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 LARCH AND BUR OAK, SHOWING TWO TYPES OP' 
 MONOPODIAL BRANCHING. 
 
 (■Sr*/.8 7 .) 
 
PLANT LIFE 
 
 CONSIDERED WITH SPECIAL REFERENCE TO 
 FORM AND FUNCTION 
 
 BY 
 
 CHARLES REID BARNES 
 
 Professor of Plant Physiology in the University of Chicago 
 
 NEW YORK 
 
 HENRY HOLT & COMPANY 
 1898 
 
Copyright, 1898, 
 
 BY 
 
 HENRY HOLT & CO. 
 
 ROUBHT DKUHHiiNI) I'KINTHR, NKV 
 
PREFACE. 
 
 In recognition of the fact that the study of botany in the 
 past has been too much a study of books about plants, numer- 
 ous laboratory manuals have been published which make pos- 
 sible the study of plants themselves. Laboratory work has 
 now become well-nigh universal. With the strenuous insist- 
 ence that this method should be used in the secondary schools, 
 there has been a growing danger that such study would de- 
 generate into mere memory training, unless the relation of 
 the facts, often entirely isolated in the pupil's mind, were 
 clearly brought out. Since laboratory study soon came to 
 include the examination of the lower plants as well as seed 
 plants, and has now begun to include some experiments in 
 their physiology, the absence of an elementary account of 
 the form and functions of plants of all groups has made itself 
 felt. I am not aware that any book at present attempts to 
 meet this need. 
 
 To the proper teaching of botany in secondary schools 
 such a book is indispensable. However capable the teacher 
 may be to gather up the facts observed in the laboratory and 
 to relate them with others so as to produce a clear concep- 
 tion of plant life, he cannot wisely rely upon the lecture for 
 pupils of 13 to 18 years. They need the printed page, 
 which appeals to eye as well as ear, if the principles and facts 
 are to be firmly grasped. 
 
 iii 
 
IV PREFA CE. 
 
 Plant Life is an attempt to exhibit the variety and pro- 
 gressive complexity of the vegetative body; to discuss the 
 more important functions; to explain the unity of plan in 
 both the structure and action of the reproductive organs ; 
 and finally to give an outline of the more striking ways in 
 which plants adapt themselves to the world about them. I 
 have made an effort to treat these subjects so that, however 
 much the student may have still to learn, he will have little 
 to unlearn ; for eradication of false notions is the despair of 
 the college teacher of science. 
 
 This is not a book to be memorized and recited. If so used it 
 is abused. It aims to be intelligible to pupils 13 to 18 years 
 of age who are engaged in genuine laboratory study — not at 
 irregular hours, without supervision, in a school desk, or at 
 home, but in a suitable laboratory, with regular time (an 
 hour and a half daily if possible), under the direction of a 
 live teacher who has studied far more botany than he is 
 trying to teach. I am aware that such conditions are yet 
 unrealized in many schools ; but they may be gradually 
 reached. That Plant Life may prove useful in botanical 
 instruction even under the most unfavorable conditions, I 
 permit myself to hope rather than to expect. 
 
 This book may be used to supplement any laboratory guide 
 or the directions prepared by the teacher. For the sake of 
 teachers who may not wish to use two books, or who lack time 
 and facilities for preparing laboratory directions, I have out- 
 lined a course of study in Appendix I which can be carried 
 out with the equipment listed in Appendix III. A description 
 of the material needed and of suitable methods of preserving 
 it forms Appendix II. Each'teacher will, of course, need to 
 modify the directions to suit the material available. I have 
 always found it easier to prepare directions to fit the material 
 than to create the material to fit the directions. The "dem- 
 onstrations " of Appendix I air intended as suggestions to the 
 
rREFA CE. V 
 
 teacher of things which it is advisable to show to pupils under 
 the compound microscope, in case inadequate equipment, 
 lack of time, or difficulty of preparation forbid class study. 
 
 I have made the directions fullest in relation to cryptogams 
 and physiology because these fields are most unfamiliar to 
 teachers at present. Further directions for the study of seed 
 plants can readily be provided from the books listed in Ap- 
 pendix IV. 
 
 For laboratory study it is necessary to select certain illus- 
 trative types and observe their structure. In the text I have 
 not specifically discussed these plants, but have treated gen- 
 eral topics so as to correlate the facts gained by a study of 
 types with others which can be readily interpreted by means 
 of the experience in the laboratory. References from the 
 bare directions of Appendix I to the paragraphs and figures 
 of the text are abundant and are intended to aid the student 
 in the comprehension of the type under observation. It may 
 be objected that he is thus aided too much. But I believe 
 that in his first steps in laboratory training the student re- 
 quires a large amount of help, and that its results are more 
 often nullified by too little assistance than by too much. 
 
 In the text I have neither sought nor avoided the use of 
 technical terms. I have refrained from making the book a 
 mere illustrated glossary. Yet I see no advantage, even for 
 young students, in repeated circumlocution, for which a 
 single word might stand. Definitions of most of the tech- 
 nical terms used may be found by means of the index ; 
 others are defined in the standard dictionaries. The careful 
 teacher will insist upon a clear understanding of the meaning 
 of terms and the accurate use of language. 
 
 I have refrained from frequent citation of plants by name 
 as examples of facts stated, chiefly because beginners are 
 rarely familiar with any plants except the commonest domes- 
 ticated ones and a few forest or shade trees. 
 
VI PREFACE. 
 
 No apology is necessary for the exclusive use of the metric 
 system. If pupils lack familiarity with it, the actual handling 
 of metric measures and weights will soon remedy this. A 
 useful chart showing the units may be obtained of the Ameri- 
 can Metrological Society, 41 East Forty-ninth Street, New 
 York, for ten cents. 
 
 Very few of the illustrations are original. In the main they 
 have been selected from a wide range of standard works with 
 especial care to secure accuracy and clearness. Whenever 
 possible the source of the figure and its magnification have 
 been given. The attention of the teacher is invited to the 
 very full description which accompanies each figure. In 
 these explanations will be found much matter which is often 
 put into subordinate paragraphs in other books. I have ob- 
 served that students are prone merely to " look at " figures, 
 and rarely study them. I therefore suggest that real study of 
 the illustrations as supplementing the text be insisted upon. 
 Sections are apt to be puzzling to beginners unless they are 
 taught how to interpret them. This can be done by requir- 
 ing them to sketch on paper or blackboard imaginary sections 
 of common objects in different planes. Articles of regular 
 form, such as a pencil, book, slate, ink bottle, desk, etc., 
 may be ''sectioned," until from sketches of sections in three 
 planes at right angles the student can construct a mental 
 image of the object. 
 
 Although divided into four parts, it has not been possible 
 to keep the subject matter of each wholly distinct, since 
 morphology, physiology and ecology are so interrelated. In- 
 deed it has been thought best to combine the morphology 
 and physiology of the reproductive organs to form Part III, 
 rather than to divide it between two. The teacher will do 
 well to see that the pupil does not neglect the abundant cross 
 references. 
 
 While the whole book is simply a restatement of widely 
 
PREFACE. VI 1 
 
 known facts, for which I am mainly indebted to general 
 treatises, monographs and shorter papers, I am constrained 
 to acknowledge for Part IV my special indebtedness to 
 Warming's Lehrbuch der bkologischen Pflanzengeographie and 
 Ludwig's Lehrbuch der Pjlanzenbiologie. 
 
 C. R. B. 
 University of Chicago. 
 
CONTENTS. 
 
 Preface 
 
 PAGE 
 
 , iii 
 
 PART I: THE PLANT BODY. 
 
 Introduction : The unit of structure 
 Chapter I. Single-celled plants and colonies 
 II. Linear and superficial aggregates 
 
 III. The thallus of the higher alg^e . 
 
 IV. The fungus body of hyphal elements 
 V. Liverworts and mosses 
 
 VI. Fernworts and seed plants 
 VII. The root .... 
 VIII. The shoot .... 
 IX. The stem .... 
 
 X. The leaves 
 
 17 
 26 
 39 
 49 
 60 
 65 
 82 
 96 
 "7 
 
 PART II : PHYSIOLOGY. 
 
 Chapter XL Introduction : The unit of function 
 XII. The maintenance of bodily form 
 
 XIII. Nutrition 
 
 XIV. Growth 
 
 XV. The movements of plants 
 
 M3 
 
 147 
 151 
 178 
 
 18S 
 
 PART III: REPRODUCTION. 
 
 Chapter XVI. Introduction : Reproductive structures . 209 
 XVII. Vegetative reproduction . . . .211 
 
 XVIII. Sexual reproduction 268 
 
 ix 
 
CONTENTS. 
 
 PART IV : ECOLOGY. 
 
 PAGE 
 
 Chapter XIX. Forms of vegetation 30S 
 
 XX. Mesophytes 312 
 
 XXI. Xerophvtes and halophytes . . . 318 
 XXII. Hydrophytes 327 
 
 XXIII. Adaptations to other plants as supports 330 
 
 XXIV. Symbiosis 333 
 
 XXV. Animals as food, foes, or friends . . 342 
 
 XXVI. Protection and distribution of spores 
 
 and seeds 352 
 
 Appendix I. Directions for laboratory study . . . 369 
 II. Directions for collecting and preserving 
 
 material 401 
 
 III. Apparatus and reagents 409 
 
 IV. Reference books 413 
 
 V. Outline of classification .... 415 
 
 Index 4*9 
 
PLANT LIFE. 
 
 PART I: THE PLANT BODY. 
 
 INTRODUCTION. 
 
 1. Units of structure. — An examination of any plant by 
 proper methods reveals the fact that it is made up of one or 
 more units of structure. The unit of structure of a brick 
 wall is the individual brick. Each has a definite shape and 
 relation to others, upon which the form of the wall depends. 
 The unit of structure of a plant is called a cell. The cells 
 have each a definite form and relation to others, and upon 
 these two factors the form of the entire plant depends. 
 
 But between the plant and the brick wall there is this im- 
 portant difference. The bricks, after being perfectly formed, 
 were put together. The cells of the plant are produced where 
 they lie and gradually groiv to a mature form and size. The 
 bricks are originally disconnected ; the plant-cells are con- 
 nected by origin, and only as they become mature do they 
 separate, if at all. 
 
 2. The cell. — A plant-cell is a minute portion of living 
 matter, called protoplasm or plasma, generally surrounded by 
 a membrane, called the cell-wall (fig. i). If the brick in 
 the previous illustration be taken to represent the protoplasm, 
 the mortar may be considered as the cell-wall. * 
 
 * This illustration must lie carried no further than to show the relation 
 of position of these two parts of a cell. 
 
2 PLANT LIFE. 
 
 3. Protoplasm. — The protoplasm is the essential part of 
 the cell. It constructs the cell-wall. Rarely, if ever, is it 
 uniform throughout, but is differentiated into distinct mem- 
 bers, each having special work to do. In the most com- 
 pletely differentiated active cells the 
 greater part of the protoplasm con- 
 sists of a finely granular or nearly 
 transparent, colorless portion, called 
 cytoplasm. Embedded in the cyto- 
 plasm are the nucleus, centrospheres 
 (figs, i and 2), and plastids (figs. 
 3 to 8). 
 
 Fig. i.-a ceil (the megaspore) 4. Cytoplasm. — This is not a 
 ^anuiar'protopiasm^'^vvhich single substance, but a mixture of 
 L^tnuintnrfnuci:' several different substances, so in- 
 ce^,^T n, The y iVn: timately mixed and so unstable that 
 ^s n fhe th c e e.rwln pl ^th r t e h P os e e' it is not possible to analyze it. 
 el the M a a d inffie n d "oo diam!- Moreover, the nature and amount 
 
 After Gufgnard. Qf t j ]e components are probably 
 
 variable. Most of the substances belong to the class of com- 
 pounds called proteids, so that cytoplasm responds to proteid 
 tests and is often spoken of as a mixture of proteids. In 
 addition there are frequently present other organic substances 
 (such as amides, carbohydrates, fats, and enzymes), and 
 always small quantities of mineral matters which appear as 
 ash when cytoplasm is completely burned. The minute 
 granules embedded in the cytoplasm are of various nature. 
 Most of them are solid substances. 
 
 5. Vacuoles. — Scarcely distinguishable from these at first 
 are the minute cavities, called vacuoles, filled with dilute 
 watery solutions of many different substances, the cell- sap. 
 In all but the youngest cells more or fewer of these bubbles 
 of water may unite to form larger ones (fig. 7). These often 
 increase so as to occupy the greater part of the space within 
 
INTKODLCI/O.V. 3 
 
 the cell-wall, being separated only by plates of protoplasm. 
 When all vacuoles fuse into one the cytoplasm is crowded as 
 a thin layer against the wall, with sometimes strands of it 
 crossing the vacuole as the remnants of the plates at an 
 earlier stage (fig. 188). 
 
 6. Nucleus. — The nucleus varies much in shape. In cells 
 whose diameters are nearly equal, it is generally spherical 
 or ovoid, but in elongated cells it may become spindle- 
 shaped or cvlindric. It is surrounded by a very delicate 
 membrane, and is composed of two sorts of substances, one 
 of which can be readily stained by certain liquid dyes, while 
 the other usually remains uncolored (fig. 2). The nucleus 
 
 Fig. 2. — A part of the same cell as in fig. i, but older, with the nucleus beginning to 
 divide. The dark thread in A, separated into pieces in />. represents the chroma 
 tin of the nucleus deeply stained, the rest of the nuclear material being unstained. 
 
 a, centrospheres. Magnified f diam. — After Cuignard. 
 
 may divide into two, a regular succession of changes in the 
 arrangement of the materials composing it characterizing this 
 process, which is commonly followed by the formation of a 
 partition-wall separating the cell into two parts, each con- 
 taining one of the daughter-nuclei. 
 
4 PLANT LIFE. 
 
 7. Centrospheres. — The centrospheres are intimately re- 
 lated to the nucleus. They are two very minute spherical 
 bodies lying in contact with it (figs, i, 2). When the 
 nucleus is about to divide one centrosphere goes to each 
 pole (fig. 2, B), and the separation of the nuclear material 
 occurs near the nuclear equator. Just as this occurs the 
 centrospheres divide, forming a pair at each pole. Two 
 accompany each daughter-nucleus. Their purpose is not 
 yet fully understood. 
 
 •••28 
 
 Fig. 
 
 Fig. 
 
 Fig. 
 
 t, showing its 
 
 wall, and some 
 il-drop. Mag- 
 
 Fig. 3. — A cell from the interior of the leaf of the 
 inclusions of the cytoplasm, z, the nucleus; c, chloropla 
 nified about ioo diam —After Zimmermann. 
 
 Fig. 4. — A, chloroplasts from the skin of the petiole of ivy; B, from the inner leaf- 
 cells of morning-glory; C, from the same cells of Achyranthes. The shaded parts 
 are protoplasm in which are embedded starch-granules, j, and proteid crystalloids, 
 k. Magnified about iooo diam. — After Zimmermann. 
 
 Fig. 5.- — Leucoplasts from a young shoot of Canna. The shaded part is protoplasm, 
 in which are embedded starch-grains, s, and proteid crystalloids, k. Magnified 
 about 1000 diam. — After Schimper. 
 
 8. Plastids. — In most cells there are also other protoplas- 
 mic structures, the plastids. In young cells these are small, 
 rounded, colorless bodies. As the cell grows older they in- 
 crease in size and number. At maturity, in cells which lie 
 near the surface of green plants, they are commonly roundish 
 or biscuit-shaped, of spongy texture, and colored yellowish- 
 
IN TROD UC TION. 5 
 
 green by a substance known as chlorophyll. These are con- 
 sequently known as chloroplasts or chlorophyll-bodies (figs. 
 3, 4). In other cells, particularly those for the storage of 
 food, they may develop into smaller, denser, flattened or 
 roundish, uncolored bodies, called leucoplasls (figs. 5, 6, 7). 
 These may act either as starch-accumulators, or in case 
 
 Fig. 6. 
 
 Fig. 7. 
 
 Fig. 6.— Part of the cell-contents of an inner cell of white potato, z, nucleus; j, 
 starch-grains, each having been formed by a leucoplast, /, which is still attached to 
 one side of the grain; k, crystalloid. Magnified abont iooo diam. — After Zimmer- 
 mann. 
 
 Fig. 7.— Leucoplasts in place in a young cell of a leaf of vanilla. /, leucoplasts; z, 
 nucleus; e, an oil-former or elaioplast. The unshaded spaces surrounded by proto- 
 plasm are vacuoles. Magnified about 1000 diam. — After Wakker. 
 
 of need, in young cells, may even be converted into chloro- 
 plasts. In other cells, particularly in highly colored parts, 
 the plastids may become of most diverse form and size, and 
 colored red or yellow, whence they are called chromoplasts 
 or color-bodies (figs. 8, 9). 
 
 9. Wall. — The cell-wall is formed by the protoplasm. 
 In green plants when first formed it consists chiefly of cell- 
 ulose, with which, as it grows older, various other substances 
 may be mixed. Some of these, such as pectin, are present 
 even in the young wall, and may increase with age; others 
 
O PLANT LIFE. 
 
 are characteristic of special changes which the wall may 
 undergo. The most noticeable changes are four: (i) Some 
 cell- walls contain suberin or cutin, fat-like substances by the 
 presence of which water and gases are hindered from passing 
 
 Fig. 8. Fig. 9. 
 
 Fig. 8.— I, chromoplasts from flower-leaves of an orchid; II, from the root of carrot; 
 III, from the fruit of mountain-ash. Embedded in the protoplasmic body of the 
 chromoplast are sometimes proteid crystalloids, /, pigment-crystals, _/", or starch- 
 grains, j. Magnified about 1000 diam. — After Schimper. 
 
 Fig. 9. — Chromoplasts from the flesh-colored shoots of the horsetail, containing the 
 coloring matter in the form of granules embedded in colorless protoplasm. Mag- 
 nified 1400 diam. — After Zimmermann. 
 
 through. The cell-walls of bottle-cork are suberized, and 
 those in the skin of the apple are cutinized. (2) Some cell- 
 walls are lignified, as, for example, those of wood by reason of 
 
 Fig. io.— A part of a thin slice lengthwise through the centre of the stem of garden- 
 balsam. The cells and vessels are elongated and are here seen from the side, show- 
 ing the thickened lines on the side walls of v, v', v", v"\ v"", and v'"". Mag- 
 nified about 400 diam. — After Duchartre. 
 
 the presence of certain substances (vanillin, coniferin, etc.). 
 They allow the ready passage of water and gases. (3) Others 
 are so transformed that, in contact with water, they swell 
 enormously, forming a mucilage or gum. These swelling 
 
INTRODUCTION. 
 
 substances are produced by the alteration of the cellulose or 
 other constituents of the original wall. (4) An excessive 
 deposit of mineral matters in tin 
 wall is known as mineralization 
 Such walls may even retain their 
 form after all organic matter is 
 burned out, as in the skin of the 
 scouring rush or horsetail. 
 
 10. Growth of the cell-wall. — 
 As the cells become older the wall 
 may increase in thickness. It must 
 also increase in area as the cells 
 grow in size. The growth in area 
 is usually accomplished by putting 
 new particles between the older 
 ones. Growth in thickness is rarely F 
 uniform. When the wall grows 
 thicker except at certain spots, these 
 remain as pits or pores in the 
 thickening layers. When only cer- 
 tain spots or lines grow thicker, 
 
 the wall shows projecting spikes, bands, or threads, which 
 give it the appearance in figs. 10, n. 
 
 c 11. — Cells from a liverwort 
 showing thickened walls A, 
 half an elater; A', a part more 
 highly magnified; B, a cell from 
 the lower part of the thallus, 
 with reticulate thickenings 
 (shaded); C, D, rhizoids with 
 isolated branched thickenings. 
 Highly magnified. — After 
 Sachs. 
 
CHAPTER I. 
 
 SINGLE-CELLED PLANTS AND COLONIES. 
 
 In the lakes and pools, in ditches and slow streams, on 
 the surface of damp rocks and wood, may be found many 
 sorts of microscopic plants, whose entire body is merely a 
 single cell. 
 
 Blue-green algae. 
 
 11. Fission-algse. — The simplest forms of these, the fission- 
 algae, have the protoplasm only slightly differentiated. The 
 central part becomes the nucleus, while the whole of the 
 remaining protoplasm is colored by the chlorophyll and a 
 blue coloring matter called phycocvanin, so that in mass these 
 algae look bluish-green or even blackish. For this reason 
 they are called blue-green algae to distinguish them from those 
 in which only the yellow-green of chlorophyll is present. 
 
 12. Gelatinous colonies. — The cell-wall may be a thin 
 sheet of cellulose, but commonly it is 
 composed of several layers, of which 
 the outer are changed into mucilage. 
 This swells into a transparent jelly 
 when wet, either becoming homo- 
 geneous or showing distinct stratifica- 
 tion. When a number of such forms 
 grow in company (fig. 12), this 
 jelly-like material blends into a single 
 
 plants seems to be em- 
 
 Fig. 12— A blue-preen aljra 
 (Gl(roca/>sa<. Single indi- 
 viduals, A, and colonies 
 
 \S' E) r °a va r ous wf s associated 
 
 Magnified 300 diam. — After 
 
 Sachs - bedded. 
 
 13. Gelatinous filament-colonies. — In other cases, instead 
 of being associated only by the adhesion of the mucilaginous 
 portion of the cell-wall, the cells, still practically inde- 
 pendent the one of the other, remain connected by the 
 
SINGLE-CELLED PLANTS AND COLONIES. 
 
 firmer portions of the wall into rows, forming irregularly 
 coiled or serpentine filaments, which are embedded in a 
 profuse gelatinous material (fig. 13). The essential inde- 
 pendence of the individual cells, even though they remain 
 connected, is shown by the fact that such a chain may be 
 
 ) 8 
 
 tKf? 
 
 Fig. 13. — Nostoc. A. a gelatinous colony, irregularly lobed. Natural size. B, a 
 portion of a serpentine filament with five heterocysts (one at each end by which it 
 was separated from the rest of the cells composing the filament, and three inter- 
 mediate ones) and the jelly belonging to it. Magnified about 400 diam. — After 
 Thuret and Janczewski. 
 
 broken up into any number of pieces and each piece will 
 retain all its powers. Here and there in the chain there 
 occur cells unlike the rest (Ji, fig. 14), called heterocysts, 
 whose function seems to be to break the chain into pieces, 
 from the growth of which independent colonies may arise. 
 The association of considerable numbers of these plants in 
 colonies gives rise to masses of jelly which vary from the size 
 of a pin-head to 2-5 centimeters in diameter. They may be 
 found adhering to water-weeds as clear- or dirty-green 
 masses, or sometimes floating free (-/, fig. 13). 
 
 14. Filaments of loose organization. — Of very near kin 
 to these plants are the oscillarias, which have received this 
 name from the pendulum-like swinging of their tips (fig. 15). 
 In them the cells remain connected more extensively and 
 more firmly, so that each is disk-shaped, and the filament is 
 much less easily separated into its component cells. More- 
 
[O 
 
 PLANT LIFE. 
 
 over the gelatinous part of the wall is much less prominent, 
 so that often it is only seen with difficulty. Even though 
 invisible, it may be detected by the slippery feel of the 
 plants when rubbed gently between the fingers. 
 
 Fig. 15. 
 
 Fig. 14. — Part of a filament ol A nab ana. h, heterocyst; a-d, successive stages in 
 the division of a cell of the filament. Magnified 540 diam. — After Strasburger. 
 
 Fig. 15. — Oscillaria. a, the tip; b, a portion of the middle of a filament. Magnified 
 540 diam. — After Strasburger. 
 
 15. Feeding habits. — The feeding habits of the oscil- 
 larias are worth notice. They are found in permanent 
 puddles and ditches where organic matter is decaying. The 
 significance of this is that some of the ancestors of the green 
 oscillarias probably had offspring which, instead of living 
 upon food prepared by means of the green coloring matter 
 (see ^[ 230), learned to utilize the organic matter in the 
 water, at first perhaps no more than the present oscillarias 
 do ; but gradually they came to live exclusively upon it. 
 As a consequence, they lost their color and became incapable 
 of existing where organic food cannot be had. 
 
 Bacteria. 
 
 16. Fission-fungi. — Along with the loss of color and 
 change of habit went a diminution in size. They have thus 
 
SINGLE-CELLED PLANTS AND COLONIES. II 
 
 become so different that they are now known as fission-fungi, 
 and popularly as bacteria, bacilli, microbes, germs, etc. 
 These plants, probably the descendants of common ancestors 
 with the fission-algae, are the smallest known organisms 
 (figs. 1 6, 17). The diameter of many sorts does not 
 
 4?V 
 
 VSf\ 
 
 %|| 
 
 gC 
 
 © % 
 
 Fig. 16. — Various bacteria, a, Micrococcus, the " blood-portent" ; i, zoogloea form 
 of the same ; c. Bacterium aceti, the ferment of vinegar ; </, Sarcina, a harmless 
 parasite of the human intestine, a, /', magnified 300 diam.; c, 2000 diam.; </, 800 
 diam.— After Kerner. 
 
 exceed .0005 of a millimeter. That would allow 175 to 
 lie side by side upon the edge of the paper on which this 
 book is printed. In many the successive divisions are 
 parallel, in others they divide the cells in two planes, ami in 
 others again in three. The cells, when they divide, separate 
 readily, in most sorts never cohering at all, but living as 
 independent cells as soon as produced. Other sorts remain 
 connected into two- to several-celled chains, sheet, or packets 
 (a, d, fig. 16). A few have their cells firmly coherent into 
 
PLANT LIFE. 
 
 a filament. As the cells are either spherical or rod-like, the 
 shape of the colony depends upon the shape of the compo- 
 nent cells and the way in which they divide (see ^[ 24). 
 
 17. Gelatin. — In the fission-fungi, as in the fission-algae, 
 considerable masses of gelatinous material are produced, in 
 which the cells may lie embedded. The films, sometimes 
 smooth, sometimes wrinkled, which appear on an infusion of 
 organic matter, are formed by the masses of bacteria which 
 become embedded in the gelatinous material produced by 
 the alteration of their cell-walls {b, fig. 16). 
 
 18. Cilia. — Most species are furnished with locomotor 
 organs consisting of fine threads of cytoplasm protruded 
 through the wall, which, by their sudden contraction on one 
 side, lash about like whips, and propel the cell by jerky, 
 darting motions through the fluid in which it swims. These 
 lashes, called cilia, may be single at the ends of the cell 
 (C, fig. 17), or many at ends or sides (A, fig. 17), or the 
 
 It * \\ 
 
 
 
 Fig. 17. — Bacteria stained to show cilia. A, cilia tufted at one end; />', cilia irregu- 
 larly distributed over body; C, cilium single at one or both ends. B. the bacillus 
 of typhoid fever; C, the bacillus of Asiatic cholera. Magnified 775 diam.— After 
 Migula. 
 
 whole cell may be covered with them like hairs (B, fig. 17). 
 They may be withdrawn or drop off when the plant comes 
 to rest, as when they form the scums previously mentioned. 
 
 These plants are most interesting on account of their 
 economic relation to health and disease, decay, fermentation, 
 etc., which cannot be discussed here.* 
 
 * For further information on these plants, see Frank/and ; Our 
 Secret Friends and Foes ; Prudden : Story of the Bacteria, Dust and 
 
SINGLE-CELLED PLANTS AND COLONIES. 
 
 13 
 
 Yellow-green algae. 
 19. Single-celled plants with chloroplasts.— Among the 
 single-celled green plants, one of the most common groups 
 
 Fig. 18. — Pleurococcus viridis. A, a single individual; B, a colony shortly after 
 division; C, the same after separation. Magnified 540 diam. — After Strasburger. 
 
 is that represented by fig. 18, which shows a representative 
 of an extensive series in which the vegetative body consists 
 of a single cell with its wall, cyto- 
 plasm, nucleus, and a few relatively 
 large chloroplasts. In this greater 
 specialization of the protoplasm, these 
 plants show the only ■ advance upon 
 the blue -green algae. The wall in 
 such as this Pleurococcus is almost 
 uniform and quite thin. 
 
 20. Colonies. — The cells are fre- 
 quently associated in 
 bedded in jelly or not. The most 
 striking and elaborate of these colo- 
 nies is formed by Volvox (fig. 19). 
 
 In this plant the colony is a hollow 
 sphere, often large enough to be seen 
 by the naked eye as a minute green ball, composed of thou- 
 sands of individuals, embedded in a common jelly, arranged 
 in a single layer at the surface. Each is connected with its 
 immediate neighbors by strands of protoplasm, and two 
 
 its Dangers, Drinking-water and Ice Supplies ; Russell: I 'airy Bacteri- 
 ology; Frankel (tr. by Linsley) : Bacteriology (medical). 
 
 1 • Fig. iq. — Volvox. 
 
 colonies, em- - ni , individuals 
 
 olony. 
 
 repre- 
 sented by the minute circles, 
 between which the protoplas- 
 mic strands form a network. 
 The large balls in the interior 
 are daughter-colonirs to be 
 set free upon the rupture and 
 death of the mother-colony. 
 Magnified about 45 diam. — 
 From Bessey. 
 
U 
 
 PLANT LIFE. 
 
 cilia are protruded into the water outside. The lashing of 
 these rolls the whole colony about. Each vegetative in- 
 dividual is entirely like the others, but those connected 
 with reproduction become specialized. 
 
 Diatoms and desmids. 
 21. Shelled plants. — Other one-celled plants constitute a 
 group known as diatoms, found in both fresh and salt waters, 
 a b c d 
 
 Fig. 20. — Various diatoms, a, Synedra ; 6, Pleurosigma : c, d, GrammatofiAora, 
 side and top views ; c. colony of Gomfihonema, with branched stalks attached to an 
 alga;y, g, single cells of same, more magnified, top and side views; A, colony of 
 Diatoma, ihe cells connected into a zigzag band ; t, k, colony and individuals (top 
 and side views) of Fragillaria : /, «/, >i, Cocconema. In m the pair is surrounded 
 by jelly preliminary to the escape of the protoplasm and the formation of two new 
 cells (auxosporesi which has been completed in «.— After Kerner. 
 
 either attached or free-swimming (figs. 20, 21). The dia- 
 toms are very various in form, and present two different 
 aspects. When seen from the side they are generally elon- 
 gated-rectangular. When looked at from above they are 
 short-cylindric, disk -shaped, boat -shaped, or variously curved 
 
S1XGLE-CELLED PLANTS AND COLONIES. 15 
 
 or angular. They are peculiar in having the cell-wall so im- 
 pregnated with silica that scarcely any organic matter is left. 
 Indeed the plants may be heated to a red heat and boiled in 
 acid without destroying the form and markings of the cell- 
 wall, so completely has it become silicified. To permit 
 growth this rigid cell-wall is constructed in two pieces which 
 fit together like the two parts of a pill-box (fig. 21). Each 
 of these pieces, or valves, is sculptured into regular patterns 
 in lines and dots, which are often so excessively minute or 
 close together as to be barely visible with the highest powers 
 of the microscope (b> fig. 20). Seen in mass, as they may 
 often be on the sides of a glass aquarium, living diatoms 
 appear yellowish-brown. The chloroplasts, which are some- 
 times single and always few, contain a brownish pigment 
 (dia/omin) in addition to the green chlorophyll. 
 
 Fig. 2i. — A single diatom (Navicula amphirhynchus). A } top view ; />, side view, 
 showing overlapping of the valves. The parts shaded by lines are the chloroplasts; 
 the dotted part the protoplasm, with nucleus about the center of cell. Magnified 
 750 diam. — After Pfitzer. 
 
 It is not uncommon for the diatoms to form colonies by 
 the adhesion of several or many individuals by means of 
 gelatinous cell-walls. These colonies are ribbon-like, or zig- 
 zag chains, or even branched filaments (//, i, fig. 20). 
 Other sorts may be attached singly or in clusters by a gelati- 
 nous stalk (e, fig. 20). In all cases the jelly, like the rest 
 of the cell-wall, is a product of the protoplasm. The slow 
 
[6 
 
 PLANT LIFE. 
 
 gliding movements of some free diatoms are due to the pro- 
 trusion of strands of cytoplasm through slits in the valves. 
 
 22. The desmids. — These form another group of one- 
 celled green alga;. They have neither the brownish color 
 nor siliceous wall characteristic of diatoms, but are bright 
 green cells of remarkably diverse and often beautiful forms. 
 As a rule the cell is flattened and is divided almost into two 
 by a deep constriction near the middle (a, b, c, e, fig. 22). 
 
 Fig. 22. — Various desmids. a, Micrasterias ; 6, Cosmarium ; c, Xanthidium ; 
 d, Closterium ; f, Staurastrum ; J, Aptogonum. Magnified about 200 diam. 
 — After Kerncr. 
 
 Often the body of the cell is covered with warts or spine-like 
 projections (b, c, fig. 22), or is prolonged into horn-like or 
 hair-like lobes. These plants also frequently cohere into 
 colonies (_/", fig. 22). In that case tooth-like projections of 
 the cell-wall may interlock. 
 
CHAPTER II. 
 
 LINEAR AND SUPERFICIAL AGGREGATES. 
 
 Obviously some of the plants mentioned in the last chapter, 
 such as the oscillarias, are colonies of cells well on the way 
 to complete union into coherent filaments whose elements are 
 attached to each other by considerable areas of the cell-wall. 
 In order clearly to understand this condition, we must con- 
 sider the mode of origin of the individual cells composing 
 the row. 
 
 23. Fission. — Under conditions unknown to us, in the 
 course of its growth a cell may divide by a process known 
 
 Fig. 22A. — A, one of the final stages in cell-division. The daughter-nuclei are still 
 connected by kinoplasmic filaments, and across the equatorial plane particles of new 
 cell-wall material are formed. A', the completion of cell-division; the daughter- 
 nuclei have rounded off and the new wall is like the lateral walls. Magnified 880 
 diam. — After Strasburger. 
 
 Fig 22B.— Three stages of division in the same cell of an orchid (£pipactis 
 palustris). The cell is occupied in great part by vacuoles, [n this case the new 
 wall forms first on one side between tin- nuclei (.! ), which gradually travel across 
 
 to the opposite side (A), the wall extending until it is complete (O. Magnified 
 about 380 diam. — After Treub. 
 
 17 
 
1 8 PLANT LIFE. 
 
 as fission. The material of the nucleus passes through a 
 complex series of changes and separates into two parts. In a 
 plane between these daughter-nuclei particles are deposited 
 to form a cell- wall (A, fig. 22A). The formation of the 
 partition-wall may occur simultaneously in all parts, or it may 
 be formed on one side first and the nuclei move across the 
 cell until it joins the lateral walls (fig. 22B). In this way an 
 isolated unicellular plant of Pleurococcus (A, fig. 18) may 
 divide into two cells so that it consists of two hemispherical 
 cells, each capable of independent growth (fig. 23, A). 
 After a time these cells may separate from each other by the 
 cracking of the original wall at the line of juncture with the 
 new partition and the cleaving of this partition parallel to its 
 surfaces into two layers, one of which covers a portion of 
 each of the thus disconnected cells (fig. 18, C). If this 
 process of division and separation goes on, the result will be 
 the production of a number of independent cells more or less 
 closely associated but not connected. 
 
 24. Cell-rows, surfaces, and masses. — In many cases, 
 however, a second division occurs in one or both cells before 
 
 Fig. 23.— Diagrams of cell division. A, division of a spherical cell into two hemi- 
 spherical cells, a, b, by the wall i. />', the same after further division in planes 2, 
 2, 3, parallel to 1. a has divided by wall 2 into a' and another cell which has again 
 divided by wall 3 into a", a", b has divided into i', b' , the inner of which has 
 elongated preparatory to a division into b", b" , as by wall 3. C, fig. A after a 
 second division, by wall 2, at right angles to 1. 
 
 separation; and sometimes even a third division takes place. 
 It is evident that the position of the later partitions deter- 
 mines the form of this temporary aggregate of cells, (a) If 
 each of the two divides in a plane parallel to the first parti- 
 
LINEAR AND SUPERFICIAL AGGREGATES. 1 9 
 
 tion, a roiv of four cells will result; the two inner cells 
 would be disks or short cylinders, while the two outer would 
 be hemispheres (fig. 23, B). (b) But if (as is actually the 
 case in Pleurococcus, B, fig. 18) the new partitions are at 
 right angles with the first, the result is a cluster of four cells, 
 each of which is a quarter of a sphere (fig. 23, C). 
 
 Should a third division occur, it is conceivable that the 
 new septa might be placed parallel to those already formed, 
 in case a ; or parallel to one set and at right angles with 
 the other, in case b ; or at right angles to both, in case c. 
 In the first instance there would be formed a row, or filament, 
 of eight cells; in the second, a sheet of eight cells; or, in the 
 third, a mass of eight cells. This exhausts the possibilities in 
 the position of successive partitions. If other divisions 
 occur, they will necessarily be more or less nearly parallel to 
 some one of the first three sets.* 
 
 The structures resulting from cell-division where the cells 
 remain united are conveniently designated as follows: (1) 
 cell-rows, filaments, or linear aggregates, arising by division 
 in one plane; (2) cell-surfaces, or superficial aggregates, 
 arising by division in two planes; (3) cell-masses, or solid 
 aggregates, arising by division in three planes. 
 
 It is manifest that there are likely to be all degrees of union 
 remaining between the cells of linear and superficial aggre- 
 gates, and that the extent and firmness of such union will 
 depend largely upon the character of the wall. As in every 
 other case, the artificial distinction between cell-colonies and 
 cell -aggregates is bridged by all manner of intermediate 
 forms. 
 
 Filamentous algae. 
 
 There is a large number of plants in which the vegetative 
 body throughout life has the form of a filament. The green 
 *The formation of partitions at angles other than 90 or l8o° to pre- 
 ceding ones would not affect the genera] result, luu would only render 
 the form of the product, as well as of the individual cells, less regular. 
 
20 
 
 PLANT LIFE. 
 
 plants of this sort live almost entirely in water or in wet 
 places, and may be conveniently designated as the filamentous 
 algce. 
 
 25. Spirogyra, etc. — Among these none are more beautiful 
 or interesting than the filamentous Conjugate, represented in 
 
 Fig. 26. 
 
 Fig. 24. — A cell from filament of Sfirogyr-a. 
 
 ch, chloroplast (there are three in this Veil); 
 
 /, pyrenoids ; k, nucleus. Magnified 200 
 
 diam. — After Straslmrgcr. 
 Kig. 25. — A cell from filament of Zygnema, 
 
 showing two stellate chloroplasts, in each of 
 
 which is a pyrenoid, with the nucleus between 
 
 them. Cytoplasm poorly shown. Magnified 
 
 550 diam. — After Sachs. 
 Fig. 26. — Two cells from filament of Zygonema, 
 
 showing the gelatinous sheath greatly swollen. 
 
 Magnified 245 diam. — After Klebs. 
 
 our waters by the genera, Spirogyra, Zygnema, Mesocarpus, 
 and some others.* They may be readily recognized, during 
 their vegetative period, by their unbranched filaments, bright 
 
 *To the Conjugate also belong tbe single-celled desraids already 
 described. 
 
LINEAR AND SUPERFICIAL AGGREGATES- 21 
 
 green color, and slippery " feel ' ' between the fingers.* Under 
 the microscope, they are at once distinguished from other 
 filamentous algse by the shape of their 
 chloroplasts. In Spirogyra these form 
 one or more fiattish, spirally wound rib- 
 bons, notched on the edges, and embedded 
 in the protoplasm near the cell-wall (ch, 
 fig. 24). In Zygnema there are generally 
 two irregularly star-shaped chloroplasts 
 (figs. 25, 26) ; while in Mesocarpus a 
 single flat, plate-like chloroplast, nearly 
 as wide as the cell, traverses its center 
 (ng- 27). f 
 
 Embedded in the chloroplasts of these 
 and other algaj are usually seen one or 
 more angular, colorless bodies, often sur- 
 rounded by a jacket of starch. These are 
 crystals of reserve proteid, known aspyre- 
 noids (/>, figs. 24, 27). Their size depends 
 upon the amount of reserve food possessed 
 by .the plant. 
 
 In these plants there is little or no dif- 
 ference between the parts of the filaments. 
 If broken into two, each part may continue 
 growing with no damage to any part 
 except the cells which were ruptured in 
 severing the plant. 
 
 26. Ulothrix, etc. — But other filamentous alga? show a 
 distinction between base and apex. In Ulothrix (fig. 301) 
 
 * This slipperiness is due to the gelatinous outer part of the cell-wall 
 (fig. 26), which is only visihle after special treatment or on examining the 
 filaments in a thin mechanical solution of Chinese ink. 
 
 f See also Ulothrix (tig. ?oi), which has in each cell a single chloro- 
 plast in the form of a thick ring. 
 
 ig. 27.— A cell from fila- 
 ment of Mesocarpus. 
 The darker body nearly 
 filling cell is the chloro- 
 plasl (lace view) in 
 which are pyrenoids, /, 
 and tannin vesicles, g. 
 1 f seen from a direction 
 at right angles it would 
 appear as a narrow 
 stripe in the center of 
 the cell, z, the nucleus. 
 Magnified about 200 
 diam.— After Zimmer- 
 
22 
 
 PLANT LIFE. 
 
 the basal cell is elongated and pointed, and is colorless, 
 because it is not furnished with chloroplasts like the others. 
 By this pointed cell the plant is loosely attached, at least 
 when young, to the substratum, while the green portion 
 waves freely in the water. Thus arises a distinction into two 
 parts, viz., the rhizoid and the thallus. 
 
 In Cladophora, Vaucheria, and their allies, the plants are 
 generally attached by a well-developed rhizoid-region, which 
 is often branched {w, fig. 28), as is also the thallus. In 
 
 iture 
 
 Fig. 28. — A young plant of I'aucheria, developing from the spore. A, 
 
 :int further develop 
 ch it attaches itsel 
 
 next the wall on all sides 
 
 spore ; B, the same after germination has begun ; (', plant further developed from 
 
 hich it attaches itself to the 
 
 spore, s/>, with growing apex, j, and rhizoid, iv, by 
 mud. The chloroplasts are numerous and close togetl 
 Magnified 28 diam.— After Sachs. 
 
 contrast with the preceding, therefore, localization of grmvth, 
 producing branching, may be observed. 
 
 27. Branching. — A branch begins by the growth in area 
 of a limited portion of the cell-wall. The pressure of the 
 contained protoplasm upon the wall causes it to bulge out- 
 ward at this point, and the convexity gradually increases as 
 the region grows until the swelling becomes an outgrowth, 
 whose further lengthening constitutes a branch similar to the 
 main filament. Growth in length may be limited to the tip 
 of the filament, or to a narrow zone including one or more 
 cells, or it may occur indifferently in any part. 
 
 28. Coenocytes. — Many algse, while externally like others, 
 which are divided into true cells, have not the units of 
 
LI X EAR AND SUPERFICIAL AGGREGATES. 2$ 
 
 structure separated by cell-walls. In Vaucheria, for example, 
 the whole of the vegetative body forms a single chamber, 
 in which lies the united protoplasm, corre- 
 sponding to many cells, as shown by the 
 numerous nuclei which are distributed through 
 it. The external walls of the cells are formed, 
 but, when the nuclei divide as growth proceeds, 
 the protoplasm does not divide, and the septa 
 or partition- walls are not formed. Such an un- 
 septate company of cells is called a ccenocyle. 
 
 In the cladophoras (fig. 29) some of the 
 normal divisions are complete, while others 
 are only nuclear divisions. Consequently the 
 cladophoras seem to be a filament of true 
 cells, but in reality each apparent cell is a 
 ccenocyte, as shown by the several nuclei in 
 each (fig. 30). 
 
 29. External segmentation. — A plant 
 body of this construction may attain con- 
 siderable size and complexity, as in Caalerpa 
 (fig. 31 ) and Acetabularia (fig. 32),* even to 
 mimicking, upon a small scale, the form of 
 leafy plants. In such cases the external walls 
 become considerably thickened, and across V,G a 9— a single 
 
 J plant of Clado- 
 
 the protoplasm and its large vacuoles, from Mora, showing 
 
 profuse monopo- 
 
 one side of the chamber to the other, run <iial branching. 
 
 Natural size. — 
 
 irregular bars of cellulose which act as braces AfUr Hauck. 
 to prevent the collapse of the outer walls (fig. ^^). 
 
 In Caulerpa, particularly, a high degree of development 
 as to external form is reached (fig. 31 ). There is a stem- 
 like axis, v-s, creeping in the mud, which bears green leaf- 
 like branches, b, on one side and clusters of colorless root- 
 
 Note carefully the scale of the figures. 
 
24 
 
 PLANT LIFE. 
 
 Fig. 31. 
 Fig. 30. — One ccenocyte from a branch of Cladophora, shi 
 
 chloroplasts ; /;, pyrenoids ; a, starch-grains; «, nuclei. 
 
 After Strasburger. 
 Fig. 31 — Part of a plant of Caulerpa. See text, r 29. Two-thirds natural size. 
 
 —After Sachs. 
 
 i-ing fifteen nuclei, ch. 
 Magnified 270 diam. — 
 
 Fig. 32. — Acetabular ia. A, an entire plant, natural size —After Woronin. A, dia- 
 grammatic longitudinal sec linn through the upper end of the stalk and the um- 
 brella-like circle of crowded branches which grow together ; «, scars left by fall of 
 an earlier whorl of short branches ; r, w, rudimentary branches ; C, the base of 
 stalk showing rhizoids for attachment, _/", and for storage, b. Magnified 20 diam. — 
 After De Bary and Strasburger. 
 
LINEAR AND SUPERFICIAL AGGREGATES. 2$ 
 
 a I >ase 
 shable, 
 
 like branches, w, on the other. Not only are 
 
 (posterior end) and an apex (anterior end) distingu 
 
 but the plant shows a difference between 
 
 an upper (dorsal) and under (ventral) 
 
 side, the leaf-like thallus lobes arising 
 
 from the dorsal side, while rhizoids 
 
 spring from the ventral side. 
 
 30. The thallus. — To the loose 
 
 aggregation Of Single Cells into Colonies Fig. 33. - Transverse section 
 
 c j c . - ., ... of axis of Caulerpa, show- 
 
 Ot definite form, as well as tO the body ing cross-bars to stiffen wall. 
 
 r lii- • ■ • Magnified about 25 diam. — 
 
 formed by their more intimate union After Murray. 
 in the linear and superficial aggregates just described, the 
 name thallus is applied. The term is most frequently applied 
 to those more complicated forms which constitute the vege- 
 tative bodies of the higher algai, which are now to be 
 described. 
 
CHAPTER III. 
 
 THE THALLUS OF THE HIGHER ALG^E. 
 
 31. From linear to solid aggregates. — From the fila- 
 mentous algae, whose body is a linear aggregate of cells, it is 
 but a step to those forms whose body is a superficial aggre- 
 gate. When JMonostroma grows from the single cell as which 
 it begins life, the cell-divisions, instead of occurring succes- 
 sively in parallel planes, are made in two planes at right 
 angles to each other. The result is a single sheet of cells 
 forming a leaf-like thallus attached to stones or other algae. 
 The broader forms are sometimes 20-25 cm - w hlc. 
 
 Ulva, a near relative, develops in much the same way, 
 but at least one series of divisions occurs in a third plane, at 
 right angles to the other two, so 
 that the body of the sea-lettuce con- 
 sists of two layers of cells. As 
 fig. 34 shows, it is very clearly dif- 
 ferentiated into rhizoid and thallus. 
 If two such layers separate from 
 each other, as they do in Entero- 
 morpha, a hollow, sac -like body is 
 formed. 
 
 So, from the linear aggregates, 
 we pass through superficial to solid 
 aggregates of a broadly extended 
 form. 
 
 The transition from linear to solid aggregates of slender 
 
 26 
 
 Fig. 34. — A small plant of Ulva 
 lactut a. the sea lettuce, show- 
 ing thallus, and rhiz..id for 
 attaching it to rocks. Natural 
 size. — From Bessey. 
 
THE THALLUS OF THE HIGHER ALGSE. 2J 
 
 form may be understood by comparing with one of the fila- 
 mentous algas a member of an isolated order of green fresh- 
 water algre, the CharacecB. 
 
 Characeae. 
 
 32. The order. — These plants constitute an outlying group 
 of considerable antiquity, having no near relatives living, yet 
 showing in the vegetative body some structural resemblance 
 to the filamentous algre, while, as a whole, their external 
 form imitates quite closely that of the higher plants (figs. 
 35, 36). The species of Chara and Nitella (the two genera 
 which make up the bulk of this order) are found in almost 
 every temperate region, growing in dense masses submerged 
 and rooting in the mud in quiet waters. They reach a height 
 of 10-75 cm - 
 
 33. External form. — The plants agree in having a central 
 axis, at certain points of which * arise lateral outgrowths of 
 two kinds. One kind forms a circle of branches, nearly like 
 the main axis, except that their growth is limited. These 
 themselves bear branches of simpler structure. The primary 
 whorled branches are the so-called " leaves," and the second- 
 ary ones which these bear are the so-called " leaflets." 
 
 Just above one of the "leaves" in each whorl is pro- 
 duced a branch precisely like the main axis, which has, like 
 it, unlimited growth. 
 
 34. The main axis. — In Nitella the axis consists of alter- 
 nately long and short cells, a very short cell occurring at each 
 point (" node") where branching occurs. The long cell 
 extends from one " node " to another. This " internodal" 
 
 * Commonly called nodes, and the intervals internodes. These terms, 
 imposed from analogies with the seed-plants, are entirely misleading from 
 a morphological point of view, as are also the names " leaves " and 
 " leaflets," applied to certain divisions of the axis, hut they have heroine 
 so fixed that it is difficult to avoid their use. 
 
28 
 
 PLANT LIFE. 
 
 F,G - 35.— Upper part of a Dlani .,{ ri v. 
 
 Krou-.h (''leaves";, and a, li;^, 1,1 '/''.' ;;;:; ] , s ':'. w . l,1 < "honied branches of limited 
 lowest being cut off. The small |„ ( |j, ' In ' ™ ncl,, ' s .." f unlimited growth, the 
 organs. Natural sire -After wtle C ' eaVes are ,eafl «* " and sex- 
 
THE THALLUS OF THE HIGHER ALGM. 2Cj 
 
 cell is, therefore, of an extraordinary length, as well as of 
 large diameter. 
 
 Fig. 36. — Upper part of a plant of Nitella. Natural 
 
30 
 
 PLANT LIFE. 
 
 35. Cortex. — Nitella and Chara are much alike, except 
 that in Chara the main axis and all its brandies are com posed 
 of a row of large cells, surrounded by a jacket of smaller ones 
 (fig. 37). The walls of these outer cells are often much 
 thickened, and incrusted with salts of lime to such an cxtmt 
 as to render the axis very brittle. Around the main axis the 
 cell-jacket is of much complexity ; it becomes more simple 
 
 ■<>x 
 
 Fig. 37. 
 
 Fig. 38. 
 
 Fig. 37.— Transverse section of the axis of Chara. a, internodal cell; b, cortical cells 
 Magnified about 30 diam. — From a drawing by C. E. Allen. 
 
 Fig. 38. — Longitudinal section of apex of axis of Chara. x, apical cell. The seg- 
 ment next below will divide into a nodal and an internodal cell ; the next one has 
 already divided and the nodal half has again divided into two internal and several 
 external (only •.; show) nodal cells. <-, </, internodal cells ; between them a node pro- 
 ducing the branches (" leaves ") e and/; and the cortical branches a, a. 6, a similar 
 branch growing up from node below, only its tip showing. Magnilied 330 diam. — 
 After Sai hs. 
 
 upon the whorled branches, and is wanting upon the ultimate 
 divisions. 
 
 While a cross-section of the axis shows a complete union 
 between the walls of the cortical cells (b, fig. 37) and the 
 central one (a, fig. 37), a study of their development shows 
 that they are originally branches of the outer cells at each 
 node, which likewise produce the circle of "leaves." The 
 
THE THALLUS OF THE HIGHER ALGM. 3 1 
 
 branches from the node above grow downward and others 
 from the node below grow upward until they meet and inter- 
 lock about the middle of the internode (fig. 38). Thus, the 
 cortical cells are not produced by division from the large 
 central cell which they cover and stiffen, but simply grow over 
 it and become united with it at a very early age, increasing 
 with its growth and undergoing division at the same time, so 
 that each cortical branch becomes multicellular. 
 
 36. Apical cell. — The axis and all its branches, in both 
 genera, are produced by the growth of a single apical cell of 
 hemispherical form (x, fig. 38). The segments, successively 
 cut off by partition-walls from its base, each divide a second 
 time. One of the cells so produced increases rapidly in size, 
 and becomes the internodal cell, while the other, by succes- 
 sive divisions and differentiation, forms the node and its ap- 
 pendages. In those branches which show unlimited growth 
 the apical cell retains its hemispherical form until death ; but 
 in the divisions with limited growth ("leaves") it becomes 
 pointed and ceases to cut off segments from the base. 
 
 37. Rhizoids. — -The structures by which the Characeos are 
 held in place are adapted to penetrate the soft mud of the 
 ponds and lakes in which they grow. From the nodes near 
 the base of the axis arise numerous colorless rhizoids, often 
 of considerable strength through thickening of the cell-walls. 
 
 The thallus shows decided increase in specialization of 
 members. This is accomplished, however, with a minimum 
 of differentiation in the cells of which the body is composed. 
 
 Polysiphonia. 
 
 In the marine alga? a still higher specialization of members 
 is reached. One of the red seaweeds may be used to show 
 the gradual advance in complexity. 
 
 38. External form. — The body oi Polysiphonia, a branch- 
 ing alga (fig. 39) which grows in abundance upon rocky 
 
32 
 
 PLANT LIFE. 
 
 seacoasts, is not divided into nodes and internodes, and the 
 branches are differently arranged from those of Chara. The 
 ^ axis is made up in its larger parts of five or 
 
 more rows of cells, the central or axial row 
 being surrounded by a jacket of at least four 
 > others (fig. 40). But these originate by 
 f i division from the central one, and are not, as 
 ' $ in Chara, merely adherent to it. It is, how- 
 Yf ever, only in the larger parts of the axis that 
 
 Fig 
 
 Fig. 39.— An entire plant of Polysiphonia, showing mode of branching. Natural 
 
 size. — After Kutzing. (See fig. 229.) 
 Fig. 40. — Transverse section of one of the branches of Polysiphonia, showing a 
 
 minute central cell with four large and four small cells surrounding it. Magnified 
 
 about 50 diam. — From a drawing by Mr. Grant Smith. 
 Fig. 41. — Apex of a branch of Polysiphonia which has nearly ceased growing. 
 
 Magnified about 100 diam. — From a drawing by Miss Rowan. 
 
 this structure appears ; at the tips even of the main axis the 
 body is a linear aggregate (fig. 41). Polysiphonia, there- 
 fore, may be looked upon as one of the simplest forms of a 
 solid aggregate. 
 
 39. Apical cell. — As in Chara, growth in length is quite 
 definitely localized, because it is the elongated terminal cell 
 of either the main or secondary axes (fig. 41) which pro- 
 duces, by division near its base, the new cells whose subse- 
 quent enlargement and division give rise to the axis. In 
 some red algae the chambers are not cells but ccenocytes, as 
 shown by the several nuclei. 
 
 40. Color. — -In this plant, as in very many of the marine 
 
THE THALLUS OF THE HIGHER ALGM. 
 
 33 
 
 alga;, there exists, in addition to the green of the chloro- 
 plasts, a special coloring matter, called phycoerythrin. To 
 the naked eye, this color overpowers the green and gives the 
 
 Fig. 42. — Upper part of a plant of Fucus Tesieulosus. r, midrib of thallus ; /, 
 bladders; s, swollen tips covered by numerous elevations, in each of which is a pit 
 (conceptacle) which contains many sex-organs. Two thirds natural size. — After 
 
 Luerssen. 
 
 plant a pink tinge. In other red algai it is often present in 
 greater quantity and variety of hue, so that brilliant reds and 
 
54 
 
 PLANT LIFE. 
 
 purples, with shadings of brown and green, mark the more 
 striking species. 
 
 Fucus. 
 
 From the very simple body of Polysiphonia to the common 
 bladder-wrack, or Fucus vesiculosus, there are all stages of 
 complexity, which cannot be traced here. 
 
 41. External form. — The body of Fucus (fig. 42), is 
 large as compared with the plants previously described. It 
 is often 75-100 cm. long by 1-2 cm. broad, of greenish - 
 
 Fig. 43. — A transverse section of the thallus of Fucus, showing midrib, r ; cortex, c ; 
 medulla, m ; and a hair-pit,/. Magnified 10 diam. — From a drawing by Mr. C. E. 
 Allen. 
 
 brown color and cartilaginous consistency. Near the base 
 the thallus is contracted into a stalk whose extremity is 
 broadened into a sucker-like disk (often lobed) which at- 
 taches the plant firmly to the wave- 
 washed rocks on which it grows. 
 Above, the thallus is flattened, with 
 a thicker rib in the middle (fig. 
 43), and branches abundantly by 
 forking. These branches, though 
 often twisted, really lie in the same 
 place as the flattening. Here and 
 there the axis shows pairs of oval 
 f.g 44 -a longitudinal section swellings, the bladders, which, by 
 $Zl?£ e nt?lp S T*l the contained gases, give greater 
 
 flattened sides oJ e body t/ ,ap,cal buoyancy tQ the pl ant s in the Water. 
 
 SWrfiSW&WE 42 - A P ical cell.-An examina- 
 toiiii^ifiESdiSS! tion of the structure of the thallus 
 -After Rostafinsk,. shows a decided differentiation of 
 
 cells, which would be expected from the large and complex 
 
THE THALLUS OF THE HIGHER ALG&. 35 
 
 form. At the apex of any growing branch is found a cluster 
 of angular cells, thin-walled, of nearly uniform size, with 
 abundant protoplasmic contents, and all in close contact. 
 ( >ne of these cells, lying in the center of the group, some- 
 what larger and of different shape from the rest {c, fig. 
 44), is constantly undergoing division, and thus cutting off 
 cells (segments) from its two inner faces (1, 2, 3, fig. 44). 
 The cells so produced undergo further divisions, forming 
 thereby all the cells of which the thallus is composed. This 
 group of dividing cells is present in all the higher plants. 
 It constitutes the " growing point " or, better, the apical (or 
 primary) merislem. The single cell from which all proceed 
 in Fucus is called the initial, or apical, cell. 
 
 43. Differentiation of cells. — But if a thin section of the 
 thallus, from an older part, be examined (fig. 45), its cells 
 will be found very different from those 
 at the apex. The cells nearer the sur- 
 face are smaller and of different form 
 from those in the interior. They are 
 also close-set, whereas those in the in- 
 terior are no longer in contact with each 
 other on all sides, but have been sep- **=> ^5^^^> 
 aratec l>v the ^rowim: oi branches from ^.i,,/.,*^. ■..-»• «••« ■• 
 
 J . ?. , f fe ,. rp , ummmmm 
 
 the cortical cells between them. 1 hese 
 
 Fi<;. 45— Diagram of a por- 
 
 filamentous branches are crossed and in- tion of fig. 44 , magnified 
 
 about 70 clum 1 cortex: 
 
 terlaced, with wide intercellular spaces, w, medulla. Thevaried 
 
 forms of the cells are due 
 
 All of these older cells have enlarged, to the different planes in 
 
 . . which the filaments are 
 
 and, instead Ol being Idled With protO- cut. The clear spaces are 
 
 filled with mucilage pro- 
 
 plasm, they will be found to have large duced by the ceff-waiis. 
 
 From a drawing by Mr. 
 
 vacuoles and heterogeneous contents. C. E. Allen. 
 The walls, also, are no longer thin and homogeneous, but 
 have become thickened and differentiated into at least two 
 layers, the outer of which is capable of swelling enormously 
 in water, while the inner layer retains its usual form. There 
 
36 
 
 PLANT LITE. 
 
 arises thus a cortex, as the outer dense part is called, and a 
 medulla or pith, as the mucilaginous and apparently isolated 
 central cells and filaments are called. At the bladders, the 
 pith becomes filled with air and other gases. 
 
 44. Special functions. — Complete examination of all parts, 
 the disk of attachment, the bladders, and the hair-pits (fig. 
 
 Fig. 46. — Several plants of Lessonia, showing tree-like thallus and branched rhizoids 
 attaching the plants to rocks, j B natural size.— After I .<• Maout & Decaisne. 
 
 43) with which many species are covered, would reveal still 
 other modes of differentiation of cells from those of the 
 apical meristem. Accompanying the change of form is 
 always specialization of function, which we can interpret 
 only in a very imperfect fashion from our own standpoint. 
 
THE THALLUS OF THE HIGHER ALGJE. 
 
 37 
 
 The compact small cells forming the surface are nutritive 
 and probably in part protective ; the bladders serve to in- 
 crease the buoyancy of the plants when the tide is in ; while 
 the abundant mucilage, formed in the interior from the cell- 
 walls, serves to retain the moisture when the plants are ex- 
 
 showing differentiation of thallus. Natural size. — 
 After !■< nnett >v Murray. 
 
 posed by the ebbing tide ; the hair-pits are functionless, so 
 far as known ; and the strong, elastic cells of the disk and 
 stalk above hold the plants in place as they sway constantly 
 back and forth in every wave of the rising or falling tide. 
 
 45. Color. — The coloring matter in the chloroplasts of 
 Fucus and other brown seaweeds is chlorophyll (green) and 
 
3$ PLANT- LIFE. 
 
 phycophoein (brown). The chloroplasts exist chiefly in the 
 cortex, which is, therefore, the food-making tissue (see ■" 230), 
 while the internal tissues are used for storage of reserve food. 
 
 46. Intercalary zones of growth. — Some of the brown 
 seaweeds, instead of growing at the tip, grow in a zone at 
 the base of the flatter part of the thallus, just above the round 
 stalk. Such growth is called intercalary growth. There can 
 be no single initial cell, but at least a zone of initials. 
 
 Some species grow to great lengths. One Australian species 
 is said to attain a length of 200-300 meters. Still others 
 have the form of a tree, the stalk-like portion representing 
 the trunk, with a crown of flattened, frond-like branches 
 above (fig. 46). 
 
 The thallus in the "gulf-weed," or " sea-grape "* (fig. 
 47), is still further differentiated into rounded, stem-like parts 
 and flattened, leaf-like ones. The bladders are berry-like 
 enlargements in the middle of short, rounded branches, and 
 the form is strikingly like that of a small herb. 
 
 * This plant is of interest, also, because from its scientific name, Sar- 
 gassum, is derived the name of that region in the North Atlantic, in the 
 loop of the Gulf Stream, the Sargasso Sea, where the plants accumulate 
 after being torn off the tropical shores on which various species grow. 
 
CHAPTER IV. 
 
 THE FUNGUS BODY OF HYPHAL ELEMENTS. 
 
 Fungi. 
 
 Fungi are plants without chlorophyll, whose body is gen- 
 erally made up of long filaments, either loosely or densely 
 interwoven and united. 
 
 47. Origin. — As the bacteria, the smallest and simplest 
 plants, were derived from the lowest algae by slow adaptation 
 to a different kind of food, so, at various points in the 
 ascending scale of algal life, certain algae have adapted them- 
 selves to the use of organic food which they could secure 
 ready-made. These, having no use for the chlorophyll and 
 chloroplasts, have gradually lost them. The adoption of the 
 habit has proved highly successful, both among the simple 
 bacteria and the more highly organized true fungi. The 
 ancestors of the present species were — how long ago no one 
 can say — probably at first chiefly, if not exclusively, aquatic. 
 Some, at the present time, have the same habit, growing in 
 infusions of organic matter. Others attach themselves to dead 
 or even living animals or plants in the water. The soil (con- 
 taining in its upper layers more or less organic matter from 
 the offal of plants and animals, or from their dead bodies) 
 and dead or living organisms furnish places of growth for a 
 great number of species which have adapted themselves to 
 other than aquatic life. 
 
 48. Hyphae.— The filaments of which the fungus body is 
 
 39 
 
40 PLANT LIFE. 
 
 composed are called hyphne. Each is the result of growth 
 from a single cell, and is comparable to the thread-like body 
 of the filamentous algae. 
 
 There is, naturally, a great variety in the hyphas of differ- 
 ent species of fungi. Some are relatively large ; others very 
 small ; some of even diameter and caliber, others irregular 
 and with unequally thickened walls ; some very thin-walled, 
 others very thick -walled. Between these extremes is to be 
 found a complete gradation. 
 
 They grow in length at the apex only. In many kinds 
 partitions are formed at more or less regular intervals, as the 
 growth in length proceeds. In others no partition-walls are 
 formed, though division of the nucleus takes place. Even 
 when transverse partitions are formed, they do not separate 
 the filaments into cells, but each chamber, or sometimes the 
 whole filament, is a coenocyte. 
 
 49. Branching. — As the hyphos elongate, branching may 
 occur. If a branch is to be formed, a limited area of the cell- 
 wall begins to grow more rapidly than the rest. This allows 
 a slight bulging of the growing region; 
 the swelling increases and soon takes 
 the form of a branch, like the main 
 axis. It may remain short or continue 
 to grow indefinitely in length. Com- 
 monly a septum is formed at the base 
 of the branch. If such a branch arises 
 first as a minute pimple, so that it 
 remains connected with the parent axis 
 
 Beer-yeast(Sacc/taro- . 
 
 cerevisi.r). «, a full- by a small neck, and has only limited 
 
 crown plant with a branch ... 
 
 'lhii(l) partially developed. /', growth 111 length, it IS Called a blld 
 
 r, colonies formed by budding, 
 
 the individuals still attached, and the process is known as budding 
 
 Magnified 750 diam.-Aftcr ,. ox e , . , ,, 
 
 Reess. (fig. 48). Such branches are usually 
 
 easily broken off, thus readily producing independent plants. 
 (See further under Reproduction, * 302.) In some species of 
 
THE FUNGUS BODY OF HYPHAL ELEMENTS. 4 1 
 
 fungi, profuse branching is the rule; in others, the branches 
 are few. 
 
 50. Mycelium. — When branching is profuse, or when a 
 considerable number of individuals grow near together, the 
 filaments often become interwoven and entangled in so com- 
 
 Fic. 4g.— A single plant of Mucor Mucedo, showing the mycelium as it developed 
 from a single spore in an infusion of dung. It bears a single erect reproductive 
 
 branch rising above the fluid. Magnified .•■■, diam. Afler Urcteld. 
 
 plex a web that it is impossible to follow a single hypha for 
 any distance. Such a mat of hyphse is called a mycelium, 
 a term which is also used to designate the vegetative hypha? 
 collectively, whether forming a felted mass or not (figs. 49, 
 50). The mycelium may be formed wholly upon the sur- 
 
42 
 
 PLANT LIFE. 
 
 face of the object upon which t he fungus lives; or parts of 
 it may be superficial, and part may penetrate that object ; or 
 all of it may be hidden within the substratum.* In some of 
 the common molds (Mucorini), the cobwebby threads lying 
 upon the surface of the substratum constitute the exposed 
 part of the mycelium, while other hyphae penetrate deeper ; 
 
 K 
 
 Fig. 50. — A section of part of the aerial body of Polyporus. s/>, hyphae running at an 
 angle to the section, cut across ; A", crystals of oxalate of lime. Magnified about 
 500 diam. Attn Vogl. 
 
 in others (Penicillium, etc.), the superficial hypha? become 
 so interwoven that they may be lifted off the substratum (as 
 from jellies, jams, syrups, etc.) as a coherent layer. But in 
 most cases, especially when the fungus grows on a solid 
 medium, the hyphae become adherent to it and permeate it 
 SO that they cannot be separated from it, even by the most 
 careful dissection. 
 
 * This non-committal term may be used to designate the material upon 
 which the vegetative part of the fungus grows, whether it be a living 
 body, a dead organism, or organic matter in solid or liquid form. 
 
THE FUNGUS BODY OF HYPHAL ELEMENTS. 43 
 
 51. Parasites. — Especially is this true of those fungi which 
 grow in the interior of living organisms. The higher plants 
 are liable to be fastened upon by parasitic fungi, and com- 
 pel led to act as hosts to their unbidden and unwelcome guests. 
 Such a host plant may be entered when a mere seedling, in 
 which case the fungus grows with its growth, or it may not 
 be attacked until older or even mature. The host may be 
 permeated in all its parts by the fungus filaments ; or certain 
 members, only, such as the leaves, flower parts or twigs, 
 
 Fig. 51.— Young hyphae of Exobasidium developing from spores, .?/, entering the 
 air-pores of the leaf of the cranberry. Others, from .</', j/", penetrate the skin 
 directly. Magnified about 600 diam — After Woronin, 
 
 may be affected. The effect of the fungus upon the host is 
 often scarcely visible to the unaided eye; sometimes a 
 local disturbance is manifested by swelling, unnatural color 
 or growth;* sometimes the affected members become dis- 
 torted and useless or are even killed ; sometimes the disease 
 is general and is followed, slowly or quickly, by general 
 death of the host. 
 
 52. Infection. — These internal parasites obtain entrance 
 
 * Sec further ""' 222, 464. 
 
44 
 
 PLANT LIFE. 
 
 to their hosts in various ways. Sometimes the young hypha, 
 growing from a special reproductive body (spore),* so minute 
 that it may easily float in the air and fall upon a leaf, creeps 
 along the surface till it finds one of the 
 microscopic openings in the skin of the 
 leaf, into which it grows (sp, fig. 51). 
 These external openings are connected 
 with irregular spaces between most of 
 the cells of the softer parts, which are 
 also the parts in which the food-supply 
 s most abundant. In these, therefore, 
 the fungus develops, breaking out to 
 the surface again to form or set free its 
 reproductive bodies. 
 
 Or, the young hyphae may excrete 
 at their tips a substance which so soft- 
 ens or dissolves the cell-walls of the 
 host that they penetrate these cells 
 readily, not only at the surface (sp' , 
 sp" , fig. 51), but in the interior. f They 
 then branch freely, often growing in 
 the spaces between the cells, often 
 passing through the cells themselves 
 
 Fig. 52— Hyphae of Fra- l h ° 
 
 metes Pitii perforating the ({\^t C2). 
 walls of a wood-cell (at c) ol v °' 3 /' 
 
 Scotch pine and destroying Plants are often attacked when mere 
 
 the primary wall ol the cell. 
 
 d .'.holes made by hypha. seedlings. Either from a bit of my- 
 
 Magnified about 800 diam. ° ' 
 
 —After r. Hanig. celium or a spore which has survived 
 
 the winter or the dry season, a hypha grows, which, almost 
 as soon as the seedling emerges from the seed, penetrates it. 
 The fungus, in these cases, may develop quickly and kill the 
 
 * See II 304 and the following. 
 
 f It is not improbable that the penetration of cell-walls is assisted by 
 such pressure as the growing hypha can exert, hut the relative action of 
 enzymes and pressure has not been determined. 
 
THE FUNGUS BODY OF HYPHAL ELEMENTS. 45 
 
 young plant (as in the "damping off" disease in green- 
 houses), or it may develop slowly and not reach maturity 
 until the host is mature. 
 
 53. Haustoria. — Those fungi which grow upon the sur- 
 faces of living plants (and those which grow in the internal 
 air-spaces) often have special branches for fastening them- 
 selves to the host or absorbing food from it. In the surface 
 
 Fig. 53. — Epidermis and a few cortical cells of cowberry with mycelium of Calyp- 
 tos/>ora occupying the intercellular spaces and pressing knob-like ends against the 
 cells from which a slender branch penetrates the wall and enlarges i 
 
 into sac-like haustoria, b, b. a, club-shaped hyphae which produce spore-mother- 
 cells, c\ in the epidermis. Magnified 420 diam.— After K. Hartig. 
 
 fungi these are usually very short, disk-like or lobed 
 branches which do not penetrate the cells of the host. In 
 other cases they are branches of minute diameter, which 
 enter the cells, and either enlarge into a knob (fig. 53) or 
 branch profusely (fig. 54). 
 
 54. Fusion. — When the hyphre of a fungus grow very 
 close together, they frequently cohere and become so 
 changed in appearance as to lose all trace of resemblance to 
 filaments. Not only fusion but thickening and division 
 
4 6 
 
 PLANT LIFE. 
 
 occur, and a section of the resulting structure has much the 
 appearance of a section of the tissues of ;i higher plant (fig. 
 55). These changes arc particularly apt to occur among the 
 superficial parts of the more massive structures among the 
 fungi, where they are necessary to impart firmness, rigidity, 
 or durability. For example : in the ergot, a fungus common 
 upon certain grasses, a portion of the mycelium is to survive 
 the winter and grow again the next season. This portion 
 
 Fig. 54. Fig. 5-.. 
 
 Fig. 54. — Branching haustoria of Peronospora. m, m, the hypha traversing an 
 intercellular space of the host; g, z, two haustoria penetrating two tills of 
 the host and branching therein. The other contents of host-cells not shown. 
 Magnified about 400 diam. — After De Bary. 
 
 Fig. 55. — A section through the mycelium of a lichen showing hypha; near upper sur- 
 face, a, and lower surface, 6, fused into a false tissue ; only in central region are tin- 
 filaments recognizable. The dark spheres are imprisoned alga;. Magnified 650 diam. 
 — After Bornet. 
 
 replaces the young ovulary of the flower (see 1" 335), and, 
 as it matures, becomes a dark-colored mass, as firm and re- 
 sistant as the grain itself (fig. 56). 
 
 The interweaving and fusion of the hypha? sometimes pro- 
 duce cord-like or strap-like structures of considerable size.. 
 The mycelia of the higher fungi frequently form them, and 
 
THE FUNGUS BODY OF HYPHAL ELEMENTS. A7 
 
 they may be found in the leaf-mold of forests or in rotten 
 stumps or between boards in wet places. 
 
 Fig. 56.— a, compact mycelium of ergot in the form of a grain-like body, replacing 
 grain of rye ; l>, the same germinating to form reproductive bodies. Natural size.— 
 After Tulasne. 
 
 54a. Lichens. — The body of lichens is a mycelium woven 
 about isolated unicellular algae, colonies, or filaments, 
 
48 PLANT LIFE. 
 
 which are thus imprisoned.* The fungus hyphae usually pre- 
 dominate and in great measure determine the form of the 
 body and its texture. Sometimes the algae are present in 
 such numbers that the hyphae seem merely distributed among 
 them. In form the body may be broad and thin (fig. 225), 
 or slender and shrub-like. In texture it may be tough and 
 leathery, with the hyphae near the surface fused into a false 
 tissue (a, b, fig. 55). When gelatinous algae, such as Nostoc 
 (see •' 13) are imprisoned, the body may be gelatinous. 
 In all cases the algae supply the fungus with food, and are in 
 turn supplied with water absorbed by the spongy mycelium. 
 (See further \\ 195, 223, 462.) 
 
 * Rarely about other small green plants. 
 
CHAPTER V. 
 
 LIVERWORTS AND MOSSES. 
 
 55. Alternation of generations. — In the liverworts and 
 mosses, as in all the plants higher in the scale, there occur 
 two well-marked phases in the course of their lives. One of 
 these phases is marked by the formation of sexual reproduc- 
 tive cells, or gametes (see *H 369), the egg and sperm, 
 whence it is called the sexual phase, or the gametophyte . The 
 other is characterized by the formation of non-sexual repro- 
 ductive cells, the spores (see "[ 304), whence it is called the 
 non-sexual phase, or sporophyte. These two phases alternate 
 with each other, the sexual reproductive cells of the game- 
 tophyte producing, under suitable conditions, the sporophyte, 
 whose non-sexual reproductive cells give rise to the game- 
 tophyte. To this regular sequence of the two phases the 
 phrase alternation of generations has been applied.* 
 
 In the higher liverworts and mosses both phases have 
 nutritive work to do, but in many this is confined to the 
 gametophyte, and in all the gametophyte carries on the 
 greater part of it. To this phase, therefore, attention is 
 first given. 
 
 Liverworts. 
 
 56. The thallus. — The form and structure of the vegeta- 
 tive body of the simplest liverworts is scarcely different from 
 
 * Rather obscure suggestions of the alternation of generations are to be 
 found among the alg;e and fungi, tint they are not definite enough to 
 warrant discussion in this book. Let the student notice, however, that 
 this feature does not appear suddenly in plant life, though introduced 
 abruptly into the account of it. 
 
 49 
 
50 
 
 PLANT LIFE. 
 
 that of some of the green algae. The body is a thallus with 
 rhizoids (fig. 57). The rhizoids are usually linear aggregates 
 
 Fig. 57. — A, plants of Riccia sorocarpa, on the ground. Gametophyte phase. Nat- 
 ural size. B, a vertical section of one of the thick lobes of the thallus, showing 
 nearly uniform structure. The thallus has nearly covered over two young sporo- 
 phytes which appear as though in the interior. Rhizoids arise from the ventral side 
 and flanks. Magnified about 25 diam. — After I5ischoff. 
 
 of cells having thin walls and little protoplasm, arising from 
 the under side and flanks of the thallus. They serve to 
 
 Fig 58.— Portion of a vertical section of the thallus of Lunularia cruciata. a, 
 dorsal, i, ventral epidermis; c, an air-pore; <•, air-chamber, from whose floor rise 
 cell-rilainrnis, ,/ ; _/, partition between adjoining air-chambers; g; colorless cells 
 containing starch, some showing net-like thickenings of the walls, others with oil- 
 bodies, //; 1, a ventral scale ; /, a rhizoid. Magnified 110 diam. — After Nestler. 
 
 fasten the thallus to the substratum, — an adaptation to the 
 terrestrial mode of life. The thallus is usually fiat and 
 
LIVERWORTS AND MOSSES. 
 
 expanded in a horizontal plane, though sometimes much 
 crisped. The simpler ones consist of several layers of uniform 
 cells* (£, fig. 57). 
 
 57. The dorsiventral thallus. — In other forms there is a 
 more decided difference between the upper and under sides 
 of the thallus. The upper cells contain chloroplasts, 
 while the under ones have none or very few. In the Mar- 
 chantia family there are large air-chambers in the upper part 
 of the thallus, from the floor of which arise filaments or 
 cactus-like rows of chlorophyll-bearing cells (fig. 58). On 
 the under side, also, are frequently found scale-like out- 
 growths (superficial aggregates), as in fig. 58, i. 
 
 A part which shows constant 
 differences between an upper (dor- 
 sal) and an under (ventral) side is 
 said to be dorsiventral, and the 
 state of being thus different is 
 termed dorsiventrality. 
 
 58. Branching. — The branching 
 of the thallus is always by forking, 
 in a single plane or direction, as in 
 Fucus, but the branches do not 
 always develop equally. Some- 
 times special branches, instead of 
 remaining horizontal, grow upright 
 and develop into peculiar forms 
 adapted to producing the sexual 
 reproductive organs (fig. 59). 
 
 59. The growing point of the thallus is usually in a notch 
 at the apex (fig. 60). There is a single apical cell of wedge 
 shape (rarely tetrahedral), from whose inner faces segments 
 are cut off (fig. 61). These, by division and growth, 
 
 oung, one mature), f< >r 
 g sex-organs. Nal ui tl 
 \ti,r Bischoff. 
 
 *Ccenocytes rarely appear in the vegetative bodies of this or any 
 higher group. 
 
52 
 
 PLANT LIFE. 
 
 produce the whole thallus. The center of the thallus is 
 generally thicker than the wings, and forms a sort of central 
 rib (B, fig. 60). 
 
 60. The shoot. — In the greater number of liverworts the 
 mature vegetative body is a shoot, which is differentiated 
 
 Fig. 60. 
 
 Fig. 61. 
 
 Fig. 60.— Surface view of growing apex of thallus of Metzgeria furcata just after 
 forking, a, primary apical cell; />, secondary apical cell of branch; c, the wing- 
 tissue between axis and branch outgrowing the apices. B, the midrib. Magnified 
 160 diam.— After Kny. 
 
 Fig. 61. — Diagram showing origin of branch in Metzgeria furcata. a, primary 
 apical cell from which the segments right and left bounded by heavy lines have 
 been cutoff. All have undergone further division. In the right-hand one the latest 
 cell-walls have been so placed as to form a wedge-shaped cell, />, which becomes 
 the apical cell of a branch. Its early formation gives the (false) appearance of 
 dichotomy. — After Kny. 
 
 into stem and leaves (figs. 62, 63). Even in such a body 
 the dorsiventral character is well marked. The stem is a 
 filiform axis of uniform cells, bearing three (rarely more or 
 fewer) rows of leaves, of which the two dorsal rows 
 are the larger, while the under leaves are much smaller, even 
 to being inconspicuous or wanting. These leaves are super- 
 ficial aggregates, consisting of uniform cells richly supplied 
 with chloroplasts, as are also the outer cells of the stem. 
 Their form is very varied and often of great beauty. They 
 are always sessile and are usually crowded so closely as to 
 overlap each other more or less, and hide the axis com- 
 pletely (fig. 63). 
 
LIVERWORTS AND MOSSES. 
 
 53 
 
 61. The origin of the leaves will be apparent upon com- 
 paring figures 64, 65, and 66. In Blasia (fig. 64) the thallus 
 is lobed, i.e., the edge has not grown equally, but continued 
 growing longer at certain 
 points. In Fossombronia ( fig. 
 65) the flattened thalloid 
 form is still evident, but the 
 lobing has become so deep 
 
 €> 
 
 Fig 62. 
 
 Fig. 63. 
 
 Fig. 62.— Gametophyte of Hazztniiti XoTce-Hollandite. Besides the ordinary- 
 branches there are slender ones (flagella) with sparse minute leaves. Naturalsize. 
 — After Lindenberg and Gottsche. 
 
 Fig. 63.— A, dorsal view; A', ventral view of a piece of fig. 6a, magnified about 12 
 diam., showing the stem, bearing two dorsal rows of large leaves and one ventral 
 row of small ones.— After I.indenberg and Gottsche. 
 
 that the almost separate parts are usually called leaves. 
 In Noteroclada (fig. 66) the central axis is still more com- 
 pact, and has lost its flat form, becoming a rounded stem 
 from whose flanks arise regular outgrowths, the leaves, each 
 of which corresponds to one of the lobes of the thallus in the 
 other forms. 
 
 Mosses. 
 
 In the mosses the complexity of the mature vegetative body 
 is somewhat greater. It is always developed as a shoot differ- 
 entiated into stem and leaves. 
 
 62. Rhizoids. — The shoot is anchored, as in the liver- 
 
54 
 
 PLANT LIFE. 
 
 Fig. 64 
 
 Fig. 64.— Part of a plant of Blasia pusilla. The flattened lobed thallus is the 
 
 gametophyte; the stalked capsules (one young:, one bursted) are two sporophytes 
 
 attached to it. Magnified 4 diam. — Alter Schiffner. 
 Fig. 65. — Gametophyte and sporophyte of Fossombronia cristata. The thallus is 
 
 so deeply lobed thai the divisions are usually called leaves. Magnified 15 diam.— 
 
 After Schiffner. 
 
 Fig. 66.— A, a gametophyte of Noteroclada, with a sporophyte attached. Natural 
 size. B, a part of the stem and a single leaf of the same, magnified about 10 diam. 
 — After Hooker. 
 
LIVERWORTS AND MOSSES. 
 
 55 
 
 worts, by numerous usually much branched rhizoids (A, fig. 
 67; iv, fig. 68). Similar filaments may be produced, often 
 in great numbers, along the stem and especially in the axils 
 of the leaves, or they may even arise from the leaves them- 
 selves, when the plants grow in dense patches or in a very 
 moist place. 
 
 Fig. 67.—.-/, gametophyte of Polytrickum commune, with rhizoids below. /?, 
 gametophyte of Hylocomium splendens, bearing three sporophytes near top. 
 Natural size. — After Kerner. 
 
 63. The stem is usually cylindrical and covered by the 
 crowded leaves. In structure it generally shows an advance 
 upon that of the liverworts in having the whole of the outer 
 region occupied by a distinct mass of mechanical tissue com- 
 posed of thick-walled cells, and, near the (enter, a strand of 
 elongated small cells, known as "conducting tissue" (fig. 
 68), though it is doubtful whether it conducts anything. 
 
56 
 
 PLANT LIFE. 
 
 Fig. 68. — Transverse section of the stem of Bryum roseum. In the center the 
 small cells make a central strand, the "conducting tissue "; the surface cells form 
 an epidermis; the next three rows within also have thick walls an. 1 strengthen the 
 stem; w, rhizoids arising from epidermis. Magnified 50 diam. — After Sachs. 
 
 Fig. 69. 
 
 Fig. 69.— A, leaf of a moss [Funaria Americana), showing central rib. Magnified 
 about 40 diam.; />', upper portion of the same leaf, highly magnified, showing 
 single layer of cells forming the blade and the narrower cells of the thick rib.— 
 After Sullivant. 
 
 Fig. 70 —Tip of leaf of a moss (Oligotrickum aligerum\ showing the thickened 
 rib, and the plate like ridges on blade and rib greatly increasing the surface of 
 nutritive tissue. Magnified about 75 diam. — After Sullivant. 
 
L 1 1 ~ER IVOR TS A iVD MOSSES. 
 
 57 
 
 64. The leaves arc also more highly developed than in 
 liverworts. They are always sessiie and are arranged in two 
 (rarely), three, or more vertical ranks along the stem, and 
 consist usually of a single sheet of chlorophyll-bearing cells, 
 the blade (figs. 69, 70), and a central rib running from base 
 to apex (frequently wanting), which is composed of elongated 
 conducting and strengthening cells (figs. 69, 70). In some 
 the amount of green tissue is increased by the formation of 
 vertical plates similar to the blade (fig. 70). 
 
 65. Branching.— The stem branches, often very profusely, 
 by the formation of lateral growing 
 points beneath the developing leaves. 
 Sometimes the growth of the lateral 
 branches, as of the original main 
 axis, is checked by the formation 
 of sexual organs. In that case a 
 new branch is likely to arise some 
 distance below the apex, so that the 
 stem is a succession of lateral 
 branches, called a sympodium (fig. 
 71). This mode of branching is 
 termed sympodial. In other cases 
 the main axis continues its growth 
 unchecked, and more or fewer 
 branches also develop. These lie 
 plainly upon the sides of a central 
 axis. This mode of branching is 
 called monopodia!. Often the 
 growth of the lateral axes is defi- 
 nitely limited and their develop- 
 ment regular, forming a pinnate 
 branch-system. If the secondary 
 axes themselves branch, there is 
 even tripinnate system, as in figure 67, B. 
 
