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 ONLY, and is subject to a fine of FIVE 
 CENTS a day thereafter. It is due on the day 
 indicated below: 
 
 2May5&4 
 
Mutants and Hybrids of the Oenotheras. 
 
 BY 
 
 D. T. MACDOUGAL 
 
 ASSISTED BY 
 
 A. M. Vail, G. H. Shull and J. K. Small 
 
 WASHINGTON, D. C. : 
 Published by the Carnegie Institution of Washington 
 
 1905 
 
Carnegie Institution of Washington, Publication No. 24, 
 
 Papers of Station for Experimental Evolution at 
 Cold Spring Harbor, New York. No. 2. 
 
 PRESS OF 
 
 HENRY E. WILKENS PRINTING CO. 
 
 WASHINGTON, D. C. 
 
 
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Mutants and Hybrids of the Oenotheras 
 
 BY D. T. MACDOUGAL 
 ASSISTED BY A. M. VAIL, G. H. SHULL,t AND J. K. SMALL 
 
 PURPOSE AND SCOPE OF INVESTIGATIONS. 
 
 The more important features of the investigations of De Vries in 
 which lines of descent were seen to originate, which embodied new 
 qualities and groupings of characters, constant and fully transmissible, 
 are now so familiar to all naturalists that no rehearsal is necessary in 
 the present paper. Early in 1902 the senior author received seeds of 
 the Lamarck's evening-primrose, and these, with seeds of various 
 species obtained directly from their native habitats in North America, 
 were cultivated in the New York Botanical Garden, in which the con- 
 ditions of soil and climate are, of course, widely different from those 
 of the botanical garden at Amsterdam, Holland. 
 
 Among other primary purposes of the cultures it was deemed of 
 great importance that the mutants should be tested as to their stability 
 when grown as biennials after the predominant habit of the genus. 
 The results of this test, together with detailed descriptions of three of 
 the mutants, have already been given in an article in which occasion 
 was taken to set forth briefly the principal tenets of the mutation theory 
 as propounded by De Vries (MacDougal, 1903). It was found that 
 the mutant forms were not only physiologically differentiated, but were 
 also easily separable from one another and from the parental type when 
 tested by accepted taxonomic criteria, and by an examination of the 
 features of their life-histories. Furthermore, all the forms came true 
 to their newly assumed groupings of characters without reversions, and 
 
 *T'he contents of this paper were presented before the weekly botanical con- 
 vention at the New York Botanical Garden, October 19, 1904. 
 
 fOf the staff of the Station for Experimental Evolution of the Carnegie 
 Institution of Washington, Cold Spring Harbor, Long Island, N. V. 
 
 Library 
 N. C. State College 
 
4 MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 exhibited only fluctuating variations of ordinary amplitude, although 
 the last-named feature was not examined by statistical methods. An 
 investigation of this feature is described in the present paper. 
 
 During the earlier cultures, plans were formulated for a somewhat 
 inclusive investigation of the genetic relationships of the various 
 members of the genus, and of the variations, or mutations, which 
 might be found to occur in O. lamarckiana in America, and in the 
 other species of the group. To this end correspondence was estab- 
 lished with collectors in various parts of America and Europe, and 
 material was obtained from such distant points as New Zealand, 
 Mexico, Holland, and Japan. A supply of paraffined paper bags was 
 furnished by Professor De Vries, and later those manufactured for the 
 Station for Experimental Evolution at Cold Spring Harbor were used 
 for inclosing the inflorescences, by which absolutely pure crops of 
 seeds of the species, as well as of the various hybrids, were obtained. 
 All sowings of seeds were made in soil sterilized in an autoclav for 
 three or four hours. A number of the parcels of earth treated in this 
 manner were moistened and kept under proper conditions, but in no 
 instance were any germinations of other Oenotheras seen. In order to 
 economize time it was found most convenient to grow the evening- 
 primroses as annuals, which may be done by germinating the seeds in 
 a propagating house and then transplanting them to the experimental 
 grounds early in May. The earlier cultures were begun about Jan- 
 uary i , but it was found that ample time for the entire development of 
 the plant was obtained if the sowings were made late in February or 
 early in March. 
 
 The portions of the general investigation in which such progress 
 has been made as to warrant the publication of the present paper are 
 as follows : 
 
 (i) Determination of the ancestral habitat and dissemination of 
 0?iagra {Oenothera) lamarckiana . 
 
 (2) Description of such species of Onagra {Oenothera} as have 
 been kept under cultivation for one or two seasons in order to facili- 
 tate observation of possible mutants. 
 
 (3) Analysis of the relationship between 0. lamarckiana and 
 other species of the genus by means of hybridizations. 
 
 (4) Estimation of the dominance of parental characters in hybrids 
 of 0. lamarckiana X 0. biennis and . lamarckiana X 0. cruciata. 
 
 (5) Determination of the recurrence and stability of mutants of 
 the Oenotheras ; description of 0. gigas as cultivated in the New 
 York Botanical Garden. 
 
 (6) Estimation of the fluctuating variability of some of the char- 
 acters of . lamarckiana^ 0. nanella, and O. rubrinervis. 
 
PLATE II. 
 
 Large-flowered Evening Primrose, figured in Barton's Flora of North America, 
 
 resembling Onagra lamarckiana. 
 
MUTANTS AND HYBRIDS OF THE OENOTHERAS. 5 
 
 DERIVATION OF ONAGRA (OENOTHERA) EAMARCKIANA. 
 
 As a result of the earlier examination of material in a few her- 
 baria in Europe and America no specimens of O. latnarckiana were 
 found that had been grown in America, and it was suggested that it 
 might have been originally native to a restricted range in Virginia 
 from which it had been exterminated. The inquiry upon this phase 
 of the investigation has been continued however, with the result that 
 many historical records, as well as some fairly well authenticated 
 material, have been found. 
 
 Barton (1821) describes an Oenothera under the name of O. 
 grandiflora in his Flora of North America, which, with the accom- 
 panying plate, well represents O. latnarckiana. (PI. II.) This plant 
 is described as " native in the woods and fields, and about habi- 
 tations, in Carolina and Georgia, flowering from May to August." 
 The fact is recalled by Barton that Elliott restricted the habitat of this 
 form "to the vicinity of habitations in South Carolina and Georgia, 
 remarking that it is certainly not indigenous in the low country." 
 
 Pursh (1814) had previously described an O. grandiflora similar 
 to that mentioned by Bartram, as "in woods and fields of Carolina," 
 and with ' ' flowers larger than any other of the North American 
 species, and of an agreeable scent." 
 
 The Floral Magazine for 1862 gives a plate of Oenothera lamarck- 
 iana with some notes on the species from which the following is 
 quoted: The one now figured was grown by Messrs. Carter & Co., 
 the well-known seedsmen of High Holborn and of the Crystal Palace 
 nursery, Forest Hill. To them we are indebted for the following- 
 particulars (Dombrain, 1862): 
 
 We received, about four years ago, some seed from Texas unnamed. When 
 we had flowered it we sent some blooms to Dr. LJndley, who pronounced it to be 
 Oenothera latnarckiana, a species we believe introduced into England by Mr. 
 Drummond. Its height is between 3 and 4 feet; it blooms the first year, is a 
 very hardy biennial, and is superior to any other Oenothera in the size and num- 
 ber of its blossoms, which measure 4 inches in diameter. 
 
 A reproduction of the same plate is to be found in L,' Illustration 
 Horticole for 1862, together with a discussion of the origin and rela- 
 tionships of the various species and a citation of the statements quoted 
 above. (Leniaire, 1862.) 
 
 A specimen in the Gray Herbarium of Harvard University was 
 examined which agrees perfectly with O. latnarckiana. From the 
 inscription, which is in Dr. Asa Gray's handwriting, it appears that 
 this plant was grown from seed in the botanical garden at Cambridge, 
 Mass., in 1862. The sheet also bears the note, ' ' Said by English hor- 
 
6 MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 ticulturists to come from Texas," and also "Oe. lamarckiana ," all by 
 Dr. Gray. It is to be noted that the date of the above culture agrees 
 with that of the Drummond plants in England mentioned above. 
 
 The second phase of the effort to trace O. lamarckiana to its 
 original habitat was directed to an examination of the material to be 
 found in the American herbaria and to excursions to some of the his- 
 torical locations. Several specimens of prime interest were encoun- 
 tered. A specimen collected by A. W. Chapman in Florida, and sent 
 by him to Europe, becoming a part of the Meissner herbarium which 
 was afterward purchased by Columbia University, was thought by 
 Professor De Vries to be 0. lamarckiana, and the mark on the sheet 
 shows that it was used by Chapman (i860, 1872, 1884) in making up 
 the description of O. bie?inis in the editions of his southern flora, in 
 which O . grandiflora Ait. was given as a synonym in the editions of 
 i860 and 1862, but does not appear in the later edition of 1897. In 
 the description he says : ' ' Varies greatly in pubescence and size of 
 flower," while the habitat is given as "Fields and waste places." 
 The elimination of the synonym from the last edition of the book can 
 not be accounted for, although the plant was presumably growing in 
 a wild condition. A duplicate of the specimen mentioned above is 
 reported by Mr. CD. Beadle to be in the Biltmore Herbarium at 
 Biltmore, N. C. A similar specimen is to be found in the herbarium 
 of the Missouri Botanical Garden. 
 
 During the visit of Professor De Vries to America in the summer 
 of 1904 he joined in the quest for specimens of O. lamarckiana and 
 called attention to a sheet of material in the herbarium of the Phila- 
 delphia Academy of Sciences, collected by C. W. Short near Lexington, 
 Ky., which he considered as 0. lamarckiana, and which was grown 
 wild in the locality recorded. 
 
 The co-operation of a number of botanists in various parts of the 
 supposed range of the species was secured and a thorough search was 
 made in the vicinity of Nashville, Tenn., by Prof. Geo. A. Martin ; 
 in the vicinity of Knoxville, Tenn., by Prof. S. M. Bain; in the 
 vicinity of Lexington, Ky., by Prof. H. Garman ; and in the vicinity 
 of Courtney, Mo., by Mr. B. F. Bush. Up to the present time, how- 
 ever, no living plants have been found that might be included within 
 the descriptions of 0. lamarckiana. 
 
 The above evidence makes it fairly conclusive, however, that the 
 large-flowered evening-primose which formed the basal material for 
 the experimental researches of De Vries is, or was, a component part 
 of the flora of North America and has been seen in the Carolinas, 
 Florida, Kentucky, and Texas during the last century, and that 
 material Irom Texas examined by Ljndley fairly represents the 
 
MUTANTS AND HYBRIDS OF THE OENOTHERAS. J 
 
 species. The main line of descent has endured practically unchanged 
 for a period of 116 years in European gardens, and was first observed 
 to exhibit mutations resulting in the production of new elementary 
 species as early as 1887, although but little doubt exists that this was 
 by no means the beginning of its period of mutability. 
 
 REDISCOVERY OF O. GRANDIFLORA (AiT.) Vail IN AMERICA. 
 
 During the course of the investigation of the records it became 
 evident that one or more large-flowered evening-primroses not recog- 
 nized in local floras had been found in southern United States at 
 various times. One of the most interesting of these discoveries was 
 that of Bartram referring to a locality on the east bank of the Alabama 
 River above Mobile and between that place and the junction of the 
 Alabama and Tombigbee rivers. He says : 
 
 Early one morning, passing along by some old uncultivated fields, a few miles 
 above Taensa, I was struck with surprise at the appearance of a blooming plant, 
 gilded with the richest golden yellow ; stepping on shore, I discovered it to be a 
 new species of the Oenothera (Oenothera grandiflora, caule erecto, ramoso, 
 piloso, 7, 8 pedalis, ioliis semi-amplexi-caulibus, lanceolatis, serratodentatis, flori- 
 bus magnis, fulgidis, sessilibus, capsulis cylindricis, 4 angulis,) perhaps the 
 most pompous and brilliant herbaceous plant yet known to exist. It is an annual 
 or biennial, rising erect seven or eight feet, branching on all sides' from near the 
 earth upwards, the lower branches extensive, and the succeeding gradually shorter 
 to the top of the plant, 'forming a pyramid in figure ; the leaves are of a broad 
 lanceolate shape, dentated or deeply serrated, terminating with a slender point, 
 and of a deep full green color; the large slender flowers that so ornament this 
 plant, are of a splendid perfect yellow color; but when they contract again before 
 they drop off, the underside of the petals next the calyx becomes of a reddish 
 flesh-color, inclining to vermilion; the flowers begin to open in the evening, are 
 fully expanded during the night, and are in their beauty next morning, but close 
 and wither before noon. There is a daily profuse succession for many weeks, 
 and one single plant at the same instant presents to view many hundred flowers. 
 I have measured these flowers above five inches in diameter; they have an agree- 
 able scent. 
 
 After leaving these splendid fields of the golden Oenothera, I passed by old 
 deserted plantations and high forests, etc. 
 
 Bartram 's expedition was undertaken "At the request of Dr. 
 Fothergill, of L,ondon, to search the Floridas and the western parts 
 of Carolina and Georgia, for the discovery of rare and useful products 
 of nature, chiefly in the vegetable kingdom. In April, 1773, I 
 embarked for Charleston, South Carolina, on board the brigantine, 
 Charleston Packet , Captain Wright , " etc . (Bartram , 1 793 , pp . 404-405 . ) 
 
 Seeds of the above plant were evidently sent to Fothergill, and 
 the following is the original description of the plant by Aiton, made 
 from specimens grown at Kevv. He says "grandiflora 2. Oe. foliis 
 ovato-lanceolatis, staniinibus declinatis, caule fruticoso, L, ' Herit. 
 
8 MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 V 
 
 stirp. nov. Tom. 2. tab. 4. Great-flowered Oenothera, Nat.' of North 
 America. Introd. 1778 by John Fothergill, M. D. Fl. July and 
 August" (Aiton, 1879). 
 
 It being deemed very important that a visit to the locality men- 
 tioned by Bartram should be made, Prof. S. M. Tracy, of Biloxi, 
 Miss., generously undertook to make the search. In accordance with 
 arrangements he proceeded up the Alabama River on August 16, 1904, 
 and five days later came upon the plant not far from the original 
 locality. Professor Tracy has kindly prepared the following report : 
 
 The locality for this plant, as given by Bartram, was " a few miles above 
 Taensa." The country immediately about Ten saw is mostly the dry, pine hills 
 common in that section, and a careful search for several miles about the town 
 did not reveal a single plant belonging to the Epilobiacese. Fort Mimms, 5 miles 
 from Tensaw on the bank of the Alabama River, was doubtless Bartram's head- 
 quarters while he was in that part of the State, but a careful search of the river 
 for some miles failed of results. Dixie Landing, 25 miles above Fort Mimms by 
 river, and 13 by road from Tensaw, was the first place where the plant was seen. 
 Immediately below the steamboat landing there is quite a stretch of abandoned 
 fields covered with a dense growth of Chamaecrista robasta from 4 to 5 feet in 
 height, and those plants are thoroughly tangled with Bradburya virginiana, which 
 makes walking exceedingly difficult. The evening-primrose was found as an occa- 
 sional plant in this growth, the first plants being seen about a quarter of a mile 
 below the landing, and others being found more or Less abundantly for more than 
 a mile down the river. When growing in the thick weeds the plants were mostly 
 erect, with simple stems, a few of which were beginning to branch at the top. A 
 few plants were found immediately on the river bank, and even on the sides of 
 the almost perpendicular bank, which is about 20 feet high, and when growing in 
 that location were, as Bartram describes them, " Rising erect 7 or 8 feet, branch- 
 ing on all sides from near the earth upwards, the lower branches extensive, and 
 the succeeding gradually shorter to the top of the plant, forming a pyramid in 
 figure." The largest plant -found measured 8 feet 9 inches in height. No small 
 plants were found, and from the root and stem characters the plant is doubtless 
 an annual. No plants were found more than 200 yards from the bank of the 
 river, and only a few plants were found in the shade of trees. Hundreds of 
 plants were examined, but no mature seed could be found. 
 
 A visit to Earle's Landing, 5 miles below Dixie Landing, showed the plant 
 to be fairly abundant there also. In nearly all cases they grew on alluvial soil, 
 which was sandy rather than heavy, and none was found near wet or marshy places. 
 The river bank was examined nearly the whole of the distance from Dixie to 
 Earle's Landing, and the plant was not rare on open ground covered with Chamae- 
 crista, but was not seen in any other location. All of the region examined was on 
 the east bank of the Alabama River. A gentleman owning land immediately 
 opposite Dixie informed me that it grew in one place on the west bank. 
 
 A large number of herbarium specimens we're prepared by Pro- 
 fessor Tracy, all of which were forwarded to the New York Botanical 
 Garden for examination, and from which seeds were obtained suitable 
 for cultures which promise to be of great service in comparisons with 
 the other large-flowered species of the evening-primroses. 
 
Ill— 111. 
 
 Fig. i. Rosette of Onagra biennis five months old. 
 
 Fig. 2. Rosette of Onagra cruciata five months old. 
 
MUTANTS AND HYBRIDS OF THE OENOTHERAS. Q 
 
 ONAGRA (OENOTHERA) BIENNIS (E.) Scop. 
 
