®i{e ^. ^, 1|m pkarg QH5GG V96 Coo w NORTH CAROLINA STATE UNIVERSITY LIBRARIES S02514745 S Date Due - A VOL. II. PL I. ANTIRRHINUM MAJUS LUTEUM RU BRO-STRIATUM With Bud Variation. Kartin.Hood StLarkinXith London.W.C VOL. II. PI. II. D. B C. A-C. -CHRYSANTHEMUM SEGETUM PLENUM D.— CHRYSANTHEMUM SEGETUM. Maran Hool&Larkir.Lifi. : .-udcT.V/',^. VOL. II. PL III. -^ O LATA. O. LAMARCKIANA. O. NANELLA MaiHu Hoad8cLarldnlitli.London.WC 1 VOL. If. PL IV. w # ^" HYOSCYAMUS PALLIDUS X NIGER. A. — H. niger. B.— H. pallidus. *trl|<. Hno^ %Lark:nI.ithI.Dndnn Wr. o z in > UJ z qE m D o z < Z u 6 < z < u q: < < -J CO < o < -J UJ tr X .ti < z < u < < _j O c *- O c J 2. < UJ z < _I z d d u z UJ q: ffi Q q: LJ > o o z UJ Q q: < o -I < Z u cr UJ Q- X UJ UJ X < UJ ■r o Z Ul O UJ q: H -I D U D m 2: o H t/) M > d X a: C/5 > (/) D U < Q- Q THE MUTATION THEORY EXPERIMENTS AND OBSERVATIONS ON THE ORIGIN OF SPECIES IN THE VEGETABLE KINGDOM BY HUGO DE VRIES PROFESSOR OF BOTANY AT AMSTERDAM TRANSLATED BY PROF. J. B. FARMER AND A. D. DARBISHIRE VOLUME II THE ORIGIN OF VARIETIES BY MUTATION WITH NUMEROUS ILLUSTRATIONS AND SIX COLORED PLATES CHICAGO THE OPEN COURT PUBLISHING COMPANY . LONDON AGENTS KEGAN I'AL L, TRENCH, TRUBNER & CO., LTD. 191O COPYRIGHT BY The Open Court Publishing Co. 1910 CONTENTS. PART I. THE ORIGIN OF HORTICULTURAL VARIF/FIES. PAGE I. The Significance of Horticultural Varieties in the Theory of Selection* 3 1. Variability in Garden Plants 3 2. The Doctrine of the Increase in Variability in One Direction Brought About by Selection 9 II. Latent and Semi-latent Characters i8 3. Evcrsporting Varieties 18 4. Half Races and Half Curves 26 5. Trifoliuni Pratense Quinqucfoliuni. An Evcrsporting Race 36 III. The different Modes of Origin of New Species 56 6. Horticultural and Systematic Varieties and Elementary Species 56 7. Progressive, Retrogressive and Degressive Formation of Species 65 IV. The Sudden Appearance and the Constancy of new Varieties 76 8. Examples of Constant Races 76 9. Sterile Varieties 8S 10. Instances of Races which Have Arisen Suddenly in Nature 95 11. Horticultural Varieties which Have Arisen Suddenly. 99 V. Atavism 104 12. Atavism by Seeds and Buds 104 13. Vilmorin's Suggestion as to the Origin of Striped Flowers 113 14. Antirrhinum Majus Striatum 120 ■ L ^v iv Contents. PAGE 15. Hesperis Matronalis 136 16. Clarkia Pulchella 144 17. Plantago Lanceolata Ramosa 148 VI. Experimental Observation of the Origin of Varieties. . 161 18. The Origin of Chrysanthemum Segetum Plenum .... 161 19. Double Flowers and Flowerheads 194 20. The Origin of Linaria Vulgaris Peloria 201 21. Heritable Pelorias 220 VII. NON-ISOLABLE RaCES .♦ 22/ 22. Trifolium Incarnatum Quadrifolium 227 23. Ranunculus Bulbosus Semi-Plenus 243 24. Variegated Leaves 265 25. Alternating Annual and Biennial Habit 291 VIII. Nutrition and Selection of Semi-Latent Characters. 307 26. Increased Nutrition Favors the Development of the Anomaly 307 27. The Influence of External Conditions and of Manur- ing 315 28. The Periodicity of Semi-Latent Characters s^3 2g. The Choice of Seeds in Selection 332 PART II. THE ORIGIN OF EVERSPORTING VARIETIES. I. Tricotylous Races 343 1. The Occurrence of Tricotyls as Half Races and Inter- mediate Races 343 2. Tricotyls, Hemi-Tricotyls and Tetracotyls 356 3. The Influence of Tricotyly on the Arrangement of Leaves 365 4. Tricotylous Half Races 379 5. Tricotylous Intermediate Races Do Not Arise by Se- lection 393 6. The Isolation of Tricotylous Intermediate Races .... 417 7. Partial Variability of Tricotyly 444 8. The Influence of External Conditions on Tricotyly . . 450 II. Syncotylous Races 457 9. Hemi-Syncotyly, Syncotyly, Amphi-Syncotyly 457 10. Helianthus Annuus Syncotyleus 466 11. Improvement of a Hemi-Syncotylous Race 476 12. Atavistic Races ■■ 481 Contents. V PAGE 13. The IiWlMciice of External Conditions on Hereditary Values 4^5 III. The Incgnstan'cy of Fasciated Races 4.S8 14. The Inheritance of Fasciations 488 15. Half Races with Heritable Fasciation 502 16. Eversporting Varieties with Heritable Fasciation ... 508 17. The Signitkance of the Atavists 514 IV. IlERiTAnLE Spiral Torsions 5-^7 18. Spiral Disposition of the Leaves 527 19. Rare Spiral Torsions 537 20. Spirally Twisted Races 54.^ 21. The SignilicaiKe of the Atavists 554 PART HI. THE RELATIONS OF THE MUTATION TiiEORV TO OTHER BRANCHES OF IXOriRY. I. The Conception of Species According to the Theory OF Mutation 5^7 1. Systematic Biology and the Theory of Mutation 567 2. Progressive, Retrogressive and Degressive Mutations. 569 3. The Theoretical Distinction Between Species and Va- rieties 578 4. The Practical Conception of Species 589 5. The Parallel Between Systematic and Sexual Relation- ship 592 II. The Range of Validity of the Doctrine of Mitation. . 599 6. The Significance of the Available Evidence 599 7. The Explanation of Adaptations (106 8. Vegetative Mutations 614 III. The Material Vehicles of the Hereditary Characters 631 9. Darwin's Pangenesis 631 10. Intracellular Pangenesis 639 11. The Pangenes as Bearers of the Hereditary Char- acters 643 IV. Geological Periods of Mutation 651 12. I he Periodicity of Progressive Mutations 651 13. Iterative I'ormation of Species 6()i 14. The Biochronic Equation 663 Index 675 LITERATURE. LIST OF THE AUTHOR'S PAPERS BEARING 0\ THE THFCORY OF MUTATION. (Sec the List at the Beginning of the First Volume.) a. Tntracclliilar Pangenesis. Translated from the German by Prof. C. Stuart Gager. Chicago: The Open Court Puh- hshing Co., 1910. b. Fhictuating VariabiHty and MutabiHty. Eine zwcigipfelige X'ariationscurvc. Roux' Archiv fur Entwicklungsmechanik clcr Organisnieii, 1895, II, Ileft I. — .\rchiv. Neerl., 1895. .Sur les courbcs Galtoniennes dcs monstruosites. Bull, sclent. France et lUl- gique, 1898, T. X.WII, p. 395. Over het omkeeren van halve Galton-curvcn. Botanisch Jaarboek, Gent, 189S. X. p. 27. Ucber Curvenselection bci Chrysanthemum segetum. Ber. d. d. bot. Ges., 1899, I'.d. XVII. Heft 3. Do zaadkweekcryen te Erfurt. Het Ncderlandsch Tuinbouwblad, 1891, p. 327. (iladiolus nanceianus, ibid., \TII, Jan. 1892. — Tulipa Greigi, ibid.. May 189-'. — Caladium, ibid., July 1892. — Caladium's van Alfred Bleu, ibid., July 1892. — Dubbele Seringen, ibid., Sept. 1892. — Grootbloemige Canna's I and II, ibid., Dec. 1892. — Amaryllis, ibid., IX, Sept. 1893. c. Spiral Torsions. Ueber die Erblichkcit der Zwangsdrehung. Ber. d. d. bot. Ges., 1889, VIII, p. 7. Eenige gevallen van Klemdraai by de Meekrap. Bot. Jaarboek, Gent, 1801. III. p. 74- Monographic der Zwangsdrehungen. Jalirb. f. wiss. Bot., 1891, XXTTT, pp. 13- 206. Plates II-Xl. Bydra.c:en tot de leer van den Klemdraai. Bot. Jaarboek, 1892, I\', \^. 145. Eiiic Mcthodc, Zwangsdrehungen aufzusuchen. Ber. d. d. bot. ("ics., 1804. Bd. XII. Heft 2. On Biastrcpsis in Its Relation to Cultivation. Annals of Botany, 1899, XIII, P- 395- d. Fasciations and Other Anomalies. Sur un spadicc tubuleux du Peperomia maculosa. .\rchiv. Neerl., 1891, T. XXI \-. p. 258. viii Literature. Over de erfelykheid der fasciatien. Bot. Jaarboek, Gent, 1894, VI, p. 72. Over de erfelykheid van synfisen. Bot. Jaarboek, 1895, \'II, p. 129. Erfelyke monstrositeiten in den ruilhandel der Bot. Tuinen. Bot. Jaarboek, 1897, IX, p. 66. Een epidemie van vergroeningen. Bot. Jaarboek, 1896, \'III, p. 66. Sur la culture des monstruosites. Cps. rs. de TAcad. des Sc, Paris, 1899. Sur la culture des fasciations des especes annuelles et bisannuelles. Revue gene- rale de botanique, 1899, T. XI, p. 136. Ueber die Abhangigkeit der Fasciation vom .Mter bei zweijahrigen Pflanzen. Bot. Centralblatt, 1899, LXXVII. Ueber die Periodicitat partieller \'ariationen. Ber. d. d. bot. Ges., 1899, XVTI, Heft 2, p. 45. Over het periodisch optreden van anomalien op monstreuze planten. Bot. Jaar- boek, 1899, XI, p. 46. Sur !a periodicite des anomalies dans les plantes monstrueuses. .\rcbiv X^eerl., Serie II, T. III. Over verdubbeling van Phyllopodien. Bot. Jaarboek, 18^93, V. p. 108. Ueber tricotyle Rassen. Ber. d. d. bot. Ges., 1902, Bd. XX, Heft 2. c. Unit-Characters. Adam's Gouden regen (Cytisus Adami). Album der Natuur, 1894. Hjbridizing of Monstrosities. Journ. Roy. Hortic. Soc, 1899. Sur la fecondation liybride de I'albumen. Cps. rs. de T.\cad. de Paris. 1899 and Ref. Biol. Centralbl., 1900. Sur la fecondation hybride de I'endosperme chez le Mais. Revue generale de botanique, 1900, T. XII, p. 129. Sur la loi de disjonction des liybrides. Cps. rs. de I'Acad. de Paris, 1900. Das Snaltungsgesetz der Bastarde. Ber. d. d. bot. Ges., 1900, Bd. XVIII, Heft" 3- Ueber erbungleicbe Kreuzungen. Ber. d. d. bot. Ges., 1900. Bd. XVTTT. Heft 9- Sur les unites des caracteres specifiques. Revue generale de botanique, 1900, T. XII, p. 257- The Law of Separation of Characters in Crosses. Journ. Roy. Hortic. Soc, 190 1, XXV, Part 3. On Artificial Atavism. Proceed. Americ. Hortic. Soc, 1902. La loi de Mexdel et les caracteres constants des hybrides. Cps. rs. de I'Acad. de Paris, 1903. Anwendung der Mutationslehre auf die Bastardirungsgcsetze. Ber. d. <1. bot. Ges., 1903, Bd. XXI, p. 45. Befruchtung und Bastardirung; ein X'ortrag, 1903. Leipsic, Veit & Co. PART I. THE ORIGIN OF HORTICULTURAL VARIETIES. I. THE SIGNIFICANCE OF HORTICULTURAL VARIETIES IN THE THEORY OF SELECTION. § I. VARIABILITY IN GARDEN PLANTS. Darwin based his theory of selection, in great part, on the well-known horticultural principle that new varie- ties are obtained by seeking for small deviations with subsequent isolation and selection. Variations which at their first appearance almost escape observation can be worked up by the skill of the gardener; in doing so varia- bility is seen to increase, and in favorable cases, very rapidly. In this way a new form arises, which answers the purposes and rewards the labors of the breeder. We have all heard how beautiful double varieties have resulted from the appearance of single flowers in which only one stamen and this often only partially was transformed into a petal. In the first volume we dealt with this practice more than once, and pointed out how liable it is to give rise to misunderstanding when applied to the elucidation of the problem of specific differentiation (Vol. I, § 23, pp. 176-185). The object of the present Part is to collate the relevant data and to show what light they throw on this all-important problem. Of course we can only go .^o far as the incomplete and scanty character of the material will allow. 4 The Significance of Horticultural Varieties. The development of the statistical treatment of varia- tion which took place after Darwin's time, allows of an altogether different conception of the phenomena than was possible some fifty years ago. It was shown that the fluctuation of characters is due to their development to a greater or less degree. But the character in ques- tion does not vary in any other than these two directions. The variation is linear (Vol. I, p. 118). It increases or diminishes but creates nothing new. New characters can arise, so to speak, alongside of it, but they arise independently of the fluctuation of the old ones. This applies to the case before us. The variations which the horticulturist looks for and then works up are not variations of the old characters ; such may indeed give rise, by selection, to improved races, but not to new types (Vol. I, p. 82). The required deviations are anomalies, as in the example of the origin of double flowers, just cited. When such an anomaly arises we may be sure that the new character already existed in the internal organization of the plant. Where it springs from and how it arose is a matter of indifference to the breeder : he has got it and can work it up. In other words : "The first condition necessary for raising a nov- elty is to possess it" (Vol. I. p. 185). , In this connection two cases are distinguished in prac- tice according as one is dealing with apparently invariable forms, or with forms exhibiting a high degree of fluctu- ating variability. In the former case all that has to be done is to isolate the novelty and to free it of possible impurities introduced by crossing. If this can be done without much difficulty the variety is perfect and con- stant from the beginning and needs only a few vears of multiplication before it can be put on the market (Vol. Variability in Garden Plants. 5 I, pp. 77-80). Many white flowered varieties afford good examples of this kind of novelty. But it is very different with the second case. A nov- elty which exhibits fluctuating variability in a high de- gree seldom makes its first appearance in a full state of development. As a rule it is very slightly developed at first. The novelty is betrayed, as the expression is, by a quite small trace or indication. From the scientific standpoint we have to regard this as a /////n^^-variant, i. e., as an extreme variant in the minus direction of the new character (Vol. I, p. 51). And it is plain that the seeds of such a variant of the new variety will, when sown in the garden, soon give the mean value of the character in Cjuestion. This process is, as we can easily see, fundamentally a phenomenon of regression (Vol. I, Figs. 18 and 19, pp. 72> and 84) ; but to the breeder it is a progressive change, and by no means an inconsiderable one, since on it the success of his operations largely depends. This apparent paradox, however, has been a great obstacle to the under- standing of these phenomena. But, to us, it explains in a very clear way the initial and rapid increase in varia- bility ; for it is obvious that an approximation to the mean value will take place much more easily and rapidly than a departure from it. The breeder can now either rest content with this ''regressive advance" ; or he can endeavor to raise the new form above its mean value by choosing plus-variants as seed-parents. But in the latter case the value of the new form remains dependent on the continuance of se- lection (Vol. I, p. 80). Notes dealing with this process of breeding are not rare in horticultural literature, but they are generally 6 The Significance of Horticultural Varieties. sliort and lack precision being much inferior in this re- spect to the accurate accounts that are given of artificial crossings. I shall bring together the most important facts that I have been able to find, in the following sec- tion (§2). In order to penetrate more deeply into these phenom- ena I have endeavored to apply this method to a series of cases. W\\\\ the help of control experiments, and by kee])i ng detailed records, I succeeded in finding out how such novelties usually develop themselves. Just as hap- pens in practice, I was successful with some cases but not witli others. And the correspondence between my results and the experience of breeders seems to me to be so com- plete that my experiments may simply be taken as in- stances of the method under discussion. I propose to distinguish, therefore, between highly variable and only slightly variable novelties. The lat- ter are generally assumed to be instances of single var- iations which arise suddenly. In the case of these I shall, therefore, only have to discuss their origin and the question of their constancy. (Chapter IV of this Part.) Much more important from the critical standpoint are the ^'arieties with a high degree of fluctuating variability, i. e., those very cases which passed for instances of the origin of new characters by artificial selection (Chapters II and VIII). As examples of this I refer to variegated leaves and to double and striped flowers. If we now compare, from a theoretical standpoint, this high variability with the normal examples which we dealt with before (Vol. I, pp. 47-52 etc.) we shall see tliat the two are not exactly the same. In variegated leaves the yellow alternates with the green, in semi-double flowers the petaloid stamens alternate with normal ones Variability in Garden Plants. 7 and so forth. Therefore we are not here deahng with the variable development of a single quality, but with the simultaneous operation, or rather with the conflict, of two qualities. For in proportion as the one or the other of them prevails the plant will be more or less variegated, double and so forth. One of the characters is the old, normal one, pertaining to the original species. The other is the new, abnormal one pertaining to the variety in pro- cess of formation, in fact the anomaly. And the conflict of these two antagonistic types affords at least a partial explanation of this extraordinary variability. The green color itself is only very slightly variable, and the pure yellow or golden varieties, in which the green is entirely absent, are equally uniform {varictatcs aureae, for example Pyrcthruin Parthcniiun aurcuni). Of ''double" forms there are two types; the ordinary highly variable more or less double sorts, and on the other hand the sterile varieties which exhibit this peculiar- ity to its full extent in all their flowers (see Ranunculus acris petaloniana, Vol. I, Fig. 40, p. 194). In this case the types with a high degree of fluctuating variability might be considered as a connecting link between two almost invariable forms, the normal single and the pet- alomanous types. If we regard this principle as an explanation of the case in point we arrive at the conception of intermediate forms zvith tzvo antagonistic characters striving for the mastery, and possessing a remarkably high degree of vari- ability as a result of this struggle. The extent of this variability differs from case to case : in the most extreme examples whole organs or even whole individuals can come exactly to resemble one of the types between Avhich they oscillate. Pure green or, on the other hand, pure 8 The Significance of H oriicnltural Varieties. yellow or even white leaves or seedlings are by no means rare in variegated varieties. But the resemblance is only superficial. The green minus variant of the variegated type does not belong to the original species, nor the yel- low plus variant to the golden variety; as may often be seen by sowing the seeds of such extreme types. I propose to call such varieties intermediate races, and if neither of the two antagonistic characters preponder- ates too much over the other, balanced races or ever- sporting varieties^ (see § 3). If we attempt to make a statistical study and graph- ical description of the variability in such intermediate forms we must obviously not expect such simple and straightforward curves as those which describe the var- iability of normal characters (Vol. I, p. 48). In prin- ciple we may expect to obtain figures which simultane- ously exhibit. the two magnitudes — that is to say com- pound curves such as have been studied by Ludwig^ Bateson, Pearson, Davenport and others. It is evi- dent that they will present very different forms according to the mutual proportion of the two characters (see be- low §§ 3-5). At the same time it is clear that in such cases selection may lead to special results which will often be due to the impossibility of transgressing the characters of the two limiting types (see § 5 and Fig. 3). The two following generalizations may be derived from the facts we have been discussing. 1. Some horticultural varieties ozve their existence to a single new character. These are usually not more vari- able than the original species and as a rule just as con- stant from seed. Very frequently the novelty consists in the loss or latency of a character of the parent spe- * See Species and Varieties, Their Origin by Mutation, p. 309. Increase in Variability in One Direction. 9 cies. In cases where the origin of such a novelty is satis- factorily known it always happened suddenly. For the combination of several characters in the same variety see Vol. I, p. 197. 2. On the oilier hand some horticultural varieties are compound types zvhich owe their existence to the associa- tion of two {or more) antagonistic characters. The two characters tend to exclude one another more or less com- pletely and struggle for the upper hand ; from this there results a very high degree of variability in their mani- festation (as in variegation, stripes, doubleness and so forth). These forms usually first appear as minus var- iants, i. e., with a slight degree of development of the abnormality in which condition they are sought for and isolated and subsequently improved by selection. The artificial production, therefore, of such a form is not a sudden one but a process of gradual improvement. Their first origin however remains unknown. §2. THE DOCTRINE OF THE INCREASE IN VARIABILITY IN ONE DIRECTION BROUGHT ABOUT BY SELECTION. One of the most attractive parts of the doctrine of selection is that according to which variability may be increased by selection. Many observations, especially in horticulture, seem to support this view ; which, if it were true would afford an almost irrefutable argument in favor of the prevailing belief in the omnipotence of natural selection fVol. I, p. 119). Varieties are said to be incipient species. Bv selecting the individuals which deviate most from the type of the species it is believed to be possible to attain first to varia- tions and then to varieties. To these is ascribed the 10 The Significance of Horticultural Varieties. tendency to become fixed and so to 1)ecome races : in the same way these races would later be transformed into species. This is the generally accepted view. This view is based, as I attempted to show in the first part of the first volume, on an unwarranted extension of Darwin's theory of selection. Darwin argued from the results obtained in horticulture; but these, at least as described in the works of the best authorities, do not seem to me to justify such an extension. According to the prevailing view, man has the power to produce any desired amelioration in any species ready to hand. All characters vary and all that need be done would be to isolate the extreme variants and to breed further from them. The process takes some time of course but in many species the experiment is already lasting about half a century. But the advances which have been made, and which are of the very greatest prac- tical importance, do not tally with this assumption. On the contrary we learn from them that for much that has been attained much has proved unattainable. The comparative studies of systematists show us that almost eveiywhere there exist unperceptible transitional stages between the smallest differences and perfectly dis- tinct species. This forms a weighty argument for, hut no proof of, the prevalent view. For we have to reckon here with transgressive variability (Vol. I, Part II, § 25, p. 430), which tends to blur the boundaries of related groups. I have indicated in the foregoing section (§1) the principles on which in my opinion an elucidation of the process in question must be based. If a small anomaly is found in a wild or cultivated species, and a new and constant form is raised from this bv selection, the whole Increase in Variability in One Direction. 11 sequence of events may have the appearance of having been gradually brought about by the free will of the ex- perimenter; whereas as a matter of fact the result was attained mainly by good luck. If we look through the literature of horticulture we shall soon see that this illusion has not taken in the really efficient breeder. He knows perfectly well that neither the beginning nor the end of such an experiment is under his control. It is only between these two limits that everything depends on his skill. The first indication of an anomaly in a pure species appears by chance; and it is a well-known rule in horti- culture that the breeder should always be on the lookout for such chance occurrences. It does not matter how small the deviation is so long as it is an anomaly (p. 4). When such a deviation has once been found it lies with the breeder to perfect it and bring it to its full develop- ment. But the ever present, more or less considerable, fluctuating variations of normal characters are of no use for this purpose ; by their means many varieties may be made better and prettier, but they can give rise to nothing really new. The best horticultural authorities are in agreement on this point. Carriere for example says : ''Lliorticul- teur ne pent faire naitre les varietes/' and in greater de- tail in reference to double flowers : "Le point de depart des fleitrs doubles est en dehors de notre puissance conime de nos calcnls; nous ne poiivons rien, on a pen pres rien, sur le fait initiatif; nous ne pouvons que le saisir lorsquil se presente; nous ne pouvons pas le provoqiier; c'est tin effet, dont la cause nous est inconnue.^^^ A well-known ^ E. A. Carriere, Production cf fixation dcs varictcs dans les vegetaux, 1865, p. 64 and p. 15. 12 The Significance of HorticitUural Varieties. English breeder, William Paul, says:^ ''He who is seeking to improve any class of plants, should watch narrowly and seize with alacrity any deviation from the fixed character However unpromising in appearance at the outset, he knows not what issues may lie concealed in a variation." Salter also said that the greatest diffi- culty lies in finding a small initial deviation ; but when this has once been found all the rest lies within our power, however small the variation mav be. And Darwin, who cites this,^ always emphasized its great importance when- ever he had occasion to refer to it. In other words, which we have already often quoted : The main condition necessary to produce a novelty is to be in possession of its first step. And yet as is well known the attempt Is not by any means alwavs successful. Sometimes the variation dis- appears without leaving a trace behind ; in which case of course all further efforts to deal with it are in vain. Unfixable deviations of this kind are, according to my experience, the occasional manifestation of latent characters. What the breeder wants to find are those cases in which the chance anomaly has already become a heritable although hidden race. \i this has happened the anomaly will, in the first place, easily manifest itself, if the conditions of life are not quite unfavorable and in the second can rapidly be developed to the level of a good horticultural variety. So far as the available data enable us to judge, breed- ing experiments of this kind always follow the same course. Hosts of examples can be found. Extensive * Confribufions to HorticiiUural Literature, 1892. Nature, Vol. 46, p. 583. "^Variations of Animals and Plants, II, p. 249. See also Part I, p. 267 et seq. Increase in Variability m One Direction. 13 sowings repeated year after year avail nothing if chance does not play its part. Anemone coronaria plena arose in the nurseries of Williamson in England as a single plant, which exhibited a slight petaloid broadening of one of the stamens.^ From the seed of this specimen a race has been started, the flowers of which became fully double in the course of a few generations. The double varieties of roses. Campanulas, and many other garden plants have arisen in the same way. I saw a bed of mignonette {Reseda odorata) some of which had double spikes, in a nursery at Erfurt. The spikes were fasciated, the flowers were broader and the whole plant fuller, more compact and handsomer than the species. The plants of this bed had been produced from the seed of two fasciated specimens which had accidentally appeared the year be- fore. The normal were weeded out and the abnormal saved and allowed to set seed with a view to putting a new variety on the market. In cases such as this, selection has a twofold object. In the first place the variety must be isolated, — that is purged of the impurities resulting from free crossing. It must also be actually improved by selection. The first indications of doubling are, as we have seen, single super- numerary petals, or in composites single supernumerary ray florets on the disc ; the first indication of a new color is often very pale ; slit leaves and petals are indicated by quite small invaginations, combs (Vol. I, p. 191) appear as small outgrowths. All these qualities had to be im- proved by selection up to the level of the mean of the character and then even perhaps beyond. An improvement of this kind, when once started, is effected not only rapidly but with increasing swiftness. Darwin, Inc. cif., TT, p. 269. 14 The Significance of Horticultural Varieties. Hence the illusion of an increase in Tariahility. The ex- planation is simply this that, as shown in the preceding section (§ 1), we first find a minus variant of the new character, which, in accordance with the law of regres- sion, approaches not tlie cliaracter of the old species but the mean value of the new variety, as soon as it is iso- lated. And this takes place easily and swiftly since the new variety in this case behaves like an improved race on the cessation of selection or under reversed selection (Vol 1, ^ 14, p. 122). The progress made by this improvement and through the purification from the results of crossing is often so rapid that it can be expressed in terms of a geometrical series. This generalization does not attain to the rank of a law, but my meaning will become clearer by citing an example. Hofmeister sowed the seeds of plants of Papaver soniniferuni polycephaluni} which he had found growing between normal examples of the species. By selecting the fruits which were richest in supernumerarv carpels, but without isolation, he effected the following- increase in the number of abnormal examples in the suc- ceeding generations : Year: 1863 1864 1865 1866 1867 Percentage of abnormal plants: 6% 17% 21% 69% 97% Geometric series: 8 16 32 64 (100) These figures, as we see, do not differ considerably from a geometric series. I do not lay much stress on the fact, but I have myself more than once obtained similar series of figures in breeding experiments. The limits that can be reached are as little under the control of the l^'eeder as the starting-points that had to "^ All gem cine Morphologic, p. 565. See our Fig. 27 on p. 13S of the first volume; also Hoffmann, Bof. Zcifg., 1881, p. 397, and Ver- LOT, Production ct fixation dcs varictcs, p. 88. Increase in Variability in One Direction. 15 be waited for. This is most forcibly brought out by the fact that numerous horticuhural varieties are still at exactly the same level as they were at the time of their introduction. The most vigorous selection continued over long periods of time has only rarely succeeded in effecting a further improvement in the same direction. We are familiar with hosts of variegated plants, but A urea vari- eties are very rare. Flowers with petalomany are sterile, and the plants can only be multiplied by vegetative meth- ods. But it is quite clear that this difficulty is by no means the cause of their rarity. Amongst composites we occa- sionally find isolated heads without tongue florets, but how small is the number of discoid varieties. I once found an example of Coreopsis tinctoria in my cultures, which exhibited only some spare ray florets, but although I isolated the plant, the abnormality did not reappear from its seed. CatacoroUa (an outward doubling of the corolla so as to form lappets) occurs almost only as a commercial race in Gloxinia superha. Fistulous compo- sites are rare; there is room on the market for monoph- yllous and laciniate varieties of many species, if only we could make them. But so long as chance does not put them into our hands, all our labor is in vain. Nevertheless, all plants no doubt possess numerous latent characters. Any culture carried out on a sufficiently large scale, or continued for several years, will give con- vincing proof. In fact it is often very difficult to keep races free from anomalies. Agrosteninia Githago, Raph- anus Rhaphanistrmn and many other species contain an almost inconceivable number. Amongst garden plants desirable novelties must obviously be rare now because they must have been already found and put on the market; 16 The Significance of Horticultural Varieties. useless and indifferent anomalies are common enough, especially in extensive cultures. When a new horticultural variety has been isolated and "fixed," that is to say improved and rid of impuri- ties by a few years' cultivation no considerable further improvement in the same direction is to be expected. Only two ways of progress are still at hand. These are to wait for the chance appearance of a new abnormality in the same strain, or to combine the new character with others by crossing. The former method is dependent on chance and therefore often unsatisfactorv. The sec- end is almost sure to succeed, and thus it is always chosen. Each new character is immediately transferred to nu- merous other varieties of the species and a corresponding number of novelties obtained in this way. Thus Le- MOiNE transferred the double flowers of a single douljle lilac to several dozen varieties, and the Cactus Dahlia was, very soon after its introduction, obtainable in almost every shade of color and doubleness. Ordinarily this process is described in the opposite way — that is to say, it is claimed that the properties of the old varieties are transferred to the new type. In this way there appears a vast series of varieties forming a new group co-exten- sive with the older forms of the original species. Thus a single new character can double the number of varieties. Petunias, Zinnias and Fuchsias are familiar examples of the application of this method in former times. Gladiolus, Begonia and many others of its recent application. The ostrich-feather Chrysanthemum (with ciliated petals) arose about thirty years ago in a single varietv (Alph. Hardy), but can now be obtained in large numbers of forms. The doctrine of the onesided increase of variability Increase in Variability in One Direction. 17 by selection is based, therefore, as far as the availal)le data enable us to decide, on the existence of strains with heritable but hitherto latent characters. Such races are highly variable, and their existence is betrayed when they first are met with, by trifling anomalies which however can easily be worked up by selection. As a result they rapidly deport from the type of the species but only be- cause they approach their nezv type : and as soon as this has been reached by isolation or exceeded by selection it is just as difficult to effect any further improvement as in ordinary improved races. These varieties cannot be evoked at will; we have to wait till they chance to ap- pear. Nor when once fully developed can we improve them further. Nothing but chance — that is to say some unknown factor — can as yet overstep these tivo limits] selection can effect no more than the most transparent illusion of any thing approaching complete control. 11. LATENT AND SEMI-LATENT CHARACTERS. § 3. EVERSPORTING VARIETIES. Before I proceed to deal with the results which have been obtained, in horticulture, with these highly variable varieties it is desirable, in order to clear up the concep- tions involved, to fix our attention on the various stages which may be interpolated between a species and a simple and constant variety derived from it. We will start from the fact that the chance appear- ance of an anomaly by no means always opens up the way to the acquisition of a novelty. One example out of many will suffice. Pitchers (Figs. 16, 106, and 109, Vol. L pp. 61, 470, 484) are usually found as quite rare and isolated variations,^ but in some species of plants, such as Magnolia and Tilia, tolerably frequently. But a vari- et}^ as rich in these structures as, for example, TrifoUum pratcnsc quinqucfoUnin is in 4- and 5-merous leaves does not exist, although it would obviously attract attention and pay the trouble of breeding experiments.- This shows that an anomaly discovered by chance may be the expression of a latent character which cannot be brought to its full state of development. Besides this ^ Over de erfelykheid van synfisen, Kruidkundig Jaarhoek, Gent, 1895, p. 129. ^A variety of Piciis rcUgiosa, with all its leaves changed into pitchers, has since been introduced into Europe by Mr. Prain^ the Director of Kew-gardens. (Note of 1910.) Eversportincj Varieties. 19 extreme but very common mode of appearance two other cases are possible, according to my experience : 1. When the seeds of an abnormal individual are sown the anomaly is repeated from time to time in a few or more individuals, remaining rare or only appearing in a feeble state of development. Selection may improve it, but only to a very inconsiderable extent. 2. Under favorable circumstances the anomaly may increase rapidly both in the degree of its development and in the number of individuals which present it. A so-called constant race is formed in the course of a few genera- tions. It is subject to a high degree of fluctuating vari- ability in respect to the character in question and is largely dependent on cultivation. I propose to term the first type of characters senii- latent and to distinguish amongst latent characters be- tween the genuine completely latent ones and those which occasionally come to light or the semi-latent ones. This term refers to the behavior of the character in the race as a whole ; a semi-latent character may remain latent in many individuals and organs and be active in others. A true latent character on the other hand only very rarely becomes active. If we study these three cases statistically, trying to plot the variation of the anomaly in the form of a curve (p. 8) we generally obtain the follow^ing results: First case. The genuine latent characters appear so rarely that they do not afford sufficient material for a curve. Second case. Semi-latent characters must be studied in combination Vv'ith their antagonistic active characters, and are expressed by half curves (Fig. 1, p. 28), from which a two-sided curve mav be derived bv selection 20 Latent a)id Scnii-Latcnt Characters. (Fig. 2, p. 34), the apex of wliich however does not become very distant from that of the half-curve. Third case. The characters are first expressible by half curves because they are uiiuus variants; but after isolation the curve very soon becomes a two-sided one with a new apex. The new variety reaches its full de- velopment and is maintained without further selection. A schematic presentation of the conflict between two antagonistic characters is given below : The normal character is: The anomaly is: I. active latent. II, active semi-latent. III. An equilibrium is maintained. IV. semi-latent active. V. latent active. I do not of course suppose that no further cases are possible, that there may not for example be various stages of semilatency. The facts at our disposal do not admit of any such definite statement. On the other hand it must be stated that the scheme I have gi\'en covers the cases ■which have been so far collected ; we shall soon see large numbers of examples of the main cases, whereas of others I have not yet found any. In the above table I obviously represents the normal, original species, and V the slightly variable and constant variety derived from it. The three other numbers repre- sent the three intermediate forms of which the two first (II and III) correspond to actuality whilst the fourth merely follows from the scheme. I am rather doubtful as to its occurrence in nature. It is necessary to introduce special names for the first two intermediate forms. I shall therefore call them both intermediate races, one of which — No. II — I shall Evcrs porting Varieties. 21 call a half race, and No. Ill a middle race. The word race is obviously not used here in the sense of an im- proved rare (Vol. I, p. 80) but simply means a heritable form. Instead of middle race I shall usually employ the more convenient term of eversporting variety.^ Two examples to which reference has already been made will serve to illuminate the foregoing discussion. EXAMPLES. VARIEGATED LEAVES. DOUBLE FLOWERS. I. Original species. Green. Simple. II. Half-race. Rarely variegated. Occasional petaloid stamens. III. Eversporting variety. Var. variegata. Var. plena. V. Constant variety. Var. aurea. Var. petalomana. The parallelism of these two groups rests on the assumption that the same character appearing in a state of full development would give rise to the constant golden and to the fully double varieties;- and that it is by their mixture with the antagonistic character that variegated and half-double varieties arise. The object of this as- sumption is solely to present the matter more clearly ; for in cases of segregation the characters behave slightly differently (see p. 124). There are many examples of half races and ever- sporting varieties ; the former constitute a very con- siderable part of the material of teratology and afford suitable material for the experimental study of monstros- ities. The same holds good for many eversporting vari- eties, and I shall have to recur to this point in the second part of this volume with especial reference to twisted stems and fasciations. Half races as a rule exhibit their ^ See Species and Varieties, Their Origin by Mutation, Chapters XI-XV, pp. 309-459- ^ See § ig and especially § 24 (on variegation). 22 Latent and Scmi-Latcnt Characters. abnormality too seldom to be of any use, or at any rate to be of more than of secondary value, in horticulture. On the other hand the eversporting varieties highly con- tribute to the diversity among horticultural plants. Nu- merous varieties with variegated leaves, with striped or double flowers, with double heads amongst the compo- sites, belong to this group. The Forinae cristatae of many ferns, the combs in the flowers of Primula sinensis, Cyc- lamen persicum, Begonia etc., the polycephaly of Papaver, the catacoroUa of Gloxinia superba, and a series of other more or less rare instances may also be adduced. It is, obviously, not necessary that all the forms named should exist for every pair of antagonistic characters. In many cases the intermediate races are absent and in others one or two of them. It is, likewise, not necessary that the pure type corresponding to a certain intermediate race should exist. We can, in such cases, very often reconstruct it by the help of analogy. The following are instances which will be described more fully later on in this part, in which the corresponding constant vari- ety is still failing. SPECIES. HALF-RACE. EVERSPORTING VARIETY. Trifolimn prateiise wild four-leaved T. p. quinqiiefoliuni. clover Trifoliuni iyicarnatum T. i. quadrifoliuju unknown. Ra7iuncuhis bu/hosus R. b. seniiplenus unknown. Chrysanthemmn inodcniui unknown C. i. plenisshnmn. Chrysanthemum segetum C. s . grandiflormn C.s. plenum. Caltha paliistris furnishes another instance; it ex- hibits in nature a half race with supernumerary petals and is represented on the market by a uniformly double sterile variety exhibiting petalomany. Camellia japonica presents the two types of doubling in different varieties. Eversporting Varieties. 23 The remarkable fistulous and monophyllous varieties, so well known as examples of partial atavism, are further instances of eversporting types (Vol. I, Fig. 38, p. 193, and Fig. 15 of this volume), together with the viviparous grasses {Poa alpiiia vivipara, Poa bulbosa vivipara, etc.) and a number of other viviparous forms such as Agave vivipara and so forth. ^ If the constant variety corre- sponding to a certain intermediate race does not exist, this latter is usually classed as a variety in the case of middle races, but as a heritable anomaly in the case of half races. It is, further, very probable that many natural spe- cies which attract attention by the high degree of vari- ability of some particular character are really in a way intermediate races, i. e., that they owe their multiformity to the co-existence of two antagonistic characters. In- stead of entering further into this very attractive subject I shall content myself wnth citing the case of Acacia diversifolia which owes its name and its nature to the conflict between the two characters of bipinnate leaves and flattened petioles without leaflets (phyllody of the stalks). The question of the constancy of these intermediate races is a very important one. I propose to deal with it when referring to individual cases in detail; and the only general statement I shall make now is that both con- stant and inconstant intermediate races exist. On the « one hand there are those cases in which an overstepping of the limits between these two races is apparently as rare as the mutations by which new species arise, and ^ See GoEBEL, Organographie, I, pp. 153-159; E. H. Hunger, Uchcr cinigc vivipare Pflauccii. Diss. Rostock, 1887. Bot. Jahresber., t888, T. XVT, 1, p. 421. and also, especial!}', Clos, in Actcs du congrcs international dc botaniquc, Paris, Sept., 1900, p. 7. 24 Latent and Scmi-Latcnt Characters. in which at least, in spite of every precaution and care, I have not yet succeeded in obtaining the one race from the other. (Trifoliiiui incarnatuni qiiadrifoluiui, T. pra- tcnse quiuqiiefolium, Ranunculus bulhosus semiplenus.) On the other hand are those races which when cultivated on a sufficiently large scale give rise every year to indi- viduals which seems to overstep the otherwise fixed lim- its of the race. These are therefore inconstant inter- mediate races. I regard this phenomenon as one of atavism, at any rate in those cases where, as in my own observations, they revert from an eversporting variety to the type of the parent species without however ac- quiring the constancy of the latter. Atavistic phenom- ena of this kind are well known in striped flowers and variegated leaves ; and I have also found very striking examples of it in Linaria vulgaris peloria and Plantayo lanceolata raniosa (§20 and § 17). Besides the cases which fall into the two categories just discussed, I succeeded in finding a third in which one intermediate race arose from the other very rarely and only in isolated cases. I have seen two cases of this so far. One was the origin of Linaria vidgaris peloria from L. V. hemipcloria (§ 20); the other was the formation of the double Chrysanthemum segetuni plenum (Plate II), from C. s. grandiflorum with 21 instead of 13 tongue-florets (§ 18). Linaria vulg. peloria is probably an intermediate race, on account of its inconstancy; whereas L. vulg. hemipeloria (with stray peloric flowers) is obviously a half race. The origin of the former from the latter presumably occurs in nature from time to time. My Chrysanthemum segetum plenum is a novelty in the horticultural sense of the term, being just as double as the double varieties of other composites; so far as I Evcrsporting Varieties. 25 know it has not as yet arisen anywhere else. It consti- tutes an eversporting variety hke a number of other double composites which are analogous to it ; and arose in my experimental garden, not from the original species, but from a variety known in the trade as C. s. grandi- floriiui, which forms a first step towards it in respect of the number of its tongue florets, and is therefore to be regarded as a half race.-^ Let us now briefly summarize the foregoing dis- cussion : 1. There exist both in the cultivated state and in nature a series of forms which are either not constant or highly variable, a state of affairs which is probably due to the interaction of two antagonistic characters. 2. Of these two characters one is to be regarded as normal, that is to say, as belonging to the parent species ; the other as the abnormal. 3. Where the former preponderates, teratological half races with their half curves are the result. 4. If the two maintain an equilibrium, there are formed what I have called middle races, intermediate races, or eversporting varieties, of which many examples are to be found amongst garden varieties and ''heritable" teratological races. 5. The high degree of fluctuating variability of the eversporting variety, its occasional discovery in nature and in cultivation, and the possibility which it affords of the working up of striking novelties by means of iso- lation and selection, afford an explanation of the major- * The numerous apices of the curves describing variation in the number of rays in composites, which have received no explanation so far, tend however to make the apphcation of this conception diffi- cult. See also the origin of Dahlia variabilis fistulosa in my cultures (§ II, p. 100. 26 Latent and Semi-Latent Characters. ity of the phenomena which led Darwin to his theory of the slow transformation of species. For at that time it was believed that the inception of this process was to be sought in the variation of a character already exist- ing, whereas as a matter of fact the variation in question is independent of the fluctuation of the existing char- acters. 6. The origin of a constant variety or a new species could be easily imagined to occur in this way : First a half race would arise from a pure race, then from this half race a middle race and lastly, from this latter, a new constant form. But this would be pure fancy, since it is without any basis of fact. Besides in many cases the intermediate stages are entirely wanting. § 4. HALF RACES AND HALF CURVES. The study of anomalies must be based on the theory that external factors can only be efficient in altering the form of the plant if the power to react to them (or the potentiality for the change) is already present.-^ ^'The induction of malformations by external causes is no more than the manifestation of latent potentialities," says Goe- BEL.- Every plant possesses a whole host of such latenV potentialities. A single plant of Plantago lanceolata may be raniosa, stipitata, and bracteata; it may have split leaves and pitchers composed of one or two leaves; and it may exhibit abnormal twisting and forked ears, or present a whole series of other anomalies. The seeds of a single self-fertilized plant will very often give rise to ^ See Intraccllulave Pangenesis, p. 194. ^GoEBEL^ Organo graphic, p. 158, Half Races and Half Curves. 27 a whole series of malformations. Many cultivated plants, such as Cyclamen, Pelargonium and Fuchsia, are particu- larly productive of such abnormalities. The internal factors may either be latent or semi- latent. In the former case the characters are either not manifested, or only exceptionally, as in the pinnate leaves of the red clover (Fig. 46) and as in the numerous cases of pitchers which have been found once, or only at long intervals, in the same species. In the second case they appear more or less regularly, often yearly, and in many specimens. For example I have observed the for- mation of pitchers on Magnolia ohovata in the various botanical gardens which I have visited; and this species as well as its near allies bears pitchers with us every year.^ In both cases these potentialities are heritable. This is proved by their frequence in the case of the semi-latent characters and rendered extremely probable in that of the latent ones by their occasional reappearance. Latent and semi-latent characters constitute zvhat we may call the otiter range of the forms of a species. The inner range of forms consists of the normal characters of a species which are exhibited during its normal life or are only induced by such common stimuli as wounds, mutilations, darkness, or the uncovering of subterranean organs and so forth. They are part of the innermost essence of the species. But the countless latent charac- ters belong just as much to the essence of the species, especially when they have formed part of tlie inner range in some remote ancestor and are therefore atavistic. And it is just this outer range which presents the best inch'ca- ^ Over de crfclykhcid van Syniisen, Bot. Jaarb. d. Gesellsch. Do- don.ica, Gent, 1895. p. 129. In the course of ten years I have observed about 100 pitchers on Magnolia. 28 Latent and Soni-Latcnt Characters. tions of descent and therefore of systematic relationship. 1 1 fuUy deserves and repays the attention given to it, as Celakovvsky's a(hiiirable papers show. It is to be hoped that others will, following the lines laid down by Hein- RiciiER. imdertaKp the task of rendering these characters more amenable to study by cultivation, and so bring an increased number of them to light. The manifestations of latent characters are so rare that they scarcely ever lend themselves to statistical study (p. 19). When they recur from time to time they are seen to be extremely vari- able, since as a rule even the rarest anomalies are not quite the same each time they appear. It is easily seen in such cases that the varia- bility is a unilateral one; but the construction of curves usually fails owing to the sparsity of the material. The half races are much more favorable in this re- spect. Here the deviations 5 6 7 Fig. T. Half Curves. A. Caltha palnstris. Curve of the num- ber of petals in 416 flowers. B, IVeigelia amahilis, Curve of the slips of the corolla in 1 145 flowers.^ are by no means so very rare. As a rule the normal character still preponderates, but material sufficient for statistical study can often be found without difficulty. It shows clearly that the variation is a unilateral one. The apex of the curve is the mean of the normal character, and the deviations all lie on the same side. And in ordinary cases they are less numerous ^Ber. d. d. hot. Gcs., Vol. XTT. 1894, p. 197, Plate X. Half Races and Half Curves. 29 the further they deviate from the type of the species. Fig. I gives a couple of examples at A and B. A gives the number of petals of Caltlia palustris in a locality not far from Hilversum; the flowers, where the species is pure, are pentamerous. But in this place there occurred flowers with 5-8 petals in the following proportions : Flowers with 5 6 7 8 Petals. Relative number 72% 21% 6% 1% Weigelia aniabilis, also, has normally pentamerous flow^ers ; but it often varies in a minus direction. I found in 1145 flowers on three bushes in our garden (Fig. IB): Number of slips in the corolla 3 4 5 Number of flowers 61 196 888 Half curves differ from the half of a normal curve because the height of the mean, i. e., the number of nor- mal cases, is too great. Such curves do not display the variability of the character given by the highest ordinate, but that of another character which is concealed in the normal flowers.^ Half- or unilateral curves are widely distributed in nature. Where they occur they point to the existence of half races. Nevertheless middle races can, under cer- tain circumstances, as we have already pointed out (p. 20) exhibit half curves; just as, on the other hand, the half * Half curves are therefore compound curves. Their apex cor- responds to the mean value of the normal character ; their flank is the expression of the semi-latent character. If the normal character, in the material at our disposal, does not vary it has no curve of its own, which accounts for the absence of a flank on the other side. This for example is the case for curves based on numbers, when the nor- mal number is constant or practically constant as in the case of the three-leaved clover or pentamerous flowers. If the normal character is distinctly, though slightly, variable, as in the case of data based on measurements, the half curve has a flank on the other side, but it is very steep. I do not propose to pursue this point any further here, since it is merely my object to show that half curves are only a special case of asymmetrical curves. 30 Latent and Semi-Latent Charaeters. curve of a half race can be tran formed into a l)ilateral curve by selection and high nutrition. 1 shall recur to this point shortly. The well-known researches of Fritz IVIuller with Abu til on give instances of half curves.^ Muller ob- tained the following figures from a culture with seeds from flowers with six petals: 145 with 5 petals, 103 with 6, and 13 with 7. Of more recent investigations we may mention those of Bateson and Pertz with Vcroniea Bu.vbauniii according to which the normal cases always composed 70-90% of the culture in spite of the selection of the extreme variants in petal-number as seed-])arents, the remaining 30-10% being composed of abnormal cases in a rapidly diminishing series.^ The fruits of Aquilecjia are pentamerous, but 6-, and still more rarely 7-merous, ones occur. The fruit of the cotton is also pentamerous, but I have found several tetramerous and occasional trimerous ones. Papaver Argemone has tetramerous flowers, but specimens with 5, and less often with 6 petals, also occur ; by sowing seeds from the latter I was not able to obtain any increase in the number. Du]:)lications of leaves, concrescence of umbel-rays in Ufnhelliferae, of the fruit stalks of Cruciferae, of the fruits themselves in the Conipositae and so forth, the adnation of an axial bud wnth its axillary branch and a number of other anomalies behave as half races. The abnormal cases, which are of course infinitely rarer than the normal ones, become rarer in proportion as they de- part from the normal. It is unnecessary to give a longer list here, I may just mention the catacorolla on the outer * Hermann Muller, Die Befnichtiing der Bhimcn, p. 450. ^ W. Bateson and Miss D. F. M. Pertz, Notes on the Inheritance of Variation in the Corolla of Veronica Buxhaumii. Proceed. Cam- bridge Phil. Soc. Vol. X, Pt. II, p. 78. Half Races and Half Curves. 31 side of the corolla in a half race of Linaria vulgaris which I have stiulied for a few generations, and for which the half curves have recently been plotted and in- vestigated by Gar JEANNE.^ It is well known that every species has a tendency, as the expression is, to vary in certain definite directions ; in these the deviations occur fairly frequently, in others either not at all or very seldom. The number of anom- alies is by no means an unlimited one for a given species, but strictly limited. One expression of this phenomenon is the fact that one species tends to produce and repeat one particular abnormality, and another species, another. This general fact, with which we are familiar in vague expressions of this kind, can be made the starting point of valuable experimental investigations. For what are we to understand by "tendency" in these cases? In my opinion simply the existence of a half race or sometimes even of an eversporting variety. These two types of races are, so far as my experience reaches, perfectly dis- tinct, and in numerous cases amenable to experimental study ; they are things with nothing intrinsically vague about them although they are sometimes blurred in their manifestation, under a superficial examination, on ac- count of the high degree of fluctuating variability which they exhibit. If we take a plant which presents this tendency to a particular anomaly and cultivate its progeny, isolating it with an eye to this tendency, we shall usually find that we are dealing with an intermediate race of the kind of which w^e have spoken. I shall refer to an instance in the fol- lowing section (§ 5) : but this will be only one out of 'A. J. M. Garjeanne, Bcohachhmgcn nnd CiiUurvcrsuchc iiber cine BliitJicnanomalic von Linaria vulgaris. Flora, 1901. Vol. 88, p. 78; with Plates IX and X. 32 Latent and Scnii-Latcnt Characters. many. It is frequently uncertain, at first at any rate, whether besides the half race, the "species" itself exists in pure condition, that is to say, a race in which the char- acter in question is not semi-latent but latent. But when, as is so often the case, the species is widely distributed but the half race is only observed locally, we are evi- dently fairly safe in assuming the separate existence of both. Anomalies which are very common in nature point to the existence of eversporting varieties ; those wdiich are rare, to half races. In the former case they are often reckoned among the characters proper to the species, as for instance the remarkable lateral fruitlets on the fruits of Tctragonia expansa, which were included by De Can- DOLLE in his diagnosis of the species, in his Prodronius.^ Other w^ell-known instances are the incomplete apetaly of Ranunculus auricomns,^ as well as the branched ears of Loliuni perenne raniosuni which seem to be relatively common everywhere in my owni country. Lenecek"'^ records lime-trees with 20-30% of their leaves trans- formed into pitchers ; and with us trees w'ith single pitchers, and others which produce large numbers of them every year are met with from time to time (Vol. I, Fig. 106, p. 470). In many cases we know both the half race and the middle race of the same, or of closely related, species. For example, there grows very commonly here a form of Plantago major (/. bracteata) which bears more or ^ A. DE Candolle, Prodromus Rcgni Vcgetabilis. See also Eich- LER, Bliithcndiagramme, II, p. 120. '^Winter, Journ. of Bot., Vol. 35, 1897, P- 406. This form also grows in our garden and in our country in the wild condition, ' O. Lenecek, Mitth. d. naturw. Vcrcins, Vienna, 1893. Found not far from Leitmcritz. Half Races and Half Curves. 33 less numerous green bracts on the lower parts of the spikes. The well-known Plantago major rosea of our gardens, all of the bracts of which are green and fairly large, constitutes the complementary, and constant, e\cr- sporting variety. Besides Papaver soninifennn polyccpli- aliim (Vol. I, Figs. 27-28, pp. 138-139) which is to be regarded as an eversporting variety, there are polyceph- alous half races of P. coimnutatum and several other spe- cies which in my cultures behave in quite a different man- ner from the former, in response to selection. Besides the favorite Varictates crisfafae of our cultivated ferns we occasionally find, in nature, wild species with a split leaf. Cclosia cristata, the cockscomb, is an exceedingly interesting eversporting variety,-^ besides which fasciated half races in numerous other genera are known. ^ But I must refrain from the citation of further instances. Just as a species can as a rule be distinguished from its nearest allies by two or several characters, so a half race can manifest as semi-latent anomalies two or more characters which are latent in the species in question. Nor is this by any means rare. In the case of characters which deviate in the opposite direction from the type of the species, ''double half-curves" may be formed which have two unequal flanks. The number of petals of Hypericum perforatum varies in this way, in this neigh- borhood, round a mean of 5 ; on the one side going fre- quently to 4 and rarely to 3, and on the other side rarely to 6. The corolla of Campanula rotund i folia often varies from 5 to 6 and 7, and rarely from 5 to 4 and 3.^ ^ See the second part of this volume. ^ Botanisch Jaarbock, Gent, i- to their race as is shown bv the fact that even after repeated selection in an atavistic direction they produce far more quadri foliate leaves than the normal red clover (or more exactly, the corresponding- wild half race of the red clover). The better the seeds are fed on the parent plant the greater is the development of the anomaly on the indi- viduals produced by them. Poor seeds give rise to ata- vists, good ones to extreme variants. My experiment extends over ten generations. It gives no support to the view that the five-leaved race was, so to speak, caught in the act of developing its character, or that it could give rise to a higher type with- out further mutation. It is a highly variable, but constant varietv. III. THE DIFFERENT MODES OF ORIGIN OF NEW SPECIES, § 6. HORTICULTURAL AND SYSTEMATIC VARIETIES AND ELEMENTARY SPECIES. The opinion has of late been often expressed, by Von Wettstein in particular, that there is no ground for the assumption that all species have arisen in the same way.^ There is no difficulty in applying this view to the theory of mutation, although one of the chief objects of this book is to show that ordinary or fluctuating variability does not provide material for the origin of new species. But this does not exclude the possibility of different modes of origin of new species. The simultaneous origin of species in groups, in definite periods, such as I have described in the case of OcnotJicra Lainarckiana, must constitute for me the main type of this process, until the origin of species has been experimentally studied in other cases. Such experiments would have to study the phe- nomenon before and during the first appearance of the new type. Inferences drawn from data obtained after its appearance can hardly be considered as decisive. This essential type explains in my opinion in the first ^ R. V. Wettstein, Dcr Saison-DimorpJiis)nus aJs Ansgangspunkt fib' die Bildung nciicr Artcn im Pftanccnrcich, Ber. d. d. bot. Ges., Vol. XIII, 1895, p. 303 ; and particularly the same author's Desccn- denztheoretische Untersiichungen; I. Unfersuclmngen i'tbcr den Sai- son-Dimorphismiis im Pftanzenreich; Denkschr. d. ]\Iat. Naturvv. Classe d. k. Akad. d. Wiss., Vienna, 1900. Horticultiwal and Systematic Varieties. 57 place the progressive origin of species, that formation of new characters to which in the main the evokition of the plant kingdom is due. On the other hand there is a whole series of other types which are now, so far as it is possible to judge, mainly confined to the lateral branches of the phyletic tree. With regard to these however we must content ourselves at present with indirect methods of investigation. Darwin's statement that varieties are incipient spe- cies is well known. So also are the words of one of the most famous authorities^ on horticulture, Verlot : Toiite variete a d\ihord existe a I'etat de variation. These two generalizations are evidently based on phenomena en- tirely different from those with which we have become familiar in Oenothera. They constitute, so to speak, the other extreme of the series. I propose therefore now to investigate the manner in which ^Variations" in the sense of so-called structural abnormalities or anomalies (and not the individuals which exhibit variation in accordance with Ouetelet^s law) arise, and how they result in the origin of ''species." But here we come across an obstacle on the very threshold of the inquiry in the manifold meanings of the word variety.^ It will soon become clear that horticultural and systematic varieties are to be considered as categories of entirely different values. But both Darwin's and Verlot 's sentences just quoted are based on data ob- tained from horticultural varieties; and we must now ^ B. Verlot, Production ct fixation dcs varictcs, 1865, p. 100. ^The general conception of this term is that formulated by Car- RiERE in the following words: "On nomnic varictc tout iudiridu qui, par quclquc caractcre que ce soit, sc distingue d'lin ou de plusieurs atitres avec lesquels on le compare et qu'on considere comme apparte- nant a un mcme type specifique {Production et fixation des varictcs, 1865, p. 6). 58 77k' Different Modes of Or'uj'ui of iicie Species. inquire how far tlieir transference to systematic varie- ties is justified.^ Tlie origin of horticultural varieties will therefore be submitted to a critical and experimental examination. But before we do this I think it advisable to consider first the meaning which is attached to the term variety in systematic works, and secondly the various ways in which species can arise. And we shall find that whilst there is no question that the mode of origin of horti- cultural varieties is often analogous to that of so-called ''good" species, this parallel is by no means so common as the present form of the doctrine of descent would lead one to believe. To begin with systematic varieties : Here we find we can draw a pretty natural line between what we called ele- mentary species on the one hand, and real systematic varieties on the other. In connection with this antithesis I think it desirable, after what has already been said on this topic in the first volume,- to lay especial stress on the fundamental dif- ference between these two conceptions. Linnaeus and his pupils describe the elementary species as varieties ; Jordan, De Bary, and others who argue from experi- mental data, refer to all forms as species. The terms ''species" and "variety" have become so familiar that it is no longer possible to effect any radical change in their definition. For their exact meaniu"- we have to refer to the works of Linnaeus himself. His * For some interesting observations relating to the origin of new forms, see the papers bv F. Krasan in Engler's BotauiscJic JaJir- hUclicr, Vol. XIII. Pts. 3-4; Vol. XXVIII, Pts. i, 2 and 5. and also his Mittlicilungcn iibcr Ciilturvcrsuchc mit Potcntilla arenaria, Graz, 1900. ^ See Vol. I, § 7, "Species, Subspecies and Varieties," especially pp. 169-172. Horticultural and Systcuiafic J'aricfics. 59 conception of them is now common property, and in my opinion our best course is to interfere with that con- ce])tion as httle as possible. There can be httle question that the difference between variants and variations is becoming more and more widely recognized. Variants are what we call individual devia- tions; they are instances of fluctuating varia1)ility. The characters which distinguish them disappear under suit- able cultivation and are therefore to be regarded as in- constant. In systematic works they are not as a rule gixen a place, or merely briefly mentioned, or, lastly, treated as a Forma, which is the lowest subdivision of tlie system; e. g., Forma alpcstris, Forma aquatica. But this can only be done when the relationship of the form is sufficiently known; lack of material in the case of exotic plants, or incomplete investigation of indigenous species of course would make this impossible, and such forms have therefore often first been described as vari- eties or even as species.^ In many cases of course the true relationship is still unknown and the systematic grouping, therefore, to be considered as provisional ; as for instance in the case of Anthyllis Viilneraria alpestris, LimoscUa aquatica caulcsccus, Carlina acaulis caulcsccns, and so forth. Bonnier's researches on Alpine plants, discussed in detail above (V^ol. I, p. 146), have demonstrated that some of these differences are not even instances of indi- vidual but of partial variability. From the two halves of a single individual can be grown the form character- istics of the plains and the Forma montana. ^ For example Ranunculus aconififolius L. in alpibus minor, caule 3-5 floro ; R. aconififolius altior Koch, caule multifloro, fol. laciniis longius acuminatis. in montibus humilioribus = 7?. plafanifolius L. mant. 79 (Koch, Synopsis, p. 12). 60 TJic Different Modes of Origin of nezv Species. But the large number of cases of forms preliminarily described as varieties but which possibly may be only variants, is one of the most considerable obstacles in this inquiry. Linnaeus himself followed two distinct rules in sub- dividing his species. According to the one the species was regarded as the type from which the varieties were derived ; according to the other, however, the species was regarded as a collective group wdiich embraced a certain number of units of equal value. The separation is sharp and definite and Linnaeus w^as obviously perfectly con- scious of its reality. In the derived varieties the series begins with /? followed by y, 8, e etc. ; it is taken for granted that the type or Forma gemiina represents the a. Li a homonomous series there is no such Forma gemiina, and the series of varieties therefore begins with a. Let us consider the two cases separately and let us begin with the second. LiNNAEUs's homonomous varieties, a, /?, y etc., are sometimes arranged in groups, and sometimes not (as in Tencriiim Poliiim, Larandnla Spica, etc.). In the former case the species falls into tw^o or several subspecies, each of which again may include one or several varieties. For instance Euphorbia exigna has two subspecies acuta and rctusa, the first of which consists of one and the second of two varieties. Beta vulgaris has the well-known sub- species rubra and Cicia; the first of these embraces five, the second two varieties. In these species there is no Forma typica or Forma genuina. The variety which is named first has no other priority over the others. In such cases the species is a group of similar com- position to that of a genus and of a family ; since in these no particular species or genus is regarded as the proto- Horticultural and Systematic Varieties. 61 type from which the rest would be merely derived forms. Species of this kind are therefore obviously and avowedly collective species. LiNDLEY, A. P. DE CaNDOLLE, AlPHONSE DE CaN- DOLLE and other eminent systematists consider the col- lective species without Forma typica to be the only really existing type. Species must be subdivided in exactly the same way as genera, says the last named of these authors in his Phytographie.^ Lindley splits up his species of roses on the same principle ; Rosa rubiginosa into 8, R. spinosissima into 9 varieties, etc. De Candolle deals with the difficult and numerous subgenera and elementary forms of Brassica in the same way in the second volume of his Systcma Vegetabiliiim. De Candolle calls the units, which in such cases are treated as varieties, "les elements de I'espece'' ;^ they are related to the species as these are to the genera and as the genera to the families. But the majority of botanists regard varieties as forms which have been derived from the species. For them the species is the type, the real entity, from which the varieties have arisen by small changes. They follow the course taken by Linnaeus who based his diagnoses, in the vast majority of cases, on one of the forms of a species and arranged the rest in a lower grade under this. The origin of the varieties from the species was simply inferred from a priori premises as I have already shown in the first volume, this origin having only been directly observed in isolated cases of horticultural prod- ucts; for the majority and certainly the most important ^ Alph. de Candolle, La Phytographie on I'art de dccrire les vegctaiix, i88o, pp. 74-82. Much of the argument set forth in the text is due to this excellent work. ^Loc. cit., p. 80. 62 TJic Different Moiirs of Oricjin of new Species. cultivated varieties are as old or even older than cultiva- tion itself. It we examine a number of such derived forms in any systematic work or llora, it immediately becomes evident that the same kind of dil'ferences recur in the most widely separated families, genera and species. Everywhere \ari- eties present series of parallel forms. The recurrence of white flowered varieties in numerous species with blue or red flowers is so familiar a phenomenon, that often all reference to them is omitted. Lixnaeus himself knew that nearly all such species had a white variety. If the color of a flower is compound, and if one of the compo- nents is lacking, a white flower with a dark center often results and is known as a J\ir. bicolor (for example C\'iio- (/lossimi officinale bicolor, Agrosfeninia coronaria bicolor) : or the dark patches are absent as in Gentiana fnnclafa concolor, which case is exactly analogous to that of Arum niaculatuni inunaculatuin. Often too, the clothing of hair is lacking either on the whole plant or, when only certain parts are densely hirsute in the "species," on these. The nomenclature of the series of parallel forms, under this heading, is par- ticularly rich in terms which all indicate the same prop- erty, as for example : Papaver dubiuni (jlabruni, Biscn- tella laez'if/ata glabra, Arabis cilia fa f/labrafa, Arabis hir- siifa glaberrinia, 1/cronica spicafa nifens, Aniygdalus Per- sica lacz'is, Eritrichiuni nanuni leiospernuun, Paconia corallina ( peregrina) leiocarpa, etc. Thornless forms are usually termed inerniis; they oc- cur in Raniincnhis ar^'cnsis. Genista gernianica, Robinia Pseud-Acacia and many others. 11ie J\irietas ciliata occurs in Cytisiis prostratus and in C. spinescens, als(^ in Lotus corniculatus, etc. A dense clothing of hair is the Horticultural ami Systematic Varieties. 63 (listingiiisliing feature of Solajium Dulcamara tomento- sum, Veronica scutellata pubescens, Melissa officinalis vil- losa, Galeopsis Ladanum canescens, Vicia lutea hirta, Lotus corniculatus hirsutus, etc. The patches of color at the base of the petals are often absent in Papaver orientale, in Erodium cicutarium and many other plants. Such names as ocliroleuca, purpuras- cens, integrifolia, serratifolia, angustifolia, latifolia de- note varieties each one of which may recur in several unrelated species. Finally I may mention the red berries which occur as a varietal character in Empetum nigrum and characterize the red variety of the gooseberry ; and the yellow berries of Atropa Belladonna lutea and Daphne Mezcreum album which are only selected examples from a long series of such varieties. All these forms differ from their species in the fact that a particular one of their characters is either devel- oped to a greater extent {hirsuta, ciliata, purpurascens,) or on the other hand very slightly developed or entirely absent. The absence of a character may also be a case of ex- treme rarity in the vegetable kingdom such as the straw- berries without runners, and the peculiar Pinus Abies aclada, with its tall absolutely unbranched stem, which has been figured by Schroter.^ Fragaria resca mono- phylla (Vol. I, Fig. ?)^, p. 193), Robinia Pseud-Acacia rnonophylla, Fra.vinus Ornus monophyllar and a mo- nophyllous form of Melilotus coerulea (Fig. 12 on page 87) belong to the same category. The varietal names enumerated above almost always occur, in svstematic works, in series which bcQin not with ^ C. ScHROTER, Die ViclgcstaJtigkcit dcr Fichtc, 1898. pp. 52-53. ^ A. Rraun, Verjuugung, § 332. Here also the earlier literature will be found : and some facts concerning? Ruhus Jdacus tnoiiof^hyllus. 64 The Different Modes of Origin of new Species. a but with /? and are therefore considered as having been derived from a Forma typica or gennina and not as being of equal vakie with this. Evidently the principle on which they are classified is borrowed from a consideration of horticultural varieties. This proceeding, however, is only justified in the relatively rare cases in which horti- cultural varieties can be demonstrated to be younger than the species. Besides this the geographical distribution of the forms in question is often employed to decide which is the species, and which are the varieties. If one particular form is wide-spread and another only local or sporadic in its appearance it is obvious that the former will be regarded as the older and therefore as the species. Often this fits in conveniently with the fact that the species was discovered earlier than the variety, so that instead of disturbing the classification in the system all that had to be done was to range the variety under the species. The exigencies of space prevent me from going into further detail here. What I have already said may suffice to show that the systematic term "variety" means two fundamentally different things to Linnaeus and the later svstematists: 1. Homonomous Forms, amongst which even Lin- naeus could not select one as a type for the others ; "Elements de I'espece" (De Candolle) or ele- mentary species. 2. Derived Forms, which are distinguished from the type of the species only by the decreased or in- creased development of a particular quality; or by its complete absence: True varieties.^ ^ Amongst these, again, the simple invariable types are to be distinguished from the intermediate or eversporting races. (See §§3-4.) Progression^ Retrogression and Degression. 65 I think it undesirable that these two types of sub- divisions of the species should continue to be denoted by the same term. The simplest plan would be to refer to the former as elementary species and only to the latter as varieties, and I hope that this limitation of the terms will come into general use. The question, however, is a purely systematic one and belongs to the department of descriptive science. For as soon as it is treated from the experimental standpoint the whole difference disappears. Many of the best vari- eties prove, when tested by sowing, to be as constant as elementary species, so that a separation on the basis of constancy is out of the question. * * * On the basis of the foregoing discussion I treat the homonomous subdivisions of the Linnean species as elementary species and eventually denote them with bi- nary names. In the case of derivative varieties, however, I prefer to make no definite choice ; I regard for example ChcHdoniiun laciniatiun Miller and Chelidoniuni majus laciniatuni as equally justifiable. And when for instance several species in the same genus have white flowered or glabrous varieties, a binary nomenclature would obviously be much too cumbrous.^ § 7. PROGRESSIVE, RETROGRESSIVE AND DEGRESSIVE FORMATION OF SPECIES. A glance at the phylogeny of the vegetable kingdom reveals the fact that all species cannot have arisen in the same way. Progressive development is due to the con- ^ For instance if specific names like that of Agrostemma nicae- cnsis for Agrostemma Githago pallida were generally used for white flowered varieties. 66 The Different Modes of Origin of neiv Species. tinual formation of new cliaractcrs, to increasing differ- entiation. Nevertheless the great nuihiforniity of spe- cies within tlie orders and families is only in part due to this progressive process, but to a large extent to an in- finite variety of combinations of characters already exist- ing. This is combined in innumerable cases with in- stances of regression ; that is, with the absence of characters which are otherwise proper to the group to which the species belongs. Sium and Berula have, for example, simple pinnate leaves within the group of the Unibelli ferae with (l(jul)ly pinnate leaves ; and tlie assump- tion is that they have arisen from the latter by a sim|)le loss. Similarly Primula acaulis stands in the middle of a group containing the Primulas, And rosace etc. with umbellate inflorescences, and the same inference is drawn as to its origin. The same is true of a host of other cases, and even for wdiole groups. For instance Delpino holds, as is well known, that the Monocotyledons have arisen from the lower Dicotyledons by the loss of a wdiole series of characters. Cases such as these are spoken of as instances of retrogressive metamorphosis. And it is probably not too much to say that there are possibly more species on the face of the earth at present that have arisen on retro- gressive than on progressive lines. The question is often debated whether, in retrogres- sion, the characters absolutely disappear or only become invisible, or latent. There is much evidence for tlie latter view, derived largely from the great varietv of atavistic structures (youth forms, subvariations on the lower internodes of lateral branches, the form of the leaf in suckers, the effects of parasites, anomalies, reversions to the ancestral form by bud-variations, etc.). Latency Progression, Retrogression and Degression. 67 is without doubt the general rule. That an actual internal loss may also occur is probable on general grounds, Init very difficult to demonstrate in a given case. For every positive result points to latency, and nothing but a nega- tive result after exhaustive investigation could warrant the conclusion that a character had absolutely disap- peared. The multiformity of species within the larger groups is also due to a phenomenon which Darwin calls parallel variation. I refer to the repeated appearance of the same new character in related or remote groups.^ Climb- ing and tendril-bearing plants, parasites, saprophytes and insectivorous plants, decussate phyllotaxy, are a few names from a vast number of instances. One of the greatest difficulties for the systematist, the question as to the mono- or polyphyletic origin of many characters is a problem of a similar nature. For example, are the siliqua and silicula in the Cruci ferae, or is the position of their embryo to be regarded as an indication of mono- or polyphyletic origin? Do the Sympetalae with an in- ferior ovary originate from other Sympetalae or from epigynous Choripetalae ? Have the Gymnosperms arisen once or oftener from the vascular Cryptogams? We do not know, because, on such points, the highest authorities are not in agreement. And so long as these differences of opinion exist it will be difficult to approach the question as to the cause of the parallel formation of specific char- acters— whether they arise from a common latent source, or afresli each time — with any hope of success. The origin of svstematic and horticultural varieties ^ On this point see also my IntraccUularc Pangenesis. English translation hy Prof. C. Stuart Gagcr (Chicago, The Open Court Publishing Co., 1910). 68 The Different Modes of Origin of new Species. is evidently due, in the vast majority of cases, to retro- gressive development or latency, as I have already at- tempted to show. There is a close analogy between the formation of these varieties and that of certain species. The origin of varieties (such as Var. hirsiitissinia, spinosissima and ciliata) as the result of the intensification of characters is a much rarer phenomenon. This form of variety, which seems to be of very little importance in the evolu- tion of the vegetable kingdom, may be called subprogres- sive, and the phenomenon of its origin subprogressive formation of species. The parallel, retrogressive, and subprogressive modes of origin have this in common that they only provide new combinations and do not contribute new units or any es- sentially new elements to the progressive evolution of the vegetable kingdom. In this respect they stand in sharp contrast to progressive formation of species. There is another series of phenomena to be mentioned here, of still less significance in the phylogeny of plants. The first of these is the manifestation of old, latent char- acters. A wdiole series of anomalies are so widely dis- tril3uted in the vegetable kingdom, or at least among flowering plants, that it is almost impossible not to as- sume a common cause for them. This cause must be a latent character that has arisen in some common ances- tor and therefore must be of great anti(|uity. The com- monest and best known example of a widely distributed anomaly of this kind is that of fasciation, instances of which in almost any desira])le number of species can be collected in the course of a few years. It appears that almost every species amongst Coni ferae and Monocotyl- edons, but especially among Dicotyledons, can exhibit Progression, Retrogression and Degression. 69 f asciations. ^ As a constant horticultural variety it occurs in Celosia cristafa; but as a specific character, so far as I know, it does not occur. This is, however, true of the almost equally widely distributed split leaves (as in Boeli- meria biloba), of adherences (Solanuin), of flowers on leaves (Helzvingia ntsci flora and others) and of numer- ous other anomalies of which Casimir de Candolle has given a valuable general account.^ He calls them "Varia- tions taxinomiqiies'' ; whereas anomalies which do not occur as specific characters such as fasciation, twisting, virescence and sterile varieties, are designated by him as ataxinomous. I take the following further instances from his list : Connation of opposites leaves, which oc- curs normally in Dipsacus, Lonicera and others, or of the cotyledons (amphisyncotyly, normal in Sieyos) ; Pitch- ers, normal in Sarracenia etc., and in the peltate leaves, as for instance Eucalyptus citriodora ; foliacious excres- cences on the leaves, normal in Senecio sagittifolius from Uruguay, and on petals, normal in Petaquia saniculae- folia and as a sport in Clarkia elegans; Synanthy in Lonicera, and so on. For our purposes, however, the question is not which anomalies can also occur as specific characters, but con- versely which specific characters can also occur as anom- alies in other species. For our task is to deal with the problem of species and especially to provide an answer to the question how far their characters can be derived from more or less widely distributed latent qualities which have existed for a long time in the vegetable king- dom or in particular groups of it. With this end in view 2 5-6. ^ See Vol. I, Figs. 34 and 35 on pp. 182-183. C. DE Candolle, Rcmarqucs sur la tcraiologie vcgctalc, 1896, pp. 70 The Different Modes of Oriijiii of uei^' Speeies. I shall supplement the examples named with a few more ; they serve to show how general this parallelism between anomalies and specific characters is. 'riuis, for example, Polxgoniiiii z'k'ipannii and Agave vk'ipava bear adven- titious buds or bulbils normally in the inflorescences; but I found them also as an anomaly in Aloe verrucosa and Saxifraga lunbrosa. A spiral involution is normally exhibited by the flowerstalks of Vallisneria and Cyclamen, and it occurs as a variety in the stalks of J uncus spiralis, and as an anomaly in Scirpus lacustris of which latter a beautiful instance came under my notice. Hypocot}'l- ous buds are, for example, normally present in Linaria and Linuni) they occur as an anomaly in Siegesbeckia^ according to Braun, and I have also observed them in Phaseolus niultiflorus. The numerous flowerbuds on the leaf stalk of Cucuinis sativus as described by Caspary- are analogous to the buds scattered on the internodes of Begonia pJiyllonianiaca. The bulbs of Gladiolus carry their lateral corms on stalks; I observed the same mode of connection as an anomaly in Hyacinthus oriental is. Masters has collected a series of teratological cases'"' of buds on leaves, which may be regarded as parallel to tlie normal instance of the same phenomenon furnished by Bryophylhnn. We see therefore that a large number of specific characters are analogous to taxinomous anomalies. 