 Fig. 71. Axis of a moss (Ortho- 
 trie It u m) showing sympodial 
 branching. .V, 5», .V 3 , • 
 ii\ e 1 lusters "I sexual organs, 
 produced at apex which check 
 the growth "I axis. Beneath 
 each a lateral growing point 
 develops, produi 
 
 the brances /•'. /•''. 6*. Magni- 
 fy d n >li. mi. Alter Bruch & 
 Scbimper. 
 
 formed a bi pinnate or 
 
58 
 
 PLANT LIFE. 
 
 66. Protonema. — In its early stages the vegetative body 
 of the hafv liverworts and the mosses is either a flat thallus, 
 similar to the mature form of the thallose liverworts, or a 
 branching filamentous body, called the protonema, almost 
 identical with the form of the filamentous algae. Upon this 
 protonema the leafy shoot arises as a lateral bud, which soon 
 outstrips it in growth and differentiates leaves. The proto- 
 nema may live for some months, but generally perishes after 
 having produced a few lealy plants. 
 
 67. Sporophyte. — The non-sexual phase in the liverworts 
 and mosses has almost no vegetative functions, and a fuller 
 
 Fig. 72. — A, two capsules of Rryum ; from the right-hand one the lid 1ms fallen, 
 showing the teeth. Magnified 5 diam />', four gametophyte shoots of Splachnunt 
 ampullaceum, bearing four sporophytes. Natural size. C, a capsule "I one <>f 
 the same sporophytes, showing enlarged apophysis, a, below the sporangium, j. 
 Magnified 10 diam. />. capsule of Splachnum luteum, with umbrella-like apo- 
 physis, a, below sporangium, .v Magnified 2 diam. 
 
 study of its structure is left for Part III. It consists at 
 maturity of a yellowish or brown spherical or cylindrical case 
 (fig. 72), which is sessile or raised upon a short or long 
 stalk and contains (a iew or) hundreds or thousands of 
 reproductive cells called spores. The base of this stalk 
 constitutes an organ called the "foot," which is embedded 
 in the gametophyte (_/", fig. 73). 
 
 68. Nutrition. — The surface of the young sporophyte, 
 when large and well developed, as it is in the higher liver- 
 worts and mosses, is green. To a limited extent, therefore, 
 it is able to make food ; but not sufficient for its needs, 
 
LIVERWORTS AND MOSSES. 
 
 59 
 
 for these arc great on account of its rapid growth and the 
 supply required as reserve for 
 
 each spore. The foot, being in 
 close contact with the tissue of 
 the gametophyte, acts as an 
 absorbing organ, receiving food 
 solutions from it. The sporo- 
 phyte thus lives, in part at least, 
 as a parasite upon the gameto- 
 phyte. 
 
 In some mosses there is a ten- 
 dency to increase the nutritive 
 work of the sporophyte by de- 
 veloping at the top of the stalk, 
 below the spore-case, a mass of 
 green tissue. InBryumfyi, fig. 
 72) this gives the capsule a pear- 
 shape, while in Splachnum {B, 
 C, D, fig. 72) it is so far de- 
 veloped as to exceed the spo- 
 rangium. In some species it is 
 expanded into a miniature um- 
 brella which, one can imagine, 
 might readily become segmented 
 into leaves. 
 
 The intimate attachment of sporophyte to gametophyte 
 continues throughout the life of the former. Sometimes the 
 gametophyte perishes at the close of the growing season, but 
 more commonly it is perennial, growing and branching at the 
 anterior end as the older posterior parts die away. 
 
 Fig. 73.— Yonni; sporophyte of Phas- 
 i urn cuspidatum. c, columella ; f, 
 foot, embedded in gametophyte stem; 
 s, seta (cells not shown); s/>s, spo- 
 rangium ; s/>, spore-mother-cells. 
 Magnified 80 diara.— After Kienitz- 
 Ge*rloff. 
 
CHAPTER VI. 
 
 FERNWORTS AND SEED-PLANTS. 
 
 Fernworts. 
 
 Among the still more complex plants, the ferns and their 
 allies, the same "alternation of generations" can be seen. 
 The two "generations," or phases, have, however, changed 
 much in relative size. Whereas in the liverworts and mosses 
 the gametophyte is much the larger and more conspicuous, as 
 well as the longer-lived, among fernworts the sexual phase is 
 so much smaller that it is seldom seen ; and in some species 
 it is almost microscopic. On the other hand, the sporophyte 
 is the phase which is usually seen and the only part popularly 
 known. 
 
 69. The gametophyte. — The vegetative body of this phase 
 of the fernworts in its best developed forms 
 is a small, flattened, green body of oblong, 
 orbicular, or cordate outline, commonly 
 less than half a centimeter in diameter, 
 rarely as much as 2 cm. (fig. 74). It is 
 strikingly like a thallose liverwort in 
 general form, being distinctly dorsiventral 
 and having rhizoids on its under side, 
 
 Fig. 74. — Ventral side of . , . 
 
 the gametophyte of a which fasten it in place. ( because of this 
 
 lem.Asplenium. The , , . . . . , . , 
 
 notched end is the an- thallOld form and because it seemed to 
 tenor. Rhizoids near , , . . ,, , 
 
 posterior emi. Tin small precede the "real plant — a popular 
 
 circles show position of , . , 
 
 male organs ; the chim- phrase meaning the sporophyte — it was 
 
 ney-like projections near ,, , ,i n- \ i-\ -\ \ .1 
 
 anterior end the female Called A />nt/// t l///l/W .) Only the Central 
 
 diam. After k r. part 01 the gametophyte consists of more 
 
 than one layer of cells. On the under side of this central 
 
 60 
 
J- /.A. VIVO NTS AND SEED-PLANTS. 
 
 61 
 
 "cushion," as it is called, are produced the sexual organs. 
 (See further under Reproduction, Tart III.) 
 
 70. Reduction of gametophyte. — In a few of the fernworts 
 the gametophyte is filamentous, or tuberous, and more or less 
 
 N 
 
 Fig. 75. — Sporophyte of a fern, Polypodiu 
 stem, hearing seenndary roots and 
 
 ilgare, showing horizontal underground 
 ■s. Natural size. — From Bessey. 
 
 completely subterranean and colorless. Such prothallia derive 
 tluir food from decaying plant-offal. 
 
 In higher plants of this group the gametophyte becomes 
 still further reduced in size and structurally simplified, until 
 in some species it is hardly more than a few cells surrounding 
 the sexual organs. These reduced forms grow by the use of 
 
62 
 
 PLAN T LIFE. 
 
 food stored in the spore from which they originate. The 
 gametophyte of such species has lost wholly its vegetative 
 character, and is restricted in function to the production of 
 the sexual organs. 
 
 71. The sporophyte. — In contrast with the smallness and 
 simplicity of the gametophyte is the relatively large size and 
 
 Fig. 76.— Embryo of Pteris aguilina, and a small part of the gametophyte, g y in 
 which its foot,/, is embedded, r, the primary root ; s. primary stem ; /, primary 
 leaf. Induced growth of the gametophyte about the foot is shown by small size and 
 numbei of cells. Much magnified. — After Hofmeister. 
 
 
 Fig. 77 — Section through embryo and gametophyte of maidenhaii fern (AdiantutH 
 Capillus-Veneris). The embryo is older than that in tig. 76. /,/, gametophyte; 
 A, rhizoids, among which are two spermaries. The eggs in three ovaries failed to 
 develop ; the other formed the embryo, E. a, primary stem, only slightly de- 
 veloped (compare s, fig. 76) ; b, primary leaf ; iu, primary mot. The part embedded 
 in the fjametophyte is the foot. Magnified about 10 diam. After Sachs. 
 
 complexity of the sporophyte (fig. 75). It is always differ- 
 entiated into stem and leaves, and, with rare exceptions, 
 roots also. This great advance in the development of the 
 sporophyte of the fernworts, as contrasted with its form in 
 their nearest of kin below, the liverworts and mosses, suggests 
 that the fernworts are a very old group ; a hint which is con- 
 firmed by the antiquity of their fossil remains. It is also 
 noteworthy that, as compared with mossworts, the chief work 
 
FEXA'irORTS AND SEED-PLANTS. 
 
 63 
 
 of nutrition has been shifted from the gametophyte to the 
 sporophyte j and this even when the gametophyte has its 
 largest size and greatest duration, while nutritive work is 
 wholly abandoned in the smaller forms. The sporophyte has 
 also become the long-lived stage, the gametophyte being 
 usually transitory (only exceptionally living more than one 
 season), while the sporophyte lives through one season in the 
 few annuals, and commonly for several or even many years. 
 
 72. The embryo. — The fertilized egg, from which the 
 sporophyte arises, develops while still embedded in the 
 gametophyte in which it is formed. Consequently the 
 embryo sporophyte is, as in the mossworts, at first surrounded 
 by the gametophyte (figs. 76, 
 77). The part of the gamet- 
 ophyte adjacent to the embryo 
 grows under the stimulus of its 
 presence, but the growth of the 
 embryo is more rapid, and it 
 consequently spreads apart the 
 gametophyte (see figs. 76, 77). 
 A portion of the embryo de- 
 velops a temporary organ, the 
 foot, which remains embedded 
 in the gametophyte until the 
 first root, stem, and leaf have 
 been formed (fig. 78). Soon 
 thereafter the gametophyte per- 
 ishes and the foot, no longer 
 useful, disappears. 
 
 73. Members. — The mature 
 sporophyte is differentiated into 
 root, stem, and leaves. The 
 important adaptations of the 
 structure and-forms of these members are so similar to those 
 
 Fig. 78 
 
 same as fiff. 77 
 
 The gametophyte, /\ seen from be- 
 low, w 11 li 1 In.-. lids ; the sporophyte 
 •-nil attached Inn with primal \ leaf", .'. 
 developed into blade and stalk ; /. the 
 primary root: .-. .1 secondary runt, 
 arising from tin- juncture oi 
 and st<-iii Magnified about 4 diam. 
 After Sachs. 
 
64 PLANT LIFE. 
 
 of the seed-plants that thay will be discussed in connection 
 with them. 
 
 Seed-plants. 
 
 Among the highest plants, those which produce seeds, the 
 differentiation of the body is essentially the same. The 
 alternation of sexual and non-sexual phases is still traceable, 
 though greatly obscured by the extreme reduction of the 
 gametophyte. This tendency to the reduction of the sexual 
 phase, which was remarked in passing from the mossworts to 
 the fernworts, continues, until in the highest seed-plants the 
 gametophyte is wholly microscopic. Even by the aid of the 
 microscope, it is possible to identify only the sexual organs 
 which it produces, and one or more cells which are, perhaps, 
 the rudiments of its vegetative body. The sporophyte, con- 
 sequently, is the only phase of the seed-plant visible to the 
 unaided eye. The relation of the gametophyte to it will be 
 explained in Part III. 
 
 The body of the sporophyte exhibits the same members, 
 viz., stem, root, and leaf, having the same general form, and 
 subject to the same modifications, as in the fernworts. To a 
 discussion of the vegetative members of the fernworts and 
 seed-plants we now turn. 
 
CHAPTER VII. 
 
 THE ROOT. 
 
 74. Analogous members. — It has been pointed out that, 
 among the lower plants, there are very many which possess 
 structures similar in form and function to the root, and 
 sometimes called by the same name. Although these parts 
 serve to hold the plant in place, and perhaps to absorb 
 material from the substratum, they are not to be looked upon 
 as homologous with the roots of the higher plants, but as 
 merely analogous with them. In the plants whose vegetative 
 body is a thallus the gametophyte is the prominent phase. 
 In no case does the gametophyte produce true roots. It is 
 not until the sporophyte becomes an independent plant that 
 true roots are found in the vegetable kingdom. It is, there- 
 fore, only among fernworts and seed-plants that these organs 
 are to be found. When the sporophyte is developed as an 
 independent plant, it becomes necessary for it to produce 
 some organ capable of holding it in place, or of absorbing 
 materials from the outside, or of doing both. The organ 
 developed to meet this need is the root. 
 
 75. Primary roots — In accordance with their origin, 
 roots are either primary or secondary. Primary roots are 
 those which are developed directly from the egg from which 
 the entire plant takes its rise. The spherical egg in most 
 of the fernworts begins its development by a division into 
 hemispheres. The hemispheres divide into quadrants ; ea< h 
 of the quadrant cells divides into two, forming octants of the 
 original egg. Division continues and the fundaments of 
 primary root, foot, stem, and one or more leaves appear 
 
 65 
 
66 
 
 PLANT LIFE. 
 
 (see fig. 76). In many of the seed-plants the egg divides 
 several times in parallel planes, forming a 
 short filament, the suspensor (figs. 79-82). 
 The terminal cell of this row may then 
 give rise to an embryo, as just described, 
 or this terminal cell and an adjacent one 
 may take part in forming the embryo. In 
 this case the terminal cell, by its divisions, 
 either produces the primary leaf or leaves, 
 t produces the primary stem and 
 r, s, ceils of the suspen- leaves ; while the second cell gives rise to 
 
 sor; a, a, fi, cells from ° 
 
 :1V H.Khiy r ^: the P rimar y stem and root > or to the 
 
 fied. -Afur Sachs. primary root alone (see figs. 80-82). 
 The two primary members formed 
 from the root hemisphere of fernworts 
 are not always permanent. The foot is 
 
 Fig. 79.— A very young or 
 
 embryo of the onion. 
 
 Fig. 80. Fig. 81. Fig. 82. 
 
 Fig. 80.— A very young embryo of shepherd's-purse. Suspensor, s, s. just completed, 
 
 and first four cells of embryo formed by division of terminal one ; the sei ond 1 ell, 
 
 />, is to produce part oi the root. Highly magnified. — After Hanstein 
 Fig. 81. — An older stage of the same. /.', embryo; /•', /■". two cells resulting from 
 
 division of b. fig. 80; *. s. suspensor. The shaded cells produce the skin and the 
 
 vascular bundles Highly magnified.— After Hanstein. 
 Fig. 82.— An older embryo of same. £, embryo; /. /, primary leaves; .9/. apex of 
 
 stem ; r, primary root ; re, first layer of root-cap; .r, suspensor. Cells shown only 
 
 in part. Less magnified than preceding.- \fter Hanstein. 
 
THE ROOT. 67 
 
 always temporary, disappearing as the embryo becomes 
 larger. It is sometimes wanting from the first. In both 
 femworts and seed-plants the primary root is rarely wanting, 
 but often short-lived, dying after the plant has established 
 itself and has formed secondary roots to take its place. In 
 many cases, however, the primary root persists throughout 
 the life of the plant. 
 
 76. Secondary roots. — Secondary roots, on the contrary, 
 are those which arise upon stem or leaf, or even upon the 
 primary root itself. In the last case they are distinguished 
 from branches of the primary root, which arise in regular 
 succession toward the apex, by originating out of this regular 
 order. Secondary roots are also called adventitious roots. 
 They may take their origin at any point upon any of the 
 members. Their point of origin will depend largely upon 
 external conditions. They are especially likely to be formed 
 upon those parts which are in contact with the substratum, 
 or from those parts which are kept moist. Upon stems they 
 are most apt to appear near the nodes. (See 1 119.) If 
 the plant as a whole is surrounded by very moist air, roots 
 may appear at any point of the surface. Secondary roots 
 arising thus upon a part of the plant exposed to the air, and 
 growing for all or part of their existence in the air, are also 
 called aerial roots. Familiar examples are to be seen about 
 the lower part of the stem of Indian corn, the English ivy, 
 the poison-oak, the trunks of palms and tree-ferns. Secon- 
 dary roots often arise in regular succession toward the grow- 
 ing apex of the stem, particularly in plants which have creep- 
 ing or subterranean stems. 
 
 77. Growing point. — Primary and secondary roots do 
 not differ materially in their structure. The early divisions 
 of the quadrant cell which produces the primary root in tern- 
 worts are so arranged that a cell shaped like a four-sided 
 pyramid is produced. This cell becomes the apical, or 
 
68 
 
 rLANT LIFE. 
 
 initial, cell. It is situated with one face directed toward the 
 apex of the root (see fig. 83), and the other three faces 
 within it. Parallel to the three inner faces partitions are 
 constantly formed in regular succession dividing this apical 
 cell into two unequal portions, so that the smaller is looked 
 upon as a segment cut off from the larger portion. If these 
 inner faces be numbered respectively 1, 2, 3, the segments 
 are constantly produced in the 
 order of the numbers. These 
 segments themselves divide to 
 form other cells, and thus give 
 rise to all the tissues of the root. 
 This mass of actively dividing 
 cells is the primary meristem or 
 growing point of the root (com- 
 pare • 101). As the older cells 
 of the primary meristem enlarge, 
 divide, and differentiate, they 
 are constantly pushing the apical 
 cell further away from the older 
 part. Not only' are segments 
 cut from the three inner faces of 
 the apical cell, but, at less fre- 
 through the extremity of a root of quen t intervals, partitions paral- 
 
 Marsiha. 1 he larjic triangular cell 1 » ' I 
 
 near center of figure is the apical le | t0 tne outer f ace f Qrm s j m j_ 
 
 cell. I lie segments from the inner 
 
 faces may be readily traced back- p u se gments. The division of 
 
 ward; thus the dotted line e< points ° 
 
 to the fourths to the sixth segment tnese sc <r ment S oiveS HSe tO 3. 
 from the posterior n.nht-hand tare "1 ° ° 
 
 apicaiceii. e/>, root -ca P (epiderm.s); s t rU cture covering the very tip 
 
 ec. cortex; c, stele; en, endodermis o • 1 
 
 (pan .,f cortex^; fie , peri. v. i. (part f the root, and connected with 
 
 of stele). Magnified about ioo diam. 
 After Van Tieghem. it for a short distance only. It 
 
 receives, therefore, the appropriate name of root-cap {ep, fig. 
 
 83). Since the cells of the surface of the root-cap are older 
 
 and firmer than the inner segments and the initial cell, and 
 
 lie in front of them, they serve to protect the more delicate 
 
 Fig. 83.— Medial, longitudinal section 
 
THE ROOT. 
 
 69 
 
 cells as the growth of those behind constantly pushes the 
 apex forward through the soil. 
 
 In seed-plants, the segments of the egg which produce the 
 
 ^v 
 
 Fig. 84. Transverse section of a young root (frown in soil, showing root-hairs with 
 adherent soil-partii les, the cortex, and the stele. Magnified about 20 diam.— After 
 Frank. 
 
 root do not divide so as to form a single apical cell, but a 
 group of initial cells, which retain tin- power of rapid division 
 and constitute a primary meristem or growing point. In all 
 other respects the development of the root from this group 
 of initials is similar to that already described. 
 
7° 
 
 PLANT LIFE. 
 
 In both cases, the differentiation of cells produced at the 
 growing point results in the formation of three characteristic 
 parts of the root, namely, (i) an outer layer or layers, the 
 epidermis ; (2) an inner region, the stele ; (3) between these, 
 the cortex. 
 
 78. 1. The epidermis usually becomes many-layered. 
 At the apex it constitutes the root-cap (ep, fig. 83). On the 
 other parts of the root it sometimes sloughs 
 off entirely, exposing the cells of the cortex 
 itself, as in the monocotyledons (lilies, 
 grasses, sedges, etc.); or, more commonly, 
 only the outer layer sloughs off, leaving the 
 innermost as the covering of the cortex. 
 
 79. (a) Root-hairs. — Those cells which 
 form the surface of the root, 
 whether they be the origina 
 epidermis or cortical ones 
 which have been exposed 
 by its loss, usually develop 
 a large number of hairs, 
 known as root-hairs (fig. 
 84). These root-hairs are 
 branches of the superficial 
 cells ( fig. 85), and maybe 
 looked upon as simple ex- 
 tensions of them, as the 
 finger of a glove is the 
 extension of its palm. Only 
 one root-hair arises from a 
 superficial cell. They arc 
 usually unbranched and without transverse partitions. Only 
 in rare cases are they wanting. They live for a shorter 
 or longer time, but are always, as compared with the 
 duration of the root, quite transient. The older part of the 
 
 Kig. 85. — Two root-hairs showing structure 
 and relation to superficial cells of root; 
 grown in water and therefore not distorted 
 as in fiji. 84. A, the younger ; />', older, 
 nearly mature. n, nucleus embedded in 
 cytoplasm; vacuole single and very large. 
 Highly magnified.— After Frank. 
 
THE ROOT. 71 
 
 root, therefore, is without root-hairs because of their death. 
 The youngest part of the root is likewise free from them, 
 because they have not yet been produced. As the root grows 
 in length, new root-hairs are continually being produced and 
 the older ones are dying at an equal rate, so that a zone 
 of hairs is found only upon the younger parts of the roots. 
 
 80. (/>) The root-cap, serving to protect the tenderer por- 
 tion of the root behind, is itself constantly exposed to injury. 
 The outer and older cells of the root-cap are, therefore, either 
 torn away through mechanical contact, having become gradu- 
 ally loosened from each other with age; or, losing their 
 active contents, they degenerate and break down into a 
 slightly mucilaginous material which facilitates the passage of 
 the root through the substratum. This degeneration or the 
 mechanical wear is repaired constantly by the formation of 
 new cells in the growing point. The thickness of the root- 
 cap, therefore, is maintained throughout its existence without 
 considerable change. It rarely becomes more than a few cell- 
 layers thick. Since its tissue is produced only by the division 
 of the apical cell or cells, it is organically connected with the 
 root only at the very tip; but it usually extends backward over 
 the root, by reason of its growth, for a considerable distance. 
 If the finger be supposed to represent the root, a short finger- 
 stall, if it were attached to the tip of the finger, might be 
 fairly taken to represent the position of the root-cap. Only 
 in rare cases is the root -cap entirely wanting. 
 
 81. 2. The stele. — Occupying the center of the root, and 
 surrounded on all sides by the cortex, is an aggregate of 
 tissues called the central cylinder, or stele (figs. 84, 86, 89). 
 The outermost layer of its cells is the peru vele (figs. 86, 88, 
 89). Within this are found strands of elongated cells or 
 cell-fusions,* called vascular bundles, or strands. These 
 
 * These are continuous chambers formed by the breaking down of the 
 partition walls between the abutting ends of cells. They are usually 
 devoid of living contents. 
 
7 2 
 
 PLANT LIFE. 
 
 bundles are of two kinds, xylem bundles and phloem bundles, 
 so placed that they alternate with each other about the 
 periphery of the stele (figs. 86, 88, 89). The xylem bundles 
 may be in contact with one another in the center, or the 
 center of the stele may be occupied by a pith (figs. 86, 89). 
 
 Fig. 86. — Transverse section of the stele and a portion of the surrounding cortex of the 
 root of calamus, j, .v, innermost layer of cortex, the endodermis, adjoining outermost 
 layer of stele, the pericycle; /. xylem bundles; ph, phloem bundles. The shaded ele- 
 ments of xylem bundles are the primary xylem ; the large ones, g, are secondary. In 
 the center of the stele and between the bundles is conjunctive tissue. Highly magnified. 
 — After Sa< lis. 
 
 The tissues of the xylem are usually lignified (see ^[ 9) 
 and, when abundant, make up what is called the wood. They 
 are the chief water-conducting elements of the older parts of 
 the root. 
 
 The tissues of the phloem are usually not lignified, and the 
 most important ones are the sieve-lubes, which conduct proteids 
 from above to the growing regions of the root. 
 
THE ROOT. 73 
 
 The number of vascular strands constituting the stele is 
 various, being as few as four or as many as forty. The 
 ordinary number, however, is from eight to twenty. (See 
 figs. 86, 89.) 
 
 82. 3. The cortex generally consists of large thin-walled 
 cells which have become partially separated from each other, 
 leaving larger or smaller intercellular spaces (figs. 86, 89). 
 Its innermost layer, bordering the stele, is usually quite 
 different from the rest, and is recognizable by its wavy, radial 
 walls, which are suberized (^[ 9). This layer is called the 
 endodermis (figs. 86, 88, 89). 
 
 83. Duration. — Even when the primary root persists 
 throughout the entire life of the plant secondary roots often 
 appear. When the primary root perishes, its functions must 
 be performed wholly by secondary roots, which are developed 
 in succession upon those parts where they are useful. The 
 secondary roots themselves may be either permanent or tran- 
 sient. In creeping plants particularly, whether growing on 
 land or in water, the functions of the root are likely to be 
 handed on to successively younger roots, the old ones perish- 
 ing and dropping off. If the roots endure for a considerable 
 time, they may retain their primitive structure and form, or 
 they may undergo secondary changes which unfit them for 
 absorbing organs, and adapt them to subserve various special 
 functions. 
 
 84. Secondary changes. — Shortly after any portion of the 
 root has ceased to increase in length, and, therefore, within 
 the first season, it ordinarily undergoes minor secondary 
 changes which may or may not be followed by more profound 
 alterations. These changes affect its primary structure in 
 various ways and to various degrees according to the parts 
 concerned. 
 
 85. 1. External secondary changes. — In some cases the 
 older roots differ from the younger in scan civ more than the 
 
74 
 
 PLANT LIFE. 
 
 loss of the external layer of cells, from which the root- 
 hairs arose. The sloughing off of this layer of cells carries 
 with it the hairs themselves and exposes the next inner layer 
 of cells, which had before become slightly altered so as to be 
 rather impervious to water. Upon their exposure, this altera- 
 tion proceeds further, so that they become almost or quite 
 incapable of being penetrated by the soil-water to which they 
 may be exposed. It follows from this that it is only the 
 younger part of the root, that is, the portion which has not 
 undergone secondary changes, which is capable of absorbing 
 water. In many roots this is the only change which occurs. 
 In a greater number certain tissues become thick-walled, so 
 that the root is also strengthened. 
 
 In a few instances, the root-cap is cast off from the tip. 
 This, however, only occurs when the growth in length of the 
 root is permanently stopped. 
 
 86. 2. Internal secondary changes. — In a large number 
 of roots, especially those 
 \ 'of dicotyledons and gym- 
 '1 nosperms, the secondary 
 changes result in increasing 
 the diameter, sometimes 
 very greatly. Increase in 
 diameter comes about by 
 the formation of concentric 
 layers of new tissue in two 
 or more regions. The new 
 
 J©" 
 
 o 
 
 Fig. 87. — Transverse section of the periphery of , 11 , _j„__j ■ u 
 
 the root ol Clusia, showing the formation of Cells aie piodliced 111 each 
 
 periderm, ec, cells of cortex: ap, the super- .:_._ l . 1, »: 
 
 ncial cells of the root (suberized); per, the region by tile resumption 
 
 periderm, its inner cells (opposite per) actively ,- ,• 1 • , • 1 
 
 &yidmgbytangentialwalls,itstw,M,ute.l.v.rs. ot active division 111 a layer 
 
 //'.snheri/.id. its innermost layer,///, the phello- r 11 1 ■ 1 
 derm. Highly magnified.— After Van Tieghe" 
 
 temporarily inactive. 
 
 :ells which had been 
 This region is then (ailed the cambium 
 or secondary tnerisiem (see^i 77). The divisions which ensue 
 in these cells are in the main parallel to the surface of 
 
THE ROOT. 
 
 75 
 
 the root, that is, they are 
 tangential divisions. 
 
 The outer growing layer 
 or cork cambium is in the 
 great majority of plants 
 formed from the cells of the 
 pericycle, but it may be 
 produced by some of the 
 cells of the cortex. In any 
 case the tissues which arise 
 from this division are of 1 *" 
 such a nature as to protect 
 the parts within. They con- 
 stitute the periderm (fig. 87), 
 
 ■Transverse section of two bundles 
 from the periphery of the stele of root of broad 
 bean (/ 'icia Faba) at the beginning of secon- 
 dary thickening. The xylem bundle, g, is 
 shaded: the phloem bundle unshaded. ?■, the 
 stelar cambium; /, the pericycle. aiso showing 
 tangential divisions in parts ; s, the endoder- 
 mis. Highly magnified. —After Haberlandt. 
 
 Fig. 89 Transverse section of thesteleol root of bean {Pkaseolus multi/hrus) shortly 
 aftei set ondary thii ki ning has b< gun r, endodermis; ,.", . peril yi le; /■. phloem bundles; 
 /, primary xylem bundles; <_• . j, ' . se< ondarj xylem; , stelar cambium; M, central pith. 
 Compare with fig. go. Highly magnified Attn Sachs. 
 
7 6 
 
 PLANT LIFE. 
 
 and are ordinarily cork-like, i.e., thin-walled and impervious 
 
 to water. Those cells which lie outside a layer of cork are 
 
 therefore cut off from a supply of food and soon perish. 
 
 The inner growing layer, or stelar cambium, is developed 
 
 within the stele and follows a 
 
 tortuous course, lying outside the 
 
 xylem and inside the phloem 
 
 bundles (fig. 88). As a result 
 
 of tangential divisions in this 
 
 region, tissues similar to those 
 
 already existing in the stele are 
 
 produced. On the outer side 
 
 the cells differentiate mainly 
 
 into the tissues of the phloem, 
 
 and on the inner side mainly 
 
 the older into those of the xylem, often 
 
 ^/ f ^S*«Ta1te b r e %VcoX" formin 8 a nearl 5' ^broken mass 
 
 ^Hs'of each (figs. 89, 90). The 
 
 lative amount of the different 
 
 tissues which make up these 
 
 ably. Compare with fig. 89, which 
 about five times as highly magnified 
 
 b, b, b, b, four primary phioem bundles; 1 eld 
 b', secondary phloem produced by 
 stelar cambium, as are the four wedges 
 
 b^^^^-iSSSfLSft bundles goes far to determine 
 l!^riS-Af^S emwedges) th e character of the mature root. 
 87. (a) Woody roots. — If mechanical tissues predominate, 
 particularly in the xylem, the root will become strong and 
 rigid, as in the case of trees and shrubs. When the root is 
 long-lived, the activity of this stelar cambium is usually 
 resumed with each season, a layer of tissue being thereby 
 added to the outside of the xylem region, and a thinner layer 
 to the inside of the phloem. The woody part, especially, 
 shows in cross-section concentric rings indicating the yearly 
 additions. Since the material produced by the stelar cam- 
 bium usually greatly increases the diameter of the root, the 
 outside parts become fissured lengthwise. Thus, in an old 
 and much-thickened root of the woody type, the periderm 
 
THE ROOT. 
 
 77 
 
 and the phloem region, with the cortex between them, if 
 anything is left of it, constitute a bark, which becomes fur- 
 rowed lengthwise, like the bark of the stems of many trees. 
 Such secondary thickening finally produces in the roots a 
 
 Fig. 91. — .-/, diagram of primary structure. /•', C, diagrams showing the results of 
 secondary thickening from the stelar cambium in the two extreme forms c, cortex ; 
 <>.•, endodermis ; />, pericycle ; ph.', primary phloem; //;'', secondary phloem; .1', 
 primary xylem ; x", secondary xylem ; cb, stelar cambium; r', secondary pith-rays ; 
 in, pith. After Van Tieghem. 
 
 structure which is almost identical with that of stems which 
 have undergone secondary thickening. (Compare ^[ 133.) 
 
 88. {!') Fleshy roots. — but if thin-walled cells are the 
 predominant products of the stelar cambium, the root often 
 becomes very thick and fleshy, as in the carrot, turnip, 
 radish, sweet potato, beet, dahlia, artichoke, etc. Such 
 roots serve the plant as storehouses of reserve food, and are 
 consequently useful to animals as food. The thin-walled 
 cells which are produced in such volume may belong to the 
 phloem region, as in the carrot and parsnip, or to the xylem, 
 as in the radish and turnip. This thickening for storage 
 purposes may affect either the primary or secondary roots, 
 or both. Other plants may develop the cortex (orchids) or 
 the pith (daffodils) to an extraordinary degree, forming 
 fleshy roots which also function as storehouses. 
 
 89. (c) Float roots. — In plants which grow in water or 
 in very wet swamps, roots are sometimes modified to serve is 
 floats. In these cases, the voluminous cortex consists of large 
 
/8 PLANT LIFE. 
 
 cells, with huge intercellular spaces which are filled with air. 
 The root thus serves to buoy up the parts of the plant to 
 which it is attached. 
 
 90. ((/) Tendrils, thorns, etc. — In a very few plants, 
 aerial roots are modified into tendrils, being slender, sensitive 
 to contact, clasping the objects which they touch, if of 
 suitable size, and thus assisting the plant to climb ; in some 
 instances they are altered into thorns, being short, rigid, and 
 sharp-pointed ; in others, being exposed to the light, they 
 develop chloroplasts, which enables them to act as organs for 
 the manufacture of food. 
 
 91. Branching. — Both primary and secondary roots may 
 branch. The mode of branching is of two sorts, either by 
 dichotomy, or by the production of lateral branches. 
 
 92. {a) Dichotomy occurs only in a few fernworts, whose 
 roots possess a single initial cell. In this case, however, 
 the single initial cell (^[ 77) is not divided into two equal 
 parts by a partition-wall, as in true, dichotomy (see ^| 103), 
 but the initial of the new branch arises from a very young 
 segment as in Metzgeria (see fig. 61). The result is a fork- 
 ing which cannot be distinguished from a true dichotomy. 
 
 93. (b) Monopodial branching. — In the common mode 
 of branching, the monopodial, the central axis grows most 
 vigorously, and bears lateral branches upon its sides. The 
 normal branches arise from lateral growing points, which 
 originate in regular succession behind the apical growing 
 point. But sometimes branches appear out of this regular 
 order. Such are called adventitious roots. (See *[ 76.) 
 
 94. Position. — Whether regular or adventitious, the posi- 
 tion of the growing points is determined by the vascular 
 bundles in the stele, since they originate opposite the xylem 
 bundles, or with definite relation to them. (See figs. 92, 
 93.) The number of vertical ranks of branches can, there- 
 fore, be predicted with some certainty from the structure of 
 
THE ROOT. 
 
 79 
 
 the root. While the angular diver- 
 gence is thus quite regular, the longi- 
 tudinal intervals at which the branches 
 will be formed, which determines 
 their distribution along the length of 
 the root, are unequal (fig. 92). 
 
 When secondary roots arise from 
 the shoot, they have a fixed relation 
 to the leaves, or they are formed 
 upon the buds produced in the axils 
 of the leaves, or they may arise at 
 indefinite points along the internodes. 
 In the first case, roots may be pro- 
 duced either opposite a leaf, or in 
 pairs, right and left of the base of the 
 leaf. 
 
 95. Origin. — The origin of root- 
 branches and of secondary roots is 
 rarely exogenous ; that is, the root is 
 not commonly produced by the divi- 
 sion of cells which lie upon the sur- 
 face of a member. In the great 
 majority of cases the origin of the 
 roots is endogenous ; that is, the for- 
 mation of the root is begun by the 
 division of cells lying in the interior 
 of the member producing it. In most 
 cases these divisions begin very near 
 to the surface of the stele, either just 
 without it, in the endodermis, or just 
 within it, in the pericycle. Soon a 
 growing point is formed (fig. 93). 
 
 /jr* 8 * -8 " 
 
 X 
 
 The rootlet is thus ii 
 completely hidden, 
 
 early stage 
 
 beinj 
 
 buried 
 
 'IG. 92. — Seedling pea. showing 
 three \ ei tii a) ranks ol brani li- 
 es aloiig the main root. These 
 
 are numbered t, 2, 3. Natural 
 size.— After Krank. 
 
So 
 
 PLANT LIFE. 
 
 beneath the cortex, through which it gradually makes its way 
 by the destruction of the tissues ahead of it, partly through 
 disorganization of the tissues by pressure, and, probably, 
 partly through actual digestion and absorption of the material 
 of these cells. When the rootlet reaches the surface it 
 emerges, therefore, from a distinct rift in the cortex (fig. 94). 
 
 Fig. 93 
 
 Fig. 93.— Transverse section of a root of a fern (7 '/,•>/.? cretica), passing through the 
 axis of a rootlet which has not yet emerged. Only the stele and three rows of cortex 
 shown, a, apical cell of rootlet, forming anteriorly the root-cap. <■/>, and posteriorly 
 the body of the root, ec, e, c, pd\ b, binary xylem bundles; /, phloem bundle with its 
 fellow opposite; /V, pericycle; at, endodermis; /, temporary digestive pouch, in 
 course of disorganization and digestion; d, cells of cortex, which will be disorgan- 
 ized as rootlet advances. Highly magnified— After Van Tieghem. 
 
 Fig. 94— The same as fig. 93, but older; not quite so much magnified. Tbe'rootlet 
 is just emerging from the parent root. /</, c, stele of the rootlet ; ec, its cortex; 
 </, disorganized cells of cortex, ec', of parent root; /-', secondary xylem; other letters 
 as in fig. 93.— After Van Tieghem. 
 
 96. External conditions. — Branching of the root is often 
 profuse, and is dependent very largely for its character upon 
 the conditions under which it takes place. In those roots 
 which penetrate the soil, it is profoundly modified by the 
 
THE ROOT. 8 I 
 
 character of the soil itself and the amount of moisture and 
 organic matter in it. 
 
 97. Buds. — New shoots may be formed by the roots, either 
 as a result of injuries, or normally. In a partially developed 
 form, these constitute buds (see ^j 101). Whether formed 
 as a result of injuries or normally, they are known as adven- 
 titious buds. They arise in the same places and develop in 
 the same way as lateral roots ; that is, they are endogenous, 
 and, as they continue to grow, burst through the cortex. 
 The shoots so produced grow in the normal manner. Very 
 rarely the growing point of the root, casting off the root- 
 cap, becomes itself the growing point of the shoot. This 
 alteration is usually the result of artificial reversal of the posi- 
 tion of the root, being brought about in some potted plants 
 by turning them upside down. 
 
CHAPTER VIII. 
 
 THE SHOOT. 
 
 98. The gametophyte shoot. — If plants could be examined 
 in the order of their development, it would be discovered 
 that the shoot has been evolved earlier than the root. It 
 makes its appearance first in the leafy liverworts and in the 
 mosses, in which the gametophyte and sporophyte each form 
 a stem. The gametophyte differentiates its secondary shoot 
 into a stem and leaves. This stem in liverworts is a slender 
 cylindrical body of very simple structure, upon whose flanks 
 arise leaves which consist of a single layer of cells only. 
 (See ^ 60. ) Neither the stem nor the leaves are homologous 
 with the stem and leaves of the higher plants. In the stem 
 itself one finds all the cells practically alike, so that little 
 differentiation of tissues has yet occurred. In mosses, how- 
 ever, the gametophyte stem shows some advance, in that its 
 tissues are clearly differentiated, the outer being transformed 
 into thick-walled cells, in order to give mechanical rigidity 
 to the stem, while the innermost, remaining slender, are 
 much elongated and serve the purpose, it may be, of con- 
 duction. (See ^[ 63.) This differentiation is naturally more 
 marked in those mosses which are erect and whose body 
 becomes largest, since in these the need for rigidity and con- 
 duction of food materials from one part to the other becomes 
 greater. In both groups the branching of the gametophyte 
 shoot is like that of the sporophyte shoot of some of the 
 higher plants, except that the branches never stand in the 
 same relation to the leaves. (See •' 65.) 
 
 82 
 
THE SHOOT. 83 
 
 99. The sporophyte shoot. — The shoot developed by the 
 sporophyte of mosses and liverworts forms no leaves, but 
 develops as a slender cylindrical stalk, at the distal end of 
 which the capsule containing the spores is formed (figs. 64, 
 73). It is rather difficult to see in this cylindrical stalk the 
 homologue of the leafy stem developed by the sporophyte of 
 the fernworts ana other plants. 
 
 The simultaneous performance of the work of nutrition and 
 of sexual reproduction proved impracticable, as shown by the 
 development of the liverworts and mosses, which are all 
 humble plants. The fernworts, originating probably at an 
 early period from the same ancestors as the liverworts, sep- 
 arated the two functions and laid the chief work of nutrition 
 upon the sporophyte. The advantage thus gained enabled 
 the extinct fernworts to develop into plants of tree-like size, 
 and to become the ancestors of all the seed plants. 
 
 The gametophyte shoot was, comparatively, a failure ; the 
 sporophyte shoot was a marked success. It has become 
 adaptable to many conditions and many functions. To 
 accomplish this its members have been extensively modified 
 in form and structure in various plants. The development 
 and mode of branching, together with the various forms 
 which the shoot assumes, are now to be discussed, to be fol- 
 lowed by an account of the two members, stem and leaf, into 
 which it is usually differentiated. 
 
 100. Primary shoot. — The shoot which develops from the 
 fertilized egg is called the primary shoot. A very few excep- 
 tional plants are found in which no primary shoot develops, 
 although there are a number of cases in which the primary 
 shoot becomes early aborted, and its pla< e taken by secondary 
 shoots arising from the root. The primary shoot normally 
 arises in fernworts from the anterior half of the egg. The 
 anterior hemisphere usually divides into two quadrants, one 
 of which develops into the primary leaf, and the other into 
 
8 4 
 
 PLANT LIFE. 
 
 the primary stem. The stem quadrant, by repeated divisions, 
 quickly specializes a central cell, which becomes the apical 
 cell of the new shoot. Ordinarily it takes the form of a 
 three-sided pyramid, whose base forms the extreme tip of the 
 developing shoot (s, fig. 76, /, fig. 95). From the three inner 
 faces, as described for the root (^f 77), segments are constantly 
 formed, whose further divisions produce all the tissues which 
 constitute the members of the mature shoot, i.e., the stem 
 and the secondary leaves. In some fern worts and in the seed 
 plants, the posterior hemisphere resulting from the first divi- 
 sion of the egg grows into a filament called the suspensor, 
 and the primary shoot develops from the anterior hemisphere. 
 (See fig. 80.) In these plants ordinarily two or more cells 
 at the apex of the primary shoot are specialized as the initial 
 cells, and from their segmentation arise the tissues of the 
 whole shoot, as in the fernworts. 
 
 Fig. 95. — Median longitudinal section through the apex of a shoot of the horsetail 
 ( Eg ui.u •turn. ,i> vense), showing primary meristem and the form of the growing point. 
 t, apical cell, from whi< h a segment, .V, has just been cut off by wall/. S' , a seg- 
 ment previously cut off, has divided by wall m. /,/"',/", successively older leaf 
 fundaments; g, the initial cell of a branch. Magnified too diam.— After Strasburger. 
 
 101. Primary meristem. — Whether the tip of the shoot 
 be occupied by a single initial cell or by a group of initials, 
 the apical region, in which the formation of new cells is 
 
THE SHOOT. 
 
 85 
 
 taking place, is called the primary meristem (fig. 95). This 
 primary meristem has no definite limit below, but passes 
 
 insensibly into the permanent tissues. The tip of the shoot 
 may be either a sharp cone or a low dome. Between these 
 forms a complete series of gradations exists. Below the apex 
 the shoot begins to show a differentiation into a central axis 
 and lateral outgrowths. The first of these to appear are 
 swellings which form the leaves. Later, above the leaf 
 fundaments may appear the fundaments of the lateral shoots. 
 
 Fig. 06. — Diagram of a section through a bud / ', the apex; i, 2, 3, 4, successively older 
 leaf fundaments; a, 6, c, successively older branch fundaments; </, e, vascular bundles. 
 —After Hansen. 
 
 The older leaves upon the sides of the axis outgrow the 
 younger ones and the developing axis, and arch over them 
 in such a way as to form a more or less compact structure, 
 which is a terminal bud. A bud is, then, an undeveloped 
 shoot, whose older leaves protect the younger, and particu- 
 larly the primary meristem (fig. 96). From the terminal 
 bud arise all the members of the primary shoot. 
 
 102. Differences from root. — From what has been said of 
 the origin of the shoot, it will be observed that it is dis- 
 
86 
 
 PLANT Lli-E. 
 
 tinguished from the root by not forming through segmenta- 
 tion from the outer faces of the initial cell or cells a many- 
 layered epidermal cap. In further contrast with the root, 
 which often has no true epidermis except the root-cap, the 
 shoot is characterized by possessing an uninterrupted epider- 
 mis over its entire surface, consisting always at first of a 
 single layer of cells. This epidermis persists as a surface 
 covering either throughout the life of the shoot, or for a long 
 period, being replaced only upon the 
 older surfaces of the axis by subsequently 
 formed protective layers. (See • 134-) 
 103. Branching. — branches of the 
 shoot arise from lateral buds, which are in 
 all respects similar to the terminal buds 
 just described. If, for any reason, the 
 terminal bud of the stem becomes de- 
 stroyed, or its growth arrested, a branch, 
 developing from a lateral bud near by, 
 may assume the position and habit of 
 the main axis, its own normal mode of 
 development being altered. In many 
 plants the death or arrest of the ter- 
 minal bud recurs at regular intervals. 
 In such plants, therefore, the main axis 
 is really a succession of lateral branches, 
 and the branching is said to be sympo- 
 dial (fig. 97). In some plants, e.g., 
 lilac, two lateral buds standing at the 
 same level may develop, if the terminal 
 one fails. In this case the shoot seems 
 to divide into two equal branches. This, 
 however, is not true, but false, or sym- 
 />(><Ii\il, dichotomy. True dichotomy, like true dichotomy of 
 the root, occurs only in those plants in which the axis has 
 
 I ig 97. Shoot of Euro- 
 pean linden, t, the last 
 internode formed by the 
 liiid of present season. 
 This dies and drops off 
 and the shoot will be 
 formed next year by the 
 last axillary bud, a, 
 which a] ipi .irs to be 
 terminal alter loss of t. 
 Half natural size.— After 
 Frank. 
 
THE SHOOT. 87 
 
 a single initial cell. The initial in these cases divides into 
 two equal parts, each of which becomes the initial of a new 
 branch. Ordinarily, however, the terminal bud develops 
 without interruption. In case it is more vigorous than any of 
 the lateral buds, the plant will have a central axis, from the sides 
 of which distinctly smaller branches arise. If, however, the 
 lateral buds are almost or quite as strong as the central one, 
 the plant seems to be broken up into branches, and, after it 
 has attained its mature form, no one can be pointed out as 
 the main axis.* Such branching is monopodia!. These two 
 types of monopodial branching and the sympodial type are 
 all illustrated in the forms attained by common forest trees. 
 (See frontispiece.) 
 
 104. Inflorescence. — Especially profuse branching com- 
 monly occurs in the parts of the seed plants where flowers are 
 produced. Such clusters of branches bearing flowers constitute 
 an inflorescence. Each sort has received a special name which 
 not only indicates the type of branching, whether sympodial 
 or monopodial, but also the relative length of the branches. 
 
 If the branching is monopodial and each lateral shoot is 
 unbranched, the inflorescence is a raceme. If the lateral 
 shoots are very short, it is a spike. If the main axis also is 
 very short, it is a head. If the main axis is short and the 
 lateral axes long, it is an umbel. If the lateral axes are of 
 unequal length, so as to bring the flowers to about the same 
 level, it is a corymb. If the branching is sympodial, various 
 forms of the cyme result. Several combinations of these 
 inflorescences are possible. f 
 
 105. Axillary buds.— Lateral buds are ordinarily formed 
 in definite relation to the leaves. They stand usually in the 
 
 * The obscurity is greatly increased by the death of more branches than 
 survive, owing to various causes resulting in poor nutrition or disease. 
 
 f For further discussion see Gray: "Structural Botany," p. 144; 
 Goebel : " Outlines of Classification," p. 407. 
 
88 
 
 PLANT LIFE. 
 
 upper angle formed by the leaf with the stem. This angle 
 is known as the axil of the leaf, and such buds are said to 
 
 Fig. 98. 
 
 Fig. 98. — I, terminal shoot of an elm. A, leaf- 
 scars; k, axillary buds. Natural size. II, 
 one of the buds cut lengthwise through 
 center, magnified 3 diam. a, young axis; 
 .", li-.it -.car; bl, youDg leaves; </■ bud-scales. 
 _ — After Behrens. 
 
 Fig. 99. — .-) , twig of red maple with ac- 
 cessory buds in addition to axillary bud. 
 B, twig ol butternut, with leaf sear. «;. small 
 axillary bud./', and larger accessory buds, 
 1. d, above axil. Natural size. — After 
 Gray. 
 
 Fig. 100.— A bit of stem of a honeysuckle 
 (Lonicera tylosteum) bearing large axillary 
 and smaller superposed accessory buds 
 above the axils of the scars, « >i, from 
 which leaves have fallen. Natural size. — 
 After Frank. 
 
 be axillary (fig. 98). Ordinarily a single bud arises in the 
 axil of each leaf. Its origin is always subsequent to that of 
 
 the leaf- fundament (figs. 95, 96). 
 
THE SHOOT. 89 
 
 There are many cases in which the lateral buds are not 
 found precisely in the axils of the leaves, but slightly to one 
 side, or at a greater or less distance above the axil (figs. 99, 
 100). 
 
 106. Extra-axillary buds. — Buds are frequently formed 
 without any relation whatever to the leaf-axil, and even on 
 the leaf itself (fig. 293). Sometimes these extra-axillary 
 buds are produced without the action of any extraordinary 
 cause, but more commonly injury of one sort or another 
 seems to act as a stimulus to the production of such buds. 
 Buds which do not originate in acropetal succession on the 
 parent shoot are called adventitious buds. 
 
 107. Adventitious buds may arise upon stems, leaves, or 
 roots. They are most commonly and abundantly produced 
 upon stems and roots. In the willows their ready production 
 is utilized for obtaining young, vigorous, and pliable shoots 
 to be used in basket-work. The few plants which produce 
 adventitious buds upon leaves, as well as the many which 
 produce them on stems, are often propagated in this way. 
 (See m 364-) 
 
 108. Dormant buds. — Many buds continue to grow with- 
 out interruption from the time of their formation, but more 
 cease to develop after they have reached a certain stage. 
 Such buds may remain dormant for a considerable period, 
 and may even be overgrown and completely enclosed by the 
 wood upon old shoots. The bud in this case grows slowly 
 and maintains itself near the surface of the wood. It is quite 
 possible that these dormant buds should for some reason 
 begin to develop later, when they are liable to be confounded 
 with adventitious buds. In case they have been buried by 
 the growth of tissues over them, the shoot which they pro- 
 duce will seem to come from the interior of the organ upon 
 which they are borne. This apparent internal origin must 
 not be confounded with the real endogenous origin of roots. 
 
90 PLANT LIFE 
 
 Since in most cases lateral buds have a definite relation to 
 the leaves, the shoots which arise from them will have a 
 similar relation. But, since many buds are produced which 
 never develop into branches, this relation is often obscure 
 and difficult to see. 
 
 109. Special forms. — The primary shoot may'grow under- 
 ground, in which case its stem usually takes a horizontal 
 direction and becomes much thickened for storage of reserve 
 food (•; 236), while its leaves are so reduced as to be scarcely 
 recognizable. Such a shoot is known as a rhizome. When 
 the primary stem is short, erect, and crowded with thickened 
 leaf bases it forms a bulb, as in the hyacinth and onion. 
 When the primary stem is short and thick, and has thin scale 
 leaves upon it, it forms a conn, as in cyclamen and Indian 
 turnip. 
 
 Branches of the specialized primary shoot may be like it, 
 as when some branches of the rhizome or corm are them- 
 selves rhizomes or corms. Others, however, will be adapted 
 to other purposes, as when aerial branches arise from rhizomes 
 to carry foliage and flowers, or when slender leafless shoots 
 called runners develop from the main axis of the strawberry 
 (fig. 297). Offsets and stolons (figs. 296, 369) are similar 
 branches likewise adapted to propagation (^[ 366). 
 
 Branches of the secondary shoots may also be different 
 from their parent axis. In different plants the shoots assume 
 the most varied forms. 
 
 Such specialized branches may be confined to a definite 
 region of the plant, or may he distributed over it. The 
 more important of these kinds of branches may now be 
 enumerated. 
 
 110. (a") Dwarf branches. — It is not uncommon to find 
 branches specialized merely by their slight development in 
 length and their capacity for being separated readily from 
 the parent shoot. Such short branches are particularly com- 
 
THE SHOOT. 
 
 91 
 
 raon among the cone-bearing trees. In these plants the 
 snort branches carry the clusters of needle leaves (figs. 10 1, 
 
 Fig. ioi. — A shoot of Scotch pine showing two regions of dwarf branches each with a 
 pair of needle leaves, and three regions oi flower branches; the flowers have fallen 
 From lower two, showing scale leaves covering the stem, Naiur.il size.— After Will- 
 komm, 
 
 102, 358). After the death of the Leaves the branches 
 themselves drop off. Somewhat similar short branehes are 
 
9 2 
 
 PLANT LIFE. 
 
 to be recognized among many deciduous trees, and, in the 
 apple, the so-called fruit spins arc 
 not dissimilar (fig. 103). 
 
 111. (/) Flowers. — The most 
 common of the specialized branches 
 among the seed plants are those 
 which constitute the flower. In 
 these the axis usually remains short, 
 the leaves are crowded, and often 
 
 Fig. .02. Fi . .03. 
 
 Fig. 102. — The base of leaves and dwarf branch of Scotch pine cut through the center 
 lengthwise. Besides the two needle leaves the dwarf branch carries a number of scale 
 leaves, d. Between the 1 ases of the needle leaves is seen the conical apex of the dwarf 
 branch, showing their lateral origin. Magnified about 4 diam. — After l.uerssen. 
 
 FlG. 103. — Twig of apple, bearing fruit spurs. A, points at which fruit was detached 
 the preceding year ; // ', leaf scars. Natural size.— After Hardy. 
 
 some of them are highly colored (fig. 104). 
 these flower branches are deciduous. 
 
 Commonly 
 
 Mag- 
 
 Pic;. 104. Fig. 105. 
 
 Fig. 104. — Flower of Sedum acre, s, sepal; /, petal; si, stamen; c, carpel 
 
 nified 3 diam— After Uaillon. 
 FlG. 105. — Piece of a twig nf asparagus ; in the axil of the scale leaf, b, arise a (lower 
 
 shoot, and three leafless needle-like branchlets. Magnified about 2 diam. — After Frank. 
 
 112. (c) Cladophylls. — A few plants have developed 
 shoots which replace leaves in function and resemble them 
 
THE SHOOT. 93 
 
 In form. These cladophylls may be either broad and flat- 
 tened, as in the "smilax" of the greenhouses, or they 
 may be slender and needle-like, as in the common garden 
 asparagus (fig. 105). In any case, since they replace leaves 
 in function, they are abundantly supplied with green color- 
 ing matter for manufacturing food. 
 
 113. (</) Bulblets. — Other branches remain undeveloped 
 as buds, but their leaves become thick and fleshy. These 
 bulblets are easily detached and serve for propagation. (See 
 ^| 364.) They are to be found in many plants. In the 
 tiger-lily they occupy the axils of the leaves (fig. 294), 
 and are modified lateral buds, while in the garden onion 
 they usually replace the flowers. 
 
 114. (c) Tubers. —Some underground shoots have their 
 ends suddenly and greatly enlarged, adapting them to the 
 storage of food. They are then called tubers. In the white 
 potato the tuber consists of several terminal internodes of 
 an elsewhere slender underground stem, the "eyes" being 
 lateral buds in the axils of minute scale leaves. In a few 
 plants tubers may even be formed above ground, as in certain 
 polygonums whose flowers are often replaced by little tubers 
 which are readily detached (fig. 106). 
 
 115. (/) Tendrils.— Some shoots take the form of slender, 
 leafless, sensitive tendrils, which assist the plant in climbing 
 by coiling about suitable objects (fig. 107). 
 
 116. (g) Thorns. — Many plants produce defensive shoots, 
 which are leafless, rigid, short, and sharp, called thorns, 
 which may be either simple or branched (fig. 108). The 
 honey-locust furnishes an excellent example of branched, or 
 compound, thorns. 
 
 Leaves themselves may be developed as tendrils or as 
 thorns, so that it must not be assumed from appearance alone 
 that such members are forms of the shoot. Observation of 
 the origin and relation of the members will reveal their true 
 
94 
 
 PLANT LIFE. 
 
 nature. If shoots, they will usually be subtended by a leaf; 
 
 if leaves, they will often have a bud or a shoot in their axils. 
 Thorns or tendrils which do 
 not arise at the nodes are 
 reckoned as shoots. 
 
 117. Duration. — Shoots are 
 either annual, biennial, or per- 
 ennial. If the entire shoot dies 
 
 Fig. 106. 
 
 Fig. 106.—.-!, upper part of a plant of Polygonum viviparum, showing flower cluster, 
 the flowers in lower hall being replaced by tubers. Two-thirds natural size. /.', a 
 fallen tuber. Magnified about 3 diam. C, a plantlet growing from tuber. Natural 
 size.— After Kn ni 1 
 
 Fig. 107. — A portion of the stem of white bryony, />', from which a tendril, ».>-, arises 
 near the leaf stalk, />, and the bud, k . 11, rigid portion of tendril ; the portion between 
 11 and tlu- portion .1, clasping the support. A, has become coiled into a spiral which 
 reverses the direction oi the coils at w and «/'. Nearly natural size.— After Sachs. 
 
 this generally involves the death of the whole plant, though 
 new adventitious shoots may arise from the roots, as in 
 sweet potatoes. In many plants, in which the shoot seems 
 
THE SHOOT. 95 
 
 to die at the close of the growing season, an underground 
 portion really survives, and sends up the new shoots. Such 
 plants, if they live for two years, are called biennials ; or, 
 if they live for several or many years, are called perennials. 
 
 Fig. 108. — Shoots of Vella sfiinosa, showing thorns. Natural s 
 
 The shoot may be composed mainly of soft tissues, and 
 persist underground, where it is protected against unfavorable 
 conditions, such as drought and cold, and especially against 
 sudden changes; or it may be composed mainly of mechan- 
 ical tissues, and be fully exposed, as are the shoots of trees. 
 In these cases the leaves generally perish and drop off an- 
 nually, but in the "evergreen" plants they live more than 
 one growing season. 
 
CHAPTER IX. 
 
 THE STEM. 
 
 118. Definition. — The shoot is almost always segmented 
 into members of two kinds, the stem and leaves. The stem 
 is the central axis of any shoot, and the leaves are lateral out- 
 growths, or branches, of it. These two members cannot be 
 accurately defined, but are in most cases readily distinguish- 
 able. Leaves commonly differ from the stem in internal 
 structure, and in their flattened form, limited growth, and 
 position, subtending the lateral shoots. (See further p. 117.) 
 
 119. Nodes and internodes. — Upon examining the surface 
 of the stem, it is almost always readily distinguishable into 
 distinct regions, the nodes and internodes. The nodes are 
 the narrow zones, often somewhat swollen (whence the name), 
 at which one or more leaves arise. The internodes are the 
 zones between the nodes. Upon watching the development 
 of the stem from the terminal bud, it will be seen that new 
 nodes and internodes are constantly emerging from its base, 
 and that the leaves formed at the nodes are successively 
 expanding. This emergence of the internodes is due to their 
 elongation. The amount of elongation, however, varies 
 greatly in different plants, and even in different parts of the 
 same plant. In many cases the internodes are considerably 
 and uniformly elongated ; the leaves are then distributed 
 along the stem at considerable and regular intervals. In other 
 cases the internodes remain very short, and the leaves are, 
 
 96 
 
THE STEM. 97 
 
 therefore, crowded. They may be so crowded as to completely 
 
 envelop the stem and hide it 
 
 from view. This is well seen 
 
 in the scale-like leaves of such 
 
 plants as the pines (fig. 101), 
 
 cedars, and arbor vitas (fig. 109). 
 
 Or, certain of the internodes 
 
 may elongate, while others 
 
 remain undeveloped. For 
 
 example, in the shepherd's- 
 
 purse, the first internodes 
 
 remain short, so that the lower 
 
 leaves are Crowded intO a tuft FlG >°9—A shoot of arbor vita; or white 
 
 cedar, showing scale leaves covering 
 Of rosette; the following inter- stem - Natural size.— After Kerner. 
 
 nodes are elongated, the corresponding leaves being scattered 
 at regular intervals; while, still higher, the internodes are 
 again shortened and the leaves brought into close clusters in 
 the flowers. 
 
 120. The consistence of the stem depends upon the relative 
 amount of mechanical tissues which it contains. Stems may 
 be designated as woody, solid, or fleshy, terms which need no 
 further definition. 
 
 121. The shape of the stem varies extremely in different 
 plants. Very commonly the stem as a whole is looked upon 
 as cylindrical, but, if carefully considered, it will be seen that 
 the diameters of successive internodes at first become gradually 
 greater, and, after maintaining this maximum for a time, grow 
 gradually less. The stem is, therefore, a cylinder with more 
 or less conical ends. If the attainment of the maximum 
 diameter is sudden, and the diminution similarly sudden, the 
 resulting stem will have the shape of a double cone. The 
 modification of such a form into the spherical is not diftic nit 
 to imagine. Striking illustrations of these extreme forms are 
 to be found among the cactuses (fig. no). 
 
93 
 
 PLANT LIFE. 
 
 122. A section of the stem commonly presents an irregu- 
 larly circular outline (fig. in). Occasionally the surface of 
 the stem is fluted or channeled, and, if these grooves or 
 channels be few and the corresponding angles prominent, the 
 section of the stem is polygonal, with three, four, five, six, or 
 more sides. 
 
 123. Habit. — As to habit, stems are commonly erect when 
 enough mechanical tissue is developed to render them suffi- 
 ciently rigid to carry not only their own weight, but that of 
 
 Jmw^ 
 
 A B 
 
 Fig. iio. — Cactuses, showing form. A, Cereus dasyacanthus. B, Echinocactus 
 horizontalis. In both the clusters of spines arise from tubercles on the stems. 
 Reduced. — After Kerner. 
 
 the leaves and other members attached to them. Other stems 
 lie flat upon the ground, to which they may or may not attach 
 themselves by the development of secondary roots. Between 
 these prostrate, or creeping, stems and the erect form every 
 conceivable position exists. The direction of growth is deter- 
 mined largely by the relation of the plant to gravity and light 
 as stimuli. (See ■ •; 285, 287.) Other stems rise into the 
 
THE STEM. 
 
 99 
 
 air, not by their own rigidity, but by the development of 
 special members for climbing purposes, such as recurved 
 spines, tendrils, sensitive leaf stalks, or even by recurved 
 normal branches. (See ^[^[115, 158.) Others wrap them- 
 selves about objects of suitable size, and are called twining 
 stems. (See • 291.) The direction of twining varies with 
 different plants, but most commonly corresponds to the 
 movement of the hands of a watch, the support being sup- 
 posed to be in the center. 
 
 124. Primary structure. — The origin of the stem-tissues 
 has already been described. (See ^j 100.) 
 
 In following the stem from apex to base it is readily 
 observed that the structure changes as the parts grow older. 
 It is possible, however, to select a point at which the stem in 
 
 Fig. hi. Fig. i 12. 
 
 Fig. hi. Diagram ol a transverse section of stem of Iberis amara, showing outline, 
 
 and paired \ asi ular bundles. The bla< k is the xylem bundle : the gray is the phloem 
 bundle. The outer line represents the epidermis : a circle including the bundles would 
 mark the limits ol the stele, with its 1 entral pith : the cortex lies between the epid« in is 
 and stele Vftei Ntfgeli 
 Fig. 1 (2.— Diagram of a transverse section ol a palm stem The epidermis is represented 
 
 by the outer line; the endodermis by the innei one, with the narrow CO It ex between 
 
 them; the stele, with numerous bundles scattered through the pith, is within the 
 endodermis. Alter Frank. 
 
 all cases attains a definite development. This point is at the 
 internode whi< h has just reached its full length. The struc- 
 ture of the stem at this point may be designated as its primary 
 structure. If a thin section be cul from such an internode, 
 
IOO PLANT LIFE. 
 
 three definite regions may be distinguished, viz.: (i) the 
 
 epidermis; (2) the cortex; (3) the stele (figs, in, 112). 
 
 125. 1. The epidermis. — This is a single layer of cells 
 forming the extreme edge of the section, being, therefore, the 
 layer which covers the surface of the stem. Here and there 
 maybe observed intercellular spaces, which permit communi- 
 cation between the outside air and similar spaces in the deeper 
 tissues of the cortex. These openings are usually bordered 
 by two specialized cells, and are called stomata. The 
 epidermal cells may be furnished with green chlorophyll 
 bodies, or these may be entirely absent. 
 
 126. 2. The cortex. — This region consists of several 
 rows of cells, usually thin-walled and not in close contact, and 
 hence abundantly provided with intercellular spaces. These 
 cells usually contain many chlorophyll bodies, to which the 
 green color common to stems is due. 
 
 The innermost layer of the cortex abutting upon the stele, 
 whose radial walls are suberized (^J 9), is usually specialized 
 to form a distinct layer of cells. This layer is the endodermis 
 (fig. 1 1 8). 
 
 127. 3. The stele. — The central region is called the 
 stele. It consists, as in the root, ordinarily of three parts. 
 Its outer layer of cells is known as the pericycle (fig. 118). 
 Within the pericycle are clusters of smaller cells, the cut ends 
 of the vascular bundles. Occupying the space between the 
 vascular bundles is the pith (figs, in, 112). 
 
 These regions of the stem are subject to various modifica- 
 tions. 
 
 128. 1. The epidermis. — While the epidermis is usually 
 a single layer of cells, it is sometimes increased to two or 
 three layers. Stomata may be entirely lacking. This is 
 especially the case in those underground and submerged 
 stems in which the stomata would be useless. The cells of 
 the epidermis are often prolonged into outgrowths of various 
 
THE STEM. 
 
 101 
 
 shapes, such as hairs, scales, and the like (figs. 113, 114; 
 see also figs. 361-365). 
 
 129. 2. The cortex. — In some plants the cortex under- 
 goes an enormous development, forming in some tubers the 
 greater part of the massive stem. 
 In other plants the cortex under- 
 goes such reduction that it con- 
 sists only of two or three layers of 
 cells. It very commonly enters 
 with the epidermis into the for- 
 
 FlG. 113 
 
 Fig. 113. — Forms of hairs from Plectranthus. a, simple pointed hair; /•, stalked 
 glandular hair; < , sessile glandular hair with secretion covering the two glandular 
 cells. Highly magnified. — After De Bary. 
 
 Fig. 114. — T-shaped hair of the wall-rlower [Cheiranthus). e, epidermis. Highly 
 magnified. — After De Bary. 
 
 mat ion of outgrowths, which are then known as emergences. 
 These emergences may take the form of rounded elevations, 
 producing a warty stem, or they may be sharp pointed 
 and either straight or curved, forming prickles (figs. 115, 
 116); or the emergence may be produced along a con- 
 tinuous line, giving rise to wings upon the stem ; or the 
 stem may be more or less covered with large pointed or 
 angular elevations, called tubercles, as in some cactuses 
 (fig. no). Very frequently the intercellular spaces of the 
 cortex are greatly enlarged, forming air passages of con- 
 siderable size. These passages may arise by mere separation 
 of the cells of the cortex, or by the destruction of those in 
 certain regions, or by a combination of these causes 
 (fig. 117). In other cases the cortical cells, instead of 
 
PLANT LIFE. 
 
 remaining thin-walled, may become greatly thickened in 
 certain regions, or even throughout the cortex. These 
 
 Fig. 115. Fig. 116. 
 
 Fig. 1 15 —Prickles on the stem of a rose. Natural size.— After Prantl. 
 
 Fig. 116.— A longitudinal section through a rose prickle in a young stage, showing Imu 
 
 the sub-epidermal (cortical) tissues enter into the structure of the emergence. Magni 
 
 fied 200 diam. — After Rauter. 
 
 Fig. 117. — Transverse section of the Stem of Elatine, showing intercellular canals, r. 
 Magnified about 15 chain.— After Reinke. 
 
 mechanical cells are likely to be aggregated in clusters or 
 strands, and serve an important purpose in strengthening 
 
THE STEM. 
 
 103 
 
 the tissues (fig. 118). In some cases vascular bundles arc 
 found in the cortex outside the stele, when they are known 
 as cortical bundles. 
 
 Fig. 118.— Transverse section of the stem of a ground [>ine (Lycoiodium complana- 
 tinu). The stele is enclosed by the endodermis, en\ />, pericycle; »'. xylem bundle; 
 ///, phloem bundle; cc', cortex, . '. mechanical tissue with thickened walls; <■/, epi- 
 dermis. In the cortex a branch stele passing out to a leaf c.n the right is cut across. 
 Magnified ioo diam.— After Sachs. 
 
 130. 3. Stele. (</) Pericycle. — The pericycle is rarely 
 wanting. It is much more frequently increased from one to 
 several layers of cells. In this case it commonly differ- 
 entiates into regions of mechanical cells with thick walls and 
 small cavities and a region of thin-walled cells. These 
 mechanical cells are either aggregated in strands opposite to 
 the vascular bundles of the stele, or they constitute a com- 
 plete zone around it. Many of the most valuable textile 
 fibers, such as those of tlax, hemp, and ramie, are obtained 
 from this region of the stem (fig. 1 19). 
 
 131. (/') Vascular bundles. — In any section of the stem 
 the number of vascular bundles in the central cylinder varies 
 greatly, not only in different plants, but c\cn in different 
 parts of the same plant. The bundles are commonly arranged 
 
104 
 
 ri.AA'T LIFE. 
 
 in pairs, a phloem (bast) bundle and a xylem (wood) bundle 
 being placed side by side, thexylem occupying the side next 
 
 Fitt. i ic).— Portion of a transverse section of the stem of flax, m, pith; //.secondary 
 xyiern forming a woody cylinder; pk, phloem ; />, bundles of mei hanical tissue (fibers) 
 among the thin-walled cells, tin- two sorts making up the cortex; ./, the epidermis. 
 Magnified about J5 diam. — After Frank. 
 
 P 
 
 Fig. 120. — Transverse section of a bundle pair from the stem of .1 begonia. 'The shaded 
 pari is the xylem bundle; the small irregular cells above are the phloem bundle; 
 between them is a zone "t urmi.itiiii: 1 • inn tern), the stelar cambium, 
 
 ulii. Ii extends also right and left oi the bundle pair. The radius of the section passes 
 through (V; C, next the center. Magnified 150 diam.— After Haberlandt. 
 
 the center of the stem, and the phloem the side next the 
 surface (figs. 1 1 1, 120). The number and position of these 
 
THE STEM. 
 
 105 
 
 bundles is, however, subject to change. In some cases 
 one of the strands surrounds the other. Commonly it 
 is the bast which surrounds the wood, as in the fernworts 
 (fig. 121). Sometimes independent phloem bundles are 
 
 Fig. 121. — Transverse section of Selaginella, showing three steles, eacli composed 
 of a xylem bundle surrounded by phloem. /, /, intercellular spaces in cortex, 
 separated from the steles only by the large-celled endodermis The cells underlying 
 the epidermis are thickened to form mechanical tissue. Magnified 150 diam.— After 
 Sachs. 
 
 found with which are associated no xylem bundles. In 
 the phloem certain cells may develop into libers, which 
 are not to be confused with the fibers occurring in the 
 pericycle. Some of these, also, are valuable in the textile 
 industries. 
 
io6 
 
 PLANT LIFE. 
 
 The paired vascular bundles within the stele occupy various 
 positions, and for purpose of location may be spoken of as 
 though single. If transverse sections of the stem are ob- 
 served, they may be seen either in a single row, roughly 
 parallel with the surface of the stem (fig. in), or in several 
 concentric rows (fig. 122), or they maybe irregularly dis- 
 posed throughout it (fig. 112). No one method ofarrange- 
 
 Fig. 122.— Transverse section of the aerial stem of an onion (A Ilium Schoenoprasum). 
 e, epidermis; ch, chlorophyll-bearing tissue of cortex; r, colorless tissue of cortex; 
 C, c'. vascular bundles (xvleni bundles black, phloem bundles dotted); sr, mechanical 
 tissues connected into a cylinder; m, pith; A, pith canal formed by destruction of 
 1 ells. Magnified 30 diam. — After Sa< lis. 
 
 ment is confined to any of the larger groups of plants, 
 although the first is characteristic of most dicotyledons, 
 while both the second and third methods are common among 
 the monocotyledons.* 
 
 * So many exceptions are found to these last statements that it is lust 
 not to indicate the arrangemenl of the bundles by the terms dicotyle- 
 donous or monocotyledonous, as has been commonly dune ; nor is it 
 possible to maintain the terms exogenous and endogenous, which have 
 long since become obsolete because misleading. 
 
THE STEM. 
 
 107 
 
 h likewise varies greatly in 
 
 to different conditions of 
 
 found enormously developed 
 
 as in some tubers, such as 
 In other plants, particularly 
 
 132. (c) Pith.— The 1 
 
 different plants according 
 growth. It is frequently found 
 in those parts of the stem which are used by the plant 
 for storing its reserve food, 
 the white potato and the yam. 
 those growing in water, it 
 suffers extreme reduction or is 
 often completely wanting, in 
 which case the bundles of the 
 stele are in close contact, and 
 the cortex usually shows a cor- 
 responding increase. In other 
 plants the cells constituting 
 the pith are greatly thickened, 
 so as to form a mechanical 
 tissue. The thickened areas 
 are usually either opposite the 
 bundles, forming a strand 
 closely adherent to their inner 
 faces, or they may extend to 
 the flanks of the bundles, thus 
 forming an arc embracing 
 each. Sometimes the thickened region becomes extended 
 between the bundles and joins the corresponding mechanical 
 tissues in the pericycle, or even those of the cortex, so as to 
 enclose completely the individual bundles (fig. 123). In 
 other plants the pith dies early and shrivels up. Very large 
 canals may thus be formed through it, or it may even dis- 
 appear entirely (fig. 122). Such early disappearance of the 
 pith produces the hollow stem characteristic of the grasses, 
 the sedges, and the various members of the sunflower family. 
 
 133. Secondary structure. — Some stems retain throughout 
 their entire existence the primary structure which has just 
 
 Fig. 123. — Transverse section Ol .1 bundle- 
 pair of Indian corn. r>, phloem bundle; 
 1. %\g, s, r, xylem bundle: p. pith; /, 
 an intercellular space formed by the 
 tearing of some of the .xylem tissues. 
 The bundle pair is surrounded by a 
 sheath of thick-walled mechanical 
 tissues. Magnified 235 diam. — After 
 Sachs. 
 
io8 
 
 PLANT LIFE. 
 
 been described, undergoing only slight changes in the char- 
 acteristics of the individual 
 tissues which compose it. 
 Thus, with age, there may be 
 a thickening of the tissues so 
 as to impart greater rigidity ; 
 or the waterproofing of the 
 exterior may be made more 
 perfect. These and similar 
 changes do not, however, 
 materially alter the structure. 
 This permanence of primary 
 structure is particularly fre- 
 quent in the stems of mono- 
 cotyledonous plants. It has 
 been observed also in some 
 dicotyledonous plants; for ex- 
 ample, in the white water lily. 
 But the stems of the great 
 majority of dicotyledonous 
 plants, as well as the conifers, 
 quickly lose their primary 
 structure, adding tissues of 
 considerable amount, so as to 
 bring about a more or less 
 striking rearrangement of the 
 iun of first formed tissues (fig. 124). 
 S^Xc^tg h ° n Atf^Tep1- 134 - Secondary meristem.- 
 
 SftA strSft xiKSS This modification of the struct- 
 
 ^^r^r^V^Z^r;;,: "re of the stem is due chiefly 
 
 SS^i&S. ^SSHSLH to the formation of one or two 
 
 AftcrTsd,iri1 ' layers of actively dividing 
 
 cells, which constitute secondary meristem or cambium, 
 
 roughly parallel to the surface. When there are two, one of 
 
THE STEM. 
 
 IO9 
 
 the layers of cambium arises nearer the (enter, the other 
 nearer the periphery of the stem. They are formed from 
 existing cells which resume their power of active growth 
 and division. The development of the tissues from the ex- 
 ternal meristem, or cork cambium, results in the formation 
 of the periderm, while the tissues arising from the internal 
 meristem, or stelar cambium, form the secondary xylem and 
 phloem (fig. 124). 
 
 135. 1. The formation of secondary cortex. — As the 
 cells of the external meristem divide, sometimes the outer 
 segments and sometimes the inner ones differentiate into 
 permanent tissues, while the other segment remains as an 
 initial for the next division. Some of the secondary tissue 
 thus produced lies outside of the generating layer, and some 
 inside (fig. 127). The secondary tissues, as a whole, con- 
 stitute the periderm. 
 
 
 Fig. 125. — A bit of a transverse section of a young stem of Scutellaria silendens at 
 the beginning of tin- formation .if periderm. <■, epidermis, some of its cells divided by 
 tangential walls, c, cortex. See tie 126. Highly magnified.— After Haberlandt. 
 
 FlG. 126.— Same as 125 but older. <•, outer half of epidermal cells; k, cork cells formed 
 by tangential divisions of inner half of epidermal cell (fig. 125) which has become pk, 
 the cork cambium; ,, cortex. Highly magnified.— Alter Haberlandt. 
 
 136. Periderm. — -The tissues formed inside the cambium 
 {phellodernt) are usually similar to the cells of the primary 
 cortex. They form intercellular spaces, and retain their 
 living contents, among which chloroplasts are often present. 
 W ith the thickening of the outer tissues, however, these 
 usually disappear. 
 
IIO PLANT LIFE. 
 
 The outside tissues of the periderm rarely remain living 
 No intercellular spaces arise between the flat cells, which 
 early lose their contents, while the walls become waterproof. 
 Such a tissue is known as cork (fig. 128). Other cells may 
 be altered into mechanical tissues by the thickening of their 
 walls and the death of the protoplasm. Zones of cork often 
 alternate in the periderm with zones of mechanical tissues 
 Since no water solution can pass through a cork zone, it is 
 evident that all parts lying outside of one are cut off from a 
 supply of nourishment, and must therefore perish sooner or 
 later. 
 
 137. Location of cork cambium. — How much will thus be 
 killed depends upon the position of the layer of cells which 
 
 Fig. 128. 
 
 Fir.. 127. — Part of a transverse se< don through the cork cambium and the tissues ii pro- 
 duces in the European elm. k, cork cells, the innermost layer still with some proto- 
 plasmic contents; pk, cork cambium; pd, secondary cortex. Highly magnified. — 
 \1te1 Haberlandt. 
 
 Fig. 128.— Part of a transverse section of young stem of cherry, showing formation of 
 periderm, e, epidermis; k, cork; ///. cork cambium, with one row of secondary 
 cortex below; ,, cortex. Highly magnified. — After Haberlandt. 
 
 becomes the generating layer. It may be formed in one 
 of three places: (a) It is sometimes in the epidermis itself 
 (fig. 125), in which case only the outer half of the epidermal 
 
77//-; STEM. HI 
 
 cells will be sloughed off.* (/>) In a majority of cases the 
 generating laver of the periderm is formed in the cortex, 
 either immediately under the epidermis (fig. 128) or in one 
 of the deeper layers (fig. 127). (c) In other instances the 
 generating layer is formed in the pericycle. If the pericycle 
 is more than one layer of cells thick, it may be formed in 
 the innermost or in any one of the external parts. In this 
 case, therefore, there will be killed all the tissues of the 
 cortex and any of the stelar tissues which lie outside the 
 portion of the pericycle from which the generating layer is 
 formed. 
 
 138. Perennials. — Plants which live for a single year have 
 usually but a small amount of periderm formed, or sometimes 
 none at all. In those, however, which are perennial, peri- 
 derm is formed not only during the first year's growth, but 
 the activity of the generating layer is resumed at the begin- 
 ning of succeeding seasons, so that annual additions are 
 made to it. In the cork oak, for example, there is an extraor- 
 dinary development of cork, which becomes so thick and 
 is so resistant to the passage of water that it serves for the 
 manufacture of stoppers. In the bottle-cork mechanical 
 tissues occur, not in zones, but in isolated patches, forming 
 the gritty masses in poor corks. 
 
 139. Secondary periderm. — The dead tissues which accu- 
 mulate from year to year upon the outside of perennial stems 
 constitute a large part of what is known as the bark. In the 
 bark of most trees one or more generating layers form in 
 addition to the first, giving rise thus to secondary periderm 
 (fig. 129). The secondary periderm may be either concentric 
 with the first, in which case the outer parts of the bark will 
 be made of concentric layers which separate readily from 
 each other ; or the new generating layer may intersect the 
 
 * The epidermis sometimes continues to grow for many years, while a 
 secondary cortex is formed under it. In this case no sloughing oft occurs. 
 
112 PLANT LIFE. 
 
 outer one, so as to isolate a mass of tissues of greater or less 
 size. When this mass is killed by the formation of a sheet 
 of cork on its inner face it gradually dries up and ultimately 
 breaks away in the form of a scale or flake (fig. 129). Hark 
 of this sort, such as that of the hickory, sycamore, or apple, 
 
 Fig. 129. — Part of a transvn^ ■., ■< iii.ii <>f the bark of cinchona. c, layers oi <<>rk 
 formed by a transient cork cambium. s, thin-walled tissues, with occasional stone 
 cells. The sheets of cork cells are lines of weakness along which the flakes of bark 
 split off. Magnified 665 diam. — After Warnecke. 
 
 is known as scaly bark. In other trees the dead outer por- 
 tions are persistent, and are only gradually worn away by 
 the action of the weather. Such persistent parts become 
 seamed or deeply furrowed lengthwise by the increased size 
 of the stem within and the constant drying and shrinking 
 of the dead parts. Such bark is called furrowed or ridgy 
 bark. 
 
THE STEM. 113 
 
 140. Lenticels. — In stems in which the generating layer 
 of the periderm is formed from the epidermis or the cortex 
 adjacent to it, the cork cells 
 produced show certain modi- 
 fications at points correspond- 
 ing to the stomata of the 
 epidermis. Here the cork 
 cells become rounded and 
 loosened from one another 
 (figs. 130, 131). The epider- 
 mis under the strain ruptures „ , , . . 
 
 1 Fir,. 130. — A bit of a transverse section of the 
 
 first at the Stoma, and exposes cortex of elder, showing a very young stage 
 
 1 in the formation of a lenticel. 1 he cortical 
 
 this powdery mass of cells c . el ,!, s imder a f " 1 ? hav f divi 4 ed tangen- 
 
 1 » tially and are ionning a loose tissue which 
 
 through a USUally biconvex > las already torn apart the guard cells 
 
 ' (See hg.. 131.) Magnified 120 diam. — After 
 
 rift, whose shape suggested 8tahl - 
 
 for the structure the name lenticel. Lenticels are formed 
 
 either beneath single stomata, or, when the stomata are not 
 
 ^^k4oM 
 
 Fig. 131. — Transverse section through .1 mature lenticel 
 Compare fig. 130. Magnified 80 diam. 
 
 uniformly distributed, beneath the clusters of stomata. When 
 the generating layer of cork is deep-seated the lenticels pro- 
 duced are without relation to the position of the stomata. 
 141. 2. The formation of secondary wood and bast.- 
 The position of the internal generating layer (the stelar cam- 
 bium) is not subject to the same variations as the external 
 
ii 4 
 
 PLANT LIFE. 
 
 one. In stems of the few monocotyledonous plants which 
 undergo secondary increase in diameter, the internal generat- 
 ing layer arises from the pericycle. Upon division the inner 
 segments, chiefly, differentiate, and from them arise new- 
 isolated bundle pairs (in which the xylem bundle surrounds 
 the phloem bundle) and new pith (fig. 132). 
 
 Fig. 132. — Portion of a transverse se< lion of a stem ol Dracaena, in process of secondary 
 thickening. <■, epidermis; I:, periderm; > . cortex, in which a bundle-pair 4 is passing 
 out to a leaf : .1 . stelar i ambium ; ; . g, vas< ular bundles ; nt, primary pith ; tt, see on- 
 dary pith. The amount of secondary thickening is shown by the radial arrangement 
 of cells of secondary pith. Magnified about 50 diam. — After Sachs. 
 
 In the many dicotyledons whose stems increase in diam- 
 eter, the stelar cambium arises between the xylem and the 
 phloem bundles of each pair, and extends across the pith 
 rays which intervene, thus forming a complete zone nearly 
 
THE STEM 
 
 115 
 
 concentric with the surface of the stem (figs. 120, 124, 133^). 
 As its cells divide, sometimes their inner, sometimes their 
 outer segments differentiate into the tissues which they then 
 
 Fig. 133. — Diagrams of transverse sections of stems illustrating modes of secondary 
 thickening. In all c, cortex; in, endodermis ; />, pencycle ; ///', primary phloem ; 
 ph.' , secondary phloem; cb, stelar cambium; .1 ', primary xylem; x", "secondary 
 xylem ; >', primary pith rays; r", secondary pith rays.— After Van Tieghem. 
 
 adjoin. Inside the generating layer between the bundles 
 there arises, therefore, secondary xylem which becomes 
 wood ; outside it, secondary phloem, or bast. Each bundle 
 is thus increased in its radial dimension (fig. 124 ). 
 
 142. Pith rays. — The generating layer in the pith rays 
 arises from the pericycle or from some part more deep- 
 seated, but in any case it connects directly with the generat- 
 ing layer between the adjacent bundles (fig. 124). In this 
 portion of the generating layer two distinct modes of develop- 
 ment are to be observed : either the tissues produced by the 
 division of the cells differentiate into pith tissue (B, fig. 133), 
 or they form secondary wood and hast corcsponding to that 
 produced between the adjacent bundles. In the latter case, 
 therefore, a complete /one or ring of secondary wood and 
 bast is formed, so that the pith occupies the center. Upon 
 the ring of secondary wood thus produced the primary wood 
 bundle projects into the pith, and upon the ring of secon- 
 dary bast the primary bast bundle projects into the rortex 
 
 (C, fig. 133). 
 
I l6 PLANT LIFE. 
 
 Intermediate between these two methods, it is common to 
 have new bundles produced by the differentiation of the 
 secondary tissues formed in the pith rays, these bundles 
 remaining separated by pith rays. In this case a xylem 
 bundle is usually first formed, followed shortly by a phloem 
 bundle outside (Z>, fig. 133). 
 
 The secondary bundles thus formed can, of course, have 
 no connection with those which enter the leaves. In this 
 they differ from the primary bundles, branches from which 
 enter each leaf. (See •[ 163.) 
 
