same during germination, and the nitrogen of seeds is all or nearly all contained in their albumi- nous ingredients." ^ Asparagin and the chief proteid of the seeds in leguminons plants have been thus compared : — Asparagin. Legumin. Difference Carbon . .... Hydrogen Nitrogen Oxygen 36.4 6.1 21.2 36.4 64.9 8.8 21.2 30.6 + 28.5 + 2.7 0.0 —5.8 "Asparagin contains less carbon and hydrogen but more oxygen than legumin and other proteids. Consequently if the whole of the nitrogen of legumin is used in the formation of asparagin, a considerable quantity of carbon and hydrogen must be given off and a certain amount of oxygen absorbed. Exactly the opposite will take place upon the conversion of asparagin into proteid." ^ 961. Products contaiDiug nitrogen. III. The alkaloids. These substances all possess the power of uniting with acids to form salts, and they are often described as basic alkaloids. Among the most important are Morphia, Quinia, and Strychnia. The number of alkaloids now known is very great, and the modes in which they are found combined in the plant are very- diverse. They are more abundant in those plants which are grown under conditions of considerable warmth, and are much more abundant in some parts of the plant than in others, as is shown by the case of morphia. Nothing is positively^ known as to their origin or proper function in the organism. It should be mentioned, however, that many of them when applied to the very plants from which they were prepared prove to be poisonous ; thus, morphia poisons the poppy. 962. Frodacts containing nitrogen. IV. Unorganized ferments. It has long been known that there must exist in certain parts of 1 Pfeffer, in Sachs's Text-Book, 1882, p. 719. For a full account by Pfcffer, see Pringsheim's Jahrbiicher, viii., 1872, p. 429 ; and Monatsbericht der Ber- lin Akadeniie, 1873, p. 780. See also Husemann and Hilger: Die Pflauzen- stoffe, i., 1882, p. 264. 366 CHA^fGES OF ORGAliriC MATTER IN THfi FLAN*. plants, notabl}- in seeds, compounds which possess the power of effecting changes in the character of starch, etc. ; but it was not until 1873 that a method was given which enables us to isolate these compounds in a state of comparative puritj'. This method is based upon their solubility in glycerin, and their ready pre- cipitation from gh'cerin solutions by means of common alcohol.^ B^- the use of this method Gorup-Besanez has been able to obtain from the seeds of vetch, flax, etc., a ferment which is soluble in water and glycerin. The substance contains 7.76 per cent of ash constituents and 4.5 per cent of nitrogen. Its solu- tions convert starch into sugar ver^' rapidly at the temperature of 20°-30° C. ; and in the presence of a dilute acid, for instance hydrochloric, it has the power of peptonizing proteids. In solu- tion, it loses its activity at 80° C, ; but if carefully dried, it can stand a temperature of 120° C. Up to the present time no fer- ment capable of effecting changes in the fats of plants has been isolated.^ 963. Baranetzkj' has shown that in the conversion of starch into sugar there are two phases : (1) the formation of dextrin, and (2), at a somewhat higher temperature, the formation of sugar. He observed an acid reaction in the ferment. 964. In the sap of Carica papaya, Wurtz and Bouchut" have isolated a peptonizing ferment which acts promptly upon albu- minoids. The juices of several tropical fruits are said to have the property of softening meats, and this action is regarded as dependent upon some unorganized ferment. 965. Besides the products alreadj' enumerated, there are some bitter and extractive matters and some coloring substances which do not naturally fall into any of the groups described. 966. From the facts which have now been presented, it is clear that the composition of the sap which escapes from a plant when it is wounded must be very complex. The juices of a plant contain all its dissolved mineral matters, gases in solution, and numerous members of both of the nitrogenous and non- nitrogenous groups already mentioned. 1 Hiifner. Journal fiir praktische Chemie, v., 1872, p. 372, and xi., 1875, p. 43. ' For a short account of the work of Kosmann (Journal de Pharmacia et de Chiraie, ser. 4, tome xxii. p. 335) and that of Krauch (Versuchs-Stationen, xxiii. p. 77), see Husemann and Hilger : Die Pflanzenstoffe, i., 1882, p. 238. * Comptes Rendus, Ixxxix. , 1879, p. 425 ; xci., 1880, p. 787. See also the following ; Duclaux : Comptes Rendus, xci. p. 731, and Hansen : Sitz. der physikmedicin. Societat zu Erlangeu, 1880. RESPIRATION. 367 RESPIRATION. 967. It has been long known that air is necessarj' for the germination of seeds. ^ In 1777 Scheele ^ pointed out that in this process, as in the breathing of animals, oxygen (called by him fire air) is consumed and carbonic acid (called by him air-acid) is given off. Two years later, Ingenhousz ^ showed tliat all plants at night give off fixed air (carbonic acid), and in 1804 Saussure proved that all plants require oxygen for their growth. In 1838 Mej-en * clearly defined the scope of respiration in plants, since which time it has been carefully examined in most of its relations. 968. The relations of gases to plants, so far as their absorp- tion and elimination are concerned, have been sufficientlj- dis- cussed in Chapter X. It is merely necessary to state at present that oxygen is readily absorbed by all parts of plants, and that the intercellular passages (519) form a means by vyhich it can traverse the whole plant very rapidly. 969. In its simplest phases respiration consists in the absorp- tion of oxj'gen, the oxidation of oxidizable organic matters, and the evolution of the products of oxidation ; namely, carbonic acid and water. Some other products are often formed in minute amount, but these may- be here disregarded. 970. Measurement of Res- piration. Eespiration can be measured very nearly by the amount of ox^^gen which dis- appears or by the amount of carbonic acid which is given off. The ordinary apparatus for examining respiration is based upon the measurement of the latter, and consists es- sentially of some application of potash-bulbs, or wash-bottles (see Fig. 163), for the interception of all evolved carbonic acid. The 1 See Malpighi ; Opera omnia, 1686. ^ Chemische Abhandlung von der Luft, 1777. 2 Experiments upon Vegetables, 1779, p. xxxvi- 4 Pflauzenphysiologie, it., 1838, p. 102. 368 CHANGES OF ORGANIC MATTER IN THE PLANT. air supplied to ttie seeds in the bell-jar, of course first carefull3' freed from every trace of carbonic acid, is drawn through by means of an aspirator, and in the bulbs all the carbonic acid derived from the germinating seeds is retained. 971. Plants in dwelling-houses. To what extent can house- plants injure the air of rooms at night? The carbonic acid which is given off by plants comes from the breaking up of assimilated matters in the various activities of the organism, such as growth, movements, etc. But the total amount of work done bj' any plant under the conditions to whicli ordinary house-plants are subjected is represented Ijy the oxidation of a very small amount of food. From the most trustworthy data it is safe to say that in the case of one hundred average house-plants the whole amount of carbonic acid resulting from such oxidation during work would not vitiate the atmosphere of a moderate-sized room to any appreciable extent ; in fact, would be exceeded by the amount evolved from a common candle burning for the same length of time. • 972. Relation of the carbonic acid given off to the oxygen absorbed. Owing to the fact that part of the carbonic acid produced during respiration is retained within the plant, and that water is formed as a product of respiration, it is difficult to determine tlie exact relations of volume of the absorbed oxjgen and the evolved carbonic acid. It is known, however, that in certain cases the amount of carbonic acid e\'olved is less than would be expected from tlje amount of oxygen absorbed. This is well shown when the germination of oily seeds is compared with that of seeds containing chiefly starch. When oily seeds germinate, the amount of carbonic acid is appreciably less than that given off by starchj' seeds. Hellriegel has shown that in one instance the fixation of oxygen amounted to an increase in weight of 1.15 percent. 973. The free oxygen of the atmosphere is ample for the respi- ratory process. Saussure-' has shown that the amount in tlie atmosphere can even be reduced one half without materiallj' interfering with the functions of the plant. Most observers have found that in pure oxygen there is an increase in the activity* of the respirq,tory function. Bert'' has conducted interesting experiments upon the effect 1 Quoted hy Pfcirer, Pllanzenphyslologie, i. p. 373. ^ For a discussion of this question, particularly witli reference to tlie lower organisms, consult Bert : La pression baromfetrique, 1878- PERIODS OF REST. 369 of pressure on the various functions, by which it appears that in ordinary air, under a pressure of six atmospheres, Mimosa per- islied quickly. In an atmosphere under high compression seeds germinated, if at all, very slowlj'. &74. Influence of temperature upon respiration. Respiration can go on at low temperatures, even near the freezing-point of water. The rate of respiration increases with rise of tempera- ture, as will be seen from the following figures for germinating beans : — ^ Tpmiicratiirfi Amount of carbonic add ±emi)erature. given off each hour. 2°C 10.56 mgi-. 6° 21.22 " 18° 32.34 " 20° 39.60 " 30° 47.52 " 975. Influence of liglit upon respiration. It is not jet known positivel}' whether light has any effect upon respiration. In some experiments there has been a sHght increase,^ in others a diminution,^ in the rate, with increased illumination ; but it is not certain whether all other factors wei-e excluded. If the produced carbonic acid does not escape readily from the tissues, respiration goes on more slowly.* 976. Periods of rest. Although all plants require oxj'gen for the performance of their normal functions, it by no means follows that when a plant is supplied with oxj'gen the normal activities will be necessarily exhibited. In the case of certain bulbs, seeds, etc., even with the most favorable surroundings, there maj' be no signs of respiratory or other activity until after the lapse of 1 Rischawi; Versuchs-Stationen, xix., 1876, p. 338. 2 Wolkoff and Mayer; Landwirtlischaftliche Jalirbiicher, 1874, Heft iv. ; Cahours : Cornptes Reiidus, Iviii., 1864, p. 1206. ^ Dumas: Annales de Chiiiiie et de Physique, ser. 5, tome iii., 1874, p. 105 ; Borodin : Just's Botan. Jahresbericht, iv., 1878, p. 920. * For the bearings of tliis upon alooliolic fermentation, which, according to Melsens, is not arrested until a pressure of 25 atmospheres of carbonic acid is reached, see Pa.steur : Annales de Chimie et de Pliysique, ser 3, tome Iii., 1858, p. 415; and Nageli: Die niederen Pilze, 1877, p. 31. Alcoholic Fermentation. This process is so intimately connected witli that of respiration that it requires a brief desci'iption at this point. Reduced to its simplest terms, it consists of the clianges which are produced in a solu- tion of sugar by the growth of a microscopic organism. This is some one of the Saccharomycetes (a group of low fungi which are propagated by a process of budding). By the growth of this fungus the solution of sugar is broken up into various products, the most noteworthy being alcohol and carbonic acid. 24 370 CHANGES OF ORGANIC MATTER IN THE PLANT. a given period of time. Tliere is little doubt that this refusal of the resting part to start is an inherited trait connected in some way with the protection of the plant against untoward influences. 977. Eespiration is accompanied by an evolution of heat. The flowers of the melon and tuberose were examined by Saus- sure, who found that in the opening of the former there was an elevation of 4 to 5 C.°, in that of the latter, .3°. Caspary detected a noticeable rise of temperature in the opening flowers of Victoria regia, and the same has been observed in flowers oC species of Cactus. 978. In those cases where it is possible to examine an organ in which the process of respiration is rapid, as in a compact cluster of flowers of Aracere, the difierence between the tem- perature of the air outside and that inside the spathe is very marked. 979. The following results bj' Senebier, obtained by two methods of experimenting, are very instructive, showing the remarkable and rapid changes of temperature in such cases. The plant in this instance was Arum maculatum. Time. Temperature of air. Temperature of spathe. C.° C.° 3 P. M 15.6 16.1 5 " U.7 17.9 5i " 15 19.8 6J " ... .16 21. C| " 14.9 21.8 7 " 14.3 21.2 9J " 15 18.5 lOJ " 14 15.7 5 A. M 14.1 14.1 Even higher differences have been observed. 980. Light is produced during the growth of certain of the lower fungi under certain conditions. The phenomenon called phosphorescence is not known in any of the higher plants.^ According to Fabre, it is associated with the absorption and consumption of oxygen, and the evolution of carbonic acid. 981. Intramoleculai' respiration. Under certain circumstances plants can continue to give off" carbonic acid when no free Dxygen is su[)plied, and when they are kept in an atmosphere 1 For an nccount of supposed cases of lunimous llowers see Balfour's Class Book of Botany, 1854, p. 676, INTIlAMOLBCULAR EESPIKATION. 371 of some other gas.^ The following experiment will illustrate this : — If a mass of active seedlings be placed in a current of some neutral gas, for instance nitrogen, tiie seedlings will continue to evolve carbonic acid. Since the amount of carbonic acid given off is greater than can be derived from the oxj'gen which might bo fairly assumed to liave been retained in the plants at the be- ginning of the experiment, the conclusion has been drawn that tlie production of this gas is at the expense of substances within the tissues containing combined oxygen. In other words, this process, which is lilie respiration in some particulars, differs from it in this respect : in ordinary respiration free oxygen enters into the plant and there oxidizes certain matters ; while in this case the molecules of certain compounds break up, and the released oxygen at once forms, with carbon, carbonic acid, which is evolved. This process is known as intramolecular respiration. 982. Wortmann^ has proved that when seedlings of Vioia Faba are placed for short periods in an atmosphere free from oxygen, they give off the same amount of carbonic acid as they do when oxygen is furnished. Hence he was naturally led to believe that all the carbonic acid produced by plants has its origin in intra- molecular respiration, and that the free oxygen of the air takes no direct part in the formation of the carbonic acid evolved. 983. But, on the other hand, Wilson' has shown that most plants evolve much larger quantities of carbonic acid when free oxygen is provided, and that Vicia Faba forms a remarkable exception to this rule. His experiments were made upon seed- lings, buds, leaves, flowers, fruits, and crj'ptogamous plants, and with uniform results. He cites Pfeffer as saying: "If an equal amount of carbonic acid were formed in both intramolecu- lar and normal respiration, this would only prove that the same 1 The same phenomenon has been observed in the case of some of the lower animals : Pfliiger (Archives fur Pliysiologie, x., 1875, p. 251) has shown that when these animals are kept in an atmosphere of nitrogen, they evolve during the first few hours nearly the same amount of carbonic acid as if they had been placed in common air. The chemical processes which cause the production and evolution of carbonic acid in the absence of free oxygen are grouped by Pfliiger under the term intramolecular respiration. 2 Arbeiten des botanischen Instituts, Wiirzburg, 1880, p. 500. ' Flora, 1882, and American Journal, xxiii., 1882, p. 423. For an interesting account of the literature of intramolecular respiration see Pfliiger's paper, men- tioned above. Observations upon the subject were made even during the last century and early in the present century. For Broughton's and Pfeffer's work see Botanische Zeitung, 1870, and Pflanzenphysiologie. 372 CHANGES OJP OEGAKIC MATTER IN THE PLANT. number of carbon affinities for oxj'gen liad been satisfied in eacli case, and would in no way indicate from whence tiie supplj' of oxygen came. And in case free oxygen was active in normal respiration, in intramolecular respiration, when free ox3-gen was absent, its full supplj' might still be obtained through constant powerful attractive forces which could take oxygen from other combinations and thus give rise to secondary changes." 984. Eriksson" has shown that a slight elevation of tempera- ture occurs during intramolecular respiration, amounting in the case of a mass of seedlings, flowers, or fruits, 125 cc. in bulk, to .l°-.3'' C. In the experiments which he made with yeast, he obtained a much larger increase of temperature. Thus, when he employed 500 cc. of a fluid containing five parts by weight of water and one part by weight of yeast, together with 10 per cent of sugar, he obtained an increase of 3°. 9 C. He found, further, that in intramolecular respiration, both in the ease of germina- tion and in that of yeast, the elevation of temperature can be noticed for one week. After this time, with diminution of the respiration, the temperature becomes the same as the surround- ing air ; but even then life is not extinct. 985. The curious experiment of introducing the smallest pos- sible amount of organized ferment into a liquid from which all air has been expelled, but which is otherwise fitted to undergo fermentation or putrefaction, has resulted in setting up one or the other of these processes, and causing the liberation of con- siderable quantities of carbonic acid. It is believed that in this case likewise the needed oxygen is supplied bj' that in the mole- cules of oxygen-compounds, which are easily broken down. 986. While the non-nitrogenous compounds are those which play the most important part in furnishing material for oxidation and the release of energy, the nitrogenous matters share in this activity. Some physiologists ^ look upon the latter as the chief matters concerned in the process of respiration, and would regard the non-nitrogenous compounds as merely supplying waste. Ac- cording to this view, asparagin is a waste product somewhat analogous to urea in animal economy. 987. From what has been said, it is plain that respiration does not consist merely in the direct absorption of oxygen and the immediate oxidation of compounds within the organism, but that it is a complicated process of which the absorption of oxy- gen and the evolution of carbonic acid are the extreme terms. 1 Untersuchungen aus dem bot. Inst, zu Tubingen, 1881, p. 105. ^ Borodin : Botanische Zeitung, 1878. CHAPTER XII. VEGETABLE GROWTH. 988. As already shown, vegetable growth consists (1) In the formation of new cells, (2) in the increase in size of previously' existing ones, or, (3) as is commonly the case, in both of these processes taking place simultaneously. In the production of new cells and in the augmentation of cells in size there are cer- tain chemical and physical phenomena which alwaj's accompany the morphological changes. 989. The chemical changes are essential!}' those which have been described under Transmutation and Respiration ; available matters change their character in order to be utilized in the for- mation and increase in size of cells. The phjsical phenomena are chiefly those which accompany oxidation ; namely, the evolu- tion of heat and the production of electrical disturbances. 990. The materials used by the plant for the formation of new structures are produced by assimilation ; and in annuals a large part of the assimilated matter is consumed in growth as soon as it is made. But, in perennials, especially in those which belong to climates where vegetation has periods of rest, a por- tion of the assimilated matter is stored up for future use. The rapiditj' of the growth from buds in the spring is due to the abundant supply of assimilated matters prepared during the pre- ceding summer. 991. Hence growth is not necessarily associated with increase in weight. In fact, in the growth of new parts from a bulb or tuber, although there is a marked increase of volume, there is, at first, an actual loss of dry substance through oxidation. More- over, one part may grow at the expense of another ; and we maj' have under certain conditions the anomaly of an increase in volume of new organs, with simultaneous but larger decrease in size of older parts, so that the result, as regards the whole, is diminution of weight. 992. Morphological changes in the cells. The two processes involved in ordinary growth, namely, increase of cells in number and in size, maj' go on together. But growing cells belong to 374 VEGETABLE GROWTH. one of two classes : either thej^ are capable of producing other cells, or, incapable of this, they develop into cells for some special offlee. To the former class belong all merismatic tissues ; (see 201) from the latter all the permanent tissues are derived. Since growing cells have such different destinies, we must ex- amine them in their earliest stage to find what they have in common. 993. The simplicity of structure in many of the lower plants is so great that a living cell can be kept under observation through- out its various stages, and through its transparent wall all the changes which go on withiu it can be noted. But the points of growth in most plants, especially those of the higher grade, are hidden bj- more superficial cells ; and upon removal of these pro- tecting parts, pathological changes are brought about at once, from exposure and mechanical injurj', and health}^ growth is arrested. In a few instances onh', such as plant-hairs and other epidermal structures, is it possible to observe directly the progress of cell-division. Growth in deeper parts must be ex- amined by an indirect method ; that is, like parts must be com- pared at different stages of development, care being taken to select those which have been kept under nearly the same ex- ternal conditions. B}' judicious selection of material for the examination of growth, specimens can be found which exhibit in a single section several different phases of cell-division. 994. When fresh material is employed, the sections are so much distorted that it is diflScult to secure satisfactory results ; in fact, the discordant views relative to the formation of cells are largely attributable to this source of error. If, however, the tissue to be examined is placed for a while in absolute alcohol, either with or without a little chromic acid, the cell-wall is rendered so much harder that the sections are not seriously distorted, and the contents of the cells are more clearlj' seen. AVhen the treatment is supplemented bj- the use of staining agents adapted to special cases, the course of development ot new cells can be followed out with comparative certainty. 996. In the protoplasm of nearly all vegetable cells there is a spheroidal or lenticular body apparently denser than the proto- plasm itself. It retains the name nucleus, given to it b}' Eobert Bi'own, who first called attention to its importance. Under ordi- nary circumstances it can readily be detected in all active cells of the higher plants. When living, it resists, like the protoplasm in which it is embedded, the entrance of all coloring agents ; but when dead it STRUCTURE OF THE NUCLEUS. 375 is at once tinged by them. Upon the application of iodine it becomes deeper brown-yellow than protoplasm, and this led Hofmeister to the belief that it is richer in albuminoidal mat- ters.^ Its behavior with digestive fluid and other reagents indi- cates that, like the nucleus in the animal kingdom, '-^ it contains a substance rich in phosphorus." 996. The surface of the nucleus generally appears to be firmer and more highly refringent than the interior mass, and in these respects is like the superficial layer of protoplasm. Even with low powers of the microscope and without reagents the inner mass of the nucleus is often seen to be far from homo- geneous, generally containing granules, which are sometimes irregular, sometimes regular in form. When a single large granule is present, it is known as the nucleolus ; when two or more, the nucleoli. These vary widely in number, size, and shape. Besides such granules, vacuoles are frequently present. Upon the application of suitable staining agents, and by the use of high powers, the nucleus, formerly thought to be nearly homogeneous, is shown to be a basic substance possessing a finely reticulated structure. At times the nucleus appears to be simply dotted throughout with fine points. 997. When the bodies which are associated with its basic sub- stance are granular, they are distinct from each other ; but when in the shape of rods, fibres, or delicate threads, they are usually conjoined to form a sort of network, or so connected together as to make a long thread which is tangled in a complicated man- ner. The basic substance of the nucleus, less highly colored by staining agents than the rest, has been called Achromatin ; while the portions which take color readilj' are termed Chromatin bj' Fleraming, nuclein * by Strasburger. During cell-division these portions of the nucleus undergo remarkable changes of shape and position, which, with the changes observable in the nucleus as a whole, can be illustrated by a few special cases taken from Strasburger's treatise, and given in nearly his words. 1 Hofmeister: Die Lehre von der Pflanzenzelle, 1867, pp. 78, 79. '^ Hoppe-Seyler: Pliysiologisclie Chemie, i. p. 8i, which contains a good account of the literature of the subject. 5 Zacharias ; Botanische Zeitung, 1881, p. 169, ^ The only objection to the temi nuclein is its previous application to the proximate chemical substance rich in phosphorus which, although a part of the nucleus, is not proved to be identical with the part which receives colors most deejily. 876 VEGETABLE GKOWTH. 998. Deyelopmeut of stomata. Each of the mother-cells from which the guardian-cells of stomata are formed contains at first a large nucleus with one large nucleolus or several small nucleoli (Fig. 164, No. 1). The nucleus grows in size and becomes gran- ular, but does not lose its identitj- in the protoplasmic mass (Fig. 164, Nos. 2, 3). At this period faint stripes appear which con- verge towards the poles of the spheroidal nucleus, while there is developed midway, at what has been well called the equator, a row of granules lying in one plane and forming a sort of disc or plate (Fig. 164, No. 4). The granules next pass for the most part in the meridian lines towards the poles, and there accumu- late to constitute new nuclei (Fig. 164, No. 5). The polar masses are connected by faint stripes, and from this stage (Fig. 164, No. 6) go rapidly to their fuller development. In them rods appear which, though somewhat curved, generally lie in the direction of the axis of the spindle, and the contour of the two masses becomes clearly defined (Fig. 164, No. 7). Next, the faint stripes thicken somewhat, while at the equator there is developed a plane of minute granules (Fig. 164, No. 8), which become confluent and form a coherent film. This soon splits into halves between which cellulose is secreted. At first the secretion takes place in spots, but it soon becomes uniform. The splitting of the film for the formation of the cellulose is similar to that of the nuclear disc, except that in the former the Fro. Ifi4. Cliaiiges in the nucleus during cell-division in the motlier-ceU of a stoma of Iris pumila. Tlie darli parts in all tlie figures represent tlie nuclein. In No. 9 the cell-division is complete. (Strasburger. ) CELL-DIVISION. 377 separation is very slight. At tlie time of the formation of the cellulose film certain nuclear tlireads may stretch as far as the wall of the mother-cell ; but often they do not extend to it, and in this case the gap is filled out by a corresponding plate from the protoplasm. The cellulose film is produced almost simul- taneously throughout the whole extent of the mother-cell, which is cut into two guardian-cells, forming a stoma (Fig. 164, No. 9).' Although the process goes on without interruption, it may be divided into three phases ; namely, (1) the arranging of the nucleolar bodies to form a disc in the middle plane of the nucleus ; (2) the splitting of the nuclear disc into two parts which pass over towards the poles, there becoming new nuclei, leaving faint meridional lines connecting them ; (3) the thickening of these lines, and the appearance of granules at the equator, so as to form a plate which divides into halves. The cellulose film secreted between these halves sooner or later goes across the cell cavitj', making a partition-wall between two new cells. The mother-cell from which guardian-cells are developed in the manner just described is itself produced in nearly the same manner from an epidermal cell. The latter contains a spherical nucleus having a diameter about two thirds that of the cell. It is not whollj^ filled with protoplasm, as is usually the case with cells capable of division, but has a very thick lining of protoplasm along the wall, and in this the nucleus is embedded. The nucleus extends completelj' across the cell- cavity, while above it and below it is cell-sap. If, now, the epidermal cell is to give rise to a new one, the nucleus passes over to one end of it and there divides into two parts, essentiall}' as before described, except that the halves remain close together. Between these new nuclei the cell disc or plate, and the cellulose plate, are successively produced, cutting the old cell into unequal parts. 999. The division of cells in cambium was examined by Stras- burger^ in young shoots of Pinus sylvestris, which had completed their growth in length and had begun to thicken. These were selected on account of their rapid development. The cambium cells of this pine have a lining of protoplasm, together with a nucleus which occupies the middle of the cell and completely fills the smaller diameter. The nucleus is nearlj^ spherical, or 1 Strasburger ; Ueber Zellbildung und ZtUtheilung, 1876, p. 110. This account is somewhat but not essentially difTerent in the editiou of 1880. 2 Ueber Zellbildung und Zelltheilung, 1876,- p. IM. 378 VEGETABLE GROWTH. somewhat lengthened in the direction of the long axis of the cell, and contains several nucleoli. When it begins to grow, these nucleoli disappear, and the characteristic striation previously de- scribed appears transverse to the direction of future division and of the nuclear disc. The latter is not clearl3- defined, and its halves do not recede from one another very far, since, in fact, there is not space for much expansion in any event. The parti- tion wall at first is confined to the space between the halves, and these are found in close contact with it, but later it extends completely across. The remarkable thickness of the radial walls of the cambium is explained by Sanio as due to the non-absorp- tion of a part of the mother-cell ; but Strasburger ascribes it to the uninterrupted nutrition of the radial wall from the contents of the cell itself. The newly formed partition- wall is thin, and cannot be shown by reagents to be double.-' 1 The student should consult Strasburger's work : Ueber den Theilungs- vorgang der Zellkerne, 1882 ; also Das botanische Praoticum, chap, xxxiv. Fig. 165. Behavior of nucleus during ceU-aivision in the eudosperm of Alliiun to illustrate the extraordinary complexity of the stained bodies. The dark lines represent the chromatin. (Flemming.) DEVELOPMENT OF POLLEN-GRAINS. 379 1000. Development of pollen-grains. This affords some of the most instructive eKainples of cell-division, and owing to the facility with which material can be procured and studied, has received much attention. (1) Sirperficiul phenomena. These, which can be easily traced without the eraplo3'ment of staining agents, are in brief as follows : At the period when the loculi of the anthers begin as minute elevations at the end of the stamen, the external laj'er of cells, which is to serve as epidermis, is underlaid by a group of small cells which give rise to the mother-cells of the pollen and to the lining of the anther itself. This group is termed the archesporium ; by division of its inner layer, large mother-cells are produced which divide to form the pollen- grains. The division of a mother-cell may give rise to two, three, or four pollen-grains, and in some cases more, according to the Fig. 166. Fritillaria Persica. Division of the mother-cells of pollen, a, early stage, in which the threads are confused; &, the segments in course of longitudinal division; c, the nuclear spindle in profile; fZ, tlie same seen from its extremity or pole; e, division of the nuclear plate; /, separation of the derivative or daughter-segments; f?, formation of the derivative tangles and the cell-plate; A, the course of the nuclear threads in the derivative nuclei; i, longitudinal extension; /c, nuclear spindle, on the right, in profile, on the left, from its extremity ; I, separation of the segments, on the left seen in pro- file, on the right from the extremity ; m, formation of the cell-plates. (Strasburger.) 380 VEGETABLli GROWTH. direction of the lines of fission. It is possible to distinguish diiferences in the mode of division which are fairly charac- teristic of Angiosperms and Gymnosperms, of Monocotyledons and Dicotyledons. Although the morphology of the tissues involved and the course of development are not yet complete!}- understood, it may be said that the formation of pollen-grains suggests throughout the mode in which the male elements are produced in the higher cryptogams. (2) Changes in the Nucleus. The following suggestions by Strasburger for demonstrating the nuclear changes in pollen- grains can be applied with few modifications to all cases of cell- division : Place the young part, in this case a yQvy young anther, in a solution of methyl-green in acetic acid, and subject it to slight pressure by which the contents of the anther-cells will be discharged. Those parts susceptible of staining will take the color readily and the different stages can be followed out sub- stantiall}' as shown in the figures. For the staining-agent above mentioned the following may be substituted, — gentian-violet in acetic acid, or nigrosin with picric acid. Preparations made with the latter can be preserved in glycerin without losing color. Another and better method is to place sections of the tissue which has been kept for a few days in absolute alcohol, in an alcoholic solution of safranin, and after twelve hours wash with absolute alcohol ; then transfer them to oil of origanum and thence to a thick solution of Damar in turpentine, for mounting. Tiy the safranin the delicate threads of the spindle are not much colored ; they take, however, a good color with hsematoxy- lin. Other combinations of coloring agents give good results.^ 1001. Cell-division in plant-hairs. The stamen-hairs of Tra- descantia Virginica afford excellent material for this examina- tion. The last or upper three cells while still young are capable of division. If the very j'oung hairs are transferred carefully to a slide on which is a three per cent solution of cane-sugar, the}- will continue the process of cell-division as shown in Fig. 167. If the specimen is a good one, and has not been much injured during its removal, it will remain active for several hours. All the examinations of cell-division require the use of high powers of the microscope, none being better for the purpose than the so-called homogeneous immersion lenses. 1002. The direction in which the new cell- wall Is laid down at the point of growth has been exhaustively examined b}- Sachs. 1 Pas botanische Practieum, 1884, p. 598. DIKECTION OF CELr.-DIVISION. 381 According to him, the planes of the walls at a point of growth maj- be thus classified : ^ — 1 "The relations of the periclinal and anticlinal planes are illustrated by the following cases : — (a) If the outline (in longitudinal section) of the growing point is a parab ola, the periclinals will constitute a system of confocal parabolas of different paranreter, the focns of the system being at the point of intersection of two lines, of which one is the direction of the axis and the other of the parameter. In this case the anticlinals, being the orthogonal trajectories of the periclinals, constitute a system of confocal parabolas, the axis and focus of which coincide with those of the periclinals. (b) If the outline of the growing point is a hyperbola, the periclinals will be confocal hyperbolas, with the same axis hut different parameter ; the anti- clinals will be confocal ellipses, with the same focus and axis as the periclinals. (c) If the outline of the growing point is an ellipse, the periclinals will be confocal ellipses ; the anticlinals will be confocal hyperbolas" (Abstract from Fig. IGT. Tradescantia Virginica. Process of cell-division in the stamen-hairs, a, with a quiescent nucleus in the lower cell, and in the upper, one which has just fin- ished its division ; 6, nucleus showing a coarse granular structure with a tendency to linear arrangement of the particles. The drawings from c to h inclusive exhibit the dilferent stages of cell-division at the following points of time : c, at 10 o'clock and 10 minutes; rf, 1020; e, 10.25; /, 10.30; g, 10.35; 7t, 10.40; i, 10.50; i, 11.10; h, 11.30- (Strasburger.) 382 VEGETABLE GROWTH. 1. Periclinal, those which exhibit in longitudinal section curves in the same direction as the surface. 2. Anticlinal, those wliich cut the surface and the periclinal walls at right angles (forming a sj'stem of orthogonal trajecto- ries for the periclinal walls). 3. Radial, those which pass through the axis of growth and cut the surface at right angles. 4. Transverse, those which cut both the axis of growth and the surface at right angles. 1003. Growth of the cell-wall. When the new cell is formed it undergoes changes in size, and often in shape and thickness. If it increases in size regularlj' at all points of the surface, it preserves, of course, its original shape ; but if its growth is irregular at different points, great modifications of form re- sult. Pollen-grains afford instances of the former method of growth, while the latter is seen in the multicellular organs, for example stems and leaves. At the growing points of the stem and leaf tiie cells when first formed are nearly alike in appear- ance ; but wide differ- ences are soon presented. The growth of a cell in size may be terminal, when it gives rise to elongated forms ; or lo- ^^"^-^ calized at a point, line, or zone, when projections and swellings of various kinds are produced.^ Arteiten des botan. Inst, in Wiirzliurg, 1878, in appendix to Text-book, 2d Eng. ed., p. 951), The student should also read Sachs's Vorlesungen, 1882, pp. 523-557. 1 These have already hcen sufficiently considered in the histological part of this volume, and it is not necessary to again call attention to the adaptations of the resultant structures to their respective kinds of work in the organism. Fig. 168. Arc-auxanometer /, tliread connecting plant witli short arm of lever a z. The weight of long arm balanced by movable weight at k. (Pfeffer.) IlECOEDiNG AUXAlJOMETfeRg. 383 1004. Measurement of growth. In some cases it is very easy to make direct measurements of the amount of increase in vol- ume ; but in general it is necessary to employ some form of appa- ratus by whicli the amount can be more or less exaggerated by a multiplier. Several forms of growth-measurers, or auxanometers, have been devised for attaining this end. The simplest consists of a fixed arc of large radius (see Fig. 168), on which a delicate arm moves up or down according to the direction in which a small wheel at the centre, to which the arm is attached, is moved by the action of a thread fastened to the plant. Care must be taken to balance the arm as perfectly as possible, in order to prevent any strain on the plant by the weight of the index. This form of apparatus is well adapted to demonstration before a class ; and if a rapidly growing seedling or strong scape is chosen for experi- ment, the movement of the arm through the arc in an hour will be sufficient to be clearly seen at a considera- ble distance. A modifica- tion of the apparatus bj' Professor Bessey reduces its cost to a mei-e trifle. Both the arc and its sup- porting radii are made of strong manila paper ; the wheel is a comrnon spool, and the arm may be a slen- der straight straw. 1005. Recording Auxano- meters. For the purpose of registering growth, several applications of the chrono- graph have been made. One of the most satisfactorj' of these consists of a slowly revolving cylinder covered with smoked paper, upon which a needle, attached to the end of a balanced thread passing over a Fig. 169. Registering auxanoraeter. The thread attached to the plant passes over ttie small wheel at x, and is balanced by a weight. The index z is balanced by the weight g ; the thread between theia goes over the wheel r. The cylinder is carried round by the clock-work, which is regulated by the pendulum weight at^. (Pfeffer.) 169 384 VEGETABLE GROWTH. wheel, leaves its trace as it ascends or descends. The wheel is caused to move b}- means of a second balanced thread which yasses over its axis, and which is fastened at one end to the growing part of the plant. 1006. Ffeffer's modification of this apparatus provides that the cylinder shall turn a short distance at regular intervals of time, so that the line made b3' the needle becomes interrupted and thus exhibits the appearance of steps ; in which the height-of the step represents the total ascent or descent of the needle during a given time, while the other line of the step merely marks the dis- tance through which the cylinder moves at the close of one of its intervals. 1007. Examples of very rapid growth are afforded by man^- fungi ; for instance the common puff-ball, which increases enor- mously in size during a single night. Shoots of bamboo have been observed at Kew to grow at the rate of two to three inches in the twenty-four hours ; and in its native habitat, Bambusa gigantea has been known to grow more than ten inches a da}'. The expansion of the leaves of Victoria regia is extremelj- rapid, under favorable conditions reaching a foot in the twenty- four hours. The scapes of many plants develop at a rapid rate, and afford excellent material for practice with the auxanometer. 1008. Conditions of growth. Vegetable growth does not take place unless there is an available supply of assimilated matter, access of free oxygen, and a sufflcientlj' high temperature. Tlie assimilated matter may be furnished to the growing parts di- rectly from green tissues, or from reservoirs where it has been stored up. In either case it must come in a state of solution to the growing cells, and hence a certain amount of water is re- quired for the transfer. That the amount of water demanded is not necessarilj- large, is shown by the starting of shoots from bulbs, tubers, etc., in the spring, even when no water has been furnished from outside. 