 Many collectors and taxonomists include a number of elementary 
 species in Onctgra biennis and attribute to it an extremely wide range 
 of fluctuating variability. On the other hand, workers who have 
 carried on cultural experiments with individuals representing a typical 
 elementary species describe it as fluctuating between very narrow limits. 
 The actual inclusion of the species is not so important, in connection 
 with the present investigation, as the degree of constancy of the various 
 strains grouped around the species and sometimes included in it. 
 
 In order to carry on observations on these points, and upon " the 
 changes produced by cultivation," upon which some systematists lay 
 so much stress, a number of plants of 0. biennis (in the strictest sense), 
 growing in uncultivated land in the New York Botanical Garden in 
 1903, were selected to form the basis of a pedigree-culture in 1904. 
 Seeds were duly harvested at the end of the season and sown in the 
 propagating house early in January. The plautlets were transferred 
 to the experimental grounds late in May and began to bloom early in 
 July. The species was thus grown as an annual during a season of 
 about nine months in soil rich with fertilizers. Furthermore, the 
 individuals were placed in rows, over a meter apart, and were kept free 
 from the competition of weeds. Briefly stated, it may be said that in 
 no single feature, nor in any instance, did these plants transgress the 
 measurements, or show different forms of organs, from those of wild 
 specimens in the vicinity. The size of the leaves, the amount of the 
 pubescence, the size of the flowers and capsules, and the formation of 
 the branches are capable of modification by soil-moisture, humidity, 
 intensity of illumination, and competition, as in thousands of other 
 well-defined species, but these modifications did not bring the species 
 nearer in aggregate character to any of the closely allied forms. Exact 
 records and observations were kept during the entire life-histories of 
 the individuals, by the aid of which the following description has 
 been prepared : 
 
 Seedling about hvo months old. — Leaves nearly glabrous ; blades 
 oval to oblong-oval, the larger ones about 10 mm. wide, obtuse at the 
 apex, each rather gradually narrowed into a petiole (fig. 1). 
 
 Seedling five months old. — Rosette open ; leaves rather copiously 
 fine-pubescent; blades oblong to elliptic, the larger ones fully 2.5 cm. 
 wide, quite approximately repand-denticulate, with the teeth more 
 pronounced at the base, acute at the apex, each narrowed into a short 
 petiole. (PI. Ill, fig. 1.) 
 
 Matitre rosette. — Leaves ample, rather copiously fine-pubescent, 
 the larger ones about 27 cm. long, 6 to 7 cm. wide ; blades oblong to 
 
10 
 
 MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 elliptic, or slightly broadened upwards, unevenly repand-denticulate 
 and mostly rather jagged-toothed near the base, the petioles relatively 
 stout. 
 
 Adult plant (Pis, IV and V). — Plant luxuriant, mostly i meter 
 tall, or less. Stem slightly uneven, but scarcely channeled, hirsute, 
 with spreading-ascending somewhat rigid hairs, copiously branched 
 throughout, the lower branches decumbent, the upper ones spreading 
 or curved upward ;* leaves very numerous, 1.5 to 2 dm. long near the 
 
 base of the stem ; blades 
 elliptic-oblanceolate to 
 elliptic-lanceolate; 
 shallowly but rather 
 prominently toothed, 
 and often jagged- 
 toothed near the base, 
 acuminate, those of the 
 upper cauline leaves 
 mostly elliptic, acute, sessile, or nearly 
 so; bracts mainly lanceolate, narrowed 
 or rounded at the base ; conic por- ■ 
 tion of the bud 14 to 18 mm. Ions-, 
 finely pubescent, the free tips of the 
 sepals about 2 mm. long ; hypanthium 
 2 to 3 cm. long, 5 to 6 mm. wide at 
 the mouth, nearly terete, sparingly 
 pubescent or glabrate ; sepals 15 to 
 20 mm. long, much shorter than the 
 tubular portion of the hypanthium, 
 petals rather delicate, 12 to 16 mm. 
 truncate or slightly emarginate at the apex; filaments 8 to 10 
 long; anthers 7 to 8 mm. long ; pistil shorter than the stamens ; 
 stigmas 4 to 5 mm. long; capsule 3 to 3.5 cm. long, 7 to 7.5 mm. in 
 diameter at the thickest point, finely pubescent, slightly curved, 
 markedly narrowed at the apex. (PI. VI.) 
 
 It is to be seen from the above description that O. biennis is 
 capable of self-fertilization by reason of the superior length of the 
 stamens, a fact that was demonstrated in the experimental grounds. 
 To secure purely fertilized seeds it was only necessary to inclose the 
 inflor escence in a parchment bag during the opening of the flowers. 
 
 *Plants growing in thickets are more spindling and have the lower branches 
 suppressed, while the young rosettes are luxuriant, with broader leaves under 
 such circumstances. 
 
 *ig. 1.- 
 
 -Onagra biennis seedling three 
 months after germination. 
 
 the free tips 4 to 5 mm. long 
 
 long, 
 mm. 
 
PLATE IV. 
 
 Onagra biennis, wild specimen, grown in competition with other meadow plants. 
 
PLATE V. 
 
MUTANTS AND HYBRIDS OF THE OENOTHERAS. II 
 
 After an examination of material in the field in America in the 
 summer of 1904, Professor De Vries informs the authors that the 
 O. biennis used in his breeding experiments at Amsterdam differs from 
 the foregoing, and is to be included with a form usually termed 
 O. biennis grandifiora by collectors. The exact relationship of the 
 two has not yet been carefully determined. 
 
 ONAGRA ARGILLICOLA Mackenzie. 
 
 Within the last year a new wild species of evening-primrose has 
 been brought to notice from the mountains of Virginia and West Vir- 
 ginia, being described by Mr. K. K. MacKenzie as " one of the most 
 noticeable and common plants on the line of the Chesapeake and Ohio 
 Railroad on both sides of the boundary line between Virginia and 
 West Virginia." It has also been collected by Mrs. L. F. Ward, at 
 "Alleghany," W. Va., and by Mr. and Mrs. E. S. Steele at Sweet 
 Springs, W. Va., and the cultures in the New York Botanical Garden 
 were begun with seeds from the latter locality. The following descrip- 
 tion has been compiled from observations on living plants of the 
 resultant cultures : 
 
 Seedling about two months old. — Leaves minutely pubescent, copi- 
 ously so near the base ; blades oblong or elliptic-oblong, the larger 
 ones less than 1 cm. wide, obtuse, each gradually narrowed into a 
 copiously pubescent petiole. 
 
 Seedling five months old. — Rosette relatively lax ; leaves minutely 
 pubescent; blades spatulate to narrowly linear-spatulate, the larger 
 ones over 25 cm. long, 2 to 2.5 cm. wide, repand, more distantly so 
 and with more pronounced teeth near the base, each gradually nar- 
 rowed into a long petiole. 
 
 Mature rosette. — Leaves numerous and conspicuously elongated ; 
 glabrous, or nearly so, except the sparingly ciliate margins, the larger 
 ones over 40 cm. long, 2 to 2.5 cm. wide ; blades broadly linear to 
 linear-spatulate, sinuate, the teeth slightly more pronounced near the 
 base; petioles relatively stout. 
 
 Adult plant. — Plant rather luxuriant, depressed in habit. Stems 
 suppressed or very short, the branches radiate, decumbent, not chan- 
 nelled, somewhat tortuous, mainly 6 to 12 dm. long, puberulent and 
 pubescent, with few spreading or ascending hairs; leaves very numerous, 
 10 to 15 cm. long on the lower part of the branches ; blades undulate, 
 or repand-denticulate, those on the lower part of the branches broadly 
 linear to narrowly linear-oblong, acute or short-acuminate, each nar- 
 rowed into a semi-terete petiole, those of the upper cauline leaves 
 similar to those of the lower, but relatively shorter and broader, and 
 
12 MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 sometimes inclined to be linear-lanceolate, sessile or short-petioled ; 
 bracts lanceolate, truncate at the base, shorter than the hypanthium ; 
 conic portion of the bud about 4 cm. long, glabrous, the free tips of 
 the sepals subulate, approximate at the base, but ascending ; hypan- 
 thium 4 to 5 cm. long, about 6 mm. wide at the mouth, ridged, gla- 
 brous ; sepals 34 to 47 mm. long, shorter than the tubular portion of 
 the hypanthium, the free tips about 6 mm. long ; petals rather firm, 
 4 to 4.5 cm. long, truncate or broadly emarginate at the apex ; fila- 
 ments 21 to 23 mm. long ; anthers 12 to 13 mm. long ; capsule 2.5 to 
 3 cm. long, about 7 mm. in diameter at the thickest, point, glabrous, 
 strongly curved, narrowed from the base to the apex. (PI. VII.) 
 
 0. argillicola is to be distinguished by the fact that it is well 
 adapted to securing cross-fertilization. When the flower-buds come 
 to the morning of the day on the evening of which they will open, the 
 pistil takes on a greatly accelerated rate of growth and pushes out of 
 the flower-buds to a length of 3 or 4 mm., bearing the unfolded stig- 
 mas in a position in which they may readily receive pollen carried by 
 the wind from neighboring flowers. It is not actually known , however, 
 whether pollination is secured in this manner, or whether insects are 
 of some aid in the matter. A similar behavior of 0. lamarckiana 
 near the close of the season is reported in Holland. The decumbent 
 or non-ascendant branches of 0. argillicola form a dense cluster which 
 gives it a very striking appearance. The main bud of the central 
 stem appears to remain dormant. 
 
 The great size of the flower of this species doubtless accounts for 
 some of the reports of the presence of 0. grandMora in the Virginias 
 and Pennsylvania, while the habit of the plant may have also sug- 
 gested some of the notions prevalent as to the variability of 0. biennis, 
 with which it may have been confused. 
 
 ONAGRA CRUCIATA (NuTT.) Small. 
 
 A number of roots and some seeds of 0. cruciata were obtained 
 from Sandy Hill, N. Y., near L,ake George, at the close of the season 
 of 1902, and early in the spring of 1903 were divided into two por- 
 tions, one of which was sent to Professor De Vries at Amsterdam, 
 Holland. Only about a dozen plants were brought to maturity in the 
 New York Botanical Garden during 1903, attention being directed 
 principally to the observations on 0. lamarckiana and its mutants. 
 
 A letter was received from Professor De Vries under date of Sep- 
 tember 19, 1903, in which he said : 
 
 Until a few -weeks ago, and before flowering, the plants were a very uniform 
 lot, with the characteristic reddish crowns and nutating tops. But now they are 
 no longer uniform. There are two very distinct types, only differing in the 
 
PLATE VI. 
 
 1 Vy 3 U ~ 5 
 
 Onagra biennis. 
 
 leaf from young rosette; 2, leaf from rosette four months old; 3, leaf from lower part of mature 
 rosette; 4, leaf from upper part of mature rosette; 5, stem-leaf; 6, bract; 7, unopened bud; 
 8, flower with petals removed; 9, petals of maximum size; 10, mature capsule. 1 to 5, one-half 
 natural size ; 6 to 10, natural size. 
 
PLATE VII. 
 
 y, 
 
 A 
 
 / 
 
 Onagra argillicola. 
 
 i, 2, leaves of young rosette ; 3, leaf from adult rosette ; 4, stem-leaf ; 5, flower with petals removed ; 
 6, bract; 7, flower-bud; 8, flower-bud immediately previous to opening, with stigma exposed; 
 9, petal ; 10, capsule. 1 to 4, one-half natural size ; 5 to 10, natural size. 
 
PLATE VI 
 
MUTANTS AND HYBRIDS OF THE OENOTHERAS. 1 3 
 
 flowers and flower-buds. Both types are to be found in the plants coming from 
 the seeds, as well as in those grown from the roots you sent me. The differences 
 are slight, but striking, absolutely individual, and without transitions. Most of 
 the individuals have broader linear petals and comparatively more rounded 
 flower-buds. The others have narrower and therefore more strictly linear 
 petals, and thicker buds. 
 
 I have also sown seed I got from Prof. B. L. Robinson, of Harvard Univer- 
 sity, gathered at Jeffrey, N. H., under the name of O. cruciata. They are wholly 
 different' from yours, being more slender, less nutating, and with a strikingly 
 longer calyx-tube. 
 
 The same facts are given in ' ' Species and Varieties : Their Origin 
 by Mutation " (De Vries, 1905, p. 589), in which it is also stated that 
 " It seems not improbable that 0. cruciata includes a group of lesser 
 unities, and might soon prove to comprise a swarm of elementary 
 species, while the original strain might even now be in a condition of 
 mutability." 
 
 The cultures of 1904 included over sixty specimens of 0. cruciata 
 which reached the adult stage, and included not only the two forms 
 which he had observed to arise from the seeds and roots sent him from 
 this place, but also the third obtained only from material from New 
 Hampshire. It is obvious, therefore, that one form arises spontane- 
 ously from one of the other two forms suddenly, and dried specimens 
 from the crop of 1903 in the New York Botanical Garden show that 
 it originated in this manner here in the first year of cultivation, 
 although the second half of the same lot of seeds sent to Professor De 
 Vries failed to give rise to it in Amsterdam. 
 
 The evidence at hand therefore seems to confirm the suggestion 
 as to the mutability of the species, but nothing may be said as to which 
 of the types constitutes the parent. The characters of the forms are 
 as follows : 
 
 No. 1 (PI. VIII) .—Adult plant robust and luxuriant. Stem 1 to 
 1.5 meters tall, copiously branched, the branches spreading, sparingly 
 hirsute, the hairs rather ascending, 1.5 to 2.5 dm. long on the lower 
 part of the stem ; blades narrowly spatulate, finely toothed near the 
 apex, coarsely and somewhat doubly toothed below the middle, each 
 narrowed into a short semi-terete petiole, those of the upper cauline 
 leaves oblong-lanceolate to lanceolate, sessile, all more or less pubes- 
 cent about the veins beneath ; bracts oblong-lanceolate, about one-half 
 as long as the hypanthium, truncate at the base ; conic portion of the 
 buds slender, 16 mm. long, or somewhat longer, sparingly pubescent, 
 the free tips of the sepals 4.5 to 5 mm. long; hypanthium slender 
 terete or nearly so, 30 or 32 mm. long, becoming glabrous, about 4 mm 
 wide at the mouth ; sepals 17 to 20 mm. long, linear-lanceolate, about 
 
14 MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 one-half as long as the tubular portion of the hypanthium, the free 
 tips 4 mm. long; petals delicate, linear or nearly so, 10 to 15 mm. 
 long, obtuse ; filament 9 to 10 mm. long ; anthers about 5 mm. long ; 
 style shorter than the stamens ; stigmas about 4 mm. long ; capsules 2 
 to 2.5 cm. long, 6 to 7 mm. in diameter at the thickest point, nearly 
 glabrous, mainly longer than the bracts. (PL IX, fig. 1.) 
 
 This form included about 52 of the individuals grown during 
 1904. The other two forms may be characterized as follows : 
 
 No. 2. — Bracts broadly lanceolate or ovate-lanceolate, round- 
 truncate at the base, about as long as the hypanthium ; conic portion 
 of the bud sparingly pubescent, 15 mm. long or less; hypanthium 
 stoutish, nearly terete, 28 to 30 mm. long, sparingly pubescent, 
 abruptly dilated at the top, and about 5 mm. wide at the mouth ; 
 sepals 14 to 15 mm. long, linear-lanceolate, about one-half as long as 
 the tubular portion of the hypanthium, the free tips about 5 mm. 
 long; petals firm, broadly linear or linear-oblong, 8.5 to 10 mm. 
 long, obtuse; filaments 8 to 9 mm. long; anthers 6 mm. long; style 
 shorter than the stamens; stigmas 6 mm. long; capsules 2.5 to 3 cm. 
 long, 7 to 8 mm. in diameter at the thickest point, with few scattered 
 hairs, slightly curved, narrowed to the apex. (PL IX, fig. 2.) Seven 
 individuals of this type were found in the cultures. 
 
 No. 3. — Bracts oblong or ovate-oblong, narrowed at the base, 
 shorter than the ovary or slightly longer ; conic portion of the buds 
 stout, 9 to 1 1 mm. long, with few scattered short hairs; hypanthium 
 slightly ribbed, stoutish, 25 to 27 mm. long, becoming glabrous, rather 
 gradually dilated at the top and about 4 mm. wide at the mouth; sepals 
 9 to 10 mm. long, much less than one-half as long as the tubular 
 portion of the hypanthium, the free tips 3 to 3.5 mm. long; petals 
 broadly linear-oblong, 6 or 7 mm. long, obtuse ; filaments 6 mm. long; 
 anthers 4 mm. long; style shorter than the stamens; stigmas 3 mm. 
 long; capsules about 2.5 cm. long, 7 to 8 mm. in diameter at the 
 thickest point, with few scattered hairs, slightly curved, narrowed to 
 the apex. (PL IX, fig. 3.) Six individuals were seen, all of which 
 completed their seasonal development much earlier than the other 
 two forms. 
 
 In the observations made during the earlier part of the develop- 
 ment of the plants nothing was recorded by which the three forms 
 might be distinguished, and hence the following characters may be 
 taken to apply to the entire lot, although it is probable that most of 
 the descriptions were made from mutant individuals. 
 