 143. Annual rings. — If the stem is perennial, year after 
 year the stelar cambium resumes its growth, adding layer 
 after layer to the secondary wood and bast. Thus most trees 
 have their shaft-like trunks formed. The generating layer 
 forms a line of weakness, especially when dividing rapidly, 
 and the parts outside separate readily from the wood. They 
 constitute the bark. 
 
 144. 3. The bark. — As has been already shown, the 
 outer part of the bark consists of the dead, dry, shriveled 
 tissues of the periderm lying outside the cork cambium. The 
 inner portions of the bark are composed of the tissues which 
 lie between the cork cambium and stelar cambium. This 
 inner part contains a greater amount of water than the outer, 
 and always some living tissues. It may consist of a part of 
 the cortex (depending upon the place of origin of the peri- 
 derm), the pericycle, and the primary and secondary bast. 
 As the tree grows older, the secondary generating layers of 
 the periderm invade the cortex and the bast, until, with 
 weathering, the bark may come to consist wholly of secondary 
 bast. It attains considerable thickness only when the loss 
 from this cause is slow. 
 
CHAPTER X. 
 
 THE LEAVES. 
 
 145. Primary leaves. — Leaves are distinguishable into 
 primary and secondary. The primary leaves arise directly 
 from the first cells produced by division of the egg. In the 
 fernworts two of the octants into which the egg divides 
 produce the primary leaf. This is entirely unlike the secondary 
 leaves, which arise upon the sides of the stem. In seed 
 plants, one, two, or more leaves develop as members of the 
 embryo, only a I'ew plants (and those probably degenerate in 
 this respect) not forming leaves before the embryo enters its 
 resting stage. 
 
 The primary leaves of seed plants are called cotyledons 
 (figs. 134, 135). They are usually transient, and not rarely 
 so distorted by acting as storage places for reserve food that 
 they do not function as foliage leaves at all. In extreme 
 cases of this kind they remain in the seed coats when the 
 embryo resumes its growth, as in pea and oak. 
 
 146. Secondary leaves are generally numerous and much 
 more conspicuous. It is these which are usually meant by 
 " leaves," unless primary leaves are specially named. 
 
 147. Development. — If the apex of the shoot is examined, 
 its progressive differentiation into stem and leaves can be 
 observed. Upon the sides of the growing point swellings of 
 various size appear, the smallest being nearest the apex (fig. 
 95). These swellings are the fundaments of the leaves, into 
 which they become transformed by further development. 
 Similar swellings appear later just above the leaf fundaments, 
 
PLANT LIFE. 
 
 which are at first not distinguishable from them, except by 
 position (fig. 96). These become the branches. Both leaf 
 and branch have their origin usually in the outer layers of the 
 shoot, and can only be distinguished by the later course of 
 development. The growth of the branch is commonly 
 indefinite, while that of the leaf is generally limited ; the 
 
 Fir.. 134. Fig. .35. 
 
 Fig. 134 A seedling oJ wheat, with grain still attached cut through lengthwise, showing 
 
 the single inim.iry li.it with its back applied to the store ot reserve food in the grain 
 (the shaded part). The tirst two secondary leaves are also developing, and the primary 
 root has extended. Magnified 4 diani Alter Kernel 
 Fr<;. 135.— Seedlings, showing primary leaves. A, a fir (. Hies orientalis); />, the dog- 
 rose; C, a morning-glory. Naturafsize. — After Kerner. 
 
 branch usually develops leaves and often buds as lateral out- 
 growths, while the leaf rarely forms buds normally ; the axis 
 of the branch is generally radial, like the parent axis, while 
 the leaf is generally flattened and dorsiventral. In most cases, 
 also, the leaf subtends the branch, both leaf and branch 
 mark those points of the stem known as the nodes. 
 
THE LEA VES. I 1 9 
 
 148. Arrangement. — Leaves appear in regular succession 
 upon the stem, the youngest being nearest the apex. Their 
 distribution along the sides of the stem, though extremely 
 various, may be reduced to two main types. Either (i) the 
 leaves are formed singly at the nodes, or (2) more than one 
 leaf occurs at each node. When the leaves are single, succes- 
 sive leaves may stand upon exactly opposite sides of the stem, 
 so that the third leaf, counting from below upwards, stands 
 over the first ; or the fourth leaf may stand over the first ; or 
 the sixth over the first, and so on. A transverse section of a 
 bud shows the mode of arrangement, and a study of such 
 sections makes it evident that each leaf appears in the widest 
 space between the two preceding leaves, i.e., where it 
 encounters the least resistance. That this is the determining 
 factor is shown by the fact that the order of arrangement may 
 be artificially altered by pressure or distortion of the bud. 
 When two or more leaves occur at each node, the members 
 of successive circles ordinarily alternate with each other. 
 This alternation is due to the same cause. 
 
 149. Form. — Leaves show a great variety of form and 
 structure. Even upon the same plant leaves of various forms 
 occur. The primary leaves are usually different from the 
 secondary leaves, both in form and size. The most abundant 
 form of secondary leaves is foliage leaves. These may be 
 very simple, as the " needles " of the pines, or differentiated 
 more completely, as in the deciduous trees. The mature form 
 of the complex foliage leaf is frequently not attained until 
 several nodes above the point at which the primary leaves 
 arise; and, if only one or two leaves are produced each 
 season, as in many ferns, the mature form may not appear lor 
 several years. 
 
 150. Foliage leaves. — A well-developed foliage leaf may 
 usually be divided into two equal parts by a plane passing 
 through its base and the axis of the stem to which it is 
 
120 
 
 PLANT LIFE. 
 
 attached, i.e., it is bilateral. Moreover, the upper and under 
 
 surfaces are usually different, i.e., it 
 
 is dorsiventral. It has three parts, 
 
 the base, the stalk, the blade (fig. 
 
 136). The leaf base is always 
 
 present, but either the leaf stalk or 
 
 the leaf blade or both maybe absent. 
 
 The leaf blade is ordinarily winged ; 
 
 indeed it is for this reason that il 
 
 W-i 
 
 Fig. 136. Fig. 137. 
 
 Fir,. 136.— Leaf of Ranunculus Ficaria. /-, leaf base; /.petiole, or leaf stalk; /, 
 
 lamina or leaf blade. Natural size. — After Prantl. 
 Fig. 137. — A leaf of a grass, with part of stem to which it is attached, s, sheath (leaf 
 
 base)attached all around node k of the stem //, /; ; /, blade ; /, the ligule, an outgrowth 
 
 from the surface. Natural size. — After Frank. 
 
 received the name " blade." Either the stalk or the base or 
 both may also be winged. 
 
 151. 1. The leaf base. — The leaf base is generally en- 
 larged so as to form a sort of cushion by which it is attached 
 to the stem. When a broad base is attached over a consider- 
 able arc of the circumference of the stem, so that it encircles 
 it more or less, the base is said to be sheathing (fig. 136). 
 In grasses, for example, the leaf base is attached over the 
 entire circumference of the stem, and enwraps it completely 
 for a considerable distance above the node (fig. 137). 
 
THE LEAVES. 
 
 121 
 
 152. Stipules. — The leaf base frequently branches. These 
 branches, commonly two in Dumber, arc called stipules (fig. 
 138). They vary from slender, awl -shaped bodies to flat- 
 
 Fir,. 138.— A growing shoot of a thorn (( 'rateegus punctata), n, leaves developed as 
 bud scales which protected the parts above when in the bud; .V, stipules. Natural 
 size. — After Reinke. 
 
 tened and leafdike ones. The stipules may remain attached 
 to the base throughout the life of the leaf, or may fall away 
 early. Usually the two are separate, but they may be united 
 with the leaf base itself, forming wings for it, as in roses 
 (fig. 139), or they may be united with one another so as to 
 form a sort of sheath encircling the stem (fig. 140). When 
 the leaf base is winged, the wings extend downward as lobes 
 more or less encircling the stem. In many cases the leaf is 
 said to be clasping (fig. 141 ). These lobes may even unite 
 on the other side of the stem, so that the stem seems to 
 penetrate the base of the blade. (See fig. 142.) When two 
 leaves occur at the same node, corresponding lobes of the 
 
PLANT LIFE 
 
 leaf bases may unite, so that the stem seems to pass through 
 the center of a leaf which extends equally on each side of 
 it. (See fig. 143.) 
 
 Fig. 139— A young flowering shoot of dog-rose, showing various forms of leaves and 
 
 transition from one to the other. «'-«*, scale leaves; Z 1 -/ 3 , foliage leaves; A'-A*, 
 
 - hracts ; the flower leaves not clearly shown. The scale leaf, «', shows a leaf base, 
 
 winged by stipules b, with only a trace of stalk and blade,;. Trace these parts into 
 
 foliage leaves, where the blade becomes compound, and subsequent reduction through 
 the series oi bracts. Natural size. — Alter I.uerssen. 
 
 153. 2. The leaf stalk.— The leaf stalk is also known 
 as the petiole. Its form is more or less cylindrical, usually 
 with a groove or channel upon the upper side. Sometimes 
 the petiole is flattened in a vertical plane, a.s in aspen poplars. 
 
THE LEAVES. 
 
 23 
 
 When this flattening is extensive, so that the petiole becomes 
 thin and leaf-like and the blade is wanting, it functions as a 
 foliage leaf (fig. 144). Not infrequent- 
 ly, the petiole is winged, as in the orange. 
 It may be entirely wanting, in which 
 case the blade arises directly from the 
 base, as in most grasses 
 
 (fig- 137). 
 
 154. 3. The leaf 
 blade. — To this part of 
 the leaf the word ' ' leaf ' ' 
 itself is frequently ap- 
 plied. In general, the 
 :he leaf blade is so broadly 
 winged as to be thin and 
 
 clasping base. flat . but ^ gradations 
 
 she. uli 
 
 forming 
 
 Potygvnu 
 
 above the sheathing leaf base . 
 cut-off leaf f: cc, the stem; ca, an axillary 
 shoot. Natural size. — Alter Frank. 
 FlG. 141.— Leaf of Tklaspi 
 Natural size. — After Prantl 
 
 Fig. 142. Fir.. 143. 
 
 Fig. 142. — Shoot of Uvularia, showing perfoliate leaves below. About half natural 
 size— After Cray. 
 
 Fig. 143. — A shoot of wild honeysuckle, showing upper leaves connate-perfoliate. 
 About half natural size.— After ( Iray 
 
124 PLANT LIFE. 
 
 exist between such forms and those that are much folded or 
 crumpled, thick and fleshy, oi even cylindrical. 
 
 Fig. 144.— A shoot of Acacia, showing at a a twice-branched (compound) leal with 
 roundish petiole ; at 6, a similar leaf with flattened blade-like petiole ; at c, phyllodia, 
 i.e., blade-like petioles without true blades. About half natural size (?). — After Frank. 
 
 If a thin blade be held between the eve and the light, two 
 parts become evident : (i ) a green tissue (mesophyll), more 
 or less opaque ; and (2) translucent "nerves" or " veins." * 
 The larger of these, usually called the " ribs," * frequently 
 form ridges upon the under surface.")" 
 
 155. Branching. — The outline of the blade is extremely 
 various. It is dependent upon the character and extent of 
 its branching, which may be either slight or extensive. 
 Slight branching gives rise to teeth of various forms (fig. 
 
 * These words must not be thought to indicate any resemblance in func- 
 tion to the same parts in animals, but only similarity of position or ap- 
 pearance. 
 
 f For further account of structure see ^[ 168. 
 
THE LEAVES. 
 
 125 
 
 145). More profound branching is evident 'in divided or 
 parted leaves (fig. 146). In 
 some blades the branching 
 is so extensive and complete 
 
 Fig. 146. 
 ) , leaf with crenate edge ; />', leaf with 
 
 ARC 
 Fig. 145- 
 Fig. 145.— Diagrams of slight leaf branching 
 
 dentate edge ; C, leaf with serrate edge. — After Bessey 
 Fit;. 146. — Leaf of A morphophallus, showing sympodial branching. Th 
 lateral axes are numbered in order. The extent of branching makes the blade divided. 
 Reduced. — After Sachs. 
 
 that the green tissue no longer fills the intervals between the 
 larger ribs, but the blade is made up of a series of independ- 
 ent portions united to a common stalk. Each ultimate 
 branch of the blade is known as a leaflet. Blades in which 
 the green tissue is continuous, even though deeply divided, 
 are called simple leases. (See figs. 136, 138, 141, 142, 145, 
 146. ) Those which are segmented into leaflets are called 
 compound leaves. (See figs. 139, 144, 147, 148, 141).) 
 
 156. Venation. — The mode of branching of the blade is 
 indicated by the main ribs which occupy the axes of growth. 
 (See ^1 169.) Study of distribution of the ribs and veins of 
 the blade, that is, of its venation or nervation, shows that 
 monopodial branching (*T 93) is the common mode, sympo- 
 dial branching occurring rarely (fig. 146). The arrangement 
 of the larger ribs may be reduced to two main types.* (1) 
 
 * Compare mode of branching of shoot, " i".;. 
 
126 
 
 PLANT LIFE. 
 
 There may be a main rib, from whose flanks arise at regular 
 intervals a series of lateral branches which may themselves 
 
 Fig. 148. Fig. 149. 
 
 Fig. 147.— A palmately branched (compound) leaf of horse chestnut. About one-fifth 
 
 natural size.— After Bessey. 
 I'ii.. 148. — A palmately branched (compound) leaf. — After ISessey. 
 FlG. Mi).— Leaflets of maidenhair fern showing dichotomous branching of veinlets, 
 
 which end free. Natural size. — After Ettingshausen. 
 
 again be branched in various ways. Such a leaf is said to be 
 pinnaiely veined (figs. 138, 151, 153). Or (2) from the top 
 of the petiole several large ribs of almost equal strength may 
 be given off. Such venation is palmate (figs. 150, 152). 
 These may be parallel (fig. 150) or radiate (fig. 152). 
 
 The distribution of the small veins or nerves shows three 
 types. They may either (1) connect with each other so as 
 to form an irregular meshed network (fig. 151); or, (2) leav- 
 ing a rib nearly at right angles, they may run parallel with 
 ea< h Other to join another large vein ; or (3) they may leave 
 
THE LEAVES. 1 27 
 
 the large vein and end free (fig. 149). In the first type the 
 finest branches of the veins, too delicate to be seen without 
 the microscope, often end free in the meshes formed by the 
 next larger branches (fig. 164). Near the margin of a blade 
 
 Fig. 150. Fig. 151. 
 
 Fig. 150— Parallel venation of leaf of Polygonatum latifolium. Natural size. — 
 After Ettingshausen. 
 
 Fig. 151. — Pinnately netted venation of leaf of a willow. Natural size.— After Ettings- 
 hausen. 
 
 the larger veins are often so connected with each other as to 
 form one or more series of arches whose convex side is 
 directed toward the margin. These forma sort of selvedge 
 and protect the leaf against tearing (fig. 153). 
 
128 
 
 PLANT LIFE. 
 
 157. Special forms. — Foliage leaves may be modified to 
 serve special purposes without wholly losing their function as 
 
 Fig. 152. — Palmately veined and branched leaf of Norway maple. About half natural 
 size. — After Kerner. 
 
 foliage. For example, the petiole may be made sensitive to 
 
 contact and adapted to wrap about slender objects, like a 
 
 tendril, as in clematis and j^fs, *t 
 
 nasturtium (fig. 154). Such 
 
 plants are called leaf-climb- — ' v 
 
 ers. 
 
 Fig. 154. 
 
 Fir.. 153 .— Pinnately veined leaf of buckthorn, with looped ribs forming a selvedge. 
 
 After Kerner. 
 Fig. 154.— Portion of a plant of the dwarf garden-nasturtium {Trofiaolum minus). 
 
 The long petiole a, ,*, ,1 of the leaf / is sensitive to contact and has coiled about 
 the support and its own stein, st. ~, axillary branch. Natural size.— After Sachs. 
 
THE LEA VES. 
 
 2 9 
 
 Some plants develop their leaves into the form of sacs or 
 pitchers. These ordinarily represent the black- of the leaf, 
 and are more or less urn- or trumpet-shaped. They may be 
 either without petiole, as in Sarracenia (fig. 155); or 
 
 A ••-;- 
 
 Fig. 155. — Pitcher-plant {Sarracenia purpurea). Leaf above A cut off to show 
 trumpet form. One-third natural size. — After Gray. 
 
 petioled, as in Utricularia | figs. 383, 384) ; or the petiole 
 may be winged to serve for foliage, as in Nepenthes ( fig. 
 382). A few plants have their leaves modified so as to serve 
 as traps, which, by their sudden movements, capture small 
 animals (figs. 386, 387, 388). 
 
 But generally the foliage function is subordinated to the 
 other work, and the leaf takes on peculiar forms, the more 
 important of which are as follows : 
 
i 3 o 
 
 PLANT LIFE. 
 
 158. (i) Tendrils. — The leaf blade alone, or some of its 
 branches, or the petiole and blade, may develop as a cylin- 
 drical body, without wings and sensi- - ,, 
 live, known as a tendril. In the pea, ^^ I^U* 
 the stipules become very large, and 
 take the function of the reduced blade 
 (fig. 156). In other plants the base 
 may be broadly winged for the same 
 purpose. 
 
 Fig. ,56. 
 
 Fig. 156.— Portion of shoot of pea, with a pmnatcly compound leaf whose upper leaflets 
 
 are modified into tendrils and the stipules greatly developed to serve as foliage. 
 About half natural size.— After Frank. 
 Fir.. 157. — Piece of the stem of locust {Robinia Pseudacacia), showing stipules in the 
 form of thorns. Natural size. — After Kerner. 
 
 159. (2) Thorns. — The leaves may develop into slender 
 conical and sharp-pointed thorns or spines, either branched 
 or unbranched (fig. 390). Sometimes the stipules alone 
 become thorns, as in locust and acacia (fig. 157). Neither 
 tendrils nor thorns can be distinguished structurally from 
 similar forms of the shoot. 
 
 160. (3) Scales. — In buds, on underground stems and 
 on various parts of the aerial stem, are found small, scale-like 
 leaves of various shapes (figs. 101, 102, 105, 109, 138, 139, 
 
THE LEAVES. 13 ' 
 
 358). These scales may represent the sheathing base only ; 
 they may be the base with the stipules (fig. 139); or they 
 may represent the leaf base and the blade. The petiole in 
 all cases is wanting. In addition to the modification of 
 form, scales, especially those that are protective, have their 
 tissues firmer and more resistant to cold and unfavorable 
 external conditions. Not infrequently the scales are covered 
 with secreting hairs, or possess glands sunk beneath their 
 surfaces, whose function is to produce and excrete resins and 
 similar materials. The inner protective scales of buds (fig. 
 98) are often covered with an abundant coating of woolly 
 hairs, which serve to prevent rapid change of temperature in 
 the interior of the bud. 
 
 161. (4) Flower leaves and bracts. — -On certain parts of 
 the stem, leaves are commonly profoundly modified to carry 
 the spore cases. They are called sporophylls (c, si, fig. 104). 
 (See ^[ 329.) Adjacent to these are others which may be 
 highly colored and adapted in form to protect the sporo- 
 phylls, and to facilitate the visits of insects (s, p, fig. 104). 
 A shoot whose leaves are thus clustered and specialized con- 
 stitutes a " flower." The leaves adjacent to the flower leaves 
 are also more or less modified in form and reduced in size. 
 They are called bracts (// •> 2 > 3. fig. 139). (See also ^[ 359.) 
 
 162. (5) Storage leaves. — Other leaves are utilized for 
 purposes of storage. For this purpose the ribs are reduced in 
 number and size, while the softer tissues of the leaf are often 
 enormously developed, and serve as the receptacles of the 
 reserve food. The primary leaves of the seed plants (coty- 
 ledons) are often much distorted by the deposit in them of 
 reserve food for the embryo. When such leaves possess 
 sheathing bases the structure resulting from the union of a 
 number of such leaves upon a short axis is called a bulb. 
 (See also ^f 109.) The leaves of buds are sometimes thick: 
 ened by the deposit of food material, and when such buds 
 
132 PLANT LIFE. 
 
 loosen from the plant they may produce a new plant, as in 
 the tiger-lily (see ^[ 361-364). Both base and blade may be 
 used for storage, as in the century-plant j or the entire leaf 
 may serve the same purpose, as in the cultivated cabbage. 
 
 163. Structure. — Three regions in each part may be dis- 
 tinguished, as in the root and stem : (1) the epidermis ; (2) 
 the cortex ; both continuous with that of the stem ; (3) the 
 Steles, continuous with those of the stem when the latter 
 contains several steles, or branches of it when the stem con- 
 tains a single stele. 
 
 164. (a) The petiole. — The structure of the petiole agrees 
 in all essentials with that of the stem (see % 124 {{.). The 
 epidermis forms the outer surface, frequently with hairs or 
 emergences (see ^[128, 129). The cortex consists of 
 rounded or cylindrical thin-walled cells, the outer layers 
 containing chlorophyll, and frequently with angles much 
 thickened for strength. Mechanical tissues forming strands 
 or bands are also frequently present in the cortex. In water 
 plants, e.g., in water-lilies, large intercellular chambers, 
 often forming extensive canals, arc present. There may be 
 a single stele, surrounded by an endodermis and containing 
 several or many vascular bundles (B, fig. 158); or there may 
 
 A />• 
 
 Fig. 158. — Diagrams of transverse sections of petioles shoving two most common 
 
 structures. A, petiole with several steles, /.'. petiole with one stele, containing a 
 number of bundle pairs. ,. cortex; en, endodermis; ///, phloem; jr, xylem ; 
 in. pith ; ' , pith rays I he letters .1 , B stand on the upper or ventral side of petiole. 
 — After Van Tieghem. 
 
 be several steles, each surrounded by a special endodermis 
 and consisting of little more than a pair of vascular bundles 
 
THE LEAVES. 
 
 133 
 
 (A, fig. 158). In transverse section the vascular bundles 
 are variously placed, being irregularly scattered, or disposed 
 in one or several groups. The single group is most common, 
 with the paired bundles placed so as to form a crescent, or 
 even a complete ring, which is flattened above or triangular. 
 The largest pair is generally median and dorsal (fig. 158), 
 with smaller ones right and left. 
 
 165. (b) The blade. — In broad leaves, the epidermis of 
 the blade is made up of tabular cells, often with wavy lateral 
 walls (fig. 159). In narrow leaves the epidermal cells are 
 
 Fig. 159. — Surface view of epidermis from under side of leaf of bracken fern {/'let is), 
 showing wavy cells, except over veins, v, where they are elongated, st, stomata. 
 The dot in each cell represents the nucleus. Highly magnified. — After Sedgwick and 
 Wilson. 
 
 longer than wide (fig. 160). Over the veins the (ells are 
 elongated parallel with the vein. The epidermal cells are 
 generally free from chloroplasts. The epidermis usually 
 consists of one layer, but in some plants becomes several 
 layered, either to serve as additional protection against eva- 
 poration or for use as a water-storing tissue. ( See • 441. ) 
 
'34 
 
 PLANT LlfE. 
 
 Hairs of many sorts, plain, stinging and glandular, and 
 of various sizes, arise from the epidermis (figs. 361-365). 
 They are essentially like similar structures on the stem (figs. 
 113, 114). 
 
 166. Stomata. — Numerous intercellular spaces bounded 
 by a pair of specialized cells, called guard cells, penetrate 
 
 Fig. 160.— Surface '.iew of epidermis from the leaf of oat, showing elongated cells (more 
 elongated over vein, >i, >:) and stomata arranged in lines. Moderately magnified. — 
 After Frank. 
 
 Fig. 161. — Perspective view of a stoma from the under epidermis of the beet leaf, show- 
 ing the sloping sides of the slit, the crescentic guard cells with chloroplasts. Highly 
 magnified.— After Frank. 
 
 Fig. 162.— Sections through stomata of beet at right angles to their length. The upper 
 figure shows the stoma open ; the lower closed. The black line represents the primary 
 wall, to which additional material, especially in the guard cells, has been added. 
 These thickenings serve by their elasticity to close the stoma. Opening is dm- to 
 turgor "i the guard cells The chloroplasts and granular protoplasm are shown. 
 Highly magnified. Alter Frank. 
 
 the epidermis. The whole apparatus is called a stoma (s/, 
 fig. 159, 160). The guard cells are crescentic, sometimes 
 with enlarged ends (fig. 160, like curved dumb-bells then), 
 
THE LEAVES. I 35 
 
 and arc sensitive to various external conditions, especially 
 light, so as to control the size of the slit-like space between 
 them by changes in their curvature (fig. 162). This slit is 
 formed, like most intercellular spaces, by the partial splitting 
 apart of the cells. It communicates with extensive intercel- 
 lular spaces in the interior. 
 
 The stomata are very numerous. In different plants, in 
 
 the space here enclosed 
 
 , the numbers usually vary 
 
 from 4000 to 30,000, sometimes, however, reaching as much 
 as 60,000 to 70,000 in the olive and rape. They are not 
 equally jlistrihuted o nJ he two si des of the le af.- being usually 
 mo re numerous j)n th e under^sidej where there arc nmrc in - 
 ternal intercellular spaces.. They may be wanting on the 
 upper side, as in lilac, begonias, and oleander. There are 
 no stomata on submerged leaves nor on the under sides of 
 floating leaves. In some plants they are found in clusters, 
 in others uniformly distributed. 
 
 167. Cortex. — -The cortex of leaves is called the meso- 
 phyll. It consists of thin-walled, active cells, for the most 
 part richly supplied with chloroplasts. In thick leaves the 
 internal cells are without them. In some leaves the cells of 
 the mesophyll are nearly uniform, but in most those near the 
 upper surface are more elongated and close set, forming one 
 or two rows, with their ends outward, while cells near the 
 lower surface are irregular in form, with large intercellular 
 spans. These tissues are known as the palisade and spongy 
 parenchyma (fig. 163). 
 
 About the steles, the cortex forms the usual endodermis 
 {gs, fig. 163), and often develops along the larger into one 
 or two strands or a sheath of mechanical tissues. These 
 tissues, together with a stele, constitute the rib or vein, often 
 so massive as to project beyond the other parts in thin leaves. 
 
136 
 
 PLANT LIFE, 
 
 168. Steles.- The steles are numerous and ramify through 
 the blade. Their structure is essentially as described for the 
 
 
 
 Fig. 163.— Diagrammatic vertical section of a leaf, 
 and stomata sp, sfi. Between upper and lower epid 
 
 pidermis, with cuticle c, c, 
 the mesophyll, with cells 
 
 ivii, 1 
 abundantly supplied with chloroplasts. The upper row of elongated cells is the pali- 
 sade parenchyma ; the rest form the spongy parenchyma, both with many intercellular 
 mmunicating with outside air through stomata. In the mesophyll lies 
 a small vein, here cut across, composed of a ventral xylern bundle v. a dorsal phloem 
 bundle ,v, surrounded by the endodermis .;,*. and the pericyclc (between e and .!,•■»')■ 
 After Sachs. 
 
 stem (•] 127). Each of the smaller consists of little more 
 than a single pair of vascular bundles. The xylem bundles 
 alone form the last branches (fig. 164), the phloem disappear- 
 ing earlier. The larger ribs may form one or two strands or 
 a complete sheath of mechanical tissues by the development 
 of the pericycle, and the bundles proper may be increased 
 by the development of secondary wood and bast. (See 
 ■" 141. 
 
THE LEAVES. 1 37 
 
 169. Growth.— The growth of the leaf is at first apical. 
 In fern-worts its tissues are produced by the continued divi- 
 
 FiG. i^. — A few meshes of the finest veins of a leaf of A nthyllis. »i , main vein ; />, />, 
 branches ; <;. .;, .;. a closed mesh ; . . ends of the finest veins within the mesh. The 
 drawing shows only the xylem bundles ; the phloem bundles accompanying them and 
 the mesophyll cells filling the meshes are not shown. Moderately magnified. — After 
 Sachs. 
 
 sion of a single apical cell, and the further division of each 
 of the segments so produced (/, fig. 76). The branches of 
 such leaves, therefore, arise in acropetal succession. In most 
 seed plants, instead of a single apical cell, there is a cluster 
 of such cells. Growth at the apex often ceases early, and is 
 replaced by growth throughout the whole extent of the leaf. 
 This intercalary growth is sometimes localized between the 
 fundament of leaf base and blade, producing the petiole 
 when one is formed. In elongated leaves without distinct 
 petiole, as in grasses and many other monocotyledons, a zone 
 of growth occupies the entire base of the blade. By the 
 division of these cells, chiefly at right angles to the length 
 
i.SS 
 
 PLANT LIFE. 
 
 of 
 
 ith 
 
 of the Made, its tissues are produced. In such plants apical 
 growth ceases so early that it can 
 be observed only in the youngest 
 stages. 
 
 170. Of branched leaves. — 
 When the leaf is to become much 
 branched, two or more new growing- 
 points develop, so that each of the 
 branches has at its apex a growing- 
 point (fig. 166). These growing- 
 points may arise from the apical 
 growing-point, or from the basal 
 one, or sometimes from both. The 
 branches will appear accordingly 
 the in acropetal or basipetal succession, 
 the or even in both as they do in the 
 The limits of the 
 growing-point are even more in- 
 definite than in the stem. The cells of which the leaf is 
 composed are produced very rapidly, and at a very early 
 stage division ceases. 
 
 171. Wintering. — In those plants which live from year to 
 year, producing new leaves each spring, the unfolding of 
 these from the winter buds is due chiefly to the enlargement 
 of cells already formed. New leaves are ordinarily produced 
 before the close of the growing season preceding that in 
 which they are expanded, and are protected in the winter 
 buds. The partly developed leaves in the bud may be flat, 
 but broad leaves are commonly folded or rolled in various 
 ways. 
 
 172. Growth limited. — The growth of the leaves is ordi- 
 narily limited, rarely extending over a single season. In a few 
 ferns and coniferous plants the leaves continue to grow for a 
 longer time. Indeed, in the curious Welwitschia (fig. 167), 
 
 Fir.. 1^.5. — Ending of a v« 
 mesophyll of a leaf, t, 
 spirally thickened cell 
 xylem ; c, c, mesophyll cells win 
 
 chioropiasts ; a, a, cells of the leaves of yarrow. 
 
 endodermis. Magnified 230 diam 
 — After Frank. 
 
THE LEAVES. 
 
 1 39 
 
 the basal growth of a single pair of persistent secondary 
 leaves is continued throughout the long life of the plant, 
 while the tips die and are frayed out. 
 
 173. Production of the other members. — Leaves give rise 
 under certain conditions to roots or to shoots. The number 
 of plants, however, in which this occurs is comparatively 
 
 FlG. 166. — Development of the pinnately compound leaf of the locust {Robinia Pseud- 
 acacia). . I , young stage, snowing on one flank the first lateral growing-point,;, 
 which is to produce the lowest leaflet. />', an older stage with the fifth growing-point 
 x just showing. A sixth is still to be developed. The hairs in A and A' are on the 
 back (under side) of the leaf, and drop off early. C*, nearly mature leaf. ./, /■', 
 magnified; c, about i natural size.— After Frank. 
 
 limited. Roots arise from leaves in precisely the same way 
 as lateral roots arise from stems (•[ 95), that is, they arc en- 
 dogenous in their origin, and develop always near the surface 
 of the steles. 
 
 When a leaf produces a shoot, it is from the epidermis or 
 from the green tissue underlying it, never from the steles. 
 Shoots thus arise from the part of the leaf corresponding to 
 that from which branches arise upon the parent shoot. 
 
 174. Secondary changes. — Leaves, like stems and roots, 
 undergo certain secondary changes, hut these are neither so 
 
140 PLANT 11 IE. 
 
 common nor so extensive as in the other two members. The 
 formation of several to many layers of cork cells upon the 
 surface of scale leaves is not uncommon. Occasionally simi- 
 lar layers of cork are formed upon the petioles of ordinal) 
 
 Fig. 167. — Welwitschia mirabilis, a coniferous plant of Africa, showing two leaves 
 which grow at base and continue to develop throughout the many years which the 
 plant lives. The tips are dead, and become worn and frayed by winds. .."j natural 
 size. — After Hooker. 
 
 foliage leaves. In some cases the large vascular bundles 
 occupying the main ribs undergo changes similar to those de- 
 scribed for the bundles of the stem (* 141), by which sec- 
 ondary wood and bast are produced. 
 
 175. Leaf fall. — One of the secondary changes of most 
 importance is the preparation for the fall of the leaf. This is 
 made by the formation of a layer of secondary meristem across 
 the leaf base at or near the point where it joins the stem. 
 The cells at this point, with the exception of those constitut- 
 ing the vascular bundles, begin a series of divisions at right 
 angles to the axis. A transverse plate of cells is thus formed, 
 some of which cells may become transformed into cork, mak- 
 ing a line of weakness ; or, without such alteration, the 
 cells may round themselves off by loosening along a definite 
 line, so that the leaf is held only by the steles. The access 
 
THE LEAVES. H r 
 
 of water to this crevice, and its freezing, serve to rupture the 
 
 remaining tissues, and thus allow the leaf to fall by its own 
 weight, or to be torn off by the wind. 
 
 The scar left by the fall of the leaf is protected either by 
 the cork already produced, or by mere drying of the exposed 
 tissues. The leaflets of compound leaves fall in like manner. 
 Sometimes provision for the leaf fall is begun as early as June, 
 as in the Kentucky coffee-tree. In other plants provision 
 for leaf-fall is begun late in the season, and in some, such as 
 the oaks, it is very imperfect, so that the leaves are finally 
 wrenched off by winter storms, or pushed off in the spring by 
 the developing buds beneath them. 
 
PART II: PHYSIOLOGY. 
 
 CHAPTER XI. 
 
 INTRODUCTION. 
 
 176. Division of labor. — The study of the external form 
 and internal structure of plants may be carried on as well 
 upon dead as upon living material. Even the observation of 
 the various stages of development requires only the examina- 
 tion of the plant as it exists at a particular moment. But the 
 plant may also be studied as a working organism. For this 
 purpose living material is indispensable. The work which 
 plants do and by which they are distinguished from non- 
 living bodies is extremely varied, and the more complex the 
 plant the more varied it is. In the preceding part the aim 
 has been to show that there exists great variety of form, and 
 that from the smaller to the larger plants there is gradually 
 increasing complexity by differentiation into tissues and 
 members. 
 
 Nutrition, respiration, growth, movement, and reproduction 
 are all executed by the single cell of the simplest plant. 
 But with specialization in structure there occurs division of 
 labor. Each kind of physiological work is known as a 
 function, and each part of the organism which does a par- 
 ticular work is called an organ. 
 
 177. Physiology and ecology. — Physiology proper treats 
 of the plant at work, discussing the different functions and 
 
 M3 
 
144 PLANT LIFE. 
 
 the way in which these are affected by external forces. In 
 its broadest sense it also treats of the relation of the plant as 
 a whole to external forces and to other living beings, both 
 plants and animals. But it is convenient to separate the 
 latter from physiology proper as ecology.* (See Part IV.) 
 
 The study of physiology proper necessitates methods of 
 controlling these external forces, carefully planned and re- 
 peated experiments, and cautious inferences. 
 
 The study of ecology requires observation in the field of 
 the adaptations of plants to prevent injury by unfavorable 
 physical conditions and the attacks of other beings, and to 
 take advantage of the favorable forces and beneficent agents. 
 
 178. Chemical and physical forces. — The functions of a 
 plant may be divided for the sake of convenience into nu- 
 trition, respiration, growth, movement, and reproduction. 
 These are largely special modes of chemical and physical 
 action. Nutrition and respiration, for example, consist 
 chiefly of a series of chemical changes ; while movement is 
 mainly a result of physical alterations in certain organs. 
 But the action of chemical and physical forces does not suffice 
 at present to explain all the phenomena of the living plant. 
 Moreover, the peculiar manifestation of these forces which 
 we call life occurs only in connection with the substance 
 which we call protoplasm. 
 
 179. The unit of function. — The functions performed by 
 the entire plant are necessarily a sum of the functions per- 
 formed by the physiological units of which it is composed. 
 As the unit of structure is the plant cell, so the unit of 
 function is the protoplasmic body of that cell. Although 
 only a portion of any plant is composed of living matter, it 
 is to that living matter only that we are to look for the seat 
 of its powers. 
 
 * Spelled in lexicons, cecology, but best usage drops the o ; sometimes 
 improperly called biology or plant biology. 
 
INTRODUCTION. 145 
 
 180. The fundamental powers of protoplasm arc tour ; it 
 is metabolic, irritable, contractile, and reproductive. 
 
 181. Metabolism. — Protoplasm is metabolic, thai is, it is 
 capable of initiating a series of chemical changes in itself and 
 in substances which come directly under its influence. These 
 changes are of two kinds. They may be constructive, i.e., 
 they may build up complex substances out of simpler ones, 
 and so fit them for use in repairing the waste caused by the 
 activity of the protoplasm; or they may be destructive, i.e., 
 they may break down complex substances into simpler, so 
 setting free the energy necessary for the work of the pro- 
 toplasm. The substances broken down may be repaired in 
 whole or in part, i.e., may take part in constructive me- 
 tabolism. Those in which no repair occurs often undergo 
 further destructive changes by which they become converted 
 into materials useless to the plant, and to be gotten rid of. 
 Metabolism, therefore, includes all the chemical changes by 
 which food is either manufactured or utilized, and by which 
 waste materials are produced and eliminated. 
 
 182. Irritability. — Protoplasm is irritable, that is, it 
 exists in such a state that it is sensitive to external influences, 
 which thereby affect the various functions of the whole 
 organism By reason of its irritability, it may even transmit 
 the effects of an external stimulus from one part to a distant 
 part. Moreover, it is capable of initiating similar changes 
 without the action of any observable external influences, and 
 is, therefore, not only irritable but automatic. 
 
 183. Contractility. — Protoplasm is contractile, that is, it 
 has the power of altering its form, of shortening in one 
 direction and elongating in another, by virtue of inherent 
 forces whose action is not understood. 
 
 184. Reproduction. — Protoplasm is reproductive, that is, 
 it is capable of so directing the chemical and physical forces 
 
I46 PLANT LIFE. 
 
 inherent in it that a new organism similar to that of which it 
 forms part may be produced. 
 
 185. Adaptation.- -The interrelation of these powers, 
 their harmonious coworking and their variation to suit the 
 varying conditions of the surrounding media (air, water, soil, 
 etc.), result in the proper performance of all the functions of 
 the plant. By means of these powers it is brought into re- 
 lation to the world about it, being adapted to other organisms 
 in whose company it lives, and enabled to withstand the 
 adverse conditions by which it is frequently threatened. 
 Every organism, indeed, must adjust itself first to the external 
 physical conditions, and, second, to other organisms. (See 
 Part IV.) 
 
 186. Physical conditions set limits upon the discharge of 
 its functions. Varying amounts of light, of heat, of moisture, 
 determine more or less rigidly how rapidly, or to what extent, 
 each function may be discharged. Every function of the 
 plant is adapted, therefore, to an upper limit, the maximum, 
 and to a lower limit, the minimum, above or below which 
 the performance of the function in question is impossible. 
 Between these limits there lies some point at which it pro- 
 ceeds most rapidly and effectively. This point is known as 
 the optimum. 
 
CHAPTER XII. 
 
 THE MAINTENANCE OF BODILY FORM. 
 
 Every plant is capable of attaining and maintaining a 
 specific form, which is not permanently altered by the direct 
 action of external forces, and is dependent upon the nature 
 of the plant itself. 
 
 187. Naked cells. — If the plant consists of a single mass 
 of naked protoplasm, it may assume a spherical or ovoid 
 shape (fig. 1 68). In attaining this form the physical forces 
 
 Fir.. iftS.— Zoospores of various Forms, 
 cilia. ./, Botrydium ; />', Draf>ai 
 Highly magnified .—After Kerner. 
 
 vimming in water by means of one or mo 
 aldia; ( ', Coieockate ; J>, CEdogoniui 
 
 constituting surface tension play a part, but the form is deter 
 mined chiefly by internal forces inherent in the protoplasm. 
 
 This is particularly well shown when such organisms extend 
 delicate protoplasmic threads, the cilia, and maintain these 
 
 i47 
 
148 
 
 PLANT LIFE. 
 
 in active motion (fig. 168), or when they extend a portion of 
 the body as a pseudopodium (fig. 169). 
 
 FlG. 169. — Plasmodia, creeping bits of naked protoplasm, showing varied shapes 
 parts are protruded or withdrawn. Highly magnified.- Artel Reiner. 
 
 188. Turgor. — If the organism be one surrounded by a 
 cell-wall, or if it be made up of a number of cells united, the 
 cell-wall itself plays a considerable part in maintaining the 
 form. This is due to the condition of the cell known as 
 turgor. When fully mature the cell-wall of each active 
 cell is lined by a more or less thick layer of living proto- 
 plasm. In the interior of the protoplasm there exist one or 
 more water chambers, the vacuoles (^[ 5). If such a cell as 
 this be measured in its normal condition, and then surrounded 
 for a few moments l>v a 10 per cent, solution of common salt, 
 reexamination will show that the vacuoles have been dimin- 
 ished, the protoplasm shrunken away from the wall, and 
 remeasurement will show that the cell has diminished both in 
 length and diameter. In its normal condition, therefore, the 
 wall was stretched by the pressure of the contents within. If 
 a cell which has been thus shrunken by immersion in a solu- 
 tion of salt be again placed in water, it may regain, in the 
 course of a few hours, its original condition, that is, it may 
 again become turgid. This would be brought about by the 
 entrance of water into the vacuoles to replace that withdrawn 
 when the cell was placed in the solution of salt. 
 
 If a thin piece of rubber tubing be connected with a pump 
 and filled with water until it is stretched, it increases its 
 
THE MAINTENANCE OF BODILY FORM. M9 
 
 diameter and length slightly, and gains, at the same time, a 
 condition of rigidity greater than in its unstretched condi- 
 tion. In a similar way turgid cells are more rigid than those 
 which are flaccid. The union of turgid cells produces a 
 member more rigid than one in which the cells are not turgid. 
 An illustration of this is to be seen in the condition of a 
 wilted, as compared with a fresh, leaf. The turgor of thin- 
 walled cells may play an important part in maintaining the 
 form and position of the parts of a plant. 
 
 189. Tissue tensions. — But turgor can affect only those cells 
 whose walls are thin and extensible. Those whose walls have 
 become thick and rigid are not stretched by this force. In 
 the larger plants, however, where both thick-walled and thin- 
 walled tissues exist, it is possible that a mass of thin-walled 
 cells may, by the united tension of its component cells, 
 stretch those tissues which are not themselves turgid. Such 
 strains in the younger regions, particularly, play an important 
 role in maintaining the form of these parts. But the tensions 
 in the older parts are generally due to the unequal growth of 
 different tissues. (See ^| 259.) 
 
 190. Mechanical rigidity. — The rigidity of the cell-wall 
 itself must be relied upon by all the larger plants. Certain 
 tissues are specialized by having their cell-walls greatly 
 thickened, and such tissue regions constitute a sort of frame- 
 work or skeleton, which is filled out by the more delicate 
 tissues. These mechanical tissues are so distributed within 
 the body as to afford frequently the maximum resistance to 
 bending and breaking strains. In the accompanying dia- 
 grams the position of the mechanical tissues is indicated in 
 transverse sections of a number of different stems (fig. 170). 
 It will be seen that they illustrate well-known mechanical 
 principles in their distribution. The hollow column (E) and 
 the [-beam (A, />', C), two of the most rigid mechanical con- 
 structions, are frequently imitated in plants. 
 
ISO 
 
 PLANT LIFE. 
 
 In stems of trees rigidity is secured not by the distribution 
 of the mechanical tissues, but by their massiveness. In them 
 the chief mechanical tissues belong to the wood, which forms 
 
 Fig. 170.— Diagrams showing the arrangement of mechanical tissues and vascular 
 bundles in the cross-section of various stems. The mechanical tissue is gray; the 
 vascular bundles black, with white dots. A, linden (young) ; B, a mint ; C, a sedge ; 
 If, a bamboo ; A, a grass. — After Kerner. 
 
 a solid column occupying the center of the body. Those 
 plants which are supported by the medium in which they 
 live, such as the aquatic plants, are usually without mechan- 
 ical tissues. 
 
CHAPTER XIII. 
 
 NUTRITION. 
 
 191. Repair and growth. — Since the body of every plant 
 is constantly wasting away by reason of its own activity, it is 
 necessary that it should be as constantly repaired. It must 
 also, for a considerable time or throughout its whole life, be 
 furnished with material which can be used in the making of 
 new parts. Without an adequate supply of food, therefore, 
 neither repair nor growth is possible. To understand what 
 materials are necessary for repairing waste and forming new 
 parts of the living plant, the constituents of a plant may be 
 determined by chemical analysis. 
 
 192. Chemical composition. — The greater portion of the 
 weight of every plant is found to be water. Of the firmer 
 parts it forms as much as 50 per cent., while of the softer 
 parts it may form 75 or even 90 per cent. The most watery 
 portions of some plant bodies, such as the juicy portions of 
 fruits and the whole body of the algae, may contain only 2 to 
 5 per cent, of solid matter. The solid material, left after 
 driving off the water at a temperature of no ('., is found to 
 consist chiefly of three elements, carbon, hydrogen, and 
 Oxygen. The most abundant element in addition to these is 
 nitrogen. If the dry substance be burned these four elements 
 are driven off in gaseous forms, and there remains a white 
 material which crumbles under pressure, the ash. An analy- 
 sis of the ash reveals the presence of sulfur and phosphorus 
 in considerable amounts, and also smaller quantities of the 
 following elements: calcium, magnesium, potassium, iron, 
 
 151 
 
152 PLANT T.TFE. 
 
 sodium, chlorine, and silicon. Of these seven, the first four 
 are found in the ash of all plants, and the remaining three 
 are very common. In addition to the elements enumerated, 
 about 25 others are known to occur in the ash of plants, but 
 only in minute quantities. 
 
 A. The water in the plant. 
 
 193. Necessity. — Since water forms such a large percent- 
 age of the weight of fresh plants, it is manifest that it must be 
 supplied in relatively large quantities, if the plant is to con- 
 tinue in an active condition. A portion of this water may 
 be used up in the chemical changes occurring in the body, 
 but it is not possible to discriminate between this and the 
 water which is necessary to furnish the proper physical con- 
 ditions of life. Water is the great solvent by which materials 
 of various kinds are carried into the plant body, and 1>\ 
 which a still greater variety within it are transported from 
 plaGe to place. Before discussing the food of plants, there- 
 fore, the relation of water to the plant may be examined. 
 
 194. Air, water, and land plants. — Some plants are not in 
 contact with water except at irregular intervals. These are 
 called air plants, and include some algae, liverworts, mosses, 
 fernworts, and seed plants. All these, however, are able to 
 live onlv in an atmosphere containing large quantities of 
 water vapor, or in those regions where they are frequently 
 sprayed with water. Water plants float upon the water, or 
 arc submerged in it. As distinguished from both air and 
 water plants, are those which normally have the mot system 
 and sometimes a portion of the stem buried in the soil, con- 
 tinually or intermittently in contact with liquid water, while 
 the shoot system is occasionally sprayed by rain. Such may 
 be called land plants. 
 
 195. Solutions in water. — In no case, however, is the 
 water in which plants are immersed, or with which they 
 
NUTRITION. 153 
 
 are sprayed, pure water. It always holds in solution sub- 
 stances derived from the atmosphere or from the soil with 
 which it has come in contact. These substances are either 
 organic or inorganic, and they enter the plant, along with 
 the water, through those organs which are adapted to ab- 
 sorption. 
 
 196. Absorption of water. — In air plants of the simpler 
 sorts, any parts exposed to the moist air or rain can absorb 
 water. In liverworts and mosses the thallus or the leaves 
 are active absorbents. In the higher plants, such as the 
 aerial orchids, the external cortex of the roots is especially 
 adapted to absorb liquid water, or to condense the water 
 vapor of the atmosphere.* In water plants the surfaces which 
 are normally in contact with the water are absorbing surfaces. 
 Such plants may be either wholly without a root system, or it 
 may be only sufficiently developed to anchor them in the 
 mud. In land plants the root system is especially adapted to 
 the absorption of water. Only minute quantities of water 
 are absorbed by the leaves and other aerial parts. The re- 
 vival of a wilted plant by spraying seems to be due more 
 largely to checking the loss of water by evaporation than to 
 the slight absorption which may occur. The root system of 
 the land plants is developed in contact with the soil. 
 
 197. Soil. — The soil consists primarily of finely divided 
 particles of rock, whose nature and size determine the quali- 
 ties by which soils are ordinarily distinguished into gravelly, 
 sandy, loamy, clayey, etc. Mixed with these rock panicles 
 is more or less organic material derived from the offal of 
 plants or animals. When decaying plant offal predominates, 
 the soil is known as vegetable mold or humus, which natu- 
 rally forms the upper layer of the soil of forests. To garden 
 or field soils, not naturally rich in organic matter, this is 
 
 * If such condensation really occurs (as is generally alleged), it does 
 not suffice to keep the plants supplied with the required amount of water. 
 
54 
 
 rLANT LIFE. 
 
 frequently added artificially. Both manure's and artificial 
 fertilizers (the latter consisting usually of dried and ground 
 animal offal) arc added chiefly for the purpose of supplying 
 compounds of nitrogen and phosphorus. 
 
 198. Soil water. — No matter how fine the soil may be, the 
 rock particles are not in close contact, but, on account of 
 their angular outline, leave spaces of greater or less size to be 
 occupied by other materials. If a soil be examined immedi- 
 ately after a heavy rain-fall, these spaces will be found com- 
 pletely occupied by rain-water. If the soil be so situated as 
 
 Fig. 171.— Diagram of a portion of soil penetrated by root hairs, h. A', arising from 
 root, ''. At =, .f, ,v' (lie hair lias grown into contact with sonic of the soil particles, /. 
 which are surrounded by water films (shaded by parallel lines), 0, o, t. The white 
 spaces are air bubbles, S, &', y, y' . When water enters the hair .it a, the thickness of 
 the film a, 3, t will be diminished, and some water will flow towards this point, re- 
 ducing all the other water films in the vicinity. Move air enters from above. When 
 rain falls, the reverse process occurs; the films thicken, and the air may be entirely 
 driven out, to return as the surplus water drains away. After S.u lis. 
 
 to be naturally drained, considerable quantities of this water 
 will disappear gradually, and the larger spaces between the 
 soil particles will be occupied partly by films of water adherent 
 to the soil grains, and partly by bubbles of air (fig. 171). 
 
 199. Salts dissolved. — The water which thus filters 
 through the soil dissolves and retains certain of its constitu- 
 ents. As the rain passes through the atmosphere it also dis- 
 
NUTRITIOX. 155 
 
 solves certain substances found therein, notably minute quan- 
 tities of ammonia and nitrous acid. By this means compounds 
 containing nitrogen are constantly being brought to the soil 
 by the rain. 
 
 200. Root absorption. — The structure of the root system 
 has been explained (% 78-82). The root hairs come into 
 close contact with the soil particles, pushing them aside 
 somewhat, and being in turn more or less deformed by their 
 resistance (z, s, fig. 171). So close does the contact of the 
 root hairs and soil grains become that many particles of the 
 soil are imbedded in the walls of the root hairs (fig. 84). 
 The root hairs are not only in contact with the soil particles, 
 but also with the films of water, which occupy the spaces be- 
 tween them (a, fig. 171). They are thus in a position for 
 absorbing water from the adjacent films. 
 
 201. Limit of absorption. — Not only is the water im- 
 mediately in contact with the root a source of supply, but 
 even that in the deeper and more distant parts of the soil. 
 For when, by the entrance of some water into the root hair, 
 the thickness of that layer has been decreased, the disturbance 
 of equilibrium causes a flow from neighboring layers to 
 equalize again the surface tensions. This goes on until the 
 films of water upon the soil grains become so thin that the 
 water particles are held too tenaciously to be pulled away by 
 the root. There remains in such exhausted soil, which seems 
 dry as dust to the touch, 2 to 1 2 per cent of water unavailable 
 for the plant. 
 
 202. Solvent action. — The root hairs also exert a slightly 
 solvent action upon the soil particles themselves by reason of 
 the carbonic acid and the acid salts which they excrete. By 
 this means various minerals, especially carbonates of lime and 
 magnesia (limestone), which could not be dissolved by the 
 water alone, may be brought into solution. 
 
 Water enters the root hairs by the physical process known 
 
156 PLANT LIFE. 
 
 as osmosis, the protoplasm, braced by the cell-wall, acting as 
 the membrane, and the cell sap of the vacuole as the denser 
 fluid of the osmotic pair. (See Physics.) 
 
 203. The development of the root system is related to 
 the character of the soil and to the amount and distribution 
 of water and organic matter within it. Branching of the 
 root system is much more profuse in the moister parts of the 
 soil, as well as in those which contain more organic matter. 
 
 204. Movement of water within the plant. — Once the 
 water has gained entrance to the plant, it must move to those 
 parts where it is to be used — i.e., to all the organs of the 
 plant, but especially to the leaves, since from these there is 
 the largest loss of water by evaporation (^[ 209). From the 
 root hairs the water passes inward through the cells of the 
 cortex, and reaches the stele. The forces which determine 
 this movement and its direction are not fully understood, 
 though osmosis probably plays a chief part. They are com- 
 prehended under the general phrase root pressure. 
 
 205. Root pressure. — The action of root pressure may be 
 demonstrated by severing a suitable stem close to the ground 
 and observing the water which flows out, after a short time, 
 from the cut end. Careful examination of the cut surface 
 will show that the water oozes out chiefly from the woody 
 parts of the stele. The force with which water is extruded 
 may be measured by attaching to the stump, by means of a 
 rubber tube, a manometer (fig. 172). In this way it may be 
 ascertained that in woody plants, such as the birch, the 
 pressure sometimes becomes equal to that of five or six 
 atmospheres. 
 
 206. Route to the leaves. — After entering the xylem 
 bundles of the roots, the water is thence transferred along the 
 stem in the same tissues, which are continuous with those of 
 the root. Since the xylem bundles form an unbroken line to 
 the most remote parts of the leaves, passing out in the ribs 
 
NUTRITION. 
 
 157 
 
 and forming the finer veins, the water may be distributed to 
 
 every part of the plant body. Within 
 
 the wood it travels chiefly in the cavities 
 
 of the large ducts or vessels, when these 
 
 are present, though the walls, also, are 
 
 saturated with it, and permit a slower 
 
 movement. These ducts, although of 
 
 great relative length (some up to 1 m.), 
 
 are not continuous tubes like the veins 
 
 of an animal, nor are they filled with 
 
 water. The water is broken into short 
 
 columns by numerous gas-bubbles, and 
 
 in ascending to any considerable height 
 
 must traverse many cell-walls. 
 
 207. Motive power. — The force by 
 which water is raised in the larger plants 
 remains yet to be ascertained. The 
 water does not flow along the ducts in a 
 continuous current, as the blood in the Fl m 
 veins, propelled by a force behind, for 
 root pressure is not adequate to push it to 
 the height attained. On the contrary, 
 during the times of most active evapo- 
 ration from the leaves, i.e., when the 
 greatest supply is needed, root pres- 
 sure becomes almost or quite negative. 
 Capillarity is also inadequate. The 
 diameter of the largest ducts is too small 
 and the friction of the water against 
 their sides consequently too great to 
 permit the movement, by this means, of ln,/ 
 a sufficient amount of water to supply the evaporation. 
 Moreover, the interruption of the water columns by gas- 
 bubbles produces surface tensions which quite overcome that 
 
 a T-tube, R, is attached by 
 a piece of rubber tubing, 
 v. The other openings are 
 closed by rubber corks, k, 
 through one of which 
 jussr-- ,1 small glass tube, 
 r, bent into two unequal 
 legs, containing mercury. 
 Through the upper should 
 pass a short piece oi glass 
 tubing drawn out to a line 
 point, to be sealed off in a 
 flame after A' is filled with 
 water. At the beginning of 
 the experiment the mercury 
 is about at the same level 
 
 in both legs. As water is 
 ton ed from tin- stump into 
 A' by toot pressure the mer- 
 lin v rives in the .inn f' 
 and falls correspondingly 
 Alter SachS, 
 
158 PLANT LIFE. 
 
 of capillarity. It has been found that the bubbles of gas 
 here mentioned often exist under negative pressure, as shown 
 by the fact that a stem cut under mercury allows the mercury 
 to ascend for some distance within the vessels. This negative 
 pressure of the gases is due to the evaporation of water from 
 the leaves, and the most recent researches point to this as a 
 very important or even the chief factor in lifting the water. 
 That the movement is not a function of living cells is shown 
 by experiments in which stems of plants have been subjected 
 to poisonous agents, or heated for many hours to a degree 
 sufficient to kill all the living cells, yet without materially 
 affecting the supply of water. 
 
 208. The loss of water. — Water is constantly evaporating 
 from the whole surface of the plant exposed to the air. Since 
 this loss is probably more or less modified by the vital activ- 
 ity of the plant, it has received the special name, transpira- 
 tion. 
 
 f — I 209. Transpiration. — In the higher plants transpiration 
 from the surface is reduced by the waterproofing of the epi- 
 dermis, so that most of it takes place from the surfaces of 
 internal cells into the intercellular spaces, wherever these 
 exist. Since the intercellular spaces are connected with each 
 other and also, through the stomata. with the outside air, 
 water vapor is constantly passing off by diffusion. The leaves, 
 affording the largest exposure, are especially organs of trans- 
 piration. After they have become fully expanded no appre- 
 ciable amount of water is lost directly from their surfaces. 
 I 210. Amount and regulation. — The amount of transpira- 
 / tion, therefore, varies with the structure of the leaf rather 
 / J than with its area. The temperature, percentage of water 
 * and movements of the air affect profoundly the rapidity of 
 transpiration. Hence arises the need of regulation by the 
 plant, to prevent excessive loss. The guard cells of the 
 stomata are irritable, so that external conditions affect their 
 
NUTRITION. 1 59 
 
 turgor, [f both arc turgid, they become curved away from 
 each other so as to increase the size of the opening between 
 them. If they are flaccid, the thick ridges along the inner 
 face of each cell straighten them, and so close the orifice 
 more or less completely (figs. 161, 162). The presence or' 
 absence of hairs upon the leaves, the existence of stomala 
 upon one or both surfaces, the sinking of the guard cells 
 below the general leaf surface, the distribution of the stomat; 
 the thickening of the leaves, their inrolling (fig. 357), or 
 revolution (fig. 359), have a decided effect upon the rate of 
 transpiration, and may be adapted to regulate it. (See 
 1T434ff.) 
 
 B. Foods in general. 
 
 211. Foods. — In addition to an adequate supply of water, 
 food is required. Materials consumed by plants as food are 
 either organic or inorganic. Organic materials are those 
 which have been produced in nature by the chemical changes 
 occurring within living bodies. Inorganic materials are those 
 formed in nature by chemical reactions not occurring in con- 
 nection with a living body. A very few of the simplest plants 
 (bacteria) have been grown by the use of inorganic materials 
 alone; only the minutest quantities of such substances are 
 utilized by most plants as food ; but large amounts are used 
 by all green plants for the manufacture of organic foods. 
 
 Organic foods are of three kinds, carbohydrates, fats, and 
 proteids. 
 
 212. Carbohydrates are substances consisting of carbon, 
 hydrogen and oxygen, so proportioned that there are 6 
 carbon molecules (or some multiple of 6) while the two latter 
 elements are combined in the ratio of two parts of hydrogen 
 to one of oxygen. Well-known examples are sugars and 
 starch. 
 
l6o PLANT LIFE. 
 
 213. Fats. — These arc likewise combinations of the same 
 three elements, but in them the hydrogen and oxygen do not 
 exist in the ratio of two to one, the oxygen being much less 
 in proportion. Some are solid at ordinary temperatures, 
 while others are fluid. They are combinations of free fatty 
 acids and glycerin. Upon the addition of an alkali, the fatty 
 acids combine with it to form soap and other compounds ot 
 less amount while the glycerin is set free Commercial ex- 
 amples of plant fats are olive oil, linseed oil, and cacao butter. 
 
 214. Proteids are foods consisting of at least five and 
 generally of six elements, namely, carbon, hydrogen, oxygen, 
 nitrogen, sulfur, and (ordinarily) phosphorus. These elements 
 are complexly combined in varying proportions. Proteids 
 are generally recognizable by their property of coagulation 
 upon the application of heat, acids, or other agents. Well- 
 known examples are the proteids forming the "white of egg." 
 Examples from the vegetable kingdom are less familiar. 
 
 Proteids always, and either carbohydrates or fats, or both, 
 must be available in order that a plant may be properly 
 nourished. Green plants obtain their food chiefly by manu- 
 facturing it out of inorganic materials taken into the plant 
 body from without. They are the only organisms, so far as 
 known, which have the power of building up organic material 
 from inorganic. They are, therefore, the ultimate source of 
 the food supply of the world. 
 
 215. Metabolism. — After suitable foods become available 
 to plants, whether by manufacture or by absorption ready- 
 made, they suffer various chemical changes both before and 
 after becoming a part of the body. The changes by which 
 foods are manufactured and assimilated and those by which 
 the products of waste are gotten rid of are all comprehended 
 under the term metabolism. 
 
NUTRITION. l6l 
 
 C. Nutrition of colorless plants. 
 
 216. Colorless plants. — By tin's really inaccurate phrase 
 are meant plants which do not possess chlorophyll, though 
 some of them are highly colored by other pigments. 
 
 The colorless plants among the thallophytes constitute two 
 large groups, known as bacteria and fungi. Among the seed 
 plants, also, are found some devoid of chlorophyll. 
 
 Many plants possessing chlorophyll show to the eye other 
 tints than green, when other pigments are present in such 
 quantity as to mask the green. This is notably the case with 
 the so-called "foliage plants," in which reds, yellows, pur- 
 ples, and browns are common. (See also ^|*[ n, 40, 45.) 
 
 Colorless plants necessarily live either upon the decomposi- 
 tion products of dead organisms, or in company with living 
 organisms. Those which live upon dead bodies, whether 
 these have lost their form completely or not, are known as 
 saprophytes. Those organisms which live in association one 
 with another are called symbionts and their relation is known 
 as symbiosis. (See Chap. XXIV.) Some symbionts are 
 antagonistic and stand in the relation of parasite and host, 
 the name parasite being applied to the organism which 
 depends for its food upon the supporting organism, called the 
 host. 
 
 217. Saprophytes and parasites may be either obligate or 
 facultative. < )bligate parasites or saprophytes are those which 
 can exist only upon living or upon dead organisms, respec- 
 tively. Facultative parasites or saprophytes are those which 
 can pass a portion of their existence upon decaying or upon 
 living organisms, respectively. They are not able, however, 
 to complete their life cycle except upon their appropriate 
 substratum. 
 
 218. Saprophytes. — Saprophytic bacteria live immersed 
 in solutions of organic material, or surrounded by films of 
 
1 62 PLANT LIFE. 
 
 fluid on the surface or in the interior of the organic material 
 upon which they flourish. Saprophytic fungi either form 
 their mycelium upon the surface of the organic matter, or, 
 more commonly, they penetrate it more or less extensively 
 by a profusely branched system of submerged hyphae. A few 
 saprophytic seed plants form at the base of the stem an en- 
 larged, tuber dike mass from whose surface great numbers of 
 profusely branched roots arise. These penetrate the decay- 
 ing material in all directions, and act as absorbing organs. 
 A few have abundantly branched underground stems and 
 have no permanent roots. 
 
 219. Digestion. — Saprophytes whose surfaces are sur- 
 rounded by food solutions have only to absorb them. Some, 
 however, have power to convert into material soluble in water 
 the solid insoluble foods with which they are in contact. 
 This is brought about either by a direct action of the proto- 
 plasm of the living plant, or by means of enzymes (•([ 237) 
 excreted by it. Such chemical changes, by means of which 
 insoluble solid materials are transformed into soluble ones 
 and are dissolved, are quite like those which occur in the di- 
 gestive tract of the higher animals, and, therefore, may Im- 
 properly termed digestion. 
 
 220. Assimilation. — After the food is absorbed, it under- 
 goes various changes, collectively known as assimilation, by 
 which it is enabled to become part of the living material of 
 the plant body.* 
 
 221. Fermentation and putrefaction. — Some saprophytes 
 produce changes in the material upon or in which they grow, 
 other than those described above. The more important 
 changes may be comprehended under the two terms fermen- 
 tation and putrefaction. Between these there is no sharp 
 
 * This is not to be confused with the manufacture of organic food by 
 green plants, to which the term assimilation is inaptly applied by most 
 writers. 
 
NUTRITION. 163 
 
 line of demarcation. Popularly the term putrefaction is ap- 
 plied to the changes in nitrogenous substances which are ac- 
 companied by offensive odors. Fermentation is commonly 
 applied to the chemical changes occurring in sugary solutions, 
 such as fruits, expressed juices, infusions, etc. Many bacteria 
 and a number of fungi, notably those known as yeasts, are 
 capable of producing fermentation in such solutions. The 
 chemical changes produced are more extensive than those 
 required for obtaining food. Ordinary brewer's yeast, for 
 example, utilizes about 5 per cent of the sugar present in the 
 solution for food, but breaks up the remaining 95 per cent 
 into carbon dioxide, alcohol, and some other less important 
 by-products. In putrefaction the by-products are commonly 
 offensive gases, among which hydrogen sulfid (H„S) predomi- 
 nates. A'arious other materials may be formed, among which 
 not infrequently are virulent poisons. These are well known 
 in certain putrefactive changes of milk, meat, etc. 
 
 222. Parasites obtain their food either by growing upon 
 the surface of the host and thrusting into its interior absorb- 
 ing organs ; or by growing wholly in the interior of the host, 
 breaking out to its surface only to form reproductive bodies. 
 
 Parasites may work little apparent harm, or they may bring 
 about local disease and death of the host. Their mode of 
 obtaining food is not essentially different from that of sapro- 
 phytes. They either digest solid foods, or absorb liquid 
 foods, prepared by the host for its own use. Among the 
 green plants there are some partial parasites, sin h as the mis- 
 tletoe, which seem to obtain from their hosts chiefly the 
 water and salts which they have absorbed. These materials 
 they themselves elaborate into food. (See further «j 465.) 
 
 D. Nutrition of green plants. 
 
 223. Raw materials. — In order that the green plants may 
 be able to manufacture their food, they require certain raw 
 
164 PLANT LIFE. 
 
 materials, which arc obtained from the medium by which 
 they are surrounded. These substances are a weak watery 
 solution of various mineral salts, and a gas, carbon dioxide. 
 
 224. Salts absorbed. — Along with the water which is 
 taken into the plant go various amounts of dissolved material, 
 a considerable portion of which consists of mineral salts. 
 When plants grow in humus, or in water or soils containing 
 organic matter, a variable amount of carbon compounds 
 suited for food may be dissolved by the water and be taken 
 up by the plant. To this extent the plant will live as a sapro- 
 phyte, and no doubt many field and garden plants have been 
 bred to require this sort of life. Among the mineral salts 
 the most important are the salts of calcium and magnesium, 
 which are present in all soils, in greater or less quantity, 
 usually in the form of nitrates, phosphates, and sulfates. 
 Compounds of two other indispensable elements, namely, 
 iron and potassium, are dissolved in soil waters. In the 
 same way at least seven additional elements are obtained by 
 plants. Besides these, other compounds to a considerable 
 number, of no use in forming food, are taken in. Silicon, 
 for example, which is found in the ash of almost all plants, is 
 of no value either as a food, or for the manufacture of food, 
 although it plays an important role in increasing the rigidity 
 of certain plants, and in protecting others from injury. 
 
 225. Selective action. — Compounds of these elements 
 exist in the water in various, though small, amounts. But 
 they are not taken into the plant in the same proportions as 
 they exist in the water. For each substance presented to the 
 plant there is a certain degree of concentration at which its 
 solutions are absorbed with greater rapidity than at any other. 
 Substances which are utilized by the plant and which, there- 
 fore, disappear as such within it by having their chemical com- 
 position altered or by being stored up in a different form 
 and so removed from solution, will enter the plant contin- 
 
NUTRITION. 165 
 
 uously so long as the supply outside exists. Substances ab- 
 sorbed by the plant and not utilized accumulate, and their 
 solutions soon attain the same degree of saturation within the 
 plant as outside, when they cease to be absorbed. It is for 
 this reason that two plants growing upon the same soil may 
 contain very unequal quantities of any important material. 
 Plants thus exert a sort of selective action, but this selection 
 is dependent upon purely physical laws, and is not directly 
 under the control of the plant. 
 
 226. Carbon dioxide. — Carbon dioxide, as such, is not 
 found in nature. It instantly combines with water to form 
 a gas known as carbonic acid gas, and this is ordinarily 
 meant when carbon dioxide is spoken of. This gas exists in 
 small quantities in the atmosphere, rarely exceeding one part 
 in twenty-five hundred, except in secluded spaces. The 
 constant currents in the atmosphere make its distribution 
 practically uniform. On account of its ready solubility, this 
 gas also exists in abundance in soil waters and in the larger 
 bodies of water constituting streams, lakes, or pools. In a 
 soil containing carbon compounds it is constantly being pro- 
 duced by decomposition. The water which passes through 
 the soil therefore has a larger percentage of this gas than the 
 air, sometimes containing as much as one per cent. 
 
 227. Absorption. — Water plants readily absorb the dis- 
 solved gas by such surfaces as are exposed to the water. 
 Floating plants have opportunity to obtain it both from the 
 water and from the atmosphere. Land plants, although 
 their roots are surrounded by a comparatively concentrated 
 solution of carbonic acid, do not take up appreciable quan- 
 tities by these organs. On the contrary, the absorption of 
 this gas seems to depend entirely upon those cells which 
 contain chlorophyll. The Stomata, which allow the internal 
 intercellular spaces free communication with the outside air, 
 are important organs, not only in regulating transpiration, 
 
1 66 PLANT LIFE. 
 
 but also in permitting the absorption of this gas. Its con- 
 tinued absorption depends upon its continuous removal from 
 the cell sap in the manufacture of carbohydrates. 
 
 228. Anabolism. — By this term arc designated the con- 
 structive processes of metabolism, by which complex sub- 
 stances are produced from simple ones. These materials 
 belong chiefly to two classes, {a) carbohydrates, (b) proteids. 
 
 229. i. Carbohydrates. — The process by which carbo- 
 hydrates are produced is called photosyntax. The conditions 
 under which photosyntax occurs are three : (a) the presence 
 of chlorophyll, (b) the action of light, and (c) the presence 
 of potassium salts. 
 
 230. (a) Chlorophyll. — Chlorophyll, as has been shown 
 in Part I, sometimes colors the whole protoplasm of the cell, 
 but is more commonly found only in certain special struc- 
 tures, the chlorophyll bodies. The real work of forming the 
 carbohydrate depends, therefore, upon the protoplasm of the 
 chlorophyll body. The purpose of the chlorophyll is to 
 absorb certain portions of the light which falls upon it. If 
 the light which has been passed through a green leaf, or a 
 solution of chlorophyll, be examined with a spectroscope, 
 seven dark bands appear in place of certain of the colored 
 rays, because these have been stopped by the chlorophyll 
 (fig. 173). ( >ne absorption hand lies between the red and the 
 orange ( 3-9 of scale, fig. 1 73), another in the orange ( 1 1-14), 
 the third, faint, in the yellow (17-20), the fourth at the 
 edge of the green (30—32), while the fifth (53-73), sixth 
 (75-93), and seventh (94-100) bands occupy most of the 
 blue and violet. These last three blend into one extremely 
 broad band, except when the light passes through very small 
 quantities of chlorophyll. 
 
 231. (6) Light. — The light absorbed by the chlorophyll 
 furnishes the energy necessary to carry on the work of taking 
 apart the carbonic acid and rearranging the molecules into a 
 
NUTRITION. 
 
 167 
 
 more complex substance. This energy cannot be supplied 
 by the plant itself. An external source of energy is therefore 
 necessary. What this source is is unimportant, provided the 
 
 Fig. 173. — The absorption spectrum of an alcoholic solution of chlorophyll. A beam 
 of sunlight passed through a prism is broadened into a strip, called the spectrum, 
 which shows different colors, according to the length of the light waves, the longest 
 appearing red and the shortest violet. Some of the light waves are stopped by 
 absorption, and at these places black lines appear (Fraunhofer lines), the more im- 
 portant being those below the letters B, <-', etc. When the sunlight passes through an 
 
 alcoholic solution it absorbs those parts of the light corresponding to the dark bands 
 
 lade visible ' 
 
 :he Fran 
 or roughly by the colors. — After Kraus. 
 
 I to VII. These absorption bands are made visible by spreading out the light ray into 
 a spectrum. The bands are located by the Fraunhofer lines, or by the artificial scale, 
 
 energy be sufficiently intense. The light of an electric arc 
 serves the purpose as well as sunlight, if its intensity be 
 equal. 
 
 232. (c) Potassium salts. — These take no part in the 
 composition of the food produced, and their exact role is not 
 understood. It is well established, however, that their 
 presence is essential to the formation of the carbohydrate. 
 
 233. The product of photosyntax. — The steps in the 
 process of the building of carbohydrates are not thoroughly 
 known. Present indications are that the material first pro- 
 duced by the rearrangement of the molecules of carbon, 
 hydrogen, and oxygen, derived from the carl ionic acid, is a 
 molecule of the simplest carbohydrate, formaldehyde. CI !..< >. 
 Several of these are then built up (by condensation and 
 polymerization) into one of the more complex carbohydrates, 
 such as cane sugar. Starch is generally the first visible prod- 
 uct and appears as minute granules in the interior of the 
 
1 68 PLANT LIFE. 
 
 chlorophyll bodies, but is probably a transformation product 
 from a sugar, to whi'ch it is closely akin (hemic ally. 
 
 234. 2. Proteids. — The formation of proteids is even 
 more obscure. Apparently at some point in the series of 
 changes following the formation of formaldehyde, molecules 
 of nitrogen are added to form an amid. Amids, especially 
 asparagin, leucin, and tyrosin, are common in plants. They 
 may also be produced by the use of carbon, hydrogen, and 
 oxygen from complex carbohydrates by katabolism (* 238). 
 They are soluble in water, crystallizable, and, hence, can be 
 carried by osmosis from cell to cell. From these, by the 
 addition of sulfur and phosphorus, proteids are formed, but 
 neither the steps in the process nor its conditions are well 
 understood. Apparently the formation of amids occurs in 
 green tissues and under the influence of light. It is probable 
 that even among the green plants the formation of proteids 
 takes place in other parts than the green tissues, as it is 
 certain that this occurs also among the colorless plants. The 
 proteids which are built up from the amids are used directly 
 in the repair of protoplasm. Since carbohydrates are neces- 
 sary to the formation of proteids, and since they can be 
 manufactured only by the green plants under the influence of 
 light, it will be seen how essential these plants are for the 
 world's food supply. 
 
 E. Storage and translocation of food. 
 
 235. Storage and transfer, -both in the colorless and 
 green plants it is necessary that the foods made or absorbed 
 should be transferred from one point to another where they 
 are to be used. The larger the plant, the more important 
 does this transfer become. In many plants, also, it is 
 desirable that a supply of reserve food be stored for use when 
 a supply is no longer available from the outside or by 
 manufacture. 
 
NUTRITION. 
 
 1 69 
 
 236. Storage. — In the higher plants storage places are 
 secured by the enlargement of roots, stems or leaves, to form 
 
 Fig. 174.— Reserve starch. .-/. two cells of a potato, showing enclosed starch grains 
 The other contents not shown. A', compound starcli grains from a grain of oats 
 Three of the component granules of a large grain are shown separately. (', starch 
 giains from a bean. All highly magnified.— After kerner. 
 
 reservoirs. Similar specialization of parts of lower plants 
 occurs. Carbohydrates are sometimes transformed into fats 
 for storage purposes, but carbo- 
 hydrate and proteid reserve food 
 is usually solid. Reserve car- 
 bohydrates usually occur in the 
 form of starch, sugar, cellulose, 
 gum, etc. Reserve proteids are 
 usually in the form of aleurone 
 grains. The starch is deposited in 
 the form of large rounded or oval 
 grains (sphere-crystals), which often 
 
 . . . Fig. 175.— Aleurone (proteid) grains. 
 
 shOW layers 0\ dillcivnt composition /. from seed oi peony. ■>. to,,,, 
 
 the outer, /'. from the middle, c, 
 and density (fig. I74). FatS OCCUr from the inner layers. //, from 
 
 . seed of castor bean a, in alcohol ; 
 in liquid form as droplets of van- b, after treatment with iodine solu- 
 tion and alcohol. In both, f, elo- 
 
 ous size, and are only rarely solid, boid; <■. crystalloid. Very highly 
 
 magnified. — After Zimmermann. 
 
 Aleurone grains are really vacuoles 
 
 filled with reserve proteids. Some of the proteids often 
 
17° PLANT LIFE. 
 
 crystallize | producing a crystalloid), and other materials are 
 frequently present, which form the globoid (fig. 175). 
 
 237. Intracellular digestion. — When solid foods, insol- 
 uble in water, are to be moved from one part of the plant to 
 another it must be done by altering them into soluble sub- 
 stances. This is accomplished by means of enzymes of differ- 
 ent kinds, adapted to effect the alteration of various foods. 
 The most abundant enzyme is diastase, which has the power 
 of altering starch into a sugar called maltose. Enzymes fitted 
 to transform proteids are also found in considerable amounts. 
 When the foods have thus been brought into a soluble condi- 
 tion, they dissolve in the water present and move from one 
 part of the plant to another, chiefly by osmosis. As any 
 given material is used up in growth or repair, or is altered 
 into another substance, a constant stream of molecules of 
 this material moves toward the point at which it is disappear- 
 ing. Thus from the food sources it is transferred to the 
 reservoirs and stored in suitable form. Thence, when needed, 
 it is redissolved after digestion and carried to the active parts 
 which utilize it. 
 
 F. Katabolism. 
 
 238. Destructive changes. — Coincident with the processes 
 which result in the formation of complex organic substance 
 out of simpler ones are those which result in its destruction. 
 The constructive processes are grouped under the term anab- 
 n/i.xm, and the destructive ones are designated as katabolism. 
 In the green plants the anabolic changes predominate (be- 
 cause of extensive photosyntax), with the result that the plant 
 accumulates organic matter ; while in colorless plants kata- 
 bolic processes predominate, with the result that the plant 
 increases in bulk, but only at the expense of organic materials 
 previously existent. In all plants, however, both the con- 
 
NUTRITION. 17 l 
 
 structive and destructive changes go on at the same time 
 and without conflict. 
 
 239. Respiration. — A series of katabolic changes is in- 
 cluded under the term respiration. It is a familiar fact that 
 the higher animals cannot live without a constant supply of 
 oxygen and a corresponding excretion of carbon dioxide. 
 This is not so generally known to be true of plants. It is, 
 nevertheless, true that no plant can live without a constant 
 supply of oxygen and a corresponding excretion of carbon 
 dioxide. The processes by which oxygen is obtained and 
 carbon dioxide excreted constitute respiration. 
 
 240. Respiratory ratio. — The ratio between the amount 
 of oxygen consumed and carbon dioxide produced varies 
 somewhat with the age and condition of the plant, as well as 
 with the circumstances under which respiration occurs. 
 Ordinarily the volume of carbon dioxide produced is approx- 
 imately equal to the volume of oxygen consumed, and the 
 
 ratio may be expressed thus: -— — 1. 
 
 241. Respiration and photosyntax. — In the green plants 
 respiration is masked in daylight by photosyntax. When- 
 ever the green parts are sufficiently illuminated, the carbon 
 dioxide produced by their respiration is consumed in the 
 formation of carbohydrates for food, lint when these parts 
 are not adequately illuminated, the process of photosyntax 
 is interrupted, and respiration can be studied. The parts 
 of plants which are free from chlorophyll, such as young 
 flowers, buds, embryos, and the like, and all the non-green 
 plants, allow the respiratory changes to be demonstrated 
 readily. 
 
 242. Aeration. — The oxygen consumed comes from the 
 atmosphere, or from the molecules of this gas dissolved in 
 water. Certain plants are adapted to aerial respiration, while 
 others are adapted to aquatic respiration, but in either case 
 
172 PLANT LIFE. 
 
 the gas used is the same. In the smaller and simpler plants 
 the protoplasm absorbs oxygen directly through the cell wall. 
 In multicellular plants, however, especially when these be- 
 come large and complex, only the superficial cells could do 
 this. The internal cells are too far from the source of supply 
 to allow an adequate amount of oxygen to reach them by 
 osmosis through other cells. In large plants, therefore, 
 intercellular spaces are provided, communicating with the 
 external air, and through these oxygen diffuses. In the 
 land plants the intercellular spaces are continued through the 
 epidermis, in which, with the guard cells, they constitute 
 the stomata (•[ 166). On the older parts of woody plants 
 which have begun to form a periderm the stomata are replaced 
 by lenticels, through which the internal intercellular spaces 
 communicate with the outer air (^[ 140). In the absence of 
 stomata or lenticels, however, the oxygen may pass through 
 any part of the surface of the plant. In submerged water 
 plants, very large intercellular spaces are formed (fig. 117), 
 permitting the existence of an internal atmosphere of con- 
 siderable amount, within whose limits gaseous exchanges may 
 occur. Oxygen may reach these intercellular spaces from 
 the water through the superficial cells. 
 
 243. Intramolecular respiration. — While free oxygen is 
 ordinarily utilized for respiration, all plants seem to be 
 capable of obtaining their supply for a short time from the 
 organic matter of the plant itself. Such respiration has there- 
 fore been called intramolecular respiration. It can exist at 
 most for a few hours without producing disease and, sooner 
 or later, the death of the plant. It is precisely parallel to 
 the similar method of respiration possible among cold-blooded 
 animals. A few plants of the simpler sort, such as the 
 bacteria, rely wholly upon combined oxygen for their respira- 
 tory supply. Such plants have adapted themselves to grow 
 in the absence of free oxygen, which, instead of facilitating 
 
NUTRITION. 1/3 
 
 their life processes, really checks them. They are known as 
 anaerobic plants. 
 
 244. Excretion. — The carbon dioxide produced by res- 
 piration, when not used for photosyntax, is gotten rid of by 
 the reverse of the methods described for the absorption of 
 oxygen. 
 
 245. Release of energy. — The purpose of respiration is 
 to set free energy required for growth and movement. While 
 plants are capable of utilizing radiant energy of the sun for 
 photosyntax, they must set free within their own bodies the 
 energy requisite for putting in place particles of new material 
 to form new parts, and for the execution of movements, 
 whether internal, such as the streaming or rotation of the 
 protoplasm, or mass movements, such as those of leaves and 
 other members, or movements of locomotion, such as those 
 of swarm pores and sperm cells. (See ^| 276 ff.) The re- 
 quired energy is set free by the decomposition of organic 
 matter. 
 
 246. Loss of weight. — As a consequence there ensues a 
 loss of weight. If a plant, such as a seedling abundantly 
 supplied with reserve food, be compelled to develop in dark- 
 ness, and so allowed to make no additional food, it may be 
 easily demonstrated that a large part, often as much as one 
 half, of its weight will be lost (as gases) in respiration. This 
 loss of weight conies primarily from the decomposition of 
 portions of the living protoplasm. These, however, are soon 
 replaced by the formation of new protoplasm from the pro- 
 teids, and these again are replaced, as already described, by 
 the use of carbohydrates and nitrogenous compounds. Ulti- 
 mately, therefore, respiration results in a diminution of the 
 reserve food, especially of the carbohydrates. 
 
 247. A vital function. — Respiration is a function of the 
 protoplasm, and does not occur simply because oxidizable 
 substances are present in the plant and oxygen is brought 
 
1^4 PLANT LIFE. 
 
 into contact with them. On the contrary, the oxygen seems 
 to enter into loose combination with protoplasm, forming 
 an extremely unstable compound which under unknown con- 
 ditions breaks down into simpler substances, setting free 
 energy. Some of these materials are again used in building 
 protoplasm, while others break down still further, ultimately 
 into water and carbon dioxide. The supply of oxygen is so 
 necessary that if a plant cannot obtain oxygen from without, 
 it will secure it by the destruction of part of its own sub- 
 stance for a time, as shown by intramolecular respiration. 
 
 248. Heat. — While this decomposition of the protoplasm 
 in ordinary respiration is not a true oxidation, it nevertheless 
 results, as oxidation does, in the evolution of heat. The 
 amount of heat produced is usually not great enough, and its 
 loss too rapid, to make it readily perceptible. Anything 
 which prevents the radiation of heat will make its measure- 
 ment possible. The germination of large quantities of seeds 
 or the blossoming of a number of flowers in a confined space 
 may raise the temperature as much as 15 or 20 above that 
 of the air. The heating of hay, grain, and similar substances, 
 which have been stored when moist, is due partly to the 
 respiratory activity of bacteria and fungi, which grow rapidly 
 under these conditions. Fermentative changes, which also 
 occur under the same conditions, add to the evolution of 
 heat. 
 
 249. Light. — A few plants also produce light. This light 
 is like that seen when phosphorus is exposed to the air in 
 darkness, or when the end of a match is lightly rubbed. 
 Phosphorescence occurs only in some bacteria and fungi. 
 When it is seen upon decaying meat, fish, or wood, it is 
 because these organisms are present. It does not arise from 
 the decaying substance itself. Several of the larger fungi, as 
 certain toadstools, have a mycelium capable of emitting this 
 phosphorescent light. 
 
NUTRITION. 1/5 
 
 250. Contrast between respiration and photosyntax. — 
 Since the processes of respiration and photosyntax in green 
 plants are so frequently confused, a contrast is here drawn 
 between them. 
 
 Respiration. Photosyntax. 
 
 Occurs in all living cells. Occurs only in green cells. 
 Indifferent to or retarded by Requires light. 
 
 light. 
 
 Consumes organic matter. Produces organic matter. 
 
 Produces carbon dioxide. Consumes carbon dioxide. 
 
 Consumes oxygen. Produces oxygen. 
 
 Sets free energy. Accumulates energy. 
 