1009. Although the process of respiration in green plants may go on for a time without free oxygen, as has been sliown by the experiments described on page 371, there is no proof that growth occurs under such circumstances. In an atmosphere of hydrogen, nitrogen, carbonic acid, or nitrous oxide, — gases which are not in themselves harmful to plants, — growth does not take place, as has been proved by experiments upon seeds and seedhngs. Detmer has shown that growth is immediately checked when the plant is deprived of free oxj'gen, but death does not ensue until RELATIONS TO TEMPERATURE. 385 al'tcM- a considerable time. During tlie period of inactivity the plant is ready to respond at once to the influence of oxygen, growth being then immediatel}' resumed. 1010. If assimilated matters and free oxygen, both essential to growth, are abundantly supplied to a plant which is kept at too low a temperature, growth does not occur. The minimum limit for growth is different for different plants, and is not the same for all organs. Again, it must be noted that there is a maximum limit of tem- perature above which growth does not take place, and this limit is also diffei'ent for different plants. Between the lower and upper limits there is, for the plants which have been thus far studied with respect to the effect of heat on growth, an optimum of temperature at which growth is most rapid. 1011. Relations of growth to temperature. The minimii.m tem- perature required for growth is generally much higher for plants of warm regions than for plants of cold climates, and there are wide differences even among plants belonging to the same climate. A few of the earliest spring plants begin their growth at or verj' near the freezing-point of water : it is thought b}' some observers that growth may, in a few cases, take place even below this point. Kjellmann states that the ma- rine algae at Spitzbergen continue to de- velop their thallus during the polar night of three months, and that most of them during this time pi'oduce theii' spores, the temperature of the sea-water being on the average one degree below zero, Centigrade.' But, on the other hand, manj- of the tropical plants ^ cultivated in hot-houses cease growing when the temperature falls below 10° or 15° C. 1012. The maximum temperatu7-e for growth is as wide in its range for different plants as the minimum. Aside from the ^ Comptes Eeudiis, Ixxx., 1875, p. 474. See also Falkenberg : Die Algen iin weitesten Sinne, in Schenk's Botanik, 1882. 2 See De Candolle : Physiologie vegetale, 1832. Fig. 170. Double-walled metallic box for keeping microscopic objects at a given temperature while under observation. (Sachs.) 25 386 VEGETABLE GROWTH. instances of plants growing in liot springs, it may be said to lie at or verj' near 60° C. The figures obtained by Sachs for the common plants he experimented upon are in general between 36° and 46° C. It is a curious fact that some tropical plants are not capable of bearing a higher temperature than a few plants of cold countries.^ 101 3. The optunum temperature for growth lies in most cases between 20° and 36° C. 1014. The following table, compiled bj^ Pfeffer, exhibits at a glance the cardinal points of temperature as they have been determined by four observers : — 1 Pfeffer: Pflanzeiiphysiologie, ii., 1881, p. 123. Fig. 171. Apparatus for keeping peedlinga in a constant temperature Tlie drum at d is an ordinary tlierrao-regulator by whicli tlie flow of illuminating gas can be controlled within narrow limits To insure still greater control, the more sensitive regulator, r. is also employed. The cylindrical vessel, z, has double walls, the space between them being filled with water. Under this vessel a very small burner is sufiicient even for optimum temperature. (Pfeffer.) RELATIONS TO LIGHT. 387 Name of Plant. Temperature for Growth. Observer. Minimum. Optimum. Maximum. °C. >=C. °0 Triticum vulgare . . (5.0 17.5 (28.7 129.7 42.5 Sachs. 1 Kbppen.^ Hordeam vulgare . 5. 28.7 37.7 Sachs. Sinapis alba . . . 0. (21. 127.4 ( 28.0 ( over 37.2 De C'andolle.3 De Vries.'l Lppidium sativum . 1.8 ( 21. 127.4 { 28. 1 below 37.2 De CandoUe. De Vries. Linum usitatissimum L8 (21. 127.4 ( 28. De CandoUe. 1 over 37.2 De Vries. Ti-ifolium repens . . 5.7 21-25. below 28. De CandoUe. Phaseolus multiflorus 9.5 33.7 46.2 Sachs. Pisum sativum . . 6.7 26.6 Kijppen. Lupinus albus . . 7.5 28. Koppen. (9.5 '9.6 (9. ( 33.7 46.2 Sachs. Zea Mais .... 32.4 Koppen. ( 21-28. 35. De CandoUe. Cucuvbita Pepo . . 13.7 33.7 46.2 Sachs. Sesamum orientale . 13. 25-28. below 45. De CandoUe. 1015. Eelations of growth to light. It i.s only under the iufln- enee of light that the plant can prepare from inorganic matter 1 Text-book, 2d Eng. ed., p. 830. 2 Warme und Pflanzensachsthum, 1870, p. 43. ^ Biblioth^que universelle d. Geneve, Archives des Sciences physiques, x.xiv., 1865, p. 243. * Materiaux pour la connaissance de rinflnencede la temperature sur les plantes. Archives Neerlandaises, v., 1870, p. 385. Koppen has given an instructive table which exhibits the relations of growth to temperature in a few common plants. The figures denote the growth in forty-eight hours of the whole descending axis of each plantlet. TemDBrature. °C. Lupinus albus. Pisum sativum Vicia Faba. Zea Mais. Triticum vulgare. 10,4 5.5 4.6 14 4 9.1 5.0 4.5 17. 11.0 5.3 6.9 21.4 25.0 25 5 9.3 3.0 41.8 24.5 31 .30.0 10.1 10.8 69.1 2S.1 40.0 27.8 11.2 18.5 59.2 26.6 SU SS.9 n.s 29.6 86.0 28.5 50.1 40.4 15 3 26.5 73.4 30 2 43.8 38.5 5.6 si.e lOi.9 31.1 43.3 38.9 8.0 49.4 914 33,6 12.9 8.0 50.2 40.3 36.5 12.6 8.7 20.7 5.4 39.6 6.1 11.2 388 VKGEtABLE GROWTH. materials for its growtli ; Imt if an adequate amount of assimilated substance has been stored up, growth can go on in the dark until this store is exhausted. It is, in fact, in the dark that nearlj- all vegetable growth takes place. It is well known that all the points of growth in the ordinary higher plants are more or less protected from the action of light. Thus, the growing tissues of buds are concealed beneath external structures ; so also is the cambium by which dicotyledons increase in thickness. 1016. When, however, a shoot develops in darkness it is apt to become much more attenuated than when it develops in light ; its leaves are etiolated, and of abnormal shape and diminished size. Such shoots are said to be " drawn." 1017. There is considerable difference in the degree to which different parts of plants are affected by the withdrawal of light, and there are also differences in this respect between different species. The effect of dai'kness upon shoots is well shown by the simple experiment of conducting a branch of some strong plant like Tropseolum or a gourd into a dark box, all its other leaves be- ing kept in the light. The effects are more striking when the shoot is a flowering one ; the internodes will be- come much drawn, the leaves will be small and blanched, the calyx will be pale, but the rest of the flower will be hardly aflected either in shape or size. It sometimes happens, however, that the flow ers will be abnormal. 1018. Tlie relations of growth to oxygen. All growth is accom- [)anied by the oxidation of assimilated substance, or food. Can growth be stimulated bj- furnishing to the plant a larger amount of oxygen than it would obtain under natural conditions? This Fio. 172, Growth of gourd in light and (Inrkness. (Sachs.) CHAKGES IN THE KATE OF GKOWTH. 389 question is not yet positively answered by any experiments. It lias been shown that some plants grow, for a time at least, more rapidly when they are subjected to a slight increase of pressure of the atmosphere by which thej' are surrounded ; but there are also a few cases which indicate that some other plants may grow more rapidly under a diminished pressure. The "resting" state of some plants cannot be shortened b^- anj' increase in the amount of oxygen furnished ; it is only after the normal time of rest has ended that any growth begins. When periods of rest cannot be disturbed by any ordinary change in the surroundings, they may be held to be conservative, since they are generally correlated with the climatic conditions of peril from cold or from dryness, under which these plants naturally' live.^ 1019. Periodical changes in the rate of growth. Even under external conditions which are as nearly constant as possible growth is not quite uniform in its rate. Thus, an extending internode grows in length at first slowly, then with gradually accelerating rapidity until a maximum of growth is reached, from which point the rate declines until with maturity of the part growth ceases. The line of growth, when given graphically, is a curve known as the great curve of growth ; and the period of rise and decline is the grand period, to distinguish this from the minor periods of accelerated growth, which appear on the curve as small fluctuations. 1020. Properties of new cells and tissues. Newly formed cells are generally' characterized bj' the possession of a certain amount of turgidit}' ; the young cell-wall exerting more or less resistance to the expansive contents within. The contents are therefore compressed to some degree by the confining wall ; the action and reaction varying, of course, with changes in the surroundings. If a part of its water be withdrawn from the cell, the com- pression is materially lessened ; while, on the other hand, an increase in the amount of water must augment it. 1021. These features have been recently re-examined b\- De Vries, who has suggested a quantitative method for determining the amount of turgidity at any given time. The method, when reduced to its simplest terms, consists in the use of solutions of ^ For a very curious aooount of experiments upon the influence of electricity upon growth, the student should see Grandeau : De I'influence de I'^lectricite atmosph^rique sur la nutrition des vegetaux, Annales de Chimie et de Phy- sique, scr. 5, tome xvi., 1879, p. 145. 390 VEGETABLE GEOWTH. salts of known strength in which the tissues are placed, and which are then allowed to act upon the contents of the cells. When the solutions are more dense than the fluids in the cavity of the cell, an exosmotie action withdraws a certain amount of the water from the cell, causing thereby a shrinking of its contents which can be easilj- observed under the microscope, or noted by curvature of the whole section. The method permits the experimenter to ascertain within narrow limits the density of the contents of a given cell, and to determine the relative degree of turgidity in different cases. When a cell undergoes no change of form upon being placed in a solution of a given strength, that solution is taken as a measure of the density of its contents.^ 1022. Tensions in cell-wall. There may frequently be observed a tension of different la3ers of the cell-wall. This can be easily demonstrated by making thin sections of any succulent tissues from which cells can be readily detached ; a curvature will be detected at the moment of cutting. 1023. Young cell-walls are elastic to a certain extent; but their limit of elasticity is easily exceeded, and then they remain in the stretched condition. When an internode is strongly, stretched in the direction of its length, it undergoes permanent elongation. This elongation may amount in some cases to three or even five per cent ; whereas the temporarj- extension in the same instances may range from seven to seventeen per cent. The extensibility diminishes, while the elasticity increases, with the age of the internode. 1024. From his experiments Sachs draws the following con- clusions regarding growing internodes : (1) After flexion they do not completely recover their straightness ; (2) one vigorous bending, and to a still greater extent repeated ones in opposite directions, leave the internode flaccid, or deprive it of its rigid- ity ; (3) when growing internodes are sharply struck, there is a sudden curvature, the concavit}- of which lies towards the direction of the blow.^ 1025. Tension of tissues. Under the ordinary circumstances of growth walls of young cells continue to be somewhat elastic 1 Pkcsmolysis. For a full account of the qunntitative action of numerous plasmolytic agents the student should consult De Vries's paper in Pringsheim's Jahrbiicher for 1884, where the effect of potassic nitrate and other snhstances upon the protoplasmic film is detailed at length. In the Laboratory at Cam- bridge, Mr. Puffer has confirmed most of De Vries's observations. 2 Sachs ; Text-hook, 2d Eng. ed., 1882, pp. 784-788. TENSION OF TISSUES. 391 and hence exhibit distinct tensions. If there is a marked dif- ference in the rate of growtli between the internal and the ex- ternal cells in any organ, as is the case in most young stems, the more superficial tissues are stretched to some extent by the internal ones ; hence arise tensions of tissues, the organ in this state being in a balanced condition, in which the equilibrium can be disturbed by slight external or internal causes. The following experiment exhibits the phenomenon of tension very strikinglj' : From a long and thrift}' young internode of grape- vine cut a piece which shall measure exactly one hundred units, for instance, millimeters. From this section, which measures exactly one hundred millimeters, carefullj- separate the epi- dermal structures in strips, and place the strips at once under an inverted glass to prevent drying ; next, separate the pith in a single unbroken piece wholly freed from the ligneous tissue. Finally, remeasure the isolated portions, and compare with the original measure of the internode. There will be found an appreciable shortening of the epidermal tissues and a marked increase in length of the pith.' The young ligneous tissue is generally shortened by its release, but this result is bj^ no means constant. The most astonishing feature is the great difference which exists between tlie length of the external tis- sues and that of the internal tissues which up to the period of isolation they had compressed. The external parts had been plainly stretched to a certain extent, while the internal had been as obviouslj' confined by them. The tensions are not only in the direction of the length, but are also transverse. Similar tensions are to be found also in foliar organs. But there are ^ The following table exhibits the remarkable differences in tension be- tween the outer and the inner parts of young shoots of Niootiana Tabacum. Each internode is first cut squarely off at both ends, and then carefully sliced lengthwise so as to separate the bark, wood, and pith from each other. Sup- posing the length of the whole internode to be one hundred units, the length of the cortex will fall short of this, while that of the pith will considerably exceed it. Number of the Internode, counting from the youngest. Length of the Isolated Tissue. Cortex. Woody part. Pith. I.-IV. V.-VII. . . . VIII.-IX. X.-XI.. . . W.l 96.9 96.5 99.5 98.5 98.9 98.5 99.5 102 9 103 5 100.9 102.4 392 VEGETABLE GROWTH. some parts, as for example most roots near their extremity, wliieh do not exhibit this phenomenon. 1026. Geotropism. Suppose a j'oung shoot to possess the ten- sion already described ; let this be placed, while growing, in an horizontal position. In consequence of its position the nutri- ent fluids will, from the force of gi'avitation, have a tendency to collect in greater amount in the cells upon its under side. Their presence on that side will not only cause an increase of turgescence there, but will offer to the growing cells a larger amount of available material for immediate use in growth. especially for lajing down the cell-wall. From one or from both of these causes there will therefore be an appreciable elon- gation of the tissues on the under side, and hence a curving up- wards will occur, which flnallj- results in the assumption of the erect position bj- the organ in question. 1027. If, on the other hand, the organ possesses little or no tension, it is conceivable that the growth would result in a cur- vature of the extremity towards the ground ; this is seen in the case of roots. The same factors produce an upward curvature where there is marked tension of tissues, and permit a down- ward curvature where there is little or no tension. It is a sig- nificant fact that in the case of certain branches from roots the direction of growth is oblique. 1028. Organs which turn towards the earth are termed geo- tropic; those which turn upwards are apogeotropic ; those which pursue in their growth oblique directions have been termed diageotropic. 1029. Heliotropism. It can be shown by exact measurement that in many cases light, especially the more refrangible part of Fig. 17a Vicia Paba Descent of root into mercury. (Sacbs.) HELIOTROPISM. 393 the spectrum, has a retarding effect upon the growth of certain parts, — for instance, upon that of shoots, — exhibiting itself in the curvature of the part towards the side of greatest iUu- mination. Such curvatures are said to be heliotropic. It is, liowever, well known that the shoots and some other parts of a few plants turn away from the light ; such are termed aphelidtropic.^ 1030. Little is known positivelj' as to the natui'e of the influ- ence which light exerts upon growth. The studies of Vines have shown that the influence is largel3- due to the modification of the turgescence of growing cells. ' ' The conditions of growing and of contractile cells are in some respects the same. Turgidit}' is essential to the proper fulfilment of the functions of both, and it has been shown that light has the power of inhibiting, more or less completel}', the activity of both. The most general case of the action of light upon growing cells has been shown to be a diminution in the rapidity of their growth. The cell with dimin- ished or arrested growth may be fairly- compared with one of the cells of a rigid motile organ. In both, the micellse of the pi'o- toplasm are in a state of stable equilibrium so that they do not jield, in the former case to the force which tends to separate tiiem, namely, the pressure of the cell contents, and in the latter to the force which tends to bring them nearer together. The theory that the action of light upon growing cells and upon those of motile organs is due to such a modification of the relations existing between the micellse of the protoplasm that the mobility of the micelloe is diminished, thus gives a satisfactorj- explana- tion of many phenomena which at first sight seem not to have much in common."^ 1031. Hydrotropism. It has been shown by several experi- menters that rootlets when developing in moist air deviate towards a moist surface. This phenomenon, whicli has been examined in detail by Sachs, is termed Hydrotropism. The 1 In order to examine the effects of the different parts of the spectrum upon the growth and movements of plants, the student should cultivate in cases of jjlass of different colors two or three seedlings, as many bulbous plants, and some well-rooted cuttings of hardy house-plants, for instance Pelargonium. Observe whether the growth is more or less rapid under blue glass, and note whether all the seedlings circumnutate in the same manner in the different cascjs. It should be borne in inind that the bulbous plant as it stai-ts has a generous supply of available food, whereas the seedling has a more scanty stoit, and the cutting very little. 2 Arbeiteii 4es hot. Irjst. in ■Wiirzburg, 1878, p. 147- 394 VEGETABLE GROWTH. accompanying figure shows an easj- method of demonstrating this mode of governing the direction of growing roots. 1032. Thermotropism. As might be expected from what has been said regarding the tensions of tissues and the facilitj- with which their balance is disturbed, the effect of warmth in govern- ing the direction of a growing organ must be considerable. Cur- vatures dependent upon temperature are called thermotropic. 1033. Assumption of definite form during growth depends, of course, chieflj' upon inherited tendencies ; but there have been experiments which show that to a slight extent it may be pos- sible hy external influences to induce special shapes of growing structures. Among the most interesting of these are the experi- ments by Pfeflfer ' upon the growth of bilateral organs in some of the lower plants, especially Marchantia ; by De Vries ^ upon 1 Arbeiten des bot. Inst, in Wilrzburg, 1871, p. 77. 2 Arbeiten des bot. Inst, in Wiii-zburg, 1872, p. 223. Pig. 174 Eontsof seedlings affected by moisture daring their descent. The ap- paratus consists of a network frame filled with moist sawdust in which the seedlings germinate. (Sachs.) FOBCE BXEKTED DURING GROWTH. 395 bilatoral symmetry ; by Vochting ' upon the modification of foliar and axial organs. 1034. The amount of force which is exerted by certain organs during their growth has been accurately measured for only a few cases. Thus Darwin ^ found that the transverse growth of the radicle of a germinating bean was able to displace a weight of 1,500 grams, or 3 lbs. 4 oz., and in another instance, 8 lbs. 8 oz. " With these facts before ns, there seems little difficulty in under- standing how a radicle penetrates the ground. The apex is pointed, and is protected by the root-cap ; the terminal growing point is rigid, and increases in length with a force equal, as far as our observations can be trusted, to the pressure of at least a quarter of a pound, probabl}' with a much greater force when prevented from bending to any side by the surrounding earth. Whilst thus increasing in length it increases in thickness, push- ing away the damp earth on all sides, with a force of above eight pounds in one case, of three pounds in another case. . . . The growing part does not therefore act like a nail when hammered into a board, but more like a wedge of wood, which, whilst slowlj^ driven into a crevice, continually expands at the same time hy the absorption of water ; and a wedge thus acting will split even a mass of rock." By means of a framework placed around the fruit of a vigor- ous squash kept under conditions most favorable to its rapid development, Clark ' estimated the force exerted by growth to be about 5,000 pounds. 1035. That external pressure can retard growth is well shown by the experiments of De Vries ' upon the formation of autumn wood (see page 138). By increasing the external pressure ex- erted by the bark he was able to diminish the calibre of the wood-cells and ducts ; whereas, bj' diminishing the pressure (by making longitudinal incisions into the bark) he was able to 1 Botanische Zeitung, 1880, p. 693. 2 The Power of Movement in Plants, 1881, y. 76. ' For a full account of this experiment, see Report of the Secretai-y of the Massachusetts Board of Agriculture for 1874. The great force exerted by the increase in size of the stems and roots of woody plants is sometimes demonstrated in an extraordinary manner by the development of seedlings in crevices. Thus, at the Marien Cemetery in Hanover, Germany, the base of a tree has dislodged the heavy stones of a strongly built tomb. One of the stones, which measures 23 X 28 X 56 inches, has been lifted upon one side to the height of five inches. The tree measures just above its base from ten to fourteen inches in diameter. 4 Flora, 1872, p. 241. 896 VEGETABLE GROWTH. cause a considerable enlargement of the similar elements. Fur- ther observations led him to the conclusion that the striking differences between spring and autumn wood, upon which the annual rings depend, are due to the greater pressure which is exerted by the bark in the latter part of the summer. CHAPTER XIII. MOVEMENTS. 1036. Most of the movements exhibited by. plants are asso- ciated with growth. In the preceding chapter attention has been called to some of these movements, especially those which are ciharacterized by a change in the direction of growing parts (see Geotropism, Hellotropism, etc.). In the present chapter it Is proposed to examine continuous and recurrent movements, and indicate to what extent these are likewise the accompaniment of growth. In the existing state of knowledge no satisfactory classifica- tion of the movements of plants can be made. The provisional one now to be followed is adopted onlj* for convenience. 1037. Locomotion, or movement of the whole organism from place to place, can be observed in some of the lower plants. One of the most interesting examples is furnished by jEtiialium septicum, which at certain stages of its existence consists of approximately pure protoplasm in a naked state. Under favor- able conditions this naked mass (the plasmodlum), which fre- quently attains considerable size, passes in a creeping manner over a moist surface, thrusting out processes in an apparently Irregular manner, sometimes retracting them, but more often bringing up to the advanced part the rest of the uneven mass. The sensitiveness of this mass to the action of external influ- ences renders it a suitable object for the examination of the essential properties of protoplasm, and man}- of the more im- portant facts relative to its movement have therefore alreadj' been given (see 550). It is important to notice particularly' that there is a rhythmical pulsation of the sap-cavities or vacuoles In the Plasmodium, dependent, it is supposed, upon the irregular absorption of water with a varying imbibition power. This spon- taneous pulsation is somewhat affected bj' external conditions ; for instance, it is increased in rate by heat and diminished b\- Bold. 1038. Portions of protoplasmic matter concerned in the repro- duction of many of the lower plants, especially those which 398 MOVEMENTS. live wholly in the water, as the algse, have the power of inde- peiideiit locomotion. This is exhibited strikingly in the motile spores, which are provided with cilia, and can thereby propel themselves fi'om place to place with considerable rapidity. Sim- ilar independent motion is shown also by the antherozoids of many of the lower and even some of the higher cryptogams. The protoplasmic movement by which such locomotion is secured is essentially identical with certain ciliary movements observed in the animal kingdom. 1039. It is a familiar fact that some minute algse, furnished either with walls of cellulose (Desmids) or cellulose impregnated with silicic acid (Diatoms), possess the power of motion, but the cause is not well understood. In the case of the skiff-shaped diatom the motion is somewhat spasmodic, and the course of the organism through the water is not in a straight line, but it is nevertheless enabled to traverse a considerable distance in a short time. Owing to the absence of an}- distinct cilia, it is difficult to conceive the mechanism of propulsion. According to Max Schultze there is a minute slit on the under side of tlie motile diatoms, and through this slit a delicate film of proto- plasmic matter projects. By contact of this motile film with surrounding objects, the diatom, as it is sui)ported in the water, is transported from place to place. These three cases of locomotion, name- ly, of (1) naked protoplasm, (2) of ciliated structures, (3) of apparentl}- closed cells, do not exhaust the list of instances of motion of vegetable organisms from place to place ; other cases are referred to the succeeding volume upon the lower plants. 1040. The movement of protoplasm with- in cell-walls has already been sufficiently examined (see 646) ; but attention should now be called to the fact that chlorophj'll granules (which are always embedded in the protoplasmic mass) frequently assume at night, or when a portion of the leaf is darkened, positions different from those which they have during strong exposure to light. This change Fio, 175. Circulation of protoplasm in hair of Gotfrd. (Sachs.) HYGEOSCOPIC MOVEMENTS. 399 of position is well observed in the tliin leaves of some mosses, the grains generally (1) gathering on the side walls under bright light, but (2) occupying the upper and lower faces of the cells when the intensity of the light is much diminished. The first mode of arrangement is termed apostrophe, the second epistrophe} 1041. Hygroscopic movements are dependent upon the property possessed by dry vegetable tissues of swelling more or less under the influence of moisture. They are most strikingly exhibited in the case of simple parts, like the filamentous appendages of the spores of Equisetum and the teeth of the peristome of certain mosses, notably that of Funaria hygrometrica. They are also seen in the long appendages of many fruits ; for example, in the awns of some grasses, in some Geraniacese, etc., where the}' serve the useful purpose of fastening the fruit with its en- closed seed in favorable soil. When the fruit falls upon moist soil, it at first lies flat ; later, the extremit}' of the appendage and the tip of the fruit form fixed points in the ground ; and then, as moisture is absorbed by the dry tissue, a spiral curva- ture throughout the whole takes place. This continues to twist the tip of the fruit down into the soil, much after the fashion of a corkscrew. This kind of movement is most surprisingly siiown in some of the grasses of South America, and in our native Stipa. In not a few instances the whole plant becomes relatively dry, lolling up into a roundish mass which becomes expanded again upon access of water. Good examples of such action are afl!brdcd ^ In some cases the aggregation of the clilorophyll granules differs somewhat from that described in the text. For a discussion of this subject, consult Frank (Botanisohe Zeitung, 1871, and Pringsheim's Jahrbiicher, viii., 1872), also Stahl (Botanische Zeitung, 1880). Sachs, Prillieux, and Famintzin have contributed much to the discussion. Fig. 176. Cross-section through the leaf of Lenina triscula, showing the position of the chlorophyll granules: A, during the day; B, during exposure to strong light; C, during the night. (Stahl.) 400 MOVEMENTS. by the so-called Resurrection plant of California (Selagi.nella lepi- dophylla) , and by the Oriental plant known as the Rose of Jericho. The latter plant, when dry and shrunken into small compass, takes the shape of an irregular ball, becomes detached from the ground where it has grown, and may be blown about over great distances ; if it has ripe seeds, these are scattered during transit. 1042. MoTements due to changes in structure during ripening of fruits. The fruit of the common Impatiens, or Touch-me- not, affords a familiar instance of the movements of this class. As it approaches maturity, the valves of the capsule become tense, each one, so to speak, holding the others in place ; and when they are disturbed by even a slight touch they separate violentlj", and bj- their spring throw the seeds to considerable distances. In some cases the mechanism is more elaborate, notably in the cucumber-like fruit of Momordica Elaterium. In this the separation of the fruit-stalk permits a sudden shrinking of the whole pericarp and a violent escape of the seeds with a viscid liquid through the opening made by the separation. The seeds are projected considerable distances from the fruit. Hildebrand ^ distinguishes between (1) dry explosive fruits (such as Violet, Witch-Hazel, and Lupinus luteus), and (2) fleshy explosive fruits (such as Impatiens, Momordica, and Cardamine hirsuta) . 1043. Revolving moTsments, or Circumnutation. The tips of all joung growing parts of the higher plants, as well as the tips of many of the lower, revolve through some orbit, either a circle or some form of the elhpse, the latter sometimes being so narrow that it becomes practically a straight line. During its revo- lution a tip bows or nods successively to all points of the compass ; whence the name nutation, or, as termed bj- Sachs, revolving nutation. Darwin, who re-examined the whole subject, has suggested a more general term, namely, circumnutation. "Circumnutation depends on one side of an organ growing quickest (probably preceded by increased turgescence) , and then another side, generally almost the opposite one, growing quickest." ^ 1044. Owing to the fact that there are numerous instances in which the revolving movements are variously modified, that is, " a movement already in progress is temporarily increased in 1 Pringsheim's Jalirbiiclier, ix., 1873, p. 235, where the whole subject is discussed in an interesting manner. 2 Darwin : Power of Movement in Plants, 1880, p. 99. CIRCUMNUTATION. 401 some one direction and temporarily diminished or arrested in other directions," it has been found convenient to discriminate between circumnutation and modified circumnutation. Darwin divides the latter into two classes of movements : (1) those dependent on innate or constitutional causes, and independent of external conditions, except that the proper ones for growth must be present ; (2) those in which the modification depends to a large extent on external agencies, such as the daily alter- nations of light and darkness, light alone, temperature, or the action of gravity. It is plain that such a division cannot be ab- solute ; in fact, numerous intermediate cases are known to exist. 1045. Methods of observation of circnmnntation. For meas- uring the rate and determining the exact direction of the move- ments of circumnutating parts when the parts are small and the movements slight, the following methods described by Dar- win 1 can be employed in nearlj' all cases where it is necessary to magnify- the amount of displacement. 1 Power of Movement in Plants, 1880, p. 6. Fig. 177. Angular movements of a leaflet of Averrhoa bilimbi during its evening descent, when going to Bleep. Temp 78-81° F. Tlie ordinates represent the angles which the leaflet made with the vertical at successive instants. A full in the curve represents an actual dropping of the leaf, and the zero line represents a vertically dependent position. Each oscillation consists of a gradual rise followed by a sudden fall. (Darwin.) 402 MOVEMENTS. A very slender filament of glass, made bj' drawing out a thin glass tube until it is no larger than a hair, is to be afHxed to the tip of the root, stem, or leaf under observation ; this is easily done by means of a quickly drying varnish, for instance shellac dissolved in alcohol. In order to mark the path made by the filament it is best to cement to the tip of the slender hair of glass a very minute bead of black sealing-wax, "behind which a bit of card with a black dot is fi.xed to a stick driven into the ground. The bead and the dot on the card are viewed througli the horizontal or vertical glass plate (according to the position of the object), and when one exactly covers the other, a dot is made on the glass plate with a sharply pointed stick dipped in thick In- dia ink. Other dots are made at short intervals of time, and these afterwards joined by straight lines. The figures thus traced are an- gular ; but if the dots are made every- one or two minutes the lines are more curvilinear, as oc- curs when radicles are allowed to trace their own course on smoked glass plates " " Whenever a great increase of the movement is not re- quired, another and in some respects a better method of obser- vation is followed. This consists in fixing two minute triangles of thin paper, about one twentieth of an inch in height, to the two ends of the attached glass filament ; and when their tips are brought into a line so that they cover one another, dots are made as before on the glass plate."' 1 It is very convenient to employ large "bell-jars, or hemispherical glasses, as glass screens upon which to recorii the dots indicating the position of the tip at any given moment. It must be remembered that in all these cases there Fig. 17R. Tracing, showing tlie conjoint circnmnutation of the liypocotyl and cotyle- dons of BrasBica oleracea during 10 hours and 45 minutes. Figure reduced to one half original scale. (Darwin.; CrilCUMNUTATION IN SEEDLINGS. 403 1046. Cii'cuiiiiiutation in seedlings. That part of the axis which is below the cot3ledons is made up of a rudinientaiy stem known as the cdulide or hypocotyl, and a rudimentary root or radicle proper. The part of the j'ouiig stemlet above the cotyledons is termed the epicotyl. In the cotyledons of the plantlet, when freed from the seed-coats, and in all parts of the young axis, slight movements can be observed. In all observations it is necessary to remove the plantlet as far as possible from disturb- ing conditions ; thus, all light must be excluded until the moment of making the observation, when only a faint light should be emplo3'ed. 1047. Two facts are easily apparent with regard to the revolv- ing radicle: (1) its extreme sensitiveness to contact; (2) its ten- dency to yield to geotropism (see 1026). 1048. The caulicle, upon emerging from the seed-coats, is often more or less arched : but it may become straight after a short time, when it can be seen to pass through an elliptical orbit by which the plane of the cotyledons is somewhat inclined suc- cessivel}' to all points of the compass. Darwin has shown that even before the liberation of the caulicle from the seed-coats, when both columns of the arch are held in the soil, the top of the arch n)oves with considerable regularit}'. It is difficult to understand how tlie summit of the arch formed by the curved caulicle can revolve when both of its supporting columns are fixed in the soil. Darwin has accepted an explanation suggested bj" Wiesner, which is brieflj' as follows : In a given internode (it must be remembered that the caulicle represents the first internode of the seedling, as shown in Volume I. page 9) there may be a zone in which the growth is equal on all sides, and which may be termed the zone of indifferent growth, while on each side of this there maj' be two others in which there is unequal growth at intervals of time. Then bj' the faster growth on one side of the arch the summit would be thrown to one side, and this process is more or less distortion produced by the best methods of projection, and in all accurate observations this must be taken into account. When seedlings are inverted so that the glass filament is held upwards, it must be noted that the influence of gravitation must come in as a modifying element. To mark the amount of influence exerted by gravitation, it is well to vary the length and weight of the filament employed. But it must be ob- served that the weight of the organ itself is the most important element in the problem. Moreover, it has been observed that all young growing parts, espe- cially the extremity of the radicle, are more or less sensitive ; and hence the course of the filament may be somewhat modified by even slight contact. 404 MOVEMENTS. would sooner or later be succeeded ]>y its reversal ; and thus the summit would be made to circumnutate. 1049. Darwin's' illustration of the movements of the parts of seedlings gives a clear idea of their sequence. " A man thrown down on his hands and knees and at the same time to one side by a load of hay falling on him, would first endeavor to get his arched back upright, wj-iggling at the same time in all directions to free himself a little from the surrounding pressure ; and this may represent the combined effects of apogeotropism and cir- cumnutation when a seed is so buried that the arched hypocotyl or epicotj'l protrudes at first in a horizontal or inclined plane. The man, still wriggling, would then raise his arched back as high as he could ; and this may represent the growth and con- tinued circumnutation of an arched hj-pocotyl or epicotyl before it has reached the surface of the ground. As soon as the man felt himself at all free, he would raise the upper part of his bod3', whilst still on his knees and still wriggling ; and this maj- repre- sent the bowing backwards of the basal leg of the arch, which in most cases aids in the withdrawal of the cotyledons from the buried and ruptured seed-coats, and the subsequent straight- ening of the whole hypocotyl or epicotyl, circumnutation still continuing." 1050. The cotyledons not only share the movement of the caulicle, but thej' have also an independent movement which is greatlj- modified by slight changes in the surroundings. Freed from their seed-coats, they move upwards and downwards in very narrow ellipses, and at diflTerent rates in different plants. Gen- erally their movement takes place only once in the course of the twenty-four hours : in Cassia tora, on an average, once in about two hours ; in Oxalis rosea, once in about three hours ; while in Ipomoea eoerulea Darwin observed the change of position to occur almost hourly. It is noticeable that the cotyledons may change the direction of their movement slightly at different times of the day, and may thus have a zigzag course during a part of the day and a nearly regular orbit during the rest. 1051 . In' some of the seedlings which have been examined with especial reference to their movements there is a joint or swelling to be detected at the base of the petiole. This is the equivalent of the pulvinus commonly found in Sensitive plants ; changes in the position of cotyledons provided with such joints depend, as in the case of sensitive leaves, upon variations in the turgescence I Power of Movement in Plants, 1880, p. 106, TWINING PLANTS. 405 of the cells composing it, wliile changes in the position of cotjle- dons devoid of them are due to unequal growth. 1052. Circumnutation of the young parts of mature plants. By methods similar to those described in 1045, it can be shown that the growing extremities of stems, branches, leaves, and their numerous modifications possess the power of movement ; in sume instances exhibiting essentiall}^ the same phenomena as those presented by the parts of the seedling, while in other cases they show differences at an early stage. The most striking of these differences is that observed in twining stems. In this case there is a greatlj' increased amplitude of the orbit through which the tip of the stem passes. Although only a special case under a general class, twining stems ma}' well receive a somewhat detailed description. 1053. Twiners are distinguished from proper climbers by the absence of au}' special organs, other than the stem itself, for grasping sup- ports ; climbers being provided with some sort of tendrils, or other help, by which the plant is held to its sur- roundings. Taking the simplest cases of twiners, such as that of the common Morning Glory, it is to be observed that (1) the revolving movement begins at the earliest moment ; (2) onlj' a few young internodes are concerned in the revolving ; (3) the revolving stem cannot twine around a smooth support (for example, a glass rod), but requires in the sui)port some degree of rough- ness ; (4) there is a limit of size to the support, different for different twiners, beyond which it cannot be grasped by the revolving stem ; (5) the dii-ection of the revolution is not tlie same for all twiners ; (6) the rate differs with the plant and with the surroundings. 1054. In the early state of a twining plant the movements are in narrow ellipses ; but with even a slight increase in size of the seedling, the transverse axis of the ellipse becomes greater, and soon the orbit is practicallj' a circle. 1055. The number of internodes concerned in the twining movement is usuallj- not more than three or four, and sometimes Fig. 179. Bevolving shoot of Morning Glory. 