11ie latter recur in related forms, but much more frequentlv in more or less remote groups. In so far as they are due to a common cause, they point to the widesj^read ^ A. Braun, Verh. d. bot. Vereins Brandcnb., XII, 1870, p. 151. ^ Caspary, Uehcr Blilthcnsprosse auf BldUcrn, Schriften d. pliys Gesellsch., Konigsberg, 1874, p. 99 and Table II. ' Masters, Vegetable Teratology, p. 170. Progression, Rctrogrcssioji and Degression. 71 existence of latent characters. I shall refer to this mode of formation of species as degressive. In it, that which arises is always something new, and often something strikingly new, hut usually without any clear relation to the progressive development on the main lines of evolu- tion. They form, rather, lateral improvements of types already existing. Degressive formation of species is therefore due to the activation of long estahlished latent characters. Of these, as Goebel has shown in his Organographies there are two types to he distinguished.^ Either the character in question was active in the earlier ancestors, or it was not. In the former case we have an instance of reversion or atavism, and moreover a genuine systematic reversion, at least inasmuch as the ancestral relation can be demon- strated. In the other case we have only the development of a specific character from a taxinomous anomaly. It is perhaps hardly necessary to state that the appli- cation of this criterion of grouping can only be effected at the present moment in a relatively small number of cases. The information at our disposal does not as yet meet the demands of such a system. On the physiolog- ical side, however, the question of prime importance is only the distinction between the chief groups; so that we will only lay stress on that point here . Bearing this limitation in mind we can summarize what we have already said, as follows: THE ORIGIN OF NEW SPECIES. A. By the formation of new characters : Progressive specific differentiation. B. A\^ithout the formation of new characters. ' K. Goebel, Organographic, Vol. I, p. 170. 72 The Different Modes of Origin of new Species, B\. By characters already existing becoming la- tent: Retrogressive specific differentiation, cases of atavism. 82- By the activation of latent characters : De- gressive specific differentiation. a. From taxinomous (latent) anomalies. b. As genuine atavism. ^3. From hybrids. 'f* 'K 'T* This list does not of course claim to be complete. There is no doubt a whole series of further types which can be more or less easily ranged under or parallel to these subdivisions. On the other hand it is at once clear that the distinction between A and B is, in the present state of our knowledge, the important thing, and more- over that it will suffice as a basis for experimental in- quiry. But before I proceed to illustrate this antithesis I will offer some remarks on the last section (Bs). New species can arise from hybrids but specific char- acters cannot arise by means of hybridization; or, we may say that with regard to the production of mutations, hy- brids behave just like ordinary species, except that ac- cording to the prevalent view they are slightly more prone to it. The existence of a vast number of species, however, is due to the various combinations of characters which also exist in closely allied or in remote species. And it is evident that, by crossing, characters can be com- bined which have not appeared in the same genealogical line but in distinct though allied species. Thus for ex- ample by crossing Oenothera rubrinervis with 0. nanella I obtained an 0. rubrinervis-nanella which has remained constant for many generations without segregation and Progression, Retrogression and Degression. 73 without reversion. xA.nd a liost of new species have doubtless arisen on similar lines. Coming now to the discussion of the difference be- tween our two groups A and B, we draw a distinction between progressive specific differentiations or tlie origin of new specific characters on the one hand, and retro- and degressive specific differentiation, which consists in the activation or latency of potentialities already in ex- istence. It is obvious that a premutation is necessaiy for pro- gressive but not for retro- and degressive difl:*erentiation. For in the case of the former the new potentialities must first arise before they can become visible externally, whilst in the case of the two latter we are only dealing with potentialities already existing. I propose therefore to apply the results obtained with Oenothera Laniarckiana and the conclusions regarding the premutation period to which we arrived, to the further elucidation of this ques- tion.^ It is of course a purely speculative discussion that we are embarking on, but one which will, in my opinion, materially help in clearing the ground. And I may therefore say, in anticipation, that this theory is supported by the experiments to be recorded in this sec- tion and most strikingly by the history of my Linaria vulgaris peloria (see § 20). I have already stated, in Vol. I, Part II, that I regard the mutational period in Oenothera Laniarekiana as a type of the mode of origin of species in general ; that is to say, of the essential form of that process, the pro- gressive type.- We often find in the vegetable kingdom analogous groups of closely related species which are ^ See Vol. I, Part II and especially § 31, p. 490. ^Vol. I, p. 259. 74 TJie Different Modes of Origin of nezv Speeies. usually ranged as elementary species of larger species, but sometimes regarded by the best authorities as "good" species. The group most closely related to our experi- mental series is that of Oenothera biennis or the subgenus Onagra ;^ more remotely connected are the groups of Hieraciuni, Rosa, etc., or of Draba verna, Viola tricolor etc. Such groups appear to us as the relics of past periods of mutation. The new forms which arise from such periodical mutations are to be regarded as homonomous subdivisions of the older species or as elementary species. It is natural in such periods not only that new specific characters should arise, but that old established latent ones should reappear more easily than at other times ; and among the mutations of Oenothera Laniarckiana our O. nanella is undoubtedly analogous to typical horticul- tural dwarf varieties, and 0. laevifolia to those systematic varieties which arise by the loss of a character. These latter, however, and similar retro- and degres- sive changes are an entirely different matter. The essen- tial condition for their production is always present, and all that is needed is the external stimulus to induce the mutation. This, it appears, need not occur periodically, nor affect several characters at the same time. New horti- cultural varieties appear at irregular intervals of time, and here and there in the area of cultivation of the spe- cies. But it is equally certain that we have to do in such such cases exclusively, or almost exclusively, with retro- gressive and degressive changes.^ Analogy and paral- lelism are universal, and their effects sometimes go so far that the characters of the species fall into the back- ground. Double flowers look -so much alike that one ^See Vol. I, p. 439; and §31, p. 490. ^I am excluding from this consideraton the effects of crossing. Progression, Retrogression and Degression. 75 often cannot 'tell, even from the best illustrations, to which genus or family a given instance belongs. I shall therefore throughout this Part attempt to describe the origin of horticultural varieties as exhaus- tively as possible. In the present state of our knowledge they form in my opinion the pattern of retrogressive and degressive formation of species; just as the mutations of OejiolJiera were the pattern of progressive changes. Together they give us some idea of the main lines along which specific differentiation takes place in nature, at the present time as well as in the past. In conclusion : Progress on the main lines of descent results from the production of new characters; but the extraordinary variety of forms results from the occa- sional disappearance of characters already existing, or from the activation of latent ones (retrogression, de- gression, atavism). IV. THE SUDDEN APPEARANCE AND THE CONSTANCY OE NEW VARIETIES. § 8. EXA]\IPLES OF CONSTANT RACES. Horticultural varieties are generally constant ; excep- tions to this rule are usually noted expressly in the text- books. Most varieties are not only constant from seed but also pure. By constant is meant that in ordinary cultivation they produce no more impurities than are un- avoidable (that is to say, at most 3%). Absolute purity means that when isolated under experimental conditions the seeds reproduce their own variety without exception. Constanc}' in this case is complete, but it is seldom of practical interest to bring either the old established sorts or the novelties to this pitch of purity, or even to find out how closely they approach it. This has, however, been repeatedly done by scientific investigators and especially by Darwin and Hoffmann.^ Insufficient familiaritv with the dancfer of chance cross- ings robbed the results of the older investigators of much of their value as evidence, except of course in those cases where the race proved constant. The large number of observations of instances of complete constancy were ob- ^ See the Riickhlick aiif mcinc CuJfurvcrsnchc of the latter author in the Botanischc ZcituivJ, t88i, and tlie hterature cited there. Ihne and ScHROTER have given a complete Hst of Hoffmann's papers in the obituary of him in Bcrichtc d. d. hot. Gesellsch., Vol. X, 1892, p. 18 of the last part. Exa}uplcs of Constant Races. 77 vioiisly made under conditions which excluded the effects of crossing. In spite of the existence of these experimental data, it is still the general view that varieties are inconstant forms. That which distinguishes them from true spe- cies is supposed to be their faculty of giving rise to occasional and not even rare reversions to the type of the species. This, moreover, is supposed to be a proof of their assumed relation to their species. Every one of course is free to choose his own defi- nition of a variety. But he wdio makes inconstancy an essential part of the definition will have to exclude a very large number — and perhaps the most important — of our horticultural varieties, and regard them as elementary species. I have spent much time in the endeavor to test the constancy of horticultural and also of wild varieties witli a view partly of directly satisfying myself as to their purity and partly of finding inconstant forms for sub- sequent experiments. I have usually started from seed but sometimes, in the case of perennial varieties, from bought plants. Whenever possible the visits of insects were excluded and the plants artificially pollinated. But in the great majority of cases pollination has to be left to bumblebees and moths, and we must be content in providing complete isolation. The most important point is the extent of the experi- ment. Absolute constancy can obviously never be di- rectly demonstrated. The space and time needed for other experiments seldom permit the bringing to flower of more than a few thousands of plants of one sort. And even if this is continued for several years the possi- bility of the occurrence of rare cases of atavism (e. g.. 78 Siiddoi .Ippcarcnicc and Constancy. once in a million) can not be excluded. The object of experimentation cannot therefore be to demonstrate ab- solute constancy. The best i)lan usually is to be content with a few hundred individuals ; it is even often impos- sible to get sufficient seed for more. Experiments on a smaller scale should only serve to confirm the results ob- tained in other cases; but even if they only do this they are, in my opinion, by no means without value. Fig. 7. Bidcns tripartito. Type without ray florets. The nearest that we can get to demonstration of ab- solute constancy is to make observations on races which grow in vast quantities in certain districts and are never- theless true to their type. In these cases the constancy is so striking as to induce many systematists to regard the form as a species. Amongst the better known ex- Examples of Constant Races. 79 amples of this are the Discoidea forms of many com- posites. MoQUiN Tandon regarded the Discoidea, i. e., the form without tongue-florets, as the Peloria of the Com- posites.^ They are generally regarded as having arisen from the Radiata forms. Sometimes the discoid form is Fig. 8. Scnecio Jacohaea L. (f. radiata). commoner than that with rays, and then the Discoidea form may be found described in systematic works as a species and the Radiata as the variety ; as for instance in Bidens tripartita (Fig. 7), and B. cernua,^ although B. ^ Teratologic vegetate, p. 179. ^ Koch, Synopsis Florae Geniiauieae, p. 309. 80 Suddoi Appcarcijicc and Constancy. grand i flora. B. bipinnata, and B. atro purpurea are well- known species with ray florets. B. tripartita and B. ccrnua arc very common in Holland and I have often tried to find or to obtain examples with ligulate florets, Fig. 9. Senecio Jacohaca discoideiis, Koch. but as yet in vain. By this fact both forms are proved to be constant as thoroughly as a proof can be. In other countries, however, the z'arictates radiatac are known to Examples of Constant Races. 81 occur. Similarly Senecio Jaeobaea lias a forina raJiala and a F. discoidea^ (I^'igs. 8 and 9) both of which grow in this country and are absolutely constant. The Discoi- deus grows in thousands of specimens in the dunes in the province of North Holland; but the Forma radiata grows equally abundantly in South Holland ; both are amongst the commonest and most widely distributed spe- cies of our flora. For twenty and more years I have had them under observation, and never saw any trace of ad- mixture or reversion ; the two varieties were always al> solutely pure in the respective localities. Of late, how- ever, there have been some cases of intermingling near the limits of their areas, probably as the result of seed transportation. The two sorts can therefore be regarded as absolutely constant.^ Matricaria Chamoniilla discoi- dca^ has proved equally constant in my experimental garden, but Murr mentions the occasional occurrence of heads with rays.'^ In 1897 I raised from the seeds of a single plant of M. discoidea 575 plants, all of which were without ligulate florets. On these I only harvested the seeds of the weakest branches of the higher orders and raised 460 plants in 1898, all of which again were with- ^ See Vol. I, p. 196. ^A valuable summary dealing with this point is given by. J. Murr, Stvahllose B Hit hen bei heimischen Kompositen, Deutsche Bot. Monatsschr., Vol. 14, 1896, pp. 161-164. See also Bofan. Jalircshcr., T. 24, 2, p. II, where rare instances of forms with rays belonging to normally discoid species and rayless flowers on normally radiata forms, are given. I cite Senecio Jaeobaea as an instance of the latter, in opposition to the observations given in the text. An attempt to discriminate half races amongst these forms (See §3, p. 18) would probably lead to valuable results. ^ For an account of the rapid spread of this form in Norway sec Jens Holmboe, Nogle Ugracsplanters Invandring i Norge, 1000. A^3'( Maga::. f. Naturv., Vol. XXXVTII, p. 187 (with map), the variety is there also fully constant. *J. Murr, loc. cif., pp. 161-164. 82 Siidifoi .appearance ami Constancy. out ligulate florets. From these plants I only harvested the poorest possible seed on the latest branches after cutting away tlie main stem and the stronger branches ; l)ut from this seed, as before, I obtained nothing but Discoidca (750 ])lants in 1899). Flowerheads without, or almost without, rays also occasionally occur in races usually normal in this respect. Examples of this have occurred in my experimental gar- den in CJirysanthonuni coronavium, Coreopsis tinctoria, Dahlia striata nana and others.^ In the first volume I cited numerous examples of constant varieties- and showed'"' that many of them were certainly one or two centuries old ; in fact as old, or probably even older than, the cultivation of their species itself. The varieties are generally as constant as the wild elementary species, of which Draba %'erna and Viola tricolor^ were cited as examples. Belonging to the same group are the two remarkable types, which Hermann MuLLER has distinguished in Iris Pseudacorus, of which the one with narrow openings to the flower is adapted for pollination by Rhingia, whilst the other is adapted for pollination by bumble bees;'"^ Irwtn Lynch has re- cently compiled a very complete and valuable list of ' Further examples are given by Murr^ loc. cit. ^ See p. ig6. Examples are afforded by GAiLLON-strawberries (Vol. I, Fig. 7, p. 34) and by Chelidonium laciniatum (Vol. I, Fig. 36, p. 190). ^ On page 183 of the first volume will be found a list of the vari- eties known to Hunting (1671) and still cultivated. * See Vol. I, Figs. 3 and 4, pp. 22 and 23. For the constancy of the elementary species of Viola tricolor see also V. B. Wittrock, Viola Studier in Acta Horti Bergiani, Vol.11, No. i, 1897 (Cultures extendiiig over three years). '^ H. MiJLLER^ Die Bcfruchtiing dcr Blumcn, p. C^. Examples of Constant Races. 83 constant varieties, based on data given b}' gardeners and botanists as well as on his own observations.^ It is a common opinion amongst gardeners that white flowered varieties are among the most constant. They are very plentiful and easy to control. From the cases as yet investigated it may be assumed that hybrids 1)e- tween them and the colored species will be colored also, and therefore soon and easily discovered ; so that in the purification or fixation of these varieties the hybrids are usually removed soon and altogether, wdiich is a very important thing for approaching constancy. Sev- eral investigators have tested the purity of white vari- eties. For instance Hildebrand- worked with white Hyacinths, Delphinium Consolida, Matthiola incana and Lathyrus odoratus; Hoffmann with Linum nsitatissi- mum album :^^ Hofmeister for thirty years with Dicjitalis parz'i flora alba;^ Prehn with Scabiosa alba;^ etc. I myself have made similar observations. I started by buying a few plants of each of some varieties of perennial species, allowing them to flower on isolated spots and then saving and sowing their seed. Wherever the isolation w^as complete all the offsiring, with a single exception (Aquilegia chrysanfha) , were white flowered. The following were the species tested in this way (I give in parentheses after each one the number of plants which were raised from their seed and observed in flower) : Cam- panula pyraniidalis alba (26) , C. pcrsicifoUa alba ( 1 044) , ^ Irwin lynch, Tlie Evolution of Plants, Journ. Roy. Hort. Soc, Vol. XXV, Pt. I, pp. 34-37, Nov. 1900. ^ HiLDEBRAND, Die Favhcu dcr Bliithcn, p. 70. ^ Hoffmann, Botan. Zcitung, 1876, p. 566. See also the very complete list of constant white varieties given by Carriere, pp. 12-13, and the literature cited there. * Hofmeister, Allgemeine Morphologic, p. 556. ^J. Prehn, Schr. Nafurzu. Vereins Holstcin, Vol. X, 1895, p. 259. 84 Sudden .Ifpcarancc and Constancy. Catananclic cocndca alba (5), Hyssopits officinalis albus (198), Lobelia syphilitica alba {537), Lychnis chalcedo- nica alba (401), Polenioniuni dissectuui album (126), Salz'ia syk'cstris alba (296). The following white vari- eties of annual species I also found to be perfectly con- stant: CJirysantheniuni covonariuni album (400), Godetia amoena, white Pearl (15), Linum usitafissimum album (779), Phlox Drummondi alba (50), Silene Armcria alba (617). Among wild species I subjected especially Ero- diuni cicutarium album, which is common in Holland, to a severe test. In this form the pigment characteristic of the species is lacking both in the leaves and in the flowers. I found the variety constant through five gen- erations in my experimental garden, not a single red plant appearing although the sowings were conducted on a very large scale. Later I collected seeds of the 7'ar. alba from another locality and found it also to be con- stant (43 specimens). Other color varieties usually prove equally pure if the seeds of plants that have been isolated are sown. In some cases this fact is so generally known that they have, on this ground, been raised to the rank of species, as, for instance, Anagallis (arzrnsis) cocvulea. In 1897 I had 25 examples of this variety flowering on an isolated spot, and from these in 1898 I had 866 plants which were without exception blue. Tetragonia expansa, whose leaves and flowers are normally reddish brown, has given rise to a pure green form which has been raised to the rank of a species under the name of T. crystallina. This I also found perfectly constant. In 1898 I sowed about 600 fruits obtained from a culture of 1897. Each fruit contains from 6 to 10 and often more seeds, which grer- minate sooner or later, some of them not until after a Examples of Constant Races. 85 few years have elapsed. In the course of the first sum- mer 3975 seeds germinated, during the second 1082, during the third 88, and during the fourth 90. All the 5235 seedlings thus raised were green without a trace of the red pigment, and belonged therefore to the T. crys- talUna. In this case, therefore, the seeds which germinate late are just as constant as those which germinate early. -^ In other cases where the constancy is just as complete but happens to be less well known, the sorts in question are "only" reo:arded as varieties. Some of these forms even seem to be wholly unknown in botanical circles,- as for instance, Silcnc Aniieria rosea whose color is inter- mediate between that of the species and that of the white variety and which is not a hybrid but an old established perfectly constant sort and just as ''good" as the other two. In 1898 I had about 4000 plants raised from the seed of isolated plants of 1897 of the Var. flore rosea in flower; they were all of the same color as the parent plants. The same result was obtained on a smaller scale in subsequent years. Clarkia pulchella cornea behaved in the same way (50 specimens). I also found the pale flowered Agrosteniina Githago nicaeensis constant (for 10 years), and Hyoscyaniiis (nigcr) pallidiis (40 spec.) 'dud Agrosteninia coronaria b (color (349 spec). Further examples of the same phenomenon are afforded by the yellow Chrysanthemwn coronarium, the varieties of the flax with white and with yellow seeds, many varieties without the dark patches at the base of the petals, which are characteristic of the species, as in Papaz'cr sonini- feruni Danehrog, Papaver comniutatnni, Madia elegans (Fig. 10) and others. ^ This is not the case with TrifoUum incarnatum quadrifolium (See § 22). ' See Bot. Zeititng, 1900, p. 234. 86 Sudden Appearance and Constancy. Another interesting^' constant variety is Chelidon'uun ma jus latipetahun. (Fig. 11), for the possession of which I am indebted to Prof. J. W. >\Ioll in Groningen. It differs from C. inajus in its petals which are so broad that their edges overlap so that they form an unbroken Fig. 10. Madia clcgans. Fig. II. A, B, Chclidonium ma jus latipctalum. C, D, CJiclido)iium niajus. crown instead of an open cross. I found it to be con- stant through several generations. The constancy of the fasciated variety of Myosofis alpestris; Victoria with its broad, many-petalled central flowers, is likewise well known, as is also that of Linaria Examples of Constant Races. 87 vulgaris tvicalcarca,^ of many glabrous forms like Lych- nis z'cspcrtina glabra, of thornless types like Datura Stra- monium incrmis- etc., all of which I have tested per- sonally. Space docs not permit of the compilation here of anything like a complete list of constant varieties. Fig. 12. Mclilotus coenilea monophyUa. Eacli leaf consists of a single blade but is more or less deeply incised. One of the lateral leaflets in the middle leaf on the right of the figure appears to be quite free. A, a bract from the inflorescence; here the leaves are least incised. ^ J. H. Wakker, Linaria vulgaris, Nederl. Kruidk. Archief, 1889, with plate X. "See Fig. 5 on page 31 of Vol. I. 88 Siiddoi Appearance and Constancy. I shall conclude by referring" to a race of MeliJotus coerulea, the possession of which I owe to the kindness of Prof. ]\I. W. Beyerinck (p. 63). Its leaflets^ are fused to a single blade in which the three main nerves still diverge from the base. The blade moreover has three distinct tips, the depth of the indentations between these being subject to considerable fluctuating variability. Not rarely the three parts are only united from the base to halfway up or less, and sometimes they are separated almost to the base and in rare cases even entirely so. All these forms may occur on the same plant. But there was no reversion in my experimental sowings ; every plant exhibited this monophylly to a greater or less ex- tent. § 9- STERILE VARIETIES. One of the greatest difficulties presented by the cur- rent doctrine of selection lies, as I have pointed out more than once in the first volume of this work, in the fact that the gradual origin of species, which is presupposed by it, has never been observed. In every case in which observations have been made sufficiently close to the origin of a new form, they indicate a sudden change. We do not find those gradual transitions which the doc- trine of selection would lead us to expect. The new form may be highly variable, and in that way the limits be- tween it and the parent species may sometimes overlap; but, as I have already shown (Vol. I, § 25, p. 430) trans- gressive variability of this kind only provides a morpho- logical transitional series and not a genetic one. My object in the present chapter is to bring together ' This form has been described by Wydler, Flora, i860, p. 56, and occasionally since. Sterile Varieties. 89 a list of further instances partly from the hterature and partly from my own observations in order to place my conclusions on a broader basis of facts. The difficulty of this task is increased by the fact that it often seems impossible to show how those cases, in which other in- vestigators believed that they had detected transitional series, are to be explained on the theory of mutation. This is especially so where the authors have simply relied on comparative investiga- tions. The results of these can usually be explained, no doubt, by the supposition of transgres- sive variability, but a proof can only be given if the phenomena in question are investigated by statistical methods. In strong contrast to these doubtful cases, however, there is a long series of observations in which the absence of transitions is practically certain. Perhaps the most striking of these are the sterile varieties which consti- tute one of the most serious ob- stacles to the current doctrine of selection, at any rate as regards its exclusive api)lication. Darwin himself repeatedly cited them as objections and examined them minutely. Fig. 13. A flower of Li- liuui candidnm plenum. The thalamus is changed into a long stalk on which the narrow per- fectly white petals are spirally arranged. 90 Siidiloi Appearance and Constancy. In the case of the vast majority of sterile varieties we know neither how, when nor wliere they arose. They are propagated hy vegetative niethiods and have heen from time immemorial. Bnt they differ from their sui)- posed parent species so markedly that they take rank with the hest varieties. Nobody suppc^ses that they have arisen gradnally. The first instance that I give is Liliuni candiduni plcnnni, a form which is on the market. It is a well- known variety, the bnlbs of wdiich are offered every year by dealers in bulbs, in their catalogues. Instead of flowers it has long stalks clothed with petals (Fig. 13). The stalk is the elongated thalamus ; the petals are nar- row and dead white, and of the color and structure of the petals of other white lilies. In each flower they continue to appear for several weeks ; the lowest may be brown and withered before the tippermost have unfolded. Figure 13 shows a fairly short flower; they are often twice as long. Stamens and carpels are never formed ; the apex consists of a compact bud of the youngest petals. We do not know how the variety first arose. It was first described by G. Vrolik in 1827, after he had al- ready seen it flowering for 20 years in the Botanical Garden in Amsterdam.^ It is therefore nearly a century old. In horticultural literature it is not referred to until much later, about 1840.- Another well-known sterile garden plant is the green Dahlia (Dahlia Tariahilis viridiflora). The flowerheads ' G. Vrolik, Over cen rankvormig,c oniivikh cling van zvittc Iclic- blooncn. Vcrhandclin^cn dcr cerste klassc v. h. k. Nederl. Institmit van Wet. te Amsterdam, Part I, 1827, pp. 295-301, with one table. The spike with five flowers figured there, is still preserved in our collection. "See Mkrat, Ann. Soc. d'hortic. de Paris, 1841-1845, and Verlot^ loc. cit., 1865, p. 91. Sterile Varieties. 91 are destitute of flowers; and the thin, transparent bracts are transformed into small green leaves. The variety is much cultivated in gardens, partly as a curiosity and partly because their green ''flowers" do not wither but remain fresh on the plant; which renders it of a decora- tive effect until far into the autumn.^ The variety arose in a crop of seedlings about the middle of the last cen- tury in Boskoop in Holland, and since then has been grown from tubers. It occasionally bears isolated red ray florets but, so far as I know, never sets seed. Some years ago I obtained what seems to be a new and hitherto undescribed form of green Dahlia through the kindness of Messrs. Zocher «& Co. in Haarlem. It is not known whence this form came because it was at first taken for the type of green Dahlia we have just been considering. It differs from this however in the fact that the green heads are not of the normal form and size but transformed into long green leaf-bearing spikes like that figured in Fig. 14 with the exception of the clump at the top. This form produced elongated flowers of this kind in great numbers in the nursery garden ; but it could never, so to speak, bring its growth to a conclusion. They grow until the autumn and often longer, and frequently attain a length of 30 centimeters and more. They behaved in exactly the same way in my garden until last year when I manured them heavily. Then there appeared from a few of the green ''flowers" in late autumn a little head at the uppermost end (Fig. 14). This unfolded, but consisted of green bracts only ; it contained neither flow- ers nor seeds. The plant is therefore perfectly sterile. Another variety closely analogous with this is the ^ See the literature in Penzig's Teratologic, TI, p. 71. 92 .f^' fy •i 1, Sudden .Ippcaraiicc and Constancy. wheat ear carnation {^Dianthus Ca- ryopliylhis spicafus). In this case we find instead of the flowers small green ears which are formed of green bracts arranged crosswise. This sterile form does not api)ear to be in general cultivation, although it is perennial ; nevertheless it turns up here and there in crops of seedlings especially of mixed varieties. I cul- tivated a plant arisen in this way ; most of the ears were sterile as usual, but some of them produced a flower at their top. From these I obtained several germinative seeds. ^ The green rose has been known from time immemorial, but the i^reen Pelargonium ::onaIc\s a.mo(\Qrn prod- uct. In both cases the petals and stamens are transformed into green leaves. They are said to be perfectly sterile, and are only propagated by cuttmgs. Many double flowers never pro- duce seed, and this is especially true of those forms which do not develop structures intermediate between sta- mens and petals, but are described as instances of Petalomania.- Ra- * After having been sown these seeds have repeated the wheat-ear variety (Note of 1909). ^ K. GoEREL, Bcitragc cur Kenntniss gc- Fig. 14. Elongated Green fiiUtcr Bliithcn, JaJirb. f. wiss. Bot., Vol. DahHa, a new variety. XVII, pp. 217-219, and elsewhere. Sterile Varieties. 93 mmcuhis acris (Vol. I, Fig. 40, p. 194), Caltha palustris. Anemone nemorosa, Hepatica triloba, Tropaeolum majus flore pleno, Clematis recta, Barbarea vulgaris floribus plenis and many others are alleged in horticultural litera- ture to be perfectly sterile. Double varieties of compo- sites also afford instances such as Achillea P tar mica, Ageratum mexicanum (some varieties), Pyrethriun ro- seiim, etc. Others, such as Anthemis nobilis, are known to bear seed from time to time and so do not belong here. Viburnum Opulns, Hydrangea hortensea, Mnscari co- niosnm plnmosum and others have become sterile by the transformation of their reproductive flowers into sterile ornamental ones. Bananas and other seedless fruits have already been dealt with in the first volume (p. 195). Many varieties of the sugar-cane never set seed, such as the Cheribon cane which is the richest in sugar. This variety, which extends over vast regions, consists of a single individual ; that is to say, it is derived from one single unknown stock plant and has always been propa- gated by cuttings or so-called Bibits only. Robinia P send- Acacia inermis^ is also said never to flower ; and is only propagated by grafting. If this sterility affects annual species or such as cannot be permanently reproduced by vegetative means, the sterile form must vanish sooner or later. Such forms hardly deserve the name of variety, and are usually spoken of as monstrosities. But, in regard to their ori- gin, they are perfectly analogous with the sterile forms of which we have already treated. In the first volume (p. 195, Fig. 41), I gave the sterile maize as such an instance. More remarkable still is the unbranched Fir {Pinus excelsa aclada or monocaulis) wdiich Sciiroter ^De Candolle, Physiologic, II, p. 735. 94 Sudden Appearance and Constancy, has described in his excellent monograph. The whole plant consists of a single branchless stem, which is merely slightly swollen at the limits of every year's growth ; the needles remain adherent for a long time.^ This form has appeared in diverse localities. Schroter records 4 examples from Italy, one from Baden, several from Westphalia, ;Mittelfranken and Bohemia, and some from Mariabrunn near Vienna. The majority of these plants reached a height of 1-2 meters, a few of them as much as 5-6 meters ; some of them are still alive RiMPAU has described an instance of sterile rye.^ Ears of this rye appeared almost every year during a period of more than ten years; they were often much and sometimes excessively branched, especially in years and localities where the rye was very thin. But as ears of this kind occurred on plants which also bore normal ones, the repeated appearance of the anomaly may per- haps be due to inheritance. And lastly, instead of giving a further record of the numerous existing sterile varieties, let me refer to Nitella syncarpa, which has recently been described by A. Ernst, and which bears, instead of oogonia, incompletely devel- oped antheridia which never produce spermatozoids.^ The examples in question w^ere observed near Ziirich, and were completely sterile. * See p. 6^ and C. Schroter. Uchcr die FicJifc (Picca cxcclsa Link) Vierteljahrsschr. d. nat. Ges. in Ziirich, Jahrg. XLIIT, 1898, Parts 2 and 3, pp. 50-53, Fig. 18. This vahia1)le work contains a very full review of the varieties, forms, and monstrosities of this highly "variable" tree. ^Deutsche laiid'Zi'irlhschafflichc Prcssc, Berlin, October 4, 1899, where photographs of monstrous ears of rye are given. ^ Alfred Ernst, Ueber Pseudo-Hcrmaphroditismus bci Nitella syncarpa. Flora, 1901, Vol. 88, Part I, with Plates I-III. Races which Hai'c Arisen Suddenly in Nature. 95 § 10. INSTANCES OF RACES WHICH HAVE ARISEN SUDDENLY IN NATURE. In nature, elementary species are, as is well known, not connected with their closest allies by transitional forms. Nevertheless fluctuating and transgressive varia- bility frequently bring about the appearance of contin- uous series, which however on closer examination espe- cially by statistical methods dissolve into perfectly dis- tinct component units. ^ In very many cases these tran- sitional forms are absolutely lacking, and the separation of a particular form as variety, subspecies, elementary species, or even species, is mainly founded on their ab- sence. The absence of transitional stages in the case of forms which have been long familiar and are widely distributed obviously tells little concerning their mode of origin. Results are more likely to follow from the investigation of those cases in which the types in question are local in occurrence and in which, therefore, if transitional stages should occur, one would expect to find them in the locality inhabited by the plant. In some instances an exhaustive and minute study of the geographical distribu- tion of certain varieties has led to the discovery of the center from which distribution took place. Ascherson and Magnus obtained a result of this kind with the pale fruited varieties of the European species of Vac- cininni and some related Ericaceae.^ In inquiries of this kind, the absence of transitions at the present time points to the conclusion that they may never have existed. ' See Vol. I, Part II, § 25, p. 430. ^ P. Ascherson and P. Magnus, J'ciiiaiidl. d. k. k. zooL-hotan. GcscUschaft in JVicn, 1891, p. 677. 96 Siiihloi Appearance and Constancy. In contradistinction to these more or less distributed varieties, there is a whole series of records scattered through the literature of cases in which a new form lias ])een found on a particular spot under circumstances wliich warrant tlie conclusion that it has arisen exactly there and fairly recently. In such cases transitional forms are always lacking, a fact which proves pretty conclu- siv^ely that such have not been produced in the origination of the form. In Part II of the first volume two cases afforded by Oenothera Laniarckiana were described in detail : I refer to the appearance of O. brcvistylis and O. lacvifolia on the original locality at Hilversum. Both species proved, when tested, to be perfectly constant from seed, without any atavism; and transitional forms were not seen in the field. If these species had arisen where I found them, their origin must have taken place between the year of the introduction of the species and the first year in which I discovered them; that is, between 1870 and 1886 (See Vol. I, p. 266). The most important and accurate observation of such an occurrence is that which has recently been recorded by Solms-Laubach, and deals with a species newly arisen from Capsclla Bnrsa Pastoris} This was found by Professor Heeger in the market ]:)lace near Landau amongst the ordinary Sh.epherd's purse and called C. Hccgcri after him, by Solms. It occurred in 1897 and 1898 in very small numbers and only on this one spot. In its vegetative parts it is exactly like C. Bursa pastoris, from which it only differs in the form of its fruits. But the differentiating characters are of the rank of some of ^ H. Graf zu Solms-Laubach, Crucifcrcn-Studicn, Botanische Zcitung, 1900, Heft X, Oct., i, 1900, pp. 167-190, Plate VTTI. Races which Have Arisen Suddenly in Nature. 97 those which serve to separate genera amongst the Cru- ci ferae. The fruits of Capsclhi Heegeri are oval, and about as thick as they are broad. The seeds are notorrhizous. The valves lack the firm anatomical structure, character- istic of the normal valve, but are soft and full of sap, a condition which may be considered as due to arrested development. On the weaker branches in the autumn, deviations from this type occur which revert more or less to that of C. Bursa; moreover the flowers and young- fruits may develop into malformations, as the result of the attacks of Cysfopus candidus, which closely resemble those of C. Bursa pastoris. The seeds of isolated plants of C. Heegeri gave rise solely to the parent type (382 examples) without rever- sion to C. Bursa. There can therefore be scarcely any doubt that C. Heegeri is a good elementary species which arose from C. Bursa in 1897, or a few years previously, somewhere near Landau. It is moreover a species which is dis- tinguished from its nearest allies by characters of far greater systematic importance than those which separate many species of known origin. I myself found a S fella ria Holosfea a petal a not far from Wageningen in Holland under similar circum- stances (1889), and also in the same year the w^ell-known Capsella Bursa Pastoris apetala^ near Horn in Lippe. But I did not succeed in obtaining seed from either of them. In 1888 I collected some seed of Lychnis vesper- tina not far from Hilversum and obtained some per- fectly glabrous plants by sowing it. The new variet\' L. V. glabra proved fully constant as soon as I was able ^ Sec Penzit,. Teratologic, T. p. 2C)y. 98 Sudilcji Appearance and Constancy. to isolate it, and has maintained itself up to the present day without ever reverting. So far as puhlished data go, forms which have sud- denly appeared in nature, or have not previously heen noticed, prove constant, provided that cross-pollination is guarded against. In the opposite case they will prove themselves pure as soon as they can be isolated. One of the oldest cases in point is the constancy of Ranun- culus arvensis inennis whicli was established by Hoff- mann.^ The majority of records refer to trees of which the larger number of varieties, if not all, according to Darwin himself, have arisen suddenly,^ such as the \veeping oak, the weeping white hawthorn, etc'^ A single specimen"* of Fagus sylvatica aspleniifolia was found in a wood in Lippe-Detmold and could be multiplied from seed. According to Loudon, Taxus haccata fasfigiafa was found in 1780 growing wild in Ireland ;'^ but no pure seedlings of it have been obtained since only one speci- men w^as observed (a female one). The above list of cases is not a rich one ; but it makes no claim to completeness. The observations in point are, with few exceptions, relatively incomplete inasmuch as there is always the possibility that the first discovery of the new species or variety may have been preceded by a long period of evolution. If we assume this to be true, the absence of transitional forms and th^ constancy of the ^ Hoffmann, Bof. Zcitung, 1878, p. 273, where several other examples will be found. ^Darwin, Variations, I, pp. 461-463. ' Further examples are given by Braun, Vcrjiingiing, p. 333 (the sudden origin of red-leaved varieties of Quercus, CoryluSj etc.). * Ratzeburg, cited by Braun in Abh. d. k. Akad. Berlin, 1859, p. 217. °L. Beissner, Handbuch dcr Nadclhohkundc, 1891, p. 169. A great number of further examples is given in this work. Horticultural Varieties Arisen Suddenly. 99 new form are the only argnnients for its sudden appear- ance. § II. HORTICULTURAL VARIETIES WHICH HAVE ARISEN SUDDENLY. It is a matter of common knowledge that horticultural varieties have very often arisen hy sports. But opinions differ on two points. One is an empirical one and relates to the question of constancy ; the other relates to the meaning of the word variety. The two points are nar- rowdy bound up with one another. If the new form is not constant and pure from seed but frequently reverts to the parent species it is usually supposed to be derived from that species and is treated as a subdivision of it. But if the new form is as constant as the parent species, the empirical means of demonstrating its relationship are lacking, and the conclusions are drawn from his- torical data and based on analogy; a proceeding which, as we all know, often leads to dift'erences of opinion. Besides the historical records the main point in sucli cases is always the proof of the constancy from seed. But inasmuch as the interest of the practical man only extends to the question whether the variety can be con- veniently multiplied by seed and is not concerned with the possibility of occasional reversions, such information, especially in older cases, can only be accepted with cau- tion. With this reservation, I propose to give a brief review of some of the better known instances. But before I do this I will call attention to a very beautiful variety which I have not yet found described nor seen in trade- catalogues, but which has appeared in my own cultures. 100 Siiddoi Appearance and Constancy. Fig. 15 represents a single Dahlia, whose ray florets are all transformed into long and broad tubes which are open above. The same thing occurs in many other com- posites, for instance in Chrysanfheinuni segetuiu fistu- losum. Coreopsis tinctoria fistulosa, etc. On the analogy of these cases I propose to call this new Dahlia, Dahlia variabilis fistulosa. This variety arose from a crop raised Fig. 15. Dahlia I'ariahilis fistulosa, a new variety which has appeared in my cultures. from the seeds of D. var. Jul. Chretien, a dwarf single Dahlia with red flowers of the color of red lead, the tubers of which I had bought in 1892 in Lyons. From the seeds which I saved in that year from this variety, I raised in 1893 several plants of which one had a white flower. I only sowed seeds of this in 1894.^ It was T have unfortunately not yet succeeded in fertilizing Dahlias artificially by their own pollen. Horticultural Varieties Arisen Suddenly. 101 in the crop thus raised that the plant whicli bore the flower head shown in Fig. 15 appeared. The color was dark carmine red, not that of red lead. The flower heads were all fistulous from the beginning of June until well into October; but the later flowers manifested the ab- normality in varying degrees. Either the base only of the tube was closed ; or only some of the ray florets had the form of a tube. The plant had to be left to free crossing with its neighbors so that no observations of real value as to its constancy could be made. Neverthe- less this was pretty considerable, for, from the seeds of my fistulosa I raised 43 plants in 1895 of which 25, that is to say more than half, had the characters of the new variety. The origin of Chelidonium laciniatuin from C. inajus was described in detail in the first volume (p. 189, Figs. 36 and 37) ; where a series of other cases will also be found. Verlot (loc. cit., p. 34) describes Ageratuni cocruleuni nanum as a novelty which is sometimes sterile, but sometimes occurs as a fertile and constant variety. Verbena hybrida, *'a fleur couronnee" arose about 1889 from the variety "a fleur d'auricule," it immediately proved constant and after only two years was put on the market by E. Fourgeot of Paris. ^ Robinia Pseud-Acacia rosea was found by Decaisne in a crop of ordinary Acacias; and Gleditschia sinensis inerniis arose in the same way, as also did Sophora japonica pendula which a])])eared in i\I. Joly's nursery garden in Paris about 1800.- In 1860 a new strawberry "Reus I'on Zuidw\k'' appeared in Boskoop. Its leaves and fruits were larger ^ See his Catalogue for 189T. Verlot. loc. cit., pp. 59. 92. 93. 2-ir 102 Siiihloi Appcanuicc and Constancy. and altogether better than any varieties then known ; it was constant from the first and spread rapidly. I shall conclnde this summary with a reference to the new species of Tomatoes which Bailey has recently described.^ He describes the oriii,in of two new forms which he has called Upright and Mikado and which arose in his cultures. They differ from one another and from the parent species by more definite and more numerous characters than many amonsf the older forms which are recognized as good species in the genus Lycopcrsicnni. They arose suddenly as usual and were propagated by seed. The observations recorded in this and the two preced- ing sections, which are far from constituting complete lists, show that the origin of varieties and of elementary species both in the garden and in the field is amenable to experimental investigation, for the phenomenon is by no means so rare as is generally believed. The botanist will investigate the indifferent and useless forms with just the same result as the profitable ones, to which alone, of course, the practical man pays attention. The cultures need not be very extensive to aft'ord novelties from time to time, though these must not be expected the first or every year. Once obtained, all that there is to be done is to isolate them as soon as they appear and pollinate them artificially. But it is far more important to go back to their ancestors, partly not to lose the historical evidence, but mainly in order to sow the seeds of these ancestors again and to find out if the novelty will be again produced, and if possible to discover the conditions which determine its appearance. l,^nf(3rtunately there are many plants which do not lend themselves to such experiments, * L. H. Bailey^ Survival of the Unlike. Horticultural Wirictics Ariscu Suddenly. 103 either because they produce no seed or yield too small a harvest when self-fertilized or because they cannot be artificially fertilized on a sufficiently large scale or be- cause the number of seeds produced, even under normal conditions, is too small. Moreover one is almost abso- lutely confined to annual or biennial species or to such perennial ones as flower freely in the first year. But in spite of these difiiculties and of the incom- pleteness of the observations made hitherto, we may safely conclude from them the possibility of an experi- mental study of the origin of horticultural varieties.^ * I shall describe an experiment of this kind with Linaria vul- garis pcloria in § 20. V. ATAVISM. §12. ATAVISM BY SEEDS AND BUDS. HoFMEiSTER ill liis AUgcuicbic Morphologic defines atavism in these words: ''The occurrence of reversions, the offspring of a variety of known origin resembhng the parent type" (p. 559). According to the meaning of the word "known" in the above definition the term atavism may embrace quite a series of phenomena of the most diverse importance. It may mean either that this origin must have been actu- ally observed, or that it can be inferred with sufficient certainty from comparative and systematic studies. If we are merely dealing with morphological questions this distinction may appear unessential, but as soon as our object is to test by experiment the results obtained, it becomes of the highest importance. For to obtain true experimental proof of atavism it is obvious that the origin of the forms should be known directly by observa- tion. The origin of a whole series of varieties and ele- mentary species from their parent forms, however, is sufficiently established by the historical evidence relating to their first appearance. It seems therefore feasible to confine our attention to such cases and to draw a distinc- tion between physiological and phylogenetic atavism. The former is reversion to actually known ancestors, the latter to systematic ancestors. Atavism by Seeds and Buds. 105 But before I proceed to examine these two forms of atavism more closely, I think it desirable to state that I here use the word ''atavism" in its narrower sense, for in its wider sense it embraces so large a group of phe- nomena that it would not be possible to deal with them all within the limits at my disposal. It seems worth while to indicate the more important of these types because they are often confused with one another and because results obtained with one form are often taken to apply to an- other, simply because they both go by the same name. We must first of all draw a sharp distinction between atavism as applied to variability and as applied to muta- bility. In the first case we are dealing with the phenom- ena presented by a single heritable character ; in the latter, with the conflict of two or more. In the improvement of races the offspring do not resemble the selected pa- rents, they always revert partly towards the mean of their ancestors. We are of course dealing in such cases with the phenomenon of regression which was fully dis- cussed in the first volume (pp. 82 and 120) ; and it would be better to refer to all those individuals of less value which are eliminated in selection as regressive and those which exceed the level attained by their parents as progressive. But it is customary to call the former atav- ists; and, as a matter of fact, they exhibit the degree of development of the characters in question as it was mani- fested by their grandparents and more remote ancestors, and not as in their parents. They could perhaps be called ''curve atavists," since this term does not suggest a reversion beyond the curves in question.^ The most fascinating section of the subject of atav- ism is that which deals wath so-called "youth" forms ^ See the pedigree of the many-rowed maize, Vol. I, p. y^,. Fig. i8. 106 Atavism. and with related phenomena. Goebel's admirable in- vestigations have demonstrated the wide distribution of these phenomena and their great importance to the theory of descent.^ It is now a matter of common knowledge that many plants, and indeed whole groups of species, exhibit characters wdien young which they either lack in the adult state, or which in later life appear only under definite circumstances. Beissner's discovery- that whole genera of cultivated Coni ferae, such as Rctinospova, are only youth-forms of other known types such as Thuya; and Reixke's investigations"' into the earlier stages of Leguminosae, as well as the work of many others, have resulted in the accumulation of a mass of information relating to this subject. Siuui and Bcrula in their early stages have the doubly pinnate and finely slit leaves of their close allies ; the thorns of Bcrhcris on the so-called suck- ers revert to the foliate form. These phenomena, how- ever, fall mostly within the sphere of systematic botany, and only concern the study of variability in so far as they are dependent on external influences. \\t must further exclude from our considerations the effects of crossing. The so-called reversions of the horticulturists which are brought about either by acci- dental crosses with the parent or by unconsciously using hybrid seed, certainly occupy a very ])rominent place in the practice of horticultural selection, but they should be rigidly excluded from scientific speculations. And ^ K. GoEBEL, Uchcr Jiigendformen von Pflanzcn und dcrcn kiinsf- lichc WicdcrJicrvorrufung.. Sit7.iingsber. d. k. bayr. Akad. d. Wiss., Vol. 26. i 2 21 12 33 63 37 3 25 5 30 77 23 . 1 3 93 96 4 96 ' 0 75 75 0 100 ! 3 1 36 37 3 97 From the red \ spikes j From tlie striped \ spikes ) I obtained a sufficient harvest of the striped and red spikes of the same plant from three individuals only. 132 Atavism. These produced in the summer of 1895 the result shown in the table on page 131. In other words, the average intensity of inheritance for striped spikes was 98% and for red ones 71%. If we compare these figures with those derived from the previous generation we do not observe any appre- ciable difference between them. In other words, the in- tensity of inlieritance exhibited by the red bud-variants is essentially the same as that of the red seed-variants. In the following year I continued this experiment through one more generation by self-fertilizing some striped and some red individuals amongst the offspring of the bud-variants. The seeds of three striped parents gave rise to 67 oft'spring that flowered, only 5% of which were red ; the seeds of the five red seed-parents, however, gave rise to 127 offspring of which 84% were red. (The percentages in the five individual groups were 71-78-84- 88 and 100.) Thus the proportions were similar to those of the previous year. ANTIRRHINUM MAJUS LUTEUM RUBRO-STRIATUM. SEED- AND BUD-VARIATIOX (ANNUAL CULTURES). Year 1896 (1895) 95% Striped Striped plant 84% Red. Red plants 1895 98% Striped (1894) Striped twigs V 71% Red. Red twigs. _j V 1894 98% Striped 1893 90% Striped plants 76% Red. 10% Red plants 1892 f Striped plant Antirrhinum Ma jus Striatum. 13 -» I have exhibited on the opposite page the whole ex- periment in the form of a pedigree. The result of our experiment can be given in yet another form. The intensity of inheritance in the finely striped spikes in successive generations produced by self- fertilization was always about 95-98%. The intensity of the inheritance of the red character in the various subdivisions of the experiment was as follows : 1. For seed variants 76% 2. For bud variants 71% 3. For the offspring of bud variants . . 8i% Average 77 % Finally I have endeavored to investigate the mode of inheritance in the case of sectorial variation ; that is, of spikes which on one lateral part bear striped flowers and on the others red ones. It is obvious that this phe- nomenon may be due to two entirely different causes. First the red flowers may be genuine bud-variants and, in such cases, they will presumably exhibit an intensity of inheritance which corresponds with that found for the bud-variants dealt with above. But it may also hap- pen that on a very coarsely striped spike some of the flowers may possess this striping in so extreme a degree that they appear uniformly red. In this case their mode of inheritance will presumably not differ from that of the remaining flowers on the same spike. The latter was the case in the only experiment which I have so far had the opportunity of making. In the summer of 1898 I employed for this purpose a broadly striped plant from the crop referred to on page 128. One side of its terminal spike bore red and the other striped flowers. There were 8 of the former and 7 of the latter. I enclosed the whole branch, before it flowered, in 134 Atavism. a bag, fertilized each flower with its own ixjlleii, and gathered the seeds separately. Five fruits of each color ripened, though some of them contained little seed. I sowed the seed in 1899 on ten separate beds; they flow- ered in Jul}'. On each bed one saw at a glance that about half the plants bore exclusively red whereas the other, slightly larger half, bore striped tiowers. I recorded the numbers separately for the ten groups ; but do not con- sider it necessary to give the separate numbers. There flowered : Average 42% From the seeds of: Plants Reds 1. Red flowers 67 'i'i% ] 2. Striped flowers 137 46% ^ * ^ jfj The result of all the experiments described above may be summarized in the following theses: \. Antirrhiniiiii inajus lutciun nibro-striahiiii (Plate I) is an inconstant race consisting of striped and of red flowered plants. 2. The striping of the commercial race varies con- tinuously, but the continuity does not include the red ones; these are separated bv a gulf from tlie striped (Fig. 22). 3. The intensity of inheritance of the finely striped plants is about 95-98%. They pass into the red type either when propagated by seeds or by buds. 4. In the same way the broadly striped indixiduals produce many more reds; the mean of three experiments fl 1-36-42) was about 30%. 5. The red plants resemble the wild ancestral form externally but are not constant as this is. The intensity of inheritance of their character is only about 70-85% ; and the remainder of their offspring revert to the striped AntirrhinuiJi Ma jus Striatum. 135 type. I have not yet observed this to happen by means of bud-variation. 6. Antirrhinuui uiajus lutcuiii does not arise from these striped and red races. 7. If we compare the forms which we have been considering,^ with the half races and middle races which we distinguished in § 3, p. 18, we hnd that between the two constant elementary species ( the systematic species, A. uiajus and the systematic variety, A. ma jus lutcum) there exist two intermediate forms which are perfectly distinct from these two, but not from one another. We can distinguish, a. Ilie eversporting variety,/], majus lutcum, striatum, ^^•ith striped flowers and a high degree of iluctuating variability, from which a faintly striped and a broadly striped race can be raised by selection. These three races however merge continuously into one another. b. The atavistic type in this race is uniformly red, but with incomplete inheritance and gives rise, when self- fertilized, in each generation to about 25% striped indi- viduals besides the red ones. In contrast with the previously described cases, the transition from the atavistic type to the eversporting variety and the reverse process here occur every vear but always with a slight gap. The red type arises from the striped race by seeds and by buds, but the striped race has, hitherto, arisen from the atavistic type only by ^The mode of inheritance in the coarsely striped individuals will have to be more closely investigated ; so also must sectorial varia- tion. Moreover the experiment should be repeated with other striped varieties, and the spotted forms investigated to see if they behave in the same way. Rut it is most important that pure cultures of the various types should be made by breeding for several generations. For this purpose the tall varieties should be chosen preferably, since they promise a much better harvest than the half-dwarf ones which I employed in my experiment. 136 Ataz'is)}!. seeds. The transition from the red to the striped oscil- lates round 25%, the transition from the striped to the red is largely dependent on the degree of striping, which points to the existence of factors as yet incompletely understood. It may perhaps be mentioned here in anticipation that the varieties of Hcsperis and Clarkia (i^ 15 and >5 16) with striped flowers behave in the same way , whilst both in Plantago (§ 17) and Linaria vulgaris peloria (§20) tlie evers])orting variety is inconstant and reverts more or less easily to the atavistic type. § 15. HESPERIS MATRONALIS. The flowers of the dame's violet are violet as the name indicates. There are three varieties on the market : a white flowered, a double, and a dwarf variety, all of which are con- stant so far as I know. A Forma lilacina and a "mixed" sort are of- fered in the catalogues. The plants are perennial; if the seed is sown in the spring, the majority of the plants Avill not flower until the following year; but if the seed is sown as soon as it ripens, or is allowed to fall on the ground instead of being harvested, the plants generally flower the next year. I have employed both of these methods at different times. I obtained my seeds in 1890 from a mixed group of white and violet flowered plants which were growing in our Botanical Garden. I grew them for two genera- Fig. 24. Hesperis matvonalis. A flow- er of the pale finely striped form, with half of one of its petals dark violet. Hcspcris iiiatronalis. 137 tions and found that the "white" were not pure white but pale hlac. Then I kept only plants of this variety through the winter, and first examined them in 1894, when they were in full flower. They flowered in isola- tion and partly pollinated themselves with their own pollen, partly were fertilized by insects. In later years also I have not enclosed this species in bags but have either grown them in an isolated position and left them to be pollinated by insects, or have had them flowering in a little greenhouse entirely built of fine metal gauze, where they fertilized themselves. My object was to test the degree of inheritance of the pale, the lilac, and the violet types separately. I shall first give a summary of my experiment. In this table, W denotes whitish, L lilac, and V violet (that is, the color of the W'ild species). The numbers in each case are per- centages of the particular culture; where the culture was too small I have omitted the numbers. HESPERIS MATRONALIS. (whitish, lilac, and violet in percentages.) 1900, 1899 38 W. 30 L. 32 V. J 50 W. 28 L. 22 V. annual and biennial 1898 92 W. 6 L. 2V. annual 1897 annual h / l r • 1895 29 W. 57 L. 14 V annual and biennial y 1 1894 I 1 Before I come to the description of this experiment it is necessary to give some more details as to the varia- bility of the color of the flower. 138 Atavism. Plants with pure white flowers such as those belong- ing to the variety Alba did not occur in my cultures. I have compared the Alba and also the Alba plena directly with my plants. Certainly the difference is sometimes very slight, especially as the petals of Alba acquire a pale lilac color when they fade. They are all gradations between the wdiitest examples and those with the full lilac color; the variability in this case is perfectly con- tinuous. But between the lilacs and the violets there is always a gap; the darkest lilacs seem to be about half as dark as the violets; intermediate stages do not occur. The vast majority of the plants have all their petals of the same color, but mixed conditions also occur. As in other cases there are striped flow^ers, sectorial and Imd- variations. Examples of these three groups appeared in various years in my cultures but only sparingly. On the striped petals the stripes were fine and rare, but they ex- hibited the dark violet hue of the original species. The instances of sectorial variation have so far been occa- sional dark flowers on pale clusters, and on the other hand flowers of which one-half of a petal was wdiitish and the other violet (Fig. 24). Bud-variations occurred on plants with very pale flowers, especially when they were richly branched and flowered on into the autumn. They were always stray twigs on the lower part of the main stems ; their flowers were all of the normal violet color. But so far I have not been able to obtain seed from them. A glance at a large bed reveals the general distribu- tion of color. At once the pale flowers are seen to be in the majority, whereas the whitish on the one hand and the lilac on the other are obviously rarer. The violet stand out conspicuously because they are not connected with the rest by any gradations. Except for this the varia- Hcspcris Matronalis. 139 tion is so continuous that it is almost impossil)le to ex- press it in numl)ers. I have tried to arrange the plants in groups and to count the numbers of each group. And I give the numbers obtained in this way, only with the object of conveying to the reader the general impression which a bed makes on the observer, for it is inevitable that the limits between the groups should be somewhat arl)itrarv. Nevertheless I trust that I have succeeded in keeping fairly well the same limits between the groups during the successive years of my experiment, and this is the most important point. For the purposes of these color valuations I picked a flowering cluster, if possible the terminal one, from each of the plants on a bed, brought them to my house and sorted them there. I made out the following more or less clearly defined groups : W. Whitish, always without stripes. VVi. Almost white ; buds and withering petals almost white. W2. White suffused with lilac, not darker when withering. [F3. Very pale lilac; buds lilac; only slightly darker when withered. L. Lilac, sometimes striped or spotted. L\. Definitely lilac, although pale; darker than Lo. Lilac; half as dark as V. V. Violet, the color of the typical species. I shall now give the composition of the culture of 1898 which was raised from the seeds of plants with whitish flowers. On July 14, I sorted 250 individuals bv the method described and found : 140 Atavism. HESPERIS FROM THE SEED OF WTTTTTSTI FLOWFRFD FT. ANTS. W^ 5% u\ Sl^'r ^v. 30% L, 4% L, 2% V 2% 92% W. 69c L. 2% V. I determined the composition of the cultures of the next year, 1899, in the same way; they were both raised from the seeds of h'lac plants. One of them (5th gen- eration) flowered partly in 1899 and partly in 1900; but the other only in 1899. The result was as follows: HESPERIS FROM THE SEEDS OF LILAC FLOWERED PLANTS. Color 1st Experiment (5th Gen.) 2d Experiment (3d Gen.) W, 3% \ 4% \ W-i 15% - 38% W 22% - 50% W. W^ 20% i 24% J V 32% = 32% V 22% = 22% V. The first list is based on 1 55 flowering plants, and the second on 219. The seeds of the whitish Hcspcris, therefore, in this experiment, produce their like with a small percentage of lilacs and violets. The seeds of lilacs, on the other hand, give rise to the three types in about equal numbers, though it must be remembered that the limit between //':] and L\ is to a certain extent arbitrary. I have not yet made a sufficient number of observa- tions on the inheritance of the violet color in this race. In the only experiment which I have carried out, only five plants flowered and they had the same color as their parents. Let us now pass on to a detailed description of the Jlcspcris Mafroiialis. 141 experiment. It began in 1894 with seven plants which had already flowered in 1893 and had been noted as lilac flowered. Many of their flowers were more or less striped, some of them produced in August the violet bud- variations mentioned above, when the rest of the flowers had been through blooming for a long time. Seed was only saved from the lilac flowered branches ; a part of it was sowed in August, the rest as soon as it was ripe. Most of it germinated in the following February and March; more than half of these plants produced stems and flowered in August. I obtained altogether 234 plants in flower of which 29% were pale, 57% were lilac and 14% normal violet. I selected the strongest plants from among the most typical of each group and transplanted them in the autumn to three as isolated spots as I could find in my garden. Here they grew freely, branched abundantly and flowered in the following year (1895) for a second time. There were three violet plants which however set very little seed. This was sown and the offspring flow- ered in the summer of 1897 in a conservatory. I took precautions to prevent their being visited by insects in order to render impossible the transference of their pollen to the other plants. As soon as the color of the flowers could be determined w^ith certainty for any plant, this was pulled up. There were, as I have already stated, only five plants and their flowers were violet. I did not allow the lilac flowered plants to flow^er in this year but kept them for the next. Of the plants with pale flowers which had been planted out separately in the autumn of 1895, only one plant flowered in 1896. Its seeds were sown immediately and gave rise to 12 ])lants which flowered in the summer of 1897; thev were all 142 Atavism. pale with no more than tlie faintest indication of the hlac color. Hie seeds were sown in pans in the autumn, the seedlings were pricked out in Xoveml^er and planted out in April 1898 on a large bed. In June 250 individ- uals flowered, and the percentage composition of the color, as given above, was determined. Then the four lilac individuals falling into the group L2 were taken up and transplanted with all possible care to the metal gauze greenhouse. Before doing so all open flowers and vouuiT fruits were of course removed. It mav be noted that in this experiment the lilac flowered individ- uals began to flower conspicuously later than the pale and violet ones. The seeds of these four plants were sown partly in October and partly in November, separately for each parent. Only one of the four resultant groups flowered in the following year (1899) ; the rest remained in the rosette stage and flowered in 1900. The proportions of the various colors were very mucli the same in the four groups. I recorded them separately but did not find any significant difl^erences. The numbers in the first column (Ist Experiment, 5th Gen.) on the table on page 140 give the composition of the whole culture. I transplanted some lilac plants of the first crop (1895), btit only kept one of them which caught my eye with its beautifully striped flowers. It grew up into a sturdy plant, flowered in 1898 in an isolated spot and set an abundance of seed. From this 219 flowering plants were raised in 1899, and their colors are recorded in the last column of the tabic on page 140 (2d Experi- ment. 3d Gen. ). If we consider the results of these experiments, ex- Hcspcris Matronalis. 14v3 tending over seven years, in their relation to other known facts we find that we can distinguish the following races : 1. Hcspcris matronalis alba, the constant commercial variety. 2a. A whitisli, pale lilac, seldom or never striped sort ([F1-W3), which can reproduce the violet color by sectorial, bud- and seed-variation ; violet seed-variation about 2% ; lilac offspring about 6%. 2b. A lilac, often striped or spotted, race which gives rise to an inconstant but mostly considerable number of whitish and violet offspring. Its color merges contin- uously into that of No. 2a, but is sharply separated from No. 3. 3. A violet variety wdiich has arisen from 2a and 2b and is presumably inconstant, on the analogy of Antirrhi- uiini iiiajus. 4. Hcspcris matronalis, the original, constant, violet species. The analogy with the corresponding races of An- tirrhinum inajus seems to me to be obvious and can be ex])ressed as follows : 1. The systematic variety which is perfectly con- stant {H. in. alba, A. niaj. lutcnm). 2. The eversporting variety with lilac or striped flowers (H. m. lilacina, A. maj. lutcnm striatum^. It can be split by selection in a plus and in a minus direction ; into a pale lilac, or finely striped race on the one hand, and on the other into the dark lilac and frequently striped dame's violet and the broadly striped snapdragon. 3. The self-colored but inconstantatavistictvpe which has the color but not the constancy of the original s])ccies. 4. The original violet, or red, perfectly constant spe- cies (Hcspcris matronalis, Antirrhinum ma jus). 144 Ataz'isjii. § i6. CLARKTA PULCHELLA. A wliite variety of this pretty red species is offered by seedsmen.-^ Besides this a striped race sometimes oc- curs which has more or less numerous red bands of vary- ing breadth on the petals.^ The red in these cases has the same intensity as that of the species. Moreover the white flowers are not pure white ; a very delicate but distinctly visible red flush can be seen on any bed of them in full flower. Sometimes occasional plants or individual flowers are somewhat richer in pigment, so that it is at once obvious that they are not pure white. I have only made an in- complete series of experiments with this plant because it does not lend itself easily to artificial fertilization and, as a rule, does not stand transplanting while in flower. But the results ob- tained suffice to demonstrate their essential correspondence with those obtained with Antirrhinum and Hcs peris. We can distinguish in this as in the other two cases between a pale race poor in stripes and a richly striped one ; moreover these two races possess the characters of the corresponding ones in the two species named. But in Clarkia the broad stripes appear chiefly as sectors, as ^ There is also a variety, Carnea, which is constant so far as my experience goes. ''See p. 119. It was referred to by Vilmorin and hy B. Verlot, Production et fixafion des varictcs, 1865, p. 64. Fig. 25. Clarkia pulchella. A white flower of which one petal and a half are dark red, while there are dark red stripes here and there on the other two petals. Clarkia PulchcUa. 145 for instance, wliolc or half petals; T shall therefore call such flowers and plants sectorial. In 1896 I had a bed of about 50 plants all of the flowers of which were whitish. The majority bore no red stripes, or only such fine ones and so rarely that they were overlooked, which is always possible since the ])lants produce very many and rapidly fading flowers. Only one ])lant stood out amongst the rest; at the end of July it bore a flower with two red petals and at the beginning of August a petal the middle third of which was also colored red. Otherwise, the bed was practically white throughout the summer. Some of the seed of the whites was saved. From the seeds of a w^hite flowered specimen I ob- tained in 1897 a culture of about 100 plants. Amongst these again there was only one sectorial example ; I saved its seeds separately although it had been fertilized by insects in the midst of the others. In the majority of these others I had not seen red stripes, but on a few of them there had been some insignificant ones. The seeds of the pale flowered plants gave rise to a generation equally poor in stripes; in 1898 I only saw one striped one amongst 30. This race therefore remained poor in red sectors as a result of a continued selection of almost white plants. From the seeds of the sectorial plant I at once ob- tained a race which was rich in red petals and red s-? ^- tions of petals, and often produced whole red flowers and twigs with red flowers only (Bud-variation). I grew it for two generations (1898 and 1899). The seeds for the first were gathered in 1897 from a seed-parent which had not been isolated; in 1898, however, I pulled up all of the non-sectorial plants whilst they were in 146 .Uaz'isiii. flower and on tlie remaining seed-parents only harvested tlie seeds from those flowers which opened after that operation. The single sectorial plant of 1897 bore one flower with one, and another with two red petals. Their seeds were harvested sejxirately and sown. The other flowers were pale; I also harvested their seed separately. The flrst named seeds, naturally few in number, gave rise in 1898 to about 40 i)lants which flowered; the latter to 200. In both groups the red stripes and sectors were remarkably numerous in comparison with the previous vear. At the end of July I found amongst the former about 25%, and amongst the latter 23Yc sectorial plants. Besides these, a plant bearing red flowers exclusively, occurred in the former group. If I had repeated these observations from time to time the two percentages would of course have been considerably increased. But in order to isolate the sectorial plants I pulled up all those which up to that time had exhibited only few and narrow stripes. As already mentioned, I harvested seed only from the fruits of those flowers which had opened after this operation. I saved two kinds of seed : one was from a number of sectorial flowers which I had marked on a large group of individuals ; the other was from a par- ticularly striking plant which I had also marked, and which had a fair number of sectorial and occasional per- fectly red flowers, exhibiting also red bud-variations on its lower branches. I harvested seeds only from the narrow striped flowers of this plant. I have one more case of sectorial variation to men- tion before I proceed to give the results obtained from this harvest. A green lateral branch in an inflorescence on an otherwise white or finely striped plant had a Clarkia Pulcliclla. 147 narrow red longitudinal line on it which was not nuich broader than a flower stalk and extended over four inter- nodes. The upper, lower, and middle flowers of the tract stood on this line ; the two former were completely red, the middle one only partly so. The two flowers oc- cupying intermediate positions but on the green side of the branch were almost white. The culture of 1899 was richer in sectorial plants than that of 1898, as the isolation of the seed-parents w^ould have led us to expect. From the mixed seeds referred to above, I had about 300 plants of which five were wdiolly red whilst the proportion of sectorial ones was 40%. The single selected seed-parent, however, gave rise to only 50 offspring which flowered, of which one was red, whilst the proportion of sectorials mounted to 70%. The average number of reds in the two cultures was 1-2% ; and that of sectorial plants 45%. These experiments show that the pale flowered plants, selected as seed-parents, give rise to a fairly constant progeny amongst which the proportion of sectorial plants is quite small. The progeny of sectorial plants, on the other hand, consists of about 45% broadly striped and 1-2^^.4 red plants, the remainder being pale tinged with red, or at any rate very poor in strii)es. The cultures of the pale fl.owered plants are ordinarilv in flower some weeks before the first stripes appear: but in the beds of sectorial plants the red may be seen among the very first flowers. Here also the white flowered ones are always in a large majority ; among a thousand flowers of this race I counted 34 striped and 8 sectorial ones, that is to say only 4% altogether. 148 Atavism. § 17. PLANTAGO LANCEOLATA RAMOSA. Plaiitago lanccoJata is one of of those plants which are remarkably rich in anomalies. Penzig mentions a considerable number of them such as leafy stalks, ears the tops of which bear tufts of foliage leaves/ forked spikes with two or more tips, torsions etc. These and many other malformations such as split leaves, pitchers consisting of one or more leaves, occur commonly in this neighborhood and also in mv cultures. It is worth men- tioning that all or nearly all of these abnormalities can occur in the same race, and sometimes indeed in a single stout individual. Evidently every plant must contain a number of latent or semi-latent characters which lie out- side its proper range of form ; these characters consti- tute, as I have already said, the outer range of the forms of the species (p. 27). A form also frequently mentioned- in the literature of the subject is one wnth branched ears {Plantago lan- ccolata rainosa).^ In this variety sessile secondary spikes are produced in the axils of the bracts at the base of the main ear. They are often small, but sometimes nearly attain the size of the central ear. Their number is highly variable. Under good conditions of cultivation each head may have from 2-7 lateral ears, but on single ears the number may rise to 20 and more (Figs. 26, 27). I have been carrying out experiments on the inheri- tance of this ra;/?o^a-character since 1887. It proved to ^I have often picked these tufts and made cuttings of them; they take most quickly and grow to strong rosettes of radical leaves, the ears arising from which may repeat the phenomenon of the tufting to a certain extent {Plantago la)iceolata coronata). ' Penzig, Teratologic, II, p. 252. ^ Kruidkundig Jaarhoek, Gent, 1897, pp. yG and 91. Plan fa go Lanceolata Ramosa. 149 be only partial. In spite of the most careful selection and isolation during the time of llowering this race every year produces plants not one of whose spikes, even when there are a hundred to the plant, exhibits the smallest trace of branching. They are obviously to be regarded as atavists. The proportion in which these atavists occur seems to be fairly constant, fluctuating however from year to year. It can be slightly increased or diminished by the choice of favorable or unfavorable seed-parents; but it does not seem possible to effect an essential and per- manent improvement by continued selection, at least not to a degree that would open a chance of altogether elim- inating the atavism. In the first years of my cultures I did not pay partic- ular attention to this phenomenon ; moreover my experi- ments were on too small a scale to afford numerical data of any value. But I found atavists as w^ell as raiiiosa- plants every year, although I always collected my seeds from the former. I did not determine the proportion until the fifth generation (1892) was reached. I should state tliat I have isolated my seed-parents every year, cutting off as many as possible of their unbranched ears before they flowered. Pollination which had to be left to the wind w^as therefore confined to the group of se- lected seed-parents, wdiose number scarcely ever ex- ceeded 10. It was as pure as it was possible to have it. I obtained the following figures : GENERATION PERCENTAGE OF ATAVISTS 5.— 1892 ^6% 6.— 1894 50%, 58%, 59% 7.— 1897 47% 8.— 1898 45%, 56%, 59% 8.— 1900 52% 150 Atavism. Plantago lanccolafa ra///c^a. therefore, produces a pro- portion of about one-half atavistic individuals every year. The variability in the fig- ures given is at least in ]:>art dependent on external in- fluences (nutrition and selec- tion). Closer examination of the individual years proves the truth of this. In 1892 I had 48 plants in flower ; nine of these plants produced split leaves and pitchers at the time when they were Ijeing transplanted, about three weeks after the seed had been sown, and seemed espe- cially desirable on this ac- count. In the summer they turned out to be all rainosa- plants with richly branched spikes. They were cultivated the following year also ; and the sixth generation was raised partly from their seed and partly from the seed har- vested in 1892 from two other seed-parents. From the latter were raised 103 plants which flowered, of which 50% were atavists, this proportion being nearly the same for the two seed-parents. In order to investi- gate this, the seeds of the individual seed-parents were, Fig. 26. Plantago lanccolafa ramosa. A whole plant. Plantago Laiiccolafa Rauiosa. 151 as usual, sown separately. The iiigher figures 58% and 59% were derived from the offspring of a plant which had been divided into two in 1893, after which one-half of it was grown on sand and the other on ordinary garden soil. I shall have to revert to the effect of this treatment on the plant itself; but it will be observed that the differential treatment had no visible effect on the offspring of the two halves. (The numbers of indi- viduals dealt with in the two cultures were 57 and 60 respectively. ) The seeds of the typical individuals of my race of 1894 I sowed in 1897 under normal conditions, as usual (seed sown in the greenhouse; seedlings pricked out into pots, and afterwards transplanted to the beds). The seed had been saved from two plants with richly branched ears. It produced a culture of 70 plants which flowered and contained 47% atavists. Whilst flowering was pro- ceeding I transplanted all the ra;// o^a-plants whose ears were only slightly branched, and marked among the re- mainder a specimen which seemed to be the most pro- fusely branched. I harvested seed from those flowers only which protruded their stigma after this separation had taken place and after the atavists had been weeded out. Seed was harvested separately from each plant. In the following summer (1898, 8th generation) it was seen that the seed of the best seed-parent had only pro- duced 45% atavists (among 100 plants that flowered). The seeds of the average seed-parents gave 56%, and those of the worst, 59%. Selection had therefore a dis- tinct, although not a very great effect. It should be re- marked that the number of average seed-parents was 8, and that of the worst ones 10. The composition of the progeny was determined separately for each seed-parent, 152 Atavism. but the differences were not greater than the extent of the experiment would lead us to expect. There were 1033 offspring from the average seed-parents and 732 from the ten worst plants. The two separate cultures which deviated most from the mean contained 37% and 65% atavists respectively. The value of 52% given Fig. 27. Plantago lanceolata ramosa. A, B, C, three branched ears. above for the same generation but grown in 1900, will be dealt with below. Bud-variations occur in this as in the inconstant races of other species, although very rarely. In such cases it is one or several lateral rosettes which vary. The struc- ture of our plant is a very simple one. The stem of the Plaiitago Lanccolata Raniosa. 153 seedling grows out into a short, somewhat obhque. rhi- zom which produces a rosette of radical leaves. Ears are formed in the axils of the higher leaves but rosettes of the second order grow out from the axils of the lower ones. In the second summer the primary and secondary rosettes behave in the same way, again producing ears above and secondary rosettes below. If the plant grows very rol^ustly it may consist of as many as 10-20 single rosettes; if it is a ramosa every rosette produces branched ears, at least on some stalks. Sometimes all the ears of the whole plant are branched, in which case it is per- fectly easy to see that there is no bud-variation. In its second year a single plant may often produce more than 50 branched ears. The culture of 1897 contained a plant which exhibited a bud-variation. The seeds of its branched ears, har- vested in the first year, had produced 89 individuals that flowered, of which ?)6 (40%) were atavists. The plant in question consisted, in the autumn of its second year, of more than 25 single rosettes which were carefully isolated, and planted separately. Only the seven strong- est ones survived this operation. I kept them all in their pots until a sufficient number of ears were visible and then planted them out on two distant beds. On the one I planted four rosettes with unbranched ears, on the other, three with branched ears. The four former pro- duced, together, over 200 strong ears, all unbranched witli the exception of a single one which bore a small lateral branch at its base. The three latter formed both unbranched and more or less richly branched inflores- cences, but during the whole summer the unbranched ears were all cut off before they flowered. The harvest from the two beds, gathered and sown separately, gave 154 Atavism. rise to two cultures in 1900. They had the following composition : Ears of seed-parent Extent of culture Atavists With branched ears Branched 44 individuals 52 % 48 % Unbranched 206 individuals 92 % 8 % The rosettes with hranchecl ears gave rise to rather more atavists than the seed of the branched inflorescences of the same plant in the first year (52% as against 40% ), which was probably due to the fact that it had a less sunny position in 1899 than in 1897. But the rosettes with unbranched ears, although they were in a good po- sition in 1899 and grew very healthily, gave a progeny dissimilar to that hitherto produced by any of the branched plants of this race (see Table on page 149 which gives the results of more than 25 individual sowings from separate seed-parents). The four lateral rosettes with unbranched ears, there- fore, formed in this case a clear instance of bud-variation, producing a race poor in branched ears. The question of the constancy of the atavists in my race is a point of considerable interest. Hitherto I ha\e found them completely constant, ^^'ith a view to test- ing this I did not weed out the atavists in the fifth gen- eration in 1894, l)ut simply cut off all their ears before the branched plants flowered, and repeated this 0])era- tion from time to time when new ears appeared before they could protrude their stamens. After the harvest I weeded out all the branched individuals ; most of the atavists survived the winter and flowered luxuriantlv in 1895 in isolation. The majority of them produced over one hundred ears per individual. I harvested the seeds separately for each seed-parent. The sowings took place in 1896 and in 1897. They riantago Lanccolata Ramosa. 