 251. Other katabolic changes. — Besides those constitut- 
 ing respiration, a considerable number of other katabolic 
 changes occurr, which are not so closely connected with 
 the vital functions of the plant. They result in the produc- 
 tion of substances which are of no further use in nutrition 
 and only of incidental value for any purpose. Such sub- 
 stances may be stored in some out of the way place, or in 
 such parts as are transient, and by the loss of these parts the 
 useless materials are gotten rid of J or they may be excreted 
 directly. The waste materials are either nitrogenous or 
 non-nitrogenous. 
 
 252. Non-nitrogenous by-products. — Among the non- 
 nitrogenous materials the most important are the carbon 
 acids. su< h as oxalic, malic, etc., the tannins, the resins, the 
 gums and the volatile oils. These substances are either by- 
 products of photosyntax, or they arise in the course of the 
 assimilation of foods. Oxalic acid is usually gotten rid of by 
 being combined with lime to form calcic oxalate, which 
 crystallizes either in the form of squarish crystals or as long 
 needles, the form depending upon the amount of water of 
 
1 7 6 
 
 PLANT LIFE. 
 
 crystallization (fig. 176). The resins, usually dissolved in 
 an oil, are generally exereted into special intercellular spaces 
 
 Fig. 176. Crystals found in plants. I, calcium carbonate; II-V, calcium oxalate; 
 II, octahedron with blunt ends; III, compound crystals from the nectary of a mallow; 
 IV, ,i, /■, needle crystals (raphides) from leaf of fuchsia ; V, cell from the fruit-Mesh 
 of a rose showing a crystal, k, embedded in an outgrowth of the cell-wall, . . All highly 
 magnified. — After Behrens. 
 
 (fig. 17 7)- 
 
 Volatile oils are secreted by glandular hairs 
 (c, fig. 113); or are formed 
 in the epidermis itself, as in 
 flowers ; or are produced in 
 chambers near the surface, 
 the cells which produce the 
 oil being disorganized to 
 form the cavity in which 
 
 Fig. [77. — Transverse section of an inter- 
 cellular receptacle for gum-resin from the the drops lie (fig. 17^)- 
 fruit of fennel. The secretion has been 
 
 dissolved out by alcohol. The shaded cells Other materials, SUCh !1S 
 lining the tube are the secretory tissue. 
 Moderately magnified.— After Tschirch. salts of lime, arc sometimes 
 
 excreted upon the surface of the plant. From glands in 
 the flower, nectar, which is a solution of sugar, is excreted 
 (figs. 179, 180). The loss of this food is compensated for 
 by its attractiveness for insects, which incidentally serve for 
 the transfer of pollen from one flower to another. Caout- 
 
NUTRITION. 
 
 177 
 
 chouc and gutta-percha occur in the milky juice of certain 
 plants. 
 
 253. Nitrogenous by-products. — Among the nitrogenous 
 waste materials the most important are the alkaloids, such as 
 
 Fir.. 178.— Section through oil-receptacles in rind of orange, a, structure at the beginning 
 of the disorganization of the oil-producing cells; />, final condition, with two drops of 
 oil occupying the cavity. Moderately magnified. —After Tschirch. 
 
 Fig 
 
 
 Fig. 180. 
 
 d surface of the cup, >/, 
 
 Fig. 179. — A flower of the red currant cut in half. The rouglu 
 
 secretes nectar. Magnified 5 diam.— After Kerner. 
 In.. 180. I, ,1 petal from the flower ol a buttercup {Ranunculus acris), showing the 
 
 nectary, n. Magnified 3 diam. II, diagram of a longitudinal section ol tin- same 
 
 through the nectary //. The tissue lining the pouch of the petal, b, secretes the drop 
 
 of nectar, /. Magnified 8 diam. After Behrens. 
 
 quinine, morphine, strychnine, nicotine, etc., which occur in 
 the seeds, bark, or leaves, and are gotten rid of when these 
 are dropped. 
 

 CHAPTER XIV. 
 
 GROWTH. 
 
 254. Definition. — The growth of plants is continued for 
 a much longer time than that of animals. In most cases it 
 is continued in some part throughout the existence of the 
 plant. There are also changes in the form of certain parts, 
 particularly of the lower plants, which must be distinguished 
 from true growth. Growth is a permanent change of form 
 accompanied usually by an increase in size. 
 
 255. Formation of new parts. — Each new cell originates 
 in the division of some previously existing cell by a partition- 
 wall.* The two cells so formed grow until they attain the 
 size of the parent cell, when one or both may continue to 
 grow until they attain a permanent form; then growth ceases. 
 Those cells which do not develop into permanent tissue, but 
 retain their power of division, constitute a mass of tissue at 
 the tip of each branch or root, the primary meristem (^[ 77, 
 101). Permanent tissue which resumes active division is 
 called secondary meristem (^[ 86, 134). It will be seen, 
 therefore, that every cell of a plant has been at some time in 
 an undeveloped or embryonal condition. 
 
 256. Phases of cell development. — The characteristics of 
 this embryonal condition are the nearly uniform and small 
 size of the cells, the relatively large nuclei, and the absence 
 or small size of the vacuoles (A, fig. 181). As the cells which 
 are destined to become the permanent tissues grow older 
 
 * To this there are only unimportant exceptions. 
 
 17S 
 
GROWTH. 
 
 179 
 
 they pass gradually from the embryonal stage into a second 
 phase of development, the stage of elongation. This stage is 
 marked by the rapid Increase of the cells in size and a much 
 less marked increase in the mass of protoplasm present. In 
 order to maintain the turgor of the cells, there is a great in- 
 crease in the volume of water, which accumulates in one or 
 
 Fig. [81. — Cells from young and mature fruit of snowberry (Symthoricarpui), seen in 
 section. ./, three young cells, very small, walls thin, inn lei relatively large, vacuoles 
 very minute; />', two, somewhat older ; larger, walls thicker, nuclei smaller, vacuoles 
 
 several. A and />' magnified 300 diam. C, a single cell, mature, magnified 
 di.1111.. inie third as much as . / and A'.- vacuole single, very large. The volume ol 
 < is more than 1500 times one of the cells in A . h , cell-wall ; p, protoplasm ; <<•, nu- 
 cleus; kk, nucleolus; s, vacuole. — After l'rantl. 
 
 more large vacuoles ((", fig. t8i ). If the organ in question 
 has an elongated form, such as the stem or the root, growth of 
 the cells takes place chiefly in the direction of its long axis, 
 although an increase also occurs in the transverse directions. 
 During this phase the tells may attain a hundred or even a 
 thousand times their former volume. Growth in length can 
 
180 PLANT LIFE. 
 
 be studied by direct observation with a microscope, but more 
 < onveniently by magnify ing the growth by mechanical means, 
 so as to observe the movements of a pointer over a scale. 
 Such an instrument is an auxanometer. Those forms of it 
 which secure a continuous record automatically are of the 
 
 Fig. 182. — Golden's auxanometer. The instrument 1 onsists of two parts, a multiplying 
 pulley and two recording rods turned by a clock. V thread from the plant passes 
 through a bent glass ,U ' ,L ' ,llu ' makes one turn around the small pulley to which it is 
 then f.isti-iu-d. Another thread makes one turn around large pulley and descends 
 to carry a pointer which slides on two guide rods. Asthe plant grows the thread 
 from it slackens and the pointer descends at a magnified rate by its own weight. Two 
 glass rods, blackened in a smoky gas-flame, are rotated by a clock to whose hour 
 spindle the frame carrying them is atta< hed. Vs thl \ pass the pointer a mark is made 
 on the smoked sulfate. The distance id the suciessive marks shows the amount of 
 growth as magnified. Permanent record may lie made by means of blue prints, using 
 the rods (which are removable) as negatives.— After Arthur. 
 
 most service (fig. 182). By imperceptible gradations these 
 
 cells pass into the third and final stage of growth, which is 
 
GROWTH. 
 
 i8i 
 
 characterized by permanent and usually irregular thickenings 
 of the wall (figs. 10, n, 52, 58). 
 
 257. Grand period of growth. — The entire duration of 
 growth of an organ is known as its grand period of growth. 
 Corresponding precisely to the phases in cell development, 
 there are three phases in the development of the organ as a 
 whole. Its growth is at first very slow, increasing gradually, 
 and then more rapidly, to a maximum, from which it falls 
 rapidly, and then more gradually, until it ceases entirely. The 
 earliest phase, the embryonal, results in so little elongation 
 that it is scarcely possible to have it recorded by the auxanom- 
 eter. The last phase, that of internal differentiation, is not 
 
 
 
 
 2V 
 
 I \ 
 
 t v 
 
 4 \ 
 
 / \ 
 
 S IX 
 
 / V 
 
 t S 
 
 4 s^ 
 
 L ^ 
 
 ^ s ^ 
 
 
 4 8 13 16 80 
 
 Fig. 183. — Curve representing the rate of growth of an internode >>f crown imperial tor 
 each day during the grand period — in this rase _'*. days. The height ol each \ ertical line 
 where it intersects the curve represents the total growth for the corresponding 24 
 hours. The numbers indicate days. The maximum growth occurred on the 6th day. 
 — After Sadis. 
 
 marked by any elongation. The accompanying curve (fig. 
 [83) therefore represents only the duration and course of the 
 phase of elongation. 
 
 258. Growing region.— The part of any one of the multi- 
 cellular plants, which is growing in length, is limited. The 
 elongating region of a root rarely exceeds a centimeter, and 
 is often not more than one halt a centimeter in length. In 
 
182 
 
 PLANT LIFE. 
 
 stems, however, the elongating part may measure twentyoreven 
 
 fifty centimeters, and in rare cases 
 much more. Figure 184 shows a 
 root, A, upon whose surface marks 
 were made 1 111111. apart. Twenty- 
 four hours later the root presents 
 the appearance of B. Only the 
 tissues in the first five spaces were 
 capable of elongation. The others 
 had passed into the third phase. 
 The second and third millimeters 
 grew most in length. The growing 
 regions of stems may be deter- 
 mined in the same way. 
 
 259. Tension of tissues. — The 
 different tissues in any organ usu- 
 ally do not grow at an equal pace, 
 and consequently certain tissues 
 are under strain, while others are 
 compressed. The curled and 
 crinkled leaves or the curved cap- 
 sules of mosses illustrate this in- 
 
 marked with fine lines of Chinese equality. It maybe present, how- 
 
 ink into 13 spaces of i millimeter l J J * 
 
 each. /:, the same root, 24 hours ever without manifesting itSt'lf ill 
 
 later, showing elongation only in ' ° 
 
 terminal 5 millimeters The rate of external form. This general COn- 
 growth is greatest m the 2d and 3d ° 
 millimeters and slow in the ,s,,,h. ( 1J, K)U jg kllOWliaS 1 1 1 C /etlSlOfl of 
 and i\\\. .Magnified 1 chain. —Alter 
 
 Prank. 
 
 /issues. If the rapidly growing 
 flower-stalk of the dandelion or the leafstalk of rhubarb 
 be carefully split lengthwise the parts will curve or even curl 
 outward. Separating the inner and outer tissues of a young 
 elder shoot and carefully measuring them shows that tin- 
 inner tissues elongate and the outer actually shorten. The 
 experiment, therefore, shows that the inner tissues really 
 grew more rapidly than the outer, but were compressed in 
 
GROWTH. 183 
 
 the uncut stem, while the outer ones were slightly stretched. 
 The strains thus set up are spoken of as longitudinal tissue 
 tensions. Similar tensions due to unequal transverse growth 
 may be shown to exist. If a thin transverse slice from the 
 fleshy leaf-stalk of the rhubarb be divided into equal parts by 
 a longitudinal cut it will be found in a few moments that the 
 halves can no longer be made to touch throughout the line of 
 the cut, because it has become convex. Both the longitudi- 
 nal. and transverse tensions may be exaggerated if the parts 
 be placed for a few moments in water. 
 
 260. Conditions of growth. — That plants may grow cer- 
 tain conditions are prerequisite. (1) There must be an ade- 
 quate supply of constructive materials. These may be derived 
 either from food recently manufactured or from that stored 
 in reservoirs, or, in the case of the colorless plants, from that 
 absorbed from without. (2) There must be a supply 0/ oxy- 
 gen for respiration. This is needed, as previously explained, 
 to set free the energy necessary for growth. (3) There must 
 be a supply of water adequate to maintain a minimum turgor 
 of the cells, without which growth cannot take place. (4) 
 A suitable temperature is required. The range of temperature 
 within which growth may take place is extensive, and varies 
 with the individual plant. In general, the upper limit may 
 be stated as about 40 C, and the lower, about o° C. The 
 minimum of plants of tropical regions is approximately io° C, 
 while the maximum for plants of the arctic or alpine regions 
 is much below 40 C. Between the maximum and minimum 
 temperatures there is an optimum temperature for each plant, 
 at which growth takes place most rapidly. For most plants 
 the optimum lies between 25" and 32 ('. 
 
 261. External conditions exercise a very important in- 
 fluence upon the rate or character of growth by reason of the 
 irritability of the protoplasm. (See further - 418.) Many 
 of these conditions act upon members of the plant so as either 
 
1 84 PLANT LIFE, 
 
 to bring about permanently unequal growth in a certain part, 
 or to cause one part to grow more or less rapidly for a time 
 than another. Such variations in growth produce curvatures 
 in the parts concerned and move members connected with 
 them. They are therefore discussed in the chapter on Move- 
 ments. Those conditions which act more generally and 
 uniformly upon a large number of plants have a tonic eflfei t 
 and serve to determine the form and mode of development of 
 members. 
 
 262. Light. — The tonic effect of light is different upon 
 different plants and even different members of the same plant. 
 
 \ 
 
 A 
 
 Fig. 1S5. — Part of the transverse sections of the stem of rye. . I. From a plant grown 
 fully exposed to light; /■'. from a "laid" plant imperfectly exposed to light, n , 
 epidermis; b, c, mechanical tissues; </, thin-walled tissues. Highly magnified.— After 
 Koch. 
 
 In general light retards growth in length. Stems grown in 
 darkness usually become excessively elongated. Those 
 which under normal illumination have internodes very 
 
GROW TIL 
 
 I8 5 
 
 short, in diminished light may have them well developed, as 
 occurs, for example, in dandelions growing in deep shade. 
 
 In general, light accelerates the growth of leaves in area. 
 Leaves of shoots grown in darkness remain small. 
 
 Light affects not only the external form but the internal 
 structure. In diminished light the cell walls do not thicken 
 normally, and mechanical tissues are weakened. " Laying" 
 of oats and such grasses is mainly due to this cause (fig. 185). 
 In weak illumination the palisade tissue of the leaves (% 167) 
 is poorly developed. 
 
 263. Light and temperature. — The combined variation 
 of light and temperature between day and night establishes a 
 daily period in the growth of all plants. The withdrawal of 
 light at night permits an increase in the rate of growth in 
 length, which reaches its maximum in some plants shortly 
 after midnight, in others not until the early morning. During 
 the day its retarding effect diminishes the rate of growth, 
 which reaches a minimum some time in the afternoon. The 
 
 5 ; ■■) 11 1 3 5 7 y 11 1 s 5 7 a 11 1 
 
 N M N 
 
 Fir.. 186.— Curve showing the daily period in the growth of a stem of rye. The vertical 
 lines represent 2-hour periods from 5 P.M. of one day to 5 a.m. of the second day. 
 the shaded parts indicating the actual hours of darkness. The horizontal lines repre- 
 sent tenths of a millimeter. The curve is drawn by taking the record from an aux- 
 anometer and laying off on the vertical line For each interval the growth shown, The 
 points arc then joined. It will be observed that the maximum rate ol growth 
 
 shortly after the period ol darkness (5 A.W I and the minimum rate alter the period of 
 most intense illumination (5 P.M.). During the experiment the thermometer varied 
 
 from [8° to 22 C. — After Frank. 
 
 minor fluctuations in temperature, as well as the generally 
 higher temperature during the day and lower during the night, 
 
186 
 
 PLANT LIFE. 
 
 introduce variations in the rate of growth, which obscure, but 
 do not counteract, the retarding influence of light. (See fig. 
 186. ) This daily period is so impressed upon the constitu- 
 tion of the plant that it maintains it for a considerable time 
 even when kept in complete darkness. Stems of sunflower, 
 after two weeks in complete darkness, still showed distinctly 
 the daily period. A similar daily period is apparent in 
 the tension of tissues which depends 
 on growth. 
 
 264. Moisture and oxygen. — The 
 amount of moisture and oxygen pres- 
 ent in the medium surrounding a 
 plant profoundly affects its form. 
 Amphibious plants, that is, those 
 which are capable of growing either 
 on land or in water, often show this 
 
 Fig. 187. — a shoot of water in a striking way. When grown sub- 
 crowfoot {Ranunculus , , . 
 aquatuis). The lower leaves merged, the leaves are usually finely 
 
 have developed under water . , 
 
 and are branched into many divided, while the 
 
 narrow divisions; the two 
 
 upper leaves have developed allowed to develop 
 
 in air and at maturity float 
 
 on the surface of the water, broad blades Scarcely 
 
 About half natural size. — 
 
 After Frank. (fig- 187). 
 
 same leaves, if 
 in the air, have 
 more than lobed 
 
 265. Mechanical pressures or strains also exert an in- 
 fluence upon the rate and mode of growth. Compression of 
 tissues retards their growth; strains accelerate it. Thus, 
 stems enclosed in plaster casts or ligatured grow more slowly 
 in thickness. Tensile strains, such as those exerted by wind 
 or weight, promote the development of mechanical tissues. 
 Petioles, which would break under a strain of 700 gm., after 
 enduring a pull of 500 gm. for five days, broke only at 1600 
 gm. Alter five days more under a strain of 1200 gm. they 
 could not be broken with less than a weight of 6500 gm. 
 
 266. Variations in rate. — There are not only variations 
 in growth in the course of each day throughout the growing 
 
growth. 187 
 
 period, but also minor variations independent, so far as 
 known, of external conditions, which are therefore called 
 spontaneous variations. Irregular variations occur from hour 
 to hour in the course of the day. Regular spontaneous 
 variations, also, occur in various organs, particularly in the 
 tendrils of climbing plants, and in the leaves of flowers and 
 buds. These regular variations, which affect different sides 
 of bilateral organs and different sectors of cylindrical ones, 
 bring about a bending of the entire organ from one side 
 to another. These curvatures produce nutation, and will 
 be further described under movements. (See ^| 283.) 
 
 267. Duration. — Even when the external conditions of 
 growth are kept as uniform as possible, growth does not con- 
 tinue for an indefinite time. Having passed through the 
 phases above named, it ceases, no matter how favorable the 
 external conditions. Yet some organs, even after growth 
 has ceased, may resume it, provided they are affected by 
 suitable stimuli. Thus, the leaf cells which have long since 
 ceased to divide may resume the power of division in the 
 neighborhood of a wound, and by division and the growth 
 of new cells may form a callus covering the wound. The 
 stimulus following fertilization also induces growth in parts 
 adjacent to the egg, as is most strikingly shown in the 
 formation of fruits of the seed plants. (See ^| 404, 409.) 
 
CHAPTER XV. 
 
 THE MOVEMENTS OF PLANTS. 
 
 268. Irritability. — Among the fundamental properties of 
 protoplasm are irritability and automatism. We know practi- 
 cally nothing of the nature of either of these properties, 
 though upon them depend all the movements executed by 
 plants. Automatism is the name given to the power in 
 virtue of which protoplasm is able to initiate internal changes 
 without the action of any external force. Irritability ex- 
 presses the power of the protoplasm to respond or react to 
 the influence of an external change. 
 
 269. Stimuli. — The external change which brings about 
 the reaction is known as a stimulus, and its application is 
 called stimulation. External forces which may act as stimuli 
 are light, heat, gravity, moisture, electricity, chemical sub- 
 stances, etc. Most of these act constantly upon plants. In 
 order that they may act as stimuli, therefore, a relatively 
 sudden change in intensity or direction must occur. Some- 
 times, however, a slow change will still produce a reaction. 
 For example, the gradual withdrawal of light may cause 
 movements of leaves. (See ^[ 297.) 
 
 270. Conditions limiting irritability. — Protoplasm is ir- 
 ritable only under certain conditions, which coincide in the 
 main with those that promote the general well-being or life 
 of the organism. The limits of temperature, moisture, and 
 the supply of oxygen, which permit irritability, are much 
 narrower than those which permit life. Thus, irritability 
 may be lost when the conditions are unfavorable, though life 
 
THE MOVEMENTS OF PLANTS. 1 89 
 
 may persist under such conditions for a long time. Irritabil- 
 ity may also be lost through fatigue, as when, after repeated 
 reaction, no response occurs to even a greatly increased 
 stimulus. Upon the return of suitable conditions, or after 
 sufficient rest, irritability may be regained. 
 
 271. Reaction. — The response of the protoplasm to a 
 stimulus is out of all proportion to the physical or chemical 
 action of the stimulus itself. The action of the stimulus upon 
 the irritable protoplasm may be roughly compared to the 
 action of the trigger niton a primed and loaded gun. It 
 sets free forces vastly in excess of those which it exerts. 
 
 272. Reaction time. — The reaction does not follow in- 
 stantly upon stimulation. The interval, which is known as 
 the reaction time, is ordinarily much longer in plants than in 
 the higher animals. In extreme cases no reaction may be 
 manifest until several hours after stimulation. In other cases, 
 however, as in the well-known sensitive plant, the move- 
 ments of the leaves follow almost instantly upon stimulation. 
 
 273. Form of reaction. — The character of the reaction is 
 not dependent upon the nature of the stimulus, but upon the 
 nature of the organ itself. It is not in the least understood 
 what the inherent peculiarities are which determine the form 
 of the reaction. In different organs exactly opposite effects 
 may be produced by the same stimulus, and the same organ 
 at different ages may respond differently to the same stimulus. 
 Thus the young internodes of the Virginia creeper {Ampe- 
 lopsis) are sharply recurved, but become erect when older. 
 The stalk bearing the flower of the peanut is erect, but as it 
 becomes older it becomes strongly retlexed, and thrusts the 
 fruit under ground. 
 
 274. Localization of irritability. — In multicellular plants 
 irritability to certain stimuli is usually localized in certain 
 organs, and often in special parts of these organs. In many 
 tendrils, for example, the free end is curved and only the 
 
190 PLANT LIFE. 
 
 concave side is irritable to contact. In the Venus' fly-trap, 
 although the whole leaf moves at the contact, only the three 
 hairs upon the upper face of each lobe are sensitive to a 
 touch. (See figs. 386, 205.) 
 
 275. Transmission of stimuli. — In these cases, as in many 
 others, the effect of the stimulus must be transmitted in some 
 way from the point of application to the cells which produce 
 movement. Much uncertainty exists as to how this is ac- 
 complished. In some cases it is doubtless done by means of 
 the connecting threads of the protoplasm from cell to cell, 
 after the analogy of a diffuse nerve. In other cases it may 
 be transmitted through certain strands of tissue by the altera- 
 tion of the hydrostatic pressure in the interior of the cells. 
 
 The movements of plants may be conveniently considered 
 as (1) movements of locomotion by single cells; (2) move- 
 ments of protoplasm within a cell-wall; or (3) mass move- 
 ments of multicellular members of the higher plants. 
 
 I. Locomotion of single cells. 
 
 276. Naked cells. — Plants which consist of a single cell 
 may be either naked or furnished with a cell wall. If naked, 
 they may exhibit either amoeboid or ciliary movements. Amoe- 
 boid movements are slow creeping movements brought about 
 by the protrusion of a portion of the protoplasm (a pseudo- 
 podium), toward which the remainder gradually flows (fig. 
 169). Ciliary movements are due to the extension of one or 
 more very slender threads, called cilia, whose rapid bending 
 in different directions propels the organism (fig. 168). 
 According to the nature of the movements, the course will 
 be zigzag or steady, accompanied by the rotation of the cell 
 on its axis. When the cell comes to rest the cilia are either 
 withdrawn or drop off. 
 
 277. Cells with a wall. — Movements of locomotion in 
 plants possessed of a cell wall are either ciliary or creeping. 
 
THE MOVEMENTS OF PLANTS. 
 
 1QI 
 
 The latter are usually due to the protrusion of processes from 
 the protoplasm through slits in the wall, as in many diatoms 
 (fig. 20). The filaments of the water slimes bend from side 
 to side, and so creep over wet surfaces very slowly (fig. 15). 
 Bacteria (fig. 17) and some diatoms move by means of cilia. 
 
 V) 
 
 A 1 
 
 II. Movement of protoplasm within a wall. 
 
 278. Streaming. — In multicellular organs it is common 
 to find the protoplasm within each active cell 
 moving about from point to point within the 
 cell. The protoplasm is filled with numerous 
 large vacuoles, so that it forms a layer next the 
 wall, with threads or ribbons extending across 
 it (fig. 188). When currents start along the 
 wall and through the strands, the motion is 
 designated as the streaming of the protoplasm. 
 These currents along any particular portion of 
 the protoplasm may run side by side and in 
 opposite directions. 
 
 279. Rotation. — When the protoplasm sur- 
 rounds a single large vacuole and thus occupies 
 only the periphery of the cell (fig. 181, C), 
 the whole mass may rotate, usually in the direc- 
 tion of its long axis. The portion immediately 
 in contact with the wall is motionless, and there 
 must necessarily be a strip between the half Fie 
 moving up and the half moving down the 
 cell, which is also quiet. Such movements are 
 called rotation of the protoplasm. It is not 
 known whether either streaming or rotation 
 has any immediate relation to the well-being 
 of the cell. 
 
 280. Cell organs. — In addition to the mass 
 movements of the protoplasm, the smaller protoplasmic bodies 
 
 A single 
 cell from a hair of 
 Chelidonium. 
 The arrows show 
 the direction of 
 movement oi the 
 protoplasm in the 
 peripheral I a y e r 
 and in the bands 
 which separate the 
 vacuoles, n, the 
 nucleus, with nu- 
 cleolus. Highly 
 magnified. — After 
 I lippel. 
 
192 PLANT LIFE. 
 
 within the cell, such as the nucleus and the chloroplasts, are 
 capable of moving about. Under moderate illumination 
 chloroplasts accumulate upon the sides of the cells most di- 
 rectly reached by the light. Under very strong illumination 
 they retreat to the walls least illuminated, or may even pile 
 up in the angles of the cell so as to shade each other (fig. 
 189). 
 
 &At 
 
 Fig. 189. — Cells from the spongy parenchyma of the leaf fo wood sorrel {Oxalis), seen 
 from the direction in which light falls on the leaf, a, position of the chloroplasts in 
 diffuse light ; /', position after short exposure to direct sunlight ; c, position after longer 
 exposure. Highly magnified. — Alter Staid. 
 
 III. Movements of multicellular members. 
 
 281. Forces. — The movements of multicellular parts may 
 be brought about either by special organs known as motor 
 organs, or by the growth of the immature parts. Motor or- 
 gans are generally responsible for the movements of mature 
 [tarts, while movements of the younger regions are generally 
 due to growth. The force exerted by the motor organs is 
 dependent upon the altered turgor of the cells of which the 
 organ is composed. If the cells upon one side lose their tur- 
 gidity, those upon the other, being unresisted, will extend 
 and bend the organ toward the side upon which the turgor 
 was diminished. It will be convenient, therefore, to dis- 
 tinguish movements due to growth and movements due to 
 variation in turgor. 
 
 282. (A) Movements of growth. — These depend upon 
 some inequality in the rate of growth of the organ concerned. 
 They are of two sorts: (1) those in which variation ingrowth 
 
THE MOVEMENTS OF PL, IX VS. I93 
 
 is produced by internal causes, called spontaneous move- 
 ments, and (2) those in which the variation in growth results 
 from stimulation by external agents, called paratonic move- 
 ments. 
 
 283. 1. Spontaneous movements. — Among spontaneous 
 movements are those in which the variation in growth occurs 
 upon different sides of a cylindrical organ, or the two faces of 
 a bilateral one. The opening of all flower and leaf buds illus- 
 trates this movement, which is called nutation. During the 
 development of the interior parts, the outer leaves (often 
 scale-like) which protect them grow more rapidly upon their 
 outer (dorsal) surfaces. They are thus pressed together into 
 a compact bud. When the internal parts are suitably de- 
 veloped a change occurs in the rate of growth of the outer 
 leaves ; their inner (ventral) faces now grow more rapidly 
 and the bud expands. Similar spontaneous variation in the 
 growth of different sides of tendrils produces a nodding or 
 waving motion, or even a rotation of the tip, by means of 
 which they are often enabled to reach a support. In most 
 tendrils the acceleration of growth travels irregularly around 
 the axis, so that their tips rotate in a roughly circular or 
 elliptical orbit from the time the tendril is two-thirds grown 
 until growth ceases. The further changes in the tendril, by 
 which it wraps the tip about the support and coils the re- 
 mainder into a double spiral, are paratonic movements in- 
 duced by contact. The rotating movements by which twin- 
 ing plants climb are also paratonic and not spontaneous. 
 
 284. 2. Paratonic movements are also of the highest im- 
 portance for the well-being of the plants concerned. By means 
 of them the different organs are developed in such situations 
 that they can properly perform their work. The stimuli 
 which influence the rate of growth are chiefly light, gravity, 
 heat, mechanical contact, and moisture. The peculiar states 
 in which a plant or an organ exists when it can respond to 
 
'94 
 
 PLANT LIFE. 
 
 the different stimuli have received different names, and those 
 names indicate the nature of the stimulus. A plant or an 
 organ is heliotropic when it reacts to the direction of the 
 rays of light falling upon it ; geo/ropic, when it reacts to the 
 force of gravity ; thermotropic, when it reacts to the presence 
 of a warm body ; hydrotropic, when it reacts to the presence 
 of a moist surface, etc. In each case the plants are said to 
 react positively when the movement is toward the source of 
 the stimulus ; negatively, when the movement is away from 
 the stimulus ; transversely, when it is transverse to the direc- 
 tion of the stimulus. These reactions are to a certain extent 
 
 ODD 
 
 Fig. 190. — Diagrams representing the transverse heliotropism of leaves of the garden 
 nasturtium (Tropaolum). Potted plants were subjected successively to light strik- 
 ing them in the direction shown by arrows. The petioles curved so .is to place the 
 blades at right angles to the incident light. — After VSchting. 
 
 related to one another, and it will be convenient, therefore, to 
 consider the effect of each stimulus upon the two common 
 forms of plant organs — namely, the radial (such as stems and 
 roots) and the dorsiventral (such as leaves). Organs are 
 sometimes physiologically dorsiventral, even though they 
 possess a radial structure ; for example, some steins behave as 
 dorsiventral organs, although they are perfectly radial in 
 structure. 
 
 285. (a) Heliotropism. — Heliotropism is the state of a plant 
 or organ when it is irritable to the direction of light rays. 
 
THE MOVEMENTS OF PLANTS. 
 
 195 
 
 Light thus plays an important part in determining the position 
 
 of organs. As a rule radial organs are either positively heli- 
 otropic, as the stems and leaf-stalks, or negatively heliotropic, 
 as the roots. Dorsiventral organs, such as leaves, are all 
 transversely heliotropic, assuming a position at right angles 
 to the incident rays, which is the most favorable position 
 possible for the manufacture of food by the green parts (fig. 
 190). Intense light, however, may bring about a different 
 reaction, so that the leaves set themselves edgewise to the 
 
 Fir,. 191. — Leaf mosaic formed by a horizontal shoot of Norway maple. The lengthen- 
 ing of the petioles of individual leaves to avoid shading of the blade is marked. 
 About one-third natural size. — After Kerner. 
 
 direction of the rays. A fixed light position is usually 
 reached by leaves by the time they become mature, and this 
 is generally at right angles to the source of greatest light 
 branches of trees show the leaves so arranged as to size and 
 position that they shade each other as little as possible, form- 
 ing the so-called leaf mosaics (figs. 191 to 193). The leaves 
 of window plants also exhibit these movements very strikingly, 
 
196 
 
 PLANT LIFE. 
 
 because usually illuminated from one side. Plants kept in 
 darkness have their leaves irregularly placed. 
 
 286. (3) Combined movements due to variations in the 
 
 Fig. hi2. — A shoot of thorn-apple or " jimson " weed, showing imperfect leaf mosaics 
 
 of tall plants formed upon the same plan as in rosettes (fig. 193). One-seventh natural 
 size. — After kerner. 
 
 amount of light or heat or both are especially exhibited by flow- 
 ers, whose opening and closing are frequently determined 
 
 mw'^M 
 
 V 
 
 Fin. 193. — A rosette of leaves ol .1 bellflower (Campanula pusilla), showing lun^tli- 
 
 ening of petioles of lower leaves so as to tarry blades from under upper leaves — 
 After Kerner. 
 
 thereby. With some plants the predominant stimulus is heat; 
 with others, light. Closed flowers of the tulip or crocus may 
 be made to open in 2 to 4 minutes by raising the temperature 
 
THE MOVEMENTS OF TLA NTS. 1 97 
 
 15 to 20 . The flowers of the white water-lily (Nymphaea) 
 and of the dandelion open in sunlight and (lose in shade. 
 By marking upon their leaves a series of equidistant parallel 
 lines with Chinese ink, and subsequently measuring the dis- 
 tances to which they have been spread, all such movements 
 can be clearly shown to be due to accelerated growth of the 
 outer or inner surfaces, respectively. The protection of the 
 flower parts or the proper discharge of the functions is secured 
 by these movements, which must not be confounded with 
 those due to the direction of light or heat rays. 
 
 '287. (c) Geotropism. — Geotropism is the state of a plant 
 or an organ when it is irritable to the action of gravity. 
 Since gravity is exerted always in the same direction, it is 
 plain that reactions to this force cannot be studied, as in the 
 case of light, by altering the absolute direction in which 
 gravity acts, but only by so changing the position of the 
 plant that the force acts in a relatively different direction. 
 The reaction to this stimulus and the fixed gravity position 
 must not be confused with the simple effect produced by the 
 weight of the parts concerned. Such effects are to be seen 
 in the downward bending of some plants with slender 
 branches, or the curvature of the flower or fruit stalks by the 
 weight of the parts. True geotropic curvatures are brought 
 about by acceleration of the growth of the irritable cells, 
 and the curvatures produced may even be contrary to the 
 direction of the force. If seedlings be grown in boxes upon 
 the rim of a wheel rotating slowly in a vertical plane, so that 
 they are successively subjected to the action of gravity in 
 relatively different directions, it will be seen that while their 
 members grow in nearly straight lines, the direction assumed 
 by the stems and roots is quite as frequently abnormal as 
 normal, because the effect of gravity which normally deter- 
 mines the direction of growth of these axes is neutralized, 
 since it now acts upon them from a new direction at each 
 
190 PLANT LIFE. 
 
 successive moment (fig. 194). If the wheel upon which 
 such seedlings are grown be rotated at a high speed, the cen- 
 
 Fig. 194. — Seedling mustard plants grown on a cube of peat, T, attached to the slowly 
 rotating axle, A, ./. of a <linnst.it. The direction of growth of roots and steins is 
 controlled 
 eliminated. 
 
 :arness of moist surfaces, the action of gravity and light being 
 ariable direction of roots and stems. At m and /'/.j aerial 
 
 hyphaj of a mold have taken direction as far from the repellant moist surfaces as pos- 
 sible. One half natural size. — After Sachs. 
 
 trifugal force will become a constant one, and, acting in 
 place of the neutralized force of gravitation, will determine 
 the direction which the stems and roots will assume. Since 
 the primary stems of most plants are negatively geotropic, 
 when grown under such conditions they will turn toward the 
 center of the wheel, while the positively geotropic roots grow 
 toward the rim. Similarly, if the wheel be rotated rapidly 
 in a horizontal plane the stem will be controlled by a com- 
 bination of the force of gravity and the centrifugal force (the 
 latter predominating if the speed is great), and will grow in- 
 ward and upward, while the roots will grow downward and 
 outward (fig. 195). 
 
 288. Transverse geotropism. — Not all stems, however, 
 are negatively geotropic, nor all roots positively geotropic. 
 
THE MOVEMENTS OF PLANTS. 
 
 I99 
 
 The central axis of both root and stem in the majority of 
 plants is so, but lateral branches of both place themselves at 
 an angle to the action of gravity, sometimes at a right angle, 
 at other times at a highly obtuse or acute angle. That is, 
 they are more or less perfectly transversely geotropic. What- 
 
 Fig. 195. — Part of centrifuge, a, the axle, rotated at a high speed by water or electric 
 motor, to which is attached the circular metal plate, r, r, carrying a disk of cork, A-. 
 To the latter are attached two seedling beans, .(, B, by means of pins; rf, the primary 
 stem; k, the primary root. Over the seedlings the cover, g, is placed to keep them 
 moist. After a few hours the lateral roots have turned into the direction of the cen- 
 trifugal force, which was sufficiently powerful to overcome that of gravity except near 
 axis of rotation, .r. One half natural size. — After Sachs. 
 
 ever the normal position of any organ, it will be regained by 
 the growing parts as rapidly as possible when the plant is 
 forcibly displaced. This can only be brought about by the 
 curvatures produced by unequal growth of the younger parts. 
 
 If a potted plant be laid upon its side for a short time and 
 then erected before any response to the stimulus occurs its 
 growing parts still curve to one side, although not so far as if 
 they had been allowed to remain in the horizontal position. 
 
 289. Grasses. — In only a few cases do the maturer parts 
 of plants regain their power of growth under the stimulus of 
 gravity. The basal portion of the intcrnodes of grasses, 
 however, remain for a long time capable of growth ; hence, 
 
200 
 
 PI.AXT LIFE. 
 
 when grasses are Mown down or trampled their stems erect 
 themselves by the geotropism of this basal growing zone 
 (fig. 196). 
 
 Vu.. 196. — Part of a wheat-stalk, showing strong geotropic curvature. The shoot was 
 placed horizontal, and the growth of the basal part of the internode with the leaf-sheath 
 connected with it was stimulated on the under side, the upper remaining short. No 
 curvature occurs in the older part of the internode. About two thirds natural size. 
 —After Pfeffe:-. 
 
 Fig 
 
 io. 107.— Root-cage, < in the lower edge of a sheet ol zim .1 little larger than the panes 
 of glass selected is formed a water-tight trough oi the same material. Two panes of 
 glass of suitable size are clamped together, with a piece of wood i cm. thick on three 
 edges to keep them separate. Seeds are sown in fine soil evenly packed between the 
 panes: these are set with the lower edge in the water-trough and a sheet of zinc is 
 used to keep out light. The cage should be slightly inclined, as shown, so as to keep 
 roots against the glass 1 rom 1 drawing by J. C. Arthur. 
 
THE MOVEMENTS OF PLANTS. 
 
 20 1 
 
 290. Root-cage. — Experiments upon the response of root- 
 lets to the stimulus of gravity upon altering their position 
 may be carried on by means of a root-cage, shown in figure 
 197. It consists essentially of two panes of glass placed close 
 together, between which, in finely sifted soil, the rootlets are 
 grown. By inclining this root- 
 cage at various angles it may be 
 shown that not only the primary 
 root, but its branches, strive to 
 regain their normal angle with 
 the direction of gravity. This 
 is illustrated in figure 198, in 
 which the dark portion of the 
 rootlets represents the growing 
 parts while the cage was in- 
 verted. They then took about 
 the same angle with the horizon 
 as when in normal position. 
 
 Many dorsiventral organs, 
 
 system of a broad 
 own in a root-cage, first in the 
 
 in the normal position. The arrow 
 
 aga 
 
 sshc 
 
 Slich as leaves, are transversely the direction in which gravity acted 
 
 the different positions. The black por- 
 
 geOtropiC, JUSt as leaves are tion of the roots were the parts growing 
 
 . during inversion. Two thirds natural 
 
 transversely hebotropic size.— After Sachs. 
 
 291. Twining plants. — The movements of twining plants 
 are due to a peculiar reaction to gravity. As the upper inter- 
 nodes of a seedling elongate they soon become too weak to 
 support themselves and bend over, becoming nearly horizon- 
 tal. When this occurs the growth of the right or left flank 
 of the stem near the bend is accelerated (whence the stem is 
 said to be laterally geotropic). The horizontal part is thus 
 swung around, twisting the stem and bringing a new Hank 
 under the influence of the stimulus. If in its continued rota- 
 tion the stem comes in contact with a nearly ere< t support 
 the free part continues to rotate, growing longer at the same 
 time, and encircles the support. The part below the point 
 
PLANT LIFE. 
 
 Fig. 199.- 
 
 a bit of the stem of the - 
 
 of contact now becomes negatively geotropic, and its growth 
 on all sides is equally accel- 
 erated. The coils are thereby 
 straightened until the stem 
 clasps the support very closely, 
 from which it is often prevented 
 from slipping by angles or out- 
 growths of various kinds, which 
 roughen the surface (fig. 199). 
 
 While gravity thus plays a 
 large part in determining the 
 
 (-^?H\ 'fffl'''ll^ position of both aerial and sub- 
 
 '^""i Tpfoj^'f terranean organs, it must be 
 
 remembered that it works con- 
 jointly with many other stimuli, 
 hop, .'showing the six angles, each The position of the members 
 
 carrying a row ot emergences, crowned 1 
 
 by a branched rigid hair with very sharp jg therefore, a resultant of the 
 
 points. Magnified 3 diam. />, three 
 
 emergences more highly magnified.- reactions to the various external 
 
 After Kemer. 
 
 forces which stimulate it. 
 292. ((/) Hydrotropism. — Hydrotropism is the state of a 
 plant or an organ when it is irritable to moisture. Hydro- 
 tropic organs may bend toward or away from a moist surface. 
 Roots are particularly sensitive to the presence of moisture. 
 If a cylinder of wire gauze be filled with damp sawdust and a 
 number of seeds planted near its surfa< e they germinate and 
 the roots start to grow in the normal direction — i. e., directly 
 downward. If now the cylinder be suspended at an angle, 
 as shown in figure 200, the roots which pass into the air, 
 stimulated by the moisture, curve toward the damp sawdust. 
 Upon entering it the stimulus ceases, and they start again to 
 grow downward, being positively geotropic. Again the 
 Stimulus of the moist surface overcomes that of gravity, and 
 they turn back to it, often threading themselves in and out 
 
THE MOVEMENTS OF PLANTS. 203 
 
 of the wire gauze. Since only one-sided action of a stimulus 
 determines direction of movement, if the air be saturated 
 they continue to react to the stimulus of gravity alone. 
 
 293. (t) Movements due to contact. — Contact, either 
 gentle or forcible, and friction act as stimuli to modify the 
 growth of many plant parts. Only rarely is the main axis of a 
 plant sensitive to mechanical stimuli, except, perhaps, to long 
 J 
 
 Fir,. 200. — Apparatus for demonstrating hydrotropism. <i. a, a zinc disk, with hooks 
 to which is attached a cylinder or trough of wire netting filled with damp sawdust. In 
 this are planted peas, g; whose routs, li, i. k, m, first descend into the air but soon turn 
 toward the damp sawdust again, m lias threaded itself in and out of the netting. — 
 After Sachs. 
 
 continued contact (or pressure) in the case of some twining 
 plants. But in many plants lateral axes in the form of ten- 
 drils (*^\ 115, 158) and leaf-stalks (^j 157) are irritable to 
 contact, even to a degree far surpassing that of our nerves of 
 touch. 
 
 If the tip of a tendril (•[ 266), while still capable of growth, 
 come in contact with a solid body, it will quickly become 
 concave on the side touched, and thus will wrap about the 
 object, if it be of suitable size. This curvature is due first to 
 the shortening of the cells upon the concave side and later 
 to unequal growth on opposite sides. Finally this effect 
 
204 PLANT LIFE. 
 
 extends to all parts of the tendril, which begins to curve. 
 As both ends are fast, it is a mechanical necessity that the 
 curves become spiral coils, both right- and left-handed, ac- 
 companied by a twisting of the tendril on its axis ( fig. 107). 
 After the coils are formed the tissues of the tendril become 
 thick-walled and rigid, so that the plant is attached to the 
 support by a series of spiral springs. 
 
 Other tendrils do not nutate, but are negatively heliotropic, 
 and by contact their tips are stimulated to develop disks 
 which apply themselves closely to the support, and send into 
 its irregularities short outgrowths from the surface cells. 
 Such plants are adapted to support themselves by walls, tree- 
 trunks, etc. The Japanese ivy and one form of the Virginia 
 creeper are notable examples. 
 
 The coiling of the leaf-stalks is not unlike the first curva- 
 tures described for tendrils (fig. 154). 
 
 294. (B) Movements of turgor.— The movements just 
 described are confined to members which are growing either 
 throughout or in some part. As turgor can affect only tis- 
 sues whose cell-walls are elastic (*j 188), the movements 
 produced directly by variation in turgor can occur in such 
 mature members only as are provided with special motor 
 organs. In almost all cases these are leaves. Stimuli which 
 regulate growth (^[ 284) may also affect motor organs, pro- 
 ducing like curvatures. But elongation of any part of a motor 
 organ by increased turgor is reversible, not permanent, (cf. 
 
 II 254)- 
 
 295. Motor organs. — The motor organ in leaves is usually 
 the leaf base (^[ 151) or a modified portion of the petiole, 
 sometimes greater but generally less in diameter than the 
 rest. Its cortex consists of large, rather thick-walled, pa- 
 renchyma cells, and the stele occupies a relatively small part 
 of the transverse section. In other parts of the petiole the 
 stele is much larger, or there may be several steles distributed 
 
THE MOVEMENTS OE PLANTS. 
 
 205 
 
 about the center. (See ^[ 164. ) 
 show the contrast. If the leaf 
 be a compound one, there are 
 usually secondary motor or- 
 gans at the base of the leaf- 
 lets, as in the leaf of the bean 
 (fig. 202). Variation in the 
 turgor of the cells of the cor- 
 tex upon one side or the other 
 produces a sharp curvature of 
 
 In figure 
 
 I and B 
 
 Fig. 201. Fig. 202. 
 
 Fig. 201. — Transverse sections through petiole of scarlet runner, ./.through the rigid 
 portion; B, through the motor organ. G, g, vascular bundles; .. cortex; w, pith; 
 r, deep channel along ventral siiU- oi petiole. Magnified about 10 diam.— After Sat hs. 
 
 Fig. 202. — Portion ol .1 scarlet runner, which, originally growing erect, has been inverted 
 for several hours, resulting in geotropic curvatures ol the primary motoi organs /', /"', 
 l n . The lowest pair oi leaves show secondary motor organs at the juncture of petiole 
 and blade. Similar ones are present in the upper compound leaves, but are not . lcarly 
 shown in the figure. The arrows show the position oi the petioles when the plant was 
 first inverted. About two thirds natural size —After Sachs. 
 
 the motor organ, which alters the position of the leaf or leaflet 
 (fig. 202). The concave surface of the motor organ is always 
 deeply wrinkled transversely, while the convex surface is 
 smooth. 
 
206 PLANT LIFE. 
 
 296. Spontaneous movements. — Only a few plants exhibit 
 spontaneous movements through the motor organs. The lat- 
 eral leaflets of the telegraph plant (s, fig. 203), under normal 
 
 conditions of rather high temperature (at 
 least 22 C), show jerky movements of 
 such direction that their tips describe an 
 irregular ellipse, which is completed in 
 1 to 3 minutes. The leaflets of the 
 clovers and oxalis show much slower 
 movements (of a few hours period), 
 which are usually obscured by the light 
 movements described in the next para- 
 
 Fig. 203. — Leaf of Hesmo- ____t, 
 diu.l gyrans. Two graph. 
 
 Sa , c r hs natural slze ~ After More commonly the turgor movements 
 are induced. The most common stimuli are light and con- 
 tact, although many others suffice to induce them. 
 
 297. Photeolic movements. — Movements produced by the 
 withdrawal of light have long been known as "sleep move- 
 ments ;" more properly, photeolic movements — that is, move- 
 ments induced by variation of light. They are best observed 
 upon the leaves of the bean family, though many other plants 
 exhibit them. Figure 204 shows the positions assumed by 
 various leaves toward nightfall. It will be seen that in 
 compound leaves the leaflets sometimes rise, so as to apply 
 their outer faces to each other ; others sink, so that the un- 
 der surfaces are in contact ; others become folded in various 
 ways. This position is maintained throughout the night. 
 Upon the increase of light in the morning, the day position 
 is assumed. The cutting off of light artificially from any of 
 these plants causes them within a short time to assume the 
 nocturnal position. Darwin suggested that the nocturnal 
 position prevents the loss of heat by radiation and consequent 
 injury from light frosts. But it is not by any means certain 
 that this is its real purpose. 
 
THE MOVEMENTS OF PLANTS. 
 
 207 
 
 298. Contact movements. — Some organs arc sensitive to 
 contact, as the leaves of Venus' fly-trap and other related 
 plants. The motor organ in the Venus' fly-trap (figs. 386, 
 205) is the cushion of tissue running along the dorsal side of 
 the leaf between the two lobes. By the sudden variation in 
 
 Fig. 204. — Photeolic movements, a, leaf of a mimosa in day position ; a', the same in 
 night position. />, leaf of Coronilla varia in day position ; />', the same in nighl po- 
 sition, r, leaf of A mor&ka fruticosa in day position ; <■'. the same in night position. 
 </, leaf of Tetragonolobus in day position ; </', same in night position, — Alter Kemer. 
 
 turgor of some of these cells the two halves of the leaf are 
 thrown quickly together when one of the six bristles upon its 
 upper surface is touched. The sensitise plant drops one of 
 its leaflets or the whole leaf quickly when stimulated by con- 
 tact, heat, or electricity. The position of the leaves when 
 
208 
 
 PLANT LIFE. 
 
 normally expanded is shown in figure 206, and their position 
 after stimulation by figure 207. The stamens (^[ 344) of 
 some flowers and the stigmas (^j 336) of others are sensitive 
 
 Fig. 206. Fir,. 207. 
 
 Fig. 205. — Part of a transverse section of a leaf of Venus' fly-trap, in, the cushion of 
 tissm- constituting the motor organ ; />, one of the sensitive bristles which, upon being 
 touched, cause the leaf to close ; /, one of the interlocking teeth. The minute pro- 
 jections over inner (ventral) surface are glands which secrete the digestive fluid and 
 later absorb the food. Magnified about 5 diam. — After Kurz. 
 
 Fig. 206. — A leaf of the sensitive plant fully expanded. Natural size. — After Duchartre. 
 
 In.. 207. — A leaf of the sensitive plant after stimulation. The motor organ at the base 
 of each leaflet has thrown it forward and upward ; the motor organs at the base of the 
 four divisions have moved them together. The motor organ at the base of the main 
 petiole has moved the whole leaf sharply downward. Natural size. — After Duchartre. 
 
 to a touch, shortening, elongating, or bending in such a way 
 as to promote pollination (*| 358). 
 
 The motor organs of the leaves of a number of the bean 
 and oxalis families also react to more violent mechanical 
 stimuli. Their movements are similar to those described in 
 U 2 97- 
 
PART III: REPRODUCTION. 
 
 CHAPTER XVI. 
 
 INTRODUCTION. 
 
 Having considered in Parts I and II the structures and 
 functions by which the nutrition of the individual is secured, 
 Part III is devoted to the consideration of the structure and 
 functions of the reproductive organs and the functions by 
 which a succession of similar individuals is insured. 
 
 One of the fundamental powers of protoplasm is its ability 
 to produce new organisms as offspring from the older ones. 
 In the simpler plants the two great functions, nutrition and 
 reproduction, are often carried on by the same cell. This 
 must always be so in the unicellular plants. In the higher 
 plants, however, these two functions become completely sep- 
 arated, organs being specialized for each, so that the func- 
 tions may be more certainly and efficiently performed. 
 
 299. Reproductive structures. — Any part capable of grow- 
 ing into a new individual may be called a reproductive body, and 
 the part on which or in which it is produ* ed is a reproductive 
 organ. If the reproductive bodies consist of one or two cells 
 only, they are usually called spores, [f they are cell-aggre- 
 gates, they are generally called brood buds or gemmce i to dis- 
 tinguish them from ordinary buds. In both cases it is neces- 
 sary that the cells to be separated from the parent should be 
 capable of growth — that is, in the condition known as the 
 embryonic phase (•[ 256). The reproductive organs pro- 
 
 209 
 
2IO PLANT LIFE. 
 
 duced by some plants are exceedingly complex and varied, 
 while others form reproductive 1 todies in very direct ways. 
 The reproductive bodies themselves are generally very simple. 
 In addition to complex reproductive organs, there are some- 
 times accessory parts by which the plant adapts its reproduc- 
 tive functions to the conditions under which it lives. Among 
 these accessory structures are many, as among the flowers of 
 seed plants, by which the aid of other plants or animals is 
 secured. 
 
 300. Vegetative and sexual reproduction. — In all the 
 diversity of organs and processes two chief methods may be 
 distinguished, called vegetative reproduction and sexual repro- 
 duction . 
 
 Vegetative reproduction consists in the formation of repro- 
 ductive bodies by processes of growth only. The modes in 
 which they arise are varied in detail, but consist essentially 
 in the production by the parent of a body, unicellular or 
 multicellular, which at maturity develops, under suitable 
 conditions, into a new plant. 
 
 Sexual reproduction consists in the formation of reproduc- 
 tive bodies by the union of two specialized cells, neither of 
 which alone is capable of developing into a new plant. 
 
CHAPTER XVII. 
 VEGETATIVE REPRODUCTION. 
 
 I. Fission and budding. 
 
 301. Fission. — In single-celled plants cell division and 
 reproduction are practically identical, since shortly after divi- 
 sion occurs the two cells so produced separate and lead an 
 independent existence (C, fig. 18). Such a method of repro- 
 duction evidently interferes little with the processes of nutri- 
 tion, which probably are scarcely even suspended during the 
 process of reproduction. 
 
 302. Budding. — A slight variation of the method of fission 
 just described is to be found in those single-celled plants, 
 such as the yeasts, whose growth is so localized as to form 
 upon one side a small enlargement which ultimately attains 
 the size of the parent, with which it is connected by a very 
 narrow neck (fig. 48). Across this neck the partition wall is 
 formed in the usual way. This becomes mucilaginous, ren- 
 dering the adhesion of the daughter cell at this point so weak 
 that it is easily separated from the parent. This method of 
 reproduction is known as budding. 
 
 303. Fragmentation. — In those plants which consist of 
 a row of cells more or less closely united, the breaking up of 
 the filaments into separate pieces, either through externa] 
 force or the death of one of the cells, may produce a number 
 of smaller colonies or of new individuals, each of which may 
 grow to full size. In some of the more looselv organized 
 filament-colonies, such as Nostoc (see • 13, and figs. 1 }, 
 14), there are specialized cells whose function seems to be 
 
 21 1 
 
212 PLANT LIFE. 
 
 to loosen pieces of definite length, which creep out of the 
 jelly, grow, and thus produce new colonies. 
 
 The greater size reached by most multicellular plants soon 
 renders impossible the continuance of this method of repro- 
 duction, except among those whose cells arc all alike. Should 
 such separation into nearly equal parts occur among more 
 highly specialized plants, it is evident that one portion might 
 easily be left without nutritive organs adapted to its needs. 
 The higher plants, therefore, specialize certain regions or 
 members, where, by division or budding or similar processes, 
 reproductive bodies may be formed. 
 
 II. Spores. 
 
 304. Sexual and non-sexual spores. — A spore is a single- 
 celled body capable of producing a new plant. Spores may 
 be formed either by a process of growth or by a sexual act — 
 i.e., the union of two cells. The former are called non- 
 sexual spores ; the latter, sexual spores. Only non-sexual 
 spores are discussed in this chapter. 
 
 305. Structure. — While a spore is generally composed of 
 one cell, the term is extended to include two- to many-celled 
 bodies which are formed in the same way as the simpler 
 ones. In fact, no clear distinction in form or structure can 
 be drawn between spores and brood-buds. (See 1" 361.) 
 
 306. Motile spores. — Spores may be either naked and 
 motile or furnished with a cell-membrane and non-motile. 
 The former are commonly produced by plants which pass all 
 or part of their lives in water, such as the algre and aquatic 
 fungi. They are usually pear-shaped and furnished with one 
 or more cilia, by means of which they swim about (fig. 168). 
 When locomotion was supposed to be a distinctive power of 
 animal bodies they were called zoospores, a name still re- 
 tained. They are also called swarm-spores. 
 
VEGE TA Tl I E REPROD UCTION. 
 
 213 
 
 When zoospores possess chlorop 
 quently do, they are aggregated at 
 the larger end, leaving the pointed 
 end to which the cilia are attached 
 colorless. Zoospores are formed 
 either in a general body-cell, not 
 visibly different from the other 
 body-cells, or in a cell specialized 
 in form and structure. In either 
 case the cell in which they are pro- 
 duced is called a zoosporangium. 
 The entire contents of the zoospo- 
 rangium may form a single zoospore, 
 or it may divide into several or 
 many. In the latter case the nu- 
 cleus divides into two or more, each 
 of which gathers about itself a por- 
 tion of the protoplasm. The zoo- 
 spores are set free by the rupture of 
 the wall of the sporangium or by 
 the solution of a portion of the wall 
 (fig. 208). They may begin to 
 move before the rupture of the wall, 
 in accomplishing which their activ- 
 ity may materially assist. They 
 then work their way out and swim 
 freely in the water. After a time 
 of movement they usually lose their 
 cilia, either withdrawing them into 
 the protoplasm or dropping them 
 off, come to rest, and begin to grow 
 into a new plant. 
 
 307. Non -motile spores are 
 formed by all classes of Land plants 
 
 l'n. 208 -Development and escape 
 
 of zoospores of an aquatic fungus 
 {Saprolegnia lactea). The ends 
 
 ot two hvph.e are shown, the ter 
 
 minal cells being goosporangia 
 
 In ,;. the protoplasm 1 
 
 ing about the numerous nui lei (no 
 
 shown). From 6 many ol tin- ZO 
 ospores have escaped through the 
 perforation in the wall near the 
 
 upper end of tin- .ell. From ."11 
 
 have est aped hut one. whk h is just 
 
 slipping through the opening ( here 
 
 in profile). Magnified 300 diam. — 
 
 Aftei kerner. 
 
 without exception. They 
 
^■4 PLANT LIFE. 
 
 are often produced in great profusion, especially by the fungi, 
 the mosses, the ferns, and the seed plants. 
 
 308. Form and structure. — Their form is exceedingly 
 various. Many are spherical or ovoid, while some are cylin- 
 drical or even needle-shaped (figs. 213, 228, 271). Irregular 
 forms, also, are not uncommon. 
 
 In structure spores are usually only single cells, specialized. 
 Each is a nucleated mass of protoplasm surrounded by 
 a cell-wall which may be either thin or thick, according 
 as the spore is destined to immediate growth, or, as a 
 resting spore, to endure for a time unfavorable conditions. 
 In some cases the wall of even the 
 ' ') JL[\ A -'Jf/fr thin-walled spores has two layers, a 
 condition which is almost universal 
 among resting spores. When the 
 wall is so differentiated the inner 
 layer is delicate, rarely thickened, 
 extensible, and composed of more or 
 less unaltered cellulose. The outer 
 layer is often irregularly thickened, 
 so that its surface is covered with 
 
 Fig. 2 oo.-Section of a mature ria ^es, WartS, Spines, Or boSSCS of 
 
 rt"el^of^fdf(co& various sorts (figs. 210, 248, 271, 
 u;r!-rVu; e t tcZ,.^'u 1 e'399)- " is brittle, as compared 
 S^pma^tT^ndiwith the inner coat, and is usually 
 ^ V ed a To«t ati so St diaS re -fe-more or less altered in composition 
 from its original cellulose nature. 
 A third layer (the epispore) is sometimes present, but this 
 is not produced by the cell which it surrounds. It is added 
 from the outside, being derived from the protoplasm sur- 
 rounding the spores after they are formed* (fig. 209). This 
 form of spore is common among the fern allies. 
 
 * This protoplasm often comes from the disorganization of some of the 
 tells around the chamber in which the spores lie. 
 
VEGETATIVE REPRODUCTION. 
 
 215 
 
 309. Food. — In almost all cases there is a supply of reserve 
 food within the spore. This reserve food varies in amount 
 with the conditions under which the spores are formed. It 
 is ordinarily greater in resting spores than in those intended 
 for immediate growth. Spores may contain chlorophyll, but 
 generally do not ; even the spores of green plants are mostly 
 without it. Its presence seems to indicate an active condition 
 of the protoplasm, and the vitality of such spores is usually 
 of short duration. It is of course absent from the spores of 
 colorless plants, such as the fungi. 
 
 Fig. 210. — Part of a vertical section of a leaf of a willow, attacked by a fungus (.!/<•/<!»//- 
 sora salicimi). eo, epidermis of upper side lifted by the young teleuto spores; /, de- 
 veloping from the spore-bed above the ends of the palisade parenchyma, />nr ; en, 
 epidermis of the under side, broken through spore-bed from which spring uredo- 
 spores, st. and paraphyses, /•. eo will also finally be ruptured to set free /. Magni- 
 fied 260 diam. — After Prantl. 
 
 310. Growth. — Spores germinate by absorbing water, thus' 
 bursting the more rigid layer or layers of the cell-wall. The 
 inner layer then grows in area to accommodate the increas- 
 ing protoplasm, which so controls the regions of growth and 
 the mode of cell division as to produce a plant of definite 
 
216 
 
 PLANT LIFE. 
 
 form. In many cases the plant produced is essentially like 
 that which gave rise to the spore. In others it is different, 
 but sooner or later in the life cycle the same form recurs. 
 Variety of bodily form is common among the fungi, in which 
 it is called pleomorphism. Among plants showing well-de- 
 fined alternation of generations ( r€ ; 55, 320), the non- 
 sexual spores are produced by one form only, and always 
 give rise to the other. 
 
 311. Origin. — Non-motile spores are either free, being 
 produced at the ends of branches specialized for that purpose, 
 or enclosed in a case called a sporangium. Often the same 
 plant forms spores by both methods at different stages in its 
 development. 
 
 Fig. 211. — Diagrams showing the formation of an acropetal sin.iicli.iiii by budding. 
 a, the spore-producing hypha : b, its terminal c < • 1 1 showing a bud which in c has ma- 
 
 tured into .1 spore ; (t, the spore < has budded, anil so on, until in h five spores have 
 been formed, numbered in order of their development.- Alter Zopf. 
 
 312. Free spores. — The formation of free spores is con 
 fined to the lower plants, and is especially characteristic of 
 the non-aquatic fungi. The branches producing spores may 
 occur singly, or, more commonly, they are aggregated at 
 certain points, forming a spore-bed (fig. 210). If the fungus 
 develops its mycelium in the interior of a host, the formation 
 of a spore-bed is often necessary to rupture the host, so that 
 
V EG ETA TIVE REP ROD UCTION. 
 
 217 
 
 the spores may be brought to the surface and set free. Thus 
 the spore-beds of parasitic fungi commonly blister the surface 
 of the host by lifting up its outer tissues (eo, fig. 210). 
 
 313. Spore-chains. — Spores maybe produced either singly 
 at the ends of the branches or in chains. When produced in 
 chains, the youngest spore may be at the base or at the apex 
 of the chain. The first method is much more common than 
 the second. In the second case each spore must arise as a 
 bud upon an older spore, budding itself to form a younger one 
 (fig. 211). The spores in such a chain are limited in number. 
 They develop rapidly, and all are loosened at about the same 
 time. Those chains which have the oldest spore at the apex 
 
 Fig. 212.— An outline showing the formation oi a basipetal spore-chain of the blue-green 
 mold i Penicillium glaucum), 6, branch oi spou- hearing hvpha. budding beneath 
 two older spores. Across the narrow net k a partition wall is formed, the spores round 
 off, and from this wall a device, .. for loosening the spores is developed. The 
 terminal spore is oldest. Highly magnified.- Alter Frank. 
 
 Fig. 213.— Longitudinal section through the edge oi a gill of a mushroom (Cofrinus) 
 after spore-formation is completed. /, interwoven hyphae ol the gill, branching to 
 form the hymenium, composed ol the paraphyses, /, the cystidia. < . anil the ba- 
 sidia, /'. The latter give rise to tour slender I nam lies, ulmsc tips enl.uge 1" lorm each 
 
 a single spore, /and. do not produce spores. Magnified 300 diam.- Alter Brefeld. 
 
 arc produced by the continued division of the branch by 
 
 transverse partitions, usually preceded by budding of the 
 apex, often described as constriction (/>, fig. 212). Beneath 
 
2l8 
 
 PLANT LIFE. 
 
 the first spore so formed another spore is produced as the first 
 grows older ; and this process continues as long as the 
 plant is able to furnish material for the making of spores. 
 In such cases, often the oldest spores are liberated while 
 new ones are being produced at the base of the chain. 
 
 A modification of the production of spores singly occurs 
 when the branch destined to produce them gives rise to 
 two to eight very slender branches, each of which enlarges 
 at the tip into a single spore, so that the main branch appears 
 to carry two to eight spores upon slender stalks. Such a 
 spore-producing branch is called a basidium (fig. 213). It is 
 the characteristic form in the higher fungi, which produce 
 conspicuous fructifications. 
 
 Fig, 214. — A, a puffball (Octaviana) halved, showing the internal chambers (shaded 
 
 dark) lined by hymenium (the narrow white border). The intervening spaces, g, 
 and the unshaded outer part are formed of interwoven hvph.i . Magnified 5 diuin. 
 />', a bird's-nest fungus (Crucibulum) halved. The similar internal chambers have- 
 been loosened by the disappearance of the intervening hyph.e immediately about the 
 hymenium (represented by radiating lines) and a wavy Stalk by which each remains 
 loosely attached. Magnified 4 diam. — After Luerssen. 
 
 314. Fructifications. — In the higher fungi whose myce- 
 lium is developed within a dead substratum many brant lies 
 are aggregated to constitute a reproductive structure or fructi- 
 fication, which is the only conspicuous part of the fungus. 
 (For an account of the vegetative parts, see ^]^[ 50, 54.) 
 
VEGE TA TI J 'E RETROD UCT10N. 
 
 219 
 
 The body of the fructification is made up of hyphae, more 
 or less interlaced and adherent, and is of a form adapted, not 
 only to break through the substratum, but also to furnish an 
 extensive surface for the spore-beds, called in these plants the 
 hymenium (fig. 213). The hymenium consists of the enlarged 
 
 Fig. 215. 
 Fig. 215. — A fructification of Clavaria 
 a i< > t\i. The hymenium covers the 
 upper part of the branches. Natural 
 size.— After Kerner. FlG. 216. 
 
 Fig. 216. — A fructification of a mushroom, Amanita phalloides. /. the cap or pileus ; 
 ?■, the veil, originally connected with edge of cap, covering the gills which radiate tnun 
 the stipe, st, to the edge of cap; vo, the volva. The surface ot the gills is covered 
 with the hymenium. Most mushrooms showing a distinct volva are poisonous. 
 Natural size. — After Kerner. 
 
 free ends of the hyphae, which are set at right angles to the 
 surface. Some, the basidia, develop 2-S slender branches 
 each of which produces at the tip a single spore. The hyme- 
 nium may be formed upon the outer surface of the fructifica- 
 tion or in internal chambers (fig. 214). In the latter case 
 
220 
 
 PLANT LIFE. 
 
 these chambers rupture at the maturity of the spores, or even 
 earlier. 
 
 The fructification may be irregularly lobed, sessile and 
 gelatinous, or much branched and cylindrical or flattened, 
 
 Fig. 217. — Fructification of Hydnum imbricatum. 
 The surface of the projecting spines on the under 
 side of the cap are covered with the hymenium. 
 Natural size. — After Kemer. 
 
 with the hymenium covering the 
 whole or the upper part of the body, 
 as in Clavaria (fig. 215)5 or it may 
 form an umbrella-like, stalked cap, 
 as In toadstools, with the hymenium 
 extending over radiating plates on 
 the under side of the cap, as in - \gari- 
 cus (fig. 216), or over spine-like pro- 
 jections in the same region, as in 
 Hydnum (fig. 217); or it maybe 
 a semicircular, sessile body projecting 
 from the substratum like a shelf or 
 bracket, with the hymenium lining 
 
 w &i 
 
 Fig. 218.— Trunk of an ash tree, 
 showing fructifications of Poly- 
 porus ig na rius. Alter a pho- 
 tograph by Von Tubeuf. 
 
 innumerable minute 
 
VEGETATIVE REPRODUCTION. 221 
 
 tubes on the under face, as in Polyporus (fig. 218) ; or it may 
 take the form of a ball, the hymenium arising as a lining 
 upon the walls of regular or irregular internal chambers, 
 which may occupy most of the interior, as in puffballs and 
 their kin (figs. 214, 219). 
 
 315. Sporangia. — Spores are also formed in the interior 
 of cells which are either free or covered by a jacket of other 
 
 Ik Hs 
 
 KW 
 
 1^ 
 
 Fig. 2ig. — Fructification of a puffball (Geaster hygrometricus) \ A , young ; />', mature, 
 the outer layer split open and recurved, the inner also broken to allow escape of 
 spores. Natural size. — After Corda. 
 
 cells. The entire structure is called a sporangium. In the 
 first case the sporangium is said to be simple. Its wall is the 
 wall of the mother cell in which the spores are produced, 
 and they are set free by its rupture (fig. 220). In the second 
 case the sporangium is said to be compound. The mother 
 cells of the spores (rarely only one mother cell) are sur- 
 rounded by others forming a jacket of greater or le>s thick- 
 ness. In the mother cells, which are differentiated from the 
 investing cells, the spores are formed as in simple sporangia. 
 As the spores mature the walls of the mother cells burst or 
 are disorganized, leaving the spores still surrounded by the 
 layer or lasers of investing cells (fig. 221). This jacket is 
 ruptured sooner or later and the spores, thus set free, are 
 distributed in various ways. (See % 475.) 
 
222 PLANT LIFE. 
 
 316. Simple sporangia. — The simple sporangium may 
 be like the general body-cells, or it may be specialized in 
 
 Fig. 220. — Longitudinal section of the simple sporangium of a mold (Mttcor). The 
 aerial hypha, //, has partitioned off a cell, .r, within which spores are produced. The 
 walls of this sporangium are studded with needle crystals of calcium oxalate. The par- 
 tition protrudes far into the end cell. Magnified 260 diam. — After Kerner. 
 
 Fig. 221. — Longitudinal section of the stem, s, of a moss gametophyte, bearing leaves, 
 b. Embedded in the stem is the sporophyte, consisting of a stalk, st , and a compound 
 sporangium, of which w is the wall, formed of a sheet of cells, enclosing the spores, 
 sp (contents not shown). Magnified 100 diam. — After Hofmeister. 
 
 form as well as in function. It may be spherical, sac-like, 
 or linear. The elongated sporangium produced by the en- 
 largement of the end of a hypha in certain fungi has received 
 a special name, ascus. The number of spores formed within 
 a simple sporangium may be two or more, up to several 
 hundred. The spores are formed like the zoospores de- 
 scribed in ^[ 306, with the difference that a wall is secreted 
 by each spore be/ore it escapes. 
 
 The rupture of the tell wall, which sets the spores free, 
 is brought about by the increase of the spores in size, or by 
 the swelling of the surplus protoplasm left after their forma- 
 tion. Preparatory to bursting, the wall is frequently altered 
 so as to be mucilaginous, or it becomes brittle. In some 
 cases a certain area is thin, which furnishes a starting-point 
 for the rupture. 
 
V EG ETA TIVE REPRODUCTION. 
 
 223 
 
 317. Arrangement. — Simple sporangia may occur singly 
 or they maybe aggregated. When 
 aggregated, they usually stand side 
 by side, and constitute a layer, 
 called the hymenium (figs. 222, 
 226). (Compare If 314.) When 
 thus aggregated (and even when 
 single) they may be enclosed by 
 a jacket formed by the coalescence 
 of sterile filaments, as in the mil- 
 dews, in which the whole structure 
 constitutes a fructification (figs. 
 223, 224, 337). In the lichens the 
 hymenium, during its earlier stages, 
 is partially enveloped by sterile 
 filaments forming a cup-like apo- 
 thecium (figs. 225, 226). In the 
 cup fungi (fig. 222) the fructifica- 
 tion, which is the only part of the 
 fungus above the substratum, is a 
 single apothecium, whose whole 
 inner face is the hymenium. In 
 an allied form, the morels (fig. 
 227), the fructification is differ- 
 entiated into a stalk carrying an 
 enlarged head marked by narrow 
 ridges separating broad shallow pits 
 over the surface of these depressed areas. In other fungi, 
 the sporangia are sunk in deep, narrow-mouthed pits with 
 which the outer part of the fructification is filled ( fig. 22S). 
 
 The simple sporangia of some of the red seaweeds show a 
 transition to the compound type in being formed by an in- 
 ternal cell of the thallus (fig. 229). The adjacent cells, how- 
 ever, do not constitute a special wall, nor are they neces- 
 
 [G. 222. — A cup fungus {Peziza 
 aurantid). A, three fructifica- 
 tions, about natural size. The 
 inner surface of the cup is covered 
 with a hymenium, a bit ol which 
 is shown' at />' in section at right 
 angles to surface. /•, paraphyses ; 
 ,;. an asms bursting to allow 
 escape of spores. Highly magni- 
 fied—After Keriler. 
 
 The hymenium extends 
 
224 
 
 PLANT LIFE. 
 
 sarily ruptured to permit the escape of the spores, being 
 often displaced in the development of the sporangium, so 
 that at maturity it is partially free. 
 
 Fig. 223. — A mildew (Erysipke communis), showing the mycelium ramifying over a 
 bit of leaf, with erect spore-bearing branches and globular fructifications, containing 
 asci. Magnified about 175 diam.— After Tulasne. 
 
 318. Compound sporangia. — Simple sporangia occur only 
 among the lower plants. In the higher plants, including 
 the mossworts, fernworts, and seed 
 plants, the sporangium is always 
 compound. 
 
 319. Development. — ( Compound 
 
 sporangia may be developed either 
 
 from superficial or from internal 
 
 .. fr ! ,m cells. As a consequence, the mature 
 
 the interior of the fructification ■ 
 
 rxa\&vn<ErysipkeHeraciei\ sporangia will be either free or more 
 
 similar to those shown in fig. 223. ' n 
 
 Each as, us contains four spores. or l ess enclosed within the tissues of 
 
 Magnified 200 diam. — After De- 
 
 Bar y. the organ by which they are borne. 
 
 A superficial cell may enlarge so as to protrude from the 
 
 surface, and divide into two parts, of which the upper cell 
 
 develops into the sporangium proper, and the lower cell into 
 
 its stalk. According to this method of development the 
 
 sporangium is a surface appendage, and may be looked upon 
 
VEGE TA 77 1 E RETROD UCTION. 
 
 225 
 
 as homologous with a hair. Sometimes the sporangia, 
 although really free, are overgrown by adjacent parts, so that 
 
 Kig. 225.— A lichen {Parmelia conspersa) growing on a stone, showing the leaf-like 
 thallus (.mycelium 1 , with many fructifications lapothecia 1 . The older ones are more 
 or less irregular and large with a narrow rim ; the younger are nearer the margin, cir- 
 cular, and nearly closed over at top. Natural size. — After Frank. 
 
 Fig. 226.— A vertical section of an apothet ium ol a li( hen 1 , \ naptychia ciliaris). h, 
 the hymenium; y, the subhymeruum, a layer. .1 densely interwoven hyphae; .-. r, the 
 sterile' hyphae which partially enclose the hymenium ; rn, the loosely woven hyphae <>t 
 the thallus; a, the algae enslaved by the fungus, Magnified about 50 diam.— After 
 
 Sachs. 
 
 they are enclosed in a chamber, whence the spores est apt- 
 after they are set free by the bursting of the sporangium. 
 
226 
 
 PLANT LIFE. 
 
 The other mode of development produces enclosed spo- 
 rangia. One or more internal cells differentiate and become 
 the mother cells of the spores. The spores, when mature, 
 
 Fig. 228. 
 
 Fir.. 227. — A fructification of the morel (Morchella esculentd). The hymenium occu- 
 pies the surface of the depressed areas. Natural size. — After Kerner. 
 
 FlG. 228.— A small bit of a section through the fructification of the ergot (Claviceps 
 purpurea), showingone ol the deep, narrow-mouthed pits, P (and part of another), 
 enclosing the asci. From the broken ascus at the right thread-like spores are escap- 
 ing. Highly magnified. 
 
 -Alter Tulasne. 
 
 will therefore be enclosed by the adjacent cells of the plant, 
 which may became altered so as to form a sort of special wall 
 more or less different from the tissue which lies farther off. 
 
VEGE TA TIVE REPROD UCTION. 
 
 227 
 
 320. The sporophyte. — Among the mossworts, fernworts, 
 and seed plants reproduction by non-sexual spores has be- 
 come so fixed and important that 
 one stage in the plant is devoted 
 especially to producing them. 
 This phase is different from that 
 producing sexual cells, the differ- 
 ence becoming greater the more 
 complex the plant. The stage set 
 apart for spore production is called 
 the sporophyte. In the moss- 
 worts the sporophyte has very 
 little green tissue, and therefore 
 carries on little nutritive work, 
 but depends for its supply of food 
 chiefly upon the sexual stage, with 
 which it is connected throughout 
 its entire existence (^| 68). In 
 the fernworts and seed plants, 
 however, the sporophyte possesses 
 extensive nutritive tissues, the 
 leaves, stems, and roots belonging 
 entirely to this stage. Sporangia 
 in these plants may be formed 
 either upon the stem or the leaves 
 — never upon the roots. 
 
 321. Liverworts. — In the 
 liverworts the sporangium is gen- 
 erally produced at the upper end 
 of a short or long stalk. It is 
 either spherical, ovoid, or short- 
 cylindrical (figs. 64, 65). The 
 spore-producing tissue occupies the greater part of the 
 interior, the wall being formed usually by a single layer of 
 
 . 229. — A branch <>i .1 rul mm- 
 
 ing tetn isp. .us. .', formed bj an 
 interna] cell of the thallus Mag 
 nifiedabout loodiam. -AfterKUtz 
 
 ing. 
 
228 
 
 PLANT LIFE. 
 
 cells. Mixed with the spore-producing cells, however, arc 
 many sterile cells, which become gradually elongated, and 
 
 spm 
 
 Fig 
 
 -The i 
 
 phyte of a peat moss {Sphagnum acuti/blium)vntb adjacent parts 
 of thegametophyte. The spun .phyte consists of a capsule, -u'. and a broad foot, sg", At 
 the stage shown in />' it is still completely enclosed in the tissues of the gametophyte, 
 viz., c, the enlarged ovary which forms the calyptra or hood, and v, the vaginule or 
 sheath surrounding the foot, ar is the neck oi the ovary. (Compare fig. 331 I The 
 ajc over the large-celled central tissue (columella) is the sporangium, fit, the false 
 stalk, produced by the gametophyte, which raises the sporopnyte. [n A, the calyptra 
 has broken, only a fragment remaining, exposing the capsule. ' d, the lid. by whose fall 
 the sporangium is exposed and the spores escape. , h, leaves oi the gametophyte : qt, 
 the false stalk. Compare figs. 67, 72. 73, in which the stalk is part oi the sporophyte. 
 . I magnified 13 diam.; /■'. 32 diam — After Schimper. 
 FlG. 231. — Longitudinal section of the young capsule of a true moss (Bryum), s, spo- 
 rangium. At this stage the mother cells 01 the spores, spin, have become free (only a 
 few are shown still enclosing the spores): tw, the wall of the sporangium, lined by 
 the remains of another layer of cells now disorganized ; < , the columella, of partly col- 
 lapsed cells ; it, intercellular space : cm, wall of the capsule : .1 n, the annuius, a ring 
 of cells which pries off the lid, at whose edge they develop : ot, the outer, in, the inner, 
 peristome, formed by the thickening of parts of the walls of certain rows of cells; >/.', 
 nutritive tissue, with chloroplasts and intercellular spaces. Magnified 25 diam. — Orig- 
 inal. 
 
VEGETATIVE REPRODUCTION. 229 
 
 in many species thicken their walls along one or more spiral 
 lines. These sterile cells are called elaters (fig. 11, A, A'). 
 They serve to entangle the spores in dusters when they are 
 set free. The sporangium opens at maturity by splitting at 
 the apex, sometimes into two, commonly into four or more, 
 parts (fig. 64). 
 
 322. Mosses. — In most mosses the sporangium is developed 
 within the enlarged upper part of the sporophyte, to which 
 the name capsule is given. In the peat mosses it is cap- or 
 thimble-shaped (fig. 230), while in most of the true mosses 
 it is a hollow cylinder (fig. 231). It opens by the falling off 
 of the sterile upper end of the capsule, which separates as a 
 lid and thus allows the spores to escape from the upper 
 end of the cylindrical sporangium. By the time the spores 
 are mature, the sterile central tissue of the capsule, which 
 forms the columella (c, fig. 231), shrivels and often almost 
 disappears, so that the capsule seems to be a cup or urn, filled 
 with loose spores. In the younger stage (fig. 232) the orig- 
 inal form is shown. 
 
 323. Ferns. — In the ferns the sporangia are usually nu- 
 merous, stalked, free, and often associated in clusters 
 called sori. They are either produced upon the under sur- 
 face of the foliage leaves or upon specialized leaves.* The 
 sori are often arranged in elongated clusters or lines 
 (fig. 2$$). Each sorus, or a (luster of them, may be pro- 
 tected by a special outgrowth from the cells in its neighbor- 
 hood, called an indusium (tigs. 233, 234). Each sporangium 
 consists of a stalk composed of two or four rows of cells ex- 
 panding above into a body composed of a single outer layer 
 enclosing the spore producing cells, and at maturity the 
 spores themselves. The walls of a row of cells more or less 
 completely encircling the body of the sporangium become 
 
 * It must l>o remembered that the entire plant, consisting of root, stem, 
 and leaves, is the homologue <>f the capsule and sialk <>!' the mossworts. 
 
230 
 
 PLANT LIFE. 
 
 irregularly thickened (sec fig. 401). The strains caused by 
 the unequal absorption and loss of water burst the sporangium 
 at some definite point. This 
 Line of dehiscence is often 
 between a pair of large sad- 
 dle-shaped cells (fig. 401). 
 
 324. Sporophylls. — In 
 many of the ferns the leaves 
 which produce sporangia are 
 not different from the foliage 
 
 Fig. 233. 
 
 Fig. 232. — Diagram of a longitudinal and transverse section of the very young capsule 
 of a true moss (Bryum). The transverse section is taken along the line A B. a, the 
 mother cells of the spores ; < . the columella ; is, intercellular space. The constriction 
 at the top marks the limit of the lid. The part below the sporangium is the neck, with 
 nutritive tissues. — Original. 
 
 Fig. 233. — A leaflet of a fern (As/- id in in) seen from the back. Eight sori are shown, 
 each covered by its own indusium, /. Magnified 2 diam. — After Sachs. 
 
 leaves. . In others, certain leaves are so specialized for 
 bearing the sporangia that they lose their nutritive function 
 in part or entirely. To such spe< ialized leaves the name 
 sporophyll is applied. 
 
 325. Horsetails. — In the horsetails the sporangia have the 
 form of sacs, varying in number from six to twelve. They 
 arise upon the lower face of a shield-shaped sporophyll (figs. 
 2 35» 2 3 () )- These sporophylls are aggregated in a close 
 cluster at the upper end of the axis, constituting what 
 
VEGETATIVE REPRODUCTION. 2$\ 
 
 may be called, properly enough, a flower.* The wall of the 
 sporangium when young is formed by three layers of cells, 
 but consists at maturity of one layer only, which, having its 
 cell-walls thickened in an irregular manner (fig. 238), tears 
 open the sporangium, usually along a vertical line. The wall 
 of the spore consists of three layers, the outer one splitting 
 into narrow strips and remaining lightly attached to the spore 
 at one point (fig. 239). To these parts of the cell-wall the 
 name elaters has also been given. (Compare 1" 321.) Their 
 
 Fig. 234. — Vertical section through the leaflet shown in fig. 233, passing through the cen- 
 ter of a sorus. e, ventral epidermis; <■', dorsal epidermis; between them the meso- 
 phyll, showing 3 veins cut across; over the central one is a cushion of tissue from 
 whose surface arise the stalked sporangia s, s. i, i, the indusium. Magnified about 30 
 diam. — After Sachs. 
 
 purpose seems to be to entangle the spores so that they may 
 not be too sparingly distributed. 
 
 326. Club-mosses. — In club-mosses the sporangia are sac - 
 like outgrowths upon the upper surface of the leaf near its 
 base, or occasionally of the axis itself jusl above the leaf. 
 Sometimes the leaves bearing them are the ordinary foliage 
 leaves ; in other species they are specialized and crowded 
 into a terminal (luster or spike (fig. 240). 
 
 327. Differentiation of spores. — Among the higher fern- 
 worts tlie spores are of two sizes : large ones, known as mega- 
 
 * This term is not generally applied to those sporophylls. Rut see defi- 
 nition of a flower, % 320, and compare tig. 237 of a " flower" of Zamia. 
 
23: 
 
 PLANT LIFE. 
 
 spore's, and much smaller ones, known rs microspores (fig. 
 241). Each kind, when it germinates, produces a sexual 
 plant, or gametophyte (■ 377), upon which, however, only 
 
 Fio. 235. 
 
 Ki<;. 
 
 Fir,. 235 Pari ol two sporophytes ol .1 horsetail {Equisetum arvense). A, the 
 spring shoots, with sheath like whorls ol leaves below and crowded sporophylls above 
 «, summer shoots, much branched, with inconspicuous leaves; nutritive work all 
 done by stems ..i these shoots. Two thirds natural size After Kerner. 
 
 Fig. 236. — Three sporophylls from the flower of a horsetail {Equisetum telmntein), 
 seen in different positions, s, the shield-shaped sporophyll ; st, its stalk attached to 
 the center of dorsal face ; sg; sporangia. Magnified about 10 diam.— After Sachs. 
 
 one sort of sexual organs is borne. The megaspores give rise 
 to plants bearing female organs only, the microspores to 
 
VEGE TA TI I 'E RETROD UC TION. 
 
 233 
 
 those bearing male organs only. A similar separation of 
 sexes in the gametophytes frequently occurs when the spores 
 are equal in size, as in Marchantia and horsetails, but it 
 
 ri<;. 237. 
 