406 MOVEMENTS. only two are involved. The iuternodes below the seat of move- ment are rigid. The revolving is associated with growth, but the growth alone is probably not the sole cause of the move- ment. 1056. It is only the young internodes which are capable of spontaneous movement ; but growth itself, unassociated with changes in the turgescence of the tissues upon the different sides,, would not be sufficient to account for the movement. It must be remembered that the j'oung stem possesses remarkable ten- sions, which are easily disturbed by slight internal as well as external causes. The increased turgescence of its cells upon one side, or their diminished turgescence on the other, or the action of both conjointl_y, followed as this is b}' an increased growth of the turgescent part, would produce sufHciefit change in the cur- vature of the stem to bring about the twining movement. 1057. When a twining stem comes in contact with a smooth support, it generall3' slides up the support, but fails to grasp it. The check which is given by a smooth support sometimes brings about a change of position in the revolving stem, which is thus described by Darwin : ' ' When a tall stick was so placed as to arrest the lower and rigid internodes of Ceropegia, at the dis- tance at first of fifteen and then of twent3'-one inches from the centre of revolution, the straight shoot slowlj' and gradually slid up the stick, so as to become more and more highly inclined, but did not pass over the summit. Then after an interval suffi- cient to have allowed of a semi-revolution, the shoot suddenly bounded from the stick, and fell over to the opposite side or point of the compass, and reassumed its previous slight inclina- tion. It now recommenced revolving in its usual course, so that after a semi-revolution it again came in contact with the stick, again slid up it, and again bounded from it and fell over to the opposite side. This movement of the shoot had a very odd ap- pearance, as if it were disgusted with its failure, but was resolved to tiy again."' 1058. Many of the common twiners of temperate climates are able to twine round very slender supports, for instance a small cord, but are unable to twine round a post or trunk of a tree. This does not, however, appear to be wholly dependent upon the amplitude of the revolution. In tropical regions some of the twiners ascend trunks of immense size, but thej- are generally assisted by adventitious roots, etc. 1 Climbing Plants, 1875, p. 21. MODIFIED CIROUMNUTATION. 407 1059. Any given twiner generally twines in one direction only ; for instance, the hop moves in the direction of the hands of a watch, or to use another expression, follows the sun ; the Morning Glory moves in an opposite direction. But there are some cases in which the direction of twining is reversed even during a comparatively short distance. In the tropics this reversal is said to be common. i 1060. The time required for the revolution of a twiner varies in different plants, and is by no means constant for the same plant at different stages of its development. In the case of the Morning Glory, the average time required for the revolution of a thrifty shoot under favorable conditions is about three hours. 1061. Twiners are affected somewhat by the amount of light received, but the revolving goes on uninterruptedly night and daj-. The increase of rate when a revolving shoot is approach- ing a window may be equal to a tenth, or somewhat more, of the whole period of the revolution. Such acceleration is very differ- ent for different plants. 1062. Modified circunmutation. The effect of the influence of light in increasing the rate of movement in a twiner is a good example of a large class of modified movements. These move- ments have alreadj' been considered in the chapter on "Growth," under the terms Heliotropism, Geotropism, etc., but must be again referred to in connection with the universal movement, circumnutation. When it is desirable to free any circumnu- tating part from the influence of a disturbing factor, for instance light, great care must be taken to avoid subjecting it to abnor- mal conditions such as result when a seedling is kept in the dark in order to free it from the influence of light on its movements. When so kept it undergoes changes of form with its blanching, and therefore little security is felt that all its behavior is normal. In the instance of green plants which demand light for their healthy activity the removal of disturbing factors is a task of considerable difficult}-. A part of the difficulty is removed by the use of some instru- ment by which the plants can be made to revolve slowlj- in a given plane, thus exposing the different sides successively to the action of the force. A simple form of this appliance is 1 Fritz Mtiller is quoted by Darwin as saying, that the stem of Davilla twines indifferently from left to right or from right to left ; and that he once saw a shoot which had ascended a tree about five inches in diameter reverse its course. 408 MOVEMENTS. known as the dinostat. It consists of a clock-work which car- ries a disc on which can be placed growing plants : by the revo- lution of this horizontal disc all parts are in turn given the same , amount of illumination. If the clock-work is so arranged as to rotate a horizontal shaft to which a growing plant can be affixed, any one part of the plant will be exposed to the influence of gravitation in precisely the same manner and to the same extent as all other parts. When circumnutation is plainly modified by unequal growth, striking disturbances are produced which have received much investigation. Among these cases are the changes of position which many peduncles undergo during the development of flow- ers and fruits. Although the extremity of the flower-stalk passes through its definite orbit, it is in some instances so affected by the greater growth of the upper side as to curve downwards, while a similar excessive growth on the under side will produce an upward curvature. De Vries, who has given much attention to these phenomena, has coined the adjectives epinastic, denoting curvature from growth on the upper side, and hyponastic, that from growth on the under side of an extending organ. Fig. 180. Disc of a clinostat covereil by a glass case g, and bearing two Windsor beans witli primary and secondary roots. NYCTITBOPJG MOVEMENTS. 409 lOGo. The ample revolving inovement is not conflned to stems, iiiit is observed in some modified branches and leaves, for ex- ample in certain ten- drils, etc. A single instance will serve to show the remarkable nature of the move- ment in the case of the tendrils of Echi- nocystis lobata, as de- scribed b}' Darwin:^ ' ' These are usually inclined at about 46° above the horizon, but they stiffen and straighten themselves so as to stand upright in a part of their circular course ; namely, when the3' approach and have to pass over the summit of the shoot from which they arise. If they had not possessed and exercised this curious power, they would infallibly have struck against the summit of the shoot and been arrested in their course. As soon as one of these tendrils with its three branches be- gins to stiffen itself and rise up verticallj', the revolving motion becomes more rajjid ; and as soon as it has passed over the point of difficulty, its motion coinciding with that from its own weight causes it to fall into its previously inclined position so quickly that the apex can be seen travelling like the hand of a gigantic clock." 1064. Jfyctitropic, or sleep, movements. The foliar organs of manj- plants assume at nightfall, or just before, positions unlike those which they have maintained during the day. In many cases the drooping of the leaves at night is suggestive of rest, and the name given by Linnaeus to this group of phenomena, namely, "the sleep of plants," seems appropriate. But in numer- ous cases the nocturnal position is one of obvious constraint, and considerable force has to be expended in lifting the leaf to 182 1 Power of Movement in Plants, 1880, p. 266. Ftg. 181. Leaf of Coronilla rosea at night, f Darwin.) FiQ. 182. Leaf of White Clover. ^, day position ; B, night position. (Darwin.) 410 MOVEMENTS. the new position. The diversitj- of positions can be only impev- I'ectly indicated bj^ the accompanying illustrations. According to Pt'effer, the sleep-movements of leaves and of cotyledons depend upon increased growth on one side of the median line of the petiole and midrib, followed after a certain interval of time bj' a corre- sponding growth on the opposite side. Thus in ordinary leaves which droop at night the depres- sion is produced bj- a slightly in- creased growth on the upper side, and the rise in the morning by a similar growth on the under side. But in the most striking cases there is a distinct appara- tus at the base of the leaf-stalk, which accom- plishes the same movement by simple turges- cence of the op- posite sides. The apparatus consists of an enl argemen t formed of cellu- lar tissue in which there is often an appre- ciable difference between the character of the cell-walls on the upper and under side of the swelling. This swelling, known as the pulvinns, permits the movement to be Fig. 183 Leaflets nfAveiTlioa bilimbi al iiiglit. CDarwin.) Fig. 184. Leaf of Acacia Farnesiana during tbe day and at night. (Darwin. ) SLEEP-MOVEMENTS. 411 continued long after the movements in joung leaves destitute of sucli an apparatus have ceased. 1065. The sleep-moTements of cotyledons are extreinel}' diverse, but in general consist in an elevation of the tips, bringing the upper faces into proximity, and sometimes into contact. It may happen also that one or more of the early leaves developed from the plumule approaches the elevated cotyledons. Dar- win has noted that in some cases tlie cotjiedons of plants, with ordinary leaves which exhibit sleep-movements, may not change their position at night, except as they do in simple circum nutation. 185 1066. The utility of the sleep-movements of leaves and cotyle- dons is believed to consist in protection from too great radiation during the night. Darwin has shown h^' simple and conclusive experiments that in the case of some plants this change of the position of leaves at the approach of a chilly night is a matter of life and death. When leaves which naturally assume nyctitropic positions are pinned or otherwise kept from changing their position, and the plant is exposed to a temperature a little below freezing, under a clear sky, into which the radiation of heat must go on rapidly from the upper surface of the leaves, serious injuries result, the leaves becoming browned and even killed ; whereas, leaves on Fig 185. Desmoilium gj'rans. A, position during the day ; B, rosltlon at night. 412 MOVEMENTS. the same plant wliich are allowed to take the protective position, escape. 1067. Sleep-movements of floral organs. Tliese are, in general, dependent, as Pfeffer has clearly shown, upon the alternate growth of the opposed surfaces. For instance in a crocus, the greater growth of the inner surface of the parts of the perianth will l)ring about an opening of the flower, whereas the greater growth of the outer surface will effect a closing. Pfefffer's method of investigation is capable of application, pro- vided one has a microscope which admits of being held with its tube horizontal. A perianth leaf is cai-efully detached without too much violence from the flower, and immediately placed in a small tube containing water, so that the expanded part may be brought within the fleld of the microscope. If fine lines are measured off upon its inner and outer surfaces in India ink, their gradually increasing distance from each other can be watched to good advantage. It can then be clearl}- seen that when the part curves outward it is owing to an increased growth upon the inner surface, and vice versa. That there is an ante- cedent turgescence is ver\- likely-, as lias been repeatedly pointed out by De Vries and others. It is probable also that in a few cases the opening and closing are dne to a temporary turges- cence unaccompanied hy much growth. Changes in illumination and in temperature are sufficient to effect the alternations of growth and of tnrgescence in delicately- constituted parts, where there is a balanced tension existing between the outer and inner tissues. 1068. Times of opening and closing in the open air. Under the ordinarj- conditions of an equable climate the times of opening and closing of the flowers of a given plant do not varj' widel3-. Hence it is possible to construct a floi'al clock which shall mark the hours with tolerable regularity. The dial at IJpsala, Sweden, suggested by Linnaeus, and that designed for Paris liy Ue Can- dolle,^ are approximately correct ; but in a climate having the sharp and sudden differences of heat and of moisture which characterize eastern North America such floral clocks are not successful. ^ The following list from De Candolle's Physiologie gives the hours of the opening of certain flowers in Paris : — Ipomoja purpurea 2 A. M. Calystcgia sepium 3-4 " Matricaria suaveoleus 4-5 " THE TELEGKAPH PLAXT. 413 1069. The Telegraph plant. The most surprising instance of rapid spontaneous movement is that which is exhibited by the lateral leaflets of Desmodium gyrans. Each complete leaf of Desmodium consists of a large terminal leaflet and two little lateral leaflets. At nigiitfall the terminal leaflets sink vertically, and the peti- oles are somewhat raised, so that the terminal leaflets are much crowded together upon the stem (see Fig. 185.) The cotyledons do not have this nyctitropic movement, but the first true leaf sleeps just as do the older ones. The lateral leaflets do not fall at night, but at the tem- perature of 36 to 38° C, or even somewhat higher, keep up, night and day, an iiTegu- lar jerking movement, which has been compared to the ticking of the second-hand of a Watch (or, formerly, to the movements of the arms of a Semaphoi-e Telegraph). The tip of the moving leaflet passes Papaver nudicaule aud most Cichoriacese ... 5 A. M. Convolvulus tricolor 5- Convolvulus siculus 6 Species of Sonchus and Hieraclum 6- Speoies of Lactuca 7 Anagallis arvensis 8 Calendula arvensis 9 Arenaria rubra 9- Meseuibryanthemum nodiflorum 10- Oniithogalum umbellatum 11 Passitiora ccerulea 12 Pyrethrum oorymbosum 2 Silene noctiflora 5- (Enothera biennis 6 Mirabilis Jalapa 6- Lychnis vespertina 7 Cereus grandiflorus 7- FiQ. 186. Desmodium gyrans, -6 (( -7 (< '< (( 10 >> 11 (( (C M. p . M 7 " 414 MOVEMENTS. through its elliptical orbit in a period of from half a minute to a minute or more, the time var3-ing greatly according to the ex- ternal conditions, but being nearly- uniform under uniform high temperature. The lateral leaflets move independentl}- of one another, one sometimes passing downwards while the other is ascending, but there is no distinct relation between them. At the base of the terminal leaflet, the base of the lateral leaf- lets, and the base of the main petiole, are pulvini, to changes in which the several movements are due. 1070. The cause of autonomic moTements not fully known. As to the cause of the periodic changes in turgescence and asso- ciated growth which give rise to " spontaneous " movements, little is at present known. The fact that in the naked protoplasm of the Plasmodium of the M3-xoni3-cetes the sap cavities exhibit a rhythmical pulsation which is thought to be dependent npon variations in the imbibition power of the protoplasm for water, throws little light upon the ultimate cause which underlies vari- able turgescence in one case and variable pulsation in the other. Although vaiiations in turgescence and associated growth are everywhere observable in joung and still parts of plants, in some instances similar phenomena can be observed, as we have just seen, in specialized organs which are no longer capable of growth. 1071. DeVries ' calls attention to the fact that organic acids or their salts, as thej- are formed in tissues, have a maikcd eflfeet upon the turgescence of the cells composing the tissue. If these compounds were produced first in the cells on one side of a shoot or other motile organ, and then in the cells next to these, and so on, the phenomena of circumnutation would be exhibited. Its cause will probably be found in chemical processes which cause the osmotic power of the cell-contents to var}'.'^ 1072. SensltiTeuess. B}- this is meant the capacitj- to react against an irritation ; thus, the root is said to be sensitive to moisture, some leaves to light, etc. But it is usual to employ- the term in a more restricted signification ; following Darwin's cautious definition, " a part or organ maj- be called sensitive, when its irritation excites movement in an adjoining part." ' The iiTitant may be shock, prolonged contact, a light touch, or a chemical agent. 1 Botanische Zeitung, 1879, pp. 830, 847, and in an independent commnni- cation. ^ Pfeffer : Periodisehen Bewegungen (1875). 8 Power of Movement in Plants, 1880, p. 191. SENSITIVENESS OF KOOTS. 415 1073. It has been shown (1024) that young shoots react, although somewhat sluggishly-, against mechanical shocli, their change of form or direction depending on the character or direc- tion of the blows received. In certain delicate tissues, especially those which possess much simplicity of structure, change of form and of direction may be produced in response to comparatively slight mechanical or chemical irritation. It is to these that the term sensitive tissues is property applied. 1074. SensltiTeness of roots. The tip of the caulicle is gen- eralty sensitive to contact and to caustics. There are, however, great differences in the degree of sensitiveness ; in some cases slight contact being sufficient to cause reaction, while in others the contact must be prolonged and accompanied b}' direct pres- sure. If the caulicle with its unformed root is placed under conditions where growth can take place with great rapidity, the sensitiveness is much impaired and sometimes is wholty lost ; it is partially lost also when the caulicle grows slowly, or is forced to grow out of season. Under natural conditions and at a normal rate of growth the tip is sensitive for about one twen- tieth of an inch. If a piece of caustic is applied to the tip (not more than 1.5 mm. from the ver^- end), the caulicle will curve away from the irritated side. The reaction is as plainly- seen in those cases where the caulicle does not elongate, but where the root itself descends. 1075. The length of the portion of these organs which reacts is about ten millimetres. The time of reaction varies for different plants, being sometimes in five hours, and, according to Darwin, almost alwaj-s within twentj'-four hours. 1076. " The curvature often amounts to a rectangle ; that is, the terminal part bends upwards until the tip, which is but little curved, projects almost horizontally. Occasionally the tip, from the continued irritation of the attached object, continues to bend lip until it forms a hook with the point directed towards the zenith, or a loop, or even a spire. After a time the radicle apparentlj" becomes accustomed to the irritation, as occurs in the case of tendrils ; for it again grows downwards, although the bit of card or other object may remahi attached to the tip." 1 1077. The tip of the radicle has been shown (1046) to be constantly circumnutating. By this movement the sensitive tip is brought into contact with different sides of minute crevices in 1 Power of Movement in Plants, 1880, p. 193. 416 MOVEMENTS. the soil/ and " as it is always endeavoring to bend to all sides, it will press on all sides, and will thus be able to discriminate between the harder and softer adjoining surfaces . . . eonse- qaentl3- it will tend to bend from the harder soil, and will thus follow the lines of least resistance." ^ 1 Darwin : Power of Movement in Plants, p. 197. 2 The two following passages should be carefully studied by the student, since they embody in a few words Darwin's summary of most of the results of his experiments upon radicles. Both passages are from the " Power of Move- ment in Plants," 1S80 ; — " We see that the course followed by a root through the soil is governed by extraordinarily complex and diversified agencies, — by geotropism acting in a different manner on the ]U'imary, secondary, and tertiary radicles, — by sensi- tiveness to contact, different in kind in the apex and in the part immediately above the apex, and apparently by sensitiveness to the varying dampness of diflereiit parts of tlie soil. These several stimuli to movement are all more powerful than geotropism, when this acts obliquely on a radicle which has been deflected irom its perpendicular downward course. The roots, moreover, of most plants are excited by light to bend either to or from it ; but as roots are not naturally exposed to the light, it is doubtful whether this sensitiveness, which is perhaps only the indirect result of the radicles being highly sensitive to other stimuli, is of any service to the plant. The direction which the apex takes at each successive period of the growth of a root ultimately ,determines its whole course ; it is therefore highly important that the apex should pursue from the first the most advantageous direction ; and we can thus understand why sensitiveness to geotropism, to contact, and to moisture, all reside in the tip, and why the tip determines the upper growing part to bend either from or to the exciting cause. A radicle may he compared with a burrowing animal such as a mole, which wishes to penetrate perpendicularly down into the ground. By continually moving his head from side to side, or circumnutating, he will feel any stone or other obstticle, as well as any difference in the hard- ness of the soil, and he will turn from that side ; if the earth is damper on one than on the other side, he will turn thitherward as a better hunting-ground. Nevertheless, after each interruption, guided by the sense of gravity, he will be able to recover his downward course and to burrow to a greater depth " (p. 199). "We believe that there is no structure in plants more wonderful, as far as its functions are concerned, than the tip of the radicle. If the tip be lightly pressed or burnt or cut, it transmits an influence to the upper adjoining part, causing it to bend away from the afl'ected side ; and, what is more surprising, the tip can distinguish between a slightly harder and softer object, by which it is slnmltaneously pressed on opposite sides. " If, Iiowever, the radicle is pi'essed by a similar object a little above the tip, the pressed part does not transmit any influence to the more distant parts, but bends abruptly towards the object. If the tip perceives the air to be moister on one side than on the other, it likewise transmits an influence to the upper adjoining part, which bends towards the source of moisture. When the Tip is' excited by light (though in the case of radicles this was ascertained in only a single instance) the adjoining part bends from the light ; but when CIRCDMNUTATION OF TENDRILS. 417 1078. SensitiTeness of steins and branches. Under ordinary conditions even twining stems are not sensitive to slight mechani- cal irritation. The reactions to moisture, light, gravitation, etc., have been already noticed, and it is now intended to call atten- tion to the extraordinar}' sensitiveness of certain tendrils, some of which are modiQed branches, while others are modified leaves or parts of leaves. 1079. Tendrils cireumnutate, and by their revolving movement reach out for a pi-oper support. Moreover, they are produced on the young and cireum- nutating ex- tremities of shoots, so that two modes of revolution are frequently to be observed simulta- neously. But in this revolving move- ment the tendrils are prevented from becoming entangled with the rest of the shoot. The manner in which this is done is thus described: " When a ten- dril, sweeping horizontallj-, conies round so that its base nears the parent stem rising above it, it stops short, rises stif- fly' upright, moves on in this position until it passes by the stem, then rapidly comes down again to the horizontal po- sition, and moves on so until it again approaches and again avoids the im- pending obstacle." ^ 1080. When a light thread is placed upon a long revolving tendril of Passiflora, Echinoeystis, or excited- by gravitation the same part bends towards the centre of gravity. In almost every case we can clearly perceive the final purpose or advantage of the several movements. Two, or perhaps more, of the exciting causes often act simultaneously on the tip, and one conquers the other, no doubt in accordance with its importance for the life of the plant. The course pursued by the radi- cle in penetrating the ground must be determined by the tip ; hence it has acquired such diverse kinds of sensitiveness. It is hardly an exaggeration to say that the tip of the radicle thus endowed, and having the power of directing the movements of the adjoining parts, acts like the brain of one of the lower animals ; the brain being seated within the anterior end of the body, receiving impressions from the sense organs, and directing the several movements" (p. 572)._ . 1 Gray : How Plants Behave, 1872, p. 18. Fig. 187. Shoot of Passiflora, showing tendrils. 27 187 418 MOVEMENTS. Sicj-os, a curvature soon takes place in the direction of the eon- tact. If the plant is in a vigorous condition and the tendiil is 30ung, a slight touch is generalh- snfHcient to cause immediate flexion. If a solid object, for instance a staff, is placed in con- tact with such a tendril, the bending and coiling takes place at once, and thus the organ is brought into close apposition with the support. 1081. As soon as the tendril has coiled around its support, a striking phenomenon is observed in the portion between the shoot and the support : it begins to twist, throwing the whole thread into a double coil, a part of which winds one way and the rest another. There can be no doubt that this comes from the action of the same force which causes the revolution in the ten- dril before it becomes attached to the support, and the further exercise of this force must necessarily produce two coils running in opposite directions. After the tendril has made fast to its suppoi-t, its structure begins to change in a remarkable manner, becoming much firmer and more elastic than before, — a provision adapting it admirably to resist sudden strains upon the main shoot from gusts of wind. 1082. But if the tendril in its revolution has failed to come in contact with anj' proper support, it is thrown into a single coil, which runs from the extremity of the tendril, and extends for a short distance, perhaps half the whole length of the organ. Sometimes, however, it simply becomes flaccid. FlO. 188. Ampelopsis quinqnefolia, or Virginia creeper. SENSITIVENESS O/.' LEAVES. 419 1083. In some cases tendrils are not sensitive to contact, but are distinctly apheliotropic, turning- away from tlie light, and in tliis wa3' securing for the plant an adequate mechanical support upon some wall or the like. Grape-vines and Virginia creeper furnish good examples of such tendrils. The branches of the tendrils of the grape-vine sometimes clasp around a slender sup- port, somewhat in the same way as an object would be grasped by a thumb and finger. The much-branched tendrils of species of Ampelopsis are also apheliotropic ; but when the tips of the branches of the tendrils come in contact with a wall, they become expanded into flat discs which cling to the surface. 1084. Sensitiveness of petioles. This can be easily examined in the common climbing species of Clematis,in Solanura jasminoides, etc. The leaves circumnutate and, in the case of compound leaves, the separate leaflets also. When 3'oung the sides of the petioles are sensitive to touch, bending towards where the pres- sure or compact is. Shortly after clasping the support by means of this bending the petioles increase in thickness, become stronger and tougher than before, and sometimes take on a structure suggestive of a rigid branch. In Gloriosa the sensitiveness is very marked in the leaf-tips, but only on the under surface of the pro- longed thread-like extremity. 1085. Sensitiveness of leaf-blades. The fly-trap of Dionsea (considered by some an appendage to the proper leaf-blade) is exquisitely sensitive to any touch upon the hairs which grow on the faces of the trap. As soon as these are touched the trap instantly closes, and the same effect follows a slight touch on the median line. A cross-section through the leaf shows that the parenchyma is thin-walled. The leaf of the small water- plant Aldrovanda has likewise been shown to be sensitive. Fig. 189. Solanura jasminoides. 420 MOVEMENTS. 'K^ '.i' 1086. The leaflets of numerous plants exhibit a peculiar degree of sensitiveness even to a slight touch. Among these are sev- eral species of Mimosa and Oxalis. The plant which has received the fullest investigation is the easily cultivated 1087. Mimosa pudica (the Sen- sitive plant) . This has compound leaves consisting cf four long leaf- lets, each of which is divided into numerous minor leaflets arranged in pairs. At the base of each leaf- let, and also at the base of the petiole, there is a pulvinus, com- posed of peculiar cells. On the upper half of the pulvinus these are thicker-walled than on the lower ; most of them contain round- ish globules made up of a strong solution of tannin in water, surrounded by a film of some albu- minoid matter. These globules are not, however, of anj' significance as concerns the motility, since thej' are found in the paren- chyma of the bark of some ligneous plants (see 953). 1088. When a fully spread leaf is touched at its extremity the manj' leaflets succes- sively close in pairs, the upper surfaces approaching and the tips falling somewhat forward ; the four branches of the leaf then draw near each other, and the main petiole inclines downwards and finally droops pas- sivelj' at the joint. The recovery from this position of col- lapse takes place in a few minutes, generally in about a quarter of an hour. Fkj. 190. Aldrovanda vesiculosa; tlie lower illustration shows the expanded leaf much enlarged. Fig, 191. Mimosa pudica. SENSITIVE PLANT. 421 1089. If an irritant is applied to a single leaflet, the opposite one may be the onl^- other affected ; or, if the effect is more pro- nounced, all the leaflets on a single division of the leaf may be closed without affecting any on the other branches. But if a still sharper impulse is given, not only will all the leaflets on a single leaf close, but other leaves on the plant may be affected. Thus it is possible bj- applying a hot needle to a single leaflet to affect all those on a small plant. A drop of strong sulphuric acid acts in the same wav.^ When a leaf of Mimosa is separated from its plant by a sharp cut through its pulvinus, and is at once placed in a saturated atmosphere, it soon recovers its normal expanded condition ; if no'.y it is touched the leaflets will collapse as usual, and at the moment of closing a drop of water can be seen exuding from the cut surface. According to Pfeffer it is possible to observe that the water comes from the parenchyma of the lower half of the pulvinus.^ 1090. According to Bert,' who made use of a thermo-electric apparatus, the pulvinus of a leaf of Mimosa in its normal condi- 1 For a study of the transmission of the shock, see Pfeffer, Pringsheim's Jahrbiicher, ix., 1873, p. 308. Some of the effects produced by irritants upon the hairs of certain insectiv- orous plants have been ah'eady described. The phenomena of aggregation then alluded to must be now treated more in detail. It is described by Pfeffer in the following words : " Suddenly the contents of the cell acteil on become clouded by a separation of minute particles which aggregate to form masses. These masses consist essentially of albuminous matters, which, from their col- lecting the coloring substance in the cell-sap, become tinged. The whole process of aggregation takes place in the cell-sap." Pfeffer points out the curious fact that while amnionic carbonate, without any other irritant, will cause this aggregation, acetic acid will make it disappear. Such changes as aggregation and variations in turgescence are connected in some way, not yet understood, with the imbibition power of protoplasm for watery fluids. The mechanical or chemical irritants which temjiorarily dimin- ish the capacity of protoplasm for retaining within the cell the maximum quantity of water will produce a distinct effect upon the tension of the cell- wall, and result in a change of its size or form, or both. The irritation thus caused can be transmitted to a distant part. The intimate relations which exist between the young cell-wall and the protoplasmic lining must not be overlooked in any consideration of the subject of sensitiveness in plants. Lastly, the continuity of protoplasm in many mobile and sensitive organs must be borne in mind in the consideration of this subject. ^ Pflanzenphysiologie, ii., 1881, p. 237. See also Pfeffer's Physiologische Untersuchungen, 1873, p. 32. 8 Comptes Rendus, Ixix., 1869, p. 895. 422 MOVEMENTS. tion is alwa^'S slightly cooler than the rest of the petiole, but upon the movement from irritation it rises in temperature ; not enough, however, to account for the raising of so con- siderable a weight as that of the leaf. 1091. Some physiologists have regarded the sen- sitiveness of the pulviuus of the Sensitive plant and of other motile parts as residing chiefly if not whol- * 192 h" in the cell-wall, while others have thought that it resided in the contractile protoplasm. It is now generallj- held to be due to some sudden variation in the osmotic power of the proto- plasm, particularh' in its peripheral portion in contact with the cell-wall, by which the turgescence of the cell is suddenly changed.^ 1092. If a plant with motile leaves is kept in darkness for a day or so, even if the temperature is fav- orable to motion, its power of movement is either greatly impaired or for a time wholly lost. A dimiuislied amount of light is sufficient to produce the same effect in the case of the Sensitive plant. 1 Compare Hofineister : Die Lehre von der Pflanzenzelle, 1867, p. 300; Briicke : Archiv fiir Anatomie, Physiologie, mid wiss. Medicin, 1848, p. 434 ; Unger : Botanische Zeitung, 1862, p.' 113 ; 1863, p. 349. Fig. 192 Traiisversesectionof themotileorganof aleiifletofOxaliscarnea. (Sachs.) Fio. 193. Vertical section tlirougli the niotilo organ of a leaflet of OxaliB carnea. (SndiB.1 SENSITIVENESS OF STAMENS. 4?,?i Sachs has given the name Phototonus to the normal motile condition resulting from alternation of clay and night. "A plant in this condition, if placed in the dark, will remain for some time (Irours or even days) in a state of phototonus, which then disappears gradually ; the plant is therefore under normal condi- tions in a state of phototonus even during the night. In the same manner a plant which has become rigid in continued dark- ness retains its rigidity for some time (hours or even days) after being exposed to light. The two conditions therefore pass over into one another onl^- slowlj"." 1093. Temporary rigidity is produced in the case of the Sensi- tive plant bj- an exposure to a temperature of 15° C. The same effect is produced bj- a temperature above 50^ C, according to Bert's observations at about 60° C. It is stated bj' him that tlie sensitiveness of Mimosa is destro^-ed by exposure to a green light, while plants placed under bell-jars of the following colors remained healtliy : white, red, j-ellow, blue, and violet.^ 1094. Sensitiveness of stamens. No better illustration of this is afforded than that given b^- stamens of the common Bar- berry. The six stamens lie curved under the arching petals, but if a filament is lightly touched it is jerked suddenly forward, bringing the anther into apposition with the pistil. 1095. The filaments of certain Compositee are sensitive. The case of the common Chicory has been thus described : The anthers are conjoined to form a tube supported upon five dis- connected filaments which are at first more or less curved out- wards. If the filaments in this condition are lightly touched thej- instantly straighten, carr3ing the anther-tube up a little higher, and thus bringing the pollen all along the stj-le which is enclosed. After a short time thej' resume their former curved condition, retracting the anther-tube to the place which it occu- pied before. It is to be observed that the irritation of a single filament excites onlj' that one, and thus the tube of anthers may be pushed over to one side for a few minutes, again recovering itself after a little while. 1096. Sparmannia Africana has a cluster of beaded filaments surrounding the pistil and variously intermingled with the sta- mens. When these are touched lightly they open out from the centre with considerable rapidity, and remain thus expanded for a certain period, after which they revert to the closed posi- tion. Somewhat the same phenomenon is to be observed in 1 Comptes Rendus, Ixx., 1870, p. 339. 424 MOVEMENTS. species of Portulaca, where the stamens, upon contact, move outwards. 1097. The gj-nandrous style of Styliduim is curved down- wards ; when it is hghth' touched it suddenly flies to the other side of the flower, although sometimes it merely- straightens itself. Sensitive lobes of the st3-le or stigma are possessed by Mimu- lus and some other Scrophulariaceae,^ bj' Martynia, and some allied plants. 1098. In all the foregoing cases the sensitiveness is greatest when the plants, or their sensitive parts, are kept at a tolerably high temperature. Sachs has sliown that the most favorable temperature for Mimosa movements is about 36° or 37° C. 1099. Effects of anaesthetics upon sensitiveness in plants. When a j'oung plant of Mimosa is placed under a bell-jar in which a sponge wet with chloroform or an equivalent anaesthetic has filled the confined atmosphere with its vapor, some of the leaflets droop and remain so, while others retain their normal position. But after a while the leaflets will be found to have lost all power of reacting to a touch ; in short, they have become insensitive. The same effect is observed in the ease of Barberry stamens. Its explanation is looked for in the changed relation of the sensitive cells to water when thej' are subjected to the influence of an anffisthetic. 1100. Plants possess no nei-Tons system. That sensitive plants mast have nerves, or their equivalent, for the recognition of im- pressions and the transmission of their influence to a somewhat distant point was formerly held by many writers, but this opinion is not now entertained by an}' physiologist.^ ' See Heckel's Memoii', Comptos Rendus, Ixxix., 1874, p. 702. " " Finally, it is impossible not to be struck with the resemblance between the foregoing movements of plants and many of the actions performed uncon- sciously by the lower animals. With plants an astonishingly small stimulus suffices ; and even with allied plants one may be highly sensitive to the slight- est continued pressure, and another highly sensitive to a slight momentary touch. The habit of moving at certain periods is inhprited both by plants and animals ; and several other points of similitude have been specified. But the most striking resemblance is the localization of their sensitiveness, and the transmission of an influence from the excited part to another, which conse- quently moves. Yet plants do not of course possess nerves or a central ner- vous system ; and we may infer that with animals such structures serve only for the more perfect ti'ansniission of impressions, and for the more complete intercommunication of the several parts" (Darwin ; Power of Movement in Plants, 1880, p. 571). CHAPTER XIV. EEPRODUCTION. 1101. In scientific as well as popular language the term indi- vidual is commonlj- applied to each anrl eveiy plant ; but if by individual is meant an organism incapable of subdivision with- out loss of its identitj-, the term as applied thus to the higher plants is obviouslj' a misnomer. It has been shown both in Vol- ume I. of this series,^ and in Fart I. of the present volume,^ that under certain circumstances an}' of the higher plants may be separated into parts, each of which may afterwards lead an inde- pendent existence. Thus buds maj- be severed from the parent plant and soon establish themselves as independent organisms, capable of increase in size, and becoming sooner or later dis- tinguishable in no wise from the stock from which they came. But there are serious difficulties in the way of regarding these separable buds as true individuals : ' each bud is the promise of a branch, and consists of parts which, under certain conditions, may be separated from each otlier. In fact, the vegetable indi- vidual is not reached in such mechanical subdivision until we come to the cells of which all the parts are composed. Nor do these satisfy completely the definition of an individual, since in exceptional cases the cell itself may spontaneoush' divide into viable parts.* 1102. In plants, individuality is more or less completely merged in community. Under normal conditions the separable parts, while still attached to their common stock, co-operate for the common good. If separated under favorable conditions they in their turn become stocks in which are combined congeries of similar separable parts, or, in other words, become individual plants, in the ordinary acceptation of the term. For instance, the tuber of the potato, which is the thickened extremity of an underground branch, possesses a certai'n number of buds, each ■ 1 Page 31(j. 2 Pages 152, 162. ^ Volume i. p. 316. * Such a phenomenon is seen in the formation of swarm-spores (or zoogo- nidia) from a terminal cell of Achlya. 426 BEPRODUCTION. of which may, in suitable soil, give rise to a thrifty plant: the new plants will in their turn produce new tubers likewise with buds, and these again new plants, and so on in unlimited succession. Nevertheless, the divisible organisms are for our present purpose convenientlj- termed vegetable individuals.^ 1103. Plants of the higher grade (Phoenogamous plants) are propagated either by buds or by seeds. In the former case, a portion of the axis with incipient leaves is separated from the parent; in the latter case, a new structure (the embrj'o), capa- ble of independent existence, is formed by means of a special apparatus, — the flower. In the flower, two sets of sexual or- gans, the stamens, constituting the androecium, and the pistils, constituting the gynoecium, produce by their conjoint action an embryo, or undeveloped plant, within the seed. Reproduction by buds is non-sexual or asexual ; that bj' the formation of an embrjo is sexual. 1104. Non-sexual reproduction (Agamogenesis) can be traced through all classes of plants, — from the higher, where it takes place through proper buds, down to the veij lowest, where it takes place by a single cell dividing spontaneously to form two or more separated individuals. 1105. Sexual reproduction (Gamogenesis) likewise can be traced through all classes of plants except the very lowest, where it has not as yet been demonstrated to exist. As the series is followed from above downwards, the flower gives place to other structures, and the seed is replaced bj- simpler bodies, known as spores. FERTILIZATION IN AXGIOSPERMS. 