 Seedling abotd two months old. — Leaves very sparingly pubescent; 
 blades oblong, elliptic or oval, the larger ones 8 to 11 mm. wide, 
 
PLATE IX. 
 
 Onagra cruciata : Buds, bracts, capsules, flowers, and petals of the three 
 elementary forms. Natural size. 
 
PLATE X. 
 
 Onagra cruciata. 
 
 leaf from young rosette ; 2, leaf from lower part of mature rosette ; 3, leaf from upper part of 
 mature rosette; 4, stem-leaf ; 5, rosette five months old ; 6, rosette two months old ; 7, rosette 
 nearly five months old, with narrower leaves. 1 to 4, half natural size; 5 to 7, natural size. 
 
MUTANTS AND HYBRIDS OF THE OENOTHERAS. 1 5 
 
 undulate, obtuse or merely acutish at the apex, each rather gradually 
 narrowed into a petiole. (PI. X, fig. 6.) 
 
 Seedlings five months old. — Rosettes not dense ; leaves glabrous or 
 nearly so, except the ciliate margins; blades spatulate, some of them 
 narrowly so, the larger ones 2 to 2.5 cm. wide, shallowly repand-dentic- 
 ulate, mostly acute, as long as the petioles or longer. (PL III, fig. 2.) 
 
 Mature rosette. — Leaves conspicuously elongated, obscurely fine- 
 pubesdent, the larger ones about 26 cm. long, 25 to 30 mm. wide; 
 blades narrowly spatulate, repand-dentate, more distantly so and with 
 prominent teeth near the base, petioles relatively slender. 
 
 All of the forms included in, and arising from, 0. crucial a are 
 capable of self-fertilization when the inflorescences are inclosed in 
 bags. So far as present information goes the species of the evening- 
 primroses native to northeastern America may be said to have compar- 
 atively small flowers and to be capable of self-fertilization, although 
 visited frequently by flying insects. The species ranging to the south- 
 ward have larger flowers, and by reason of the superior length of the 
 pistils are adapted to cross-fertilization, although it is not definitely 
 known that self-fertilization does not ensue. In 0. argillicola the early 
 protrusion of the stigmatic surfaces from the unopened flower-bud 
 has the appearance of a positive adaptation for securing pollen from 
 other flowers, by the agency of wind, gravity, or insects. 
 
 HYBRIDS. 
 
 Among the crosses made in the New York Botanical Garden 
 during 1903, that of 0. lamarckiana X 0. cruciata and the reciprocal 
 were attempted. The first only was successful, as the castration of 
 the flowers of 0. cruciata was not accomplished sufficiently early to 
 prevent self-fertilization. Likewise the removal of the stamens of 
 0. lajiiarckiaua was not done in such manner as to exclude the action 
 of its own pollen and the pistil-parent appeared as a pure strain in the 
 cultures. 
 
 0. lamarckiana X 0. cruciata. — A detailed study of the hybrids 
 obtained by the pollination of 0. lamarckiana by 0. cruciata was made 
 by De Vries, but the pollen-parent was evidently a highly variable 
 hybrid race which bore the general vegetative characters of the 
 true cruciata, but which showed a fluctuating variability in its flowers, 
 from an atavistic obcordate form of petal to others of the slender 
 cruciata type. The form in question is known in Europe as Oeno- 
 thera cruciata varia and is held by De Vries to be probably a hybrid of 
 0. maricata and cruciata. (De Vries, 1903, pp. 100-110, 593 _6 33-) 
 
l6 MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 The individuals of the hybrid as made in the New York Botanical 
 Garden in 1903 were seen to be furnished with narrower leaves in the 
 earliest stage of the seedlings, all of which but one were destroyed by 
 insects before the main axis was formed. The plant was recognizable 
 at some distance throughout its entire existence by its light yellowish- 
 green color. The leaves of the young rosettes were ovate-lanceolate, 
 obscurely and remotely repand-denticulate, blunt at the apex, with the 
 laminae extending down the petioles to the bases in the form of wings 
 1 to 2 mm. in width. (Plate XII.) 
 
 The leaves of the mature rosette were narrowly lanceolate-oblong, 
 being broadest above the middle and tapering to both ends, with the 
 petioles winged. The laminae were approximately denticulate in the 
 apical portion and irregularly so in the basal half. All of the leaves 
 of the rosette and stem were minutely pubescent. 
 
 The stem attained a height of about 55 cm. and bore a number 
 of short, spreading branches arising from the base of the main stem 
 and reaching half of its length. Numerous shorter branches arose 
 from the entire stem from a short distance above the base. The 
 apical portions of all branches were tinged with red. The stem leaves 
 were narrowly oblong-lanceolate, tapering to both ends and acute at 
 both ends; 9 to 11 cm. long, and 14 to 17 mm. wide. The terminal 
 rosettes were dense, close, symmetrical, and spreading. The first 
 flower was shown on August 12, about six weeks later than the begin- 
 ning of the blooming of either parent. 
 
 The petals were recurved after the manner of 0. cniciata and were 
 from 9 to 1 1 mm. long, varying from linear-oblong to irregularly 
 obcordate or truncate, being entire, obscurely emarginate or irregu- 
 larly notched near the apex. Furthermore, these various forms might 
 be illustrated in a single flower (see Plate XII, figs. 6a, ya, and 8). 
 The definite tips of the calyx-segments were spreading in the bud and 
 were 3 to 15 mm. long. The stamens varied in length, being 
 shorter than the pistils in some flowers, and longer in others. The 
 ovaries were about 9 mm. long, slightly hirsute, and the hypanthium 
 was glabrous. The bracts were lanceolate-acuminate. The calyx- 
 segments were much shorter than the hypanthium. The hypanthium 
 showed a purplish tinge and the petals were flesh-color, except at the 
 tips. The capsules were rounded, obscurely angled, 20 mm. long 
 and 4 to 5 mm. in thickness, tapering from near the base to the tip, 
 and bearing a few spreading hairs. (PI. X.) 
 
 This hybrid agrees quite well with 0. critciata varia as described 
 by De Vries, which he thought was a hybrid between muricata and 
 cruciata. Whether it is actually identical with this form can not be 
 
PLATE XI 
 
 ,:^.. 
 
 U 
 
 '*c*t&yr 4 
 
 
 *"« 
 
 ^w 
 
 
 
 
 'jH* 
 
 Adult specimen of the hybrid Onagra lamarckiana X Onagra cruciata (No. 3.21). 
 
PLATE XII. 
 
 7a 
 
 8 
 
 9 
 
 Onagra lamarckiana X Onagra cruciata (No. 3.21). 
 
 1, leaf from young rosette; 2, leaf from median portion of mature rosette ; 3, leaf from upper portio 
 of mature rosette; 4, stem-leaf; 5, bract; 6, flower with petals removed (see 6a); 7, flowe 
 with petals removed (see 7a); 8, petals of mininum size ; 9, unopened tlower-bud ; 10, capsule 
 1 to 4, one-half natural size; 5 to 10, natural size. 
 
MUTANTS AND HYBRIDS OF THE OENOTHERAS. I J 
 
 definitely stated, since no living material of the latter has been exam- 
 ined. The only characters of the hybrid clearly derived from the 
 pistil-parent are the relative length of the main axis and the general 
 habit of branching. It is to be said on the other hand that the cruciata 
 characters to which the general aspect of the plant is largely due are 
 without exception more or less modified. The relative length of the 
 stamens and pistils was seen to vary so that some of the flowers were 
 capable of self-pollination, while in others the chance of pollination 
 without the aid of external agencies was extremely small, so that it 
 might be said that in some branches of the plant the lamarckiana 
 character was dominant, while in others the cruciata self-fertilizing 
 capacity was shown. A similar range of partial variability will be 
 described in one of the hybrid races of the O. lamarckiana X 0. biennis. 
 O. lamarckiana X O. biennis. — The results of the crosses made in 
 the New York Botanical Garden were much more diversified than 
 those made by De Vries, who obtained what he designates as a 
 typical unilateral hybrid as a result of fertilization of 0. lamarckiana 
 by O. biennis grandiflora. He says (De Vries, 1903, p. 31) : 
 
 The hybrid of Oenothera biennis (O. biennis grandiflora) and O. lamarckiana 
 resembles the first so strongly that they can hardly be distinguished from one 
 another. I have made this cross partly in 1894 and partly in the summer of 1899, 
 and in the last-named year partly with 0. lamarckiana from my own cultures, 
 and partly from the same species grown from purchased seeds. In all cases I 
 used O. lamarckiana as the mother. The stamens were taken from flowers of 
 plants in the open (from unopened buds), and from plants of my own cultures 
 in the last-named period. The bastards were of a single type, and were inter- 
 changeable with O. biennis (O. biennis grandiflora) , not only in the rosettes, 
 but also in the flowers and ripe fruit. I had about 50 flowering plants in 1895, 
 and about 70 -f- 60 in the two series in 1899, making altogether about 180 speci- 
 mens in bloom in addition to some with young stems and rosettes only (bien- 
 nials). Some differences were seen, but they were not so marked or so important 
 that a description could be made of them. 
 
 I harvested some seeds in 1895, which were secured by artificial pollination, 
 and the second generation was grown from these in the summer of 1896. These 
 repeated, in the 50 specimens coming into bloom, only the characteristics of the 
 first-named parent (biennis). 
 
 Similarly the pollination of 0. lamarckiana by 0. mnricata resulted 
 in a monotypic unilateral hybrid which approximated the pollen- 
 parent. 
 
 Four distinct types were distinguishable in the hybrid in New 
 York, and the different forms could be recognized in a very early 
 stage of the seedlings. All of the individuals were easily seen to be 
 grouped around the types mentioned, and no intermediate or inter- 
 grading forms were found. The number of individuals brought to 
 
l8 MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 maturity was comparatively small, and the possibility is not excluded 
 that a culture of several hundred plants might include still other 
 forms. In fact, the very differences between the results of the hybrid- 
 izations, as carried out in Amsterdam and New York, suggest that the 
 manner in which the various qualities in the two parents are grouped 
 in the progeny might be capable of a wide range of variation. Many 
 indications lead to the suggestion that the dominancy and prevalency, 
 latency, and recessivity of any character may be more or less influenced 
 by the conditions attendant upon the hybridization ; the operative fac- 
 tors might include individual qualities as well as external conditions. 
 In addition to the hybrid individuals several specimens of the pistil- 
 parent, lamarckiana, and one of its mutants appeared in the cultures, 
 indicating that self-fertilization was not entirely prevented. This 
 might be accounted for in two ways. Castration might not have been 
 performed early enough to prevent the action of pollen being scattered 
 from a bursting anther upon a mature stigma while the operation was 
 being performed. Then, again, the possibility was not wholly excluded 
 that pollen from the bursting anthers which fell upon the bracts 
 inclosed in the parchment bags might have been carried to the stigmas 
 by currents of air caused by the compression or expansion of the 
 parchment bags. At any rate, the appearance of individuals of the 
 pistil-parent type may betaken as presumptive evidence that such self- 
 pollination occurred by some method, although the appearance of 
 individuals of the parental type in hybrids is well known. 
 
 (I) A type represented by individual No. 2.1 (PL XIII, fig. 1) 
 showed a rosette of deeply dull-green leaves, more or less crinkled 
 and irregular in form and margin. In all about twelve plants of this 
 type were seen, although but five reached a stage sufficiently advanced 
 to send up a central stem. The rosettes were sparse and the leaves 
 thick and fleshy, and almost glabrous, except that some were minutely 
 pubescent on the veins beneath. The leaves of the rosettes varied 
 from narrowly linear in the earlier stages to linear-lanceolate with 
 obtuse apices, and to oblong-spatulate, broadest above the middle, 
 and acutish in some individuals. The laminae were revolute and 
 irregularly denticulate and formed narrow wings nearly to the base of 
 the petioles. 
 
 The main axis of the hybrid individuals reached a height of 15 
 or 20 cm. , at which stage in the development elongation ceased and the 
 lateral branches became very active ; in some instances no noticeable 
 elongation of the main axis occurred. Branches of this were more 
 rounded in outline and bore leaves of a structure somewhat more 
 
PLATE XIII. 
 
 Fig. i. Rosette five months old of No. 2.1 of the hybrid Onagra 
 lamarckiana X Onagra biennis. 
 
 Fig. 2. Rosette five months old of No. 2.27 of the hybrid Onagra 
 lamarckiana X Onagra biennis. 
 
MUTANTS AND HYBRIDS OF THE OENOTHERAS. IO, 
 
 nearly conforming to normal types in a manner comparable to that of 
 the parent, as noted above. These leaves were ovate- denticulate, 
 abruptly acute, slightly crinkled, and were minutely pubescent. The 
 terminal rosettes were dense and symmetrical and flower-buds were 
 developed, the first of which opened on August 12. About this time 
 some large rosettes were formed from lateral buds near the bases of 
 the stems, which were composed of oblong-lanceolate leaves, slightly 
 crinkled and denticulate and tapering to both ends. The entire 
 plant was tinged with red, and most deeply so in the upper branches. 
 (PL XVII, fig. 4O 
 
 The petals were deeply emarginate, 28 to 30 mm. long and 30 to 
 35 mm. wide, being broader than long in all instances. The segments 
 of the calyx were 30 mm. in length, being less than half the length of 
 the hypanthium, which measured about 38 mm. The ovary was 10 
 mm. long and, with the hypanthium, bore a number of scattered hairs. 
 Perhaps the most noticeable feature of this type was the variability of 
 the relative length of the stamens and pistils. The pistils were fairly 
 constant in length, but in some flowers the stamens were shorter and 
 therefore not adapted to self-fertilization, while in others the anthers 
 were above the stigmas, thus insuring self-pollination. No correlated 
 structures were observed. 
 
 The capsules were about 2 cm. long, 5 to 6 mm. wide below the 
 middle, oblong, tapering from near the base, obscurely angled and 
 channeled, sparingly pubescent with both long and short scattered 
 hairs. 
 
 The exceptional, forms of leaves exhibited by this type were found 
 to be accompanied and probably caused by the presence of a fungus, 
 which seemed to attack this type only of the hybrid progeny. Similar 
 effects in 0. lamarckiana have not yet come under observation, but 
 young rosettes of 0. biennis, together with mature plants coming into 
 bloom, were found growing wild in some waste park-land near the New 
 York Botanical Garden on August 21 , 1904. The leaves of these plants 
 were closely similar to those of the pathological hybrid individual in 
 general appearance, and furnished the curious parallel of showing 
 a partial return to the normal form near the upper ends of the branches. 
 Rosettes of the type described were transplanted to pots in the experi- 
 mental house and the terminal portions of the leaves cut away in 
 accordance with garden practice. Within a few days several leaves 
 were seen to show an abundance of yellowish spermagonia, which 
 appeared to belong to Aecidium peckii De Toni, although aecidia were 
 not found. 
 
20 MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 (II) A second type was represented by individual No. 2.27, in 
 which the leaves of the rosettes were finely pubescent on July 1 ; the 
 rosettes were widely spreading and the leaves finely pubescent in 
 specimens examined on that day. The laminae were lanceolate-oblong 
 acute at the apex and broadest above the middle, gradually narrowing 
 to the broad petiole and decurrent upon it to its base ; approximately 
 denticulate, crinkled between the secondary veins, more or less spotted 
 with reddish areas. (PL XIII, fig. 2.) 
 
 Stems were sent up, which, upon examination on July 13, showed 
 leaves of a dark bluish-green tinge, the laminae becoming convex 
 upwardly owing to the unecpial growth of the midrib. The stems 
 were dotted with the reddish bases of the hairs. The apices of the 
 main stem and of its branches formed close and symmetrical rosettes, 
 in approximation of the structures shown by lamarckiana. 
 
 The general habit of the shoot was much like that of biennis, the 
 basal branches being long. The central stem, however, was irregu- 
 larly compressed and was of a zigzag form. 
 
 The flowers exhibited the following characters: Corolla-segments 
 2.2 cm. long, 2.5 to 3 cm. broad ; catyx-segments 2.7 cm. long, more 
 than half the length of the hypanthium; hypauthium 3.5 cm. long, 
 slightly pubescent with scattered spreading hairs ; ovary 6 mm. long, 
 also pubescent with scattered spreading hairs ; anthers and stigma as 
 long as corolla, included, stigma variously 4 to 6 lobed. Bracts nearly 
 as long as the hypanthium. 
 
 Capsules about 13 mm. long, w r ith greatest diameter 6 to 7 mm., 
 the greatest length being about twice the thickness ; ovoid-oblong, 
 tapering in upper portion to obtuse apex ; not angled ; slightly 
 channeled; sparingly pubescent with appressed hairs. (PI. XV, fig. 2.) 
 
 (III) The third type of the hybrid was represented by individual 
 No. 2.24, in which the rosette was easily recognizable in the early 
 stages and was dense, with the leaves lying flat on the ground when 
 examined on July 1. The leaves were finely pubescent, with broadly 
 ovate laminae, the laminae more or less crinkled, acutish or obtuse at 
 the apex, broadest in the middle, more or less abruptly narrowed into 
 the broadly margined petiole, which is narrowly winged at the base. 
 These organs were approximately denticulate toward the apex, and 
 irregularly dentate at the base, with reddish petioles and the laminae 
 sparingly spotted with red. (PI. XIV, fig. 1.) 
 