 Fig. 237- -A, the " flower " of a seed plant (Zamia muricata). It is 1 omposed of 
 crowded sporophylls, of which one is represented in A' as seen from the side. It has 
 
 a stalk capped by a hexagonal tup, .>. with numerous sporangia, 1 . on the under side. 
 . I , natural size. ' ti, magnified about 6 diam Aftei Karsten, 
 Fio. 23S. — A bit of a section of the wall of a sporangium of a horsetail The cells of 
 the outer layer thi< ken their walls along spiral lines. The two inner layers of CI 
 
 become disorganized at maturity ol the sporangium. Magnified 250 diam \tt.r 
 
 ( 'ainpbell. 
 
 I'll.. 239.— Two spores of a horsetail [Eguisetum arvense); one showing thi elaters 
 open, as when dry, the other with them coiled, as when moist. Magnified 25 diam. — 
 After Kerner. 
 
234 
 
 PLANT LIFE. 
 
 always occurs when they are unequal. A corresponding dif- 
 ference in size is often found between the sporangia con- 
 taining small spores (microsporatigia) and those containing 
 large spores (megasporangia) (figs. 241, 242 1. 
 
 The sex terms, male and female, applicable primarily to 
 the sex cells, arc applied also to the organs and to the plants 
 
 240. 
 
 Fig. 240. — Sporophyte of a club-moss (Lycopodium clavatnm). The horizontal stem 
 is densely covered with leaves ; those OB the erect branch become small and few tor a 
 space: these are succeeded by broader leaves, the sporophylls, crowded in a dense 
 spike, s. Half natural size.— After I'rantl. 
 
 Fig. 241. — Section through three sori of an aquatic femwort {Salvinia natans). 
 Each is covered by a double indusium. r, /. two sori consisting of sporangia con- 
 taining microspores <see tig. 242); <». a sorus consisting of sporangia, each containing 
 one megaspore. M agnified 10 diain. After Sachs. 
 
 which bear them, so that the microspores are said to produce 
 male plants, and the megaspores female plants. For a fur- 
 ther account of the gametophyte, see • 386, 394, 393. 
 
 328. Seed plants. — In the seed plants this differentiation 
 of the spores is always found. The microspores are called 
 
VEGE TA TI I r E REP ROD UCTION. 
 
 235 
 
 pollen, and the megaspores are called embryo-sacs * The mi- 
 crosporangia and megasporangia, also, are always different in 
 form and structure, and the leaves upon which they are usually 
 borne are also of two distinct forms. In no case do sporo- 
 phylls perform nutritive work; they are always specialized. 
 Those leaves which bear microsporangia are called stamens^ 
 and the leaves which produce the megasporangia are called 
 
 Fig. 242. — A, a microsporangium of Salvinia seen from the outside. It contain?; (<^ 
 microspores. />', four spores from A, surrounded by hardened frothy mucilage. C, 
 median longitudinal section of a megasporangium, showing structure oj wall at matu- 
 rity, and the single spherical megasporc, with its proper wall (black line) and a thick 
 frothy epispore ill 368). A and C magnified 55 diam. B, magnified 250 diam.— After 
 Strasburger. 
 
 carpels* (figs. 245, 250, 251). In spite of these special 
 names, it must be carefully borne in mind that the sporangia 
 and sporophylls of the seed plants are not different from those 
 of the fernworts or mossworts in any essential particular. 
 
 329. The sporophylls of the seed plants are usually aggre- 
 gated by the failure of the internodes of the axis to lengthen 
 as much as between the foliage leaves. Very often, also, the 
 
 * These special names were given because the seed plants were first 
 studied, and it was long before the real nature of the pans and theii n la 
 tion to similar ones in the lower plants were known. The terms are still 
 in use, and are likely to continue to be used for convenient e. 
 
236 
 
 PLANT LIFE. 
 
 leaves adjacent are modified in form and color to adapt them 
 to securing the dispersal of the pollen by various agents, 
 especially insects. Such a shoot bearing sporophylls and 
 accessory leaves is called a. flower (*\ 330). As a similar 
 aggregation of the sporophylls occurs in horsetails and many 
 club-mosses (figs. 235, 240), it is evident that the flower is 
 not distinctive of the seed plants, though it attains the highest 
 specialization among them.* 
 
 The parts and functions of the flower of seed plants are 
 now to be discussed. 
 
 The Flower. 
 
 330. A flower, in its simplest form, may consist of an axis 
 bearing only a single sporophyll (fig. 243). A flower usually 
 consists of a shortened axis, the torus, bearing several sporo- 
 phylls and several accessory floral leaves (figs. 104, 244). 
 
 Fie z 43 . 
 
 Ho. -M3-— -'. a single flower ; /.', a portion of the flower cluster of A risarum r»/i,'<"''. 
 
 The flower is composed of one stamen only. Magnified slightly.— After Kngler. 
 Fir.. 244- A Mower of linden, halved; showing a pestle-like pistil. Magnified about 3 
 
 diam. — After Reiner. 
 
 The sporophylls arc known as essential organs, the accessory 
 leaves as the perianth and bracts. 
 
 The essential organs are of two sorts, stamens and carpels. 
 In any flower they may be all stamens or all carpels, or may 
 
 * It is for this reason that the term see J plants is preferred to Jlozuering 
 plants. 
 
VEGETATIVE REPRODUCTION. 237 
 
 include both sorts of sporophylls. The perianth may be com- 
 posed of one or two kinds of Leaves, often bright-colored. If 
 
 there are two sorts, those next the sporophylls are generally 
 highly colored, and constitute the corolla. Each leaf of the 
 corolla, when distinct, is a petal. The leaves below the co- 
 rolla are often green. They constitute the calyx, and each, 
 when distinct, is a sepal. 
 
 331. Carpels. — The leaves (sporophylls) bearing the 
 ovules (megasporangia) are called carpels. They ma\ In- 
 flattened ; or so curved that in the course of their develop- 
 ment the edges unite and a cavity is more or less perfectly 
 enclosed; or neighboring carpels may grow together in such 
 a way as to form a case. Such hollow structures, whether 
 composed of one or more carpels, are often somewhat pestle- 
 shaped, whence they early received the name pistil (fig. 244). 
 A flower whose only essential organs are pistils is called pis- 
 tillate. The sporangia arise usually upon the ventral (inner) 
 face or the edges of the carpels. In the open carpel they are 
 exposed, but in the closed carpels they are completely shut 
 in, except for a narrow opening which sometimes remains, by 
 which the interior cavity communicates with the outside air. 
 
 332. Ovules. — Among seed plants the sporangia which the 
 carpels bear are universally known as ovules, a name given to 
 them under the supposition that they were the eggs which, 
 upon fertilization, produce new plants. Though they are not 
 in any respect comparable to the real eggs (since the) are 
 produced by the non-sexual or sporophyte phase), the name 
 is retained for convenience. 
 
 333. Gymnosperms and angiosperms. — When the changes 
 through which the ovule passes are complete, it bee nines the 
 seed. When the ovules are produced upon the free stirfai e of 
 an open carpel, the seeds are, therefore, exposed. On the 
 contrary, when the ovules are borne within a closed pistil 
 (formed by one or mure carpels) the seeds are developed 
 
2 3 8 
 
 PLANT LIFE. 
 
 within this case, by which they are protected until mature, or 
 longer. 
 
 These two methods of seed pioduction form the basis for 
 the separation of the seed-bearing plants into two great groups, 
 one known as gymnosperms, or plants with naked seeds, the 
 other as the angiosperms, or plants with encased seeds. 
 Open carpels are found exclusively among the gymnosperms, 
 to which belong the cone- bearing, mostly evergreen, trees, 
 while the closed pistils are chiefly found among angiosperms, 
 to which belong the majority of garden and field plants and 
 the deciduous forest trees. 
 
 334. The simplest form of carpel occurs in Cycas (fig. 
 245), in which the ovules are borne on the edges near the 
 bases of leaves which somewhat resemble the foliage leaves, 
 and form a whorl between preceding and succeeding whorls 
 of foliage leaves upon the main axis. The carpel of most 
 gymnosperms is a scale from 
 whose upper surface arises a 
 similar fleshy scale, the pla- 
 centa, bearing two ovules 
 upon its ventral (upper or in- 
 
 FlG. 245. Fir.. 246. 
 
 Fig. 245. — An ovule-bearing leaf or carpel of Cycas r*wfl/Kfa, showing 4 ovules near 
 base, replacing the 1t.uu lies. ( hi the right above, a young seed. About one qu liter 
 natural size.— After Sachs. 
 
 Fk; 246 —A young cone-scale (placenta) of Scotch pine showing the two ovules; the 
 latter halved parallel to the scale, showing the body of ovule and the prolonged integ- 
 ument forming the micropyle, in. The scale is attached at /». Magnified about 8 
 diam. After Kerner. 
 
VEGETA TIVE REP ROD I r C2 'ION. 
 
 239 
 
 ner) face (fig. 246). In such cases the carpels are generally 
 aggregated in close spirals near the end of a thickish axis, 
 and finally ripen into a cone (tigs. 341, 358), which gives 
 the name to one of the largest orders of gymnosperms, the 
 
 Fig. 247. — .-/, shoot <>f the yew ( lux us baccata) with three ripe seeds, each surrounded 
 by a fleshy aril. Natural size. B, ovule with its tip projecting from the scale leaves 
 dt the shoot it terminates. ( . the same, halved, showing the body of ovule (sporan- 
 gium] and the lone; tube-like integument. O, young seed ol same, with aril partly 
 formed. E, mature seed, halved. The central (white) body is the embryo; around 
 it (dotted) the food ; then the seed coat; then the aril (white!. A', C, /'.A', slightly 
 magnified. — After Kemer. 
 
 Conifers. (See further ^| 404.) The ovules of some gym- 
 nosperms are not borne by carpels, but each terminates an 
 axis, as in the yew (fig. 247). 
 
 335. The closed pistils of angiosperms are usually distin- 
 
240 
 
 PLANT LIFE. 
 
 guishable into (i) an enlarged basal part, the ovular?,* con- 
 taining the ovules, surmounted by (2) a slender part of vari- 
 able length, the style, which is terminated by (3) a rough, 
 sticky, or branched part, the stigma. (See figs. 250, 258.) 
 
 336. The stigma may take the form of a knob, a ridge, 
 a straight or wavy line, or be lobed or branched. However 
 compact, it is usually roughened by the prolongation of 
 its surface cells into rounded, pointed, or hair-like exten- 
 sions (figs. 248, 283), which frequently 
 secrete a sticky fluid. Its purpose is 
 to secure the adhesion of the pollen 
 spores brought to it by various agents, 
 among the most important of which are 
 the wind and insects. 
 
 337. The style may be thick or 
 slender, long or short, branched or un- 
 branched, hollow or solid. It is fre- 
 quently wanting, so that the stigma is 
 said to be sessile upon the ovulary. 
 
 338. Simple and compound pistils. 
 ^fromV^gl*! com —When several carpels are present in 
 
 to C Sch Z r£"&i f^'Cd! one flower the >' may form as many 
 ZSL^&vFSaZ separate simple pistils as there are car- 
 #ft&ffi£E-£ P<*s. ^ numerous, the axis will -be 
 After straslurger. enlarged or elongated to accommodate 
 
 them. (See ^[ 360.) Instead of forming separate pistils, 
 
 * This part was early called the ovary (a name which is still in general 
 use), meaning the organ which produces eggs, under the impression that 
 the ovules ( = little eggs) were like the eggs of birds, an idea which was 
 further carried out in the name albumen given to the fond stored in the 
 seed. (See ' ,T 403, 407. ) To avoid confusion with the true ovary (1 388), 
 in which the real egg is produced (^ 387), I here suggest the name ovu- 
 lary — i.e., the organ which produces ovules. The word ovule, though as 
 had in etymology as ovary, is convenient, and does not lead to any con- 
 fusion. 
 
V EG ETA TIVE RE PROD UCTION. 
 
 24I 
 
 the carpels may be united to form a single compound pistil. 
 This union is commonly brought about (1) by the actual 
 growing together of the parts in a very young stage, so that 
 the cells interlock and become partially or completely united; 
 or (2) the carpels develop, not as separate- parts, but as a 
 ring of tissue growing up from the surface of the axis; or, 
 (3), a portion of each carpel develops separately, and later 
 these distinct parts may be lifted by the growth of the ring 
 of tissue beneath them (fig. 249). 
 
 339. The union * of the carpels may be only at the base ; 
 or it may involve the entire ovulary, leaving the styles free; 
 
 Fig. 249. Fig. 250. Fir,. 251. 
 
 Fig. 249. — Pistil of white hellebore (Veratrwn album) showing time carpels separate 
 
 above only. Magnified about <• diam. After llerg and Schmidt. 
 Fig. 250. — Calvx and pistil of the manna ash (Fraxinus ornus) showing calyx leaves 
 
 united at base and carpels united throughout, the slightly 2-lobed stigma only giving 
 
 external evidence of their number. Magnified several diam.— After Berg and Schmidt. 
 Fig. 251.— Pistil of white potato halved transversely, showing two carpels united at 
 
 center where their edges form ,1 large placenta on whose surface the ovules arise. 
 
 Magnified several diam— After ICeraer. 
 
 or the union may be complete, with the exception ot the 
 
 stigmas, or it may involve even them (tig. 250). Union may 
 take place in such a way that the edge of each carpel meets 
 its fellow and the edges of neighboring carpels in the center 
 of the compound pistil (fig. 251). In this case the ovulary 
 
 * This phrase may It used for convenience in all cases, oven of those 
 
 pistils in which the carpels were- at no time separate, 
 
24- 
 
 PLANT LIFE. 
 
 is divided into as many chambers as there are component 
 carpels, and the partition by which the chambers are sepa- 
 rated represents the adjacent parts of the two carpels. Or 
 the carpels may unite with each other at their edges only, so 
 -rr'sr-^^Tj^s, that the line of union is at the outside 
 ^^ s— cg^l ^^^ of the pistil. In this case the ovulary 
 will have a single chamber. In both these 
 
 FlG. 252. — A transverse . 
 
 section of the capsule of methods of union the normal number of 
 
 shepherd's purse. The , 
 
 pistil consists ,,f two chambers in the ovulary may be increased 
 
 carpels, at whose united 
 
 edges two placenta: are by OlltglOWths from the Carpels them- 
 
 formed carrying the 
 
 ovules (now seeds). The selves, as in figure 252, where Jrom the 
 
 partition from one pla- 
 centa to the other is an united edges of the carpels a plate of tis- 
 
 outgrowth (false parti- 
 tion) and not part of the sue has grown out to meet a correspond- 
 
 carpel. Magnified about 
 
 6 diam.— After Bessey. ing one from the other side, so that what 
 should be a one-chambered pistil has become two-chambered. 
 (Compare also fig. 276.) Even simple pistils are subject to 
 such subdivision of their interior (fig. 253). 
 
 Fig. 253. Fig. 254. 
 
 Fig. 253. — Lower half of the pistil of Astragalus canadensis. It consists oi only one 
 carpel, but is divided into two chambers by a false partition, an outgrowth from the 
 midrib of the leaf. Magnified several diam — Alter dray. 
 
 Fig. 254— Two stages in the development of the ovule of the currant, ./.a median 
 longitudinal section ol a young ovule; n, the sporangium; //.inner integument be- 
 ginning to develop as .1 nng at base oi n ; .'/, the fundament of the outer integument ; 
 »r, the mother cell of the niegaspores ; /,', a similar section of tin sporangium alone, 
 older, showing »/', ;//", «/'", the daughter cells of m ; ///'". only becomes a perfect 
 spore; m' and m 1 ' do not develop further and become destroyed. Contents of cells 
 not shown. Magnified 350 diam. — After Warming. 
 
 340. Ovules. — An ovule consists of a megasporangium 
 partially enveloped by one or two outgrowths from beneath. 
 
VEGETATIVE REPRODUCTION. 243 
 
 The sporangium forms the body of the ovule (fig. 254). In 
 the interior the mother cells of the megaspores are differen- 
 tiated early, the outer tissues forming the wall of the sporan- 
 gium (fig. 254). In a few ovules as many as 20 to 40 mega- 
 spores begin to develop ; in most only one to' four. Even 
 when several megaspores begin to form it is rare for more 
 than one to reach perfection ; the remainder disappear 
 almost completely. 
 
 341. Indehiscence. — The megaspore never escapes from 
 the sporangium ; a condition which necessitates many adapta- 
 tions. (See further « r 358, 414). The protection of the 
 megaspore by the sporangium renders a thick wall unneces- 
 sary. For this reason the megaspore looks more like a cavity 
 in the ovule than like a spore. Because an embryo appears 
 later inside this apparent cavity, the megaspore of seed plants 
 has long been called the emhryo-sac. 
 
 342. Integuments. — The sporangium is surrounded by 
 one or two integuments. These arise as outgrowths from 
 
 the tissues adjacent. If the spo- ^-^ w 
 
 rangium is to have two coats, the *r* | L 
 
 inner appears first as a low ring A, V /'/'■Jf""' I 
 
 around its base gradually growing , ^"y 
 
 up around it ; the outer shortly , ^^^ 
 
 appears in the same way (fig. 255). 
 
 _, . 11 1 Fig. 255.— Two very young ovules 
 
 I hese integuments, as well as the of the California puppy ,/„/,. 
 
 scholtzia I, seen from the outside. 
 sporangium, often grow unsvm- /•'. somewhat older than 
 
 . '. the sporangium ; fc, the inner in- 
 
 metncally, so that at the maturity tegument; /■>■, the outer integu 
 
 ment; ///, the -ulk. Magnified 
 Of the megaspore the OVUle is Often [4odiam Mtei Duchartre. 
 
 variously curved (figs. 254, 255, 256). The megaspore it- 
 self may be distorted by this means so as to lose still more 
 its likeness to a spore. 
 
 343. Location. — Ovules are borne either upon the axis 
 itself or upon the carpels. When they are borne upon 
 the axis they may be either uncovered, as in the yew 
 
244 
 
 PLANT LIFE. 
 
 among gymnosperms (fig. 247), or the carpels* may form 
 a covering, as in angiosperms. In these plants the ovule 
 may terminate the axis, as in sunflower and buckwheat 
 families (fig. 257); or the ovules may be lateral upon 
 the surface of an enlargement of the axis within the ovulary, 
 as in pinks and primroses (fig. 258). 
 
 It is usual, however, for the ovules to arise upon a carpel, 
 either singly or in clusters which occupy definite portions of 
 its surface. The cushion or ridge from which the ovules 
 arise is called the placenta. In the pines the placenta is a 
 
 Fir;. 256. — Diagrams of median longitudinal sections of three sorts of ovules to show 
 curvatures due to unsymmetric growth. A, a straight, />', an inverted, C, a bent ovule. 
 In all: _/, the stalk; X-, the sporangium; //, the inner integument; at, the outer in- 
 tegument ; m, the micropyle ; c, the base of the sporangium where the integuments 
 arise (called the chalaza); r, the ridge (rhaphe) formed by the union of stalk and outer 
 integument ; em, the megaspore. As C develops further em may become sharply bent 
 on itself.— After l'rantl. 
 
 scale-like outgrowth from the upper surface of the carpel, 
 bearing two ovules (fig. 246), and as the cones mature these 
 gradually outgrow the carpels and constitute the main por- 
 tion of tlie ripened cone. To such placentas the ovules are 
 
 attached by one side ; they are therefore entirely sessile. The 
 
 •Although the enclosing leaves in this case do not bear the sporangia, 
 and are, therefore, not strictly sporophylls, their similarity in form renders 
 it convenient to retain the name carpel even for those pistils in which 
 they are a mere roof over a convex or hollowed axis bearing the ovules. 
 (See fig. 25S.) 
 
VEGETA TIVE REPRODUCTION. 
 
 ••15 
 
 placenta in angiosperms commonly consists of a cushion of 
 tissue usually at the united edges of the carpel or carpels, [f 
 the carpels are united into a compound pistil, the placentas 
 will be cither isolated, as ridges upon the inner face of the 
 wall of the ovulary (fig. 25 2 J, 
 or aggregated at its center 
 (fig. 251). Occasionally the 
 ovules arise upon the entire 
 inner face of the carpels, as in 
 the gentians. 
 
 Fig. 257. 
 
 Fig. 258. 
 
 Fig. 257.— A median longitudinal section through the flower of Klu-um undulatutn, 
 s, a sepal; /. a petal; n. a, n, anthers; «, stigma; /. ovulary; kk, sporangium, 
 which, with the two integuments over it, forms the single ovule terminating the axis ; 
 </>; nectary Magnified about 10 diam. — After Sachs. 
 
 Fig. 258. -Pimpernel lAmtgnUu arvensis). A, median longitudinal section ol a 
 young flower-bud ; /.sepal; c, corolla, just beginning to develop ; .(.anther; A", car- 
 pels growing over A. tne apex ol the axis. />', median longitudinal section ol the 
 
 pistil. . . the carpels, forming a root over S, the axis on which ovules are beginning 
 
 to develop, and growing up to form a columnar style at whose apex is the stigma, '.. 
 (', the same, older. ,S, the enlarged apex of the axis showing six ovules, Sk, in sec- 
 tion; gr. the style: n, the stigma, on which arc lodged pollen grains, p. All magni- 
 fied.— After Sachs. 
 
 344. Stamens.— A stamen is a leaf (sporophyll) of the 
 seed plants which bears the microsporangia, or pollen sacs. 
 The flowers whose essential organs are all stamens are said to 
 
246 
 
 PLANT LIFE. 
 
 be staminate. Rarely a single stamen constitutes a flower. 
 Except for the crowding, the stamens are arranged like all the 
 other leaves of the plant, arising on the axis alternately, or 
 in one or more circles. The stamens exhibit great diversity 
 of form and size. Each usually consists of two parts, a stalk, 
 called the filament, bearing an enlarged portion, called the 
 anther. 
 
 345. The filament may be long or short, slender or thick, 
 rounded or flattened. It may be entirely wanting, in which 
 case the anther is sessile. 
 
 346. The anther is usually larger than the filament and 
 commonly two-lobed, having the sporangia located in the 
 thicker parts. The sterile tissue between the sporangia is 
 called the connective (fig. 262). This appears usually as a 
 mere continuation of the filament, but sometimes is prolonged 
 beyond the body of the anther, as an appendage (fig. 259). 
 
 Fig. 260. 
 
 Fi<;. 259. — Anther of the sweet violet (Viola odor,tta), showing the connective pro- 
 longed into a triangular tip. Magnified about 5 chain- After Knurr 
 
 I ig - \ ut 1 1.1 of thyme ( Thytnui serpyllum), showing broad connective. Magni- 
 fied about 5 diam. — After (Center, 
 
 I'M.. 261. — Anther of the sage {Salvia <>/'//, inalis). Opposite a the filament proper is 
 jointed to the elongated connective which has one perfect anther-lobe on the upper 
 end; on the other the sporangia do not develop. Magnified about 5 diam.— After 
 K, enter. 
 
 It is sometimes broad, so that the sporangial lobes are widely 
 separated (fig. 260), and may even be so long and slender as 
 to seem a part of the filament (fig. 261). 
 
VEGE TA TIVE REP ROD UCTIOM. 
 
 M7 
 
 347. Sporangia.— The anther bears from 1-12 micro- 
 sporangia upon its surface, or wholly or partly sunk in its 
 
 Fig. 262.— Transverse section of the anther of thorn-apple (Datura Stramonium). 
 c, connective, with a small stele embedded in parenchyma ; a, />, a, /, the four spo- 
 rangia, arranged in pairs showing pollen grains. When the sporangia break, the walls 
 rupture at the groove between a and /. Magnified about 25 diam. —After Frank. 
 
 tissues. In most anthers the sporangia are either 2 or 4 
 
 (fig. 262). When there are four they are often paired, and 
 
 each pair may become confluent by 
 
 the absorption of the portion of the 
 
 anther tissue between them (fig. 263). 
 
 This occurs about the same time that 
 
 the outer wall bursts in order to set 
 
 free the spores. Such anthers, at the 
 
 time of opening, are apparently two- 
 
 chambered. In those which contain 
 
 only two sporangia, the two may open Fig. 263. -Trans verse section of 
 
 . . bursted anther of a lily (Bu- 
 
 independently, or they may become tomus umbeiiatus). Sporangia 
 
 n , , have ruptured at z, so th.it the 
 
 confluent, so that at maturity they two pairs have each formed a 
 
 single cai itv. The coi 
 may seem to constitute a single is relatively small; in the centei 
 
 a single stele. Magnified about 
 chamber. 2odiam. mm Sachs 
 
 348. Dehiscence. — The opening of the 1 hambers occurs in 
 
 one of three ways : by pores, by slits, or by valves. (1) A small 
 
 area of the outer wall is absorbed or breaks away so that the 
 
2 4 8 
 
 PLANT /.//■/■:. 
 
 pollen spores sift out through the pore so formed (fig. 264) ; 
 or (2) a crack begins at one point and extends lengthwise of 
 the sporangium, in which case the anther is said to open by 
 slits (figs. 259, 260, 261) ; or (3) the break occurs along a 
 line considerably curved, and the flap (valve) thus loosened 
 curls up or lifts so as to allow the escape of the spores (fig. 
 265). All three methods are dependent upon some special 
 
 Fig. 265. 
 
 Fie. 264. — Anther and pollen of a Rhododendron. A, the anther, opening by pores at 
 the end and allowing the pollen to escape. Magnified 8 diam. //.pollen grains ad- 
 herent in four-, (tetrads) as formed in the mother tells: the tetrads an- held together by 
 a stirkv material which draws nut i 1 1 1 . . cobwebby threads as they are separated. Mag- 
 nified 50 diam. — After Kernel 
 
 FlG. 205. A flower oi cinnamon, halved. The calyx and stamens are raised on a cup 
 developed around the pistil. The anthers open bj uplifted valves, one for each spo- 
 rangium, which lure are arranged in two stories instead of in pairs side by side. Mag- 
 
 nilied about 7 diam. — After 1. 
 
 structure of the wall of the sporangium at the lines of rup- 
 ture. 
 
 349. Union. — The stamens are not infrequently united 
 with each other or with some of the neighboring leaves of 
 the flower. They may l>e united to ea< h other by their fila- 
 
i "/•/<//•; ta ri i •/•; retrod uction. 
 
 249 
 
 merits only, or by their anthers only, or throughout their 
 
 whole length. Union with the pistil or pistils is rather un- 
 common, but union with the corolla or calyx is very frequent. 
 The union of stamens may be real or apparent. They may 
 develop independently anil later 
 cohere by their adjacent edges 
 (fig. 266). Or they may begin 
 development separately and be 
 subsequently raised by the growth 
 of a ring of tissue of the torus 
 (•[360), so that the free portions 
 arise from the top of a shorter or 
 longer tube. "When the stamens 
 and corolla, arising independently, 
 are carried up together by the 
 growth of such a zone of the axis, 
 the stamens appear to arise from 
 the surface of the corolla (fig. 
 267). 
 
 350. Branching. — The sta- 
 mens frequently branch, and this 
 is difficult to distinguish from the 
 displacement by basal growth just 
 described, except by studying 
 their development. When sta- 
 mens branch a single fundament appears, on which later arise 
 smaller knob-like elevations, the fundaments of the branches, 
 each with its own growing point. (See figs. 268, 269, 270; 
 also • 171 and figs. 146, 166 on branching of loaves, of 
 which this is only a spe< ial case.) 
 
 351. Pollen grains. — The microspores produced in the 
 sporangia of the stamen are at maturity single cells. Their 
 forms and walls are various, being round, ovoid, or even 
 
 angular, with the surface smooth, grooved, or roughened, with 
 
 sunflc 
 
 The stamens of one of the 
 family (Cosmos bi/>hi- 
 natus). A, stamen tube formed by 
 five stamens coherent by their an- 
 thers around the style; the fila- 
 ments with a tuft of hairs about the 
 middle. />'. the same, but stamens 
 only; the tube has been slit along 
 one side and opened out Hat; seen 
 from the inside, Connective pro- 
 longed; dehiscence by slits Mag- 
 nified about 7 diam. After Baillon. 
 
PLAiXT LIFE. 
 
 few or many bosses, points, or ridges, as in other spores 
 (A-D, fig. 271). In the pines the outer layer of the wall 
 
 G'g-^s 
 
 Kig 1*67. Fig. 269. 
 
 Fig. 267. — Corolla of Alcanna tinctoria slit and laid open, showing almost sessile 
 stamens united with corolla above the middle of tube, s, scale-like outgrowth from 
 corolla. The tube between .v and the notches at edge of corolla result from the growth 
 of a ring of tissue beneath the five fundaments of the corolla which produce the five 
 corolla lobes c. Having grown so tar, a ring of tissue inside, on which the stamen fun- 
 daments were developing, became involved in this upward growth, and thus the sta- 
 mens were carried up and arise just above j. Magnified 4 diam. — After Berg and 
 Schmidt. 
 
 Fig. 268. -Very young flower of Hypericum perforatum, seen from above, showing 
 s, sepals; /•, fundaments of petals ; a, a, a, fundaments of the three stamens, each al- 
 ready with two lateral growing points, the fundaments of branches, appearing; g; fun- 
 daments of 3 carpels. Compare with figs. 269 and 270. Magnified about 50 diam. — 
 After Frank. 
 
 Fig. 269, An older stage of fig, 268, showing only the fundaments of stamens, a, and 
 of carpc-K. g: < in the- latter at the angles appear the fundaments of the three styles. 
 Many branches of a have begun. Compare tig. 270. Magnified about 50 diam. 
 — After Frank. 
 
 forms two bladdery swellings which make the spore relatively 
 lighter (E, fig. 271). The pollen spores arise in the spo- 
 rangia in fours in each mother cell, as described in ^j 306. 
 (See also fig. 264.) They are either dry and powdery when 
 
VEGETA TIVE REPRODUCTION. 
 
 251 
 
 ng to 
 
 the sporangia burst, or are mois 
 
 each other in larger or smaller 
 
 clusters (fig. 264). Sometimes, 
 
 as in orchids and milkweeds, they 
 
 are all held together in one mass 
 
 by the remnants of the mother 
 
 cells in which they were formed, 
 
 and are attached to a part of the 
 
 tissue of the anther which carries 
 
 the mass as a stalk or handle (figs. 
 
 272, 273). Dry spores are usually FlG 
 
 adapted to distribution by wind; fSSdtf-^lf^o? 
 
 while the adherent spores are t^t^T^^t^. 
 
 adapted to carriage by small ani- L%^ Fra M k agnified ab ° Ul 3 ***' 
 
 mals, especially insects. (See further^]" 481.) 
 
 352. Germination in place. — By the time the sporangia 
 
 270. - Mature condition of the 
 
 Fig. 271.— Pollen grains. A, white water lily (Nymf h ten alba). B, a thistle (Ctrswm 
 >ii-mo>aU-). C.a mallow {Hibiscus ternatus). D, dandelion {Tat 
 cinale). Magnified 200 diam.— After Kerner. E, pine, showing bladdery enlarge- 
 ments, *,*,oi the outer layer of the cell-wall. The central portion is the body of the 
 
 spore filled with protoplasm with a large nucleus. Kroin it is separated a lenticulai 
 cell, /'. the rudiment ot tile gainetuphyte. Magnified 400 diam -Alter Strasburgei 
 
 are old enough to release the spores, the latter have already 
 germinated and begun to form a new sexual plant, the male 
 gametophyte. Thus the spores of the non-sexual plant give 
 
252 
 
 PLANT LIFE. 
 
 rise to a plant of the other or sexual phase ; the sporophyte 
 produces the gametophyte. (For a description of the plant 
 thus formed see * 3 85.) 
 
 353. Perianth. — The perianth is not present in any 
 
 Fig. 272. — A, hanging flower of milkweed, seen from the side. The petals are sharply 
 reflexed. Natural size. />, the upper part of same, magnified about 2} diam., with 
 two of the appendages, ,/. ol the stamens cut off and the front of the anther wall dis- 
 sected away to show its two pollen masses. C, two pollen masses from neighboring 
 anthers connected to a dip, by which they may be attached to the foot of an insect. 
 Magnified about S diam. /». foot of an insect with pollen masses attached. In (and 
 D the pollen masses are inverted as compared with their position in . / and /•'. — After 
 Kerner. 
 
 gymnosperms (^[ 2,2,2,), except in a rudimentary form in a 
 few species of the highest order. In angiosperms the 
 perianth, which is rarely wanting, is primarily for the 
 protection of the sporophylls. As in all cases where leaves 
 are produced rapidly and in dose proximity on a short 
 axis, they grow during their earl] Stages more rapidly 
 upon the outer face than the inner. They are, therefore, 
 concave inward and closely pressed together, forming a hud. 
 At a certain stage the growth upon the two faces of the 
 
VEGETATIVE REPRODUCTION. 253 
 
 perianth becomes equal, and later is more rapid upon the 
 
 inner face than the outer. At this time Jt$$b> 
 
 the flower unfolds, the perianth spreading Jf ^$$ 
 
 more or less and exposing the stamens jpjr 
 
 and pistils within. These variations in g ^^ ctl 
 
 growth are often repeated, the stimulus ^fT 
 
 being light or heat or both, when it is Fic.273 -Pollen massfrom 
 
 ,1 an orchid. The pollen 
 
 necessary to protect the spores against gndns are arrang ed in 
 unfavorable weather. Such flowers open legated at 7he C end r< of g a 
 
 j 1 , . • \ c ii • 1 stalk, cd, terminating in 
 
 and close several times before their leaves an enlarged sticky disk, 
 
 . , /c , , w oei \ e.bymeansof which the 
 
 wither. (See also % 286.) p() n en mass adheres to 
 
 354. Calyx and corolla. — The leaves of ?^&?m.— Arur lngie°r Ut 
 the perianth are usually arranged upon the torus in two or 
 more circles or in a low spiral. They may be all alike or 
 differentiated into two series, an outer and an inner. In the 
 latter case those of the outer row or rows constitute the calyx, 
 and the inner set the corolla. 
 
 355. The calyx. — The calyx leaves, or sepals, are generally 
 green and possess a great variety of form. When separate, 
 the sepals are usually sessile and broad, with more or less 
 pointed apex. The sepals are often apparently united in the 
 manner already described for the stamens, the originally 
 separate portions appearing as teeth or lobes at the rim of a 
 cup or tube, or some similar structure. Occasionally the 
 sepals are not persistent, but tall as the bud opens or shortly 
 thereafter. More commonly, however, the calyx, especially 
 when undivided, remains throughout the entire development 
 of the flower, and often of the fruit. 
 
 356. The corolla. — The inner set of perianth leaves, the 
 petals, constitutes the corolla. The corolla presents a greater 
 variety of form and color than does the calyx. The petals 
 may be sessile or have a short or long stalk (fig. 274). The 
 corolla ma) develop a cup or tube, as described tor the calyx, 
 with teeth or lobes representing the petals (c, c, fig. 267). It 
 
'54 
 
 PLANT LIFE. 
 
 may be lifted on a common tube with the calyx from which 
 it then seems to arise ; or it may be raised 
 with the stamens, which then seem to be 
 attached to it, as in figure 267 ; or stamens, 
 corolla, and calyx may be lifted together 
 (figs. 288, 355). The corolla is ordinarily 
 not persistent, usually falling or withering 
 shortly after the microspores have been 
 lodged upon the stigma. 
 
 357. Irregularity. — Both corolla and 
 ig. 274.— Outline of a calyx are often radiallv symmetrical — i. e., 
 
 petal of Lychnis, 
 
 showing long stalk the parts surrounding the center of the 
 
 and an outgrowth, n, 1 
 
 the Hguie. Compare stem are of equal size and like shape, 
 
 fjpr rM Aftpr T .nprQ- 
 
 scn 
 
 37. — After Luers- 
 
 md may be divided into several like halves 
 by radial planes (figs. 275, 276). But often the symmetry 
 of the calyx, and still more frequently that of the corolla, 
 
 Fig. 275. 
 
 Fig 276. 
 
 Fir.. 275. — A flower of the flax, halved ; showing radial symmetry. See fig. 276. Magni- 
 fied 2 diam— After liessey. 
 
 FlG. 2-(k — Diagram showing the arrangement of the parts of a flower of flax. Outer 
 circle, 5 sepals ; second, 5 petals; third, 5 stamens; fourth, 5 carpels, each divided by a 
 false partition into 2 chambers. Five different radial planes will, therefore, divide this 
 flower into halves.— After Bessey. 
 
 is so altered by unequal growth of the parts that the flower 
 can be divided into like halves by only one, or at most two, 
 
VEGE TA TI I r E KEPKOD UCTION. 
 
 255 
 
 planes; or it may even be entirely unsymmetrical. This 
 unlikeness in the size and shape of the accessory leaves not 
 infrequently extends to the sporophylls (figs. 277, 278). 
 
 The irregular form and color of the perianth (when other 
 than green), including the variegation of the ground color 
 by lines and spots, seem to be dependent upon the relation of 
 the flower to insects. (See further ^[ 484. ) 
 
 Fig. 277. — An unopened Sower of tlie sweet pea, halved ; showing bilateral symmetry 
 
 (irregularity. Slightly enlarged.— After Hessey. 
 FlG. 278. — Diagram showing the arrangement of the parts of the flower of sweet pea. 
 
 Outer circle, calyx >5-lobed> ; second, 5 petals, the two lower united; third, 10 stamens, 
 
 9 united by filaments, 1 separate ; center, one carpel. Only one plane will divide this 
 
 flower into halves. — After l'.essey. 
 
 358. Pollination. — Since the megaspore is enclosed per- 
 manently by the ovule, and in angiosperms the ovules are 
 again enclosed by the pistil, it is necessary that the male plant 
 growing from the pollen spores be developed in the neighbor- 
 hood of the ovule whose megaspore produces a female plant. 
 (See ^jl" 341, 3S6.) To insure this a portion of the pistil 
 forms a receptive surface, the stigma, upon which the pollen 
 spores may be readily lodged. It is advantageous, also, to 
 have the pollen spores of one flower lodged upon the stigma 
 in another flower of the same sort rather than upon the 
 stigma of the same flower. The process of lodgment of 
 pollen on a stigma is (ailed pollination. If the pollen from 
 one flower is tarried to the pistil of another, it is tailed 
 cross-pollination. * To secure pollination, and espei iallv 
 
 * Since fertilization of the egg i- tin- ultimate object of pollination and 
 
256 
 
 FLA. XT LIFE. 
 
 cross-pollination, the agency of wind or water or insects is 
 
 employed. To the peculiarities of these various agents, 
 flowers adapt themselves in character of pollen, color, nectar, 
 odor, form of parts, time of development of stamens and 
 stigma, etc. For an account of these see € • 477-482. 
 359. Bracts. — In the immediate neighborhood of the 
 perianth the leaves are usually modi- 
 fied at least in form and size, and 
 not infrequently in color. The 
 leaves in whose axils the flowers 
 arise are called bracts, as are also 
 those which subtend branches of the 
 inflorescence (//', //", // 3 , fig. 139). 
 The axis of the flower, when 
 elongated beneath it, usually bears 
 one or more bractlets. 
 
 The bract is sometimes large and 
 surrounds the entire inflorescence, 
 as in Indian turnip (fig. 279) and 
 the calla, when it may be vari- 
 ously colored. Highly colored 
 bracts occur in the scarlet sage 
 
 Fig. 279.— Inflorescence of Indian and, with incOHSpicUOUS flowers, 
 turnip (.1 s/uuiia), surrounded 
 
 by a large striped and mottled in poinsettia and painted cup, 
 
 bract, the spatke. Natural size. 
 
 —After Gray. while the four large whitish bracts 
 
 of dogwood are the only conspicuous part of the inflores- 
 cence (fig. 280). 
 
 Bracts are aggregated to form an involucre beneath a head 
 (T 104), as in the sunflower family (figs. 2S1, 409), or an 
 umbel (^[ 104), as in the parsnip. The perianth may be 
 almost or quite wanting, and the bracts and bractlets may 
 be the only protective leaves for the sporophylls, as in the 
 
 generally its final result, the terms close- or self-fertilization and cross- 
 fertilization were formerly used. The word pollination is preferable. 
 
VEGETATIVE REPRODUCTION. 2$y 
 
 Fig. 280. — Inflorescence of the dogwood (Cor nits florida\ showing four white bracts 
 below- it, giving the whole cluster the aspect of a single (lower. Two thirds natural 
 size.— After Baillon. 
 
 Fig. 281.— Inflorescence oi yarrow {Achillea millefolium). A, seen from above; /■', 
 in longitudinal Bection. r, bracts, forming the involucre ; d, bra< 1- in whose axils the 
 flowers stand; ra, the ray flowers; »//, the disk flowers; .. corolla; '.ovulary; 1, 
 stigmas; >, the common torus. A magnified about 8 diam. ; B, about 15 diam Vftei 
 
2 5 8 
 
 PLANT LIFE. 
 
 grasses (fig. 282). Bracelets sometimes form a sort of second 
 calyx beneath the true calyx, as in hollyhock. In the straw- 
 berry and its kin, the somewhat similar extra whorl of leaves 
 
 Fig. 282. 
 
 Fig. 283. 
 
 Fig. 284. 
 
 Fig. 282. — A single flower of wheat, showing two chaffy bracts, />, v, which protect it. 
 For the parts of the flower see fig. 2S3. Magnified about 5 diam. — After Luerssen. 
 
 Fig. 283. — The flower of wheat with bracts removed, showing two fleshy bractlets, c, c, 
 the lodicules, which at time of blossoming swell and open the bracts. Three stamens, 
 and a carpel with two styles and feathery stigmas constitute the flower proper. Magni- 
 fied about 5 diam. — After Luerssen. 
 
 Fig. 284. — Outline of the flower of strawberry, seen from beneath, c, corolla ; k, calyx; 
 k', epicalyx, formed by the union of the stipules of the sepals. Slightly reduced. — 
 After Luerssen. 
 
 belongs to the calyx, being the stipules of the calyx leaves 
 united in the course of development (fig. 284). 
 
 The " cup " of the acorn, the "shuck " of the beechnut, 
 and the "bur" of the chestnut represent late-developed out- 
 growths beneath the flower or the flower cluster, which be- 
 come scaly or spiny as the nut develops, and serve to protect 
 the forming fruits. 
 
 360. The torus. — In the vicinity of the flower leaves the 
 internodes of the stem are rarely developed, so that the nodes 
 from which the flower leaves arise are close together. More- 
 over, the axis is usually enlarged, so as to give greater space 
 for the numerous leaves. This enlarged portion is called the 
 receptacle or torus. When the leaves are removed or fall 
 naturally the torus shows ordinarily a rounded or conical sur- 
 face, with close-set scars left by their bases (fig. 285). When 
 
I 'EGE TA TI I '£ REP ROD UCTION. 
 
 259 
 
 a great number of sporophylls are to be borne, the torus is 
 elongated, as in the mousetail (fig. 286); or greatly enlarged, 
 
 Fig. 285. Fig. 286. 
 
 Fig. 2S5— The torus of a flower of stonecrop (Sedum tematum), with the leaves re- 
 moved to show scars ; two leaves of each kind shown a, sepal ; />, petal ; c, stamen ; 
 ii, carpel. Magnified several diam. — After Gray. 
 
 Fig, 286.— Flower of mousetail {Afyosurus mittimus), halved; showing s, spurred 
 sepal : st, stamen ; st' , a staminode or sterile stamen, having the position and form of 
 a petal ; t, elongated torus covered with carpels, some of which are cut through. Mag- 
 nified several diam— After Engler. 
 
 FlG. 2S7.— Flower of the strawberry, halved; showing elongated and thickened torus. 
 Magnified about 3 diam.- After Bessey, 
 
 as in the strawberry (fig. 287); or transformed into ;i cup, as 
 in the rose (fig. 288). 
 
 When flowers in large numbers nre very closely associated, 
 
!6o 
 
 PLANT LIFE. 
 
 as in a head (• 104). the receptacles arc joined to form a 
 large common receptacle, as in the sunflower and its allies 
 (fig. 281). The receptacle in such plants may he a cone, 
 a dome (fig. 409), or a more or less flattened disk. In the 
 
 Fig. 288. Fig. 289. 
 
 Fig. 288. — Flower of sweetbrier rose, halved; showing urn-shaped torus. Compare fig. 
 
 139. Natural size. — Attn- Bessey. 
 I ■ , Tin- inflorescence of fig. halved lengthwise; showing common torus on 
 
 whose interior surface many flowers are formed. Two fig wasps are near the opening 
 of the flower chamber, one outside, while the other has just crawled in among the 
 flowers. Natural size. — After Kerner. 
 
 fig the common receptacle is pear-shaped, with the edges 
 almost meeting above and the flowers distributed over the 
 inner face of the fleshy sac (fig. 289). 
 
 III. Brood buds, etc. 
 
 361. Definition. — Single-celled spores pass without any 
 sharp distinction into the multicellular bodies known as brood 
 buds. For convenience, however, brood buds maybe de- 
 fined as multicellular (sometimes unicellular) bodies capable 
 
 of producing a new plant of the same phase as that from 
 which they arise. Since this is a distinction for conve- 
 nience merely, it is not desirable to distinguish brood buds 
 
VEGETATIVE REPRODUCTION. 26l 
 
 from spores until the mossworts are reached, in which the 
 alternation of phase is well marked. In their simplest form 
 such buds consist of a single cell, though more commonly 
 they are two- to several-celled. Some or all of their cells are 
 in the embryonic stage (^] 256). Like spores, they are sup- 
 plied with reserve food. 
 
 362. Simple forms. — The form of brood buds is various. 
 When not differentiated into distinct organs, they are club- 
 shaped, lenticular, or spherical. In some thalloid liverworts 
 (Marchantia and Lunularid) they are produced on the surface 
 of the thallus, surrounded wholly or on one side by an out- 
 growth from the surface forming a cup or a crescentic ledge 
 (figs. 59, 290, 291). In some mosses brood buds arise from 
 
 Fig. 290. — Thallus of Marchantia, seen from above, showing the cups containing brood 
 buds. See fig. 291. Natural size. — Alter Kerner. 
 
 the apex of the stem, either in cup-like clusters of leaves or 
 exposed (A,A f , fig. 292); in others they are smaller and 
 simpler and are developed upon the leaves (B, B\ fig. 292). 
 In all the mossworts they belong to the gametophyte. 
 
 363. Shoots. — In femwortS and seed plants the brood buds 
 belong to the sporophyte. In the latter they are espe< iallj 
 abundant, and often reach considerable size ami complexity 
 before being separated from the parent, usually consisting of 
 a short axis with a growing point and at least rudimentary 
 
262 
 
 PLANT LIFE. 
 
 91. Fin. 2152. 
 
 the development of a brood bud of Marchantia ; 
 
 ill seen from 
 
 Fig. 
 
 Fig. 291. — Six stages 
 side. I, very young 
 
 older, terminal cell divided trans- 
 versely. Ill, IV, V, successively older stages. VI. mature, cells not shown: two 
 growing points localized on right and left edges. I-V, magnified about 250 diam.; 
 VI, about 25 diam. — After Sachs. 
 
 Fig. 292. — Brood buds of mosses. A , upper part of the stem of Aulacomnium audio- 
 gynu m . with a cluster of brood buds at apex (magnified about 8 diam.), one of which is 
 enlarged 120 diam. in A', />', tip of leaf of Syrrkopodon sender (magnified about i" 
 diam.) showing brood buds ; />", some more enlarged labout 40 diam.). — After Kerner. 
 
 Fig. 293. — Young plants developing from adventitious buds on leaves of a fern (Aspic 
 vhich they readily separate to form 
 
 muni i>ulbi/,-r iiniK from ■ 
 size. />', magnified 2 diam. 
 
 plants. A, natural 
 
VEGETA TIVE RETROD L'CTION. 
 
 263 
 
 leaves. They generally arise upon the stem, more 
 
 from the leaves or the root. Upon 
 
 the stem they usually take the place of 
 
 shoots of other forms, developing from 
 
 axillary buds (figs. 294, 296). If 
 
 formed on leaf or root it is always from 
 
 adventitious buds (fig. 293). 
 
 Every possible gradation exists, from 
 the simplest to those with well-de- 
 veloped members, constituting a plant 
 of some size. They may be artificially 
 grouped as follows : 
 
 364. {a) Buds. — In these the axis 
 is short and the leaves scale-like. When 
 most highly developed the quantity of 
 reserve food is considerable and the 
 
 rarely 
 
 Fig. 294. — Fleshy buds in axils 
 of the leaves of a lily (I. ili- 
 um bulbi/eruiti). Some- 
 what reduced. — After Van 
 Tieghem. 
 
 .y^ 
 
 v\/f 
 
 t. 
 
 
 3M : 
 
 jL_I- 
 
 1 
 
 Fig. 295.— Pond weed iPolamogeton crispus). Detachment o) spe< i.il shoots, hibenuu - 
 
 ula, which are to hibernate under water. The plant ./ has one oi these shoots at the 
 tip; B lias just loosened one, /;, which is sinking to the bottom. Two thirds natural 
 size.— After Kemer. 
 
264 
 
 PLANT LIFE. 
 
 parts of the bud are often distorted 
 by the enlargement of the tissues 
 to contain the food. The fleshy 
 buds which readily separate from 
 the axils of the leaves of some 
 garden lilies (fig. 294), and those 
 which replace the flowers in some 
 cultivated onions, are well known. 
 (Compare also fig. 106.) 
 
 365. (/') Hibernacula. — Some- 
 what similar but more highly de- 
 
 Fig. 296.— A plant of stonecrop [Sedum dasyfihyllum). Offsets are produced near the 
 base on short brandies o, o ; at the tip of longer branches, o' ; and in place of the flow- 
 ers, o". Natural size.— After Kerner. 
 
 Fig. 297.— Formation of runners in the strawberry. ,t, the mother plant ; b, voung plant 
 formed at tip of first runner; c, plantlet at tip of second ; a third has put out from c. 
 Slightly reduced.— After Seubert. 
 
VEGET. I I'l I E RETROD UCTION. 
 
 265 
 
 veloped brood buds are formed at the approach of winter 
 about the base of the stem in many perennials with her- 
 baceous tops. These are separated by the death of the parent 
 stem and produce new plants 
 in the spring. Some aquatics 
 show a similar habit, dropping 
 short shoots to the bottom of 
 the water in autumn, which 
 are to grow in the spring (fig. 
 
 295)- 
 
 366. (r) Offsets, etc. — 
 Some plants produce special 
 branches, either underground 
 or aerial, which develop at 
 their extremities new plants or 
 special structures for their for- 
 mation. The housedeek or live- 
 forever (fig. 369) and stonecrop 
 (fig. 296) reproduce themselves 
 by offsets. These are short 
 branches with a rosette of 
 leaves at the tip which is read- 
 ily detached and rolls away, 
 to take root at the first oppor- 
 tunity and establish a new 
 
 plant. The Strawberry and Fig. 298.— A plant of eel-grass (Vallisne- 
 
 ria spiralis) forming new plants, a, b, at 
 
 eel-gl'aSS form long leafleSS tips of runners, arising from axils of lower 
 leaves. One third natural size. \tu-r 
 
 branches which take root at the Schnizlein. 
 
 tip and produce new plants, the slender runner subsequently 
 perishing (figs. 297. 298). The white potato forms at the 
 end of slender underground branches elongated tubers upon 
 which are numerous buds, any one of which, nourished by 
 the reserve food in the tuber, may produce a new shoot. 
 The slender stem by which the tuber is connected with 
 
266 
 
 PLANT LIFE 
 
 the main axis perishes at the end of the growing season 
 (fig. 299). 
 
 367. (d) Cuttings or scions.— Closely related to this 
 mode of reproduction is that by the separation of fleshy 
 
 Fig. 299. — A seedling potato plant. ( is the baseoi the stum, below whi< h is the primary 
 root. r. The primary leaves < t, are still present. The early leaves,./! rlre not so much 
 branched as later ones will In-. In the axils of the lower leaves arise the branchi 
 with scale leaves, e'e, and secondary roots, 1 . The tips of these branches, when 
 illuminated, bear foliage leaves, /' ; but usually they thicken into tubers,//., which 
 have scale leaves, e'i , in whose axil bud an formed, the o-called " eyes " of 
 
 the tul hi Natural size. — After Duchartre. 
 
 members, upon which are subsequently developed adventi- 
 tious buds, which give rise to new plants. The thick leaves 
 of Bryophyllum are often Mown off by storms, and produce 
 
 new plants from buds formed at the teeth along the edge. 
 
I 'EGE TA Tl I £ RETROD UCTION. 
 
 267 
 
 Some species of Kleinia, natives of Cape Colony, have fleshy 
 Stems, jointed at intervals, so that they easily break there. 
 When broken off by an accident, the piece rolls away, takes 
 root from the under side, and sends up shoots from the upper. 
 
 Advantage is taken of this power of severed parts to form 
 adventitious roots and shoots in the artificial propagation of 
 domestic plants. Suitable portions of shoots or leaves for 
 the development of new plants under proper conditions are 
 called cuttings, scions, or "buds." They may generally be 
 grown in water or soil ; or they may be securely fastened in 
 a slit or wound in another plant. The latter process is 
 known as grafting or budding, according to the form of the 
 implanted part. Indeed brood buds in general may be 
 looked upon as natural cuttings or scions. 
 
 368. Branching. — A further modification of this method 
 of reproduction is to be 
 served in the formation 
 new individuals through pro- 
 gressive death of the older 
 parts. If a plant, dying thus, 
 be a branching one, death will 
 sever the branches as it reaches 
 them sooner or later, and 
 each branch then becomes an 
 independent plant. This is 
 seen in its simplest form in 
 those plants which have a hori- 
 zontal branching thallus whose p 
 base dies as the apex elongates Fig. 300.— Outline of a thaiius of u„>- 
 
 \ 1 • • chant ia geminata. The base D is 
 
 (fig. 300). It IS common in dying as the apices are growing and 
 
 branching. Wheti death reaches the 
 plants with underground Creep- first fork there will be two independent 
 
 plants; at the second there will be four, 
 
 mg* stems which send up aerial andsoon. 
 
 leaves or shoots annually, as do the ferns of temperate regions 
 
 and main glasses and mints. 
 
CHAPTER XVIII. 
 
 SEXUAL REPRODUCTION. 
 
 369. Cell union. — All methods of sexual reproduction 
 consist in the formation of a single cell by the union of two 
 specialized cells, known, respectively, as the male gamete and 
 the female gamete. The essential step in their union is the 
 coalescence of the nuclei. The cell thus formed is capable 
 of developing into a new plant under suitable conditions, 
 and is, consequently, a spore. Such sexually produced spores 
 must not be confounded with non-sexual spores (see ^[ 304). 
 
 370. Origin. — It is scarcely to be doubted that the earliest 
 methods of reproduction were vegetative, and that sexuality 
 has been acquired by a gradual modification of cells previ- 
 ously devoted wholly to ordinary processes of growth. The 
 probable history of the origin of sexual cells and sex organs 
 can onlv be inferred from the fact that the simplest plants 
 show no sexuality, others show imperfect sexuality, and still 
 others complete sexuality. The data are very imperfect, but 
 they enable us to form at least an intelligent idea of how 
 sexuality may have been acquired. 
 
 Theory of sexuality. 
 
 371. Rejuvenescence. — Among the processes of growth 
 in the simpler plants, especially the fission-algne (^[ 11), one 
 of the most striking is that known as rejuvenescence. In this 
 process the protoplasm of the cell escapes from the cell-wall, 
 and acquires special motor organs known as cilia, which en- 
 
 268 
 
SEXUAL REPRODUCTION. 269 
 
 able it to swim rapidly, but apparently aimlessly, through the 
 water. In this form it is essentially a zoospore. (See ^ 306.) 
 After having moved about for a variable time and perhaps 
 increased its volume by growth, it loses its cilia, surrounds 
 itself again with a cell-wall, and resumes its ordinary mode of 
 life. In filaments of some multicellular algae a similar process 
 occurs. The contents of any cell may escape by the solution 
 of the cell-wall and become a zoospore. After swimming 
 about for a time the zoospore may come to rest, secrete a 
 cell-wall, and by repeated divisions in one plane produce an 
 individual similar to the parent. (See ^| 24.) It is evident 
 that such a method would give rise economically to a con- 
 siderable number of individuals. The process is essentially 
 the separation of the filament into pieces, each being the 
 contents of a single cell. 
 
 372. Conjugation. — In other filamentous algae the cell- 
 contents, instead of escaping as a single zoospore, divide into 
 two or more zoospores. If, while these are still active, two 
 accidentally collide, the possibility of their adherence and 
 and the fusion of the two into one is conceivable. Such 
 fusion actually occurs among the zoospores of alga;, and is 
 (ailed conjugation, but in observed cases it follows a definite 
 method, and is not merely accidental. It is probable, how- 
 ever, that the first occurrence of conjugation was accidental, 
 and that it has become fixed and definite because those indi- 
 viduals in which it occurred with most certainty and regular- 
 ity thereby produced the most vigorous offspring. 
 
 373. Imperfect sexuality. — In the alga Ulothrix, we have 
 a plant in which many of the processes just described still 
 occur. It produces zoospores of two kinds: (1) large ones, 
 with four cilia (C, fig. 301), formed in pairs in each cell (B) ; 
 (2) small ones, having two (rarely four) cilia, and arising 
 eight or sixteen from each mother cell (D). Both these sorts 
 of zoospores will grow, after a period of swimming, into new 
 
270 
 
 PLANT LIFE. 
 
 plants, though the small ones produce very slender, weak fila- 
 ments (fig. 302). Beside the zoospores, Ulothrix produces, 
 under certain conditions, gametes, which are precisely like 
 
 Fir,. 301. — Ulothrix zonata. .1, a young filament with rhizoid cell, r, at base. B, bit 
 of a filament from whose cells large zoospores are escaping through a pore in the side- 
 wall. C, a single large zoospore. D, bit of a filament from whose cells small zoo- 
 spores lor gametes 1 are esi aping / ■', small zoospores lor gametes . /•', gametes con- 
 jugating, (r, same, conjugation complete. //. zygote, before formation of wall to 
 become a resting spore. Magnified 4S2 diam. — After Dodel-Port. 
 
 the small zoospores in appearance. But their behavior is 
 different. They usually conjugate freely in pairs and produce 
 resting spores. If, however, they do not conjugate, each 
 
SEXUAL REPRODUCTION. 
 
 2 7 I 
 
 may round itself off and, alone, become a resting spore. 
 These resting spores, after a dormant period, germinate and 
 develop into new plants. 
 
 In llothrix, therefore, the gametes are imperfectly sexual. 
 Failing to conjugate, as many do, they may still develop into 
 new individuals. A con- 
 sideration of the appearance 
 and behavior of the gametes 
 leaves little doubt that they 
 are merely small zoospores 
 which have acquired imper- 
 fectly the habit of conjuga- 
 tion and retained partially 
 the power of independent 
 growth. 
 
 374. Further develop- 
 ment. — -The perfecting of 
 reproductive methods fol- 
 lowed the two lines just sug- 
 gested. On the one hand, 
 complete sexuality was ac- 
 
 Fir.. 302.— Sporelings of Ulothrix zon.it*. 
 quired by certain Cells, while a, a young plant from a large zoospore. 
 
 />, young plants from small zoospores which 
 Others Were more Completely germinated without leaving the mother cell. 
 
 Magnified 4S2 diam.— After Dodel-Port. 
 
 specialized as non-sexual re- 
 productive bodies. The latter have already been discussed 
 
 (T3°4ff-)- 
 
 Tracing now only the line of sexual development, it is 
 probable that the first step in this differentiation was the 
 failure of some of the zoospores to escape from the cell pro- 
 ducing them. From this point two lines of development 
 diverge. 
 
 375. 1. Isogamy. — Along one of these lines, the zoo- 
 spores ceased to form cilia, and became non motile sex 
 cells, in some cases similar in form and function, and in others 
 
272 
 
 PLANT LIFE 
 
 like 
 
 in form but unlike in behavior. This leads to the com- 
 pletest form of conjugation, as seen 
 in Mesocarpus, Spirogyra, and other 
 Conjugate. (See *[ 25.) In these 
 the contents of one cell of a filament 
 enter those of another either by a 
 partial solution of the partition-wall 
 between them or by the formation of 
 a tube-like outgrowth from one or 
 both of the cells concerned, so that 
 when these tubes come in contact and 
 have their ends absorbed the contents 
 of one cell passes over into that of 
 the other (fig. 303). The cells con- 
 jugating in this way may he either 
 neighboring cells of the same fila- 
 ment or cells of different filaments 
 brought into proximity by acccident. 
 
 Fig. 303 —Conjugation of .S> iro- , 
 
 gymquinina. The cells a, a' In the course of development in this 
 
 are just forming the conjugat- . . , . 
 
 ing tube; the contents not yet direction conjugation reaches its 
 fully reorganized as gametes. _ i ■ i 
 
 The body protoplasm is not highest perfection, being secured with 
 
 shown in these two cells, ... . , . 
 
 though it is in the others such certainty that non-sexual methods 
 
 (compare fig. 25, of another . 
 
 species of Spirogyra). The are almost entirelv abandoned. 
 
 cells b, b' have completed the «.„„_,, „, 
 
 tube ; the ends have been dis- 376. 2. Heterogamy. — i he second 
 
 solved and the contents of b 
 
 is passing over into b' . This lj ne of development Was followed In- 
 process is nearly completed in 
 
 cells c, c'. 2, 2, zygotes, with other algae, and the method proved so 
 
 protecting wall, thereby pre- ... , - 
 
 paredto become resting spores, efficient that it became the dominant 
 
 Magnified 150 diam. — After 
 
 Strasburger. one in the plant kingdom. Among 
 
 these algre there occurred a differentiation of the zoospores. 
 The first step in this differentiation was an increase in size 
 of one of the sex cells, so that they differed both in action 
 and in form. To distinguish one from the other the larger 
 sex cell is called the female cell, or egg, and the smaller, the 
 male cell, or sperm. A further difference arose in the com- 
 
SEXUAL REPRODUCTION. 
 
 273 
 
 plete loss of motility by the female cell (fig. 304). When 
 these differences exist in the sex cells their union is no 
 longer called conjugation, but fertilization, the active male 
 cell being said to fertilize the quiescent female ( ell. 
 
 377. Sex organs. — A further stage in the development of 
 sexuality is reached when the cells producing the sperms or 
 
 Fig 
 carpus. /■. sperm 
 
 Differentiation of gametes in some marine algae 
 lost 
 
 1. ./. 1 
 the extreme "I difference in she in gametes. All magnified equally (about 700 diam.), 
 
 egg of Za 
 
 before fertilization which is about to occur in (/ 
 
 ke gametes of Keto- 
 ne egg loses its cilia and rounds itself 
 . sperm, _/. egg of incus. This is 
 
 the eggs are differentiated. The cell or the Organ producing 
 the egg has been known by various names in different groups 
 of plants. An appropriate general name for it, without refer- 
 ence to its structure, is the ovary. (See further* 335.) 
 
274 PLANT LIFE. 
 
 The male organ was called the antheridium, from the idea 
 that it was like the anther of seed-plants, which was once 
 supposed to be the male organ of the flower. There is no 
 special objection to the name, but a more appropriate one for 
 it is the spermary, since these male cells are known as the 
 spermatozoids or, briefly, the sperms. 
 
 The final step in the development of sexuality is the restric- 
 tion of the formation of sex organs to a certain phase in the 
 life history of the plant, which is therefore known as the 
 sexual phase, or gametophyte, the remaining phase or phases 
 being called, for the sake of distinction, non-sexual, and con- 
 stituting the sporophyte. The gametophyte alternates with 
 the sporophyte, giving rise to the phenomenon known as the 
 "alternation of generations." (See % 55.) 
 
 378. Directive agents. — To secure the union of the male 
 and female cells, the male gamete must be directed to the 
 female. By what means this is accomplished is not fully 
 known. Organic acids and sugar exercise such an influence 
 on certain sperms that they swim towards the source of these 
 substances. The wide distribution of such compounds sug- 
 gests that probably their presence in the female gamete may 
 render it attractive. W this is true, the sperms exhibit a spe- 
 cial irritability towards these materials, whose diffusion acts 
 as a stimulus. 
 
 Isogamy. 
 
 Sexual reproduction, as developed among existing plants, 
 shows two main types, known as isogamy and heterogamy. 
 
 379. Isogamy is thai mode of sexual union in which the 
 size and form of the gametes is alike. In some cases the 
 behavior also of both male and female isalike, while in others 
 the male shows a greater power of movement. When both 
 are equally motile and escape from the cell, conjugation occurs 
 wherever they happen to come in contact. The form is usually 
 
SEX i A L KEF ROD UCTION. 
 
 ?75 
 
 pear-like {E, fig. 301). The protoplasm at the narrower end 
 is more transparent and hears two or more 
 cilia ; while the larger end is occupied hy 
 the reserve food and particularly the chloro- 
 plasts, if present. Union of free motile 
 gametes occurs by gradual coalescence, be- 
 ginning at the pointed, transparent end {F, 
 fig. 301). When the conjugation is com- 
 plete the resulting spore (zygote) usually 
 acquires a spherical form, soon secretes about 
 itself a wall, and either begins to grow at 
 once into a new plant or thickens the wall 
 and becomes dormant for a time as a resting 
 spore. In other cases the form of the 
 gametes is determined only by the shape of 
 the cell, from which they do not escape. The 
 entire cell contents constitutes the gamete 
 (figs. 303, 304). In such plants both 
 gametes may be equally motile and meet 
 in a branch, the conjugating tube, to form a 
 spore, as in Mesocarpus (fig. 304) ; or the 
 male gamete may be motile and migrate from the cell in 
 which it is produced, through the conjugating tube into the 
 cell containing the female gamete, with which it fuses, as in 
 Spirogyra (l^. 303). 
 
 The spore thus formed may be a resting spore, in which 
 case it secretes about itself a thick wall, and remains dormant 
 for several weeks or months. In the plants just referred to, 
 the spores, funned in early summer, with the remnants of the 
 parent cell-walls about them, sink to the bottom of the water, 
 and do not germinate till the next spring. 
 
 Fig. 305. — Conjugation 
 of Mesocarpus. The 
 contents of the two 
 upper cells are accu- 
 mulating in the con- 
 jugating tube to form 
 a zygote, which is 
 complete in the 
 lower tube. Magni- 
 fied about 150 diam. 
 — After DeHary. 
 
276 
 
 FLAX J- LIFE. 
 
 Heterogamy. 
 
 Heterogamy is that mode of sexual union in which the sex 
 cells are unlike, being differentiated into sperms and eggs. 
 
 380. The sperms. — The body of the sperm is the cell 
 nucleus, surrounded by a small amount of protoplasm which is 
 often extended into one or more cilia (fig. 306). The more 
 complete the differentiation of the sperm the smaller, as a 
 rule, is the amount of body protoplasm. Whether or not the 
 sperm is motile depends upon the conditions to which it has 
 become adapted. Whenever motile, fertilization must occur 
 in the presence of water of amount sufficient to permit the 
 sperm to swim to the egg. 
 
 Fig. 306. — Sperms of various plants, showing variety of form, t, Volvox aureus; 
 1, Vaucheria synandra . ;, Ckarafragilis ; 4, Fucus serratus ; 5, Marchantia 
 7, Marsilia vestita. Magnified kk»i 
 
 polymorpha : 6, Equisetum Telmatei 
 diam. — After Mbbius 
 
 The spermary may produce only one sperm (fig. 307), or 
 its contents may divide into many (fig. 310). When single, 
 
SEX I A 1 REPROD UCT10N 
 
 2/7 
 
 the form of the sperm is usually that of the cell in which it 
 is produced. U it is set free, it may become globular, and 
 have slow amoeboid movements, or it may be entirely im- 
 motile. In the latter case it must depend upon the move- 
 ments of the water into which it escapes for transference to 
 the vicinity of the egg. The sperm may be ovoid and fur- 
 nished at the end with one or more cilia ; or elongated and 
 bent or coiled one or more times. The elongated forms 
 have almost invariably two to many cilia (fig. 306). 
 
 381. The spermary. — The organ in which the sperms are 
 produced is the spermary or antheridium. It is either simple 
 or compound. A simple spermary consists of a single cell 
 whose contents is transformed into one or more sperms. 
 Simple spermaries occur only in algae and fungi, and by 
 reduction among seed- plants. (See ^[ 
 3S5.) If more than one sperm is to be 
 formed, the nucleus, originally single, 
 becomes divided into as many parts as 
 there are to be sperms (sometimes into 
 more than become mature). The total 
 number of sperms produced by a plant is 
 related somewhat to the number of eggs, 
 but particularly to the chances of the 
 sperms reaching the egg. 
 
 If there is but a 
 
 Fig. 307.- The sex organs 
 
 ingle sperm iormeu of Peronospora. /;, 
 
 ' hvplia which has devel- 
 
 bv each spermary, either the number ot oped at the end the 
 
 spermaries is great or some adaptation 
 
 exists for the certain transfer of the sperm 
 
 to the e^g. In Cystopus and its allies, 
 
 for instance, a branch of the spermary 
 
 grows into the ovary, through which the 
 
 sperm passes to the egg (fig. 307). 
 
 A simple spermary arises either by the 
 
 egg (the centra] 
 dark sphere <'.■'. hypha 
 which lias developed the 
 
 spermary. >:. who 
 toplasm, constituting .1 
 single sperm, is passing 
 through the fertilizing 
 tube (a branch ol the 
 
 Magnified $50 diam 
 Aftei DeBary. 
 
 differentiation of 
 
 one of the ordinary cells, or of a special lateral branch, as in 
 
2 78 
 
 PLANT LIFE. 
 
 the filamentous algae and fungi (figs. 307, 308). In the 
 thallus of multicellular algas it may be the terminal cell of a 
 
 a A 
 
 Fig. 308. — Sex organs of water flannel {I'aucheria sessilis). A, a portion of filament 
 with two lateral branches, a, Ag. In a the spermary has already heen divided from 
 the body cavity by a partition wall. In r'x , a partition will form at juncture with main 
 axis (see fig. /■). when . , becomes the ovary. B, the ovary, mature, having opened 
 and extruded .v/, a portion of the protoplasm.. What remains is the egg. The chloro- 
 plasts have accumulated, leaving a clear receptive spot opposite entrance of ovary. ( , 
 sperms, which escape at maturity from A, <i. D, ovary with egg about to be fertil- 
 ized; the sperms have collected at the opening. A, />', /», magnified about ioodiam. 
 C, magnified much more (about 350 diam.?). A, />, after Sachs; />', C, after Prings- 
 heim. 
 
 branch or, in the leaf-like forms, a cluster of surface cells. 
 In Fucus the spermaries (figs. 309, 310) are terminal cells 
 of much-branched hairs which J 
 
 develop from the surface cells 
 of a narrow-mouthed pit like 
 
 
 Fig. 309.— A portion of a branched hair from a conceptacle of bladder wrack (/■:,, us 
 vesicutosus). The darker cells are the spermaries. Magnified 160 diam. — After 
 Thuret. 
 
 Fig. 310. — Spermaries of Fucus vesiculosus, showing the escape of the sperms. Magni- 
 fied 350 diam. — After Thuret. 
 
SEX UA L RE PROD UCTIOX, 
 
 279 
 
 that for the ovaries (fig, 326). (See also fig. 42.) The 
 sperms are set free by the rupture of the wall of the spermary. 
 382. A compound spermary consists of one or more cells 
 in which the sperms are to be produced (each correspond in- 
 to a simple spermary), surrounded by a wall formed of a 
 single layer of cells (rarely more). Compound spermaries 
 are found only in Characese, mossworts, and higher plants. 
 The spermary is a spherical or elongated sac, raised upon a 
 stalk, or sessile ; free upon the surface of the plant, or sunk 
 in a pit (fig. 311). The cell in which each sperm is formed 
 
 Fig. 
 
 longitudinal section ot a male head of Marchantia. t, portion of 
 
 thallus ; ha, enlarged head or receptacle; a, spermaries, sunk in pits opening at 0. 
 Magnified about 15 diam. />', compound spermary. a/, its wall, surrounding the 
 immense number oi minute regularly arranged sperm mother cells; st, its stalk. 
 Magnified about & 1 diam. —After Sai hs. 
 
 is called a "sperm mother cell." Each contains a single 
 nucleus which enlarges to form the sperm of that cell (fig. 
 312). The sperms arc set free by the breaking down of the 
 walls of the mother cells at about the same time that the 
 outer wall of the spermary is ruptured by the destruction of 
 one or more of its cells. 
 
 The form of the vegetative body of the gametophyte in all 
 
2 SO 
 
 PLANT LIFE. 
 
 but the seed plants was described in Part I. The forms of 
 the spermaries are as follows: 
 
 383. Chara. — The compound spermary of Chara (fig. 
 313) consists of a spheri< al case composed of four triangular, 
 plate-like cells; from the inner face of each projects a 
 handle-like cell to whose end are attached 24 filaments, each 
 composed of 100-200 disk-shaped cells. Each of these con- 
 
 Fig. 312. — Development of a sperm of a liverwort I Pellia epiphylla\. n, mother cell 
 with nucleus, the latter approaching the wall ; 6 to h, nucleus elongating and curving 
 into an arc, and finally a spiral coil; e, an edge view, showing origin of cilia from 
 peripheral protoplasm ; /, also an edge view; k, mature sperm, free. Magnified iooo 
 diam. — After ( luignard. 
 
 tains a sperm; so that each spermary produces 20,000- 
 40,000 sperms. 
 
 384. Mossworts and fernworts. — In the mossworts the 
 
 spermary is a stalked body, whose internal cells are the sperm 
 mother cells, the outer laver forming the spermary wall (fig. 
 
 In the fernworts the spermary is sessile and the number of 
 mother cells is much smaller (fig. 314), corresponding to the 
 reduction in size of the gametophyte (see • 395)- When 
 the gametophyte is greatly reduced, as in the club-mosseSj 
 a single spermary only is formed, which is even larger 
 than the rest of the gametophyte (fig. 315). 
 
 385. Seed plants. — In the seed plants the male gameto- 
 phyte begins to be formed before the microspore leaves the 
 sporangium. In gymnosperms the spore divides into two to 
 six cells, one or two of which represent the vegetative part 
 
SEXUAL REPRODUCTION. 
 
 28l 
 
 Chara. bear- 
 
 ol" the gametophyte and the others the spermary (fig. 316). 
 In angiosperms the vegetative part seems to have vanished 
 and the two cells which are formed constitute the spermary, 
 the smaller representing 
 the sperm cells and the 
 larger the wall cells (fig. 
 317; compare fig. 315). 
 Sometimes, indeed, the 
 smaller cell is only repre- 
 sented by a nucleus, no 
 partition wall being pres- 
 ent. Thus, the spermary 
 in all seed plants has almost 
 become a simple one again 
 by reduction from the com- 
 pound spermary of their 
 ancestors 
 
 reduction of the male game- 
 tophyte, that is, to a sex 
 organ alone, almost all trace 
 of resemblance to a plant 
 has been lost, and it is diffi- 
 cult to think of the pollen- 
 grain (microspore) as pro- 
 ducing a real plant. This 
 male plant, though ex- 
 tremely small and simple 
 even when mature, is the 
 exact homologue of the 
 larger male plant produced 
 by the spores of the mosses, ferns, horsetails and selaginellas. 
 386. Pollen tube. -The maturity of the male gametophyte 
 is reached only alter the microspore has been caught by the 
 moist surface | fluid in the micropvle or on the stigma | pro- 
 
 By this extreme Fig. 313.— A, part of a "leaf 
 
 ing sexual organs. /\ leaf; p. undeveloped 
 "leaflets"; 0', leaflet; /3", leaflets of the 
 branch, sc; the dark oval body is the ovary 
 containing the fertilized egg; ,v, five cortical 
 cells which have grown spirally around the 
 ovary proper and become adherent to it ; 
 they terminate in . , the five crown cells, be- 
 tween which the sperm makes its way to the 
 egg; ,1. the spermary, showing four of the 
 s toothed plates of which its wall is composed, 
 and the center ot each to which on the inside 
 the handle cell is attached. Magnified 33 
 diam. /•'. longitudinal section through young 
 "node" of a "leaf " of ( lhara, showing origin 
 and young stage ot sexual organs. / and in 
 stand in the c omers ot the adjacent tnternodal 
 .ells; between them is the thin nodal cell 
 
 from which arise ;< and the sexual organs .vX- 
 and ,1 ; br, cortical tells co 
 is the young ovary not yet overgrown by the 
 cortical cells at its side's. ,,. the spermary, 
 
 shows four wall cells outside, from which 
 their handle cells have just been divided; 
 all too young to shew relative sizes or shapes. 
 Magnified 2 1" diam Alter Sat hs. 
 
282 
 
 PLANT LIFE. 
 
 vided to receive it. The wall cell remains undivided and 
 grows to form an unseptate filament, called the "pollen 
 tube" (figs. 317, 318, 319, 321, 322, 323). In gymno- 
 
 Fig. 314. 
 
 Fig. 314. — Vertical median section of the mature spermary of a fern [Adiantutn 
 capillvs-veneris). /. adjacent cells of gametophyte (figs. 74, 77) j , ( , spermary, show- 
 ing wall composed of three cells, the two lower (above and below letter a) being ring- 
 like. The chloroplasts have accumulated on the inner face. The interior cell, origi- 
 nally single, has divided into a number, the sperm mother cells, which at this stage are 
 loosened and contain each a fully developed coiled sperm. Magnified 550 diam. — 
 After Sachs. 
 
 Fig. 315. — A vertical median section of the gametophyte of Selaginella stolonifera. 
 />, a single cell representing the vegetative part of the gametophyte (compare figs. 74, 
 314) ; w, the cells forming the wall of tile spermary; ,f, the mother cells of the sperms, 
 each containing one sperm and now loosened from each other. The gametophyte with 
 its single spermary scarcely exceeds the size of the microspore which produces it and 
 therefore only just bursts the outer wall of the spore. The solution of the wall cells 
 w allows the sperms to escape. Magnified 640 diam. — After Strasburger. 
 
 Fig. 316.— Diagram of the gametophyte of the larch (Larijc Europaa), formed in the 
 microspore. /, the vegetative cell ; st , two stalk cells of the spermary; s, cell whose 
 nucleus subsequently divides to form two sperms (the walls of the mother cells not 
 forming) ; w, the wall of the spermary which remains undivided. Compare fig. 315. 
 
 sperms this penetrates the megasporangium (ovule body) and 
 reaches the female gametophyte on whose surface are formed 
 the ovaries (figs. 319, 320, 321, 322). In the course of its 
 development the sperm cell loosens itself and migrates down 
 the tube. Its nucleus is set free by the disorganization of the 
 wall of the cell (if formed) and usually undergoes division, 
 thus making two or more sperms (figs. 321, 322). These 
 escape through the ruptured wall of the end of the tube, 
 pass between the neck cells of the ovary and so fertilize the 
 
 egg (11 39 3> fi g- 32i)- 
 
 In angiosperms, in order that the sperm may reach the 
 egg, the pollen tube must grow through the tissues of the 
 stigma and style, or pass down the style canal to the interior 
 
SEX UA L REP ROD UCTION. 
 
 283 
 
 of the ovulary, then through the micropyle (fig. 323), and 
 finally penetrate the megasporangium. The sperm nucleus 
 then fuses with the egg nucleus (see ^[ 369). 
 
 Fig. 317- 
 
 Fig. 31 
 
 Fig. 319. 
 
 Fig. 317. — Gametophyte of the pinesap (Monotrofla Hypopitys). <?, microspore show- 
 ing two cells; the smaller being the sperm cell and the larger corresponding to the 
 wall of the spermary, undivided. /■. the same, 6 hours later, showing the pollen tube 
 developed from the larger cell. The smaller one has become disorganized ami its 
 nucleus isttll undivided into sperms! and that of the larger cell have migrated into the 
 tube. Magnified too diam. — After Strasburger. 
 
 FlG. 318. — One stage in the fertilization of the egg of an orchid {Orchis latifolta). The 
 pollen tube, /», has entered the narrow micropyle, «/, of an ovule, and reached the 
 megaspore e, the upper half of which only is shown with three eggs (two imp rfi 1 1), 
 In the pollen tube, just above and below the entrance of the micropyle, are the two 
 sperms, s. s' . Magnified 3in.di.1m. After Strasburger. 
 
 1 1 11. Longitudinal section through the ovule oi the larch and the placental scale 
 to which it is attached. /, placental stale; ^, vascular bundles; ;/. megasporangium ; 
 i, integument; . , female gametophyte inside megaspore wln.se limit is shown b) oval 
 line; ,;, ovary;/, pollen-tube. Magnified 14 diam. — After Strasburger, 
 
 The growth of the spermary as a tube within which the 
 sperms may migrate to the egg is necessary because the female 
 gametophyte is forced to develop within the megaspore, 
 which is not released from the sporangium. In angiosperms 
 the further enclosure of the megasporangia in the sporophyll 
 (carpel) makes it necessary for the tube to be sufficiently long 
 
284 
 
 PL A. XT LIFE. 
 
 to traverse the pistil. Pollen tubes may, therefore, grow 
 10-15 cm. in length. Usually the older part of the tube dies 
 
 Fig. 322. 
 
 Fir,. 320. — Anterior fourth of female gam'etophyte of spruce {Picea exceka), showing 
 two ovaries. <\ tissue ot gametophyte (endosperm); a, egg; k. nucleus oi egg; /;, 
 neck of ovary (the line does not reach the neck, which is situated in a depression of the 
 plant below // : the shading shows the side (d this slope); kz, neck canal cell. See fig. 
 321. Magnified 50 diam. -After Strasburger. 
 
 Fig. 321.— A portion of the ovary of the spruce, seen as in fig j ■■ but magnified 165 
 
 diam. The cell kz of lie,. 320 has bei mm .h -. u j.ini/ed to make way for the pollen 
 tube,/, which has pushed between the neck cells and reached the egg, r, into which 
 one of the sperms in its tip is about to enter, g, tissue of the female gametophyte.— 
 After Strasburger. 
 Fig. 322. Upper part of ovule of red cedar, with integument removed. >ni, mega- 
 sporangium ; ctl, female gametophyte with three ovaries oi .11 luster of six ; /, pollen 
 tube. Each ovary shows an elongated egg and above the small neck cells. The left- 
 hand pollen tube has two sperms about to pass between neck cells into an egg. Magni- 
 fied 67 diam.— After Strasburger. 
 
 as the tip advances. The food needed is chiefly derived 
 from the cells of the stigma and style which it disorganizes. 
 
SEXUAL REPRODUCTION. 
 
 285 
 
 387. The egg. — The egg is larger than the sperm, usually 
 non-motile and fixed. In aquatic algre the egg is sometimes 
 
 Fig. 323. — Diagram of a lun^iti.iuni.il >cl tii.n of a pistil with one ovule, s, stigma, on 
 which are lodged two pollen grains ; ; . style ; a, 01 ulary ; /. >/, at, //, together form 
 
 the Ovule ; /, stalk ; //, niega>poi,mgium ; ,; /', outer integument ; //. inner integument ; 
 r. megaspure. will) nucleus which is to develop later into vegetative part ol female 
 plant; i, antipodal cells ; k, egg, and near by another ; m, micropyle j /, polli 
 
 entering it and reaching egg. -Alter I.ucrssen. 
 
 free, escaping from the ovary in which it is produced, and 
 being fertilized by the sperms, which arc likewise tree in the 
 water, as in Fucus (fig. 324). Sometimes the egg itself is 
 ciliatedand hence motile. In these cases it meets the motile 
 sperms in the water. 
 
 The form of the egg is much less variable than that of the 
 
(86 
 
 PLANT LIFE. 
 
 sperm. It is almost always ovoid or globular. The small 
 amount of body protoplasm of the sperm may be looked upon 
 as merely accessory. That of the egg, however, is usually 
 abundant and well supplied with reserve food, and it takes 
 part after fertilization in the formation of the new plant. 
 
 388. The ovary. — The organ in which theegg is produced 
 is the ovary (oogonium, carpogonium, or archegonium). 
 Usually but one egg is produced in each ovary, though as 
 many as eight are formed in the Fucacere 
 (fig. 327). The ovary is either simple 
 or compound. 
 
 389. A simple ovary consists of a 
 single cell, the bulk of whose proto- 
 plasm becomes one egg (or several).. ($ 
 
 324. Fig. 325. 
 
 Fig. 324. — Egg of Fiichs as it floats in sea-water, surrounded by many sperms, one of 
 which eventually plunges into it, unites with its nucleus and so fertilizes it. Magnified 
 350 diam. — After Thuret. 
 
 Fi<;. 325. — Portion of two ovaries of an alga {Spkeerofilea annulina). The upper part 
 contains two eggs, and a number of sperms which have entered through the pore at 
 the side. The lower egg of the two shows the receptive spot above. A sperm is 
 partially imbedded in the protoplasm of this part in process of fertilization The 
 egg in the lower ovary has been fertilized and has secreted a thick wall, thus becom- 
 ing a resting spore. Magnified 500 diam. — After Colin. 
 
 A portion of the protoplasm of the ovary is almost invariably 
 excluded from the egg (B, fig. 308). The sperms reach the 
 egg either through an opening formed in the wall of the 
 ovary (D, fig. 308, 325), or through a tube formed by the 
 spermary, which penetrates the ovary (fig. 307). 
 
SEX UA L REPR OD U CTION. 
 
 287 
 
 Simple ovaries occur only in the algseand fungi, where they 
 are known as oogonia or carpogonia. They are either pro- 
 duced by the modification of one of the cells of a filament 
 (fig. 325), or they are the terminal cell of a special branch 
 (fig. 308). Usually the ovary is decidedly larger than the or- 
 dinary vegetative cells. The fertilized egg often becomes a 
 resting spore (fig. 325). 
 
 in the higher algae, especially the marine algae, the ovaries 
 are often aggregated in special pits, the conceptacles, as in 
 
 m 
 
 Fig. 326.- A section through a female conceptacle of bladder wrack (Fucks vesiculo- 
 sits); showing form <il pit. the numerous hairs with which it is lined, and ovaries in 
 various stages . . t development. In the tissue about the pit note the cortex oi densely 
 plated cells and the loose network of filaments in the interior. Magnified 50 diam. — 
 After Thuret. 
 