1106. Flowering plants are naturally divided into Angio- sperms and Gymnosperms : the former are distinguished by the possession of a closed ovary in which the ovules are contained. The latter have no closed ovar3-, and hence the ovules are naked. A part of the reproductive ajiparatus is simpler in Gymnosperms than in Angiosperras ; but owing to certain practical difficulties in the treatment of microscopic material, the demonstration of the reproductive process is less easy in the former than in the hitter. It is proposed, therefore, to begin with an examination of the reproductive process, or fertilization, of Angiosperms. 1 The view has been held by some that all the derivatives from one seed, whether united or separated, constitute collectively a single individual. STRUCTURE OF THE PISTIL. 427 1107. Three subjects inust be biieflj- reviewed before enter- ing upon the stud}- of the process itself; namely, the pistil, the ovule, and the pollen-grain . For all details regarding particu- lars of form and special morphological relations, pages 249-285 of Volume I., and Chapter IV. of the present volume may be consulted. 1108. The aiigiospermous pistil (see Fig. 196) consists of a closed ovary containing the ovules, which is generally prolonged into a slender organ known as the style. Eitiier some portion of the style, or, when tiiis is wanting, some portion of the ovai y, is furnished with a peculiar secreting surface known as the stigma. The manifold shapes of ovar}-, style, and stigma have been suf- flcientl}- described in Volume I., and the microscopic structure of each has been examined in a general waj- in Part I. of the present volume. From what was there said, it will be remem- bered that the form and structure of pistil and stamens have intimate relations to the transfer of pollen and its reception by the stigma. 1109. The stigmatic secretion. The surface from which this exudes may exist as an expanse of considerable extent, or it may have the form of single or double lines, or be reduced even to a mere point. The extent of the stigmatie surface bears a fixed relation to the number of ovules in the ovary. At a certain period in the development of the flower, the stigma, which up to that time mav have been apparently free from moisture, becomes covered with a glutinous secretion of a saccharine nature. At this period, known as that of ma- turit}-, the stigma is from its stickiness likely to catch and retain upon its surface any pollen which may fall thereon. The secretion is generally slightly acid ^ in reaction, and is as variable in the amount of sugar which it contains as ordinary nectar. 1110. The pollen-grains of angiosperms when set free from the cells in which they are produced may become completely^ isolated (simple grains), or they may remain firmly coherent in clusters of four (Typha, Rhododendron, etc.), eight, sixteen, thirty-two, or even, as in some species of Acacia, sixty-four ("compound grains"). In many Orchidacese the grains are more or less compactly fastened together into masses bj- a glu- tinous matter forming pollinia, and much the same grouping into masses occurs in Asclepiadacese. 1 Van Tieghem : Traite de Botaniiiue, 1884, p. 850. 428 KEPEODUCTION. 1111. Sh'uctnre of pollen-grains.^ The grains consist of sin- gle cells having a firm membrane and heterogeneous contents. Tiie membrane is rarely single (as in Zostera), being generally composed of two coats, — an outer, the extine (called exine by Sehacht), and an inner, the inline. The extine maj- be smooth, but it is frequently beset with protuberances of some kind, points, prickles, or other sculpturings, which ma^- be characteristic of genera or even larger groups. It is also provided generally with one or more partial or complete perforations, which aj-e of course fully closed 113- the inline which is pressed up against them. The number of these perforations is constant in certain groups of plants : for instance, one in most monocotyledonous plants ; two in Ficus, Justicia, Belopeione ; three in Onagracese, Geraniaceaj, Compositse ; four to six in Impatiens, Dlmus, and Alnus ; many in Nyctaginacese, Convolvulaceae, Malvaceae, and some Caryophyllacese. Under the action of concentrated sul- phuric acid the intine is destroyed, while the extine generally remains unchanged except in color.^ When the pollen of Thunbergia is acted on by strong sulphuric acid, the destruction of the intine permits the extine to uncoil as a band. In no case did Sehacht detect an\- perforation of the intine. 1112. The contents of a pollen-grain are (1) protoplasmic mat- ter; (2) granular food materials, such as starch, oil, and, ac- cording to Sehacht, inulin ; (3) dissolved food matters, sugar and dextrin. These heterogeneous contents form what was formerly called the fovilla. In the granular protoplasmic matter of pollen-grains it is pos- sible to demonstrate the existence of a nucleus, and in some cases two nuclei can be made out distinctly. It is considered well established'' that the single nucleus which exists in the simple grain at the period of its se[)aration froin the mother-cell divides in most cases into two nuclei of unequal size. The larger of the two fragmental nuclei remains with no change ; while the smaller may become partitioned off from the rest of the cell either by a true cell-wall or bj- a peripheral film of protoplasm, and may later divide and form a group of two or four minute cells. ' Tliese details are summarized chiefly from Schacht's exhaustive treatise on the subject in Pringsheim's Jahrbiicher, ii., 1860, p. 109. 2 In some cases a double membrane can be shown in the extine, for instance CEnothera, where the extine separates into a true extine and an intcxtine. ' Rtrasburger : Ueber Befruehtimg und Zelltheilung, 1878. See also Quarterly Journal of Microscopical Science, 1880, p. 19. POLLEN-GRAINS. 429 1113. The pollen-grains of manj' plants burst when placed in water, and the fovUla escapes as a slightlj- coherent mass which soon becomes more diffused and allows the finer granules to pass into the water, where thej^ immediately exhibit the Brownian movement, common to all minute particles suspended in a liquid. "■ 1114. If pollen-grains are placed in a solution of sugar in- stead of in pure water, they will increase somewhat in size ; and in a few hours, if the specimen is kept at the right tem- perature, there will appear at some point of the surface of each grain a minute tube, which by great care can be cultivated in a proper medium until it attains a length of several millimeters.^ 1115. The pollen-grains of TulipaGesneriana emit their tubes in a 1 to 3 per cent solution of cane-sugar ; the following require a somewhat stronger syrup : Leucojum sestivum and Narcissus poeticus, 3 to 5 per cent; most orchids, 5 to 10 per cent; Con- vallaria majalis, 5 to 20 per cent ; Iris sibirica, 30 to 40 per cent.' 1 For an extfniled account of the speculations once based upon the occur- rence in water of motion of the particles of the fovilla, the reader should consult Meyen: Pflanzenphysiologie, iii., 1839, pp. 192 ct seq. ; and also the reinarltable treatise by Robert Brown. 2 Schleiden states that pollen-grains which come accidentally in contact with nectar readily send out tubes ; and that we often find at the base of the flower a whole mass of confervoid web, which consists of entangled pollen- tubes emitted in this manner (Principles of Scientific Botany, 1849, p. 408). ' Strasburger: Das botanische Practicum, 1884, p. 511. Fig. 194. a, young pollen-gi'ain of AUium flstnlosum, before its division ; b, after tlie division of tlie nucleus: c, after the division of the protoplasm; f?, young pollen-grain of Monotropa Hypoi>itys divided; e, same eniitfiiig its tube, into which the two nuclei pass; /. coalescent grains of the pollen of Platanthera bifolia during their division ; g^ formation of the pollen-tube of Orchis mascula, into which the two nuclei pass. (Stras- burger .J 430 EEPRODUCTIOK. 1116. When a pollen-grain is deposited upon a fitting stigma,' at the period when the stigmatic secretion is suffleientlj* abun- dant, it increases somewhat in size, and soon ^ a tube,' sometimes more than one, is thrust forth and passes immediately into the loose tissue of the stigmatic surface. The tube consists of a protrusion of the inline, and its place of emerging is at some one of the perforations of the cxtine. In some instances the wall separating the larger and the smaller fragments of the original nucleus of the pollen-grain becomes absorbed, and then the two nuclei make their way into the tube as it is prolonged. During its descent the pollen-tube is slender, of about the same calibre throughout, and has extremely thin walls. It extends through the conducting tissue of the style, being nourished by the nutrient matter secreted from the cells of that tissue, until it at last reaches the cavity of the ovary. 1117. According to Capus,* the extent of the stigmatic surface bears a definite relation to that of the conductive tissue of the style, one surface being in fact a mere expansion of the other ; and the volume of the conductive tissue of the sti'le is governed by the number of ovules which are to be fertilized. Thus, in a 1 All interesting account of the artificial fertilization of certain plants of the Poppy family after removal of the stigmas is given liy Hooker in " Tho Gardeners' Chronicle," 1847. It is not known that the experiments have yet heen repeated. " According to Gartner, the emission of the pollen-tuhe begins in some cases in half a minute after the pollen has heen applied to the stigma ; but in some others, as in Mirabilis Jalapa and in the Malvaceae, it takes from 24 to 36 hours. ' Amici, in 182i!, appears to have been the first to detect the pollen-tube. His earliest observations were made ujion Portulaca oleracea. * Annales des Sc. nat., ser. 6, tome vii. p. 204. Fig. 195. Apparatus for cultivating pollen-grains, etc. Tlie object is placed on tit tinder side of a glass cover over the circle at a. If necessary, air can be drawn throug!a the tube. A simpler contrivance may be ni;ide from a piece of moist pasteboard. DESCENT OF THE POLLEN-TUBE. 431 pistil with a large number of ovules the stigmatic surface is large, as is also the amount of conductive tissue of the stj-ie through which the pollen-tubes are to descend. 1118. The conductive tissue through which the pollen-tube descends, and by which it is nourished, is formed at the stigma by a modification of epidermal ceUs, and below this arises from modifications in the parenchyma ; in the style it may constitute a solid mass of delicate cells, sometimes with walls which have undergone the mucilaginous modification, or it may simply line the hollow tube which is frequently found, as in the pistil of the violet. 1119. The time required for the descent of the pollen-tube de- pends upon the length and character of the path the tube is to traverse, and is verj- different in different cases. Hofmeister states that in Croons vernus, with a style which is from one to two inches in length or sometimes more, the tube reaches the ovary in from one to three days. Schleiden ^ gives the following times required for descent of the tube : Cereus grandiflorus, having a style nine inches long, a few hours ; Colchicum autnmnale, with a stj'le thirteen inches long, twelve hours. In some other cases (certain orchids) it is weeks before the end of the tube lias descended for even a very short distance. 1120. A single pollen-grain of some flowers can emit more than one pollen-tube : thus Amici has seen twent}' to thirty' tubes proceed from one grain. Pollen-tubes sometimes branch in their course downward. 1121. The length of tii^ae during which pollen-grains can preserve their vitality has been determined for a few cases : ^ 1 Schleiden: Principles of Scientific Botany, 1849, p. 407. 2 Gartner, quoted by Mohl: Vegetable Cell, p. 134. Fig 196. Diagram of a longitudinal section of an nvary liaving only one ovule with basal placentation, designed to exhibit the course of the pnllen-tube from the stigma to the summit of the embryonal sac above the oosphere. Tlie ovule is auatropous, and is inserted, as is usually the case in Composite. (Luerssen.) 432 EEPKODUCTION. Those of Hibiscus Trionum at least three daj-s after removal from the anther ; those of Cheiranthus Cheiri, fourteen dajs ; those of Camellia, Cannabis, Zea, and Fhoenix dactylifera (Date), one year. 1122. Althougb each ovule requires for its impregnation only one pollen-tube, the number of pollen-grains in flowers which open at maturitj' is far in excess of the number of ovules. The ratio has been ascertained in a few cases, among which are the following: Cereus grandiflorus,' 250,000 grains of pollen to 30,000 ovules ; Wistaria sinensis,^ about 7,000 grains of pollen to each ovule ; Hibiscus Tiionura,' 4,8G3 grains of pol- len to about 30 ovules. In some other cases, for instance Geum urbanum,^ the excess of pollen over ovules is about 10 : 1. 1123. The localization of the conductive tissue in the ovary itself is sometimes ver}- marked ; thus in ovaries with parietal placentation, the ovarian walls in the immediate vicinitj- of the ovules are seen to be distinctly conductive, while in those with axile placentation, the modified tissue is found in the axis. Capus distinguishes the following varieties of conductive pla- centae : (1) with a smooth surface, the micropyle being close to the placenta, e. g., Solanum ; (2) papillar, the papilte either simple or compound, sometimes serving to guide the pollen-tube to the micropyle, e. g., some Cucurbitaceee ; (3) hairy, the hairs sometimes secreting a mucus or even breaking down into a gelatinous mass through which the pollen-tube maj' penetrate with facility, e. g., some Aroids. Special names were formerly given to peculiar forms of the conductive tissue, but the terms now possess no utility. For special examples of the forms, the reader must consult the practical exercises at the end of this volume. 1124. Structure of the ovule. As shown on page 175, the ovules arise as minute protuberances at some part of the ova- rian wall or upon the axis of the ovary. In orchids the pro- tuberance consists of only a single row of cells ; but in most 1 Morren. ^ Gardeners' Chronicle, 1846, p. 771. 5 Kblreuter : Vorliiufige Nachricht (quoted by Balfour : Class Book of Botany, p. 564). * Gartner ; Beitrage zur Kenntniss, p. 346 (quoted by Darwin in "Effects of Cross and Self Fertilization in the Vegetable Kingdom," p. 377). The following are some of Hassall's determinations of the number of pollen- grains (Annals of Nat. Hist, viii., 1842, p. 108): Dandelion, 243,600 grains ; a flower of Peony, with 174 stamens each containing 21,000 pollen-grains, 3,654,000 ; while in s, plant of Rhododendron the number of grains was esti- mated to be 72,620,000. STRUCTXJUE OF THE OVULE. 433 197 other cases several rows of cells are superposed, forming the body known in morphology as the nncleus of the ovule. This, to avoid the possibility of even slight confusion, will be now spoken of as the nucellus. That this distinction is necessarj-, will appear from the fact that in one of the large cells of this body there is a true cell-nucleus which under- goes remarkable changes, all of which I must be described. It should there- fore be remembered that in the fol- lowing discussion the term nucellus means exactly that which in Volume 1. page 277 is called nucleus of the ovule. 1125. Around the nucellus there is developed in most in- stances a double ring, which soon nearly invests it, forming an inner and an outer coat. Attention has been called in Volume I. to the fact that the integuments of the ovule do not conipletel3- invest the nucel- lus, but that there is at its true apex an orifice known as the foramen or microp3'le. It has also been shown that bj- a peculiar distortion during its development the ovule may be so bent round upon its support, the funiculus, as to have the micropyle present itself towards the placental attachment. Hence, when the apex of the ovule is spoken of, the micro- pylar extremity is meant. 1126. At the micropj-lar extremity of the forming ovule, a single cell, beneath the surface (except in orchids and some saprophytes) , elongates in the direction of the length of the ovule, and by one or sometimes many transverse and vertical partitions becomes divided into segments of unequal size. The lowest segment continues the elongation and the enlargement of the structure thus formed within the ovule, known as tlie embryo Fig. 197. Longitudinal section of the amphitropous ovule of Baptisi.i australis. (Van Tieghem.) Fio. 198. Longitudinal Bection of the anatropous ovale of Mimosa pudica. (Van TieghemJ, 28 484 EEPEODUCTION. sac. During the subsequent development of the ovule the embryonal sac continues to increase in size, often irregularly, and displaces or obliterates by absorp- tion many of the cells around it. 1127. At an early period in the de- velopment of the embryonal sac it is completely filled with protoplasm con- taining a cell-nucleus. This nucleus di- vides, and the two new nuclei are soon found at opposite ends of the sac, where each divides into four nuclei. Between the two groups of four nuclei there may be a vacuole of considerable size. The next stage is marked by the pas- sage of a nucleus from each extremit3- of the embrj'onal sac towards its centre, where they become united to form a sec- ondary nucleus. 1128. The nuclei at the lower end of the sac become surrounded with other protoplasmic matter, and later by cell-walls ; they then consti- tute what have been termed the antipodal cells. At the upper end of the sac, also, the three nuclei become surrounded by Fig. 199. Longitudinal section of theortliotropouB ovule of Polygonum divaricatum. /«, funicnlns; te, tlie two integuments; nu, the nucellus, ■whose summit is prolonged towards the mi(Top,vJe. mi ; se, the emhryoiial sac. (Strasburger.) F]a. 200. Polygonum divarioatum. Summit of the ovule with the apex of the em- bryo sac, and the complete embryonal apparatus, e, the oospore; s, one of the syner- gidae, the other being hidden from view. (Strasl>urger.) Fig. 201. Polygonum divaricatum. Summitof the ovule, showing the encroachment of the embryo sac upon the adjoining cells. (Strasburger.) CHANGES IN THE 003PHERE. 435 more or less protoplasmic matter, but are not invested by a true cell-wall ; these have been termed the egg-apparatus. Two of these naked nu- cleated bodies are somewhat attenuated at their upper part and rounded below ; the slender portion contains the nucleus, the rounded a vacuole. The bodies are termed the synergidoB. The remaining cell is near the lower extremity of the two just de- scribed, and is known as the oosphere. All of these parts are shown in the fig- ures. Such, then, is the structure of the em- br3-onal sac and of the egg-apparatus, when the extremit}' of the pollen-tube emerges into the cavitj- of the ovary and comes in contact with the niicrop3-le, or foramen. It has been shown bj"^ Stras- burger, that when contact takes place be- tween the pollen-tube and the summit of the embryonal sac, one of the sj-nergidse changes its character ; its rather clear pro- toplasm becomes turbid, its vacuole and nucleus vanish, and with a slight con- traction the mass becomes finelj' granu- lar, after which it ma3- wliollj- disappear. At this time the oosphere also undergoes the following changes : it clothes itself with a thin film of cellulose, and in its protoplasmic mass a well-marked nucleus, probably derived as such from the pollen- tube, appears by the side of the nucleus of the oosphere, sometimes of the same size, sometimes smaller. The two nuclei blend, forming a single ovoid body, with distinct or with confluent nucleoli. Even if at first distinct the nucleoli may be- come confiuent at a later period. The Fig. 202. Synergidaj prolonged across the membrane of the embryonal sac. a, 6, c, from Gladiolus communis ; dt from Bartonia aurea. a, plane perpendicular to the plane of the symmetry of the ovule ; b. In the plane of symmetry j c, after separation of the three parts; c2. (Strasburger.) Fig- 203. Oapsella Bursa-pastoris. Two embryos with cotyledons distinctly devel- oped. B more advanced than A. (Luerssen.) 436 REPRODUCTION. Other sjnergide remains unchanged, or passes Uirongli neai'ly the same changes as those described. It should be said that in some instances the pollen-tnbe passes down without apparentl3- affect- ing the sjnergidaa to anj' very marked extent, but producing its influence di- rectly* upon the oosphere. 1129. These changes now described in the oosphere are known collectively as those of fertilization or impregnation ; tlie fertilized or impregnated oosphere is termed an oospore. It passes through a series of changes bj- which a second cell is formed, then others in a linear series, or in a more complex chain, termed the proembryo or suspensor. In some cases, however, no suspensor at all is produced. Fig. 20i. Capsella Biirsa^paBtoris. Embryo developed more than in Fig. 203. A longitudinal section showing cotyleQons, kb ; v, point of growth; e, suspensor ; p/, plerom ; p and pe, periblem ; (?, anil d'-, dermatogen ; A^, and h^. root-cap. (Hanstein.) Fig. 205. Camelina pativa. a, two-celled embrjo, much exceeded in size by the long suspensor. Capsella Bursa- pa storis, the figures &, r, showing different stages in the development of the embryo; b,c,fJ, aspects of the embryo divided into quadrants; e,f,gi different views of the embryo at the formation of the dermatogen ; i, longitudinal sec- tion showing further divisions and the formation of the periblem and plerom; A", same as j, but given in perspective; /, longitudinal, m, transverse, section of the same em- bryo at a later stage ; n, perspective view of embryo at a little earlier stage than / and m; o,^, r, later stages; g, same embryo seen from below, exhibiting the first divisions near the suspensor; s, s', s", cells nearest the suspensor, (7..ucrssen, after Praz- mowski.) ■ ■ - - . FERTILIZATION IN GYMNOSPERMS. 437 1130. The terminal cell of the suspensor is followed by the initial cell or cells of tlie embryo proper ; the different stages of the development of the embryo can be traced in the ovale of one of our most common weeds, Capsella (compare Figs. 203-205). The case above described is a simple one, but may ser\'e as a type of all normal cases of fertilization in angiosperms, the innu- merable deviations from which cannot be further alluded to here.^ 1131. With the changes in the embryo sac there are concomi- tant changes in the whole nucellus and its integuments. A certain amount of food of some kind (sec 509) is stored either in the sac or in the developing tissues around it, constituting the so-called albumen of the seed. The food within the develop- ing embryo sac is termed endosperm ; if around it, perisperm. But the changes do not stop with the ovule as k, ripens into a seed ; they go on also in the surrounding parts. In fact, as soon as fertilization has begun, the flower wilts, and in most cases the external organs fall. The ovar}', sometimes with associated parts such as the calyx, the receptacle, etc., passes through changes by which it becomes the fruit. FERTILIZATION IN GYMNOSPERMS. 1132. The chief differences between the reproduction in these plants and that in those just described are in the preliminar3- development of the pollen and the ovule. 1133. Pollen of gym- nosperrns. The grain is distinctlj' divided by a curved partition into two portions, and one of these portions is fre- quently divided in much the same way into two parts. Comparison of this pollen with that of '■ The student is urged to study with great care the masterly treatise by Strasburger, Ueber Befruohtung und Zelltheilung, 1873, and the more succinct account in his Practicum, 1884. Fig. 206. A, pollen-grains of Biota before their escape from the pollen-sac. I, fresh, // and III swollen by water; the exHiie e having split off, the protoplasmic contents are seen. B, .pollen-grains of Pinus pinaster before their escape from the pollen-sac; a elde and a dorsal view. (Sachs.) 438 EEPEODUCTION. angiosperms shows that in the latter the nucleus divides, but that the division stops here, no true dividing-wall being formed. 1134. Ovule of (jymiiosperms. Ttie ovule is always ortliotropous. It has an integument which is sometimes prolonged so as to form a flesly tube communicating with the nucellus. The nucellus, like that of angiosperms, contains an embryonal sac ; at an early stage this is filled with endosperm, which it will be remembered is not developed in angiosperms until after fertilization. Some of the upper cells of the endosperm are rather larger than the others, elongated in the direction of the axis of the ovule, and each surmounted b}- a " rosette " of minute cells which comes between the group and the summit of the embrj'o sac. These large cells, with their rosettes, are termed cor- pusculea. These corpuscules are considered oospheres. Around them in the embryo sac there ap- pears to be nothing corresponding strictl}' to the synergidas, the an- tipodal cells, etc., observed in the angiosperms, although some ho- mologies have been pointed out. In some cases, like that figured, there is a sort of depression at the summit of the endosperm, which has been called the pollinic chamber. 1135. Contact of pollen with the ovule. As the name indi- cates, the gymnosperms are naked seeded ; no stigma or style inter- venes between the pollen and the ovule. When the divided pollen of the gymnosperm falls upon the micropyle of the ovule, It Fig. 207. PoUen-graiii of Ceratozamia longifolia. A, grain with partial partitions ; B, the same emitting its tube, ps, which has ruptured the outer coat; y, minute inactive cells. (Juranyi.) Fig. 208. Longitudinal section of the nucellus of the naked ovule of Juniperus Virginiaiia. 71, nucellus; se, membrane of the embryonal sac; c, endosperm; c, cor- puscles ; p, a pollen-grain which has protruded its large tube as far as the corpuscles. (Sirasburger.> FERTILIZATION IN GYMNOSPERMS. 439 finds there a certain amount of moisture by means of wliich a tube is formed from one of the large cells. This extends directly Into the tissue of the nucellus, coming sooner or later into con- tact with the summit of the embryonal sac, and then affecting the corpuscules below. From the fertilized corpuscule tlie embrjo is developed.^ ' For the purpose of affording some means of comparison of the methods of reproduction in iiowering plants and in tliose of a lower grade, the following brief notes concerning the reproduction in several of the groups of Cryptogams have been inserted : — (1) No sexual reproduction has yet been demonstrated in the very lowest forms of vegetntion. Such plants are tenned Protophytes. The fungi which are associated with fermentation and putrefaction, and certain of the simplest algae, are examples of the group. In the study of the Protophytes the beginner can examine with profit the cells of common yeast. Care should be taken to distinguish between the cells of the plant and the grains of starch with which compressed yeast is generally associated. The simplt; one-celled plants with chlorophyll which belong to this group can be found in almost any stagnant water. They are spherical, and aie fre- quently grouped in twos or fours. ( 2 ) The sexual process in Zygophytes is characterized by the confluence of the protoplasmic masses of two very similar cells by which a new mass is formed as the starting-point of the new indi- vidual. In most of these, zygojihytes there is no plain distinction of sex. Some of the lower moulds and many of the filamentous algae are examples of the group. Excellent specimens for study may be found in stagnant or slow-running water in spring and through the suni- mei'. By careful search it is possible to detect cases in which the process of conjugation has advanced somewhat : such specimens can be kept under ob- servation by having the slide sufficiently warm and constantly supplied with fresh water, when the different stages of conjugation and of cell-division may be examined. 209 Fig. 209. Spirogyra, illustrating the mode of fertilization in the Zygojiliytes. Approximating cells of two filaments produce extensions which become conjoined ; tlie ■protoplasmic masses in these cells become confluent, forming a single mass wliich after escaping becomes clothed with a cell-wall and develops into a filamentous chain of cells. Ill this case there is no appreciable distinction of sex. 440 EEPRO0UCTIOK. 113G. It was formerh- thought that no clear gradations could be detected between the"^ flowering plants and . the higher groups (3) Oophytes. In this group a mass of protoplasm, known as an oosphere, is fertilized by specialized threads or slender masses of protoplasmic matter termed antherozoids, coming from another part of the same or of another plant. By contact with these an- therozoids the oosphere he- comes an oospore, the start- ing-point of a newindividuah In this group, of which Fucus or rock-weed may he taken as an example, the fertilization is direct. In the examination of this group the student may em- ploy the common rock-weed which carpets the boulders along tlie coast. Sections should be made in the un- even pustulated part of the frond, aud in a vertical di- rection. Good preparations can be obtained from mate- rial which has been dried or from that which has been kept in alcohol, and winter specimens will be found especially good. Some of the species are dioicious, having the male elements in the conceptacles » /It^fisH '^ on one plant and the female elements in those upon an- other. (4) Carpophytes. The simplest plants of this het- erogeneous group are illus- trated by Fig. 211. The oosphere is contained in a specialized organ (the car- pogonium), which is fre- quently prolonged to form a style-like process (the tri- cKogyne). The antherozoids ^1^ are carried by water to this process, and fertilization results ; the product of Fig. 210. Fucua, illustrating the fertilization of an oophyte. a, section throngli a conceptaclo exhibiting the reproductive organs; b anil c, the obspheres in different stages of development; d, antheridia with a single antherozoid ((/); e, an oSsphere surrounded by antherozoids; ./•, an oosphere gei-niinaling. (Thuret ) FjG. 211. Nemalion. I.-IV., a carpophyte. I., a branch showing antheridia, n, and a rarpogonium, o, with the triohogyne, t (e, spemiatium). V., Lejolisia exhibiting a, an- theridium, c, carpogonium.and/, ripe fruit; e, an escaping spore. (Thuret and Bornet.) 210 EEPEODtrCTION IN CRYPTOGAMS. 441 of flowcrless plants. Comparative investigations liave, however, siiovvn that such gradations do exist, and that the chain of exist- fevtilization is shown in the figure. Of the more complicated cases this is not the place to speak ; their treatment, as well as that of all the simpler forms, may be looked for in Volume III. Specimens for this demonstration of the different stages of reproduction are to be procured at different seasons. As will be seen from the figure, most of the features are so nearly supei-ficial as to need no particular sections for their exhibition. / (5) True mosses and their allies are characterized by the posses,sion of au archegonium or flask-shaped body containing a central cell in which is the oosphere. The oosphere i.s fertilized by immediate contact with antherozoids ■which are formed in antheridia ; as a result of the fertilization, there is produced a spore-case filled with spores. In the examination of the fructification of a moss, the plant must be taken at an early stage, and search must be made for the sexual organs by remo\ al of the flower-like cluster of leaves at the summit of the minute 2. stalk. If the removal is success- fully performed, and the plant is in the right condition, a group of threads like those shown in the figure will be plainly seen. Among these are to be foTmd some flask-like bodies, the arche- gonia, and either on the same receptacle or on another plant of the same species the male organs, one of which, greatly magnified, is shown in Fig. 212. Under a very high power the escaping antherozoids can be seen. When fertilization has taken place, the archegoniuui goes on in its development, be- coming, after many intermediate steps, the capsule or "fruit" of the moss, covered by a sort of hood or cap, and tightly closed at its mouth by a lid. Reniioval of the lid discloses the teeth of the mouth (peristome) and the spores within. Upon germina- tion, a spore gives rise to slei.der filaments among which is pro- duced the minute moss-plaut with the sexual organs figured in the sketch. Fig. 212. Funaria Srgrometrica, a moss. 1. Longitudinal section through the npper part of the plant with archegi>nla, a, anrl leaves, *. 2. Anthetidium bursting acd allowing escape of the antherozoids, a. (Thom^.) 442 EEPEODUCTION. ences is practican3' unbroken, reaching from the lowest to th( highest forms. The character of this evidence will appear in the succeeding volume of this scries. (6) True ferns exhibit the following phenomena of fertilization. On the hack of the frond there are formed spores in spore-cases, which are variously- grouped and protected. The spores on reaching a fit surface soon give rise to thin films (pro- thalli), on the nndei side of which are pro- duced the sexual or- gans, all of which are shown in the figures. As a result of the pro- cess of fertilization there is produced afem-plant, which at its adult age bears the spores ahove spoken of. In au\' greenhouse where ferns are kept it is easy to procure, hy careful search on the soil of the flower-pots, abundance of the pro- thalli in differentstages. The most minute of these exhibit the sexual organs just forming, while those which are more advanced give all the features shown in the figures. The stu- dent m ust observe that on the surface of the soil in the flower-])Ots many other growths are to he found, and care must be taken not to con- found other flat films (belonging, forin stance, to Hepaticije) with the prothalli of the ferns. Sections through the prothallus will exhibit the sexual organs in diflFerent stages of development. The best material is procured by the cultivation of Fig. 213. Protliallus of a fern, exiiibiling tlie reproiluctive organs. At the sinus of tlie heart-shaped film are to be seen the archegoiiia, one of which, more higlily mag- nifleil, is displayed in section in A. B, an enlarged antheridium with escaping anthero- zoids. (Luerssen.) SEXUAL AND NON-SEXUAL KEPKODUCTION. 443 1137. Contrast between non-sexual and sexual reproduction as regards results. In non-sexual reproduction a certain poition of living matter is separated from the rest of the living matter of the plant, and, coming under favorable conditions, pursues an independent existence ; in sexual reproduction, two portions of living matter, from different parts of the organism or from different organisms, unite to constitute a new individual. fern-spores. On a piece of unglazed earthenware, for instance a broken flower- pot, wfiich has been first boiled for a time in water to destroy any injurious moulds, a few spores are to be lightly dusted. If the whole is covered by a bell-jar and kept dark and warm, after a certain time the delicate films will be detected and can then be traced through their development. (7) Some of the allies of the ferns produce spores of more than one sort, differing in size and subsequent devel- opment. The larger spores, known as macrospores, give rise to an included prothallus which subsequently becomes exposed at one portion, where there is developed an archegonium (or sometimes more than one). Previous to or coin- cident with this development there is formed within the spore-walls a peculiar tissue which has been termed the endo- sperm, and which is regarded as the homologue of the endosperm in gymno- spermous seeds. The smaller spores are denominated microspores, and pursue a peculiar coui'se of development. One of the cells (seldom more than one) remains essentially unchanged, while the others give rise to the mother-cells of the antherozoids. It is therefore thought proper to consider the sterile cell as the homologue of a rudimentary male prothallus, and the others of rudimentary antheiidia. From the mother- cells are i)roduced, sooner or later, the antherozoids by which the archegonium is fertilized. If these allies of the ferns are compared with the angiosperms, wide differ- ences are found to exist which can be bridged over, in part at least, by the gynmosperms. Hence, in some systems of classification the gymnosperms are placed between the angiosperms and cryptogams instead of between the mono- cotyledons and dicotyledons. Fig. 214. Selaginella. A, F, microspores in different stages of formation of the aniherlilia G, antlieroznid ; H, axile longitudinal section of a macrospore six weeks after fertilization, but before germination; v, rudimentary prothallus of tlie micro- spore; p, prothallus of the macrospore with three arcUegonia; enci, endosperm; e, exosporium. (Pfeffer.) 444 EEPEODUCTION. 1138. The new individual, for instance a bud, arising from non-sexual reproduction, generallj- repeats in itself all the pecu- liarities of the organism from which it took its origin ; the new individual, the seed or spore, arising from sexual reproduction, usually differs in some particulars from the organism or organ- isms b}' which it was produced. 1139. Hence, in the higher plants individual peculiarities are perpetuable by bud-rei)roductiou, whereas the seed gives rise to variations. If the horticulturist wishes to keep the descendants of a given stock true to all the characters which give them value, he relies upon some method of multiph'ing the plant by buds ; if, on the contrar3', he desires to induce or increase some varia- tion from the stock, he makes use of seeds. 1140. The ordinarj- horticultural operations by which buds are severed from the parent stock and suitably placed for further advantageous development are : (1) layering, — the fastening a blanch in earth, so that while j'et connected with its main stem it may form new roots and afterwards live independently of the stem ; (2) the forcing of cuttings or slips, which in con- genial soil will produce a supply of roots ; (3) grafting, or the transfer of a shoot (a scion) from the parent plant to some other plant by which it can be nourished ; (4) budding, the transfer of a single bud to another plant (see 426). 1141. While iu most cases buds produce shoots or plants very closely resembling the parent, it sometimes happens that re- markable variations arise. These are known as bud-variations, and are commonly called sports. In general, when once origi- nated they are perpetuable by any of the processes of ■ bud- propagation just described, but are not likely to be reproduced by seed. From the long list of them given by Darwin only a few familiar cases are here mentioned : (1) the moss-rose, from the Provence rose (Rosa eeutifolia) ; (2) Pelargonium, giving rise to numerous varieties ; (3) Dianthus, Sweet William, Car- nations, and Pinks, which vary very widely in cuttings from a single plant. 1142. Many of the cases of sports, especially those wliich have descended from hybrids, are attributable to reversion to an ances- tral form ; a few seem to be dependent on changes in the sur- roundings ; while others have been attributed to the influence exerted b^- a graft. 1143. Ordinarily the scion produces no marked effect upon the stock, and, conversely, the stock exerts no effect upon the shoot growing from the scion. But when, for instance, some of the CYTISCS ADAMI. 445 variegated forms of Abutilon Iiave been grafted on green-lea\ed stocks, they have been known to affect man^- of the subsequent shoots. Such cases are known as graft-hybrids. The most remarkable example is that of Cytisiis Adami, a form midway between Cytisus laburnum and purpureiis. Of this plant Darwin says : " Throughout Europe, iu different soils and under different climates, branches on this tree have repeatedly and suddenlv re- verted to both parent species in their flowers and leaves. To behold mingled on the same tree tufts of dingy red, bright j-el- low, and puj'ple flowers, borne on branches having widely differ- ent leaves and manner of growth, is a surprisiug sight. The same raceme sometimes bears two kinds of flowers, and I have seen a single flower exactly divided in halves, one side being- bright yellow and the other purple ; so that one half of the standard-petal was yellow and of larger size, and the other half purple and smaller. In another flower the whole corolla was bright yellow, but exactly half the calyx was purple. In an- other, one of the dingy-red wing-petals had a liright j-ellow narrow stripe on it ; and lastly, in another flower one of the stamens, which had become slightly foliaceous, was half yellow and half purple ; so that the tendency to segregation of char- acter or reversion aflfects even single parts and organs. The most remarkalile fact about this tree is that in its intermediate state, even when growing near both its parent species, it is quite sterile ; but when the flowers become pure j-ellow or pure purple they yield seed." Passing over the views expressed by many that Cytisns Adami is a hybrid produced by seed, the account of its origin, quoted hy Darwin, is here given. M. Adam inserted a shield of Cytisus laburnum in the stem of C. purpureus ; the bud lay dormant a year and then produced a shoot which was rather more vigorous than those of C. purpureus ; this shoot was propagated and the plants therefi'om were sold as a varietj- of Cytisus |)urpureus, before they had come into flower.^ 1 The account of the budding was published after they had flowered, but before this extraordinary tendency to reversion had been manifested. Upon a review of tlie testimony Darwin was inclined to accept the foregoing account of the origin of Cytisus Adami as a graft-hybrid as true. Other cases are to be placed in the same category. For a full statement of bud-variations and graft-hybrids the student sliould read: Darwin, Variation in Animals and Plants under Domestication, 1868, vol. 1, chap. xi. ; also Foeke, Die Pflanzen-mischlinge, 1881, p. 519. In the latter is an interesting account of the mixed oranges (Bizarria). Con- sult also Braun, On the Phenomenon of Rejuvenescence in Nature (Pay Society, 1853) ; and numerous papers by Caspary. 446 KEPRODUCTION. 1144. Apogamy. The prothallus which develops from a fern- spore bears upon its under side the sexual organs ; from their interaction a bud is produced which grows into the fern-plant. Farlow^ has shown that in some cases the prothallus can give rise to a bud without sexual intervention. De Bary * has traced out the connection between this mode of budding and that which is found in certain other plants. To the abnormal budding of the prothallus and homologous structures he has given the name apogamy. 