 The basal branches were nearly as long as the main axis. A por- 
 tion of the stem immediately above the base was devoid of branches. 
 The upper part of the stem bore numerous erect branches. The stems 
 were deeply channeled and of a reddish color in the lower portions, 
 
PLATE XIV. 
 
 Fig. i. Rosette five months old of No. 2.24 of the hybrid 
 Onagra lamarckiana X Onagra biennis. 
 
 Fig. 2. Rosette five months old of No. 2.32 of the hybrid 
 Onagra lamarckiana X Onagra biennis. 
 

 
PLATE XV. 
 
 Fig. i. Adult plant of 2.1 of the hybrid Onagra Iamarckiana : Onagra 
 biennis, showing basal rosette, pathological leaves, normal leaves on 
 upper part of stem, buds, and flowers. 
 
 Fig. 2. Onagra Iamarckiana X Onagra biennis No. 2.24 at left, 
 
 No. 2.27 at right. 
 
MUTANTS AND HYBRIDS OF THE OENOTHERAS. 21 
 
 being distinctly paler in the terminal parts, which were of a yellowish - 
 green color. All of the stems and branches were terminated by tufted 
 rosettes. The following characters were exhibited by the flowers 
 (PI. XVII, fig. 5): 
 
 Petals 27 to 31 mm. long and 27 to 33 mm. wide, deeply emargi- 
 nate ; calyx-segments 30 mm. long, being more than half the length 
 of the hypanthium, which was 48 mm. in length, slender, and gla- 
 brous, except for a few scattering hairs; ovary 12 mm. long, glabrous, 
 except for a few scattered hairs ; stamens nearly as long as the 
 pistil. The capsules were 29 to 32 mm. long, 6 to 7 mm. in thick- 
 ness, being about four times as long as broad, distinctly four-angled, 
 and shallowly channeled ; oblong and narrowed in the apical region ; 
 sparingly appressed pubescent. This type was noted as producing 
 perfect seeds in apparently smaller numbers than the other types of the 
 hybrid, although some branches bore several well-filled capsules. 
 (PI. XV, fig. 2.) 
 
 (IV) A fourth type was represented by individual No. 2.32, 
 which was not recognized in the rosette stage, although the leaves 
 are much narrower than in 0. biennis, and are not so deeply toothed 
 in the basal portion. The aspect of the adult plant (PI. XIV, fig. 2) is 
 very marked, however, and it is easily recognizable. The lateral 
 branches are numerous and nearly as long as the main axis, with the 
 stems deeply channeled. The larger leaves of the rosette are narrowly 
 oblong-lanceolate and yellowish-green, with prominent reddish mid- 
 veins. The stem leaves are lanceolate and broadest about the middle 
 and deeply toothed. The entire plant is pubescent and shows a tinge 
 of reddish color even when young, which becomes much intensified 
 with age. (PI. XIV, fig. 2.) 
 
 The bracts are oblong-ovate, the hypanthium longer than its seg- 
 ments ; the petals are about 20 mm. long and 24 mm. wide, with wedge- 
 shaped bases. The stamens, pistil and petals are about of the same 
 length. The green capsules are about 26 to 27 mm. long and 6 to 7 mm. 
 thick, oblong, tapering from near the base to the narrow apex, and 
 shining green, being only sparingly pubescent. The general outline of 
 the capsules is irregular ; in cross-section they appear distinctly four- 
 angled. (PI. XVI, fig. 3.) 
 
 Seven individuals of this type were brought to maturity and all 
 conformed, with only minor divergences, to the above structures. 
 
 The hybrid progeny in the cultures made in the New York Botanical 
 Garden and in Amsterdam was thus seen to include a series of types 
 which ranged, in the aggregate of characters included, from those 
 
PLATE XVI. 
 
 /, 
 
 // 
 
 Stem leaves, bracts, petals, capsules, and flowers of Onagra biennis and of two of 
 the four hybrid types of Onagra lamarckiana X Onagra biennis. 
 
 i, Onagra biennis ; 2, No. 2.27; 3, No. 2.32. Stem-leaves one-fourth natural size; remainder of 
 
 figures five-eighths natural size. 
 
PLATE XVII. 
 
 Stem-leaves, bracts, petals, capsules, and flowers of Onagra lamarckiana, and of two 
 of the four hybrid types of Onagra lamarckiana X Onagra biennis. 
 
 4, No. 2.1; 5, No. 2.24; 6, Onagra lamarckiana. Stem-leaves one-fourth natural size; remainder 
 
 of figures five-eighths natural size. 
 
22 MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 representing pure strains of both parents through goneoclinic forms 
 to intermediates in which the parental characters were more or less 
 equally apparent. 
 
 Although the great difficulties attendant upon a valuation of the 
 characters occurring in hybrids were appreciated, it was concluded 
 that such an estimation expressed in tabulated form would be the best 
 method of expression of the dominance of the various characters. 
 
 Hurst selected twenty anatomical characters which were assigned 
 equal value, and included such features as the habit of growth, and 
 form and shape of the leaves and other organs, and upon the preva- 
 lence of these characters the degree of relationship of the hybrid to 
 the parent was estimated. (Hurst, 1900.) 
 
 Peter made a tabulated list of the external characters of the 
 hybrids of the hawk weed, in which these characters were classed as 
 unilateral, goneoclinic, or intermediate with respect to the corre- 
 sponding features of the two parents. The dominance of an3 r given 
 character was calculated from its occurrence in the entire list of 
 plants examined. (Peter, 1884.) 
 
 Mathematical expressions of the dominance 7 of qualities are in 
 themselves misleading unless based upon actual physical measure- 
 ments taken by statistical methods from a number of individuals to 
 eliminate errors. Then, again, the estimation of the development of 
 a paired character presents one of the greatest difficulties encountered 
 in the study of hybrids. Authors are by no* means agreed as to what 
 constitutes absolute dominance. Until within the last few years a char- 
 acter was regarded as dominant by most writers onl} r when it appeared 
 in the hybrid as an exact reproduction of the parental quality. The 
 most recent discussion upon this subject that has come to notice is 
 that of Correns, who takes the ground that a character apparently 
 representing the parental quality to 75 per cent of its full power may 
 be considered as dominant, when occurring to the extent of 25 to 75 
 per cent as intermediate, and below 25 per cent as recessive. (Cor- 
 rens, 1903.) 
 
 This author calls attention to the fact that fully dominant charac- 
 ters occur but rarely, and cites examples of Hyoscyamus and Bryonia. 
 
 The comparatively small number of individuals (33) of the hybrid 
 between O. lamarckiana and 0. biennis which were brought to ma- 
 turity did not give extended opportunities for statistical work, and the 
 number of characters taken into account included many not suscep- 
 tible of direct physical measurement. It was decided, therefore, to 
 express the descriptions in taxonomic terms arranged in tabulated 
 form to serve as a graphic illustration of the general complexion of 
 
MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 23 
 
 the types embraced by the hybrid. In this scheme it was found most 
 convenient to apply the terminology generally used to designate the 
 aspect of an individual to that of the separate characters, and qualities 
 which were fully dominant and accurate representations of the paren- 
 tal forms were placed under the heading of ' ' unilateral ; ' ' those which 
 approximated the type of one parent closely, but did not represent it 
 sufficiently to be identical with it in ordinary descriptive work, were 
 classed as "goneoclinic " to that type, while those in which an average 
 of the paired characters was apparent were placed under ' ' interme- 
 diate." It is evident that the "intermediate" of Correns would 
 embrace both the " intermediate " of the above classification and the 
 goneoclinic departure from it on either hand. Goneoclinism may well 
 be the extreme of fluctuating variability instead of a modification of 
 a group-quality. The scheme used below has been found most con- 
 venient for this special discussion, but it is not urged as the best 
 method for the general estimation of hybrids. 
 
 Tabulated analysis of the characters occurring in the various types of the hybrid 
 Onagra lamarckiana X Onagra biennis. 
 
 No. 2.1. 
 
 
 Unilateral. 
 
 Goneoclinic. 
 
 Intermediate. 
 
 Goneoclinic. 
 
 Unilateral. 
 
 
 To lamarckiana. 
 
 To biennis. 
 
 
 
 
 
 
 Leaves dull -green, 
 fleshy, narrow, 
 with irregular out- 
 lines, affected by 
 parasite. 
 
 Lower leaves thick, 
 
 Stems and 
 leaves. 
 
 Flowers and 
 fruits. 
 
 Leaves crinkled. 
 
 Termin a 1 ro- 
 settes symmet- 
 rical. 
 
 Upper leaves 
 ovate, denticu- 
 late. 
 
 Capsules taper- 
 ing to near 
 apex, short, 
 and thick. 
 
 
 
 Relative length 
 of stamens and 
 pistils variable. 
 
 
 waxy, affected by 
 parasite. 
 
 Calyx -segments 
 shorter than hyp- 
 anthium. 
 
 
 
 The notable feature of the structure of this type consists of the forms of 
 leaves exhibited by the stem. The rosettes and leaves of the stem which are 
 attacked by the fungus are almost exact counterparts of those of O. biennis, 
 while the upper portions of the shoot bear foliage-organs, very similar to tihose 
 of O. lamarckiana. The tendency to being attacked by the fungus seemed con- 
 fined wholly to this type, -which is entirely unlike the remainder of the progeny in 
 characters not affected by the parasite. 
 
2 4 
 
 MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 Tabulated analysis of the characters occurring in the various types oj the hybrid 
 Onagra lamarckiana X Onagra biennis — Continued. 
 
 No. 2.32. 
 
 
 Unilateral. Goneoclinic. 
 
 Intermediate. 
 
 Goneoclinic. 
 
 Unilateral. 
 
 
 To lamarckiana. 
 
 To biennis. 
 
 
 Leaves crinkled. 
 
 Stems chan- 
 neled. 
 
 Terminal ro- 
 settes symmet- 
 rical. 
 
 Ovary sparing- 
 ly pubescent. 
 
 
 
 
 Leaves narrow, not 
 
 
 
 
 M 
 
 deeply toothed. 
 
 Leaves narrow, deep- 
 ly toothed. 
 
 Branches long and 
 numerous. 
 
 Relative length of hy- 
 panthium to calyx- 
 segments 31 : 4 1 . 
 
 Bracts oblong-ovate; 
 
 petals wedge-shaped 
 
 at base. 
 Stamens as long as 
 
 pistils ; pistils as long 
 
 as petals. 
 
 leaves. 
 
 
 
 
 
 » 
 
 Capsule oblong, 
 tapering at 
 apex. 
 
 Hypanthium of 
 average length 
 of parents. 
 
 Petals wider 
 than long. 
 
 Capsule four- 
 angled and 
 tapering at 
 apex. 
 
 fruits. 
 
 
 Entire plant becoming deeply tinged with red when mature. 
 
 No. 2.24. 
 
 Rosettes 
 
 Leaves crinkled. 
 
 Yo u n g leaves 
 
 Mature rosettes Yo u n g leaves 
 
 
 
 
 broadly ovate, 
 
 dense, spread- 
 
 denticulate. 
 
 
 
 
 acutish or ob- 
 
 ing. 
 
 Basal portion of 
 
 
 
 
 tuse at apex. 
 
 Leaves broad, 
 rounded at 
 apex. 
 
 older leaves 
 irregularly 
 denticulate, 
 tapering to 
 petiole. 
 
 
 Stems and 
 leaves. 
 
 
 
 
 Leaves ovate- 
 
 Basal branches as long 
 as main axis. 
 
 hanging down, 
 
 
 
 lanceola te, 
 
 
 densely ar- 
 
 
 
 denticulate 
 
 
 
 ranged. 
 
 
 
 throughout. 
 
 
 
 Upper branches 
 
 
 
 
 
 
 erect, spread- 
 
 
 
 
 
 Flowers and 
 
 ing. 
 Bracts subcor- 
 
 Capsule nearly 
 
 Petals interme- 
 
 Hypa n t h i u m 
 
 Terminal rosettes 
 
 fruits. 
 
 date, oblong- 
 
 glabrous, ta- 
 
 diate i n size 
 
 thin. 
 
 tufted. 
 
 
 lanceolate, 
 
 pering from 
 
 and in relation 
 
 
 Rela tive length of 
 
 
 acutish, or 
 
 near base, 
 
 of length and 
 
 
 hypanthium and 
 
 
 acuminate. 
 
 slightly chan- 
 neled. 
 
 breadth. 
 
 
 * calyx-segments as in 
 
 biennis. 
 Relative length of 
 stamens and pistil as 
 in biennis. 
 Capsule distinctly 
 four-angled. 
 
 Among the characters noted above, all may be traced to the influence of one 
 or other of the parents directly, except that of the excessively long and thin 
 hypanthium. This organ sustains the proportions of some of the large-flowered 
 relatives of 0. lamarckiana, 
 
 Library 
 
MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 25 
 
 Tabulated analysis of the characters occurring in the various types of the hybrid 
 Onagra lamarckiana X Onagra biennis— Continued. 
 
 
 
 Nc 
 
 . 2.27. 
 
 
 
 
 Unilateral. 
 
 Goneoclinic. 
 
 Intermediate. 
 
 Goneoclinic. 
 
 Unilateral. 
 
 
 To lamarckiana. 
 
 To b 
 
 lennis. 
 
 Rosettes 
 
 Leaves crinkled. 
 
 Mature rosettes 
 
 
 Young leaves 
 oblong-lanceo- 
 
 Leaves spotted 
 with red. 
 
 
 
 dense, leaves 
 
 
 
 
 with long 
 
 
 late, tapering 
 
 Leaves of ma- 
 
 
 
 petioles. 
 
 
 at base. 
 
 ture rosettes, 
 lanceolate - ob- 
 long. 
 
 Stems and 
 
 Leaves crinkled. 
 
 
 Length of stem- 
 leaves average 
 
 
 leaves. 
 
 Terminal ro- 
 
 
 ture rosette not 
 
 
 
 settes dense 
 
 
 of parents. 
 
 so deeply and 
 
 
 
 and regular, 
 
 
 
 regularly den- 
 
 
 
 leaves deeply 
 
 
 
 ticulate as in 
 
 
 
 green. 
 
 
 
 biennis. 
 Basal branches 
 not as long as 
 main axis. 
 
 
 Flowers and 
 
 Basal portion of 
 petals rounded. 
 
 
 Petals with 
 
 
 
 fruits. 
 
 acute, irregu- 
 
 length greater 
 
 
 pistils of same 
 
 
 
 larly denticu- 
 
 than width. 
 
 
 length ; capa- 
 
 • 
 
 
 late, rounded 
 
 Superficial ex- 
 
 
 ble of self-fer- 
 
 
 
 or obscurely 
 
 tension aver- 
 
 
 tilization. 
 
 
 
 cordate at base. 
 
 age of parents. 
 
 
 
 
 
 Capsule ovoid- • 
 
 Capsule pubes- 
 cent, obscure- 
 ly channeled. 
 
 
 
 The stems were irregularly compressed with a zigzag outline, in a manner 
 reminiscent of those of 0. rubrinervis. The upper leaves of the rosettes and of 
 the stems were strongly convexed upwardly, due to the unequal growth of the 
 laminae and midrib. The oalyx-segments were relatively shorter than in either of 
 the parents. The entire shoot of the adult plant was deeply tinged with red. 
 
 It is to be seen from the foregoing that the hybrid 0. lamarckiana X 
 0. biennis obtained from the crosses made in New York includes four 
 distinct and separate forms, none of which are identical with the uni- 
 lateral monotypic hybrid obtained in the same cross in Amsterdam. 
 In the last-named form the qualities of the pollen-parent were fully 
 dominant throughout, while in the four types the qualities of the 
 two parents exhibit diversified mosaics of dominancy and latency 
 of the parental characteristics. 
 
 One of the American types, No. 2.1 (PL XVII, fig. 4). was 
 characterized by a predisposition to the attacks of a fungal parasite, 
 Aecidium peckii. The portions of the plant affected exhibited structures 
 quite similar to those of the pollen-parent when affected by the same 
 organism. Organs not directly attacked by the fungus showed such 
 
26 MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 distinctive form as to make it certain that the diseased plants were not 
 simply pathological individuals of one of the other types, but that the 
 hybrid included a strain incapable of resisting the attacks of the fungus. 
 The entire crop of seeds obtained by the cross in the previous year 
 were sown in a single seed-pan, and this strain was seen to be affected 
 even in the first foliage-leaf, while all of the others were found to be 
 wholly immune. The whole pathological effect may be said to be due 
 to the dominance of qualities of biennis. L,eaves not directly attacked 
 by fungus, on the other hand, exhibited a predominance of qualities 
 characteristic of O. lamarckiana. The variable length of the stamens 
 and pistils may, however, most reasonably be ascribed to the patho- 
 logical condition. 
 