155 gave rise respectively to three and six cultures derived from the nine seed-parents. Each culture consisted of from 35 to 100 plants, making together 600 flowering individuals bearing 4000 inflorescences. These were un- branched without exception. The question suggests itself, whether the seed-atavists and the bud-atavists belong to the same type. On the one hand it is possible that the constancy of the former is not always so al)solute as it appeared in my experiment. On the other hand, lM-anched Imd-variants might occa- sionally appear in the race derived from the atavistic l)ud-variants, and such might have been the cause of the occurrence of branched individuals (8%) in my culture of 1900. But further investigations are necessary to provide a satisfactory answer to this question. Plantago lanccolata ramosa, therefore, gives rise to atavistic individuals, cither by seed (about 30%) or by buds (very seldom) which are either absolutely, or at least in a high degree, constant from seed. It still remains to describe briefly the fluctuating vari- ability of our race of plantains. This is considerable, and conforms to the common laws; especially is it de- pendent to a large extent on external conditions and, within certain limits, capable of being altered by selec- tion. The observations, which I now shall give, refer to true ;'a///6>^a-plants, and not to atavists and bud-varia- tions. The variability of this race corresponds with that of other monstrous races inasmuch as the curve describ- ing it is dimorphic.^ During Jnly and August 1893 I ^ Sur Ics conrhcs galtonicnncs dc3 monstruositcs. Bull. Scientif. de la France et de la Bclgiqne, public par A. Giard, XXVII, 1(896, P- 397- 156 Atavism. i:)ickc(l all the ears of a small group of plants, and ob- tained the following figures: Ears without any branching . . . 191 Ears with one lateral ear 80 Ears with two lateral ears .... 136 Ears with three lateral ears .... 93 Ears with four lateral ears .... 33 Ears with five lateral ears .... 12 Sum of ears 545 The degree of branching in this group was fairly low; nevertheless the apex of the curve of the atavistic ears is distinct from that of the branched ones. This l)henomenon could indeed be easily observed, even with- out any counting, on account of the relative scarcity of heads bearing a single lateral ear, a fact which I have also observed repeatedly since. This is a character of the eversporting variety and suggests the possibility that the one-branched ears which are so common in nature (where the ra/7/c.9a-form, as is well knowni, is not at all rare) presumably constitute the half race; but I have not investigated this point. The number of compound ears per plant, and the degree of branching in each, are to a great extent de- pendent on the conditions of life. The stronger the growth of the whole plant, and the richer the foliage, the more pronounced will the anomaly be. Therefore, a more profuse branching of the individual ears usually goes hand in hand with a richness of branched inflores- cences. The branching also manifests a certain periodic- ity. The young plants almost always begin with un- branched ears ; it is not until later that the monstrosity appears, gradually increasing in strength. Then towards the end of the summer I often observed a diminution in the amount of branching and often the formation of Plantago Lanccolata Ramosa. 157 more numerous nnbranched ears. In the second summer often almost all the ears on healthy individuals are branched even when their number reaches 50-60 per plant. In the first year I found that as a rule there were 10-20 branched ears, and sometimes as many as 30 or even more occurred on each plant. In fact we may assume that, on the average, and with ordinary methods of cultivation, about one-third of the ears will be branched during the first summer; for instance, in 1898 I found amongst 439 ears on 30 individuals 136 or 31% which were branched. It goes without saying that the atavistic individuals were excluded from these countings. I have also made some direct experiments to deter- mine the influence of individual vigor on the develop- ment of the anomaly. In the first place I have grown ^•ery weak plants and have then got them to grow stronger gradually. For this purpose I made use of the plantain's well-known property of producing buds from its roots. As the roots are all very thin, the plantlets obtained in this way are very weak at first, nor do they grow up as quickly as seedlings. For the purpose of this experiment I selected (March 1893) ten plants which had had 10-25 branched ears each in the previous year. I pulled them out of the ground, cut ofif the mass of their roots and planted these, throwing away the rosettes and any leaf-buds that might be present. I put the roots of each individual straight into the ground without separating them. Radical buds were produced in hundreds, often so many from one bundle of roots that there was not room for all of them to develop. In the middle of June, that is, after about three months, they began to flower. At first there were onlv 40% branched ears, with onlv one or two lateral 158 Jtaz'isni. ears (on the 46 first flowerstalks). In tlie next 100 the proportion mounted to 60^/cy and 3-4 partite inflores- cences also occurred. Later on, alxxit the middle of July, the first stalks with five lateral ears appeared, and the number of branched ears gradually increased to 70%, and in August the strongest rosette had 67 ears of which 52 were branched, i. e., about 78%. A question at one time much discussed was whether adventitious buds had the power to reproduce the varia- tions and anomalies of the parent plant. At that time malformations were not regarded as heritable, but since the inheritance of monstrosities has become generally recognized,-^ it must be considered evident that • adven- titious buds will behave like normal ones ; and the only question that can arise is whether they are more liable to produce bud-variations or not. If they are weak the abnormal character will be less pronounced; but if their strength is equal to that of ordinary buds the abnormal character must be developed to the same extent. It is therefore almost superfluous to lay much stress on the reproduction of the branched ears from tlie radical shoots of our plantain. The rest of my experiments deal with divided plants. In the spring of 1893 I selected for this purpose two fine rosettes that had survived the winter and which had proved to be particularly rich in branched ears in the previous year. Both plants were divided as equally as possible into halves. Of the first plants one-half was planted in sand and of the other one-half was ])ut in the shadow of a tree, the control halves of both plants being cultivated under ordinary conditions for the pur]wse of "^Erfch'ke Monstrositcitcn, Kruidknndig Jaarboek, Gent. 1897, p. 62. Plantago LaiiccolatLi Ruinosa. 159 comparison. At the l)eginning of the period of flowering no difference was discernil^le in either experiment be- tween the two halves, but it gracktally became visible during the course of the summer. I picked off all the ears from the culture in sand at the end of July and at the end of August ; here is a record of them : Number of lateral ears per primary ear Totals 0 12 3 4 5 July 28th ^^^^^-^ 3 3 4 6 3 1 20 / Control 9 7 9 6 0 0 31 48 Aug. 31st -i^^^"^^ 14 10 12 8 3 1 i Control 12 2 10 7 6 2 39 The difference though slight is distinct. It is more clearly l)rought out if the mean number of lateral ears per primary ear is calculated. In August in the plants on sand this was 1.5, in the control half 2. A similar effect was produced by shade which exerted a most deleterious effect on the whole growth of my experimental plants as will be seen from the small number of ears produced. I obtained the following figures in the same way as in the previous experiment. Number of lateral ears per primary'- ear Totals 0 1 2 3 4 S 6 July 28th -i^^hade 7 6 2 7 5 2 0 29 i Control 1 1 2 8 19 20 1 52 Ausr 31st -^ ^^^^^^ 15 1 1 2 0 0 0 19 ( Control 21 9 20 16 10 3 0 79 The mean numl)er of subsidiary ears per primary ear in August in the shadow half was 0.5 and in the control half 2.0. In conclusion, the results of the whole series of ex- periments which has lasted over more than ten years may be summarized as follows : The Plantago lancrolafa ramosa of ]iiy experiment constitutes an '^inconstanf 160 Atavism. middle race or eversporting variety: that is to say, a race zi'hich produces in every generation a fairly constant proportion of at ovists. This proportion is about 50%. The segregation of atavists occurs regularly in gen- erations grown from seed, but sometimes also in those grown by means of bud-variation. The atavists are per- fectly, or at least very nearly, constant. The true representatives of the race (i. e., all other than atavists) produce both unbranched and more or less profusely branched ears, and are largely dependent, in regard to this character, on their environment and their individual vigor (fluctuating variability). The stronger the plant and the more favorable the conditions the more pronounced is the anomaly.-^ ^Compare the behavior of Papaver somnifcvum polyccphahim in Vol. I, Part I, § i6, p. 138; and also the end of this part. VI. EXPERIMENTAL OBSERVATION OF THE ORIGIN OF VARIETIES. § i8. THE ORIGIN OF CHRYSANTHEMUM SEGETUM. PLENUM. (See Plate II.) The double corn marigold constitutes a new variety which has recently arisen in my cultures. It has never occurred before. Chrysanthcuium scgctiun is, of course, a favorite annual garden plant, and so is a variety of it called C. scgctum grandiflonnn. A form called C. scgc- titrin Gloria is announced amongst this year's novelties } its flowers are said to attain a diameter of 10 centimeters, but it is not double. If a double form ever had appeared, it would without any doubt have been put on the market as a noteworthy improvement, even as the double vari- eties of Chrysantlicinum inodonun and other composites are so widely grown. My ''conquest," as the breeders of hyacinths in Haar- lem call their novelties, is the counterpart of the well- known CJirysanthcniuni inodoruin plciiissiinwn. It is inferior to it in the matter of color, inasmuch as white flowers are always in greater favor than }'ellow ones. The doubling of the heads of composites is never so perfect that tubular florets are completely absent from all inflorescences. Nevertheless it frequenth' looks as if this were so (Fig. 28) ; but if we look a little closer we ^ Seed-catalogue of Haage and Schmidt in Erfurt, tqoo. 162 Observation of the Origin of Varieties. will always find between the tongue florets, more or less numerous tubular florets which are hidden from view by the others. Moreover, the degree of doubling is to a considerable extent subject to fluctuating variability; one plant has more and another fewer, transformed florets. Fig. 28. Clirysanthcmnm inodorum plcniss'nnum. A plant with a high degree of doubling in the inflorescences, and, consequently, perfectly sterile. This is an important point, for the white tongue florets of C. inodorum plenissimmn are female and inflorescences such as those shown in Fig. 28 and Fig. 34C on page 184 set absolutely no seed. The variety is therefore main- Tlic Origin of CJirysiUithcuiiim Scgetiuii Flciiuni. 163 tained by saving seed from plants such as those figured in Fig. 34 A and B, p. 184. These remarks also apply to my new Chrysanthcinuiii scgctuin plenum. Many specimens set absolutely no seed because the doubling has gone too far. For the same reason others afford only a meagre harvest. Too drastic a selection at the beginning of the flowering period would destroy any prospect of a harvest and might even result in the extinction of the variety. Moreover plants with a high degree of ''doubling" produce no pollen for the fertilization of the others, because they are almost exclusively female ; so that they can take no part in the perpetuation of the race in this way either. My novelty is probably the first horticultural variety which has arisen in an experimental culture. By this I mean that pure fertilization has been insured since the beginning of the culture and that exact and detailed records of the course of the experiment have been kept every year. Moreover the selection of the seed-parents has constantly been carried out from the verv beijinnini?-, with a view to the same ideal. Selection began in 1897, the "double" race was obtained in 1900. The selection occupied, therefore, a period of three years. The corn marigold, being a composite, is admirablv adapted to form the material for a statistical investi- gation of its variability. The number of ray florets fluctuate in accordance with the well-known law of Lun- wiG based on Braun and Sciiimper's series. By this means the exact composition of a culture can be ex- pressed in figures and plotted graphically by recording a sufficient number of inflorescences. The course of the selective process can in this way be displayed in all its 164 Observation of the Origin of Varieties. details. Although an explanation of Braun-Schimper's series is still wanting, each of the numbers in it (e. g., 13, 21, etc.) may figure as a specific character; that is, it may be the constant mean for a particular species. On the other hand they may constitute stages of variation or characterize races whose nature is still unknown to us. We must therefore limit ourselves to a purely em- pirical description. It seems desirable to give a general outline of the significance of my ex- periment before I proceed to describe the details. The corn marigold is \ery common in cornfields over the greater part of Europe, as also its German names '' Saativiicherblume' and "gelbe Kornbhune' im- ply. It has thirteen ray florets in the inflorescence and fluctuates around this number according to Que- telet's law. A commercial variety, called Chrysanthe- miirn segetiun grandiflo- rwn, whose origin is not known, is distinguished by the possession of larger and more numerous tongue florets.-^ So far as my experience goes, bought seeds of this vari- ety, give rise to a mixture of this and of ordinary C. scgctiun, no doubt on account of the fact that in the nurseries both are grown close together, for practical ^ RiJMPLER, Vilmorin's Blumeng'drtnerei, 1896, II, p. 507. Fig. 29. Chrysanthemum segetum plenum. An almost completely double inflorescence. See also Plate II. The Origin of Clirysatithcmum Scgctiim Plcniun. 165 reasons. In botanical gardens, too, both sorts are often grown together; and, frequently, simply under the name of C scgetiim. This mixed asseml)lage gives rise to a dimorphic curve ;-^ but the two groups of individuals which com- pose it can easily be isolated by selection. Then the C. scgeUim grandiflonun proves to have a mean of 21 ligulate florets, around which variation practically takes place in the same way as in the 13-rayed race (i. e., the wild species), except that it has a tendency to multiply the number of rays beyond the limits of a normal Quete- let's curve ; a fact which indicates discontinuous varia- tion.^ This slight indication was the starting point for my experiment. In 1897 I chose a seed-parent with 34 rays for the 1898 crop, and reached 49 rays.^ Proceeding in the same way I reached 67 in 1899 and about 90 in 1900 in the best inflorescences. Up till 1899 the ligulate florets only appeared in the circumference, the disc con- sisting solely of tubular florets. In this year, however, there appeared 2 or 3 ligulate florets in the midst of the disc of a few flow^rheads on a single plant. This was the first indication of the double race. Therefore I only sowed the seeds of this one plant in 1900, and from that the race was fully developed (Plate II). Apart of course from eliminating the possible effects of crossing, it needed no further selection ; a too rigid selection was moreover ^ Eine ::weigipfclige Van'ationscurve, Archiv fiir Entvvickelungs- mechanik der Organismen, Leipsic, 1895, p. 52. ^Compare the half curves (p. 26) and the note on page 29. See also Uchcr halhc Galton-Curven als Zeichcn discontimiirUcher J'aria- Hon. Berichte d. deutschen hot. Gesellschaft, Vol. XT I, p. 197. ^ Uchcr Cun'cnsclccfion bei Chrysanthemum scgctum. Same jour- nal, 1899, Vol. XVTI. p. 84. 166 Obscri'Litioii of the Origin of raricfics. to be avoided on account of the sterility of the most highly modified individuals. My cultures embraced, as a rule, a hundred indi\'id- uals each, but sometimes a few hundreds. There can hardly be a doubt that if I had carried out more extensive sowings I should have attained my object at least one year earlier. But the more stringent the selection is, the smaller are both the harvest and consequently the next year's crop. Of course the reader will ask, has this transition been a gradual or a sudden one ? I consider it sudden ; but much depends on the meaning that we attach to the w^ords. At any rate the change did not occupy centuries, as is comnionly supposed by the current theory of selec- tion; it did not even require one decade. Three years were sufficient in a culture of no more than a few square meters in extent. I now come to the details of the experiment and shall first give a short description of the original wild species. The species does not grow around Amsterdam. The herbarium material collected by me in various parts of the Netherlands points to the general occurrence of a mean number of 13 rays. Heixsius plotted curves from plants from two localities in the province of North Bra- bant, and obtained the following numbers. The first row relates to plants which were collected near Vucht, the second to a collection from Hintham.^ NUMRER OF LIGULATE FLORETS (l. F.) IN THE NETHERLANDS, L. F. 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 Vucht 0 1 13 5 3 8 18 78 37 22 11 17 2 3 3 0 Hintham 10998 15 14 33 94 101000 ^ Bcr. d. d. hot. Gcs., Vol. XVII, p. 87. 1 have already exhihited the variation in hoth localities united into a single curve in Vol. I (See p. 152, Fig. 2,2). The Origin of Clirysaiitlicniiim Scyctmii Flciiiiiii. 167 In all 221 and 104 flowers were examined. The curves are mononiorphic and symmetrical. The same is true of this species in Thuringia. Ludwic. gives tlie following data derived from 1000 plants col- lected at Brotterode.^ DATA FROM THURINGIA. L. F. 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 Inflorescences 1 6 3 25 46 141 529 129 47 30 15 12 8 6 2 We may therefore assume that the mean number of rays for the wild corn-marigold is 13. I investigated the mixed race occurring in botanical gardens for the first time in 1892. The result proved to 12 13 14 15 16 17 18 19 20 21 22 23 0 I 14 13 4 6 9 7 10 12 20 1 0 Fig. 30. Chrysanthemum segetum. Mixed crop. Curve of the ray-florets in the primary inflorescences of 97 indi- viduals in 1892. The upper series of figures gives the number of rays, the lower series the number of those in- dividuals possessing the scale character written above it.' l)e a dimorphic curve (Fig. 30), which at the time was the first compound curve to appear in botanical literature.'" I had obtained the seed for the experiment by exchange from a number of botanical gardens. I mixed it thor- oughly and sowed it on a single bed, where 97 plants ^ F. LuDWiG. Ueher Vanafionscurven mid Variationsilachen, Bot. Centralbl., Vol. FXIV, 1895, p. 5. Also F. Ludwig. Die pAanzUchen Fariatiotiscuncii und die Gouss'sche Wahrscheinliehkeitseurve; same journal, Vol. LXXIII, 1898, p. 71 (p- 16 of the ofl'print). "From the Archiv f. Entzvickelungsmechanik, he. eit., p. 58. ^ Archiv fiir Entivickelungsmeehanik, 1895, loc. eit. See also Ludwig in Botan. Centralbl., Vol. LXIV, 1895, p. 71. 168 Observation of the Origin of Varieties. flowered altogether. I picked off and recorded a head from each of these during the course of the summer. On every plant I selected the terminal inflorescence of the main stem as soon as it opened ; plants in which this failed were pulled up before they flowered. Only pri- mary inflorescences were, therefore, employed, and the curve obtained was an index of individual variability, that is to say each unit in it represented a whole plant. The figures obtained are represented in the following series; The upper row gives the number of ligulate florets (L. F.) per inflorescence; the lower, the number of individuals which possessed these numbers. VARIATION IN NUMBER OF RAYS IN C. SEGETUM^ 1892. L. F. 12 13 14 15 16 17 18 19 20 21 22 Individuals 1 14 13 4 6 9 7 10 12 20 1 The curve based on this series of figures is given in Fig. 30. One of its two apices corresponds to that of the wild species, the other to that of the curve for Chry- santhennun Leucantheniiun and C. inodonun. My next task was to separate the components from this mixture and to do this in such a way as to place their existence in the mixture beyond doubt. On account of the inevitable interference of insects in pollination it seemed to me impossible to do this for both supposed races at the same time, so I determined to isolate the 13-rayed form first, and the 21 -rayed later on from a new mixed crop. I devoted the two years 1893 and 1894 to the former inquiry. With this object in view, I eradicated every indi- vidual of the mixed crop of 1892 wiiich had more than 13 rays, as soon as I had counted the rays on its terminal flowerhead. In this way only 15 plants were saved, of which one had 12 and the rest 13 ligulate florets; the rest The Origin of Chrysanthemum Segetum Plenum. 169 were removed so early that there was no danger of these 15 being fertihzed by them. These plants flowered abun- dantly from their lateral shoots but exhibited no tendency to form a curve with an apex at 21. They were there- fore sufficiently pure representatives of the supposed race. In September I harvested the seeds of the 13-rayed plants which I had spared, and sowed half of them in the 12 13 A 17 18 19 20 21 22 23 24 25 26 27 28 B Fig. 31. A. Chrysanthemum segetum. B. Chrysanthemum segetum grandiRorum (after purification). Curves of the races after isolation. A, Curve of the 13-rayed race in 1894. B, Curve of the 21-rayed race in 1897. The ordinates give the number of individuals with like number of ray-florets in the primary inflorescences of the individual plants. The numbers of ray-florets them- selves are given below the abscissa. following spring (1893). I raised 162 flowering indi- viduals, and recorded the numbers of rays on their ter- minal heads. The curve representing this generation was steep, monomorphic and symmetrical (see Fig. 31 A for 1894), and agrees satisfactorily with the curves, given above, for the plants from the wild locality (p. 167 and Fig. 32, Vol. I, p. 152). Therefore there can be no 170 Observation of the Origin of Juirieties. doubt tliat the wild form exists in the mixtures grown in botanical gardens. But in order to strengthen this proof I have cultivated the isolated race for one more generation. For this purpose I selected three vigorous plants from amongst the 1893 crop whose terminal in- florescences had 12 ray-florets, and left them to be fer- tilized by themselves and by their like after all plants with 13 or more rays had been eradicated. From these three seed-parents I harvested the seed separately and raised three families, in 1894, on different beds. The rays of the terminal inflorescences were recorded, and the experiment brought to an end. I shall now give the results of these three counts made in 1894 together with that of 1893. It will be seen that the series of figures correspond with one an- other exactly ; at any rate as nearly as is necessary for the object of this experiment. The composition of the four cultures in the two generations was as much the same as we should expect four samples of an ordinary species to be. THE 13-RAYED RACE. VARIATION IN NUMBER OF RAYS^ IN TWO GENERATIONS. Ray-florets 8 9 10 11 12 13 14 15 16 17 18] 19 20 21 1893 210 7 13 94 25 7712030 1894. First family 0 0 0 1 10 59 18 2 3 4 1 0 2 1 " Second" 00 14 1189 115002 100 " Third " 01 2 3 10 73 21 1200000 Total, 1894 0 1 3 8 31 221 50 8 5 4 3 1 2 1 The total for 1894 is given in the form of a curve in Fig. 31 A. The whole number of individuals dealt with in this year was 338.^ In order to isolate the 21 -rayed race out of the same ^ For a detailed comparison of the curves of the two years see Archil' fiir Entwickelungsmech., II, 1895, loc. cit., p. 62. The Origin of Chrysanthemum Segetum Plenum. 171 mixture, I had to provide more seed because the previous stock had been completely exhausted. I procured it in the same way, by exchange from botanical gardens, and from a similar number of them (about 20). It was not to be expected that the identical form of curve would be obtained again, because the relative height of the two apices obviously depends on the proportion in which the two constituent races are mixed ; and this must be left to chance. I was therefore curious to find out whether the 13-rayed race alone was cultivated in some gardens and the 21 -rayed exclusively in others. With this object I sowed the various samples separately, and on a sufficient space to bring as many specimens to flower as possible. I then recorded the terminal inflorescence of each plant. From no single garden had a pure race been sent, neither of the 13-rayed nor of the 21 -rayed form. In every case both forms were found mixed and in the most diverse proportions. The mixed race was therefore the only one generally cultivated at that time. The variation in the number of ray-florets in the ter- minal inflorescences of the 589 individuals of the whole culture of this mixed race from the botanical gardens in 1805 was as follows: L. F. 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 Individuals 7 3 3 5 14 153 77 60 55 31 33 39 41 56 10 1 0 0 1 That is to say, the same apices as in 1892; but in this series the 13-rayed race is obviously more strongly rep- resented than the other. With a view to discovering also the character of the race which is sold as Chrysanthemum segetum grandi- florum, I sowed a quantity of its seed. When the plants flowered in July an extraordinary variety of forms was exhibited bv the liq;ulate florets. These were in some 172 Observation of the Origin of Varieties. cases very short, in others very long; in some cases so narrow that they did not touch one another, in others more than twice as broad as those of the wild form. The color varied between golden and straw yellow, the tips of the florets were entire or indented, and so forth. This was sufficient to indicate the presence of several races. With regard to the num1)er of ray-florets the differences were not so great, as in the mixtures we have already dealt with. There was only one perfectly dis- tinct apex, that at 21. The other at 13 was more or less obscured. It was obvious that the commercial race was the 21 -rayed one, and that it had been adulterated by admixture with the other only as much as is unavoid- able and therefore admitted in all cultivation on a large scale. The terminal inflorescences of the 282 plants of this culture of C. segetwn grandifloruin were recorded with the following result : L. F. 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Individuals 10 0 1 1 27 27 24 31 30 21 29 24 58 7 0 1 These figures confirm what I have said and show that the 21 -rayed race of C. s. grandiflorum contains an ad- mixture of a relatively small number (which probably fluctuates from year to year) of the 13-rayed race. My next task was to isolate from this mixture the 21 -rayed race, whose existence had so far been merely inferred. I devoted the two following years to this in- quiry, and in the summer of 1895 selected the necessary seed-parents from the mixed crop. We here encounter an obstacle in the shape of trans- gressive variability, to which we have already referred,-^ and wdiich has often raised difficulties in the earlier in- 'See Vol. I, Part I, p. 56; and Part IT, §25, p. 430. The Or'ujin of Chrysanthciuuin Scgciiuii Plcmiui. 173 vestigations. In order to bring this phenomenon into bolder relief let us imagine that the isolation has already taken place and the new race isolated. In other words let us examine Fig. 31 (p. 169) and the data from which this is derived (pp. 170 and 176). Let us first fix our attention on the ordinate at 21. It contains only indi- viduals of the 21 -rayed race. But in 1894 a single ex- treme variant appeared, which, although it belonged to the 13-rayed race, nevertheless had as many as 21 rays (p. 170). If the cultures of 1893 and 1894 had been more extensive the number of these extreme variants would obviously have been greater. For the ordinates 20, 19, 18, etc., it is still more evident that individuals of both races can occur. If we choose plants which have 21 or more ligulate florets in their terminal inflorescences we cannot at all be certain that they all belong to the race which is be- ing sought. And if they are left to pollinate one an- other, or if their seeds are mixed in the harvest, there is small likelihood of the strain being pure. Amongst the majority of pure seed-parents a number of individ- uals of inferior value may exist and it is necessary to remove these as soon as possible, at any rate before the harvest. The possibility of doing this is afforded by the later flowers. By means of them a curve can be de- termined for each plant, and in this way values can be obtained which are independent of the chances in- separably connected with small numbers. The curves describing the separate parts of one individual are called its ^'part-curves." I have therefore plotted such curves of all the individuals selected at the beginning of the flow- ering period as having 21 and more ravs in their ter- 174 Observation of the Origin of Wirieties. niinal inflorescences. Tlie result proved my view to be correct and showed the necessity of the correction which it had suggested, h'or there were 22 plants which, al- though their terminai inflorescences were 21 -raved, had a part-curve with an apex at L3-14. The following are the data as obtained at the end of August : L. F. 12 13 14 15 16 17 18 19 20 21 Lateral flowerheads of 22 indiv. 2 54 58 51 28 19 19 12 2 2 These plants therefore belonged to the 13-rayed race, and were consequently eradicated. Besides these, there were five plants with doubtful curves ; tliey were also not retained. All that was left was a group of 6 individuals whose curves seemed to me sufficiently distinct and certain to justify the harvesting of their seed. The following line gives the sum of their data : L. F. 12 13 14 15 16 17 18 19 20 21 22 Lateral flowerheads of 6 indiv. 0 1 3 5 4 6 11 21 30 29 1 All in all there were 111 inflorescences.-^ If the terminal inflorescences of these plants (5 with 21, 1 with 26 rays ) had been included, the maximum would have been exactly at 21. Seed was saved only from these six plants for the 189.6 crop. It was harvested separately from each parent. The fertilization of these plants had not been wholly pure, because the rejected plants referred to above could not be recognized nor removed before the latter part of August, and because flowers which bloom in Sep- tember set hardly any seed with us. Kacli of the six crops actually gave a curve which liad a distinct maxi- mum at 21, but only one of them (No. 1) wholly lacked ' The curve is figured in Bcv. d. d. hot. Gcs.,Yo\. XVIL Plate \\l. Fig. 2^. The Origin of Chrysanthciniun Scgctum Plcniun. 175 the other maximum, without however heing symmetrical. Even in this group the race was therefore still far from heing pure. Below I give the curve for the offs])ring of the single hest seed-parent together with the sum of the curves representing the offspring of the five remain- ing seed-parents (Nos. 2-6). These curves therefore refer to the initial culture of the 21-raycd race (1896). L. F. 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 No. 1 0 1 0 3 9 15 15 22 30 33 36 64 123 15 5 0 Nos. 2-6 1 5 11 12 70 84 69 92 79 77 114 150 416 46 3 1 All in all 370 plants were recorded for No. 1 and 1220 foi- Nos. 2-6. Only the first named group, that is to say the off- s])ring of the plant numhered 1 in 1895, was used for the continuation of the experiment, and from it the hest seed-parents for the purification of the race were selected on the hasis of an examination of their lateral hranches. These were two plants the lateral floAv^rheads of which gave the following curves (1896) : L. F. 12 13 14 15 16 17 18 19 20 21 22 No. 1« 01143220330 No. 1^ 000000203 14 0 Of the two. No. 1/; most ohviouslv l)elonf>-s to the race I was looking for. I harvested only the seeds of these two plants, and sowed them separately in the following year. In har- vesting this seed I confined myself to flowers which had hloomed after the other plants had heen removed and had therefore heen pollinated with their own or similar l^ollen. The result corresponded with mv expectation, for in the following summer the race was pure on hoth beds. 176 Observation of the Oriyin of Varieties. This is seen at a glance from the two series that fol- low and from Fig. 31 B which relates to the second group. The data were obtained in the same way as in previous years, only the terminal inflorescence of the main stem of each plant being recorded. The character of the second generation of the 21 -rayed race in 1897 was, therefore, as follows : L. F. 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 32 No. 1« 0012023 41 41200000 ^o.l b 1 3 0 3 7 14 43 142 43 21 11 5 3 1 0 1 Both groups are very symmetrical, a fact which can be immediately seen in Fig. 31 B which is even more regular than the corresponding figure of the 13-rayed race (Fig. 31 A). There were only 56 flowering off- spring of No. la but 298 of No. 1^. If I had not limited myself in the previous year to such a small number of seeds, I should have had to sow the seed either of less suitable individuals or from flowers on the same plants which had opened earlier, i. e., which had been pollinated with inferior pollen. In tliat case my race would have been just as incompletely pure in 1897 as it had been in 1896. I have convinced myself, by special experiments with such seed, of the correctness of this view, but do not consider the details worth print- ing. ^ By tin's result the isolation of the races supposed to exist in the mixture, was accomplished. Let us therefore once more examine Fig. 30 on page 167 and Fig. 31 on page 169. The first thing that we see is that the maxima are the same in both figures; they lie at 13 and 21. The ^ Races differing in their number of ray-florets can be mixed by crossing {Bcr. d. dcutschcn hot. Ges., Vol. XVJI, p. 92). This mix- ture is an extremely interesting phenomenon in many respects, but needs a closer investigation. The Origin of Chrysanthcimun Scgctwn Plcnwn. \77 explanation suggested by the double curve has thus been fully substantiated by the result of selection. On the other hand it is perfectly plain that the dimorphic curve is not simply the sum of the two monomorphic ones. The mixed assemblage does not simply contain the two mixed races, either in equal parts or in any other pro- portion. It cannot be synthesized from its components. This is proved by two circumstances : on the one hand by those parts of the curve that lie outside the maximum ordinates, on the other by the middle part. The two component curves begin at 7 and end at 28 {2>2) and their sum should do so too. But the curve of the mixed race is limited by 11 and 23. This is seen more clearly by looking at the ordinates 12 and 22, since there are far too few individuals in these in Fig. 30. Thus we see that the limits of the curves are, so to speak, "drawn in" in the mixture. On the contrarv the individuals are heaped up between the two apices. Moreover in this part there is a secondary maximum. This is seen at 17, but in the commercial mixture of 1895 falls on 16-^ ac- cording to the figures given above (see p. 172). We come noiv to the double race. It is a well-known saying amongst horticulturists, that any one who wishes to obtain novelties must be eagerly on the lookout for small differences (See Vol. I. Part I, p. 185, and this volume, § 2, p. 9). If these deviations are not cases of fluctuating variability but strike the eye by the fact that they are much rarer than these, it is probable that they are the external manifestations of semi-latent characters. If this is actually the case it is further probable that tlie character can be brought bv isolation and selection to ^ i6 (= 3 + 5 + 8) is one of the subsidiary numbers in Lud- wic/s law. Tlie question arises whether by the crossing- of two pure races these subsidiary numbers may arise elsewhere also. 178 Obscrz'afioji of the Oriyiii of raricfics. partial if not to complete predominance. The success of the experiment of course depends on factors still unknown to us, for it is by no means always successful. My belief in these principles, which Darwin himself often refers to, led me to pay special attention, from the very outset of my experiment, to part-curves, i. e., to curves derived from the lateral flowers of the single plants (seep. 173). It is useless to give the numerous cases which afforded no indication of a latent character, and so I will proceed at once to that plant which was the first to do so. It was a specimen of the 21 -rayed race of 1896, which had 21 ray-florets in its terminal in- florescences and gave the following part-curve on the 12th of August : L. F. 14 15 16 17 18 19 20 21 22 No. 1^ 1 1 2 2 2 3 0 3 4 I refer to this plant as No. Ir^ in order to indicate that it belonged to the same culture as Nos. la and 1^ whose part-curves were given on page 175. It agrees with those two plants in the fact that there is not a trace of a maximum at 13; but it differs from them and from all the other plants that were examined on the same bed, by the possession of four flowers with 22 rays. On no other plant was there a single lateral flower with more than 21 ra3^s. This indication was no doubt pretty small. It would not have been discovered but for the counting of the ligulate florets. Without this statistical method of in- vestigation it would certainly never have been grasped, for the plant Ir grew in a culture of about 1500 speci- mens. It was noted first, along with 500 others, as hav- ^ Berichte d. d. hot. Gcs., Vol. XVII, p. 91, where No ir is given as No. 12 in the series. The Origin of Chrysantliciniiiu Scgctuui Floiuin. 179 ino- 21 rays in the terminal inflorescence, and as thus coni])lying with the main condition for the new race. By means of the grouping of the figures for the offspring, that of one seed-parent (1895, No. 1 of page 175) was first proved to be far better than that of the five other parents. Then amongst this chosen group the inchviduals with tlie largest number of florets in their terminal heads were selected and amongst the best of these was found the one which gave the faint indication already described. CHRYSANTHEMUM SEGETUM GRANDIFLORUM. ANCESTORS OF THE DOUBLE RACE. YEAR I'LANT NUMBER OF RAYS IN TERMINAL INFLORESCENCE ADVANCE 1895 No. 1 21 1896 No. U 21 1897 34 13 1858 48 14 1899 66 18 1900 Alaximum 101 35 But small though this indication was, it sufficed to bring the latent character to light. All that was still ne- cessary was to carry the process of selection on through three years in the same direction and on similar prin- ciples. I chose only one seed-parent each year for the continuation of the experiment, isolated it together with some of the next best as early as possible, and harvested its seeds separately from those of its neighbors. Com- pletely isolated plants of Clirysanflicinimi scgctiiin usually set so little seed that it is impossible to rely on them, and therefore fertilization has to be effected to a certain ex- tent by inferior individuals. If this were not the case my object would most certainly have been reached earlier. 180 Observation of the Origin of Varieties. CHRYSANTHEMUM SEGETUM PLENUM. (See page 182.) CURVES OF RAYS IN THE ANCESTRAL GENERATIONS^ (Only the terminal inflorescence of each individual was employed in plotting these curves.) T.F. 14 15 16 17 18 19 20 21 22 23,24 25,26 27 28 29 30 18962 15 15 22 30 33 36 64 123 15 5 0 1897 2 1 2 1 0 12 10 169 102 45 30 19 21 3 1 2 1 1898 1 2 10 17 17 20 21 30 17 13 10 11 1899 1 1 1 0 0 3 2 9 6 6 7 3 (continued.) T.F. 31 32 33 34 '35 36 37 38 39 40 41 42:43 44 45 46 1897 1 0 0 1 1898 6 9 13 21 6 3 5 3 1 2 0 0 0 0 0 2 1899 8 12 13 12 14 10 10 8 6 7 4 8 6 1 10 6 1900 1 0 0 1 1 1 0 0 1 0 1 2 1 0 (continued.) T.F. 47 0 48 1 49 50 51 52 53 54 55 56 57 58 59 60 61 62 1898 1899 4 4 2 2 2 0 2 0 1 0 2 0 0 0 0 1 1900 4 0 0 2 0 1 1 2 0 1 0 2 0 0 0 1 (continued.) T.F. 63 64 65 66 67 68 69 70 71 72 73 74 75 99 101 1899 1900 0 1 0 0 0 1 1 0 1 0 1 0 0 0 1 1 1 1 1 1 ^ These series of figures, with the exception of those for 1896 are exhibited in the form of curves in Fig. 32. ^For the complete curve of 1896 see page 175. The individuals with 10-13 rays are left out here. The Origin of Chrysanthcinuui Scgctum Plenum. 181 Chance may also be unfavorable in another respect. It often happens that the best plant is not sufficiently vigorous to be chosen as seed-parent, but fortunately this 12 15 18 21 24 27 30 33 36 39 42 45 48 51 54 57 CO 63 66 69 72 75 78 81 84 87 90 93 96 99 102 1897. 1898. .AA. .yzx 1899. -.a. J::. 26 66 1900. ntMx M 12 15 18 21 24 27 30 33 36 39 42 45 48 61 54 5^ 60 63 66 69 72 75 78 81 84 87 90 93 96 99 l02 Fig. 32. Ancestral generations of Chrysantlicmum scgctum plcuimi. Curves of the number of rays in the terminal inflorescences in the several individuals of the genera- tions of 1897- 1900. For the numbers themselves see page 180. The seed-parent of 1896 was 21-rayed (X at the top of the 1897 curve) ; the other chosen seed-parents are indicated in the various curves by a X over the appro- priate ordinate. The original plant, from which the culture was derived, was the individual grown in 1895 as No. I (p. 175) from which No. ic arose in 1896, and from the seeds of this came the culture of 1897. difficulty did not present itself in the experiment under consideration, partly because of the favorable conditions of culture. 182 Observation of the Origin of Varieties. The progress was uniform and regular and the sim- plest index of it is the series of successive seed-parents. The number of ray-florets in the terminal inflorescences of my selected plants in successive years was as shown in the table on page 179. The progress can be seen still better from the curves which I have plotted of the terminal inflorescences in the \arious generations. The reader is referred to the table on page 180 and Fig, 32 on page 181. The original ])lant of 1895 referred to as No. 1 arose from a seed which, as already stated, was obtained by exchange from a botanical garden. Indeed this particular lot of seed came from Groningen but produced a mixture the curve of which would obviously not have any special interest. The cultures of the subsequent years were every time the offspring of a single individual whose fertilization by its like had been insured as much as possible. The following considerations arise out of an inspec- tion of Fig. 32. The curve of 1897 was monomorphic like that of the typical examples of the 21-rayed race (Fig. 31 B, p. 169) ; but it was markedly asymmetrical, a fact which afforded a pretty strong indication that the race could be improved by selection in the plus direction. It confirmed the expec- tation based on the part-curve of the parent of this culture. The curve of 1898 relates to the offspring of the 34- rayed plant of 1897. In it new maxima appear. These conform with Ludwig's law, for the}^ lie on the figures of the well-known Braun-Schimper or Fibonacci se- ries. One of them is at 34 (= 13 + 21) which belongs to the primary series: the other is at 26 (= 5 + 8+ 13) which is one of the subsidiary numbers. The maximum TJic Origin of Chrysanthctuiiin Scgctum Plciiuiii. 183 in this year was offered by a plant with 48 rays which was healthy enough to be chosen as a seed-parent. But this hgin-e lies very close to the next figure in the series (13 + 34 = 47). The maximum at 21 has disappeared, but the form of the curve clearly indicates its participa- tion in the composition of the whole. In the following year the advance was much less consid- erable. The maxima at 26 and 34 and that near 47 became more distinct, but the maxi- mum number of rays increased to 67. At the same time an- other still more important dif- ference appeared since now for the first time ligulate florets appeared between the tubular florets of the disc. This only occurred on a single plant and not till the beginning of Sep- tember. This plant had 66 rays in its terminal inflores- cence, and was one of those which had been selected as seed- l^arents, and accordingly isolated at the beginning of the flowering period. On account of its possession of this first sign of real doubling it was chosen for the continua- tion of the experiment in 1900, to the exclusion of all the rest. Tt is well known that in other species of this genus (e. g., Chrysaiiflicniuiii ludicum and C. iiiodoniiii) tlie doubling consists in exactly the same phenomenon. In Fig- 33- Chrysanthemum se- gefiim t>lcnum. One of the six inflorescences which in 1899 first exhib- ited true ''doubHng." The figure represents the par- ent plant of the "double" variety. 184 Observation of the Origin of Varieties. the midst of the tubuhir llorets (Fig. 34A) Hgulate florets are developed (Fig. 34B). If the ''doubhng" is carried very far the former are completely covered by the latter (Fig. 34C), and can only be seen by pulling out the ligulate florets or by turning them aside. If this is done a large number (and not merely a few scattered ones, as might perhaps be expected) of tubular yellow corollas Fi2, both kinds of ligulate florets were counted to- gether. The two flowers with 99 and 101 ligulate flo- rets respectively were to all appearance almost entirely double. The ''doubling" was also exhibited on the lateral branches. When these were in full flower, I selected the twelve best ''double" plants and pulled up the rest. The lateral inflorescences of the rejected plants gave a curve w^hose maximum was at 47 (= 13 -\- 34) in accordance with the indications referred to above and apparent in Fig. 2)2. The worst flower had only 28, the best one 94 rays. The average of the wdiole lot was 47; but the curve, in spite of the coincidence of the mean and the maximum was not symmetrical. Altogether the rays of 378 inflorescences were counted. As was to be expected, the selected seed-parents ex- hibited great differences in the degree of "doubling" in the lateral inflorescences. On some this was inconsider- able. On others the mean was from 2-5 disc-ton <>ues per inflorescence whilst on two a niean of 1 1 was counted. One plant bore nothing but wdiolly double flowers. It had seven flowers on which 279 disc-tongues were counted, giving an average of 40. In consequence of this the plant w^as absolutely sterile ; it bloomed well afterwards, but in spite of every care I could not get a single seed from it. But the finest specimens of C . in- odorum plcnissiniuni are also known to set no seed. Like- wise the two plants whose lateral flowers had on the average 11 disc-tongues, set no seed. The Origin of Chrysanthciuiun Segetum Plenum. 187 We thus see that the hmit has been reached. Any fnrtlier impro\'enient of the race will only increase the number of doubles and consequently of sterile individ- uals. Seed-parents therefore must always be chosen amongst the plants with the same degree of ''doubling" as in this year (1900). In this respect my new race be- haved, immediately after its origin, exactly like the old- established Chrysantheniwn inodonun plenissimuni} It still remains to give some account of the general conditions of fertilization of the seed-parents in the vari- ous years. No doubt the experiment would have been purer and more demonstrative if the corn marigold were capable of self-fertilization. But this either does not occur at all, or only to a totally inadequate extent. Each year I have therefore left a group of a few selected plants to flower together after the eradication of the rest; and have been obliged to content myself with collecting the seed of each in a separate package. Future experiments will have to determine what the effect of this crossing m.ay have been on the progress of the race. Meanwhile it may be of interest to place on record the number of ])lants which have flowered together each year, showing the stringency of selection to which they were subjected. In the summer of 1895 the original parent of the whole race, which was raised from seeds obtained by ex- change (1895, No. 1), could not be isolated until late and then incompletely, but as the plants flowering at the same time also belonged to the 21 -rayed race the curve of the offspring was very "pure" in this respect (p. 176). In the next year the number of seed-bearers was reduced, about the middle of August, to three very vigorous indi- ^ The Matricaria Uore tofo alho plcnissimo , described by ^fuN- TiNG in 187 1, the best specimens of which also set no seed, was prob- ably the same variety {Waarc Ocffcningc dcr Plantcn, p. 527). 188 Observation of the Origin of Varieties. viduals whicli had 21, 21, and 22 rays respectively, in their terminal inflorescences. One of those with 21 served for the continuation of the experiment but all three had exhibited correspondingly high numbers in their lateral flowers. The fertilization in this year was therefore sufficiently pure. This was not the case in 1897. The 34-rayed seed- parent of that year was pollinated at first amongst all the other plants, and later amongst the rest of the selected ones which were however as many as 25 in number. It set so little seed that it was impossible to rely solely on the seed due to the later pollinations (i. e., the purest seed) for next year's crop. The two maxima of the curve of 1898 are therefore, at least to some extent, due to mixed pollination (Fig. 32 under 1898). In 1898 I selected the seeds for the continuance of the race in two periods on the chosen seed-parent after having marked the flow^ers separately for them. The first harvest was from flowers which had bloomed be- fore the removal of the rest, the second from those which had bloomed later. The latter must therefore have been fertilized by the seven remaining seed-parents whose ter- minal inflorescences, however, all had had more than 34 rays (the numbers were 35-36-37-38-39-40 and 46). The two specimens were sown separately and their curves determined ; but no essential difference between them could be detected, either in their limits, or in their means, or in their general shape. The seed-parent of 1899 with 66 rays and with the first 1-3 ligulate florets on its discs (Fig. 33), belonged to the first series, the 67-rayed plant shown in the table on page 180 for 1899, however, to the second. In the summer of 1899, tov/ards the end of July, I 1 he Origin of Chrysanthemiun Scgctnm Plenum. 189 saved 17 seed-parents with 48-67 rays in their terminal inflorescence. From these I collected the seed from the flowers which bloomed in July separately from those whose flowers had opened after the selection had taken place. But from the former specimen I raised only three plants that flowered (with 41-44-47 rays in their terminal head), which evidently could have no effect on the shape of the curve and were soon removed. Fertili- zation in 1899 therefore was again very pure. Having arrived at the end of the account of our ex- periment, all that remains is to compare the course of the selective process in this case with the ordinary pro- cess of selection carried out in the improvement of agri- cultural plants. I refer the reader to Fritz Mueller's experiment with the many-rowed maize already de- scribed.-^ That the difference is essential will be clear from the description given. In the case of the maize the object was to intensify the racial character (12-14 rows) as much as possible by selection; in the case of the Chry- santhemum the object was to uncover a latent character and to bring this to its full development. In the first case a visible character that had been known for ages had to be increased as much as possible; in the second, according to current conceptions at least, a new char- acter had to be called forth. The 26-28 rowed ears fall within the range of fluctuation of the 12-14 rowed race; and they would without doubt have appeared within it without any selection, if cultures of sufficient extent, which could be calculated beforehand, had been grown (Vol. I, p. 162). Without any doubt my crop of 1807 would have ^ See the pedigree in Vol. I, Fig. i8, p. jt^. 190 Observation of the Origin of I'arictics. "iven rise immediatelv to flowerheads with central li""ii- late florets if it had been on a sufficiently large scale. But it would not have produced them in a proportion which could be predicted l)v Quetelet's law, but accord- ing to the principles of discontinuous variation which are still unknow'n to us. The course of the improvement is different in the two cases. The results obtained with the maize conform to the law of regression, the increase in the number of rows in the ears becoming slower and more difificult to secure, the further we get from the starting-point. Ex- actly the reverse is the case in the Chrysanthcnnini. The i:>rogress was continuous and did not materially change until 1899, when the first central ligulate florets appeared. Then it took a leap, all the offspring of this plant having more or less double flowers. More strictly speaking, the leap had already taken place, the plant with the first central ligulate florets (Fig. ZZ) having already crossed the threshold. Its offspring behaved like the offspring of a pure race, such as for instance C. inodoruni plcnis- simnm. A break therefore occurred, and obviously before 1899; either in tlie origin of the seeds of 1898 from which the plant in question arose, or even earlier. And since C. inodornni plenissinuun has maintained itself for many years without selection, it is probable that the new C. scgctnni plenum will do the same. But the reverse was the case with the maize which reverted to the old form within a few years after the cessation of selection (Vol. I, p. 125). Hitherto I have taken the number of ray-florets in the terminal inflorescence almost exclusively as a character of the whole plant, and the curves have been plotted The Origin of CJirysanthcmuni Scgciwu Plciiimi. 191 from tlie figures ol)tained in this way. But there is, as we liave already seen, another method of estimating the indivi(hial vahie of a plant, namely that based on a de- termination of the mean character of as many fiowers as possible on a single individual. This raises two points for consideration : first the mode of branching of the corn marigold, and secondly the influence of the devia- tion of the individual from the mean of its race. The mode of branching in Chrwsaiitlicinuni scgcfum is as follows. The main stem which arises from the plumule bears two groups of branches; strong ones at its base from the axils of the radical leaves; and, higher up, weaker ones whose vigor first gradually increases and then decreases, as they succeed one another from below upwards. This applies both to their length and to the number and strength of their secondary branches. These secondary branches are, therefore, of the third order; they often bear branchlets of the fourth and even of the fifth order. The flowers that bloom in July, with us, are mostly of the second order, those blooming in August and September of the third and fourth. In the course of the summer, and with the flowers on tlie successively higher orders of branches variabilitv is seen to manifest a general decrease. The sides of the curve are, so to speak, drawn in ; the curve itself be- comes narrower. The amount of deviation of the various individuals from the mean of the race decreases, and the mean consequently comes to stand out more boldlv. This is of especial importance in cases in which a curve has been shifted laterally by stringent selection (such as Fig. 32, p. 181) where it might remain doubtful what the shape of the curves would have been if selection had 192 Observation of the Origin of Varieties. effected nothing more than the isolation of the individ- uals of the new race. \Yq have therefore to examine the ''late summer" curves of the 13-rayed, 21 -rayed and double races. Let us begin with the first. The extreme limits of the curve of this race at the ])eginning of August were 11 and 21 ray-florets. These numbers gradually decreased until September, when only heads with 13 and 14 rays were formed. In the next year at the end of July the limits were 10-19, but in August 12-14. I examined the 21-rayed race, with reference to this character, in the summer of 1898, dealing with the indi- viduals which had been saved for seed. The data for three of the plants^ are summarized in the following table : PLANT FLOWERS NUMBER MIN. MED. MA? A. Terminal 1 48 September 1st 32 29 33 45 October 10th 42 18 27 36 November 1st 28 19 26 31 B. Terminal 1 — 35 — September 1st 36 24 28 36 October 10th 33 16 22 27 November 1st 23 15 21 25 C. Terminal 1 — 46 — September 1st 14 26 28 35 October 10th 18 18 26 30 November 1st 8 21 23 28 We see that the numbers gradually shift in the direc- tion of the maximum at 21 (in the case of one plant actually reaching it), without any indication of the max- imum at 13 of the other race. The plants dealt with, therefore, clearly belonged to the 21-rayed race. ^ Over hct periodisch optreden der anomaVicn op monstreuze planten. Kruidkundig Jaarboek, Gent, XI, 1899, PP- 57-58. The Origin of Chrysanthcinum Scgctum Plcninn. 193 This was apparently no longer the case in the follow- ing summer. The following are the records of five plants taken in late summer : TERMINAL INFL. MIN. MED. MAX. A 67 33 39 50 B 55 31 42 50 C 51 37 47 54 D 50 33 51 60 D 33 40 51 E 66 38 47 62 E — 32 43 52 D' and E' were counted 6 weeks later on the same plants as D and E. The plant E is the seed-parent in Fig. ?)2, p. 181, under 1899, marked with a X- The figures may be regarded as the expression of a tendency to fall back on the secondary maximum at 47 (= 13 + 34), and the same result was reached by the other count- ings, which it is not worth while to reproduce here. In the following year (1900) the maximum of the lateral inflorescences was still higher. I give the data derived from three plants which were "double" and con- sequently sterile, and of the four next best which were chosen as seedparents. MIN. MED. MAX. Sterile I. 72 87 100 II. 48 62 94 III. 46 56 79 Seed-parent I. 47 63 76 II. 51 62 91 III. 44 60 94 IV. 46 56 86 The curve of the ''double" race thus seems to have its maximum at about 55 (=21 +34). The possi- bility of attaining higher mean numbers seems to be 194 Observation of the Origin of J\irictics. cxcliKle(i l)v tlic sterility of the more perfectly double l)lants. Let us uow l)rielly suuiniarize the results of this ex- perinient. There is, on the market, a 21 -rayed race of the normally 13-rayed Chrysanthcnunn scgctwn. It is not strictly pure, but can easily be made so; it bears the name C. scgctum grandiflornni. From a plant which, in lcS95, caught my attention by a few 22-rayed lateral flowers, I succeeded in raising, by a process of selection, a hitherto unknown race with double flowerheads, the new C. scgctum plenum (Plate II). The course of this process is exhibited in Fig. 32, p. 181, in which tlie X X X X indicate the individuals selected as seed- parents for each succeeding generation. C. scgctum plciuim behaves with regard to its double character, exactly like the double commercial varieties of other species of the same genus (C inodorum, C. indicum etc.). The new variety was therefore obtained by bringing to light a character latent in C. scgctum grandifJorum. § 19. DOUBLE FLOWERS AND FLOWERHEADS. The experiment described in the foregoing section (^ 18) justifies an attempt to form some conception of the manner in which this phenomenon of ''doubling," which is widely distributed among cultivated composites, may have arisen in other cases. If we examine the facts closely we shall discover in the majority of cases an extraordinarily close agreement with our own specimen, at least so far as the absence of scientific observations admits the possibility of a comparison. There are, it is true, certain abnormal types of ''doul)- ling," such as the de\'elopment of secondary flowerheads Double Flowers and Flowerheads. 195 (Cineraria), the transformation of the httle yellow disc- florets into long white tubes (Pyrethnmi, see Fig. 36) etc. We shall however leave such cases out of considera- tion ; they may be regarded provisionally as cases of spurious doubling. The genuine 'Vloubling," on the other hand, as ex- hibited by the most diverse species, presents a very marked agreement with the conditions found in Cliry- santheuiuin segetiun. Indications of a tendency to "doub- ling" occur both in forms of which a double variety is not offered by seedsmen and in those of which such are already on the market. For instance in 1892 I ob- served occasional tube-florets more or less completely transformed into ligulate florets in a culture of Bideus (jrandiflora in my garden. In other cases the variation is only seen when curves are plotted. For example I obtained the following very asymmetrical curve from a culture of the single variety of Clirysaiifhenium coro- nariimi, a favorite garden plant whose double form has long been known (Fig. 35). 130 flowers on 25 plants of a single crop were recorded, the flower at the top of the main stem and those on the primary branches alone being taken into account. I found : Ligulate florets 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 Inflorescences 10 1 2 2 12 25 19 21 IS 14 6 7 2 3 That is to say, 18 on one side of the mean and S7 on the other, with a faint indication of a second maximum at the next figure in the Braun-Sciiimper series, 21. It is clear that the (l(ml)le variety of this species could prol)- ably be obtained from these plants, exactly in the same way as in C. segefiim. These considerations evidently lead to the hypothesis that the secondary maxima on the positive side of Lud- 196 Observation of the Origin of Varieties. wig's ray-curves^ may also indicate the existence of a latent character, which, if it could be made active, might perhaps give rise to the double variety of the species. If we now examine the double varieties of the com- posites, we see that the structure of their inflorescences corresponds in every detail with that of Chrysanthenunn segetuni plenum. The amount of doubling is always Fig- 35- Chrysanthemum coronarium. highly variable. The best cases reveal no tube florets as in the case of Chrysantheniuni inodoruni in Fig. 34, p. 184. But if one looks between the ligulate florets small yellow tubes will be found in no inconsiderable quantity. This is true of Calendula officinalis and many other species. Such flowerheads are usually sterile, for ^ May not the secondary maxima on the negative side similarly indicate the variety without ray-florets, the Var. discoidca (See §8, pp. 78-79 and Fig. 9, p. 80). Double Flowers and Flozverheads. 197 the Hgulate florets are female, and inasmuch as very often all the flowerheads on a single plant attain to this degree of doubling" the best variants cannot serve as seed-parents. But two further types are always found with yellow discs which are either unifcjrm (Fig. 34A) or contain scattered ligulate florets amongst the tubular ones, as is so often seen in Chrysantheniwn uidicuni and Zinnia elegans. The double Bellis perennis also, if grown from seeds, is highly variable in this respect. These two types are fertile and therefore constitute the seed- parents of the variet}^; if the plants with central ligulate florets (see p. 185) furnish sufficient seed the harvest is saved exclusively from them ; but they often set little or hardly any seed. This unavoidable restriction in the choice of the seed- parents and the frequent difficulties of selection depen- dent on it account for the fact that bought samples of the seed of double composites often give rise to only a relatively small proportion of the desired type, as has long been known^ to be, and still is, the case {Chrysan- thennnn coronariuni sometimes only 50%, Centaurea Cyanus 40-50%, Tagctes ofricana with rare exceptions double etc.).^ Many double varieties of composites seem to be al- most as old as horticulture itself (See Vol. I, p. 183). According to the oldest accounts the degree of doubling and the range of its variation were formerly the same as now. Finally I have to mention the fact that bud- and sec- torial variations are found in tliis case as well as in others. ^ E. g., Pyrcthrum roscum. Dahlia, Chrysanthemum indicum, ac- cording to Verlot, Production ct fixation dcs varictcs, i(S65, p. 83. ^ See the catalogues of Penary, and Haaoe & Schmidt of Er- furt, Veitch & Sons of London and Sutton & Co. 198 Ubscrvatwii of the Ujicjiii of I 'arictics. I refer to a very beautiful instance of the latter (Fig. 36) which I owe to the kindness of Mr. Ernst H. Krelage in Haarlem. The origin of double flowers in other groups of flow- ering plants has probably occurred on similar lines with that of double inflorescences. I restrict myself to a con- sideration of doubling by the transformation of stamens into petals, that is, the petalody of the stamens, referring the reader for an account of the other types of doubling to Goebel's well-known monograph.^ Occasional petaloid stamens occur fairly commonly both in culture and in nature ; they are so well known that it is not necessary to cite special instances. The curve which represents this variation is unilateral, indi- cating thereby the existence of a latent or semi-latent character.- The attempt to render this active may be made, and if it succeeds'^' the origin of a double variety may be expected. Double varieties of this kind tend to vary in the same way as those of composites. If, for instance, the com- mercial Varietates plenae of Clarkia pulchella, Clarkia clccjans. Phlox Dnnnmondi and others are examined, almost all the intermediate stages between nearly hemi- spherical double flowers and flowers wnth normal sta- mens are met with. In such cases it is usually obvious that favoral)le conditions tend to increase ''doubling," a fact which has been known for a lono- time in the case of Anfliciuis nobilis, of some species of N^arcissus, * K. GoEr.Ki., Bcitr'dge ziir Kenntniss gcfiilUcr BU'ithcn, in Prings- iieim's Jahrb. f. wiss. Bot., Vol. ly, 1886, p. 207. ^ Ueher halhe Galton-Curvcn ah Zeichen discontimdrlicher Varia- tion. Ber. d. d. bot. Ges., Vol. XII, 1894, P- i97- "Which is, however, by no means always the case. See the ex- periment with Ranunculus bulhosus in §23 of this part. Double Fhru'crs and PlozvcrJicads. 199 and other bulbous plants.^ There is a certain periocHcity in this case too ; for sometimes the hrst, but more usually the later, flowers are less double than those which bloom in the height of the flowering period. This fact is well known to breeders,- especially in the case of certain double varieties of Begonia in which seeds can only be saved from the autumn flowers. Fig. 36. PyrctJiniin roscum, from the nursery of Messrs. Krelage & Son in Haarlem (1899). I" one half (the rear half in A, the left in B) the inflorescence is made "double" by the elongation of the tube-florets ; in the other half it is "single." A, oblique view ; B, section. The majority of double varieties are constant from seed, even in the case of trees and shrubs (varieties of the peach and the apple for instance),'^ others appear to be only slightly so, and others not at all (Pruniis spi- ^LiNDLEY, Theory of Horticulture, p. S33- ^ Carriere. Production ct fixation dcs varlctcs, 1865, pp. 66 and 67 {Camellia alba plena, incarnata, Fuchsia, etc.). ^ Verlot, loc. cit., p. 83. 200 Observation of the Origin of Varieties. nosa).^ For instance, 80% is the figure given for Dian- thiis CaryophylluSy^ and double varieties of Campanula are said always to produce a certain number of single plants. In the case of double stocks one may reckon on between 50-60% double offspring according to the treat- ment and selection of the seed. Pot culture favors "doub- 1 mg. "3 The transformation of stamens into petals often goes so far that no pollen is formed. When this oc- curs the stigma of the double flower must be fertilized with the pol- len of a single flower or left to be pollinated by insects. The result is that the race gives rise to both forms every year. For instance Pa- paver nudicaule auran- tiacum plenum, the seeds of which give rise to between 40 and 60% of double -flowered speci- mens every year. It is the other way round with the double Petunia whose capsules are usually mal- formed ; but they develop a few stamens, with the pollen from which the stigmas of single flowers are dusted, ^Ibid. ^ Seed catalogue of D. Sachs, Quedlinburg, 1890-91. (Dianfhus Caryophylliis c. ft. Margaritae, novelty 1889). ^ Chate, Culture pratique des Giroftees. Nobbe. Botaji. Central- blatt, Vol. XXXII, 1887, p. 253. Fig. 37. Anemone coronaria, "The Bride." Double on one side, single on the other. From the cultures of Messrs. E. H. Krelage & Son of Haarlem. The Origin of Linaria Vulgaris Peloria. 201 preferably after castration. The seeds collected after this operation are said to give from 25 to 40% double plants the number varying directly with the care with which the castration was carried out. Double flowers are also subject to sectorial and bud- variation. A chestnut tree {Acsculus Hippocastaniun) at Geneva, a single branch of which has borne double flowers for many years, ^ is perhaps the best known ex- ample of the latter, whilst our Fig. ^7 gives an interest- ing case of the former. It is a flower of the pure white Ancjjioiie coronaria, "The Bride," which, like the Py- rcthruin, I owe to the kindness of Mr. Krelage. It grew in a bed of the single variety ; the plant which bore it had exclusively single flowers with the exception of this one. On the one half there w^ere stamens only, as is shown by the figure; in the other half, however, the vast majority of stamens were transformed into narrow petals, just as happens all round the stigma in the double form. The single variety frequently exhibits more or less definite traces of doubling, and from these Messrs. Krelage have succeeded in producing a double sort and putting it on the market. But a sectorial variation like that figured has only been observed once in the course of many years. § 20. THE ORIGIN OF LINARIA VULGARIS PELORIA. About ten years after the appearance of the first edition of Darwin's Origin of Species (1859) Hof- ^A. P. DE Candolle, Physiologie vegetate, 1832, II, p. 479, and Alph. de Candolle, Geographie hotanique, 1855, II, p. 1080. This tree stood in the garden of M. Saladin de Bude near Geneva. Many cuttings made from tlie double-flowered branch have been distrib- uted. 202 Obscrz'afiou of the Origin of Varieties. MEiSTER wrote the following words at the end of his account of pelorias.^ *'One of the most remarkable features of the varia- tions of plants is, without question, the sharpness and suddenness of the origin of profound deviations from the normal form of structures such as we see it in the phe- nomena just considered, in many analogous cases, and especially in the formation of monstrosities. The new form does not come into existence by the gradual sum- mation of small deviations in one direction, during suc- ceeding generations; it appears all at once, perfectly distinct from the original form." This highly important and perfectly correct state- ment rests even now simply on the absence of transi- tional forms, and does not rest on direct observation. If the peloria had originated by a gradual process it would be reasonable to suppose that at least in some of the relatively numerous instances the intermediate steps w^ould have been found ; but as this was not the case it was concluded that they did not exist and therefore that the origin of the variety had been immediate.- But it is hardly necessary to point out that nothing short of direct observation can furnish the final proof. Direct observation will moreover inaugurate a new stage in the study of this remarkable phenomenon, by making ^W. HoFMEiSTER, Allgcmeine Morphologic der Gciv'dchse, 1868, p. 564. ^ On the pelorias of Linaria, especially of L. spuria, see H. VocHTiNG, Uebcr Blilthcnanomalicn, Jahrb. fi'ir wiss. Botan., Vol. XXXI, No. 3, 1893, and L. Jost, Bliithenanomalien bei Linaria spuria, Biolog. Centralblatt, Vol. XIX, 1899, p. 145. Also J. H. Wakker, Over pelorien, Ned. Kruidk. Archief, Vol. V, p. i, July 1889, with Plate X. P. VuiLLEMiN, Monstruosites ches le Linaria vulgaris, Bull. Soc. Sc, Nancy, Dec. 1893, with one plate (Vol. XIII, 1894, P- 33)- W. and A Bateson, On Variations in the Floral Symmetry, Journ. Linn. Soc. Bot., Vol. 28, 1871, p. 381. The Orig'ui of Linaria Vulgaris Pcloria. 203 accessible to investigation the mode of its appearance and the external canses to which it is due. For these reasons I have endeavored to induce the occurrence of the Pcloria from the ordinary form in my experimental garden. It is obvious that the success of such an experiment, at least at first, is dependent on chance. This chance hov^ever can be favored by making the cultures as extensive as possible, and by widely vari- able conditions of life. Fortune has favored mc, and after seven years' work my object has been attained. Th^Pcloria appeared quite suddenly in the fifth and sixth generation of my culture. The signification of my observations will be more properly understood if I premise my account of them with a short gen- eral and historical account of the subject, referring the reader for the litera- ture to the following section (§21) and to Penzig's Teratologic} Peloric flowers in Linaria vulgaris- were first dis- covered, as is well known, in 1742 by Zioberg on an island near Upsala and described by Linn.eus in the Fig. 38. A, B, Linaria vulgaris. C, D, Peloric fli)\vers. ^O. Penzig, PUanzcn-Teratologic, Vol. II, p. 195. ^ The Pclorias have five spurs: Pcloria ncctaria. Rut there is also a Pcloria ancctaria in which the tlowcrs are regular hut without spurs. See Penzig, loc. cit., and Verlot, Production dcs varictcs, p. 90. This variety is nearly sterile, setting very little seed, but it breeds true. 204 Observation of the Origin of Varieties. Amoenitates aeademicae} The plant grew there together with the ordinary Linaria and formed a ''constant" race Fig. 39. Linaria vulgaris peloria. A richly branched stem of a plant of the second generation. Raised in 1898 from seed of the first generation of 1897 and photographed in August 1900. All flowers are peloric. through propagation l)y the buds on its roots. All the flowers of this plant were peloric (as in Fig. 39). Lin- ^ Amocn. acad., I, p. 55, p. 280 (1744). See Moquin-Tandon, PHancen-Teratologie, 1842, p. 170, and Hofmeister, he. cit., p. 563. The Origin of Linaria Vulgaris Peloria. 205 N^us described this form, which was new then, under the name of Peloria, derived from the Greek TrikMp, a monster. It was not till later that the occasional occurrence of isolated peloric flowers on the ordinary Linaria vulgaris was noticed. Moreover in the course of time further speci- mens of the true Peloria were found scattered over most of Europe. Such plants have been brought into cultivation by many investigators. They have remained constant and could be propagated by means of their numerous radical buds. In the occasional cases in wdiich the plants apparently reverted to the one-spurred form it is possible that some roots of the ordinary L. vul- garis were accidentally trans- planted amongst the roots of the peloric specimen. So many descriptions of the flowers ex- ist that I think it is hardly necessary to repeat them. In Fig. 39, however, will be seen a freely branched specimen of our plant. I have also given a figure of a spike of the ordinary Linaria vulgaris in Fig. 40, for the sake of comparison. The common opinion of those who have worked with the Peloria is that it is in a high degree sterile. The Fig. 40. Linaria vulgaris. A normal flowering stem. 206 Observation of the Origin of Varieties. pdlen is poorly developed and the capsule is practically atrophied; but not to such an extent that fertile seeds are never produced, as some investigators seem to think, ^ for some attcm])ts to harvest seed have been successful. W^iLLDEXow records an experiment in which such seed lias given rise almost exclusively to peloric plants. - The Peloria, or Linaria vulgaris peloria is character- ized by the fact that all its flowers are peloric. This character is, it is true, subject to considerable fluctuating variability, especially in the number and degree of devel- opment of the spurs. But I never found normal one- spurred flowers amongst them, although since 1894 I was able to observe in my cultures several hundreds of peloric flowers every year, and in favorable years even many thousands of tliem. Besides this Peloria, as already stated, there are some- times found on the ordinary Linaria vulgaris isolated peloric structures, which are subject to a high degree of fluctuating variability (Fig. 41). The most usual case is a single flower on a plant which does not bear anotlier afterwards during the whole course of the summer. Sometimes I found 2 or even 3 peloric flowers on the same plant, both in the wild and in the cultivated state, ])ut seldom a larger number. It often happens that an individual which has produced the abnormality in its first vear will not produce a single one in the second, although it branches more freely and bears many more flowers ; on the other hand the abnormality sometimes reappears. Such isolated pelorias are not limited to any particular position f' although in my garden they usually occurred ^ Verlot, Production et fixation des varictcs, p. 90. ' De Candolle. Physiologic vcgctalc, IT, p. 692. My experience is in full agreement with that of Wim.denow. (See p. 216.) ' See Pexzig, loc. cit., p. 195 The Origin of Linaria Vulgaris Peloria. 207 on the highest lateral twig below the main flDwer- spike. The qnestion snggests itself, Is the power of i)ro- dncing isolated peloric flowers inherent in all plants of Linaria vulgaris} Or are there two races, one with and one without this faculty? This question seems not to have been investigated as yet. From the observations already described it must be concluded that this point can never be de- termined in the field, for the absence of the abnormality on ]:)articular days, or even in par- ticular years proves nothing in itself. Personally I think it likely that both kinds exist and that there are localities for Li- naria vulgaris in which these ab- normalities are never found. Holland however is not one of these. By paying attention to them when out on an expe- dition, one will find isolated pe- loric specimens fairly frequently and in the most diverse localities. When I wanted a specimen to photograph for an illustration (Fig. 41), I asked my wife to look for one in the neighborhood, and it was not long before I had one. The power to produce them is, therefore, widely distributed in this country; and also obviously heritable although in a latent state as a rule. Whether or no there are localities in which this character does not occur, I cannot tell. Fig-. 41. Linaria vulgaris hcinipcloria. Branch of a normal flowered plant with a single peloric flower. Zandpoort, Aug. 1900. a, normal one- spurred flower, b, a Pe- loria. 208 Observation of the Origin of Varieties, So long as it is not certain whether a Linaria vulgaris apeloria exists, I propose to call the plants with this power provisionally L. vulgaris heniipeloria (Fig. 41). This name of course refers hoth to those plants on which iso- lated peloric flowers have been observed, and to their offspring. Cases of true Peloria (Fig. 39) are also occasionally seen in this country in the wild condition. A few local- ities for it are recorded in the Floras. I myself had some plants from a spot near Zandvoort in 1874, but since then it has not been found there again. Only one new locality has since become known to me, and this was near Oldenzaal (1896). It is of course not known whether the Peloria occurred spontaneously in these var- ious localities and had not been introduced from else- where, but its high degree of infertility makes the likeli- hood of such an introduction very remote. For the purposes of my experiment I transplanted some plants from the country into my garden in the summer of 1886. I selected plants with occasional pel- oric flowers and freed their roots as carefully as possible of fragments of roots whose connection with the hemi- peloric plants was not absolutely certain. The plants came from Gooiland. I also collected, at the same time, the Linaria vulgaris with Catacorolla,^ and obtained the three-spurred variety (see § 8, p. 87) from Dr. Wakker. These three forms flowered together in the following summer in my garden. In 1888 I sowed the seeds which I had collected in 1887, to produce the second generation, but the plants did not flower till 1889 and again in 1890. In the first year a single peloric flower was produced amongst in- ^ See Chapter TT of this part, §4, p. 31. The Origin of Linaria Vulgaris Pcloria. 209 numerable flowers with a single spur ; in the second year, however, two appeared. I collected the seeds of these plants in 1889. From this I raised the third generation in 1890. Here again the plants did not flower till the second year, and again there was one case of a Pcloria amongst thousands of normal flowers. I harvested the fruits of this peloric plant separately and it furnished me with sufficient seed for the culture of 1892. This year I adopted the plan of sowing the seeds in pans, containing good garden soil, in the greenhouse of my laboratory. Hitherto I had simply sown the seed in the bed, for which method, however, a much larger quantity of seed is required. The seedlings were planted out singly in pots containing richly manured soil as soon as they began to develop a hypocotylous bud ; then they were kept under glass, and were not transferred to the open bed until June. The result was that they not only flowered in the first year, but did so very luxuriantly. There were about twenty individuals in all. On one of these I saw a single peloric flower at the end of August. In the autumn I pulled up all the plants except two, one of which had exhibited the peloria. These two plants flowered in the following year in complete isola- tion, a profusion of flowers being borne on the freely branched stems, but they did not then develop a single peloric flower. They produced 13cc of seeds, an abun- dant harvest. I sowed a small proportion of this in the following year, and as it gave rise to the Linaria vul- garis pcloria I was looking for, I sowed the rest in 1896, and some again in 1899. Before we proceed to give an account of this main section of the experiment let us briefly summarize the 210 Observation of the Origin of Varieties. results obtained in the years 1886-1893. They com- prise four generations, each of which produced only one or two peloric flowers amongst thousands of normal ones. The anomaly, therefore, seems to recur every year and is obviously due to the existence of some her- itable semi-latent potentiality which only very seldom becomes active. This result of the experiment supports the conclu- sion based on the repeated occurrence of isolated peloric flowers in nature. Linaria vulgaris hemipeloria is thereby shown to be a heritable form. The question whether it is identical with Linaria vulgaris itself, or constitutes a variety or a race of this, cannot be answered for the present. From it my L. vulgaris peloria arose, as I shall now show. In order to make this part of my experiment more easily intelligible I shall first describe it in the form of a pedigree. This contains the four generations already dealt with, and two further ones of the Hemipeloria (1-6), together with the first, second, and third genera- tions of wholly peloric plants (I-III). The meanings of the abbreviations are : h and H: Linaria vulgaris hemipeloria. p: " ** peloria, 1st generation. P: '• " " 2d and 3d generations. Wherever necessary the number of plants is prefixed to these letters either in absolute numbers or in percent- ages. For the fifth and sixth generation I have, as will be seen, made repeated sowings in various years. The sign (-) means that the examples in question were the same as in the previous year, and bore seed a second time. Finally I have denoted by H the two plants of 1893 which in their second year produced the seed from The Or'Kj'ui of Linaria Vulgaris Pcloria. 211 which the L. vulgaris pcloria first arose. These H plants were therefore the parents of the peloric race. PEDIGREE OF THE ORIGIN OF LINARIA VULGARIS PELORIA, GENERATION III 1899 annual II 1898 annual I-II 1897 annual and biennial 6 1895, 1897 annual 5 1894, 1896, 1899 annual 4 1892-93 biennial 3 1890-91 biennial 2 1888-89 biennial 1 1886-87 biennial H a.nd. h = Hemipeloria; p and P = Peloria. 28 T' 4- 4 /^ 7.S /^ 4- 4 // Z P -Vhh (2) 15 // + 2 /> 6 // 4- 1 /• 1895 I 57 A -f 1 /» 1897 h + 1% p 1894 1896 // + 1% p 1899 h h We will hegin the ftirther account of the experiment with the parent plants (//) of the peloric race (1893). As I had not of course observed anything extraordinary up to that time I only sowed a little of its seed. This was done in pans in the greenhouse; the young plants were transferred into pots with manured soil until they were planted out in June. As a result of this treatment 212 Observation of the Origin of Varieties. they all flowered in the first year, — 58 plants in all, of which 45 were dicotylous and 13 tricotyloiis. Amongst the dicotyls there were eleven plants, each of which bore one, two, or three peloric flowers, while in one case a peloric flower replaced a whole raceme. Amongst the tricotyls I did not find any such flowers^, partly because the majority of these were removed by the middle of August; but there appeared amongst them one plant which bore peloric flowers exclusively on all of its stems and their branches. It bore no seed in spite of repeated careful pollination, partly with pollen from the neigh- boring plants ; it survived the winter and flowered freely in the following year, again producing exclusively peloric flowers. This experiment seemed to suggest that the Peloria arose from the hemipeloric parent in a proportion of about 1-2%. So in order to obtain closer knowledge of this proportion, I made a larger sowing in 1896 from the same lot of seed, and was able to plant out about 1850 seedlings in pots. By the middle of July some wholly peloric individuals had appeared, which were promptly taken up and transferred to a remote part of the garden. The further examples of Peloria which appeared from time to time, were planted beside them. By the middle of August all healthy plants were in flower and were recorded. There were altogether 16 totally peloric plants and 1759 with ordinary flowers, and here and there occasional peloric structures. This gives a total of 1775 plants which flowered, of which \% (strictly speaking 0.9%) belonged to the new peloric variety. For the harvest the flowers of the best peloric plants were enclosed in parchment bags and each fertilized with The Origin of Linaria Vulgaris Pcloria. 213 the pollen of another peloric plant. I also selected a beautiful hemipeloric plant which bore a profusion of flowers, one of the earlier of which was peloric. It set a quantity of seed after self-pollination.^ I repeated the experiment in 1899 with the rest of the seed of the parent plant H, and obtained the same result, as was to be expected. I raised slightly over 300 flower- ing plants, of which 3 were wholly peloric; that is to say, a proportion of 1% again. I observed on the rest a certain number of stray peloric flowers during the course of about two months. These three cultures constituted the fifth generation of my experiment. The sixth generation therefore could be raised from the seeds of the hemipeloric plants in it. I did this partly in 1895 from the plants of 1894, and partly in 1897 from those of 1896. The plants which bore the seed had flowered in bags and had been fertilized partly by their own pollen and partly by pollen which I had transferred from one seed-parent to the other. In both cases the mutation was repeated. Wholly peloric individuals again arose from hemipeloric ances- tors, in spite of the smallness of the crops occasioned by the poorness of the harvest. In 1895 I raised 17 flowering individuals from seeds of the dicotylous plants mentioned on page 559; two of them were wholly peloric, all their flowers being of this type. In 1897 I sowed the seed of the fine hemipeloric plant of 1896 referred to above, but obtained only 7 flowering individuals, one of which again, however, was wholly peloric. I come now to the consideration of the question as ' This frequently fails in Linaria vulgaris, but sometimes succeeds more or less completely on very vigorous plants. 