1145. PartUenogenesis ^ is the production of an embryo with- out the intervention of pollen (or the equivalent of pollen in the lower plants). Coelebogyne ilicifolia, a species belonging to the order Euphorbiacese, has been known to produce seeds with more than one embryo, and without access of pollen. It has been held by some that the embryos in this case are formed fi-om oospheres which had not been fertilized, but investigations by Strasbiirger indicate that they are adventitious outgrowths from the cellular tissue of the nucellus, and are outside of, not in, the embryo-sac. In some other cases examined, Strasburger regards the forma- tion of embryos outside the embryo-sac as dependent upon the fertilization of the ocisphere, but in only one case of this kind did he observe any embiyo form also from the fertilized oospore. 1146. Polyembryony, the production of two or more viable embryos in a seed after the manner just described, is of frequent occurrence in oranges, onions, and -Funkia (Day Lily). 1147. Fertilization in different degrees of consanguinity. It has been shown in Volume I. that " no two individuals are exactly alike ; and offspring of the same stock may differ (or in their progeny may come to differ) strikingly in some particulars. So two or more forms wliich would have been regarded as wholly distinct are sometimes proved to be of one species by evi- dence of their common origin, or more commonly are inferred 1 Quart. Jouru. Mic. Science, xiv., 1874, ji. 266 ; Proceedings Am. Acad., ix. p. 68. ^ Botanische Zeitung, 1878, p. 449 cl seq. 3 Braun: Ueter Parthenogenesis bci Pllanzen, 1857; Hanstein : Die Parthe- nogenesis der Coelebogyne ilicifolia, 1877 ; Hanstein : Botanische Abhand- lungen, 1877 ; Strasburger : Befruchtung und Zelltheilung, 1878. Cases of partlienogenesis occur in the lower plants, where they have been followed out in cultures continued for a considerable time. Their consideration belongs to the next volume of this series. For an account of parthenogenesis in animals, see Balfour ; Treatise on Comparative Embryology, 1880 ; also Brooks on Heredity, 1883, p. 65. CLOSE AND CEOSS FERTILIZATION. 447 to be SO from the observation of a series of intermediate forms which bridge over the differences. Only observation can inform us how much difference is compatible with a comnion origin. The general result of observation is that plants and animals breed true from generation to generation within certain somewhat indeterminate limits of variation ; that those individuals which resemble each other within such limits interbreed freely-, while those with wider differences do not. Hence, on the one hand, the naturalist recognizes Varieties or differences within the species, and on the other. Genera and other superior associations indicative of remoter relationship of the species themselves." " Most varieties originate in the seed, and therefore the foun- dation for them, whatever it ma_y be, is laid in sexual reproduc- tion. . . . Upon the general principle that progeny inherits or tends to inherit the whole character of the parent, all varieties must have a tendency to be reproduced bj- seed. But the in- heritance of the new features of the immediate parent will com- monly be overborne by atavism ; that is, the tendency to inherit from grandparents, great-grandparents, etc. Atavism, acting through a long line of ancestry, is generally more powerful than the hereditj- of a single generation. But when the offspring does inherit the peculiarities of the immediate parent, or a part of them, its offspring has a redoubled tendency to do the same, and the next generation still more ; for the tendencies to be like par- ent, grandparent, and great-grandparent now all conspire to this result and overpower the influence of a remoter ancestrj-." ^ 1148. The reproductive elements in a complete flower may combine to produce an embryo. In this case the pollen and ovule have originated upon a single shoot, within verj' narrow limits of difference as regards the time, place, and conditions of their development, and the result of their union is what might be expected, — a close copj' of the parent plant. The fecunda- tion of a flower by its own pollen is termed close-fertilization, or self-fertilization. 1149. In cross-fertilization the pollen fertilizing the ovule of a flower comes from another flower of the same species, and here the reproductive elements have been developed under dissimilar conditions. lloO. In hybridization the pollen comes from a flower of a different species ; and in this case the conditions, external and 1 Volame I. pp. 318, 319. The student is urged to review carefully the following sections also in that volume ; 619 to 640, and 657 to 662 inclusive. 448 REPRODUCTION. internal, under which the reproductive elements have been pro- duced are widely dissimilar. The mechanism bj- which close-fertilization is secured in some instances and absolutely prevented in others has been fully explained in Volume I. The account of the mechanism is now to be supplemented b3- a statement of the results of reproductioQ in the different degrees of relationship. 1151. The results of close-fertilization contrasted with those of cross-fertilization. It has long been known to cultivators of plants, that in order to keep the desirable varieties which are under cultivation " true to seed " they must be close bred ; that is, all pollen from other varieties of the same species must be excluded. The whole subject is best illustrated b^- reference to the numerous experiments bj' Darwin ; the exhaustive nature of which is indicated l)y an account of a single series given nearly in his own words. 1152. The plants experimented upon in all cases were raised from earefullj- ripened seed, and, when read}- to flower, were placed under nets with meshes of one tenth of an inch in diame- ter, in order that all pollen-carrying insects might be excluded. A plant of Ipomcea purpurea (Morning Glory), growing in the greenhouse, was protected in the manner just described, after ten of its flowers had been fertilized by pollen from their own sta- mens, and ten others by pollen fiom a distinct plant of the same species. The seeds from the first ten flowers may be termed self -fertilized, those from the other ten, crossed. The two kinds of seeds were placed on damp sand on opposite sides of a glass tumbler covered hy a glass plate, with a partition between the seeds, and the glass was put in a warm place. As often as a pair of seeds germinated they were put on opposite sides of a pot, with a superficial partition between them, and the same procedure was followed until five or more seedlings of exactly the same age were planted on the opposite sides of several pots. The soil in the pots in which the plants grew was well mixed, and the plants on the two sides were alwaj-s watered at the same time ; thus the seedlings were subjected to practically the same conditions from a ver\' earlj' stage. In the same manner self-fertilized and crossed seeds were secured during ten generations. The results, so far as these can be shown by measurement of the plants, are exhibited in the following table : ^ — Darwin : Effects of Cross and Self Fertilization, 1S76, p.- 62. CLOSE AMD CROSS FEKTILIZATION CONTKASTED. 4-19 IpOM(EA puepcrea. •s "S.S , <4-i O >=!rS=a: Number of the •555 |1 "Eh: fl ill 5 Generation. '^K, Sis alfi ^^-"S n' Pl SB s3:P4.S c tig;= K& 'A i)eared, they w-ere pre- cisely like those of the female parent, L. speciosum. The first bud opened on the 7th of August, and proved a magnificent flower, nine and a half inches in diameter, resembling L. auratum in fiagrance and foim, and the most biil- liant varieties of L. speciosum in color. In the following year it measured nearly twelve inches from tip to tip of the extended petals ; and in England it has since reached fourteen inches. ... In this one instance the experiment had been a great success; but of the i-emaining fifty hybrids, not one produced a flower in the least distinguishable from that of the pure L. speciosum. The 458 BEPKODUCTION. 1182. Focke has shown that hj-bi'iils between remotely related species are generally delicate and difficult of cultivation, but that those which result from nearlj- related species are remarkable for the vigor of their vegetative organs. Niigeli has also pointed out that the latter have a somewhat longer lease of life than the parents ; thus annuals can become biennials or even perennials. 1183. Hj'brids between closelj' related species usuallj' have larger or more showy flowers than either of the parents, but their reproductive organs are much weaker. Tliis diminution of fer- tilitj- maj' be complete, but it is usually only i)artial. The pollen- grains are generally fewer and often less developed, the ovules are less likely to afford sound germs. As a rule, the stamens are more affected than the pistils. 1184. Derivative hybrids are the offspring resulting from a union of a b3brid with one of the parent forms, or with another hj'brid from a different source. In the former case there is fre- quentlj' observed a marked tendency towards reversion, which may be heightened by repeated experiments in the same direc- tion, until at last it is complete. ^ 1185. Hj-brids and their offspring exhibit a marked tendency to varj'. This fact is utilized by horticulturists in the production of new varieties. Varieties thus produced must, however, be perpetuated by other means than b^' seed.^ influence of the alien pollen was shown, as before noticed, in the markings of the stem, and also in a diniiiiished power of seed-bearing ; but this was all. " In the next year, wishing to see if the male parent would not make his influence appear more distinctly in the second generation, I fertilized several of these fifty hybrids with the pollen of L. auratum, precisely as their fe- male parent had been fertilized. The crop of seed was extremely scanty ; but there was enough to produce eight or ten young bulbs. Of these, when they bloomed, one bore a flower combining the features of both parents ; but, though large, it was far inferior to L. Parkmanni in foriu and color. The remaining flowers were not distinguishable from those of the pure L. speciosum" (Bulletin of the Bussey Institution, ii., 1878, p. 161). 1 For a full treatment of this subject, the student should examine Nageli's treatise in Sitzungsberichte der Konigl.-bayer.-Akad. der Wissenschaften zu Muiichen, 1865, ii. ; and that by Focke, PHauzen-mischlinge, 1881. 2 For a full account of the variation of hybrids, the student should see Kaudin, Ann. des Sc. nat., s^r. 4, 1863, tome xix. For a study of the influence of foreign pollen on the form of the fruit, see a paper by Maximowicz : St. Petersb. Acad. Sui. Bull, xvii., 1872 col. 275. CHAPTER XV. THE SEED AND ITS GERMINATION. 1186. Thus far this treatise has dealt chiefly with the phenom- ena presented by the organs of adult plants, especially while these are in a healthj- state. It is necessarj' to consider in con- clusion a special case ; namely, that of tlie seed, and the earliest phases of its independent existence. 1187. When a fertilized ovule approaches maturity, its activi- ties become notably lessened in degree until, with perfect yipe- ness of the seed, the embrj-o manifests no indication of life. In a few cases the seed is so precocious that it will germinate even before it is deta(!hed from the parent plant ; but there is usually a period of suspended activity. 1188. Two views are held as to the nature of the life of the embryo during this period of arrested activity: (1) that it is simply' potential, and may be roughly compared to the fire in a match, ready to manifest itself under favorable conditions ; (2) that it is a sluggish, dormant state, which differs from active life only in degree. 1189. From the first point of view it is easy to regard the seed as representing a certain amount of potential energy' indi- rectly derived from solar radiance, and held for a time in a con- dition from which it ma3' be released in many ways : thus, it may be liberated bj' rapid combustion, as when corn is burned for fuel ; bj" slow oxidation, as when seeds decaj" ; or by the act of germination. 1190. The second view takes into account, although it does not explain, the slight changes which take place in certain seeds and some other parts, especially buds, during what has been called the resting state. 1191. It has been stated (976) that many seeds cannot be made to start into active growth, even under the most favorable external conditions, until after the lapse of a definite period. Nothing is j-et known as to the exact structural and other changes ■which go on by virtue of this peculiarity. 460 THE SEED AND ITS GEUMIXATION. 1192. Ripening of frnits and seeds. The structural changes attending this process, taken together, result in adaptations for providing the embryo with an ample supply of food, for giving it adequate protection during its resting state, and for securing its dissemination. 1193. The chemical changes comprise chiefly the storing up of a sufficiency of food of a proper character to support the embryo for a time. In pulpy fruits they are mostly associated with the consumption of a certain amount of oxygen and the liberation of more or less carbonic acid. Many of the chemical changes can go on after the separation of the fruit or seed from the parent plant. In the ripening of pulp3- fruits the important changes in texture are attended by the formation of sugars, acids, etc., and by modifications in the character of the walls of cells. 1194. Dissemination is most frequently secured by (1) some meclianism for transport by air, water, fleece, or plumage ; (2) the construction of some expulsive apparatus ; (3j the existence of certain attractions of taste, color, and odor, by which the seeds are made the food of birds. In the last case the germ itself, protected against the action of digestive juices, is often carried to great distances from the parent plant. 1195. Ripeness of seeds. The embryo is sometimes viable, or capable of independent life, at a very earl^' stage. Immature seeds are of course deficient in tiieir suppl}- of proper food for the embryo, which is onl3- imperfectly developed, and their in- teguments are not yet adapted to protect the germ adequately. But in certain instances such seeds ma^- germinate, giving rise to strong and healthy plants. Cohn ' has shown that seeds which are not perfectly ripe germinate somewhat sooner tiian tiiose which are more mature ; this moans that the store of food is in a condition which admits of immediate use. He has further pointed out that seeds separated from the plant, but still enclosed in the pericarp, ripen ; and he believes that those seeds which have reached a medium stage of ripeness germinate most readily. " Viability does not coincide with ripeness ; it precedes it." ^ 1196. Shortly before the period of ripening, the part which 1 Flora, 1849, p. 481. 2 There is some reason to believe that in the case of certain cultivated vege- tables unripe seeds may give rise to earlier varieties than come from ripe seeds. For numerous citations from the extensive literature of the subject see a paper by the author in the Report of the Secretary of the Massachusetts Board of Agriculture for 1878. VITALITY OF SEEDS. 461 connects the fruit or seed with the parent plant undergoes marlied changes, -which ultimately effect or permit complete separation of tlie seed from the plant without anj' injurj-. The process of separation has been compared to that bj' which the leaf is de- tached from the branch in the autumn. 1197. How long can a seed retain its vitality? Some seeds perish shortly after separation from the parent unless they are at once planted, while others preserve their vitality' for long periods. In experiments by De Candolle seeds of three hun- dred and sixtj'-eight species of plants were kept in the same place and under the same conditions for fifteen years. The following results are recorded : — Of 1 Balsaminacese 1 came up, or 100 per cent. " 10 MalTaceje 5 " " " 50 " " " 45 LeguiuinosaB 9 " " " 20 " " " SOLabiatae 1 « <> .. gj <. .. " 10 Scrophulariaceae " " " 10 Umbelliferae " " " 16 CaryophyllacesE " " " 32 Gramineae " " " 34 Craciferse " " " 45 Compositae " " 1198. Daubeny, Henslow, and Lindley found that the seeds of a species of Colutea germinated when fortj'-three years old, and those of a Coronilla when forty-two years old. Thej' ascertained that the seeds of plants belonging to twent3' genera experimented on, germinated after from twenty to twenty-nine j'ears' separa- tion from the parent plant.-' There is no unquestioned evidence that wheat-grains from the wrappings of mummies have been made to germinate.'^ 1 Report of the British Association for the Advancement of Science, 1850, p. 165. 2 The following notes of cases of prolonged vitality may be of interest : — M. R. Brown ra'a dit avoir fait germer des graines de Nelumbium specio- sum extraites par lui de I'herbier de Sloane, c'est-k-dire ayant an moins 150 ans (De Candolle: Geographie Botanique raisonnfe, 1865, p. 542). Seeds of Nelumbium (jaune) have sprouted after they had been in the ground for a century (Lyell's Second Visit to the United States, ii., 1849, p. ?28). The gi-ains of wheat found in mummy-wrappings are uniformly blackened as if by slo-vv charring (eremacmisis), and there is no evidence of a trustworthy character that such seeds have ever been made to germinate. The account hy Count von Sternberg of the germination of -wheat supposed to have been procured at the unrolling of a mummy will be found in Isis, 1836, col. 716-717. 462 THE SEED AND ITS GERMINATION. GERMINATION. 1199. Germination,^ the process by which an embrj-o unfolds its parts, is complete when the plantlet can lead an independent existence. 1200. The conditions necessary for germination are (1) moist- ure, (2) free ox3gen, (3) warmth. 1201. The amount of water required to initiate the process of germination is, in general, that which will completely saturate and soften the seed. Germination does, however, begin in cer- tain cases even when onlj- the radicle and the albumen direetlj- around it have become soaked. The amount of water requisite for the saturation of a seed has been determined for a large immber of plants, and will be seen by a comparison of the results to vary within wide limits, depend- ing on the percentage of water already present and the character of the albumen. It is plain that in vei-y exact determinations account must be taken of the possibility of a loss by the seed of a portion of its contents while in water ; in three days this amounts in the common bean to a little over two per cent. The cereals require a comparatively small amount of water for satu- ration, while leguminous seeds absorb a much larger quantity.^ 1 It is well to distinguish between two stages in the process of germination, (1) that marked by the protrusion of the first rootlet, (2) the subsequent de- velopment of the embryo into an independent plant. The reason for making this distinction is, that most of the experiments upon the relations of tempera- ture, etc., to germination have usually terminated at the first stage ; whereas the vigor of the plantlet as seen at a later stage is aii important factor in deducing results to guide practice in sowing seeds. 2 The table below, by Hoffmann (Versuchs-Stationcn, vii., 1865, p. hi), has a parallel column of results obtained at Tharandt (Nobbe: Samenkunde, p. 119); Species. Percentage of liquid water absorbed. Observations by Hoffmann. Observations at Tliarandt. 44. 45.6 46.9 67.7 69.8 92.1 104. 1068 117.5 120.6 126.7 39.8 60. 167. J a. 96. it. 71. 105.3 89. Wheat Buckwheat Oats Windsor beaa Peas ABSOEPTION OF "WATER BY SEEDS. 463 1202. The increase of seeds in size accompanying the absorp- tion of water is ascertained by placing them from time to time in a narrow graduated cylinder, pouring over enough water to completely cover them, and noting the heiglit at which the water stands ; then pouring it into another graduated glass and accurately measuring it. The difference in amount of water in each case indicates the volume of the seeds. The work must be done expeditiously in order to avoid the eri-or arising from absorption during the period of measuring; but this error in any case is slight. 1203. The following results may be of interest and serve as a guide to the student.^ 65.418 grams of air-dried peas, having a volume of 43 cubic centimetres, were soaked in water at a temperature of 19°- 21° C. The soaked seeds were at each measurement carefully dried by blotting-paper : — Time. 1. In absolute figures. 2. In percentages. Weight. Volume. Weight. Volume. 14 hours . . . 41 ■' ... 70 " ... 46.41 gr. 8.02 " 8.52 " 46 cc. 19 " 7 " 70.9 12.3 13 107 44.1 16.3 70 hours . . . 62.95 gr. 72 cc. 96.2 167.4 The gain iu weight in 70 hours was therefore 96 per cent, and in volume 167 per cent. In another experiment the changes were as follows : Phaseolus vulgaris gained in weight, in 48 hours, 100.7 per cent, and in volume, 134.14 per cent. In still another experiment, with the same species, the gain in weight in 72 hours was 114.5 per cent (or, taking into account some loss bj^ extraction, 117.5 per cent) , and in volume, 140.9 per cent. The gain in volume is con- siderablj' greater than the gain in weight.^ 1 Nobbe : Handbuch der Samenkunde, 1876, p. 122. 2 It must be noted that in many dry seeds, for instance between the coty- ledons of some peas and beans, there are cavities which must be filled before there can be any marked increase of volume (Nobbe : Handbuch der Samen- kunde, 1876, p. 125). 464 THE SEED AND ITS GERMINATION. 1204. The greater part of the increase in weight and volume from the absorption of water bj' dry seeds takes place in a short time ; for example : — Phaseolus vulgaris. Increase in weight. Increase in volume. In 6 hours " 9 " 13.99 per cent. 18.63 " " 49.42 " " 3.35 " " 28.28 percent. 13.10 " " 62.07 " " 3.45 " " " 23 " " 28 " After this there was very little gain either in weight or volume. 1205. Access of free oxygen must be provided to secure germination. Even if all other conditions are favorable, germi- nation does not take place in pure water devoid of any free oxygen, or in an atmosphere of nitrogen. 1206. The oxygen accessible to the seed must be diluted to about the degree found in common atmospheric air, although it is not necessary that the dilution should be made with nitrogen, as is the case with air. Boehm ^ has shown that a mixture of proper proportions of hydrogen and oxj'gen answers about as well as a mixture of nitrogen and oxygen for germination of seeds, provided it is furnished to them under ordinary atmos- pheric pressure. That the degree of pressure is an important factor, is proved by Bert's'' experiments. Barley gave the following results : — Percentage germinated. In ordinary air (76 cm. pressure) 84 In air 50 " " ... • • • ^^ 25 " " ; ; 28 6 " " 10 The proportion of oxygen to nitrogen in atmospheric air is approximately 1 : 5 (oxygen, 21, nitrogen, 79 parts). 1207. The temperature requisite for germination to begin differs considerably in different species. The lowest tempera- ture recorded is the following, noted by Uloth : « In a perfectly dark ice-cellar seeds of Acer platanoides sprouted on ice, the rootlets penetrating to a depth of 5 to 7.5 cm. into the dense 1 Sitzbev. : Wien Akad., Ixviii., 1873, p. 132. ^ Comptes Eendus, Ixxvi., 187,5, p. 1493. ' Flora, 1871, p. 185. TEMPERATTJEE REQUISITE FOR GERMINATION. 465 clear ice ; the seeds themselves being in hollows on its surface. The temperatiire must of couree be given as 0° C. Uloth found also that wheat-grains germinaterl in the same cellar upon pieces of ice. Kerner ^ placed seeds with some earth in glass tubes and exposed them to the cold springs on the edge of snow-fields in Alpine regions. He found that the seeds of most Alpine plants could germinate at 2° C, and that some might even at 0°. It was shown that at all growing points there is some lieat evolved. In Uloth's observations, above noted, attention is called to the fact that the rootlets descended into solid ice in a number of cj'lindrical cavities which they melted out for themselves. 1208. The minimum temperature for germination of the seeds of many plants in common cultivation is given by Haberlandt ^ as 4°. 75 C. (although some can start even below this). Be- tween 4°. 75 and 10".5 we have the minimum temperature for Indian corn, timoth\' grass, sunflower; between 10°. 5 and 15°. 6, that for tobacco and squash ; between 15°.6 and 18°.5, that for cucumber and melon. 1209. The maximum temperature, or that bejond which germi- nation cannot begin, differs greatl}- in different species. Haber- landt has shown that degree of ripeness, freshness, the " race," and several other influences considerably modify the result. The maximum temperature for a few of the more common plants is here noted : — c°. Wheat, vye, barley, oats, peas, timothy grass, cabbage, poppy, flax, and tobacco 31-37 Eed clover, lucerne, buckwheat, and sunflower 37.5-44 Indian corn, millet, squash, cucumber, and sugar melon .... 44-50 In no case was germination observed above 50° C. 1210. Between the minimum temperature below which and the maximum temperature above which germination of a cer- tain kind of plant does not ordinaril}' take place there lies an optimum, temperature ; that is, the degree at which germina- tion begins most speedily.^ The short table on the following page is by Sachs : — 1 Berichte der naturw-med. Vereines in. Innsbruck, 1873, and Botanische Zeitung, 1873, p. 437. 2 Versuchs-Stationen, xvii. p. 104. ' The diff'erence in regard to the degree of warmth demanded by seeds of the same species raised in different climates has been examined by Schiibeler (Die Culturpflanzen ISTovwegens, 1862, p. 27). 30 466 THE SEED AND ITS GEKMESTATION. Minimum, Maximum. Optimum. Barley Wheat Scarlet nmner . . . Indian corn .... Squash 5° 5° 9.05 9.05 11° 38° 42° 46° 46° 46° 23° 29° 33° 33° 33° 1211. The time required after planting for germination to begin, a point indicated by the protrusion of the radicle, has been determined ^ for a large number of plants. A few exam- ples are here mentioned : — Indian com. Eed clover. Birch. Atl6°C 144 hours. 32 hours. 120 hours. " 25°C 56 " 24 " 24 " " 31° C ~ . 48 " 24 " 24 " " 37°.5 C 48 " 24 " 24 " " 440 C 80 " 72 " 1212. The influence of light upon the earliest stages of germi- nation has been shown by careful investigations to be inappre- ciable so far as most plants are concerned.^ The unqualified statement found in some works/ that light is in general prejudicial to germination, is not borne out by facts. 1213. TMe phenomena of germination are : (1) forcible absorp- tion of water, (2) absorption of oxygen, (3) solution of nutrient matters, (4) their transfer to points of consumption, (5) their employment in building up new parts. After the initial step these processes may go on simultaneously. 1214. The enormous imbibition power of dry seeds can be demonstrated by confining sound seeds in a strong receptacle to which water can obtain access. If a closed manometer is attached, the pressure they exert can be measured. Boehm * 1 Versuchs-Stationen, xvii., 1874, p. 104 ; and Storer : Bulletin Bussev Inst., 1884. •' 2 Hoffmann : Jahresher., iiber Agricultur-Chem., 1864, p. 110. 3 Ingenhousz ; Senebier, Physiologie vdgetale, iii. 1800, p. 396'; Johnston's Lectures on Agricultural Chemistry, 1842, p. 194. 4 Muller: Botan. Unters. ii., 1872, p. 29, quoted hy Nobbe (Hand- buch der Samenkunde, p. 118). Similar experiments at Welleslev College gare results somewhat lower than this. ° PHENOMENA OF GERMINATION. 467 found that peas in swelling could overcome a pressure of 18 atmospheres, corresponding to a height of the mercurial column of 13.5 metres. 1215. The influence of oxygen upon the absorption of water bj' the seed is not marked, as will be seen by the following experiment : ' — 200 fresh seeds of red clover were placed in pure water for 20 hours ; 200 more were placed in water into which oxygen gas was conducted ; 200 more in water through which carbonic acid gas was conducted for a while and then the water covered with a layer of oil to exclude the air. The results, so far as swelling is concerned, were as follows : — Seeds in water 83 per cent swollen. " " with oxygen .... 86 " " " " " carbonic acid . . 71 " " 1216. The oxygen absorbed by seeds in germination was thought by Schonbein to undergo the active or ozone modifica- tion. By his experiments the seeds of two plants, Cynara Scol^'- mus and Scorzonera Hispanica, were shown to possess to a con- siderable degree the power of converting atmospheric oxygen into ozone. 1217. Oily seeds absorb a large amount of oxygen. Siewert has pointed out the fact that the neutral oil of the rape-seed very soon after access of oxygen and water to it possesses an acid reaction. Oleic acid can absorb at ordinary temperatures about twenty times its volume of oxygen. 1218. Nutrient matters must become liquid before they can be utihzed bj' the embryo. Some of these in the form in which they are stored up in seeds are soluble in water ; such are tlie sugars, dextrin, and a part of the albumin. The other nutrient matters, such as starch, the oils, and most nitrogenous sub- stances, must undergo changes before they can enter into solu- tion. Some of these changes have already been alluded to in Chapter XI., and are here presented in brief review. 1219. The conversion of starch into soluble matters is eflfected in the seed bj' means of one or more " ferments." In the pro- cess of malting,^ which consists essentially in forcing germination up to the point of protrusion of the radicle and then checking it, the starch appears to undergo little change. But if the ground malted grains are kept in water of a temperature of 68° C. for 1 TSTobbe : Handbuch der Samenkiinde, 1876, pp. 102, 103. 2 See Watts's Dictionary of Clieniistry, under " Beer." 468 THE SEED AND ITS GEKMINATION. two hours, all the starch will be found to have been converted into and dissolved as soluble carboh3-drates, sugar, and dextrin. The change in this case is attributed to the ferment, diastase, one part of which, it is claimed, can convert two thousand parts of starch into sugar. It will be noted that in the pro- cess above described the temperature (68° C.) is much higher than that at which ordinary germination proceeds. Dubrunfaut^ has given the name maltin to a ferment far more active than diastase, found in all germinating cereals. This is able to convert into a soluble state from one hundred thousand to two hundred thousand times its weight of starch. It forms with tannic acid an insoluble compound which retains its power for a long time. In good barley meal there is one per cent of maltin. 1220. The oil in oily seeds is in germination carried through a long series of changes. It is first transformed into starch, and then follows the same course as starch, already described.^ 1221. Van Tieghem has shown that oleaginous albumen, rich in aleuron, has an activity of its own which enables it to digest itself, so to speak, and thus become at once fit for the embryo to use ; on the other hand starchy albumen and cellulosic albu- men must be first acted on by the embryo, and thus become dissolved and ready for use.^ 1222. The changes which take place in a germinating seed are accompanied bj' direct or indirect oxidation of a portion of the nutrient matters, a release of energy, and an evolution of carbonic acid.* The amount of COj given oflT by germinating seeds and the rise of temperature serve as measures of the process of oxidation. 1223. It is not proved that germination can be hastened by chemical means. Experiments with dilute chlorine water seem to show that the time can be somewhat lessened, but the results are discordant.^ 1224. It has been asserted recently that the presence of mi- crobes, the minute organisms to which putrefaction is due, is 1 Coniptes Renclus, Ixvi., ji. 274. 2 Peters, Versuchs-Stationen, iii., 1861, p. 1 ; MiiQtz, Ann. de Chimie et de Physique, s^r. i, tome xxii. p. 472. 3 Ann. des Se. nat., ser. 6, tome iv., 1877, p. 189. 4 For the changes in the horny endosperm of the date palm see Sachs, Botanische Zeitung, 1862, p. 241. 5 See M. Carey Lea, American Journal of Science, xxvii., 1864, p. 373, and xliii., 1867, p. 197. FIRE-WEEDS. 469 essential to the beginning of the process of germination. It is ' said that in soil which has been completely sterilized, that is, freed from microbes or their germs, seeds provided with all other requisites for germination will fail to sprout. These experiments by Duclauxi have not been repeated by other observers. 1225. The appearance of abundant crops of certain plants upon ground recently cleared by Are is one of the most note- worthy phenomena in connection with germination. At the North, two plants have obtained, par excellence^ the name of "fire-weeds;" namely, Erechtites hieracifolia, and the more common willow-herb, or Epilobium angiistifolium. They are later replaced by shrubs, and later still by soft-wooded trees, which are characteristic of burnt districts. The following sug- gestions have been made in regard to their appearance : (1) that the seeds have been long buried in the soil, under conditions which have preserved their vitalit}', but which did not permit them to germinate ; (2j that the seeds find their way to the ground of a clearing which affords, in the ash released from wood by burning, a soil most fit for germination. But no exact observations have jet been made upon the subject. ^ Comptes Eeudus, c, 1885, p. 67. CHAPTER XVI. KESISTANCE OP PLANTS TO UNTOWARD INFLUENCES. 1226. Claude Bernard has shown that life presents itself under three forms: (1) latent, dormant, or inactive, illustrated bj' the seed ; (2) variable, or oscillating, exemplified by the plant during periods of apparent rest, when its activities are nearly suspended, but when, in fact, some chemical changes are going on, though very slight in degree ; (3) active, or free, exhibited by a plant in full vigor. It has been repeatedly pointed out in previous chapters that during their resting periods seeds and other parts can be sub- jected to the action of influences which would destroy the life of plants in full activity.^ 1227. Inquiry as to the kind and amount of injury caused to active plants by hurtful agents must deal with the influence of extremes of temperature, too intense light, improper food, poi- sons, and mechanical agents. Many of these injurious influences and their effects upon special parts of the plant have already been alluded to in previous chapters ; bnt it is proper to con- sider them now with regard to the whole organism. 1228. Effects of too high temperature upon the plaut. Here, as in most other cases, there is wide diversity among plants, depending upon their constitutional peculiarities ; thus, plants of the tropics not onl}' demand higher temperatures than those of 1 For some account of various recent views in regard to the nature of life, the student is referred to the following works : Herbert Spencer, Principles of Biology, 1870; Claude Bernard, LeQons sur les Phenomfenes dela Vie communs aux Animaux et aux Vegetaux, 1879; and Nageli's recent treatises. For an interesting account of the reactions of living matter to very dilute solutions of certain substances which ai'e poisonous when used in greater strength, see Loew and Bolcorny. These investigators use a dilute alkaline solution of argentic nitrate in the discrimination between living and dead protoplasm ; upon api)lication of the reagent the former turns black, the latter remains uncolored. The solution is made by mixing 1 cc. of a one per cent solution of the nitrate in distilled water with an equal amount of a solution containing 13 parts of potassio hydrate solution, 10 parts of ammonia, and 77 parts of distilled water (Pfliiger's Archiv. xxv., 1881, p. 150). EXTREMES OF HEAT AND COLD. 471 colder climates for the exercise of their normal functions, but they will also gcnerall3- sustain much higher degrees of heat with- out injury. The differences of temperature in favor of tropical plants are not, however, always ver}- marlved. The following table ' indicates sufliciently the highest tempera- tures which a few common plants can bear. The line at the top shows what were the immediate surroundings of the plants ex- perimented upon ; the columns marl«:ed A show tlae highest temperatures short of proving fatal ; tliose marked B, the low- est fatal temperatures. The plants were exposed to the high temperatures from fifteen to thirtj' minutes. iiame of Plant. Koots in -water, stems in air. Koots in soil, stems in air. Plant in water. A. B. A. B. A. B. °C. o o o Zea Mais 45.5 47. 50.1 52.2 46. 46.8 Tropseolum majus Citrus Auvantium 45.5 47.8 47. 50.5 50.5 52. 44.1 50.3 45.8 52.5 Phaseolus vulgaris 45.5 47. 50. 51.5 1229. After a plant has been subjected to too high a tempera- ture, its foliage wilts and soon becomes dry ; and its leaves, having once taken on a scorched appearance, are unable to recover their turgescence. it may happen, however, that the injury does not proceed so fai as to affect the latent or even the partially developed buds ; if this is the case, partial recovery takes place through their unfolding. The curious fact^ that many algse can resist very high temperatures has been already adverted to (see 566). 1230. Effects of cold upon the plant. Certain plants are seri- ously injured by low temperatures which are considerably above the freezing-point of water, but these are exceptional cases. Most northern plants can readily endure cold, provided tlieir tissues are not frozen. Frost produces very different effects upon different plants. In some of our familiar spring plants the leaves may be frozen and thawed without apparent mischief, but in general the thawing must take place slowly ; if it proceeds rapidly, the plant may be 1 De Vries: ArcWves Neerlaiidaises, v., 1870. 2 Consult also American Journal of Science and Arts, xliv., 1867, p. 152. 472 UNTOWARD INFLUENCES. irreparably injured. Tiiere are well-linown cases in which plants ma^- be thawed quickh' without serious injury.^ 1231. Goppert^ and others have shown that the flowers of certain orchids, turned blue by the formation of indigo in their cells when they are slightly frozen and suddenly thawed, will preserve their usual colors unchanged if made to thaw very slowly.' 1232. As to the length of time during which the vitality of a frozen plant persists, we have no exact observations ; but it is stated that after the recession of a glacier in Chamouni sev- eral plants which had been covered bj- ice for at least four years resumed their growth.* 1233. It is still an open question whether much of the injury to certain plants by^ freezing is not strictly mechanical, resulting from the expansion during the formation of ice in the cells. ^ 1234. " WinterkiUin^." The destruction of many plants by exposure to the influences of a variable winter is sometimes attributed to the injurious effects of drying winds rather than to cold alone. It has been shown (748) that the amount of water absorbed by roots -is governed largely by the temperature of the soil. Although the exhalation of moisture from the leaves of evergreens in winter is not large, it is, however, suflncient to create a certain demand upon the soil for a supply. This de- mand, slight as it is, is of course greater during very dry weather ; and it is from this that the injuries may be supposed largely to result. 1235. The behavior of certain plants during exposure to low temperatures afl"ords some of the best illustrations of the adap- tation of vegetation to its surroundings ; and the question as to increasing the tolerance of a given species or variety to the 1 Sachs has shown that the leaves of cabbage, turnip, and certain beans frozen at a temperature of from — 5° C. to — 7° C, and placed in water at 0° C, are immediately covered with a crust of ice, upon the slow disappearance of which they resume their former turgescence (Versuchs-Stationen, ii. 1860, p. 167). If such frozen leaves are placed in water of 7.5° C. they become flaccid immediately, '■^ Botanische Zeitung, 1871, p. 399. ' According to Kunisch (qimted by Pfeffer : Pfianzenphysiologie, ii., p. 436), this blue discoloration is observed when the flowers, placed in an atmos- phere of carbonic acid, are subjected to a freezing temperature ; in this case, of course, the indigo is produced from chromogen without free oxygen. < Botanische Zeitung, 1843, p. 13. 6 Hoffmann (Grundziige der Pflanzenklimatologie, 1875, p. 325) attributes a part of ihe mechanical injury from freezing to the separation from the cell- sap of the air previously contained therein. IMPROPER FOOD AND POISONS. 473 untoward influence of cold, hy careful selection of seed for a series of years, lias been successfully answered by cultivators in some northern countries of Europe.^ 1236. Among the protective adaptations of seeclhngs to cold is that described by DeVries,^ who has noted that in certain instances there is a marked retraction of tiie caulicle into the ground upon the approach of a lower temperature. The with- drawal is due to the contraction of the cellular tissue composing the root. 1237. Effects of too intense light upon the plant. All otlier conditions being natural, living plants containing chlorophyll can perform their functions normallj- when placed in the brightest sunlight." Even when the rays of liglit are moderately concen- trated upon the foliage by a large convex lens there is no seri- ous disturbance of function. But when, as in Piingsheim's experiments (see 824), the sunlight is rendered very intense, assimilation is arrested and destruction of the protoplasm soon ensues. 1238. Effects of improper food upon the plant. It has been shown (Chapters VIII. and X.) that certain substances are in- dispensable to the healthful growth of plants ; and it has further been pointed out that most of these substances may be offered to the plant in excess with no marked results. It sliould now be noted that a few of these substances, notably nitrogen com- pounds, applied in excess may induce a more luxuriant growth than is desirable to the cultivator. Penhallow * and others have jTOinted out that certain maladies of plants are largely' dependent upon malnutrition. In such maladies fungi are frequent con- comitants, in many cases invading plants already enfeebled by improper or insufficient food ; in others, obviously causing by their presence and activity the diseased conditions. 1239. Effects of poisons upon the plant. Noxious Gases. The most hurtful of these, considered from a practical point of view, come as products of the combustion of inferior sorts of coal, 1 Schubeler (see note on page 465). For an account of the formation of ice in plants, and the diiferent degrees of temperature at which it takes place, consult Miiller : Landwirthschaftl. Jahrbiicher, ix., 18S0. 2 Botanisclie Zeitung, 1879, p. 649. Haberlandt has also examined the same mechanism to some extent. " It is a familiar fact that many plants thrive best in deeply shaded glens. Success in the cultivation of such plants is attained only by regarding their natural condition. * Houghton Farm Experiment Department, series 3, no. iii. 474 UNTOWARD INFLUENCES. especially those which contain sulphur compounds as impurities.^ Formerly, in the vicinity of large chemical factories, the escaping gases were productive of wide-spread injury to vegetation ; but improved methods of manufacture have diminished this evil to a considerable extent. 