 A second form, No. 2.32 (PI. XVI, fig. 3), reproduces the biennis- 
 characters of the bracts, relative dimensions of the pistils, stamens, 
 and petals quite exactly, and shows only slight departures from this 
 parent in the habit of branching and form and margins of the leaves. 
 The relative measurement of the hypanthium and of the petals are 
 alike in the parents and remain the same in the hybrid. Only one 
 character seems to have been transmitted unchanged from the lamarck- 
 iana parent, while the stems are channeled something after the manner 
 of this parent, and some crinkling of the leaves is present. In this 
 instance the qualities of biennis predominates strongly in the hybrid, 
 and the qualities inherited from the other parent are of comparatively 
 minor physiological importance. It is notable, however, that the 
 general aspect of this plant is very different from that of biennis, 
 although the taxonomic analysis yields so little actual anatomical 
 divergence. This is partly due to the unusual reddish color present 
 in the leaves and stems. 
 
 A third type, No. 2.24 (PI. XVII, fig. 5), was characterized by 
 the combination of parental qualities in such manner as to constitute 
 intermediates. The characters of the form, size, and structure of the 
 stems and leaves made a mosaic of modifications from both parents, in 
 which it would be difficult to assign greater importance to one over 
 the other. The hypanthium exhibited a length greater than that of 
 either parent, while the ovary was less pubescent than either. The 
 amount of red color present in the stems and branches was much 
 greater than that of either parent and is only duplicated among some 
 of the related species of the genus. 
 
 The form and structure of the bracts and the crinkling of the 
 leaves were transmitted unchanged to the individual ; the size and 
 form of the petals were intermediate, and the relative length of the 
 calyx-segments and hypanthium of biennis were found. It was notable 
 
PLATE XVUI. 
 
 Onagra gigas. 
 
 leaf from middle of main stem ; 2, leaf from main stem ; 3, bract from one of the lowermost flowers ; 
 4, flower with petals removed ; 5, petal ; 6, leaf from lower part of rosette five months old ; 7, leaf 
 from upper part of rosette five months old ; 8, capsules. 1, 2, 3, 4, 5, and 8, five-eighths natural size; 
 6 and 7. one-fourth natural size. 
 
MUTANTS AND HYBRIDS OF THE OENOTHERAS. 27 
 
 that the spread of foliar surfaces and the density of arrangement of 
 the leaves was similar to lamarckiana, while the form, incisions in the 
 margin, and arrangement at apices of branches were similar to biennis. 
 In the same manner the capsule was nearly glabrous, but was found 
 to be distinctly four-angled. 
 
 A fourth type, No. 2. 2 7, bore flowers not easily distinguishable from 
 the pollen-parent, being capable of self-fertilization, but with the parts 
 of the flower of greater size. From the other parent the unequal growth 
 of the leaves, which results in the crinkling of the laminae is shown 
 with a modification which causes convexities and concavities. 
 
 The symmetrical terminal rosettes are also a lamarckiana charac- 
 ter of the entire laminae. An analysis of the remaining characters show 
 that nearly all are combinations of parental qualities. Perhaps the 
 most remarkable feature of this type is the appearance of qualities 
 usually exhibited only by species allied to the parents and not by the 
 parents directly. Among these may be mentioned the zigzag forma- 
 tion of the stem and the red coloration of the shoot. 
 
 In view of the above results it is evident that a repetition of 
 the crosses between the mutant derivatives of 0. lamarckiana and 0. 
 biennis would yield much of interest. De Vries has repeatedly called 
 attention to the fact that the prevalency of the parental types in crosses 
 of mutants with each other and with the parental form may be altered 
 by nutritive conditions, and it may well be supposed that a similar 
 state of affairs may be found to exist in the hybrid described above. 
 
 It will be of interest to trace the dominancy of the separate charac- 
 ters of the two parents throughout the hybrid considered as a whole. 
 Of these the one that may be seen earliest in the development of the 
 plantlets is the density of the rosettes due to the rapidity with which 
 the leaves on the shortened internodes of the young stems appear, and 
 their duration. Every individual in the hybrid, without exception, 
 showed a heavy rosette composed of about 12 to 20 leaves, after the 
 manner of lamarckiana. Plantlets of biennis of a similar age never 
 bore more than half that number. The character in question depends 
 upon the activity of the internode ; the dominant character entails a 
 more rapid succession of development in these members, as no differ- 
 ence could be detected in the duration of the individual leaves. 
 While the character itself would be classed as meristic in its nature, 
 yet it is really seen to rest upon a real and constant physiological 
 quality. In addition to the rate of growth, it is not improbable that 
 the greater density of the dominant rosette may be due in part to the 
 development of a greater number of internodes before the elongated 
 flowering shoot is sent up. 
 
28 MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 The leaves of all rosettes of the hybrid showed laminae variously- 
 crinkled, caused by the unequal growth of the mesophjdlary and fibro- 
 vascular tracts of the laminae, a character which is well marked and 
 constant in 0. lamarckiana, but which was not seen in 0. biennis in 
 any of the cultures, although it has been seen in a few wild specimens 
 which were growing luxuriantly. Furthermore, the crinkling of the 
 leaves was exhibited in the stem-leaves of the entire hybrid. In one 
 type, that illustrated by 2.27 and consisting of two individuals, a 
 further lack of correlation in the growth of the tissues of the leaf was 
 exhibited, which consisted in an excess growth of the midrib over 
 that of the wings of the laminae, giving it an upward convexity which 
 might easily be converted into the reverse form. This was present in 
 both the rosette and stem-leaves. 
 
 The forms of leaves were so diversely intermediate that it is not pos- 
 sible to point to any important dominancies in this respect, except such 
 as are found in the types of terminal rosettes exhibited by stems and 
 branches. One, a regular, flattened, and symmetrical rosette, charac- 
 teristic of lamarckiana, was dominant in all individuals except those 
 of 2.24, which bore tufted rosettes in the five individuals included 
 with it. 
 
 The branching habit of 0. biennis, by which secondary members 
 were borne on all parts of the main axis, decreasing in length upwardly, 
 showed exactly the complementary prevalency, being present in all 
 individuals with terminal rosettes of the pattern of 0. lamarckiana. 
 Type No. 2.24, which bore bie?inis rosettes, gave off large basal 
 branches, and the upper part of the main axis was more densely 
 branched than in 0. lamarckiana, so that the habit of the pistil-parent 
 in this particular was not exhibited in pure form by any member of 
 the hybrid. 
 
 Stems of rounded cross-section were found to be more prevalent 
 than those with deep channeling, the latter occurring on only five indi- 
 viduals of the hybrid. 
 
 The capacity for self-fertilization as indicated by the relative 
 length of the stamens and pistil was dominant in all types, except that 
 of 2.1, or in about 29 out of the 33 individuals examined. A sharp 
 separation with regard to this character may be detected in securing 
 pure fertilizations. In order to obtain capsules with pure seeds it is 
 but necessary to inclose the inflorescences of 0. biennis in the parch- 
 ment bags and the pollen will fall on the stigmatic surfaces without 
 the intervention of any agency whatever except gravity. On the other 
 hand, 0. lamarckiana rarely sets seeds unless pollen is transferred to 
 the stigmas by insects or by hand, although in the open air the same 
 purpose is sometimes accomplished by the wind. 
 
MUTANTS AND HYBRIDS OF THE OENOTHERAS. 20, 
 
 The calyx-segments are relatively much shorter than the hypan- 
 thium in all individuals of the hybrid showing a dominance of a char- 
 acter of O. biennis, although the actual length of the latter is greater 
 in some individuals than in either parent. The other features of the 
 flowers were variously intermediate. The elongated capsule was pres- 
 ent in all of the individuals of the hybrid, except in the two included 
 in the type of No. 2.27. 
 
 OCCURRENCE OF MUTANTS. 
 
 Among the progeny arising from the cross between 0. lamarckiana 
 and 0. biennis were two individuals which, as early as July 1, were 
 seen to be separable by the variously erect leaves with long petioles 
 in the rosettes. The rosettes were sparse, and the leaves were oblong- 
 lanceolate, obtuse at the apex, broadest about the middle, and more 
 or less abruptly narrowing to the petiole, upon which the narrow 
 wings of the laminae extended nearly to the base. The basal portions 
 of the leaves were deeply and irregularly denticulate. The members 
 of the rosette were minutely pubescent. On July 13 these plants had 
 sent up shoots which soon bore the characteristic leaves, bracts, and 
 flowers of 0. rubrinervis, a mutant which was originally observed by 
 De Vries in 1887. 
 
 The occurrence of mutants in hybrids in which one of the parents 
 appears as a pure strain has long been known and has been described 
 at length by Professor De Vries as occurring at numerous times in 
 his cultures. He found that about 1 per cent of the hybrid progeny 
 of 0. lamarckiana X 0. nanella was composed of mutants, and that 
 about 2 per cent of the hybrid progeny between various older species 
 were mutants in a series of tests made in 1896-1900. (De Vries, 1903, 
 pp. 425, 426.) 
 
 0. rubrinervis was observed by De Vries to arise in the hybrid 
 progeny of 0. lamarckiana X nanella, 0. lata X nanella, 0. lata X 
 lamarckiana, 0. lataX brevistylis, 0. nanella X brevistylis, 0. scintillans 
 X nanella, and 0. lamarckiana X scintillans, to which must be added 
 the experience related above, by which this species was also found in 
 the descendants of 0. lamarckiana X biennis. 
 
 The facts recorded by De Vries indicate that the mutability of the 
 various forms of the evening-primrose is not modified by crossing in 
 any manner. It is a matter of interest in this connection that he has 
 also established the conclusion that the number and amplitude of 
 fluctuating variations exhibited by parental forms are not increased 
 or materially modified in the hybrids. 
 
30 MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 The designation of an individual from a hybrid progeny as a 
 mutant is unsafe, unless, as in the evening- primroses, the characters 
 of the mutants have been established by previous observations. It is 
 quite possible that mutants may have appeared in hybrids at various 
 times, thus giving basis for the assumption that new qualities were 
 seen to appear as a result of the hybridization. 
 
 A second occurrence of O. rubrinervis as a possible mutant was 
 noted in a lot of plantlets grown from seeds obtained from the botan- 
 ical garden at Upsala early in 1904. The seeds were sown in germi- 
 nating pans on March 28, 1904, and four individuals were transplanted 
 to the experimental grounds on May 28 and began to send up shoots 
 early in July. Of these, two were undoubted types of 0. rubrinervis , 
 corresponding to this form in all particulars. 
 
 In reply to the inquiry as to the derivation of the seed from which 
 the above plants were grown, Prof. F. R. Kj ell man, director of the 
 botanical garden at Upsala, replied as follows under date of August 
 8, 1904: 
 
 The seeds of Oenothera lamarckiana, which you received from this botanical 
 garden, were gathered from plants grown in a cool house from seeds obtained 
 from Professor De Vries. Some Oenotheras of other species were growing near 
 these plants, upon which account the possibility of hybridization was not ex- 
 cluded. Pure seeds of the new species of Oenothera may, in my opinion, only 
 be obtained from Professor De Vries. 
 
 In view of theabove record, therefore, it may only be said that the 
 specimens of O. rubrinervis in this culture owe their origin either to 
 an actual mutation, or to the pollination of 0. lamarckiana by 0. 
 rubrinervis . Professor Kjellman did not state whether or not any of 
 the new species were included in the lot growing near 0. lamarckiana, 
 although the negative presumption seems warranted. 
 
 Still a third occurrence of the same species is to be noted, for 
 which all explanation is lacking at the present time. A package of 
 seeds under the label of " Statice Japonica " were received from the 
 botanical garden at Tokyo, in 1903. After germination, four of the 
 seedlings were transplanted to small pots in accordance with the usual 
 custom with new accessions to the New York Botanical Garden. 
 Attention was not called to the peculiar appearance of these plants 
 until early in May, when they formed rosettes 2 dm. in diameter, and 
 were unmistakably 0. rubrinervis. I was not able to trace the history 
 of the seed-package and learn whether all of the seeds were of the same 
 kind or not. If by mistake a package of seeds of Onagra had been 
 sown under the above label, the rubrinervis which was with it would 
 
MUTANTS AND HYBRIDS OF THE OENOTHERAS. 3 1 
 
 have germinated first, as the seeds are very easily awakened from the 
 dormant condition, and a half dozen of these would have been trans- 
 planted to small pots by the gardener and the remainder would have 
 been destroyed in accordance with the usual custom. A still further 
 possibility lies in the fact that ordinary seeds are sown in mixtures of 
 potting soil that has not been sterilized, and might have contained 
 some seeds of this species from the cultures made in the New York 
 Botanical Garden for the previous year. 
 
 The chief purpose of the earlier studies of the senior author of the 
 present paper was to make comparative studies of the parent-form with 
 its mutant derivatives, and also to test the stability of all of the types 
 concerned when cultivated under climatic conditions widely different 
 from those under which the mutants arose. Previously to the cul- 
 tures of 1904 less than a dozen of the various forms were brought to 
 maturity, and no attention was given to the possible occurrence of 
 mutants among the seedlings, although many might have been present. 
 Thus DeVries found 600 mutants in 50,000 seedlings from lamarckiana , 
 although he has pointed out that it would be possible to have exten- 
 sive plantations of seedlings which included no divergent forms. 
 Still another factor in the matter consisted in the inexperience of the 
 experimenter. The discovery of the mutants in the seedling stage 
 when only two or three small leaves are present is difficult for the first 
 time, although after becoming accustomed to the typical forms and 
 learning the aspect of the things to be looked for it is compara- 
 tively easy to recognize the better-known mutant types. Even then 
 the mutants previously seen are much more readily distinguished than 
 those known only by descriptions. This matter of practical observa- 
 tion depends greatly upon the plain mechanical fact that the selection 
 of the various forms is generally done in the seed-pans in which ger- 
 mination occurred in order to save the labor necessary in transplanting 
 them to small pots. 
 
 After the major ends of the cultures had been reached in the 
 summer of 1904, and the newly -grown crops of seed were nearly 
 mature, the chances of losing any of the forms under cultivation by 
 accident was reduced to a minimum, and all of the seeds remaining on 
 hand were sown in pans of sterilized soil in order to make separate 
 observations upon the occurrence of mutants. Several thousands of 
 seeds of 0. lamarckiana of the crop of 1901 from the botanical garden 
 of Amsterdam, and of the same species of the crop of 1903 from the New 
 York Botanical Garden, were germinated in the above manner. In 
 addition, a few hundred seeds of 0. gigas o f the crop of 1903 from the 
 botanical garden of Amsterdam were sown 
 
32 MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 The seedlings of the last-named species show a wide divergence 
 in the juvenile leaves, which is partially continued even in the foliar 
 organs of the mature plant, although it is not believed that these 
 divergences may be grouped in separate strains of the species. Con- 
 sequently several selections were made from the cultures which, how- 
 ever, were soon found to be well within the limits of the type. 
 
 The results obtained from 0. lamarckiana were of much greater 
 interest. Mutants were found in the seedlings grown directly from 
 the seeds from the garden at Amsterdam, and also from those of 1904 
 from the New York Botanical Garden. As early as October 1, 1904, 
 O. albida, 0. elliptica, and 0. scintillans were recognizable in the plant- 
 lets grown from seeds produced in New York and Amsterdam. 
 Later, gigas, nanella, oblonga, and subovata were found. In addition 
 to these seven known mutants which had been seen to originate 
 previously in Amsterdam, seven other forms could be distinguished 
 which could not be identified with any forms heretofore observed by 
 Professor De Vries or the authors. It is therefore justifiable to say 
 that so far as present information goes the range of mutability of the 
 parent-species has been extended under the conditions under which it 
 has been cultivated in America. A comparative examination of the 
 cultures in the two localities brings out the fact that the plants grown 
 in New York were much more vigorous and active than those in 
 Amsterdam, and the suggestion lies close at hand that whatever the 
 causes may be that induce changes in the qualities of a species, the 
 actual environment in which such mutative alterations ensue is one 
 that has a majority of the factors favorable to vegetative development 
 as well as to plentiful seed-production. The limited number of facts 
 brought to light by the mutation cultures certainly support the sug- 
 gestion in question, which, it is to be noted, is in direct opposition to 
 the conclusion of Darwin that new types arise most plentifully in 
 response to adverse circumstances. 
 
 In conjunction with the foregoing it is to be recalled that seeds of 
 0. lamarckiana obtained from Vilmorin-Andrieux et Cie., in France, 
 by De Vries, produced some 0. nanella when sown in the botanical 
 garden at Amsterdam in 1899. (De Vries, 1903, p. 459.) 
 
 It is to be seen, therefore, that 0. lamarckiana. is still in a mutable 
 condition in various portions of its widely extended range. The 
 results of the more recent cultures made in the botanical garden at 
 Amsterdam leads, however, to the conclusion that 0. lamarckiana 'has 
 lost the capacity for producing 0. lata, laevifolia, and brevistylis. De 
 Vries also found that the capacity for mutability inherited by rubri- 
 
Plate xix. 
 
 Fig. i. Onagra lamarckiana and Onagra nanella in bloom. 
 
 Photographed at 6 a. m., August g' 1904. 
 
 
 
 $m. 
 
 % 
 
 Fig. 2. Onagra lamarckiana X Onagra biennis. 
 No. 2.32 at left and right in foreground; No. 2.24 in center. 
 