214 Observation of the Oricjiii of J\v'ictics. to whellier the mutants are immediately constant from seed. An almost insurmountable obstacle in tlie way of providing an answer to this question is the low fertility, or rather the almost complete sterility, of the peloric flowers. Practically no results can be obtained with self-pollination, and when artificially fertilized with one another's pollen the majority of the flowers set no seed. I have pollinated thousands of flowers in the course of several years, only to obtain a little over one hundred fertile seeds. Under these circumstances it is obviously diflicult to avoid mistakes ; stray pollen grains may happen to reach the stigma from distant groups of normal plants, by the agency of insects, or in the operation of artificial pollination.^ These circtimstances evidently tend to in- validate the conclusion in cases in which the abnormality would seem to be incompletely inherited. Only three of the wholly peloric plants of 1896 set seed in that year. From this seed only 8 plants were raised ; five of them had one-spurred flowers and 3 were wholly peloric. I kept the peloric plants of 1896 through the winter, and took much trouble in 1897 in the attempt to fertilize their flowers. Every other day I pollinated all the open flowers with pollen from two other seed- parents. I obtained a very small quantity of seed most of which was empty (0.2 cc). About 100 seeds ger- minated, but some of the young plants were so weak that they soon died. 79 plants flowered most of which were Axry \-igorous and branched freely ; 75 were wdiollv peloric, and 4 normal, the latter being removed as soon as possible. The former exhibited great variability in the structure of their flowers, but did not produce a single one-spurred corolla. During July and August they ^ Such crosses give normal one-spurred individuals. The Oriyin of Luiaria Vulgaris Pcloria. 215 filled an entire bed of over 3 square meters in extent, with hundreds of vigorous spikes which bore exclusively peloric flowers. I again obtained only a very small harvest from this bed (0.3 cc) ; it was the result partly of artificial and partly of insect pollination, the plants flowering in suffi- cient isolation. Very few of the seeds germinated (1899) and only Z2 plants flowered; 28 of them were peloric but 4 were normal. The progeny of the peloric race was therefore a mixed one, in the three experiments which were continued over two generations. It consisted altogether of 3 -|- 75 -f- 28 ^106 peloric and 5 + 4 + 4=13 normal (including hemipeloric) individuals, a total of 119 with about 10% atavists. Willdenow (see p. 206) also found the peloria character inherited, though incompletely. As already stated, however, insufficient isolation may have played some part in bringing about this result, but hardly to such a degree that we might infer from our experiments that the peloria comes true. If we now look back over this experiment, which occupied 13 years, its result may be summarized as fol- lows : 1. Uiiaria Tulgaris hcinipclona is a race with an in- herited semi-latent character, which manifests it- self from time to time among thousands of flow- ers, but seldom in more than one instance on a plant. It is widely distributed in the wild state. 2. From it the Liuaria vulgaris pcloria may arise but the conditions under which this happens are not yet understood. 3. This origin is a mutation : it takes place suddenly, and without any visible preparation. Especially 216 Observation of the Origin of Varieties. in those individuals from the seeds of which the mutation arises the latent character is not more highly or more often developed than in the rest of the race. 4. The mutation is repeated in successive genera- tions. I observed it for two years, but did not follow it further. 5. The mutation occurred in about 1% of the indi- viduals. 6. The new character was exhibited by the mutants, in a full state of development, in all their flowers ; although it was subject to considerable fluctuating variability. 7. The mutants are to a large extent, perhaps even perfectly, constant from seed. The intensity of inheritance observed was about 90%, but it is probably more. * * * Let us next see how these results can be applied to the explanation of the occurrence of the Pcloria in the free state. Wholly peloric plants have been found wild bv numerous botanists and in the most diverse localities; but, so far as the published information extends, always as rarities. They maintained themselves during a larger or shorter period of years by means of their radical buds, perhaps produced some scanty seed but could not spread nor reach new localities by this means. They must there- fore have originated in each case in the spot where they were found. I imagine that this origin is determined everywhere by the same general laws, and thence conclude that it occurs in the wild state in the same manner as in the particular case observed by me, i. e., from Linaria viil- The Origin of Liiiaria Vulyaris Pcloria. 217 (jaris liciiii pel aria, and always suddenly. The very gen- eral occurrence of this race and the fact that intermediate forms between it and the fully developed Pcloria have never been mentioned by botanists, give support to this h}pothesis If this view is correct we have here a mutation which is not limited to a period but continues to appear from time to time during the course of the ages. Its appear- ance in every single case is independent of the others, at least so far as external conditions are concerned. In this sense it is polyphyletic. A point which favors this view is the fact that it is not a member of a definite group of mutations as are the subspecies of Draba vcrna, Viola tricolor and others. Linaria vulgaris, it is true, frequently gives rise to other kinds of variations such as the Pcloria ancctaria and the Catacorolla, both of which have occasionally appeared in my own cultures, but nothing is on record concerning the relation between these and the Pcloria nectaria which I have studied. If we compare these results with those which we have described above for Antirrhinum inajus striatum (§ 14, p. 134), we see that Linaria vulg. hemipcloria is obviously a half race; and that L. vulg. pcloria, whose partial con- stancy seems analogous to that of the striped snapdragon, may perhaps be regarded as parallel to this. These two races fluctuate so as to approach one another, so to speak, occasionally overstepping the common boundary either in single flowers (L. vulg. hemipcloria) or in whole plants (L. vulg. pcloria). * * * We now come to the most important ]:)oint to which our results and conclusions lead us — namely the com- 218 Obscrvalion of the Or'ujin of ]\iviciics. parison of this mutation with those of Oenothera La- inarekiana. The two processes have several features in common, but possess others which are mere or less strongly opposed. The points of similarity are : the sudden and imnie- diate origin, the repeated appearance, the mutation- coefficient of about 1% (see Vol I, Part II, § 14, p. 2>^7), the completeness of the new type, and its high degree of heritability. These common characters justify the description of the origin of Linaria vulgaris peloria as a mutation.^ But it is a mutation of a special kind. The structural change does not extend to all parts of the plant, but is confined to the flowers ; in their youth the two types cannot be distinguished. In the mutations of Oenothera Laniarckiana the new characters are analogous to the specific characters of related species already existing; in the case of Linaria no such analogy exists. On the contrary the new character in Linaria occurs as a variety in numerous other species, and even in distantly related ^ Linnaeus, as is well known, expressed the view that the Peloria is a hybrid between the common Linaria vulgaris and some other im- known plant. Its comparative sterility favored this view, but as the second of the two parents could not be found this view has since been given up. Here, however, I might discuss the possibility that L. vnlg. hemipcloria might be a cross between L. vulgaris (apeloria) and L. vulg. peloria. If this were so the appearance of the latter from the former would perhaps have to be regarded not as a muta- tion, but as a segregative process in a hybrid race. If this view were true the Peloria should first have arisen from the Apeloria, without the mediation of the Pleuiipeloria, a process which has still to be observed. It is, however, no more than a pure assumption that the hybrid ApeloriaY, Peloria would be a Heuiipeloria; in fact our knowledge of other cases would lead us to suppose that it would be like one of the parents, in this case the Apeloria, and so long as there is no direct information on any of these points a further dis- cussion of this view seems barren. Moreover it is by no means cer- tain that Linaria vulgaris apeloria exists at all, or ever has existed; the variety, in this genus particularly, may well be older than the species. The Origin of Linaria J^ulgaris Pcloria. 219 plants. Lastly the mutation in Linaria does not appear along with others in space and time, but occasionally, and scattered perhaps over the whole area of the parent form and probably over the whole period of the life of this race. The mutations of Oenothera Laniarekiana necessi- tated the assumption of a definite premutation, but the origin of the Peloria is obviously a phenomenon of a different kind. Peloria is often regarded as an instance of atavism.^ The c(^rrectness of this interpretation obviously depends primarily on whether this term is used in a narrow or a broad sense. Atavism is a reversion to ancestral char- acters ; in the narrow sense to the complete type of par- ticular ancestors, in the wider it refers only to single characters. But it is clear that the spurs which form a distinctive character of the genus Linaria must be older than the species L. vulgaris, which cannot therefore have had ancestors without the spur but with the other char- acters of the species; so that L. vulgaris aneetaria can occupy no place in the series of ancestors. The sym- metry is ever so much older and L. vulgaris with regular flowers has certainly never existed amongst the ancestors of the common toadflax. Moreover the sterilitv of the peloric plants does not favor such a view. If the Peloria must be regarded as atavistic, this view can mean no more than the assertion that it has arisen by the loss or latency of a character of the common Linaria. Therefore we are concerned here with a retro- gressive mutation, and the question arises, how far the difi^erences between this case and the progressive muta- tions with which we have become familiar in Oenothera * See L. JosT, Biolog. Cenfralbl, 1899. p. 149. 220 Ohscrz'ation of the Origin of Varieties. are tliiis to be explained. The explanation is so simple that it follows directly from the preceding discussion. It is merely necessary to point out that the most impor- tant condition for a character to become latent is its pres- ence; and this explains how it is possible that the Pcloria so often appears over the whole area of distribution of the species. Neither a premutation nor a period of muta- tion is necessary for such an occurrence. If the loss or latency (for the inner potentiality is ob- viously not lost but only becomes inactive) affects single flowers we have a partial atavism, but if it affects the whole plant we have the complete and heritable Peloria. It is on this basis that the atavistic phenomena of the striped flowers, of the many-spiked Plantago (§17, p. 148) and of the peloric Linaria fall in line. They are retrogressive phenomena, reversions to ancient charac- ters wdiich have externally become lost but are still pres- ent in a latent state. Their agreement with one another on the one hand, and their contrast with the progressive mutations of Oenothera Laniarckiana, on the other, thus receive a satisfactory explanation. §21. HERITABLE PELORTAS. Pelorias are very rarely met with in nature as a specific character. As an instance I may quote Mentha aqiiatica, the apical flowers of which according to Schim- per's discovery are always regular and consequently peloric,^ and the orchid Uropediinn Lindenii, which is regarded as the peloric form of Cypripedinni caudatuinr ^ A. Braun, Ahh. d. Berliner Akad., 1859, p 112; and Delpino, Mem. R. Instit. di Sci., Bologna, 5 Ser., Vol. I, 1890, p. 269. ''A. Brogniart, Ann. Sc. naf., 3 Ser.l, Vol. XIII, p. 113 (Plate 2) ; and J. M. Janse, Maandblad voor N atuurwetenschap p en , Vol. XIV, No. 3, 1887, p. 29. Uroped'mm Lindenii appears to be by no Heritable Pelorias. 221 In a state of cultivation peloric races are also very rare, and the common Gloxinia superba erecta with its numer- ous color varieties and hybrids is the best generally known cultivated example.^ Our present knowledge of the origin of Linaria vul- garis peloria as described in the foregoing pages, justifies us in attempting to form some idea concerning the origin of such forms in these perfectly analogous cases and also to sketch the details of this idea on a basis, or back- ground of facts. But there are still difficulties in the way. The low fertility and the incomplete constancy of the Peloria distinguish it from true species.^ Most systematists would evidently not consider L. vulgaris peloria to be a true species unless the common L. vulgaris were ex- tinct. Besides the examples named, there is a whole series of heritable cases of peloria, which either appear as rare anomalies, or are familiar cultivated races, and repeat the abnormality regularly and in a fairly large number of individuals every year.^ In both cases, however, the development of the anomaly is, as usual, in a high degree dependent on external conditions. There are, as we have stated in the foregoing section means rare in Colombia (South America) ; it was discovered there by Linden in 1843 (Linden, Pescatorca, Iconographie dcs Orchi- dees, i860, Plate IL ^ The spurless varieties of certain species of Viola and Tropae- olum may also be regarded as pelorias : see the following page. ^ From this point of view it would be very important to know whether the Mentha and Uropcdium cited are perfectly constant, that is, never produce atavists without pelorias. ^Tt is extrernely doubtful whether, besides these, there are pelorias, the origin of which is solely due to external influences and docs not need the existence of a corresponding internal poten- tialitv. 222 Observation of the Origin of Variety. (§20), various kinds of pelorias according as one or another form of the petals of the parent species has be- come the one which prevails in the subspecies. In spur- bearing species they are distinguished as Peloria nec- toria and anectaria. Both possess a very low degree of fertility but are, so far as is known, heritable. Peloric flowers without spurs are well known in Linaria,^ An- tirrhinum,- Viola,'^ Tropaeoliun,'^ etc.^ There are few heritable peloric races beyond those which have been named. The best known are Corydalis solida peloria which in Godron's experiments^' was found to transmit the abnormality through a series of genera- tions, and Digitalis purpurea monstrosa (Fig. 42). This latter, the peloric foxglove, has been a favorite garden plant for a long time, and has often been the subject of morphological investigations. The oldest descriptions and figuies are due to my predecessor G. Vrolik, whose preparations are still to be seen in the collection at Amster- dam.'*' Since his time the variety has been cultivated in our botanical garden more or less regularly, and is still growing there. ^ It is very constant; its peloric flowers ^ C. Billot, Annotations a la Flore de France et d'AUemagne, quoted in Bot. Zeitung, 1872, p. 278. ''J. T. C. Ratzeburg, Animadversiones ad peloriarum indolem, 1825, Plate I, Figs. 64-76. ^J. C CosTERUS, Pclories du Viola tricolor, Archiv. Neerl., Vol. XXIV, p. 142, Table II; De Candolle, Organographies PL 45. * E. VON Freyhold, Ueher Pelorienbildung bei Tropacoluui adnn- cum, Botan. Zeitung, 1872, p. 725 and Plate IX. "D. A. GoDRON, Mem. Acad. Stanislas, 1865 and 1868 {Delphi- nium chinense, etc). ® GoDRON, loc. cit., 1868, pp. 3-8, Cultures from 1862-68, with more than fifty peloric plants. " G. Vrolik, Ueher cine sonderhare Wucherung der Blunien bei Digitalis purpurea. Flora, i844,p. i. Plates I and II; also Fortge- setzte Beohachtungen iiber die ProlHication von Digitalis purpurea, Flore, 1846, p. 97, Plates I and II. ^ The following selection of references may be of use: W. F. R. Her if able Pclorias. 223 are, however, highly variable and only too frequently accompanied by other malformations. The commonest of these are an increase in the number of organs, the formation of catacorollas and the production of a secon- dary raceme from the axis of the flower. These are the cases which are most commonly described and figured in literature. In order to find more regu- lar and even perfectly pentamerous flowers we must look to the tops of the weak lateral branches of vigorous plants (Fig. 42) ; these hardly ever proliferate, are often still pleiomerous, but there will also occur amongst them flowers with a per- fectly regular corolla with five lips and five erect stamens. The peloric flowers of Digitalis purpurea are always terminal, whether they occur on the main stem or on branches. The same is true of most other Serophu- SiTRiNGAR, Plantaardige Monstruositcltcn, K. Akad. v. Wetenscli., Amsterdam, 1873, 2d. R., Vol. VII, Plates I-TI P. Magnus, Digitalis purpurea, Sitzungsber. Prov. Brandenb., Vol. XXII, 1880, p. J. C. CosTERUs, Teratologische Verschynsclen by Digitalis pur- purea, Ned. Kruidk. Archief, 1885. Plate VII. Angel Gallardo, Fasciaeion, Proliferacion y Sinantia. Ann. ]\Tiis. Nacion., Buenos Aires, Vol. VI, p. 37, PI. 3; also Sohre aiguiias aunmaJias de Digitalis purpurea (witli complete bibliograpby), same journal, Vol. VII, pp. 37-72. Fig. 42. Digitalis purpurea mou- strosa. A lateral brancb witb a terminal pentamerous pcloria. 224 Observation of flic Origin of Varieties. lariaccae,^ and of many other families, especially or- chids.- The relation between this position and the reg- ular form of the flower is still without a proper explana- tion; and the question whether the anomaly is due to high nutrition or to the absence of the factor which determines the bilateral symmetry or both, still awaits a definitive answer. Laterally situated peloric flowers are very rare but sometimes occur as we have seen in Linaria Fig. 43. Antirrhinum ma jus. A, Peloric flower from the middle of an otherwise normal raceme, August 1899. Two slips of the corolla stand erect ; the other three are bent downward. B, Normal flower of the same spike. vulgaris hernipeloria (Fig. 41, p. 207), and as is shown by Antirrhimun ma jus (Fig. 43), etc. Of great impor- tance, also, is the hitherto little noticed fact that in Digi- talis and one or two other cases, the peloric terminal flower opens first of all, whilst the order of opening of all the other flowers on the stem is normal, i. e., acro- petal. ^EiCHLER, Bliithendiagramme, I, p. 208. ''Pfitzer, in Engler and Prantl's Natilrl. PHanaen-Familicn: Orchid., p. 61. For further information on pelorias of Orchids see Penzig, Mem. Soc. naf. Sc. Cherbourg, Volj XXIX,, 1894, pp. 79-i04- Heritable Pelorias. - 225 Peloric flowers occur as chance anomalies in a large number of plants. A speciment of Scrophiilaria nodosa which I have had growing for the last ten years pro- duced them abundantly. On the other hand my cul- tures of Antirrh'uium iiiajus although of twelve years duration and carefully guarded gave rise to no UKjre than two peloric flowers, one of whicli is shown in Fig. 43A. Both sprang from the middle of the racemes, that is, they were lateral. I have also observed occasional cases of peloria on Aesculus Hippocastanwn, Melain- pyriini pratense, Orohanche Galii,^ Cytisus Labiirmiin, etc. In my cultures of 1892 a peloric flower occurred on a plant of Lnpinus hit ens. The tube-shaped peloric flowers of the cultivated Calceolarias are also well known. In these and similar cases the mode of inheritance has still to be investigated. In this respect the observations of Peyritsch are of great importance He has shown that in the case of peloria in Leonuriis Cardiaca, an an- nual Labiate, the anomaly can be reproduced from seed whether this originates from the peloric or the normal flowers of the same plant. Feyritsch's memoir is one of the most valuable of those which deal with peloria, and is indeed an almost complete monograph so far as the Labiates are con- cerned.- He has also investigated the influence of the environment on the anomaly as occurring in a series of Labiates.^ I select the following observations for notice here : ^ See also W. F. R. Surtngar, Orohanche Gain, Ned. Kriiidk. Archief. 1874, Vol. I, p. 330, Plate 18. ^ T. Peyritsch. Uehcr Pcloricn hci Lahiafcn, Sitzber. d. k. Akad. d. Wis?.. Vienna, Vol. XT., Part T, 1869, p. 34.^ Pk-^tes T-VT ; and Vol. XLTI. 1st secticn, 1870, p. 497, Plates I-Vlll. "J. Peyritsch, Unfcrsuch. i'lher die Actiologic pclorischcr BU'iicn- 226 Obscri'ation of the Origin of Varieties. Lamium maeiilatiiin and Galeohdolon lutciim commonly produce peloric flowers in the neighborhood of Vienna. They often bear them every year on the same plant, but one or more years are sometimes skipped. A sunny position increases the number of anomalous flowers whilst dense shade diminishes it ; consequently one locality often furnishes instances of peloria in several species of Lab- iates (e. g., Calaiiiintha and others), whilst the same species growing together in another locality will not pro- duce a sinerle svmmetrical flower or onlv verv few. When- ever the conditions affecting a plant were improved by cutting down timl)er, peloria occurred in profusion, and the transference of a plant to a sunny spot in a garden often resulted in its appearance. Other authors, and particularly Vuillemin/ also assert that the conditions of life play an important part in inducing the anomaly, provided that the inherited potentiality for it is present. hildiingen, Denkschr. d. k. Akad., Vienna, Vol. XXXVIII, Part TI, 1877, with Plates I-VIII. See also Goebel, Organographie, I, p. 163. ^ Loc. cit., 1894, p. 33. VII. NON-ISOLABLE RACES. § 22. TRIFOLIUM INCARNATUM QUADRIFOLIUM. Few experiences are so well fitted for enabling us to obtain an insight into the nature of specific characters as the failure of an experiment in selection. I am not speak- ing of practical experiments because in such cases the breeder is often disappointed by the fact that the result is not superior to what he has already, or is not suitable for cultivation on a large scale from other causes. This kind of failure only concerns the practical breeder and does not affect the scientific investigator. The object of the latter is simply to find out whether a race specified beforehand can be obtained or not. According to the theory of selection almost anything ought to be obtainable. Almost all characters manifest fluctuating variability to the extent requisite for selection. If the range of variation is considerable, selection should proceed rapidly; if it is within narrower limits it should merely require longer series of generations; and if, more- over, the familiar but undemonstrated opinion is assumed that fluctuating variability increases as the result of the selectixe ])rocess, there is no reason why in any given case the attempt to breed a desired race should not suc- ceed. But this discussion, in my opinion, onlv applies to ordinary fluctuating variability, and if thus limited, I 228 Non-Isolablc Races. willingly agree with the prevailing view. In the sphere of mutability, on the other hand, matters are entirely ditlerent. Here species, subspecies, varieties, races, etc. arise by mutations which are induced by rendering active a hitherto latent or semi-latent character. The first con- dition for a desired mutation therefore is the existence of the character in question in a latent or semi-latent state. Without this nothing can be achieved, at least in the present state of science, and it is only in the case of semi-latency that we can have any sort of evidence that the desired character is present. Horticultural breeders are well known to be continually on the lookout for any such indication.^ But the presence of a latent character is not of itself sufficient, according to my experience, to insure the suc- cess of an experiment in selection. For many an experi- ment has failed in spite of years of labor. This proves nothing in itself, because it is often due to lack of sufficient experience, and this experience can only be acquired by carrying out a successful experiment in an analogous case ; in other words, by making exactly the same experiment with a related plant, preferably with another species of the same genus. For this reason I have more than once endeavored to breed a race analogous to one already existing in a closely related species of the same group, which is either on the market, or has appeared in my own cultures. Ex- perience has taught me that the end may often be attained with greater or less ease according to circumstances; Init that in many other cases, so it appears, insurmountable obstacles bar the wav. A very definite and simple case is afforded by the * See Vol. T, Part T, § 25. p. 188; and this volume, Part I, § 2, p. 9. Trifoliuni Incarnatiun Quadrifoliuiii. 229 attempt to breed a five-leafed race of the crimson clover {Trifolinin incarnatuni) analog- ous to the hve-leafed race of the red clover (Trifolinin pratcnsc) which has already been described (§ 5, p. 36). I started the ex- periment in 1894; since then I have devoted a great amount of trouble to the task without any result, until in 1900 I gave it up. The attempt simply does not suc- ceed, with my material at any rate. The object was worth a great effort. At first I believed that I had artificially made the five- leaved red clover, or as it is often expressed, that I had cre- ated it. The gradual develop- ment of my theory, however, led me to doubt the correctness of this opinion. It seemed possible that I had merelv found the race already existing in nature, but in a condition in which it was not recognizable as such. Eight years however had gone by since the beginning of that culture, and it was practically out of the question to go back to it. I re- Tig. 44. TnfoUnm incar- 1 1 i.1 r , 1 , natiini. A flowering solved therefore to endeavor to branch with a single 4- raise a new five-leafed clover and ^^^'-'^^^ ^^'''^^\ ^'^^ .''^^^"'^ , . of an experiment in se- selected the crniison clover. This lection lasting six years. 230 Kon-hokiblc Races. choice was largely determined by the fact that there were no published records of 4- or 5- foliate leaves of this clover,^ which means that the character, if present in a latent state, is much rarer than in the red clover. I take this opportunity of calling attention to the inestimable value of PENZio's^'Teratology." This lies per- haps rather on the negative than on the positive side, for it is of course possible to collect the main literature relating to a given question oneself, although not witli- out the expenditure of a great amount of time; but if one is not a teratologist by profession, it seems hardly possible without some such help, to satisfy oneself that ^•^ Fig. 45. Trifolium incarnatum, 4- foliate leaves, the middle one with incomplete segregation of a lateral leaflet. absolutely no records relating to a particular phenomenon exist. The first step in a purely scientific breeding experi- ment evidently is to find out whether the deviation in question has occurred before, and if so, whether it is rare or common. My belief is that the commoner anomalies are heritable characters with a high index of inheritance (often about 30-40% or more), but that the rarer ones are the occasional expressions of latent or semi-latent characters. These are also inherited in their latent state, and if they turn u]) here and there this latent condition must ])robably be widely distributed. ' O. Penzig. Piiansenteratologic , Vol. T, 1890, p. 385, where T. incarnatum is not even mentioned. Trifoliiun hicaniatuiii Oiiadrifoliimi. 231 If Trifoliiun iiicarnatimi with 4- foliate leaves had often been mentioned it would therefore seem probable that a five-lea\ed race of it occurs in nature, although just as little separated from the ordinary crimson clover as the five-leaved race of the ordinary clover is from this. Latent characters, in my opinion, are often older than the species which bear them. I regard the division of the leaf into four blades in this case as an atavistic phenom- enon, and I believe that this latent potentiality is as old as the whole group of clovers with trifoliate leaves {Tvifoliuin, Medico f/o, Mclilotus etc.), that is, older than the individual gen- era of this group. In many spe- cies this power of reproducing quadri foliate leaves may have been completely lost, for it is mentioned in Penzig's book only for a relatively small number of them. In others, however, it has ])ersisted to the present day. If the trifoliate leaves of the clovers are derived from Papilionaceae with pinnate ones, the multi foliate leaves which they occasionally produce must evidently be re- garded as atavistic phenomena. The correctness of this view is proved by those very rare cases in which, in the races in question, ])innate leaves appear instead of the ordinary multi foliate ones. I have observed this from time to time in my Trifoliuni pratcuse qiiijigncfoliitm (Fig. 46) and the same thing has been found bv other authors in Trifoliuni in in us and Tri folium re pens. I have mvself found 4- and 5-foliate leaves in Mcdi- Fig. 46. Trifoliuni f^ratensc. An atavistic pinnate leaf. 232 Non-Isolabic Races. cogo liipuliua, whilst Braun has observed them In M. safk'a. They are well known in T. pratcnsc and T. rcpeus, and Wydler has recorded 4-foliate leaves in Lotus major and Tctragonolobiis biflonis. In some suc- cessive sowings which 1 made with Medicago lupulina I found the character to be inherited although in a mod- erate degree only, but I have not continued the experi- ment. But let us return to the crimson clover. The question is, what prospects were present at the beginning of the ex])eriment, and what may be expected from such ex- periments in general ? There are three main possibilities to be considered. We may find at the beginning of the experiment (See § 3 p. 20) : 1. A race which often exhibits the anomaly in ques- tion, and bears it as a heritable character, i. e., an ever- sporting variety; 2. A half-race with a semi-latent anomaly v/hich is only occasionally manifested; 3. An ordinary plant of the species with the character in question in a latent condition. In the first case the race already exists and all that is necessary is to isolate it ; in the second it may possibly be obtained : in the last there is little prospect of doing so. In order to present a clearer idea of the mutual rela- tions of these three cases let us examine TrifoUuui repens and T. pratense. That the anomaly is by no means A-ery rare is testified in both cases by the popular belief in the so-called lucky four-leaved clover as well as by common experience. If looked for in a field of clover, or in a meadow, or along the roadside, a four-leaved clover will be found from time to time. If repeated attempts are made to find them they will certainly prove to be rare Trifolmni Incarnatum Quadrifoliuui. 2^^ but not so rare as we might have imagined. I have found them ahnost every year, and often (juite soon after I had been asked for one. On the other hand there is on the market the 5-fohate T. rcpcns atropnrpurcum which is often cultivated in gardens for its dark brown leaves, and for T. pratcnse I have described the five-leaved form in detail in § 5. Plants of T. pratcnse are sometimes found in the field with two or more 4- or multi foliate leaves. I found one in 1866 in the Cronesteyn estate near Leyden, and an- other in 1886 near Loosdrecht. The first had several 4-foliate leaves, and also some 5-6-foliate ones. I se- cured the former but did not cultivate it; the latter formed the starting point of my race. In view of my present knowledge I must assume that in both cases the plants already belonged to the race when I found them ; and I also consider it as probable that this race had arisen on these very spots, or at least not far from them.^ Whether the same race can also be produced from the occasional stray four-leaved clovers I do not, of course, know ; but I anticipate that the attempt would sometimes succeed and at other times fail. If this view is confirmed by future experiments we shall have proof of the exist- ence of the two races, the eversporting variety and the half-race, existing simultaneously within the limits of a single species. For the present we must be satisfied with the knowledge that there exists a race rich in anomalous leaves in the red and in the white clover, and one in the crimson clover which bears the character only in the semi-latent state. I shall now proceed to the description of the latter. In the winter of 1894-95 I bought a kilo of the seed A polyphyletic origin, therefore, as in Linaria vulgaris pelon'a. 234 Non-Isolable Races. of the ordinary crimson clover and sowed part of it on a bed of about five square meters. Two of the seedhngs were tricotylous and one was tetracotylous, and these were transplanted to a special bed as soon as possible in the hope that tWey would exhibit the desired abnor- mality. This hope was based on the principle of the correlation between different kinds of anomalies.^ If a plant exhibits an anomaly in its early stages it will, ac- cording to this principle, be more likely than any other individual in the same culture to give rise to other devia- tions later on. In this particular case my expectation was fulfilled, for the tetracotylous plant produced one 4-foliate and one 5-foliate leaf in the course of the sum- mer. Such were not found on any other plant, either during the course of the experiment or at the end of July when the plants were in full bloom and were pulled up and minutely examined. There wxre about a thousand plants. I left the three selected specimens to flower together and sowed their seeds in April 1896. Over 600 seedlings came up, all of them with only two cotyledons. In all of them the first leaf was single, which is the general rule in clovers (Fig. 47 A). The second and third leaves developed in May; they were quite normally trifoliate, with tlie exception of one, of which one of the three leaflets was split laterally, although not completely di- vided. The form of this blade was similar to that figured in Fig. 45 B. About 250 individuals of the whole group were planted out. The seed had been sown in pans ; the young plants were transplanted into pots and were planted in the beds ir the middle of May. At the end of June, ^ Eine Methode, Zwangsdrehungen aufzusuchcn, Ber. d. d. bot. Ges., Vol. XII, 1894, p. 25. Trifoliuni Incarnatum QiiadrifoUuui. 235 at the beginning of the flowering period, several incH- viduals exhibited one or more 4-fohate leaves ; the anom- aly was therefore a heritable one. Moreover the multiplication of the blades had also increased considerably as the result of selection, as the following figures prove. These refer to the offspring of that seed-parent which had already exhibited the anomaly in the previous year. There were 90 of them ; among the offspring of the tricotylous parents ''4-leaves" were not entirely absent, but they were relatively scarce, and Fig. 47. Trifoliuni incarnatum. A, a seedling with normal primary leaf. B — D, seedlings with 2- and 3-foliate leaves. The former arise from the larger ; the latter from the smallest seeds. the whole group was consequently pulled up at the be- ginning of the following period. About 73 (58 out of 90) of the rest were perfectly normal without any in- crease of the number of leaflets. On the average they had about 10 stems and 100 leaves per plant. The re- maining plants formed a half-curve^ of the following composition. The first row gives the number of 4- or 5-foliate leaves per plant, and the second the number of *§ 4, p. 26; and Uebcr halbe Galton-Curvcn, Ber. d. d. hot. Ges., 1894, Vol. XII, p. 197. 236 Non-Isolablc Races. individuals on which these numbers were observed f cul- ture of 1896): Abnormal leaves 0 1 23456789 Individuals 58 10 12 4 2 2 1 0 0 1 The 58 normal plants were pulled up. Of the rest four were weak and died; there remained 28 which all flowered together. Their seed was harvested separately after the number of 4- and 5-foliate leaves on each parent had been recorded. In March 1897 I sowed a part of this seed in pans, separately for each seed-parent. The object of this was to find out whether there was any difference between the individual seed-parents with regard to the number of anomalous offspring which they produced. From an examination of the pans it was easily seen that the ab- normality had already appeared in the primary leaves of some of the seedlings. In the great majority of cases these were perfectly normal, consisting of one leaflet as in the whole of the previous generation. In some cases however this primary leaf consisted of two or three leaflets (Fig. 47 B-C). Such occurred in the crops raised from 6 of the 21 plants whose seeds had been sown. Each seed-parent had given a crop of about 300 seed- lings. Five of the crops contained not more than 2 ab- normal seedlings, but the remaining one had a very large number, namely 14 amongst 335 seedlings or about 4%. It is worthy of notice that the parent of this crop had only had two 4-foliate leaves itself and thus had not given the least sign that it would produce offspring with so much higher a degree of the abnormality. Moreover I could not find any relation between the number of ab- normal leaves on the other seed-parents and the pro- portion of abnormal offspring raised from their seeds. Tri folium Incarnatinn Ouadrifoliuiu. 22>7 llie plant with nine 4- or 5-foliate leaves did not give rise to a single anomaly amongst 300 seedlings. Amongst breeders of animals it is generally recog- nized that the visible characters of an animal are of very little use as an indication of its value for breeding. The offspring which the animal has already produced afford a much more reliable indication. On the basis of the choice of the seedlings, the 14 abnormal offspring of the seed-parent with 4% were planted out in the beds in June 1897, together with the seven next best plants. The latter produced very few 4- to 5-foliate leaves per plant, the first 0 and 1 in eleven cases, but 9, 9 and 4 in three cases. There was there- fore no marked advance on the previous year in this respect. The progress was just as inconsiderable in the harvest of that year. The percentage of abnormal individuals amongst the seedlings ranged in 1898 between 1 and 4% and in one case reached 6%. On the other hand all the (19) seed-parents investigated had at least one and usu- ally two or more seedlings with a divided primary leaf. But here again no relation was manifested between the number of abnormal seedlings and the number of 4- or 5-foliate leaves on the seed-parents which produced them. 227 seedlings were planted out, most of which were perfectly normal at the time of flowering. I obtained the following half-curve (1898) : Number of multifoliate leaves per plant: 0 12 3 4 5 Individuals: 188 29 7 1 1 1 That is to say, about 20% of individuals with the inherited anomaly in from 1 to 5 of the whole number 238 Ko)i-Is()lablc Races. of leaves counted on tlie plant (about 100). The numbers were therefore smaller in this than in the previous year. For this culture I had planted out the normal and ab- normal seedlings of the most abnormal seed-parents and some abnormal seedlings of the remaining seed-parents. No essential difference between these three groups could be detected when they were recorded at the time of flow- ermg. Pitclier formati(^n was observed ])oth amongst the seedlings and during the later stages; tliis is another indication of correlation amongst the vari(xis characters. In the summer of 1898, 41 of the selected plants fur- nished a sufficient quantity of seed. In the following s])ring I determined the proportions of seedlings with compound primary leaves in the crops from each of these parents and reckoned them in percentages. The compo- sition of the 1898 harvest with respect to this character was : Percentage of abnormal offsprino; 0 1 2 3 4 5 8 11 15 16 20 24 27 Parents 3 12 7542121 11 11 That is to say, a considerable advance which at once becomes evident if this series of figures is com])ared with that given above for the 1897 harvest (1-4 and 6%). This advance has moreover taken place in spite of the falling off in llie number of 4-foliate leaves in tlie seed- parents. In the spring of 1899 I only selected seedlings with trifoliate primary leaves for transplanting (see Fig. 47C), and only from amongst the offspring of the four seed- ])arents with from 15-24Vr abnormal oft'spring. At the time of flowering, however, my hopes were disappointed. In the middle of July there were amongst 120 richlv branched flowering plants 45% without the anomalv, Trifoliiun lucaniatuiii Oiiadrifoliuiii. 239 27% with a single abnormal leaf each, and 28% with two to four 4- to 5-foliate leaves each. That is to say, 55% abnormals as against 20% in the previous year — which indicated a marked advance. But my hope of obtaining a leaf with mure than five leaflets was not fulfilled. In spite of repeated search I never found one. Nor did I obtain plants rich in four- bladed leaves; for there were none with more than four of them. Therefore I have since abandoned the hope of breed- ing a race of four-leaved clover, corresponding to my Trifoliwn pratcnse qidnqucfoHum, from this material. A striking feature of this experiment is the ajjparent absence of a relation between the degree of al)normality of the adult plants and that of the seedlings. For the paucity of four-bladed leaves in the grown plants seems incompatible with the abundance of multi foliate primary leaves in the seedlings from which they grew. The failing of this relation has led me to the dis- covery of a most remarkable connection between this variability and the size of the seeds, for the smallest seeds are those which give rise in the largest number to compound primary leaves. Small seeds germinate somewhat later than larger ones and also give rise to weaker plants. It had often struck me that the selection of the most abnormal of the seedlings was frustrated by the fact that many of the indixiduals with compound primary leaves were too weak to be planted out, or died soon after tlie process. It also struck me that all the seedlings in a pan could not be recorded at the same time. At first view the plants ap- pear to germinate very regularly, and hundreds in the same pan seem to unfold their leaves at the same moment. 240 Noii-Isolablc Races. At this point they were recorded and, if the first leaf was single, were usually pulled up. Those which were saved were usually weaker, more stunted and backward in growth. Several had not yet unfolded their first leaves, and amongst them a great number of the anom- alies were found when the examination was repeated a few days afterwards. I then convinced myself by a very simple experiment of the correctness of these conclusions. All that was necessary was to isolate the large and the small seeds in a sample and to sow them separately. But as there is no absolute limit between the two it was necessarv to know how many seeds should be separated out, as the smallest. And this can only be done by the number of anomalies, i. e., compound primary leaves, they produce. I therefore selected a sample of seed whose capacity for producing anomalies I already knew. This was 15%; the sample was derived from a single seed-parent. I separated the seeds into three categories, small, inter- mediate and large. All in all there were 217 seeds of which 17 did not germinate. The characters of those which did are as follows : Number of divisions in the primary leaf. 1 2 3 2-3 Small seeds 31 9 16 12.5 % Intermediate seeds 50 2 1 1.5% Large seeds 88 2 1 1.5% 169 13 18 15.5 % It will be seen that almost all the abnormal seedlings are derived from the smallest seeds. The seedlings from the large seeds had, with a single exception which was an abnormal one, unfolded their primary leaves in May, and fourteen days after the seed had been sown ; the same TrifoUiuii Incarnatuni Ouadvifoliuin. 241 is true of the intcniicdiate seeds with the exception of four, two of which were a1)normal. 11 normal plantlets developed from the smallest seeds in the same time; the 9 other normal and the 25 abnormal ones did not unfold their first leaf until the third week.^ These facts show further that the number of seed- lings with abnormal primary leaves does not depend simply on the degree of fixation of the variety. It de- pends mainly on the proportion of small seeds. This, however, in its turn, depends on the size of the harvest. Fig. 48. Trifolium incarnatum. Monstrous seedlings from the smaller seeds. A, B, D, with two to four primary leaves ; C, with a double leaf with broad flat peduncle. In the 41 samples which composed the harvest of 1898 there were 8 with 8-27% abnormals ; these samples con- sisted of from 0.3 to 1.5 cc. of seed. The remaining samples consisted of from 2 to 5 cc. of seed and the n.umber of abnormals produced ranged between 0 and 5%. From these facts we see that the weaker individ- * In stocks also the seeds which produce plants with double flowers and those which give rise to "singles" have difl^erent rates of germination, as is well known. An investigation of the seeds ot inconstant varieties, or, as they are usually described, varieties which have not "yet" been fixed, would be certain to reward the inquirer with many interesting discoveries. 242 Nou-Isolablc Races. iials, whicli gave a poorer harvest, gave rise to the larg- est number of abnormals amongst their offspring. I have repeated the same experiment with the harvest of 1899, with the seeds of four separate seed-parents, but as I did not know their capacity for producing abnormals in advance, the difference was not so striking. The large seeds gave rise to 2-4%, the small ones to 3-1 3 7^ abnor- mals. Altogether seedlings from 2758 large and from 617 small seeds were examined. Two questions present themselves in connection with the interpretation of these experiments: (1) Can the position in which the small seeds are chiefly produced on the plant, be determined?-^ (2) Are the germs of the small seeds perhaps the better nourished ones ; is there, for instance, just as much nutriment brought to them as to the large seeds, but must they, for want of room or for other reasons, utilize it in some other way? I recommend these problems for further study, and may perhaps in the mean time record a few facts bear- ing on them wdiich I have observed. In the crimson clover, monstrosities occur much more frequentl}' among the seedlings from small tlian among those from large seeds. The latter are almost all perfectly normal. The small seeds often produce plants with supernumerary cotyledons, or with two or more primary leaves (instead of one) or with divided peduncles, symphyses in the leaves and other malformations (Fig. 48). Unfortunately it is often difficult to keep these individuals alive and to bring them to flower. Let us now cast a final glance over the whole course of the experiment. ^ Tn stocks. Jiccordin.f^ to Chate, Culture dcs Giroflccs, the seeds which produce double-flowered plants arise chiefl\- from the lower half of the pods of the strongest racemes of the plant. Ranunculus Bulbosus ScinipUiius. 243 A crimson clover plant w itli some quadri foliate leaves was ()])taine(l by the selection of tricotylous and tetra- cotylous seedlings in conformity with previously studied laws of correlation. The anomaly proved to be heritable and has maintained itself until now, during six genera- tions (1895-1900). It was improved by selection but only within very narrow^ limits. Plants with more than five leaflets per leaf have not as yet arisen, nor have ])lants bearing ten or more 4- to 5- foliate leaves, and it is nearly always the ''small" seeds which give rise to seedlings with compound primary leaves. But the chief result is that the desired race, rich in 4-foliate leaves, "T. incarnatuni quinqucfoUuni" anal- ogous with Trifoliuni prafcnse quinqucfoUuni^ did not arise. ^ § 23. RANUNCULUS BULBOSUS SEMIPLENUS. Double flowers are common phenomena amongst the buttercups.- They occur not only in the cultivated Ra- nunculi ( R. asiaticus) but also in several wnld species. The doubling may be either complete and brought about by petalomania as in the Ranunculus acris shown in Fig. 40, Vol. I, p. 194; or it may be more or less incomplete when caused by the transformation of a varying numl)er of stamens into petals (R. acris, R. auriconius, R. Philo- notis, R. re pens etc.). In Ranunculus bulbosus, the bulbous buttercup, the ^ The same thing no doubt occurs also in other cases. The at- tempt to breed from occasional anomalies a constant race endowed with the particular variation, in some cases succeeds, but in others does not. For instance I have for many years endeavored to raise from the occasional polycephaly in Palaver commutatum a race with as beautiful crowns as those which characterize the famihar Paf^oi'cr sonmifcnun polycephalum (see Vol. I. p. 138, Fig. 27), but in vain. ^ See Penzig, Pflancenteratologie, Vol. I, pp. 181-189. 244 Non-I salable Races. stamens are often (either all, or only some of them) transformed into petals with the result that dense double flowers are produced.^ These have been described by Fig. 49. Ranunculus hulhosus scmiphnus. A, the bulb; A' and A", its leaves from the axils of which the flower- ing stems S arise ; E, terminal flower of the main stem ; S, secondary flowers partly broken off; T, tertiary flow- ers. (See p. 256). various authors.- In the neighborhood of Amsterdam this variety does not occur, so far as I know. On the ^ Loc. cif., p. 185. Fasciated stems with broadened terminal flow- ers are also met with occasionally in the Ranunculus bulbosus in Holland. ^Compare the Ranunculus bulbosus Alcae of Naples, described by Terracciano, Nov. Atti d. R. Instif. Napoli, 1895, Vol. VIII, No. 7. Rannnciiliis Biilbosus Scuiiplcmis. 245 other hand on plants growing as they often do in sandy locaHties, the flowers often possess a slightly increased number of petals. In these abnormal flowers there are usually six or, rarely, seven petals, very seldom more than 10-12. They are as a rule ordinary petals, but there sometimes occur some that are much smaller and narrower and are ob- viously metamorphosed stamens. This metamorphosis is often only partial, and the famil- iar intermediate stages are exhib- ited. The abortive stamens are usually to be found among the most peripheral ones ; but they are not necessarily the outermost ones, di- rectly adjoining the corolla.-^ The potentiality of this doubling is therefore present in a semi-latent condition in the wild plants of this species growing in this neighbor- hood. I regard this race, therefore, as a half race in contradistinction to the normal double race which is only known to me from the pub- lished records. Obviously the two possess the same character; which Fig. 50. Ranunculus bul- bosus scniiplcnus. A flower with 31 petals (partly petalodic sta- mens) ; the only one amongst 4425 flowers. It occurred on a qua- ternary branch in my culture of October, 1892. See the series of figures on page 252. is, however, active in the one case but latent or semi-latent in the other. It seemed to me important to discover whether it was possible to obtain the double from the half race by selec- tion. According to the views advanced in this work this should be possible, but not every attempt need neces- sarily be successful. But if it does succeed the change ^See GoEBEL, Jalirb. f. wiss. Bot., Vol. XVII, pp. 217-219. 246 Non-Isolahlc Races. must be brought about suddenly, and, under ordinary conditions of culture, be effected in the course of a few years. In this way the double variety may have arisen from time to time in the wild state; and in the same manner the present half race may perhaps, in the course of time, undergo this change. This transformation, how^ever, cannot be simply the result of careful selection. A mutation is needed; and we know as little about the causes of mutations as about the method of inducing them artiiicially. Mutations are known to occur wn'th moderate frequency both in breed- ing experiments and in nature, but, up to the present, their occurrence has been a matter of chance (§§10 and 11, pp. 95-103). In my experiment such a mutation did not occur, although it extended over five generations.^ The half race was distinctly improved by repeated and very strin- gent selection. It became at the end very rich in extreme or almost extreme variants, but it was just in these that it proved to be so remarkably constant. In its five gen- erations it reached a point which did not seem to me likely to be exceeded by further selection. It produced occasional flowers with more than 15 petals, and a single one with 31, but the mean number of the petals in its selected individuals did not exceed 9-10. The double variety did not arise from it, in spite of everv effort. * The fluctuating variability of the semi-latent character m Ranun- culus hulbosus sonif^lenus seems to cover a much wider range of forms than in Trifolium. Tlicre the extremes are 3 and 7 leaflets ; in the buttercup they are 5 and 31 and perhaps more petals. From this it does not. however, follow that the variation is greater in the one case than in the other, but only that the variation is expressed by a larger number of divisions in the latter case, i. e., that there are more scale characters in the curve. RaniiHculiis Bulbosiis Sciiiiplcnus. 247 I conclude, therefore, that in this case the half race cannot be transformed into the double race by simple selection, but only by an internal change — a mutation — the external causes of which are still unknown to us. Proceeding now to the detailed description of my experiment, I begin with the half race in the conditions in which I originally found it in nature. I found the half race growing in 1886 and 1887 in a sunny and sandy spot not far from Hilversum, where I have often seen it since. The bulbous buttercup grew there in abundance ; most of the flowers were normal, but a considerable number had more than five petals. I shall refer to these latter for convenience of expression as pleiopetalous. For several years I have recorded the flowers in that iocality. I give the records of 1886 and 1887, each of which relate to 300-400 flowers. The data are given as percentages. Number of petals 5 6 7 8 9 10 11 12 13 14 Flowers in 1886 91.5 5.5 1.2 0.6 0.6 0 0 0.3 0 0.3 Flowers in 1887 90 7 2 0 0.5 0 0.5 0 0 0 The two series^ agree as closely as could be expected and the records for the other years also fall in line. The maximum of the curve (see Fig. 51 H) is over the normal number of petals ; and from it the curve falls rapidly. It is a so-called half GALTON-curve. Flowers with less than five petals do not occur in this locality. The great steepness of this curve is due to the fact that on many of the plants no pleiopetalous flowers were found on the days when the observations were made. But this does not mean that the lialf race is mixed with ^ Uehcr halhe GaUon-Curven ah Zeichcn discontinuirJichcr J^an'a- fioii. Ber. d. d. bot. Gescllschaft, Vol. XI T, 1894. p. 197. where some of the scries of figures ofivcn below can also be found. 248 Non-Isolablc Races. a pure race with five petals only. For the plants in ques- tion were either weaklings, or exhibited pleiopetalous llowers on other days. I was often able to observe that on many plants six-petalled flowers occur on one day but not on another. The 6-7-petalled flowers are found from the beginning of the flowering period, but the higher figures do not occur till later, as is also known to be the case in other instances of double flowers. In 1887 I moved some plants in which the abnormal- itv was well developed, to my garden, v^diere they flowered again in the following summer and set seed. These plants constitute the first generation of my experiment. Since then I have sown seed every year, but only part of the plants, sometimes one-half, sometimes two-thirds, pro- duced flowering stems in the first year, and I have always confined my attention to these, throwing away those which did not bloom during the summer. I have some- times kept some of the best examples of the half race through the winter for secondary experiments, but I shall return to these later on. During the period 1889-1892 the second to the fifth generation of the half race were grown in this manner, the extent of the cultures being gradually increased. I always harvested my seed from the most abnormal in- dividuals, which I selected by simply cutting off the flowers with five petals from all the plants. The numbers of these on the individual plants were recorded in some years but not in others. Pollination was left to the bees, but no definite effects of cross-fertilization have been traceable in the results of the experiments. The first two years of the experiment (1889 and 1890) need only a brief reference. Plants without pleio- petalous flowers or with only very few, were removed Ranunculus Bulbosus Scniiplcnus. 249 as soon as possible, or were deprived of their flowers: of the rest, only the seeds of flowers with six and more ])etals were saved. But this process is not one of selec- tion, as will be shown by means of some special experi- ments which were instituted later. The result of selection could be seen in 1891 in the best examples of the half race, but in 1892 (the fiftli generation of the culture) in nearly all the plants. The number of petals increased in every respect. The apex H 1887. Fig. 51. Ranimcuhis bulbosus semiplenus. Experiments in selection during the period 1887-1802. H 1887, curve of the wild form; E 1891, curve of the abnormal plants in 1891 ; A 1891, curve of the selected seed-parents in 1891. 1892, curve of the whole crop in August 1892. The num- bers at the base refer to the number of petals per flower. of the curve shifted to 9 and 10 petals and even further; that is to say, the mean of the half race (9-10 petals) was separated by selection from that of the pure s])ecies (5 petals), a point which is rather striking because this was not effected in my experiment with Trifoliuni in- carnatum. The course of the whole experiment is ex- hil)ite(l graphically in Fig. 51 which is composed of four curves. The first (H 1887) exhibits the countings given 250 Non-I salable Races. above, which were made in the original locahty. Then there are two curves for 1891. In this year I had a ciikure of about four square meters from which I re- moved, about the beginning of August all plants which had not produced any pleiopetalous flowers as well as those which had not yet bloomed. For two weeks I counted every flower which appeared on the remaining specimens. They amounted to 128 and the various de- grees of the anomaly were distributed over them as follows : Number of petals 5 6 7 8 9 10 11 12 13 Number of flowers 45 24 28 17 8 4 0 1 1 The curve E 1891 in Fig. 51 is based on these figures. It is a half curve like the previous one, but without the steep apex. The disappearance of this is due partly to cultivation and to the repeated selection, but partly also to the fact that the individuals with the smallest numljer of pleiopetalous flowers had been removed before the counting took place. After these data had been determined I carried out a still further selection. Several plants had not produced a single flower with more than seven petals. These were removed in the middle of August and observations on the rest were continued. There were 18 plants, all of which were selected for seed-parents as being the best representatives of the race. I counted all the flowers which bloomed from August 15 to 31, and obtained the following numbers '} Number of petals 5 6 7 8 9 10 11 12 13 14 Number of flowers 9 17 39 64 45 37 15 9 6 2 * In the preliminary account of this experiment, mentioned above, this series is given separately in two curves, one of which refers to the most abnormal plant, the other to the rest. Raminciiliis Bulbosus Sciiiiplcinis. 251 Total 243. The curve (Fig. 51, A 1891) has he- come two-sided. It has no maximum at 5 hut a very definitely pronounced one at 8. It is composed of oh- servations made on 18 plants which differ little from one another. Individuals with these characters occurred neither in the original locality nor at the beginning of my experiment. The sowing, in 1892, of the seeds of these selected individuals gave rise to above 300 plants which were coming into flower from July 21 to August 31. The curve for 1892 in Fig. 51 refers to these. Those which flow^ered later were examined separately and will be de- scribed afterwards. On all the flowers which opened l)etween the dates named the petals were counted, and the numbers entered in my notebook separately for each plant. I give the totals, which relate to 4425 flowers. The numbers of petals were distributed over these as follows : Petals 5 6 7 8 9 10 11 12 13 14 15 16-31 Flowers 409 532 638 690 764 599 414 212 80 29 18 20 The curve which is now an index of the degree of de- velopment of the whole race, agrees fairly closely with that of the selected seed-parents of the previous year (1891), as can be seen from a comparison of the curves A 1891 and 1892 in Fig. 51. The apex of the curve, however, has advanced a whole petal. There has been no regression as is the case in the selection of active char- acters, but a progression such as is usually characteristic of the selection of semi-latent characters. The change in the right half of the curve is also im- portant although not given in Fig. 51. It consists in the occurrence of more extreme variants. In the previous 252 Non-Isolablc Races. generation there were no flowers with more than 14 petals. Now there are 38, distributed as follows : Petals 15 16 17 18 19 20 21 22 23 31 Number of flowers 18 8 5 2 1 1 1 0 1 1 It should be noted, however, that they were found amongst a group of 4425, and therefore only amount to about 1% (0.86%). But as not a single one w^as found in 1891 amongst 243 flowers, a genuine, although only a slight, advance has taken place. The great majority of the 295 plants which were flowering in August and formed the 1892 culture, had 5 6 7 8 9 10 II 12 13 14 15 Fg. 52. Ranunculus hulhosus semiplenus. Composition of the fifth generation in 1892. A, the curve of some "ata- vists" ; M, the curve of intermediate individuals ; V, the group of extreme variants. The figures refer to the number of petals per flower. individual curves whose maximum was at 9. But amongst their number were variants and extreme variants also. On the one hand there were *'atavists" with a maximum on the ordinate of five petals, i. e,, with a one-sided curve, as in those from the original locality ; on the other hand there were variants on the plus side which bore on the average eleven petals per flow^er. In one case even a mean of 13 petals was reached. These curves were two-sided, and not, as in the five-leaved race of the red clover, in- Ranunculus Bulbosus Seuiiplenus. 253 versely one-sided. But we are dealing here merely with a cumulative effect within a half race and not with an isolated, fully developed race. I have chosen a number of variants from the two categories, have added up the number of their petals, and obtained the following data : Petals: 5 6 7 8 9 10 11 12 13 14 15 16 17 18 23 Number of flowers y^.- 66 34 21 18 15 11 7 2 0 0 10 0 0 0 " M: 13 14 22 28 51 26 16 12 6 4 2 1 0 1 0 V: 9 11 26 39 62 79 148 84 30 8 4 3 2 1 1 These data are exhibited graphically in Fig. 52. They relate to three small groups of individuals, chosen in such a way that the curves of the individual plants did not exhibit any considerable deviations from the mean of the group. A is the curve of the twelve atavists extracted from the whole series of observations; the maxima of all their curves were at 5 petals. M is a curve represent- ing ten plants grown from the seeds of a single seed- parent. V is the curve composed of all the plants the apex of whose individual curves lay above 10. There were 22 of them altogether; the apices of their curves were at 11, with three exceptions which were at 12 and 13, l)ut tliese curves did not exercise anv marked effect on tlie shape of the average curve of the whole group. If Fig. 51 and Fig. 52 are compared a most remark- able similarity will be observed. The latter figure gives tlie composition of my race at the end of a process of selection extending over five generations, the former re- lates to the separate stages in this process. This mutual resemblance lies in the fact that the original half curve (Fig. 51, H 1887) continues to appear throughout the process, although it is a little flattened; it occurs in 18Q1 (Fig. 51, E 1891) and also in 1892 (Fig. 52 A). Ata- vistic fluctuation therefore is still exhibited l)v mv race 254 Non-Isolablc Races. in spite of the repeated selection.^ The curve ]\1 has a more normal shape than the corresponding curve "1892'' in h'ig. 51 ; which is ohviously due to the fact that the former represents a homogeneous group whilst the latter is a composite curve embracing all the groups of tliis culture. Curve V is related to curve M as it would be if we were dealing with ordinary fluctuating variability ; it is simply shifted to one side.^ It seems obvious that the race could still be improved by sowing the seeds of those seed-parents the apices of whose curves are at 11, i. e., that these curves could be shifted still further to the right. I have made some such sowings since 1892, but only on a small scale and not without interruption. They w^ere not intended as a con- tinuation of the experiment. The number of petals per flower increased slightly, but the type itself Avas not es- sentially altered. I especially never saw a trace of any- thing like the origin of a double flower. In order to find out wdiether there was any likelihood that the type of my race would in the near future mani- fest an improvement I made the following calculation. ' The 295 plants of wdiich the culture of 1892 consisted, arose from the seeds of 21 seed-parents. I selected tlie ten best of these parental groups and plotted the curves for all the ofl^spring of each seed-parent. The curves proved to differ very little from one another. Tlieir apices all fell over nine petals, with one exception, wliicli was over ten. I should say that in making the calcula- tion I have left the groups which contained less than 300 ^ Whereas as a result of the selection of active characters the whole curve is shifted; see Vol. T. p. 73, Fig. 18, and the third part of the first volume. ^ .Sec Yn]. T. Fie:. tt6. on page 536. Ranunculus Bulbosus Scmiplcnus. 255 flowers out of consideration. But even these did not manifest any notable differences. I then compared these ten curves with the part-curves determined from the parents themselves (i e., with the number of flowers counted on the seed-parents) and found no correlation. As a matter of fact the seed-parent with the smallest number of pleiopetalous flowers had the offspring with the largest number. The following four curves of the offspring of four seed-parents are extracted from my records. Under M are given the numbers of petals in the seed-parents of 1891. M NUMBER OF PETALS PER FLOWER — 5 6 7 8 9 10 11 12 13 14 15 16 17 18-23 Totals C 5—10 37 47 81 81 85 102 47 31 6 3 4 10 0 525 C 6—10 25 67 80 75 117 77 75 45 30 10 6 1 2 3 613 C 6—11 54 53 62 78 87 60 59 37 10 4 4 1 1 1 511 C 7—11 52 57 76 77 95 64 26 13 0 0 0 0 0 0 460 Another fact which points in the same direction is that the plant which seemed to be far the best in the summer of 1891, inasmuch as the apex of its curve was over 11-12 petals, had offspring whose character cor- responded exactly with that of the whole culture of 1892. The improvement on the seed-parent therefore did not justify the expectation of a real advance. For these reasons I then discontinued the experiment. It seemed to me that the iinpossihUity of raising the double race from my half race by simple selection z^'as placed beyond all doubt. This result could only be ex- pected from a further mutation. The extensi\-e material afforded by these cultures has been utilized to find out how far the number of petals per flower in tlie half race is determined, apart fn^m selection, bv internal causes, and how far bv external. 256 Non-Isolahlc Races. I found it to be dependent only to a very slight degree on the former but in a high degree on the latter. The first question that presented itself was: To what principles of distribution does the number of petals on the individual plants correspond. Is this number de- termined by the situation of the flower or by external factors or by both? With regard to the position of the flower Braun in his Verjunguiig distinguishes between a strengthening and a weakening system of branching. In the former the branches increase in strength, though often but slightly, with each new degree of division; in the latter each secondary branch is weaker than the branch on which it is borne. Ranuncithis bulbosus be- longs to the former category (see Fig. 49 on page 244). The main stem (E) is surpassed by the vigorous lateral shoots (S), which arise directly from the tuber, and these in their turn are excelled by their own (tertiary) branches (T in the figure). The same thing continues with further growth until ultimately the process is re- versed and weaker branchlets are produced. The more vigorous a branch is, the larger and stronger, as a rule, will be its flower. If we now compare the number of petals on the flowers of this half race, with their position on the branches of the various orders, we are often struck by an apparently definite correlation. But this is only due to the fact that such cases produce a more vivid impression than the opposite ones. When a detailed record is made the latter are found to be just as numerous as the former. In September 1892 I determined the number of petals, and the position on the plant, of 1197 flowers on 82 plants ; and plotted a curve for each position. Here how- ever I only give the means of the curves. Ranunculus Bulbosus Scmiplenus. 257 A. B. NUMBER OF FLOWERS PETALS PER FLC On the ma-n stem: 1. Terminal flower 75 697 9.3 2. Secondary flowers 221 2005 9.1 3. Tertiary 134 1237 9.3 From the tuber: 4. Secondary flowers 259 2419 9.3 5. Tertiary 397 3716 9.4 6. Quaternary " 111 1014 9.1 1197 11088 9.3 It is evident that the number of petals in the various groups is practically the same.-^ Even the seeds of pleiopetalous flov^ers are by no means better. In gathering the harvest of 1891 I col- lected the seed on each plant in a separate bag with ref- erence to the number of petals of the flowers. The flow- ers were labelled for this purpose at the time of flowering. In the culture of 1892, therefore, the plants were arranged in groups, first according to their seed-parents, and sec- ondly according to the petal-number of the flowers from which the seed had been gathered. I then grouped all of the figures by the latter character and obtained the fol- lowing result : NUMBER OF PETALS IN THE FLOWERS WHICH FURNISHED THE SEED C5-7 C 8 C 9 C 10-11 C 12-14 ' In the weakening sj'^stem of 1)ranching on the other hand the contrary seems to be the rule; so for instance in my cultures of Sa/^o- naria officinalis with 5-10 petals, in Chrysantlicmum scgctnm ( § 18) etc. 'The mean is slightly lower here than in the previous table be- cause that only refers to countings made in September. (See later.) MEAN NUMBER NUMBER OF PETALS OF FLOWERS OF THE OFFSPRING^ COUNTED 8.3 932 8.7 1072 8.5 1217 8.6 1420 8.7 919 Average 8.6 Total 5560 25S X 0)1-1 salable Races. Here again there is no discernible correlation. I have obtained the same result in other years. From this we see that in this case at least selection must not be founded on the different llowers of a plant but on the individual plants. However, the possible influence of the various grades of branching independently of the number of petals remains to be investigated. But whereas no internal causes were found which determined the pleiopetaly in the individual flowers, the external causes could be discovered the more readily. This character follows the general rule; for the higlier the nutrition and the more favorable the environment the more petals are produced per flower. The following experiments and ol)servations will prove this. I shall first refer to an observation for which un- fortunately I can give no numerical corroboration, but which may throw some light on the independence of the character of the flowers, of the order of branching. In the summer of 1892 when I examined all the flowers of my culture, and recorded the number of their petals twice a week, I was struck by the fact that the high numbers fell on particular days whilst on other days only low or intermediate numbers were observed. This would seem to indicate that during the development of the flowers in May and June pleiopetaly is influenced by weather conditions, in such a way that flowers which are in the susceptible period of their development during fine weather wn'll produce more petals, quite independently of the order of the branch which bears them. This conclusion is supported by another set of obser- vations. In September 1892 the flowers, on the wliole, produced more petals than they did in August of tlie same vear. Or. to be more accurate, the number was sfreater Raniuiculiis Buibusiis Sciiiiplciiiis. 259 on those plants which opened their first flower in Se])- teniber, than on those which had already begun to flower in July and August. The number of individuals of the former group was 77; they produced 1134 flowers du- ring the period ending with the beginning of November, •when I stopped recording. In the other grou]) there were 295 plants which flowered, and they produced 4425 flow- ers. The distribution was as follows:^ Petals: S 6 7 8 9 10 11 12 13 14 15 16-31 Oldest plants. 409 532 638 690 764 599 414 212 80 29 18 20 September plants: 40 52 126 165 204 215 177 104 35 8 4 0 Fig. 53. Raiiiuiculiis bulbosus semiplcnus. A, curve of the plants Howering in August; S, curve of those flowering in September. The ligures at the base refer to the num- ber of petals per flower. These figures are exhibited graphically in Fig. ^Z ; they have been reduced for convenience of comparison so that the numbers in the two groups are about the same. The apex of the curve of the early flowering plants is over the 9; it is the same curve which has already been given in Fig. 51 on page 249 for the year 1(S92. The other curve has its apex over the 10, and also remains above the other curve in the right half of its course. The cause of this difference can only lie in the re- tarded germination. Fither the seeds which germinate later are intrinsically more productive of pleiopetalous ^ See above, p. 2"'? yi?n Fig. :;? ^892). 260 Non-Isolablc Races. flowers^ (like the small, late-germinating seeds of the crimson clover), or germination in the height of the summer in better and particularly in warmer weather favors development in such a way that the flowers are richer in petals ; for the plants which flowered in July and August, germinated for the largest part during the cold and unfavorable weather experienced in May shortly after they had been sown. I first made an experiment to determine the influence of nutrition on pleiopetaly in 1890. I had wintered the selected plants of 1889, and in ]\Iarch transplanted half of them on a bed of pure sand, and the other half on a bed of ordinary garden soil. Only two-thirds (i. e., 12) of the plants of the former lot flowered, whilst all of the latter did. On the sandy bed I counted the petals of all the flowers and about twice their number on the control bed by simply picking off all the open flowers on alternate days. I examined in all 75 and 147 flowers respectively. The following is the result reckoned in percentages for convenience of comparison : Number of petals: 5 6 7 8 9 10 On the bed of sand* 73 23 4 0 0 0 On garden soil: 53 26 14 5 1 1 The plants on the better soil produce distinctly fewer five-petalled and more 7-10 petalled flowers. It is per- haps permissible to conclude from this that the steep drop of the curve from the wild locality, where the soil was sandy is, to a large extent at any rate, due to low nutri- tion. For presumably the same plants would exhibit a higher degree of pleiopetaly if grown on better soil and * With regard to this, it would be of great interest to find out in this and other plants the degree of development of the anomaly in such individuals which do not germinate until two or three years after the sowing of the seed Ranunculus Bulbosus Scuiiplcnus. 261 so give rise to a less steep curve, just as in the experiment under consideration. I made a corresponding experiment in the summer of 1891, on the effect of manured and unmanured garden soil, with the race w^hich was by that time consideraljly improved (Fig. 51 and page 250). The manuring was done with guano ; the two beds lay next to one another and were of the same size. On each was sown half of the harvest of several plants which had been very i)ro- ductive of pleiopetalous flowers in 1890. In the course of the summer 159 flowers on the unmanured bed opened and were recorded and 376 on the manured. The rela- tion between these two numbers is the best measure of the effect of the manure. The results, reckoned in percent- sl^-o, cii V- cxj iv/iiv^vv o . Petals: 5 6 7 8 9 10 11 12 13 14 Without manure: 12 15 25 21 12 10 3 1 1 0 With guano: 14 15 17 21 14 9 4 3 2 1 Without manure the apex of the curve Avas over the 7 and there were very few flowers with more than eleven petals : with manure the apex was over the 8, and there were distinctly more pleiopetalous flowers. In both the above experiments the control material consisted of other individuals than those used for the experiment itself. It is possible, however, to subject the same plant alternately to favorable and unfavorable in- fluences, and when this is done the same result is ob- tained as in the previous cases. With this object I trans- planted a series of the best plants of 1892 to a very drv bed in the spring of 1893. I left them there, and did not water them although the weather was continuallv dry. They suffered visibly under this treatment and some of them even produced fewer flowers than in the PLANTS NUMBER OF FLOWERS 1892 1893 No. 1 25 14 No. 2 43 19 No. 3 9 14 No. 4 44 5 No. 5 12 18 No. 6 16 21 .OWER DIFFERENCES 1893 9 2 5 4 6 4 5 3 8 2 8 1 262 Noii-Isolablc Races. previous summer. T have a record, which has been al- ready alluded to, of the number of petals of all the flowers of each of the plants of 1892 ; these were recorded in the same way in 1893. But I only give here the mean numbers of petals per flower. MEAN NUMBER OF PETALS PER 1892 11 9 10 8 10 9 The anomaly was thus diminished on every single ])lant as the result of transplanting to dry earth. The results of all these experiments prove that the production of more than five petals in a flower is inde- pendent of the position of this flower on the plant, but on the other hand is dependent in a high degree on the external conditions under which the particular flower passes its early stages, i. e., the most susceptible period of its existence. The number of petals varies directly with the vigor of the ])lant, the moisture and richness of the soil, the warmness of the weather and even the amount of sunshine during this suscepti1)le period. Cultivation in the garden is therefore bound to con- vert the steep half curve of the wild locality (Fig. 51 for 1887) into a flatter one which will gradually extend to higher numbers of petals and will ultimately develop a new apex. This process, however, takes place more conveniently and more certainly, if the cultivation is combined with selection (see the same figure). The latter process picks Ranunculus Bulbosus Scniipicnus. 203 out the plants which iiiaiiifcst the anuiualy most abun- dantly and most strongly ; these must, however, according to the facts given, as a rule, ])e the l)est nourished ones, i. e., the most faxored In' their en\ironment. For on the same l)ed, even if it has been uniformly prepared with the greatest care, the conditions under which neighboring plants grow are often very different. One seed may germinate in a place in wdiich moisture is better retained ; another may germinate in almost dry soil. Some germi- nate on warm and tine days and are in consecjuence ahead of their less favored brothers for their whole li\-es; and so on.^ And so it is that the several plants from seeds of the same seed-parent sown on the same day and on the same bed, are necessarily exposed to diverse condi- tions of life. Amongst them selection picks out the best and therefore, at least as a general rule, the most highly nourished ones. Selection, so to speak, only precipitates the operation of these external factors ; as we have pointed out before in connection wkh Papavcr soninifciinn poly- ccphalunir Selection and cultivation have, therefore, worked in the same direction in my experiment for four genera- tions. They have about doubled the mean number of l)etals per flower, having brought it, in fact, to 9-10; they have produced, amongst several hundred plants and several thousand flowers, no more than three flow^ers with more than twenty petals (C 21. C 23 and C 31), i. e., not essentially more than w^ould be expected according to Ouetelet'.s law^ from the actual mean and the am])litude of variation. These flow^ers occurred perfectly fortui- touslv on plants which were not particularly favored oth- erwise, the means of the curves being only 10 for each ' See Vol. T, p. 138. ' See Vol. T. p. 140. 264 Non-I salable Races. of the three plants. We are thus justified in concKuhng that hy the selection of these plants as seed-parents the mean of the race might further be slightly improved during the course of some years, but that these extreme variants afforded no more hope than did the others, of the attainment of the double race. Cultivation and selection cooperate in the direction of the desired end; they lead the half race measurably fur- ther on this line, but it is not through them that the object can be attained. The half race remains a half race, in spite of every effort and care, the semi-latent character expresses itself oftener and oftener, but it does not succeed in becoming the equal of the normal active characters, i. e., in constituting the mean character of a new race, independent of the continuance of selection and favorable cultural conditions. To arrive at this result a process of an entirely differ- ent nature is evidently required. According to the cur- rent theory of selection the goal would be reached if the experiment could be continued for tens or hundreds of years. But the course of the experiment we have de- scribed does not support this view ; it shows, on the con- trary, that all that can ever be gained by nutrition and selection has already been secured in these five genera- tions. The actual result is the production of an elite race which has a mean number of 9 petals in the flowers, under the favorable conditions of culture which obtained ; and gives rise, according to environmental conditions, on the one hand, to better variants (with a mean of about 11-13, or perhaps a few more, petals) while, on the other, it throw^s off atavists with a half Galton curve (see Fig. 52 on page 252). It is my opinion, however, that if the culture of the Variegated Leaves. 265 half race were stil! continued, the double race would some day appear quite suddenly, and that it would then, after a short but sufficient isolation, persist as a constant, though highly variable, race.^ § 24. VARIEGATED LEAVES. Variegated plants have long been great favorites in the garden, and their great instability has contributed largely to the development of the horticultural concep- tion of a variety, for the variations in their col(.)r pattern are practically unlimited. Hardly any two leaves are alike, and many species have a whole series of dappled and flecked varieties. They also possess the striking property of continually and conspicuously reverting to the species to which they belong. Such reversions occur either amongst seedlings or as bud-variations, and since on shrubs and trees these latter often remain for many years and not rarely in more than one instance on the same plant, they can be seen by every one. In this way these bud-variations have come to be regarded as a suf- ficient proof of the idea that varieties are derivative and unstable structures, which always tend to revert to their parent species. Especially in the first half of the eighteenth century were plants with speckled and striped leaves very much sought after.^ About that time the well-known English gardener Thomas Fairchild possessed more than one hundred varieties of them in his garden, and afterwards ScHLECiiTENDAHL published a list from which it can be seen that variegation is distributed over the whole ^T. e., as an eversporting variety with a wide amplitude of varia- tion which however would not alter in the course of the generations. 'Meyen, PHanzen-Patholog'ic , 1841, p 282. 266 Non-Isohihlc Races. vegetable kingdom and occurs in all the larger groups and especially in most families of flowering plants.^ At that time some of the most widely cultivated forms were the ribbon grass, Phragmitcs anindinacca z'aricgata, and the variegated holly. Ilex Aquifoliwn. Both are still much grown in gardens, the ribbon grass being rela- tively uniform, the holly highly variable. Of the latter there is a variety with white-edged leaves, besides the ordinary one with flecked leaves. Phraginites is differ- ent in many respects from genuine variegated plants and is much less variable in its character. The Ilex, however, is highly variable and often bears green shoots which may soon supersede the others on account of the greater facility with which they can obtain nourishment. A fine variegated bush of this species, or of any other, may be- come entirely green, whenever the green branches are not cut away every year. Thus it is probable that many specimens of the holly, which are now quite green, were originally variegated and were bought and planted as such. On closer examination we often find on them an occasional variegated twig which proves the correctness of this supposition. This is also the case with the horse chestnut, of wdiich many older trees still living were planted at a time when the variegated variety was in special favor. Since then their foliage has become green and their original character is no longer seen. But an occasional checkered branch, or even the numerous small twigs with white leaves along the main stem, betrays the original variegated condition of the specimen. In the same way many cases of single variegated twigs on green bushes and trees are not to be regarded as the indi- * ScHLECHTENDAHL, Luinaea, 1830, V, p. 494. Very little seems to be known about variegated mosses and thallophytes. Variegated Leaves. 267 cation of something new but as a reminiscence of times long past when these varieties were in general favor. Variegation is classified under several headings. In the first place there are the yellow and the white varieties. In the former the chlorophyll is only insufficiently pro- duced, but in the latter even the xanthophyll or carotin is lacking;^ and a more or less abortive development of the chloroplasts is usually correlated with the absence of these pigments.^ Further we distinguish marginate, flecked and striped sorts. The former seem to constitute a variety for them- selves and are much rarer than the latter ; they appear to be good races, that is, to be as constant as any ordinary garden, variety, but I shall have little to say about them in this part. The most characteristic and best known example of them is the white bordered holly to which we have already referred."^ Whether a plant is flecked or striped depends as a rule on the mode of venation of the leaves. Many varie- gated monocotyledons have striped leaves {Agave, Con- vallaria luajalis, Phoriniiun tenax, Tradescantia re pens, etc.) whereas the dicotyledons are usually flecked or streaked. The incomplete development of the chloroph}ll ob- ^ See T. Tammes, Ueber Carotin, Flora, 1900. ^For further information on this point see the elaborate ana- tomical studies of A. Zimmermann, Ucber die ChromatopJwrcn in panacJiirtcn BlUttcrn, in Beitrage zur Morphologie und Physiologie der Pflanzenzelle, Heft II, 1891, pp. 81-111, and Ber. d. d. hot. Ges. VIII, 1890, p. 95. Also H. TiMPE, Beitrage cur Kcnntniss dcr Panachining, Inaug.