 Fucus (figs. 42, 326). Here the ovary is formed by the en- 
 largement of the terminal cell of a two-celled outgrowth from 
 the surface (\'\y;. 327). The eight eggs are set free and are 
 fertilized in the water 1>\ the motile sperms (fig. 324). They 
 grow at once into new plants. 
 
 The simple ovary is surrounded in Chara (fig. 313) by a 
 jacket of spirally coiled cells, which grow up from beneath it 
 and make it look as though it were compound (•' 390). 
 
288 
 
 PLANT LIFE. 
 
 The most highly developed simple ovary (the carpogonium) 
 occurs in the red algae, in which it is often differentiated into 
 the ovary proper (which does not always form a distinct egg | 
 and a long branch, the receptive apparatus, or trichogyne, 
 to which the sperm adheres and through which its nucleus 
 
 Fig 329. 
 
 Fig. 327. Ovary of bladder wrack (Funis vesicuiosus), with some of the hairs. The 
 ovary is raised on a stalk cell ; it contains 8 eggs, of which 6 are shown. Magnified 
 160 diam. After Thuret. 
 
 Fig. 328.— The ovary of a red alga {Nemalion multifidum). A , in process of ferti- 
 lization, rco, egg nucleus (a dark chromoplast lying near); sp, sperm which has ad- 
 hered to the trichogyne t and caused the absorption of the wall there : ns, the sperm 
 nucleus on the way down the iii. Imumh- /•'. ,1 later stage, no and ns about to unite. 
 Magnified about 600 diam. — After Wille. 
 
 I'ii. \ In. null nt .1 red sf.iweed ( rolyslfihoniti ofiaca) bearing cystocarps (the 
 
 black dots). See fig. 330. Natural size. — After ECUtzing. 
 
 travels to the ovary proper (fig. 328). The result of fertiliza- 
 tion is the production, often by a very complicated process 
 of growth, of a spore-producing body, the cystocarp (figs. 
 329, 330). The cystocarp is, in part, the homologue of the 
 sporophyte phase of higher plants. From its interior non- 
 
SEX UA L RE PR OD UCTION. 
 
 289 
 
 sexual spores arise (fig. 330), which produce the gametophyte 
 again. 
 
 390. A compound ovary consists of a central row of cells 
 (each of which is homologous with a simple ovary) surrounded 
 
 Fig. 330. — A , a bit of a red seaweed bearing a mature cystocarp ; seen from the side. 
 The spores show through the translucent wall. />'. a diagram of a section through the 
 same, showing spores as enlarged terminal cells of twigs arising from a basal cell of the 
 cystocarp. The shaded parts arise from the fertilized egg (= a sporophyte), the case 
 developing by induced growth. Magnified 25 diam. — After Falkenberg. 
 
 by a wall composed of one or more layers of cells. Of the 
 central cells only the lowest produces an egg. The upper 
 ones break down into mucilage, by the swelling of which the 
 ovary is opened, and by its escape in whole or part a canal is 
 formed leading to the egg (fig. 332). Down this canal the 
 sperms make their way, and one fertilizes the egg. 
 
 The compound ovary is known as an archegonium. When 
 best developed, it is a flask-shaped structure [f\i;. 331) con- 
 sisting of a body and a neck. In the body is the cell con- 
 taining the egg. Compound ovaries may be stalked, sessile, 
 or sunk in the tissues of the gametophyte. They are found 
 only in mossworts, fernworts, ami seed plants. In the latter. 
 however, they are simplified out of all likeness to the form 
 dese lilted. 
 
 391. Mossworts. — When the gametophyte is differentiated 
 into stem and [eaves, as in mossworts alone, they are formed 
 upon the stem. Usually several are developed in the same 
 neighborhood, when they are generally protected by over- 
 
290 
 
 PLANT LIFE. 
 
 arching leaves (fig. 331). In the same cluster there may be 
 spermaries, or these may be on a different part of the same 
 plant, or on another plant. 
 
 Fig 33" 
 
 Fig. 332. 
 
 Fig. 331.— Longitudinal section through the tip of a shoot of a moss (Funaria hygro- 
 metrica). st, stem ; />, leaves protecting the ovaries a. Magnified ioo diam.— After 
 Sachs. 
 
 Fig. 332. — A vertical section of the gametophyte of a fern ( Pteris serrulata). g, vege- 
 tative tissue of gametophyte, with chloroplasts ; e, .body of ovary sunk in gameto- 
 phyte. surrounding the spherical egg; «, neck projecting and curved; /«. mucilage 
 formed by disorganization of canal cells and escaping, having pushed apart terminal 
 cells of neck. Magnified 260 diam. — After Strasburger. 
 
 392. Fernworts and seed plants. — When the gametophyte 
 is a thallus, as in fernworts and seed plants, the ovaries are 
 borne on the surface of the thallus, partially or wholly sunk 
 in its tissue. In the ferns, they arise upon the under surface, 
 near the anterior end (fig. 74), and have the neck only pro- 
 jecting (fig. 332). In the horsetails the ovary is still more 
 deeply sunk. In the selaginellas the gametophytes are male 
 and female, the male arising from the microspores (fig. 315) 
 and the female from the megaspores (fig. 333). Both are 
 small, scarcely larger than the spores in which they grow. 
 The ovary is completely sunk in the female gametophyte and 
 
SEXUAL REPRODUCTION. 
 
 2 9 I 
 
 is much simplified, the neck-cells and the egg being the only 
 distinct parts of maturity. 
 
 393. Gymnosperms. — In the gymnosperms the female 
 gametophyte is not large enough to burst the megaspore which 
 
 spin 
 
 Fig. 333. — Longitudinal section of the female gametophyte of Selaginella Martensii. 
 //, d, (/, the body of gametophyte; »-, r, rhizoids (rudimentary) on its surface; a, an 
 Ovary whose egg failed of fertilization; e, embryo developed from fertilized egg; its 
 Cell-structure is not shown, but the various members are begun ; .r, suspensor ; st, stem; 
 /, /, primary leaves ; rt, root; /, foot ; e ', a younger embryo, with cell-structure shown, 
 the letter standing in large suspensor cell ; spnt, wall of megaspore. Magnified 12c 
 diam.- After Ffeffer. 
 
 remains enclosed in the sporangium. Upon its surface are 
 formed several ovaries, each reduced to an egg and two to four 
 tiers of neck-cells (figs. 320, 321). 
 
 394. Angiosperms. — In the angiosperms the female gam- 
 etophyte is so simplified that it is represented only by a few 
 cells, among which may be recognized at least one egg (e, 
 fig. 334), and possibly two others, s, s. The ovary has been 
 reduced to nothing but an egg, and the full development of 
 the gametophyte seems to be delayed until after the egg is 
 
2 9 2 
 
 PLANT LIFE. 
 
 fertilized. In these plants, therefore, we return to a con- 
 dition which is scarcely an alternation of sexual and spore- 
 producing phases, because the 
 sexual phase is nearly obliterated 
 by reduction. 
 
 395. Relative size of gameto- 
 phyte and sporophyte. — The ac- 
 companying diagram (fig. 335) may 
 roughly illustrate the history of 
 
 Fig. 334. 
 
 Fig. 335- 
 
 Fig. 334.— End oi megaspore ol I\<Iy^ouii /// liivaricatum. e, egg; s, s, synergi- 
 dx, probably sterile eggs. Below e the nucleus from whose divisions arise the cells 
 "I the belated gametophyte Magnified 540 diam Alter Strasburger. 
 
 Fio J35 Diagram representing the reduction of gametophyte and increase in sporo- 
 phyte from lower to higher plants, a, green alga- ; /-, red alga-: r. liverworts; </, 
 mosses; e, ferns ; y, club-mosses; .i,-, gymnosperms ; /;. angiosperms. Original. 
 
 development of these phases in the vegetable kingdom. 
 
 The gametophyte phase is represented by the dotted area. 
 It has its greatest development in the lower algse and fungi, 
 where it constitutes the whole, diminishes at first slowly and 
 then rapidly. After the fernworts are passed it constitutes a 
 relatively inconsiderable part of the plant and almost disap- 
 pears among angiosperms. Of the sporophyte, represented 
 by the white area, the reverse is true. The lines (tossing 
 the diagram at various levels show by their length in the 
 white and black areas the relative importance of the two 
 phases in the groups indicated. 
 
SEXUA L REPROD UCT10N. 
 
 293 
 
 Loss of sexuality. 
 
 396. Among fungi. — Though descended from ancestors 
 possessing sexual organs, certain groups of plants have lost this 
 mode Ox" reproduction and rely wholly upon non-sexual 
 methods. Such are the higher 
 fungi. The lower forms only 
 have sexual organs. These fungi 
 show their- relation to algae by 
 retaining in part or wholly aqua- 
 tic habits. In Cysiopus, for ex- 
 ample, at a certain stage zo- 
 ospores are produced ; and these 
 are generally characteristic of 
 aquatic plants, though Cystopus 
 has become a parasite upon land 
 plants. Many aquatic fungi are 
 known, most of which grow 
 upon dead plants or animals 
 (espe< ially insects) which have 
 fallen into the water. Not only 
 do many of these lower forms 
 produce zoospores, but the form 
 of their sex-organs and mode 
 of union remind one immedi- 
 ately of similar structure and 
 action in common algae. Com- 
 pare, for example, the sex- organs 
 in Vaucheria (fig. 308) and those oi Achlya (fig. 336). 
 
 Some fungi possess sex-organs which are functionless, 
 although the egg de\ elops as though it had been fertilized I fig. 
 336). But in most, all trace of sexual organs has disappeared, 
 though many produi e spore-bearing structures, the fructifica- 
 
 Fig. 336. — A. Functionless 
 of a fungus (Achlya <■ 
 
 with 'i eggs . 
 spermaries from branches ol same 
 liyplia form fertilizing tube which re- 
 mains closed. /•'. eggs which have 
 tini; spuii's w itliout ferti- 
 lization. M.i.unilu-il .■!•-•. iliam. — After 
 s.n hs. 
 
294 PLANT LIFE. 
 
 tions ( c 314) which are homologous with those known to arise 
 from the fertilized egg and adja< ent parts. In all these cases 
 the fructification may be considered the homologue of the 
 sporophyte of higher plants, for, even though its origin is 
 now purely vegetative, this has come about by reduction from 
 more perfect ancestors. 
 
 397. Apogamy. — In certain of the higher plants sexual re- 
 production is sometimes replaced by a process of budding, 
 which differs from reproduction by brood buds ( c 361 ff . ) 
 in giving rise to the other phase from that on \vhi< h the bud 
 arises. Some ferns, for example, regularly produce upon the 
 gametophyte a bud which grows into a sporophyte, the sex- 
 organs being functionless. This process is called apogamy. 
 
 398. Polyembryony. — Among the seed-plants a budding 
 of the megasporangium, instead of the fertilization of the egg, 
 ma}- produce an embryo. Except that the embryo so pro- 
 duced suspends its growth and becomes a part of a seed, such 
 reproduction is in no way different from that by brood buds 
 (^[ 361 ff.) It is common in the orange, and often results in 
 the formation of more than one embryo in the seed. 
 
 Results of sexual union. 
 
 The immediate result of the coalescence of a male and a 
 female gamete is the formation of a cell capable of producing 
 a new plant, i.e . a spore. The first step toward this is the 
 formation of a wall about the spore. It may then grow at 
 once into a new plant, or it may remain dormant for a longer 
 or shorter time. 
 
 399. Resting spores. — In the latter case it is called a 
 "resting spore." To protect itself, it thickens its-wall, often 
 very greatly. It may then escape from the parent by the 
 breaking of the ovary in which it lies, but more commonly it 
 remains enclosed until set free by the death of the parent 
 
SEXUAL REPRODUCTION. 295 
 
 and the decay of the ovary. Such are the resting spores of 
 Spirogyrciy Mucin-, Cystopus, and Chara.* 
 
 400. Embryo. — In the other case the sexually produced 
 spore develops at once. Except in the brown seaweeds, 
 whose eggs are ejected into the water before fertilization, the 
 spore remains enclosed in the ovary, within which it begins 
 to form an embryo. 
 
 401. Induced growth. — As a consequence of this develop- 
 ment, growth is induced in the ovary itself and the parts 
 adjacent. In the mildews the ovary produces one or more 
 asci (fig. 224), while the hyphae near by branch profusely and 
 cover the developing internal parts with a thick false tissue 
 (figs. 223, 337), the whole constituting a fructification. In 
 
 Fig. 337. — Formation of t he " fruit" in a mildew (Rrysiphe Cichoriacearum). a, 
 threads of mycelium ; i, spermary ; r, ovary ; </. the ovary after fertilization, show- 
 ing tin branches from hypha beneath ovary covering it; e, later stage, showing 
 these branches coalescent and dividing by partitions to form a false tissue. (Com- 
 pare fig. 223.) Highly magnified. — After < Ersted. 
 
 red seaweeds the ovary and adjacent parts finally form the 
 cystocarp (fig. 330). In mosses the ovary grows extensively 
 (fig. 33$), but is finally torn loose and carried up on the 
 embryo and becomes the loose hood, which is usually lost 
 early. The stem also enlarges beneath the ovary and forms 
 a sheath around the embryo (fig. 338), which grows down- 
 ward into the parent though not organically connected with 
 
 *It should be remembered that thick-walled "resting -ion-" arc also 
 formed vegetatively. Sec ■ jo8 
 
ig6 
 
 PLANT LIFE. 
 
 it. At the same time the neighboring leaves are stimulated 
 to increased growth. 
 
 In fernworts the sexual plant is stimulated by the growth 
 
 of the embryo within it, and enlarges considerably. 
 
 But it is soon outgrown by the young sporophyte, 
 
 to which it supplies nourishment until leaves are 
 
 produced and it is able to feed itself (figs. 76, 77 
 
 78). 
 
 402. Seed.— In all but the seed plants the de- 
 velopment of the embryo is uninterrupted until 
 a mature sporophyte is 
 formed. In seed-plants 
 the embryo develops to a 
 stage, and then 
 
 Fig. 338. Development of the embryo sporophyte of a moss {Funaria hygro- 
 metrica\ A, longitudinal section ol the ovary, <5, £, A, shortly after fertilization 
 of egg which has developed into the embryo, ol which J is the apical growing point 
 and /' the b isal, or foot ; /., /.. body of ovary ; //, tile base of the neck. /•', longi- 
 tudinal section through apex of stem and leaves. Two Ovaries are seen ; one has 
 failed of fertilization ; the other, c, has enlarged I" a< i ommodate the embryo, _/", de- 
 veloping inside it ; //. its neck, now withered. ( ', longitudinal section of same, older; 
 f, the embryo has grown downward into the apex ot sirni : tin- ovary, . . has still 
 
 further enlarged and indeed outgrow n the embryo, forming a bladdery case around 
 
 its base and elsewhere a close sheath for it ; /;, the neck. Around the embryo, where 
 it enters the stem, the latter has grown up as a sheath to whose edge the base of 
 ovarv is still attached. A little later the ovary will be torn off at this point and will 
 !„• lifted on !h. elongating sporophyte as a dry membranous sheath, the calyptra. 
 .1 , magnified 500 diam. ; />' and C' about 65 diam. — After Sachs. 
 
SEXUA L RETROD UCTION. 
 
 297 
 
 ceases to grow. With suitable protection and food-supply 
 
 it is then cast off as a seed (see further «[ 408), and usu- 
 ally after a dormant period continues its development until 
 mature. 
 
 403. In gymnosperms. — The growth of the embryo from 
 the egg in the gymnosperms stimulates the whole gameto- 
 phyte. This grows as rapidly as the embryo, which pushes 
 its way into it and remains completely surrounded by it (fig. 
 339). The whole ovule is also stimulated to growth. The 
 sporangium increases for a time, but is so crowded between 
 the growing gametophyte within and the hardening integu- 
 ment without that it is mostly absorbed (fig. 339). The in- 
 tegument grows for a time 
 to accommodate the struc- 
 tures within, but its tissues 
 finally become in whole or 
 in part thick-walled, form- 
 ing the seed- coat. In a few 
 gymnosperms (Cycas) its 
 
 h 
 
 Ki<;. 339. Fig. 340. 
 
 Fig. 33q. — Longitudinal section of the seed of silvrr fir i.//>/V.v /V, / 7 n.it, i\, showing 
 
 straight embryo with several primary leaves in center of the endosperm (dotted); 
 
 m, the micropyle, The integument lias become the testa (shaded with radial lines). 
 
 Between the testa and endosperm are the remains of the sporangium. Magnified 
 
 about 5 diani Alter Kerner. 
 FlG. 340. — Longitudinal section <il seed ,.1 , nail's. //, hilum (scar of attach 
 
 ment); w, micropyle ; t, outer fleshy layei ol integument; //and 1V1, two hard 
 
 layers,,) same ; f, thin eap-like remnant of sporangium ; /, gametophyte enlarged 
 
 forming the 1 ndosperm : ,». eggs which faili ,1 ol I, rtili/ation ; <-w, embryo produt ed 
 by a fertilized egg. Two thirds natural size. After Luerssen, 
 
 outer parts become fleshy, and the seed looks like a large 
 cherry. In the yew a second fleshy integument (an aril) 
 grows up around the hard seed (fig. 247). At maturity the 
 seed of gymnosperms thus consists of the embryo within 
 (fig. 340, em) surrounded by the gametophyte, />, whose cells 
 
298 
 
 PLANT LIFE. 
 
 become filled with reserve food, constituting then the so-called 
 endosperm; around this is the remnant of the sporangium, 
 when more than a mere membrane, likewise stored with food, 
 and <alled the perisperm ; while over all is the hardened in- 
 tegument or iesta, often of unlike layers, /, if, in. 
 
 404. Fruit. — In the conifers the sporophylls hearing the 
 ovules and the axis from which they arise also grow. As tin- 
 ovule is becoming the seed each sporophyll enlarges, but 
 especially the placental out- 
 growth (set' • 334), and the 
 whole number, together with 
 the enlarged axis, form the 
 cone (fig. 341, 358). Some- 
 times (as in the junipers) the 
 sporophylls become fleshy and 
 adherent, forming a berry-like 
 body. 
 
 34'- 
 
 .;(-•• 
 
 Fig. 341.— A mature cone ol .1 pine (Pinus sylvestris), the upper quarter cut away. 
 sq, s</\ the placenta] si ales ; g; seeds ; <•«/, embryo in a seed, lust below the pla- 
 cental scale which bears the lower seed e, may be seen part of the carpellary scale 
 in section. Magnified about 2 diam. From liessey. 
 
 Fig 342. — A placental scale of pine {P. sylvestris) seen from above; showing two 
 winged seeds in place. .1/, micropyle ; «'//. limit oi si ed ; the parts beyond are Rat 
 wings, formed by the splitting off of a layer ol tissue from the surface of the scale. 
 Magnified about ; diam. Vtoxa Bessey. 
 
SEXUAL REPRODUCTION. 299 
 
 When firm at maturity the cone scales open on drying, and 
 the seeds, each with a wing attached, split off from the scale 
 (fig. 342) and are shaken out. 
 
 405. In angiosperms the development of the embryo 
 stimulates the belated female plant to complete its growth, 
 and the megaspore (embryo-sac) is soon entirely filled by it. 
 This late-forming gametophyte is called endosperm, as in the 
 pines. 
 
 406. Endosperm. — The growing endosperm and the 
 embryo sporophyte, which it surrounds, crowd upon the 
 sporangium. This may, therefore, partly or wholly dis- 
 appear. If, when the full size of the endosperm is reached, 
 the embryo continues to grow, it may crowd upon the endo- 
 sperm until a part or all of it is absorbed. The embryo 
 sooner or later passes into a resting stage and ceases to en- 
 large. In this dormant condition it remains for a time whose 
 duration is chiefly determined by external conditions. 
 
 407. Food. — The tissue of the endosperm is utilized by 
 the parent sporophyte as a storehouse of food for the use of 
 the embryo sporophyte when it resumes growth. If the 
 embryo displaces the endosperm, it absorbs the reserve food 
 therein, consisting of starch, oil, or aleurone grains (^[ 236). 
 In case any tissue belonging to the sporangium remains, this 
 also is utilized for storage. To distinguish it from the endo- 
 sperm it is called perisperm. It is only occasionally present 
 in any amount in this group of plants. 
 
 408. The integuments of the ovule at the same time en- 
 large, and finally become differentiated in such fashion as to 
 ((institute the seed-coats. The ripened seed, therefore, con- 
 sists of the following parts: ( 1 ) in the interior, occupying 
 various positions and of exceedingly variable relative size, the 
 embryo; (2) immediate) \ around this, the endosperm or peri- 
 sperm, or both; but either or both may be so shrunken 
 and emptied as to be recognizable only by microscopic ex- 
 
300 
 
 PLANT LIFE. 
 
 ami nation ; (3) upon the exterior, one or two integuments 
 more or less readily distinguishable from each other (figs. 
 343> 344, 345)- 
 
 Fig. 743.— Longitudinal section of fruit of black pepper, containing a single seed. /V, 
 pericarp, showing two layers (the outer unshaded, the inner shaded by radial lines); 
 sc, seed-coats ; em, embryo, surrounded by en, the endosperm ; /, perisperm. Mag- 
 nified about 5 diam. — After Baillon. 
 
 Fig. 344.— Seed of pansy, entire and halved, the latter showing the straight embryo, 
 the endosperm (white and dotted), the seed-coats ; m, micropyle. Magnified about 
 10 diam. — After Baillon. 
 
 409. Fruit. — The growth of the embryo 
 excites not only the tissues of the ovule to 
 further development, but also the sporophylls 
 (carpels) bearing the ovules, and not infre- 
 quently even more remote parts. The carpels 
 (PAytoiaVta an< ^ tne * r contents and adherent parts, when 
 halved* ^show' fully developed, constitute the fruit. The car- 
 
 b°rfo U nelt the P e,s are tnen knOWD as the pericarp. The 
 and" neai-'b/sur 5 changes \vlii< h the parts undergo are chiefly 
 "ndosperm! of two sorts — an increase in size and an altera- 
 dtam! — ''After ti 011 °f texture. The increase in size requires 
 no special explanation. The carpels may be- 
 come dry at maturity, or may thicken and become soft and 
 fleshy, or even juicy. In accordance with these differences, 
 two sorts of fruits are recognized, namely, dry fruits and 
 fleshy fruits. Between these, however, there is no sharp line 
 of demarcation. 
 
 410. Dry fruits. — If the pistil contain only one or two 
 
SEXUAL REPRODUCTION. 
 
 30I 
 
 seeds, it very often does not open at maturity. Consequently, 
 the seed-coats ordinarily remain thin, and the protective 
 function is put upon the pericarp. In some cases the carpel 
 becomes adherent at an early stage to the surface of the 
 ovule, and at maturity the pericarp is so firmly attached that 
 it can scarcely be distinguished from the seed-coats them- 
 selves. Such a change takes place in the fruit of most grasses, 
 and the grain so formed is ordinarily mistaken for a seed 
 (fig. 346). When dry fruits are one-seeded and indehiscent 
 
 12 34 
 
 Fig. 346.— A small portion from the margin of a transverse section of grain of oats, 
 1, 2, pericarp; 3, seed-coats; 4, remains of the sporangium : 5-7, endosperm ; 5. 
 gluten cells; 6, cells containing large compound starch-grains (compare fig. 174) at 
 7 richer in gluten, with less starch. Magnified about 325 diam.— After Harz. 
 
 the pericarp usually bears whatever special contrivances are 
 necessary for the distribution of the seeds. (See further ^[ 
 489 {{.^ If, however, the pericarp contains many seeds, it 
 generally breaks at maturity to allow the loosened seeds to 
 escape. The extent and position of the opening into the 
 seed chamber or chambers are extremely various. In some 
 cases the openings are so small as to be mere slits or pores 
 (fig. 347). In others a more or less circular line of breakage 
 forms a little door or valve which opens and closes with 
 
302 
 
 PLANT LIFE. 
 
 changes of moisture (fig. 348). In other cases the pericarp 
 splits lengthwise into two or more pieces (fig. 340), or, less 
 
 Fig. 347. 
 
 Fig. 348. 
 
 Fig. 347. — Ripe capsules of a wintergreen (Pyrola c/itoran//ta), showing dehiscence 
 by pores. The opening is a short split at the middle of the base of each carpel. 
 
 Natural size— After Kerner. 
 Fie;. 348. — Ripe capsules of a bellflower (Campanula ra/>u>uuloides), showing 
 small reflexed valves. Natural size. — After Kerner. 
 
 Fig. 34g.—/f, capsule of violet split open at maturity, the seeds still attached to the 
 parietal placenta;. />', three pods of Lotus corniculatus ; a, just beginning to 
 1 r,<. k ; 6, split throughout, with the pie< es somewhat twisted ; < , empty ol seeds, the 
 two pieces fully dried and twisted. Natural size.— After Baillon. 
 
SEXUAL REPRODUCTION 
 
 303 
 
 often, cracks transversely so as to loosen a lid (fig. 350). In 
 the former case, if it is composed of two or more carpels, 
 (1) the carpels may separate from each other along their 
 original line of coalescence. If these carpels so separated 
 contain only one or two seeds, they may remain indehiscent 
 and behave like the simple pistils previously described ; but 
 
 Fig. 350. 
 
 Fig. 350 — Ripe capsule of pimpernell {Anagallis arvensis), opening by a lid. 
 
 Magnified several diam. — After Baillon. 
 Fig. 351. — Diagrams showing three modes in which capsules break as seen in trans- 
 
 vt-rse sections. A, septicidal dehiscence; B, loculicidal dehiscence ; C, septifragal 
 
 dehiscence. Modified from Prantl. 
 
 if they contain several to many seeds, they also break along 
 their inner edges (A, fig. 351). Or, (2) the carpels may 
 split along the middle, ami also at the center of the ovulai v 
 if it is more than one-chambered (B, fig. 351 ; A, fig. 349). 
 Or, (3) the outer parts of the carpel may split away from the 
 placentae, thus exposing the seeds (C, fig. 351). 
 
 411. Fleshy fruits. — The changes which produce fleshy 
 fruits consist in the transformation of certain parts of the 
 pericarp into masses of thin- walled juicy cells. Other parts 
 may remain unchanged, or may even become hardened. The 
 inner part ot the pericarp sometimes becomes of a stony 
 hardness, while the outer portion becomessoft and juicy. Such 
 
304 
 
 PLANT LIFE. 
 
 changes produce a fruit like that of the peach or the cherry. 
 The pericarp encloses a single seed 
 with delicate brown seed coats whose 
 protective function has been com- 
 pletely usurped by the stone (fig. 
 352). In other cases, while the 
 inner face becomes stony, the outer 
 becomes fibrous, tough, and dry, as 
 in the almond, walnut, and hickory 
 nut. The outer part in the last even 
 
 Fig. 352.— Fruit of the cherry, breaks regularly into four pieces 
 
 halved, e, epidermis of peri- _,_.... . . _ 
 
 carp; m, fleshy layer of Such frUltS flimisll a transition frOU 
 pericarp ; en, stony layer of 
 
 pencarp; .?, seed; cot, one the most perfect fleshy fruits to the 
 
 of the pair of thickened seed- . . 
 
 leaves of embryo. Natural dry fruits. In other cases the placentas 
 
 size. — After Focke. . , 
 
 become very much enlarged, and the 
 whole of the pericarp becomes fleshy, as in the tomato. In 
 others the outer part of the pericarp is hard and firm, while 
 the inner becomes pulpy, as in the pumpkin and squash. 
 
 412. Accessory fruits. — Parts adjacent to the carpels, 
 either flower leaves or axis or both, stimulated to growth, 
 frequently enter into the formation of 
 fleshy fruits. These may be accompanied 
 by either a fleshy or a dry pericarp. In 
 the wintergreen berry the calyx grows 
 thick and fleshy and surrounds a dry peri- 
 carp, which cracks at maturity (fig. 353). 
 In the strawberry (fig. 287) the torus be- 
 comes greatly enlarged and fleshy, while 
 the minute, one-seeded, dry fruits are 
 scattered over its surface, imitating small 
 seeds. The fig has the same parts, with 
 the torus concave, instead of convex (fig. 
 289). The apple consists of a fleshy torus carrying at its 
 free end the withered calyx and enclosing the tough, thin 
 
 Fig. 353. — Fruit of 
 wintergreen (Ga ul- 
 theria procum- 
 
 fie/is), halved, show- 
 ing thin (dry) peri- 
 carp, surrounded by 
 thickened fleshy 
 caly x. Magnified 
 about 2 diam. — After 
 Gray. 
 
SEXUAL REPRl >/' < 'CTK >JV 
 
 305 
 
 pericarp | fig. 354). In the blackberry the receptacle be- 
 comes fleshy, and each pistil forms a minute fruit like a 
 
 Fig. 354. — Fruit of the apple. A, halved longitudinally; 
 pericarp, enclosing seeds ; g, vascular bundles of the tit 
 calyx leaves. One hall natural size.— After Focke. 
 
 alved transversely. /, 
 torus entering k, the 
 
 cherry, adherent to its neighbors and to the pulpy torus. The 
 raspberry is like it, except that the adherent mass of fruits 
 separates as a cap from a firm torus (fig. 355). 
 
 413. Multiple fruits. — If the flowers form a crowded in- 
 florescence, either dry or fleshy fruits may be closely crowded 
 at maturity. Under these conditions fleshy fruits frequently 
 become adherent, and may thus constitute a multiple fruit 
 quite similar in form to the fruit formed by the aggregated 
 
 Fig. 355 
 
 Fig. 356. 
 
 Fir.. 3H5. — Vertical section of a flower of raspberry (Rubus idtrus), showing numerous 
 pistils which form the caplike fruit over the enlarged torus; olla, and 
 
 calvx all united .it base. Magnified about 2 <li. 
 Fig. 156.— A, pistillate flower cluster ol white 1 
 
 Natural si/e Alt. i P.aillon. 
 
 Alter kerne 
 ilberry; B, multiple fruit from same 
 
306 PLANT LIFE. 
 
 carpels of a single flower. Compare the multiple fruit of the 
 mulberry (each section from a separate flower whose floral 
 leaves and pistil both become pulp}-; fig. 356) with such an 
 aggregate fruit as the blackberry, in which each section is 
 one pistil out of the many belonging to a separate flower (fig. 
 355). The pineapple is similar to the mulberry in origin. 
 
 Even more remote parts are stimulated to development by 
 fertilization of the egg. The stem bearing the flower gen- 
 erally grows and becomes stronger, to carry the fruit, espe- 
 cially if large. The minute bractlets sometimes become 
 highly developed beneath the fruit. The cup of the acorn 
 and the husk of the hazelnut originate in this way as the 
 nuts form. The similar husk of the beechnut and chestnut 
 encloses more than one fruit. 
 
 414. Distributive arrangements. — Since the seed plants 
 abandoned the distribution of the megaspores and form both 
 the gametophyte and the new sporophyte within the tissues 
 of the old, it became necessary to adopt some other method 
 whereby the young can be so scattered as to prevent them 
 from coming into sharp competition with the parents. This 
 distribution occurs at the time of maturity of the seed, i.e., 
 when the embryo has become dormant, and the food store 
 and protective coverings have been completed. The devices 
 by which seeds are scattered are dependent upon the number 
 and character of the seeds and the nature of the pericarp. 
 Thus, one-seeded, indehiscent fruits must be scattered by the 
 structures arising upon the surface of the pericarp or its ad- 
 herent parts. On the contrary, seeds which escape from the 
 pericarp have the distributive structures developed by the 
 seed coats themselves. For distribution plants adapt them- 
 selves so as to employ the agency of the wind, water, and 
 animals, or they develop special mechanisms for casting off 
 the seed as a projectile. A consideration of these adapta- 
 tions belongs to ecology. (See Chap. XXVI.) 
 
PART IV: ECOLOGY. 
 
 415. Definition. — Physiology, in its broadest sense, may 
 be divided into physiology proper and ecology. Ecology 
 is that portion of botanical science which treats of the rela- 
 tions of the plant to the forces and beings of the world about 
 it, as distinguished from physiology proper, which treats 
 of the relation of the plant as a whole to the chemical and 
 physical forces within it. The forces without the plant 
 necessarily limit and modify the action of the forces within 
 it; consequently it is quite impossible to draw a sharp dis- 
 tinction between those subjects which belong to ecology and 
 those which belong to physiology proper. Parts II and IV, 
 therefore, will be found to overlap in many places. Several 
 of the subjects already treated under physiology belong in 
 part to the present section. for example, the movements 
 of plants are due not to internal causes alone, but to internal 
 causes as modified by external conditions. In this part only 
 a bare outline of the adaptations of plants in form and habit 
 to their physical surroundings and to other living beings i an 
 be given. 
 
 307 
 
I. NUTRITIVE ADAPTATIONS, 
 
 | I. ADAPTATIONS OF FORM AND STRUCTURE 
 TO ENVIRONMENT. 
 
 CHAPTER XIX. 
 
 FORMS OF VEGETATION. 
 
 416. Adaptation. — The various physical conditions which 
 make up the "climate" of any particular region of the 
 earth's surface, together with the nature of the substratum 
 upon or in which the plant grows, largely control the form 
 and functions of the plants found in that region. Stated in 
 other words, plants, in order to exist at all, are compelled to 
 adapt themselves to the places in which they grow. This 
 compulsion is on pain of death. 
 
 417. The struggle for existence. — The competition be- 
 tween plants is intense. Only a very small portion of the 
 seedlings which start in any particular area can come to 
 maturity. Far the greater number will be killed by being 
 robbed of light and of water by the overshadowing leaves 
 and interlacing roots of their companions. Since such com- 
 petition exists, it is evident that only those best suited to the 
 conditions under which they 'grow will have any chance 
 whatever to survive. 
 
 Not only are individuals subject to this competition, but 
 all individuals of a particular kind (a species) may be de- 
 stroyed in any region through the competition of other 
 species better suited to the conditions of that region. 
 
FORMS OF VEGETATION. 309 
 
 Through this competition between species one kind may be 
 forced to migrate to some different region in order to main- 
 tain itself. The capacity of a plant to adapt itself to a differ- 
 ent environment determines the possibility of its occupying 
 a new region, for here it must come into competition with 
 other sorts, and can only maintain itself if it is capable of so 
 modifying its form and structure as to adapt them to the new 
 conditions, and that as well as or better than the occupants 
 it finds in possession. In the beginning it was probably by 
 competition between species that water plants were gradually 
 adapted to an amphibious life, and then to a terrestrial life, 
 all the while advancing in complexity; later some green 
 plants adapted themselves to a parasitic or saprophytic life ; 
 plants of moist regions gradually moved out and occupied 
 even the deserts ; plants loving the shade adapted themselves 
 to the direct light of the sun ; and so on, until all parts of 
 the earth's surface and even considerable depths of the ocean 
 have been occupied. 
 
 418. Environment.— In order to understand the variety 
 of factors which are acting upon any particular plant, it will 
 be instructive to consider the conditions which surround the 
 ordinary land plant. A portion of such a plant is imbedded 
 in the soil, and the remainder rises into the air. The sub- 
 terranean part is profoundly influenced by the size and form 
 of the soil particles, as well as by their chemical composition. 
 It is exposed to contact with water varying in amount, some- 
 times from day to day and always from time to time during 
 the year, holding many substances in solution in varying 
 amounts and kinds at different periods. It is subject, also, 
 to variations of temperature from day to day and from season 
 to season. 
 
 The aerial part of such a plant is exposed to greater or 
 less variations of temperature from hour to hour, from day 
 to night, from day to day, and from season to season. It is 
 
3IO PLANT LIFE. 
 
 exposed to light varying in intensity from day to night and 
 from day to day, and to light differing in direction from hour 
 to hour of each day. It is enveloped by fogs or mists, or is 
 pelted by rain, hail, sleet, or snow, and sometimes com- 
 pletely buried in ice or snow. 
 
 A plant has little or no power to alter any of the agents 
 which act upon it, but it must be able to withstand the in- 
 jurious ones, or even to turn them to its advantage. It 
 would be difficult to conceive a more complex set of factors 
 to which adjustment must be effected ; and the more since 
 these conditions are combined with each other in an infinite 
 variety of ways. Because the physical conditions vary in 
 different parts of the earth's surface, the vegetation in each 
 region differs from that in others. 
 
 In any particular locality certain conditions of water, soil, 
 air, temperature, light, and precipitation are likely to be as- 
 sociated. It is possible, in a somewhat arbitrary way, to 
 recognize four general sets of conditions to which plants must 
 adapt themselves, in each of which the water supply is the 
 predominant factor. It should be understood clearly, how- 
 ever, that these sets of conditions pass into each other im- 
 perceptibly. Corresponding to these four sets of external 
 conditions, we may recognize certain characteristics in plant 
 form and structure, which are likely to be as>ociated, and it 
 thus becomes possible to distinguish four forms of vegetation 
 corresponding to the four sets of external conditions. 
 
 419. The first set of conditions consists of those charac- 
 terized by no extremes. Both the air and the soil are moder- 
 ately moist; the precipitation is distributed through the 
 year, or at least through the growing season ; there is no ex- 
 cess of salts in the water or in the soil ; the soil is usually 
 enriched with organic matter, often in considerable amount. 
 The plants which grow under these conditions are the ones 
 most familiar to people in the fertile regions of temperate 
 
FORMS OF VEGETATION. 3 11 
 
 climates. These may be reckoned as the average, or mean, 
 plants, and are therefore called technically mesophytes. 
 
 420. A second set of conditions is characterized by de- 
 ficient water supply throughout the year, the amount of water 
 present in the soil often being less than 10$. Such regions 
 may be considered as regions of continuous drought. The 
 plants adapted to these conditions are known as drought 
 plants, or xerophytes. 
 
 421. A third set of conditions, prevailing over compara- 
 tively limited regions, is characterized by an excess of salts in 
 Ike soil or water. These salts are chiefly sodium chloride 
 (NaCl, common salt), gypsum (CaSOj, and magnesium 
 chloride (MgCl). Plants which can live under these condi- 
 tions are known as salt plants, or halophytes. 
 
 422. A fourth set of conditions is characterized by an 
 excess of water. The plants grow wholly or partly surrounded 
 by water, or their roots are imbedded in a soil supersaturated 
 with water, that is, containing at least 8o$. Such plants are 
 called water plants, or hydrophytes. 
 
 It will be noticed that the first three groups, namely, meso- 
 phytes, xerophytes, and halophytes, are essentially land plants 
 in distinction from the fourth group, which are water plants. 
 
CHAPTER XX. 
 
 MESOPHYTES. 
 
 423. I. Mesophytes show certain general relations to ex- 
 ternal conditions, many of which are also shared by other 
 forms. Except to these minor variations in the environment, 
 they show no special adaptations ; or, rather, they are looked 
 upon as the normal plants, and the ways in which others 
 differ from them are spoken of as special adaptations. In 
 reality, however, the general methods by which they adapt 
 themselves to their environment, which are now to be con- 
 sidered, are quite as much special adaptations as those shown 
 by plants living in extreme climates. These adaptations will 
 be discussed in relation to each of the main factors of the 
 environment. 
 
 424. i. Air. — The composition of the air varies little from 
 place to place. It is only in those regions in which it is 
 rendered impure by artificial means, such as the vicinity of 
 cities and factories, and in the few isolated regions in which 
 it is vitiated by natural means, as in volcanic regions, that 
 any special adjustments may be looked for. Artificial vitia- 
 tion of the air kills off certain plants. A few plants have 
 adapted themselves to air in the neighborhood of fumaroles, 
 where they are subjected to vapors containing large amounts 
 of sulphurous acid. Whatever special adaptations are found 
 are internal, since only the very simplest plants find it pos- 
 sible to live in such conditions. 
 
 The movements of die air, however, influence profoundly 
 
 312 
 
MESOPHYTES. 313 
 
 the form of plants. This they do indirectly by the shifting 
 of sands in sandy regions, and by their effect upon the pre- 
 cipitation and upon the moisture of the atmosphere. Winds 
 increase evaporation from the soil and from the surface of 
 plants, and thus directly influence form. Trees growing in 
 wind-swept regions are always low, bushy-branched, with 
 the trunk and limbs inclined to leeward. The twigs on the 
 windward side are often dead. Forests in wind-swept regions 
 often thin out to windward, the trees becoming smaller and 
 smaller, finally being replaced by bushes which become 
 sparser until no woody vegetation is present. The leaves 
 upon such plants are small and often peculiarly spotted. 
 These effects upon the form have been ascribed to the me- 
 chanical action of the air, to the presence of salts when in the 
 neighborhood of the ocean or salt lakes, and to the reduced 
 temperature ; but probably none of these causes is to be 
 looked upon as so efficient as the drying brought about by 
 the prevalent wind. 
 
 425. 2. Light. — Light affects plants directly through its 
 influence upon their nutrition and upon the evaporation of 
 water from their surfaces. In this way it affects (1) the rate 
 of development. For example, the blossoming of flowers 
 and the production of leaves occur earlier upon the sunward 
 side of a tree or shrub than upon the other side. In the 
 same cultivated crops of the north and south there will often 
 be several days' difference in the total number between sow- 
 ing and maturing. Thus barley at northern Norway, in 68° N. 
 lat., matures in 89 days, while at Schonen, in 56 N. lat., it 
 matures in 100 days. Since the total hours of illumination 
 must be about equal, the longer days of the north enable the 
 plants to produce more food, and so to mature more rapidly. 
 The forcing of vegetables under glass by the aid of electric light 
 during the night depends upon the same principle. (2) The 
 form of plant parts is directly influenced by light. Plants accus- 
 
314 J PLANT LIFE. 
 
 tomed to the direct sunlight and those accustomed to shad-' 
 show profound differences in habit. Light plants are stocky and 
 compact ; their stems are inclined to be woody, the leaves 
 are usually folded or crisped aud often set at an acute angle 
 with the direction of the light, and the surfaces are frequently 
 hairy. In contrast, shade plants are slender and sprawling; 
 their stems often thin and weak ; the leaves flat and smooth 
 and set transverse to the direction of the light-rays, while the 
 surface is slightly, if at all, hairy. (3 ) In inte rnal structure ; 
 ,- ajso, there are decided differences, particularly!!! the le a ves. 
 (See %" 167, 438.) The leaves of light plants usually have a 
 thick epidermis, often shiny, with lateral walls straight ; the 
 stomata are frequently confined to the under side and often 
 ,sunk; the palisade cells are elongated, sometimes forming 
 
 (two or three layers and occasionally appearing on both faces 
 of the leaf. The shade plants, on the contrary, have a thin 
 epidermis, often containing chlorophyll, with lateral walls 
 often very wavy ; the stomata are produced on both sides of 
 the leaves, and the palisade tissues are poorly developed. 
 Light plants frequently have red cell-sap, especially in the 
 epidermis of smooth plants, and their colors are always 
 deeper, especially in the plants of high latitudes. Shade 
 plants, on the other hand, are usually pale, rarely high- 
 colored. 
 
 426. 3. Temperature. — Temperature exercises an im- 
 portant influence upon plants, both upon their aerial and sub- 
 terranean parts. The temperature of the air is really much 
 more important in controlling the adaptations, and con- 
 sequently the geographic distribution, of plants than is light. 
 The reason for this is to be found in the much more unequal 
 distribution of temperature in various regions of the earth's 
 surface. Moreover, temperature' affects every vital function 
 of the plant, for each of which a maximum, minimum, and 
 optimum point maybe determined. (See ^[ 186, 263.) The 
 
MESOPHYTES. 3^ 
 
 variations in temperature to which plants are subjected require 
 special adaptations. 
 
 427. (a) Protection against changes of temperature. — 
 These adaptations arc to be found in the presence of special 
 cell-contents, such as oils or resins, which reduce the liability 
 of those cells to freezing ; in the reduction of the amount of 
 water in cells so that less damage results from freezing ; and, 
 finally, in the presence of poor conductors of heat, such as 
 scale-leaves and hairs in profusion, a jacket of old withered 
 leaves, etc., all of which insure slow thawing if the plant is 
 frozen. The winter buds of trees in temperate climates 
 illustrate all of these adaptations. 
 
 428. (l>) A dormant period is necessitated by low tem- 
 perature during part of the year in temperate and arctic cli- 
 mates. The period of vegetation in the higher latitudes is 
 often very short. The same conditions prevail at high alti- 
 tudes, with the same effects. In these regions, therefore, the 
 plants are almost all perennials. In many cases the rudiments 
 of flowers are formed in the year preceding that in which 
 they are developed, in order that full opportunity may be 
 given for the ripening of the seeds and fruits in the short 
 growing season. Some plants adapt themselves to short 
 periods of vegetation by the presence of evergreen leaves, 
 which are ready at the first opportunity to resume their work 
 of food manufacture. 
 
 429. ( c ) The form of plants is modified by the tem- 
 perature of the air and soil. Tow temperatures are also 
 likely to bring about the formation of dwarf plants. 
 
 430. (d The rate of development is strikingly influenced 
 by variations in the temperature of the soil. The soil heat is 
 derived from the sun and from the decomposition of organic 
 matter within it. The sun is far the most important source. 
 The amount of lnat absorbed varies with the exposure of the 
 soil, its color, porosity, amount of water, and the duration of 
 
3I<3 PLANT LIFE. 
 
 the sun's rays. The influence of the temperature of the soil 
 
 is mainly indirect, acting through its effect on the water 
 supply of the plant. 
 
 431. (c) Moisture and precipitation. — The amount of 
 moisture in the atmosphere largely determines the amount of 
 evaporation from the surface of the plant. The relative 
 amount of moisture in the atmosphere is exceedingly variable, 
 and bears a direct relation to its temperature. Indeed, so 
 closely related are the conditions of temperature, light, and 
 moisture in the air, that the adaptations of shade plants, 
 mentioned above, may be considered as the sum of the 
 effects due to these three factors. It is difficult, if not im- 
 possible at present, to say which are the effects of light and 
 which of evaporation. 
 
 Precipitation affects plants chiefly as it influences water 
 supply. A few plants only of the higher forms are able to 
 absorb moisture directly from the air, except as a last resort. 
 (See % 196.) Many of the lower plants, such as the algae, 
 lichens, and mosses, absorb rain instantly by their aerial 
 parts. Some plants have adapted themselves to frequent and 
 prolonged rainfall, bearing it often for months at a time ; 
 other plants under such conditions lose their leaves very 
 quickly. Rain-loving plants have their leaves furnished with 
 elongated tips or with grooves and hairs to carry off the rain 
 quickly. Their surfaces, also, are not readily wetted by water. 
 Others protect themselves against the rain by adjusting the 
 direction of their leaves to it so that a heavy, splashing rain 
 strikes them at an acute angle. Others, by a movement of 
 their leaves as soon as the sky is clouded, avoid injury from 
 heavy rains. The branching of leaves in certain cases may 
 be looked upon as a protection against heavy rainfall. 
 
 The snow cover through cold periods is for many plants 
 essential as a protection against low temperatures during the 
 dormant period. Others have adapted themselves to growing 
 
MESOPHYTES. 3'7 
 
 even in the midst of snow, putting forth their leaves and 
 blossoms while still surrounded by melting snow. 
 
 432. ( /') Soil. — Both the chemical composition and the 
 physical properties of the soil affect plants. The latter arc, 
 however, by far the most important. Here, again, the reason 
 is to be found in the relation of the physical qualities of soil 
 to the water supply. 
 
 The water which permeates the soil takes up from it certain 
 substances, and becomes thus a dilute solution of various 
 salts. That the salts thus present in the soil water may affect 
 the form of the plant is strikingly shown in the occurrence 
 of certain species of a genus only upon soils containing lime, 
 while others of the same genus are found only in soils free 
 from lime. When the local distribution of corresponding 
 species of the same genus within the same region is deter- 
 mined by the presence or absence of lime in the soil, com- 
 parison of them indicates the general effect of lime salts upon 
 the plant. Plants growing upon lime are usually stronger 
 and more densely hairy, often hoary, while those on other 
 soils are smooth or furnished with glandular hairs. The 
 lime-loving plants have bluish-green leaves, as contrasted 
 with the grass-green. Their leaves are also more numerous 
 and more deeply branched, the flowers larger and their colors 
 dulkr and paler. 
 
CHAPTER XXI. 
 
 XEROPHYTES AND HALOPHYTES. 
 
 433. II. Xerophytes. — The plants of dry regions blend 
 by imperceptible gradations with the mesophytes. They 
 reach their best development in desert and rocky regions. 
 Some, especially of the lower forms, grow in such situations 
 that they must adapt themselves to become so dry at certain 
 periods that they may be powdered. Such, for example, are 
 a few algae, many lichens, mosses, and a few fernworts. 
 Adaptations in these cases must be looked for in the character 
 of the cell contents. 
 
 Other plants must adapt themselves to endure dry periods, 
 such as those occurring from day to day, or between the wet 
 and dry seasons, by retaining in their bodies sufficient water 
 to sustain life. The following are some of the chief methods 
 by which plants adapt themselves to periodic or continuous 
 drought. 
 
 A. Adaptations for reducing transpiration. 
 
 434. i. Periodic reduction of surface exposed. — -The 
 dying away of an annual plant after forming its seed may be 
 looked upon as an adaptation of this sort. Little evaporation 
 occurs from the surface of the seed, which is thus adapted to 
 withstand prolonged dryness. Perennial plants accomplish 
 the same results when their annual shoots die off and leave 
 only the rhizomes, tubers, and similar parts buried in the soil. 
 Perennial plants with perennial shoots may drop their leaves 
 
 318 
 
XEROPHYTES AND HALOPHYTES. 319 
 
 during the dry period and form them again upon the return 
 of the growing season. The fall of leaves in our woody vege- 
 tation is a similar adaptation to the cold season. The rolling 
 or curling of leaves is a common mode of avoiding evapora- 
 tion. It is common in grasses ( fig. 357) and mosses. 
 
 435. 2. The constant reduc- 
 tion of exposed surface. — This 
 B ^fl^ may be secured among the leaves 
 
 by reducing them either in area 
 f or in number or both, or by much 
 ranching, with little green tissue 
 
 A 
 Fig. 357. — Transverse sections of a gra>-s leaf (Lasiagrostis). .1, open; A', rolled, 
 when dry. The white plates are the ribs of mechanical tissue above and below a 
 stele, one in each ridge ; the shaded areas are green tissue. The Stomata are located 
 low on the sides of the narrow grooves between the ridges, so that when the leaf is 
 rolled, evaporation through them is hindered. Magnified 16 diam. — After Kerner. 
 
 Plants wi th bris t je-sh npr-' 1 "'■ "—d ie-shaped leav es (tigs. 10 1, 
 358), those with permanently rolled leaves (fig. 359), or 
 those with scale-like leaves I fig. 100 ) show thev arious phases 
 
 of such adaptations^ KxtrenuT reduction oTsurface is secured 
 
 by suppression of leaves. In this case any further adaptation 
 depends upon the stems, which must also provide fornutritive 
 work. The.se may take the form of leaves 1 see € 112); 
 or the branches may be thick, rigid, and fleshy 1 fig. 360) ; 
 or they may be thread-like or needle-shaped, as in the aspara- 
 gus (fig. 105) ; or the stems themselves may reduce their area 
 by becoming fleshy and cylindrical, prismatic, or spheroidal, 
 as in the various forms of Cereus and melon <a<tuses (fig. 
 1 10). 
 
 436. 3. Movements of parts to reduce the illumina- 
 tion. — Certain lea\es are adapted to a permanent profile 
 position, that is, with the edges turned toward the sky. 
 
320 
 
 PLANT LIFE. 
 
 instead of the surfaces. (See ^| 285.) Others assume a 
 profile position when the illu- 
 mination becomes too intense. 
 These positions, by placing the 
 leaf surface oblique to the di- 
 rection of the light rays, reduce 
 the amount of evaporation very 
 considerably. 
 
 437. 4 Coverings, consist- 
 ing of living or dead scale- 
 leaves, stipules, leaf-bases or 
 entire leaves, reduce transpira- 
 tion by obstructing the free ex- 
 change of air, or by holding 
 water and so keeping moist the 
 surfaces they cover. 
 
 438. 5. Structural modifi- 
 cations. — ■ These may occur 
 either in the epidermis- or some 
 internal tissues. (a) The epi- 
 dermis may greatly reduce evap- 
 oration by the formation of 
 hairs in such profusion as to 
 form a cover for the surface 
 (figs. 361-364). Hairs in- 
 tended to protect from evap- 
 oration are usually dead and 
 
 filled with air. Reflecting light from many points, they look 
 white, and the surface seems hoary, or woolly, or silky. 
 Hairs in the form of scales which overlap reduce the rate of 
 evaporation by covering the stomata (fig. 365). -Iuirther__ 
 adaptations~ot the epidermis are to be found in the pres- 
 ence of a thick cuticle (fig. 367); the water-proofing of 
 the whole of4he outer wall of the epidermis; the develop- 
 
 . — Shoot of larch, with ripe 
 showing needle-shaped leaves 
 on dwarf branches ; scale leaves on 
 main axis ; carpellary scales just peep- 
 ing from between placental scales of 
 cone. Natural size. — After Ke 
 
XEROPHYTES AND HA l.OPH YTES. 
 
 321 
 
 ment of two or more layers of epidermal cells (fig. 370) ; or 
 the excretion of wax or of varii+*ff upon the surface of the epi- 
 
 FTOXrs: 
 
 
 Fig. 359. — Transverse section of a leaf of a heath {Tylanthus ericoides), showing 
 revolute form. The stomata are on the under (concave) surface among the hairs, 
 winch still further impede the transpiration. Magnified 130 diam. — After Kerner. 
 
 dermis. The latter often becomes very thick, giving to the 
 leaves a shiny appearance. Wax is usually in the form of a 
 
 Fig. 36 
 
 Fig. 360. — Prickly pear ( >puntia vulgaris) with Battened jointed stem and no 
 
 leaves. About one fourth natural size, After Frank, 
 Fu;. 361.— Multicellular hairs ol edelweiss, MagnifU d about 50 diam.— After Kerner, 
 Fir.. 362. — Silky unicellular hairs ol Convolvulus Cntorum. Magnified about $" 
 
 ili.1111 Ml. 1 K( ii" 1 
 
3 22 
 
 PLANT LIFE. 
 
 --:' : \ ' 
 
 bluish-white powder, which can be readily wiped off with the 
 
 ringers, as from the surface 
 of fruits, such as plums or 
 grapes, the leaf of cab- 
 bage, or the stalk of sugar- 
 cane (fig. 366). The in- 
 ^ terior layers of the wall 6T 
 ■ the epidermis are some- 
 - — ttmeT'coivverted into rhu- 
 ~~cTTage, which retards the 
 evaporation ~rjf — -avuU£.i\__ 
 ^J£he__ sinking of" the sto- 
 mata below the general 
 
 Fig. 363. 
 
 wr 
 
 
 Fig. 363.- Stellate hairs <>f /h<i/:i 
 Thomasii, seen from above. 
 Magnified about 50 <li. 
 
 After kerner. 
 
 Fig. 364. — T-shaped hairs of Ar- 
 temisia mutellina. Magnified 
 about 50 diam.— After Kerner. 
 
 1, . 565 Shieldlike si .<l<--s of an 
 1 1 /■:/,., ix "'>■■■ ■• 
 
 folia), seen from above. Mag- 
 nified about ;•> diam.— After 
 Kerner. 
 
 level (fig. 367), their arrangement in pits (fig. 368) or in 
 "groTTves (fig. 357), and their restriction to the under side of 
 the leaf (fig. 359) may be looked upon as further epidermal 
 
XEROPHYTES AND HALOPHYTES. 
 
 323 
 
 ,ni1-ipfntjnnc tp r^dll^w^yapnrririrm In the leaVCS of SOUK' 
 
 xerophytes the guard cells of the stomata are motile only 
 when young, becoming thick-walled and fixed when the leaf 
 is mature. The stoma itself sometimes becomes closed, also. 
 
 Fig. 366.- -Portion of a transverse section through a node of sugar-cane, showing rods 
 of wax secreted by the epidermis. Magnified 142 diam.— After I »e Bary. 
 
 FlG. 367. — Transverse section of a portion of the margin of a leaf of Aloe socotrina. 
 1. thick cuticle; below,, cutinized layers of wall of epidermis,*'/; /, parenchyma 
 cells with chloroplasts ; . r. a crystal cell with needle crystals ot oxalate of lime; sp, 
 
 fuard cells of stoma, sunk below surface : .;, intercellular space under stoma. Magni- 
 ed about 175 diam. — After Tschirch. 
 
 _{&L- l'he internal tissues of the leaves may be more compact. 
 This reduces transpirationby restricting thelil'ea of llie-air 
 passa ges. Such dense structure is secured by multiplying 
 th e number of the palisaTrrr iTTycrs and by the "Tub re regular 
 form of the spongy parenchyma (fig. 359 and ^' 167). 
 
 B. Adaptations for taking up water. 
 
 439. Absorption. — 1. Some plants are adapted to im- 
 mediate absorption of moisture in the air or of liquid water 
 falling en their aerial parts. Such are. usually, the 
 algae, In hens, and mosses which -row in exposed situations. 
 2. Certain of the higher plants are furnished with hairs 
 adapted to the prompl absorption of rain or dew, e.g., Spanish 
 
324 
 
 PLANT LIFE. 
 
 moss. 3. < Uhcr plants adapt aerial routs to the absorption of 
 
 moisture from the air, as well as falling water. (See ^ 196.) 
 4. Many are surrounded by the bases of dead leaves, which 
 act as a sponge for absorbing water, and supply it gradually 
 to the stem or younger leaves. Living leaves, sometimes 
 singly, sometimes in clusters, form cuplike or tubular struc- 
 
 
 Fk;. 368.— Portion of a vertical section of leaf of oleander. <■/, epidermis of upper 
 face; e/>' , same of lower face with stomata, s, in deep pits with numerous hairs, t: 
 pal, palisade parenchyma in two layers; ,r/, spongy parenchyma; //, /;', hypoderma 
 adapted to water storage. Chloroplasts shown only in left-hand side of figure. 
 Magnified about 175 diani. — After Van Tieghem. 
 
 tures, acting as water receptacles, from which it can be 
 absorbed as required. Such adaptations occur chiefly in 
 epiphytes. (See" 454-) 5- Many xerophytes develop ex- 
 ceedingly long tap roots, which penetrate the soil deeply 
 to a permanent water supply. 
 
XEROPHYTES AND HALOPH YTES. 325 
 
 C. Adaptations for storing water. 
 
 440. 1 . Special cell contents. — The simplest of these adap- 
 tations is the presence of mucilage in the cells, arising from 
 the cell-wall or developed in the cell-sap of various parts. 
 (See *j" 5.) The presence of acids, tannins, and salts perhaps 
 aids in the retention of water. 
 
 441. 2. Water-storing tissues. — (a) Fleshy plants, or 
 succulents, are those which thicken their parts by the develop- 
 ment of an unusual amount of parenchyma, which contains 
 a large quantity of cell-sap, and usually much mucilage. 
 These thin-walled, mucilage-containing tissues form a reser- 
 voir for the storing of water. In such plants the epidermis 
 is very strongly water-proofed; the stems are thick, cylin- 
 drical, prismatic or spheroidal ; the leaves are wanting, or they 
 are thick and fleshy, cylindrical or broad (fig. 369), and 
 arranged in rosettes. 
 
 (U) In non-succulents, 
 the epidermis itself may 
 be greatly developed as 
 a water-storing tissue, 
 or it may form great 
 numbers of bladdery 
 hairs which are richly 
 
 supplied with water, as FlG , 3 , 9 ._ A 3Trfto«£k \sL* 
 in the well-known "ice- ^SVSSSPfoKS 5*?e3KF 
 
 ,i„„, •• ._ ,,.i,;,.k ,k., branches, these become detached and form in- 
 piam, on \\nun lilt, dependent plants. About one half natural size.— 
 
 hairs glisten like ice. After Gray. 
 
 In the first case, the epidermis, instead of forming a single 
 layer of cells, ma) develop into several layers, the lower ones 
 large and thin-walled, as in begonias, figs, and peppers I fig. 
 370). The cells immediately under the epidermis sometimes 
 become transformed into a water-storing tissue, as in the 
 oleanders (fig. 368); or strips of tissue extending from the 
 
326 
 
 PLANT J.ll-F. 
 
 upper to the lower side of the leaf may act as reservoirs 
 
 of water. 
 
 442. 3. Tubers and bulbs. — These forms of the shoot 
 in which the parenchyma is 
 abundant and richly supplied 
 with water may also be 
 counted, in part at least, as an 
 adaptation for water-storage. 
 443. III. Halophytes. — 
 The salt-loving plants arc, 
 in most of their characters, 
 strikingly similar to the xero- 
 phytes. This similarity is to 
 be explained probably by the 
 difficulty of securing a suita- 
 ble water supply. They grow 
 near the ocean, upon the 
 shores of salt lakes, by salt 
 springs, and in the interior 
 of the great continents in old 
 lake basins in which the salts 
 have accumulated by the 
 rains. A few of the halophytes 
 are trees and shrubs, with 
 leathery leaves, but almost all 
 are succulents. In habit thev 
 
 Fig 370. — Strip from a vertical section of 
 leal "I Peperomia trichocarpa. ./, from 
 afreshleaf; w, water-storing tissue, com- ov»n*»rallv In™ nft*»n ,-.-,.,> 1, 
 
 posed of the multiple epidermis of the arC ,^lUiall\ IOW, otUll ( Ucp- 
 
 upper side ;*, chlorophyll-bearing cells; • j, ( jj , fl « ■,,,(! 
 
 s, spongy parenchyma with sparse chloro- " J 6» " ll " nnii\, iksiij aiiu 
 
 plastS and much water. /.'. tin- same after ____, _, 1 , . #.___ ,1,, . ,„ f 1 ^„,. c . 
 
 four days" tr.mspirati,,,, at ,s ,.. C. The nl(>r « <" lesstiailsllH Cllt lea\ CS 
 
 tissue w is much collapsed, the walls being „_ i , __. . 4 i, ii i__ ,, i 
 
 |,l..it.-,i : .also shrunken, but « as before, and stems; the cells large and 
 
 S ified about 5 ° diam - Vfl - Haber - thin-walled, containing com- 
 paratively little chlorophyll and abundantly supplied with 
 water, with few and small intercellular spaces and the surface 
 generally smooth. 
 
CHAPTER XXII. 
 
 HYDROPHYTES. 
 
 444. IV. Hydrophytes may be divided into three groups : 
 i. Slime plants, which grow in the mud or slime at the bot- 
 tom of bodies of water. Here belong many algae, especially 
 
 itoms, man\- species of low fungi, and bacteria in great 
 numbers. 2. Submersed plants, either free or attached. 
 Many alga?, including both the diatoms and the filamentous 
 algae, are found floating in the water at various heights, 
 sometimes near the surface, sometimes more deeply submersed. 
 Since their substance is heavier than water, their capacity to 
 sustain themselves depends upon the production of gases in 
 the interior of the cells, or upon the presence of gases en- 
 tangled among their filaments. A few of the higher plants 
 are also found submerged and free, such as the bladder-worts. 
 The number of free-floating plants of the larger kinds is 
 small compared with those attached. The higher algae, 
 moss-worts, fern-worts, and seed plants are usually fastened 
 in the mud or to sticks and stones. The thallus of the algae 
 is usually profoundly branched and the shoots of the mosses 
 are richly supplied with leaves. All of the submerged fern- 
 worts and seed plants are characterized by a very thin -walled 
 epidermis, the absence of stomata, and the extensive surface 
 due to the very profuse branching of the stems or leaves, or 
 to the great number of these, or to both. In all cases the 
 extensive green surfa< e may be looked upon as an adaptation 
 to securing carbon dioxide and the manufacture of sufficient 
 
 327 
 
328 PLANT LIFE. 
 
 food by means of the weak light in a situation where there is 
 no danger from lack of water. 3. Floating or p artly sub- 
 mersedpltuils, either free or attached. Many of the Tilamerr^- 
 tous algae ahTT~TiTattmis float free at the surface. The chief 
 characteristics of the higher floating plants which root in the 
 mud are these : their floating leaves are simple, little branched 
 or not at all, roundish or elliptical in form, leathery, and the 
 surface not easily wetted ; stomata are present only on the 
 upper surface, and the leaf stalks are adapted in length 
 to the depth of the water in which they grow ; the woody 
 tissues are either entirely absent or poorly developed, be- 
 cause there is no occasion for the transportation of water, 
 nor need of rigidity, since the medium in which they grow 
 supports most of the weight. 
 
 445. Light. — Green water plants are limited in their 
 distribution by the depth to which light can penetrate water. 
 This does not exceed even in pure waters four or five hundred 
 meters. No seed plants have been found at a greater depth 
 than thirty meters, and few algae at a greater depth than 
 forty meters. Plants which are brought up by dredging 
 from lower depths than this are usually those which have 
 been detached and sunk. 
 
 446. The temperature of the water is very much less sub- 
 ject to variation than that of the air, never falling, except 
 at the surface, below 0.5 C* 
 
 447. The movements of the water are of much importance 
 to plants in bringing air and food materials to them. These 
 movements are wave movements, or surf, and currents. 
 Plants growing within the limits of wave action are often 
 damaged or torn away by the waves. The Sargasso Sea is 
 marked by an accumulation of such plants, mainly of brown 
 
 * The minimum temperature of the deeper water is usually stated as 4 
 C, but many observations upon Lake Mendota by Birge have shown that 
 in winter it falls nearly to zero, even at a depth of eighteen meters. 
 
HYDROPHYTES. 329 
 
 algas, which have been swept to the quieter parts of the North 
 Atlantic by currents after having been detached by the waves. 
 Such plants may often live for a long time and may even 
 continue their development. 
 
 Plants adapt themselves to currents, such as those in fresh- 
 water streams, by their slender form, which is characteristic 
 of plants in flowing waters, as seen in filamentous alga? and 
 the much divided leaves of higher plants. Currents of water 
 act as a stimulus upon certain plants, producing a direct 
 reaction in the mode of growth. 
 
 448. The composition of the water affects chiefly the dis- 
 tribution of plants, in a manner similar to the presence of 
 salts in the soil. In the ocean waters the percentage of salts 
 is extremely variable in different regions ; in some places it 
 is as low as 0.5 per cent. , while in others it reaches 4 per cent. 
 In fresh waters the differences in kind and amount of dis- 
 solved salts are chiefly due to differences in the soils which 
 the streams drain. 
 
8 II. ADAPTATIONS TO OTHER PLANTS. 
 
 449. Plant associations. — Each set of external conditions 
 brings about the association of certain plants with each other, 
 because they have adapted themselves to those conditions. 
 The four groups just considered may be looked upon as plant 
 societies of the most general kind. Within each of these 
 four it is possible to distinguish a number of smaller societies 
 determined by a more limited range of conditions. 
 
 Besides these plant associations, however, there are those 
 which are determined by the relation of the plants to each 
 other, as affording mechanical support, or assistance in the 
 work of nutrition. The plant associations of this kind only 
 are now to be considered. 
 
 CHAPTER XXIII. 
 
 ADAPTATIONS TO OTHER PLANTS AS SUPPORTS. 
 
 Certain plants serve others as carriers, acting purely as 
 mechanical supports. To these supports plants have adapted 
 themselves in various ways. In many instances dead objects 
 of similar form may serve the same purpose. 'Hie supported 
 plants are, therefore, partly independent of the others, though 
 in most instances in nature they rely upon living supports. 
 
 450. i. Climbing plants. — Climbing plants are those 
 which develop lateral organs, sensitive to contact, which be- 
 come recurved or coil about a support of suitable form and 
 
 33" 
 
ADAPTATIONS TO OTHER PLANTS. 331 
 
 si/o, or form adhesive disks by means of which they cling to 
 rough surfaces. These lateral organs are forms either of 
 leaves or lateral shoots, and are known as tendrils (figs. 107, 
 156). (For their form see % 115, 158; for their action, 
 II 266, 293.) 
 
 451. 2. Clambering plants are those which form lateral 
 organs not sensitive to contact, and by means of them sup- 
 port themselves on adjacent plants. Recurved leaves, shoots, 
 and prickles (fig. 115) may serve these purposes. 
 
 452. 3. Twining plants are those which have adapted 
 their shoots to winding about a support of suitable size. (See 
 If 291.) 
 
 453. 4. Root climbers have adapted their aerial roots to 
 attaching the plant to rough surfaces. (See 1" 90.) All of 
 these organs are structures belonging to the sporophyte, and, 
 therefore, are found only in fernworts and seed plants. 
 
 454. 5. Epiphytes.— Tins name is rather loosely applied 
 to those plants which are attached to others for mechanical 
 support, and do not derive food from them. All kinds of 
 plants have representatives in this group. Algae, diatoms, 
 and other small water plants attach themselves to other alga; 
 and the higher water plants. Lichens, liverworts, mosses, 
 ferns, orchids, bromelias, etc., are abundant upon trees. 
 Epiphytes are attached by hair-like rhizoids, or by hold-fasts, 
 which apply themselves to the roughnesses or even penetrate 
 the outer dead parts, but do not absorb from the living tis- 
 sues of the supporting plant either water or food materials. 
 The water supply is provided for (1) by adaptations for ab- 
 sorbing rain or dew, mists, or even dampness, instantly, either 
 by the surface, as in algae, mosses, and lichens, or by means of 
 hairs, as in the Spanish moss and other seed plants; (2) by 
 adaptations to catch the water in living or dead leaves and 
 hold it, either by capillarity or as a vessel, long after pre- 
 cipitation has ceased. Many of the simpler epiphytes are 
 
33 2 PLANT LIFE. 
 
 adapted to become dry without injury, while the larger ones 
 are inhabitants of moist tropical regions, where the danger 
 of drying is avoided and it is possible to obtain an adequate 
 water supply. Their food materials are derived entirely 
 from the air and the water which falls upon them, while the 
 mineral salts are obtained from the dust which has been 
 carried by the air and accumulated upon the surface of the 
 supporting plant, or among the mass of dead and decaying 
 leaves and other debris about the base of the epiphyte. Or- 
 ganic matter from the decay of the older parts may also be 
 reabsorbed. 
 
 An adaptation to this mode of life is marked in the repro- 
 ductive bodies. Of all epiphytes the seeds or spores are 
 either light and carried by the wind ; or the seeds are sticky 
 and carried by birds and other animals ; or they are eaten by 
 birds and voided upon the trees where they are adapted to 
 germinate. 
 
CHAPTER XXIV. 
 
 SYMBIOSIS. 
 
 455. Living contact. — Not only are different species as- 
 sociated through the influence of similar surroundings which 
 they find congenial, but certain plants adapt themselves to 
 such an intimate relation with others that they live in imme- 
 diate contact with them. This intimate association is known 
 as symbiosis. When the parties to symbiosis stand to each 
 other in the relation of partners, each furnishing certain 
 materials or conditions advantageous to the other, the asso- 
 ciation is called mulualistic symbiosis or mutualism. When the 
 relation of the parties is that of master and slave, one indi- 
 vidual deriving advantage from the labor of the other and in 
 return furnishing it suitable conditions for existence, the 
 association is a form of mutualism known as helotism. Finally, 
 when the relation of the parties is that of an unwilling host 
 and an unwelcome guest, one individual being fastened upon 
 by the other from whose presence it is unable to free itself, 
 the symbiosis is called parasitism. (See ^[^[ 51, 52, 53, 
 222.) 
 
 A. Mutualism. 
 
 456. 1. Between plants of the same species. — Mutual- 
 ism may occur between individuals of the same species. 
 Illustrations of this are to be seen in the massing of the 
 lower alg?e into colonies, in some of which certain individuals 
 may be differentiated from others for the purpose of carrying 
 on a function of advantage to the colony. (See 12, 13, 
 
 333 
 
334 PLANT LIFE. 
 
 20.) In a somewhat similar way certain bacteria are found 
 always massed into colonies, constituting a sort of thallus of 
 
 Fig. 371. — A, serpent-like colonies of Chondromyces serpens, composed of numerous 
 rod-shaped individuals, B, a, which multiply by fission, />, and secrete a mass of jelly 
 which holds them together. A magnified 45 diam.; B, 750 diam.- After Thaxter. 
 
 characteristic outline (fig. 371). In the higher fungi, also, 
 the mycelium may be looked upon as a thallus formed by the 
 aggregation of many individuals ; for, while it is possible to 
 have a mycelium produced from the development of a single 
 spore, it is not common. The mycelium is generally the 
 result of the union of hyphse (see •; 50) arising from many 
 spores. Even in such cases the mycelium may constitute 
 a single body, and may give rise to a single fructification. 
 
 457. 2. Between plants of different species. — Mutual- 
 ism is more common between plants of different species. It 
 takes the following forms: 
 
 458. (a) Lodgers. — The higher plants often shelter 
 'various species of lower ones within their intercellular cham- 
 bers, or in pockets formed by lobes or bladders of various 
 sorts. This relation is especially common between water 
 plants and algre. Species of Nostoc live in the intercellular 
 spaces of liverworts and duck-weeds, in the cortex of the 
 roots of some land plants, and in the bladdery leaf-lobes of 
 liverworts. Some species of the higher alga?, also, are 
 frequently associated with other species to which they attach 
 themselves. That they are not merely epiphytic (see *" 454) 
 is shown by the fact that certain species are found only upon 
 certain other species, while they do not grow upon other 
 
.9 YMBIOSIS. 
 
 335 
 
 plants which would furnish them similar external conditions 
 (fig. 372). 
 
 LJ % 
 
 A />' 
 
 Fig. 372. Fig. 373. 
 
 Fig. 372. — A portion of a filament of an alga (Ectocarpus^ showing at <( another alga 
 [Entoderma Wittrockii) which has embedded itself in the cell-wall. Magnified 480 
 diam. — After Wille. 
 Fig. 373.— A , a tuft of rootlets of white poplar forming mycorhiza. Natural size. /•'. 
 a portion of a transverse section of one of these rootlets, showing the mantle of fungus 
 mycelium and the growth of the hyphae also in some of the outer cells of the root. 
 Magnified ifiu diam.— After Kerner. 
 
 459. (/') Mycorhiza. — Mutualism between the roots of the 
 seed plants and certain fungi is common. Such a combina- 
 tion of root and fungus is called a mycorhiza. The fungus 
 forms a jacket over the outside of the root (figs. 373, 374), 
 taking the place and work of the root hairs by means of 
 strands of hyphae extending from the surface of the fungus 
 jacket (fig. 374) ; or it grows inside the cells of the cortex 
 anil epidermis, forming knotted masses (fig. 375); or it is 
 • onfined to certain definite portions of the roots, forming 
 upon them swellings from the si/.e of a hazelnut to the size 
 of a man's head. The first form is especially common upon 
 the roots of the oak, elm, walnut, apple, pear, maple, ash, and 
 related trees It has also been found 11)1011 the roots ^\ a 
 large number of herbaceous plants. The second form belongs 
 
336 
 
 PLANT LIFE. 
 
 chiefly to the heaths and orchids. The third form grows 
 upon alders, bayberry, etc. 
 
 460. (c) Root tubercles of Leguminosse. — A peculiar case 
 
 of mutualism appears in the bean family between the roots 
 
 and bacteria. The latter produce upon 
 
 the roots small swellings from the size 
 
 of a grain of wheat to that of a hazelnut 
 
 (fig. 376). The presence of these 
 
 *IG. 375- 
 Fig. 374.— Tip of a rootlet of beech {Fagus sylvatica) with fungus mantle, the 
 hyphae acting as absorbing organs in place of root hairs. Magnified too diam. — After 
 Frank. 
 FlG. 375. - Mycorhiza of orchids. A, diagram of a longitudinal section of a root ; /, /, 
 the cells of cortex filled with hyphae of fungus; i-, stele. Magnified about 20 diam. 
 />', a bit of longitudinal section of root of Ffeottia, near the tap. <■, epidermis ; /, a 
 series of cortical cells filled with fungus. Into the ceil a (nearer the tip of root) the 
 hyphae are just entering; in the cells above /', recently entered, they have only formed 
 a small knot about the nucleus. Magnified about 200 diam.— After Frank. 
 
 bacteria, in away yet unexplained, certainly enables the plant 
 to use free nitrogen from the atmosphere, while other plants 
 are required to obtain it in combination from the soil. The 
 enrichment of the soil by growing clover and similar crops 
 upon it and plowing them under is explained by their ability 
 thus to accumulate nitrogen from the air. 
 
 461. 3. Between plants and animals. -Mutualism also 
 
S YMBIOSIS. 
 
 337 
 
 occurs between plants and animals. Various species of plants 
 attach themselves to ani- 
 mals by which they are 
 carried about. The plant 
 is thus aided in obtaining 
 the materials for food, 
 and not infrequently the 
 plant conceals the animal 
 from another which seeks 
 it as prey. In this way 
 certain crabs are hidden 
 by algne attached to them. 
 One of the most striking 
 cases of protective m imicry 
 is that in which an Aus- 
 tralian fish has acquired 
 surface outgrowths which 
 imitate almost precisely the 
 appearance of brown sea- 
 weeds, so that, when quiet, Fig. 376.— a young cl 
 
 . , , ,., cles, t, on the roc 
 
 it looks like a stone to Uoff. 
 
 which seaweeds had attached themselves. Thus it often 
 
 escapes its enemies, as does the crab with its 
 
 mask of real seaweeds. 
 
 B. Helotism. 
 462. 1. Fungi and algae. — Helotism 
 exists between fungi and algae, constituting 
 
 F Hd?S; "Ealnil the bodies known as lichens, in which the 
 '• fungus is the master and the alga the slave. 
 (See ^[ 54</, and fig. 377.) The same 
 fungus may be found enslaving more than 
 one species of algae even within the same mycelium. The 
 prOtonema of mosses or even the leaves of some small 
 
 enveloping an alga, 
 us. Mag- 
 nified 950 diam. — 
 After Kemer. 
 
333 
 
 PLANT LIFE. 
 
 plants may be surrounded by a mycelium. The enslaved 
 green plants are generally unicellular or filamentous algae. It" 
 the latter are the species whose colonies produce voluminous 
 gelatine, the texture of the lichen body is gelatinous ; other- 
 wise it is tough and leathery. Some 
 of the fungi which ordinarily associ- 
 ate themselves with alga? to form 
 
 "^^ f /^ff?^'- - i y ' uncns ma y cx ' st *" ree as sa i )r °- 
 
 phytes. The alga itself influences 
 the form of the thallus more or less 
 profoundly according to its relative 
 amount. The same fungus associ- 
 ated with different algre produces 
 lichens which are described as dif- 
 ferent species, or even as different 
 genera. 
 
 463. 2. Animals and algae. — 
 Helotism exists between animals 
 and algae. Various simple animals, 
 such as radiolaria stentors, hydras, 
 sponges, echinoderms, and worms, 
 
 ^ radiolarian iLithn- 
 cercus annularis), one of the 
 microscopic single-celled animals 
 with a siliceous skeleton, .V, 
 formed by the outer portions of 
 the protoplasm, E, which is sep- 
 arated from the internal proto- 
 plasm, J, by a perforated cap- 
 sule, < ; mi, nucleus; fed, 
 threadlike protrusions of the 
 protoplasm. Embedded in the 
 
 outer protoplasm, E, are numer- 
 ous "yellow cells," Z, each with 
 its own cell-wall, nucleus, and 
 chloroplasts. These are an alga, 
 
 aXLaAZooxanthellanutricola. enclose algae in their bodies and 
 
 Highly magnified. — After 
 
 Butschli. 
 
 manufacture. The al 
 cellular forms which 
 division (fig. 378). 
 
 utilize the products of their food 
 , r a: thus enslaved are all minute uni- 
 multiply within the animal body by 
 
 C. Parasitism. 
 
 464. 1. Fungi. — A very large number of colorless plants 
 have adapted themselves to live upon living plants or ani- 
 mals which they force to act as their unwilling hosts. By 
 the presence of the parasite the normal functions of the host 
 or its normal growth or both are more or less seriously inter- 
 fered with, so as to produce disease, slight or grave, local or 
 
SYMBIOSIS. 339 
 
 general, according to the circumstances. Many animals are 
 
 Fig. 379.— Roots of a yellow Gerardia, G, attached to the root of a blueberry bush, B. 
 They enlarge at the points of contact and there send haustoria into the host root. 
 Natural size.— After Gray. 
 
 thus preyed upon by bacteria and fungi. Most communi- 
 cable diseases, such as typhoid fever, diphtheria, and tuber- 
 
 n dodder twining about a hop stem. All but the uppermost coils 
 show the groups of wartlike swellings trom whi< h haustoria pi ni trate the host stem. 
 Natural 51 v : I ■■ rm nation ol ame. Thi are arranged in ordi 1 
 
 from right to left, tn the lasl ound a suitable support and has 
 
 absorbed all the reserve food in the thicl nd, which has withered and died, 
 
 freeing the plant from the ground. Magnified 1 Vfter Kerner. 
 
34Q 
 
 PLANT LIFE. 
 
 culosis, are known to be due to the transfer of the parasite 
 from the diseased individual to the healthy one. In a similar 
 way bacteria live as parasites upon green plants, causing 
 disease and often death. The number of bacterial diseases 
 among plants is relatively small, for comparatively few bacteria 
 have been able to adapt themselves to living in the acid cell- 
 sap of plants. The number of diseases of plants due to 
 parasitic fungi, on the contrary, is very large. (For the mode 
 by which parasitic fungi gain entrance to the bodies of their 
 hosts, see % 52.) 
 
 465. 2. Seed plants. — A few seed plants have adapted 
 themselves to a parasitic life upon others. Some may be 
 reckoned as semi-parasitic, having 
 still green leaves and true roots. 
 In addition, however, special organs 
 are developed for attaching the 
 parasite to the roots of other plants, 
 from which at least a water supply 
 and probably food materials are 
 absorbed (fig. 379). Other semi- 
 parasites, such as the mistletoe, at- 
 tach themselves to the host above 
 ground, and have no true roots of 
 their own. Some parasitic seed 
 plants twine about their hosts, into 
 which they send absorbing organs 
 by means of which they derive all 
 their food from the host. Such is 
 the yellow parasitic vine, known as 
 dodder (fig. 380, A). These plants 
 germinate in the ground, and as seedlings possess true roots, 
 but after attaching themselves to the host the lower part 
 of the stem dies away so that the true roots are transient (fig. 
 380, B). Some root parasites begin to germinate upon the 
 
 Fig. 3S1. — A twig infested with a 
 parasitic seed plant {Apodan- 
 thes) whose body is hidden un- 
 der the bark of the host, through 
 whi( h a short branch bearing a 
 few scale leaves and a single 
 flower bursts. Natural size. — 
 After Kerner. 
 
SYMBIOSIS. 34 l 
 
 ground, but do not pass beyond the first stages of develop- 
 ment unless in contact with the root of the host by which 
 they are normally sustained. Under these conditions they 
 then form a conedike enlargement, which unites with the 
 cortex of the host root and penetrates to the stele. From 
 this conical stem arise the aerial shoots. Other parasites 
 form a network or even a complete hollow cylinder outside 
 the wood of the host and under the bark. From this 
 curious body the few flowers break through the bark and 
 appear upon the surface of the root or stem of the host, quite 
 as though they were a part of it (fig. 381). 
 
§ III. ADAPTATIONS TO ANIMALS. 
 
 CHAPTER XXV. 
 
 ANIMALS AS FOOD, FOES, OR FRIENDS. 
 
 I. Carnivorous plants. 
 
 466. Nitrogen supply. — The ordinary source from which 
 green plants obtain nitrogen for the making of their food is 
 the nitrogen compounds dissolved in the soil water. Plants 
 which live where the soil water contains little or no nitroge- 
 nous material are forced to resort to another source of sup- 
 ply. Some plants solve the problem by entrapping animals, 
 deriving from their bodies the desired nitrogen compounds. 
 Such plants are called carnivorous plants, or, since the bulk 
 of their catch consists of insects, insectivorous plants. The 
 catching of animals is done 
 
 467. i. By pitfalls and traps. — (a) The various pitcher 
 plants furnish a fine example of well-devised pitfalls. The 
 leaves of these plants have a deep, trumpetlike tube making 
 up the body of the leaf; or they carry at the end of a long 
 petiole a deep cup with a lid, as in the tropical pitcher plants 
 (fig. 382 ; see also fig. 155). The tube is one-third or half 
 full of water, in which are always found numbers of dead or 
 dying insects. The sides of the tube without art' often made 
 attractive by gaudy colors or by lines of sweet secretion, 
 which draw both flying and crawling insects. Within, its 
 surfaces are either excessively smooth, so as to afford no 
 
 342 
 
ANIMALS AS FOOD, FOES, OR FRIENDS. 343 
 
 foothold to an insect attempting to crawl out ; or covered by 
 stiff, downward-pointing hairs to oppose its passage; or the 
 side of the tube is filled 
 with thin translucent spots 
 through which the cap- 
 tives vainly strive to fly, 
 while the real opening is 
 concealed. By one or 
 other of these means the 
 prey is prevented from 
 escaping, and sooner or 
 later is drowned in the 
 liquid. In this liquid 
 digestive enzymes or bac 
 teria quickly dissolve the 
 softer parts of the insect 
 bodies, and the soluble 
 portions are absorbed by 
 the leaf. 
 
 {b) The bladderwort, 
 which abounds in quiet 
 pools, furnishes an ex- 
 cellent illustration Of traps Flr - 382— A, trumpet-shaped sessile leaf of Sar- 
 racenia variolaris, snowing thin membran- 
 (fiUS. 78':, ^84). UnOll m,s windows in the meshes of the veins of 
 \ © o 01 o ~tj 1 the hood which arches over the mouth of the 
 
 the leaves are numerous trumpet. /;, cup-shaped petioied leal .if .\v- 
 
 pentkes villosa, with elevated lid and margin 
 minute bladders, each ribbed. One-third natural size.— After Kerner. 
 
 with a small opening about which divergent hairs serve as 
 
 guides to the entrance. The entrance is lightly closed by a 
 
 flap of membrane, which is readily lifted by minute water 
 
 animals. After they have passed through the opening the 
 
 membrane drops behind them, ami is stiff enough to prevent 
 
 their escape. Death ensues sooner or later, and absorbing 
 
 hairs on the inner face of the trap take up the nutritive 
 
 materials. 
 
344 
 
 PLANT LIFE. 
 
 468. 2. By adhesive surfaces. — Animals are also cap- 
 tured by adhesive surfaces. These surfaces are covered by a 
 
 ■S\ I. ..v -:■ 
 
 m3^ 
 
 .%i. 
 