1240. Sulphurous acid, formed by combustion of sulphur in the open air, produces, even when existing in the air in the pro- portion of only one part in 9,000, the following effects upon leaves : their blades shrivel from the tips, become grayish yel- low, and soon drj' so that they fall off at a slight touch. The phenomena observed are somewhat lil^e those occurring at the time of the fall of the leaf in autumn. Yet in the experiments by Turner and Christison mentioned in the note,^ the amount of sulphurous gas present in the air was so small as to escape detection by smell. H^-drochloric acid gas, nitric acid in vapor, and chlorine are also very destructive to plants, even when in such minute amounts as to be unnoticed on account of their odor. Injurious effects are often produced upon shade trees by the leakage of illuminating gas from street mains. 1241. Wardian Cases. In 1829 Ward accidentally discovered that plants could thrive in tightly closed cases, in which there could not be any interchange of the air with the outside atmos- phere.' This discovery led him to institute experiments rela- 1 E. Angus Smith : Air and liain, 1872, pp. 465, 553. 2 For accounts of experiments in this interesting field, the student may consult the following works : Turner and Christison, Edinburgh Medical and Surgical Journal, xxviii. p. 356; and Gladstone iu Report of British Association for Advancement of Science, 1850. 3 N. B. Ward : On the Growth of Plants in Closely Glazed Cases, 1852. The table on the following page, based on researches by T. W. Harris, shows the agents, the effects of which were tried upon chlorophyll, and the results in each case as to the extrusion of chlorophyll pigment (see 772). The figures in the third column indicate results as follows ; — 1. Chlorophyll grains large and well defined. Sponge-like stracture evi- dent. One or two globules of large size on almo.st eveiy grain ; sometimes almost as large as the grain itself, which is colorless or nearly so. 2. Globules still plentiful but smaller ; frequently several on each grain. Structure of the grains evident. The protoplasm in this and the two following grades (3 and 4) is often contracted by the chemicals used, rendering the result more or less obscure. 3. Globules small, and fewer than in 2. Grains still retain some coloring- matter in their substance, and are not so well defined either in form or structure. 4. Globules few; only seen on a few grains. Structure of the grain not defined, but under a high power it frequently has a granular and sometimes a NOXIOUS GASES. 475 tive to the systematic cultivation of plants in such cases in the impure air of manufacturing towns. In the glass cases, now- stellate appearance. In the latter case each grain la generally surrounded by an irregular mass of colored protoplasm, these miusses being often connected together b}' threads. This stellate structure is also often brought out after dissolving out all the coloring-matter by prolonged treatment with benzoic acid. 5. No result. Agent. Time of Action. Eesnlt. «i 1 i/nr/w\ ,1 ( Grains bleached, but form Alcohol (95 %) 1 day. i •' ( remains. Steam 1 hour. 2 Boiled in H^O 7 min. 2 " then cold in HCl . . . 2 days. 3-)o^, , „ " HNO3 . . . 2 " 3[ ,'i?r/'y'^ Benzoic Acid. 2 " 3 3 s*^"^*"- H2SO4 cone 1 " Specimen destroyed. HjSO^ dilute 1 " 3 HNO3 cone. . . 1 " Protoplasm contracted. HNO3 dilute . 1 " 1 HCl 1 " 2 HCl + HNO3 (3 parts HGl.l part HNO3) 1 " | ^™*°£™ "'"'''"'"" H2SO4 + HCl (equal parts) 2 " 3 H2SO4 -f HNO3 " 2 " 3 H2SO4 + HCl -I-HNO3 (equal parts) . . 2 " 3 HCaHaOa 7 " 3 H2C2O4 7 " 3 H3PO4 7 " 2 H.AH4O. (Tartaric acid) jS^^g'*^-;!*} 7 " 2 H2Cr04 7 " 4 Picric Acid 7 " 4 Citric Acid 7 " 3 Boracic Acid . . 7 " 3 •t, • A -J ( sat. sol. in a sol. of lA parts ) - ,, . Benzoic Acid I n^^hPOi to 100 H^O } ^ ^ Benzoic Acid 2 " Grains bleached. Salicylic Acid 3 " 3 Na5HP04 6 " 5 Na(NH4)HP04 6 " 5 NaHS04 6 " 5 t Grains destroyed and pig- NaOH 2 " } ment diffused through ' the protoplasm. NH4OH 2 " 5 K2CO3 2 " .5 ! Grains swell and become homogeneous, but no extrusion or escape of the pigment. 476 UNTOWARD INFLUENCES. eveiywhere known as Wardian cases, the plants are supplied with sufficient water, and the atmosphere is practicallj- satu- rated with moisture. When exposed to sunlight, the plants in tlie cases can carrj' on all the operations of assimilation, growth, and respiration. Comparing the conditions which surround the plants in a Wardian case with tliose which prevail in a furnace-heated house, it is plain that the plants in the case are placed in what is es- sentiall3- a humid tropical climate, while those in the house are exposed to excessive dryness, and to an atmosphere which maj- contain minute traces of the poisonous gases arising from combustion. 1242. lyiqu'ids and Solids. Comparativelj' few substances except those possessing strong acid or alkaline properties are injurious to a plant. As indicated in 683, preparations of arsenic which are extensively employed for the destruction of insects upon crops in cultivated fields are not absorbed b^- plants to an appreciable extent. This is further illustrated by the impunity with which various other insecticides can be applied to green- house plants. 1243. Numerous experiments, more curious than profitable, have been made to test the effect of poisonous alkaloids upon vegetation. Manj' observers have proved that some plants yielding poisonous alkaloids may be poisoned by applications to their roots of solutions of the ver}' alkaloids which the^' have themselves produced ; thus morphia may poison the poppy (see 961). Strasburger^ saj's that. morphia speedily kills motile spores. Kiihne^ has noted that the protoplasmic movement in the stamen-hairs of Tradescantia is not wholly arrested, even after many hours, I)}- a solution of veratrin ; and Pfeffer^ has observed that the cells in sections of certain fleshy roots are not killed even when immersed for several days in a saturated solution of morphia acetate. As Frank * suggests, these discrepancies in effects depend on the differences in the power possessed by the various parts in the absorption of such matters. 1244. Effects of mechanical injuries upon the plant. The most important of these are caused by destructive fungi. The destruc- 1 Wirkung des Liclitcs und der Wiirme aiif Sclnviirmsporen, 1878, p. 2 Uiitersiichungmi uber das Protoplasma, 1864, p. 100. 8 Pflauzenphysiologie, ii., 1881, p. 454. * Pflaazenkrankheiten, 1879. LIGHTNING. 477 tion primarily affects the cell-contents, and later the cell-wall. It is very highly probable that in certain cases various pro- ducts of decomposition arising from the progress of the fungi may themselves prove poisonous to contiguous parts of the plant. One of the most important problems of practical horticulture and agriculture is the search for efficient means b\' wliich invad- ing fungi may be destroyed without at the same time injuring the host-plant to which they have attached themselves.' 1245. The presence of certain fungi in plants sometimes gives rise to abnormal growths and to various distortions. When once their disturbing influence is felt, the subsequent growth may be affected for a long time, and the malformations become of an extraordinary character. 1246. Considerable distortions are often produced by bites or other injuries by insects.^ Galls — for instance those of the oak and willow — are among the most noteworth3' instances of this kind. 1247. The effects of lightning upon trees have been examined bj' manj^ observers. Cohn * and C'oliadon * have pointed out some of the characteristic injuries sustained bj- species of poplar, elm, and oak, stating that the stroke does not usnall3' affect the summit of the first two, but that oaks are frequently struck at their uppermost branches. The course of the injurj' is often spiral, winding around the trunk in stripes which involve part of the sap-wood and bark. It is not now believed that any species of trees are exempt from injury from lightning, although the ash was formerly thought to possess a remarkable degree of immunity. 1248. Partial or complete blanching of otherwise healthy leaves exposed to light has been regarded by some observers as an indi- cation of a diseased condition. In some cases the blanching is dependent upon a lack of iron in the soil (see 791), bnt in others it appears to be strictly hei-editary, being propagable both by bud and by seed. Nothing is known, however, as to its causes in these cases, and they are generally referred to the unsatis- factory category of sports. It is worthy of notice that a considerable proportion of the so-called variegated plants, especially of those which have only ' For an account of some experiments in this field, see Frank : Pflanzen- krankheiten, 1879 ; and Nohbe : Haudlnich der Samenknnde. 2 For a bibliography of this subject, see Frank's PHanzenkrankheiten. 8 Denkschrift. d. Schles. Ges. f. vaterl. KuU. Breslau, 1853, p. 267. * Mem. de la Soc. de Phys. et d' Hist. Nat. de Genfeve, 1872, p. 501. 478 UNTOWARD INPLTTESrCES. white spots intermingled with the green of the leaf, come from eastern Asia, notably from Japan.' 1249. The lease of life of any given plant is fixed primarily by the inherited character:^ hence we have annuals, biennials, and perennials ; but these differences are not in all cases abso- lute, in some thej^ are even ill-defined. The lease of life is modified secondarily bj' external influences, which have been sufficiently discussed in the present volume. In conclusion, attention should be called again to the fact (see Chapter V.) that in many instances the duration of the life of the plant Is determined largely by mechanical factors, especially the strength of materials. 1 Morren : Heredity de la Panaehure, 1865, p. 7; Frank : Pflanzenkrank- heiten, p. 465. 2 The student should examine Minot on "Life and Growth." GLOSSARIAL INDEX. GLOSSAHIAL INDEX. The numbers following the titles refer to pages. An italicized page-number indicates that the term which it follows is defined on the page to which it refers. Absolute alcohol (C^HoO), use of, as a medium, 5, 9. Absorption, chemical, by soils, 243; de- pendence of rate of, upon temperature, 279; of ammonia by leaves, 332, 341; of aqueous vapor by leaves, 283 ; of carbonic acid b}' plants, 299; of gases by water, 300 n. ; of liquids through roots, 230; of moisture by soils, 239; of oxygen during germination, 465; of saline matters from soils by roots, 244; of water by seeds, 463; of water during germination, 466; of water previous to metastasis, 267 ; relation of transpiration to, 279; through the cut end of a stem, 263. Absorption-bands, 292, 293. Acetic acid (HC2H3O2), as a reagent, 9, 54; as a mounting-medium with glj'cerin, 21. Achromatin {optui, I bear), 451. ^sculiu (CsiHj^Oia), 302. jEthalium septicum, composition of pro- toplasm of, 197; locomotion of, 397; preparation of Plasmodium of, for ex- amination, 196. Agamogenesis (a, without; yaiJ.o^t mar- riage; yereo-is, origin), 426. Age of trees, 140. Aggregation, 340, 343, 421, n. Air, composition of, 303; contained in a plant, 100 ; contained in fresh woods, 261; removal of, from specimens, 9. Air-passages, 100. Air-plants. See Epiphytes. Albumen of the seed, 181. Albumin, diffusion of, 223; of plants, 363. Albuminoids, 325, n. ; formation of, in tlie plant, 335 ; tests for, 28 ; transfer of, 356. AlburnLim. See Sap-Wood. Alcohol (CjHoO), action of, upon cer- tain parasites aud saprophytes, 294; action of, upon chlorophyll, 41, 290^ use of, as a medium, 5; use of, as a preserving and hardening agent, 9 ; use of, in prepar.ition of specimens for mounting, 23; use of, in removing air from spt-cimens, 9. Aldrovanda, 344. Aleurone grains (a\evpov, wheaten flour), 47. See also Protein Granules. Algae, absorption by, 230; growth of certain, at low temperatures, 385; in hot springs, 205. Alkaloids, 327, 365; cannot be utilized by plants, 335; effect of, upon plants, 365, 476. Alkanna (alkanet root), 18, 363, n. Alum (K2Al2[S02]4 -I- 24 H2O or [NH,], Al20e[SOj4-|-24H20), 10. Aluminium, occurrence of, in plants, 256. Amides, occurrence of, in grasses, 336. Amidoplasts (ajauAov, starch; irXda-a-oi, I form), name proposed by Errera for leucoplastids. Ammonia (NH^OH), absorption of, by leaves, 332, 341; absorption of, by soils, 243; formation of, in putrefac- tion, 333. 31 482 GLOSSARIAL INDEX. Ammonia-earmin, 16. Amoeboid movement of protoplasm (iM^"^^', change; eMos, form), 201. Aiiiyiogenic bodies (ajttuAof, starch ; y^v- "aii, I produce), 43. See also Leuco- plastids. Amyloid (a/auAor, starch; ei'Sos, form),32,n. Anaesthetics, effect of, upon protoplasmic movements, 211; effect of, upon the Sensitive plant, 424. Anaplast (ii'airAao-o-a), I shape), 287, n. Androecium (aiojp, » man ; oIkos, a house), 426. Angiosperms (iwetor, vessel; trirep/xa^ a seed), fertilization in, 426. Angle formed by the union of a branch and the trunk, 193. Anilin blue, action of, upon callus, 94. Anilin chloride, use of, as a test for lig- nin, 10, 37. Anilin sulphate (2 [CcHsNHjJSOjHj), use of, as a test for lignin, 10, 37. Animals, occurrence of chlorophyll in, 288. Annual growth of roots, 114; of stems, 137, 139. Annular markings (annulus, a ring), 30, 85. Anther (ii^fliipdi, flowery), development of the, 171. Antheridia, 441, n. Antherozoids, 440, «., 441, n. Anticlinal planes (afri, against; k>^Cveiv [/t\ivu], to incline), 382. Antipodal cells (avrC, against; n-oiJs, a foot), 434. Apheliotropic curvatures (i-iro, from; ^^105, the sun; Tp6irot, a turn), 393. Apical cell in roots of the higher crj'pto- gams, 117. Apogamy (dTrd, without; ya/ios, mar- riage), 446. Apogeotropic organs (iwo, from ; 7% the earth; rpdiros, a turn), 392. Apospory (iird, without; airopot, seed), the substitution, in reproduction, of budding for asexual spore-formation. Apostrophe (iird, from; "ip'xjirj, a turn- ing), 399. Apposition theory concerning the growth of the cell-wall, 219. Approach grafting, 152. Aquatics, absorption by, 230 ; epidermis of, 67. Aqueous tissue. See Water Tissue. Arabin (2CoH,„Oii-|-H20), 358. Archegonium, 441, »., 442, »., 443, ». Archesporium (ipxv, beginning; o-irdpos, seed), 17J, n., 379. Areolated dots {areola, a small, open place), 30, 82. Argentic nitrate (AgNOa), 10. Arsenic, occurrence of, in plants, 256 ; use of compounds of, as insecticides, 476. Artificial cell, 226. Asexual reproduction, 426, 444. Ash, amountof,in plants, 236,247; compo- sition of, in plants, 247 ; of autumn and spring leaves compared, 281; office of the different constituents in plants, 252. Asparagin (UHsN^Os-f-HjO), 10, 364, 372. Asphalt-cement, 20, 24. Assimilating system of the plant, 285. Assimilation, 185, 284; a process of re- duction, 285, 320 ; chlorophj 11 acts as a screen in, 323; conditions for, 285; contrasted with respiration, 356 ; course of transfer of the products of, 356; Draper's experiments upon, 310; early history of, 323 ; effect of artificial light upon, 316; formic aldehyde hypothe- sis, 322; free oxygen not necessary for, 318; influence of colored light upon, 310 ; measure of activity of, by the bacterial method, 315; measure- ment of the amount of, 312; portion of the spectrum causing maximum activity in, 314; practical study of, 305; products of, 320; products of, necessary for growth, 384; raw ma- terials required for, 299; relations of carbonic acid to, 318; relations of tem- perature to, 316 ; storing of products of, in perennials, 373. Atavism (atavus, an ancestor), 447. Atom, 213, n. Auric chloride (AuCU), 10. Automatic (autonomic) movements, 413. Autoplast (aiiTot, self; irAao-o-io, I form), 287, n. Autumn wood, 138, 395. Autumnal changes in color in leaves, 297. Auxanometers (aifiicri!, increase ; p-irpov, measure), 383. Bacteria, measurement of activity of assimilation by, 315. Balsam, Canada, 22; Copaiba, 363; of Fir, 363; of Peru, 363; of Tolu, 363. Balsams, 97, 3fi3. Barium, occurrence of, in plants, 256. GLOSSARIAL INDEX. 483 Baik, HI, 149. Basifugal growth (basis, base; fugo, I flee), 158. Basipetal growth (basis, base; peto, I move toward), 156. Bassorin (CHuOj), 358. Bast-fibres, 87 ; clinging fogetlier of, in inner barlt, 147; in cribose portions of fibro-vascular bnndles, 10-1; forming sheaths of collateral bundles, 12;j; re- actions of, 90; separation of, from the stem, 147; size of, 90; solubility of, 33. ft. ; strength of, 18y. Beale's carrain, 17. Benzol (CgHg), a s^Avent for fats, 10; use of, in preparation of specimens for mounting, 23; use of, in section- cutting, 3; use of, in treatment of the chlorophyll pigment, 291. Benzol-balsam, 23. Bibulous paper, use of, 5. BicoUateral bundles, 104 ; in stems, 123. Bifacal arrangement of leaf-parenchy- ma, 158. Biformes {biforis, having two doors), 53, n. Blanching of leaves, 254, 297, 477. Blastocolla (/3A<'i'"s. shoot; "o^^". g'le), the balsam produced on buds by glan- dular hairs. Bleaching processes, 11. Bleeding of plants, 264. Bloom, 67, 294. Bordered pits, 30, 82 Boron, occurrence of, in plants, 256. Branches, rudimentary and transformed, 153. Branching of roots, 115, 232. Bristles, 69. Bromine, occurrence of, in plants, 256. Brownian movement, 429. Budding, 152, 444. Buds on leaves, 162. Bud-variations, 444. Bundle-sheath, 104. Burnettizing, 142. Byblis, 345. C-EsiuM, occurrence of, in plants, 256. Caffeine (C,H,„N,0.,), 327. Calcareous soils, 239. Calcic chloride (CaClj), use of, as a clearing agent, 10 ; use of, as a mount- ing medium, 21; use of, in the meas- urement of transpiration, 274. Calcic hypochlorite (CaCl^Oj), use of, as a bleaching agent, 11. Calcium, occurrence of compounds of, in p ants, 39, 54, 247, 337 ; office of, and its compounds in the plant, 253. Calli.s, as a means of healing plant wounds, 150; in sieve-cells, 93. Calyptrogen (icaWn-rpa, a cover; ynwia, I produce), 107, n. Cambiform cells, 122. Cambium, 104, 123, 135, 136; cell- division in, 377. Cambium-ring, 1-37. Cambium libres, 81, it. Camera lucida, 4. Camphors, 363. Canada balsam, 22. Cane-sugar (Cyfl^fi^^, amount of, in plants, 359; diffusion of, 223; test for, 52. Capillary water, 242. Caramel", diffusion of, 222, 223. Carbohydrates, 51, 357 ; transfer of, 356. Carbolic acid (C„H, .OH), use of, as a clearing agent, 167; use of, as a test for lignin, 11, 37. Carbon, appropriation of, by plants, 285 Carbon distdphide (CS,), 11. Carbonates, test for, 9, 54. Carbonic acid (used in this work as a term for carbon dio.xide, CO2), absorp- tion of, by plants, 209, 305; amount of, decomposed in assimilation, 319; amount of, decomposed by plants pro^ portional to the disti'ibution of effective caloric energ}' in light, 314; amount of, in natural waters, 300; amount of, in rain-water, 299, 300, v.; amount of, most favorable to assimilation, 319; effect of a large supply of, upon vege- tation, 304, 318; roots do not take up, 300. Carmin, 16 ; with picric ncid, 17. Carnivorous plants, 338. Carpogonium, 440, n. Carpophytes, reproduction in, 440, n. Casein of plants, 363. Castor-oil, use of, as a medium, 6. Caulicle (cnuliculus. a small stem), 403,- movements of the, 403; sensitiveness of the, 415; structure of the, 106, 118. Caustic soda. See Sodic Hydrate. Cell, 25; an osmotic apparatus, 229; origin of name. 25. Cell-division, 374; directions of, 380; in plant-hairs, 380; in the cambium 484 GLOSSARIAL INDEX. of Pinus, 377 ; in the development of pollen-grains, 379 ; in the formation cf stomata, 376 ; method of demonstra- tion of, 380. Cell-plate, 376. Cell-sap, carboh^'drafes in the, 51 ; color of the, in flowers, 170; color of the, masks that of chlorophyll, 294. . Cells, animal, analogous to vegetable, 220; elassitication of, 56, 59; develop- ment of, 58; method of determining the density of the contents of, 390; morphological changes in, during growth, 373; turgidity of newly formed, 383. Cellular system, 57, 60, 102. Cellulose (CoHioOs), composition of, 31; formation of, in cell-division, 376 ; oc- currence of, -with crystals, 54; rela- tions of, to moisture, 219; solubility of the modifications of, 33, «., 35, n. ; spe- cific gravity of, 145; stability of, 354, 357; tests for, 8, 11, 15, 31. See also Cell-wall. Cell-wall, capacity of the, for transfer of water, 258 ; direction in which the, is laid down, 380; formation of, 2J, 218; growth of, 218, 355; mai'kings of the, 29; modifications of the, 34; plates of the, in cork-cells, 38; rela- tions of the, to protoplasm, 218 ; rela- tive amount of space occupied by the, in fresh wood, 261; structure of, 29, 257; tensions in the, 390. Central cylinder, changes in the, 113; structure of the, 110. Centric arrangement of leaf-parenchyma, 158. Cerasin, 358. Chemical absorption by soils, 243. Chemical rays of the spectrum, 308 ; least efficient in assimilation, 310, 311, 313. Cherry-wood, use of, in testing for lig- nin, 14. Chloral hj'drate (CCIsCHCOH],), 11, 42. Chlorine, occurrence of, iu plants, 247 ; office of, in the plant, 254. Chloroform (CHCI3), effect of, upon protoplasmic movements, 211; effect of, upon the Sensitive plant, 424 ; use of, in preparation of specimens for mounting, 23. Chloroform-balsam, 23. Chloroiodide of zijic, 8, 33. Chloroleucites. See Ghloroplastids. Chlorophyll body (xAupos, green ; ^u'AA.oi', leaf), 41. Chlorophyll granules, 28, 41, 286; action of alcohol upon, 41; action of darkness upon, 42; action of hydrochloric acid upon, 230, 475, n.\ action of steam upon, 230, 475, «.; action of various agents upon, 474, w. ; break- ing up of, at autumn, 298; formation of, 287; in epidermal cells, 67; in evergreen leaves, 298; occurrence of, 288; position of the, during the day and at night, 398 ; ?ringsheim's study of, 13, 289; stroma of, 290; structure of, 289. Chlorophyll pigment, 41, 286; aBSence of, in certain plants, 234; changes in the, at autumn, 237; color of a solu- tion of the, not permanent, 296; ex- traction of the, 290; fluorescence of the, 234; in Floridese, 295; spectrum ofthe, 292, 313. Clilorophyllan, 291, n., 292, n. Ghloroplastids (x^'*'P°^» green ; n-Aatro-u, I form), 41. See also Chlorophyll Granules. Chlorosis, 297. Chromatin (xP"**"! color), 375, 378. Chroniatophores {KP<^t^°- [gen. xp-*'^'^'"^^], color; op6iii^ I bear), 41. w., 287, ■«. Chromic acid (CrOa', action of, upon the cell-wall, 11, 39. Ohromoleucites. See Chromoplastids. Chromoplastids (xP'^**". color; 7rA.ao-criu, I form), 41, 287. Cilia (cilium, an eyelash), movements by means of, 398. Cinchona, bast-fibres of, 148, n. Circumnutation (circum, around; nuta^ tio, a nodding), 400; in seedlings, 403; methods of observation of, 401; modi- fied, 401, 407; of the radicle, 403, 415; of tendrils, 417; of the young parts of mature plants, 405. Citric acid (CeHsOr). 360. Clathrate cells (clathri, a lattice), the name given by Mohl to cribriform cells. Clayey soil, 238. Clearing agents, 7, 10, 11. Cleft of a stoma, 269. Climate, adaptations of plants to a drv, 289. Climbing plants, 405. Glinostat (i^^. nipple), 101. Equilibrium of water in the cell, 258. Equisetum {equus, a horse; meta \jieta\, hair), epidermis of, 154; stem of, 154. Erythrophyll (epuflpos, red; i)>uAAoy, leaf), 291, n. ; 297. Ether (C«H,„0), effect of, upon proto- plasmic movements, 211; a solvent for fats, 12. Ether (of space), 306. Ethereal oils, 362. Etiolation, 288, 291, 295, 388. Etiolin„291; spectrum of, 296. Evaporation, compared with transpira- tion, 275; from an animal membrane, 275; from soils, 241; from the surface of a plant, 257; relation of growth to, 271, K. ; relation of rain-fall to, 242. Evergreen leaves, 164 ; changes of chlo- rophyll granules in, at autumn, 298. Exine. iSee Extine. Exogenous stems (ff", outside; ttwia, I produce), 129. Exosmoae (tfu, outside ; i\Kov, a leaf), the fundamental tissue of the leaf. Mestom, 191. Metacellulose, 35, n. Metals found in plants, 2i7, 255. Metaplasm (fterii, in the midst of ; irXiaiia, that whieli is foi'med), the name given by Haustein to the granular substances mingled with protoplasm. Methyl-green, 19, 380. Metastasis (/xeracTTaa-ty, a removing). See Transnmtation. Methyl-violet " BliBBBB," 19. Micellae, 212, 257, 393; attractions of, 212, 218. Micrometer, 3. Micro-millimeter, 4. Micropyle (nutpdj, small; iriiAij, orifice), 433. Microscope, 1. Microsomata (^ixpos, small ; rrufia, body), 2U. Microspectroscope, 292. Microspore, 443, n. Microtome, use of the, in section-cut- ting, 3. Mikroskopirlack, 24. Milk-sacs, 99. Millon's reagent (.\cid Nitrate of Mer- cury), 13, 28, 33. Mimosa pndica, 42D. Mineralization, 34, 39. Mirror of microscope, 2. Modifications of the cell-wall, 34. Moisture, effect of amount of, in the air upon transpiration, 275; effect of forests upon the amount of, in the air, 281; effect of, upon the direction of growth, 393 ; exhalation of, by desert plants, 276 ; relations of proto- plasm to, 209; relations of soils to, 239. See also Water. Molecule, 212, n. Monocotyledons, distribution of mechan- ical elements in, 191 ; secondary struc- ture of stems of, 135; stems of, 129; types of stems of, 133. Morphia (diHwNOs + HiO), 327, 365, 476. Mosses, absorbing organs in, 117; aid the soil in retention of waler, 282; leaves of, 164 ; reproduction in, 441 , «. ; stems of, 154. Mother cells, of pollen, 171, 379; of sto- mafa, 72, 376. Mounting-media, £0. Movements, cause of autonomic, ni,t fully known, 414; due to changes in structure during ripening of fruits, 400; hygroscopic, 399; of ciliated structures, 398; of Desmids, 398; of Diatoms, 398; of leaves, 419; of proto- plasm, 199, 398; of seedlings, 403; of the Telegraph plant, 413; of tendrils, 409, 417; of twining plants, 405; of young parts of mature plants, 405; revolving, 400; sleep, 409; sleep, of cotyledons, 411; sleep, of floral or- gans, 412; spontaneous, 413; utility of i-leep, 411. Mucedin, 364. Mucilage, conversion of the cell-wall inlo, 34; in the cell-sap, 51; solubility of vegetable, 33, Mucilage-cells, 99. Jlucilaginous modification of paren- chyma cells, 63. Mucus, 220. Mulder's hypothesis concerning the ori- gin of albuminoids, 326, n. Multiple epidermis, 67. Myxomjcetes, 196, 414. Naeg ELI'S HYPOTHESIS conccmlng the structure of organized bodies, 212. Nascent tissue (nnscens, arising). See Meristem. Natural grafts, 152. Nectar, 451; protection of, from the visits of unwelcome insects, 455 ; secre- tion of, 452 ; specific gravity of, 452. Nectar-glands, 161, 451. Nectar guides or spots, 453. Nectaries, 452. Negative geotropism, 392. Negative heliotropism, 393. Nepenthes, 349. Nervation of seed-coats, 180. Nerves of leaves, 156. Nickel, occurrence of, in plants, 256. Niggl's test for lignin, 13. 492 glossakiaij index. Nigi-osin, 19, 380. Nitrates, as a source of plant-food, 335; test foi-, 326, n. Nitric acid (HNOa), 13; as a source of plant-food, 335. Nitrogen, amount of, in plants, 327; amount of, in rain-water, 331 ; appro- priation of, by plants, 325, 330 ; com- parative needs of wild and cultivated plants for, 334:; compounds of, in the atmosphere, 331; in coloring-matters of leaves, 292; in the soil, 333; mode of formation of atmospheric com- pounds of, 332; sources of, for plants, 327. Non-sexual reproduction, 426, 444. Nucellus, 175, 182, 433. Nuclear disc, 376. Nuclear spindle, 376. Nuclein, 375, 376, 378. Nucleus, 25, »., 28, 199, 220, 374; be- havior of the, with reagents, 375 ; dem- onstration of changes in the, in the development of pollen-grains, 380; structure of the, 375. Nucleus cellulfe, 27, n. See Nucleus. Nucleus of a starch-granule. See Hilum. Nucleus of the ovule. See Nucellus. Nucleolus, 28, 375. Nutation {nutatio, a nodding), 400. Nutrition, 355. Nyctitropic movements (yt$ [gen. vuktos], night; Tpdiros, a turn), 409. Oaks, histological classification of, 143, ).. Objectives, 2. Odors, of flowers, 454; of wood, 142. Oil in seeds, 331. Oil of cloves, 3, 23. Oleic acid (CieHsiO,), 360. Oleiu (C„H,„40„), 360. Olive-oil, use of, in experiments on pro- toplasmic movements, 211. Oophytes, reproduction in, 440, n. Oosphere (uov, an egg; o''<>aipa, a sphere), 435, 440, ?.., 441, n. Oospore {ioy, au egg; o-Trdpos, seed), 436, 440, n. Open bundles, 104. Opening and closing of flowers, 412. Orange "K," 19. Orchids, trachi Ms in roots of, 109. Organ, 102, ISO; rank of an, 186, w. Organic acids, effect of, upon turges- cence, 414. Organic matter, appropriation of, by the plant, 337; changes of, in the plant, 354. Organic products, classification of, 357. Osmic acid (perosmic acid) (OsOj), 14, 46. Osmometer (ua/ids, impulse ; iierpov, mea-. sui-e), 224. Osmosis (u(riu.ds, impulse), 221, 224. Osmotic equivalent, 225. Osmundacese, stems of, 154. Ovary {ovum, an egg), arrangement of fibro-vascular bundles in au inferior, 174; arrangement of fibro-vascular bundles in a superior, 173; structure of the, 172; varieties of conductive placeiitie in an, 432. Ovules, changes iu the fertilization of, 435; development of, 433; formation of, 175 ; ripening of, 178 ; structure of the, in angiosperms, 432 ; structure of the, in gymnosperms, 438. Ozone, 304. Oxalates, test for, 9, 54. Oxalic acid (CjHA), 360. Oxidation, 355. Oxygen, an agent in the disintegration of rocks, 237 ; amount of, absorbed during respiration, 368; ainount of, evolved in assimilation, 319; necessary for germination, 464; necessary for protoplasmic movements, 210; of air ample for respiration, 368; relations of growth to, 388; required bv roots, 245. Palisade-cei.ls, 61, 159. Pahnate venation in leaves (palmatus, bearing the mark of a hand), 157. Palmatin (CiiHrnOc), 360. Palmitic aciil (CoHsjOi), 360. Palms, fibro-vascular bundles in, 130, 131. Paper-pulp, inanufacture of, 145. Paracellulose, 35. Paraffin, use of, in section-cutting, 3. Parallel venation in leaves, 156. Parasites (n-apatriTo?, one who lives at another's expense), 289, 338; chloro- phyll lacking in certain, 204; food of, 338; roots of, 116; union between, and their hosLs, 153, 338. Parchment paper, 32, n. use of, in making osmometer, 224. Parenchyma (iropeyi^^eio, I pour in beside), GLOSSARIAL INDEX. 493 67, 60; elements of, GO; forms of tells of, 61; in the fiiscicular sj-stera, 102; of the flower, 170; of the fi-iiit, 176; of the leaf, IDS; of the petiole, 160: of the stem, 119, 124; sclerotic, 62; thin-walled, 62. Parthenogenesis (7rap0eVo?, a virgin • yimTK, production), 416. Path of water through tl.e plant, 259. Peatj- soils, 2:JU. Pectin bodies, 358. Pcctose, 34, n., 358. Pellicle-membrane, 227. Perennials, storing of assimilated matter in, 373. Periblem (wcpi^Ktijia, a covering), 105, 118, 155. Pericambium, 113. Periclinal planes (irepi, around ; kAiVu, I incline), 382. Periderm (irepi, around; Swa, skin) 75. Periodic movements of organs, 409. Peripheral tissue of rootlets, 108. Perisperm (ircpi, around; ajrep/ia, the seed), 437. Peristome, 441, n. Perosmic acid. See Osmic Acid. Petiole {pctiolus, a little foot),x paren- chyma of the, 160; sensitiveness of •the, 419. Pfeffer's experiments with artificial cells, 226. Phelloderni (.^eXWs, cork; Sepiio., skin), 75, 148, n. Phellogen (e\K6s, cork; yemiia, I pro- duce), 74, 148. Phenol. See Carbolic Acid. Phloem ((JiXoco's, inner bark), 104. Phloroglucin (CnlloOs), use of, as a test for lignin, 14, 37. Pliosphoi-us, occurrence of, in plant-ash, 247; office of, in the plant, 253. Phosphorescence, 370. Phototonup, 423. Phycocyanine (0i)Ko?, sea-weed; Kvavo^, . dark blue), 295. Phycoijrythrine (i/iij/co?, sea-weed; ipv- 9p6z, red), 295. Phycopha'ine (<^C/eo?, se.i-weed; <^aid?, brown), 295. Piiycoxanthine (<^u«oy, sea-weed ; ^av66g, yellow), 295. Phyllocladia (u\kow, leaf; KAaSos, a young branch), 280. Phylloc>'anin (ilHiAAof, leaf; Kuaj-osjdark bluc),"290. Phyllodia (^vAAaJSijs, like leaves), 280. PIn'llopliore (if>iiAAoi', leaf ; (jiopcia, I bear) 132. ' Phyllo.'cantUin ("(nJAAor, leaf; frn'SoV, yel- low), 290. Pl]y^ical properties of soils, 239. Picric acid (C„H3[N02]30H), 18. Pililerous layer (pilus, hair; fero, I bear), 108. Pinguicula, 345. Pinnate venation in leaves (pinnatus, featliered), 157. Pistils, changes of, in ripening, 176; fibru-vascular hurdles in, 173; scn^i- tiveness of, 424; structure of angio- spermous, 427. Pith, 124; solubility of, 34, re. Planes of the cell-wall at the point of growth, 381. Plasmolysis (n-Aao-na, what has been formed : Ajicris, a loosing), 390, n. Plasmolytic agents, 27, n., 390; effect of, upon protoplasm, 210. Plastids (irAao-o-o), I form), 40, 287. Pleon (irAtW, full), 212. Plerom (jrAijpcofia, that which fills), J05, 118. Poisons, effects of, upon plants, 473. Polarizing apparatus, 4. Pollen (pollen, fine flour), amount of, pi'oduced by flowers, 432; bursting of grains of, in water, 429; contents of grains of, 428; development of, 171, 379; effect of sugar solutions on grains of, 429; of angiosperms, 427; of g}'mnosperms, 437; structure of, 428;"vi(ality of, 431. Pollen-tube, emission of the, 430; time required for descent of the, 431. P, Uinia, 427. Pollinic chamber, 438. Polyembiyony (iroAiis, many; ip-^pvov, embryo), 446. Ponceau, 19. Poplar, glands on leaf of the, 161. Potash (KOH), diffusion of, 222; use of, as a reagent, 6 ; use of, in examina- tion of chloroplastids, 42; use of, in section-cutting, 3, n. Potassic acetate (KC2H3O2), use of, as a mounting-medium, 21. Potassic bichromate (IV2Cr207), 14, Potassic chlorate (KCIO3), 14. Potassic ferrocyanide (K,Fe[CN]G), use of, in making precipitation-mem- branes, 225. Potassic nitrate (KNO3), 15, 390, n. 494 GLOSSARIAL INDEX. Potassium, occurrence of, in plants, 2i7; office of, in the plant, 252. Potential energy, 307. Precipitation-membrane, 225. Preparation of specimens, 21. Preservation of wood, 142. Pressure, effect of atmospheric, upon germinati(m, 309, 464; effect of atmos- pheric, upon growth, 389; effect of, upon movements of protoplasm, 208 ; growth retarded by external, 395; of sap in the stem, 264. Prickles, 69. Primary cortex, 119. Primary membrane, 36. Primary structure, 105; of the root, 106; of the stem, 119. Primine {primus, first), 178. Primordial tissues, 58. Primordial utricle, 27, u., 220. Procambium, 104. Prosenchyma (n-pd?, near; eyxviia, an in- fusion), characteristics of, 58, 76; in the fascicular system, 102. Proteids,28, 326, "n.; formation of, in the plant, 335. Protein basis, 46. Protein granules, 44; classification of, in seeds, 182. Prothalli, 442, n. Protogenic development (irpuros, first; yevfoM, I produce), 99, /i. Protophytes, 439, n. Protoplasm (irpSiTo^, first; TrAacr/xa, what has been formed), amoeboid movement of, 201; appearance of, 26; chemical properties of, 197; circuliition of, 199, 398; composition of, 28, 197 ; continuity of, in cells, 214; discrimination between living and dead, 10, 470, n. ; effect of mechanical irritation upon, 208; ex- amination of, 106, 198, 202; film of, envelops many crystals, 54; historical note regarding, 219; in young cells, 198; movements of naked, 2(10, 201, 397 ; movements of, dependent on the absorption of moisture, 212, n.; nitro- gen in, 325 ; passage of, through imper- forate cell-walls, 217; physical proper- ties of, 197 ; rate of movements of, 200; reaction of, 198; relations of, to anaesthetics, 211; relations of, to elec- tricity, 207; relations of, to gravita- tion, 209; relations of, to light, 206; relations of, to moisture, 209; relations of, to plasmolytic agents, 210; rela- tions of, to temperature, 201; rela- tions of, to various gases, 210; rela- tions of the cell-wall to, 218; rotation of, 21)0; structure of, 2U; tests tor, 28; vitality of, in seeds and spores, 205; water contained in, 198, 257. Pulsation of vacuoles, 397. Pulvini (pulvinus, a cushion), 160, 404, 410 ; continuity of protoplasui in the cells of, 215; "in the Sensitive plant, 420 ; in the Telegraph plaut, 414. Putrefaction, results of, 333. Pyrenoids (impiji', a kernel ; elSos, form), 287, n. QUEKCITKIN (C33H30O,), 362. Quinia (CaoHaNzO^ -|- HjO), 327, 365. Radial bundle, 104. Radial planes, 382. Radicle, 118; movements of the, 403: structure of, 106. Rain-fall, efliect of forests upon the, 282. Rain-water, gases in, 300, n.; nitrogen compounds in, 331. Ranvier's picrocarmin, 17. Raphides {pait-ii [gen. pai5os], a needle), 52. Razor, use of the, in section-cutting, 3. Reagents, 4; employment of, 6. Receptacles for secretions, 97, 110. Recording auxaiiometer, 383. Red anilin, 19. Rejuvenescence (re, again ; juvenesoo, 1 become young), the formation of a single new cell from the protoplasm of a cell already in existence. Repair of waste, 355. Reproduction, 425; by budding, 444; contrast between methods of, as re- gards results, 443; in cryptogams, 439, ■«.; methods of, 426. Reserve protein matters, 44. Resin-cells, 97. Resins, 98, 36:!; detection of, 12. Respiration, 355, 356, 367 ; accompanied by evoluti' n of heat, 370; contrasted with assimilation, 356; early history of, 367; influence of light and temper- ature upon, 369 ; intramolecular, 370. Resting state, 3(19, 389, 459. Resiu'rection plant, 399. Retention of moisture by soils, 239. Reticulated markings, .'iO, So. Reticulated venation in leaves. 156. GLOSSAKIAL INDEX. 493 Revolving nutation, 400, Rhizogenic cells (pifa, a root; yewata, I produce), 115, 7i. Rhizuids (p'S'". a root ; eXSos, like), 117, 230. Rhizomes (ptf"»j^a, that which has taken root), structure of, 153. Rhodospermin (foSov, rose ; trwipiia, seed,) 295. Ripening of fruits and seeds, 460. Rocks, disintegration of, 237. Root-cap, lOG, 107. Root-hairs, 108; corrosive action of, 246; distortion of, 231; increase the absorbing surface of a root, 231; meth- od of obtaining for study, 109 ; num- ber of, on different plants, 231 ; office of, in absorption, 231; size of, 231; walls of, 108, 109. Roots, absorption by, 230, 244 ; amount of branching of, 232; ceutral cylinder of, 110; colors of, 116; cortex of, 110; crown, 153; depth to which branching of, occurs, 233; extent of, 232, 235; formation of, 107, 155; from leaves, 162; growth of, 107; influence of the soil upon, 234; of cryptogams, 116; of orchids, 109; 0X3'gen needed by, 245; parasitic, 116; piliferous layer of, 108; primary structure of, lOG; secondary structure of, 112; types of branching of, 115, n. Roridula, 345. Rose of Jericho, 400. Rosolic acid. iSee Corallin. Rotation of protoplasm, 200. Rubidium, occurrence of, in plants, 256. Rudimentary branches, 153. Russia matting, 147. Russow's potash-alcohol, 7. Safka.mn (Cj,H,„N,), 19, 380. Salicin tC,sH,gO,), 362. Saline matters, absorption of, by roots, 244. Sandy soil, 2-38. Sap, amount of, in plants, 265; flow of, from plants, 264; pressure of, 264, 265. Saprophytes (o-mrpo!, putrid; ^urdi', a plant)! 289, 294, 337. Sap-wood, 141. Sarcode, 220. Sarracenia, 347. Scalariform markings {scalm-ia, a lad- der; forma, form), 30, 84. Scales, 69. Schizogenic development (<^x^'fw, I cleave; ytwia, I produce), 99, n. Schleitn, 220. Schulze's macerating liquid, 14, 38, 39. Schulze's reagent, 9, 33, 76, 77, n. Schweizer's reagent, 12, 15, 32. Scion, 152, 444. Sclerenchyma (o-kAtjpo?, hard; iyx"t^°-y ^" infusion), 87. Sclerotic parenchvraa (ir/cXrjpds, hard), 62. Secondary liber, 113. Secondary structure, 105; of roots, 112; of steins, 135. Secondary wood, 113. Secretions, of nectar, 451; receptacles for, 97, 110 ; stigmatic, 427. Section-cutting, 3. Sectmdine (secundus, second), 178. Seeds, albuminous and exalbuminous, 181 ; arrested activity of, 459 ; changes during the ripening of, 460; dissemina- tion of, 400, 460; food in, 182, 437, 467; germination of, 462; germination of oily and starchy, compared, 368; im- mature, 460; increase of, in size, upon the absorption of water, 463 ; integu- ments of, 178; minute structure of, 178; protein granules in, 182; ripeness of, 460; vitality of, 205, 461. Selenium, occurrence of, in plants, 256. Sensitiveness, 414: effect of anajsthetics upon, 424; of leaf-blades, 419; of peti- oles, 419; of roots, 415; of stamens, 423; of stems and branches, 417; of styles, 424 Sensitive plant, 420, 424. Sensitive tissues, 415. Shell-lac, 24. Sieve-cells, 91, 103, 112; contents of, 94; development of, 122; of cryptogams, 94; of gymnosperms, 94; size of, 92. Sieve-plates, 91, 92. Sieve-pores, 91, 93. Sieve-tubes. See Sieve-cells. Silica (SiOj), deposits of, in plants, 39. Silicium, ofiice of, in the plant, 255. Silphium laciniatum, arrangement of parenchyma in the leaf of, 160. Silver, occurrence of, in plants, 256. Simple hairs. 68. Simple microscn]ie, 1. Simple pistils, 173. Sleep-movements, 409 ; of cotyledons, 411; of floral organs, 412; utility of, 411. 496 GLOSSAEIAL INDEX. Slides (slips), 2. Sodic chloride (NaCl), 15; diffusion of, 222, 223. Sodic hydrate (NaOH), use of, as a reagent, 7; use of, in the manufacture of paper-pulp, 147. Sodic hypochlorite (NaClO), 11. Sodium, can partly replace potassium in plants, 255; occurrence of, in plants, 217. Soft bast, the unlignified cells of the liber portion of a fibre- vascular bundle. Soils, absorption of heat by, 245; ab- sorption and retention of moisture by, 239, 282; chemical absorption by, 243; classification of, 238; condensation of gases by, 244; effect of transpiration upon, 283; evaporation from, 241,282; filtration through, 242; formation of, 237; influence of, upon roots, 234; in- fluence of, upon transpiration, 270; mechanical ingredients of, 239; nitro- gen available to plants in, 333 ; pliysi- cal properties of, 239; root-absorption of saline matters from, 244; tempera- ture of, 245; transportation of, by water, 238. Solanum Fseudocapsicum, coloring- matters in berries of, 177. Solid yellow, 10. Sources of nitrogen for the plant, 327. Specilic gravity of wood, 144. Spectrum, classification of the raj's of the, 308 ; effect of the rai's of the, upon protoplasmic movement, 206 ; effect of the raj's of the, upon transpiration, 278; of chlorophyll, 292, 313. Spermoderm ((nrep/io, seed ; Sipiid, skin), 178. Spliieraphides ((n^aipa, sphere; pa^is, needle), 53. Sphere-ci'ystals, 53. Spines, GO. Spiral markings, 30, 84. Spongiole {sponyiula, a little sponge), 230. Spongy cortex, 120. Spongy parenchvma, 61. Sports. 444. Spring wood, 138, 396; transfer of water thro;igh, 258. Staining agents, 15; effect of, upon pro- toplasm, 210. Stamens {stamen, a thread), development of, 171; sensitiveness of, 423. Starch, amount of, in plants, 357; ap- pearance of, when examined with polarized light, 60 ; conversion of, into sugar, 357, 467; composition of, 60; first visible product of assimilation, 321; in latex, 96; in seeds, 182; pres- ence of, in chloroplastids, 42; produc- tion of, in a plant dependent on potas- sium, 262; solubility of, 49; structure of, 47; tests for, 8, 50. Starch cellulose, 50. Starch generators. See Leucoplastids. Steam, action of, on chlorophyll gran- ules, 290, 475, n. Stearic acid (OisHjoO,), 360. Stearin (CsjHnoOs), 360. Stellate hairs (steila, a star), 69. Stellate scales, 69. Stems, 118; bleeding of, 264; course of fibro-vascular bundles in, 125; cortex of, 119; development of, 124; dicoty- ledonous (exogenous), 123, 136 ; epider- mis of, 119; tibro-vascular bundles of, 120; injuries of, 149; monocotyle- donous (endogenous), 129, 133, 135; of mosses, 154 ; of vascular crypto- gams, 154; pith of, 124; pressure of sap in, 264; primary structure of, 119; secondary structure of, 135; sensitive- ness of, 417 ; transfer of water through, 258 ; wilting of cut, 263. Stereom (o-Tepeds, firm), 191. Stigma (crnyiid, a mark made by a pointed instrument), 427 ; character of the cells of the, 172; extent of surface of the, 427, 430. Stigmatic secretion, 427. Stock, 152. Stomata (ordna, the mouth), 70, 268; de- velopment of, 72, 376 ; guardian cells of, 70, 269; mechanism of, 269; occur- rence of, 70, n., 71, n., 72; passage of gases through, 303 ; relations of, to exter al influences, 270; size of, 71.' Stratification, 30. Striation, 30. Stroina (crTpinii, a bed), 198. Strontium, occurrence of, in plants, 2-56. Structural characters of wood, 146, re. Strychnia (CnHmN.Oa), 365. Style (stilus, a style), 427; character of the cells of the, 172; conductive tissue of, 431 : sensitiveness of, 424. Suberification {subei\ cork; facio, I make), 34, 38. Suberin, 38; tests for, 7, 14, 39. Submerged phsenogams, leaves of, 161. Substitute fibres, 80. Sugar, diffusion of, 222; effect of a solu GLOSSABIAL INDEX. 