-Diss., Gottingen, 1900. * Marginate forms are commonly supposed by gardeners to be more stable than flecked ones. This fact was noted by Morren in 1865. (Hercditc de la panachure, Bull. Acad. roy. Belg., T. XTX. 2d series, p. 225). Verlot however maintains the opposite opinion (Dcs J\vtc- tes, 1865, p. 74). For information relating to variegated varieties of Ilex see Focke, Abh. d. Naturw. Ver. zu Bremen, Vol. V, pp. 401-404- 268 Noii-lsolablc Races. viouslv results in an insufficient assimilation of carljonic acid gas. Thus the variegated parts grow less vigor- ously and are less resistant than the corresponding green ones. The Cy perns altcrnifolius of our greenhouses, the Aspidistra elafior and a number of other favorite varie- ties show this clearly. Arundo donax often attains a height of three or more meters whereas its striped vari- ety is scarcely half that height. Leaves of the variegated Aspidistra very often have one of their longitudinal halves green, but the other colorless. In such cases the leaf is distorted owing to the insufficient growth of the colorless half. The same thing happens in many other cases. The yellow leaves and parts of leaves, however, are not entirely without the green coloring matter, nor wholly without the power of assimilation. Most of them give a green extract when put into alcohol, and if examined under the microscope patches of green tissue can be found here and there, especially near the veins. The power to sustain life, however, is often lacking and the leaves die shortly after their growth is completed. Therefore, a high degree of the anomaly is not in favor, because the plants which possess it often become disfigured by the edges of their leaves turning brown. Many plants in which the variegation has gone too far die in their very early stages, while others have not sufficient strength to flower and bear seed. This latter circumstance is of special interest because it follows that plants with a high degree of variegation as a rule can have no part in the propagation of the variety.-^ In the opinion of some ^ It is perhaps scarcely necessary to state that these remarks do not apply to brown and purple leaves or those with red spots. For information on this point see Stahl's excellent article Uebcr bunte Laubhldtter, Ann. Jard. Bot. Buitenzorj^., Vol. XTII, Ft. 2, 1896, p. 137. Variegated Leaves. 269 authors another fact is connected with this, viz., that varieties which have both variegated leaves and d(juble flowers are much rarer than would have been expected from the prevalence of these two anomalies in horti- culture.^ In variegated plants, as is well known, not only the leaves are flecked. Their stems and calices are also often variegated, and the same is true of the fruits (pears, grapes, the siliquae of cabbage, Barharea vulgaris, CJiei- ranthus Cheiri, Alyssnm maritimtim, Acer, Ilex, Aego- podiiun, Ligusticum, etc. ).^ I have also sometimes found galls on variegated oaks to be variegated, especially in the case of the beautiful orbicular galls of Cynips Kollari. I shall now proceed to the important question of the inheritance of this abnormality or the degree of fixing as it is usually called. As already stated I shall exclude from consideration the white-flecked''^ and the marginate forms of variegation, and shall confine myself to the ordinary cases of yellow variegated leaves. I shall give the numerical proofs of my conclusions later, and shall now proceed to deal with the question whether variegated sorts are half races or intermediate races (see Chapter II of this part). In my opinion the great majority of the variegated garden varieties are intermediate races, as for instance Barharea vidgaris; whereas wild plants which occasion- ally present this character represent half races. Their * B. VerloTj Stir la production ef la fixation dcs varictcs dans Ics pJantes d'ornement, 1865, p. 75. Also Morren, Hcrcditc dc la pana- ihure, loc. cit., p. 226. ''Morren, loc. cit., p. 233. ' I have not myself made any observations on this phenomenon ( Albicatio, Albinismiis) and the published records of it arc very scanty. The fine white-variegated Humuhts japonicns varicgafus would be well worth experimenting with. 270 Non-Isolablc Races. multiformity and instal^ility corroborate this view. It is only the commonness of variegated sorts and the great interest which attaches to them which l)rings them to be regarded as analogous to the best constant varieties. Moreover this ^•iew is supported by tlie general opinion that a complete development of the yellow color would characterise the supposed constant variety, but that it would at the same time of necessity lead to the destruc- tion of the ])lants. In this conception variegation is re- garded as an incomplete anomaly whose complete con- dition would im'olve its own destruction : Imt this view is incorrect.-^ Complete yellow varieties are not only pos- sil)le and capa1)le of existence but actually well known in horticulture, although the numl)er of such forms is small. Instances can be found in seedsmen's catalogues; e. g., Sambucus nigra aiirca and Fraxmiis excelsior aiirea, also the aurea varieties of Chrysantheniuiu carinatuin, Mira- hilis Jalapa, Scabiosa atropurpnrea, Humiilus japoniciis (hifesceiis) etc. These plants, so far as I know, are all either yellowish-green or golden-yellow.- They also ap- pear to be very constant and never or very seldom to revert to the green type. I have made a number of ex- perimental sowings on a large scale of the seeds of the ordinary golden-yellow variety of Clirysanfheiiiiiui Par- theuiunv' (Matricaria exiuiia nana coiiipacta foliis aureis Horf.) and did not find amongst the many hundred ex- amples a single atavist : neither green nor variegated seed- lings occurred. But amongst other commercial seeds I have not found so great a degree of purity, the admixture ^ See § 3 of this part (pp. 18-26). "T have not grown all the above forms myself; and it should be noticed that the name aureus does not always relate to uniformly colored sorts, e. g., Agave stn'aia aurea. ^ViLMORiN, BJumeng'drtuerei, Vol. TT. p. 509. J\iricgafcil Lcaz'cs. 27\ of green plants, liowcver, not being larger tlian niigiit as a rule be expected from commercial seeds. For in- stance, StcUaria grauiinca aiirca gave only 28% and Myo- sofis alpcsfris com pacta foliis aiircis only 3% of green seedlings. But even in tliese cultures tbere were no variegated plants. Tlie fact tbat tbe anrca varieties give a green extract in alcohol and contain sufficient chlorophyll for their nutrition does not need special mention. Fig. 54. Thymus Scrpylluni. The ordinary Thyme; a phmt with a variegated branch H. The aurea varieties and the velU^w variegated sorts owe their character to the masking of the green pigmeni by the yellow which is developed in the former case all over the leaf, and in the latter only in certain tracts. The majority of variegated plants arc anal(^gous to those numerous half races which manifest their anomaly ( wliich may be doubling, pitcher formation, tlie production of 272 Noji-Isolable Races. qiiadn" foliate leaves, etc.) only in isolated organs and parts of organs. Some sorts I regard as analogous to the double varieties, whilst the aurca varieties are probably just as constant as the Varietatcs discoidcac and as the best elementary species. The very general occurrence of variegated plants points to the conclusion that the latent capacity for varie- gation is widely distributed throughout the vegetable kingdom. Moreover the fact that branches and whole plants with this character are met with every year in new species both in the garden and the field points in the same direction. In this connection I may mention the fact that forms with white variegated or wdiite- or yellow- edged leaves occur only rarely. I observed an instance of the latter in a wnld specimen of Oenothera Lainarck- iana (1887, see. Vol. I, p. 480) and of the former I found specimens in Spiraea Ulmaria, Calluna vulgaris, TrifoJium pratcnse, Lychnis diurna in 1886 and 1887 in the neighborhood of Hilversum. In the above mentioned years I found 3^ellow variegated plants of Planfac/o major, Phalaris arnndinacea, Rhinanfhns major, Erica Tetralix, Urtica nrens, Hypericum perforahini, Trifoliitni pra- tcnse, Hieracitini Pilosella, Rubiis frnticosns. Polygonum Convolvulus and Genm nrhanum. In 1869 I found a beautiful variegated specimen of Arnica montana in the Thuringian Forest and later one of Plantago lanceolata in Saxon Switzerland, and one of Thymus Serpyllum near Wyk aan Zee in Holland (Fig. 54), and I have since frequently found occasional variegated specimens of other wild species. In the same way they appeared in my own cultures where there can be no question ])ut that they have been preceded by many generations of purelv green ancestors; so for instance in Chrysanthe- Variegated Leaves. 273 mnm segetuiu, Antirrhimtm niajiis, Polygonum fago- pynini, Linaria I'ldgaris, Silene noctiflora etc. The large scale on which I have conducted my ex- periments with Oenothera Lamarckiana has enabled me to watch the origin of variegated forms in that species more closely. Here they appear almost every year from green ancestors, and in the most widely different experi- mental families and elementary species.^ Instances of it I found in the main Lamarckiana families, first in the original wild locality, then in 1889, 1890, 1892, 1895, 1898 and 1899 in my cultures, arising from series of seed-parents which were in every case green plants ; also in 0. ruhrinervis in 1891, 1893 and 1894; in 0. laevifolia in 1891, 1894 and 1899; in O. suhlincaris in 1896; in 0. lata in 1890 and 1899; in O. nancUa in 1890, 1896 and 1899; in O. scintillans in 1898 and so on; also from the crosses 0. lata X O. criiciata and O. Lamarck- iana X O. Lamarckiana criiciata and others. In 1899 only eight variegated plants arose in my whole cultures which consisted of over five thousand plants of Oeno- thera, that is, between 0.1 and 0.2%. But in the field the anomaly was evidently much rarer. One of the most striking phenomena presented by variegated plants is the so-called twig or bud-variation. From a bud a branch arises which is unlike the whole of the rest of the plant in the character of its variegation, and in this case both variegated plants bearing green twigs occur and conversely plants which have hitherto been green may bear stray variegated branches. In both cases a latent potentiality is manifested. The appearance of green branches on variegated plants is generally regarded as a case of atavism, that is ^ See also Vol. T, p. 480. 274 Non-Isolahlc Races. reversion to the parental form. It is especially common on woody species and in shrubs. Ei'onymus japonica, Oucrciis pcdiinctilata, Weigelia amahilis, Corniis sail- guinea and many others afford well-known examples. Others are found amongst perennials and perhaps best of all in Arabis alpiua. I may cite as further instances partly from the literature on the subject and partly from my own observations: Castanca vesca, Kevria japonica, Acsculns Hippocastanmn, Yucca pendida aiirea, Ulnnts cainpestris, Zca Mays, Rubus fruticosus and so on. Tlie green branches can obtain nutrition better than the variegated ones. Therefore they grow^ more vig- orously and become stronger during the course of years, and very often overgrow the others. As a rule all their leaves and branches are pure green, and they look as if they had entirely lost the capacity for varie- gation. But this is not the case, for sometimes we see single variegated twigs on these green branches. Arabis alpina is especially instructive in this connection, for it often gives rise to variations from its buds, and since it is easy to separate these and cultivate them further. Analogous cases of this double reversion, as it may be called, were observed bv me in 1893 in Castanca vcsca varlcgata and Kcrria japonica varicgata which bore a little variegated twig on a green branch; and the same has been observed in other cases. The deficient nutrition frequently makes the varie- gated leaves smaller than the green ones. If the pigment IS mainly absent in the margin of the leaves this becomes too small for the middle area and the whole leaf becomes crumpled. A unilateral checking of the growth leads to a corresponding bending. It is due to these circum- stances that the habitus of variegated plants is often so Variegated Leaves. 275 different from that of the typical form, Init as soon as reversion occurs through bufl-variation all these second- ary characters are dispersed at once, the green leaves be- coming dattened out, assuming the normal form, and often attaining twice the size of the variegated ones. In this way the reverted branch easily strikes the eye. I ob- served this most beautifully in Casfanea vesca and Uliiius caiiipestris, but Kerria japojiica and many other species show it as well. The question which btids are most likely to give rise to atavistic branches has been much discussed, and the general opinion seems to be that the rhizome and the adventitious buds on the roots are most prone to rever- sion. Thus Glechoina hederaceinn variegatum often pro- duces green rtmners^ whereas the variegated Tussilago Farfara breeds true from its runners. For the last ten years I have had a variegated plant of Riibiis fniticosns which has produced both green and variegated plants from its radical buds In proportions which vary according to conditions, and to the year. It seems to me probable that the weaker buds are most likely to give rise to ata- vists : but since this results in the production of green branches which grow much more vigorotisly than the neighboring variegated ones, it is not easy to decide this point.- Variegated branches on green plants are almost as common. It is the general idea amongst gardeners that the numerous variegated varieties of woody plants have, wn'th few exceptions, arisen in this way. One of these ^Verlot, he. cit., p. 78. ' Tn papers on this subject we often come across an expression of the opinion that it is the strongest branches which become green ; but this view, no doubt, is largely due to a misapprehension of the relation between the cause and its effect, as explained in the text. 276 A^oji-Isolablc Races. exceptions is lJ\vgcIia aiuabilis varicgata which was raised by Van Houtte^ from the seed of the green variety; another is the variegated grape raised by Knight.- In many cases a record of the original dis- covery has been preserved. Thus Wolff^ states that he found a variegated branch on a bush of Spiraea opuli- folia ; the leaves were whitish green with a sulphur yel- low margin, marked here and there with dark green flecks. The new form was easily multiplied by cuttings and appeared on the market as Spiraea opulifolia hetero- phylla foL aitr. marg. In nature bud-variations of this kind are also occa- sionally found, and it seems that this is almost the only bud-variation which is met with amongst wild plants, for usually this phenomenon is observed as a case of re- version on cultivated varieties or on hybrids. I myself have found very beautiful and large variegated twigs in Qiiercns pednncnlata, Betula alba and Fagus syhatica in the forests near Hilversum; in each case there was one large variegated branch on an otherwise green tree amongst hundreds or even thousands of perfectly green individuals. On the variegated branches the variegation often ap- pears unilaterally. The anomaly is developed laterally or unilaterally, or to use a more accurate expression, sectorially. For in the vertical projection of the branch there is usually only one sector which is variegated ; some- times one-half, sometimes one-third, and often even a smaller section of the circumference of the stem being affected.^ The sectorial variation behaves in the same ^Verlot, loc. cit., p. 74. *De Candolle, Physiologic, II, p. 73\. ^Garteniiora, Vol. XXXIX, 1890, p. 9- *A study of sectorial variation in relation to the divisions in the Variegated Leaves. 277 way in this case as in that of the striped flowers. The buds in the axils of the leaves on the variegated sectors usually produce variegated branches, but those of the green sectors green ones. Breeders take this fact into consideration in the choice of buds for use in the multi- plication of variegated forms, as we have already seen.^ It seems that the bud-variations, that is to say both the progressive (producing variegation) and the retrogres- sive or atavistic ones, are generally the result of a pre- ceding sectorial variation. But in most cases all traces of the latter are soon lost. In Quercus pediincidata I ob- served, as I have already mentioned, a variegated twig on a green bush. In this case the variegation extended on to the bark and the color of the branches of the pre- ceding years could thus still be recognized. The main branch proved to be unilaterally variegated and the varie- gated twig arose from this side. The branches at the other side were green (Hilversum 1886). When the leaves are arranged in two rows as in Castanca irsca, UUniis caiiipestris etc. the leaves on one side of the branch may be variegated and on the other, green. In such cases I found the lateral twigs on the older parts on the green side to be entirely green and those on the variegated side entirely variegated ; but I might repeat here that there is still a tendency in the green branches, even if only a slight one, to produce variegated leaves. The contrast between green and variegated is therefore not nearly so great as would appear at first sight. We have now to consider the question of the in- fluence of external conditions on the degree of variega- apical cells would be of great interest, especially in the Conifers and vascular Cryptogams (e. g., Junipcrus, Adianthuin, Selagiiiclla etc.). * See Salter's method, Vol. T, Part I. p. 147. 278 NoH-I soluble Races. tion.-^ On this point the hterature is rich in contradictory information. This contrachction is probably mainly due to the fact already mentioned that the green parts are so very much stronger than the variegated ones. This strikes the eye so forcibly that the idea easily arises that the strongest parts of the variegated plants are most liable to become green and the weakest branches of green plants most likely to become variegated. In my opinion, however, this conclusion is incorrect. The relative vigor is determined by the anomaly, but from this it by no means follows that the anomaly, in its turn, is determined by it. So far as my experience goes the reverse is the case, and variegation forms no exception to the general rule fur semi-latent characters, that favorable conditions increase the intensity of the anomaly. The best instance that I know is furnished by the variegated horse-radish (Cochlearia Aruioracca varie- gafa), which with unfavorable treatment is almost green, but under glass or in a cold frame may even become en- tirely white. Plants growing in the open in a sunny posi- tion are often beautifully variegated, wdiereas in shady positions they are a much darker green. The same is true according to Schlechtendahl of Plectogync I'arie- (/afa on the leaves of which a greater or lesser number of white stripes can be induced at will by merely trans- planting* it.- Fragaria indica variegata is a favorite plant for hanging-baskets. If one wishes it to be nicely variegated it must be planted in good dry soil, not too loamy or calcareous.'''' The same is true of the striped sorts of the ordinary strawberries, in which, as Ver- ' E. Laurent, Sur Voriginc des varictcs fanachecs. Bull. Soc. R. Bot. Belgiquc, Vol. XXXIX, 1900, pp. 6-9. ■ Bot. Zcitung, 1855, p. 558. ^\^tlmorin-Andrieux,, Flrurs dc plcinc tcrrc, p. 408. Varicyatcd Leaves. IIS) LOT^ says, "L(if panaclinvc pent s'obtcnir pour uiiisi dire a rolonte,'' by merely growing them in a dry position. A dry position is however at the same time as a rule a sunny one, whereas a damp one, as a rule, is shaded. Experiments which I have conducted with these and several other variegated sorts of various species, in order to determine the influence of daily and profuse watering in full sunlight on variegation, have been without any positive result. On the other hand I succeeded with Tradcscantia repens in controlling the proportion of yel- low and green stripes. In this experiment I cultivated the plants in pots and simply removed the pots to better or less well-lighted parts of the greenhouse without alter- ing the soil or the amount of water I gave them. The more intense the light the more variegated were the new leaves that were formed.- On variegated shrubs we often see that in the better lighted parts variegation is more intense and in the shader ones less pronounced. Even variegated conifers such as the Junipertis, may show this, and it is well known to be the case with Sarnhucns nigra. The variegation in myr- tles with striped leaves is also dependent on nutrition ;"' and various authors and gardeners hold that the soil and position exert a more or less important influence on the degree of variegation.^ Pclargoniinn f:onaIe, Conval- laria luajalts, Mentha aquafica, Phalaris arundinaeea. Phlox decussata and others are given as instances.'' Such ^ Verlot, loc. cit., p. 76. " For facts relating to the influence of galls on variegation in nupoforiuDi cannalnuum see Vol. I, p. 407. " Meyen, Pflanzen-Pathologic, p. 287. * As for instance Salter, quoted in Darwtn", J^ariations. TT. pp. 263-264. ^' Darwin^ he. cit., I, p. 390: TT. p. 263. 280 Non-Isolahle Races. plants are often entirely green during years of improper treatment, but with due care can be restored to the varie- gated condition.^ The degree of variegation is not only dependent upon the conditions of growth but also on the time of the year. If we look closely at variegated plants in green-houses we shall see that the branches which arise in summer are beautifully flecked, whereas those which arise in \vinter, w^hen they get less light, are much greener and sometimes even quite green. This at least is true in our climate ; but one must remember that the leaves formed in sum- mer remain on the shrubs through the winter, and undergo no further change in their variegation. There- fore it is not the general appearance which is dependent on the time of the year. Ouercus pednncidata argcnteo- picta is green in spring, but becomes white or variegated later on.^ Young plants are often still green in spring even .though later they may become variegated, as for instance, Symphytum, Barharea vulgaris, etc.*^ I have observed in a culture of Gciim nrhamim, which I have kept up during several years, that the variegated speci- mens gradually develop green leaves in the autumn and lose the variegated ones. In winter they were almost completely green, but as soon as life awoke in the spring they began to develop flecked leaves again, and through- out the whole summer they were fully variegated. They behaved in this way throughout every winter of their life. On the other hand a variety of the ornamental curly cale with yellow-veined leaves is beautifully varie- * Verlot, loc. cit., p. 75. 'L. Beissner, Knospcnvariation, IMittli. d. deutsch. Dendrolog. Gesellsch., No. 4, 1895. ' Verlot, loc. cit., p. yS. Variegated Leaves. 281 gated in late autumn and winter but becomes completely green in summer.-^ In all these observations there was no question of bud- \'ariation. Of the causes of this phenomenon little is known. On the other hand it is generally recognized that if resting buds on variegated plants are allowed to grow vigorously they often develop into completely white or yellow so-called chlorotic branches; — I mean those buds which on green sorts would develop into strong succu- lent shoots under similar inducements, but the chlorosis soon puts an end to this development. Adventitious buds which arise from the stem a little above the soil fre- quently give rise to chlorotic branches, either after the stems have been cut down or when the leaves have been eaten by snails, or from some other cause. Aescidus Hippocastanum is the best known example, so also are Evonyinus japoniciis, Pelargonium zonale, Azalea ja- ponica, Aiicuba japonica, Ilex Aquifoliuin ; also Spiraea callosa, Kerria japonica, Vinca major,^ Hydrangea lior- tensis,^ Fagiis sylvatica,'^ Uliniis caiupesfris/^ Cormis san- guiueaS' Saiiibuciis nigra,^ Myrtns communis tarantina,'^ Zea Mays etc. The inheritance of variegation through seeds is one of the most interesting phenomena presented by this ^ H. MoLTscH, Uchcr die Panachi'irc des Kohls. Ber. d. d. l)ot. Gesellsch., Vol. XIX, 1901, p. z^- ^ Verlot. loc. fit., p. 75. Here also will be found information relating to Glechoma hcderacea. ^ MoRREN, Hcrcdite, loc. cit., p. 230. Here also Pclargoniiivi iii- (juiiians. * According to Schleiden, after being damaged by snails, cited by Morren, loc. cit., p. 227. ^ Ulmus, Cornus and Samlniciis according to my own observa- tions. Moreover I have seen such branches on almost all the above named varieties. 'G. Arcangeli, Bull. Soc. Bat. Ifal., 1895, PP- 16-18. 282 Non-Isolahlc Races. wliole set of facts. The variegated sorts are nearly all more or less constant; sometimes to a very small and sometimes to a very large extent. This character has been subjected to what we may call an automatic selec- tion, for every gardener naturally plants out only varie- gated specimens neglecting the green ones ; also it is customary to cut away the green twigs which arise by bud-variation. Here we have a sort of unconscious se- lection which has however been exercised in the same direction for many years, and in many cases through some centuries. And what has been effected by this continued selec- tion? Absolutely nothing. At least, so far as we know, nothing more than maintaining the variegated varieties and keeping them in a fairly pure condition. But nothing like fixation has resulted ; that is to say, the varieties continue to produce atavists when grown from seed, and moreover, the pure and constant varieties which corre- spond to them have not been obtained. For in this case these varieties, as we stated above, would have to be the pure yellow ones, such as are known to gardeners under the name of mire a forms. All in all there are in our gardens, perhaps twenty or thirty, or even a few more of these aurea forms ; and this number is as nothing compared with the almost un- limited series of variegated forms. Moreover exactly those variegated forms which have been cultivated most carefully and for the longest time have not given rise to aiirea varieties.-^ From this discussion I draw the conclusion that con- tinued selection with variegated plants will not of itself lead to the production of constant forms. For this, ^ See the list on page 270. Variegated Leaves. 283 sometliing else is necessary, and this something chance alone can. provide, \\niat we want is the transition frnm one race to another, a transition, which according tu my opinion, cannot be effected gradually, but takes place suddenly from as yet unknown causes; we have, in fact, to wait for a mutation. The longer a variegated plant has been in cultiva- tion the more strongly does the fact that it has not pro- gressed support this conclusion. The best instance is afforded by the familiar Rocket^ which is one of the oldest, favorite and most widely distributed variegated plants in cultivation, and which is often seen to escape from gardens (Barbarea vulgaris variegata). The plant is cultivated almost solely for its variegated leaves, al- though it is a kind of cress. It is biennial and sufficiently constant ; it is usually grown from seed, although it can also be propagated by division. Only a small percentage of the seedlings are found to be variegated. Amongst a thousand growni from seeds which I had harvested myself from isolated variegated plants, I found only one per cent variegated and ninety-nine per cent plants whose cotyledons and first leaves were pure green. No white or yellow seedlings occurred. Of the greens a large proportion developed later into variegated plants, as was to be expected." But the variety can by no means be regarded as fully fixed. Very many variegated varieties, especially of annual and biennial plants, come true to seed. AIorren, Car- RiERE'*^ and other authors have drawn \\\) lists, and much information relating to the subject can be gathered from ^ Vilmorin-Andrieux, FIcui's dc plcinc tcrrc. p. 387. ^According to Morren. Hcrcditc, Inc. ci'f.. p. 229, from 70-90% of the seedlings become variegated in later life. ^ E. A. Carriere, Prodttctinu rf fixation drs varictcs, 1865. p. 14. 284 Non-I salable Races. seedsmen's catalogues. Such statements relate, of course, only to practical and not to absolute constancy. It suf- fices that the harvests justify a reasonable hope that a certain number of variegated individuals will occur amongst the seedlings. Information as to the magni- tude of this proportion is rarely given. Godron found Acer striatum varicgatum to repeat the anomaly in only one-third of its seedlings.^ Viviand-Morel found only occasional variegated specimens amongst five hundred seedlings of Hedera Helix variegata and only one amongst fifty of variegated Yucca, the majority being green. ^ Pepin states that the seeds of Sophora japonic a foVus raricgatis always give rise to more variegated than green plants '? but in the case of these and similar data we know nothing, as a rule, as to whether the seeds have been derived from individuals which had been isolated. Pollock sowed the seeds of a variegated plant of Ballofa nigra which he had found wild and obtained thirty per cent variegated seedlings. In the next generation the seeds of these, however, gave 60% of variegated indi- viduals.^ The plant is now on the market and from the commercial seed I raised 25% variegated and 75% green plants. The seeds of a variegated specimen of Chrysan- themum inodormn found near Amsterdam produced 65 plants in my garden, of which 5% were variegated whilst 17 produced spotted leaves during the course of the summer, and the rest were green (1893). From the seeds of a variegated Luuaria biennis I raised green plants onl>; (1893) and I obtained the same result in ^Mem. Acad. Stanislas, 1873. ^ Lyon horticolc, 1893, p. 144. 'Verlot^ loc. cit., p. 75. * Darwin^ Variations of Animals and Plants, T, p. 409. Variegated Leaves. 285 1896 from some self-fertilized variegated Oenothera La- niarckiana, although these two sorts are ordinarily con- stant from seed. Variegated Oenothera rubrinervis gave rise to 20% variegated seedlings (1892), but on a repe- tition of the experiment with another plant (1893) all the offspring were green. In sectorial variegation we might expect the seeds of the variegated sectors to give rise to more variegated plants than those of the green ones. The only informa- tion relating to this question as far as I know is due to Heinsius.^ He found a stem of Dianthus harhatns, one of the longitudinal halves of which was variegated, whilst the other w^as colored in the ordinary way. During the flowering period the plant was protected from insects by gauze and artificially fertilized, each flower being polli- nated wath pollen from another in the same longitudinal half. On the one half the capsules were white, on the other green ; both produced ripe seed. The seeds of the white fruits produced seedlings without chloroi)hyll but the seedlings from green capsules were the normal green. In 1888 I myself collected the green and the variegated fruits of a sectorial main stem of Oenothera Lamarckiana separately. The seeds of the former gave rise almost exclusively to green plants, those of the latter to a large proportion of variegated ones. In the summer of 1895 I saved the fruits from a green and from a variegated branch of the same plant of this species, but both sets of seeds gave about the same very small proportion of varie- gated specimens, viz., 2%. In the summer of 1898 I conducted a more exhaustive research with sectorial variegation in Oenothera La- ^ H. W. Heinsius in the Proceedinp^s of the Gcnootschap ter hevordcring dcr Natuur- Genees- en H eclkunde te Amsterdam, fleet- ing of May 7, 1898. 286 Non-Isolablc Races luarchiana. In the normal families of my cultures some specimens that happened to be variegated had, after arti- ficial self-fertilization, given rise to no more than two per cent of variegated offspring and in the next genera- tion the same proportion was repeated, the conditions be- ino- the same. From these I selected in 1898 the four finest young plants, planted them out a meter a])art, and thereby obtained strong, richly-branched individuals, of which some were slightly, and others strongly, variegated. On all of them the flow^ers from which T intended to sa\-c seed were artificially and purely fertilized with their own pollen. On each of the four plants I first fertilized flowers on the pure green and afterwards some on the variegated lateral branches. Amongst 675 seedlings of the former and 1300 of the latter group the seeds pro- duced the following percentages of yellow and variegated seedlings : PERCENTAGE IN VARIEGATED SEEDLINGS PLANTS GREEN BRANCHES VARIEGATED BRANCHES No. 1 0-0 % 1 % No. 2 — 3 No. 3 0-0 4-12-18 No. 4 0-0 6-9-45-100 Eacli num1)er refers to a separate l^ranch The six greens gave rise, as we see, to green seedlings only, but the varies^ated ones to a laro;er or smaller number of seedlings with this character. The figures 1, 3, 4, and 45 in the last column relate to the slightly variegated branches ; the rest to those with this character more strongly developed. The latter therefore gave a higher percentage of variegated offspring. The variegated seed- linijs had either vellow or flecked cotvledons, or ^reen cotyledons and flecked leaves, and of these three groups there were 68% of the first, 12% of the second and 20% Variegated Leaves. 287 of the third group. The more yellow seedlings there were in a group the more variegated specimens did it, as a rule, also contain. I collected tlie seeds of a yellow fruit separately ; only eleven of these germinated but these had all pure yellow cotyledons. On the other hand striped fruits had percentages of variegated seedlings which varied greatly, and this was also true of the striped parts of capsules when their seeds were harvested sepa- rately. Lastly the seeds of green capsules produced only green seedlings. The color of the seedlings is therefore to a larsfe ex- tent determined by the color of that part of the mother plant wln'ch produced the seed (and also the pollen). I made a further investigation of the seedlings from seeds of green and variegated branches of individual plants in various other species, after artificial isolation had been secured, either by means of parchment bags, or by planting the plants some distance apart, or by making them flower at different times. ^ I obtained the following percentages of variegated and yellow seedlings : SEEDS OF CREEX VAKIEC.ATED BRANCHES BRANCHES A. Commercial variegated races; Arabis alpina 2-10 % 90 % Helianthiis annutis 0 " 100 " P.. Occasional finds: Lamium album 0 '• 3 " Ceuin nrbamiDi 0.3 " 4 " Silene noctiflora (5 ") (34 ") The high percentage of green plants in Arah'xs alpina corresponds presumably to the readiness with wliicli tliis species produces bud-variations, variegated branches l)e- _ ^ Tn SUcnc nncfi/lora only was fertilization left to the free agency of insects. 288 Non-Isolahle Races. ing easily produced by green plants and green branches by variegated ones. Now let us consider the yellow seedlings of variegated plants. They appear, it is true, to be mutants, but, as a matter of fact, they are the extreme variants which, how- ever, do not attain to their goal but perish in the attempt, for tliey are too poor in chlorophyll and are thereby des- tined to die early. Nearly all of them die without so much as having unfolded their first leaves, or sometimes even their cotyledons. They constitute the extreme limit of a long series of variegated forms, but have, so to speak, followed a wrong direction. They are by no means rare ; for instance they are well known in the holly. Ilex Aquifolhim, and they often result in a very considerable loss amongst the seedlings raised from the seed of variegated plants. It is not, however, variegated plants only which pro- duce such seedlings; green plants do so only too often, and this even occurs in families cultivated for experi- mental purposes when the cultures are pure green and have been so for many years or did not produce more than an occasional variegated leaf or twig. If in such cases the seeds of the single seed-parents are sown sepa- rately the proportions in which variegated seedlings oc- cur in the various groups are found to vary greatly. Some species appear never to produce them, for In- stance the tricotylous races of Cannabis safk'a, Mcrcu- rialis annua, and Pliacclia tanacetifolia which I have cultivated, although I have sown the seeds of several hundreds of individual plants separateh^ in the course of some years. In other species they are very rare ; in some, however, the percentage of yellow seedlings is so con- siderable as to become a real nuisance. Thus, for in- Variegated Leaves. 289 stance, the highest numbers (not to mention the numer- ous smaller ones) that I found amongst the seedlings of individual seed-parents were as folows : YELLOW OR WHITE SEEDLINGS Aiilirrhinuin viajiis 5-6 % Clarkia pulchella 9-13 " Papaver Rhoeas 15-30 " Polygonum Fagopyruin 8-12 " Scrophularia nodosa 10-15 " Trifolium incarnafnin 4-6 ' ' Chrysanthenimn segetuvi 13 " Lijiaria vulgaris 25 " Trifolimn pi'atejise 13 " Oenothera Latnarckiana 20 " In many other species I have, as yet, found not more than one or two per cent of yellow seedlings from the seeds of individual parents. Therefore I presume that this extreme variation is brought about, besides by the heritable potentiality, by causes similar to those in operation amongst the variants in the small seeds of Trifolhun incar- natuiJi (p. 239). In some cases, as for instance Polygonum Fa- gopyruin and Trifolium incarnatum it struck me that the higher numbers were more frequent than some of the lower ones. This was especially the case in Papaver rupifragum, amongst the offspring of a single parent plant. This plant was selected as l)cing a 0.1. 3 6 9 12 15 18 21 24 Fig. 55. Papaver rupifragum. Pro- portion of yellow seedlings among the seeds of 54 green plants. These plants themselves were the off- spring of a single green parent plant. The two first ordinatcs are slightly reduced. The figures 3, 6, 9, etc.. signify 2-4, 5-7, 8-10% yellow seedlings and so forth. 290 Noji-Isolablc Races. tricotylous specimen and had been raised from seed ob- tained in excliange; it flowered in 1893 in complete iso- lation and produced 6% yellow seedlings amongst its off- spring. I planted out about 60 of the green plants which grew to healthy individuals in 1899. I left the pollina- tion to insects but saved the seeds of each plant separately and then counted the number of yellow seedlings for each in a lot of 300.' Y. S. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 22 24 27 30 Ex. 27 6 1 1 1 0 0 0 1 1 2 3 1 1 2 4 0 3 1 0 0 1 Or 27 63 0 4 5 6 31001 "V. S." signifies the yellow seedlings in each lot of seed and ''Ex." the number of plants which exhibited this proportion amongst their seedlings. In the lower line from 2% onwards these are arranged in groups of 3 in order to emphasize the general result. The num- bers of this last row are plotted in Fig. 55. This curve is similar to the curves of monstrosities wdiich have been subjected to a selection extending over many years. ^ Even as these, it consists of a half curve and of a bilateral curve. It indicates therefore the selection of a latent character which in this particular case started with the choice of a tricotylous plant which happened to be a partictilarly suitable one.^ The observations and experiments which we have described or passed in review show that variegated plants constitute a group of forms which in spite of being se- lected for years or even for a century have manifested no further improvement in the quality and constancy of ^ See the second section and Sur les coiirhes golfouiennes dcs monstniositcs. Bull. sc. de la France et de la Bclgiquc, published by A. GiARD, Vol. XXVII, April 1896, p. 396. ^ See Uchcr einc Methode, Zivangsdrchungen aufziisuchcn, Ber. d. d. hot. Ges., Vol. XII, 1894, p. 25. Altcrnatincj Annual and Biennial Habit. 291 their peculiar character than many of the most recently arisen variegated sorts. They are highly varialjle and give rise in many cases almost every year to green des- cendants, on the one hand, and to pure yellow, on the other. The former are regarded as atavists, the latter, however, are only variants and not mutants, since so far as the observations extend they give no hope that they will ever form the basis of a pure yellow race. These, the true aurca varieties, have only arisen in relatively very rare cases ; possibly from variegated types but without showing any evidence to support this supposition. The capacity for producing variegated leaves or yel- low seedlings is more widely distributed in the vegetable kingdom in a latent and semi-latent condition than per- haps any other character. § 25. ALTERNATING ANNUAL AND BIENNL\L HABIT. One of the strongest pieces of evidence for the doc- trine of mutation is the phenomenon in beets which is called bolting or shooting. It can be observed in almost every field of beets. Occasional plants- are seen to de- velop a stem in the first year, to flower and to bear seed. They store no sugar or other food-stuffs or at any rate onlv to a verv slipiit extent in their roots which become correspondingly woody. They are useless for practical purposes. On good fields about 1% of the plants ordi- narily behave like this, and more rarely a smaller pcv- centage of the whole crop. Under unfavorable circum- stances, however, their number often increases consider- ably ; reaching for instance from ten to twenty per cent and sometimes still more. No farmer uses the seeds of such annual plants for 292 Non-Isolable Races. sowing. They obviously offer too great a prospect of a repetition of the evil. Moreover the seeds of these bolters cannot, either by chance or carelessness, get mixed up with those of the biennial beets because they ripen a year earlier. Thus in every generation an absolutely rigid selection of biennial examples as seed-parents takes place, and must have taken place as long as the culture of beets has proceeded on rational lines. Nevertheless these bolters have not disappeared. Stringent selection has failed to eliminate them. More- over as far as historical data enable us to decide, the proportion of bolters remains about the same. In ref- erence to this case at any rate we are therefore fully justified in stating that selection cannot effect in the course of a long period of time what it fails to bring about within a few years. This belief is w^idely and firmly held by beet-farmers. They are always in search of new means of combating this evil ; but the mere selection of biennial beets is con- sidered to be without prospect of success. Rimpau has endeavored to attain this end by raising a triennial race, by selecting the so-called laggers, i. e., plants which have not flowered in the second year;^ but most agriculturists content themselves with making the conditions of culture as unfavorable as possible to this evil.^ These laggers are in a sense analogous to the bolters, inasmuch as they have been eliminated by the normal ]3rocess of selection since the time when beets were first ^W. Rimpau^ Das Aufschiessen dcr RnnkcIrUhcn, Landwirtsch. Jahrbiicher, Vol. V, 1876, p. 31, and Vol. IX, 1880, p. 191. By the same author, Das Saniciischiesscn dcr Ruben, Deutsche Landvv. Presse, Jahrg. XXI, No. 102, Dec. 22, 1894, P- 984- ^A list of the most important papers on the subject is given by RuMKER. Die Ziickcrriihenzuchtung der Gegenzvart, Blatter fiir Zuckerriibenbau, 1894, PP- 22-23. Alternating Annual and Biennial Habit. 293 cultivated and have nevertheless not been extirpated. The general opinion of botanists is that the represen- tatives of the main line of the evolution of plants have been for the most part perennials. From these the an- nual and biennial forms must have arisen independently in the various families and groups; and it is furtlicr natural to suppose that the biennials arose first and that the annuals arose from them. If this is true the pro- duction of a biennial from an annual or of a perennial by one of these two would have to be regarded as a phenomenon of reversion.^ Instances of such atavism seem to occur very generally in the vegetable kingdom, but progressive transitions, that is to say, those that take place in the opposite direction, are also by no means rare.- From the abundant literature on this point I select two cases which seem to me the most important. Pha- seoliis rmiltiflonis {Ph. coecinens L.) is, with us, an annual plant, producing occasionally, however, a bulbous root which can be wintered and by means of which the plant can be perpetuated. Von Wettstein/^ to whom ^we owe our knowledge of this phenomenon, has obtained plants which lived four years, and in my own experi- mental garden I have succeeded in wintering several such Phaseohts tubers. Von Wettstein's view is that we are dealing here with the transformation of a peren- ^ Many, however, hold the opposite view. See Darwin, Varia- tions, II, p. 5; and Rimpau^ loc. cit. ' See the works relating to this snhject by Irmtsch and Warming. Also HiLDEBRAND in Engler's Botan. Jahrb., IT, 1882, pp. 51-135; with regard to different sorts of beets: F. SciiiNnLER in Bof. Ccntral- blatt, 1891, Nos. 14 and 15, and the literature cited there. ^ R. VON Wettstein, Die InnovationsvcrJiiiltnissc von Phascolus coecinens L. (=: Ph. multiflorus IVilld.), Oesterr. hot. Zeitschrift. 1897, No. 12, 1898, No. I. 294 Non-lsolablc Races. nial species into an annual one.^ The careful experiments of Briem lead to the same conclusion ; for he succeeded in wintering the sugar beet after it had borne seed and in inducing in this way the same plant to bear seed a second and sometimes even a third time.- All that was necessary to bring this about was that the beet in question should continue to increase in thickness"* and accumulate, in its new rings of tissue, the necessary quantity of sugar and other food-stuffs. Tt is known that summer wheat can be changed into winter wheat"* by a selective process, and that the con- verse process may also take place ;^ also that a perennial sort of rye is occasionally raised in Russia besides the ordinary annual rye.^ Numerous annual species also give rise to biennial and perennial forms such as Arabis dcn- fata and Dclpliiniuin ConsoVida-? and as a general rule interferences of various kinds with the normal vital pro- cesses of the plant are considered tu be the causes of these changes.'^ "^ Loc. cif., p. II. " F. Strohmer, H. BRIE^[ and A. Stift. Uchcr mehrj'dhrige Zuckerriiben und deren Naclicurhf, Oesterr.-Ungar. Zeitschr. fiir Ziickerindiistrie, Pt. 4, 1900, with Plate XV. " For facts relating to this growth in thickness see Die ahnonnale Entstchnng sccunddrey Gczvcbc in Pringsh. Jahrb. fiir wissensch. Bot., Vol. XXII, 1890, p. 35; and Plate III, Fig. 14. * Numerous illustrations of the question dealt with in the text are furnished from agricultural experience by C. Fruwirth. Die Ziielitting der laudzvirtschaftlichen Culturpflanzen, 1901, p. 146. ^Darwin, Animals and Plants, I. p. 33:^. *^ A. Batalin, Das Perenniren des Roggens. A ver^^ important paper dealing with these questions is H. C. Schellenberc/s Grau- hiindcns Getreidcvarietdten, Ber. d. Schweiz. bot. Gesellschaft, Part X, 1900. "Theod. TTolm. On the Vitality of Some Annual Plants^ Amer. Journal of Science, Vol. XLII. 1891, p. 304. *'W. Bartos, Zeitsclirift f. Zuckerindustrie in Bolimen, Vol. XII, 1898, p. 456. Alternating Annnal and Biennial Habit. 295 Conversely many perennial plants which under nor- mal conditions llower the second year after germination for the first time, can be induced by favorable cultiva- tion to flower in the first summer, though this does not always succeed with every individual. In this way many ])erennial species are treated in horticultural practice ?is annuals, and I myself have cultivated a whole series of plants more or less regularly as such ; for instance, Achillea Millefolium, Hesperis niatronalis, Lychnis z'cs- pertina glabra, Picris hieracioides, Trifoliuni pratense quinquefoliuni and others. Let us proceed now to our more immediate subject, the phenomenon of the occurrence of many species partly in annual and partly in biennial specimens. Such plants are regarded by descriptive systematists as biennials, as, for instance, the name Oenothera biennis indicates; for, under the less favorable conditions which usually obtain in the field the great majority of the specimens will be biennials. In my opinion this view is quite correct, but the bien- nial s])ecies in cjuestion must possess the capacity of grow- ing as annuals, in a semi-latent condition. Moreover this capacity does not seem to be universal, but to be con- fined to particular races. For instance, Koch's Synopsis Florae Gernianicae et Heheticae (3d ed. 1857) and Gre- NiER and GoDROX in the Flore de France (1852) give Dipsacus syh'cstris as an annual, whilst I myself have hitherto only been able to raise biennial races of it from seeds derived from numerous different sources, and in spite of the fact that I modified the culture in every con- ceivable direction in the hope of making them annual. It is highly probable that many species exist in certain 296 Non-Isolablc Races. regions as pure biennials, in others as annuals, and in still others in a mixture of these two forms. ^ Inasmuch therefore as the biennial habit is to be re- garded as the character of the species and the annual habit as the anomaly, the latter is likely to follow the general rule according to which the development of the anomaly is favored by improved conditions of life. And the experiments which I propose to describe in this sec- tion prove the correctness of this view. However, there is an apparent contradiction, for, as is well known, Rimpau has shown in the case of the beet that every retardation or interruption of the growth, whether it occurs during germination or just after the seed comes up or at a later stage of the development of the plant, favors the production of the seed in the first year of the plant's life.^ But in this case it only appears that we are dealing with conditions favorable to the production of the anom- aly whereas in reality we are concerned with the stimulus necessary for the manifestation of this bolting. As it is not very easy to make this difference clear I shall select an instance of a pure biennial race^ which lacks the power of giving rise to annual specimens. I refer to my cul- tures of Dipsacus sylvestris. This race can be sown at any period of the year, and the plants will always remain rosettes until the end of the next winter and develop a stem in the spring of their second year. According to whether the sowing was made in the spring or in the summer or not till autumn are the rosettes vigorous or ^ Instances of this are given by J Costantin, Les vegetaux et les milieux cosmiques, Paris, 1898, pp. 28 f. ^ Landw. Jahrbiicher, passim, 1880, p. 194. ' On Biastrepsis and Its Relation to Cultivation, Annals of Bot- any, Vol. XIII, No. LI, Sept. 1899, p. 395. Altoiiai'uuj Annual and Biciuiial Habit. 297 weak, but this treatment has no effect on the period at which the stem w ill be developed. If the seeds are sown in ]\larcli in the greenhouse and the seedlings are picked out early into pots and planted out in May or June, we get vigorous rosettes with abundant lea\'es, but not a single stem in the first year. If the seeds are sown in September in the greenhouse, soon after harvesting, the rosettes remain weak until winter, but nevertheless de- velop a stem in the following spring. By sowing the seed in late autumn in the open ground, however, the plants will develop only a single pair of leaves above the cotyledons and they can be induced to pass through the winter without producing their stems in the spring. In this case they pass through the whole of the summer as rosettes, become extraordinarily vigorous and do not develop a flowering stem until after the second winter. These experiments show that a definite stimulus is necessary for the production of a stem. Under the con- ditions of my own experiments it seems to be the winter which exerts the stimulus and that it can do so at any age of the plant except the very young stages when only the first two leaves are unfolded. But without this stim- ulus no stem is formed. The experience of beet cultivators goes to show that the chief cause of the bolting is the night frosts of the spring. Manifestly they exert an effect on the young plants similar to that produced by the winter. It is a fact generally known that the percentage of bolters is high in direct proportion as the seed was sown earlv ; crops which have been sown late are sometimes perfectly free from this defect. Rimpau showed that if a small section of a field which has been sown early is co\-ered over wnth a sheet every night that threatens to be frosty. 298 Non-Isolablc Races. tlie occurrence of bolters is considerably diminished; in one experiment for instance from 7 to 4%.^ Other results point in the same direction. Heuze^ in his valuable little book on the oil plants,^ says with regard to the rape (Brassica Napus olcifcra), that in the north of France it should not be sown before the middle of July or after the middle of August, for in the latter case the plants will not be strong enough to sur- vive the winter, and in the former too large a proportion will set seed in the first year. The same thing is true of a whole series of other biennial plants Ixjth cultivated and wild ; those which germinate late become biennial ; of those which germinate early a greater portion become annual, the earlier the sowing or the germination took place. In these cases we are not concerned with the induction of bolting by night frosts, or by any other stimulus, but with a case of inherited variability. It is true that the beet possesses this variability also, but the general con- ditions in this species are much complicated thereby. That we have to deal with a phenomenon of inheritance is proved by the fact that the annual form can easily be fixed by selection, without, however, attaining a state of absolute purity. Rimpau sowed the seed of bolters,'" and by always selecting seeds ripened in the first vear, he obtained in the fourth generation a race whose seeds when sown on the 31st of March produced annual ])lants only and which in the fifth generation, when sown on the 5th of April, w^as as constant an annual as the normal ^ W. Rimpau, Das Aufschiessen dcr Rtinkelriihen, Landwirtsch. Jahrbiicher, i88o, p. 192. "L. Heuze, Lcs plantes oleagineuses, Bibliotheque du cultivateiir, Paris, 2d ed., p. 16. " Loc. cif., p. 197. Alternating Annual and Biennial Habit. 299 beet, sown at the same time, was biennial. The same is true with other species. Seeds of the wild Daueiis Carota saved from annual plants gave me a large pro- portion of annuals; but seeds from plants which had come through the winter gave a predominant proportion of biennials. On the other hand selection does not seem to lead to the production of annual races which would be free from occasional atavism. It is my custom now to cultivate my Oenothera Laniarckiana and its derivative species mostly as annuals. Many of these cultures have been continued for six or more generations by means of the seeds of annual specimens only. Nevertheless every year there occur occasional and sometimes several bien- nial plants amongst them. Aster Tripoliiini^ is usually given as an annual in the floras, but with us it is represented by specimens which pass through the winter as well as by plants which flower in the first summer. In experimental sowings in the garden I obtained roughly equal numbers of the two types; but if I sowed the seed in March or April in the greenhouse the plants developed stems in the first year almost without exception. They were, as a rule, covered with glass every night until June, and thus protected from night frosts, and they were well treated also in other respects, especially by transplanting them soon after germination into rich well-manured garden soil. For according to my experience one of the best means of inducing biennial plants to behave as annuals is to give them plenty of manure, provided of course that the ^KocH, Synopsis Florae Germanicac et Hclvcticac, p. 361. Gke- NiER ET GoDRON, Flove dc Fvancc, Vol. II, p. 102; Kaksch. I'adc- mccum hotanicum etc. 300 Noii-IsokWlc Races. capacity to do this is present in them in a semi-latent state. ^ With Oenothera Laiiiarckiana I have made some more extensive experiments on accelerating the development of the stem by improving the conditions of growth. In the wild state this plant consists chiefly of biennials, Init partly also of annual and of triennial individuals. Under experimental conditions, however, the duration of its life seems to depend more on external influences than on the choice of seeds. I have especially tested the distance between the plants, the sunniness of the position, and the richness of the soil. In 1888 I selected some seeds of my biennial stock plants of the Lamarckiana family of 1886-1887,- in order to investigate the effect of the degree of separation of .he plants in the bed. For this purpose I selected four adjacent beds of similar contents with regard to soil and manure, sowed the seeds in the middle of April fairly thickly in rows, and weeded them out during germina- tion in such a way that on two beds the plants stood at moderate distances, on one fiu'ther apart, and on a third more closely. In the summer up to the middle of September I recorded the number of individuals with stems and the number of the rosettes. The sum of the two obviously affords a measure of the distances between the plants. The extent of each bed was 13 square meters. The figures are : "^ Sur la culture des monstruositcs, Comptcs rcndiis de I'Ac. d. Sc, Paris, January, 1899; Sur la culture dcs fasciatious dcs cspcccs annuclles et bisannuelles, Revne generalc de botanique, Vol. XT. 1899, P- 136; and Ueher die Abhangigkeit dcr Fasciation vom Alter hei sweijdhrigen Piianzen, Botanisches Centralblatt, Vol. LXXVII, 1899. ' See the pedigree in Vol. T, p. 224. Alternating Annual and Biennial Habit. 301 PLANTS PER PERCENTAGE OF PLANTS RKn PT ANTS SQUARE METER WITH STEMS No. 1 1350 100 23 % " 2 and 3 630 + 650 50 43 " " 4 380 30 58 " That is to say, the closer the plants are together, and the less room each one has, as a result of this, for the unfolding of its leaves, the smaller is the number of annual plants. In the following year I repeated this experiment, but this time with the seeds of annual plants. The result was, however, the same. There were 1188 plants on one bed of 13 square meters, that is, about 90 per square meter; of these 20% were annuals. On the other bed of the same size there wxre 348 plants (or 27 per square meter) and 54% developed stems. I repeated the same experiment once more, in 1890, with the seeds of an annual plant of 1889. On tlie one bed there were 40 plants per square meter, of which 17% were annual. On the control bed there were only ten plants in the same area, and of these 72% produced stems in the first summer; the extent of the bed in both cases was 5 square meters. In 1891 I investigated the influence of the distance between the plants in an experiment with Oenothera laez'ifolia, raised from the seeds of an annual race which had been selected for three generations.^ The two beds were of the same size, had the same aspect and the same soil, and both received a similar and liberal dressing of guano. They were sown in the middle of May on the same day, but at the end of July they contained 195 and 638 plants respectively (per each 6.S square meters). As a result of this, the bed in wliich the plants were far See the pedigree in Vol. I, p. 224. 302 Xo)i-Isolablc Races. apart had 162 plants which developed stems, whilst on iliat in which they were close together there were 145. The ditlerence between the two reckoned as a percentage of the whole culture is of course more striking, viz., 83% as against 20%. More important, however, is the fact that per each square meter in absolute numl)ers more annual individuals are produced when the plants are grown far apart than when they are grown more densely and therefore in larger numbers. When view^ed in this way the result points to the great importance of sowing seeds thinly in experimental cultures. Experiments with shading are met with the difficulty that the young plants cannot stand it very well, even when, as in my experiments, the shadow is that of trees. The experiment was conducted at the same time as that of 1890, referred to above, on a similar scale and by growing the plants far apart; it produced about 46% annuals as against 72% in the control experiment al- ready mentioned. By far the best means, however, of increasing tlie proportion of annual plants or even of securing their exclusive production, is to sow the seed and keep the young plants under glass. In doing so the seed can be sown in March or April in un-manured sterilized soil, and the seedlings may be pricked out singly into pots containing richly manured soil after the appearance of the third or fourth leaf. In this condition they remain under glass until the end of May, at least during the nights and on cloudy days, and can then be turned out of the pots without breaking the ball of earth round the roots and transplanted to the place where they are to grow. Treate 1 in this way almost all the plants behave Alternating Annual and Biennial Habit. 303 as annuals, and of late I have grown all my cultures by this method or by some .slight modification of it. In order to determine the effect of the soil on the development of the stem I have compared the difference l)etween plants grown on manured and unmanured beds, and also the difference between plants grown on barren sand and on fertile soil. The first of these two exi)eri- ments I have made with the Oenothera laevifolia. I used seeds which I had saved in 1890 from the third annual generation of my culture (see Vol. I, p. 273). The seeds were sown in the middle of May on three beds of 3/4 scjuare meters each. They were adjacent to one another, had the same soil, a similar exposure, and so forth. The seedlings were thinned out early, to 100 per bed, in such a way that the distances between them were as uniform as possible. The sole difference lay in the kind of manure which they received, which in No. 1 was nothing, in No. 2 a quarter of a kilo of guano, and in No. 3 a quarter of a kilo of hornmeal. In the second bed, therefore, the manure was rich in phosphatef and in the third in nitrogen. On the 30th of July 1 recorded the plants w'ith the following result : PLANTS ANNUALS No. 1. Without manure 100 n% No. 2. With guano 98 90% No. 3. With hornmeal 108 94 f^ In spite, therefore, of the fact that the race had been selected for three years the proportion of annual plants on the bed without manure was only 77 per cent, wliilst this proportion was considerably increased by the addi- tion of manure, and more bv the addition of nitroq:en than by that of phosphates. Further experiments with dif- ferent quantities of the same manure showed that the 304 Non-Isolablc Races. amounts employed in this experiment (about 80 grams per square meter) should not be exceeded, that is to say, that the result cannot be improved by still heavier ma- nuring. For the experiment with sand I dug in my experi- mental garden a bed of 13 square meters in extent and one-half a meter deep, and filled it with ordinary fine sand. On this bed and on a neighboring one of the same size I sowed seed of Oenothera Laniarckiana in the sum- mer of 1899. The control bed was not manured but contained a very fertile soil ; the seed was sown in the middle of April. 1lie sand of the bed bordered immediately on the rich soil of the path which surrounded it.-" Therefore the plants at the margin could thrust their lateral roots into this, and thus obtain richer food than the more central rows. This circumstance showed very important results during the course of June, for wdiile many flower- ing stems were produced towards the outside of the l)ed, hardly any occurred in the middle. It was not until the middle of July that the development of stems set in here also. Curiously enough this occurred in almost every instance at exactly the same time. In the middle of August among the 82 plants of the outer rows about 60% had developed stems, whilst in the middle there were 133 rosettes amongst 203 plants, that is to say about 24% of annual specimens. We see that the dis- tances between the plants in this experiment were very considerable, for on 13 square meters there were only 285 plants. Even at the end of the summer they hardly touched one another. In the control experiment in which ^ In subsequent years I have separated the sand from the earth by boards. AlUiiiat'uKj J initial and Biennial Ilahil. 305 the distance between the plants was praclically the same there were about the same number of plants that devel- oped stems as there were on the margin of the sand bed, in fact a little less, 53% amongst 348 plants. Our main result therefore is that the proportion of plants wdiich developed stems in the center of the sand bed is 34% as against the 53% and 60% amongst the plants on the margin of this bed and in the control bed respectively. Equally striking w^as the sudden change in the behavior of the central plants in July. This pointed to some special cause. I suspected that it was connected with the growth of the roots and that these about this time had penetrated the layer of sand and reached the fertile earth beneath it. When I dug up the roots at the conclusion of the experiment I found that these were, as a matter of fact, longer than half a meter and had branched freely below the level of the sand. In order to find out whether this was the real cause of the development of the stems I made an experiment in 1891 with a bed in which the layer of sand was much deeper (one meter). A part of the original sand bed wliich was only one-half meter deep, and a neighboring bed filled with ordinary good garden soil served as con- trol. This time the bed was surrounded by boards and, consequently, there w^as no difference in the behavior of the central and marginal plants. For this experiment I used the seeds of a culture of Oenothera ruhnnerris which had been cultivated as an annual for two genera- tions (seeds of 1890 of the pedigree of Vol. I. p. 273). The sowing took place in May 1891. At the end of July I recorded the plants on the three beds, each of which was 3 square meters in extent. 306 No)i-Isolablc Races. ^LANTS ANNUALS 161 21 % 226 50 " 131 98 " Sand-bed, 1 meter deep 2 Garden-soil On the control bed the distances between the plants were somewhat greater, but as practically they did not touch one another on the sand bed this fact does not signify. The seeds employed in this experiment gave a larger proportion of annual specimens than did those of the previous one. Tlie main result is that the proportion of plants which produce stems in their hrst year can Ije reduced to about one-half by cultivation in a bed with half a meter of sand, and to less than a quarter by culti- vating in a meter of sand. The results of the foregoing experiments prove that biennial species which possess, in a semi-latent state, the capacity to produce annual specimens, can be induced to manifest this anomaly to a much greater extent by sup- plying them with more food. Crowding of plants, sha- ding, lack of manure, or cultivation on sand, favor tlie production of biennials ; but the more space, light and nourishment in the soil there is at the disposal of the individual plants the greater will be the number of those which will produce stems, flower and ripen their seed in their first summer. The stimulus of the winter or spring frosts, which in other cases induces the young plants to develop stems, is without effect here ; for under the described conditions even seeds sown in the middle of May in the open ground may give rise almost exclu- sively to annual plants. Continued selection, however, fails either to fix the biennial races and to free them of annual specimens, or to free the annual races of biennial individuals. VIII. NUTRITION AND SELECTION OF SEMI- LATENT CHARACTERS. § 26. INCREASED NUTRITION FAVORS THE DEVELOP- MENT OF THE ANOxMALY. Fluctuating variability is a phenomenon of nutrition, whereas mutability is the result of hitherto unknown causes (Vol. I, p. 575). This statement, which is per- haps the sharpest expression of the contrast between fluctuating or continuous variability on the one hand and occasional sudden transitions from one species into another on the other, has been discussed more than once in this work. It is equally true for the variability oi semi-latent characters as for that of normal ones. This side of the statement has also been already alluded to. and I have cited many instances in order to prove its truth. Everywhere nutrition and variability are so in- timately connected that the physiology of the latter ])hc- nomenon can hardly be dealt with without discussing its relation to the former. Artificial selection is the choice of the better nour- ished individuals, except of course, when selection is carried out in the negative direction (Vol. I, p. 142). In the first volume I cited as a proof of this generaliza- tion an experiment with a semi-latent character. The number of accessory carpels of Papai'cr sonniifcniin polyccpliahiin was shown to be dependent on selection 308 Nutrition and Selection. and, to a no less extent, on nutrition. In the third part of the first vohime, the curve representing the length of tlie fruits in OcnotJicra and the curves of the rays of cer- tain Umbelli ferae and Compositae also proved that these two factors operate in the same direction. Active and semi-latent characters are thus shown to behave in the same way with regard to these two factors. Since, however, the extraordinary variability of semi- latent characters (of which an account has been given in § 2 of this part, p. 9), is one of the strongest supports of the doctrine of selection, it seems to me that it is worth while to attempt to make the relation between this phe- nomenon and nutrition specially clear. In this last chap- ter I will therefore deal with a series of facts gathered partly from the literature of the subject and partly from my own observations, which all point more or less defi- nitely to the conclusion that semi-latent characters are largely dependent on the external conditions of life. External influences exert their effect on the develop- ment of organs during their youth, that is to say during the so-called susceptible period. After the character of the organ has been definitely established in this period, the further development cannot affect it. The number of leaflets in a clover leaf, of the petals of Ranunculus hulhosus, of the accessory carpels of Papaver are finally determined in this period; but the conditions of life at the critical moment are not the only factor. The accu- mulated effects of previous influences have also com- bined to determine the individual strength of the organ or of the individual ; and the part which this latter factor plays in the determination of the degree of development of the deviating character is sometimes greater and some- times less than that of the immediate external conditions. Nutrition Favors the Anomaly 309 The most susceptible stage seems to be that of the young embryo in the ripening seed, for external in- linences show their greatest effect on seed-plants. But they also play a part in vegetative methods of propagation and operate in the same direction, though as a rule with less intensity. The gap between anomalies and normal active characters is bridged by a complete series of normal, la- tent characters. These too are de- pendent on external conditions in just the same way as the other two are. As a general rule we may state that, within the specific range of its character, the form of an organ is determined by external physical influences.^ As an instance let me cite the result of some experiments with the germination of potato seeds.- The first leaves of the seedlings are simple (Fig. 56), and the follow- ing ones gradually approach the peculiar pinnate form of those of the grown plant. If the germina- tion takes place in the garden, in full sunlight, the plant develops quickly and the various steps in the development of the leaf- form ^ Keimungsgeschichfe der Kartoffelsamen in Landvvirthsch. Jalir- biicher, VII. Jahrg., 1878, p. 35. 'Lor. cif., p. 35. Fig. 56. Seedling of po- tato grown under un- favorable conditions of light. From i to 6 the form of the leaf increases in complica- tion, but from 8 to 12 it decreases again. Cultivated in a room in 1876. 310 Nutrition luuI Sclcctio)i. follow rapidly on one another. But if the conditions are iinfa\orable, as in a room, differentiation proceeds more slowly. The internodes tend to become abnormally long, to produce too little wood, the leaves develop small pin- nules only, and in very unfavorable conditions I have sometimes observed an interruption in the series of leaf- forms on the stem. Above the lyrate leaves simple ones were again formed, the series turning backwards.^ These phenomena are much better illustrated in those cases in which the first leaves are more compound than the later ones; for instance in the species of Acacia which produces phyllodes in reference to which Goebel's im- portant investigations have thrown so much light on the relation between embryonic forms and external condi- tions.- I have already referred to this above; but I might now mention a figure of a seedling of Acacia verticillata which, after it had already reached the stage of producing phyllodes, was induced to repeat the bi- pinnate form of the embryonic leaves by unfavorable conditions. In the same w^ay the production of linear or arrow-shaped leaves of Sagittaria sagittifolia and that of the perforated leaves of Monstera dcliciosa and others was shown to be dependent on external conditions. In- sufficient nutrition tends to bring about a recurrence of tlie embryonic form, and it seems to be a secondary (|uestion whether this is the simpler or the more com- plicated. The Campanula rotund i folia studied by Goe- BEL, the flowerstalk of which changed from the linear to the heart-shaped form of leaves,^ is perhaps the best ^ See also E. Roze, La transmission des formes ancestralcs dans Ics vcgetaux, Journ. d. Bot., Annee X, Nos. i and 2, 1896. ^ K. GoEBEL, Organogra-phie der Pflanzen, I, p. 150. Fig. 105. ' GoEBEL, Flora, 1896. Vol. LXII, Pt. I. Nutrition Favors the Anoniaty. 311 known example. In the case of the Conifers Beissner has also shown that insufficient nutrition, for instance l)y cultivation in puts, can lead to a protracted reten- tion of the embryonic form.^ In Eucalyptus Globulus and Acacia cornigera stems which have been cut down produce branches which repeat the embryonic form of leaves, which are sessile in the one species and thornless and destitute of the so-called ant-bread appendages in the other.- Exactly the same general conditions obtain in the development of anomalies, that is to say of those char- acters which are only exceptionally or never developed in the normal life of the species. Here again their pre- cise nature seems to be a matter of indifference, that is to say, whether they are harmful or harmless; in either case they are under the influence of external conditions. Instances of deleterious characters are furnished bv varie- gated leaves and by flowers and flowerheads which have become sterile b}^ doubling (see §§ 19 and 24). The same is also true of real monstrosities, such as fascia- tion and twisting, as we shall see in the next chai)ter ; and of new characters, reversionary phenomena, pro- gressive and retrogressive variations of which I shall give a series of instances in the following section (§ 27). It is true both of half races and of middle races : in both it is the older or specific character which is intensified by unfavorable conditions, whilst the anomaly or the vouni>er character is intensified bv favorable ones. Ob- \iously there is only a small step from these two races characterized by the semi-latency of the former or the ^L. Betssner, Handbuch der NadelhoJzhuiidc. See also Bot. Zeitung, 1890, p. 539. 'F. HiLDEBRAND, BotilU. Zcituilg, 1892, p. 5. 312 Nutrition and Selection. latter character to the true elementary species in which the character of the parent species has become completely latent, for in this case the variation of the new character of course conforms to the general laws of variability. We have studied this relation of variability to nutri- tion from various points of view in our researches with the half races of Trifoliiiin incarnatnni quadrifolinin and Ranunculus bulbosus scniiplenns, but especially with the true middle races, Trifolinm pratense qidnquefoliuni, and Chrysanthcminn segetuni plenum as well as with anal- ogous groups. Fig. 57. Lysimachia vulgaris. Transverse sections of two buds which were to develop into upright stems in winter. A, quaternary, and B, trimerous symmetry. It should be remembered that in all these cases we are dealing with variability in the restricted sense and not with mutability. How one race is transformed into another, we do not know. The phenomenon is as yet far too rare and has not yet been adequately investigated. The variability of the eversporting races is of the trans- gressive kind; but it does not lead, as a rule, to muta- bility. Finally I wish to illustrate by means of a scheme the relation between the variability of semi-latent characters and the external conditions of life, and I select as material Nutritiun Favors the Anuiualy 313 for this the disposition of the leaves of Lysiinachia vul- garis (Fig. 59). This species has opposite leaves as a rule, but often occurs with quaternary and ternary whorls. With regard to this character the species he- haves as a half race, in this neighborhood at any rate. If we examine the rhizome in the spring we find tlie vegetative buds growing vertically upwards under the top soil or moss and ready for sprouting. At this period it can easily be seen that all of the buds have their scales Fig. 58. Scheme to illustrate the relation between external conditions and anom- aly. Shifting of the apex of the curve. A, the effect of high nutrition ; B, the effect of unfavorable conditions. The (a) and (b) curves illustrate the dis- position of the leaves of the stems of Lysimachia vulgaris ; a, after high, b, after low nutrition. (See the figures on page 314.) Fig. 59. Lysimachia vulga- ris. Rhizome buds which would develop into stems. A, thick, with quaternary bud ; B, thin, with ternary whorls in the interior of the bud. The visible scales show a decussate arrangement in both cases. (For diagram see Fig. 57.) in a decussate arrangement at the lower end (Fig. 59), but within the bud the disposition of the leaves is different. In this region the structure is that which will be mani- fested by the growing stem in the summer. The thickness of the future stem is correlated with that of the upright subterranean shoot, and on it depends the disposition of the leaves. The weakest shoots have the leaves arranged in opposite pairs, the stronger ones in trimerous and the strongest of all in tetramerous 314 Nutrition and Selection, whorls. This character of the stem, which must be defi- nitely determined by microscopical examination, can, how- ever, be predicted with sufficient accuracy by the thick- ness of the shoot. Of course, the same relation obtains in the summer when the contrast strikes the eye far more forcibly, and then we see that the lateral branches of ternary and quaternary stems have almost without ex- ception decussate leaves, obviously because they are the weakest of all. If the plant is taken into cultivation it is easy to mod- ify the proportions of the various sorts of stems by suit- able treatment, although vegetative methods of propaga- tion alone are employed ; but it must be remembered that the buds for the following year are already completely laid down in October, and that the disposition of their leaves is therefore finally decided at that time. The ac- tual disposition in any given year is therefore deter- mined by external conditions which prevailed in the pre- vious year. The curves in Fig. 58 are plotted from observations which gave the following results. In March 1890, 1 planted out a group of rhizomes in a favorable position in my garden, and in June I noted the two-, three- and four- whorled stems, which therefore had been laid down under the influence of the unfavorable conditions which ob- tained in 1899. In the following summer I repeated the observations and thus formed an estimate of the efTect of growth under more favorable circumstances (better soil and more light). The results were: RECORDS FOR WHORLS 2- 3- 4-MEROUS TOTALS Summer, 1890 35 21 2 58 1891 17 40 10 67 The apex is seen to be shifted from stems with oppo- External Conditions and Manuring. 315 site leaves to stems with trimeroiis whorls (Fig. 58 /; and a)- The arrow A in I^ig. 58 iiidicates the result of im- proved conditions, the arrow B that of more unfavoraljle ones. The figure therefore not only illustrates a particular case Imt is a graphic representation of our thesis that high nutrition favors the production of the anomaly. This scheme can be applied to a long series of cases, both of anomalies that occur in the field and of highly variable horticultural varieties. The best known example is furnished by the tricolored pansy Viola tricolor ma- xima. Here, as every gardener knows, the spring and early summer flowers have larger, much broader and more intensely colored petals than those of late summer.-^ The greater drought and the gradual exhaustion of ma- nure around the plants are the causes. The same general- ization applies to numerous cases to some of which we will refer in the following section. § 27. THE INFLUENCE OF EXTERNAL CONDITIONS AND OF MANURING. J. CosTANTiN has dealt with the relation between the plant and its environment in a book devoted to this ques- tion.- In it he treats of the influence of the environment both on the normal characters of the plant and also on varieties and anomalies. An immense range of facts and observations is thus made accessible to the student. ^V. B. WiTTROCK, Viola-Studier, Acta Horti Bergiani, Vol. II, 1897, Nos. I and 2. See also Verlot, loc. cit., pp. 46-47. "J. CosTANTiN, Les vcgctaux ct Ics milieux cosniiqucs. Bibl. scientif. Internationale, 1898. The earlier writings of tiiis author have been dealt with in our first volume (p. 99). 316 Nutrition and Selection. \\'e shall here confine ourselves to true anomalies, that is, to semi-latent characters,^ and will start with some instances of plants which are propagated vegeta- tively. First let us look at the continued growth at the top of the inflorescence of the white clover (Fig. 60), an anomaly which is fairly rare in this region, but which has been intensified considerably by favorable cultivation in my garden. Fig. 60 affords instances of this anomaly selected from a vast number of available cases.^ Elonga- tion of an inflorescence into an ear-shaped peduncle, pro- liferation or formation of two inflorescences, one above the other, on the same stem, and the appearance of small clusters in the place of the individual flowers accompanied by an increase of the bracts are some of the more impor- tant instances. In the summer of 1890 I found near Hilversum a specimen which bore a single flower on the elongated axis of one of its inflorescences. I transplanted it to my garden, sowed the seeds in the following year and obtained a few "perumbellate" inflorescences. Again I collected the best seeds and sowed them in 1891. When the plants flowered about 2% of the several thousands of inflorescences had proliferated, most of them belonged to the type shown in Fig. 60 B, others to the rarer types A, C and D. T then selected the best plant, isolated it completely, and made certain that all the branches really belonged to it. After this I divided it, planted out the ])arts, and let them grow as strong as possible. In this ^ The methods of cultivation suitable for producing pure white flowers on colored varieties of Syn'nga in winter, and the well-known blue coloration in the Horfensias are widely different. (See Verlot, he. cit., pp. 60-61). ^ The anomalies in question have long since been dealt with in the literature of the subject, and have been collated by Penzig, in Teratologie, I, p. 387. External Conditions and Manuriiig. 317 way I filled two beds of about two square meters each in the summer of 1892. They gave a very characteristic half curve when the inflorescences were plotted according to the number of flowers on that part of the axis which had proliferated. These numbers varied from 0 to 10 and were distributed as follows (August 1892) : NUMBER OF FLOWERS ON THE PROLONGATION OF THE AXIS Inflorescences 0123456789 On the 1st bed 325 83 66 51 36 36 18 7 6 1 " " 2nd bed 403 97 62 35 46 20 20 14 11 3 0 11 Totals 1 0 630 2 1 721 Fig. 6o. Trifolium repens perumhellatum. Four different inflorescences from the same culture, 1891. A, with thick continuation of the main axis ; B, the continuation thin and sparsely covered with flowers ; C and D, with three- fold continuation. We see that one-half of the inflorescences on this plant had proliferated this time, partly as the result of selection, partly on account of improved cultivation. Most 318 Xutrition and Selection. of the perumbellate inflorescences appeared in July. Be- fore July there were 21%, in July 47%, in August 38%, and tliis last record was made on over 500 inflorescences. I contini^ed the experiment by planting out some of the creeping stems of this plant into two other beds, of which one consisted of good garden soil, the other of dry sandy soil. In this year under less favorable conditions of growth, the proportion of anomalies was less . Amongst about 300 inflorescences in each bed 6% had elongated on the sand bed and 12% on the control bed. On the former the plants were small, their leaves being smaller and paler and less numerous than the normal. This experiment shows that the proportion of anom- alous inflorescences is to a very large extent determined by external conditions even when the method of propa- gation is purely vegetative. In the literature of this subject we sometimes come across the view that anomalies are favored by improved external conditions because more nutriment is necessary for their development, and the fasciations, and the multi- plication of the number of leaves, leaflets, etc., are given as instances. As a matter of fact even when the anom- aly consists in a reduction of parts the same relation ob- tains. This is shown by the second instance that I shall give. This is Potcntilla anscrina, of which I found some plants with occasional tetramerous flowers near Hilver- sum in 1889 among the ordinary pentamerous ones. I planted them out and divided them, and in the summer of 1891 I selected the best specimens and made sure that all the runners were still organically connected. In 1892 I planted out one-half of tliis on a manured bed and the other half on an unmanured bed adjacent to it. From the middle of July to the beginning of August, External Conditions and Manurinij. 319 I counted the sepals of all the flowers. There were about 2500 on the manured bed, and about 1500 on the un- manured. Amongst them were many with five and f(jur sepals, and about 20 with 3, but none with fewer tiian 3 or more than 5. Here again, a pronounced half curve was the result. I have reckoned together the i)roportion of 3-4-merous flowers for the individual counts, and at each stage in the counting collected all the flowers wliich had opened since the preceding one. The counts were made when possible every fourth day, or, when the num- ber of flowers was too small, at greater intervals. The result was as follows : PROPORTION OF 3-4-MEROUS FLOWERS IN %. June July Augus. Day: 19 23 27 15 9 13 17 21 25 29 2 Manured: 7 13 24 28 34 39 50 65 49 49 43 27 % Unmanured: — — 7 — 20 33 39 — 42 49 46 44 % We see that the proportion of anomalies increased on both beds gradually throughout the summer, reached its maximum in the second half of July, and then sank again. On the manured bed, however, this proportion amounted to 65% of the whole and on the unmanured bed to 49% of the flowers counted (160 and 224 flowers in the two cases respectively). In this case, therefore, both the periodicity and the relation to the external con- ditions are in all essentials the same as in the case of the wliite clover. In this latter case a plant which T had raised from seed served as material; but in tliat of PotcntiUa a specimen which T liad collected in tlie fleld. I shall now deal as briefly as possible with a series of further instances, emphasizing as before that the ex- ternal influences have the results in question only when the particular cliaracters are already present in the semi- 320 Nutrition and Selection. latent condition. On completely latent characters no effect can be produced; we are dealing solely with half and intermediate races. '*In other specimens, however, this is obviously not the case," says Goebel, ''they retain their normal form even when grown in rich soil ; the high nutrition operates on the malformation, not as a cause, but as a releasing factor."