 Fig. 383. — A bladderwort {Utricularia Grafiana), showing an aerial flower stalk 
 carrying an open flower and a second one above from which the corolla lias fallen. 
 Some stems bear numerous, finely branched leaves, /■, and others the large bladders, 
 />'. See fig. 384. A shoot of a' smaller species is shown at a, with bladders and 
 leu is on same stem. About two-thirds natural size.— After Kerner. 
 
 sticky fluid secreted by numerous glandular hairs, and upon 
 these many small insects may be found dead. In many 
 
ANIMALS AS FOOD, FOES, OK FRIENDS. 345 
 
 cases the softer parts of the insect bodies are digested and 
 absorbed. It should be noted, however, that adhesive sur- 
 
 Fig. 384. B Fig. 385- A 
 
 Fig. 384. — A bladder of Utricularia vulgaris, halved lengthwise, with an imprisoned 
 
 crustacean, Cyclops, a to b, opening, with hairs, //, i, about it; b to c, cushion-like 
 
 rim, b-c part cut through, d-e surface on which the flap,./, rests, opening inwards only ; 
 
 g, wall of bladder set with absorbing hairs within and glandular hairs without ; k, the 
 
 stalk (secondary petiole). Magnified 20 diam. — After Cohn. 
 Fig. 3S5.— Two leaves of sun-dew I Drosera rotundifolia). A, in expanded position 
 
 showing the tentacles. B, shortly after the capture of an insect. The tentacles on the 
 
 right half are indexed to bring the glandular tips in contact with the prey. Magnified 
 
 z\ diam. — Alter Kerner. 
 
 faces are also merely protective against the visits of unwel- 
 come guests, who steal nectar or pollen. (See ^[ 488.) 
 
 469. 3. By move- 
 ments of traps and 
 adhesive surfaces. — 
 Somewhat more 
 complex methods of 
 capture are exhibited 
 by leaves which have 
 special movements 
 connected with traps 
 or sticky surfaces. 
 The sundew of our 
 swamps has the edges 
 and surface of the leaves covered 
 
 -Sgf? 
 
 Fir.. 386.— Cluster of leaves at the base of flower stalk 
 of Venus' fly-trap {Dioncea muscf/ula). One-half 
 
 natural size.- Alter Drude. 
 
 r ith many outgrowths, 
 
346 
 
 PLANT LIFE. 
 
 each of which is tipped by a large gland (fig. 385). The 
 clear, glistening fluid, a large drop of which is secreted 
 by each gland, is sticky enough 
 to entangle even insects of con- 
 siderable size, which alight upon 
 the leaves. The viscid secretion 
 envelops the struggling insect, and 
 at the same time the branches of 
 the leaves bend slowly inward 
 until more and more of the sticky 
 glands are thrust upon it. The 
 character of the secretion then 
 changes. It becomes 
 more watery and 
 contains ferments 
 which soon digest 
 the softer parts of the 
 
 Fig 187. — .-/, blooming plant <>f Aldrovandia vesiculosa. Natural size. Vfter 
 Drude. B, a single circle ol leaves seen from the center above, slum-inn stalk ami 
 two semicircular lobes. Magnified] diam V.fter Caspary. 
 
 Fig. 388. Transverse section through closed trap of A Idrovandia, showing on inner 
 face long sensitive hairs and many absorption hairs. Only the central part is three 
 layers of cells thick; abroad margin is only one cell thick. Compare appearance in 
 ''■ fig- :< s 7- Magnified 2<> diam. — After Caspary. 
 
 body. These are absorbed, and play an important part in 
 the nutrition of the plant. 
 
 Dioncea (fig. 386) and its water mate, Aldrovandia (fig. 
 387), have leaves whose blades are somewhat like a spring 
 
ANIMALS AS FOOD, FOES, OR FRIENDS. 347 
 
 trap. The blade is two-lobed, with a hinge along the middle 
 (figs. 205, 388;. The hinge is in reality a cushion of tissue 
 upon the back, which quickly throws the two halves of the 
 leaf together when the sensitive hairs on the inner face 
 of the trap are touched. The movement is sudden enough 
 in Dioncea to catch the slow-flying insect, or, in Aldrovandia, 
 the minute water animal. The prey is prevented from escap- 
 ing by the interlocking, toothdike lobes along the edges 
 of the leaf. Digestion and absorption of the nitrogenous 
 materials follow.* 
 
 II. Herbivorous animals. 
 
 470. Protection. — While a really insignificant number of 
 minute animals are eaten by plants, a very large number of 
 plants find it necessary to protect themselves in some way 
 against destruction by browsing animals, insects, snails, 
 and slugs. Since the animal world relies for its food 
 supply ultimately upon the green plants, it is plain that 
 no such protective measures are completely effective. The 
 protection, therefore, may be looked upon as a protection 
 against extermination rather than against injury. As pro- 
 tective adaptations against browsing animals are usually 
 reckoned : 
 
 471. 1. Armor, in the form of hard, leathery, sharp- 
 edged, woollv, bristly, or sticky parts, especially leaves 
 (figs. 361, 362, 364, 389); or thorns (figs. 157, 390), prickles 
 ( fig. 115), or stinging hairs | fig. 391). 
 
 *Travesties upon these strange methods of nutrition appear periodically 
 in newspapers, and plants of remarkable size and forbidding aspect are 
 represented as capturing birds, animals, and even men, thai venture into 
 their neighborhood. It should be noted, therefore, that in all cases the 
 plants which capture animal food entrap only the smaller animal-, scarcely 
 any of them, except those caught by the pitcher plants, larger than the 
 
 common house fly. 
 
348 
 
 PLANT LIFE. 
 
 472. 2. Distasteful or injurious substances, such as 
 volatile oils, camphors, acids, tannins, alkaloids, etc. The 
 milky juice of plants like milkweeds, which e 
 
 often contain acrid substances, may also be 
 protective. 
 
 473. 3. Mimicry. — Certain plants which 
 are not distasteful or disagreeable have 
 adopted the same form of leaves and stem 
 and the general habit of those which graz- 
 ing animals have found distasteful. This 
 
 mimicry causes them to be 
 avoided, as well as the really 
 hurtful ones which they imitate. 
 
 Fig. 389. 
 
 Fig. 390. 
 
 Fig. 389. — Edge of a leaf of a sedge (Carex strii t,i), showing alternate epidermal cells 
 pointed and underlaid by two layers of mechanical cells. Magnified 200 diam.— After 
 Kerner. 
 
 Fig. 390. — Part of a shoot of barberry in spring showing leaves of preceding year as 
 persistent three-pointed thorns, in whose axils the buds are developing into the sea- 
 son's siioots. Natural size. — After Kerner. 
 
 Fig. 391. — A stinging hair of the nettle {JJrticd) t in longitudinal section, x, emerg- 
 ence in which the single-celled hair abc is sunk below <il<. The knoblike apex < is 
 easily broken off because the cell wall just below it is thin and brittle. The oblique 
 cutting edge left pierces the skin like a hypodermic needle and some of the acrid cell 
 contents enters the wound, causing intense itching. Magnified 60 diam. — After 
 Frank. 
 
 474. 4. Ants. — In the tropics particularly, certain plants 
 
ANIMALS AS FOOD, FOES, OR FN I ENDS. 349 
 
 secure themselves from the attacks both of browsing ani 
 inals and leaf-cutting insects 
 by encouraging the presence 
 of colonies of warlike ants 
 upon them and making pro- 
 vision for their defenders' 
 wants. A very large number 
 of species * protect themselves 
 in this way. For the ants 
 the plants provide (a) nectar, 
 
 Fig. 392. 
 
 Fig J93. 
 
 Fig. 392.-P.it of a section through the cushion («•', fie;, 303I at base ol leal ol ( 'ecropia, 
 showing the velvet} hairs with which it is covered, and among them the egg-like 
 bodies, rich in proteids and fats, whi< h the ants collect and cany into their nests in the 
 interior of the stem. Magnified about mcliam. After Schimper. 
 
 Fig J93 \pr\ ol the hollow stem of a young Cecropia. a, the thin spot above a 
 leaf, whii h al lias bei 11 gnawed through by the ants to make their nest in the cavity 
 ol the stem : 1 . the I u hion at lias,- ,.1 I, .it si'.ilk where food bodies grow. See fig. 39--. 
 Two-thirds natural size. Alter Schimper. 
 
 similar to that secreted in the flower, i.e., a watery solution 
 of various sugars, but secreted by nectaries outside the 
 flower ; (//) fodder, in the form of hairs (fig. 392), often of 
 peculiar form, richly supplied with nutritive substances, 
 
 More- than three thousand arc listed by Delpino. 
 
;;o 
 
 PLANT LIFE. 
 
 growing from special parts of the surface, which are regularly 
 eaten by the ants and grow again, so that a constant supply is 
 at hand; (c) divel/ings of various sorts. Certain plants have 
 the stems hollow throughout, with special modification of the 
 structure at certain spots, so that an entrance to these hollows 
 may be readily made (fig. 393). In others, portions of the 
 internodes are much enlarged and hollow ; sometimes only 
 the internodes in the region of the flower clusters are thus 
 transformed. In other plants chambers are produced by the 
 bladdery enlargement of the under part of the leaf near the 
 midrib (fig. 394). In some acacias the stipules are developed 
 
 as massive thorns, which 
 
 the ants inhabit. 
 
 475. Domatia. — Somewhat sim- 
 ilar dwelling places, though less 
 perfect, are provided by many 
 plants for the mites. These dwell- 
 
 lii 
 
 r 
 
 Fig. 304. 
 
 395- 
 
 Fk;. 394. — Under side of the base of the leaf blade of Tococa lancifolia, showing 
 bladder on each side of midrib, each with entrance at a, a. Natural size. (?)— After 
 Si lumunii 
 
 Fig. 395— Domatia on under side of leaves. A, between midrib and laterals of 
 Psychotria. 8, between midrib and lateral of the linden ( Tilia Europaa). Magni- 
 fied about 5 diam.— After LundstriSm. 
 
 ing places are in the form of minute shelters usually upon the 
 under side of the leaves. They are generally formed by hairs 
 roofing over an angle of the veins, or by various outgrowths, 
 folds and pits (fig. 395). Their significance is not at all 
 clear. 
 
ANIMALS AS FOOD, fiOES, OR FRIENDS. 35 1 
 
 476. 5. Crystals. — Plants protect themselves against soft- 
 bodied animals, such as snails and slugs, by means of the 
 sharp-pointed crystals which are present in the leaves of 
 many species. According to Stahl, all tissues containing 
 these crystals are avoided by such animals, but will be readily 
 eaten by them after the crystals are removed. 
 
II. REPRODUCTIVE ADAPTATIONS. 
 
 CHAPTER XXVI. 
 
 PROTECTION AND DISTRIBUTION OF SPORES 
 AND SEEDS. 
 
 The present knowledge of reproductive adaptations among 
 the flowerless plants is very imperfect, though probably many 
 exist. This chapter must, therefore, discuss chiefly the 
 adaptations in the more complicated reproductive structures 
 of seed plants which have been most studied, with only 
 incidental allusions to such arrangements in the lower plants. 
 
 I. Protection against bad weather. 
 
 477. By movements. — Spores unfitted to resist low tem- 
 peratures or wetting must be protected from rain, cold, and 
 similar conditions. When nectar is secreted in the flower as 
 an attraction to insects it is liable to be washed out by rain 
 unless access of water to the interior of the flower is pre- 
 vented. To avoid these dangers, many plants upon the 
 approach of unfavorable weather bend their leaves so as to 
 close the flower (fig. 396), or arch the stalk so as to turn the 
 blossom into such a position that the rain or snow will not 
 reach the sporangia or the nectaries. These movements of 
 the leaves and stalk are combined in various ways to meet 
 the needs of each particular form. All of them are growth 
 
 352 
 
DISTRIBUTION OF SPORES AND SEEDS. 353 
 
 movements, brought about by variations in light and tem- 
 perature, which act as stimuli. (See ^| 286.) 
 
 II. Adaptation to distribution of spores. 
 The fact that spores are found in every group of plants 
 from the lowest to the highest makes it probable that a great 
 
 Fig. 396. ''"■ 3^7 
 
 Fig. 396.— A, flower of California poppy (Eschscholtzia), opened in sunshine ; /•'. the 
 
 same, closed in wet weather. Natural size. -After Kerner 
 Fig. V17. A, aerial liypha of Pilobolus crystallinus, with sporangium. The liypha is 
 
 swollen beneath the sporangium and very turgid. />'. the same with sporangium torn 
 
 off at base and being shot away by the violent escape of the mucilaginous contents uf 
 
 the hypha. Magnified about lodiam. After Kerner. 
 
 variety of ways will have been adopted by plants to secure 
 their distribution. The more important ways may be grouped 
 as follows : 
 
 478. 1. By turgor and tension. — Among the fungi, spores 
 are often projected from the spore case by the pressure upon 
 
354 
 
 PLANT LIFE. 
 
 it of neighboring cells, increasing until the sporangium 
 
 ruptures suddenly ami the spores are shot out like projectiles. 
 In some cases the whole sporangium is thrown off in this 
 fashion, often to the distance of a meter or more (fig. 397). 
 
 Fig. 
 
 B 
 
 Fig. 398. 
 
 Fig. 398.— A, a fly killed by the fly fungus {Empusa Muscce), stuck to wall by hypha 
 and surrounded by'a halo of the spores. Two-thirds natural size. B, hvph.v projecting 
 into the air from the body of the fly, from whose tips spores are being shot off. 
 Several are shown in various stages of development. The turgor of the enlarged end 
 of hvpha finally ruptures the atta< hment ol the spore and it is shot off surrounded by 
 the mucilaginous contents which cause it to adhere to any object struck. Magnified 
 200 diam. "" C, a spore enveloped in mucilage. Magnified 420 diam — After Kcrner. 
 
 Fig. 399. — A, spore chain from a fructification {acidiuni) of the cranberry rust 
 (Calyptrospora). s, s, mature warty spores separated by an intermediate cell, w, 
 which has arisen by the division of the spore fundament by a transverse wall into a large 
 upper and a small lower cell. The upper becomes the spore and the lower thi 
 mediate cell which elongates, loses its contents, and dies ; its wall becomes mucilagi- 
 nous and so loosens the spores. Magnified 420 diam.— After Hartig. B, three spores 
 at tip of an acropetal chain ; the terminal spore therefore smallest A disjunctor, </, 
 has been formed between the layers of the partition wall and lias forced them apart 
 The white area between two lowest shows area formerly connected. ;/, nuileus. 
 Magnified 520 diam.- After Woronin. 
 
 The fungus which attacks and kills house flies in summer 
 casts off the single spore from the end of the stalk carrying 
 it by the bursting of the end of this stalk through excessive 
 turgor (fig. 398). With the spore goes the contents of the 
 
DISTRIBUTIOX OF STORES AiYD SEEDS. 
 
 355 
 
 stalk, so that it is surrounded by a mass of mucilage, thus 
 enabling it to adhere to any object which it strikes. 
 
 Filaments carrying the spores often twist upon drying 
 and thus jerk off the spores ;is they suddenly slip past some 
 obstruction. When spores are produced in chains, either 
 the walls of a special cell or a layer of the cell-wall between 
 them may act as a separator by its alteration into mucilage 
 (A, fig. 399). In some cases the spores are wedged apart by 
 the secretion, between the layers of the wall joining them, of 
 a cellulose plug which gradually elongates into a slender 
 spindle to whose tips the spores are so slightly attached that 
 the lightest breath carries them away (B, fig. 399). The 
 elaters of the liverworts (fig. n and c 321) serve in some 
 cases to sling out the spores when the capsule bursts ; in other 
 cases, as in Marchantia, they entangle the spores, insuring 
 gradual and preventing too sparing distribution. The teeth 
 around the mouth of the capsule of mosses serve to distribute 
 the spores at opportune intervals, instead of having them 
 emptied out all at once. In some mosses the teeth are erect 
 or recurved when dry, but upon being moistened they arch 
 over the mouth, thus 
 forming a nearly closed 
 cover (fig. 400). < hints 
 have the teeth arched 
 over the mouth when 
 dry or permanently fas- 
 tened together by their 
 tips, thus narrowing the 
 opening and allowing 
 the spores to sift out 
 between them. In some 
 cases the teeth, by their 
 form and hygroscopic curvatures, serve to sling out the spores 
 to a short distance. In many ferns the annulus of the spo- 
 
 Fig. 4<>" Capsules "i .1 m<.ss [Grimmia) afier 
 fall of lid. .-J, teeth erect when dry. leaving cap- 
 Bule widely open ; /•'. the same in damp weather. 
 Magnified about 10 diam. After Kerner. 
 
356 
 
 PLANT LIFE. 
 
 rangium tends to straighten itself upon drying, thus rupturing 
 the sporangium. After bending backward for some distance 
 until the tear gapes wide, it suddenly straightens and hurls 
 the spores to a considerable distance (fig. 4or). 
 
 Fig. 401.— Sporangia of the male fern (Aspidium Filix-mas) scattering the spores. 
 A, closed; A', burst by the drying of the annulus ; (', the annulus after becoming 
 strongly recurved is just returning to a nearly straight form and the spores are thereby 
 being hurled toward />'. Magnitied about 65 diam. — After Kerner. 
 
 479. 2. By water. — In perfectly quiet water, distribution 
 of spores depends solely upon their own motor organs. Only 
 zoospores (see ^| 306) are so furnished. For these a film of 
 water is sufficient, and they may swim some distance over 
 what appear to be merely moist surfaces. Most of the algae 
 and fungi living in water form zoospores. Their production 
 is often controlled by external conditions, the formation of 
 new individuals being thus provided for when the old are 
 threatened with destruction. 
 
 In flowing water and by currents, non-motile spores are 
 readily distributed. Even such relatively heavy spores as 
 the resting spores of algae may be carried long distances by 
 water currents. The microspores ( pollen) of aquatic seed 
 plants are sometimes carried to the stigma by water currents, 
 as in Vallisneria | fig. 402). 
 
 480. 3. By air currents. — Spores may be readily carried 
 by the air on account of their small size and their ability to 
 
DISTRIBUTION OF SPOKES AND SEEDS. 357 
 
 withstand dryness. Must spores float in the air for some time 
 like dust particles, and the slightest current is adequate to 
 lift many and carry them along. Spores of most non-aquatiG 
 
 Fie. 402.— Pollination of eel-grass (I'allisneyia spiralis}. The large flower is a pis- 
 tillate one. with stigmas .'ringed on under side. About it are floating staminate flow- 
 ers in various stages of development, having broken from submersed stems which 
 bore them. The ones on the right and left have the boat-shaped perianth lobes turned 
 back, stamens mature, and pollen exposed ; one has floated so that the pollen is 
 brought into contact with the stigma of the pistillate flower. Magnified 10 diam. — 
 After Kerner. 
 
 fungi, mosses, and fernworts are distributed by air currents. 
 The microspores of some seed plants, especially the common 
 forest trees, are carried in this way. 
 
 481. 4. By animals, especially insects. — It is the seed 
 plants, particularly, which have adapted themselves to the 
 distribution of spores by this means. The development of 
 the male plants in this group must be completed in tin- 
 neighborhood of the female plants, tor the reason explained 
 in ^[ 386. The microspores must, therefore, be carried to 
 the ovules of gymnospenns or to the stigmas of angiosperms 
 
35 8 PLANT LIFE. 
 
 and lodged there. It has been clearly shown not only that 
 adaptations for securing this result have been developed, but 
 also that there have arisen various ingenious adaptations to 
 sec ure cross-polli nation and to prevent close-pollination. 
 (See \ 358.) Some of these may be here enumerated. 
 
 482. Adaptations for cross-pollination. — (a) The sepa- 
 ration of the stamens and pistils, staminate flowers and pistil- 
 late flowers being produced upon the same plant or even upon 
 different plants of the same species ; (I>) the early ripening of 
 the stamens so that they discharge their spores before the 
 stigma of the same flower is exposed or receptive, or vice 
 versa; (c) arrangements preventing the pollen from reaching 
 the stigma of the same flower, vvhi< h vary according to the 
 different modes by which the transfer of the pollen is made; 
 (J , the failure of fertilization to occur when close-pollination 
 happens. In such cases the pollen is said to be impotent. 
 This means that the male plants are either not completely 
 formed by it, or that their sperms do not stimulate the egg 
 to development. 
 
 483. Adaptations for close-pollination. — But close-pollin- 
 ation, even though it results in weaker offspring, is better 
 than entire failure to produce progeny. Therefore, some 
 plants permit close-pollination in the event of failure to 
 secure cross-pollination, while a few have adaptations which 
 insure it. Our common violets produce in the late spring 
 and early summer in< onspicuous blossoms which do not open, 
 containing stamens with few pollen grains. These flowers, 
 however, produce seed abundantly, and always by close- 
 pollination. Various other species have similar arrange 
 ments. 
 
 484. Adaptations to insects.— The adaptations to secure 
 cross pollination through the visits of insects are so numerou 
 and so varied, and the advantage in the number and weight 
 of seeds produced is so marked, that for most seed plants 
 
DISTRIBUTION OF SPORES AND SEEDS. 359 
 
 cross-pollination must be considered the far more desirable 
 process. Flowers are adapted to insect visitors in the follow- 
 ing ways : 
 
 485. (</) Food. — They provide for their visitors edible 
 substances, such as nectar and pollen,* material for nest 
 building, shelters, or breeding places. 
 
 486. (b) Advertisements. — They advertise the presence 
 of such attractions in two ways, which are sometimes com- 
 bined, and insects accustomed to visit flowers quickly learn 
 to know what the advertisements mean. (i) By color. 
 Flowers are so colored as to attract notice ; and this is 
 further secured by the large size of individual flowers or by 
 massing many small flowers into close clusters. (ii) By odor. 
 Odors are due to volatile oils, usually in the epidermis of the 
 petals or sepals, often curiously localized. Dusk- and night- 
 blooming plants often have heavy odors. 
 
 487. (c) Form and position of parts. — Many plants by 
 the form of their flower leaves provide landing places for 
 welcome visitors. Guides to the location of the nectar, in 
 the form of grooves, folds, hairs, lines of color, etc., are 
 often present. The form and position of the stamens and 
 pistils is often such as to insure the desired transfer of pollen. 
 These positions may be permanent or they may be secured 
 by movements at opportune times. Among the movements 
 are those due to turgor and those due to the presence of 
 motor organs. In a very large number of cases, by the form 
 of the flower-leaves and the essential organs the plant is 
 adapted to visitation by particular insects, and if these are 
 not present, or it their access is denied, constant failure to set 
 seeds is the result. Thus one may distinguish plants adapted 
 to bees, moths, butterflies, flies, birds, or even snails. 
 
 488. (d) Exclusion of unwelcome visitors. — In addition to 
 
 * The microspores are often produced in great excess of the plant's own 
 
 needs. 
 
360 
 
 PLANT LIFE. 
 
 provision for welcome guests must be enumerated the meth- 
 ods of excluding unwelcome guests, which on account of their 
 size and habits are unable to bring about the desired transfer 
 of the pollen, while at the same time they rob the plant of 
 nectar or pollen provided for more acceptable visitors. 
 
 Fk;. 403. — Flower of Cobeea scandens,b&\\eA\ showing tufts of hairs on the base of 
 the filaments, of which there are five ; these close the bottom of the corolla cup where 
 nectar is secreted against intruders. Three-fifths natural size. — After Kerner. 
 
 (i) Various obstructions with- 
 in the flower may render ac- 
 cess to the nectar impossible 
 to the smaller and weaker in- 
 sects, while allowing others 
 to reach it. Such obstruc- 
 tions are formed by folds, 
 hairs, and other outgrowths 
 upon the flower leaves or the 
 essential organs (fig. 403). 
 (ii) Obstructions outside the 
 /lower may exclude crawling 
 
 Fig. 404.— Flower of a saxifrage .{Saxi/rapa insects. Such are sticky Slir- 
 controversa), protected against invasion J 
 
 by the numerous sticky glandular hairs on f aces an( J hairs (fig. 404), 
 the flower stalk, ovulary, and calyx. Mag- v ° ^ T /» 
 
 nified several diam.— After Kerner. nioatS about the Stem formed 
 
 by cup-shaped leaves holding water, or those formed by 
 
 water in which swamp plants grow. (iii) The time of bloom- 
 
DISTRIBUTION OF SPORES AND SEEDS. 36 1 
 
 ing also prevents the visits of any insects except those flying 
 at that particular season. 
 
 III. Adaptations to the distribution of seeds. 
 
 489. After the ripening of the seed various devices and 
 forces operate to scatter them at as great a distance as pos- 
 sible from the parent, so that the young plants will not come 
 into competition with the old ones or with each other. This 
 object, which is secured in lower plants by the distribution 
 of the spores, can only be attained in seed plants by scatter- 
 ing the seed, because the megaspore is not set free ; the ga- 
 
 Fir,. 405.— Elastic valves for slinging seeds. A, fruit of wild geranium (G. /,i/«.r/r,-) 
 with 1 11 -i-Msii-m , ,il\ \ I In live 1 arpels surround an elongated torus, from which the) 
 break first at bottom ; curling upward suddenly they sling the seed out oi the basal 
 part which has cracked along the inner side. B, fruit ol touch-me-not \lmpatiens 
 noli-me tangere), one sound, the other bursted 'riK-i.nin.-ls have curled up elasti- 
 cally from the base and slung out the seeds. Natural size. Aftei Kemer. 
 
 metophyte is consequently developed within the sporophyte ; 
 and the embryo sporophyte is likewise enclosed by the old 
 
 sporoph] te (See ■ .108.) 
 
362 PLANT LIFE. 
 
 The methods by which distribution is secured may be 
 
 grouped as follows : 
 
 490. 1 . Distribution by tension and turgor. — Some plants 
 (e.g., witch hazel) as they ripen the pericarp, alter its tissues 
 in such a way that the contained seeds are compressed when 
 the pericarp dries, and after it opens they are pinched out 
 from the narrowing valves, as a wet apple or melon seed may 
 be shot from between the thumb and finger. In others 
 (e.g., touch-me-not and cranesbill) the parts of the peri- 
 carp shorten on one side until the strain breaks them loose, 
 when they become suddenly elastically curled and sling 
 the seeds contained to a considerable distance (fig. 405). 
 Somewhat similar causes, i.e., curvatures due to unequal 
 shrinkage or swelling of the tissues, enable some fruits 
 with long awn or bristles to creep over the ground or to 
 bury themselves in it when al- 
 ternately moistened and dried 
 (fig. 406). The pericarp of the 
 squirting cucumber is so dis- 
 tended by the almost liquid 
 pulp surrounding the seeds that 
 it ejects the mass through the 
 opening formed by its separa- 
 tion from the axis. 
 
 491. 2. Distribution by 
 water. — In some plants this 
 is secured by the fact that the 
 fruits open only when moist- 
 ened. In such cases the seeds .. , _. ..,.,. 
 
 lie 406.— Pieces mli> which the fruit of 
 
 may be either Washed OUt from storksbill breaks. There are five ol 
 
 J these each corresponding to .1 carpel and 
 
 the opening pods by rain, or arranged on the sides <.i a prolonged 
 
 1 ° ' - torus as in A , fig 405. A, when dry the 
 
 may be loosened in many beak is spiraHy .-..iie.!: a, when moist. 
 
 ' - I lie l>asc is hard and very slurp. .Magin- 
 
 other ways. The seeds are Bed about a diam.— After Noll. 
 
 thus set free at the time best suited to their prompt germi- 
 
DISTRIBUTION OF SPOKES AND SEEDS. 
 
 363 
 
 nation. Some plants, adapted to distribution by water, are 
 provided with floats. These floats may eonsist either of the 
 enlarged and bladdery pericarp (or some portion of it), or 
 of the spongy, air-filled seed coat. The fruits or seeds are 
 thus made more buoyant and float upon the surface instead of 
 sinking as usual. Naturally, water-loving plants are chiefly 
 adapted to distribution in this manner. 
 
 492. 3. Distribution by winds. — Some plants which secure 
 their distribution by winds are only lightly attached to the soil 
 at maturity, so that they 
 are readily uprooted and 
 carried bodily, when dry, 
 for considerable distances 
 by the wind. The transfer 
 is facilitated by the incurv- 
 ing of the branches upon 
 drying, so that the uprooted 
 plant is more or less spheri- 
 cal in outline, or by the fact 
 that the plant is normally 
 spherical by the propor- 
 tion of the branches. Such 
 plants are known as " tum- 
 ble weeds.'* Singly or ag- 
 gregated in large bundles 
 they arc rolled over plains 
 and prairies for long dis- 
 tances, shaking out their 
 seeds as they go, or open- 
 ing their fruits when moist- 
 ened. Another adaptation 
 for distribution by the 
 wind is the small size of some seeds. Thoseofsome orchids 
 are so diminutive that it takes 500,000 to weigh 1 gram. 
 
 Fig. 107.— Seeds ol an 1 ■'■ > **\ 
 
 with cells ol seed coal bladdery and filled with 
 air. These seeds are eje< ted From the < apsule 
 by the contortions ol the hairs on its inner 
 faces which curve and twist as the moisture in 
 the ah varii s. Magnified diam Ifter 
 
3^4 
 
 PLANT LIFE. 
 
 Such minute seeds are readily blown long distances by 
 the wind. Relative lightness is also secured by the con- 
 struction of some seeds, which are surrounded by a volu- 
 minous coat containing many large air spaces (fig. 407). 
 Outgrowths from parts of the seed coat or pericarp also secure 
 the same end. In such cases the fall of the fruit or seed 
 though the air is so retarded that it may be carried laterally 
 some distance by the wind. No seeds, however small, float 
 long in quiet air, since buoyancy is derived only from air- 
 
 Fro. 408. — Fruits with wings. A , fruits of ailanthus tree (A . gla miulosus), each carpel 
 with double wing. />', truits oi a maple tree, each carpel with a single wing. Natural 
 size. — After Kerner. 
 
 containing tissues. A flattened form of the fruit or seed is 
 very common, and this form is often exaggerated by the 
 formation of wings, i.e., of thin outgrowths from the surface 
 (fig. 408). The center of gravity in such cases is so placed 
 that the plane of flattening will be nearly horizontal when the 
 seed falls. These fruits or seeds sink from 1 to 30 times as 
 slowly as the same bodies without the wing. Sometimes spe- 
 cialized persistent flower leaves, either corolla or calyx, are 
 used for this purpose, as in dandelion and thistle (fig. 409). 
 
DISTRIBUTION OF SPORES AND SEEDS. 365 
 
 Hairs of the most various origin arc produced in such 
 numbers and position as to form either parachutes or tangled 
 woolly envelopes to the fruit or sec Is ( figs. 410, 41 1). 
 
 Fig. 41" 
 
 Fig. 409.— Heads of fruits of the dandelion; single fruits falling, exposing common 
 
 torus and involucre. Natural size.— After Kernel . 
 Fig. 410. — Fruits of a willow, burst, and allowing the seeds, each with .1 tuft of silky 
 
 hairs (coma), to escape. Natural size. — After Kerner. 
 
 493. 4. Distribution by animals. — To secure this there 
 arc two general methods observable. (</) The seed or fruit 
 is cither adapted for transport by adhering to the both- of the 
 animal ; or (b) the seeds are surrounded by edible parts, and at 
 the same time so protected against the digestive juices that 
 they may pass uninjured through the alimentary canal. A few 
 plants are distributed by animals which collect and hide their 
 fruits or seeds (e.g., the squirrels 1. The adhesion of fruitsor 
 seeds to animals, especially to those which are provided with 
 
3 66 
 
 PLANT LIFE. 
 
 -A fruit of Barbadoes cotton, open, exposing the voluminous hairs (commer- 
 cial cotton) which clothe the seeds. Natural size. — After Kerner. 
 
 Fig. 
 
 412. 
 
 Fig. 
 
 Fig. 412. — Fruit of Agritnonia, halved; showing torus, carrying calyx and withered 
 stamens above, covered with hooks, and enclosing the hard peril irp, with a single 
 seed. A pistil which did not mature lies to the right. Compare torus in tig. 288. 
 Magnified about 8 diam. — After Baillon. 
 
 FlG. 413. — Fruit of tick trefoil {Desmodium Canadense). A, pods which separate into 
 sections, each containing one seed. They are covered with stiff hooked hairs, some 
 of which are shown enlarged at />'. A, natural size. />', magnified about 20 diam. — 
 After Kerner. 
 
DISTRIBUTION OF SPORES AND SEEDS. 367 
 
 fur, is generally secured either by surfaces made adhesive by 
 the sticky secretion from glandular hairs, or by the develop- 
 ment of outgrowths in the form of hooks or barbed prickles 
 (figs 412,413, 414,415). A few water animals and wading 
 birds distribute seeds which . 
 happen to fall into the mud 
 by the adhesion of this mud 
 to their bodies. 
 
 The fleshy fruits with edible 
 parts are usually colored to 
 attract the notice of the fruit- 
 eating animals. Seeds which 
 escape crushing by the teeth or 
 grinding in the gizzard are apt 
 to be in condition to germi- 
 nate when voided. The seeds 
 of the mistletoe are separated 
 from the pulp of the berry by 
 the birds which eat them, Fig. 414. Fig. 4 i S . 
 
 nnrl eriVtiner rr> the* Kill or« FlG ' 4J4-— A, cluster of fruits of Spanish 
 aiHl, Sticking tO tile Dill, are needles {Bidens bipinnata). A. a single 
 m-i'i„.,1 riff ,-m the> KronoViao fruit enlarged, show in< barbed awns, rep- 
 Wipea OH Oil tile Drancnes resenting the calyx lobes, by which it aS- 
 
 nf trpp« whprp thMV rr*>rmi heres - ,l ' animals - A > natural size; A', 
 
 OI trees, Wliere tney germi- magnified 2i diam.— After Kerner. 
 
 n _j. FlG. 415. — Fruit of cockle-bur ( Kanthium 
 
 u <* tCl strumarium), halved, showing two seeds, 
 
 'l'h.> nrl'ii.tQtinn nf nlontc tn the u .PP er " f which usually germinates a 
 
 1 ne adaptation ot plants to NL . ar i ater ,i, an t i le lower. Natural size 
 any one of these agents of AfterArthur - 
 
 distribution is likely to be more or less effective with other 
 agents. For example, the tufts of hairs which increase the 
 buoyancy of the seed in air would be equally effective 
 should the seed chance to alight upon water, or they may 
 suffice to entangle the seed in the fur of animals. 
 
 494. Adaptations for germination. — Adaptations for dis- 
 tribution not infrequently also secure advantage in germina- 
 tion. It is important for man) seeds that they be anchored 
 to the ground when they have once been transported, so that 
 
368 PLANT LIFE. 
 
 they may not be subject to further disturbance. Such an- 
 chorage is sometimes secured by the transformation of the 
 outer layer of cells into mucilage, so that the seed, upon be- 
 coming wet, is stuck fast to the soil ; or by the tufts ot hair 
 which, once wetted, cling to the surface of the earth ; or by 
 barbed bristles and hygroscopic awns which, having become 
 entangled among the grass, work a pointed seed body deeper 
 by every change of moisture (fig. 406). 
 
 Study of plants in relation to their surroundings, therefore, 
 yields the conclusion that these organisms are wonderfully 
 plastic, responding either temporarily or permanently to 
 every change in conditions. It is greatly to be desired that 
 the too common thought of plants as only things to be clas- 
 sified may be replaced by the conception of them as beings at 
 work, to be studied alive. 
 
APPENDIX I. 
 DIRECTIONS FOR LABORATORY STUDY. 
 
 Part I : Morphology. 
 
 I. ALG^E. 
 
 A. PLEUROCOCCUS 
 
 i. Examine with a lens pieces of bark bearing Pleurococcus 
 and similar algae. Note the irregular distribution of the green 
 granular heaps of plants. Is there any similarity to the distri- 
 bution of higher plants over uncultivated areas? 
 
 2. After soaking a piece of bark for a few minutes, scrape off 
 with the nail or a dull knife blade some of the green material, 
 spread it as well as possible in a drop of water on a slip of glass, 
 cover it with a piece of thin glass, avoiding air-bubbles, and 
 examine with a lens. Observe the minuteness of some of the 
 specks, which are mostly single plants. The larger ones are 
 clusters of plants. 
 
 3. Demonstration. Examine slide under a high power and 
 observe the form and color of single plants. Notice many con- 
 sisting of two or more cells still joined together, resulting from 
 cell division. (If 19, fig. 18.) 
 
 B. NOSTOC or RIVULARIA. 
 
 1. Observe the size and form of the colonies, and the consist- 
 ence of the jelly enclosing them. (" 13.) 
 
 2. Crush a bit of a A r ostoc colony or a whole one of Rivularia 
 between two glass slips, remove the upper slip, cover with water 
 and observe the coiled (Nostoc) or radiating straight filaments 
 (Rivularia) embedded in the jelly. (Figs. 13, 14.) 
 
 369 
 
37° APPENDIX. 
 
 C. OSCILLARIA. 
 
 1. Observe the color of a bit of Oscillaria; contrast it with that 
 of Pleurococcus. (•[ n.) 
 
 2. With needles tease out the specimen in a drop of water on a 
 glass slip; observe the delicate thread-like form. (Fig. 15.) 
 
 3. Transfer a bit of living Oscillaria to a small glass dish or 
 white individual butter plate with a little water; protect it from 
 drying up with a cover; 24 hours later observe the position of 
 the filaments. (•[ 14.) 
 
 4. Demonstration. Dip a considerable mass of Oscillaria in hot 
 water for a moment and put in a white butter plate with as small 
 a quantity of water as will cover it. As the water evaporates 
 observe the color deposited on the dish at the edge of the water. 
 
 or no 
 
 D. SPIROGYRA. 
 
 If fresh material is available examine a few filaments in a white 
 dish for color. If preserved material is used, stain red by 
 immersing for a few minutes in eosin (cheap red ink will answer). 
 
 Examine with a lens. Observe: 
 
 1. Length; whether broken or whole; whether with or without 
 branches. 
 
 2. The delicate partitions, like white lines, crossing the green 
 (or red) filaments, dividing the protoplasm of one cell from 
 another. Can the form of the chforoplasts be seen? (Cf. fig. 24.) 
 This can be readily seen only in the larger species. (T 25.) 
 
 3. Demonstration. Mount a few fresh filaments in water. 
 Show under moderate power the form of the chloroplasts; the 
 reserve food nodules; the nucleus. (Fig. 24.) 
 
 4. Examine conjugating specimens with a lens after staining. 
 Observe the conjugating tubes connecting two filaments like rungs 
 of a ladder (Tf 361); the zygotes or zygospores (^[365) as blackish 
 dots in some cells. Are they in one filament only or in both ? 
 
 5. Demonstration. Mount conjugating filaments and show 
 the conjugating tubes and zygospores. (If 375, fig. 303.) 
 
 E. CLADOPHORA. 
 
 If fresh material is at hand observe in a white dish; if pre- 
 served specimens are used stain for a few minutes in eosin. 
 I. How is the plant attached? 
 
DIRECTIONS FOR LIBOR A TORY STUDY. 3/1 
 
 2. Observe form and particularly the abundant branching. 
 Can a single main axis be traced ? How many branches arise at 
 one point ? (Fig. 29.) 
 
 3. Demonstration. Kill and fix the protoplasm of some fila- 
 ments of Cladophora by placing them in chrom-acetic acid 
 (water, 990 parts; chromic acid, 7 parts; acetic acid, 3 parts) for 
 1 hour; wash out the acid by placing them in running water 
 for several hours (6-24) or in a large dish of water changed 
 several times in the course of 24 hours; stain by placing them in 
 alcoholic borax-carmine or hematoxylin for several hours. 
 Mount in water. Examine with high power of microscope. 
 Each segment of the filament will be seen to contain several 
 nuclei (more deeply stained than the body protoplasm and the 
 numerous chloroplasts), showing the segments to be camocytes and 
 not true cells. (1[ 28.) 
 
 F. STONEWORT (Ckara sp.). 
 
 Place the plant in a glass dish with clean water. Set it over a 
 black background if preserved (and therefore colorless) material 
 is used. If fresh, a white dish furnishes a good background. 
 
 1. From the base of the axis carefully remove the mud by 
 washing. Observe the colorless rhizoids. (IT 37-) 
 
 2. In the body of the plant observe (a) the central axis; {/>) the 
 whorls of lateral dwarf branches ("leaves") at intervals 
 ("nodes"); (c) the single lateral axes arising among the 
 whorled dwarf branches. (1[ 33, fig. 35.) 
 
 3. Trace the main axis to its tip. Compare the distance be- 
 tween whorls toward the tip. How do they stand close to tip? 
 Dissect away the outer ones successively. What is within ? 
 
 4. Demonstration. Prepare or obtain a longitudinal section of 
 the apex of the axis, and show under compound microscope the 
 apical cell and the differentiation and growth of its successive 
 segments. (T[ 39, fig. 38.) 
 
 5. Compare the length of the various lateral axes. Compare 
 the tip of any of the long lateral axes with that of the main axis. 
 What do the observations show as to the duration of growth of 
 these ? 
 
 6. Compare the length of old and young dwarf branches. 
 Compare their tips with those of either lateral or main axes. 
 What do these observations show as to the duration of growth 
 of the dwarf branches? Observe the form and distribution of 
 the branchlets. Can they continue to grow in length? 
 
37 '2 APPENDIX. 
 
 7. Hold a bit of the main axis (use decalcified plants) between 
 the halves of a piece of pith and with a very sharp knife or a 
 razor cut a transverse section of the axis. Mount on a slide in 
 water with cover glass, and examine with lens. Observe the 
 central cell, surrounded by a row of cortical cells. (Fig. 37.) 
 
 8. Trace the course of the rows of cortical cells by examining 
 the surface of the axis with lens. Note the short projecting cells 
 which roughen the surface. (If 35.) 
 
 9. Demonstration. If fresh material is available mount a living 
 rhizoid in water and show the rotation of the lumpy protoplasm. 
 
 10. On the lower whorled branches observe the black ovoid 
 resting spores, surrounded by a paler cortex, with a crown of five 
 cells at the free end. Study these on successively higher and 
 higher branches, and observe differences in color, and finally of 
 shape. What is the form of the youngest (ovary) ? (T[ 389, fig. 
 3I3-) 
 
 11. Examine at the same time the spherical spermaries (orange 
 or scarlet in fresh specimens) which are found with some ovaries. 
 Why are they absent on older branches ? Can any trace of them 
 be found? (If 383, fig. 313.) 
 
 12. Demonstration. Mount young ovaries and show the central 
 cylindric egg ; the five cortical cells, straight in the youngest, 
 spirally twisted in old«r ones, terminated by five crown cells, 
 between which the sperms make their way to the egg. 
 
 Mount entire spermary; also on another slide one teased out 
 with needles ; show the eight wall cells, united by zigzag edges, 
 each carrying a handle-cell on its inner face, from which arise 
 numerous filaments composed of disk-like cells each containing 
 one sperm. 
 
 G. POLYSIPHONIA (/'. variegata). 
 
 Place a plant in a glass dish over a black or white background. 
 Observe 
 
 1. The form of the body and the mode of branching. (Fig. 39.) 
 
 2. The mode of attachment at the base, if specimens are entire. 
 
 3. Demonstration. Mount the tip of one of the branches and 
 show the high, dome-shaped apical cell, with segments cut off 
 successively from its base, to be later themselves divided 
 longitudinally. (If 39, fig. 41.) 
 
 4. Cut a transverse section of a medium sized axis and observe 
 the four large peripheral cells, surrounding a central cell; the 
 latter to be seen only under compound microscope. (Tf 3S, fig. 40.) 
 
DIRECTIONS FOR LABORATORY STUDY. 373 
 
 5. On some plants observe that the smaller branches are 
 swollen here and there with more opaque contents at these 
 points. These are the tetrasporangia. Compare their size as they 
 are traced tip-wards. What do you infer as to their origin ? 
 (IT 317. fig- 22Q) 
 
 6. Demonstration. Mount tetrasporic branches and show the 
 tetraspores. 
 
 The sexual reproduction is so specialized that beginners should 
 not be perplexed with it. (See p. 288.) 
 
 H. BLADDER WRACK {Fucus vesiculosa). 
 
 Place plant in a glass dish or a pan of water. Observe 
 
 1. The general form of the body or thallus; its mode of branch- 
 ing. (IT 41.) 
 
 2. The thicker central region forming a midrib, with thinner 
 wings. (Figs. 42, 43.) 
 
 3. Downwards, the thickening of rib and death of wings to 
 form stalk near base. 
 
 4. The lobed attachment disk at base of stalk. 
 
 5. The swollen regions of the wings here and there. Cut into 
 one of these and observe that it is a bladder. 
 
 6. The notched tips of some branches ; the enlarged and more 
 or less distorted tips of most, forming the receptacles. 
 
 7. Scattered on the thallus minute elevations, from which pro- 
 trude through an opening at the top a tuft of fine hairs. These 
 are the mouths of the hair pits. 
 
 8. Crowded on the receptacles, larger warts with a hole at top 
 and similar protruding hairs. These are the mouths of larger 
 pits, conceptacles, which contain the sex-organs. 
 
 Cut two thin transverse sections of the thallus, one through the 
 bladder and the other through the general thallus. The latter 
 should include a hair pit. Examine them with a lens and observe 
 
 9. In the latter, the denser outer tissues ; the cortical region ; 
 the looser inner ones, of elongated threads and much mucilage, 
 the medullary region ; the thicker denser midrib ; the form of the 
 hair pit. 
 
 10. Note the difference between the structure of the bladder 
 and the unswollen wing. Which region is altered to form the 
 bladder ? 
 
 Cut thin transverse sections through the center of the recepta- 
 
374 APPENDIX. 
 
 cles of male and female plants. If another species than Finns 
 vesicuhsus is used (e.g., F. platycarpus) both sex-organs will be 
 found in same conceptacle. If the sexes were not collected 
 separately and marked they can only be recognized after cutting 
 sections by the descriptions and figures given. Observe 
 
 ii. The form and size of conceptacles. Compare with hair 
 pit. 
 
 12. In male conceptacles, the crowded and tufted hairs, some 
 of whose terminal cells are spermaries. (If 381, figs. 309, 310.) 
 
 13. In female conceptacles, the ovaries of various sizes. The 
 larger ones are mature. (IT 3S9, figs. 324, 326, 327.) 
 
 14. Demonstration. Mount very thin sections of male and 
 female conceptacles or some of the teased out hairs from them 
 and show : 
 
 The oval spermaries, filled with rounded sperms. 
 The ovaries, young and old ; in the latter, the eight crowded 
 and therefore angular eggs, which round off on escape.* 
 
 II. FUNGI. 
 
 A. BLACK MOLD {Rhizopus nigricans). 
 
 Before any white or black dots appear on the mold, examine 
 the vegetative hyplm. ("" 48.) These are of two kinds, (a) those 
 running over the surface of the bread ; (b) those penetrating it. 
 
 1. Examine a. Lift up a few threads with a needle and mount 
 them in water. Study with a lens. Are they white or colorless? 
 Why then is the body composed of them (the mycelium, ^[ 50) 
 white ? 
 
 2. Examine /'. With needles tease out hyphrc from a bit of 
 bread in water ; free them as far as possible from the debris and 
 mount. Compare with a. 
 
 After mold has begun to show black dots (sporangia ) examine. 
 
 3. Determine how the branches are placed which bear the spo- 
 rangia, i Fig. 49. ) 
 
 4. Compare the white (young) and black (mature) sporangia. 
 Can you find the very smallest ones? 
 
 * If fresh material can be obtained demonstrate the sperms and eggs after escape from 
 spermary and ovary. Expose a plant with mature receptacles which has been in sea 
 water (01 1 ; pi 1 cent solution oi sea salt) to the air for a few hours: mount in sea 
 water on a slide some of the orange exudation which appears at the mouths of male con- 
 ceptacles. The water will be found filled with spei maries from which are escaping 
 motile sperms. The same treatment with female plants will demonstrate the eggs. By 
 mixing drops of water containing sperms and eggs the process of fertilization maybe 
 watched. 
 
DIRECTIONS FOR LABORATORY STUDY. 3/5 
 
 5. Snip off a few ripe sporangia with scissors, handling them 
 cautiously to avoid breaking or tangling them ; mount in alcohol * 
 and examine. Crush (if not already broken) and observe numer- 
 ous dust-like particles, the spores, which escape. 
 
 6. Demonstration. Mount a full grown but immature sporan- 
 gium and show the structure of sporangium with septum grown 
 up into it forming the columella ; the spores. (1[ 316, fig. 220.) 
 
 B. WHITE RUST (Cystopus portulaca). 
 
 1. Demonstration. Boil a leaf of purslane for a minute or two 
 in s% potassic hydrate. Tease apart the tissues of leaf with 
 needles on a slide, mount and show the mycelium of the fungus, 
 consisting of tangled hyphae ramifying among the cells of leaf. 
 
 (IT 51. 52.) 
 
 Examine a dried leaf. Observe 
 
 2. The white blisters {spore beets) here and there on the surface ; 
 the thin membrane (the epidermis of the leaf) by which they are 
 covered ; in older blisters the cracking and final disappearance of 
 this skin. (IT 312, fig 210. ) 
 
 3. The white powdery spores which jar out or can be dislodged 
 with needle. 
 
 4. Demonstration. Cut a transverse section through one of 
 these spore beds and show the close set ends of hyphae producing 
 the spores in chains. (IT 313. ) 
 
 5. Cut a transverse section of the leaf or stem, mount and 
 observe the numerous dark dots scattered through the tissues of 
 the host. These are the resting spores with thick opaque walls. 
 
 6. Demonstration. Show in a similar section the spermaries 
 and ovaries, and the various stages in the maturing of the fertil- 
 ized egg into the resting spore. 
 
 C. MILDEW {Microsphara Friesii, or Erysiphe communis). 
 
 Examine dried leaf bearing mildew. Observe 
 
 1. The whitish interlacing hyphne on surface of leaf, forming 
 the mycelium. (If 50.) 
 
 2. The distribution of the fungus ; does it cover the whole leaf 
 or only occur in patches ? Compare the earlier and later gathered 
 leaves as to this. 
 
 •Because water will not readily wet them. Replace alcohol as it evaporates j it does 
 so rapidly. 
 
376 APPENDIX. 
 
 3. The pulverulent appearance on the younger leaves, due to 
 spores. 
 
 4. Demonstration. Scrape a bit of the mycelium from the sur- 
 face of the leaf after moistening it for a few minutes with a 5$ 
 solution of potassic hydrate. Mount and show (a) the colorless 
 branching hyphae ; (6) the erect branches bearing the spores ; (c) 
 the spores. 
 
 7. Examine as before one of the older leaves. Observe the 
 yellowish dots scattered over the mycelium, the immature fruits. 
 (U 401, fig. 337.) Associated with these the black mature fruits. 
 These contain sporangia with spores. (*\\ 317, fig. 223.) 
 
 8. Demonstration. Mount and crush under cover glass some 
 mature fruits ; show the sporangia (asci) and their contained 
 spores. (Fig. 224.) 
 
 D. CUP-FUNGUS (Peziza sp.). 
 
 1. The mycelium penetrates the earth or rotting wood on which 
 the fructification appears and cannot be dissected out. Only the 
 reproductive parts (T[ 317) are to be examined. Observe the size, 
 shape, and color of the cup. The red and orange cups usually 
 lose their color in preserved specimens. 
 
 Cut a thin section from a piece of the cup at right angles to 
 inner surface. Mount. Observe 
 
 2. The dense upper layer of parallel hyphae (hytnenium), with 
 rows of black specks. The latter are the spores in the long 
 parallel sporangia (asci). (H 317, fig. 222.) 
 
 3. The lower layer, less dense, of tangled hyphae. 
 
 4. Demonstration. In a very thin vertical section show (a) the 
 hymenium, with paraphyses, asci, and ascospores ; (o) the looser 
 lower layers of interwoven hyphae. 
 
 E. LICHEN (Physcia stellaris). 
 
 Soften the plants by soaking them in water for a few minutes. 
 Observe 
 
 1. The mycelium, forming a connected leaf-like lobed thallus. 
 Compare as many other forms as are available. (*} 54a, fig. 225.) 
 
 2. Compare the color when dry and wet. In the latter condi- 
 tion, the mycelium is more translucent and the imprisoned green 
 algae show through more plainly. (Figs. 55, 377.) 
 
 3. The tufts of hyphae extending from lower surface to bark, 
 the holdfasts or rliidnes. 
 
DIRECTIONS FOR LABORATORY STUDY. 377 
 
 4. Occupying the central region on the upper surface, the 
 round colored disks, apothecia. Compare the form of the younger 
 ones nearer the margin. What change occurs as they grow 
 older? (1 317, n g- 22 5-) 
 
 5. Here and there, minute black specks, the mouths of sacs 
 sunk in the thallus, called spermogouia. 
 
 Cut a vertical section through an apothecium and a part of the 
 thallus on each side. Observe 
 
 6. The layers of the thallus; above and below, dense layers, the 
 upper and lower cortical layers ; between them, the medullary 
 hirer, with green alga distributed unequally through it. 
 
 7. The form of the apothecium : its broad short stalk and 
 rim; the convex surface of the disk. Is this more convex than 
 before cutting ? How shown ? Why? 
 
 8. The layers of the apothecium; the upper (liymenium) of ver- 
 tical parallel sporangia containing rows of black dots, the spores ; 
 the second {sub-hymenium) of fine, pale, tangled hyphae; the third 
 (medullary layer) with green alga:; the lower cortical layer. (Fig. 
 226 ) 
 
 9. Demonstration. In a very thin vertical section of apothe- 
 cium show the sporangia (asci) and ascospores; the paraphyses. 
 
 10. Compare apothecium with the cup of Peziza. How are 
 they different? Do these differences seem important? (Figs. 
 222, 226.) 
 
 F. MUSHROOM (Agaricus sp.). 
 
 1. The mycelium of this plant consists of rope- or ribbon-like 
 strands of hypha ramifying extensively in the substratum. The 
 fructification only is here studied (Tf 314). Examine this part 
 fresh or in water. Observe in a mature one the two parts, stalk 
 and cap. (Fig. 216.) 
 
 2. With a sharp long-bladed knife or razor cut the cap and 
 stalk lengthwise through center. Is the stalk hollow through- 
 out? Or is the central part only of different texture from outer ? 
 Determine differences of texture by teasing apart the hyphse with 
 needles. 
 
 3. Cut off stalk close under the cap. Turn the latter under side 
 up. Observe the radial plates (gills) extending from margin to 
 stalk. Do all reach the stalk ? 
 
 4. Examine the young fructifications. Ry cutting them length- 
 wise observe the formation of the chamber from whose roof the 
 
378 APPENDIX. 
 
 gills develop; the floor becomes thinner as the chamber enlarges, 
 and finally ruptures, exposing the gills. Does any part of this 
 floor (called the veil) adhere to the stalk or the edge of cap on 
 mature fructifications ? 
 
 5. If fresh mature fructifications are available cut away the 
 stalk and place the cap on a piece of black paper,* gills down, 
 resting on the stump of stalk, cover with a tumbler or bell jar, 
 and examine after 24 hours the spore print formed by the great 
 number of spores which have fallen from the surface of the gills. 
 
 6. Demonstration. Cut a very thin transverse section of a gill 
 and show the hymenium covering the surface, with basidia carry- 
 ing the free spores. (Fig. 213.) 
 
 7. Compare with mushroom various other fructifications of 
 related fungi {Hydnum, Boletus, Polyporus, Clavaria). Observe 
 the various forms by which extensive surface is secured for the 
 hymenium. (T[ 314, figs. 215, 217, 218.) 
 
 III. BRYOPHYTES. 
 A. THALLOSE LIVERWORT {Marchantia polymorph*). 
 
 Examine an entire plant in water. Observe 
 
 1. The flattened horizontal body {thallus) with central line, the 
 midrib, and thinner wings on each side. 
 
 2. The notched apex (the apical cell is at the base of this 
 notch). (% 59.) 
 
 3. The mode of branching {dichotomous). Examine the tips 
 and find one just branched. Do not confuse with notch of apex; 
 when a tip branches there will soon appear two notches. Does 
 the branch appear on the side of the older thallus, or are the 
 branches equal at first ? Are they equal when older? (If 58.) 
 
 4. The green lens-shaped bodies {brood-buds) growing at certain 
 spots along the midrib, surrounded by an outgrowth which forms 
 a cup-like rim about the cluster. Remove a brood-bud and ob- 
 serve its form, especially in full grown ones the two opposite 
 notches, the growing points. (1J 362, fig. 290.) 
 
 5. The air chambers {areola) of the upper part of the thallus, 
 showing through the skin, best seen in older parts and with a 
 lens. What is their form ? Are they all alike ? (If 57.) 
 
 * If the gills are light colored ; if dark colored use white paper. 
 
D IKE C I 'IONS FOK L A BORA'l 'OK V SI' UD Y. S79 
 
 6. The openings into the air chambers, in the skin over each 
 one. 
 
 7. Compare the under surface with the upper. Observe the 
 numerous hairs. Discover the difference in place of origin and 
 direction of growth of these. (^[ 56.) 
 
 8. Carefully pull off with forceps as many of these hairs as 
 possible and notice the dark-colored overlapping outgrowths 
 along the midrib, curving outward as they are followed forward, 
 attached along their edges. These are the so called "leaves." 
 
 Cut a transverse section of the thallus through a brood-bud 
 cup. Observe 
 
 9. The origin of the brood-buds (only the younger still remain- 
 ing) over the midrib. 
 
 10. The difference between tissue of upper and under parts of 
 thallus. (If fresh plants are available observe especially the 
 difference in color.) 
 
 12. Demonstration. Cut a very thin transverse section of the 
 thallus. Select a part passing through stoma and show 
 
 (1) The air-chamber; its roof, the skin, with chimney-like 
 stoma in center; its sides a vertical plate of cells; its floor, with 
 branched filaments of chlorophyll-bearing cells. (Fig. 58.) 
 
 (2) The large-celled colorless tissue forming the lower half of 
 section; the sections of "leaves" arising near midrib and con- 
 cave towards center. 
 
 The sexual branches are so peculiar and specialized that the 
 beginner ought not to be puzzled with them. 
 
 B. LEAFY LIVERWORT (Porella platyphylla). 
 
 1. In what position do the plants grow with reference to the 
 substratum ? 
 
 Disentangle carefully a single plant.* Observe 
 
 2. The growing apex ; the dying base; the distinctly dorsiven- 
 tral habit. Enumerate the differences between the upper and 
 under sides. (*[ 60.) 
 
 3. The mode of branching : a central axis, with lateral 
 branches, themselves with lateral branches ; i.e., monopodial and 
 bipinnate. (If 65.) 
 
 4. The yellowish or brownish stem, covered with leaves 
 unequally distributed. 
 
 * If dry, first soften by placing plants in hot water for a few minutes. 
 
3^0 APPENDIX. 
 
 5. The two rows of large leaves on the upper flanks of the 
 stem. How do they overlap? Turn the shoot over and note a 
 third row of small underleaves in the center below ; also right 
 and left the lobes of the upper leaves. Determine the form of 
 the under and upper leaves. Make an enlarged paper pattern of 
 the latter showing how their ventral lobes are arranged. (Figs. 
 62, 63.) 
 
 6. Demonstration. Mount a leaf and point out the uniformity 
 of cells and their abundant chloroplasts. 
 
 7. Examine male plants* and observe the male branches: 
 short, abundant near the anterior end of main and lateral axes, 
 with crowded, closely overlapping leaves, the anterior ones often 
 pale. 
 
 8. Cut off a male branch ; dissect leaves carefully and observe 
 in the axil of each leaf a spherical yellowish body on a slender 
 stalk, the spermary. (^ 3S2, fig. 311, B.) 
 
 9. Demonstration. Mount a mature but unbroken spermary 
 and show the single layer of cells forming a wall enclosing an 
 opaque mass of sperms. If fresh, the spermary may rupture on 
 being put into water and the sperms swim about rapidly in the 
 field of the microscope. 
 
 10. Examine a female plant. On the under side observe very 
 short lateral branches, bearing a pear-shaped tumid sac, the 
 perianth. How is it constructed at the free end ? 
 
 11. Examine old perianths; observe partly projecting from 
 such the mature sporophyte, consisting of a brown spherical capsule 
 on a pale slender stalk (seta). (The capsule is often bursted ; if 
 so, determine into how many pieces (valves) it splits.) To what 
 is the stalk attached ? (T[ 32, figs. 64, 65.) 
 
 12. Examine successively younger female branches (to be 
 found toward the anterior end) and note various stages of devel- 
 opment of the sporophyte. Find a young sporophyte, differenti- 
 ated into stalk and capsule, but still enveloped by a thin mem- 
 brane, formed by the enlarged body of ovary and surmounted by 
 a brown bristle, the neck of the ovary. Determine what becomes 
 of this membrane {calyptra). 
 
 13. Demonstration. Select the youngest female branch with 
 well grown perianth, cut a median longitudinal section, or dissect 
 away the perianth, mount, and show the group of several ovaries ; 
 some with canal cells in place, others with canal cells disorgan- 
 
 * The sexual organs are bome on different plants. 
 
DIRECTIONS FOR LABORATORY STUDY. 3^1 
 
 ized making an open canal to the egg, and others, perhaps, with 
 an embryo sporophyte in the enlarged body. (1[ 391, fig. 331.) 
 
 14. Demonstration. From a mature capsule mount and show 
 spores and elaters. (Fig. II, A.) 
 
 C. MOSS [Mnium cuspidatum). 
 
 Examine plants with capsules attached. Observe the two 
 connected plants : 
 
 1. The leafy stemmed plant or gametophyte. (*i\ 55.) 
 
 2. The slender plant attached to its tip, the sporophyte, consist- 
 ing of a wire-like stalk, the seta, enlarged above to form the 
 hanging capsule. ("IH67, 322.) 
 
 3. Boil for a few minutes in 5 per cent, potassic hydrate, rinse 
 in water and gently pull sporophyte until it separates from the 
 gametophyte. Observe the smooth pointed end which was sunk 
 in gametophyte. If properly separated no sign of tearing can be 
 seen. (Fig. 73.) 
 
 Examine gametophyte in water. Observe 
 
 4. The differentiation of the body into stem and leaves. 
 
 5. The brown hairs (r/iizou/s) about the stem, which attach 
 plant to ground. Do they branch ? (If 62.) 
 
 6. The strength of the stem ; test it by breaking it with a 
 lengthwise pull. Cut a thin transverse section and observe dark 
 colored mechanical tissues in outer region. (H 63, fig. 68.) 
 
 7. The form and structure of the foliage leaves : note midrib 
 of mechanical cells (test strength); lamina of one layer of cells 
 large enough to be visible under lens ; border of mechanical cells, 
 some projecting pretty regularly as teeth. (^[64, fig. 69.) 
 
 8. Smaller, scale-like leaves on part of the stem. 
 Examine sporophyte with mature capsule. Observe 
 
 9. The slender seta. 
 
 10. The thin yellow inverted capsule, from whose end a piece 
 has fallen leaving it open. (T 322, fig. 72.) 
 
 11. About the edge of the capsule a fringe of pointed projec- 
 tions, teeth, curved inward, constituting the peristome. Break off 
 these outer teeth and notice the pale fringed membrane within, 
 forming the inner peristome or endostome. (Figs. 72, 231.) 
 
 12. Among these, or to be pressed out of capsule, many fine 
 spores. 
 
 13. Demons/ration. Cut off on a slide the end of the capsule as 
 a ring, with peristome attached. Divide this ring into halves. 
 
382 APPENDIX. 
 
 Holding one half with needle cut off the peristome close to cap- 
 sule. This allows the teeth to float away from membrane. Turn 
 other half with convex side up, cover all pieces, and show the 
 peristome, endostome, and spores. 
 
 Examine young sporophytes of this or other mosses. Observe 
 
 14. The cylindrical form of the embryo sporophyte. 
 
 15. The hood covering its apex and carried up by it until the 
 developing capsule forces it off. (If 401, fig. 338.) 
 
 16. The lid which falls off to open capsule. 
 
 17. Examine on young gametophytes the sex organs. Dissect 
 with needles the tufts of leaves at apex of stem* and search for 
 (a) Transparent oval sacs, the empty spermaries ; and similar 
 opaque greenish or whitish ones, in which sperms are still en- 
 closed. (1[ 384, fig. 311, B). (b) Flask-shaped bodies, with a long 
 neck and short stalk, the ovaries. These may always be found, 
 withered somewhat, at the tip of a stem where a young sporo- 
 phyte is developing. (IT 391, fig. 331.) 
 
 Numerous hairs, paraphyses, of no known function, may be 
 found intermixed with the sex organs. 
 
 19. Demonstration. With dissection as above, mount spermary 
 and ovary. Show (a) in spermary, the stalk, the wall, the sperm 
 cells ; {b) in ovary, the stalk, body, neck, canal, and egg. 
 
 IV. PTERIDOPHYTES. 
 A. MAIDENHAIR FERN {Adiantum pe datum). 
 
 I. The gametophyte. 
 
 1. Observe its shape and size ; the notch at the growing point 
 (anterior end) ; the dying (posterior) end ; the thicker central 
 region, with thin wings. [*\] 69.) 
 
 2. On the under side, a cluster of rhizoids near the posterior 
 end. 
 
 3. Compare this plant with the thallus of Marchantia. 
 
 4. Demonstration. Mount a gametophyte underside up, and 
 show (a) among the rhizoids the spherical spermaries ; {/>) nearer 
 the apex the chimney-like necks of the ovaries. 
 
 If gametophytes with young sporophytes attached are available, 
 observe 
 
 * In some species the male organs form at the apex of the axis disk-like clusters, sur- 
 rounded by leaves, the whole reminding one in form of a miniature sunflower-head, 
 while the female organs occur in smaller numbers (3-6) in the bud-like clusters of leaves 
 at the apex of other stems. 
 
DIRECTIONS FOR LABORATORY STUDY. 383 
 
 5. That the young sporophyte is fastened to the under side of 
 the gametophyte. (U 72, figs. 76-78.) 
 II. The sporophyte. 
 Taking the underground parts in a dish of water, observe 
 
 1. The slender wire-like roots. How are they branched ? (^[ 91 
 ff.) Where are they attached to the stem? Trace an unbroken 
 one to the tip. The following points can only be seen on roots 
 carefully gathered and cleaned. What difference of color near 
 tip? Can you find many fine tangled root hairs? Where present ? 
 Where absent? (H 79.) 
 
 2. Demonstration. Cut a longitudinal median section of a root 
 tip and show the tetrahedral (triangulai in section) apical cell ; 
 the segments cut off from inner faces producing root tissues, 
 those from outer face producing the root-cap. (U 77, fig. S3.) 
 
 Cut a transverse section of an old root, mount and observe 
 
 3. The outer brown mechanical tissues (also used for storage). 
 (H85.) 
 
 4. The central whitish tissue, chiefly the stele, in which the 
 visible openings are the larger vessels. (If 81.) 
 
 5. In what position does the stem naturally stand ? Observe 
 its occasional branching H[ 103) ; the surface covered with chaffy 
 scales (![ 128) ; the growing apex and dying base. 
 
 6. Its nodes and internodes ; the nodes are indicated by the 
 attachment of a single leaf at each ; the internodes are the inter- 
 vals between the nodes. How are the leaves placed? (^[ 119.) 
 
 Cut a transverse section of the stem and observe 
 
 7. The outer brown mechanical tissues (also used for storage). 
 
 (IT 129.) 
 
 8. The circular, oval, or C-shaped white tissues, most of which 
 belong to the stele. Trace the course of the stele through at least 
 two internodes by cutting a series of rather thick (1 mm.) sec- 
 tions, observing the mode in which the stele branches to pass out 
 into a leaf. Cut also a longitudinal section through the base of 
 a leaf stalk and trace course of stele. (H1[ 130, 131.) 
 
 Taking a perfect leaf, dried under pressure, observe 
 
 9. The stalk or petiole, with its branches. Note the mode of 
 branching; the petiole divides into two equal'divergent branches ; 
 each of these forks, one branch carrying leaflets while the other 
 again forks, and so on. (^[1[ 153, 155.) 
 
 10. The hardness of the mechanical tissues at surface of polished 
 petiole. 
 
3^4 APPENDIX. 
 
 ii. The leaflets. Note [a) shape, as to outline and margin, 
 comparing basal, median, and terminal leaflets of any branch ; 
 (b) the veins, containing branches of the stele ; (<r)the green tissues 
 between the veins. (1[ 154.) 
 
 12. Demonstration. Strip off a bit of epidermis, mount and show 
 (a) the irregular form of epidermal cells; (/<) the intercellular 
 openings with guard cells (stomata). (" w , 165, 166.) 
 
 13. Demonstration. Cut a very thin vertical section of a leaf 
 at right angles to veins, and show (a) the upper and lower layer 
 of cells forming the epidermis; (b) the green parenchyma cells with 
 intercellular spaces; (c) the section of the vein composed of the 
 stele with mechanical tissues above and below it. (1T^[ 167, 168.) 
 
 14. At the edges of the leaflets on the under side crescentic 
 brown spots, sort. (Tf 323.) 
 
 15. Boil a leaflet for a minute in water. With a needle turn 
 back a flap which covers the sorus, the indusium; observe that 
 it is a specialized portion of the edge of leaflet. 
 
 16. On the under side of the indusium, a mass of yellowish 
 spheroidal bodies, the sporangia. Scrape away most of them and 
 notice the relation of their points of attachment to the veins. 
 
 Mount some of the sporangia and observe 
 
 17. Their shape; the stalk by which they were attached. (Fig. 
 401.) 
 
 18. The darker ridge, annulus, which serves to burst them 
 when mature. (Fig. 401.) 
 
 in. Study the manner of bursting. Tear a bit of indusium from 
 a dried specimen previously soaked in water, removing most of 
 the sporangia. Allow it to dry while watching it-with a lens, 
 illuminating from above. 
 
 20. Demonstration. Mount sporangia and spores and show 
 their structure, especially the annulus. 
 
 B. HORSETAIL {Equisetum arvense). 
 
 I. The gametophyte cannot be readily obtained, and differs 
 from that of the fern mainly in having erect branches, with the 
 sex organs on the upper side and always on separate plants.* 
 
 II. The sporophyte. Taking the underground parts in water, 
 observe 
 
 * See Goebel, Outlines of Classification, figs. 210, 211; Campbell, Mosses and Ferns, 
 fig. 220; Sachs, Physiology of Plants, figs. 425, 426. 
 
DIRECTIONS FOR LABORATORY STUDY. 385 
 
 1. The slender roots (all secondary); their places of origin. 
 (1" 7°-) (Structure quite like ferns.) 
 
 2. The stem; its nodes and internodes; longitudinal shallow 
 furrows and low ridges. 
 
 3. At each node a toothed sheath (representing a circle of 
 leaves not distinct from each other), best seen on younger region. 
 
 Cut a transverse section of the stem; mount; observe 
 
 4. A circle of large air-canals, one opposite each furrow. Trace 
 these lengthwise in an internode. Do they pass the node? 
 (1 129.) 
 
 5. Within the circle of air canals, the tissues constitute the stele. 
 Opposite each surface ridge, a cluster of small cells looking 
 denser than adjacent tissues. These are the cut ends of the 
 vascular bundles. (Tf 131.) 
 
 (If underground stems are lacking make out this structure in 
 the aerial ones, which differ mainly in being hollow.) 
 
 Examine one of the flesh-colored aerial shoots in water (fig. 
 235, A). Observe 
 
 6. Similar distinction into nodes and internodes. Break the 
 stem by a lengthwise pull. Where does it break? There is an 
 intercalary zone of growth at the base of internode. (Compare 
 leaves, ^[ 169.) 
 
 7. The large sheath at each node, the leaves. Each tooth 
 represents a scale leaf. Note relation of teeth to ridges of 
 stem and to those of sheath next above or below. (Tf 160.) 
 
 8. The different leaves near apex, separate, but whorled and 
 crowded in a cone; these are the sporophylls. (HIT. 324, 325, fig. 
 235.) Note the lowermost whorl united and forming a sort of 
 collar.* 
 
 Dissect off several sporophylls in a small dish of water and 
 observe 
 
 9. Their parts, the stalk, the head ; hexagonal form of head 
 due to crowding. 
 
 10. The six to ten thin sacs under the head and parallel with 
 stalk, the sporangia. (Fig. 236.) 
 
 11. Tear open a sporangium. Leave the spores in a pile on one 
 slide and mount a bit of the wall on another. In the latter ob- 
 serve the cells with thread-like spiral thickenings on the walls; 
 
 * This may be considered a primitive periantli (.1353) and gives added reason tor 
 calling the whole cluster a Bower. 
 
386 APPENDIX. 
 
 an arrangement to burst the sporangium when mature. (Fig. 
 238.) 
 
 Breathe on the dry mass of spores. Watch the squirming 
 movements. 
 
 12. Demonstration. Mount a few spores in water and others 
 dry, and show the elaters ; strips of the outer walls of spores, 
 loosened but wrapped around spores when moist, straightened 
 out when dry. (Fig. 239.) 
 
 Examine the green branched shoots (fig. 235, B). Compare struc- 
 ture with other shoots, noting differences. Observe 
 
 13. Profuse branching and the arrangement of the branches and 
 branchlets. 
 
 14. Cut a longitudinal section through the base of a branch. 
 Observe that the branches arise from the stem above the origin 
 of leaves and burst through the sheath. 
 
 15. That the nutritive work depends on the stem, not on the 
 leaves, which lack green tissue. 
 
 16. The roughness of the surface. Rub branches on a metal 
 surface and observe that they scratch it, on account of silica in 
 walls of surface cells. 
 
 C. SELAGINELLA (.V. rupestris). 
 
 I. Gametophytes, male and female, are extremely reduced, 
 scarcely bursting the wall of the spores producing them. See 
 
 IT! 384. 392, figs. 315, 333. 
 
 II. Sporophyte. 
 
 Examine in water an entire plant. (If previously dry it should 
 be boiled for a few minutes in water.) Observe 
 
 1. The yellow thread-like secondary roots arising at various 
 points from the stem. (Structure like fern.) 
 
 2. The branched shoots; note method ; lateral branches arising 
 from side of mother shoot, i.e., monopodial branching. 
 
 3. The crowded foliage leaves. Mow arranged ? (See p. 97.) 
 
 4. The sporophylls. Search for ends of branches having leaves 
 in four vertical ranks. Compare form of these leaves with foliage 
 leaves. Observe 
 
 5. In their axils large yellow sacs, the sporangia ; some con- 
 taining 
 
 6. One to three large spores, the megaspores; more abundant 
 than similar sporangia containing 
 
DIRECTIONS FOR LABORATORY STUDY. 387 
 
 7. Numerous small spores, the microspores. Microsporangia are 
 usually at tip or base of spike and are often difficult to find if 
 material is not collected at proper season. (1H[ 326, 327.) 
 
 V. SPERMATOPHYTES.* 
 
 A. PINE (Pinus sylvestris). 
 
 Examine a shoot showing at least the growth of present year 
 and that 01 the preceding. Observe 
 
 1. Two kinds 01 axes : (a) the main axis of the shoot, with un- 
 limited growth, now terminated by a conical bud ; (/') the very 
 short lateral axes of limned growth, dwarf branches, each bear- 
 ing two «to/A-/.'i(-r.i. ("| no, rig. 101.) 
 
 2. The six forms of leaves. Scudy the shape and structure of 
 each. (a) the slender green leaves, needles ; (b) the scales closely 
 covering the older parts of the stem, in whose axils arise the 
 dwarf branches carrying the needle-leaves ,- (c) the thin broad 
 scales on the dwarf branches, enwrapping the bases of the needle- 
 leaves (best seen about the leaves on the young shoot) ; (d) the 
 scales protecting the apical bud (If 160) ; (<•) the two forms of 
 sporangium-bearing leaves, sporophylls, in the two sorts of flowers 
 (see further 4 and 9). 
 
 3. Dissect the scales carefully from a large terminal bud and 
 compare the interior parts with those of the shoot which bears it. 
 Can you make out the corresponding members? If not, it is 
 because the bud is too young. Use a bud taken from the tree in 
 summer or autumn and these points can be seen best. What is a 
 bud? (p. 85.) 
 
 4. Examine the sporophylls. Observe the two kinds : (a) 
 Numerous oval clusters of yellowish bodies, the micro-sporophylls 
 or stamens, about the base of the young shoots (fig. 101), now 
 called a staminate flower ; (b) a single cluster of mega-sporoph vlls 
 about the apex of one or two short lateral branches arising just 
 below terminal bud of a young shoot and extending a little beyond 
 it, forming the pistillate flower. (■[*[ 331, 344.) 
 
 5. Study the arrangement of the staminate flowers on the axis. 
 Compare the position of each cluster of sporophylls (flower} with 
 
 * In this group the sporophytes only can be studied without the compound microscope. 
 tophytes sec demonstration 
 
388 APPENDIX. 
 
 that of the dwarf shoots on the upper part of the same axis. 
 What is a flower? (p. 236.) 
 
 6. Dissect off a single micro-sporophyll (stamen) from one of 
 the staminate flowers. Observe the broad short stalk ; the thin 
 upturned end ; the two large sacs, sporangia, on the under side. 
 Tear open these and observe the innumerable small spores, 
 microspores (or pollen grains). 
 
 7. Demonstration. Mount mature microspores in water and show 
 (<7) the spore itself (the central body) with two bladdery enlarge- 
 ments of the outer wall to secure buoyancy in air ; [b) the immature 
 male gametophyte inside, consisting of two cells, the smaller rep- 
 resenting the vegetative part (a mere rudiment) and the larger the 
 spermary, simple by reduction. (If 385.) 
 
 8. Examine a pistillate flower. Observe that it shows from the 
 surface two kinds of leaves: (a) thin ones with toothed edge, the 
 so-called bracts ; (l>) thick fleshy ones with a prominent point, the 
 carpels. These are probably two parts of one structure, the 
 sporophyll, which is deeply divided ; but there is wide difference of 
 opinion as to the exact nature of the bracts and carpels. 
 
 9. Dissect out a carpel and observe (</) the broad attachment ; 
 (/>) the ridge on the upper side (keel) extending into a prominent 
 point ; (c) the two enlargements on the upper side near the base, 
 the ovules, and their oblique position. The ovules consist of an 
 integument and a sporangium containing a single megaspore. 
 Note the opening in the integument (micropyle) at the end nearest 
 the base of the carpel, with two prolongations right and left. 
 (Fig. 246.) 
 
 10. Examine a year-old cone. Observe the excessive growth 
 of the carpels as compared with the bracts. Can you find the 
 latter by cutting the cone smoothly lengthwise through the cen- 
 ter ? Note the woody texture of all parts. (If 404, fig. 341.) 
 
 11. Dissect out an entire carpel. Observe the obliquely placed 
 ovules (Fig. 342). 
 
 12. Cut a thin longitudinal section of the ovules and the carpel. 
 Observe the sporangium surrounded by the integument prolonged 
 beyond it at the orifice ; inside the sporangium a cavity, the 
 interior of the megaspore, now partly filled with the young female 
 gametophyte. (Compare fig. 319.) 
 
 13. Demonstration. In a similar section show these parts under 
 compound microscope, especially (a) the female gametophyte, 
 growing inside the spore which has not escaped from the sporan- 
 
DIRECTIONS FOR LABORATORY STUDY. 389 
 
 giuni; (/•) microspores lodged about the mouth of integument, the 
 spermary often forming a tube. (T| 386.) 
 
 Examine a 2-year-old (mature) cone. Observe 
 
 14. The extreme woodiness of the cone, especially the carpels 
 which are spread apart when dry. y\ 404.) 
 
 15. On the upper surface of some carpels, two thin wing-like 
 scales, with a seed attached. 
 
 16. Time the fall of winged seed from the extreme height to 
 which you can reach. Time its fall after removing wing. How 
 will this aid in distributing seed ? (H 492.) 
 
 Bisect a seed lengthwise, parallel to flatter faces. Observe 
 
 17. The firm seed-coat, which is the integument of the ovule 
 grown and ripened. 
 
 iS. Enclosed by the coat a white tissue loaded with starch and 
 oil, the endosperm, which is the enlarged female gametophyte. In 
 the center of this the embryo sporophyte which grew from one of 
 the eggs produced by the female gametophyte, after the egg was 
 fertilized. Note that the tissues of the sporangium have disap- 
 peared, having been crowded and absorbed. (T 403.) 
 
 19. Dissect out the embryo from another seed. Observe that 
 it is already differentiated into a slender stem, and six primary 
 leaves about its apex. (Fig. 339.) 
 
 B. MARSH MARIGOLD (Caltha palustris). 
 
 1. Examine the roots. Observe (a) their surface, wrinkled 
 from shortening; (/') their structure. 
 
 2. Cut a transverse section as in fern; observe that mechanical 
 tissues are wanting. 
 
 3. Bisect longitudinally the base of a plant. Observe, as shown 
 by the origin of leaves, the variable length of internodes; at 
 base the internodes are very short so that leaves are crowded; 
 in the middle the internodes are long and leaves distant; above, 
 the internodes become shorter until, in the flower, they are not 
 developed and the leaves are very much crowded. (^[ 119.) 
 
 Study one of the well developed foliage leaves (*1 150). Ob 
 serve 
 
 4. The broad rounded blade with slight branches (teeth) at the 
 margin. 
 
 5. The long slender stalk, petiole, gradually passing into 
 
39° APPENDIX. 
 
 6. The sheathing base, in upper leaves branched to form two 
 stipules. 
 
 7. Examine and compare the various forms of leaves: {a) the 
 lowest, having sheathing bases without petiole or blade, passing 
 gradually into (b) the best developed foliage leaves; (c) these near 
 the flowers losing petiole and diminishing blade, becoming bracts; 
 (d) the yellow perianth leaves ; (<r) next within these the yel- 
 lowish stamens (micro-sporophylls); (/) the flattened pod-like 
 green carpels (mega-sporophylls) each forming a simple pistil. 
 (11 160, 161.) 
 
 8. Bisect a flower lengthwise. Observe the three sorts of 
 leaves, perianth, stamens, and carpels; their relation to each 
 other and their insertion separately on the enlarged stem, the 
 torus. Separate some from an old flower and note the scars left 
 by their fall. (1 330.) 
 
 9. Are perianth leaves similar, or of two sorts? (1 354.) 
 
 10. Dissect off a stamen. Observe the two parts: (a) the slender 
 stalk, filament, and (b) the enlarged part, anther. Note in the 
 anther the two lobes, each with a shallow groove marking the 
 position of the two pairs of sporangia. Tear open the sporangia 
 with a needle and observe the innumerable microspores (pollen 
 grains) which they contain. Examine a naturally bursted anther 
 and determine how they open. (HI 345-348.) 
 
 11. Demonstration. Cut a thin section of an anther from a bud 
 and show (a) the four sporangia, in pairs, entirely distinct, and 
 the point at which they become confluent as they burst; (b) the 
 pollen grains. (1 351.) 
 
 Dissect off and examine a pistil. (1 33S.) Observe 
 
 12. At the apex the roughened area, the stigma (1 336), sessile 
 (1 337) upon 
 
 13. The enlarged part, the ovulary (I335). Observe its flat- 
 tened form and the groove along one edge. Split it along this 
 line, flatten it out carefully and note the ovules attached to the 
 edges. (1 343.) 
 
 14. Cut several transverse sections of the pistil and observe the 
 thickened edges of the carpel, forming the placenta, to which 
 ovules are attached. Compare sections. Are all ovules attached 
 to same edge ? 
 
 15. Demonstration. Prepare a longitudinal section of an ovule 
 of a lily and show the two integuments; the sporangium, enclos- 
 ing the single megaspore, or embryo sac. (H 340, 394.) 
 
DIRECTIONS FOR LABORATORY STUDY. 391 
 
 Study and compare the flower and leaves of the sweet pea 
 (Lat/iyrus odoratus), apple, fuchsia, and garden lily. 
 
 For the study of primary roots and root hairs, primary stem 
 and primary leaves, germinate Indian corn, scarlet runner or any 
 bean, in clean damp pint- sawdust, and grow until plants are sev- 
 eral inches high, watching stages of development. 
 
 For forms of stems examine white potato (tuber); onion (bull)); 
 Indian turnip or Cyclamen (corm); morning glory or hop (twin- 
 ing); white clover (creeping). 
 
 For structure of stems, study Indian corn (monocotyledon, with 
 no secondary thickening), cucumber or pumpkin (dicotyledon, 
 with no secondary thickening), and young sunflower (dicotyledon, 
 with secondary thickening). Compare transverse sections. 
 
 For lenticels and the formation of periderm, examine the twigs 
 of plum, cherry, elder or box-elder. 
 
 For buds examine large winter buds of hickory, horsechestnut, 
 or poplar. 
 
 Part II: Physiology. 
 
 1. To show the existence of turgor in the individual cell. (•" 188.) 
 Mount a bit of Spirogyra under microscope; observe position of 
 
 chlorophyll bands. Irrigate with 5 per cent, solution of salt and 
 note effect. 
 
 (If Spirogyra is not at hand use hairs on stamens of Trades- 
 cantia ; or the epidermis, filled with purple cell sap, from the 
 under side of the leaves of the cultivated 7"radescantia (" wander- 
 ing Jew"); or the hairs of geranium leaves.) 
 
 2. To show effect of turgor of cells on rigidity of young parts <<>//- 
 taining no mechanical tissues, t". iSS.) 
 
 Remove carefully a young plant with vigorous primary r<>,»t 
 grown in sawdust or sand. Lay in water for a few minutes. 
 Note rigidity. Transfer to 5 per cent, salt solution for a few 
 minutes. Again note rigidity. What has happened? Remove 
 to water again for 15 min. What is the result? 
 
 3. To show the existence of longitudinal tensions of tissues due to 
 unequal growth or turgor. (" 259.) 
 
 A. Cut a young internode of elder 10 cm. long, making ends 
 as square as possible. Measure accurately. Remove wood all 
 around and measure pith. Place pith in an atmosphere satu- 
 
392 APPENDIX. 
 
 rated with moisture and measure after i hour. Compare meas- 
 urements. (If elder is not at hand use young shoots of grape, 
 wild or cultivated.) 
 