MUTANTS AND HYBRIDS OF THE OENOTHERAS. 33 
 
 nervis, by which it was able to give rise to nanella, no longer exists. 
 The loss of mutability has been noted to be accompanied by an acqui- 
 sition of the Mendelian procedure in the hybridization of these two 
 forms. (De Vries, 1903, pp. 458, 460.) 
 
 The discovery of single plants presumably derived from an ances- 
 tral mutation, or of a few plants as mutants from a parent, suggest 
 that in some instances the period of mutability of a species may 
 include only a single season, and these brief periods may recur at 
 intervals concerning which information is totally lacking. In the case 
 of Oenotheras, however, the first mutants in bloom were found in 1887, 
 which shows that the parents from which they were derived perfected 
 their seeds in 1885. The recurrence of various mutants has been noted 
 in every succeedingyear, including 1904, and it is to be seen, therefore, 
 that this species has been in a mutable condition for twenty years. 
 How much earlier mutants have been formed than the date given 
 above cannot be surmised. The continuance of the capacity for muta- 
 bility is open to actual observation, however, and it may be possible 
 within fthe next few years for the botanist to actually witness the 
 closing of the mutative period in this plant which has furnished 
 material so rich in practical and theoretical results. The procedure of 
 O. lamarckiana is supposed by De Vries to be similar to that which 
 has been followed by Draba and Viola in the productions of the 
 swarms of species now recognized. (De Vries, 1905.) 
 
 During the cultures of 1902- 1903 O. lamarckiana, O. nanella, and 
 O. rubrinervis were grown as biennials for purposes of comparison 
 with the behavior of other species. During 1904, however, seeds were 
 sown in the propagating houses about the first of the year and the 
 plantlets, after being properly transferred from smaller to larger pots, 
 were placed in the soil in the experimental grounds in the latter part 
 of May. No marked difference between the two series could be 
 detected. It was noted that 0. gigas, however, has more thoroughly 
 established itself in the biennial habit and that not half of the plants 
 grown as annuals actually produced flowers or seeds in 1904. 
 
 The estimation of the general hardiness or fitness of the parental 
 form and of the mutants, with a view to the determination of their rel- 
 ative value if thrown into a competitive struggle for existence, is not 
 to be too lightly made. O. lamarckiana has not spread over any part 
 of North America having the climate of New York, and its cultivation 
 in this locality must bring into contact many factors inoperative in its 
 natural habitat. Tests made under such conditions must be accepted 
 most guardedly. A general description of some of the more striking 
 characteristics of the various forms will be of some value, however. 
 
34 
 
 MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 The rosettes of 0. lamarckiana and 0. rubrinervis which failed to 
 send up flowering shoots in 1903 endured the following winter, which 
 was of maximum severity, and began growth in a normal manner in 
 the spring of 1904, but were uprooted to make room for a new series of 
 experiments. 
 
 No actual difference has been found in the power of producing 
 pollen among the parent-form, the mutants grown in the New York 
 Botanical Garden, and the other American species. All produce an 
 abundant crop of pollen, and show many faulty grains. 0. rubrinervis 
 was found to produce a greater number of capsules, and the seeds ger- 
 minated more readily than those of the parent-form, the plants reaching 
 maturity earlier than 0. lamarckiana. O. gigas, on the other hand, 
 grows more slowly than the parent-form, as stated above, although it 
 
 Fig. 2. Seedlings of Onagra gigas, about Ave weeks old, showing variations 
 
 in forms of leaves. 
 
 produces seeds abundantly, which show a high percentage of germina- 
 tion. Both species are supposed by De Vries to be quite equal to the 
 parental type in vigor, or perhaps to excel it. The latter suggestion 
 is supported by the marked reproductive capacity of these forms in 
 hybridizations When crossed with the parental form or with other 
 mutants, the dominance of the characters of 0. gigas and O. rubri- 
 nervis is especially marked, most so in the case of 0. gigas. 
 
 In continuation of the work carried on in previous cultures obser- 
 vations of 0. gigas were made for the purpose of placing on record an 
 exact description of its characteristics as grown in America. The 
 formal descriptions of the parental type andO. rubrinervis and O.nanella 
 have already proved useful in the various phases of the present investi- 
 gation. (MacDougal, 1903.) 
 
PLATE XX. 
 
 Fig. i. Onagra gigas in bloom. 
 
 Photographed at 7 a. m., August 9, 1904. 
 
 Fig. 2. Rosettes ot Onagra gigas six months old, show ing diverse forms ol lea\ es. 
 

 
PLATE XXI. 
 
 Onagra rubrinervis. 
 
 Photographed at 6.30 a. m., August 9, 1904- 
 
PLATE XXII. 
 
 A series of leaves taken from near the middle of the basal branches ol On 
 lamarckiana and Onagra rubrinervis, illustrating the nearest approach to 
 identity in leaf-form. The two lower rows are Onagra rubrinervis ; the two 
 upper Onagra lamarckiana. 
 
MUTANTS AND HYBRIDS OF THE OENOTHERAS. 35 
 
 ONAGRA (OENOTHERA) GlGAS. 
 
 Seedling about two months old. — Leaves finely but rather copiously 
 pubescent ; blades various ; those of the earlier leaves narrowly or 
 broadly oblong, those of the later leaves broadly oval, suborbicular, 
 or ovate-orbicular, mainly 3 to 4 cm. wide, abruptly narrowed at the 
 base, or truncate, longer than the petiole. 
 
 Seedling five months old. — Rosettes rather dense; leaves copiously 
 fine-pubescent; blades broadly oblong, oval, or ovate, varying to 
 obovate, the larger ones 2.5 cm. wide, distantly denticulate, obtuse or 
 nearly acutish at apex, markedly longer than petiole. (PI. XX, fig. 2.) 
 
 Mature rosette. — Leaves ample, finely pubescent all over, the 
 larger ones about 28 cm. long, 9 to 10 cm. wide ; blades ovate and 
 prominently glandular-denticulate, or with an ovate terminal lobe and 
 several large basal teeth, or tooth-like lobes, with petioles very stout. 
 
 Adult plant. — Plant very stout and luxuriant. Stem channeled, 
 branched near the base, and mainly below the middle, the branches 
 assurgent or ascending, like the main stem hirsute, the hairs com- 
 monly widely spreading ; leaves finely pubescent, 1 to 2 dm. long, on 
 the lower part of the stem, numerous ; blades shallowly and rather 
 remotely toothed, those of the lower cauline leaves oblong-spatulate to 
 oblong, acute at the apex, each narrowed into a semi-terete, margined 
 petiole, those of the upper leaves broadly oblong to oblong-ovate, acute 
 or abruptly short-acuminate, sessile or nearly so ; bracts ovate-lanceo- 
 late, cordate or subcordate at the base; conic portion of the bud about 
 3.5 cm. long, finely pubescent, with short, spreading hairs, the free tips 
 of the sepals 6 to 7 mm. long ; hypanthium 4 to 4.5 cm. long, about 
 
 7 mm. wide at the mouth, slightly ribbed ; sepals 4 to 4.5 cm. long, 
 about as long as the tubular portion of the hypanthium, the free tips 
 
 8 to 9 mm. long; petals firm, 4.5 to 5 cm. long, truncate or slightly 
 emarginate at the apex; filaments 18 to 20 mm. long ; anthers 15 to 
 16 mm. long; pistil longer than the stamen ; stigma 6 to 7 mm. long ; 
 capsule about 2 mm. long, 7 to 8 mm. in diameter at thickest point, 
 finely pubescent all over, scarcely narrowed at apex. (PL XVIII.) 
 
36 MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 STATISTICAL COMPARISONS OF ONAGRA (OENOTHERA) LAMARCK- 
 IANA WITH TWO OF ITS MUTANTS .* 
 
 So general is the experience in garden practice that a variety 
 which has been improved by selection rapidly loses its improved 
 character upon the cessation of the selective process that the sta- 
 bility of any modification which is discovered either in nature or 
 under cultivation demands the fullest possible proof. The mutation - 
 theory is so diametrically opposed to Galton's law of ancestral 
 heredity that it needs especial investigation from the same standpoint 
 and by the same methods by which this law was established. Accord- 
 ing to Galton's law the offspring shows a certain definite degree of 
 inheritance from each generation of its ancestors, one-half from its 
 parents, one-quarter from its grandparents, one-eighth from its great - 
 grandparents, and so on. (Gal ton, 1889.) As a consequence of this 
 law the children of extreme parents are on the average less extreme 
 than their parents, because their preparental ancestry is on the average 
 more mediocre. The departure of the offspring from the mean con- 
 dition of the race to which it belongs toward the extreme condition of 
 its parents has been designated ' ' regression. ' ' One of the most serious 
 criticisms which has been made upon De Vries's conclusions has been 
 that of Weldon , who points out that no satisfactory evidence has been 
 presented to prove the completeness of regression, in the Galtonian 
 sense, in the Onagra mutants. For, unless such regression is com- 
 plete, these mutants could not maintain themselves distinct from the 
 parental type except through the agency of man in guarding pollina- 
 tion and in selection, a fact which wtmld deprive them of all signifi- 
 cance in the explanation of evolution. (Weldon, 1902.) 
 
 To test quantitatively the continuity or discontinuity of a few of 
 the differential characters of the Onagra mutants, and to begin the 
 work which, when continued for several years, will forever set at rest 
 the question of the completeness of Galtonian regression, the investi- 
 gation the results of which are reported in this section were undertaken. 
 The number of specimens available for study was not sufficient for the 
 most satisfactory statistical work, but the results offer a number of 
 suggestive lines for future investigation. 
 
 As all the characters chosen for this investigation are notably 
 affected by the physical conditions to which the plants are subjected, 
 it should be pointed out that all these specimens were grown near 
 each other in an experimental garden which presents nearly uniform 
 conditions throughout, and that they were planted at the uniform 
 
 *Prepared by G. H. Shull. 
 
MUTANTS AND HYBRIDS OF THE OENOTHERAS. ^J 
 
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 53 i. 
 
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38 MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 distance from each other of one meter, thus allowing each specimen 
 sufficient space to express its characteristic physiological nature 
 unmodified by complex interrelations with other plants. 
 
 The stature of Onagra nanella. — The character which most strik- 
 ingly differentiates 0. nanella from its parent-form, O. lamarck- 
 iana, is that from which it has so appropriately received its name. 
 The great difference in height between these two species may be seen 
 in the photograph (PI. XIX, fig. 1), which represents a typical speci- 
 men of each. The results of measuring 23 specimens of O. nanella 
 and 34 of 0. lamarckiana are seriated in the form of curves of equal 
 area in fig. 3. It will be observed in this figure that not only are the 
 two curves quite distinct, but that they are separated by a wide gap. 
 The discontinuity is tremendously in excess of the probable errors, 
 the distance between the means of the two curves being more than 
 forty times the sum of the probable errors of the means. The heights 
 of Onagra nanella group themselves about the mean value 22.81 ±1 .02 
 cm., with a range from 7 cm. to 35 cm., and those of O. lamarckiana 
 about the mean value 88.68 ± 0.55 cm., with a range from 77 cm. to 
 96 cm. The other constants present quite as interesting differences. 
 Although the mean height of O. nanella is only one-fourth as great as 
 that of 0. lamarckiana, the standard deviation, <r, is considerably 
 greater, being 7.26 ± 0.72 cm. in the former and only 4.76 ± 0.39 cm. 
 in the latter. As the mean and the standard deviation are combined 
 
 in the formula ^^, to form the coefficient of variability, the latter 
 
 constant shows an even more remarkable difference between these two 
 forms than do the means. The coefficient of variability in the height 
 of Onagra nanella is notably high, 31.84 ± 3.16 per cent., while that 
 in O. lamarckiana is quite as notably low, 5.37 ± 0.44 per cent. This 
 is particularly interesting, as will be seen later, in its agreement with 
 the fact that in most of the characters chosen for this study the 
 mutant is significantly more variable than the parent-form. 
 
 The branching habit of Onagra rubrinervis. — The nature of the 
 branching of O. rubrinervis as compared with that of 0. lamarck- 
 iana is such as to give it a very characteristic aspect. On the average 
 about twice as many of the axillary buds develop branches and these 
 branches have a greater average length. In both species there is a 
 whorl of long lateral branches surrounding the base of the main axis. 
 In . rubrinervis the central axis bears numerous branches roughly 
 correlated with their position on the axis in such a way as to give the 
 plant as a whole a distinctly conical form. In 0. lamarckiana, on the 
 other hand, the branches arising from the central axis are less numer- 
 
MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 39 
 
 ous, shorter, and evidently less closely correlated with their position 
 on the axis, but show a tendency to group themselves somewhat above 
 the base, so that the plant resembles the framework of an inverted 
 umbrella. (Cf. PL XIX, fig. i, and PL XXI.) 
 
 
 
 
 
 
 
 
 
 
 
 fc 
 
 
 o 
 
 1 
 
 to 
 
 o 
 
 !- 
 O 
 
 1 
 O 
 
 1 
 
 c* 
 
 o 
 
 1 
 
 cs 
 
 T 
 
 s? 
 
 1 
 
 o 
 
 — 
 
 1 
 
 CO 
 
 1 
 
 O 
 -* 
 
 so 
 1 
 
 CO 
 
 o 
 
 Cr* 
 
 1 
 
 CO 
 CO 
 
 o 
 
 55 
 
 1 
 
 $ 
 
 Si 
 
 1 
 
 in 
 
 • 
 
 3 
 
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 Si 
 
 N 
 
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 T 
 
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 T 
 
 CO 
 
 T 
 
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 1 
 
 •2 *-■ 
 
 £ s 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 > f* 
 
 s O 
 
 O ... 
 
 . CO 
 
 •2 = 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 A 
 
 
 ma and 0. rubrine 
 VI., 20.70 ± 0.49; <r, 8.24 
 t.O ±1.7 per cent. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 i 
 
 . 
 
 
 
 
 
 
 
 
 
 V/ 
 
 
 y //, 
 
 
 
 / / 
 
 
 y A 
 
 nches in Onagra lamarcki 
 arckiana : Range, 11 to 25; J 
 ± 1.04; <r, ti.:!4 ±0.78; 0. V., 1' 
 
 
 
 
 
 
 
 
 
 / 
 
 ' // / 
 
 h 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 \\\ 
 
 \ \ N 
 
 \X\ 
 
 n In number of lateral bri 
 Ines rising to left. 0. lam 
 .v.- i;an'_T,:;l to 62; M., 42.35 
 
 
 
 
 
 
 
 M 
 
 §§ 
 
 
 
 MS 
 
 \V\ 
 
 
 \V\ 
 
 s^ 
 
 
 \V\ 
 
 
 
 
 
 
 
 
 
 
 
 s$ 
 
 
 
 
 
 
 
 
 
 
 
 
 B a « 
 
 2 ^ M 
 
 
 
 
 
 
 
 
 
 
 v 
 
 \\ 
 
 a. 4. \ 
 shadei 
 0. rt*6 
 
 
 
 
 
 
 
 
 
 
 
 £ 
 
 C5 00 I- 
 
 to lO 
 
4Q 
 
 MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 Although such a character as this is too largely influenced by the 
 individual physiological vigor to be of any value as a diagnostic char- 
 acter, the difference of aspect between the lots of plants of these two 
 species was so striking that it was thought interesting to give it quan- 
 titative expression. A comparison of the number of lateral branches 
 shows complete discontinuity between the two species in this regard, 
 the range in O. lamarckiana being from n to 25, and in 0. rubrinervis 
 from 34 to 62. Curves of equal area representing the variation in the 
 number of branches of 17 specimens of 0. rubrinervis and of 20 speci- 
 mens of 0. lamarckiana selected by lot, are shown in fig. 4. The 
 constants of these curves are as follows : 
 
 Onagra lamarckiana. 
 Onagra rubrinervis . . 
 
 M 
 
 ean. 
 
 Meters. 
 
 20.70 ± 0.49 
 42.35 ± 1.04 
 
 Standard deviation. 
 
 Meters. 
 
 324 ± 0.35 
 6.34 ± 0.73 
 
 Coefficient of variability. 
 
 Per cent. 
 
 15.7 ± 1.7 
 15.0 ±1.7 
 
 If, instead of the number of branches, we consider the total branch- 
 length, the results are in some respects more striking still, for in gen- 
 eral the branches are longer in 0. rubrinervis than in O. lamarckiana. 
 This did not prove invariably true, however, and the discontinuity 
 which should have been increased by this difference in average length 
 is lost through the occurrence of a specimen of 0. r ub rinervis having 
 a total branch-length of only 7.79 meters, though it had 39 branches. 
 This is well within the range of total branch-length of 0. lamarckiana, 
 which varied in this respect between 3.65 meters and 8.41 meters. 
 The greatest length of branches observed in any specimen of 0. rubri- 
 nervis was 29.98 meters. The variability in regard to total branch 
 length is presented graphically in fig. 5. The constants of these 
 curves are as follows : 
 
 Onagra lamarckiana. 
 Onagra rubrinervis. . . 
 
 M 
 
 ean. 
 
 Meters. 
 
 6.68 ± 0.20 
 18.19 ± 1.30! 
 
 Standard deviation. 
 