^ It is a familiar fact that many garden plants de- teriorate if they are allowed to remain for a long time in the same place. They exhaust the soil and must, therefore, be moved from time to time. This is true, for instance, of Pansies, Anemones,- Dahlias, Petunias,'^ the crested forms of many ferns^ and so on. Morren planted out a specimen of Saxifraga decipiens which had hitherto borne normal flowers on stony ground, into good garden soil. In this it grew very vigorously, formed larger flowers than before, and manifested at first a slight transformation of its stamens into petals which, however, increased gradually during the course of the summer until ultimately the flowers became entirely double.'^ In Hedychinni coronariuni the structure of the flowers is also shown to be dependent on nutrition.^ Wild apples and medlars lose their thorns in a few years if they are transplanted to gardens, '^ and Carlina acaulis becomes the so-called Var. canlcscens, in rich soil, a fact which has already been recorded by Wolff in his Theo- ' K. GoEBEL, Or^anographie, I, p. 159. Various instances are also given by Burkill, Journ. Linn. Soc. Bot., Vol. XXXI, 1895, pp. 2i8fif. ■ Vilmorin-Andrieux, Les fleurs de pleine terre, p. 87. ^HiLDEBRAND, Bcv. d. d. hot. Gcs., Vol. XIV, 1896, p. 327. *L6wE, cited by Goebel, loc. cit. ''Bull. Acad. R. Bdg., Vol. XVII, Pt. T, p. 424. •^ Fr. Muller, Flora, 1889, Pt. Ill, pp. 34''^-352, PL 16. ' De Canpolle, Physiblogie vcgctalc, II, p. 721. External Conditions and Manuvinij, 321 ria gcncrationis. The branching of the ears of Triticuni tiirgiduni coniposititni (Vol. I, p. 125) and the carpello- niania of Papavcr soninifcruni (Vol. I, p. 138) are to a very large extent dependent on external conditions. Double poppies become almost single under unfa\oraljle conditions; I have observed this in Papavcr soninifcruni naniini album in my own cultures. Again the doulJe Saponaria officinalis plena seems to become single after transplantation, but subsequently to regain its double character.^ The ordinary Saponaria officinalis often forms hexamerous flowers in this neighborhood. These were, however, more numerous in my cultures under good than under bad treatment. The studies of Pey- RiTSCH on the influence of the cutting down of wood- bands on peloric varieties has already been referred to (§21, p. 225). On a lime tree in the vicinity of Baarn pitchers are produced every year; but I always found them on the open sunny side and never in parts of the tree where the branches were shaded by neighboring trees. The color is also well known to be very dependent on external conditions. Achillea Mille folium rosea will only form its fine red inflorescences in a sunny position; if this is shaded the color is pale or absent, as I have myself often observed. Inflorescences grown in the dark re- main quite white, even when they would otherwise have been red. The same is true of Begonia semperflorcns atropiirpiirea J'^ernon, whose brown red foliage cannot, so to speak, stand the smallest amount of shadow. In this case I have succeeded in making some plants almost quite green Iw shading them during tlicir }-<>uth. The * MuNTTNC, JVaarc Ocffniinficii dcr Planfni, 1671, p. 5fN'>. Al^;o In my garden. 322 Nutrition and Selection. color of Aiiiarantiis tricolor, the variety of whose color is its only claim to popularity, is dependent on external conditions.^ Zca Mays forms more bi-sexual panicles and ears when the seed has germinated at a high temperature. Ranunculus bulbosus scniiplcnus (§ 22>y p. 258) forms more petals if it germinates in the summer than if it germinates in spring. Summer wheat can, as is well known, be transformed into winter wheat by sowing it in autumn, although, as it appears, only in a small pro- ])ortion of individuals.- Amongst the cultivated Begonias we sometimes find bi-sexual flowers which are the result of the appearance of stamens in female flowers; in them the inferior fruits become more or less completely superior and other anom- alies make their appearance.'^ For the last 12 years I have grown such a specimen of Begonia Sedcni (B. boli- viensis X B. Pcarcci) which I have gradually multiplied by dividing its tubers. In the summer of 1890 I marked the tubers which produced the smallest numbers of such transformed flowers and planted them out in 1891 into a bed which was more richly manured and better situated than the rest. As a result of this they produced a con- siderably larger number of anomalous flowers than the control specimens. Lnpinus lutens sometimes produces twisted inflorescences.^ Seeds of such flowers collected in the field and sown in the garden did not repeat the anomaly ; but in the next generation it reappeared as the * Vilmorin-Andrieux, Lcs fleurs de pleine terre, p. 64. ^ MoNNiER, cited by Darwin^ Variations, I, p. 333. ^ P. Magnus, Sitzher. d. hot. Ver. d. Prov. Brandenburg, XXVI, 1884, p. 72, Table II, and Penzig, Teratologie, I, p. 500. * Monographic der Zwan^sdreJnin^cn, Jahrb. f. wiss. Bot., i8gi, Vol. xxiii, p. 107, PI. IX. The Fcriodicity of Scmi-Latcnt Characters. ol^ result of heavier manuring and better treatment (1890- 1892). Of a kindred nature, proljaljly, is the well-known fact that anomalies are more abundant in certain years than in others. Munting records this for Liliiiin criien- iiiui plciiinn'^ a.nd KiCKX for pitchers, of which there was in the neighborhood of Gent, in Belgium, something like an epidemic in 1848 in the tobacco fields, and in 1851 in Rosa Gallica and Rosa centifolia? In the neighbor- hood of Freiburg there was an extraordinary abundance of floral malformations in the summer of 1866.'"' In France the hot and dry summer of 1893 brought out a large number of these, and Gagnepain records a long series of anomalies which he observed at that time."^ The year 1845 was a great year for peloric Calceolarias, 1862 for central umbels in Auricula (in England). For ten years I have observed the formation of pitchers in Mag- nolia ohovata and that of hermaphrodite flowers in Salix aurita. In both these cases the frequency varied greatly with the year, although the specimens which were exam- ined closely every year, were growing in our garden. I sliall not extend this list which the reader may easily c(3mplete either by personal observations or from the alnindant literature on the subject. § 28. THE PERTODTCTTY OE SEAII-LATENT CHARACTERS. The immediate external conditions which obtain dur- ing the susceptible period of develoj^mcnt do not consti- tute the sole factor which determines the greater or less ^Hunting, loc. cif., p. 501. 'J. KiCKX, Bull. Acad. Roy. Bclgiquc, Vol. XVHI, Pt. I, p. 591. ' HiLDERKAND. Bot. ZcitUUg, 1866, p. 239. * Bull. Soc. Bot. France, Vol. XL, 1893, pp. 309-312. 324 Nutrition and Selection. visible development of semi-latent characters. Of almost equal inii)cjrtance is the individual strength of the young- plant, which, however, is the result of the operation of external factors during preceding periods of time, which may be weeks or months or even years. The stronger a bud is, the more is it liable to produce anomalies. This phenomenon is most clearly seen in the periodic- ity of the manifestation of anomalies by the same plant, and in the parallel between this manifestation and the gradual increase and subsequent decline in strength, either of the whole individual or of the succeeding orders of its branches.-^ This periodicity has been exhaustively studied in the five-leaved clover, and we have become familiar with instances of it in several other species. It remains now therefore to examine the nature of this process from a more general point of view. For this let us select a concrete instance. In gardens a double form of Chelidonhini majus is often found in which, as a rule, the doubling is only slight, and seldom consists in the production of more than 16-20 petals per flower (Fig. 61). On the plants in my cultures this doubling regularly increases from the spring until the summer, both on the main stems of plants in their first year and on the lateral stems of plants that have been wintered. For instance in May all the flow- ers were single, i. e., with four petals (Fig. 61 A). With June the number began to increase, and many flowers with 6 and 7 and occasional ones with as many as 10 petals occurred : whilst in the second half of June the majority had 12 to 14 and some 15 and 16 petals. Every year * Over hct pcriodlsch opfredcn dcr anomaJicn of> movsfrcuce planten. Bot. Jaarb., Gent, Vol. XI, 1899, p. 46, and Ucber die Pcrio- dicitdf der partiellen Variationen, Ber. d. d. bot. Ges., Vol. XVII, 1899, p. 45. * The Periodicity of Semi-Latent Characters. 325 the doubling was seen to increase in intensity in the same way. Braun, in his great work on the rejuvenescence of plants, has discussed the part played by periodicity in normal development with great thoroughness and clear- ness.^ In the whole plant and also in the sej^arate orders of branches the vigor of life goes up and down. The in- Fig. 6i. Chelidonium ma jus plenum. A, a normal flower with four petals ; B and C, flowers with five petals ; D, a flower with eight well-developed petals and two petaloid stamens. 1-5, the transition between stamens and petals. dividual strength of the plant is perpetually fluctuating, affecting the size of the leaves, the length and thickness of the internodes, the number of leaflets in compound leaves, the number of rays in the umbels, the ramifica- tions in the inflorescences, the number of florets in the ^A. Braun, Verjiingiing, pp. 23-55. 75-76. 90 etc. See further: Heinricher. Biolog. Ccntralhlatt, Vol. XVI. No. i. pp. 13-14. Po- KORNY, Sitcbcr. d. Acad. d. Wiss., Vienna, 1875, Vol. 72, pp. 527-547. 326 Nutrition and Selection. flowerheads of composites, and so forth. Every shoot has its cycle. It begins with simple or atavistic forms, then gradually manifests the characters which are pecu- liar to the species in their full development, and gradually reverts. From the primary shoot this cycle is transmitted to the secondary shoots and from these to the branches of still higher orders. In this process the latter may become stronger or weaker in comparison with the main shoot, or even of equal strength. As a rule the branches are weaker than the main shoot ; those which are not fall into two categories according to Braun^ strengthened shoots and repeating shoots {Erstarkungssprosse and Wiedcrlwlungssprossc).^ Spikes and racemes are the best known instances of weakened shoots ; their apical flowers, if such are present, are in advance of all the rest in their development as for instance in the peloric Digitalis. In the red clover the main shoot consists of a short upright rhizome, whereas the lateral branches gradually increase in strength and develop into flowering- stems. In Tctragonia cxpansa the main shoot is always short and erect, terminating with a flower. The secon- dary shoots often grow to more than a meter in length and are much stronger. Instances of strengthening shoots are the lateral branches which arise from the axils of the radical leaves of many plants (Ranunculns bulbosus), or from the middle part of the stem (Chry- santlicnnim scgctuin and Trifolinni incarnatum) ; also the forked inflorescences as in Saponaria officinalis. Re- ]:>eating shoots are often runners, and then we have what Braun calls ^'repetitional generations," as in Valeriana officinalis, LysiniacJiia vulgaris, etc. See § 22,, p. 256. The Periodicity of Semi-Latent Characters. 327 Space does not permit the extension of this hst;^ moreover all I am concerned with here is to show that this scheme also holds good for the distribution of anom- alies on the plant. Unfortunately it often can not be exactly applied because it is complicated with the effect of external influences. Every shoot and system of branches has its susceptible period, during which the external factors which happen to prevail favor the pro- duction of the anomaly, or the type of the species, ac- cording to their nature. But apart from these numerous fluctuations the rule holds good wdiere the material is suf^ciently plentiful to justify the neglect of exceptions. In a culture of Specularia Speculum which I had in 1892 I found the flowers to be partly tetramerous and partly pentamerous. The pentamerous ones occurred at the top of the stem and of the strongest branches of the second order, whilst all the remaining flowers were tetramerous. A similar difference between apical and lateral flowers is exhibited as a normal character by Adoxa Moschatellina and by many other plants. The Pimis sylvestris of this neighborhood often has its needles combined into groups of three instead of groups of two. Each such group of needles, as is well known, belongs to a single dwarf shoot or spur. I found that the tri- foliate spurs occurred almost exclusively on the stronger branches, and chiefly at their upper Q\\i\ ; but where they did occur they were numerous and closely, packed. As a rule it is the main stem itself which bears them, but sometimes the strongest branches do so as well. 11iere occurred up to 15 trifoliate spurs on the same one year's growth of the stem, all close to the a])cx. mixed with ^ On tlie question of periodicity in the branching of cereals see ScHRiBAi'x in Journal d' Agriculture pratique, 1800. and Rimpau in Laiidzi'irthsch. Jahrbiichcr, Vol. XXIX. p. 589. 328 Nutrition and Selection. numerous bifoliate ones. Pimis Pinaster exhibits the same phenomenon. In different years the frequency of its occurrence varies greatly. Camellia japonica with striped flowers, is striped mainly in November and December; but if it flowers in April, it produces only self-colored ones.-^ A form of Trifoliiuii repcns produced pitchers in my garden al- most every year in no inconsiderable numbers and in great variety of forms. But they never occurred except in the spring;- just as the lime bears its pitchers chiefly on the first leaves of the branches and Saxifraga crassi- folia on the lower abbreviated and leafy part of the flower peduncle.^ Ulniiis caiiipestris, on the other hand, forms its pitchers chiefly from the strongest leaves in the middle and upper part of the branches. It is in this middle region of the branches that anom- alies are most commonly found, either exclusively or chiefly. Thus Fritz Muller describes a Begonia from Brazil, of the height of a man, which bore little append- ages at the base of the leaf blade, ^ which were usually not more than 1-3, and sometimes from 5-50 mm. long. Thev were onlv found on the fourth to the tenth leaf, in one case from the second to the fifth leaf, of the upright stem ; and occurred at the same height on every anom- alous stem, both in the garden and in the field. In May 1890 I observed a group of Epilobium hir- sutiiin, the numerous and still young stems of which were for the most part forked. These divisions occurred always about the same height and did not recur during ^Verlot, loc. fit., p. 67. J. C. CosTE'^us, Bekertjes aan de eindhlaadjes van Trifolium repens. Botan. Jaarboek, Gent, 1892, p. 13, PI. I. ^T. Tammes, Kon. Akad. d. Wetensch., Amsterdam, 1903. * Fr. Muller, Ber. d. d. Ges., Vol. V, p. 44. The Periodicity of Semi-Latent Characters. 329 the course of the summer. They were spHt fasciations, but the division had gone somewhat deeper, as was vis- ible by the individual leaves being torn from below up- wards with one half adhering to the one arm of the fork and the other half inserted on the other arm. Such leaves occurred on several shoots, but, as already stated, always at the same height on the plant. The lower end of many racemose inflorescences is a favorite place for anomalies. Thus slightly double varieties of Gladiolus bear double flowers almost always in this position only. The racemes of Primus Padiis bear lateral racemes in this position almost exclusively; and, in other cases, it is also only in this position that tetramerous flowers are borne. Many double varieties are known to bear single flowers at the end of the flow- ering period, and sometimes also at the beginning. These flowers alone set seed, while the double ones are sterile. It is well known amongst horticulturists that in multi- plying perennials and bulbs by seed, the value of the plants cannot definitely be estimated in the first year in which they flower. It is not until the second or the third year of the flowering that their qualities are dis- played to their full advantage. Many specimens of Chrysantheimun indicwn, which when raised from seed, are only half double in the first year, will develop double flowers in the second year if grown from cuttings.^ The varieties with tricolored leaves of Pelargonium ::onale tricolor do not exhibit their full range of color until the second year after their seed is sown.- To breeders of tulips, hyacinths and other bulbous plants this rule is well known. *Reid and Bornemann*3 Catalogue, 1891, p. 20. Sutton's Catalogue, 1891, p. 77. 330 Nutrition and Selection. The rule for ordinary branching is that the anomaly diminishes with the higher orders of branching, omitting from consideration, of course, the strengthening and repetitional shoots. Every one knows the beautiful case of Myosotis azorica Victoria {M. alpestris var.), Avhich has been on the market for many years, and was de- scribed bv ]\1 AGNUS. -^ This heritable anomaly has a verv much extended flower at the top of its main axis, often consisting of more than 10 and sometimes over 20 petals in one row. The number of sepals and stamens has cor- respondingly increased. The subsequent flowers of the inflorescence have become much less compound and the number of petals gradually diminishes during the course of the flowering period, until finally only pentamerous and hexamerous flowers are produced. Chrysantheniuni inodoriini plenissiniiiin manifests a similar periodicity, and the number of petals in Ficaria ranunculoides and Ccntaurea Cyanus are in the same manner dependent on the order of branching.- Veronica Biixbawnii, according to Bateson and Pertz, bears the largest number of anomalous flowers at the beginning of the flowering pe- riod, that is to say, just before it is at its height.^ il/v<^- surus niijiinius bears the more single flowers the w^eaker these are.^ A number of similar cases have already been ccjllected by Munting in the seventeenth century, and recently by Burkill amongst others.'"* ^ Verhandl. d. Bot. Ver. d. Prov. Brandenburg, XXIV, 1882, p. 119, PI IV. "J. Mac Leod, Botanisch Jaabock, Gent, 1899, Vol. XI. ^\y. Bateson and Miss Pertz, Notes on the Inherilonee of Vari- ation in the Corolla of Veronica Biixbaumii, Proceed. Cambridge Phil. Soc, X, Part 2, p. 78 (1898). *H. MiJLLER, Nature, Vol. XXVI, 1882, p. 81. ^ A. Munting, Waare oeffeninge, 1671 ; J. IT. Burkill, Linnaean Soc. Journ. Bot., Vol. XXXI, 1895. p. 216. The Periodicity of Semi-Latent Characters. iM Tagetes africana and T. signata often first exhibit single flowerheads only, but subsequently double ones in increasing numbers on the same plants. The same thing can be seen in Zinnia elegans, and in Althaea rosea the flowers are sometimes seen to become more double as we proceed up the stem. Weak lateral buds in variable races often exhibit a special tendency to atavistic variations. This is true of the branches of the highest orders, of the accessory shoots, which are formed in addition to the normal axil- lary bud, of resting buds, etc. But it should be remem- bered that it is just these buds which often develop into very strong branches and become the succulent shoots which tend to reproduce the anomaly rather than the specific type. I have already referred to this exception above. CapscllaHeegeri, the new species described by Solms/ produces reversions to C. Bursa pastoris on its weak lat- eral branches and, according to the same author, the same phenomenon is exhibited by those varieties of Nas- turtium palustre which have been lumped together into the genus Tetrapoma. Papaver somnifernm polycepha- him produces flowers without any accessory carpel almost exclusively on the very weak branches which arise from the main stem towards the end of the year when the lateral branches have been cut away. The peloric flowers of Digitalis purpurea are monstrously developed at the apex of the stem and on the strongest lateral branches ; but on the weaker ones they are simple and very regular (Fig. 42, p. 223). Such buds can often be induced to develop by cutting ^ H. Graf zu Solms-Laubach, Crucifcrcnstudicn. Botan. Zci- tnns:, 1900, Pt. X, p. 167. 332 Nutrition and Selection. down the main stem; and by this means we can often obtain the desired variations, as Goebel has shown, unless the anomaly is too much favored by a very vig- orous growth. § 29. THE CHOICE OF SEEDS IN SELECTION. From the periodical changes in the tendency of the plant to produce anomalies, we might expect a corre- sponding periodicity in the seeds. ^ The seeds of flowers which have bloomed under favorable circumstances should produce more anomalous individuals, those of the weaker branches, on the other hand, more atavistic ones. This expectation, however, is only to a slight extent fulfilled, and the latent capacity of the seeds seems to be regulated much more by factors other than those determining the periodicity of the parent plant. Our knowledge of this subject is, however, still in its infancy. Nevertheless there is a whole series of facts which are worth collating because they are likely to serve as a stimulus to further investigation. In doing so, it should be emphasized that in the selection of seeds we are con- cerned with variability and not with mutability, and in most cases, in fact, with the extreme fluctuating varia- bility of semi-latent characters. It is only a strong, well-developed seed, furnished with a healthy germ and richly supplied with food mate- rial that can give rise to the very strongest plant in a healthy culture. Doubtless, of course, the differences between the individual seeds are to a large extent levelled down during the first weeks after sowing; but this is not always the case. Obviously the most favorable condi- ^ C. Fruwtrth, Die Ziichfung dcr JandzvirthschaftUchen Ciiltur- t^Hanacn, 1901, p. 102. The Choice of Seeds in Selection. 333 tions can only give the best possible result when they are combined with the highest germinal capacity. For this reason in agricultural practice and occasion- ally also in horticulture special attention is often paid to the individual seed. The points to which attention is paid are, on the one hand, the size and weight of the individual seeds and, on the other, the place of their origin on the parent plant. The practice of selection in cereals consists essentiallv in the choice of the larjjest and heaviest seeds, or more strictly, in the elimina- tion of the smaller ones by winnowing machines or other devices.^ When the object is to produce small families to serve as the stocks of new races, meas- urement and weig-hin"- of the individual seeds is rec- ommended by the best authorities, and special trays for determiningtheir A ff weight have been devised.- Fig. 62. Clumps of fruits of the sugar beet ; half schematic. A, two ripe chnnps on a stem ; B, one of these cut longitudinally show- ing the three seeds in the three special fruits.^ An important advance in the method of selection has been made in recent years by Van de Velde who ^ See Von Rumker, Getreidccuclifung, 1889, and Von Rumker, Dcr wirthschaftliche Mchnvcrth gutcr Culturvarictiitcu unci ausgc- Icsenen Saatgutes, Arbeiten der D. Landw. Gesellsch., 1898. Pt. '36, p. 127. "VoN RiJMKER, Joiirn. fiir Landwirthschaft, 39. Jahrg., Pt. 2, p. 129. ^The specimens from which this drawing was made T owe to the kindness of Messrs. Kuhn & Co., beet seedsmen in Naarden, Holland. They were taken from selected beets of the very high 334 Xufritioii ami Selection. has studied the relation between the size of the seeds and rapidity of germination.^ As a rule the larger seeds germinate faster than the smaller ones; and thus their weight favors the production of strong plants in more than one way. Moreover, as has long been know^n, tlie seeds which germinate the first are the best and produce the finest plants. When harvesting of flower seeds has to be done in the field, the first seeds often fall out before tlie harvest ; they germinate easily and usually do so at once ; and we all know that from such seeds the finest specimens may be produced. In fact for certain definite species the handbooks recommend the practice of allow- ing them to sow themselves, since this self-sow^ing leads to much better results than are obtained even from seed carefully harvested at the proper time. The question as to where the best seeds occur on the ])lant is one that has been much discussed. Let us con- sider the sugar beet as our first instance. In this species 2-5 or more fruits are associated to form a so-called clump (Fig. 62), in which the upper flower produces the larg- est seed Fig. 62 b) ; whilst tlie lateral seeds of the same clump are less fine and markedly smaller and differ amongst themselves very much in size.^ This phenom- enon has been recently subjected by Briem to an exhaus- tive investigation.^ He sowed the clumps, and planted out their individual seedlings separately in a row. In percentage value of from 18.9 to 20.1% of sugar, and with roots weighing 900-1100 grams. ^Van de Velde, Invlocd van dc grootte der caden op dc kiniiiiig. Botanisch Jaarb. Gent, 1898, pp. 109-131. ' Kriinungsgeschichfr dcr Zurkcrri'ihc, Landw. Jalirb.. VTTT, 1R70, P- 14, ' H. Brtem. Sludicu i'lhcr Saincnri'ihcn, clncm Riibcnknauc} cnf- stammcnd. Oestcrr.-Ungar. Zeitsclir. f. Zuckerindustrie und Land- wirthsch., 1900, Pts. TT, TV, and W. The Choice of Seeds in Selection. 335 this way the plantlets derived from a single clump c(juld he compared with one another throughout the wliolc course of their development. The largest seed becomes the largest seedling which produces the finest beet, and lastly the most fertile seed-parent. The relative weights of the five seedlings of a clump at the end of germination were as follows: 100 — 7A — 67 — 51 — 46. The heaviest seedling weighed 5.8 milligrams. The full-grown beets derived from a single clump weighed in one case 1156, 859, 574, 344, 310 grams, and they furnished respectively 241, 167, 202, 239, 104 grams of seed at the end of their second year. E. ScHAAF considers a very important advantage of the so-called "cutting"-culture in beets to be the exclusive development of the largest seed of each clump which is effected by the close proximity of the plants during the production of the clumps.^ Amongst cereals the matter has been most thoroughly investigated and I refer the reader to the literature on the subject which I have already cited. Tlie heaviest grains are situated at the middle or somewhat below the middle of the ear. Fruwirth showed this to be true for barley, rye, wheat, spelt, and also for maize.- There l)roved to be certain subordinate differences characteristic of the various varieties and species.'^ Bruyning found that in oats the low^er grains of the lateral ears are far ^ E. ScHAAF, Blatter fur Zuckerriibcnbau, Jahrg. VTT. No. 24, Dec. 1900. ■ C. Fruwirth, Uehcr den Sltz des sehiversten Korues in den Fruelifsflinden heim Getreide, in Wollnv's lM-)rschun.u:cii auf deni Gebicte der Agric.-Physik, XV, 1892, p. 49. " E. NoTHWANG, Unters. i'lher die J^ertheihinv d. Korner(^e:i.'ieIifes an Roggendhren, Diss., Leipsic, 1893; Bot. CcntralblaU. 189s, II. p. 263. 336 Nutrition and Selection. better than the upper ones/ and the same is true of other species of cereals. Lastly some reference should be made to those cases in which individual seeds possess the peculiarity of germinating late, and of remaining one or more years in the soil, as for instance the small seeds of various species of clover. In Xanthium canadcnsc each fruit contains two seeds, one of which germinates after the first win- ter, the other not until after the second.- \Mien we are dealing with semi-latent or, in general, with highly variable characters, a selection of seeds either by their size and weight or by their place of origin on the plant is to be recommended in many cases, and the general rule seems to be that the place of origin of the best seeds will also be that of the desired variants. There are some cases in which this rule does not apply, such as we have seen in Trifoliwn incarnatuin, where it is the smallest late germinating seeds wdiich contain the best representatives of the four-leaved half race. In Chelidoniuni majns plcmim the single flowers bloom first, and the double ones later, as we have seen in the preceding section (§ 28). I have harvested the seeds of both and sown them separately; but found no difference in respect of the doubling amongst the off- spring. Bateson and Miss Pertz'^ also failed to find any difference in respect of doubling amongst the off- spring of nomial and abnormal flowers of the same plant with Veronica Buxhaumii. In Oenothera Lamarck- iana I found about the same percentage of annual and ^ F. F. Bruyning, Proefnemingen met havervarieteitcn, Wage- ningen, 1900. ^T. C. Arthi'R, Proceedings Ann. Meeting Soc. Agric., Science. August, 1895. ' W. Bateson and Miss Pertz, loc. cit., p. 79. The Choice of Seeds in Selection. 337 biennial individuals from the upper and hjwer fruits of the same spike. In Viola tricolor maxima the small sum- mer iiowers furnish the main quantity of seed. It never occurs to a seed collector to regard them as of less value than the first seeds. In many double plants, especially in Begonia, it is practically only the flowers which bloom last that produce pollen and set seed. This seed is always sown without any detrimental result to the degree of doubling of the variety. On the other hand it is generally regarded as desirable to harvest the lower seeds of the inflorescence in the cox- comb, Celosia cristata ; and in the case of the crested spe- cies of ferns {Varictates cristatae) the spores which are found on the dissected leaves, and still more on the tips of such leaves, are regarded as the best, although spores found on the other parts of the leaves will certainly re- peat the anomaly.^ Another instance which has been studied by many investigators is furnished by the stocks, whose double varieties have been known for a very long time, for a century at least, to consist in each generation, of double and single plants in about equal numl^ers.- Tbe former are absolutely sterile, lacking pistils and pollen as a result of their petalomania (see Vol. I, p. 194), so that only the latter can play a part in the con- tinuation of the race. There are certain differences be- tween the seeds which produce the single and the double specimens. The latter are heavier and germinate more quickly,^ and the young plants can be sorted out in the ^ See the long list of references given by Goebel, Organo^raf^hic, I, p. 158; Verlot, loc. cit., p. 97; Carkiere, loc. cit., p. 67; Kencelv Rridgmann, Ann. Sc. nat., 4 Seric. Vol. XVI, p. 367; C. T. Druerv. Jonin. Roy. Hart. Soc, Vol. XII, III, 1890, p. 517, etc. " E. Chate Fils, Culture pratique des giroHees, Paris, Biblioth. de I'horticulteur praticien. ^NoBBE, Botan. Centralhlatt, Vol. XXXII, 1887, p. 253. 338 Nutrition mid Selection. beds long l^efore they exliibit l)iulsJ The lower pods on the main stem and on the principal branches as well as the lower two-thirds of each pod furnish on the average more double than single plants; the upper sec- tions of the pod and the pods of weaker branches yield more single ones. The proportion of double plants in the harvest can be increased to about 60% cither l^y lim- iting the production of seed by means of culture in pots, or by pruning; and in the best nurseries the finer sorts are usually subjected to this treatment. If the seeds are kept through some years the proportion of double seedlings gradually increases, because the mortality is greater amongst seeds that were destined to produce singles. It is stated that in the case of the Balsam and many other double flowered varieties the seeds are rounder and fuller and also smoother than those of the corre- sponding single sorts. The ''double" seeds of Petunia are said to germinate later than the single ones, so at least I have been told by nursery men at Erfurt. In the Composites the central seeds of the disc in double vari- eties are said to be more likely to repeat the anomaly than the marginal ones. All these statements should, however, be regarded critically, and many of them are in need of experimental confirmation. - Nevertheless the general rule is that the various seeds of a plant may give rise to offspring of widely different degrees of individual vigor, according to the place of their origin on the parent plant, their size and their ^ This process which is carried out by children is called csimplcr, in France. The matter stands in need of closer investigation, ^ Peyritsch has collected references to the earlier literature re- lating to this point. Ziir Aetiologie pclorischcr Bliithciibildiiiigcn, Abhandl. k. k. Akad. Wien, 1877, pp. 135-136. The Choice of Seeds in Selection. 339 weight ; and that, in accordance with the rules which we have ah'eady enunciated, a greater or less development of the varietal character is correlated with these degrees of strength. PART II. THE ORIGIN OF EVERSPORTING VARIETIES. I. TRICOTYLOUS RACES. § I. THE OCCURRENCE OF TRICOT YLS AS HALF RACES AND INTERMEDIATE RACES. In the chapter on latent and semi-latent characters in the first part of this volume, I have discussed the differ- ence between half races and intermediate races. It is not in the possession of certain elementary characters that they differ one from another ; in this respect they are identical. They possess exactly the same characters and in the same numbers. That feature, however, which constitutes the point of difference, is semi-latent in the half race, that is to say manifests itself only rarely and in occasional individuals, one in every thousand for in- stance. In the intermediate race, on the other hand, it is active and equivalent to the character to which in the half race it is, as it were, subordinate. Considered with regard to the features which distinguish them, both races, therefore, possess two elementary characters, which, how- ever, cannot be expressed simultaneously in the same organ but are mutually exclusive. In an ideal intermediate race, these two antagonistic characters would be of exactly equal value; that is to say, half of the individuals would exhibit the one. and the other half the other character. \\'hether such ideal races actually exist in nature is an open (|uestinn, since as a rule one of the two characters is more or less easilv 344 TricotyloHS Races. manifested than the other. ^Moreover those cases would have to be excluded in which either the conditions of life or some selection of the race could have exerted an influence in one direction or the other; for, as we have seen, intermediate races are very susceptible to both these groups of factors. Among the intermediate races known to me the tri- cotylous and syncotylous forms approach most closely this ideal picture.^ For, in pure cultures, they furnish as a rule 50% dicotylous and 50% tricotylous or syn- cotylous seedlings. By altering the conditions of growth as well as by selection this proportion can be easily and greatly modified in both directions, almost to the ex- clusion of one or other of the two types. But such treat- ment leaves the essential nature of the intermediate race untouched. It neither reverts to the half race when subjected to selection, nor is it possible to derive a con- stant and pure tricotylous variety from it.- As far as I know, there are hardly any references to tricotylous races in botanical literature, and the possi- bility of the existence of tricotylous intermediate races seems never to have been discussed. In this part, how- ever, I shall describe some instances of such races in order to demonstrate their existence and to study their characters. In the period from 1892 to 1897 I succeeded in producing such races from half a dozen very different species. I wanted also to include in this inquiry some pure tricotylous and pure dicotylous races, that is to say, races the seedlings of which were in the first case ex- clusively tricotylous and in the latter exclusively dicotyl- ^ See my preliminary note Ueber tricotyle Rassen in Ber. d. d. bot. Ges., 1902, Vol. XX, p. 45. ^ See the scheme on page 24. Tricotyls as Half Races and Intcruicdiatc Races. 345 Otis. But hitherto I have not discovered a single in- stance of the former, and have only obtained one in- stance of the latter.^ Before I proceed to a detailed description of my races and cultures it seems desirable to give a general account of the manner in which tricotylous seedlings are found, and how the desired half and intermediate races may be most easily derived from them. It is well known that amongst the seedlings of dicot- ylous species occasionally individuals are found with three seed leaves. It is only necessary to look over a seed-bed in the garden in spring in order to find in- stances of these. The more extensive the sowing and the more careful our search the greater \n'\\\ be the num- ber of tricotylous seedlings found. Some species pro- duce them in greater, oth- ers in smaller proportions ; and they can often be found even in the smaller pot-cultures of the greenhouse, but in many cases I have had to sow 10,000 or 20,000 seeds of a species before finding a single individual which showed any variation in this direction. But numerous species seem to produce one or several tricotyls in every hundred or thousand seedlings. Fig. 62,. Antiryhimim ma jus. A C, D, seedlings with 2, 3. and 4 cotyledons. B, with a deeply cleft cotyledon. * My Helianthus aninius syncofylcus has not produced a single tricotylous plant in the ten years during which 1 have often counted hundreds or even thousands of seedlings every year. On the other hand they occasionally occur in Helianthus auituus i-arirgalus and some other varieties of the sunflower. 346 Tricotyloiis Races. If the variants are rare, they are as a rule normal tricotyls; but if they are more numerous the type is usually seen to be varialjle both in the minus and in tlie plus direction. For convenience of expression we may regard a tricotylous seedling as having arisen Ijy the doubling of one of the two cotyledons of a dicotyledon by splitting, just as is so frequently observed in foliage leaves. Smaller degrees of the splitting would lead to variations in the niinus direction; but if the splitting affects both cotyledons there arise variations in the plus direction, which, if the doubling is complete, result in the origin of tetracotyls (Fig. 63 D). A seedling with one normal and one split seed-leaf is called a hemi- tricotyl •} one with two split seed-leaves, or with three of which one is split, is called a hemi-tetracotyl. In the same way hemi-pentacotyls, and so on, may be found ; but the deviations become rarer as they are more remote from the pure tricotylous type. If we make a collection of all these forms it is easy to construct a continuous series which extends from the pure type, on one side, through stages characterized by more or less deep fission, to the dicotyls ; and in the other direction in a similar manner to the tetracotyls and, if the material is extensive, even further, to the pentacotyls, and so on. Fig. 64 exhibits such a series derived from Oenothera hirfella, the unsplit seed-leaf of each plantlet being omitted. But obviously even here the forms fig- ured are only a selection from a much more complete series. If we imagine those cotyledons which have been cut off in these figures to be split also, the series would represent the transition from the tricotyls to the tetra- cotyls. ^Berirhfe d. d. hot. Gcs., 1894, Vol. XTT, p. 26. Tricotyls as Half Races and Intermediate Races. 347 A series of this kind is, however, a purely iiKjrpho- logical one and neither physiological nor statistical. If we wish to obtain this, we must not merely pay attention to the forms, but also to the frequency of their occur- rence. In doing so the first striking fact is that all the aberrant forms taken together, constitute only a very small percentage of the total number, even smaller some- times than the figures already given. Therefore, if we construct a frequency curve the dicotyls produce a high peak and the curve extends from this only in one direc- tion and is therefore a so-called half curve. ^ Further, amongst the aberrant forms themselves, the various forms occur in widely different proportions. The hemi-tricotyls are far rarer than the tricotyls ; the num- ber of all the hemi-tricotylous types together often does not amount to as much as that of the pure tricotyls. Deep clefts are somewhat less rare than shallow ones; and we often see specimens wdiich at first seem to be purely tricotylous but which, when the peduncles of the cotyledons gradually elongate, turn out to be deeply cleft. This is particularly evident in Amarantus spcciosiis and Antirrhinuin majus (Fig. 63 B), in which the closer juxtaposition of two of the cotyledons betrays the fact that they arise from a common stalk. Hemi-tetracotyls are always much rarer than tricotyls in sowings from commercial seed as w^ell as in selected races. Neverthe- less some species seem to be richer in them than others. If we plot such a frequency distribution we obtain a two-peaked curve which has a small secondary apex over the ordinate for the tricotyls, besides the main one for the dicotyls. Thus T found a crop of 800 seedlings of Cannabis sativa of 1894 to have the following com- ' See above, p. 26. 348 Tricotylous Races. position, tlie proportion of tricotyls (that is to say all the aberrant forms of the series) being about 10%. :OTYLS HEMITRIC. TRICOT. HEMI-TETR ACOTYLS AND TETRACOTYLS 726 24 46 4 90.8 3.0 5.7 0.5 Or in % If we wish to make ordinates for the various degrees of cleavage we are met by tlie difficulty presented by the choice of the limits of such arbitrary groups. This diffi- Fig. 64. Oenothera hirfella. Intermediate forms between the dicotylous seedling (A) and a tricotylous one (G). The normal cotyledon has been cut away from each plant. Cultivated in 1900. culty is partly due to the fact that the stalks of the cotyledons continue to grow for some time after the cotvledons themselves have assumed their definitive form. Tricotyls as Half Races and Intermediate Races. 349 But as a rule we find the general relations to be such as are exhibited in Figure 65. This curve has a form which is also commonly seen in other anomalies.-^ Whilst dicotyly is a character without variation tri- cotyly is one which exhibits a very high degree of fluc- tuation. The limit between dicotyls and the extreme minus variants of the tricotyls can always be easily and certainly observed ; because the apex of the cotyledon is the first part of it to assume its definitive form, and a cleft in this apex, however small, can be clearly seen. There is therefore no fear that the rarity of such ex- tremes might be due to im- perfect observation. The limits between the remaining smaller groups are blurred and arbitrary. But this dif- ficulty disappears in the eval- uation of the degree of in- heritance, because all the seedlings which exhibit cleav- age in one or both cotyledons are united into a single group and treated as tri- cotyls in the larger sense. I shall denote the dicotyl- ous seedlings of tliese races as atavists.- In the sowings ^ See Chapter TV of this part, and Sur Irs courhcs gaJtonicf.ucs dcs fiionsfruositrs, in tlie Bull. Scientif. dc la France et de la Bel- gique, published by A. Giard, Vol. XXVIl, 1896, p. 397. " See above, p. 104. 29. Die. Hemitricot. Trie. Tetraeot. Fig. 65. Schematic representa- tion of the fluctuating varia- bility of tricotyly. The tri- cotyls and the dicotyls con- stitute the two apexes, the hemi-tricotyls and tetracotyls (together with the hemi- tetracotyls) constitute the re- maining ordinates. 350 Tricotylous Races. of commercial seed the application of this term would not, of course, be justified; but in my cultures, which, almost without exception, were started by the selection of tricotylous individuals, this term is obviously fully justified. Moreover, in this way, the word dicotyl is left to its pure systematic signification. And, as in some other cases, atavism is here seen to be an oscillation be- tween two empirically known extremes.^ So far as my experience goes, tricotylous seedlings are much commoner amongst cultivated species than amongst wild ones, and even amongst the latter they usually occur from seeds saved in botanical gardens and ^'ery seldom from those collected in the field. Amongst cultivated plants, again, they are commoner amongst spe- cies which are grown on a large scale than on a small one. Thus I have obtained my intermediate races from amongst the former, partly from agricultural and partly from horticultural species. As an instance of the former I may mention the hemp and of the latter the snap-dragon and the wild poppy. But besides these I discovered a rich tricotylous race in my Oenothera hirtella, an entirely new species which was found quite by chance in my garden. It is not impossible that cultivation on a large scale favors the origin of new races. A profusion of instances of some anomaly in a species either in the field or in cultivation, suggests the presence of an intermediate racer a scarcity, however, that of a half race, as is especially well known to be true in the case of fasciations. Tricotyly conforms strictly to this rule. From seeds obtained from the trade or by exchange ^ See page io8. * See page 32. Tricotyls as Half Races and Intermediate Races. 351 we rarely get more than low percentages; but it is obvious that we should not expect all the seed-parents in the held to furnish the same number of tricotylous seedlings. Com- mercial seed is almost certain to be a mixture and to }'ield a mean proportion, which may perhaps be much lower than the seed of those specimens would yield. which were the richest in tricotylous offspring. It fol- lows from this that we can only form a proper estimate if we select a group of plants among our first sowing and harvest their seeds separately, if possible after tak- ing the precaution of preventing too much cross-fertili- zation by Insects. It is obvious that in such a culture a choice will have to be made, and as a rule the tricotyls, using this term in its widest sense, will be selected. From the separate harvest of these selected specimens, individ- ual hereditary coefficients may then be obtained. In spite of every precaution, the choice of the plants will depend mainly on chance, for, as we shall see later, tricotyls are by no means more likely to reproduce the anomaly than some of the dicotyls. On the contrary, plants much better in this respect sometimes occur among these: but we have at present no other means of dis- covering them except by growing their seed. Experience however has shown that if we allow a fairly large group to ripen their seed we may become independent of chance in so far that we can be fairly sure that at least some seedparents will give a relatively high proportion, pro- vided of course that the original mixture contains such amongst its components. It will soon be seen that in spite of all apparent intermediate degrees, two main groups can be distinguished. In one of them we find only low individual values, from 0 to 3%, or very little over; in the second, on the other liand. besides these 352 Tricotyloiis Races. some higher ones which not rarely attain a value of 10% to 20 % and in rare cases even of 30% to 40 %. Whenever the cultivation in the garden gives no ground for the assumption of special influences the differ- ence between the values derived from the original com- mercial samples of seed and the self -harvested seed of the first year must be attributed almost exclusively to the fact that the commercial seed was a mixture whilst the self -harvested crops matured in isolation. But since mixtures of this kind have been the rule during the gen- erations which preceded the purchase of the commercial, horticultural or agricultural, seeds, it is evident that those species which contain a number of rich seed-parents every year, will give a higher percentage of tricotyls in the mixture than others. Thus the percentage compo- sition of commercial seed gives some idea of what may be expected from it by subsequent culture. In the following sections (§§2-8) I shall describe my experiments on these two groups in detail. Here, however, I will give the main result. It is this: By far the largest number of spacies contain only a half race in respect to tricotyly, but some few also con- tain, besides this, the intermediate race. If the latter is present in commercial seed or in seed obtained by ex- change, it can be easily and speedily isolated; but if it is not present years of selection cannot bring it out. The half race and the intermediate race are, here as else- where, perfectly distinct things, which do not merge into one another, or if they do, they do so only by chance. Sometimes, but on the whole very seldom, an indi- cation of the likelihood of obtaining tricotylous inter- mediate races may be afforded in nurseries and in agri- culture. This consists in species with a decussate ar- Tricotyls as Half Races and Intermediate Races. 353 rangement of the leaves in the exhibition of trimerous whorls on the stems in the later life of the plant. I paid great attention to this point at the beginning of my ex- periments when I visited the great nurseries at Erfurt. Here the ternary individuals of Antirrhinum ma jus in the fields impressed me greatly. They were not con- sidered by the gardeners as worth any attention, but they formed the foundation for my first tricotylous inter- mediate race. The difference between tricotylous half and inter- mediate races lies in their percentage composition and not in the visible characters of the individuals. Neither the number nor the cleavage of the cotyledons on a single individual is decisive. As a rule tricotylous specimens of both races tend to produce a richer harvest of the tricotyls than the atavists of the same race; but expe- rience shows that the difference is only a small one ; and, further, that tricotyls, even those of a high productive ca- pacity, are often surpassed in this respect by some of their atavistic brethren. The chief point is, however, that both the half race and the intermediate race are composed of both types of individuals ; in the former the tricotyls are rare, whereas in the latter, under normal circumstances, both forms appear in about equal numbers. Moreover, both races contain all the stages of hemi-tricotyls, and, although these are rarer, of hemi-tetracotyls also. It is not possible, therefore, to tell from a single plant to which race it belongs. Only its ancestry can deter- mine this; and if this is unknown, we have to reach the decision by means of subsequent breeding. It is an ex- treme case of the transgressive variability which was discussed in the first volume.^ The forms composing a 'Vol. I, Part II, §25, pp. 430 ff. 354 Tricot\loiis Races. half race occur in the intermediate race also, and as a rule all of them in every sowing, provided it is not too small. On the other hand, if the half race is cultivated on a sufficiently large scale, it will contain all the forms of the intermediate race. There is no morphological limit between the two, although the physiological one is perfectly definite, and in my experiments has never been 15 ?0 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 1 0 1 2 1 1 6 9 10 7 16 13 13 15 3 1 0. Fig. 67. Oenothera hirtella. Tricotyloiis intermediate race ; curve of hereditary capacities of plants of 1896, including both atavists and tricotyls. The ca- pacities oscillate between 15 and 95%. The meaning ef the figures is the same as in Fig. 66. 0.1 0.4 0.7 1.0 1.3 1.6 1.9 2.2 2.6 2.8 3.1 3.6 3.7 26 16 14 10 9 3 6 8 0 0 0 11. Fig. 66. Oenothera ruhr'i- nervis. Tricotylous half race. Curve of the he- reditary capacities of the plants of 1894. The highest of these was Z-7%- The upper row of figures relates to the percentage composition in tricotyls, the lower to the numbers of seed-parents with this composition. The ordi- nates have the same signification as these latter figures.^ overstepped. The tricotyls of the half race do not lead on to the intermediate race, nor do the atavists of this race lead on to the half race. The two races are just ^ The percentage figures are calculated, in this experiment, from counts made on 300 seedlings from each plant ; but the number of ordinates is reduced to one-third. Therefore o.i means, o — 0.2; 0.4, 0.3 — 0.5 and so on. The tricotylous race-s of Dracocephaluin uwlda- ricum and Penstemon gentionoi'des gave similar curves. (Harvest of 1894). Tricotyls as Half Races and Intcniicdiatc Races. 355 as sharply and unalterably separated as, in the first part of this volume, we saw was the case in numerous in- stances, and especially in the tive-leaved race of the red clover. Nothing less than a mutation can effect the transition between the two, but I have not yet had the good fortune to observe such an occurrence. In these experiments therefore the differences be- tween individuals to which attention has to be paid are their hereditary values ; and whether they themselves have two, or three or cleft cotyledons is a matter of sec- ondary importance. In my cultures the selection of tri- cotyls as seed-parents has been the general rule, since this practice on the one hand increases the probability of excluding specimens wnth a low^ hereditary capacity, and on the other, of including those with the high ; but the increase of this chance is only a small one, as the frequent cultures I have made from atavists clearly show (see below, § 6). For a half race the curve describing these values is a half curve. The vast majority of individuals have either nothing, or little else, but dicotylous oft'spring; and the numbers of individuals with the larger numbers of tricotylous offspring decrease rapidly (Fig. 66). These curves may be improved in the same way as those of other half races, viz., by the selection of individuals witli the highest value, as we have seen in Raintnculus bitl- bostis scimplemis (see § 23, of the first part of this volume, p. 249). Curves describing tliese values in intermediate races usually have their maximum ordinates at 50% ; they are, however, liable to be much altered by selection and ex- ternal conditions. Fig. 67 is a curve of this kind f<^r Oenothera Jiirfella, whose apex is at about 65%. If 356 Tricofylous Races, from a group like this the plants with the smallest values are selected for the continuation of the culture, values which are equal to or even smaller than the best ones of the half race can be obtained. Here also the variability is of the transgressive kind; but it does not result in the transition from one race to the other. Half races and intermediate races are, therefore, with regard both to the forms of their individuals and the magnitude of their hereditary capacities highly variable races. On the other hand they are perfectly constant inasmuch as neither race can be transformed into the other artificially. They behave like the majority of ever- sporting races of other anomalies. ■"• § 2. TRICOTYLS, HEMI-TRICOTYLS, AND TETRACOTYLS. The opinion, prevalent amongst gardeners, that hy- brids are intermediate in form between their parents, and that intermediate types, therefore, should be regarded as hybrids, might easily lead to the assumption that the hemi-tricotyls are hybrids between tricotyls and dicotyls. Intermediate they are without any doubt, especially when the cotyledons are cleft over half their length. But the occurrence of a continuous series of intermediate forms between di- and tricotylous plants proves the incorrect- ness of this view, or at least indicates that it does not cover all the facts. The question has to be decided by experiment. For this reason I have made a series of crosses between dicotyls of a half race, and tricotyls of the corresponding intermediate race. Although I always paid especial attention to the occurrence of hemi-tricot- ylous seedlings amongst their results, they were just as ^ See above, p. 22. Tricotyls, Hemi-tricotyls, and Tefracotyls. 357 rare amongst the hybrids as in other cuhures. The hy- brids are ahiiost without exception dicotylous, although of course occasional hemi-tricotyls and tricotyls occur amongst them, just as they do in the half races. There is therefore no ground for the supposition that seedlings with cleft leaves should be of a hybrid nature. They are simply variants of the tricotylous type. The occurrence of seedlings in which both the cotyledons are cleft or doubled, favors this view. They cannot possibly be regarded as hybrids ; they occur so regularly and abun- Fig. 68. Silene odontipetala. A, a hemi-tricotylous, B, a tricotylous, and C, a tetracotylous seedling", 1900. dantly in tricotylous intermediate races that they must be simply regarded as plus variants of the same character. Moreover the fact that one or the other of the seed leaves in a tetracotyl may be cleft also, supports this view. Such a cleavage results in the origin of pentacotyls and hexacotyls which, however, will be, obviously, very rare. True pentacotyls, arisen by such a cleavage, I have seen, for instance, in Scrophularia nodosa, Aniarantus spcci- osns, Oenothera Laniarekiana and Papaver Rlweas (Fig. 69. ) 358 Tricolyloiis Races. Henii-tricotyls and tetracotyls are, as we have al- read)' stated, as a rule rarer than tricotyls, even when we inckide all the juiims and phis variants of these groups. This can be observed in bought samples of seed ; but better if we sow the seed of plants grown from such a sample separately. Thus, for instance, I found in 1892 among the seeds of a plant of A spent I a azurca setosa 3 hemi-tricotyls, 15 tricotyls and 3 tetracotyls among 1170 seedlings, and in the crop derived from another individual of the same culture 2 hemi-tricotvls and 5 Fig. 69. Papaver Rhocas. Semi-double cultivated form. Dicotylous, liemi-tricotylous, tricotylous, tctracotylous, and pentacotylous seedlings; from the seeds of 1899. tricotyls amongst 550 seedlings. Further, I found in 1892, amongst 13,000 seedlings of Ainarantits spcciosus 202 hemi-tricotyls, 245 tricotyls, and 22 tetracotyls and hemi-tetracotyls. In the former group the cleavage was shallow in 47 cases, deep in 97 and intermediate in 58. The same general result was obtained in other plants. To obtain a further knowledge of tricotyls and hemi- tricotyls we must cultivate them furtlier, allow them to flower separately, and compare the composition of their progeny with that of the tricotylous individuals from the Tricotyls, Hcini-tricotyh, and fcfracotyls. 359 same culture. In doing su we find that they do not tend to reproduce their own type, but beliave, as a rule, in the same wav as tricotvls. Minor (luantitative differences may occur, but of qualitative there are none. At any rate it seems impossible to isolate and fix these two sub- sidiary types and obtain pure hemi-tricotylous or tricotyl- ous races. I propose to deal first with the hemitricotyls. 1 ha\e repeatedly isolated them and tested their hereditary capa- city, especially in Auiaraiitiis spcciosiis and Cajuiabis satiz'o. In Ainaraiitus, if we plant out some hemi-t'ricotyls and some tricotyls, the highest values are sometimes ob- tained for the former, and sometimes for the latter ; l)ut only with slight differences. For instance, in the harvest of 1892 the value of 20,000 seedlings was a mean of 2% for the former, and 3.5% for the latter. Moreover there were slightly more hemi-tricot}'ls than tricotyls amongst the former, the difference, however, was only 0.1% in 10,000 seedlings of each group, and in this figure the various degrees of cleavage were, moreover, lumped together. In 1892 to 1895 I then grew the hemi-tricotyls and the tricotyls separately for tliree fur- ther generations, always selecting the individuals with the highest hereditary capacities. In these four years the highest values obtained varied for the hemi-tricotyls from 4.2 to 8.5% with a mean of 5.5%, and for the tricotyls from 3.6% to 7.4% with a mean of 5.7%. From these figures it seems to make practically no difference whether hemi-tricotyls or tricotyls are selected as seed-parents. Of Cannabis satira I had in the summer of 1894 a bed of each of the two types. The hemi-tricotyls gave values varying from 1 to 26%, and the tricotyls from 4 to 14% ; with means therefore of 1 1 and 9%. In Pcnstcnion 360 Tricofxious Races. Ljcntianoidcs the cleft forms gave a mean of 2.8%, but the tricotyls a mean of 2.9%. On the whole, therefore, there are no essential differences in hereditary capacity between the hemi-tricotylous and tricotylous examples of the same races. Moreover we shall see later that this rule must be true, when we shall find that even the atavists in the pure races do not differ essentially in these values from the tricotyls (see § 6). We now come to the tetracotyls. Experiments here meet with the diffi- culty of distinguishing the true types from others. For, occasionally, double seedlings or twins occur. In these the axis is more or less deeply cleft; it looks as if two seedlings had fused together side by side. If the cleavage extends downwards into the hypocotylous region there are two separate groups of seed-leaves and these are frequently at Fig. 70. Acer Pseudo-Plafanus. A tetracotylous seedling, the axis of which spHts above the cotyledon. In the cleft two leaves are seen, the lower part of whose stalks are grown to- gether, back to back. (Spring, 1887). different heights. There is obviously no danger of confusing such cases with tetracotyls, although the twin seedling does actually bear four seed leaves (Fig. 71). But if the division affects only the part of the axis above the seed-leaves, these Tricot yls, Ilciiii-lricotyls, and Tctracotyls. 361 stand in a whorl and the seedhng cannot be distinguished from those in whicli the seed-leaves and not the axis have divided. Only after further growth its true nature can be decided. If, huwever, the doubling is continued with- out splitting of the stem, peculiar fasciated plants may \)Q the result. In such cases the real state of affairs often remains hidden. In Ainarantus spcciosiis especially, I have often ob- served such twins (Fig. 71), and also in Datura Stra- moniuin, Acer Pseud o-Plataniis (Fig. 70) etc.^ Fig. 72 represents a section of a stem of a tetracotylous plant of Fig. 71. Seedlings of Amarantus speciosiis. A, tetracotyl- ous ; B, twin, each of the split halves of the axis bearing two seed-leaves ; C, twin, one of whose halves is tricotyl- OLis ; D, hemi-pentacotylous seedling, the sole instance of this case in a culture of over 20,000 seedlings ; E, Tri- syncotylous plant. Harvest of 1893. Amarantus speciosus, which split at a considerable height above the insertion of the cotyledons and bore in the fork two leaves the midrib of which had grown together on the dorsal side up to within a short distance of the apex. In the axils of these leaves small branches were seen with a little terminal inflorescence and a small leaf inserted below this. Above this point the two branches of the fork were of normal growth. Fig. 70 represents ^ See L. J. Leger's exhaustive work on the anomalies in the seed- lings of Acer Pseudo-Platanus. Bull. Soc. Linn. Normandic, 1889, p. 199. with plate. 362 TricctMlo^'is Races. a seedling of Acer Pseudo-Platanus with four seed-leaves which I found in the spring of 1887 in a forest and trans- planted to my garden. Here it developed its stem. As soon as this had definitely split, and just before the cotyl- edons were about to fall away I dried this specimen in order to keep and photograph it. It is obvious that such twins do not belong to the tricotyl- ous race, that is to say, that their anomaly is due to some other elementarv character. Therefore they should not be counted when recording the seedlings, nor be used as seed- parents. But as their nature can only be determined for cer- tain in some cases, it is not al- ways possible to take this pre- caution ; and the fact that the hereditary values obtained from tetracotylous individuals are sometimes worse than those from the corresponding trico- tyls may in part be due to this circumstance. For the rest tetracotyls do not in any essential respect be- have differently in inheritance from the tricotyls. From their seeds are produced, besides the atavists, mainly tricotyls, with hemi-tricotyls and tetracotyls in the usual dimin- ishing proportions. My tricotylous half race of Scvopliu- Fig. 72. Amarantus specio- sus. Forking of a stem of a tetracotylous plant with two leaves in the fork which have grown together dorsally. The figure shows also their axillary twigs. Tricot y Is, Ucmi-tricotyls, and Tcfrocotyls. 363 laria nodosa produced, in the harvest of 1894, a mean of 2% and a maximum of 5.5% tricotyls per seed-parent. I harvested the seeds from two tetracotyls and ol^tained 0.5% and 3% tricotyls. Amongst the 2000 seedhngs wliich these cultures contained, there were 30 tricotyls, 3 hemi-tricotyls and only 2 tetracotyls. On the other hand a tetracotylous plant of Aspcrula a-ziirca gave 7% and the corres]:)onding tricotylous seed- ]:)a rents only 2%, in 1892. Of this 7%, there were 5% tricotylous, 1% tetracotylous, and 1% hemi-tricotylous. I bred tlie tetracotyls of Aniarantiis speciosus for two s^enerations, in 1893 and 1894. In the summer of 1893, 9 tetracotylous plants were left to flower; 3 proved to be fasciated, but the rest gave values varying from 1 to 7.5% with a mean of 5%. I counted for each seed- parent 500-1000 seedlings. The corresponding tricotyl- ous culture gave values from 2.5% to 7.5%, that is, a mean of 4.5%; from each of the 15 seed-parents from 700 to 1000 seedlings being examined. We see there is practically no difference between the two cases. Together the tetracotylous parents produced only 6 tetracotylous offspring among 4000 seedlings, and the tricotyls 13 among 10,000; that is to say, they behaved in regard to this character as variants of the same race. I then selected the tetracotylous offspring of the tetracotvlous seed-parents for a continuation of the race in 1894, but observed no further progress, the percentage in tetra- cotyls being only 0.2%. The question suggests itself whether the proportion of tetracotylous seedlings, perhaps, simph- obevs the laws of proba1)ility. The splitting of a cotyledon may be im- agined to be distributed at random over a group of sav 100 individuals, and we mav ask. how manv times a 364 Tricotylous Races. seedling will have two such divisions and so become a tetracotyl or hemi-tetracotyl. If, for instance, 50 divi- sions are distributed over 100 seedlings, with 200 cotyl- edons, hov/ often may we expect a single plant to present two such divisions? In the same way the expectation of pentacot3ds may be calculated. Without going closely into this calcula- tion, it is obvious that the proportion of tetracotyls will, on the whole, increase with that of the tricotyls indepen- dently of course of the nature of the species in question. As a matter of fact we do not observe such an independ- ence. Some species are relatively rare in tetracotyls wdiilst others produce them more abundantly. Thus An- tirrhinuin inajns never gave more than 1% to 2% of tetracotyls (Fig. 63 D, p. 345), although the proportion of tricotyls was as much as 79%. Oenothera hirtcUa, Scrophularia nodosa, and Cannabis sativa are also poor in tetracotyls. The latter produced only 1 to 3.5% of them, even when the wdiole value amounted to 63% (in 20 individual records). On the other hand, other species, or at any rate the races of them wdiich I observed, pro- duced tetracotyls abundantl}^ I have grouped together w'ell over 100 separate rec- ords from my cultures of 1894-1896, in wdiich the hemi- tricotyls, tricotyls and tetracotyls w^ere recorded sep- arately for each sowing, which almost always consisted of about 300 seeds. From these I have especially cal- culated, besides the percentage composition in split-leaved seedlings, the proportion of these to the tetracotyls; and I eive below^ the number of tetracotvls per 100 tricotvls in the wn'der sense of that term. This proportion varied in Amarantns speciosns, for 2-10% tricotyls, and in Can- nabis safh'a for 6-52%, between 1 and 7%. In Mer- Tricot y!s, Hcini-tricotyls, and Tefracotyls. 365 ciirialis annua for 8-86% tricotyls between 1 and 16% ; in Silcne inflata for 27-73%, in Clarkia pulchclla for 6-16% and in HclicJirysiun bracteatuni for 3-41% tri- cotyls, from 2 to 28%. In the individnal records this ratio is obviously subject to considerable fluctuation on account of the small number of tetracotyls in the indi- vidual crops, and for a proper estimation of this ratio cultures on a much larger scale and especially designed for this end would be necessary. Here I shall content myself with giving an experimental series obtained with Clarkia pulchclla, which shows roughly how the ratio of tetracotyls to tricotyls increases with the number of the latter. Percentage ratio of tricotyls 6 7 14 16 27 55 62 63 Number of tetracotyls per every 100 tricotyls ... 15 5 26 5 10 18 22 20 Similar figures were obtained with Phacclia fanaccti- folia, Papavcr Rhocas, HclicJirysiun bracteatuni and Mercnrialis annua. § 3. THE INFLUENCE OF TRICOTYLY ON THE ARRANGE- MENT OF LEAVES. Elementary characters are not as a rule betrayed by a single external characteristic, but by several. In most cases one of these can easily be recognized as the primary one, and the rest are then termed secondary. In other cases a doubt may arise as to which should be regarded as primary and wdiich as secondary. White-flowered varieties of red or blue species often exhibit the absence of color in the fruits as well as in the leaves or the stem. Moreover they can frequently be recognized as early as in the seedling stage by their pure green color. My new 366 Tricot yl oils Races. Oenotheras differ from the parent species in several char- acters; nevertheless each arises siuklenly with its char- acters complete. From this fact we conclude that all of them must be regarded as the expression of a single m- ternal change. A single new elementary character can thus affect more or less profoundly a whole group of older internal characters. We will regard tricotyly, for the present at any rate, as the primarv expression of a definite internal factor wliich occurs in the latent state in large numbers of di cotvledons. though not necessarily in all. It also occurs, although as yet in a small group of cases, in the active :? ^-'-^ Fig. 7^. Scrophi'.lan'a nodosa. A tricotyloiis seedling with the first whorl of leaves which is ternary also; C, the cotyl- edons, l-'rom the harvest of 1899. State alongside dicotyly. On this point of view the qties- tion suggests itself whether this internal factor will per- ha])s also betray itself during the later life of the plant. I^ricotvly results in an abnormal arrangement of the seed-leaves, and thus it is only natural to expect that its internal cause may lead to anomalies in the disposition of the foliage leaves as well. As a matter of fact, this is the case. In the first place, in species with decussate leaves, the arrangement of the leaves in whorls of three may continue upwards from the cotvledons fFig. 73V This may be limited to Tricofyly ami iJic AvnuKjaiioil of I. caves. 367 the lower whorls, or continue in all (^t them. \n the first case the transition between the two arrangements is often effected by intermediate stages, such as cleft leaves.^ Other disturbances of the disposition of the leaves also can follow on tricotyly, amongst the most important of which are twisted and fasciated stems as well as the pro- duction of so-called terminal leaves. In the following- paragraphs I shall describe some of the most important of these \-arious phenomena which have occurred fre- quently, and in many cases almost regularly, in my ex- periments.- It seems desirable to state beforehand that the anom- alies in question exhibit an obAious genetic C(Minection with the splitting or duplication of the cotyledons, al- though this relation needs closer investigation. Other malformations of structure no doubt are also met with amongst tricotylous individuals (for instance, variegated leaves, prolification of flowers and flowerheads), but not more abundantly than elsewhere. ]\Ioreo\er it is by no means a rule that in all species the same anomalies should occur amongst tricotyls. It a])pears, on the contrary, that certain species, (or at any rate, certain commercial races of them), have a marked preference for definite ab- normalities, since both torsions and fasciations appear relatively abundantly amongst certain species, but rarely amongst others. In the same way su1)terminal leaves lia\-e hitherto ])een observed in c|uite a limited number of instances onlv. On this relation between tricotyly and abnormalities in the disposition of the subsequent leaves T lia\e based ^ Delpino, Tcoria dcUa Fillotassi. 'Further facts will be found in Eiiir Mcthodc, ZwauiisdrchuuQ,cn aufcusiichni. Rer. <\. '1. hot. Ges., 1894. Vol. XII. p. J3. 368 Tricotylous Races. a simple method of searching for such anomalies. Fas- ciations are so common in nature and in the garden that special means for obtaining them are not required; but twisting is much rarer and ordinarily it is only by a lucky chance that we meet with an instance of it.^ If we wish to become independent of this chance we must have re- course to the culture of variations of cotyledons, because such will offer a greater likelihood of furnishing the de- sired anomaly than other examples of the same species. In the first, or at least in the second, generation we may count on finding them, if the extent of the experiment is sufficiently great, and once obtained, they can easily be further improved by ordinary selection. A single in- stance will suffice. ]\IoRREN found a very fine specimen of twisting in Dracoccphaluui spcciosnm in a meadow not far from Liege, ^ and wdien I read his description I be- came extremely anxious to investigate such a case of torsion in this species, or at any rate in this genus. For this purpose I selected Dracoccphahun moldavicuin, which, being an annual, seemed more suitable. In the spring of 1892 I selected a single hemi-tricotylous seed- ling found in a sowing of commercial seed (a little less than 20,000 seedlings), and from this bred a race wdiich in the first year exhibited nothing remarkable but pro- duced fasciations in the second year and traces of twist- ing in the third, and finally, in the fourth, some very fine instances of spiral torsion. One of these had the whole main stem transformed into a screw (Fig. 74). Fortunately in such experiments, the aim can be attained, as a rule, in a much smaller number of years. ^Monographic dcr Zzcan^sdyeJiun^cu. Prixcsheim's Jahrb. f. wiss. Bot., Vol. XXIII, p. ii6. ""Bull. Acad. Roy. BcJg., Vol. XVIII, p. zy. Tricotyiy and the Arrangement of Leaves. 369 Tricotylous s|)cciincns of species willi ;i decussate arrangement of their leaxes very often produce tlie lower leaves of the stem in whorls of three. Sometimes this extends all the way up, or at least to the inflorescence, Fig. 74. Dracocephahim moldaviciun. Twisting of the main stem as the result of a breeding experiment ex- tending over four years. (Compare below Fig. 82.) sometimes, however, it reverts to the decussate arrancre- ment sooner or later as we proceed ui)wards. Very often also the latter follows immediately on the seed-leaves (Fig. 76 B). All such cases can often be observed in J/ 0 Tricotxious Races. the same culture from the seeds of a single seed-parent. This is especially the case in Anfirrliiniiin iiiajiis and ScropJiularia nodosa, in which species I have often pre- ferred as seed-parents, the tricotyls, whose first whorls were trimerous. Nevertheless they have not, as a rule, proved the better qualified to continue the character of tlie race. Further instances are afforded by Dipsaciis sylvestris, Lychnis fidgcns, Dracoccphaluin nioldavicunu Dianthus harbafus and so on. Tn the spring of 1887 T had some tricotylous seed- lings of Acer Psetido-Plata- niis: two of them are now high trees, whose trunks bear their branches in trimerous whorls. The lateral branches of ternary main stems tend, as a rule, to revert to the de- cussate arrangement. Sub- terranean runners, (for in- stance in Valeriana officina- lis) and the secondary stems which are produced at the Dianthus barbafits), afford, Fig- 75- FciStts syhatica. Tri- cotylous seedlings. A, with a ternary whorl of the first leaves ; B, with a leaf with two apices and a divided vein. level of the ground (e. g.. however, numerous exceptions. In tricotylous cultures, dicotylous individuals some- times become ternary later. Thus I possess a plant with ternary whorls of Aesculus Hippocastanuni (now 13 years old), which only had two cotyledons, and from the same crop a plant which was tricotylous but has since produced leaves on the decussate plan only. In ]:)Otli specimens the change in the disposition of the leaves Tricotyly and the Amuigciiicfit of Leaves. 371 toDk place before the cotyledons were dead. \\\ Dipsaeiis syl-i'esfris tors its, a race which is usually ricli in lernar\- in(h\ iduals, these are almost without exception decussate in early youth. On the boundary between the 2- and 3-merous whorls 2!/2-nierous ones not infrequently occur. I mean whorls with one normal and one more or less deeply cleft leaf. All degrees of cleavage (or symphysis) may occur. In the tricotylous races of Antirrhiniiui ma jus and Serophu- laria nodosa they are particularly abundant, and merge Fig. yG. Mercnrialis annua. A, normal seedling; C, cotyl- edons, (i) the first, and (2) the second pair of leaves; B, a tricotylous seedling the first two leaves of which stand opposite one another (1900). into the decussate arrangement in the first or second or in some later whorl. In the choice of seed-parents I have always paid attention to this point, although it has onl}- a secondary effect upon the result. Further instances of cleft leaves in the transition from tricotyly to the later normal arrangement were afforded me by Dianthiis barbatiis. Lychnis vespertina, Polygonum Fagopyrum, CoUinsia he- terophylla, Anagallis grandiflora and in large quantities by Fagus sylvatica (Fig. 75) as well as by many other species. As the phenomenon is quite common when more extensive sowings are made and as, especially in 372 Tricot \lous Races. perennial plants, the transition from one mode of ar- rangement to the other has been frequently observed on the same axis, as Delfino has shown, I need not enter further into it now. Sometimes it happens also that the main stem of a tricotylous plant bears its leaves in quaternary w-horls (Scabiosa atvo purpurea). Fasciations are a frequent consequence of tricotyly, though they sometimes do not ai)pear until late in the life of the plant. Merciirialis an- nua and Ajuaranfus speciosus furnished a series of instances nearly every year during sev- eral years of culture. In the former species they usually appear low on the stem ; in the latter not below the in- florescence (See Fig. 83, p. 399). My tricotylous race of Mercurialis annua furnished almost all forms of fasciation. Fig. 77 represents a tricotylous plant whose stem was split from the first node after the cotyledons, and was therefore Fig. yy. Mercurialis annua. A, tricotj'lous seedling with split stem; B, a seedling the first whorl of leaves of which was ternary ; C, hemi- tricotylous plant (1900). only fasciated in the epicotvl- ous internode. Between this condition and a flat stem one centimeter broad, and much contorted, all inter- mediate stages are presented by this species. In the spring of 1887 I collected a large group of hemi-tricotyl- ous, tricotvlous and tetracotvlous seedlings fSee Fisf. 70) of Acer Pseudo-PIafanus not far from Hilversum and grew them for several years. Most of them I threw Tricotyly and the Arrangement of Leaves. c>7^ away as soon as they rexerted to the decussate arrange- ment of their leaves, but seven of these trees are still alive, two with ternary stems (p. 370), two with a de- cussate arrangement of the leaves, and one with a much flattened main stem. This last one began with three cotyledons; it then became decussate, and in its second year (1889) became ternary again. In the autumn of the following year it began to flatten out, formed three five-leaved whorls and began to split when laying down the winter bud. I then broke off all the terminal buds except one, which in the spring of 1891, during sub- sequent growth, split into three flat twigs of which again two were removed. In the following summer the fasciation recurred, and also, after splitting in the win- ter, in the next year (1892), and again in 1893. Every time the forked branches were reduced to one. The divisions became much rarer, later on, and the older sec- tions of the stem which were at first flat gradually be- came cylindrical, as usually happens in fasciation when it afl^ects trees. ^ On tricotylous specimens I also observed flattened stems in Antirrhhinm ma jus, Artemisia Ahsynthium, Sca- hiosa atropiirpurea, Dianthus pliimariiis, CoUinsia hetero- pliylla, C. grandiflora, C. violacea and Tetragonia ex- pansa (Fig. 78) ; and amongst tetracotyls in ScropJui- laria nodosa and Colli nisia z'iolacea and other species.- In many cultures I have observed that fasciations are more common amongst tricotylous plants than amongst dicotylous ones, but I shall only deal in detail with an experiment on Aspenda aziirea. In the spring of 1892 I selected the hemi-tricotylous, tricotylous and tetra- '^ Kruidk. Jaarh. Gent, 1894, Plate XI, {Abies excelsa). ^Ber. d. d. hot. Gcs., Vol. XII, p. 36. 374 Tricot yloiis Races. cotyKjiis seedlings from conunercial seed of this pretty little annual (Fig. 79). I cultivated them and saved their seeds and in the following year planted out the variants and the atavists separately. There were 37 of the former group and 15 atavists. From the former there arose 28 flattened stems and branches ; from the Fig-. 78. Tetragonia expansa. A, branch split by forking: B, comb-bke expanded terminal flower of a flattened main stem. latter only four, that is to say, a proportion of 75% and 27% respectively. It should be mentioned that all the variants among the seedlings were planted out and that some of these gave rise to rather weak plants, whilst of the atavists I selected the strongest seedlings only. These, however, in spite of their greater individual strength and Tricotyly ami the .Irramjcmcul of I.raics. 37? in spite of their origin from IricoLylous parents, prt^duced considerably fewer fasciations than the triccjtyls. We come now to the spiral torsions. Idiese occurred in several of my tricotylous races nearly every year since 1893, and often in considerable numbers. As a rule they Fig. 79. Aspcrula azurea. l*"ig". «So. Mclaiiipyniiit pratensc'. Tetracotylous plant with spiral arrangement of leaves (iiSS/). consisted of fairly long, much twisted sections of the main stem, or of the stronger lateral branches which abutted above and below on the normal or decussate sections. They bore their leaves sometimes in a \ery steep spiral and sometimes in an unbroken line on one 376 Tricotylous Races. side of the stem.^ I found these torsions not only in my own races but also on tricotylous individuals raised from commercial seed of Anagallis grandifiora, Collinsia bicolor, C.heterophylla, C.violacea, Dianthus phunarius, Fcdia scorpioides, Scabiosa atropiirpurea nana, Silene noctiflora and Zinnia clcgans. Also in the second gen- eration of Aspenila azurea sctosa and Viscaria ocidata? Fig. 8i. Antirrhinum majiis. Seedlings with terminal leaves A, tricotylous ; the others are atavists from the same race. A, B, with a single terminal leaf; C, the two leaves of the first whorl fused laterally and placed termi- nally; D, a terminal pitcher formed of two leaves. Lastly I wish to refer to a tetracot3dous plant of Melainpyrum pratense (Fig. 80), whose first leaves above the cotyledons, instead of being decussate, were arranged in a very irregular spiral. I found it in the summer of 1887 growing wild not far from 'S Graveland. It is important, because it shows that even a splitting of both * F'gured in Ber. d. d. hot. Ges., Vol. XII, PI. II, Figs. 9 and 10. ^ Ber. d. d. hot. Ges., loc. cit., pp. 32-35 ; see the figures on Plate II of this article. Tricot yl\ and flic Avnuiijciiioit of Leaves. Z77 the cotyledons and especially a splitting equally deep on the two sides may involve an alteration in the disposition of the leaves. This, of course, is by no means a neces- sary consequence, but the present case indicates that the internal cause is not necessarily limited in its operation to the cotyledons. Terminal leaves have hitherto been regarded by tera- tologists as very rare occurrences, but my tricotylous races of Antirrhlnnin uiajiis have afforded me the oppor- tunity of observing them repeatedly and in hundreds of specimens (Fig. 81). A well-known instance is the great terminal leaf of Gcsiicra Gcroltiana described by Morren and reproduced by Masters/ This specimen bears only one normal pair of leaves, and above these an erect leaf of double the normal size. In the figure we can see the node at which this is inserted; and the simplest explanation of this remarkable phenomenon is that, for some reason or other, the growth of the second leaf of the pair, as well as that of the terminal bud was impeded in early youth. Ber- noulli mentions a similar apparently terminal leaf of Coffca arabica, and was able in this case to confirm the correctness of this supposition by microscopical obser- vation.^ He also describes a shoot of Fuchsia iiiacro- stcmina which bore a funnel-shaped leaf at the top. The races of the Snap-dragon, which we have already mentioned bear every variety of these structures. These may consist of single or of double leaves, or of leaves grown together in the shape of a funnel. All inter- mediate stages between these and the normal plants oc- 'Ch. Morren. Bull Acad. BcJo., Vol. XVTT. Part IT. p. 2>^7\ M. T. Masters, Vegetable Teratology, p. 88, Fig. 40. ^ G. Bernoulli, Ueher scheinhar terminale Blatter, Botan. Zei- tnng, 1869, p. 19. 378 Tricotyloiis Races. cur. These anomalies are found especially on the seed- lings and usually replace the first or second whurl of leaves and rarely the third or a higher one. In the spring of 1894 I had a large crop of the red flowered variety which produced about l^c of these abnormali- ties amongst many hundred seedlings. In subsequent years I had even larger numbers. In the spring of 1897, for instance, I had about 10/6 in very extensive sowings of a tricotylous race with striped flowers. The most important cases are, of course, those in which the rudi- ments of the opposite leaf and of the terminal bud can be clearly seen with the naked eye alongside the terminal leaf. I have frequently planted out such plantlets in the hope of growing them for my experiments, but usually without success. Either they did not develop a main stem at all, or only a delicate one ; often there arose from the axil of one of the lower leaves or of one of the cotyledons a lateral branch which, however, remained weakly. Sometimes the organ situated opposite the terminal leaf is somewhat better developed, but usually it cannot be seen withotit the help of a microscope. If the terminal structure has only one vein I regard it as a single leaf (Fig. 81 B). But if it has two points \vith a double or divided midrib (Fig. 81 C) it obviously represents the two leaves of a pair. Sometimes these are fused together laterally; the peduncle is, however, considerably broad- ened and its point of insertion clearly recognizable. Fre- quently, however, the peduncles are fused at their base, at both sides, and form a little tube which embraces the terminal bud. If the concrescence is of considerable extent terminal ascidiae are the result, which, in most Tricotylotts Half Races. 379 cases, can he clearly recognized as consisting of two leaves (Fig. 81 D). The fact that so rare a teratological phenomenon should occur so regularly in two well-known varieties of the same species, — the one uniform red, and the other striped yellow and red — means perhaps that the char- acter in question has existed for a long time in the Snap- dragon and will be found, after a close investigation, to exist in other cultivated varieties also and possibly even in the wild ancestral form. Of course the fact that I found them in a tricotylous race need not necessarily indicate a causal relation between this character and tricotyly, because, at the beginning of my cultures, I started by selecting the tricotyls and continued the race from their seeds alone. If such a relation did exist the fact that the anomaly occurs both on dicotylous and on tricotylous individuals would be very important, for it would show that it is not the visible tricotyly itself, but some corresponding internal character, which must be regarded as the cause. It is to be hoped that the abund- ance in which the anomaly can now be obtained will render possible a closer examination of this problem. § 4. TRICOTYLOUS HALF RACES. Occasional tricotylous seedlings will be found among samples of seed in very many species. All that is neces- sary, therefore, to start a culture is to buy a sufficient quantity of seed and to sow it. The seed will either give no aberrant forms, or very few, or a considerable number. In the first case the possibility of obtaining tricotyls still remains open if a larger quantity of seed is sown. In the second case the variants can be used as 380 Tricotylous Races. the point of departure for the race ; they offer the prospect of provi(hiig a half race. In the third case we may ex- pect to obtain an intermediate race rich in tricotyls. Ahnost every year I have made experiments of this kind, but I was especially engaged with them in the spring of 1895. At that time I sowed about 20 grams of each of 40 species of annual plants, or in the case of very small seeds a somewhat smaller quantity, so as to investigate several thousand seedlings of each kind. I shall now give a list of the species falling into the third category, species, that is, which gave so large a number of aberrant forms as to justify the expectation of an intermediate race — an expectation which has, as a rule, been fulfilled, as we shall see in the following section (§5). TRICOTYLS FROM BOUGHT SEED. (Spring, 1895.) <^ TTTT i'^ X T:> C* DICOT- HEMI- TRICOT- TETRA- SPECIES YLS TRICOTYLS YLS COTYLS Chrysanthemum inodortim , plenissimum . . . . 