497 tion of, on pollen-grains, 429; in the cell-sap, 52; use of, as a reagent, 15, 199. Sugar group of non-nitrogenous prod- ucts, 358. Sulphur, appropriation of, by the plant, 255, 281, 336; in the ash of plants, 217. Sulphuric acid (H2SO4), effect of, upon cellulose, 15, 31 ; effect of, upon cuti- nized membranes, 39; use of, as a sol- vent for callus, 93. Sulphurous acid (SO2), effects of, upon leaves, 474. Superior ovaries, arrangement of the tibro-vascular bundles in, 173. Suspensor, 436. Synergidae (o-ui/epydt, working together), 435. Syntagma ((riii-TaYiua, that which is put together in order), 213, n. Synthesis of albuminous matters in the plant, 335. Systems, 102. Tabasiieer, 39, n. Tagma (riyiia, a company), 213, re. Taniiate of gelatin used in the formation of Traube's cell, 226. Tannin (CuHicOo), diffusion of, 222; in pulvinua of Mimosa, 361, 420; occur- rence of, in plants, 361; tests foi", 12, 14. Tapetum (tnpete, a carpet), 171, n. Tartaric acid (CiHoOc), 360. Teasel. See Dipsacus. Tegmen (teffinen, a covering), 178. Telegraph plant, 413. Temperature, effect of, upon absorption by soils, 240; effects of too high, upon ■ plants, 470 ; elevation of, during intra- molecular respiration, 372; influence of, upon absorption by roots, 245 ; influ- ence of, upon assimilation, 306, 316; influence of, upon respiration, 369; in- fluence of, upon transpiration, 277; of air inside a spathe, 370; of pulvinus of Mimosa, 421 ; producing rigidity in Sensitive plant, 423; relations of growth to, 385 ; relations of protoplasm to, 201 ; relations of soils to, 245 ; rela- tions of, to germination, 464. Tendrils, circumnutation of, 409, 417. Tensions of the cell-wall and tissues, 390. Terpene (CioHio), 362. 3Z Tertiary formations in the root, 115. Testa (testa, a shell), 178. Tetrad (Terpis, four), 171. TUallium, occurrence of, in plants, 256, Thallophytes, 164, 440. Tharandt normal-culture solution, 250. Thermotropic curvatures, 394. Thermotropism {eep/idy, heat; rpdiroi, a turn), 394. Thiersch's borax-carmin, 17. Thiersch's oxalic-acid carmin, 17. Times of opening and closing of flowers, 412. Tin, occurrence of, in plants, 256. Tissues, 102; classilication of, 187; con- ducting power of ligneous, 261; cribri- form, 91; depth to which light pene- trates, 309 ; hardening of, 9, 11 ; rela tions of water to, 257; sensitive, 415; tension of, 390. Titanium occurrence of, in plants, 256. Trabecular ducts (trabecula, a little beam), 86. Trachea; (rpaxeia, rough), 82, 84. See also Vessels. Ti-acheal cells, 81. Tracheal portion of a flbro-vascular bundle, 104. Tracheids, 82; in roots of orchids, 109; in stems, 121; size of, 143; walls of, 84. Transfer of water through the plant, 257 ; compared with that through porous inorganic substances, 262, n. ; effect of exposing a cut surface to the air upon, 263; effect of motion upon, 263; path of, 269 ; rate of, 259, 26 1 . Transformed branches, 153. Transformed cells, 56. Transmutation, 354, 355, Transpiration, 266; amount of water given off in, 271, 275, 281; apparatus for registering, 273; checks upon, 280; compared with evaporation proper, 275; effect of various salts upon, 279; effect of heat upon, 277; effect of light upon, 277; effect of mechani- cal shock upon, 278 ; effect of moisture in the air upon, 275; effect of nature of the soil upon, 276; effects of, upon the air, 281 ; effects of, upon the plant, 281; effects of, upon tlie soil, 283; experiments upon, 273; methods of measuring, 272 ; relation of age of leaves to, 279; relation of, to ab'^orp- tion, 279; relative amounts of, from opposite sides of a leaf, 274. 498 GLOSSAKIAL INDEX. Transverse planes, 382. Trees, age of, 139. Triclioblast (epi'f [gen. rpixos], hair; fi\a.(TT6t, shoot), a name proposed by Sachs for such idioblasts as are es- pecially distinguished by size and branching. Trichogyne, 440, 7t. Trichom'es («p.f, hair), 66, 68, 2f0. Triiiitrophenic acid. See Picric Acid. Triolein. See Olein. Tripalniatin. See Palmatin. Tristearin. See Stearin. Trommer's test for dextrin, 61. Trophoplast (Tpo(f)di, a feeder; irAio-o-io, I form), 287. Tiillen. See Tyloses. Turgescence, effect of organic acids upon, 414. Turpentine (CioHi„), use of, in prepara- tion of specimens for mounting, 23. Twining plants, 405. Tyloses (tvAos, a protuberance), 87. Typical cells. See Fundamental Cells. Unorganized FERaiEsxs, 366. Utricularia, 346. Vacuoles, 26, 177, 200, 212. n., 280, 375, 307. Variegated plants, 477. Varieties, 447. Variety-hybrids, 456. Vascular system. See Fibro-vascular System. Vasculose, 36, n. Vasif orm elements (ms, vessel ; forma, form), 81. Vasiform wood-cells. See Tracheids. Vegetable acids, 360. Vegetable mucus, occurrence of, in plants, 358; test for, 15. Vegetable parchment, 32, n. Venation of leaves, 156. Vesque's method of producing crystals, 55. Vessels, 55, 77, 82, 84; classified, 60; size of, 86. Viola tricolor, coloring-matters in flowers of, 170. Vitality of seeds, 205, 461. Vitellin, 364. Wardian cases, 474. Water, absorbed previous to metasta- sis, 267; absorption of gases by, 300, n. ; action of steam upon chlorophyll, 290, 475, n. ; an agent in the formation of soils, 237 ; amount of, contained in plants, 236 ; amount of, given off in transpiration, 271 ; amount of, required for germination, 462; direction in ■which tissues most readily conduct, 262, n.; effect of absorption of, upon seeds, 463 ; effect of, upon protoplas- mic movements, 209; effect of, upon opening and dosii'g of stomata, 270; equilibrium of, in the plant, 258; ex- udation of, from uninjured parts of plants, 267 ; method of determining amount of, in dry wood, 261 ; rate of ascent of, in stems, 261, 263 ; relations of, to tissues, 257 ; relative amount of space occupied by, in fresh wood, 261; transfer of, in plants, 257, 269 ; trans- port of soils by, 238; use of, as a medium, 5; use of, as a mounting- medium, 21. See also Moisture. Water-culture, 248; directions for, 249; first application of method of, 249 ; so- lutions for, 250. Water-plants, size of, 188; structure of land-plants compared with that of, 257. Water-pores, 73. Water tissue, 62, 280. Waxy coatings upon the epidermis, 66. White chlorophyll, 322. White lead as a v.irnish, 24. Wiesner's tests for lignin, 10, 14, 37. Wild plants, supply of nitrogen to, 334. Wilting of leaves, 471. Winterkilling, 472. Withering of stems, how prevented, 263. Wood, autumn, 138, 395; color of, 141; density of, 144; identification of, by histological features, 145, n. ; odor of, 142; preservation of, 142; spring, 138, 395; structural characters of , 146, n. Wood-cells, 57, 78, 82; size of, 86, ■«., 143. See also Tracheids. Wood elements, inclination of, to the axes of trees, 143. Wood-fibre used for paper-pulp, 145. Wood-parenchyma, 77. Woodward's carmin, 17. Woody fibres, 57, SO. See also Wood- cells. Woody rings, 114, 137; demarcation between, 139 ; size of, 140 ; two, formed in a single year, 139. Work of the plant, 185. GLOSSARIAL INDEX. 49y Works of reference relating to insectiv- orous plants, 351; relating to niicro- scupe manipulation and micro-chem- istry, 24; relating to tiie cell and its modifications, 55; relating to the his- tology of tlie organs of vegetation, 165. Wounds of plants, healing of, 150. Xanthic flower coloes {lofSos, yel- low), 454. Xanthophyll (fovSof, yelloiv; ijivWoir, leaf), 290, 291, 297. Xerophilous plants (fepo'5, dry; (jiiKiai, I love), 280, li,. Xylem {(vkov, wood), 104. Zinc, occurrence of, in plants, 255; re- lated to changes of form in the plant, 256. Zygophytcs, reproduction in, 439, n. PRACTICAL EXERCISES. SUGGESTIONS FOR STUDIES IN HISTOLOGY AND PHYSIOLOGY OF PHJENOGAMS. The following hints are designed chiefly' to aid students who have at their command the simplei- appliances described in the foregoing pages. In addition to the simplei- exercises there ai-e also suggested a few which are quite within the power of students having access to a small chemical laboratory' and a small cabinet of physical apparatus. The chemical and pliysical outfits now found in rnan3' of our high schools will prove ample for the successful prosecution of these experiments. HISTOLOGICAL PRACTICE. Material for study. The supply of material for histology should be abundant and of the best quality-, all inferior or imj^er- fect specimens being carefully excluded. It (except that dis- tinctl}' referred to s,a fresh) should be collected at proper seasons and preserved at once in strong alcohol, great care being exer- cised to have every specimen accurately labelled ; name, locality, time of gathering, etc., being noted. When alcoholic material is required for immediate use in the preparation of sections, it can be softened, if necessary, by soaking in pure water, as directed in 37. Delineation. When a satisfactory section or preparation has been secured, the student should make an accurate drawing of its essential features. The employment of a camera lucida (12) insures correct proportions in all parts of the sketch, and is always to be recommended. Drawings made by its aid are con- veniently designated by the following abbreviated term, udnai. del. It may seem scarcely necessary to caution students against obscuring any part of their histological sketches by meaningless shading ; a few clean and clear outlines suffice to express the character of the preparation better than any attempt to give the Qffects of light and shade. There are some exceptions to this i! STUDIES IN HISTOLOGY. broad statement ; for instance, preparations of nascent flowers are shown equallj- well bj- shaded figures, and the same is true of maiij- pollen-grains, etc. The use of slips of drawing-paper of uniform size and the arrangement of these under appropriate heads will render the keeping of a systematic record of work much easier. Permanent preparations. In most cases the sections or other preparations should be permanently mounted in some suitable preservative medium, and properly labelled with the name of the plant and of the special part exhibited, date of preparation, medium in which it is mounted, etc. The drawings should be numbered or labelled to correspond with the permanent prepa- rations. Histological elements, their modifications and combinations. In the following enumeration of the more important elements the sequence is (1) form, (2) contents, (3) distribution, (4) development. FOEMS OF THE STRUCTURAL ELEMENTS AND SIMPLE TISSUES. 1. Pakenchyma Proper and its Chief Modifications. (a) Soak a few peas or beans in water until they become soft enough to be cut without difficulty, remove the seed-coats, and make with a wet razor (see 8) three very thin sections through the cotyledons. These sections for comparison should be at right angles to one another, in order to exhibit the length, breadth, and thickness of the cells. On removing them from the knife or razor (by means of a camel's-hair brash), float them in water and move them genth' about, in order to detach the cell-contents which have partly escaped fiom the cut cells. When the sections appear clear, transfer them to the middle of a glass slide, add a little pure water and cover with thin glass, being very careful to exclude all air-bubbles. If the sections are thin and wholly free from bubbles of air, compare the outlines of the cells with one another, making drawings of the specimens. (b) Make similar sections (1) through the pulp of an}^ unripe fruit — apple, pear, snow-berry, etc. ; (2) through the pith of Elder, Lilac, or any soft shoots ; (3) through the pulp of any succulent leaves, for instance those of Sedum, Purslane, or Beoonia. PARENCHYMA AND ITS MODIFICATIONS. 3 (c) Make a transverse and a vertical section through the petiole of &uy water-Ill^', or through the soft interior of any rush (Juncus). (c?) When, after considerable practice, the student succeeds in making veri/ thin sections of the foregoing plants, let the reagents for the demonstration of cellulose be applied to them, as directed in 143. It is not superfluous to State (1) that success in the application of these and most of the other reagents employed under the microscope is generally preceded by man}- failures, and (2) that carelessness in the use of some of the reagents maj' irreparably ruin the microscope lenses. /Sclerotic Parenchyma. Excellent material can be obtained from the flesh of pears and quinces (see 211 and Fig. 40). From the tougii shells of man^- sorts of nuts and seeds (see Fig. 41) good preparations can be made bj- the method described in 495. For the Canada balsam there recommended good shellac can be advantageously- substituted. Gollenchyma cells are well exhibited hy cross-sections of the stem of any common Labiate, for instance Spearmint, or of the stem of almost any of the Umbelliferae (see 216). Ajppl}' dilute hydrochloric acid to the sections. Wood parenchyma cells are easily obtained hy careful macer- ation (70). Dilute solutions of iSchulze's liquid are preferable to strong, although much slower in action. Excellent material is afforded by most of the oaks and other Jiard woods (see 254, 255). Nearly all possible intermediate forms can be found by careful search. Apply the tests for"lignin" (154). Use also upon different specimens red and blue coal-tar colors. II. Epidermal Cells. (a) Examine a film removed from the upper surface of some fleshy leaf; for instance, Sednra, the cultivated Cotyledon or Eccheveria, Purslane, or Begonia, etc. (h) Compare the cells of this film with those found on the upper surface of a shining petal; e. g., that of Buttercup or Poppy. 4 STUDIES IN HISTOLOGY. (c) Remove a moderate!}- thin film from the young stem or branch of some Cactus, and examhie the exposed surface of th6 epidermal cells for ciitinizatioii (156 and 224). Apply anj- of the coal-tar colors to similar fragments, and note differences of tint. (d) Examine the " bloom" (226) on the following: (1) stem of Indian corn, (2) stem of castor-oil plant, (3) leaf of cabbage, (4) frnit of plum, juniper, or M^-rica cerifera (Bayberr}-). («) Make a thin vertical section through the leaf of Ficus elastica (India-rubber plant), noting the epidermis and c^'stoliths (see 164 and Fig. 6). (/■) Examine the examples of multiple epidermis afforded by manj- of the cultivated species of Begonia. Trichomes. (a) Examine the velvet}' petals of anj- flower, and compare their ver}' short trichomes, or haii's, with those on downy, rough, and bristlj- stems and leaves. (6) Examine also a I'ertical section of a young rose-prickle. The varietj- of glandular trichomes at hand in anj- locality is so great that no special directions need be given for their selection. (c) Eoot-hairs are easily obtained b}- allowing the seeds of flax, or the grains of corn, wheat, etc., to germinate on wet filtering-paper, or even on moist glass. Stomata (pp. 70-73). For the proper studj- of these a mi- crometer eye-piece (11) is very necessarj'. By its emploj-ment the dimensions of individual stomata and the number of stomata on a given space can be easily determined. Sections of stomata are made best by aid of the processes of imbedding (8). Examination of the table by Weiss (page 71) will afford hints as to the selection of large stomata for examina- tion in section. Watir-pores and rifts (242). {a) Water-pores are furnished bj- the tips of the teeth of the leaves from some species of Fuchsia. Sections sliowing their constituent cells are best made verticall}' and lengthwise through the leaf. Tropseolum, or the so-called Garden Nasturtium, also gives good examples. (5) Compare with these water-pores tiie iiTegular rifts in the leaves of some grasses ; for instance, Indian corn. PROSEN'CIIYMATIC WOOD-ELEMENTS. 6 III. CORK-Cl!LLS. For the exfimination of these cells, the student should begin ■with the soft and close-textured "velvet" cork procurable at any apothecary shop. Let the sections be made in at least two directions at right angles to each other, and if possible let them pass through one of the lines of demarcation of the cork : note anj- dift'erences of shape and size presented by the cells at that place. The young steins of an}' of our common currants give in cross- section excellent illustrations of cork-cells (see pages 74-76) and of their development. Test these and similar specimens of cork-cells for the presence of cutin or suberin (see 26, u4, 161). IV. Prosen-chvmatic Woori-ELBMKNTS. These elements (see pages 78-87) can be studied to best ad- vantage after very careful maceration, as directed in 70. Long wood-cells, woody fibres, and trachesE (or ducts), arc easil}' separable from each other by such chemical means, and arc generalU' identified with facility. Abundant material for the demonstration of tracheae is afi'onled b^" the fibro- vascular bundles (198) of herbs and b^' the ligneous parts of our common trees otlier than the Coniferoe. There appears to be no special need of specifying the ligneous plants which can be most successfully employed for demonstrations of the wood}' elements. Magnolias, Tulip-tree, woody Leguminosse and Rosaceae, Urticacese, and Cupuliferae are all satisfactory as sources of material. Good examples of tracheids are procurable from species of Coniferae, such as Pines, Firs, Spruces, etc. These should be examined in all stages of development and from all points of view, particular attention being directed to tiie marked difference between the radial and tangential aspects of the cells. Cells which have been separated from each other mechanically and have not been previously acted on by chemicals should be studied with reference to their behavior under the action of iodine and other reagents, it being possible to demonstrate the existence of thin layers or " plates " which compose the wall. Iodine colors the fresh cells jellow ; investigation shows, how- ever, that the inner wall or plate of the cell is not much, if at all, colored b}- the reagent, the color being confined to an outer and a middle wall or plate. When the cells thus treated with iodine are touched with concentrated sulphuric acid, the outer and middle plates remain yellow, while the inner plate turns b STUDIES IN HISTOLOGY. blue. Soon the inner and middle [jlates dissolve, the outer not being attacked until somewhat later. If Schulze's macerating solution (full strength) is employed, the outei' plate dissolves quicklj-, but the others are not much affected for some time. Careful management of these powerful solvents is demanded to insure even a moderate degree of success in this demonstration. V. Bast-Fibhes. Isolation of these cells is easil3- effected bj- teasing with needles under the dissecting microscope. The use of macerating solu- tions for this purpose is also admissible, but the results are not quite so satisfactory as with the wood-elements. Examination of the table on page 90 shows the wide difference which exists between the dimensions of the raw fibres and their structural elements, iuto which they can be separated mechanicallv. Most bast-fibres take the coal-tar colors very well, and it would be best for the student (without giving too much time to it) to note the different effects which are produced on various fibres bj' the colors described on page 19. The changes produced in the dimensions of the fibres by dilute acids should also be observed. After this preliminary practice the reactions given on page 90 should be carefully repeated with such material as is at hand. Full directious for the preparation and use of the prescribed reagents will be found in the introductory chapter. Lastly, de- terminations of the average dimensious of the commercial fibres, flax, hemp, jute, etc., should be carefully made. VI. Ceibeose-Cells on Sieve-Cells. These can be very easil}' demonstrated in thin vertical sec- tions of the stems of anj- large Cucurbitaceous plants ; for in- stance, squashes, melons, etc. If the student fails to detect iu fresh material forms similar to those shown in P'ig. 73, a little tincture of iodine should be added to the specimen, iu order to contract the lining and other contents of the cells. By this reagent the contents become more or less distinctl}- colored, and the discrimination between the cells and the surrounding tissues is generally very plain. In other common plants, grape-vines, etc., the detection of cribrosc-cells is not always easy, but a diligent search will bring out these characteristic constituents of soft bast. The study of the structure of the sieve-plates requires the use of much higher powers of the microscope than most beginners LATEX-CELLS. 7 are likeh' to possess. Much can, however, be done in the ex- amination of the callus h\ the emploj'inent of the reagents mentioned in 282 and 283. The student should not fail to sub- mit a thin section showing the larger cribrose-cells to the action of concentrated sulphuric acid, and remove in this waj' the whole of the cell-wall, leaving (if the manipulation has been careful) the contents slightl^y connected together and showing the inter- communication between the cells. VII. Latex-Cells. Latex-cells are abundant for demonstration in many wild and cultivated plants ; but few afford material better adapted to the use of beginners than the greenhouse plant. Euphorbia splen- dens. Other cultivated species of the same genus are about as good. With the younger and softer stems of this plant one has merely to secure thin sections through their outer or cortical portion, when, in a good section, the latox-tubes can be found ramifying irregularly. The peculiar dumb-bell shaped grains in the tubes form a characteristic feature. When a thin section of an}- tissue containing latex-tubes is gently heated in a dilute solution of potassic hydrate, or for a shorter time in a stronger solution, the parts become so much softened that the tubes can be easily separated from the sur- rounding tissue, after which they can be floated on to a fresh slide and examined bv themselves. Abundant material for the study of latex-cells is furnished by plants of the followmg groups : LobeliacesB, Campanulacese, Liguliflorse, and many Papaveracese. VIII. Special Eeoeptaoles for Secretions. These are constantly met with in sections of many stems, leaves, and fruits. A few examples for study are here given. (a) Crystal-cells. Look for these in the leaves of the Araceee, Onagraces?, and Chenopodiaceae, and in the bark of almost any of the ligneous Rosacese (Pomese), where they arc especially associated with the bast-fibres. (J) Hesin-cells and resin-reservoirs are found in the bark of many Coniferse and UrabeUiferse, etc., in the leaves of Rutacese, Hypericacese, and Myrtacese. (c) Tannin receptacles are found in very many kinds of bark. For the detection of tannin, solutions of potassic chromate or ammonic chromate may be employed, a brown color beino- 8 STUDIES IN HISTOLOGY. pi-oniptlj produced. This test is preferable in some respects to tiie solutions of iron alluded to in 69. Intercellular spaces of various shapes and sizes containing air, or air and water, are met with in many of the plants already enumerated. The most interesting are found in monocotyledo- nous plants, notably Aracese and Juncacese. CELL-CONTENTS. I. Pkotoplasm. No better material for the demonstration of the physical and chemical properties of protoplasm in its active state can be em- ployed by a beginner than the young stamen-hairs of Spiderwort. Several garden species of Spiderwort are available for this pur- pose, especially Tradescantia Virginica and pilosa. The green- house species can also be employed. If none of these are at hand, any young large plant-hairs with thin transparent walls will answer for the demonstration. If the hairs are sufficient!}' j-oung, the protoplasm appears as a nearly- transparent mass fllhng the cell-cavity ; but even when they are only slightly advanced in development the mass +iecomes honey-combed by sap-cavities or vacuoles. With further development these be- come confluent, and traversed here and there by slender threads ; the wall of the cell, however, as long as it is alive, being lined by a delicate film of protoplasm. When the protoplasm exists in a cell only in the latter condi- tion, it is well to place the cell in a solution of sugar (a five per- cent one will answer) or in dilute glycerin. By this means the protoplasmic lining is contracted somewhat by the withdrawal of water from its cavity, and in shrinking from the wall its shriv- elled contour can be easily distinguished. It is best for a beginner to use in his early demonstrations very young plant-hairs in which the vacuoles do not occupy much space within the cell. The cells composing the growing points of most roots, stems, and leaves are too small for satisfactory study at the very outset ; it is well to defer the examination of the protoplasm in these until its reactions have been clearly demonstrated in young plant-hairs. Directions for the demonstration of active protoplasm can be found in section 124. The tests there given should be repeated b}' the student four or five times with different kinds of cells, PLASTIDS. 9 after which the effect upon fresh material of potassic hydrate, both the concentrated and the dilute solutions, should be care- fully watched. In these examinations it will be well to practise ■with the reagents without lifting the cover-glass (see 17 and 20). II. Chlohoplastids. Examine the chlorophyll granules (see page 41) in the fol- lowing material : — (a) The parencliyma cells of any thick leaves, for instance those of Purslane, Begonia, etc., noting in the drawing the rela- tive size and abundance of the granules in different cells. (b) The epidermis of the same leaves, noting in what cells, if any, the granules are found. Examine also the green bodies in the leaves of an^' true moss, and in any filamentous alga, «. g., Spirogyra, and the cotyledons of the following seeds for any green granules : sunflower, maple, and pine. Raise three seedlings of flax and pine. Let one of the seed- lings of each be kept in darkness, to the second seedling of each give onlj' a very little light, to the third give as much light as possible ; and when the plumules have begun to develop, examine the cotyledons and young stems for any color-granules. Do well-blanched celery petioles contain chlorophyll? To answer this, examine the base, middle, and summit of the leaf- stalk. The next three studies can be advantageouslj' deferred until after that of starch. III. Leucoplastids. These bodies (see 174) require for their detection very careful manipulation, but by following the directions given on page 44 they can usually' be macje out without much difficulty. For the pseudo-bulb of Phajus, which is there recommended, the same oi'gan in almost any of the cultivated exotic orchids may be substituted. IV. Chromoplastids. These can be examined in any of the colored fruits ; for instance, in winter, the berries of Solanum Pseudocapsicum (Jerusalem Cherry) may be used (as directed in 498). The granules tliere found should be compared with colored granules in the petals of almost any flower. For examination of the color- granules in flowers, common pansies answer very well (see 477.) 10 STUDIES IN HISTOLOGY. V. PiiOTEiN Granules (pages 44-47 and 182). Examine thin sections of the endosperm of the seed of Ricinus after the specimen has been treated as directed in 176, and also of the seed of BevthoUetia (Brazil-nut) . Permanent preparations from the latter should be made as directed on page 47. Search also for cubical crystalloids in the cells just under the skin of a potato-tuber. VI. Starch. In the examination of starch (pages 47 and 181) make thin sections of (a) a potato-tube)', (b) the cereal grains figured in the pages cited, (c) seeds of the pea and bean. Detach some medium-sized starch-granules and measure them with the micrometer ; after this applj' a solution of iodine, em- plo\-ing the most dilute one which will impart a decided color to the granules. Is the color given b}' iodine permanent? Does exposure of the colored specimen to light make anj- difference in permanence of color ? In all cases note very carefully- any appearance of stratifica- tion which the different granules present, and determine the distinctive characters by which each of the common commercial starches can be recognized, such as rice-starch (toilet-powder), laundrj- starch (either wheat or potato), etc. After sufficient familiarity has been acquired b3' an examination of all the kinds of starch figured in Part I., try to identif}' nnder the microscope specimens of laundry starch and of various kinds of flour. Can starch be detected in the following : — ■ Seeds of flax and mustard? Roots of beets and turnips? Pulp of the ripe and the unripe apple? Bark of willow and maple ? Young shoots of pine ? For the detection of starch in minute amount in chlorophyll granules the directions given on page 42 must be carefully followed. From this time on, the character of the granules seen in any specimen should be determined by iodine and the result noted in the drawing. CRYSTALS, CAKBOHYDRATES, AND OIL-GLOBULES. 11 VI r. Ckystals. In many of the sections alreatl\' spoken of, for instance those of Begonia, single crystals and clusters of crystals have at- tracted attention. For a brief stnd}' of different forms of crystals (see pages 52-55) the ft)llowing are very serviceable : petioles of Begonia, scales of onion, leaves of Tradescantia, Fuchsia, and the common " C'alla" (Richardia), bark of many woody plants. If a thin section of the leaf of almost any Araceous plant, for instance " Calla," is placed in a little water under the micro- scope, it frequently happens that the discharge of acicular crystals (raphides), described on page 52, can be seen without difficulty. Apply to the specimens containing crj'stals the two reagents spoken of in the table on page 54, and carefull}- note results. Repeat Vesque's experiment (188). vni. Carbohydrates dissolved in the Cell-Sap. (a) Inulin (183) is deposited from its solution in eell-sap whenever the cells are placed for a time in alcohol or even in glvcerin. Its characteristic forms are not likely to be mistaken for anything else met with in the tissues. Excellent material is afforded not only hy the common Dahlia, but by Cichory and Dandelion (see Fig. 35). (b) The sugars. Examine a thin section of beet-root by the method described in IB-l. Compare with it a thin section of any ripe fruit. IX. Other Cell-contents. Oil Grlobides, sometimes of large size, but generally minute, are to be looked for in those seeds which do not contain starch (compare 511). Examine in these the effect of ether on the par- ticles of oil, and also make sections through the leaves of St. John's-wort, Rue, and Dictamnus, and through the rind of an orange or lemon to determine the shape of the receptacles con- taining oily matters. liesins, etc. For a study of these, proceed as directed in 56, employing .young shoots of Pine. Tannin, etc. For the detection of tannin, solutions of iron (see 59) maj- be used ; but the results are generally more satisfactory when a solution of potassio or ammonic dichromate is employed. The color imparted to tlie cells containing much tannin is brownish 12 STUDIES IN HISTOLOGY. or even almost black. The student should examine the very peculiai' globules of tannin-solution fonnd in the sensitive pnlvi- nus, or cushion, at the base of the petiole of Mimosa (Sensitive plant). Similar globules have been detected in different barks. DISTRIBUTION OF THE HISTOLOGICAL ELEMENTS. The various histological elements after being examined as directed in Chapter II. should be investigated with regard to their mutual relations. It is advisable to begin with the skele- ton or framework of the plant, afterwards taking up the latex- cells, etc. As shown in Chapter III., the framework of the higher plants, which we are now to consider, consists of fibro-vascular bundles variously arranged and conjoined. The bundles, which in some cases may run for some distance as isolated threads, and in others exist as compact masses, are surrounded witli larger or smaller amounts of cellular tissue, the exterior portions of which are si)eciall3' adapted to come into contact with the surroundings of the plant. I. Srni'CTnRE of Fibro-vascular Bukdlf.s. For the demonstration of the structure of fibro-vascular bundles, seedlings of the following plants will aflbrd good material: Bean, Indian corn, Castor-oil plant, and Squasli. The roots of these plants give examples of radial bundles (313), in which the strands of liber and of wood are in ditferent radii, wiiilo from their stems (including the hypocotyledonarv stem of the bean, castor-oil, and squash) may be obtained excellent illustrations of collateral bundles. The sections for displaying the structure of the bundles are best made in the three directions, transverse, vertical-tangential, and vertical-i'adial. In a few cases sections made obliquely to the axis of the organ are instructive ; but unless great care is exercised in observing all their relations, they may be ratlier misleading. In all cases examine fully the character of the bundle-sheath (see 212). The student should not be satisfied with anything less than a clear interpretation of all the structural elements which he meets in a given bundle. If the structure of a bundle is not revealed by the sections already prepared, fresh ones should be made and carefully compared with the others, and FIBKO-VASCULAE BUNDLES. 13 with the figures in Part I. In order to identify some of the structural elements composing a bundle, it is sometimes advis- able to resort to cautious maceration (see 70), so that the parts may be isolated. It has been found advantageous, in a few in- stances, to verj' securely fasten the section under examination to thin rubber membrane by means of the best "rubber" cement or marine glue, and then subject the membrane and section to- gether to the action of the macerating liquid, great care being exercised to have the process gradual. After the maceration is complete, the membrane is removed from the liquid, washed, and then slowly stretched until the adherent wood-elements are somewhat torn apart. It will be obser\ed that by this method their former relations need not be greatly disturbed. After examining the fibro-vascular bundles in the seedlings above named, proceed to the study of the bundles in the roots, stems, and leaves of two adult herbaceous plants, for instance Indian corn and Bean, in order to ascertain what differences, if an^', exist in the composition of the bundles in a given organ at different periods of growth. It was stated in 309 that the simplest form of a fibro-vascular bundle consists of nierel}' a few tracheal cells (or sometimes tra- cheae) together with some cribrose or sieve cells. The student should search for tracheids, which may occur disconnected from any bundle ; as for example in the stems of species of Salicornia (a seaside plant of succulent texture), and in the petiole and pitchers of Nepenthes. Tracheids occur also, often in a con- tinuous layer, as a sheath of the aerial roots of orchids. Sieve- tubes may be looked for at a little distance from the bundles in the stems of potato and tobacco, where they occur in the periphery of the pith. Two supplementary studies are strongly' advised : (1) of the bundles in ferns, (2) of those in aquatic phsenogams. In the former, " concentric '' bundles are met with ; in the latter, rudi- mentary bundles. II. COUKSB OF THE BUNDLES. The course of the fibro-vascular bundles can be traced in some cases, especially in young and rather juicy stems, like those of Impatiens, with little or no difficulty ; but it is generally neces- sary to treat somewhat thick sections of the stem under ex- amination by a macerating liquid, for instance potassic hydrate, after which the course can be made out. In most cases the course of the bundles can also be made out b^- series of sections 14 STUDIES IK HISTOLOGY. made at different points in tbe organ, care being taken to arrange the sections in tlieir proper sequencs. The following material will be nseful for practice in the deter- mination of the course of the bundles : j'oung shoots of Clematis, Vitis, and Pliaseolus (all dicotyledons) ; and, after these, shoots of Spiderwort, the rootstock of Convallaria (Lily of the Valley), or of Smilacina, and if possible the bud of a young palm. The course of the bundles in leaves and dry fruits can be easily demonstrated by " skeletonizing" them. This is effected by keeping the leaves for a long time in a dilute solution of calcic hypochlorite (see 50). DEVELOPMENT OF THE ELEMENTS. This must be examined in the youngest seedlings of the plants now spoken of. The sections must be through the growing points, and should be well cleared by one of the processes de- scribed in 16 or 24. For the development of special structural elements, for example latex-cells, see Part I. HISTOLOGY OF THE VARIOUS ORGANS. I. The Root. The student may use, for demonstration of the histolog}- of the root-tip, anj- seedlings which have been grown either in water or on a clean support, and are therefore free from grains of earth. Root-hairs are best examined on seedlings sprouted upon moist sponge or bibulous paper. n. The Stem. It is advised that the student now prepai'e, in addition to the sections of stems previously examined, sections through two and three j-ear old shoots of any common dicotyledon, and note all differences which exist between the different woodj' elements forming the rings, and all changes in the bast. The growth of cambium should be carefully examined in the j'oung shoots of Pine and of Oak. For the study of the secondary changes in the bark, the twigs of black currant or of white birch afford good material, the successive changes being easily followed. The occurrence of true cork in out-of-the-way places is illus- trated by Catalpa, Professor Barnes reporting that it sometimes occurs between the annual layers in the stem of Catalpa speciosa. Other cases should be looked for. LEAF AND FLOWER. 15 III. The Leaf. The leaf presents fe\y difficulties in histological manipnlation. For all necessary details consult pp. 155-164. The foUowiug plants atToi'd excellent material for studj' : — Of the centric arrangement of parenchj-ina in the blade, Trit- icurn vulgare, Acorus, and many of the Cactaceaa. Of the bifacial arrangement of parenclyma, many plants with flat horizontal leaves. IV. The Flower. It is assumed that the student has thoroughly familiarized himself with the morphology of the simpler flowers as explained in Volume I., and has acquired some facilitj' in examining, as there directed, those of more complicated structure. The stud}' of the microscopic anatomy of all the floral organs in their adult state should precede any attempt to examine their development. Since the flower should be examined in all stages of its development, it is well to select for stud}' onlj- those flow- ers which can be readily obtained in large numbers, and further- more, bj' preference, those which are not thickl}' covered with hairs. The common weeds Lepidium Virginicum and Capsella Bursa-pastoris afford excellent material for the study of the flower and its development, and have the signal advantage of being niucli alike in tlie most essential respects, yet possessing minor differences which are not likely to be overlooked. An exhaustive examination of the histology' of the organs of the flower should begin with the study of the sepals, the other organs being taken up in their turn, and the following points receiving special attention : (1) the possible occurrence of stom- ata upon all the parts of the blossom ; (2) the peculiarities in the proper epidermal cells of the petals ; (3) the character of the parench3'ma in all parts of the flower, and all diff'erences in the nature of the cell contents, notably the plastids ; (4) the charac- ter and the distribution of the fibro-vascular bundles in their course from the pedicel to their ultimate attenuated ramifications in the several organs. /Stamens. The character of the pollen demands special atten- tion, and its examination should be followed by a comparison between as many kinds as possible taken from various flowers. The character of the integuments and the contents of the grains should also be demonstrated. 16 STUDIES IN HISTOLOGY. The pistil requires little special study, except in regard to its development. It will be well to examine the conductive tissue of the style and trace it down to the ovarian walls. (Other minute matters connected with the stamens and pistils are con- sidered under "Fertilization.") V. Development of the Flowee. From the j'oungest flower-cluster of any plant having indeter- minate inflorescence, for instance that of Lepidium or Capsella, cut squarely off a short piece of the tip, place it on a glass slide in a little alcohol, in order to remove the air, and cover with thin glass. (If the student has an air-pump, the specimen can be placed at once in water on the slide, and then subjected to the action of a partial vacuum, which will of course free the whole preparation from any air-bubbles.) After the air has been removed, add water, and if the specimen requires clearing, as is usuallj' the case, some potassa. On gently warming the slide the specimen will grow somewhat darker, but after a time will be made tolerabh* clear. If not, proceed as directed in 25. The specimen, if a good one and well prepared, ought to show all the relations of the several flowers of the cluster to each other. Prepare a second specimen b^- removing the flowers in succession under the dissecting lens, beginning with the larger, and placing them in a row wliich will comprise all the stages of development. AVith the material thus obtained, which it is well to keep moist with glj-cerin, the examination of all the different parts can be successfully carried out. The stud}' will be far more instructive if the student makes a parallel series with an allied species. Comparison of the two species above mentioned shows exactly when and where some of the parts are arrested in development. VI. Development of the Pollen. The examination of the anther for this study should begin at a very early stage in the growth of the flower, and particular attention should be given to the cells wiiich line the pollen cavi- ties. Great advantage is gained from the skilful employment of staining agents, by which the parts are brought out more clearly (see 77 et seq.). All changes in the character of the nucleus of the grains during their differentiation demand for their identification the use of staining agents without the pre- vious application of potassa. STEUCTUEE OF THE SEED. 17 VII. Dkvelopment of Ovules. Ill this examination the wall of the ovary must he reinoved, and the minute eminences which are to become the ovules ob- served in their earliest stage. The successive external produc- tions which are to become the integuments of the ovule should be traced with great care. It is also well to examine minutely the clianges in form of the embi-yonal sac in the nucleus (or nucelhis) of the ovule. These will be further adverted to under " Fertilization." VIII. Minute Stuucture of the Seed. Since in the previous exercises some parts of the seed have been alread3- examined, it is necessaiy here merely' to call atten- tion to the desirability of studying the character of the integu- ments in at least two common and a few exceptional cases. For the former, no seeds are better than tliose of the common Bean, Pea, or Lupine. After a clear idea lias been obtained of the nature of the cells, which compose the greater part of the two integuments, tlie student should make careful sections through the hilura in order to display the peculiar sac-like body tliere seen. For the exceptional types of integuments, examine the seeds of Flax (showing the gelatinous modification, etc.), or better, if tliej' can be procured, the seeds of CoUomia and Cot- ton. It will be well also to examine tlie closely united ovarian and ovular coats in the common grains, like Wheat or Indian corn. The student should examine as many seeds as possible, includ- ing those containing much, little, and no starch, and observe also whether or not there is any difference between ripe and unripe seeds in tlie amount of starch which tlie.y contain. He should examine the contents of the cells nearest the integuments in any of the seeds above mentioned, and ascertain the relative amount of albuminoid matters present compared with those in the cells in the interior of the seed. Further micr.oscopic examination of the seed is to be taken up when germination is studied. 