 B. Split a scape of dandelion lengthwise with a sharp knife 
 into four strips. Note immediate effect upon their form. Lay 
 the strips in water for a few minutes. Observe form. Transfer 
 them to 5 per cent, salt solution. What effect? What causes 
 these changes of curvature? (The young stems (hypocotyls) of 
 castor bean may be substituted for dandelion scapes but are not 
 so responsive.) 
 
 4. To show the existence of transverse tensions of tissues due to 
 unequal growth. 
 
 A. From a piece of willow or poplar stem separate a ring of 
 bark 1 cm. wide, slitting it on one side only, taking care not to 
 stretch it. Keep it in a moist atmosphere for a few minutes, 
 and then replace it. Does it meet about the wood ? 
 
 B. Cut a slice about 2 mm. thick from the end of a stalk of 
 rhubarb. Bisect this and keep the halves for a few minutes in a 
 moist atmosphere, then place severed edges together. Do they 
 touch throughout ? 
 
 5. To show the location of root hairs and especially their adhesion 
 to soil particles. (H 79, 200.) 
 
 Germinate wheat in sand and when seedlings have several 
 strong roots dig up carefully; shake sharply in water; note 
 where soil clings most tenaciously. Brush away most of this 
 with camelhair brush and examine a bit of this part of root under 
 a low power of microscope. Observe distortion of root hairs, 
 and particles of sand partly embedded in them. 
 
 6. To show excretion of acid salts by roots, (^f 202.) 
 
 Fill a wide-mouthed bottle holding 250 cc. with tap water; add 
 2-3 drops of ammonia and several drops of phenolphtalein.* 
 If the water does not now remain pink add a drop or two more of 
 ammonia. Select a vigorous seedling bean grown in sawdust; 
 rinse roots well to remove impurities. 
 
 Cut in two a cork which fits the bottle; in the halves cut two 
 corresponding notches of such size that with a little cotton for 
 packing the plant will be firmly held. Place the plant with 
 
 * An indicator for acids, colorless when a fluid in which it is dissolved is acid, rose 
 pink or darker when alkaline. For use the crystallized phenolphtalein is dissolved in 
 alcohol. 
 
DIRECTIONS FOR LA BORA TORY STUDY. 393 
 
 enough cotton to secure it in the cut cork and set in bottle with 
 roots immersed. 
 
 As the plant grows from day to day watch for the dis- 
 appearance of color in the solution, whicn will indicate when the 
 alkaline fluid has become acid. Arrange a control experiment in 
 exactly the same way, but without plant. Surround each bottle 
 with opaque shade of heavy paper, to avoid effect of light on the 
 roots and fluid. 
 
 7. To show the corrosion of carbonate of lime by the carbonic acid 
 excreted by the roots. (T 202.) 
 
 Cover a polished marble slab to a depth of 5 cm. with clean 
 sand, in which plant corn or beans. After the plants are 10-15 
 cm. high, remove sand carefully and rinse off the marble. 
 Examine the surface by reflected light. A little graphite rubbed 
 into lines etched by roots will make them more readily visible. 
 
 8. To show root pressure as a factor in the movement of water in 
 plants. (Tf 205, fig. 172.) 
 
 Cut off the stem of an actively growing plant (plants of castor 
 bean and tomato 25-30 cm. high are especially recommended) 
 a short distance above the soil and fasten tightly to the stump, 
 by means of rubber tubing, a piece of glass tubing a meter long, 
 and about the diameter of the stump. Add enough water to rise 
 10 cm. above the rubber connection. Keep roots well watered and 
 mark the height of the water in tube from time to time until it 
 reaches the top or begins to fall. Does the water rise from the first ? 
 
 A more satisfactory record may be reached by attaching to the 
 stump a T-t UDe as shown in fig. 172. To the horizontal arm 
 attach a mercury manometer. (A manometer may be readily 
 constructed by bending a glass tube, about 5 mm. diameter (3 
 mm. bore) and 80 cm. long, upon itself 30 cm. from one end, so 
 that it forms a u with unequal legs 3-4 cm. apart. Bend 5 cm. 
 of the end of the short leg at right angles, in the plane of the U- 
 Tie the legs to a piece of cork between the legs near top, so that 
 the tube will not be easily broken by the leverage of the legs <'ii 
 the bottom bend.) Fill the space between stump and mercury 
 with water. In the third arm insert a short tube drawn out to .1 
 slender point to permit the escape of air and extra water. Seal 
 this with flame after filling. There must be at least 15 cm. of 
 mercury in (J portion of manometer. At beginning mark, with a 
 bit of gummed paper, height of mercury in each leg ; measure 
 difference at intervals thereafter until mercury begins to fall. 
 
394 APPENDIX. 
 
 9. To show that water is not absorbed by leaves in quantity ade- 
 quate to supply evaporation. (^[ 196.) 
 
 Cut off a vigorous shoot of a plant with abundant foliage ; 
 close end of stem with grafting wax ; expose to sunlight until 
 slightly wilted ; then immerse it in water. Does the plant recover 
 its turgidity ? 
 
 10. To show that many leaves are not wetted by -water. (*[ 210.) 
 Immerse various sorts of leaves in water. Does the water wet 
 
 the surface? What is the cause of the silvery reflection of light 
 from the surfaces of some ? What relation does this repulsion of 
 water have to blocking of stomata by rain? 
 
 11. To show the loss of -water by evaporation. (If 208.) 
 
 Clean and dry the surface of a pot in which a thrifty single- 
 stemmed plant is growing ; close the hole in the bottom with a 
 cork ; with a brush paint the whole surface with a thick layer of 
 melted paraffin. Cut out'a piece of stiff paper which will fit 
 around stem and just cover the soil in pot. Using this as a pat- 
 tern cut a cover for the soil from a sheet of lead ; slit the cover 
 from the central hole to circumference ; adjust it around plant 
 and cement all cracks with grafting wax.* Weigh. Weigh again 
 at intervals of 24 hours, for 4 days. 
 
 12. To show the variation in the rate of evaporation due to the 
 difference in structure of the organ. (^\^\ 209, 438.) 
 
 Compare as shown by shrinkage or by loss of weight, (a) 
 Through cork tissue and without it. Take two potatoes ; peel 
 one ; expose side by side ; compare day by day. (b) Through skin. 
 Compare in same way two apples, (c) Through stomata. Take 
 three equal leaves of oleander; of one close the stomata (which 
 are on under side only) with a thin coat of grafting wax, or cocoa- 
 butter melted and brushed on (taking care not to kill cells by 
 having wax too hot) ; coat the upper surface of second in same 
 way ; leave third uncovered. Compare day by day. 
 
 13. To show the conditions affecting evaporation. (^T 210.) 
 Construct a potometer as follows : Bend the central stem of a 
 
 T-tube until it is parallel with the cross piece. Fit into the lower 
 opening of the straight leg a capillary tube 30-40 cm. long, with 
 3 cm. of each end bent at right angles to the main part and in 
 opposite directions. Into the bent leg fit a shoot of a thrifty 
 plant cut off under water, at the same time filling the j-t"be with 
 
 *Or the pot can be set in a tin vessel which it fits and the lead cover luted to this. 
 
DIRECTIONS FOR LABORATORY STUDY. 395 
 
 water. (To accomplish this bend the shoot to be cut of? so that 
 the place of the cut is submerged in a deep pan of water. Fit it 
 in tube without exposing cut surface at all to air.) Dip the lower 
 end of the capillary tube in water and allow apparatus to stand 
 until capillary tube fills with water. Remove the water for a 
 moment and allow a bubble r cm. long to enter ; time it as it 
 moves between a series of equidistant marks on capillary tube. 
 Try the rate under various conditions of light, temperature, and 
 moisture acting on shoot. 
 
 14. To show the lifting power of evaporation. (^[ 207.) 
 
 Cut off under water a shoot from a thrifty plant ; fasten it air- 
 tight in the end of a piece of glass tubing 30 cm. long, of appro- 
 priate diameter, by means of a piece of rubber tubing slipped 
 over the end of the stem, taking care not to expose the cut end to 
 air. Fill glass tube with water before fitting in plant ; erect the 
 whole with lower end of tube dipping in a cup of mercury. Set 
 in light and note height of mercury in 1-48 hours. 
 
 15. To show loss of liquid water when absorption is great and 
 evaporation slow. 
 
 Grow seedlings of wheat or oats until 5-10 cm. high ; then 
 cover with a glass bell for an hour or two. Where do drops of 
 water appear ? Why? 
 
 16. To show roughly the path of evaporation stream in woody 
 plants. (U 206.) 
 
 A. From a leafy shoot of a woody plant remove a ring of bark 
 5 mm. wide. Protect the exposed surface against drying with 
 grafting wax. Observe whether the leaves wilt or not, and if 
 they wilt, the time required. 
 
 B. With a knife or fine saw cut a little over half through the 
 stem of a plant of the same sort used in A ; 1 cm. above this cut 
 make a similar one on the opposite side. The two must be so 
 placed and of such a depth that all the tissues are severed. Sup- 
 port the branch or stiffen it against breaking by bandaging it with 
 strips of wood. Make same observations as in ./. Examine the 
 pith. Is it alive ? Dues it contain water ? 1 n what tissues, there- 
 fore, do you infer water travels to leaves? 
 
 17. To show restoration and maintenance of an interrupted evap- 
 oration stream. 
 
 Fit a well wilted shoot into the short arm of an unequal U-tubc 
 filled with water to the level of the short end. Allow it to stand 
 for half an hour. Does the shoot recover? If not, pour nun ut \ 
 
39^ APPENDIX. 
 
 into the longer arm until it stands 10 cm. above its level in the 
 short arm. Does the shoot now recover turgor ? Why? Allow 
 it to stand for some days. Does the level of the mercury change ? 
 
 18. To show in what tissues food most readily travels. (U 235.) 
 Girdle as in experiment 16 A a shoot of willow. Cut it off 5 
 
 cm. below ring. Place shoot in water. After some weeks note 
 where new roots are formed. Why? 
 
 19. To show the permeability of stomata for air and their com- 
 munication -with the system of intercellular spaces. (^T*[ 167, 227.) 
 
 Fasten a leaf with a long petiole air-tight in a rubber cork, 
 through which also passes a short glass tube. Fit the cork into 
 a bottle holding sufficient water to cover end of petiole. Attach 
 a filter pump or air pump to glass tube. Observe whether air 
 bubbles leave the end of the leaf stalk. 
 
 Reverse the leaf, so that the blade is immersed, and make same 
 observation. Where do bubbles appear ? Is there any difference 
 between upper and lower sides? 
 
 20. To show the depth to which light may penetrate green tissues. 
 
 a 231.) 
 
 Take a cylindrical pasteboard or metal tube, closed at one end 
 and having a cover which will fit over the closed end. In the 
 end and in the cover cut corresponding holes 1 cm. in diam. Mark 
 side and cover when in place so that holes can be made to coin- 
 cide. On the bottom place a part of a leaf which will cover hole. 
 Slip on cover and observe whether light is transmitted through 
 leaf. Add successive pieces of leaf until no more light passes. 
 What is the color of last light seen ? The examination must be 
 made with direct sunlight, and light completely excluded from the 
 eye except that which passes through the instrument. 
 
 21. Method for detecting considerable quantities of starch in plant 
 organs. (1 233.) 
 
 Boil a few leaves of various plants for a few minutes. Place 
 in alcohol at about 6o° C. until all chlorophyll is dissolved.* 
 Bring the leaves into a tincture of iodine, diluted to a bright 
 brown, for half an hour. The leaves or parts containing starch 
 will become bluish, dark blue, or black, according to amount of 
 starch present. 
 
 22. To show that manufacture of starch occurs only in cells directly 
 illuminated. ("[ 231.) 
 
 * Do not heat over open flame, but set bottle, loosely corked, in a vessel of hot water. 
 
DIRECTIONS FOR LABORATORY STUDY. 397 
 
 Darken portions of some leaves of a plant previously found to 
 show starch in its leaves (sunflower, bean, tomato, or nasturtium) 
 by attaching two plates of cork on opposite sides by means of 
 two pins driven through both and the leaf. On the afternoon of 
 the following day, if sunny, cut off the leaves and test for starch. 
 What has become of starch in cells under the cork? 
 
 23. To shozu that oxygen is a by-product of photosyntax, ("]f 250.) 
 Collect the gas mixture evolved from a vessel full of aquatic 
 
 plants by inverting over them a funnel to whose tip is connected 
 a test tube filled with water to be displaced by the rising gases. 
 Keep the plants in sunlight. When the tube is filled, test the 
 contents for oxygen by inserting a glowing splinter. 
 
 24. To show the effect of light and temperature on photosyntax, 
 using the rate of evolution of oxygen as an index. 
 
 Fasten a shoot of a water plant (Elodea , Myriopkyllum, or Cerat- 
 ophyllum) 10 cm. long to a glass rod and immerse in tap water so 
 that the cuf end is uppermost. Set in sunlight and observe the 
 bubbles rising from the end of stem.* Determine rate at which 
 they rise by counting the number given off in a certain short 
 time. Continue the observation until the rate is approximately 
 uniform. Shade the shoot and determine rate. Return to sun- 
 light and determine rate. Put a piece of ice in the water and de- 
 termine again. 
 
 25. To show the digestion of starch by diastase. (*[ 237.) 
 Powder a handful of malt in a mortar or obtain ground malt. 
 
 To 25 grams of the powder add 100 cc. of water; stir well to- 
 gether; allow mixture to stand (with occasional stirring) one to 
 two hours; filter; preserve the filtrate. Take 1 gm. of starch 
 and rub it up in a dish with 5 cc. water; pour this into gjjj^c. of 
 boiling water, stirring as it enters. With 25 cc. of this paste mix 
 thoroughly 5 cc. of the filtrate (which contains diastase extracted 
 from the malt). Test a small portion of the mixture at once for 
 starch by adding a few drops of tincture of iodine, and similar 
 portions at intervals of half an hour until starch reaction ceases. 
 Taste the remaining paste. Into what has the starch been con- 
 verted ? 
 
 26. To show evolution of C0% by respiration of leaves and 
 /lowers, (f 239. ) 
 
 * If several bubbles arise at once, remove shoot from water, dry the cut end of Stem 
 with filter paper and coat it with a thin layer of grafting wax ; then perforate thi^ wax 
 with a line needle point so a.s to offer one ail lot gases. 
 
39^ APPENDIX. 
 
 Provide a piece of plate glass and a bell jar with ground rim, 
 of suitable size to cover a blooming plant growing in a pot. 
 Alongside the pot place a shallow dish of baryta-water ; cover 
 both with the bell, daubing its edge with vaseline to make con- 
 tact with glass plate air-tight. Place in darkness. Note film of 
 barium carbonate on surface of water after a day. Conduct a 
 control experiment, identical but for the absence of plant. Is 
 more or less barium carbonate formed? Why darken? 
 
 27. To show evolution of CO2 by respiration of seedlings. 
 
 Fill a wide-mouthed glass jar or bottle of 1 liter capacity one- 
 third full of peas and beans which have been swollen for a day 
 in water, then rinsed thoroughly in 5 per cent, formalin 
 and again rinsed in water. Cork or cover tightly. After 24-48 
 hours remove cover and thrust in a burning match or candle 
 attached to a wire. If C0 2 has been produced it will extinguish 
 flame. Test also by lowering into jar a vessel of baryta-water. 
 If precipitate or film forms it shows presence of C0 2 . 
 
 28. To show the evolution of heat during respiration. (^| 248.) 
 Take three-fifths the amount of dry wheat required to fill two 
 
 3-inch flower pots ; swell in water over night ; rinse one half in form- 
 alin as above ; kill the other by boiling in water for five minutes. 
 Stop bottom hole in pot with a cork; fill one with dead, the other 
 with living seeds, and bring the two to same temperature by run- 
 ning water through the dead and hot one. Insert a thermometer 
 in the center of each mass of seeds ; place both under one box 
 or bell jar. Observe changes of temperature for two days.* 
 
 29. To measure the rate of growth in length. 
 
 Construct an auxanometer as follows : Take a board 30 cm. 
 square, a common spool, a wheat or oat straw 35 cm. long, and a 
 piece of glass tubing 5 cm. long, which will just allow spool to 
 revolve easily on it. Close one end of the glass tube by holding 
 it in the flame of a Bunsen burner ; when hot spread it enough 
 to stop spool from passing over end, by pressing it endwise 
 against a piece of iron. With a fine saw cut a section 5 mm. 
 thick from middle of spool, thus making a wheel. File a groove 
 in edge of this wheel, deep enough to carry a thread. Slip wheel 
 on glass tube and fasten it in board near lower left corner so 
 deep that spool-wheel will revolve smoothly but have no un- 
 
 * Compare thermometers previously to see that they register alike ; if not ascertain 
 the correction. Greater differences in temperature of seeds will be observed if pots are 
 surrounded with cotton batting. 
 
DIRECTIOXS FOR LABORATORY STUDY. 399 
 
 necessary play. On the board, with hole for glass tube as a 
 center, mark an arc of 90 degrees. The radius of the arc should 
 be a multiple of the radius of wheel. Divide arc into half centi- 
 meters. Attach wheat straw to wheel as a pointer. 
 
 To the tip of a growing seedling bean fasten a thread by a slip 
 noose. Pass thread over wheel once and to its free end attach a 
 light weight — just enough to turn wheel and pointer when plant 
 is lifted. Set pointer at o and at intervals read the multiplied 
 growth. By taking observations at regular intervals determine 
 the rate of growth of stem for a week. What regular variation 
 can you discover ? 
 
 30. To show the necessity of respiration for growth. (^[^[242, 245.) 
 Germinate a number of beans in sawdust. Select eight with 
 
 straight roots about 2 cm. long. Clean and dry the surface 
 slightly by brushing with frayed edges of strips of filter paper, 
 taking care not to expose roots so long that they are injured by 
 dry air. With a very fine sablehair brush and thick Chinese (or 
 waterproof black drawing) ink, mark each root by distinct lines 
 into ten spaces 1 mm. apart, commencing with tip. This can be 
 done most conveniently by pinning the seedling to a strip of soft 
 wood and laying alongside the root a ruler whose graduated edge 
 has been blunted by a plane until it is about 2 mm. thick. 
 
 Pin half the seedlings to a strip of soft wood set into a jar 
 partly filled with wet sawdust, so that the roots will be vertical 
 in damp air. Put the other half into a similar jar and cover them 
 with water recently boiled and cooled. After 24 hours, remeasure 
 and compare total growth. (See also exp. 31.) 
 
 31. To determine the zone of maximum growth in roots and stems. 
 (1 258.) 
 
 A. Observe the four seedlings of exp. 30, whose roots grew in 
 moist air. Which spaces grew most? 
 
 B. Mark several upper internodes of a bean plant in a similar 
 way, but at 5 mm. intervals. After 4S hours observe how many 
 have elongated and which have grown mosti 
 
 32. To show the effect of gravity as a stimulus on roots. (" * 287- 
 290.) 
 
 Arrange the marked root of a seedling bean as in exp. 30, ex- 
 cept that the root is horizontal, and a pin just above the extrem- 
 ity murks its position. After 24 hours observe curvature and 
 which spaces have become curved. Compare with those which 
 have grown most. 
 
400 APPENDIX. 
 
 33. To show the effect of gravity as a stimulus on growing regions 
 of upright leaves and items. (^[^[ 2S7-29O.) 
 
 A. Support an onion, roots down, in a vessel of water so that 
 it is half immersed, until the leaves are about 10 cm. long. Then 
 turn it so that leaves are horizontal and observe where curvature 
 occurs. 
 
 B. Cover the bottom of a deep dish about 25 cm. long with a 
 layer of wet sand, and bank this against one end to the top. Into 
 this bank stick horizontally several grass stems having at least 
 one node ; cover with a glass plate. After 24-48 hours observe 
 curvature. Cut a longitudinal section of the node and observe 
 the part of the leaf-sheath in this curvature. 
 
 34. To show the effect of direction of light as a stimulus on leaves. 
 
 (IT 285.) 
 
 Set a potted plant (geranium, sunflower, nasturtium, or mallow) 
 in the dark for 24 hours ; then place it before a window, shading 
 it so that light reaches it chiefly from one direction. Mark certain 
 leaves and record the position of the plane of the blade ; 24 hours 
 later observe the position and compare with first. 
 
 35. To show effect of direction of light as a stimulus upon stems 
 and roots. (H 285.) 
 
 Grow seedlings of white mustard thus : Tie loosely over the 
 mouth of a jelly-glass a double piece of fine bobbinnet; fill vessel 
 with tap water to the net, on which place seeds ; set in dark, re- 
 placing water as it evaporates, until seedlings are 3 cm. high, 
 with roots as long or longer. Then place in a box, blackened 
 inside, into which light is admitted, through a hole 4-5 cm. 
 in diameter, at right angles to stems and roots. Observe curva- 
 tures 24 hours later. 
 
 36. To show effect of intensity of light as a stimulus on certain 
 leaves. (^[ 297.) 
 
 Observe the position of the leaflets of white, red, or sweet 
 clover, bean, locust, or oxalis at 3 p.m., 6 P.M., at dusk (or after 
 nightfall by using a lantern) and at 8 A.M. In the morning darken 
 with a box a plant showing these movements. After an hour or 
 two, observe the position of leaflets. 
 
 37. To show effect of contact as a stimulus to tendrils. (TJ 293.) 
 Stroke with a pencil the concave side of the tip of a tendril of 
 
 passion vine, squash, wild cucumber, or balsam-apple, on a warm 
 day or in a hothouse, and observe curvature which follows in a 
 few minutes. 
 
APPENDIX II. 
 
 DIRECTIONS FOR COLLECTING AND 
 PRESERVING MATERIAL. 
 
 Those who cannot collect the plants they require can orcki them from the Camhridge 
 Botanical Supply Co., 1286 Massachusetts av., Cambridge, Mass. Orders should be 
 placed in advance of the collecting season to insure obtaining the material. 
 
 Pleurococcus. — For this and similar one-celled algae, collect pieces 
 of shaded fence boards near the ground, or flakes of bark from 
 the north side of trees in groves and parks, which show a bright 
 yellow-green color. These may be preserved dry. 
 
 Oscillaria. — Search in drippings about watering troughs, city 
 gutters where water stands, or any open drain which contains 
 organic matter decaying in stagnant water. A glass jar or 
 aquarium in which water plants have decayed will usually con- 
 tain this plant. It may be recognized by its bluish or blackish 
 green color, and often occurs in coherent films or thicker masses. 
 It may be obtained fresh at any time of year, either out doors or 
 in the laboratory. ■ 
 
 Rivularia. — Collect in midsummer or later the larger water 
 plants to whose leaves and stems adhere jelly-like lumps of a 
 dirty green color, from the size of a pinhead to 1-2 cm. in 
 diameter. The margins of lakes, pools, and slow streams furnish 
 the best localities. 
 
 Nostoc colonies form similar jelly masses, commonly larger and 
 free floating or attached. Preserve both like the following. 
 
 Spirogyra or Zygnema. — Search in spring or early summer in slow 
 streams fed by springs. It will be recognized when in vegetative 
 condition by rich green color and slippery " feel." Under the 
 microscope the form of the chloroplasts will show the genus. 
 
 401 
 
402 APPENDIX. 
 
 (See 1[ 25.) When conjugating it often loses the deep green and 
 becomes yellowish, and the filaments seem to be double. 
 
 This condition can be recognized under the lens. Spirogyra 
 may often be obtained all through the year in pools and springs. 
 It should De preserved in the following solution: Camphor water 
 50 cc; water 50 cc; glacial acetic acid 0.5 cc. ; copper nitrate 
 2 gm.; copper chloride 2 gm. 
 
 Cladophora. — Species of this genus may be found attached to 
 sticks and stones at the edge of lakes or pools. It often covers 
 these completely with a thick mat of long, yellowish green, 
 branched filaments. It may be found throughout the growing 
 season. For winter use preserve in same solution as above. 
 
 Chara. — Several species are common in shallow ponds and lakes, 
 in water 0.2-1 meter deep, rooting in the mud, often in company 
 with Myriophyllum and Ceratophyllum, two seed plants, the latter 
 of which may readily be mistaken for it by novices. But these 
 plants are usually bright green while Chara is dull or dirty green, 
 or even whitish (especially when dry) from the coating of lime, 
 which also renders it brittle and harsh to the touch. Careful in- 
 spection of its form and a section of the axis at once enables one 
 to recognize it. (See figs. 35. 37.) Specimens should be gathered 
 when the spermaries on the lower branches (" leaves ")are orange. 
 Pull up the plants carefully, wash off as much as possible of the 
 mud which clings to the delicate, colorless rhizoids. The basal 
 part of the axis should be put in a separate jar from the rest. 
 Put a few plants into 2 per cent, chromic acid, and allow them to 
 remain 24 hours todissolve off lime with which they are incrusted. 
 After pouring off the acid and rinsing them thoroughly, soak 
 them in a large vessel of water for 24 hours, changing water 
 several times (or allow water to run over them slowly for six 
 hours) to remove acid. Preserve in 70 per cent, alcohol. Plants 
 may be preserved in formalin or 70 per cent, alcohol, in long 
 jars so as to entangle them as little as possible. If brittle from 
 alcohol (as they often are) before removing them from jar for 
 distribution pour off alcohol and cover with water for a few 
 minutes. 
 
 Polysiphonia. — All species are marine, and any common species 
 will serve. They are found in reddish brown, feathery tufts 2- 
 10 cm. high, on other larger sea-weeds, or on piles and stones, 
 about low-water mark. They collapse completely when with- 
 drawn from the water. 
 
COLLECTING AND PRESERVING MATERIAL. 4,0$ 
 
 The plants should be fixed in one per cent, chromic acid (or in a 
 saturated solution of picric acid in sea-water) for 12-24 hours, 
 washed in sea-water as described for Chara, and hardened in 40, 
 60 and 80 per cent, alcohol successively, remaining in each 6- 
 24 hours. They may be preserved in the latter. They may also 
 be preserved in formalin. 
 
 Fucus. — All species are marine and any one will serve. The 
 commonest is Fucus vesiculosus (fig. 42), which may be found on 
 rocks between tide marks. It is of olive-brown color, with 
 swollen tips to many of the branches, and bladders in pairs along 
 the thallus. Plants may be obtained fresh at almost any season. 
 Various species of brown sea-weed may be found fresh at the 
 fish stores of all large cities, whither they are sent as packing. 
 
 Mucor or Rhizopus. — Saturate a piece of bread with water and 
 keep it under a bell jar, in a warm place, for a few days. 
 Several species of molds will appear, the most common of which 
 is the black mold, Rhizopus nigricans. This may be recognized 
 by its white fluffy mycelium, on which arise tufts of erect hyphae 
 developing at tips spherical sporangia, at first white, later black. 
 These tufts occur at intervals along a stolon-like hypha. The 
 same mold may be found on rotting vegetables and fruits, 
 especially sweet potatoes and lemons, and may be raised more 
 rapidly on bread by sowing spores. It will be followed by the 
 green mold, Penicillium glaucum, and often later by other 
 species. . Since the plants may be grown promptly, the material 
 used should be living. 
 
 Microsphaera or Uncinula or Erysiphe. — Any species of mildew 
 will answer. Microsphara grows everywhere on the leaves of 
 the cultivated lilac. Erysiphe is abundant on the leaves of blue 
 or white vervain {Verbena hastata and V. urticafolia) and many 
 Compositae. Uncinula attacks leaves of many willows. About 
 midsummer, when the fungus has a white powdery aspect, gather 
 leaves and dry them under light pressure. Later, gather leaves 
 of the same species showing yellow and black dots (the fruits) on 
 the mycelium. Preserve in the same way. 
 
 Cystopus portulacae. — This species is abundant throughout the 
 summer on leaves and stems of purslane (Portulaca oleracea) 
 which grows in every garden and cornfield. Another s; 
 grows in late spring on shepherd's-purse (Cipse//,i bursa-pastoris) 
 and another on the pigweeds (AmarantAus sp.). Anyone will 
 answer. The species on Capsella (Cystopus candidus) only oc- 
 
404 APPENDIX. 
 
 casionally forms resting spores in that host. They may be found 
 in abundance in the flowers of radish which become much enlarged 
 and distorted when this fungus is parasitic thereon. All species 
 may be known by the white blisters formed by lifting the skin of 
 the host. Preserve in formalin or alcohol leaves and stems of 
 host bearing blisters. Some may also be dried. 
 
 Peziza. — The cup fungi grow on earth or fallen rotting leaves, 
 twigs or trunks, in woods. The fructifications may be at once 
 recognized by their cup-like form. The inner surface of the cup 
 is often bright colored, red or orange, brown or black. The 
 mycelium is hidden in the substratum. They may be collected in 
 spring and summer and preserved in formalin or 70 per cent, 
 alcohol. 
 
 Lichens. — Any common foliose species which forms apothecia 
 abundantly will answer. A bright gray species with black apo- 
 thecia (Physcia stclluris) is abundant on tree trunks, as is also a 
 yellowish species with orange apothecia {Theloschistes polycarpa). 
 These may be collected at any convenient time, and kept dry. 
 Besides these, collect other foliose forms; also species of Cladonia 
 growing on the ground, with body much lobed and the apothecia 
 coral-red knobs on upright gray stalks; also species of Ustiea, 
 clothing the branches of trees with gray-green shrub-like or hair- 
 like tufts. 
 
 Mushroom. — Any species with cap and gills will answer. They 
 may be found in woods throughout the summer and especially 
 in late summer or autumn during a rainy season following 
 drought. Only the fructification need be collected. Select a 
 small firm species with well defined stalk, cap and gills. Col- 
 lect fructifications in all stages of development from young to 
 mature. Preserve as soon as gathered in formalin or 70 per cent, 
 alcohol. 
 
 Other Hymenomycetes. — Collect fleshy cap fungi with hanging 
 points instead of gills {Hydnum, fig. 217), or intersecting plates 
 forming tubes {Boletus). Preserve these as mushroom. Collect 
 also the woody bracket fungi (Polyporus, fig. 218), which grow on 
 rotten trees and fallen limbs, showing innumerable fine tubes 
 underneath. Preserve dry. Also the much branched firm- 
 fleshed Clavaria (fig. 215). Preserve as mushroom. All will be 
 found in damp woods. 
 
 Marchantia. — Common on wet ground and rocks, or even in 
 drier places among grass in the shade of walls or fences. It 
 
COLLECTING AND PRESERVING MATERIAL. 405 
 
 may be recognized by flattish green body about 1 cm. wide and 
 5-8 cm. long, attached by silky hairs. At some times it bears on 
 the upper surface sessile cups containing green grains, and sends 
 up erect slender sexual branches which spread out into flat heads 
 6-8 mm. across, some scalloped at edge and some with finger-like 
 rays. When cups or sexual branches are present no other liver- 
 wort can be mistaken for it. A very similar one, except in these 
 parts (Conocephalus conicus) may be distinguished by its larger 
 size and larger stomata, looking like needle pricks over the sur- 
 face, while those of Marchantia are just visible. It may be used 
 for the vegetative parts. Collect in July. Free from dirt as 
 much as possible, and preserve in formalin or 70$ alcohol. 
 
 Porella. — Abundant everywhere on the bases of trees especially 
 in low grounds or wet bottom lands. It may be recognized by 
 its dirty-green pinnately branched shoots, 1-2 mm. wide, with 
 crowded overlapping rounded leaves. The plants are always in- 
 tricately interwoven. Flakes of the bark may be peeled off with 
 a broad knife or chisel, taking care not to tear up the plants into 
 too small patches. Collect in summer. Preserve dry, after dry- 
 ing under light pressure. Some should be kept in formalin or 
 alcohol for demonstration of finer structure of sex organs. 
 
 Mnium. — Any species of the genus will do. The commonest 
 species eastward is M. cuspidatum. It is abundant everywhere in 
 patches on shady banks and in open woods about the bases of 
 trees. It may be recognized by the yellow or orange oval cap- 
 sule, thin and irregularly wrinkled when dry, horizontal or pen- 
 dent on a stalk 2-3 cm. long. The leaves are broadly oval, with 
 fine sharp teeth under lens, and a distinct midrib. When moist 
 the leaves are rather pale green, ahd not crowded or overlapping. 
 When dry the clump is a dull, dirty green, and the leaves are 
 much curled and twisted, expanding quickly when wetted. The 
 male and female organs are in the same cluster, at the apex of 
 the axis. Under the microscope the species may be recognized 
 by the oraitgt- inner peristome with double rows of perforations 
 in the membrane below the segments. Preserve as directed fur 
 Porella. Almost any similar moss will serve equally well, espe- 
 cially the common species of Bryum, 
 
 Equisetum. — The gametophytes are not readily obtainable. The 
 sporophytes of the common E. arvinse grows on dry sandy banks, 
 often on railroad embankments. The underground stems send 
 up in spring (April-May) unbranched flesh colored shoots 5 mm. 
 
406 APPEXDIX. 
 
 in diameter and 10-25 cm. high, with brown scale-like sheaths at 
 the nodes. These shoots terminate in a cone-like cluster of 
 sporophylls. Later in the season from the same underground 
 stems, grow green much branched shoots, looking somewhat like- 
 miniature pines, the main lateral axes being produced in whorls 
 at the nodes. Collect both sorts of aerial shoots with under- 
 ground shoots and roots attached. Preserve the flesh-colored 
 and underground shoots and a few green shoots in alcohol or 
 formalin ; most of the green shoots may be dried under light 
 pressure between drying paper or newspaper. 
 
 Adiantum. — Gametophytes of any fern will answer. They are 
 flat green heart-shaped bodies 2-5 mm. in diameter, attached to 
 soil by rhizoids. They may be collected on fern pots or grown 
 in greenhouses, or may be obtained from supply company named. 
 Especial care should be taken to have some young sporo- 
 phytes still attached to gametophytes. The sporophytes of 
 the maidenhair fern are easily recognized by the peculiarly 
 branched leaf. The stem is wholly underground. Each leaf 
 has a slender polished stalk which forks into two equal 
 branches ; these fork, one branch of each pair growing straight 
 and bearing leaflets while the other again forks in the same way ; 
 and so on until 4-8 branches have been formed on each half. 
 Collect underground stems and roots, loosening them gently and 
 washing off dirt carefully to avoid destroying all root tips and 
 hairs. Preserve these in alcohol or formalin. Gather leaves 
 when the crescent-shaped fruit dots at edges of leaflets are yel- 
 lowish brown (August). Preserve by drying, spreading out 
 each leaf to show its mode of branching clearly. 
 
 Selaginella. — A wild species', S. rupestris, grows abundantly on 
 dry bare hills and rocks. It forms grayish-green, much branched 
 tufts, 3-8 cm. high, with narrow bristle-tipped appressed 
 leaves, and resembles in aspect a large rigid moss. Many 
 branches are terminated by a sharply quadrangular spike of 
 sporophylls, about 1 cm. long. Several exotic species are com- 
 monly cultivated in greenhouses and window gardens, where 
 they produce sporangia abundantly. Any species will answer. 
 Collect the wild plant about July. Specimens may be preserved 
 dry or in alcohol or formalin. 
 
 Pinus. — Any species will answer. The Scotch pine is so widely 
 planted that it is often easiest to collect. The leaves are grayish 
 
COLLECTING AND PRESERVING MATERIAL. API 
 
 green, in pairs, 5-10 cm. long; cones small, about 5 cm. long, 
 the ends of scales bearing a conspicuous protuberance, long and 
 recurved on the basal scales. The Austrian pine, also widely 
 planted, has dark green longer leaves (10-15 cm -)» larger cones, 
 with no recurved bosses. The flowers are of two sorts and 
 should be watched for in spring (May) as new shoots appear. 
 The staminate flowers form conspicuous yellow clusters at the 
 base of the young shoots, and should be collected as soon as the 
 sporangia begin to shed the spores. The pistillate flowers are 
 quite inconspicuous, small oval clusters (5-7 mm. long) pro- 
 jecting slightly beyond the tip of the young shoots. The tree 
 bearing staminate flowers usually bears few pistillate ones, and 
 vice versa. Collect shoots bearing each kind of flowers, cutting 
 far enough back to include the leaves of the previous year. Pre- 
 serve in alcohol or formalin. Collect also year-old and two-year- 
 old cones. Preserve the former (green) in fluid; the latter 
 (mature) dry. 
 
 Caltha. — This plant is common in wet meadows and swamps 
 northward. It is 15-30 cm. high, smooth, with rather coarse 
 hollow ribbed stems, orbicular or kidney-shaped alternate leaves, 
 with broad clasping base to the petiole, and numerous bright 
 yellow flowers 20-25 mm. in diameter, produced for two weeks 
 or more in April or May. Gather entire plant; wash the roots. 
 Preserve a few plants and an extra supply of flowers and fruits 
 in alcohol or formalin. Dry most of the entire plants. 
 
 Lathyrus. — The sweet pea is grown in almost every flower gar- 
 den and is known everywhere. Preserve flowers and leaves in 
 summer in alcohol or formalin. 
 
 Stems. — The various sorts recommended may be collected at 
 any convenient time and preserved in fluid. 
 
 Seeds. — The nmsi useful seeds for laboratory work are Indian corn, 
 wheat, buckwheat, castor bean ( Ricinus), white lupine, {Lupinusal- 
 dus), scarlet runner (Phaseolus), broad bean {Vicia faba), hemp, 
 white mustard. These should be obtained fresh each year, as they 
 deteriorate more or less with age. Those which cannot be had 
 everywhere (such, perhaps, as lupine, castor bean, scarlel 
 runner, and broad bean) may be purchased of seedsmen in Large 
 cities. See advertisements in magazines. 
 
 Potted plants. — Such as arc grown in window gardens or all 
 greenhouses will suffice. A commercial greenhouse, if accessi- 
 
408 APPENDIX. 
 
 ble, will raise tomato, castor-bean, bean, and sunflower plants as 
 ordered, and will furnish active young plants at any season re- 
 quired, in case pupils cannot grow them either at school or home. 
 Malt. — Can be obtained ground or unground at any brewery, 
 or may be made by sprouting barley until the seedlings appear 
 and then drying at about ioo C. 
 
APPENDIX III. 
 APPARATUS AND REAGENTS. 
 
 The chemicals required are so few that in most cases they 
 may be most conveniently obtained through local dealers. It is 
 desirable, however, to order apparatus from dealers who make a 
 specialty of manufacturing or supplying optical, chemical, and 
 physical apparatus. Schools are entitled to import such appara- 
 tus free of duty, and by doing so through importing firms a large 
 part of the cost may be saved. The list is given here for its 
 convenience as a summary. The amounts necessary are not 
 specified as they vary with the size of classes, and the teacher 
 who is prepared to conduct the experiments can readily deter- 
 mine how much is needed. 
 
 CHEMICALS. 
 
 Acetic acid. — Used for fixing protoplasm. 
 
 Alcohol. — Large schools should buy in barrel lots free of reve- 
 nue tax. For regulations apply to the revenue collector of the 
 district in which the school is situated, or to the Secretary of the 
 Treasury. 
 
 Ammonium hydrate (ammonia). 
 
 Barium hydrate, — For making baryta water; or this can be ob- 
 tained fresh as needed from druggist. 
 
 Chromic acid. — Used in fixing and decalcifying. 
 
 Corn starch. — As prepared for table or laundry. 
 
 Formalin. — This is a 40 per. cent solution of formaldehyde in 
 water. Dilute solutions can be prepared as needed. Mosl 
 plants require a 10 per cent solution, i.e., formalin 1 part, water 
 9 parts. 
 
 Grafting 7cax. — Made as follows : Melt together resin (by 
 
 409 
 
4IO APPENDIX. 
 
 weight) 4 parts, beeswax 2 parts, tallow i part; mix well; pour 
 into a pail of cold water; grease the hands and " pull " till nearly 
 white. In using it should be handled with greased fingers to 
 prevent its sticking to them. 
 
 Iodine. — Either solid, from which the tincture can be prepared 
 by dissolving a few flakes in alcohol, or the tincture may be pur- 
 chased. 
 
 Mercury. — For directions for keeping it clean and dry, see 
 Botanical Gazette 22 : 471. Dec. 1896. 
 
 Paraffin. — A common quality, melting at about 65 C. 
 
 Phenolphtalein. — A few grams will last a long time. 
 
 Potassic hydrate. — May be bought in sticks and the solution 
 made, but it is more convenient to buy the liquor potasses of 
 druggists. 
 
 Sodium chloride. — Table salt is pure enough. 
 
 Vaseline. 
 
 APPARATUS FOR MORPHOLOGY. 
 
 Dissecting microscopes. — Each pupil should be provided with one. 
 A most effective low-priced dissecting microscope was designed 
 by the author and is manufactured by several firms. In no case 
 has the author any financial interest in the instruments. The 
 stand T I, manufactured by the Bausch & Lomb Optical Co., 
 Rochester, N. Y., with i-inch lens, and a similar one by Queen 
 & Co., Philadelphia, have been approved by the designer. Many 
 forms offered to schools by jobbers are not worth buying. 
 
 Compound microscopes. — The school should be supplied with at 
 least one good compound microscope for demonstrations, and as 
 many more as can be profitably used. If the teacher is capable 
 of using such instruments properly he will be able to select it 
 wisely with such advice as he may obtain from personal acquaint- 
 ances on whose judgment he can rely. Schools are advised to 
 deal only with manufacturers of established reputation. 
 
 Scalpels. — Each pupil should be provided with a sharp knife 
 with slender blade for dissection. It is desirable for the school 
 to furnish scalpels of suitable form. The slender blades, 3-3.5 
 cm. long on cutting edge, are recommended. 
 
 Forceps. — Straight form, with smooth points, will be found use- 
 ful, though not indispensable. 
 
 Needles. — Each pupil should have a pair of needles (No. 6, 
 
APPARATUS AND REAGENTS. 41 I 
 
 sharps) with the eye end set into a soft pine penholder or similar 
 handle. They must be kept sharp on a fine oil-stone. 
 
 Drawing mad-rials. — A medium pencil (No. 3 or M) and a very 
 hard one (No. 6 or 6 H) should be used and kept sharp. Slips of 
 heaviest linen ledger paper (120 lb.) cut 14 X 8 cm. are recom- 
 mended. Only one drawing should be put on a slip. 
 
 APPARATUS FOR PHYSIOLOGY. 
 
 Since much of the apparatus needs to be put together by the 
 student, the requisites are mainly tools and a good supply of tub- 
 ing, both glass and rubber, bottles, and bell jars. The following 
 will enable the foregoing experiments to be carried out. 
 
 Tools. — Hammer, fine saw, three or four chisels, assorted files, 
 brace and assorted bits, screw-driver, smoothing plane, with a 
 supply of nails (especially finishing nails) and screws will be 
 found most useful. 
 
 Glass tubing. — A little capillary tubing (0.5 mm. bore) will 
 be needed. Most used sizes are 5 mm. (3 mm. bore), 7 mm. 
 (5 mm. bore.) Some larger sizes (13 and 19 mm.) will also be 
 useful. 
 
 Rubber tubing. — 3 and 5 mm. bore mostly ; some of 10 and 15 
 mm. bore. 
 
 Bottles. — Wide-mouthed, various sizes, up to 1 liter. 
 
 Tumblers. — Jelly glasses answer well. Odd lids and glass dishes 
 from homes and stores can be made useful. 
 
 Corks. — Assorted sizes. Several rubber stoppers, sizes S, 10, 12, 
 3-hole, are desirable. 
 
 Bell Jars. — Several sizes are necessary ; 1; X 20 and 20 X 30 cm. 
 will be found useful; also at least one 30 X 50 1 in. All should 
 have ground rim and tubulure at top. 
 
 Funnels. — Glass, assorted sizes. <>, 8, and u cm. diam. are 
 most used ; there should also be two or three larger ones. 
 
 filter paper. — Buy cut filters 15 and iS cm. in diameter. 
 
 Thermometers. — Should be graduated in degrees, — io° to -f- ioo° 
 C, with milk-glass scale. 
 
 Test tubes. — 2 X 15 cm. is a convenient size. 
 
 T -tubes. — Two sizes. 5 and 10 mm. bore. 
 
 Bunsen burners. — If gas is not available, gasolene burners 
 should be substituted. 
 
412 APPENDIX. 
 
 Marble-. — A plate 25 X 25 X 2.5 cm., polished on both sides. It 
 can be re-polished after etching and used as often as desired. 
 
 Filter pump. — Can be used if water service is available, or if a 
 head of 5 m. can be secured by tank. Korting's is excellent. 
 
 Rulers. — 30 cm. long, graduated in millimeters. 
 
 Brushes. — Camelhair brush of large size, and sablehair, smallest, 
 are useful. 
 
 Pius. 
 
 Tin tube. — 3 X 15 cm. See experiment 20. 
 
 Absorbent cotton. — Also a roll of cotton batting. 
 
 Sheet lead. — Light weight, used by plumbers. 
 
 Plate glass. — Cut into pieces 20, 25, and 35 cm. square. 
 
 Pine sawdust and clean sand. — For germinating seeds. 
 
APPENDIX IV. 
 REFERENCE BOOKS. 
 
 The following books will be found useful to teacher or pupil or 
 both, and are recommended as suitable reference books for the 
 school library. The list is not intended to be exhaustive, nor 
 does it include books for popular reading. 
 
 FOR GENERAL REFERENCE. 
 
 Kerner: Natural history of plants. New York: Henry Holt & 
 Co. $15.00. (Translated by Oliver.) 
 
 Strasburger, Noll, Schenck and Schimper : Text-book of 
 botany. New York : The Macmillan Co. $4.50. (Trans- 
 lated by Porter.) 
 
 Bennett and Murray : Handbook of cryptogamic botany. New 
 York: Longmans, Green & Co. $5.00. 
 
 Vines : A student's text-book of botany. New York : The Mac- 
 millan Co. $3.75. 
 
 Sachs : Lectures on the physiology of plants. New York : The 
 Macmillan Co. $7.00. (Translated by Ward.) 
 
 Goebel : Outlines of classification and special morphology. NY w 
 York : The Macmillan Co. $5.50. (Translated by Garnsey 
 and Balfour.) 
 
 Warming: Handbook of systematic botany. New York: The 
 Macmillan Co. $3.75. (Translated by Potter.) 
 
 Gray : Systematic botany. New York : The American Book Co. 
 $2.00. 
 
 Bessey : Botany, Advanced Course. New York : Henry Holt & 
 Co. $2.20. 
 
 Geddes : Chapters in modern botany. New York: Charles 
 Scribner's Sons. $1.25. 
 
 413 
 
414 APPENDIX. 
 
 Warming: Lehrbuch der iikologischen Pflanzengeographie. Ber- 
 lin: Gebr. Borntrager. (A German translation by Knoblauch. 
 An English translation is now in preparation.) 
 
 PfeFFER : Pflanzenphysiologie. Ed. II., vol. I. Leipzig: Wil- 
 helm Engelmann. M. 20. (An English translation is now in 
 preparation by Dr. A. J. Ewart.) 
 
 Vines : Lectures on the physiology of plants. New York : The 
 Macmillan Co. $5.00. 
 
 Goodale : Physiological botany. New York: The American 
 Book Co. $2.00. 
 
 FOR LABORATORY DIRECTIONS. 
 
 Bergen: Elements of botany. Boston: Ginn & Co. $1.10. 
 
 Spalding : Introduction to botany. Boston : D. C. Heath & Co. 
 80 cts. 
 
 Macbride : Lessons in elementary botany. Boston : Allyn & 
 Bacon. 60 cts. 
 
 MacDougal : Experimental plant physiology. New York : Henry 
 Holt & Co. $1.00. 
 
 Arthur : Laboratory exercises in vegetable physiology. Lafay- 
 ette, Ind.: Kimmel & Herbert. (Pamphlet.) 35 cts. 
 
 Darwin and Acton : Practical physiology. New York : The 
 Macmillan Co. $1.60. 
 
 Arthur. Barnes and Coulter : Plant dissection. New York : 
 Henry Holt & Co. $1.20. 
 
APPENDIX V. 
 OUTLINE OF CLASSIFICATION. 
 
 In the foregoing work no endeavor has been made to present 
 any scheme of classification, but only to develop certain principles 
 in logical fashion. As a supplement the following general classi- 
 fication, adapted mainly from Strasburger, Noll, Schenck and 
 Schimper's Lehrbuch der Botanik, may be useful in showing the 
 relationship of the more important plants named in the text and 
 appendices. 
 
 All classification is more or less artificial. The purpose of such 
 an outline is to indicate roughly the present knowledge of kinship 
 among plants. Even were knowledge perfect it would naturally 
 be impossible to do this in a linear arrangement such as is neces- 
 sary in a book. Moreover, knowledge is far from complete. It 
 is to be expected, for example, that ultimately botanists will be 
 able to express much more accurately the relationship between 
 the groups of fungi and the algae than is now possible. Then, 
 the various groups of fungi will be ranked alongside the green 
 plants to which they are most akin, as is now done in the Schizo- 
 phyta, instead of being constituted a class by themselves. 
 
 The following classification differs more or less from all others 
 in details. Like them, it is merely tentative, and will be modified 
 as knowledge increases. Only in the most general divisions will 
 all schemes be found similar. 
 
 Subkingdom I. THALLOPHYTA. Thallophytes. 
 
 Class I. Myxomycetes. Slime molds. 
 Class II. Schizophyta. Fission plants. 
 
 Order I. Schizophycece. Fission alga?. Blue-green algae. 
 
 Nostoc. Rivularia. Oscillaria. 
 Order 2. Schitomycetes. Fission fungi. 
 Bacteria. 
 
 415 
 
416 
 
 APPENDIX. 
 
 Class III. Diatomeae. Diatoms. 
 
 Class IV. Peridineae. Often ranked as animals. 
 
 Class V. Conjugate. Brook silks and desmids. 
 
 Spirogyra. Zygnema. Mesocarpus. Desmids. 
 Class VI. Chlorophyceae. Green algae. 
 Order I. Protococcales. 
 
 Pleurococcus. Volvox. 
 Order 2. Cottfervoidales. Confervoid algae. 
 Ulothrix. Cladophora. Ulva. 
 Order 3. Siphonales. 
 
 Vaucheria. Caulerpa. Acetabularia. 
 Class VII. Phaeophyceae. Brown algae. 
 Order 1. Phaosforales. 1 
 
 Lessonia. 
 Order 2. Fucales. 1 
 
 Fucus. Sargassum. 
 Order 3. Dictyotales. 
 Class VIII. Rhodophyceae. Red algae. 
 
 Orders numerous. Polysiphonia. 
 Class IX. Characeae. Stoneworts. 
 Chara. Nitella. 
 Class X. Hyphomycetes. True fungi. 
 
 A. Phycomycetes. Algoid fungi. 
 
 Heterogamous Series. 
 Sub-class I. Oomycetes. 
 Orders numerous. Cys- 
 topus. 
 
 B. Mesomycetes. 
 Sporangiate Series 
 Sub-class III. Hemiasci. 
 Yeast. 
 
 C. Mycomycetes 
 Sporangiate Series. 
 Sub-class V. Ascomycetes. 
 Witch-broom fungus. Mil- 
 dews. Truffles. Penicil- 
 lium. Cup-fungi. Morels. 
 Class XI. Lichenes. Lichens. 
 
 Physcia. Theloschistes 
 1 Various larger species known as tangles, kelp, r 
 
 Isogamous Series. 
 Sub-class II. Zygomycetes. 
 Orders numerous. 
 
 Mucor. Rhizopus. Em- 
 pusa. 
 Intermediate fungi. 
 
 Non-sporangiate Series. 
 Sub-class IV. Hettribasidii. 
 Brand fungi. Smuts. 
 Higher fungi. 
 
 Non-sporangiate Series. 
 Sub-class VI. Basidiomy- 
 
 cetes. 
 Rusts. Cap-fungi. Poly- 
 porei. Puff-balls. 
 
 .k-weed, bladder-wratk. 
 
OUTLINE OF CLASSIFICATION. 417 
 
 Subkingdom II. BRYOPHYTA. Bryophytes. Mossworts. 
 
 Class I. Hepaticae. Liverworts. 
 Order 1. Ric dales. 
 
 Riccia. 
 Order 2. Marchantiales. Liverworts. 
 
 Marchantia. Lunularia. 
 Order 3. Anthocerotales. Horned liverworts. 
 Order 4. Jungermanniales. Leafy liverworts. Scale mosses. 
 
 Porella. 
 Class II. Husci. Mosses. 
 
 Order 1. Sphagna Us. Peat mosses. 
 
 Sphagnum. 
 Order 2. Andreaales. 
 Order 3. Archidiales. 
 Order 4. Bryales. True mosses. 
 
 Bryum. Mnium. Hypnum. 
 
 Subkingdom III. PTERIDOPHYTA. Pteridophytes. 
 Fernworts. 
 
 Class I. Filicineae. 
 
 Order 1. Filicales. True ferns. 
 
 Adiantum. Pteris. Aspidium. Asplenium. 
 Order 2. Hydropteridales. Water ferns. 
 Class II. Equisetineae. Horsetails. Scouring rushes. 
 
 Equisetum. 
 Class III. Lycopodineae. 
 
 Order 1. Lycopodiales. Ground pines. 
 
 Lycopodium. 
 
 Order 2. Selaginellales. Club mosses. 
 
 Selaginella. 
 
 Subkingdom IV. SPERMATOPHYTA. Seed plants. 
 
 Class I. Gymnospermae. Gymnosperms. 
 Order 1. Cycadales. Cycads. 
 Cycas. 
 
41 8 APPENDIX. 
 
 Order 2. Coniferales. 
 
 Pines, spruces, larches, firs, etc. 
 Order 3. Gnetales. 
 
 Welwitschia. 
 Class II. Angiospermae. Angiosperms. 
 
 Sub-class I. Monocotyledon.es. Monocotyledons. 
 
 Orders several. Lilies, irises, grasses, sedges, rushes, 
 palms. 
 Sub-class II. Dicotyledones. Dicotyledons. 
 
 Orders numerous. Most herbs with net-veined leaves, 
 deciduous shrubs and trees. 
 
INDEX. 
 
 All references are to pages. When there are two or more references to the 
 same topic, figures in bold-face indicate the definition or chief discussion of the 
 subject. Italic figures indicate illustrations. 
 
 Absorption, carbon dioxide 165 ; 
 water 74, 153, 155, 323 
 
 Acacia, leaves I : ' t 
 
 Acetabularia 23, l'4 
 
 Achillea, inflorescence 257 
 
 Achlya, sex organs 293 
 
 Acids, carbon 175 
 
 Adaptations 146, 308 
 
 Adiantum 382; embryo 62, 68; 
 leaf 126; spermary 282 
 
 Aeration 171 
 
 Agaricus 377, 404 
 
 Agrimonia, fruit 866 
 
 Ailanthus, fruit 864 
 
 Air, distributing seeds 363; dis- 
 tributing spores 356; effect of 
 composition 312 ; effect of 
 moisture in 316; -plants 152 
 
 Alcanna, corolla 250 
 
 Aldrovandia ..'}>: 
 
 Aleurone grains 169 
 
 Algae, eggs ?86, 288; fission 8; 
 gametes 278; imprisoned 338, 
 877 ; in other water plants 33 1 
 
 Alkaloids 177 
 
 Allium, stem 106 
 
 Aloe, epidermis 828 
 
 Alternation of generations 49. 
 60 
 
 Amanita, fructification 219 
 
 Amorpha, sleep movement .'". v 
 
 Amorphophallus, leaf 125 
 
 Anabaena 10 
 
 Anabolism 166 
 
 Anagallis, fruit SOS; pistil :','> 
 
 Anaptychia, apothecium 
 
 Angiosperms 237; ovary 291; 
 
 seed 299; sperr.iary 281 
 Animals, and plants 336, 338, 
 
 342; distributing seeds 365; 
 
 distributing spores 357 
 Anther 246 
 
 Anthyllis, venation 137 
 Ants and plants 348 
 Apical cell, Cha.ra.SO, 31; Funis 
 
 34', liverworts 51; Polysipho- 
 
 nia 32; root 67, 6S; shoot 84 
 Apodanthes S40 
 Apogamy 294 
 Apparatus 409 
 Apple, fruit S05 
 Arbor vitae, shoot 97 
 Archegonium 289 
 Arisarum, flower 
 Armor, protective 347 
 Artemisia, hail 
 Ash, pistil of .;/ 
 Asparagus, branches 92 
 Aspidium, pinnule 280; s.irus 
 
 281; sporangium 
 Asplenium, buds 262; gamete* 
 
 phyte 60 
 Assimilation 1 62 
 
 Astragalus, pistil 
 A ulai omnium, brood bud 
 Automatism u^. 188 
 Auxanometer isn 
 
 Bai tei ia to, //. 12 
 Bacterium aceti // 
 Balsam, stem 6 
 I tai berry, thori 
 
 ,19 
 
420 
 
 INDEX. 
 
 Bark 111, 116 
 
 Bast, secondary 113 
 
 Bazzania 53 
 
 Bean, geotropic roots 199, 201 
 
 Beech, mycorhiza 336 
 
 Beet, stoma 184 
 
 Begonia, stem bundle 104 
 
 Bellflower, fruit 802; leaf ro- 
 sette 196 
 
 Bidens, fruit 367 
 
 Bird's-nest fungus 218 
 
 Blackberry 305 
 
 Bladderwort 343. 344, 345 
 
 Blade, leaf 123; structure of 
 leaf 133 
 
 Blasia 54 
 
 Boletus 404 
 
 Books, reference 413 
 
 Bracts 131, 236, 256 
 
 Branches, dwarf 90, 91, 92 
 
 Branching 22; of leaves 122, 
 124, 125, 126, 128, 138; of liv- 
 erworts 51; of mosses 57; re- 
 production by 267; of root 78; 
 of shoot 86; of stamens 249 
 
 Brood buds 260 
 
 Bryony, tendril 94 
 
 Br yum, capsule 58, 228, 280; 
 section of stem 56 
 
 Buckthorn, leaf 128 
 
 Buds, 85, 88; adventitious 89; 
 axillary 87; dormant 89; on 
 roots 81; reproductive 263; 
 shoot 85 
 
 Budding 40, 211, 267 
 
 Bulb 90, 326 
 
 Bulblets 93 
 
 Bundles, vascular 71, 72, 100, 
 103, 114, 132, 136 
 
 Butomus, anther 248 
 
 Butternut, buds 88 
 
 Cactus, forms 98 
 
 Calamus, root 72 
 
 Caltha 389. 407 
 
 Calyptospora, haustoria ^5; 
 spores 854 
 
 Calyx 237, 253 
 
 Campanula, fruit 302; leaf ro- 
 sette 196 
 
 Canna, leucoplasts 4 
 
 Capsella, embyro 66; pistil 242 
 
 Carbohydrates 159; manufac- 
 ture 166 
 
 Carbon dioxide, absorption 165 
 
 Carex, leaf edge 348 
 
 Carnivorous plants 342 
 
 Carpels 235, 236, 237 
 
 Carpogonium 287 
 
 Carrot, chromoplasts 6 
 
 Caulerpa 23, 24, 25 
 
 Cecropia, stem 349 
 
 Cedar, gametophytes 284 
 
 Cell 1; division 17, 18; naked 
 147; wall 5 
 
 Centrifuge 199 
 
 Centrospheres 4 
 
 Cereus, shoot 98 
 
 Chara27, 2S, 30,2,11, 402; ovary 
 281; spermary 2S0, 881 
 
 Characeae 27 
 
 Cheiranthus, hairs 101 
 
 Chelidonium, hair cell 191 
 
 Chemotaxis 274 
 
 Cherry, cork cambium 110; 
 fruit 304 
 
 Chlorophyll, function 166; spec- 
 trum 166, 16? 
 
 Chloroplasts 4, 5, 21; move- 
 ments 192 
 
 Chondromyces, colonies 884 
 
 Chromoplasts 5 
 
 Cilia 12, 147, 190 
 
 Cinchona, bark 112; stem 108 
 
 Cinnamon, flower 248 
 
 Cladonia 377 
 
 Cladophora 22, 28, .'./, 370, 402 
 
 Cladophylls 92 
 
 Classification 415 
 
 Clavaria, fructification 219, 404 
 
 Claviceps, fructification /.'. ' 
 
 Climate, relation of plants to 
 308 
 
 Climbers 330 
 
 Close-pollination, adaptations 
 for 358 
 
 Clover, root tubercles 337 
 
 Club-mosses, sporangia 231 
 
 Clusia, periderm of root 74 
 
 Cobsea, flower 360 
 
 Cockle-bur, fruit 367 
 
 Ccenocytes 22 
 
JXDEX. 
 
 421 
 
 Cohesion, carpels 241; stamens 
 248 
 
 Cold, protection against 315 
 
 Colonies, gelatinous 8 
 
 Color, significance 359 
 
 Conducting tissues 156 
 
 Cone, pine 998 
 
 Conifers, fruit 29S 
 
 Conjugatae 16, 20 
 
 Conjugation 269, 274 
 
 Contact movements 203 
 
 Contractility 145 
 
 Convolvulus, hairs 321 
 
 Coprinus, gill 217 
 
 Cosmos, stamens 249 
 
 Cotton, fruit 366 
 
 Cotyledons 117 
 
 Cork 110; cambium no 
 
 Corm 90 
 
 Corn, stem bundles 107 
 
 Cornus, inflorescence 257 
 
 Corolla 237, 253 
 
 Coronilla. sleep movement 207 
 
 Cortex, Chara 30; leaves 135; 
 root 72, 73; secondary 109; 
 stem 100, 109 
 
 Cranberry rust, spore chain 354 
 
 Crataegus, stipules 121 
 
 Cross-pollination 255; adapta- 
 tions for 358 
 
 Crucibulum 21S 
 
 Crystals 175, 176, 351 
 
 Cup fungus 223 
 
 Currant, nectary 177; ovules 
 
 Cuscuta 889 
 
 Cutin 6 
 
 Cuttings 266 
 
 Cycas, carpel 238; seed 897 
 
 Cystocarps, Polysipbonia 988, 
 
 £89 
 Cystopus 277, 375, 403 
 Cytoplasm 2 
 
 Dandelion, fruit 866 
 
 Datura, anther 248; leaf mo- 
 saic 196 
 
 Dehiscence, anthers 247; fruit 
 301, 80S, 808 
 
 Development, phases of 178 
 
 Desmids 16 
 
 Desmodium fruit 366 
 
 Diatoms 14, 16 
 
 Dichotomy 78, 86 
 
 Digestion 162; intracellular 170 
 
 Dionaea 346; leaf 208, 34-5 
 
 Distribution, of seeds 361; of 
 
 spores 353 
 Dodder 889 
 
 Dogwood, inflorescence 257 
 Domatia 350 
 Dorsiventrality 57 
 Draba, hairs 822 
 Dracaena, stem 114 
 Drosera, leaves 345 
 Duration, of root 73; of shoot 
 
 94 
 
 Echinocactus, shoot 98 
 
 Ecology 144, 307 
 
 Edelweiss, hairs 321 
 
 Eel grass, runners 265 
 
 Egg 285 
 
 Elaeagnus, scales 322 
 
 Elaters 7, 355 
 
 Elatine, stem 102 
 
 Elder, lenticel US 
 
 Elm, buds 88; cork cambium 
 
 110 
 Emergences 101, 102, 802 
 Embryo 62, 63, 66,289,291, 295, 
 
 296, 297, 300, 304; sac 243, 
 
 244 
 Empusa 354 
 Endodermis, root 72, 75, 77; 
 
 stem 100, 115 
 Endosperm 298, 299 
 Energv, released by respiration 
 
 173 ' 
 Entoderma in alga 
 Enzymes 162 
 Epidermis, adaptations 320; of 
 
 leaf 133; of root 70; of stem 
 
 100, 101 
 Epipactis, cell division 17 
 Epiphytes 331 
 Epispore 214 
 Equisetum 230, 282, 384; apical 
 
 bud 8J t ; sporangium wall 988) 
 
 spore- 
 Ergot, fructification .;?. 
 Erysiphe 924, 375; f™' 1 
 
422 
 
 INDEX. 
 
 Eschscholtzia, ovules 243; pro- 
 tection of stamens 353 
 Excretion 173 
 Exobasidium 43 
 
 Fagus, mycorhiza &?<? 
 
 Fats 160 
 
 Fennel, resin receptacle 176 
 
 Fermentation 162 
 
 Fern, maidenhair 3S2, 406 
 
 Fernworts 60; ovary 290; sper- 
 mary 280, 282; sporangium 
 229, 356 
 
 Fertilization 255, 285 
 
 Fig, inflorescence 260 
 
 Filament 246 
 
 Fir, seed 297; seedling 118 
 
 Fission 17, 211 
 
 Flax, stem 104 
 
 Flower 92, 236; leaves 131; 
 movements 196 
 
 Fly fungus 354 
 
 Fly trap, leaves 208, 345 
 
 Foliage 119 
 
 Food, for insects 359; insects as 
 342; with spores 215 
 
 Foods 159; manufacture 166, 
 16S; storage 16S; transloca- 
 tion 168 
 
 Fossombronia 54 
 
 Fragmentation 211 
 
 Fraxinus, pistil 241 
 
 Freezing, protection against 
 315 
 
 Fructifications 218 
 
 Fruits, accessory 304; adapta- 
 tions to distribution of seed 
 361; of angiosperms 300; dry 
 300; fleshy 303, 3(17; of gym- 
 nosperms 298; multiple 305 
 
 Fucus 33, 34, 373, 4°3; egg 286; 
 ovary 287, 288; spermary 278 
 
 Funaria, leaf 56; development 
 of sporophyte 206; ovary 290 
 
 Function 143; limits to 146; unit 
 of 144 
 
 Fungi 39, 213, 216 ff., 335, 337, 
 338; fission 10; loss of sex- 
 uality 293 
 
 Fusion, of hyphae 45; of sta- 
 mens 249 
 
 Gametophyte 49; of fernworts 
 60; of liverworts 58, 54; of 
 
 mosses 55; reduction 61, 292; 
 of seed plants 64; shoot 82 
 
 Gaultheria, fruit S04 
 
 Gelatin 6, 12 
 
 Gemmae 260 
 
 Geotropism 197 
 
 Gerardia, parasitic SS9 
 
 Germination, adaptations to 
 367; of pollen 251 
 
 Glceocapsa S 
 
 Grafting 267 
 
 Grain 301 
 
 Grasses, geotropic node 199, 
 200; lea.H20; rolling of leaves 
 S19 
 
 Grimmia, capsules 855 
 
 Growth 151, 178; conditions of 
 183; daily period 1S5; dura- 
 tion 187; grand period 1S1 ; 
 induced 295; intercalary 38; 
 of leaves 137, 138; localiza- 
 tion of 22; measuring 180; 
 movements due to 192; of cell 
 wall 7; of spores 215; region 
 of 181; spontaneous varia- 
 tions in 1S7 
 
 Gymnosperms 237; ovary 291; 
 seed 297; spermary 280, 282 
 
 Hairs 320, 821, 822, 347; absorb- 
 ing 323; glandular 360; of 
 stem 101 
 
 Halophytes 311, 326 
 
 I laustoria 45, 46 
 
 Heat from respiration 174 
 
 Heatli, rolled leaf 821 
 
 Heliotropism 194 
 
 Hellebore, pistil .' :} 1 
 
 Helotism 333, 337 
 
 Heterocysts 9 
 
 Heterogamy 271, 276 
 Hibernacula 204 
 Honeysuckle, buds SS; leaves 
 
 128 
 Hop, emergences 202 
 Horse-chestnut, leaf 126 
 Horsetails 384, 405; sporangia 
 
 230, 232; sporangium wall 
 
 §88; spores ..;.; 
 
 
INDEX. 
 
 423 
 
 Host 161 
 
 Houseleek S25 
 
 Hydnum, fructification 220, 404 
 
 1 [ydrophytes 311, 327 
 
 Hydrotropism 202; apparatus 
 SOS 
 
 II ylocomium 56 
 
 Hyphse 39; branching 40; fu- 
 sion 45 
 
 Indian turnip, inflorescence 256 
 Infection with fungi 43 
 Inflorescence S7 
 Insects, adaptations of flowers 
 
 to 358; distributing spores 
 
 357; exclusion of 359; as food 
 
 342 
 Integuments, of ovule 243; of 
 
 seed 299 
 Internodes 96; of Chara 27 
 Involucre 256 
 
 Irregularity 254; purpose 359 
 Irritability 145, 183, 188, 274; 
 
 localization 189 
 Isogamy 271, 274 
 Ivy, chloroplasts 4 
 
 Katabolism 170, 175 
 
 Land plants 152, 311 
 
 Larch, gametophyte 282, 283; 
 shoot 320 
 
 Lasiagrostis, rolling of leaf S19 
 
 Lathyrus 407 
 
 Leaves, adaptation 314, 320; 
 arrangement 119; base 120; 
 blade 123; development 117; 
 fall of 140; form 119; growth 
 137. 138; of mosses 57; origin 
 53; pine 91, 92; primary 117; 
 secondary 117; stalk 122; 
 structure 132, 189; suppres- 
 sion 319; as water recepta- 
 cles 324 
 
 Leguminosfe, root tubercles 336 
 
 Lenticels 113 
 
 Leucoplasts .'/, 5 
 
 Lichens J'., 47, .'.'.7, 337 
 
 Light, effect on growth [84, 
 185; effect on form 313; effect 
 on water plants 33S; escaping 
 
 319; produced by plants 17c 
 
 relation to photosyntax 166 
 Lignification 6 
 Lily, anther .'/,S; buds 262 
 Lime, effect of 317 
 Linden, domatia 350; shoot 86 
 Liverwort 49, 378, 379, 404, 405; 
 
 sporangium 227 
 Locomotion 190 
 Locust, development of leaf 
 
 139; stipule thorns ISO 
 Lodgers 334 
 Lonicera, buds S8 
 Lotus, fruit SOS 
 Lunularia %9, 50 
 Lychnis, petal 254; stigma 2j0 
 Lycopodium, stem 103 
 
 Malt 40S 
 
 Maple, buds 88; fruits S24; leaf 
 188; mosaic 195 
 
 Marchantia 378, 404; elaters 7 
 rhizoids 7; spermarv 979 
 thallus 267; brood-buds 262 
 thallus 261 
 
 Marigold, marsh 389, 407 
 
 Marsilia, root tip 68 
 
 Mechanical tissues 149; devel- 
 opment of 1S6 
 
 Mechanics of body 149 
 
 Megasporangium 234 
 
 Megaspore 231; of lily .' 
 
 Melampsora, spore beds 215 
 
 Meristem, primary 35; of root 
 68; of shoot 84; secondary 74, 
 108 
 
 M>s, 1, arpus 21; conjugating 
 
 Mesophytes 311, 312 
 Metabolism 145, 215 
 Metzgeria ■'•-' 
 Micrococcus // 
 Microsphaera 375, 403 
 Microsporangium 234 
 M i< rospores 231 
 
 Mildew :."/. 375, 403; fru • 
 
 Milkweed, Bowers 252; pollen 
 
 mass 
 Mimicry 3 p 
 
 Mimosa, leaves 208; sleep 
 movement ."- , 
 
424 
 
 INDEX. 
 
 Mineralization 7 
 
 Mnium 381, 405 
 
 Moisture, effect on growth 186 
 
 Monopodial branching, of root 
 7S; of shoot 87 
 
 Monostroma 26 
 
 Monotropa, pollen tube 283 
 
 Morchella, fructification 286 
 
 Morning glory, chloroplasts 4; 
 seedling US 
 
 Mosaic, leaf 195, 106 
 
 Mosses 53, 3S1; brood buds.?'/'.'; 
 sporangium 229; teeth 355; 
 sporophyte 822 
 
 Mossworts, ovary 289; sper- 
 mary 2S0 
 
 Motor organs 192, 295 
 
 Mountain ash, chromoplasts 6 
 
 Mousetail, flower 259 
 
 Movements 188; combined 196; 
 contact 203, 207; for entrap- 
 ping animals 345; of water, 
 effect on plants 328; para- 
 tonic 193; photeolic 206; spon- 
 taneous 193, 206; to protect 
 spores 352 
 
 Mucor 41, 403; sporangium 222 
 
 Mulberry 306; flower and fruit 
 305 
 
 Mushroom 377, 404; gill SI? 
 
 Mustard seedlings, geotropic/.%? 
 
 Mutualism 333 
 
 Mycelium 41 
 
 Mycorhiza 335, 336 
 
 Myosurus, flower 259 
 
 Nectar 176; guides to 359 
 
 Nectaries 177 
 
 Nemalion, ovary 288 
 
 Nettle hair 348 
 
 Nitella 27, ."■> 
 
 Nitrogen, supply 342 
 
 Nodes 96; of Chara 27 
 
 Nostoc 9, 369, 401 
 
 Noteroclada 54 
 
 Nucleus 3 
 
 Nutation 193 
 
 Nutrition 151; of Oscillaria 10 
 
 Oats, cell from leaf 4; epider- 
 mis 134 
 
 Odor, cause 176; purpose 359 
 
 Offsets 90, 265 
 
 Oils 176 
 
 Oleander, leaf 824 
 
 Oleaster, scales 822 
 
 Oligotrichum, leaf 56 
 
 Onion, embryo 56; stem 106 
 
 Oogonium 287 
 
 Opuntia 321 
 
 Orange, oil receptacle 177 
 
 Orchid, chromoplast 6; light 
 seeds 363; mycorhiza 886 ; 
 pollen tube 283 
 
 Organ 143 
 
 Origin of roots 79 
 
 Orthotrichum, branching 57 
 
 Oscillaria 10, 370, 401 
 
 Osmosis 156 
 
 Ovary 240, 273, 286 
 
 ( Hulury 240 
 
 Ovules 237, 242, 243, 244; dia- 
 grams 285 
 
 Oxalis, cells 102 
 
 Oxygen, effect on growth 186; 
 supply 171 
 
 Pansy, seed 300 
 
 Parasites 43, 161, 163 
 
 Parasitism 333, 338 
 
 Parmelia, thallus 825 
 
 Pea, flower 255; growth of root 
 182 ; leaf tendrils 130 ; root 
 branches 79; sweet 407 
 
 Pellia, sperms 280 
 
 Peperomia, water storing 326 
 
 Pepper, fruit 800 
 
 Perennials in 
 
 Perianth 236, 252 
 
 Pericarp 300; adaptations to 
 distribution of seeds 3(12 
 
 Pericycle, root 71 ; stem 100, 
 103' 
 
 Periderm, root 74, 75; second- 
 ary in; stem 109 
 
 Perisperm 29S, 299 
 
 Peronospora, haustoria 46; sex 
 organs 87? 
 
 Petal 237 
 
 Petiole 122; scarlet runner 105', 
 sensitive 128; structure 132 
 
 Peziza 223, 376, 404 
 
INDEX. 
 
 425 
 
 Phascum, sporophyte 59 
 Phaseolus, motor organs 905; 
 
 stele of root 75, 76 
 Phelloderm 109 
 Phloem, bundle of root 72 ; 
 
 secondary 109 
 Photosyntax 166; product 167; 
 
 and respiration 171, 175 
 Phycocyanin 8 
 Phycoerythrin 33 
 Phycophaein 3S 
 Phyllodia I:', 
 Phyllotaxy 119 
 Physcia 376, 404 
 Physiology 143; apparatus 411; 
 
 experiments 391 
 Phytolacca seed 300 
 Pilobolus, abjection of sporan- 
 gium S5S 
 Pilularia, megaspore 214 
 Pimpernel, fruit SOS; pistil £45 
 Pine 387, 406; carpel 238; cone 
 
 298 ; shoot 91 ; wood, pene- 
 trated by hyphae 44 
 Pineapple 306 
 Pine sap 988 
 Pistil 237; diagram £85; simple 
 
 and compound 240 
 Pitcher plants 129, 342, S48 
 Pitfalls 342 
 
 Pith, rays 115; stem 107 
 Placenta 244 
 Plasmodia 14S 
 Plastids 4 
 
 Plectranthus, hairs 101 
 Pleurococcus 13, 369, 401 
 Pokeberry, seed SOO 
 Pollen, grains 249, 250 ; tube 
 
 ."/", 281, ?8S, ?84, 886 
 Pollination 255, 358 
 Polyembryony 294 
 Polygonatum, leaf VB7 
 Polygonum, megaspore 
 
 Stipules /.'./; tubers U) 
 Poly podium 61 
 Polyporus 4.! ; fructification 
 
 i£0, 404 
 Polysiphonia 31, St, 372, 402; 
 
 cystocarps $88, £89 ; tetra- 
 
 s pores .'.',' 
 Folytrichum 55 
 
 Pondweed, hibernacula 268 
 
 Poplar, mycorhiza 335 
 
 Poppy, ovules 243; protection 
 
 of stamens 353 
 Porella 379, 405 
 Potassium salts, relation to 
 
 photosyntax 167 
 Potato, pistil 241 ; starch 5 ; 
 
 seedling ?66 
 Pressure, effect on growth 186; 
 
 root 156 
 Prickles 101, K/J, 347 
 Proteids 160; grains 169; manu- 
 facture 168 
 Prothallium 60 
 Protonema, mosses 58 
 Protoplasm 2; movements 191; 
 
 naked 147; powers 145 
 Psychotria, domatia 350 
 Pteris, embryo 62 ; origin of 
 
 root SO; ovary 290 
 Puff ball 214, 221 
 Putrefaction 162 
 Pyrenoids 21 
 Pyrola, fruit 302 
 
 Radiolarian and algae 33S 
 
 Rainfall, adaptations to 316 
 
 Ranunculus, leaf 120; nectary 
 177 
 
 Raspberry 305 
 
 Reaction 189 
 
 Reagents 409 
 
 Rejuvenescence 268 
 
 Repair 151 
 
 Reproduction 145, 209; adapta- 
 tions 352; sexual 268; vegeta- 
 tive 211 
 
 Resins 176 
 
 Respiration 171; intramolecular 
 172 
 
 Rheum, flower .">■'' 
 
 Rhizoids 22; Chara 31; liver- 
 worts 50; mosses 53 
 
 Rhizome 90 
 
 Rhizopus 374, 403 
 
 Rhododendron, anthers and 
 pollen . '/.'' 
 
 Riccia 50 
 
 Rigidity, how secured 149 
 
 Rings, annual, of stem 116 
 
426 
 
 INDEX. 
 
 Rivularia 369, 401 
 
 Robinia, thorns ISO 
 
 Root 65; adaptations 156; ad- 
 ventitious 267 ; aerial 324 ; 
 cage 200, 201; cap 68, 70, 71; 
 climbers 331 ; differences 
 from shoot 85 ; fleshy 77 ; 
 float 77; hairs 69, 70; hairs 
 and soil 154; hairs, solvent 
 action 155; origin from leaves 
 139 ; parasitic 889 ; pressure 
 156; pressure, apparatus for 
 157; primary 65; secondary 
 67 ; tap 324 ; tendrils 78 ; 
 thorns 7S ; tubercles 336 ; 
 woody 76 
 
 Rose, flower 260; leaves 122 ; 
 prickle 102; seedling IIS 
 
 Rotation of protoplasm 191 
 
 Runner 90, 265 
 
 Rye, daily period of growth 
 185; stem IS 4 
 
 Sage, anther 247 
 Salts in water 154, 164 
 Salvinia, sporangium 285 
 Saprolegnia, zoospores 213 
 Saprophytes 161 
 Sarcina 11 
 Sargassum 37, 38 
 Saxifrage, flower 360 
 Scales 320, 322; leaf 130 
 Scarlet runner, motor organs 
 
 205 
 Scions 266 
 
 Scutellaria, cortex 109 
 Secretion receptacles 176, 177 
 Sedge, leaf edge 848 
 Sedum, flower .'/..', 259; offsets 
 
 .<•■; 
 
 Seed 296, 407; in angiosperms 
 
 299; distribution 306, 361; in 
 gymnosperms 297 
 
 Seed plants, ovary 290 ; para- 
 sitic 340 ; spermary 280 ; 
 spores and sporangia 234 
 
 Selaginella 386, 406 ; female 
 gametophyte 291 ; male ga- 
 metophyte 282; stem 105 
 
 Selection, power of 164 
 
 Sempervivum 826 
 
 Sepal 238, 253 
 
 Sex organs 273 
 
 Sexuality, imperfect 269; loss 
 of 293; origin 268 
 
 Shepherd's purse, embryo 66; 
 pistil 242 
 
 Shoot 82; differences from root 
 S5; from leaves 139; liver- 
 worts 52; primary 83 
 
 Sleep movements 206 
 
 Soil 153; effect of temperature 
 of 315 ; effect of physical 
 characters 317; limits of ab- 
 sorption from 155 ; salts in 
 154; water in 154 
 
 Solutions, water 152 
 
 Spadix 256 
 
 Spathe 256 
 
 Spermary 274, 277 
 
 Sperms 276 
 
 Sphseroplea, gametes, 286 
 
 Sphagnum, sporophyte 228 
 
 Spirogyra 20, 370, 401 ; conju- 
 gating 272 
 
 Splachnum, capsules 58 
 
 Sporangia 216, 221; of anther 
 247; of fern 356 
 
 Spore 212; chains 217; diagram 
 216; germinating 4- : '< non- 
 sexual 212; of Penicillium 211 ; 
 of Filularia 214; protection 
 352; resting 294; sexual 268 
 
 Sporophylls 131, 230 
 
 Sporophyte 49, 227, 292; fern- 
 worts 62; mosses 58, 59, :::; 
 shoot 83; seed plants 64 
 
 Spruce, ovaries 284 
 
 Stamens 235, 236, 245 
 
 Starch, manufacture 167 ; re- 
 serve 169 
 
 Stem 96; climbing 99; erect 98 
 forms of xerophytic 319; o 
 mosses 55, 56; prostrate 98 
 sections 99, 102, 108, 104, 105 
 106, 108, 114; shape 97; struc 
 ture 99; twining 99 
 
 Stele, of leaves 136; of root 71; 
 of stem 100, 103 
 
 Stigma 240 
 
 Stimulus 188; transmission of 
 190 
 
INDEX. 
 
 427 
 
 Stipules 121 
 
 St. John's wort, stamens 250, 
 251 
 
 Stolon 90 
 
 Stomata 134; sunken 322 
 
 Stonecrop, flower 259; offsets 
 264 
 
 Storage 107; of foods 168, 169; 
 in leaves 131; in roots 77 
 
 Strawberry, flower 258, 259; 
 runners 264 
 
 Streaming of protoplasm 191 
 
 Style 240 
 
 Suberin 6 
 
 Sugar, manufacture 167 ; re- 
 serve 169 
 
 Sugar cane, epidermis 323 
 
 Sundew, leaves 345 
 
 Suspensor 66, 291 
 
 Symbionts 161 
 
 Symbiosis 161, 333 
 
 Symphoricarpus, fruit cells 179 
 
 Sympodial branching, in moss 
 57; in shoot of seed plants 86 
 
 Syrrhopodon, brood buds 262 
 
 Telegraph plant, leaf 206 
 Temperature, effect on growth 
 
 185; on form 314; on water 
 
 plants 328 
 Tendril, of bryony 94; leaf 130; 
 
 movement of 203; shoot 93 
 Tension, distributing seeds 
 
 362; distributing spores 355; 
 
 of tissues 149, 182 
 Tetragonolobus, sleep move- 
 ments 207 
 Tetrasporangia, of Polysi- 
 
 phonia .'.',' 
 Thallus 22, 25; of Fucus 34; of 
 
 liverworts 49 
 Thickening, secondary, of root 
 
 74, 77; of stem 107, 115 
 Thlaspi, leaf VSS 
 Thorn apple, anther 248 
 Thorns 347; leaf 130; shoot 93; 
 
 of Veil a 96 
 Thyme, anther 247 
 Tococa, base of leaf 350 
 Torus 236, 258 
 Traction, effect on growth 186 
 
 Trametes 44 
 Transfer of foods 168 
 Transpiration 158; adaptations 
 
 for reducing 318 
 Traps 343 
 
 Trefoil, fruit of tick $66 
 Tropaeolum, leaf 128 
 Tubers 93, 326 
 Turgor 148; distributing seeds 
 
 362; distributing spores 353; 
 
 movements 204 
 Twiners 201, 331 
 Tylanthus, leaf 321 
 
 Ulothrix 21; reproduction 270, 
 
 271; zoospores 269 
 Ulva 26 
 Uncinula 403 
 Urtica, hair 348 
 Utricularia 343, 344, 345 
 Uvularia, leaves 128 
 
 Vacuoles 2, 179 
 
 Vallisneria, distribution of 
 
 spores 356, 857; runners 265 
 Vanda, light seeds 868 
 Vanilla, leucoplasts 5 
 Varnish, on epidermis 321 
 Vascular bundles 71, 72, 100, 
 
 103, 114, 132, 136 
 Vaucheria 22, 23 ; sex organs 
 
 278 
 Vella, thorns 95 
 Venation, leaves 125, 127, 137, 
 
 13S 
 Veratrum, pistil .'.;/ 
 Vicia, vascular bundles of root 
 
 75 
 Violet, anther 2 40; fruit /.v.' 
 
 Water, absorption 153, 323 ; 
 distributing seeds 362; dis- 
 tributing spores 356 ; effect 
 of composition 329; effect of 
 movements 32S; force raising 
 157; loss 158; movement 150; 
 necessity 152 ; path of 156 ; 
 percentage 151 ; -plants 152, 
 327; salts in K14; storing 325 
 
 Waste products 175 
 
 Wax, on epidermis 321 
 
428 
 
 INDEX. 
 
 Weight, loss of 173 
 Welwitschia 140 
 Willow, fruit S65; leaf 127 
 Wind, distributing seeds 363; 
 
 distributing spores 356; effect 
 
 on form 313 
 Wings to fruits 364 
 Wintergreen, fruit 302, 304 
 Wheat, flower 258; geotropic 
 
 stem 200; seedling 11S 
 Wood, in root 71; secondary 113 
 
 Xanthium, fruit 367 
 
 Xerophytes 311, 318 
 Xylern bundles, of root 72; sec 
 ondary 109 
 
 Yarrow, inflorescence 257 
 
 Yeast, beer 40 
 
 Yew ovule and fruit 239 
 
 Zamia, flower 233 
 Zea. stem bundles 107 
 Zoospores i^T, 212 
 Zygnema 20, 401 
 
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