1000 3 32 0 Silene orientalis alba . 3000 3 7 0 Papaver Rhoeas fl. ple7W 3000 1 15 1 Clarkia pulchella alba 4000 5 5 0 Glaiiciuni liiteiim 16000 0 15 0 Nigella hispanica alba 10000 0 15 0 Phacelia iaiiacetifolia . . 16000 8 18 0 Helichrysiim bracteatuni 35000 9 16 3 With the exception of Silene, Glauciniu and Nigella, I have raised intermediate races from all these sowings. As I have already mentioned, hemi-tricotyls and tetra- cotyls are seen to be rarer than the typical tricotyls. A sample of seed of Lobelia Erinus, grown in the spring of 1902, had a very high proportion of tricotyls, viz., 31 in 100 seedlings. Tricotylous Half Races. 381 Very small proportions of tricotyls were yielded by Silene hirsnta, which only produced 3 in 80,000 seed- lings. The following species produced from 1-2 speci- mens in every 10,000 seedlings: Argemone grandiflora, Aster tenelhis, Clarkia elcgans, Godctia amoena, Hyos- cyarnus pic t us, Silene Aruieria, and others. I observed no tricotyls at all in sowings of the same extent of Argemone mexicana, Datnra laevis, Hyoscyanius albus, Nigella damascenaj Phacelia texana etc. I tested 800 seeds of each of 8 species of Cerinfhe, and only obtained a single tricotylous plant in C. bicolor, C. gymnandra and C. major. The seeds mentioned were all obtained from the nursery of Messrs. Haage & Schmidt in Erfurt. It is not unlikely that if the seeds were bought from other nurseries, different results could be obtained, especially from firms who do not exchange seed with the nurseries at Erfurt. Similarly the seeds of wild species occasionally pro- duce tricotyls, but, as it seems, only in very small quan- tities, and they have hitherto given no promise of yield- ing an intermediate race. As instances I mention Ra- phanus Raplianisfrnni and Epilobinm hirsiitum, of which species I found 1-2 tricotyls in large crops. If the seeds of wild species come from botanical gardens the pro- portion of tricotyls is sometimes greater; for instance in Silene nocti flora (1892) it was about 20 in 10,000 seedlings. Amongst trees I have hitherto found tri- cotylous seedlings abundantly in Acer Pseudo-Plafanus and Fagns sylvatica and also in Robin i a Pseud-Acacia and Ulmus campestris. In order to test the hereditary capacity of the cotyle- don variants in such crops, I have frequently planted 382 Tricofyloiis Races. them out and allowed them to flower in isolation. Higher ])roportions are thus obtained : for instance in cultivated species in Cclosia crisfafa 2^c , in Clirysaii- thcniuin Mycoiiis 1-2^6, in Oenothera longifolia V/( , O. mollissiina V/o , O. uudulaia, 1%, Xylopleunini tetra- pteriun 2%, Podolcpis gracilis 2^/c, Tctragonia expansa 2%, Veronica longifolia 4%; and amongst wild species in Chenopodiujn album 1%, Thrincia hirfa 1%, and so forth, the two latter having been grow for three genera- tions. Further instances will be afforded by the be- irinnines of mv cultures to be mentioned below. If we compare the proportions just given, excluding those species which are so rich in tricotyls that they probablv contain an intermediate race, we find from 0-2 tricotyls in about every 10,000 seeds, from mate- rial which lias been bought or obtained by exchange or collected in the field, whilst the harvest obtained after the isolation of the tricotyls, contains from 1-2%. The orisfinal mixtures, therefore, must have contained the seed of many individuals witliout tricotylous offspring. Besides the hereditary capacity of bought seed and of the tricotyls raised from it after artificial fertilization, we have to consider the question whether this capacity can be increased by a selection extending over several eenerations, or whether it maintains itself without chang- ing. As I have already stated, the conclusion derived from mv experiments is that the answer may fall into one of two categories. In some species selection may soon lead to a proportion of 50% tricotyls and more ; in others, this does not take ])lace even if the selection is continued for many years. Obviously this depends on the (|ue>^tion whether an intermediate race is present in tlie given sample of seed, or not. If it is there, it Tricofyloits Half Races. 383 can l)e isolated immediately; if it is not, no amount of selection will bring it aliout. The experiments in whicli isolation succeeded will be described in § 6; but the ex- periments which failed fall into two groups, according to whether it could be decided immediately, or not until much later, that an intermediate race could not be raised. In the former group fall those cultures in which there was no progress at all, or so small a one that I had to give them up after three or four generations. For if, after this time, a proportion of no more than from 1 to 2 or at most 4% is reached, or if in the case of higher proi)ortions the ratio fluctuates greatly but does not ex- hibit a regular increase, how many years of work would it take l)efore we can be certain that nothing can be at- tained ? These briefer experiments will form the sub- ject of this section. In the second group fall two cultures which I have continued for a considerable time, namely Ainarantus speciosus through nine generaiions and Scrophidaria no- dosa through ten. Neither now leaves any hope of ever becoming successful (see >^ 3) ; but, as I have already said in the first part of this volume (p. 227), it is just the experiments in selection that fail, which give us the deepest insight into the nature of elementary characters. I shall now proceed to the description of my ex- periments; and I shall confine myself to those which were instituted with the express hope of breeding a tricotylous intermediate race, and were continued f(^r 3 or 4 generations with this sole object in view, until it l)ecame evident that only a half race was present. The extent of the cultures varied greatly, according to the importance which I attached to them at tlie l)cginning. In the fir<^t place T shall deal witli Ocuothcra nihrinrnis. 384 Tricotylons Races. Oenothera nibrincri'is. In the pedigree of the Laevi- folia family on p. 273 of the first volume, the origin of two specimens of 0. rubrinervis is recorded for the year 1889. In the generations which were raised from these two mutants, no tricotyls were at first observed (1890- 1891). They first appeared in the spring of 1892, and with them the culture of the tricotylous half race began. I selected the tricotyls from amongst thousands of seed- lings and planted them out singly in pots with well manured soil. I obtained 22 strong plants which flowered freely in an isolated spot. The seeds were saved sep- arately from each parent, each of which was labelled according to its individual vigor. The five strongest plants gave respectively 1.5, 1.9, 2.3, 2.6, and 2.8% trico- tyls amongst from 700 to 900 seedlings. The remainder, the weaker plants, only 0-1% With an average of 0.7% amongst 8000 seedlings. The value 2.8% was obtained from a very vigorous plant; in the three following gen- erations it has hardly been reached again, in spite of selection, and never was really exceeded. The ofl^spring of only the five best plants were planted out and in all cases only tricotylous individuals. There were about 70 of them and they were potted singly and well manured (1893). In the middle of May they were planted out into the bed at distances of about 30 centimeters apart, wdiere they flowered in isolation in August, and could be mutually fertilized by insects. In the spring of 1894 the seed of each plant was sown sep- arately, and when the cotyledons had completely unfolded the seedlings were recorded, 300 for each parent but 1000 or more in the 20 which appeared to be the best. Altogether 45,000 seedlings were recorded, and amongst these w^ere 170 tricotyls, i. e., about 0.4%. Of these Tricotyloiis Half Races. 385 12 were hemi-tricotyls and one was a tetracotylous speci- men. There were also some few syncotylous ones. The ratio from the best seed-parents was no more than from 0.8% to 1.1%. The tricotylous offspring of these and of some with from 0.5 to 0.6% were planted out in the same way as in the previous year, provided they were strong little plants. This time the inflorescence of each plant was guarded against the visits of insects by means of a parchment bag and artificially fertilized in the hope of thus isolating individuals producing higher propor- tions. On page 354 I have plotted, in Fig. 66, a curve of the harvest of 1894, based on the records made in the spring of 1895. There were two seed-parents wdiich manifested an advance on the previous year, inasmuch as their ratio was 3.5% and Z.7%, but the difference was only a very inconsiderable one. In all, there were 87 seed- parents. As I had planted the offspring ot the individual grandparents of 1893 together in groups in 1894, I could now make a selection not only betw^een the parents but also between the grandparents. The grandchildren of those grandparents only, whose offspring had pro- duced the highest mean proportion, were planted out. By means of such a selection of grandparents the pedi- gree becomes an individual one in spite of the size of the mltures, embracing, in each generation the offspring of one selected individual only. The method, therefore, unites this principle with the greater certainty that can be obtained by extensive cultures and a double selection. I have also applied it to a number of other cases. From one grandparent with 1%, therefore, and from six of its offspring with from 0.9% to 2.1% 54 tricotvl- ous specimens in all were planted out ( 1895). From the 386 Tricotylous Races. beginning of the flowering period all these were covered witli fine gauze, guarded from the visits of insects and artificially fertilized every day or every other day. About 300 seedlings of each plant were recorded. The ratios were from 0 to \.2^/o with an average of 0.8%. Two parents had 1.4% and one 2%, that is to say, that here again there was no progress. The offspring of the six parents fell into groups between which the differences were but slight (3 with 0.7%, and 3 with 0.8% on the average). In the list which follows I have collected the highest values that were obtained in the course of these genera- tions. , SPRING OF ^ 1893 1894 1895 1896 Highest values 2.8 % i.l % 3.7 % 2.0 % Selected seed-parents 2.8% 1.0% 2.1% — These figures show a fluctuation within fairly nar- row limits, but no essential advance in the course of four generations. It seemed therefore to be useless to carry the experiment further. It is certainly probable that, in the course of time, further selection might have brought about some slight improvement; but obviously this would have been of little significance, and at any rate there was no prospect of ever obtaining a race with 50% tricotyls. Chcnopodhiiu olbuiii. A tricotylous plant flowered in 1889, In isolation in my garden, and produced 1% tri- cotyls in the spring of 1890 amongst about 1000 seed- lings. Four of these were cultivated further, but their seeds gave rise again to no more than 1%. The third generation Avas therefore not better than the second. Dracocephahiiu inoldaviciim (Fig. 82). In the spring TricotyloHS Half Races. 387 of 1892 I obtained only a single henii-tricotyl from about 20,000 bought seeds. The seeds of this plant gave rise in 1893 to five tricotyls and two hemi-tricotyls among 4000 seedlings, that is, about 0.2 7©. Their seeds were harvested separately, and as the expectation of tricotyls was a small one, great quantities of it were sown. I recorded from 800 to 2900 from each, i. e., altogether about 15,000 seedlings, and found the ratio of tricotyls (and hemi-tricotyls) to be from 0.2 to 0.4%. It did not, therefore, seem justified to make a selection among the individual seed-parents. In 1894, 12 tricotyls the stems of which had remained ternarv, and twelve specimens with normal decussate stems were planted out. Several beauti- ful fasciations and occasional cases of spiral torsion oc- curred in this culture (p. 369) . The seeds were harvested sep- arately. In the spring of 1895 they again produced only from 0.1 to 0.4% of tricotyls. Seventeen specimens from the seed pans with from 0.2 to 0.4% were planted out about a meter apart, but tl^e seeds produced, in 1896, scarcely any tricotyls and only from five seed-parents, the pro- portion being from 0.3 to 0.7%. In tlie course of four generations selection had, there- fore, brought about practically no advance. Fig-. 82. Dracocef^halum mol- davkiim. A whole plant. 388 Tricotyloiis Races. LxcJuiis fill gens. The tricotylous seedlings of this species are as a rule weakly ; their culture, therefore, is difficult and their harvest poor. In 1892 I had a tri- cotylous plant whose seeds gave a proportion of 5%. From these I reached, in the spring of 1894, a ratio of 13% containing one tetracotylous plant; most of the tricotyls afterwards remained ternary. In 1895 they produced tricotyls in proportions varying from 3 to 11%, with a mean of 6%. In the next, i. e., the fifth genera- tion (spring of 1896), I counted from 2 to 8% tricotyls per seed-parent, and from a particular individual 21 tri- cotyls amongst 110 seedlings, i. e., about 19%. But the numl)er of seedlings in this case was too small to signify a real advance. Penstemon gentianoides. In 1892 I had raised four tricotylous plants from bought seed. They produced respectively 0.3, 1.0, 2.6 and 3%^ tricotyls in 1893. I planted out the tricotylous seedlings of the best seed- parent, but only six managed to flower. Their seeds gave ratios varying from 4% to 12% (March 1892), with a mean of 7%. The tricotylous seedlings of those seed- parents only which had ratios above 10% were planted out. Of these 8 tricotyls, 6 hemi-tricotyls and 2 tetra- cotyls have flowered. The seeds of the former gave ratios of tricotyls, ranging from 0 to 2>.Z% with a mean of 2.8%; the hemi-tricotyls from 1.27^) to 2.4% with a mean of 4.8% ; and the four tetracotyls 10% and 11%-, amongst which, however, only a single seedling had four cotyledons. The offspring of both of these tetracotyls and of the best of the remaining seed-parents were planted out in 1895. Only in the case of eight plants, however, w^as the harvest a sufficient one and gave a ratio which as a rule was between 0 and 12% and which Tricotyloiis Half Races. 389 attained its niaximuni in 15%. The latter occurred amongst the 300 seedlings from the seeds of a daughter plant of one of the two tetracotylous grandparents. In the last three generations the maximum ratios were, therefore, 12, 11 and 15%, indicating no advance of any significance. Polygonum Convolvulus. A tricotylous plant flow- ered in 1888, in isolation, in my garden. Its seeds gave rise to normal seedlings only (1889). From their seeds, ahout 4000 in all, 1450 seedlings were raised, and 12 of them were tricotylous, i. e., 1% (1890). I harvested the seeds of six tricotylous plants separately, and ohtained ratios from 1 % to 2.4% in sowings of about 1000 seeds each. Of these, 12 seed-parents produced only about 1% in the next generation in the spring of 1892; two of them, however, produced 1.5 and 2%. Seventeen plants were planted out. In their crop (April 1893) the proportion of tricot3ds varied from 0.5 to 2% in lots of 200 and 400 seedlings, and twelve tricotyls succeeded in flowering. The next generation (April 1894) contained, in the best cases, 2.8% tricotyls ; the next one, 0 to 2% from 8 seed-parents (1895) ; and the last, or ninth, again 2% only. Silcne conica. In 1892 I had a few tricotyls in flower from seed received by exchange from another botanical e^arden. Their seed ^-ave 3 tricotvls pmonest 1000 seedlings. I planted these out, together with some dicotylous seedlings, and in May 1894 I had from 0.2 to 1% tricotvls in everv lot of 350 to 800 seedlino^s. Eii^ht tricotyls were planted out and in the spring of 1895 their harvest gave a proportion of only 2% and less. From these T obtained in 1895 a fourth generation, 390 Tricot yl oils Races. the seeds of tour seed-parents producinj^- no tricotyls and those of one, 2 amongst 500 atavists. Silcnc conoidca, like the foregoing species, was ob- tained by exchange in 1892 and gave a snigle tricotylous seedling. In the following spring I had abotit as nian\' tricotylous seedlings as in the previous species ; and in the succeeding generation (1894) 3% tricotylous plants amongst 407 seedlings from seeds of a single tricotylous seed-parent. Only these 12 tricotyls were then planted out; and their seeds were harvested separately in late summer. In every lot I recorded from 300 to 900 seed- lings and only in two cases, where the har\ est had 1)een too small, so few as 200. The sowings contained, as a rule, from 0.5 to 1.5% and only in one case, amongst 316 seedlings, 3% tricotyls. All the vigorous tricotylous seedlings were planted out in such a way that the off- spring of the individual seed-parents stood in grou])s. Hieir seed was harvested from each seed-parent and sown separately; and the proportion of tricotylous inch- viduals was determined for each among 300 seedlings. This proportion fluctuated, for the 26 seed-parents, l^e- tween 0 and 4.2%. The separate groups manifested no relation to the .hereditary index of their several seed- parents. The off"spring of parents with 0.5% and also of those with 2% and 3%, had, as a rule, 0.6%. On the other hand the offspring of seed-parents with a mean of 1 % exhibited this mean ratio of 1 %. again, and the highest figure obtained in this experiment, 4.2% oc- curred amongst them. The maximum values in the three succeeding genera- tions were therefore 3, 3 and 4%, i. e., they were fairly constant. In Silcnc uocfiflora, also, I have studied tricotyly TricotyluHs Half Races. 391 through the course of four generations (1891-1894), and found it heritable to the extent of from 1 to 2%, but I have not made any detailed records. Spinacia olcracca. The spinach also contains tri- cotylous seedlings. I employed the Dutch spinach with smooth round seeds without thorns, a fine and perfectly constant type. In 1892 I found a tricotylous specimen, and grew this amongst some normal i)lants, because the species is dioecious. When the harvest was first exam- ined there proved to be five tricotyls and one hemi-tricotyl amongst 1000 seedlings, i. e., 0.6%. Then the best tri- cotyls v^^ere selected from several thousand seedlings ; thirteen being met with. During the flowering period, several of them proved to be monoecious, a phenomenon which sometimes occurs in this species and has been ob- served also in Cannabis sativa, Mercttrialis annua, and others. I harvested the seeds separately from 5 female or monoecious plants, and obtained ratios of 0, 0, 0, 1 and 2% tricotyls amongst the seedlings, of which only 4 managed to flower. They were one male and 3 female plants which latter set an abundance of seed. They gave ratios of 0, 0 and 2%, the latter occurring amongst 430 seedlings. In the summer of 1895 the tricotyls flowered, and I collected the harvests of the various female plants separately, and thiis was able to determine the proportion of tricotyls for each parent in the spring of 1896. This fluctuated between 0 and 3% and in one case reached 4% (mean 1.5%). Summary: The results of the experiments described show that, in the cases dealt wn'th, a stringent selection, extending over three years, failed to effect any definite and certainly any considerable advance. The individual instances fall into two categories ; as a rule the propor- 392 7^ricotylons Races. tion of tricotyls was 1 to 2% and reached 3 and 4% so rarely that these numbers must perhaps be regarded as the extreme results of the errors of observation which are bound to occur in such countings. In two species the ratio was about 10 to 15%, but these were both perennial forms which, in my annual cultures set but little seed. They were Lychnis fulgcns, from 1892 to 1895, with 5 — 13 — 11 and 8 — 19% tricotyls and Pcnstemon gentianoidcs in the same years with 3 — 12 — 11 and 15%. They should perhaps be excluded from further considera- tion. Summarizing my data therefore (with the omis- sion of these cases) we obtain a very uniform picture of the inheritance of tricotyly in half races under con- tinued selection. INHERITANCE OF TRICOTYLY IN HALF RACES UNDER CONTINUAL SELECTION. FIRST GENERA- TION MAXIMUM VALUES IN THE SPRINGS OF ■. 1890 1891 1 2.4 1892 2 1893 2.8 0.2 2 0.3 3 0.6 1894 1.1 0.4 2.8 1 3 2 1895 3.7 0.4 2 2 4 2 1896 Oenothera rubrvnervis . . Chenopodium album . . . Dracocephalum moldavicum Polygomim Convolvulus Silene conica " conoidea .... Spinacia oleracea .... 1892 1889 1892 1888 1892 1892 1892 1 1 2 0.7 0.4 4 Thus we see that tricotylous half races exist which even under the most stringent selection can produce only small percentages of this anomaly. So far as we can conclude from indirect data, half races of this kind ap- pear to be widely distributed in the vegetable kingdom. Samples of seed, whether they be bought or collected in Tricofylous Races Do Not Arise by Selection. 393 the garden or in the field, which give rise to no more than occasional aberrant forms amongst about 10,000 seed- lings, as a rule strongly suggest the existence of such half races. § 5. TRICOTYLOUS INTERMEDIATE RACES DO NOT ARISE BY SELECTION. In the first part of the first volume I brought to- gether a long series of facts from botanical and horti- cultural and, most important of all, from agricultural literature, w^hich afforded sufficient proof that specific characters do not arise by selection. Applied to tricotyly, the truth of this generalization is demonstrated by the results of the experiments de- scribed in the foregoing section (§4) and summarized in the table on the preceding page. This result is in com- plete agreement with my experience in regard to the origin of species and constant races in other cases. In contrast to these the so-called improved races of the agriculturists which have arisen by artificial and re- peated selection are constant only to a small extent (Von Rumker). On the other hand the so-called heritable or constant races do not arise by selection, with however much acumen and perseverance it may be prosecuted.^ The distinguishing terms are, I admit, not very practical and open to much criticism. The two kinds of races which they indicate are, however, absolutely distinct things, among wild plants as well as among cultivated species; but, unfortunately, if we only have a single in- dividual before us we cannot, as a rule, determine to which of the two types it belongs. Only its progeny can decide, and even this, often not until after the lapse of ^ See Vol. I, p. 106. 394 Tricotylous Races. several generations. But, at the l^eginning of our cen- tury, we stand only on the threshold on which systematic botany must be raised from a comparative to an experi- mental science. The experiments described in the foregoing section (§ 4) cover four generations as a rule, i. e., a selection of tricotylous plants four times repeated, and thrice re- peated for those with apparently the highest values. It may, however, be allowable to suppose that stray un- favorable individuals occurred amongst the selected ones and that a selection of longer duration might possibly be crowned with success. In order to determine this point I have, as I have stated above on page 383, continued the experiment with two species, to which I have lately added a third, through about ten generations. I devoted every possible care to the selection and carried it out on as large a scale as could be desired. The result was a genuine progress which amounted in both cases from one or two per cent to a value which reached in the seeds of some rare seed- parents, even as much as 25%. But from the character of an intermediate race with a mean value of 50% the races are still far removed, and every circumstance points to the conclusion that it is simply impossible to reach this by the method (as yet the only available one) w^hich was employed. The two plants used in these experiments were Ama- rantiis speciosus and Scrophularia nodosa. The former is an annual garden plant, much in favor on account of its height and its red foliage (Fig. 83) ; the second is a wild perennial species which is very common in this neighborhood. It flowers in its first year and can be easily cultivated as an annual. In the previous section Tricotyloiis Races Do Not Arise by Selection. 395 (§ 4) these two species were omitted from consideration in order to describe the experiments here in their en- tirety. The hope which I cherished at the beginning of these experiments has not been fulfilled, it is true; but I think that a brief notice of it will serve a useful purpose. The present form of the theory of selection would justify the expectation that a continued selection of the tricotyl- ous individuals would result in a race which should, year after year, produce tricotyls in continually increas- ing quantities, until ultimately a new variety or sub- species would arise, composed solely of such individuals. This form of the theory is very accommodating. If we have regard to the law of regression (Vol. I, p. 83), the mean of the race always lags further behind the indi- viduals which have been and are to be selected ; so that, as a matter of fact we never attain to the type of a new and constant race. But if we neglect this law, as is now frequently done, w^e might expect that continual and uniform progress, which alone could account on the ground of the theory of selection for the origin of spe- cies in the vegetable and animal kingdom. And lastly we might assume an increase of variability in the chosen direction by means of selection, an hypothesis wdiich, as I har-e shown in the first part (p. 9), is entirely unsup- ported by evidence. The first of these hypotheses would lead us to ex- pect a variable tricotylous race, never becoming perfectly constant, a thoroughbred race in the agricultural sense of the word. The second would lead us to expect a con- tinuous and uninterrupted increase in tricotylous indi- viduals resulting in a constant tricotylous subspecies. The third would point to a gradual acceleration of the 396 Tricotyloiis Races. process. As a matter of fact neither one nor the other has occurred. If we would speak of a thoroughhrcd race I only obtained a thoroughbred half race with a mean value of no more than 10 to 15% wdiich remains dependent on the selection of seed-parents with about 25%, and is perhaps capable of some very small further improvement. The second hypothesis is so remote from facts that as yet it hardly admits of being tested ; my experiments at any rate, lend no support to it. Rather might they be taken to be in favor of the third view ; for the progress does actually seem to become gradually more rapid after the first few years. But then it should be remembered that selection is at first a ver}^ difficult matter, the tricotyls being still very rare, and for a large part delicate and unfit for further cultivation. In sub- sequent years there are hundreds of tricotyls from which the strongest may be selected ; and we can even limit ourselves to the best specimens produced by the best parents and grandparents, and thus carry out a much more stringent selection. In reality the acceleration of the progress is thus brought about by a practical im- provement in method and not by a biological increase in variability. At first I entertained the hope that even if these ex- pectations were not justified some relation between varia- bility and mutability might perhaps exist. ^ I imagined that the capacity for producing mutations might be con- ditioned by external influences and therefore might it- self be a variable character. The diversity amongst the mutation-coefficients of my Oenotheras seemed to sup- ])ort this view.^ Moreover the external conditions which * See my Intracellular Pangenesis. "" See Vol. I, p. 337. Tricotyloiis Races Do Not Arise by Selection. 397 shift the variabiHty in the half race in the plus direction might perhaps be the same as those which would lead to a mutation and thereby to the sudden origin of a rich intermediate race. This would, in fact, perhaps, constitute the smallest step amongst all the possible forms of mutation.^ If a mutation were ultimately to be in- duced by an improvement in the external conditions and by the choice of individuals thus modified in the desired direction,- it should most easily occur on the limits be- tween the half race and the corresponding intermediate race. My hope was, therefore, that an intermediate race would suddenly arise from my improved half race and at first give about 50%, and then, by further culture, yield still higher numbers, perhaps even 80 to 90%. This hope was based on the analogous case of the origin of Chrysanthennun segetum plcmim from C. segctwn grandiflorum ; for in this way tricotylous races behave when they happen to be found and are isolated (see § 6). A step of this kind I have, however, not yet observed. In the case of both species I have determined the heredi- tary capacity of as many as 300 seed-parents in a single year, but without result. I have employed every device of culture and in Scropludaria I sowed the seeds of the second and sometimes those of the third year of the life of the plant ; but every advance was followed by a step in the reverse direction. I believe that I have tried everv- thing that was possible to me at the time, and I liave continued to make every conceival^le effort in spite of the * See p. 20 ; with regard to premutation. Vol. I, p. 490; and with regard to varieties and subspecies, p. 64 of this vohime. ^Alimentation ct selection. VoUunc jubilaire de la Societe de Biologic, 1899; and Vol._ I, p. 142 of this work where the statement is made that "selection is the choice of the best nourished individ- uals." 398 Tricotyloiis Races. fact that the goal l)ecame ever more obviously unattain- able; but nothing I did was of any avail. The half races remained half races, and the prospect of attaining an intermediate race is no greater now than it was at tlie beginning.^ I shall proceed now to the description of my two ex- periments. Amarantus spcciosus (Fig. 83). In 1889 I had a tricotylous and a hemi-tricotylous specimen of this fine garden plant, w^hich usually attains a height of from VA to 2 meters. They flowered together, but far removed from any other specimens of the same genus. ^ I har- vested the seeds separately, but only sowed those of the hemi-tricotylous plant. This had a small comb-shaped extension of the summit of the raceme as is showni in Fig. 83, and as it afterwards often occurred in this race. Its seeds gave rise to four tricotyls and one hemi-tricotyl amongst 110 seedlings, that is, a proportion of about 4.5%. The degree of inheritance therefore proved to be greater than in most of the other half races investi- gated (^4). The culture was, however, unfavorable, since only one hemi-tricotylous plant could be brought to flower, and since therefore a number of atavists had to be cultivated with it as a precautionary measure: but I only saved the seed of tlie hemi-tricotylous plant. This produced 6 tricotylous and 5 hemi-tricotylous seedlings amongst 250, that is, about 4.5% or the same amount as in the previous generation. This time, however, T could plant out the aberrant forms only and I managed to keep the majority of them alive. Only one, however, ' Mutations must, nevertheless, have external causes, and these must be found some day, but perhaps by some other means. ^ Amarantns spcciosus is regarded by some authors as a sub- species of A. paniculaliis. Tricotylous Races Po Xol Jrisc by Selection. 399 flowered. It was a richly branched compact tricotylous specimen, which was only a meter high. It set an abundance of seed, which produced a proportion of hemi- tricotyls and tricotyls, much greater than that attained Fig. 83. Amaraiitus speciosus. Top of a plant of two meters height from tlic tricotylous half race. in the previous generation. There were 89 aberrant forms amongst 700 seedlings, that is, about 13%. A very considerable advance had therefore been made 400 Tricotylous Races. in the fourth generation (1892) and this has been main- tained since that time in spite of considerable fluctuation. Up till that time my selection had been limited by the fact that only hemi-tricotyls had survived to become seed- parents. From this point onwards I had both hemi- tricotyls and tricotyls in abundance. For the next four years I selected in these two directions, and maintained a tricotylous and hemi-tricotylous race simultaneously (1892-1896), but as no essential difference was mani- fested between the two I abandoned the hemi-tricotylous race, as stated in § 2, and only went on with the tricotyl- ous one. The account which follows relates solely to this. But before I proceed with it I wish to call attention to some facts relating to the method of culture. The seed was sown in sterilized soil in pans ; the soil was not manured. As soon as the cotyledons had fully unfolded and before the first leaf was visible, the seedlings were recorded. All, or nearly all, of the dicotylous ones were destroyed and only the aberrant forms saved. Of the latter I chose what I considered to be a sufficient number of the strongest specimens, and planted them singly in pots with heavily manured soil. The best manures for this purpose are nitrogenous ones. If the number per- mits it, two tricotyls are put in each pot, of which the weaker is subsequently killed out. This transplantation takes place in April or May ; the pots are kept under glass in the garden until June, during the nights at any rate. Then the plants are planted out into the bed at distances of from 20 to 30 centimeters, and the larger lateral branches are cut off in order that the plants may not interfere with one another. The plants are monoecious, the male and female flowers standing close together. Self-fertilization seems to be the rule; for isolated plants Tricotyloiis Races Do Not Arise by Selection. 401 set as much seed as those grown in groups. The seeds do not fall out and as soon as the desired quantity is ripe the whole raceme is cut off and rubbed between the hands. One cubic centimeter per plant, and often less, is suffi- cient for next year's seed ; as a rule I obtained about 4 to 5 cubic centimeters from each individual. After the transplantation of the seedlings the length of the cotyledons, and of their stalks especially, increases considerably. In this way it may happen that specimens which, at their first examination, appeared to be pure tricotyls are found to have two of their cotyledons united at the base, and therefore to be deeply cleft hemi-tricotyls. I have as a rule removed such specimens when I discov- ered them, and not cultivated them further, although this is not actually necessary. In the summer of 1892 I had 11 tricotylous speci- mens which flowered in a group as far removed as pos- sible from the hemi-tricotylous culture already men- tioned. The harvest gave a maximum of 11.9% tricotyls, but on the average only 1 to 6.5% with a mean of 3.5%. In 1893 I planted out the purely tricotylous seedlings only of a seed-parent with a hereditary value of 6.3%. I saved the seeds of 15 plants, examined between 500 and 1000 seedlings per seed-parent, and obtained values which fluc- tuated between 2.6% and 7.4%; mean 4.7% (1894). I selected the parent with 7.4% for the continuation of the race and only planted out the best tricotylous speci- mens from amongst its offspring. I had 44 tricotyls amongst 1000 seedlings to choose from; besides these tliere were 31 hemi-tricotyls and one tetracotyl. I re- peated the evaluation of the ratio with 4000 seedlings and found 7.2%, that is to say, about the same value. At the end of the summer of 1894 my culture con- 402 Tricotylous Races. sisted of the 20 best tricotyls only, and 16 of these ripened their seeds. In this generation, however, there was a considerable step back, for the individual parents varied between 0.5% and 3.7% ; and one parent had not a single aberrant form amongst 200 seedlings. The mean was 1.8%. The seeds of the five best plants were again sown and 1000 seedlings from each examined. The values were now 2.6 — 2.8 — 3.2 — 3.2 and 3.6%. In the following years I endeavored to determine the cause of this re- turn by a series of collateral experiments, but without success. The variability of the hereditary value in such races obviously depends in great part on causes which we do not yet understand. I now planted out the tricotylous offspring of two plants with 3.2 and 3.6%, but in two separate groups in order to be able to confine the selection to the offspring of one of them later, if desired. These cultures consisted of 12 and 13 tricotyls, no essential difference between them being manifested. The values calculated from the batches of 300 seedlings from each seed-parent were : SEED- VALUES CALCULATED FROM THE OFFSPRING PARENT (Spring, 1896) with 3.2 % 1.3 1.7 1.7 2.0 2.3 2.3 2.7 2.7 2.7 3.0 4.0 5.5 with 3.6% 0.7 0.7 1.0 1.3 1.7 2.0 2.7 2.7 3.0 3.0 3.7 4.7 5.3 The mean for both cases was therefore about 2.5% (actually 2.5% and 2.7% respectively). This experi- ment proves how little effect an enlargement of the ex- tent of the cultures has in such an experiment in selection, for if I had only dealt with the offspring of one of the two parents, the result would obviously not have been essentially different. In the summer of 1896 I did not go on w^ith this cul- ture, but tried to find out whether by planting out a con- Tricotylous Races Do Not Arise by Selection. 403 siderably larger number of individuals, I could yet im- prove the prospects of success. For this purpose 1 se- lected the two plants of 1895 which seemed to be the best, and for which I had found the highest values in the spring of 1896, viz., 5.3% and 5.5%. In order to have a large crop to select from, I sowed 15 culjic centimeters of seed, and raised from 15,000 to 20,000 seedlings, of which the strongest tricotyls and hemi- tricotyls were planted out singly in pots, and later put out in the beds. Three sowings were made, at the end of March, at the end of April and in the middle of May, in the hope of possibly increasing thereby the varialjility and the prospect of a mutation. Furthermore, within the three groups, widely different positions, different degrees of remoteness of the individual plants, and different treatment in the matter of pruning, obtained. Many plants gave more than 30 cubic centimeters of seed each, but more than ten cubic centimeters was never saved. Altogether I saved the seeds of about 450 plants, and sowed them separately. For each seed-parent 300 seedlings were recorded in 1898; and the proportion of tricotyls was calculated from these data. The result was, however, that a very great difference was seen to exist between the two grandparents of 1895; the one with the \'alue of 5.3% proved to be a bad stock plant. Amongst its offspring, of which there were 30, the ratio was greater than 3% in ten cases only, and on the average it was 0.3 — 0.5%.' And this in spite of the treatment, which, though varied, was the best that could be given, and in spite of the complete exclusion of atavists. The second grandparent, with the value of 5.5%, proved as fortunate in its progeny as the former had been unfortunate. Its offspring had all been sown to- 4U4 Tricotyloiis Races. gether, and planted out under the same average treat- ment on the same bed and on the same day. About 140 plants set seed abundantly. On the average, however, this culture was not better than those of the previous years, for it only yielded a ratio of 4.5%; but the range of variability was much greater. Eight plants occurred, the hereditary coefficients of which exceeded all previous ones. Of these, six were 14 to 17%, one 21%, and one 25%. Here the possibility of a sudden advance seemed to open up. Before I give the whole series of figures, I wish to make one further observation. If in the year 1897 I had not cultivated 450 plants, but only, let us say, one- third, I would have limited myself to the offspring of the grandparent with 5.5%, although the value is only apparently greater than the other, because the difference lies within the limits of observational error. I would then have obtained precisely the same result with only one-third of the labor. In other words, neither the se- lection of tricotyls as seed-parents, nor the attention paid to the hereditary values, although this excludes the poor- est tricotyls in spite of the latitude of possible errors, can make the experiment independent of chance. Noth- ing less than carrying out the experiments on a much larger scale can effect this. But the results of the two following generations will show that even in the present very favorable case, no real or permanent advance was effected. The values obtained, in the spring of 1898, for the 140 offspring of the best parent of 1895, which itself had a value of 5.5%, are distributed as follows: (P refers to the figures in percentages and A to the cor re- Tricotylous Races Do Not Arise by Selection. 405 spending number of offspring which manifested these numbers amongst their seeds). P 1 2 3 4 5 6 7 8 9 10 11 12 13 U 15 16 17 21 25 A 16 27 30 18 18 11 6 4 2 2 2 3 2 1 2 1 2 1 l This series only relates to the tricotyls selected for my experiment. If I had planted out the whole progeny of the parent in question without selection, the number of low values would most certainly have been somewhat larger; and the apex of the curve would perhaps have stood over the 0 instead of over 3%. But the chief point in this series is that from 3% onwards the figures regu- larly and continually diminish in such a way that the two extreme variants with 21% and 25% round off the series continuously; i. e., in the ordinary manner pecu- liar to physiological curves. It is obvious that they do not stand in discontinuous relations to it. In the estimation of the higher individual values a latitude of 5% must be allowed, i. e., the figure 15 de- notes a real capacity of from 10 to 20%, the figure 2? one of from 20 to 30%. In the case of extreme devia- tions it is always well to assume that these errors may have operated in the same direction. We may only state, therefore, that by means of a cultivation through eight generations, a ratio of 20% has been attained. But whether or not this is the limit, we do not know. Also, it is uncertain whether the parent with 25% was reallv better than those with 15 to 21%. But it is certain that the best seed-plant, as judged by its hereditarv value must be one of this group. Therefore, at this stage in the development of our race, the process of selection has become much more certain than before and less dependent on chance. It is only necessary not to limit our choice to those which 406 Tricotyloiis Races. appear to be the very best, but to cultivate also some of the next best seed-parents for the continuation of the race. Of the culture of 1897 I selected five, viz., those with 16, 17, 17, 21 and 25%. In order to allow as manv different external factors as possible to come into play, I sowed the following generation in two subsequent years (1898 and 1899), and in the first year in two separate lots, one in the middle of April and one in the middle of May. Altogether somewhat over 400 tricotylous plants were planted in this year, and the hereditary capacity was determined on 300 seedlings in each lot. But in spite of every care, the result was a return to ])revious values, and this in the case of every one of the five parents. The mean value for all of them was only 2%; the five highest values were 9.6 — 10.6 — 10 — 11 — 11% mostly amongst the offspring of the same grand- parent (E in the following table). Below I give a short review of the values found separately for each individual grandparent of 1897. The countings were made in the spring of 1899. A. Grandparents in 1897 A Their values in spring 1898 . B. Parents sown on April 21st, 1898: Their values in spring 1899: Maximum Mean C. Parents sown on May 7th, 1898: Their values in spring 1899: Maximum . 9.6 6.6 4.6 6.3 7.3 Mean 4.1 2.2 2.1 2.5 2.5 Mean of the two series ... 2.8 1.5 1.4 1.8 3.6 The two grandparents with 16 and 25% must there- for be regarded as the best ; and it must be supposed that the five exceptionally high figures were brought about A B C D E 16 17 17 21 25 5.3 2.6 3.0 3.3 11.0 15 0.8 0.7 1.1 4.7 Tricotyloiis Races Do Not Arise by Selection. 407 by peculiarly favorable circumstances which were not repeated in the following year. The repetition of tlie experiment in 1899 gave prac- tically the same result. All in all, in the ten generations of my experiment, there occurred neither a sudden nor a gradual transition to an intermediate race. And lastly let me summarize the whole culture in a simple table which gives only the mean and the highest value for each generation as well as the value for the seed-parent selected for the continuation of the race. GENERA- TION YEAR OF FLOWERING VALUES FOUND IN THE FOLLOWING SPRING MEAN MAXIMUM SEED-PARENT I. 1889 4.5 II. 1890 — 4.5 III. 1891 13 IV. 1892 3.5 11.8 6.3 V. 1893 4.7 7.4 7.4 VI. 1894 1.8 3.6 3.6 VII. 1895 2.5 5.5 5.5 VIII. (450 Ex . ) 1897 4 25 16-25 IX. (400 Ex .) 1898 2 11 — The whole series, with the exception of the maximum figures for 1897 rather indicates a fluctuating around a constant mean value than a steady progress under the influence of selection. Scrophularia nodosa. Of this species a series of forms occurs. Their characters have been given in the Prodrouius of De Candolle. The leaves are broadly cordate or only rounded at the base, with little teeth of almost uniform size, or very coarsely and irregularly indented, and tiie fruits are large or small. The form with cordate, tiniformly toothed leaves is very common, in this neighborhood, and, so far as I know, the only 408 Tricotylo us Races. one that occurs. The form with coarselv dissected leaves rounded at the base, and small flowers and fruits, is the one employed in my experiments (Fig. 84). In the summer of 1901 I planted out large numbers of both types in my garden, after a close examination of their characters. Both are, as far as my experience extends, quite constant for many gen- erations, i. e., they are good subspecies. My culture began in 1890 with the seeds of a tricotylous plant from our botanical gar- den, which, in the following year, produced, besides a num- ber of atavists, four plants with three cotyledons and a main stem with ternary whorls up to the inflorescence (1891). From the seeds of one of these plants I again obtained in the summer of 1892 some tricotylous seed- lings, the majority of which, however, became decussate af- terwards. Only two of them remained ternary throughout the summer, and these were the only ones which I allowed to flower. Among their seed I counted 780 and 1000 seed- lings respectively, and found the value in each case to be 1%. In 1893, 16 tricotylous plants flowered and constituted the fourth generation of my race. Their seeds were saved separately and produced a mean of from 1 to 2%, Fig. 84. Scrophularia nodosa. Main stem of the tricotyl- ous half race with ternary whorls of leaves. Tricotylous Races Do Not Arise by Selection. 409 in the best cases 2.4 to 4.1 and 5.4%. The counts were made on 700, 800 and 2000 seedHngs. These three plants had, however, decussate leaves on their main stems, and this shows that the disposition of leaves on the stem is of subordinate value in selection. In the later genera- tions I have always selected the ternary individuals where possible, but have not found that they are any better than the others. In the summer of 1894 tricotylous seedlings of the seed-parent w^ith 5.4% were planted out. I saved the seeds of 25 plants separately, and in the following spring examined from 300 to 500 seedlings in each crop. The values were essentially the same as in the previous year, and varied between 0.5% and 5.5% with a mean of 2% : and the five best gave 3.6 — 3.8 — 4.0 — 4.2 and 5.5%; the three last values are based on counts of 1000, 1500 and 2000 seedlings. It was only the offspring of these parents that were planted out in 1895, and only those with three cotyledons and with a first whorl of three leaves (Fig. 73, p. 366). By planting them out in three groups in the following spring, a selection was made possible which related to the grandparents. Those with 4.0 to 4.2% gave offspring with 1.3 to 5% with a mean of 3% ; (from 12 parents and from counts of groups of 300 seedlings). The grandparent with 5.5% proved to be considerably better. Its twelve offspring had 2 to 8%, with a mean of 4.5%. Seedlings of this group only were planted out in 1896 and only tricotylous specimens with ternary lower whorls, from parents with 6 — 6 and 8%. They were in all 72 strong plants each of which gave a sufficient harvest for the calculation of their hereditary values in groups of 300 seedlings. The parent with 8% gave 2 to 15%, with 410 Tricotylous Races. a mean of 6%. The two other parents 2 to 10% and 3 to 14%, with means of 6 and 7%. Obviously the difference was not sufficiently considerable to base a se- lection among the grandparents upon. On the other hand it was evident that the race had been improved by the process of selection wdiich now extended over six generations ; and this improvement w^as afterwards main- tained. For the culture of 1897 I selected the tricotylous off- spring of three seed-parents with 11 — 11 and 15% tri- cotylous offspring, and planted out 100 of them, which were all strong plants with a ternary first whorl of leaves. The harvest was recorded in the spring of 1898 in the usual way. The three parents, however, which were now grandparents, again showed no essential difference in their offspring. VALUE FOR VALUE FOR THE PARENTS NUMBER THE GRANDPARENTS MIN. MED. MAX. OF PARENTS 11% 2 7 15 20 11% 3 7.5 15 24 15% 4 8.5 13 28 Here again the figures were the same as in the i)rc- vious generation. Although, as we have seen, the selection of grand- parents, in this case, afforded no reliable ground from which an improvement of the race could be started, yet this must be the case whenever the hereditary capacity of the grandparent is much influenced by fortuitous cir- cumstances which affect the selection of the seeds. There- fore the special object of such selection is mainly to ex- clude such cases as much as possible from the main trunk of the pedigree, by simply not planting out their seed lings. Tricotylous Races Do Not Arise by Selection. 411 But when the values of several parents do not differ so greatly from one another that the differences fall out- side the limits of prohable error, individuals should be planted out every year from all of the best parents. This would, however, necessitate an increase of the cultures on too large a scale. Nevertheless I extended my culture as far as possible in the summer of 1898 on this principle, and saved the seeds of 300 plants separately. The result of the 300 counts which were made on these lots of seeds, embracing 300 seedlings for each lot, corresponded with my expectations to this extent that one of the grandparents proved to be by far the best. Its hereditary value was 14%, that of its offspring had a mean of 20%, and for two individuals even 25 to 27%. Moreover, outside the limits of this group, this race also showed an increase in hereditary capacity. The harvest of 1898 contained the seeds of 300 tri- cotylous plants, which in their turn had been raised from 15 parents with values from 10 to 15%. The results were as follows (expressed in percentages) : Parents 10 10 10 10 10 10 11 11 12 12 13 13 U 15 15 ^rr . \ Mean . 8 10 10 11 14 19 10 15 11 16 10 13 20 14 14 (JiTsprine^ - ^ ^ ( Max. . 8 11 20 20 27 26 19 25 20 24 21 21 27 21 22 Number of offspring 1 2 19 28 11 6 8 9 27 6 36 32 12 64 39 The mean of the whole series of counts was 12% and denoted a considerable increase in the character of the race. Let us now compare this series of figures with that given on page 405 for Amarantus speciostis. That series relates to the hereditary coefficients of 140, this to those of 300 plants, which in the former case belong to the 8th, and in this one to the 9th generation. Both series, therefore are the result of a selection which extended 412 Tricotylous Races. over a sufficiently long period of time to justify the expec- tation that a definite result would be obtained. They exhibit, however, one striking difference. The mean of the figures for Aniarantns is between 2 — 3%, and this renders it not improbable that, if the coefficients of the atavists could have been incorporated in the curve, its apex would have been at 0, that is to say, that a unilateral or so-called half curve would have been the result. But the apex of the Scrophiilaria curve is at 12% and varies amongst the individual families from 8 to 20%, indi- cating thereby the possibility of an isolation of a separate apex for the tricotylous specimens. In other words, the tricotylous half race of Aniaran- tus behaves, during this long period of selection, in es- sentially the same w^ay as at the beginning (table p. 407), whereas Scrophiilaria behaves like other half races im- proved by selection. The scheme representing the in- fluence of selection on the half race of Ranunculus biil- bosns scmiplcnns (Fig. 52 on page 252 of this volume) would apply equally to this case. The explanation of this difference in behavior is per- haps to be sought in the assumption that in Scrophiilaria tricotyly has only been indirectly improved. I am re- ferring to the case of Trifolium incarnatuiu quadrifoVmm which I described above on page 239. In that case the smallest seeds gave rise to the largest number of aberrant seedlings. If the production of small seeds could be increased by selection the number of seedlings with com- pound primordial leaves would also be increased. It seems possible that in Scrophiilaria similar factors were at work, since the cliaracter involved need not, of course, necessarily be the size of the seeds. The repeated selec- tion of tricotyls would not, on this assumption lead di- Tricotylous Races Do Not Arise by Selection. 413 rectly to the increase of this character, but to a supposed change in the structure of the seeds which would favor the anomaly. Whether or no this supposition is correct I do not know, but it is a fact that the fruits and seeds of my race have gradually become smaller; and that it is the plants producing the largest number of tricotyls which bear the smallest fruits and seeds, I find repeatedly noted in my records. At any rate we are here in touch with a principle which may be applicable to other cases also. A selection may produce its effect on an unknown character which in its turn will affect the character actually dealt with. With regard to the extent of my culture of 1898 it is further worth remarking that it shows that, in general, the extent of the cultures is by no means so important a factor as is usually supposed. If I had confined myself to experimenting with three or five seed-parents, as for in- stance in Amaranfus in 1897 (p. 406), I should have chosen the best ones according to their hereditary co- efficients ; and it was exactly amongst these that the best of all occurred as the series on page 41 1 shows. Increased extent of the experiment deepens one's insight into the processes involved, but does not hasten the improvement of the race ; although it is never advisable to confine one- self to experimenting with one single seed-parent, if this can be avoided. The next generation, the 10th and at present the last, has repeated the progress observed in the ninth. Here again the race of Scrophiilaria behaved differently from that of Amarantiis. I confined myself to the progeny of the plants of 1897 which exhibited the value of 14%, and amongst the offspring of which the mean attained 20%. From these I selected five specimens with 22 — 23 414 TricofyloKS Races. — 23) — 25 and 27^0. I planted out 165 tricotylous seed- lings from amongst their offspring in pots, as soon as they proved themselves also to be ternary in tlieir lirst whorls of leaves. In the following whorls about half of them reverted to the decussate arrangement. These were thrown away, and only 72 plants which remained ternary were ultimately planted out. They were fairly uniformly distributed over the crops of the five parents. From these 72 plants, 72 values, in five groups, were calculated in the following spring (1900). The lowest values, arranged in a series corresponding with the in- creasing values of the five parents, now grandparents, were 9, 8, 13, 8 and 11%, the means 16, 17, 18, 17, and 19%, and the maxima 19, 22, 26, 22 and 26%. As we see the five groups did not exhibit any essential differ- ence. The mean value of the previous generation, 12%, had now been exceeded, but the maximum remained the same. Let us now summarize the whole experiment in the following table : GENERA- TION YEAR OF FLOWER INC VALUES FOUND IN THE SPRING LOWEST MEAN FOLLOWING HIGHEST I. 1890 II. 1891 — III. 1892 1 IV. 1893 0-0.3 1-2 5.4 V. 1894 0.5 2 5.5 VI. 1895 2 4.5 8 VII. 1896 2-3 6-7 14-15 VIII. 1897 2-3 7-8 15 IX. 1898 2 12 25-27 X. 1899 8 16-19 26 Progress is, as we can see, a continual one. and the selection has been, although perhaps only indirectly, (p. Tricot ylous Races Do Not Arise by Selection. 415 412), successful throughout. Nevertheless an interme- diate race has not arisen, either graduall)' or by means of a sudden jump. The progress in the last two years was more rapid than before as the result of increased strin- gency of selection, without, how^ever, affording any in- dication that the mean of 50% was likely soon to be reached. Oenothera Bcrteriana. Besides the two cultures men- tioned which were begun in the first years of my ex- periments in selection, I have cultivated yet a third race with the same object. This race was one in whicli the intercrossing of the various individuals could always be avoided. There is, however, no ground for fear that occasional unavoidal^le crosses in Aniarantns and Scro- pJi III aria had any considerable effect on the selection pro- cess; for both species must be fertilized almost entirely with their own pollen on acount of the great number of their flowers which are open at the same time ; and they are, when thus fertilized, perfectly fertile as isolated in- dividuals show. Moreover what is spoiled by crossing is eliminated bv selection. But the evidence is more satisfactory if self-fertiliza- tion can be insured. This occurs in Oenothera Bcrteriana. Its flowers form perfectly normal fruits and seeds, when the \isits of insects are excluded. I enclosed my plants in a cage of fine metal gauze. Some years I have fer- tilized them artificially in it ; but this is quite superfluous, because when the flower withers the stigrna bends down- wards and thus reaches the pollen. Tn the two last sum- mers the cage was shut from the beginning of the flow- ering period until the seed began to ripen. Nevertheless they all produced fruits with scarcely an exception. These fruits contained an abundance of seed, and a few from 416 Tricotylous Races. each plant are sufficient, and this is a great advantage as compared with the laborious process of harvesting in Scrophularia. My culture began in the summer of 1896. At that time the prospect of obtaining an intermediate race in the other two races had already become very remote. From some plants in our botanical garden I saved seeds which produced 13 tricotyls, 4 hemi-tricotyls and one tetracotyl amongst 300 seedlings, i. e., 6%. This figure was considerably higher than most of the values of my half races mentioned on page 392, and about as high as the value attained by Amarantiis and Scropluilaria at that time. At the same time six other species of Oeno- thera were tested with reference to their production of tricotyls. I found from 0 to 1 and 2% and therefore selected the 0. Berteriana. In the spring of 1897, tri- cotyls only were potted singly, and planted out in July in the beds. Their hereditary values were determined in the following year in the case of 15 plants. They fluctu- ated between 1 and 12% and exhibited a mean of 4%. In the following generation, 1898, I was able to plant out about 60 strong tricotyls, and since that time I have con- ducted the cultures on this scale wath only slight modi- fications. 15 tricotyls from the plant with 12%, and 45 from those wnth 6 to 7% were planted out. The former group, however, proved to be no better than the latter. The values of these plants varied from 2 to 16%, with a mean of 4%. The best of the five other groups, how- ever, had values varying from 6 to 16%, with a mean of 8% (from 10 separate crops). The remainder varied between 4 and 11, with a mean of 6%. I selected the three best parents whose values were 15, 16 and 16%, and T planted out the strongest tricotylous ofifspring of The Isolation of Tricotylous Intermediate Races. 417 each (1899). This year 77 plants gave a sufficient har- vest, the figures for the three groups (each derived from a single grandparent) did not exhibit any differences worth mentioning. The minimum was 2^/c, the mean 12, and the highest value 25%. Therefore a consider- able advance on the preceding generation had taken place. In 1900 I had only 31 plants, bearing seed, which were cultivated in the same way as in the previous year. They constituted three groups, each from a single grandparent, but without exhibiting any differences worth considera- tion. The hereditary values varied between 5 and 17% and their mean was 10 to 13%. The culture of the last year (1901) embraced 40 plants, the values of which varied between 0 and 21 and had a mean of 10%. The result, like that of the two foregoing species, may now be summarized in tabular form. VALUES DETERMINED IN THE FOLLOWING GENERA- TION YEAR OF FLOWERING MEAN SPRING HIGHEST SEED-PARENTS I. 1896 — 6 II. 1897 4 12 12 III. 1898 4-8 16 15-16 IV. 1899 12 25 23-25 V. 1900 10-13 16-17 U VI. 1901 10 21 The prospect of raising an intermediate race seems therefore in this experiment to be as small as in Amaran- tus and Scrophularia. § 6. THE ISOLATION OF TRICOTYLOUS INTERMEDIATE RACES. It is just as easy to isolate an intermediate race from seed which has been bought or obtained from any other source if it happens to be already present in it, as it is 418 l^i-icofyloiis luicrs. difficult to raise one if it is not. Isolation can be effected in two to three generations as a rule, in fact as soon as the hereditary values of the plants raised from the original mixture of seed have been determined. Very little care and no artificial fertilization at all is necessary for this purpose. It takes place as quickly in dioecious wind-fertilized flowers, such as the hemp, as in self- fertilizing species enclosed in bags or cages. In the choice of species and varieties one obviously has not a free hand. We must first search for cases in which the desired races ha])pen to be present, and for this purpose sowings of considerable extent have to be made. If lots of ten to twenty grams of seed, according to the size of the individual grains, are sown, it can be seen soon after germination whether the species is likely to produce a tricotylous intermediate race or not. The oc- currence of 1 to 2 tricotyls amongst about 10,000 normal seedlings does not justify this expectation, but that of one or more per thousand does as a rule. The cultures of my half races mentioned in § 4 (p. 392) had begun in 1892 or earlier, and in the spring of 1895 there could be no doubt that I should not obtain any intermediate races from them. I resolved therefore to seek them elsewhere, and selected for this purpose about forty species and varieties of garden plants, which were chiefly annuals. The result of this sov/ing, which was conducted on a large scale, has already been given on page 380. Most of the sorts contained too few tri- cotylous seedlings. Only 8 offered the prospect of giving rise to an intermediate race, and of these I had to reject three for various reasons. The remaining five, however, fulfilled my expectations. Before I proceed to the description of my experiments The Isolation of Tricotylous Intermediate Races. 419 it is desirable, in connection with what was said in the first part of this volume, to consider what we should expect to occur in the isolation of such intermediate races as may happen to be present. The intermediate race does not differ from the ordinary types or half races in any visible characters, but only in the frequency of tricotylous specimens. If the tricotylous individuals are selected for culture from crops raised from bought seed, it is by no means certain that these and these only belong to the intermediate race, if indeed such exists at all. For in addition to this, the half race is almost always present, and this, as we know, also contains some tricotyls. On the other hand the intermediate race always produces atavists and usually in considerable numbers. Provided therefore that the crop contains an intermediate race, some of the dicotyls and some of the tricotyls would be- long to it ; but the prospect of obtaining it from the latter w^ill obviously be greater than from the former. For this reason I select, whenever possible, tricotyls only for trans- plantation. All that then remains to be done is to save their seeds separately from each plant and to determine their hereditary values in the harvest. If any of these are especially high they belong to the intermediate race, and all the res! are thrown away inasmuch as they in- clude the half race and the doubtful cases. Ordinarily the race is by this time perfectly pure and can be improved by selection on the ordinary lines. As a rule, the means of the curves describing my intermediate races, lie be- tween 50 and 60%, and can be brought as high as cSO to 90% by selection in occasional individuals. In contradistinction to the unsuccessful experiments described in the previous section there can be no doubt in these successful cases that we are not dealing with the 420 Tricotyloiis Races. selection of the extreme variants of ordinary fluctuating variability. Even the doctrine of unilateral increase in variability as a result of selection is of no help in this case (see § 2, p. 9), for selection could hardly operate so rapidly as to produce its whole effect in a single gen- eration. The old saying of gardeners that the first con- dition necessary for the production of a novelty is to possess it already, also applies to these purely experi- mental races (Vol. I, p. 185 and elsewhere). If the tri- cotylous race does not already exist it cannot, at present at any rate, be either isolated or bred. A high percentage in tricotyls is seldom found in wild species. The highest value I have yet found oc- curred in Linaria vulgaris in the spring of 1894 in a sow- ing of the seed of a hemipeloric plant of the race that I was cultivating at that time (see p. 211). There were 59 tricotyls amongst the 425 seedlings, i. e., 14%. Amongst commercial seed the prospect of obtaining intermediate races seems to me to be the greatest, as I have already stated, in those sorts which are cultivated on a large scale in the field or in the garden. It is much smaller in those varieties of flowers which are only grown on a small scale every year. Moreover it seems obvious that cul- tivation on a large scale should favor the origin of new races. If the intermediate race, which is being sought for, exists in some sample of seed, we may expect to find mean, bettei or inferior representatives of it. If the former is the case the mean character of the race, that is about 50 to 60% of tricotyly is attained at once, and this occurs in the majority of cases, as might be expected and as the table at the conclusion of this section Avill show (p. 439). Individuals with a higher productive The Isolation of Tricotyloiis Intcnncdiate Races. 421 capacity are rarely found at first. I came across an instance of one only once, at the beginning of my experi- ment with the syncotylous Helianthiis anniius (see the following chapter). If individuals with low hereditary ca- pacities are found, those with mean values can as a rule be easily raised from them, for they are to be regarded simply as minus variants of the race sought for; and will therefore, in conformity with the law of regression, revert to this value even if selection be only suspended (see above, p. 5). Experience shows, and the table al- ready referred to will demonstrate, that one or two gen- erations are, as a rule, sufficient for the attainment of values of 50 to 60%. Before I proceed to a detailed description of my ex- periments I will give a few instances to show the course which these experiments in the isolation of tricotylous intermediate races follow. The attaimncnt of the mean value. On page 380 I have given, in a small table, the numbers of tricotyls which I found in some samples of seed in the spring of 1895. For some of these species these tricotyls were planted out and their seeds saved separately and sown. I obtained values from 12 to 19% in the best individuals (s])ring 1896), and on the rest, as a rule, much fewer. These were regarded as belonging to the half race or as of doubtful significance. The tricotyls from tlic best ])arents were now (1896) planted out, and the hereditary value for each was calculated in the following spring. Below I gi\e a resume of these figures in groups of 0 — 2, v^ — 7, 8 — 129; , with means of 1 — 5 — 10% and so forth, for convenience of comparison, and indicate, f(^r each such reduced value, the number of individuals which exhibited it. 422 I'ricotxlous Races. ISOLATION OF TRICOTVLOrS RACES. HEREDITARY VALUES OF THE SECOND GENERATION. FIRST GENER- 1 5 10 15 20 25 30 35 40 45 50 55 60 65 ATION C/a t k ia p u Ich ell a 16 r^ 0 1 1714734 2 1422 rap'iver Rhoeas 18% 0 0 2854310001 Papaver Rhoeas 19% 0 0 11821440] Phaceliatanaceti folia 14%033113 8 6 4 2 2 2 It is easily seen that in such cultures the choice of specimens which belong undoubtedly to the intermediate race is made possible. All plants with a low hereditary \alue are simply rejected, since the possibility exists that among them may be hidden In-ljrids between the two races. The high values are free from this doubt and indicate the pure race we are searching for. Thoroughbred races. Under this term those races are included in agriculture which have been considerably improved by stringent selection. In the first part of the first volume we have seen that they remain de]:)endent on continued selection, and do not really become constant. For studying the features of such races, the tricotylous intermediate races afford most suitable material, for, after reaching the mean value of about 50%, we may select the extreme variants, and, by their culture, improve the race much farther. As instances I choose Mercurialis annua, a large agricultural crop, and Silenc infJafa, which I derived from seed introduced with cereals. Botli cul- tures were started in 1892, and reached a hereditary value of 55% in the harvest of 1894. From ])lants with this value I raised a fourth generation, which oft'ered me the following figures : The Isolation of Trkotyloiis Inlcnncdialc Races. 423 SELECTIOxN' OF THOROUGHBRED TKICOTVLOI'S RACES. llEkEDITAKV VALLES OF THE BEST TRICOTVLOUS SEKD-l'AkENTS UE THE FOURTH GENERATION. THIRD GENER. 25 30 35 40 45 50 55 60 (o 70 75 80 85 ATION jMercuria/is ainiiia 55% 12 2 12 12 3 1 Silene inflata 55% 10234444711 It \\ ill be seen that regression did not accompany this ..election, because the parent plants deviated too little as vet from the mean of the new race. On the other Irmd the high values of 75-85% were immediately reached, and this obviously indicates a considerable advance. These instances, taken together with the table which will be given on page 439, are sufficient to indicate the method by which tricotylous intermediate races, if they are at all present, can be isolated and improved. They will facilitate the understanding of the detailed description of my experiments. These obviously present, according to the species investigated, greater or less deviations from the instances given, but as a rule they are not essential ones. Therefore I shall give these descriptions as briefly as possible. But before doing so I wish once more to lay emphasis on the fact that these cases are thoroughly distinct from those in which only half races are present, and from which, after several generations, often no more than 2 to 4% and only very rarely as much as 20% was reached, as maximum figures (see table on page 392). Oenothera hirtella. Under this name I cultivate a tricotylous race which I obtained by chance from bought seed. In 1895 I was growing some samples of seed of Oenothera Laniarckiana and allied species which had 424 Tricotylous Races. either been bought or obtained by exchange, in order to compare them with my own strains. In the autumn I saved the seed of a number of separate specimens and sowed it in the hope of finding a tricotylous intermediate race amongst them, inasmuch as my own races and vari- eties offered no prospect of producing them, as has al- ready been mentioned for a special case, that of Oeno- thera ruhriiiervis (p. 383). This hope was fulfilled by a single specimen, all the remaining lots of seed giving the usual very low values of from 0 to 4%. This specimen was a plant which was noticed by some striking distinc- tive marks. It was taller and slenderer in growth than all the other species, more than 2 meters high, with a long raceme interrupted in places by the failure of some of the lower buds. Its flowers were of the size and structure of those of 0. biennis and, like this form, were self- fertilized within the buds before their opening. Its pro- geny have kept true to this type through a series of gen- erations. This stray plant produced from its seeds, in a lot of 300 seedlings, 7% tricotyls, and in another estimation, amongst 2430 seedlings, 8% tricotyls, of which 143 were tricotyls in the restricted sense, 59 were hemi-tricotyls, and 4 tetracotyls. Whether the parent itself had three cotyledons, I do not of course know. Of this crop the tricotylous seedlings only, and of these only the strongest, were planted out on the 2d of April, 1896. In the middle of July, some few days be- fore they flowered, the whole bed was covered with a great cage of fine cloth. The cloth was removed at the beginning of September and at the same time all the open flowers and buds were removed from the plants. Seeds were saved separately from 54 individuals and 300 The Isolation of Tricotylons Intermediate Races. 425 seedlings were counted from each lot. The result was a very remarkable one. With a single exception the fig- ures formed a close series of which the mean was 7%, whilst the great majority of figures lay between 2 and 12%. (Two parents with 0.5 and 1.0 and three with 13, 14, and 17%.) Besides these there was a single plant which stood far from the others in the series. It had produced 56% tricotyls, i. e., more than half of its seeds were tricotylous. For the sake of greater certainty this value was determined twice. The percentage value calculated from a lot of 768 seedlings was 58% ; from another of 657 seedlings 54% ; with a mean of 56% for 1492 seedlings. This one plant, therefore, had a hereditary value which corresponded closely with the mean value which we should expect the intermediate race sought for to possess. Of course the experiment was continued from the seeds of this plant only. The seedlings of all the other parents, tricotyls as well as dicotyls, were thrown away. Two courses were now open to me, either simply to maintain the race, or to endeavor to improve it by further selection. In the former case, selection would have to be avoided as much as possible, and we should have to harvest and sow the seeds of all the specimens mixed together, and in planting out the seedlings be careful not to give preference to the tricotyls. I have not done this ; but as is my custom, I have harvested and recorded the seeds of each individual separately and only planted out the seedlings of the best parents, that is to say the parents with the highest hereditary values, for the continuation of the race. In the summer of 1897. 37 tricotylous offspring of the 426 Tricotylous Races. parent with the value of 56^0 flowered in a cage of metal gauze. The values, calculated in the usual way from the harvest, gave a good curve, whose mean was 72^0. The lowest percentage of tricotyls was now 38%, the three highest 83 — 83 and 89^0, that is to say, a very consider- able advance. Atavistic seedlings of the same parent were also planted out. but they naturally exhibited a somewhat smaller advance. In the following year, 1898, I did not sow the seeds of the plant with 89%, but from various considerations those of one with 66%. The reason for this choice was that the plant had flowered early and that the harvest had been increased thereby. The parents with the higher values had flowered too late or set too little seed, and it would have been very dangerous to have continued the experiment along this line. Moreover there was no longer any particular interest in improving the race fur- ther. The mean value has been lessened thereby to about 40%, and the maximum to 74%. Cannabis sativa. I propose to deal now with two cultures of dicEcious plants, Cannabis and Mercurialis. In these cases self-fertilization is impossible; neverthe- less the isolation of the intermediate races was effected as easily and almost as quickly as in Oenothera. Without doubt self-fertilization has in such experiments, when- ever feasible, the high value which is usually assigned to it ; but the experiments now to be described show that it can often be dispensed with, as well. This result is very important, because it makes isolation and selection pos- sible in species in wdiich an artificial fertilization of every single seed-parent would increase the labor bevond meas- The Isolation of Tricotyloiis Intciinediatc Races. 427 lire. Such a task I have, therefore, only undertaken with a single species, Antirrhinum inajiis. Only some varieties of hemp seem to include tricotyl- ous intermediate races. Amongst those which I have tested I have found such a one in the giant hemp only. In the spring of 1893 I sowed a large quantity of seed of this species, but was only able to bring 7 tricotylous plants to maturity. Unfortunately the majority of them were male, and there was but a single female plant. This, how- ever, produced four tricotyls amongst 126 seedlings. In 1894 two of these were female and two male. The seeds of the former were saved separately and yielded 15 and 9% tricotyls amongst 400 and 600 seedlings respectively. For the continuation of the race, onlv the tricotvlous seedlings of the parent with 15% were planted out (1895). There were 29 plants, of which 10 bore seed. Their values were 19—31—38—40—43—47—48—50— 52 and 63%. As we see they attained the mean value of the intermediate race and even exceeded it in one case, (63% amongst 316 seedlings). The tricotylous ofifspring of this individual alone were planted out (1896). Of these, 38 specimens set seed, and from this the values of the individual parents were calculated. I reduced them, as usual to groups with 40 — 45 and 50% etc.. as a mean value, and found the 38 offspring of the parent with 63% to be distributed as folows : Proportion of tricotyls 40 AS 50 55 60 65 70 75 80 Number of seed -parents 5 5 3105 5 2 2 1 The mean of the series is at about 55%, and the series therefore constitutes a good instance of a young, isolated race whicli, however, has not yet been improved to anv considerable extent bv selection. 428 Tricol\Ious Races. In 1897 I continued the culture for the purpose of improving the race. I sowed the seeds of four plants which had 65 — 66 — 67 nd 707© tricotyls, and managed to bring 60 tricotylous plants to maturity, of which 26 set seed. Their hereditary values varied between 35 and 90%, their mean being 74%. This mdicates a satisfac- tory advance. Mercurial is annua. In 1892 I possessed two tricotyl- ous plants, one a female, the other a male, wdiich had been raised from species that had been obtained in ex- change from some botanical garden. The yield was very poor; only 14 seeds germinated and they had two cotyl- edons each (1893). In saving their seeds I did not isolate them and found 2% tricotyls amongst the 1100 seedlings which were raised in the following spring (1894). Besides these several tricotyls had come up in the bed from seeds which had fallen out, so that I had altogether 18 female and a corresponding number of male tricotyls. This culture gave the expected result. The hereditary values calculated for the individual seed- parents were distributed regularly between 1 and 55%, the five highest being 31—34—41—52 and 55%. The intermediate race had therefore been isolated at least in these latter specimens. In 1895 I only planted out tri- cotylous seedlings from the one parent Avith 55%. Of course it was uncertain in this case whether the pollen had been produced by plants belonging to the intermediate race. But the values calculated in the spring of 1896 suggested that the race w^as fairly pure. I have already given this series of figures above (p. 423). The mean was at 67, the maximum had increased to 86%. In 1896 the tricotyls of two parents, whose values were 78 and 81%, were planted out in lots of 25 and 20 The Isohiliun of Tricotylous Intcnncdiatc Races. 429 respectively. The values tor the two groups did not differ essentially, and were (listril)uted hctween 51 and 92^0, and the mean of the 2? plants (the rest had heen male) was 73%. The race had, therefore, in compari- son with the previous year, undergone a further im- provement. It was continued one year more in the same way (1897). 12 female and several male tricotylous off- spring of the parent with 92% were planted out, and the values calculated from these were found to be distributed between 65 and 91%, with a mean of 78%. We see, therefore, that after the figure 55% had been reached in the harvest of 1894 the mean value rose in the three following years of the experiment to 67, 73 and 78%. Clarkia pulchella, Fig. 85. It was in the spring of 1895 that I made the extensive sowings of horticultural seeds to which I have already referred, for the purpose of isolating tricotylous intermediate races. The seeds of Clarkia pulchella alba produced about 1% tricotyls. v30 of these flowered, but only 18 of them produced suf- ficient seed. Two of them had hereditary values of 14 and 16%, the rest from 0 to 7%, with a mean of 4%. In 1896 only the tricotyls of the parent with 16% were planted out. There were 39 of these, and for all of them a value could be calculated. These values have been oiven on page 422, and were above 50% for eight plants. The intermediate race, therefore, was already represented by several specimens. In 1897 I planted out only the tricotylous seedlings of the ])lant with 64%, and saved the seeds of 39 of them. Their hereditary values were distributed be- 430 Tricotylous Races. tween 16 and 79% and gave a mean of 49%. The race could therefore be regarded now as perfectly pure. Hclichrysiuii hractcatuni conipositum, Fig. 86. From the same set of sowings as that which contained Clarkia, I planted out some tricotylous seedlings of HclicJirysiun. There was a relatively large number of them, and alto- gether 19 set seed. For each one the value was calcu- Fig. 85. Clarkia piilchcUa alba. A flowering sprig. lated se])arately. In the case of 15 plants these were distributed between 2 and 8% and exhibited a mean of 4% ; but there were higher figures besides, viz., 12 — 12 — 16 and 41%. The latter plant was obviously a repre- sentative of the intermediate race sought for; the re- mainder were thrown away as doubtful, although if there had not happened to be such a faA^orable plant The Isolation of Tricofyloiis hitcniicdiatc Races. 431 among them all, the plant with 16% would, no doubt, have offered me as good a prospect as the corresponding plant of Clarkia. The chosen plant was remarkable for the large proportion of tetracotyls and the low proportion of hemi-tricotyls which it produced. There were 1 1 % of the former, and only 1 % of the latter. This peculiarity has reappeared amongst its descendants, especially with regard to the tetracotyls. In 1895 I planted out on separate beds tricotyls and tetracotyls of the parent with 41% only. Among the tricotyls ^2 plants set plenty of seed. Of these one produced only 6% tri- cotyls, amongst the rest the values were distributed between 13 and 43%, and their mean was at 26%. The tetracotyls gave similar numbers, em- bracing 19 plants with from 14 to 42% and a mean of 25% ; besides these there was one plant with as much as 51%. This latter fact must ob\iously be at- tributed to a fortunate chance, and we may conclude that the tetracotyls are not more likely, nor on tlie other hand less so, to produce tricotyls tlian the tricotyls themselves, but that they ob- viously belong to the same race, i. e., tliat their character is brought about bv the same elc- mentary factor. Tlie proportion of tetracotylous seed- lings in this culture was very high, but not higher tlian the ratio recorded for the first generation. For tlie continuation of the race onlv seedlings of the Fig. 86. HcUchry- suni bractcatuni conif>osifu}n. A flowering stem of a plant of the tri- cotylous interme- diate race. 432 Tricotyloiis Races. tetracotjv'lous parent with 31% were planted out. Ilere again both the tricotylous and tetracotylous plantlets were used, but this time not in separate lots Seeds of Z7 plants were saved and sown, and they gave values which did not differ essentially from those obtained in the fore- going year. They were distributed fairly regularly be- tween 16 and 52% and had a mean of 35%, i. e., the mean vahie had undergone a considerable increase. Antirrhinum niajns. It was with this plant that I made one of my first experiments in the production of tricotylous races, and the fact that the progress in this case was much slower than in later cultures, may well Ije ascribed to the less extensive experience which I had at that time. I am now inclined to regard the practice of selecting from an insufficient number of seed-parents, and also of inadequate manuring as some of the causes. Nevertheless I shall describe the experiment because it ultimately led to a genuine tricotylous race. On the other hand it may not be unimportant to show that, if a repe- tition of my tricotylous cultures is made, the attainment of the end must not always be expected to be reached in two or three generations. I have attempted to isolate tricotylous races from two varieties of the Snap-dragon. First from tlie striped variety mentioned on page 120 of this volume, and figured in Plate I; but as the success attamed with this after four generations (1892-1896), was not so great as in the other case, and 45% had not been exceeded, I did not proceed further with it. Therefore I shall confine my description to the latter. It was a dark red half- dwarf variety. In 1892 I had four tricotylous plants from bought seed, and from their seeds obtained in the following The Isolation of Tricotylous Interuiediatc Races. 433 spring" (1893) the proportions 2 — 4 — 7 and 7*/o of tri- cotylous seedlings, counted in lots of from 300 to 500. I only planted out the seedlings of one of the plants with 7 Jo, but the experiment was not successful, and only three tricotylous plants gave a sufficient quantity of seed. Their hereditary values were 2 — 8 and S/c. The seed- lings of one of the best plants were planted out in 1894. In this year I had twelve tricotylous plants for which I could calculate the values. With two exceptions, they were distributed between 7 and 19%, but the exceptions attained 2?) and 25%, the mean of the whole group being 13%. In 1895 the tricotylous seedlings of the two best parents were planted out in separate groups. The mean numbers of these differed considerably ; but both attained a proportion of 41% as maximum. The parent with 23% had produced offspring the values of which were distributed between 7 and 31% (18 plants with a mean of 17% and one plant with 41% tricotylous grand- children; whilst the parent with 25% gave values from 15 to 31% amongst 12 offspring, with a mean of 26%, and two specimens with 41%. In conformity with the principles of selection of the grandparents, the three plants with 41% were not regarded as analogous, and only the offspring of the parent with 25% and with a mean, calculated from its grandchildren, of 26% were planted out. The progeny of the third plant with 41 % were considered as of inferior value and thrown away. In the following spring, when the values were cal- culated, no essential difference could be detected between the two grou]:)s of my culture of 1806. In percentage calculated from lots of 300 seedlings these figures were as follows : 434 Tricotyloits Races. VALUES OF THE OFFSPRING NUMBER OF P 4 PTTNT LOWEST MIDDLE HIGHEST SEED-PARENTS A 41% 31 45 67 16 B 41*7^ 22 50 79 22 Since these two cultures may be regarded as typical of ordinary intermediate races, not subjected to improve- ment by selection, I will give the full series of figures for one of them (B). They are as follows: 56 58 59 71 79 60 60 SO 51 55 55 55 41 42 46 47 47 35 36 39 22 25 W^ritten in this way the figures show, without any further treatment, a group in the form of a curve the apex of which was between 50 and 55%.