18 STUDIES IN PHYSIOLOGY. PRACTICAL EXERCISES IN VEGETABLE PHYSIOLOGY. This course of cxpei'iineuts in Vegetable Phj-siology is divided into two parts : the first series comprises a few exercises wliicli can be undertaken bj- any one liaving only the simplest appli- ances ; the second requires more complicated apparatus. The first series, if faithfully and intelligently followed, should place the student in possession of the leading facts regarding the prin- cipal activities of the plant ; while the second series should ac- quaint him with the chief methods employed for the investigation of the special offices of the organs of the plant, and fix the principal results in his mind. It should, however, be frankly stated that for the proper and satisfactorj' performance of the experiments detailed in this second or special series the student should first become familiar with the ordinary methods of chemi- cal and ph^'sical manipulation, and have at command the funda- mental principles of chemistry and of phj'sics. FIRST SEEIES. In this series are discussed experimentally the following car- dinal topics : (1) The behavior of protoplasm in a living cell; (2) The gain in substance by assimilation and the loss of sub- stance by growth ; (3) The chief conditions under which plants assimilate ; (4) The dependence of the principal activities of the plant upon certain external conditions. The experiments can be conducted with the following ap- pliances : — 1. A small balance with weights ranging from twenty grams to one centigram. If a balance is not procurable, ordinary hand- scales with horn or brass pans will answer verj- well. 2. A water-bath, or in place of it a small porcelain-lined kettle of one or two pints capacity, fitting into a larger iron kettle. Water placed in the larger kettle prevents the inner one from being heated above the boiling-point of water. 3. Haifa dozen test-tube's. 4. Three or four pieces of glass tubing, six inches long. 5. A small camel's-hair pencil, and India ink. 6. Pieces of colored glass or colored gelatin (red, yellow, green, blue, violet), six inches square or larger. MOVEMENTS OP PROTOPLASM. 19 For the first studj-, the examination of protoplasm, a micro- scope magnifying from two hundred to six hundred diameter?, will be required, together with a small outfit of slides and covers ; and for the examination of growth a zinc box constructed as directed in "The Dependence of Growth upon Heat." I. The Behavior of Protoplasm in a Living Vegetable Cell. For all necessary details as to the chemical reactions of proto- plasm, see 124 and the exercise on page 8 of this "Praxis." At present it is proposed to call attention to the various Movements of Protoplasm. (a) Material. The delicate hairs from the young leaves of almost any pubescent plant will serve for the demonstration of these movements, but the following are recommended on account of their abundance and excellence : stamen-hairs of Spiderwort (Tradescantia), hairs from the 3"oung leaves of squash and nettle, and from the velvet}- leaves of many culti- vated exotics. (5) Preparation of specimens. Remove b}- needles, forceps, or scalpel a very little of the epidermis witii its attached hairs, and place it at once in a little water on a glass slide. In placing the thin glass cover on the specimen be careful to exclude all air- bubbles and not to crush the (jells. If necessary, put a fragment of glass under one edge of the cover, to lighten the pressure on the object. If the hairs are suitable for the examination, the delicate threads of protoplasm ought to be distinctly seen through the cell-walls, and, after a little time, a movement of translucent granules should be seen in them. If, after a few moments, no movement can be detected, warm the slide a little with the hand and again observe. If no movement should now be seen, add to the water on the slide a little dilute glycerin ; this causes slight contraction of the protoplasmic lining of the cell, and probablj' the movement can then be observed in the threads. If not, do not waste time over the specimen, but try a fresh one. A power of 200 diameters will answer for this work, but one of 500 is better. (c) Questions to be answered hy the specimen. If the student has secured a good preparation, in which the movement of gran- nies in the threads can be .seen distinctly, he can easily answer the following queries : What is the rate of motion of the gran- nies at the temperature of the room? Do the threads remain 20 STUDIES IN PHYSIOLOGY. unchanged in shape ? Do any grannies pass from one cell to the next one? Where is the motion fastest? While the observations ai'e in progress, bo careful not to allow the preparation to become dr3- : add a little water ocoasionall}-, and note whether the rate of motion is increased or diminished for the next minute or so. (d) Questions to be answered by experiment. (1) What effect upon the rate of protoplasmic movement does increase of tem- perature produce? In order to keep the slide with the specimen, prepared as above, from touching the metallic stage of the microscope, place under each end of it a piece of thick pasteboard, and then clamp it down firml}' b}' means of the stage-clips, so that it cannot be easil}- displaced. After the slide has been in position for a few minutes, note the rate of movement of the granules at the ordinary temperature of the room. When this has been accu- rately determined, place near the specimen, on the slide, a coin or other small piece of metal which has been heated to 40° C, and note the change of rate. Afterwards apply more and more heat bj' a second and a third application of tlie coin, heated each time higher by immersion in hot water, and note the result. Of course this very simple method of experiment does not allow one to determine the exact temperature to which the specimen is heated, but its temperature is onl^" a little lower than that of the coin. For exact experiments employ the apparatus described in 557 or 558. (2) What effect upon the rate of movement does a decrease of temperature cause? Prepare a fresh specimen as directed under (6), lower the tem- perature of the slide by the application of a coin which has been immersed in ice-water, and note all changes in the rate of move- ment. Still lower temperatures are easily secured bj' placing in a small copper cup on the slide (an ordinary copper cartridge- shell answers very well) a mixture of ice and salt. If in either of the preceding experiments the motion of the granules has been arrested, endeavor, by reversing the applica- tion, to re-establish movement : thus, if the movement was ar- rested at the higher temperature, apply cold ; if it was arrested by cold, apply heat. ASSIMILATION AND GROWTH. 21 II. The Gain in Substance by Assimilation, and the Loss of Sub- stance DURING GllOWTH. Select a number of beans (Windsor, Horticultural, Lima, or white), of nearly the same size, weigli ten of tliem, and diy tliem cai-efully in a water-bath to ascertain tlie amount of water wliicii tliey contain. Take two other lots of ten each, weigh them careful!}", plant thein on moist blotting-paper or wet sponge, and keep tliem in a warm place until they have sprouted. When the beans have fairly started, suspend them over tli,e surface oi water, with their roots in it, as directed in 669. From this timj on, keep one set of the seedlings in tlie light and the other set in the dark, being careful in each case that the water is supplied in sufficient quantity to make up for all loss by evapoi-ation, and that it is changed every third day. Let all the conditions undir which the two sets are cultivated be as nearl}' alike as possil ), with the single exception that light is present in one case ai^d completel}' absent in the other. In a couple of weeks the two sets of seedlings will have become large enough for further study : the set grown in the light will be green and thriftj-, tha others may be as large, but they will have a ytllow, unhealthy appearance. Remove the two sets from the water and carefully dry them separately over the water-bath as directed in the case of the seeds. When they do not further lose weight, weigh carefulb/. Compare the weight of the dried seedhngs with the weight o? the dried seeds. III. The Chief Conditions of Assimilation. In the examination of these, repeat with great care the expepl ments detailed on page 305. IV. The Dependence of Gr.owTH ui'on Heat. This ma^- be shown in the following manner: Take a sheet oi tin or zinc about 6 to 8 inches in width and 24 inches in length. Turn up its ends at right angles 6 inches. Turn them once more at right angles, rather less than half an inch at the top and two and a half inches at the bottom. This last turn will hold a sheet of glass which will form the fourth side of a bos', narrower by two inches at the bottom than at the top ; that is, the glass side will not be vertical, but inclined. Cut out a piece of wire-gauze of the right size for the bottom, and either solder or rivet it in place. Fill this box with well-moistened sawdust. Flant a row of six or eight large Windsor beans in regular order 22 STUDIES IN PHYSIOLOGY. iu the sawdust, near the glass side, so that the tip of each radicle will stait down about one fourth of an inch from it. If the glass is proporl}- inolincd, the radicle will quickly press itself against it and thus be the more roadil3' seen and studied in its subse- quent growth. Wlien the radicles are about two inches in length, withdraw them, and by tlie aid of a fine carael's-hair brush and India ink mark them off with precision at regular intervals of one or two millimeters, then place each in the same place and position from which it was taken. It will be found that only tlftir tips grow ; the marks above the tips remaining the same distance apart. Put a thermometer in the sawdust in order to observe the tem- perature, upon which it will be found the rate of growth depends. Place the seedlings near the stoA'c or over a register where the temperature of the sawdust can be gradually raised to from 28° to 30° C. Having previously measured and noted the exact length of the radicle of each plant, observe its increase, while the temperature remains constant, for a given period of saj- from five to ten hours. Next place the case containing tlie seedlings in an improvised ice-chest (any box which can be well closed will answer), and when the temperature has been reduced to 10° C, or nearlj- that, measure the roots carefully again. Hold this degree of cold as nearlj- constant as possible for five or ten hours, whichever may have been the period of time in the first ease. Compare the growth in the two periods and note the difference. SECOND SERIES. — SPECIAL EXPERIMENTS. I. Diffusion. Place a tumbler containing an inch or two of pure water upon a firm shelf where it will not be subject to any jarring, and put in it a vial filled to the brim with some colored liquid, for instance blue or purple ink. Then by means of a tube or " thistle-funnel" resting on the bottom of the tumbler pour into the tumbler water enough to come up to the mouth of the vial, and verjj^ cautiously add more until the mouth is covered to a depth of about an incli. If the pouring has been skilfullj' done, there will be scarcely any of the inJc mixed with the surrounding water. Let the apparatus stand undisturbed for a week or so, and note anj- changes in the color which maj- be observed from day to day. Try the same experiment with a saturated solution of common salt in place of the ink, and at intervals of three daj's cautiously OSMOSE. 23 remove a little of the water from the bottom of the tumbler by means of a small tube or pipette, and test it for chlorides. II. Osmose. Diffusiox through a Membrane. Scoop out a small cavity in a fleshy root, for instance that of a carrot, and carefullj- dry it with a cloth. Then fill it with fine sugar, and let the root stand in some place where it will not be disturbed. Note any changes which take place in the sugar and in the condition of the root. By comparative examinations of the tissues removed and those remaining, ascertain whether any of the sugar has entered the cells. Tie a thin, sound piece of parchment paper (or, better still, parchment) over the mouth of a thistle-funnel, and fill the bulb of the funnel with a strong solution of common salt. Then sus- pend the funnel in pure water, so tliat the level of the water outside corresponds to that of the brine inside, and keep the ap- paratus in a warm place, noting an^- change of level of the liquid in the funnel tube. Trj- other substances in the tube ; for in- stance, dilute potassic hydrate, concentrated potassic hj-drate, sj-rup, and diy powdered gum-arabic. Carefull}' examine the upper surface of the leaf of Lilac, Olean- der, or Echeveria for the presence of stomata, and if none are found, make the following trial witli a good, sound, young leaf, being careful to see that the plant is well watered. Put a drop of water on the upper surface of the leaf, and dust upon it either finely powdered sugar or salt, until the drop has taken up all it can, and the mass looks nearly- dry ; then blow off the residue, and cover the leaf or plant witii a bell-jar. Keep it in a warm place and water well. Observe in the course of a few hours, and at frequent intervals during the next four or five da3-s, any changes which the spot of sugar undergoes. It is a good plan to prepare several such spots with difl['erent substances. III. Pelliolk PEEOirrrATES. — Tuaube's Artificial Cei.l. Dissolve 5 grams of pure potassic ferrocyanide in 100 cubic centimeters of pure water. Place some of the solution in a test- tube having a foot, and drop into the tube a small fragment of moist chloride of copper. Observe the changes which take place in the shape of the film which instantly forms around the frag- ment. Try the same experiment with a saturated solution of potassic ferrocyanide, and afterwards with solutions containing respectivelj' 1 and 10 per cent of the ferrocyanide. 24 STUDIES IN PHYSIOLOGY. What effects are proclueed when a solution of potassic ferro- cyanide is shaken up with a solution of copper chloride? The pellicle precipitates can be further examined as directed on page 226. Calcic chloride and sodic carbonate can be einploj-ed in the examination instead of the substances there mentioned. IV. Pfeffer's Artificial Cell. Repeat Pfeffer's experiments (page 227), with all the precau- tions tliere advised. In ever^- case where a manometer, or pressure-gauge, is to be used, corrections must be made for temperature and for baro- metric pressure according to the directions given in such works as Bunsen's " Gasometr3-.'' V. Absorption of Water. Moisten one side of a perfectly- flat, thin i)iece of hard wood, for instance the holly-wood used for scroll-sawing, and note anj' change of form which occurs. What effect is produced by moistening, in the same way, the other side of the wood? Fill a strong stone bottle with large dry seeds of known weight, for instance beans, and put it in a pail of water so that the water can pass into its moutli. If the bottle should break in a few hours, remove quickly with blotting-paper all the outside moisture from the seeds, and determine their increase in weight due to absorption of water. Place a thermometer bulb in a tumbler half full of dry starch ; slowly add to this water of exactly the same temperature, and note any change of temperature which accompanies the absorp- tion of the water by the starch. Weigh a fleshy root, and carefully drj- it in a water-bath, to determine the amount of water which can be expelled at 100" C. Then raise the temperature of the root to somewhat above 100° C, by carefully heating it in a sand-bath, and observe any loss of weight. Determine also the amount of water contained in a fibrous root of Indian corn, a small woody stem, " dry " wood, leaves of Indian corn, Begonia, and Sedum, the pulp of an apple, grains of wheat. After the above substances have been thoroughly dried and weighed, immerse them in water for one hour, wipe them as diy as possible bj' means of blotting-paper, and weigh again. How much water can each absorb in one hour? In like manner as- certain how much they will absorb in ten hours and in twentj-- four hours. RELATIONS OF THE PLANT TO WATER. 26 VI. Eoot-Absoeptiox. Repeat the following experiments bj' Olilert : — Cut off tlie so-called spongioles, the very tips of the roots of sonnd seedlings which have been cultivated for a few days upon moist sand or sponge (or, better still, with all the roots in water), and cover the wounds with asphalt-varnish. The wounded end of the root must be quickly dried with blotting-paper before the varnish is applied. Then put the roots of the plant again upon tlieir moist support or in water, and endeavor to answer by care- ful observation the question : Does or does not the plant absorb enough water for its needs without tlie " spongioles"? Cultivate seedlings of one or two plants, for instance radish and wheat, upon (1) rather dr^- sand ; (2) moist sand ; (3) wet sand, or upon blotting-paper of these three degrees of moisture, and notice if there is any appreciable difference in the number of root-hairs produced. Can the development of the hairs be in- creased bj' increasing slightly the temperature of the support? VII. Root Puessuke. Cut off squarely' the stem of a young dahlia or sunflower well rooted in a flower-pot of moderate size, and to the stump fasten immediatelj' a T-tube, with its pressure-gauge as directed on page 264. Ascertain tlie pressure shown by the mercurial gauge at intervals of an hour, and determine also the effect of chang- ing the temperature of the soil in the flower-pot. VIII. Stem Pkessure. Apply a pressure-gauge to the cut stem of some woody plant well established in a flower-pot (for instance, a strong rose), and ascertain the amount of pressure exerted bj' the sap. In the winter time or early spring try the experiments referred to on pages 2G4-267. IX. Transfer of Water through Stems. Eepeat De Vries's experiments described on page 263. For these, stems of sunflower and tobacco answer very well, while tliose of heliotrope are not very good. Ascertain the height to which a color (as anilin red) will rise in the cut stem of a young woody plant under different conditions of warmth, exposure of the leaves to light, etc. Repeat the experiment with a strip ot blotting-paper, described on page 260. Try the foregoing 26 STUDIES IN HISTOLOGY. with the substitution of a salt of lithium for the dye, and deter- mine the rate of ascent. It will be well for the student at this point to review carefully the principal facts regarding the amount of moisture which the atmosphere can take up at different temperatures. In all trans- piration experiments he should determine the percentage of moisture in the atmosphere to which the leaves of the plants are exposed, and for this purpose the well-known Hygrodeik, or Hygrophant, may be employed. But if only the simple wet and dry thermometer bulbs are at hand, the student can find all necessary data for his calculations in the tables published by the Smithsonian Institution. Place in a watch-glass under the microscope water contaiuing finely powdered ind'go, and immerse in it the clean-cut surface of a leafy shoot. Observe in which direction the indigo particles move. X. TuAxspinATioN, OE Exhalation. Kepeat the following experiment devised by Henslow : " Take six or eight of the largest, healthiest leaves j'ou can find, two tumblers filled to within an inch of the top with water, two emptj' dry tumblers, and two pieces of card each large enough to cover the mouth of the tumbler. In the middle of each card bore three or four small holes just wide enough to allow the petiole of a leaf to pass through. Let the petioles hang suffi- ciently deep in the water when the cards are put upon the tum- blers containing it. Having arranged matters thus, turn the empty tumblers upside down, one over each card, so as to cover tlie blade of the leaves. Place one pair of tumblers in the sun- shine, the other pair in a shady place. In five or ten minutes examine the inverted tumblers." Tic a piece of thin rubber-cloth around the flower-pot and lower part of the stem of any young leaf)' |)lant, and weigh the whole upon a common balance capable of turning with a deci- gram, under a lead of two or three kilograms. If notliing better can be procured, one of the best forms of small platform balance will answer. A thistle-funnel should be tied up with the stem, so that water can be supplied to the plant as required. Ascer- tain the amount of transpiration from the foliage of the plant during twenty-four hours under the following conditions : (1) at a temperature not falling below 60° F. (about 1G° C.) ; (2) at a temperature not rising above 40° F. (about 4° C). What is the loss of moisture in one hour under direct exposure to the brightest sunlight? Note temperature and moisture in the ASH OF PLANTS. 27 air. What is tlie effect upon transpiration of placing the flower- pot in some cruslied ice, tlie temperature of the air remaining about the same as before ? Determine the minimum, maximum, and optimum temperature for transpiration of any suitable herbaceous plant, for example, a Pelargonium (House Geranium). XI. Extravasation fkom Leaves. Cover a young healthy plant of Indian corn or wheat with a bell-jar, being careful to keep it warm. If, after a little time, a drop of water should appear at the tip of any of the leaves, remove it by blotting-paper, and replace the bell-jar. What is the lowest temperature at which water is thus given oflT by young leaves of the above plants ? If a j'oung Caladium is at hand, examine the tip of the leaf for the jet of water (page 268) which can sometimes be seen. If the plant is a suitable one, and the jet can be seen at all, ascertain the lowest temperature at which it is ejected. XII. Incombustible Matters in the Plant. Burn upon platinum foil (free access of air being permitted), known weights of the following substances, and weigh the ash left in each- case : (1) oak-wood, (2) pine-wood, (3) a young leaf of an}- plant, (4) a much older leaf of the same plant (for instance raspberry), and (5) some grains of Indian corn. If no platinum foil is at hand, burn the substance in a hard glass tube open at both ends and held slightly inclined in the flame of an alcohol lamp or of a Bunsen burner. If the glass tube is used instead of platinum foil, weigh the tube and the substance together before heating, and afterwards weigh tube and ash together to obtain the difierence in weight. XIII. Examination of the Ash of Plants. If the student has facilities for conducting qualitative chemical analyses, he would do well to examine the ash of the following plants : Sugar-beet, Buckwheat, and Oat. If he has had sufficient practice in quantitative chemical analysis to warrant it, an examination of the ash of some one of the plants which have been spoken of in GC4 and 665 would form a useful exercise. The investigation of the ash of a single species at different seasons is recommended. 28 STUDIES IN PHYSIOLOGY. XIV. Wateii-Cultuue. In the study of water-culture no plants can be more easily managed than buckwheat and Indian corn. Secure good seed- lings, and treat them as described in G6'J. After the plants have become well established in their new surroundings, use for the nutrient liquid the following solutions in a fixed order, and with the precautions laid down on page 249. 1. Well-water, or other drinking-water. 2. Distilled water with potassic nitrate. 3. b& a " " chloride. 4. a (.i, " raagnesic sulphaie. 5. (C it. " calcic chloride. 6. i^ a " " sulphate. 7. a ii " potassic phosphate. 8. Nutrient solution I. (672). 9. ti fci II. (673). 10 . Distilled water alone. XV". Assimilation Phopee. Chlorophyll and other coloring-matters. Make a solution of the pigment hy placing bruised leaves of grass in strong alcohol for a few hours, and keeping them from the light. It is well to prepare at least ten ounces of the strong extract, which can be used in all the following experiments. Examine the color of about an ounce of the above extract held in a small vial. What is its color by transmitted and by re- flected light? In the latter examination it is better to throw a strong light from a burning-glass or double convex lens upon the surface of the liquid. How long will the liquid keep its color in the strong light? Treat, as directed in 774, one ounce of the extract which has not been exposed to light, and place the turbid mixture aside in a dark place until it becomes clear. What are the colors of the upper and the lower layer into which it separates ? If a microspectroscope is available, make on paper projections of the spectra of the following substances: (1) Chlorophyll solu- tion, (2) the upper layer of the liquid just mentioned, and (3) the lower layer of the Lc^uid. Examine also the spectrum of a thin green leaf. If possible, examine the colors of autumnal leaves, and of alcoholic extracts from colored flowers and colored fruits. ASSIMILATION. 29 Place a few red sea-weeds in pure watei-, and let them remain there for ten hours. What is the color of the water by (1) trans- mitted light? (2) by reflected light? Extract tlie coloring-matter of red sea-weeds by means of alcohol, and compare the alcoholic with the aqueous solution. What is the color of an alcoholic extract of tlie bruised tissues of Mouotropa uniflora? Etiolation. Keep seedlings in a warm, dark place until they have lost their green color, and then, having removed some of their leaves for immediate examination, place the plants, with the remaining leaves attached, in the light, ilake alcoholic extracts of the blanched leaves and of the gi'een ones, comparing them from all points of view. Examine pine seedlings grown in complete darkness, and ascer- tain the nature of the pigment which their green cells contain. Carbonic acid and assimilation. Compare at the end of two or three weeks the dry weights of two seedlings grown under the following conditions : Both the seedlings have furnished to them exactly the same kind and amount of soil, and are provided with equal amounts of nutrient solutions at corresponding times ; both are placed under tubulated bell-jars, and have the same amount of moisture in the atmosphere to which tliey are exposed. The seedling in one bell-jar obtains a supply of carbonic acid gas, since there is an opening in the jar through which the en- closed air communicates with that outside containing its normal proportion of carbonic acid. The seedling in the other jar lias no carbonic acid supplied, since a cup which contains potas- sic hydrate deprives the air already in the jar of all its carbonic acid, and an open receptacle, filled with pumice-stone satu- rated with potassic hjdrate, removes all carbonic acid from any air entering the jar. One plant is thus furnished with enough available carbonic acid, the other is in an atmosphere wholly free from it. In a modification of the foregoing experiment, supply a known quantity of carbonic acid in aqueous solution to the soil of the second plant, being careful to prevent hj means of a cover of rubber-cloth any escape of the carbonic acid from the soil of the flower-pot into the air of the jar, and after a few days compare the weights of the plants as before. Can a water plant derive its carbonic acid from water contain- ing a small amount of sodic bicarbonate in solution ? Add to the normal air contained in a freshl}' filled bell-jar, in which a seedling is growing, a known quantity' of pure carbonic 30 STUDIES IN PHYSIOLOGY. acid.^ Later, double and quadruple the quantity added, and observe the eflfect produced upon the plant. Experiment with different species of ferns and club mosses in tlie same manner. Observe in another series of experiments the elfeet of sunlight in modifying the influence of an excess of carbonic acid gas in the atmosphere. The measure of assimilatioe acticity is to be found either in the amount of pure oxj-gen evolved in assimihition, or in the amount of carbonic acid decomposed in it. 1. Determinations depending upon tjie amount of oxygen evolved : The gas which is given olf during assimilation, espe- cially by water plants, is never absolutely pure oxygen ; but since it contains so small a proportion of other matters under most circumstances which the student is likely to meet, the amount of it evolved may be taken safely as the approximate measure of assimilation. The method of measurement by count- ing bubbles emitted by water plants in water (see 814) is alwa^-s practicable and easy of execution. The evolved gf.s can be easily collected in any convenient in\erted receptacle. If the gas collected and measured is analyzed eudiometrically, as dir3cted in Bunsen's '' Gasometry," the determination leaves kittle to be desired. 2. Determinations depending upon the amount of carbonic acid decomposed. To the air contained in a glass vessel in- verted over mercury a known quantity of carbonic acid is added. The plant previously placed in the receptacle decomposes a part of this, and after a given time the amount decomposed is ascer- tained by measurement of the carbonic acid that remains. Effects of different gases upon assimilation. A few plants and two or three small Wardian cases, or, better, capacious bell- ja.rs, will answer for this study. Select only sound plants for examination, and be careful to liave those in one bell-jar as nearl3- as possible of the same size and strength as those in the others. Let tiie air in one of the jars be ordinar}' atmospheric air ; to that in the others add a known but small quantity of one of the fol- lowing gases ; namely, (1) common coal gas ; (2) sulphurous acid ; (3) chlorine. Compare the growth and vigor of the plants from time to time, and observe whetlier insolation makes any diflference in the appearance of the i)lants exposed to the gases mentioned. 1 In all cases where an additional amount of gas is introduced into a bell- jiir, allowancp must be made in some way for the possible increase of pressure. For the necessary correction in these cases, and for other details regarding the management of gases, consult Bnnsen's " Gasometry." RESPJ RATION. 31 XV'I. Rekpiiiation. The meiisure of this process is usually found in the amount of carbonic acid given off by plants. The methods of deter- mination of this amount are, although apparently simple, open to some objections ; but by the exercise of great care in the management of the simple appliances, their results are in gen- eral trustworthj^ The carbonic acid which is given off b}' the plant ma^- be measured in one of the two following ways: (1) A current of air freed from all its carbonic acid by means of wash-bottles con ■ taining potassic hydrate is allowed to pass into a receptacle in which are confined the plants to be examined. The air with- drawn from this receptacle passes slowl3' through Liebig's potash bulbs in which are held a known amount of potassic hydrate. At the conclusion of the observation the amount of carbonic acid which has been given off liy the plants and been taken up bj- the potassic hydrate in the bulbs can be accnrately determined. (2) The current of air which is withdrawn from the receptacle containing the plant is permitted to pass very slowly through a long slightly inclined tube in which is held a solution of pure baric hydrate. As the bubbles of gas pass through this liquid and give up their carbonic acid, thej- cause an abundant precipi- tation of baric carbonate in it. The second method, which is essentially that of Pettenkofer, yields unifprm results, and is in general to be preferred to the first. It is better applicable to ol)servations upon intramolecular respiration ; in which, as pointed out in 981, some gas hke nitrogen or hydrogen, wholly free from any trace of oxygen, is allowed to come in contact with plants or parts of plants, and the amount of carbonic acid given off is determined as in the former case. Interesting results are obtained by placing in the receptacle very young seedlings, or buds which have just begun to unfold. XVII. Growth. The measurement of growth. Growth can be satisfactorily measured in the three following ways, each of which is adapted to particular instances : — 1. Direct measurement. Determ.ine the place and rate of growth of young internodes of an}- rapidly developing plant, for instance Morning Glory, by marking the whole space of the internodes into equal intervals, and subsequently determining 32 STUDIES IN PHYSIOLOGY. the actual injrease in distance between any two or more lines. In all cases mark the part under examinatiou with good India- ink, making clear, narrow lines. To avoid any possible error caused by influence of lines marked only on one side, make lines on both sides of a part whenever possible. To measure the growth of leaves, use the method spoken of on page 156. 2. Measitrement hij a micrometer eye-j:iece. With the tube of the microscope kept perfectly horizontal, examine the position of a line of India-ink, upon a perianth leaf of Crocus, or upon the root-cap of Windsor bean. Observe the space which the image of the line appears to pass through in a given time, and refer this to the previously determined values of the spaces of the micrometer. 3. Measurement by an index, (a) On a simple arc. For this use the simple and admirable modification of Sachs's aux- anometer, devised by Bessej- (American Naturalist). {b) On a recording drum. A slender brass or steel shaft is attached to the hour-spindle of a cheap clock, and from the shaft is suspended firmly a stiff pasteboard drum of about the same size. This revolves with the spindle, and if well made is carried without any^ appreciable vibration. A piece of glazed paper of the size of the drum is moistened, and a little mucilage placed on one edge, so that when the paper is rolled around the drum, its edges can be firmly fastened together. Be careful to have the seam in the paper so placed as to avoid any catching of the needle index attached to the plant. When the paper on the drum is dry, it is smoked lightlj' and evenly over a smoky turpentine flame. The needle at the tip of the index is now placed against the smoked paper so as to press lightly upon it, and, as the drum revolves, leave a clean mark. When a suffi- ciently long record has been registered, the paper is carefully removed and dipped in (not brushed with) a solution of common rosin in alcohol, which upon drj-ing prevents any of the lamp- black IVom coming oflT. Two corrections are necessary with this simple apparatus : (1) for the cnrve of the descending needle at the end of the radius ; (2) for anj' changes in the position of the needle caused by the varying amount of moisture in the air. For recording temperature, it is possible to use a metallic thermometer with a long index, and have the two records side by side. It is well, however, to liave the needle for the ther- mometer give a different mark in order to prevent any subsequent confusion. MOVEMENTS OF PLANTS. 33 The proper methods of examining the formation of new cells in a simple case are indicated in the studies upon a stamen-hair of Tradescantia noted on page 380. XVIII. Movements op Plants. The student is advised to select some one plant in a vigorous condition and make a thorough examination of all the phenomena of movement which it presents. The plants named below are among the best for such an examination, and they can be made to grow even under rather unfavorable conditions, like those afforded by schoolrooms. Spontaneous movements. Desmodium gj'rans, the Morning Glory, or Hop, maj' be used. The first requires a high tem- perature and a fair amount of moisture in the air in order to exhibit its peculiar movements satisfactorily. Movements following shock. The Sensitive plant (Mimosa pudica) should be observed. It can be experimented upon with various kinds of irritants, both mechanical and chemical, at various temperatures, and under the influence of anaesthetics. For the experiments with aneesthetics only verj' young plants are suitable, and they cannot well be used afterwards for other investigations. In the case of all of the above plants note anj' changes which the leaves undergo during the day and at the approach of night. The details given in 1045 suffice to indicate the general method of exaggerating by means of slender glass threads the slow and slight movements of plants, and do not need fvirther treatment here. For observations with such threads, the following plants are very useful : seedlings of the Morning Glorj', clover, cress, cabbage, and sunflower. XIX. Tension of Tissues. Make sections of young internodes as directed in 1025, secur- ing in every case accurate measurements of all the parts, both before and after their separation. It wiU be well to examine in like manner a large number of young roots, stems, leaves, and parts of flowers, noting in all cases the age of the part examined. XX. Insectivokous Plants. In the study of these plants the student is advised to read carefuUj' Mr. Darwin's work on the subject, and verify, by means 34 STUDIES IN PHYSIOLOGY. of good specimens of Drosera rotundifolia, the facts there re- corded. Students are reminded that Mr. Darwin's observations were made witli the simplest appliances, and with a degree of care never excelled. For independent stud^' abundant material may be found in the common iSarraceuias of the North and South, in regard to which very much still remains to be learned. XXI. Ceoss-Feetilization. For this study, repeat the observations of Darwin as thes' are given in his work on Cross and Self Fertilization ; or if that is not at hand, as they are brieflj- stated in the abstract in the present volume, pages 448-450. XXII. Hybiudizing. With the precautions given on page 456 the student should be able to undertake experiments in hybridizing species of the following common genera, all of which lend themselves readily to this process : Nicotiana, Verbascum, Lilium, etc. Be care- ful to exclude foreign pollen in all cases. XXI II. The Eu'exisg of Fiiuits and Sheds. Good material for this studj' is afforded by the following plants : Solanum, Impatiens, Pyrus, Prunus, and Tecoma. XXIV. Gerjitnatiiik. Select sound seeds of some common plant, for instance beans or Indian corn, and test witli them the truth of the following statements: (1) Water is essential to germination. (2) Germi- nation cannot begin without access of free oxj-gon. (i) Seeds of the plants selected require the same temperature for the be- ginning of germination. (4) When the process of germination has once begun, light is necessary to any increase of the plant in dry substance (compare experiment Series 1, No. II.). (5) Car- bonic acid is constantly given off during germination. (C) In some cases carbonic acid will continue to be evolved even when no more oxygen is supplied (compare intramolecular respira- tion). (7) The temperature of germinating seeds is higher than that of the surrounding atmosphere (compare respiration). What is the optimum amount of water required for the speedy germination of the following seeds, — Windsor beans, peas, clover, squash, and sunflower? EFFECTS OF FROST. 35 What is the optimum amount of oxygen required? Wliat is the optimum temperature required ? Compare the precocity of unripe and ripe seeds of any plant. XXV. Effects of fkost. Wrap up a leaf of Begonia in thin ruhber-cloth, to protect it from moisture, and place it in a freezing mixture of powdered ice and salt. After an hour examine the tissues of the leaf with special reference to any mechanical injurj' which they may have sustained. Having completed this preliminary study, proceed to the examination of anj' well-developed seedlings, and note in every case (1) the effect produced upon the parts which have been quickly thawed ; (2) the effect where thawing has been allowed to go on very slowly. Freeze any strong seedlings and after a time thaw them slowly. Place them then under favorable conditions for growth, in order to ascertain whether their vitality has been destroj'ed. In cases where death of the part or plant ensues, does it appear to come from the freezing or from the thawing? 36 Table of measuUkS. Measures of Length. Inches. Meter . 39.37079 Millimeter .... 0.03937 Micro-m lliraeter {/j.} tl e unit of microscopic measurement . Measures of Capacity. 0.000039 Pints. Cubic Inches. | Liter . . . 1.761 61.02705 Cubie centimeter or m Uiter .00176 . . 0.06103 Measure of Weight Grains. Gram . 15.43235 Measures of Temperaturk. Centigi-ade, or Celsius. Fahrenheit. R6ainur. Centigrade, or Celsius. Fahrenheit R6amur. o o o o o o +100 + 212 +80 + 16 +60.8 +12.8 no 104 72 15 59 12 80 176 64 14 57.2 11.2 70 158 56 13 55.4 10.4 60 140 48 12 53.6 9.6 50 122 40. 11 51.8 8.8 49 120.2 39.2 10 50 8 48 118.4 38.4 9 48.2 7.2 47 116.6 37.6 8 46.4 6.4 46 114.8 36.8 7 44.6 5.6 46 113 36 6 42.8 4.8 44 111.2 35.2 5 41 4 43 109.4 34.4 4 39.2 3.2 42 107.6 33.6 3 37.4 2.4 41 105.8 32.8 2 35.6 1.6 40 104 32 +1 +33.8 +0.8 39 102.2 31.2 --32 38 100.4 30.4 —1 --30.2 —0.8 37 98.6 29.6 2 28.4 1.6 36 96.8 28.8 3 26.6 2.4 35 95 28 4 24.8 3.2 34 93.2 27.2 5 23 4 33 91.4 26.4 6 21.2 4.8 32 89.6 25.6 7 19.4 5.6 31 87.8 24.8 8 17.6 6.4 30 86 24 9 15.8 7.2 29 84.2 23.2 10 14 8 28 82,4 22.4 11 12.2 8.8 27 80.6 21.6 12 10.4 9.6 26 78.8 20.8 13 86 10.4 25 77 20 14 6.8 11.2 24 75.2 19.2 15 5. 12 23 73.4 18.4 16 3.2 12.8 22 71.6 17.6 17 1.4 13.6 21 69.8 16.8 18 —0.4 14.4 20 68 16 19 2.2 15.2 19 66.2 15.2 20 4 16 18 64.4 14.4 30 22 24 17 62.6 13.6 —40 —40 —32 '\! i5 -\\^\\\«4&&\N\\\^\\'«4*^\\Nci««.\\\\&-^^^ 'I