 Meters. 
 
 1.35 ±0.14 
 7.95 ±;0.92 
 
 Coefficient of variability. 
 
 Per cent. 
 
 20.2 ± 2.2 
 43.7 ±5.1 
 
 This comparison shows a remarkable difference throughout, the 
 most important feature probably being the fact that the coefficient of 
 variability in total branch-length is more than twice as great in O. 
 rubrinervis as in 0. lamarckiana. 
 
 The size and shape of the leaves of Onagra rubrinervis, — Much 
 more important taxonomically than stature and branching are the 
 leaf-characters, and it is just here that statistical study encounters the 
 most serious obstacles in seeking a satisfactory basis. In the first 
 
MUTANTS AND HYBRIDS OF THE OENOTHERAS. 41 
 
 place, some of the leaf-characters are]incapable"of quantitative expres- 
 sion, such as the degree of crinkling of the leaf, which is a striking, 
 though not an absolutely distinctive feature of the leaf of 0. lamarck- 
 iana. Some leaves of O. rtibrinervis are also crinkled, but it is a gen- 
 
 70 
 
 66 
 
 m 
 
 m 
 
 60 
 
 45 
 
 40 
 
 35 
 
 :;o 
 
 35 
 
 20 
 
 15 
 
 10 
 
 Fig. 5. Variation in total branch-length of Onagra lamarckiana and O. 
 rubrinervis. O. lamarckiana: Range, 3.65 to 8.48 meters; M., 6.68 + 0.20 
 meters; <r, 1.85 ± 0.14 meters; C. V., 20.2 ± 2.2 per cent. O. rubrinervis: 
 Range, 7.79 to 29.98 meters; M., 18.19 ± 1.30 meters; a, 7.95 ±0.92 meters; 
 C. V., 43.7 ±5.1 per cent. 
 
 eral character of the leaf of 0. lamarckiana and only occasional in 
 0. rubrinervis. Other characters, although measurable, present tech- 
 nical difficulties incommensurate with the value of the results, as, for 
 instance, leaf-thickness and degree of pubescence. The leaf of 0. 
 
42 
 
 MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 45 
 
 50 
 
 95 
 100 
 
 120 " "145 
 125 150 
 
 Fig. 6. Variation in leaf-length of Onagra 
 lamarckiana and O. rubrinervis. O. 
 lamarckiana : R.,49to 137 mni. ; M.,96.85 
 ± 0. 42 mm. ; o-, 13.08 ± 0.30 mm. ; C. V., 
 13.60 ± 0.81 per cent. O. rubrinervis : R., 
 63 to 142 mm. ; M., 97.99 ± 0.34 mm. ; o-,12.87 
 ± 0.24 mm. ; C. V., 12.62 ± 0.24 per cent . 
 
 lamarckiana is noticeably thicker 
 than that of 0. rubrinervis. So- 
 called qualitative differences are 
 usually compounds of several meas- 
 urable characters, any one of which 
 is a wholly unsatisfactory measure of 
 the quality, while only one, two, or 
 several at most of these measurable 
 characters can be dealt with mathe- 
 matically at a time. Leaf- form is 
 a character of this kind. Not only 
 is the relation of length to breadth 
 important, but the relative posi- 
 tion of the widest part of the leaf, 
 the angles of apex and base, and 
 indeed the curvature of the mar- 
 gin at every point from petiole to 
 apex, enter as essential features of 
 leaf- form, and no tangible mathe- 
 matical expression can be devised 
 to represent it. Confining ourselves 
 to a single measurable character, 
 such as leaf length or breadth, 
 there is still another difficulty which 
 must be met. The leaf is a differen- 
 tiated organ and there is no exact 
 homology between any two leaves. 
 In a plant which has but few leaves 
 this is strikingly evident, and no 
 leaf on a stem which has ten leaves 
 corresponds exactly to any leaf on 
 another plant of the same species 
 which carries but nine leaves. In 
 plants with numerous leaves, as 
 in the various species of Onagra, 
 the degree of differentiation between 
 adjacent leaves is so slight that 
 they may be treated as homotypic 
 without appreciable error, provided 
 as nearly as possible the corre- 
 sponding parts of the various speci- 
 mens are used as the source of 
 leaves for the study. 
 
MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 43 
 
 The leaves chosen for this comparative study were taken from a 
 point about two-fifths of the distance from the proximal toward the 
 distal end of the long lateral branches mentioned above as forming 
 a whorl about the base of the main axis. The number of such 
 branches borne by each specimen allowed the collection of a suffi- 
 ciently large number of leaves by taking them from a very short sec- 
 tion of each branch, so 
 that the error due to 
 differentiation is insig- 
 nificant compared with 
 the ' 'chance' 'variation. 
 From 20 to 30 leaves 
 were taken from each 
 of 20 specimens of each 
 species, and the width, 
 and the length from the 
 base of the petiole to 
 the apex, were meas- 
 ured in the fresh con- 
 dition. The length and 
 width were then com- 
 bined for each leaf in 
 the ratio, width -5- 
 length, this being the 
 simplest possible ap- 
 proximation to a sat- 
 isfactory mathematical 
 expression for leaf- 
 form. The curves 
 shown in figs. 6, 7 
 and 8 compare graph- 
 ically the results of 
 these measurements. It 
 will be noted on refer- 
 ence to fig. 6 that the 
 length of the leaves 
 in the two species is 
 almost identical, while 
 fig. 7 shows that with respect to the width of leaf they are quite 
 different, though not discontinuous. In consequence of the approxi- 
 mate identity in leaf-length the ratio representing leaf- form corresponds 
 closely with the leaf-width in the character and degree of overlapping 
 of its curves, as will be seen on comparing figs. 7 and 8. 
 
 Fig. 7. Variation in leaf-width of Onagrarubrinervis and 
 O. lamarckiana. O. rubrinervis: R.,17 to 10mm.; M . 
 29.736 ± 0.098 mm.; <r, 3.589 ± 0.069 mm.; C. V., 12.07 ± 0.28 
 percent. O. lamarckiana : R., 24 to 50 mm. ; M., 37.H17 
 ± 0.137 mm. ; o-, 4.248 ± 0.097 mm. ; C. V., 11.29 ± 0.26 per 
 cent. 
 
44 
 
 MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 The constants of these curves, which represent the variations of 
 the two populations, each taken as a whole, are as follows: 
 
 
 Mean. 
 
 Standard deviation. 
 
 Coefficient of variability. 
 
 Variation in length of leaf : 
 
 Onagra lamarckiana 
 
 Millimeters. 
 
 96.15 +0.42 
 97.99 ±0.34 
 
 37.617 + 0.137 
 29.736 ± 0.098 
 
 Per cent. 
 
 39.964 + 0.123 
 30.077 ± 0.084 
 
 Millimeters. 
 13.08 +0.30 
 12.37 +0.24 
 
 4.248 + 0.097 
 3.589 + 0.069 
 
 Per cent. 
 3.811 + 0.087 
 3.098 + 0.056 
 
 Per cent. 
 
 13.60 + 0.31 
 12 62 + 24 
 
 Variation in width of leaf : 
 
 Onagra lamarckiana 
 
 11.29 + 0.26 
 12 07+023 
 
 Variation in the ratio between 
 width and length: 
 
 Onagra lamarckiana 
 
 9.53 + 0.22 
 10 30 + 20 
 
 
 
 Considering the great variability of leaves, it would not be 
 expected that two species so closely related would exhibit complete 
 discontinuity in size of leaf or in the ratio between width and length. 
 It is not so much the extreme types of leaves which give to a plant its 
 characteristic appearance and appeal to the systematist, as the type to 
 which the majority of the leaves belong. The mean values of the 
 various leaf-characters for each individual would much more nearly 
 represent the conditions as seen by the descriptive botanist. For this 
 reason it seemed important to compare the means of length, width, 
 and form of leaves in the individual plants of the two species. The 
 results are represented in figs. 9, 10, and 11, and show that there is 
 approximate identity in the mean length of the leaf, but complete dis- 
 continuity in both mean widths and the mean ratios of width to length. 
 The constants were not determined for these curves, as an inspection 
 of the curves together with a statement of the ranges will sufficiently 
 indicate the nature and degree of discontinuity present. 
 
 The ranges of mean values of the leaf-characters in the individ- 
 ual plants were as follows : 
 
 
 Length. 
 
 Width. 
 
 Width-=-length. 
 
 
 Millimeters. 
 
 88.42-112.32 
 86.28-107.15 
 
 Millimeters. 
 
 33.74-41.64 
 25.93-32.53 
 
 Per cent. 
 34.62-44.41 
 25 30 32 54 
 
 
 
 
 It will be noted that the break between the mean values of leaf- 
 width and that between the mean ratios of width to length are slight 
 but sufficient. If a larger number of specimens had been used the 
 range would have been extended somewhat and it is not improbable 
 that they would overlap some, and yet the unsatisfactory character of 
 
MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 45 
 
 the ratio of width to length as a measure of leaf- form would not allow 
 us to infer from such overlapping that the two species are not abso- 
 lutely distinct with respect to the form of the leaves. This fact will 
 become convincingly apparent upon reference to Plate XXII, in which 
 
 35 30 35 40 45 - 50 55 
 
 Fig. 8. Variation in ratio of width to length in the leaves of Onagra 
 rubrinervis and O.lamarckiana, expressed in per cents. 0- rubrinervis: 
 Range, 20-48; M., 30.077 ±0.084; <r, 3.098 ± .056 ; C. V., 10.30 ± 0.20 per cent. 
 O. lamarcUana: Range, 28-53 ; M.. S9.961 ±0.123; <r,3.811 ±0.087; C. V., 
 9.53 ± 0.22 per cent. 
 
 are contrasted the leaves from the specimen of 0. lamarckiana having 
 the minimum mean ratio and those of the specimen of 0. rubriiu 
 having the maximum mean ratio. According to this statistical meas- 
 
4 6 
 
 MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 ure, these two lots of leaves are the most nearly identical in form of any 
 two plants, belonging to these two species, which were investigated. 
 If to the difference of outlines as shown in the plate could be added the 
 marked crinkling of the lamarckiana leaves, a character which disap- 
 pears on pressing, the discontinuity would be even more obvious. 
 
 Interpretation of statistical results. — In reviewing the results of this 
 study one feature stands out prominently, which appears to the writer 
 to be of more fundamental significance than the mere determination of 
 the differences in superficial characters of the several species under 
 consideration. This feature will be apparent upon a comparison of 
 the coefficients of variability throughout. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 A 
 
 \ / 
 
 
 
 
 
 
 
 
 
 
 
 
 \Yv 
 
 
 
 
 
 
 
 
 
 
 ^ 
 
 ^ 
 
 / \ 
 
 'A 
 
 
 
 
 
 
 
 
 
 ^XA 
 
 &§ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 /// 
 
 /// 
 
 
 
 
 
 
 
 
 
 
 . 
 
 \ 
 
 / 
 
 
 b 
 
 k 
 
 
 85-87 8S-90 91-93 94-96 97-99 100-102 103-105 106-108 109-111 112-114 115-117 
 
 Fig. 9. Variation in the mean length of leaves in Onagra rubrinervis and O. la- 
 marckiana. Curve for O. rubrinervis shaded with lines rising to the right. Range, 
 O. rubrinervis, 86.28 to 107.15 mm. ; O. lamarckiana, 88.42 to 112.32 mm. 
 
 The variability of the mutant is significantly higher than that of 
 Onagra lamarckiana in four of the six characters considered. In the 
 number of lateral branches, one of the remaining two characters, the 
 excess in favor of . lamarckiana is far within the probable error, and 
 therefore has no significance. Only in regard to the leaf-length of 0. 
 rubrinervis is there a significantly higher variability in O. lamarckiana 
 than in its mutant, and this is a character in which the mutant pre- 
 sents no material difference from its parent, the difference between 
 the mean lengths of leaves in the two species being only i.i mm. in 
 excess of the sum of the probable errors. 
 
 Probably related to the same causes which determine this greater 
 variability of the mutants is the fact that there is a lower degree of 
 correlation between the length and breadth of the leaves of 0. rubri- 
 nervis than in 0. lamarckiana. Correlation tables of these two charac- 
 
MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 47 
 
 ters are shown in figs. 12 and 13. The lesser correlation of the for- 
 mer isapparent to the eye in the more scattered distribution of the 
 variates. The coefficients of correlation are as follows : Onagra la- 
 marckiana, 0.7916 ± 0.0090; Onagra rubrinervis, 0.6604 ± 0.0119. 
 This is simply another way of expressing the fact that the leaf-form of 
 O. rubrinervis is more variable than that of its parent-species. 
 
 If increased variability and decreased correlation be, as here indi- 
 cated, a general feature of those characters in which a mutant departs 
 markedly from the parental condition, how is it to be interpreted? It 
 is hinted by Weldon ('02) that these mutants are possibly the result of 
 selection and isolation. No one can deny that there has been selec- 
 tion and isolation in their culture, but it may be questioned whether 
 
 35-26 27-28 29-30 31-32 33-34 35-36 37-38 3'J— 10 11-42 
 
 Fig. 10. Variation in the mean width of leaves of Onagra rubrinervis and O. 
 lamarckiana. Curve for O. rubrinervis shaded with lines rising to the right. Kange : 
 O. rubrinervis, 25.93 to 32.53 mm.; O. lamarckiana, 33.71 to 41.64 mm. 
 
 these processes have been carried on to such an extent as to explain 
 the peculiar behavior of the mutants as compared with that of an 
 extreme variate. This question will not be satisfactorily answered 
 until a newly arisen mutant shall be subjected to various conditions 
 of cross and self fertilization, and the results are studied statistically. 
 It seems fair to assume that there has been a more discriminating 
 selection in the case of the several mutants than in O. lamarckiana. It 
 is therefore something of a surprise, if Weldon's suggestion be true, 
 to find the latter less variable in nearly every character studied. This 
 surprise is due to what may be a false assumption, namely, that selec- 
 tion necessarily operates to lessen variability. Is it not conceivable 
 
4 8 
 
 MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 that the selection of an extreme condition may result in increased 
 variability even after several generations ? 
 
 The supposed effects of self and cross fertilization can hardly be 
 assumed as of any consequence in this connection, for both species 
 have been self- fertilized during a number of generations. Just what 
 effect this has had upon their variability is not known. De Vries 
 does not think that cross-fertilization, even hybridization, has any 
 appreciable influence on the frequency of origin of a given mutation 
 in a mutating species. (De Vries, 1901, p. 211-212; 1903, p. 425-426.) 
 
 85-86 87-38 39-30 31-33 33-34 35-36 37-38 39-40 41-43 43-44 
 
 Fig. 11.— Variation in the mean ratio between width and length of leaves in 
 Onagra rubrinervis and O. lamarckiana. Curve for O. rubrinervis shaded 
 with lines rising to the right. Range : O. rubrinervis, 25.30 to 32.54 per cent.; O. 
 lamarckiana, 34.62 to 44.41 per cent. 
 
 Weismann (1892) maintained in his earlier works that all heredi- 
 tary variation is due to cross-fertilization, but more lately he has 
 withdrawn from this extreme position, and now considers amphimixis 
 " nicht alsdie eigentliche Wurzel der Variation selbst, denn diese kann 
 unmbglich auf einen blossen Austausch der Ide, sie muss vielmehr 
 auf einer Veranderung der Ide beruhen." He even looks upon cross- 
 fertilization as a process by which the range of variation is lessened, 
 and the variable forms which he thinks may arise at each " Neuanpas- 
 sung," are condensed into a species and rendered constant. (Weis- 
 mann, 1902, 2:235.) 
 
MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 49 
 
 Darwin performed a large number of experiments to test the 
 effect of self and cross fertilization, but his object was to determine the 
 advantages or disadvantages as measured by height, productivity, etc., 
 rather than the effect on variability. The number of specimens used by 
 him in each species studied was hardly sufficient to allow conclusions 
 of value regarding variability , but he infers that variations are primarily 
 
 
 
 
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 61 1 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Fig. 12. Correlation table of length and width of leaf in Onagra rubrinervis. 
 Width of leaf subject, length relative ; p = 0.6604 ± 0.0119. 
 
 due to differences of environmental conditions, and that cross-fertiliza- 
 tion tends to produce uniformity when these variations are slight, and 
 to increase the diversity when the variations are considerable. These 
 questions need thorough reinvestigation, and their discussion is futile 
 until such investigation is made. (Darwin, 1876, p. 452.) 
 
 If the Onagra mutants are not the result of selection and isola- 
 tion, acting within the field of applicability of known laws of 
 variation and heredity, but are really, as they have been called by 
 certain German writers, ' ' correlation-breakers, ' ' may not the increased 
 
50 
 
 MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 variability and decreased correlation be explained by the newness of 
 the species, which may be assumed to want that perfect adjustment to 
 their surroundings which an older species has acquired through the 
 cumulative effects of long-continued adaptive reactions, aided by 
 natural selection — i. e. , by the elimination of the unadapted ? This 
 
 
 
 
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 439 
 
 Fig. 13. Correlation table of length and width of leaf in Onagra 
 lamarckiana. Width of leaf subject, length relative ; p = 
 0.7916 ± 0.0090. 
 
 question also can be answered only by experimentation and observa- 
 tion continued through a series of }'ears. 
 
 It appears highly desirable that the statistical study of O. lamarck- 
 iana and its mutants should be continued during a series of years, 
 and that similar studies should be made of other mutating and mutant 
 species. The exact status of the mutants with regard to their varia- 
 bility and capacity for self-maintenance may be most conclusively 
 determined by the use of the methods entailed in such work. 
 
MUTANTS AND HYBRIDS OF THE OENOTHERAS. 51 
 
 GENERAL SUMMARY. 
 
 A brief resumi of the more salient features of the foregoing 
 paper will serve to emphasize the contributions made to the subject 
 during the course of the experimental work described. 
 
 A continuance of the effort to trace the nativity of 0. lamarckiana 
 has resulted in the discovery of records and specimens that appear 
 fairly conclusive that it is a true and independent species native to 
 America, although the matter is not decided with the finality afforded 
 by living specimens observed in the field. That this species has re- 
 mained unchanged during a period of a hundred and sixteen years is 
 established beyond doubt, and renders the matter of its nativity of com- 
 paratively little importance as to the standing of the mutants derived 
 from it. Perhaps no plant is known in which the purity of the strain 
 has been so critically examined as Lamarck's evening-primrose. Some 
 of the mutants are derivatives, most of which have become separated 
 from the parent-form by the acquisition of new characters, while others 
 are of a retrogressive character. Many of the new unit-characters dis- 
 played are not known in any of the other members of the natural group, 
 and thus may not be regarded as degressive acquisitions, or as due to 
 the retraction of a retrogressive step taken in the previous history of 
 the parent-species. 
 
 The material used as O. bie?inis in the investigation described in 
 Die Mutationstheorie proves to be a large-flowered species, which 
 has probably been known to many workers as 0. biennis grandiflora. 
 The uniformly unilateral character of the cross between this species and 
 0. lamarckiana (O. lamarckianaX O. biennis grandiflora) which was 
 an unitypic hybrid very similar to the poll en -parent, a result which led 
 De Vries to the conclusion that O. lamarckiana was a direct derivative 
 of the latter, probably by mutation. A re-examination of the evi- 
 dence, however, recalls that the cross with muricata was similarly 
 unilateral to the latter when used as a pollen-parent, and it is evident 
 that too much weight must not be given to the conclusion in question 
 until confirmatory evidence is obtained. 
 
 A consideration of the groupings of characters leads to the con- 
 clusion that O. grandiflora Ait., 0. lamarckiana Ser., and O.argiUi- 
 cola MacKenzie are much more closely related to one another by ana- 
 tomical characters and physiological traits than to biennis or any 
 other member of the genus. Furthermore, the ranges of the three 
 species mentioned appear to be more or less identical, or overlapping. 
 
 O. grandiflora Ait. had been seen by but few botanists in a living 
 condition in America, and its place in the American flora had become 
 
52 MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 a matter of much doubt, but field expeditions guided by descriptions 
 from Bartram's travels in 1776 resulted in a rediscovery of the species 
 in a spot not far from the original locality. This found, the confusion 
 which had arisen as to the separation of this species and 0. lamarck- 
 iana is cleared up. 
 
 The cultures of the evening-primroses made in the New York 
 Botanical Garden show that two or more elementary species are 
 grouped under some of the specific names as ordinarily accepted. 
 The failure to recognize these elements has resulted in the prevalent 
 opinions as to the wide range of fluctuating variability exhibited by 
 these plants. This is especially true of O. biennis , which has enjoyed 
 a reputation for variation not justifiable by systematic and orderly 
 observations made on plants grown under various conditions. One of 
 the forms, apparently typical of the true O. biennis now under culti- 
 vation, is in a mutative condition, but description of the derivatives 
 is reserved until they have completed a cycle of development. 
 
 O. cruciata as it exists at the present time in the cultures in the 
 New York Botanical Garden, and in the Botanical Garden of Amster- 
 dam is composed of three elementary species, which are fairly distinct 
 and without intergrading forms. A careful analysis of the occurrence 
 of the group leads to the inevitable conclusion that one of the forms 
 is in a mutating condition. 
 
 It is evident that in the investigations of native species for 
 possible mutating forms, the first and most important task to be 
 completed is that of the resolution of the forms selected into their 
 elementary constituents. Otherwise the seed obtained from plants 
 belonging to separate strains might well give an appearance of 
 variability not justifiable by the facts. Mutations, therefore, may be 
 taken as properly authenticated only when appearing in guarded 
 pedigree-cultures from seeds produced by a known individual, which 
 should be preserved for comparison. Discussions of mutants secured 
 under other conditions may serve an important purpose in offering 
 clues which will be useful in the selection of research material, but 
 can have no direct or actual value as a contribution to the subject. 
 
 The evening-primroses of eastern North America, from which 
 probably all of the forms cultivated in Europe are derived, may be 
 divided into two groups — a group including O. biennis, muricata, 
 octkesiana, and cruciata, in which the flowers are comparatively small, 
 and in which self-pollination is possible and frequent. The second 
 group, including species native to a region farther south, comprises 0. 
 argillicola, 0. grandiflora, and O. lamarckiana , in which the flowers are 
 large and the stamens are much shorter than the pistil, a condition 
 which with some accessory structures favors cross -pollination. 
 
MUTANTS AND HYBRIDS OF THE OENOTHERAS. 53 
 
 The hybrid O. lamarckiana X O. cruciata consisted of a single 
 type in which the characters of the pollen-parent were largely domi- 
 nant, although none of them were transmitted unchanged. A singu- 
 lar union of characters was shown in the relative lengths of the sta- 
 mens and pistils, a feature favoring cross and self fertilization. Some 
 of the flowers bore stamens shorter than the pistils, while in others 
 these organs were of equal length. Many of the modifications of the 
 predominating characters were dependent upon and were modified by 
 the alterations in the general stature of the plant. This hybrid corre- 
 sponds quite closely with the descriptions of 0. cruciata varza, a 
 supposed hybrid of 0. cruciata and 0. muricata given by De Vries. 
 
 The hybrid of 0. lamarckiana X 0. biennis was of a pleiotypic 
 character, being composed of four well-differentiated types with no inter- 
 grading forms. This result differs widely from that obtained by De 
 Vries in hybrids with 0. biennis grandiilora and 0. muricata as the 
 pollen-parent. In both of the last-named instances the result of the 
 cross was a unitypic hybrid closely unilateral to the pollen-parent. 
 In 0. lamarckiana X 0. biennis some characters of both parents were 
 transmitted to all of the four types of the hybrid, but the greater num- 
 ber of the active characters were those of the pollen-parent. 
 
 A remarkable predisposition or weakness to the attack of a 
 fungal parasite was exhibited by one of the types. The habit of ine- 
 quality of growth of the laminae resulting in crinkling, characteristic 
 of lamarckiana, was transmitted to all individuals of the four types of 
 the hybrid. The symmetrical form of the terminal rosettes of lamarck- 
 iana was transmitted unchanged to two of the types. No other char- 
 acters of the pistil-parent were inherited in their entirety, although a 
 number of qualities, approximating those of lamarckiana sufficiently to 
 be termed " dominant" by some authors, were seen. Three of the 
 types were goneoclinic to the pollen-parent, while the fourth (No. 2.24) 
 may be fairly taken as furnishing an example of an intermediate form, so 
 far as such estimations may be taken to be of value. The zigzag stem, 
 No. 2.27, is an example of the dominancy of a feature usually latent in 
 the pistil-parent, but exhibited by one of its mutants, rubrinervis. The 
 capacity for self-fertilization was dominant in three of the types, but 
 in the fourth a variability between cross and self fertilization was 
 indicated by the varying relative lengths of the stamens and pistils . It 
 is to be noted in this connection t'iat 0. brcvistylis, one of the mutants 
 of 0. lamarckiana Mas a pistil shoiierthan its stamens, and is therefore 
 adapted to self-fertilization, although no actual physiological predis- 
 position in the matter is found. 
 
54 MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 The recurrence of known mutants of 0. lamarckianawas observed. 
 O. mbrinervis appeared among the hybrid progeny of O. lamarck- 
 iana X 0. biennis, in which imperfect castration had been accomplished 
 and the parental strain appeared in the cultures. It appears therefore 
 that the mutant may be considered as a derivative of the one parent 
 purely, although the possibility is not excluded that it might have come 
 as a hybrid strain, as has been observed by De Vries in several crosses. 
 Better authenticated mutants were seen to arise from seeds obtained 
 from purely fertilized plants of O. lamarckiana grown in the botanical 
 garden at Amsterdam in igoi ; also from seeds of the same species 
 gathered in the New York Botanical Garden in 1903 after similar 
 precautions had been observed. 0. albida , 'scintillans , gigas, oblonga, 
 subovata, and O.elliptica were found among the mutants, offering evi- 
 dence of the indubitable occurrence of the mutants in purely fertilized 
 seeds, and also that O. lamarckiana has not reached the end of its 
 mutative period. Furthermore, seven forms not definitely assignable 
 to any of the known mutants of this parent were found, showing that 
 the range of the mutability of the species had been extended by 
 unknown causes, but which were included in an environment of 
 cultural conditions extremely favorable to rapid and vigorous growth 
 and development. It seems safe to assume, therefore, that mutation 
 is induced, or at least increased, by favorable, not adverse conditions, 
 though the duration of the experiments has not been sufficient to 
 permit an analysis of this phase of the subject. 
 
 0. gigas, the species most recently tested in the mutation -cultures 
 in New York, was seen to agree in stature and habit with the indi- 
 viduals grown in the original locality at Amsterdam. Only about 
 half of the individuals could be brought into bloom during the first 
 season, although it was extended to ten months by special methods of 
 culture — a fact in accord with the behavior of the plant in De Vries 's 
 cultures. The constancy of the species also extends to its variability 
 as to the forms of the leaves, an'attribute also previously recognized. 
 
 The results of the statistical studies show that some of the unit- 
 characters of the mutants have a much greater variability than the 
 corresponding features of the parent-form, and the greater amplitude 
 of the fluctuations is coupled with a decreased correlation. 
 
 Thus the coefficient of variability of the height of the shoot of 
 7ianella is 31.84 ± 3.16 percent, while that of lamarckiana is 5.37 db 
 0.44 per cent. The coefficient of variability for the number of branches 
 of mbrinervis is 15.0 zfc 1.7 per cent, and for the total length of the 
 branches is 43.7 =k 5.1 per cent, and for the ratio between width and 
 length of the leaves is 10.30 ± 0.20 per cent ; for the number of 
 
MUTANTS AND HYBRIDS OF THE OENOTHERAS. 55 
 
 branches of lamarckiana 15.7 ± 1.7 per cent, for the total length of the 
 branches 20.2 ± 2.2 per cent, and for the ratio between the width 
 and length of the leaves 9.53 =b 0.22 per cent. 
 
 The great variability of the mutants does not, however, seem to 
 result in any diminution of the gap that separates them from the 
 parent form, and no movement in this direction has been observed in 
 the long period which has elapsed since the new species came into 
 existence. Thus the heights of 0. nanella group themselves about the 
 mean value of 22.81 d= 1.02 cm., with a range from 7 to 35 cm., while 
 those of 0. lamarckiana group themselves about the mean of 88.68 dz 
 0.55 cm., with a range from 77 to 96 cm. The number of branches 
 per individual of lamarckiana ranged from n to 25, while that of 
 rubrinervis was 34 to 62. The actual discontinuity is somewhat more 
 fully expressed, however, by a comparison of the numerous features 
 which elude measurements to be seen in Plate XXII, in which leaves 
 from the specimens of lamarckiana and rubrinervis which approached 
 each other most nearly are shown. The actual discontinuity between 
 the retrograde variety, 0. nanella, and its parent in the leading feature 
 of height of stem is even more marked than the gap between the 
 various unit-characters of rubrinervis and lamarckiana. 
 
 Recurring again to the amplitude of the fluctuations in the 
 mutants, it is to be said that it is doubtless much greater in the leaf- 
 forms of the retrograde variety, 0. nanella, than in any which have been 
 measured, if the entire mass of foliage is taken into account, since in a 
 certain mid-stage in the rosette it is practically impossible to distinguish 
 it from the parent, although fully distinct as to form and size of the 
 leaves in the very young and very old rosettes. The very range of 
 variation may be in itself a character of the mutants, in which case no 
 reason could be given for its existence, any more than reasons could be 
 given for the existence of any other unit-character. Similar diffi- 
 culties might be encountered in seeking an explanation of the com- 
 parative amplitude of variation of any group of related forms. 
 
56 MUTANTS AND HYBRIDS OF THE OENOTHERAS. 
 
 BIBLIOGRAPHY. 
 
 Aiton, William. 
 
 1789. Hortus kewensis; or, a catalogue of the plants cultivated in the Royal 
 Botanic Garden at Kew. 2: 2. London, 1789. 
 
 Barton, William P. C. 
 
 1821. A flora of North America. 1 : 21-24, p'- 6. Philadelphia, 1821. 
 
 Bartram, William. 
 
 1793. Travels through North and South Carolina, Georgia, East and West 
 Florida, the Cherokee country, the extensive territories of the Mus- 
 cogulges or Creek Confederacy, and the country of the Chactaws. 
 Dublin, 1793 (reprinted from the Philadelphia edition of 1791). 
 
 Chapman, A. W. 
 
 1860. Flora of the Southern United States. New York, i860. 
 
 1884. Flora of the Southern United States. Second edition. New York, 
 
 1884. 
 1897. Flora of the Southern United States. Third edition. Cambridge, 
 Mass., 1897. 
 CorrEns, C. 
 
 1903. Ueber die dorninirenden Merkmale der Bastarde. Ber. d. Deut. Bot. 
 Gesell., 2 1 : 133, 1903. Also, Weitere Beitrage zur Kenntnis der 
 dorninirenden Merkmale und der Mosaikbildung der Bastarde. 
 Same journal, 21: 195, 1903. 
 
 Darwin, Charles. 
 
 1876. The effects of cross- and self-fertilization in the vegetable kingdom. 
 482 pages. London, 1876. 
 
 De Vries, Hugo. 
 
 1901. Die Mutationstheorie. Versuche und Beobachtungen iiber die Entsteh- 
 
 ung von Arten im Pflanzenreich. Erster Band. Die Entstehung 
 der Arten durch Mutation. 648 pages, 8 plates. Leipzig, 1901. 
 
 1902. Die Mutationstheorie. Versuche und Beobachtungen iiber die Entsteh- 
 
 ung der Arten im Pflanzenreich. Zweiter Band. Die Bastardi- 
 rung." Erste Lieferung. Pages 1-240. Leipzig, 1902. 
 
 1903. Die Mutationstheorie. Versuche und Beobachtungen iiber die Entsteh- 
 
 ung von Arten im Pflanzenreich. Zweiter Band. Elementare 
 Bastardlehre. Pages 241-751, 4 plates. Leipzig, 1903. 
 1905. Species and varieties: their origin by mutation. Edited by D. T. 
 MacDougal, xviii 847 pp. Chicago and London, 1905. 
 
 Dome-rain, H. H. 
 
 1862. Lamarck's evening primrose, Oenothera lamarckiana. The Floral 
 Magazine, 2: plate 78 (with accompanying text). 1862. 
 
 Galton, Francis. 
 
 1889. Natural inheritance, ix + 259 pp. London, 1889. 
 
 Hurst, C. C. 
 
 1 900. Notes on some experiments in hybridization and cross-breeding. The 
 Journal of the Royal Horticultural Society (London), 24: 90-126. 
 Ap., 1900. 
 
 Lemaire, Charles. 
 
 1862. Oenothera Lamarckiana. LTHustration Horticole, 9: plate 318 (with 
 accompanying text). 1862. 
 
.MUTANTS AND HYBRIDS OF THE OENOTHERAS. 57 
 
 MacDougal, D. T. 
 
 1903. Mutation in plants. The American Naturalist, 37: 737-770. N 1903. 
 [1 Ja., 1904]. 
 Peter, A. 
 
 1 884. Tabelle iiber die Procentsatze der bei den Bastarden der Piloselloiden 
 unterschiedenen Merkmale. Botanische Jahrbiicher fur Systematik, 
 Pflanzengesohichte und Pflanzengeographie, 5: 246-251. 1884. 
 Pursh, Frederick. 
 
 1814. Flora Americae Septentrionalis ; or, a systematic arrangement and 
 description of the plants of North America. 261. London, 1814. 
 
 Vaie, Anna Murray. 
 
 1905. Onagra grandiflora (Ait.), a species to be included in the North 
 American Flora. Torreya, 5 : 9-10, Ja. 1905. 
 
 Weldon, W. F. R. 
 
 1902. Professor de Vries on the origin of species. Biometrika, 1 : 365-374, 
 Ap., 1902. 
 
 Weismann, August. 
 
 1892. Aufsatze iiber Vererbung und verwandte biologische Fragen. 848 
 
 pages. Jena, 1892. 
 1902. Vortrage iiber Descendenztheorie gehalten an der Universitat zu 
 
 Freiburg im Breisgau. Zweiter Band. 462 pages, 3 plates. Jena, 
 
 1902. 
 
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