^ I planted out the grandchildren of the plant B only, and selected for this purpose (1897) the two parents with 71 and 79%. The two cultures consisted of tri- cotylous plants only, flowered on separate beds, fertili- zation being left to the agency of insects, however, as in ])revious years. The result of the determination of the values in the spring of 1898 was as follows: HEREDITARY VALUES OF THE OFFSPRING NUMBER OF LOWEST MIDDLE HIGHEST SEED-PARENTS C 71% 34 62 74 23 D 79% 48 64 79 24 In comparison with the previous year, therefore, an advance had taken place in the mean values but not in the maximum. ^ It is my custom to plot the harvest raised from each parent and from each grandparent in this way. When grouped in this manner the figures display the result very graphically; and immediately show whether it falls outside the limits of observational error ; and whether therefore the existence of differences between the individuals is shown bevond doubt. The Isolation of Tricotylous Intermediate Raees. 435 Let us now summarize the whole culture, which ex- tended over six years. We obtain the following series: VALUES IN THE HARVESTS OF 1892 1893 1894 1895 1896 1897 Highest value 7 8 25 41 79 79 Mean " 5 6 13 26 50 64 Lowest " 2.2 7 15 22 48 x\s already stated, the intermediate race had therefore, in this case been isolated only gradually from the mix- ture, chieih' as the result of the originally small extent of the cultures. Papaver Rlweas. In 1895 I selected 21 tricotylous seedlings from a sowing of the double garden variety of this plant with mixed colors. They yielded an abun- dance of seed, which gave the following percentage of tricotyls, counted in groups of 300 seedlings each : 18 19 19 20 12 12 7 7 8 4 4 4 4 6 0.5 1 1 1 1 1 2 This group plainly exhibits two sections, a half curve with an apex at 1 % and 4 seed-parents with the proportion of 18 to 20%. Obviously these four belong to the inter- mediate race sought for, whilst the rest are partly hybrids between the two races. The best tricotylous seedlings of the two parents with 18 and 19% were planted out in 1896. They flowered and set an abundance of seed. The determination of the hereditary values from lots of 300 seedlings each gave a result for one of the two parents, with 24 offspring, of 10 to 56% with a mean of 19%, and for the other from 10 to 53% with a mean of 26%. Seedlings were planted out from the two best 436 Tvicotyloiis Races. plants of these groups and the result in the following spring, 1898, was 23 to 65%, with a mean of 40% among 17 seed-parents, and 26 to 75%, with a mean of 47%, amongst 13. Phacclia tanacetifolia, Fig. 87. My race arose from the same set of bought seed which included Clarkia, Hcli- chrysuui and Papaver. In the summer of 1895 I had 20 tricotylous plants, raised from bought seed, in flower. Their values constituted a two-fold group like that which occurred in Papaver, Three seed-parents had 12 — 12 and 14%, but the rest had values between 1 and 10%; the three former were alone used as the basis of my race. The three cultures derived from them gave 30 — 6 and 9 separate harvests, which were evaluated in the spring of 1897 in the usual way. The lowest, middle and highest values for the three groups were 5 — 26 — 58, 21—28—42, and 6—14 — 16%. Obviously the two first grand-parents had given better offspring than the last one. I selected the former group for the continuation of the race, employing the two best plants with 54 and 58%. They gave two groups of tricotylous plants, the harvests from which exhibited a great advance on the average, but which did not differ essentially from one another. With the exception of the extremes these fig- ures constituted a closely circumscribed group of 35 val- ues distributed between 35 and 72%, with a mean of 57%. The extremes were 20 and 22%, and on the other side 80 — 85 and 90%. The two former figures, which were probably the result of incomplete isolation, occurred in the same group. The higher figures, however, were distributed over the offspring of both grandparents. Obviously the mean value of 57% of the intermediate The Isolation of Tricotylous hitciincdiatc Races. 437 race had been attained, and therefore I did not continue the culture. Silcnc inflata, Fig. 88. I obtained this race by pure chance. The stock plant was one of that series of forms which I had taken into cultivation, during the course of many years, for the purpose of finding species in a mu- Fig. 87. Phacelia tanacetifolia. A llowering sprig. Fig. 88. Silcnc inflata, A whole plant. table state (Vol. I, p. 271). A single specimen which had come up from seed of weeds, accidentally imported with cereals into our harbor, was transplanted into my experimental garden. The seed from this plant produced a proportion of 3% tricotyls, and when it flowered again in 1893, one of 4%. The tricotyls of the first harvest 438 Tricotyloiis Races. were planted out in the summer uf 1893 and eight of them yielded an ample quantity of seed. In each lot, of from 200 to 1300 seedlings, I counted the percentage of tricotvls and found most of them to be distributed be- tween 2 and 15%, the highest numbers being 24 and 32^0 (these latter amongst 1300 and 1060 seedlings re- spectively). The mean w^as 11%. Therefore the original plant obviously belonged to a tricotylous intermediate race, a fact which, however, was only pro\'ed by the behavior of its descendants. In the spring of 1894 I only planted out the tricotyl- ous ofl'spring of a parent with 32%, and obtained 22 ])Iants which set seed. From these I obtained in the following year 22 hereditary values which were distrib- uted between 26 and 55% and reached a mean of 37%. There were three individuals with 5^1 — 55 and 55%. We see that the mean was higher than the corresponding \alue of the parent plant, and from this we conclude that regression did not take place in the direction of 0, but towards the other side ; and this is exactly what should happen in the isolation of new races from their mix- tures. In the summer of 1895 I planted out tricotylous off- spring from the two parents with 55% ; I kept them in two groups and determined their values from the har- vests of 31 individuals. There was no essential differ- ence between the two groups ; the numbers were dis- tributed between 26 and 73 and their mean was 53%. The mean had, therefore, reached the value of the parent, and the race could be regarded as an intermediate race, isolated but not yet subjected to selection. For the next generation I selected the tricotylous offspring of three plants with 66 — 68 and 73%. Of The Isolation of Tricolyloiis I iilcnncdiafc Races. 439 these plants 25 set seed, Init the culture was iinsueeess- ful in this year, owing to adverse circumstances, and only a few of the plants produced more than 200 fertile seeds. The values, therefore, were not very exact, but formed a close group ranging between 18 and 56%, with a mean of 32%. It will be seen that in spite of the selection a general retrogression had taken place. Suunnary. If we look at the results of the experi- ments which have been described, we are struck by the fact that a certain group of hereditary values appears much more commonly than others. These are the fig- ures ranging round 55%, and this value is usually reached at the conclusion of the second generation or, in less favorable experiments, at the conclusion of the third or fourth. A\'ith a view to emphasizing this fact I have grouped the whole series of experiments in such a way that the figures round 55% are brought together in one column : ISOLATION OF TRICOTYLOUS INTERMEDIATE RACES. HIGHEST HEREDITARY VALUES EXPRESSED IN PERCENTAGES FOR THE SUCCESSIVE GENERATIONS. Anfirr/iinujn tnajus . Mercurialis annua . Silcne in flat a . Cannabis sativa . Clarkia pulchella . Helichrysiiin bracteaiurn Papaver Rhoeas . Phacelia tanacetifolia Oenothera hirtella FIRST GEN- ERATION 1892 1892 1892 1893 1895 1895 1895 1895 1895 1-50' 7 I I I 8 0 3 3 I I I 25 2 32 15 16 41 20 — 1 I ' 14 I i 8 ABOUT 55 9r 41 55 55 52-63 64 51 56 58 56 60-95 fr 79 86 73 80 79 52 75 90 89 79 92 56 90 91 In this table the first column gives the year in which the experiments began, either with the selection of tri- 440 Tricotylous Races. cotylous seedlings from seed which had l)cen bought or obtained from some other source, or with plants which had been found by chance (Oenothera, Silene). Where necessary, this year is denoted in the table by I (first generation). The numbers which succeed each other in the row to the right of it refer to the first and the follow- ing generations. Thus for instance in Clarkia there were as many as 16% tricotyls in the harvest of the first gen- eration, 64 in those of the second and 79 in the third. The point which this table is intended to illustrate is best brought out by a comparison with the series of figures given on page 392 for the half races. In that case, a selection continued from four to six years, did not bring this value, as a rule, further than 2 to 4%, and only in exceptional cases attained 15 to 20%. In this case, on the other hand, 55% is attained in two or three generations. In the half race a continuation of the selection would presumably not have led to any con- siderable increase, a fact which is demonstrated by the experiments with Amarantiis and Scrophularia which were continued over a longer period of time.. In this case, however, selection is as a rule very effective, inas- much as it can increase the best representatives of the race, in a veiy short time, to a hereditary capacity of 80 to 90%. Therefore there can be no doubt that entirely differ- ent factors are at work in these two cases. In the former there occurred only races with half curves on which se- lection has little effect. In this case, however, tliere oc- ciu-red, besides these, the highly variable intermediate races which are extraordinarily susceptible to selection and to external conditions of life. They were easily isolated, either because one or more examples of them The Isolation of Tricotylous Iiitciiucdiatc Races. 441 were already present in the (^-iginal sanii)le of seed, ov l)ecaiise between the interme(hate and the half races hy- brids were met with, by the snbsequent segregation of wliich the race w^as produced. In the first experiments the isolation of the tricotyl- ous intermediate race took from three to four genera- tions. Later when I started tlie experiments on a larger scale, the number was reduced to two years. Further selection brought it up, in one year as a rule, to 70 — 80% and sometimes even to 90%, either immediately in the course of another year, or after two generations. Unfavorable conditions of life led to exceptions, or even to retrogression ; but only Helichrysuin and Silcne ex- hibited this feature. Cannabis, Mercurial is and Antir- rhinum maintained a value of 80 — 90% under continued selection, and it is quite probable that even 100% might have been attained in occasional individuals. The mean figures of the wdiole group correspond, as a rule, to these maximum values. They maintained themselves at about 55%, but are liable to be increased by selection or dimin- ished by unfavorable conditions. Lastlv, it should be noted that the ni>ures for these intermediate races are so far removed from those of the half races (p. 392), that all suspicion as to the possible effect of occasional errors in the choice of the samples is excluded ; in other words, that hereditary z'aines from 1 to 5% or ez'cn of 5 to 20 9^ , // they are maintained in spite of selection, may he regarded as characteristic of half races, whilst values of 40 to 60% . idioi found in separate crops, may be taken to indicate the presence of intermediate races. A\nien an intermediate race is isolated from an orig- inal sample of seed, it is separated from the half race 442 Tricotylous Races. which is also present, for hardly ever is the intermediate race found pure hy itself. As far as I know, at least, there is no species of plants which has so much as half of its seedlings showing three cotyledons, without being selected. If we study the process of separation by the statistical method, we find that two curves, a half curve with an apex at 0, and a bilateral curve with an apex at 50 — 55%, can be distinguished from one another. Some- times in one or other of the transitional generations both curves can be more or less clearly seen side by side, constituting a so-called dimorphic curve. I have fre- quently observed this in these experiments, and have, in some cases referred to it. Dimorphic curves of this kind are best obtained in the transitional generations by planting out dicotylous as well as tricotylous seedlings ; for, as was mentioned before, it is very likely that many dicotyls will belong to the half race and most of the tricotyls to the intermediate race. But if the latter is once isolated, all the individuals belong to it, independently of the question whether they have tw^o or three or cleft cotyledons. In this stage a dimorphism of this kind is no longer to be expected, un- less selection is continued in two different directions.-^ As an instance of this let me cite the case of my cul- ture of Mercnrialis annua in 1895 (see the table on page 439), inasmuch as this species, being dioecious, would be expected to exhibit a levelling of the differential char- acters. The plant with a value of 55% in 1894 could obviously have been partly cross-fertilized. Its offspring had in their seeds the following hereditarv values : Witli regard to this question compare the analogous experi- ments witli H ^liantluis anmius syncotylcus (II, §ii). 81 82 86 72 74 76 78 66 67 . 44 48 50 34 35 36 40 21 22 24 25 18 20 The Isolation of Tricofylous Inicnncdiatc Races. 443 A. Tricotylous offspring B. Dicotylous offspring -I 21 22 24 25 25 [ 18 20 The group is therefore dimorphic, the intermediate race is not yet pure. I found the same conditions to obtain in other cases. In Clarkia pidchella also, the atavists reverted when sown in 1897 alongside the tricotylous culture already mentioned and from seed of the same parent. This parent already had a hereditary value of 64%, but was the first in this race with a high figure, and therefore still belonged to the transitional period. The values are arranged in groups of 5 to 15, 15 to 25 etc., and the number of individuals which fall into each group are given under the mean percentage number, i. e., 10, 20 etc. Proportion of tricotyls in percentage 10 20 30 40 50 60 70 80 Number of tricotylous individuals 02588 12 3 1 Number of atavistic individuals 4 13 911 0 2 — — The mean for the tricotylous individuals is 49%, for the atavists 30%. The race once isolated, the atavists obviously still have smaller values than the tricotyls ; but the difference is never more than a small one, and the curve for the two races together will have only one apex. In Oeno- thera hirtella I examined a series of values of the atavistic offspring as well as the tricotylous offspring of the same parent of 1896 which had a value of 56%. This parent had been self-fertilized, the visits of insects havine been excluded : and so were all its offspring. I shall group the values in tlie same wav as above. 444 Tricotylous Races. Proportion of tricotyls in percentages 10 20 30 40 50 60 70 80 90 Number of tricotylous individuals — — — 1 6111-ilO 1 Number of atavistic individuals 1 0 4 3 10 1111 6 0 Calculated for the whole progeny 1 0 4 4 19 27 32 21 1 The average value for the tricotyls is 72^0 and of the atavists 60%, which latter figure is of itself high enough for an intermediate race. The last row was obtained l\v means of a correction of the values of the tricotyls, since too small a number of these had been cultivated in com])arison with the atavists. The whole curve is ob- viously monomorphic although much flattened. A curve with such a great amplitude indicates a cor- responding high variability and therefore also a consider- able susceptibility to external influences, as we have found in several instances to be the case with intermediate races. To this great amplitude also the fact is due that se- lection, however stringent, never cjuite eliminates the lower values. Even when the apex of the curve is be- tween 60 and 70%, values as low as 25% may still occur. In such cases the curve has a ''sweep" to the atavistic side, and thus differs most conspicuously from the curves of the half race, the shape of which might be considered as its mirrored image ; but as I shall come back to this point when I deal with syncotylous races, I shall not give any instances now. § 7. PARTIAL VARIABILITY OF TRICOTYLY. In experiments with tricotylous races the hereditary capacity or value is, as we have seen, the main character subjected to selection. This term indicates the number of tricotylous seedlings in the harvest. The seeds of each individual are saved and sown separately, and then recorded after germination. Whether the individual it- Partial Variability of Tricotyly. 445 self has two or three or merely cleft seed-leaves is a question of minor importance, and does no more than furnish a suggestion in starting the experiment. On the average, atavists and hemi-tricotyls are, without doubt, of less value in this respect than tricotyls and. tetracotyls ; but the differences are too small to warrant a choice of seed-parents on this ground. The determination of the hereditary value depends, therefore, largely on the extent of the crops. The larger this is for any one individual, the more closely will the value found correspond to that which would be derived from an imaginary harvest, consisting of an infinite num- ber of seeds. Therefore, the best plan would be to make the plants grow as vigorously as possible, and to save the seeds of all fruits from as many branches and sprigs as possible. In practice, however, this cannot be done, since it is far more important to grow as many indi- viduals as possible in a given space. The more numerous the individuals are, the more stringent the selection be- comes ; and, wdiat is far more interesting, at least in working with mixtures, the greater is the prospect of finding any desired particular sort. Unbranched, or al- most unbranched, plants wnth terminal inflorescences only, obviously need much less room than much branched in- dividuals; and larger harvests require relatively too much time to gather. The best plan, therefore, would be to collect only just so much seed from each individual as is necessary for sowing in the following year. These considerations suggest the question whether different groups of fruits are alike in regard to hereditary capacity or whether they exhibit, perhaps, considerable differences. Shall we find this capacity to be different on the branches from what it is on the main stem? Will 446 Tricotylous Races. tlie earlier seeds give different values from those given l)y the later ones? Has the character of tlie year in which the harvest is made any such influence amongst perennial plants? Obviously these cjuestions must be answered if the individual harvests are to be limited in the interest of the experiment. In the last two sections of the first part of this vol- ume we have seen that semi-latent characters manifest a certain periodicity in their distribution over the plant, and also that the choice of seeds on the plant plays some part in the process of selection. The question is, how do the tricotylous races behave in this respect? The general rule seems to be that a bud, whether of a branch or of a flower, is more likely to reproduce an anomaly, the more vigorous it is (p. 324). Therefore with an increase in the degree of branching the expecta- tion of the occurrence of anomalies decreases (p. 329). The first or lower fruits of an inflorescence will be stronger than the higher ones, and the fruits on the weak lateral sprigs of the primary and secondary branches may as well be thrown aw-ay. There is no ground for supposing that the flower buds behave difl^erently from the vegetative parts. The best instance of the phenomena in question is afforded by profuseh- branched S]:)ecimens of the twisted race, Dip- sacus syh'cstris tarsus. The torsion affects the middle ])ortion of the main stem, but neither its upper nor lower extremity. Tt is repeated on the strongest branches situ- ated on the middle of the stem, and on these only in their middle parts, and excluding the weaker ones. The stronger a stem or a branch is. the greater is the extent of the twisted part. Tn tlie 1)ranches it is always con- fined to sinHe internodes, \\liereas the stem mav fre- Partial J^ariability of Tricofyly. 447 qiiently be entirely transformed. Branches of the second order exhil)it no more tlian traces of the anomaly. If we apply this instance to the distrilmtion of tri- cotylous seeds on a plant, we shcjnld conclude tliat the lower part of the terminal inflorescence of the main stem would produce the highest proportion of tricotylous seed- lings; but the flowers and fruits themselves are lateral branches, and so the question arises, how far we are justified in expecting this. In species like Oenothera and Antirrhinum, which have a primary inflorescence rich in flowers and in seeds, I have usually limited myself to this and, where possible, to its lower and middle parts. In Heliehrysuni to the flowerheads which open first, in Clarkia and Phaeelia to as many of the earlier flowering branches as would pro- vide a sufficient quantity of seed, and so on. The question is whether these first fruits possess the same hereditary capacity as would be found from the largest number of fruits that could be gathered on the plant. With a view to determining this point I have insti- tuted a number of subsidiary experiments. The answer has been in the afi^rmati^'e throughout. Certainlv there are small differences ; these, however, seldom fall out- side the latitude of 5% which is the limit of observational error. I shall now present the results of these experi- ments in a condensed form. y\ first experiment was conducted with Oenothera hirtella, which fertilizes itself in parchment bags with- out artificial aid. In the summer of 1898 I planted out seven tricotylous seedlings of one parent with a heredi- tary value of 66% at distances of about a meter apart, allowed them to branch freely and to develop into vig- orous plants, enclosed the flowers in parchment bags and 448 Tricotylous Races. harvested and examined the seeds for each indivicUial branch separately. Only slight differences were pre- sented by the values obtained, and I shall therefore only give the means. T determined the values of the inflores- cences of the main stem and found the average to be 38% ; for the strong lateral stems produced from the axils of the rosette (see Fig. 55, Vol. I, p. 302) I found it to be 45% ; for the upper branches of the stem (see Fig. 49, Vol. I, p. 282), however, 47% (calculated from 24 determinations), and for the lower branches of the stem, which in :;his species tend to be very much weaker, 52% (in eight counts). The distribution of the differ- ences, therefore, was different from what would have been expected. They show that in this case, the harvest from the primary inflorescence gives a somewhat lower value than the whole harvest of the plant in question would have given. In Dracoccphalum moldavicnm, where the values are always small, I collected, in the summer of 1895, the seeds of all specimens from the main stem and lateral branches separately, but found no difference (0.4% for both). In Amarantus speciosus the seeds from the terminal panicle regularly gave somewhat higher values than those from the lower branches, but with very slight differences only (1892). The average calculated from 20 plants was 2.8% for the former and 1.7%; for the latter. In many of my experiments I have saved the seeds which ripened first, separately from those which ripened later: e. g., Amarantus speciosus, Scrophularia nodosa, MerciiriaJis annua, Antirrhinum majus, Silene inflata, and others. No differences of any importance were found in this way. Deviations are sometimes found in larger series, but only such as can be attributed to the Partial Variability of Tricotyly. 449 unavoidable errors in the samples of seed. In Mcrcit- rialis annua I have for several years recorded the seed- lings which came up from the first seeds that fell exit on the bed. In this species, as is well known, the fruits open suddenly and scatter their seeds about. These counts gave essentially the same results as those obtained later from seeds harvested and sown by hand. I often made use of them to obtain a preliminary idea concerning the extent of the improvement to be expected. My custom is to limit the separate harvests to the desired quantity of seed, by cutting back during the period of growth, and by stopping the saving of seed as soon as a sufficient quantity has been secured. For this purpose I have estimated this amount from the result obtained in the first generation, in the case of each species. Moreover I have frequently compared such gatherings with much more extensive ones, obtained either bv not cutting the plants back or by not ceasing to save the seed before all of it was ripe. In this way Aniarantns spc- ciosiis often gave higher values from a smaller harvest, but tlie differences were slight and the exceptions many. Cannabis saliva gave the same values from large plants bearing more than 100 cubic centimeters of seed each, as from average or weaker individuals. In such large crops, saved without limitation and amounting to 80 — 110 cc. of seed the average was 11%, but in croi)s of 20 — 35 cc. it w^as 14%. The cultures were made in 1S*^)4 and the same happened in other years. In Oenothera rubrincrvis the value was seen to decrease as the size of the harvest increased, but only in degrees of one-tenth per cent, on the average, amongst numerous individual trials. 11ic same occurred in ScropJuilaria nodosa. This latter s]~)ecies, as well as Silcnc inflafa, is a per- 450 Tricotylous Races. cnnial form ; and therefore both of them afford material for comparing the harvest of the same plant as produced in successive years. Here again I failed to find differences of any significance. I have given above the values de- rived in 1892 and 1893 from a single plant of Silcne, which flowered in isolation ; they were 3 and 4% for these two years. In ScropJudaria I made a series of ob- servations at the beginning of my cultures when the hered- itarv values were still small, and repeated them in the period of 1896-1899, when they had become higher (15% and more). In these years, 1897, 1898 and 1899 six plants gave the following values, the bracketed number referring to the second year: A 22 (25), B 25 (17), C 22 (17), D 23 (25), E 27 (25), F 23 (22). Ob- viously these figures do not justify a conclusion as to any diminution or increase in the ratio in which tricotyls are produced. The result of all of these experiments is such as to justify my practice of limiting the individual harvest to the quantity of seed necessary for sowing. § 8. THE INFLUENCE OF EXTERNAL CONDITIONS ON TRICOTYLY. Which seeds in a fruit produce aberrant seedlings? This question is at once one of the most simple and one of the most difficult presented by experimental breeding. If some day we could succeed in solving it and thereby make a control of this process possible, much light would be thrown on a whole series of phenomena connected with the origin of races. In dealing with this question we are thrown back on Qgg cells and pollen grains and the problem at once Influence of External Conditions on Tricotyly. 451 becomes a double one. To these is added a third factor, namely the union of the two germ cells, which may itself be influenced by outward conditions in different ways. I have gone into the questions only so far as was necessary for the choice of the conditions of my experi- ments. The course of these has, as a rule, been very regular. The results of selection seldom have been dis- turbed, to any great extent, by other influences. Some- times, however, this did obviously occur ; and it is exactly experiments of this kind which justify us in ascribing an important part to external conditions in the determi- nation of the proportion of tricotylous seedlings. But when, from these facts, we proceed to analyze this in- fluence, we do not succeed in making experiments in which the same influences have the same results. Two instances will suffice. Under very peculiar con- ditions which affected the whole growth of the plant, the hereditary capacity of my race of Ainarantus spc- ciosus suddenly rose, in 1891, from 4.5 to 13%, with- out, however, maintaining that proportion even under selection (p. 407). On the other hand, in the summer of 1896 the whole culture of SUcnc inflata underwent considerable deterioration as the result of unfavorable conditions, the mean of all values falling from 53 to 32%. One year may obviously affect the plants quite differently from another, even when the treatment to which they are subjected is as uniform as possible. The effect is perhaps produced in the early stages of the plant, perhaps also in the development of the sexual cells and at the time of fertilization. Abundant starting-points for further investigations may here be found. As a rule the likelihood of obtaining anomalies in- creases with the vigor of the seeds which produce them 452 Tricotylous Races. (p. 332). It is natural to inquire, therefore, whether this vigor of the seeds can be increased by improved nutri- tion of the plant. Unfortunately we must, in such cases, be content with averages, and these obviously give much smaller differences than the single extreme cases. Some- times I found that the external conditions exerted a con- siderable influence, but, as a rule, I could not detect any difference. In the first place I shall refer to the effects of manu- ring. The prevailing opinion is that manuring with ni- trates favors the development of leaves, but that phos- phates favor flowers and fruits. As a nitrate manure I employed horn-meal combined with dried guano and as phosphate manure the ordinary superphosphate; but I find that the former usually produces more abundant flowering and a larger harvest of seed than the latter. In 1899 I instituted a comparative experiment with Oeno- thera Jiirfella by planting out the seedlings of a single self-fertilized plant. During the period of flowering each inflorescence was guarded from the visits of insects by a parchment bag. The nitrate plants grew more ra])idly and luxuriantly at first than those on the phosphate bed. Moreover they began to flower somewhat earlier, and consequently set more seed; for fertilization must be stopped before all the flowerbuds have opened, since in our climate flowers which open in September have not time enough left to ripen their seed. The harvest for each individual plant was examined separately, and from this was calculated, in the way we have so frequently described, the percentage value for each plant. In the following summary these are associ- ated in groups of from 15-25, 26-35, 36-45; the means of the groups being 20, 30, 40 etc. Influence of Extenial Conditions on Tricotyly. 453 HEREDITARY VALUES IN OENOTHERA HIRTELLA IN 1899. Percentage values 10 20 30 40 50 60 70 80 90 After manuringf with nitrates 0 8 17 12 9 5 2 2 1 After manuring with phosphates 129 14 78511 The number of individuals in the first experiment is 56, in the second 48; average harvest per plant, 3.5 and 2.5 cc. The seed was collected from the terminal spike only. The mean value for the nitrate plants was 37%, for those manured with phosphates, 44%. The parent of all these plants had had a value of 66%. Manuring with superphosphate has therefore, in this case, in an otherwise uniform culture, been more favor- able to the production of tricotylous seedlings than ma- nuring with hornmeal. I found exactly the same result in the same year with Helichrysuni bracfeafuni. I planted out tricotylous seed- lings only of a single parent with 11%. I determined and arranged the values as before and found : HEREDITARY VALUES IN HELICHRYSUM BRACTEATUM IN 1899. Percentage values 10 20 30 40 50 Mean After manuring with nitrates 2 22 18 5 1 26% After manuring with phosphates 1 5 20 11 2 32% Number of individuals 48 and 39. The grow tli on the nitrate bed was very luxuriant ; the leaves were dark- green, and the flowers abundant. On the phosphate bed the plants were yellowish-green, very little branched, and with fewer ripe flowerheads. Indeed, onh' 39 (^f the 50 plants which had been set out set sufficient seed. Results as definite as these are not, however, always obtained, especially when a comparison is instituted not between individual plants raised from seed, but between the various parts of a single individual obtained bv di- viding it. I conducted such an experiment with Oeno- 454 Tricoiylous Races. fJicra {Kuciffia) glaiica in 1899, Ijut counted 5% tri- cotyls, both on tlie phosphate and on the nitrate half. I obtained the same result in ScropJiularia nodosa by growing one half in ordinary garden soil and the other in sand, both yielding 1% (1894). The two first experiments on the inliuence of manure show that an increase in the number of tricotyls is as- sociated with a diminution of the yield. The same result can also be obtained if the harvest of the individual plants is reduced in other ways. In Oenothera hirtella I adopted two methods of doing this, late sowing and culture in pots throughout the whole summer. Tricotylous seed- lings of a single parent (with 66%) were planted out. In one of the two groups the sowing had taken place in March, in the other at the beginning of May (1898). Some plants of the former sowing were kept in pots of 15 centimeters filled with well-manured garden soil throughout the whole summer. Fertilization took place in parchment bags and the individual crops, recorded and evaluated in the usual way, gave the following result : HEREDITARY VALUES IN OENOTHERA HIRTELLA IN 1898. Percentage values 10 20 30 40 50 60 70 Mean Normal culture After sowing in May After culture in pots Number of plants experimented with 18, 36 and 19. We see therefore in this case a definite though small increase in the number of tricotyls. The mean of the harvest for the normal culture was Z.'b cc, for the late culture 2.5, for the pot-culture 4.5 cc. This latter had therefore not had the expected result of making the yield smaller, and as, nevertheless, the proportion of 1 4 4 3 5 0 1 ?,7% 0 0 10 14 11 1 0 41% 0 0 3 5 7 4 0 47% Injiiioicc of External Conditions on Tricotyly. 455 tricotyls has increased, it is plain tiiat the factors under- lying- these differences are by no means simple. This is further shown by the fact that a repetition of the experiments does not always produce the same result. Thus in Ainaranttis speciosus (1897), and ScropJiularia nodosa (1898), I was not able to observe any influence exerted by the various external conditions on the propor- tion of tricotyls, although the experiments were carried out on a large scale. I also found that if I sowed sam- ples from the same lot of seed in two successive years, the mean ratio of tricotvls in the harvest of the two cultures was the same, (e. g., Oenothera hirtella, 1898 and 1899). Moreover, unfavorable conditions can sometimes, by diminishing the yield, lead to an increase in the per- centage values. This is shown by an experiment which I made in 1898 with Antirrhimnn ma jus. I covered half of my culture with a cage made of fine metal gauze painted black, after the plants had developed a stem of 10 centimeters above the cotyledons. Within the cage it was considerably darker than outside, and the plants grew very wxakly, produced only few branches, and de- veloped but a small number of flowers and fruits on the terminal spikes. Fertilization was artificial, and all the plants were guarded from the visits of insects. The yield In the cage was 0.5 cc. per plant, and outside 1 cc. per plant. In the former case as many fruits as possible were gathered but in the latter the upper flowers of the spike were not fertilized. The material used in this experiment consisted exclusively of the offspring of a single parent of 1897 which had had a value of 14%, but tricotylous and dicotylous seedlings were both used, each group being planted half within the cage and half 1^ 10 20 30 40 Mean 0 4 2 2 2 20% 5 8 4 1 4 14% 0 3 2 3 4 35% 1 U 9 14% Tricotylous Races. 456 outside. I collected the seeds and determined the values in the same way as usual, and obtained the figures which appear in the following summary: HEREDITARY VALUES IN ANTIRRHINUM MAJUS. Percentage values Dicotyls in the shade Dicotyls in the sun Tricotyls in the shade Tricotyls in the sun Number of seed-parents 10, 21, 12 and 24. We see that in both cases the proportion of tricotyls was considerably increased by cultivation in the shade. The experiments which we have passed in review in this section prove that the proportion of tricotyls in the offspring may be considerably modified by external in- fluences, especially in eversporting varieties, but within certain limits. The differences are such as cannot be neglected in comparative experiments and cultures, and show the importance of carrying out the latter under as constant conditions as possible. In general it must be assumed that a treatment, favorable to the individual flowers and seeds, will increase the production of tri- cotylous seedlings, but the question as to the nature of this relation in the individual cases must, for the present, remain unanswered. 11. SYNCOTYLOUS RACES. § 9. HEMI-SYNCOTYLY, SYNCOTYLY, AMPHI-SYNCOTYLY. Alongside seedlings with split or double cotyledons there occur others, the seed-leaves of which have fused so as to form one single organ. They are, however, much rarer, but not so rare that they cannot be found every vear, at least in some sowing or other. Tricotyls may be found in the proportion say, of one in a thousand, but syncotyls, as a rule, only one in tens of thousands of seedlings. In the sowings of 1895 which we have already men- tioned (p. 380), I found, amongst more than 250,000 seedlings of 40 species, only 10 syncotyls as against 150 tricotyls. Where they occur more abundantly this is due to inheritance, for as soon as the syncotyls are allowed to flower in isolation and their seeds are saved separately, it is found that they inherit their character in almost the same degree as do tricotyls. Instances of syncotyls were afforded me by Aster fcncUus, Clarkia clegans, C. pidchella, Cerinthe gym- nandva, Chrysanthcinuin Myconis, Hclichrysuin hractca- fujji, Phacdia tanacetifoUa, Silene hirsiifa, AnagaUis gran- diflora, EpUohhmi hirsuUim, Hesperis matronalis, Pent- stciunn gentianoides, Rohinia Pseud- Acacia, and many other forms -} but always in small proportions. A few * Further instances are given by H. B. Gruppy, Irregularity of Soiiu^ Cotyledons, Science Gossip, N. S., Vol. II, 1895, p. 171. 458 Syncotylous Races. species, however, produced them more abundantly. Among these were the following which produced the proportions of syncotyls from the seeds of single individuals, indi- cated by the attached figures: Oenothera (Kneiffia) glaiica 16% (Figs. 89 and 90), Picris hieracioides 8%, Valeriana alba 3%. Dahlia variabilis and Sycios angu- lata were also found to be rich in syncotylous seedlings, Fig. 89. Oenothera glauca. A plant which produces an abundance of syncotylous seedHngs. and in Centranfhus inacrosiphon I found 37% of them amongst the seeds of a single syncotylous plant. -^ By syncotyls we mean, in the strict sense of the term, those individuals whose seed-leaves are completely, or almost completely, fused together along one side. Smaller degrees of fusion are called hemi-syncotyls, and they constitute an uninterrupted series between normal di- ^ Eine Methode, Zwangsdrehungen aufzusuchen, Ber. d. d. hot. Ges., Vol. XII, 1894, P- 25. Heini-Syncotyly, Syncotyly, AmpJii-Syncotyly. 459 cotyls and types in which the fusion has extended to the very tip- The lesser degrees of fusion are usually rarer than the greater, and, therefore, in order to get a fairly complete series of transitional forms, cultures from the seeds of selected individuals are required. It is often very difficult, especially in forms with stalked cotyledons, to distinguish between the lowest grades of fusion and pure dicotyls. If the crops are recorded before the cotyledons and their peduncles have grown to their full extent, it may easily happen that occasional seedlings. Fig. 90. Oenothera glauca. Syncotylons seedlings. A and B, ordinary syncotyls ; C and D, pitcher-shaped syncotyls or amphi-syncotyls. which, after further growth, will prove to b hemi-syn- cotylous, are mistaken for dicotyls. The hemi-syncotyls constitute the minus variants of the series, the corresponding plus variants being the amphi-syncotyls of double or two-sided syncotyls (amphi- cotyls). In these latter cases the cotyledons are fused on both sides, often more on one side than the other, sometimes equally high on both sides. The cotyledons constitute a pitcher (Fig. 90 C and D, and Fig. 91) which is either cylindrical or urn-shaped or disc-shaped, 460 Syncotyloiis Races. according- to the breadth of the cotyledons on the normal plant. I found instances of these remarkable and pretty structures almost every year in HeliantJms annuus syii- cotylcus and in larger numbers in Mercurialis annua and Ccntvanthns macrosiphon,^ and also occasionally in An- tirrhinum majus, Sinapis alba, etc. The fusion of these cotyledons sometimes results in a pressure being exerted on the plumule and interfering with its growth, and we often find that syncotyls grow slower than normal seedlings, at least at first, and that Fig. QT. Raphanus Raphanistrum. A cotyl pitcher ex- panded in the form of a disc. A, from the side ; B, the same, seen obliquely from above and showing the plumule. amphi-syncotyls are especially backward. The extent of this influence cannot, as yet, be measured ; but the fact that syncotyls are so much rarer than tricotyls may per- haps be explained by this check on their growth. Some- times the plumule breaks sideways through the cotyl- pitcher by splitting its lower part (Cenfranfhus macrosi- phon, Mercurialis annua) . Sometimes it succeeds, although very late, in elongating in the normal direction. In Helianfhus annuus I have sometimes operated upon such ' Figured in Bcr. d. d. hot. Ges., Vol. XTT, PI. TT, Figs. 3 and 4. Hcnii-Syncotyly, Syncotyly, Auiphi-Syncotyly. 461 ])itc]iers by splitting them up along one side with a sharp knife, as soon as I saw that the plant would not grow without this help. By this means I succeeded in bringing the plants to flower, but they were weak, thin-stemmed individuals. The growth of the plumule is often entirely sus- pended, both in ordinary unilateral syncotyls and in pitcher-like structures. In such cases the seedlings live much longer than usual, the cotyledons grow to a great size, often twice the normal, but finally the plant dies without producing a stem. This occurred frequently in Hclianthus annuus and Dahlia variabilis, and less often Fig. 92. Polygonum Convolvulus. Instances of tri-syn- cotylous seedlings with various degrees of splitting and fusion. in Penstcrnon gcntianoides and Cannabis sativa. In the two latter species one or two leaves were sometimes de- veloped, but after that the terminal bud ceased to grow, whilst those leaves attained an abnormal size and thick- ness (Fig. 93). In such cases the question arises whether the inhibition of the growth may not, both here and elsewhere, have some other cause also. Syncotyly may be combined with tricotyly, and since, as we have seen, the fluctuating variability of both pre- sents a long series of forms, the multiformity will be much greater still in the series of the so-called tri-syn- cotyls. Thus, for instance, in Polygoniun Conrolvulns 462 Sxucofvloiis Races. (Fig. 92), and also in Chciiopodinm album, Thrbicia Jiirta, etc. Between svncotyly and disturbances in the normal arrangement of leaves in the later life of a plant, there \/ / Fig. 93. Cannabis sativa. A, a seed- ling which unfolded its cotyledons in April, but up till June had formed no plumule ; B, another with two abnormally large and thick first leaves, the terminal bud of which underwent no further growth. Both are from a culture, in the remain- ing seedlings of which the length of the stem had become 10-20 centi- meters during the same time (1894). Fig 94. Fagns syhatica. Syncotylous seedling with much elongated epicotylous internode and abnormal development of the plu- mule. is a close connection, as there was in the case of tricotyly. Frequently this disturbance is only a small one (Fig. 94) ; but in species with a decussate arrangement of the leaves or at anv rate of the first leaves, there often follows on Hoin-Syncofyly, Syucolyly, .hnplii-Syncotyly. 463 the syncotylous organ a node with only one leaf, which then usually stands opposite to this structure. I have frequently observed such cases in Mercurialis annua (Fig*. 95) and Hclianthus annuns} Further disturbances ma / then follow, such as unequal size of the two leaves Fiut perhaps they were the weakest individuals and contracted the disease for this reason. III. THE INCONSTANCY OF FASCIATED RACES. § 14. THE INHERITANCE OF FASCIATIONS. Fasciations are amongst the commonest anomalies which occur in the vegetable kingdom.^ Until about ten years ago the prevailing opinion concerning them, as in- deed in regard to monstrosities in general, was that they were not heritable but owed their origin to external in- fluences only. The coxcomb, Celosia cristata, was con- sidered an exception to this rule. It was, however, well known that the phenomenon occurred more frequently among certain species than among others ; but the con- ception that some plants possessed a greater tendency to the production of such anomalies than others was taken for a sufficient explanation of this fact. But since I have succeeded, in the case of a series of apparently fortuitous fasciations, in establishing, by iso- lation and selection, races in which the deviation is re- peated regularly and in a considerable number of indi- viduals, it has become evident that we are concerned here with heritable qualities which are handed on from one generation to another in certain strains of individuals, and which really differ from the characters of ordinary varieties only in the fact that they are always accom- panied by reversions. It never happens that every branch ^ See A. Gallardo, Fasciaci'on, Proliferacion y Sinantia. Anales del Mnseo Nacional de Buenos Aires, Vol. VI, pp. 37-45. Tlic InlicriUuicc of Fasciations. 489 on a sufficiently branched individual is fasciated, any more than that all the individuals in a large crop produce the anomaly without exception. The Cclosia cristata, which comes closest to perfection in this respect, is only an ap- parent exception to the rule. Fasciations, therefore, afford valuable material for the study of inconstant characters. Moreover they are Fig. 104. Ears of r3^e with two and three tops, such as are sometimes found in mowing the fields (1891). known everywhere, can be procured by everybody, and are fairly easy to cultivate ; and the successful cultures give rise to beautiful instances of fasciation in a third or even in a greater proportion of the individuals. There is a complete series of transitional forms between the atavists and the most abnormal specimens, inasmuch as the broadening of the axis can be either very slioht or 490 The Inconsta}icy of Fasciated Races. very considerable, and all the intermediate stages can often be observed on the lateral branches of a single plant. The most important result which can be deduced from the experiments which follow is the discovery that the afcrt'isfs or noii-fasciatcd individiials of the race can only he regarded as reversions in the morphological sense; but that physiologically considered, that is, as transmitters Fig. 105. Ranuuciihis biilbosus. A fasciated stem which has grown up from a broadened rosette of radical leaves. The terminal flower is also broadened and split. Hilver- sum, 1894. of fasciations, they are scarcely inferior to the best fas- ciated specimens of the race. The character in question is only latent in them, or rather only temporarily invisible ; perhaps simply not developed by reason of the absence of some necessarv external factors. The atavists do not, so to speak, depart from the race, as do those of Oenothera scintillans; the race con- The Inheritance of Fasciations. 491 stitutes a uniforni group of individuals and only differs from constant races or true varieties by the extraordi- narily high degree of variability of its distinguishing character. This degree of variability relates not only to the degree of expansion of the axis, but also to the manner in which the anomaly is manifested. First we have to Fig. ]o6. Viola tricolor maxima, the garden pansy. A forked flower stalk arising from the axil of a double leaf {a, a) ; .yand.y, the outer stipules; s , the inner un- split stipules of this leaf. The continuation of the main axis has been bent down laterally, {b). distinguish between the split branches and the fasciated branches scnsn sfricfo. Split ears of the rye are some- times found in the fields (Fig. 104) and then preserved by the country folk. The axis of these ears may be divided once or oftener, the parts above the division being perfectly normal themselves. Or again the haulm 492 The Iiiconstaucy of Fasciafcd Races. below the ear may be split and produce two ordinary ears side by side. Amongst other plants also forkings of this kind are by no means rare, but as a rule they occur associated with typical fasciations. The latter are of the same breadth from below, that is to say in the strict sense ribbon-shaped, or they begin with a cylindrical form below, and gradually flatten out towards the top. The latter case is the normal one ; from it the former has been derived. This may occur either on an axis of two or more years of age, or on the lateral branches of stems which are themselves fasciated. Axes of two or more years of age begin by being circular in transverse section, and can, in the same summer, obtain a maximum breadth which they then retain in later years. This is observed especially in stems which arise from a rosette of radical leaves developed in the preceding year (Crepis biennis, Aster Tripoliuni, Picris hieracioides, Pri- inula japonica, Raminciihis bulbosus [Fig. 105] etc.). In trees and shrubs and especially in firs (Abies excelsa) a fasciation that has once appeared, frequently reappears for several years in succession.^ The lateral branches of fasciated axes often have an expanded base and then grow on without further increase in breadth. Like the base of a lateral twig, a leaf on a fasciation can undergo expansion in its youth. In this way there arise broader, more or less deeply split, leaves, not infre- quently even with similarly expanded or split -axillary twigs (Fig. 106) ; or again the germs may be split and parted quite early, and two or more leaves arise in this way instead of a single one. Especially when the leaves * C. DE Candolle. Fasciation che:: un Sapin, Archiv. Sc. phys. et nat., tScSq, Vol. XXT. p. 95. PI. TT ; and Over de erfcJykhcid der fasciaticiij Botan. Jaarboek, 1894, PI. XI. The Inheritance of Fasciations. 493 are arranged in whorls, this kind of niulli])hcalion looks very striking (Fig. 107). If we examine the growing point of a fasciated shoot, the abnormal conformation can already be distinguished. Fig. 107. The Madder. Ruhia tinctortim. Fasciated stems with an increased number of leaves in the whorls, found in a madder field near Ouwerkerk and broken off at the rhizome (1890). Where the fasciations are very broad this was to be ex-' pected, as for instance in the case of Scdiiiu rcflcxuiu cristatiiiu figured in the first volume (Figs. 34-35, ])p. 494 Tlic lucoiistancy of Fasciatcd Races, 182-183). Expanded combs of this kind are often seen at the top of inflorescences, especially in Veronica longi- Fig. io8. J^croiiica longifoJia. Inflorescence with tlie tip expanded in the form of a comh. folia (Fig. 108), Ainarantus speciosus (Fig. 83, p. 399), Oeiinfliera Lamarckiana and 0. brei'isfylis, etc. The Jii/irri/aiicc of j'asciatiojis. 495 Tliese phenomena have l)een more closely investigated by Nestler who regularly found inside the terminal bud of a fasciated branch a line of fasciation instead of a point, in other words a growing comb instead of a grow- ing cone.-^ The leaves arising from this latter are pro- duced in ver}' large numbers and in an abnormal arrange- ment, and in consequence of this, the disposition of the leaves on fasciated stems tends to be extremely irregular ; but although this subject is obviously very important in its bea'-hig on the whole question of phyllotaxy, it still awaits a thorough investigation. In this respect it would be particularly valuable t^o make a study of fasciations in conifers, for our knowledge of the normal structure of tlieir cone of vegetation is much more extensive than it is in regard to that of angiosperms.- Moreover there is no lack of material, for Cryptoineria japonica 111011- sfrosa and the fasciated varieties of several other species are on the market (Fig. 109). Besides the cases of ordinary fasciation, and of those in which the surface may be bent by unequal secondary growth, there are some cases of most peculiar conforma- tion which hitherto have been very little investigated. It is not known whether these are the expressions of the same internal character or whether they must be referred to special factors. Their morphological structure is in favor of the latter view : but the former is supported by tlic fact that they have hitherto always been observed in conjunction with ordinarv fasciations, i. e., in si")ecies which are particularly liable to them. Exam])les are af- forded by the multi-radiate and annulate fasciations. ' A. Nestt.er. Uiifcrsuchiiuf^cii iihrr Fascialioiiru. Ocstcrr. botan. Zeitschrift. 189-I. No. off., with 2 plates TT. DiNGLER. Ziiiu Schcitekvachstlmm dcr Gvnuwsf^cnncu. Bcr. d. d. hot. Ge.s., Vol. IV, icS86, p 18. 496 The Inconsttnicy of Fasciated Races. In tlic rine lasciations tlic vco-etative cone is trans- formed into an annular wall which ultimately develops into a smaller or larger funnel. I found these remarkable structures re- peatedly in my cultures of Veronica longifolia, where they remained quite small, scarcely reaching a centimeter.^ On the other hand I have observed a funnel -like structure in Pcpcroinia maculosa of more than a decimeter in length. - Some of the best known instances of ring fascia- tions occur in Taraxa- cum officinale ; these have frequently been described and I have myself often had the opportunity of in- vestigating them.^ With- a thick, tube - like Fig. 109. Crytomeria japonica mon- strosa. A commercial variety very rich in fasciations. a, laterally ex- panded tip of a branch producing a normal twig at d by means of splitting; b and c, further fascia- tions of this branch. ni flower - stalk, often as many as 10 to 20 slender stalks arise, each in the axil of a leaf and each ^ A. Nestler, Ueher Ringfasciation, Sitzungsber. d. k. Acad. d. Wiss., Wien, Vol. CIII, Part I, 1894, Plates I-II. ' Sur un spadice tuhuleux du Pcperomia maculosa. Archives Neer- landaises d. sc. ex. et nat, Vol. XXIV, p. 258, PI. XTI. Afterw^ards the anomaly occurred again on the same plant (1892). ^ MiCHELis, Bofan. Zcitung, 1873, p. 334; 1885, p. 440. Further literature will be found in Nestler's paper already cited. For Helian- The Inheritance of Fasciations. 497 bearing" a more or less normal inflfMxscence. From the seeds of such an individual, I have for many years culti- vated a large bed containing over 100 plants which, how- ever, only produced ordinary fasciations, but no ring- fasciations. Sometimes I have found radiate fasciations in my cultures of Amarantus speciosus alongside of the more Fig. no. Amarantus speciosus. Tri-radiate peaks of inflorescences. common, ordinary fasciations.^ The tip of the inflores- cence was not flattened, but tri- or sometimes quadri- radiate (Fig. 110). In Digitalis In tea I have observed a similar case, and in Celosia cristafa I found a good thus auuuus, see Paul Richter, Bcr d. d. hot. Gcs., 1890, Vol. VTTT, p. 231, PI. XVI. Oz'cr de erfclyhhcld van fasciaticu, Botanisch Jaarboek, Gent, 1894, P- 90. 498 The Inconstancy of Fasciatcd Races. instance of a quadri-radiate apex on a branched indi- vidual (1893). Tri-radiate fasciated heads have often been found in Composites ; for instance in Chrysanthe- niiun LcucantJiennim, HcUanthns annuus and Erigcron hcUidiflorus. In the latter species these have occurred with tolerable frequency in my garden. All these cases are greatly in need of a closer investigation. For the production of a fasciation the presence of the internal factor is not of itself sufficient. Favorable con- ditions of life are also quite necessary. The stronger a plant or a branch is, the more liable is it to expand and flatten out. This is best seen in those biennial or peren- nial plants which occasionally have the power of flower- ing in the first year. If they do this, either only small fasciations, or none at all, are developed, whilst it is amongst the specimens which remain in the rosette stage during the first year and do not develop their stem till the second, i. e., after they have undergone considerable increase in strength, that the most numerous and finest fasciations will be found. Thus, for instance, I obtained through the kindness of Professor Lagerheim from Stockholm seeds of a fasciated plant of Hicraciuni iiiu- bcllafmn. and in the summer of 1901 I had from these a bed with nearly a hundred plants without a trace of fasciation. Some plants, however, did not make a stem that year but, after they had survived the winter, pro- duced in the following spring some beautiful expanded stems with comb-shaped inflorescences at the top. The same occurred in my cultures of Aster TripoUuni, Picris hieracioides, Oenothera Lamarck'iana and others. The first species, when grown as an annual, developed tall stems which remained fairly cylindrical in the lower part, and then began to flatten, without, however, attaining TJic InJicritaiicc of I'ascialioiis. -1-99 a greater l)rea(lth tlian about 2.5 centimeters; Ijiit in large cultures there were sometimes as many as 60 or 70/^ of such broadened shoots. When grown as a biennial, h(nv- e\'er, the hearts of the rosettes gradually expand in the first autumn or during the winter, and from these, stems are produced which sometimes attain a very considerable breadth. Thus, for instance, in the summer of 1895 I measured some of from 3-6 centimeters. Picris hicra- cioidcs seldom produces fasciations in the first year, and when it does they are not broad ; whilst the stems i)ro- duced m the second year from the broadened rosettes of radical leaves ordinarily afford some of the finest in- stances of this anomaly.^ Just as the age of the various individuals of a culture has a great effect on the production and development of the fasciations, so also has the time of the year at w^hich the seed is sown. Many biennial or perennial plants which quickly manifest the character of the race when sown early, remain apparently normal if the sowing was made late, and they cannot grow out to sufficient strength before winter. My fasciated races of Crepis biennis and Taraxacum officinale are very instructive in this connec- tion. Sowings of Crepis, made in April and May, gave from 30-40% of fasciated individuals. Sowings made at the end of Ji-ily produced 20% only, and those made in September none at all. Similarly, Taraxacum officiiiale, when sown in spring, produced 13 to 27% of fasciations. whilst a sowing made in August did not produce even so much as a single flattened flower-stalk. \^ur la ciillurc dcs monstruositcs, Compt. rend., Paris, Jan. 1899; Sur la culture dcs fasciations dcs espcccs aiinucllcs ct bisa)i)ii(cllcs, Revue gen. d. Bot., 1899, Vol. XI, p. 136; and Ucbcr die Ahhdni^ig- kcit dcr Fasciation vom Alter bei czi'eijdhrigcii PHanzen, Botanisclies Ccntralblatt, 1899, Vol. LXXVII. 500 The Inconstancy of Fasciafcd Races. In races of this kind all conditions of the environ- ment are of importance. By crowding, the proportion of fasciated individuals can be reduced, for instance, from Fig. III. Agrostemma Githago. A plant the main axis of which had been cut off at o. The cotyl- edons have dropped off at C and C. Their axial twigs are fasciated, and instead of producing decussate leaves, bear multiple whorls. They split occasionally at the nodes, forming forks with branches at (/, b, c, d, e and /. Just above f the calyx of the flower is spiral (kk), and fused with the uppermost fo- liage leaf (b), by which the flower stalk is seen to be twisted. (1892.) 40 to 5%. Even if the number of fasciations is calcu- lated per area of the bed, a small number of specimens give a prospect of obtaining more- fasciations than a Tlie Inheritance of Fasciations. 501 larger number planted on the same area, but too close to- gether. The number of fasciations can be diminished by cultivation on sterile sand and increased by the addi- tion of manure. The most numerous and the finest in- stances of the anomaly are produced by cultivation in pots with heavy manuring and by subsequent trans])lan- tation to the beds; and so forth. -^ Further, a considerable effect can be exerted on the production of fasciations, as upon that of monstrosities in general, by pruning and by the selection of buds which accompanies this process. Thus, Goebel says in his Or- ganograpliie^ that fasciations can be artificially produced by diverting the ''sap" with great intensity into a lateral bud which would otherwise have obtained only a small quantity of it. It is for this reason that fasciations are particularly abundant on adventitious branches and shoots from cut stems. Even in annual plants such as Phaseoliis ynultiflorus and Vicia Faha, fasciation can be induced by cutting off the plant above the cotyledons. A plant which is peculiarly suitable for the demonstration of this method is Agrostemma Githago, which in my cultures always produced an abundance of anomalies, but did so with greater certainty when I had removed the main stem, just above the cotyledons or the first pair of leaves. The axillary buds, which, as a rule, do not develop, grew out under this treatment and frequently became fasciated (Fig. 111). The phenomena of periodicity are also associated with the effects of nutrition. Lateral branches of fasciated shoots are usually of normal structure; but broadened ones not infrequently occur amongst them. If they do, ^ Botan. Ccniralhlatt, 1899, he. cit. ''Vol. I, p. 234. 502 The Inconstancy of Fasciatcd Races. they manifest a certain order in their disposition since they are usually found in that region where other normal and ahnormal characters also attain the maximum of their development.-^ This phenomenon which can easily be demonstrated in the fasciated race of Tetragonia cx- pansa, is, however, in need of more thorough investi- gation. But the chief point seems to me to be, as Goebel ]Dointed out in his work to which we have already re- ferred, that the latent factor for the production of anom- alies must be present in all those parts of the plant in which external influences are able to induce fasciations or anomalies. If this is absent no amount of manipula- tion is of any avail. It seems, however, that the factor for the production of fasciations is pretty generally dis- tributed throughout the vegetable kingdom; though it is not so general but that there are certain groups in which it does not occur. It is a curious fact that fascia- tions are much commoner amongst dicotyledons than amongst monocotyledons, although some very well-known instances are ]:)resented by the latter {Asparagus, LUiitin, Fritillaria, Orchis). § 15. HALF RACES WITH HERITABLE FASCIATION. It is only by conducting special breeding experiments that we can discover for certain whether fasciation is heritable in a given species, and to what extent. If, however, such cultures are made, we shall soon find that these anomalies fall into two categories which are per- fectly analogous to the half races and eversporting vari- ^ See T. Tammes, Ucher die Pcriodicit'dt morphohgischer Er- scheinungcn bci den Pflanzcn_ Kon. Acad. v. Wet., Amsterdam. 1903. Half Races zvitli Heritable l-asciation. 503 cties distinguished in the first part of this \-uhinie ( p. 18). In the former case the anomahes are rare and their fre- quency can not be increased by selection to any consider- able extent. In the second case the fasciations occur even in the held in obviously larger numbers ; and it is only necessary to isolate the examples in question in order to be in immediate possession of a race producing fasciations abundantly. These experiments are perfectly analogous to those which we have described in the case of other anomalies and especially to those relating to tricotylous and syncotylous cultures (see page 343). Nevertheless, in the case of fasciations, we have by no means so strin- gent a character to select by, as is presented by the per- centage hereditary values, calculated from the seedlings of tricotylous races, and therefore the subsequent devel- opment of the race after the initial isolation is a matter of much greater difficulty. Postponing the consideration of the eversporting vari- eties or intermediate races to the next section, let us here attempt to obtain some insight into the races in which the anomaly occurs more rarely. Unfortunately, in many instances the available data are not yet sufficient to enable us to decide with perfect certainty to which of the two t\ pes a given case belongs. Fasciations occur in so many commercial varieties that they are accessible to everybody ; sometimes even the variety owes its name to the frequency of this character, as, for instance, the Sword-elder (Sanibiiciis nigra fas- cia fa) ; or it may be an almost constant attri])ute of the cultivated sorts, as in the Japanese spindle-tree {Ez'0}i\- imis japojiica. Fig. 112). When the varieties are either largely or exclusively multiplied in the vegetative way, it is possible that the anomaly, although only heritable 504 The Inconstancy of Fasciated Races. to a slight degree, may be memifested frequently; as, for instance, in Lilium speciosiun album corymbifloriun and in the so-called sword-shaped variety of Fritillaria hnpcrialis. The well-known monstrous species of Cactus should also be referred to here (C peruviamis nion- strosus). Experimental estimations of the constancy Fig. 112. Evonymus japonica. A fasciated much-split twig of this common garden plant. A, B, growth in 1898; C, D, in 1900. Photographed, Aug. 1900, from life. of these abnormalities from seed do not yet seem to have been made. The same general conditions obtain amongst many species of trees and shrubs, of which any collector can easily obtain a fasciated sprig. As instances from my own collection I mention Fraxinns excelsior, Alnus c/liifi- nosa, Crataegus nigra, Azalea indica, Rohinia Pseud- Half Races nnth Heritable Fasciatioii. 505 Acacia, Salix purpurea^ Sali.v alba, Spiraea callosa atro- purpiirea. Moreover I have obtained, by the kiiKhiess of Prof. W. Jo HAN N SEN of Copenhagen, beautiful broad Fig. 113. HeliantliKS tuhcrosus. A fasciated stem which is spHt into two ahiiost equal fork-branches b and c, at the node marked a. From the fork there arise two leaves d the mid-ribs of which have fused along their dorsal side/ fasciations of the underground stems or runners of Spi~ raea sorbifolia from the nursery of Air. Zeiner Lassen in Helsingor. Instances of the same fasciations have I have also observed this remarkable occurrence of fusing by the backs in leaves in the forks of split twigs, in Robinia Pscud- Acacia and Evonymiis japonica (Pkingsheim, Jahrb. f. zviss. Bot., XXIII, p. 81) and also in Collinsia hcteropJiylla (1892), Epilobiiiiii InrsHfiiin (1892), Echhim vtilgarc (1892), CJirysantlicmum scgctum (i(S92). AgrostemmaGithago (1892 and 1894), Acer Pscudo-Platanus (1891), Crcpis biennis (1893), Aniarantus speciosiis (1894), Mercu- rialis annua (1894) and Lamiuni purpureuni (1895). 506 TJic Inconstancy of Fasciatcd Races. been described and figured by Caspary and therefore appear to be fairly abundant in this species.^ In perennial weeds fasciations also occur freely, and here we may often observe that the phenomenon is re- peated more or less regularly in successive years on the same specimens or groups of specimens. For instance, we have in the botanical gardens at Amsterdam a plant of Sonchus pahistris on which I first observed a splendid tall broadened stem in 1890. Since then the plant has pro- duced almost every year one or several such structures, sometimes 2 meters in height, sometimes not more than 1 meter,and attaining a breadth of 6 centimeters by a thick- ness of 1. These stems are cylindrical at the level of the ground, but flatten out grad- ually upw^ards. Similar instances were afforded by Aconituui Xa- pcllus, and Hclianthus tubc- rosns (Fig. 113) in our gar- den, by Jiisticia siipcrha in the greenhouse, and l)y Agri- mania Eiipatoriiim and Chrysanthemum Leiicanthenuini in the field. I frequently observed fasciations in annual and biennial species, and usually in the course of several years in the same locality; for instance in Raphaniis R. Caspary, Eiiie gehandcrte Wiirzel von Spiraea sorhifolia L., Schriften d. Physik. Oec. Ges. Konigsberg, 1878, XIX, p. 149. Plate IV. As a matter of fact, however, it was not a root; see Pexzig, Teratologic, I, p. 421. Fig. 114. Plantago lanceolata. Ears which have spHt one, two or three times. Cultures of 1894 and 1895. Half Races zvifh Heritable Fasciafion. 507 Raplianistruni, Pedicularis palitstris and Oenothera hi- cuuis. In my cultures of Aiiiarantus speciosiiSy Helian- i/iiis aiuiiius and Oenothera Laniarckiana, the anomaly was reproduced almost every year through the course of ten years. -^ One of the best known instances is afforded by the sugar-beet, fasciated speci- mens of which can be found almost every year in the fields. We frequently find amongst them quite long, broad and wholh^ flat stems. In spite of the obvious fact that they are not selected as seed-parents they recur regularly, and this fact is sufficient to demonstrate the heritability of the anom- aly. I have further to men- tion Plant ago lanceolata, the variety ra//zo^a of which I have described in detail in the first part of this vol- ume (page 148) and which I have cultivated every year since 1889. It sometimes produces split ears (Fig. 114), especially amongst the inflorescences which are not branched at their base, i. e., the atavistic ones. In this ^ Furtlier details relating to this subject and more instances of the phenomenon will be found in Oz^cr dc crfclykhcid dcr fasciati'cii, Botanisch Jaarboek Gent, 1894, p. "^2. Fig. 1 15. Artemisia Ahsynthium. A fasciated branch which has been heavily bent in conse- quence. 508 The Inconstancy of Fasciated Races. race the anomaly is obviously in the latent condition and only to a slight extent heritable. N. IMezzana records an instance of a fasciated stem of Ciicurbita Pcpo, the upper part of which gradually be- came broader over about a meter of its length, and was thickly set with leaves and flowers. The phenomenon was observed on a number of specimens which had been raised from seed of the same fruit and Mezzana con- cludes from this fact that the anomaly is inherited.-^ The fact that I have frequently observed such fasciations in my own cultures of Cnciirbita supports this conclusion. In Artcniisia Absynthinin also, fasciations are sometimes very common as I observed in 1883 (Fig. 115), 1887, 1888, 1889 and 1890, and the phenomenon was repeated from seed in 1889 and 1891.- The remarkable forms which the fasciated branches of this species so frequently assume offer a profitable subject for future inquiry. § i6. EVERSPORTING VARIETIES WITH HERITABLE FASCIATION. Some wild species produce, in certain districts at least, a much higher proportion of fasciated examples than others do. According to my experience, such cases sug- gest the occurrence of heritable races, the individuals of which are mixed with those of the normal species or occasionally occur by themselves alone. So far as I am aware, such races do not consist exclusively of fasciated plants, but partly of these and partly of normal ones. Without cultivation the latter cannot be distinguished from the normal plants of the species in question, and ^ N. Mezzaxa, Sopra nn caso d'l fasciacione ncl fusto di Ciicur- bita Pepo, Bull. d. Soc. Bot. Italiana, Florence, 1899, pp. 268-273. ^ Botan. Jaarh. Gent, 1894, p. 97. Eversportlng Varieties with Heritable Fasciation. 509 therefore we can not directly see whether both races or only the first grow in the particular locality; but their great rarity points to the mixed condition. The heritable races which have hitherto been found and isolated in this way, behave like eversporting vari- eties inasmuch as each generation consists both of fasci- ated individuals and of atavists, even under conditions of the most stringent selection. Moreover the proportion of these two types appears to be pretty constant, at least under similar conditions of life. As a rule, there are about 40% fasciated individuals and 60% atavists. Higher percentages of the former occur only under favorable circumstances, whilst the proportion of the latter very easily increases under unsuitable conditions of culture, in spite of selection. The first instance that I shall describe was afforded by Crepis biennis, an exclusively biennial plant, fasciated • stems of which have been frequently observed in various localities in Holland. The starting point of my culture consisted in two fasciations, which I found in May 1886, in a meadow near Hilversum, amongst hundreds of normal plants of Crepis. The broadening of their stems was small and limited to the top. I collected ripe seed in this meadow in June, but from normal plants only. Whether all or only some of these belonged to the ever- sporting race I was in search of could, of course, not be determined then. This seed furnished in the following year about one hundred plants, of which three were already fasciated in the rosette stage, whilst in the following year nine more of them developed more or less flattened stems or branches. The total proportion, therefore, was 12%. In order to make perfectlv sure, T retained only the first 510 The Inconstancy of Fascia ted Races. mentioned specimens as seed-parents and destroyed the rest before they flowered. These three plants therefore formed the l)eginning of my race. Denoting the wild specimens of 1886 as tlie first generation, the second grew in 1887 and 1888, the third in 1889 and 1890, and so on. This third one con- sisted of 120 plants, of which 48 or about 40 ^r already exhibited a comb-shaped linear growing point in tlie heart of their rosettes in the winter. This comi) was in some specimens as much as six centimeters long. I se- lected the three finest fasciations as seed-parents and re- moved the rest before flowering. The fourth generation raised from this seed produced a slightly lower propor- tion of fasciations, containing, as it did, only 30% of them. In the fifth generation a further reduction took place, viz., to 24%.^ The sixth generation (1895-1896) was very rich in fasciations, and in ten plants out of the 40, produced a growing comb of from 4 to 7 centimeters. Unfortunately the remaining fasciations of less degree mostly died in the winter before they were recorded, so that an exact percentage value can not be given. Never- theless it was obvious that the character of the race had been displayed oftener than in the previous generation. In the following, viz., the seventh generation, I also re- corded only the expanded rosettes before the winter, and found ten of them amongst 49 plants, that is about 20%. The eighth generation was not sown till 1902, and only on a verv small scale. The combs became visible during the winter 1902-3. Tf we summarize the results which we have described, we see that the seed collected in the field, without selec- tion, gave about 12% fasciated ofi^spring, whilst the seeds * Bofanisch Jaarhoek, Gent, 1894. p. 80, and 1897, P- 66. Ez'crsporting J^aricfics ivifh Heritable fasciation. 511 of the best cultivated individuals gave values l^etween 10 and 20%, in the course of the five generations which followed. These would probably have been higher if the cultures had been larger and tlie external conditions more favorable, and especially if a closer searcli liad been made for smaller fasciations on the lateral l)ranches. We may therefore regard the constitution of this race as fairly constant under normal conditions, and put it on the average al)out 30-40%. No doubt, this fi^'ure is somewhat lower tlian the normal value of tricotylous intermediate races which we described in the second chapter of tliis part. In that case the value was about 55% ; but this difference does not seem to be of great significance, especially wlicn we remember that tricotvlv is alreadv determined in the seed- lings, whilst a long period of time elapses between the ripening of the seed of the fasciated plants and the mani- festation of its character, during which period all sorts of external influences may be affecting the result. A second difference between tricotvlous and fasciated races also demands brief notice. In the former, selection soon led to a transgression of the original normal value ; and values of 70 to 90% were often reached or even sur- passed without much trouble. In the fasciated races, on the other hand, it is very difficult to raise the value above about 40%. The ex])lanation of this seems to me to be as follows : In my tricotylous races a twofold se- lection took place, inasmuch as, first, the tricotvlous in- dividuals were selected for subsequent cultivation, and, secondly, a selection was based on the proportion of tri- cotylous individuals amongst their seeds. By the selec- tion of the parents with the highest hereditarv values, this A'alue itself was seen to increase in the following 512 The Inconstancy of Fasciated Races. generation. In the fasciated races, on the other hand, we are obhged to hmit our selection to the best represen- tatives of the anomaly; but there is no further reason to suppose that these also possess the highest hereditary values. Thus, an essential part of the selective process as applied to the tricotyls is omitted in this case. This is mainly due to the impossibility of calculating the hered- itary values in the seed pans, and the fact that these would need cultivation on a very large scale in the gar- den. In order to calculate the hereditary values for only 20 seed-parents from lots of only 100 offspring each — and even this would hardly give reliable results — 80 square meters of the garden would have to be devoted to Crepis, and this can scarcely be done in an ordinary garden. It is to be hoped that institutions will soon be erected where such determinations can be carried out.^ Besides Crepis biennis I discovered one or two other species behaving in the same way and succeeded in rais- ing eversporting varieties from them.- The first to be mentioned is Aster Tripoliiim, of which I obtained a splendid fasciated example with ripe fruits in the autumn of 1900, from this neighborhood. At first I grew the plant as an annual and reached only a low proportion of fasciated individuals as a result of this. The fisfure was 7% for the fourth generation. In the fifth generation, however, in the summer of 1894, the plants were sub- jected to better treatment, and more than half of them produced fasciated stems, amongst which many were more than 3-4 centimeters broad. I shall deal with My experimental garden contains 75 beds of about 4 square meters each. ^ BotaniscJi Jaarbock, Gent, 1894, and Bull Scicnfifique de la France et dc la Bclgiquc, public par A. Giard, XXVII, 1896. p. 402. Evers porting Varieties with Heritable Pasciation. 513 Geranium molle faseiatmn in the next section. Of this race, one-third consists, as a rule, of inthviduals with fasciated hranches. In 1895 I was growing its sixth generation. I have also cultivated six generations of Taraxacum officinale fasciatuin. This species, as a rule, produces 30%, and sometimes more, of fasciated individ- uals. Beautiful instances of fasciation have been fur- nished almost every year, since 1885, by Tetragonia ex- pansa in the botanical garden in ^Amsterdam, and the proportion of these was, in the fourth and fifth genera- tions after isolation, slightly over 50%. The same general behavior w^as observed in my fas- ciated races of Thrincia hirta, Veronica longifolia, Hes- peris matronalis, Picris hieracioides etc. From these data wx may draw the general conclu- sion that such races, after having been isolated and sub- jected to good treatment, and by the selection of the finest instances of fasciations as seed-parents, consist of a little less than one-half of fasciated individuals, and of a little more of apparently normal, atavistic, plants. This proportion, however, depends to a large extent on ex- ternal conditions. By means of suita])le cultivation it can be considerably increased, but on cessation of this care it soon sinks to quite low values. Many of the known instances of fasciations probably behave in the same way. For instance Kornicke has grown for many years a perfectly constant race of a fasciated pea (Pisum safiT'iun) in Poppelsdorf. and Rnr- PAU has informed me that he cultivated this fasciated race from seeds during several years in good garden soil and found it constant. The result of sowing the seed of Sedum reflexum cristatuiu (Vol. T, p. 183), in this garden, was the reappearance of the abnormality in large 514 TJic Inconstancy of Fascia fed Races. numbers. To this group, also Asparagus officinalis and several other species seem to belong. § 17. THE SIGNIFICANCE OF THE ATAVISTS. As we have seen in the first section of this chapter (page 490) a proper understanding of what is meant by atavism is a necessary basis for the discussion of our appreciation of the inheritance of fasciations, and of anomalies in general. Here, the atavists are not indi- viduals which step out of the race; on the contrary, they are to be regarded merel}^ as specimens in which, from some external cause or other, the anomaly is not mani- fested during their lifetime. In the selection for the continuation of the race they are, of course, not usually ])referred, but as a matter of fact they may serve just as well for this purpose as the fasciated individuals them- selves. Extensive investigations are still to be carried out before a complete and proper understanding of the prin- ciples which underlie these phenomena can be attained. The knowledge however, which we already possess, ap- pears to me to be sufiPicient to demonstrate the correctness of the generalization just enunciated. In the first place I mentioned the remarkable fact that the anomalv can re- main latent during a whole generation without disap- pearing forever or even becoming noticeably diminished. Sometimes indeed two or several generations can be skipped in this way. Let me give some instances as proof of this.^ In the fall of 1887 I collected some seed of Tetragoma cxpansa from fruits on very broad stems and obtained, in the following years, 1888-1890, three further "^ Botanisch laarhoek, Gent, 1894. The Significance of the Atarists. 515 generations which produced a greater or les.^ number of fasciations. The seeds of the finest fasciations of 1890, however, produced nothing but normal plants in 1891 which did not exhibit the anomaly, even on a single lateral branch. They were weak plants and it lucjked as if the anomaly were lost once and for all; Imt seeds of these plants produced in the following year, 1892, fourteen plants, of which seven were fasciated. Six of them had 1 — 1 — 2 — 2 — 3 — 3 broadened stems, and one plant had as much as four large fasciations. More- over the lateral branches were so much affected by the anomaly that I found about one-third of them to be modified in this way. Since that time the anomaly has remained constant in this strain. In the third generation of my race of Aniarantus speciosus (1891) the fascia- tions were also absent, but returned in the fourth and fifth generations in 30 and 50% of the indixiduals. In HeUanthiis annmis they were also absent from the third generation (1889), whilst the fourth contained about 20% of fasciated individuals, and the anomaly has since remamed constant. In the maize I observed fasciated ears in 2 cultivated race in the years 1888, 1889, 1892 and 1893, but not in the generation of 1891, between these. From the seed of a very broad stem of Picvis hieracioidcs (1887) I raised three generations under unfavorable conditions, and they did not produce a trace of the anomaly on many hundreds of branches and stems. Tt was not until the fourth generation that the anomaly reappeared, although only t(^ a slight extent. Besides this strain I have cultivated a race of biennial individuals, and these have presented fine Instances of fasciations in greater or less abundance in e\'ery generation.-^ ^ Revue generalc dr hotan'ujnc. 1899, Vol. XT. p. T36. 516 Tlic hicoiistancy of Fasciatcd Races. In the summer of 1895 I isolated some of the atavists of my race of Crcpis biennis described above, before they flowered.^ The seeds were sown in the following year and produced over 350 plants. About 20% of these ex- hibited the comb-like structure in the center of the ro- settes, and this line sometimes reached a length of five centimeters. Thus we see that the seeds of the atavists may produce fasciations in about the same quantities as do the selected fasciated individuals. Inasmuch as the monstrosity frequently lowers the strength of the plant, it might perhaps even be advisable to choose the seeds of the atavists or of individuals which are only fasciated on their lateral branches. A further proof of the view' that the atavists are only fasciated individuals with their character in a latent con- dition is afforded by experiments on the effect of thor- ough manuring. For the individuals which under normal favorable circumstances behave as atavists can be in- duced bv it to a relatively considerable development of fasciations. In 1895 I made such an experiment with my strain of Crcpis biennis fasciata which then contained some 20 to 40% of fasciated individuals every year. I manured a group of 41 plants with an abundance of horn- meal. At the time of ripening only six of these lacked the anomaly, i. e., 85% instead of 40% were fasciated. The plants stood fairly close together, at distances of about 20 centimeters apart. If I had given them enough room I should probably have succeeded in inducing the anomaly in every one of them.- The fasciated commercial race of Celosia cristata, * Botanisch Jaarhoek, Gent, 1897, p. 66. ^ Botanisch Jaarhoelz, 1897, p. 66; and Bull. Scicntif., loc. cit, Vol. XXVII, p. 413. The Significance of the Atavists. 517 generally known as the coxcomb, is peculiarly well suitccl for an investigation of atavism. The great combs pro- duced by this favorite garden plant are merely the se- lected well treated and highly nourished individuals, i e., the extreme plus variants of the race.^ All the rest are thrown away in their early stages by the gardener; but if we wish to know how the race really behaves, we must Fig. ii6. Celosia cristata. An almost entire plant under poor treatment. Top comb-shaped but small ; most of the lateral branches were also broadened at their tips. make sowings ourselves and plant out all the individuals without selection, and cultivate them further. It is well known that in this way we obtain numerous plants with branched stems and with a much lower degree of the antjmaly (Figs. 116 and 117). By the selection of these minus variants for further cultivation one might expect, ^ For the mode of cultivation suitable for this variety see !Mol- ler's Deutsche Garteii-zeitting, 1892, p. 200. 518 Ihc lucunsfaiicy of FasciafccI Races. as Solms-Laubacii suggests, to ultimately obtain the un- fasciated original form of this highly moditied plant. ^ But according to the view laid down in this book, a mu- tation would be necessary for this ; and, so far as we know, these ap- pear only very seldom and fortui- tously, unless we happen to meet with a plant in a mutational period. During the years 1893-1897 I endeavored to obtain a race devoid of fasciations, but in vain ; and in- asmuch as the general rule is that fa\'orable circumstances increase the production of the anomalies, and as correspondingly the worst nourished and w^eakest individuals have alwavs borne the smallest fas- ciations, I w^as ultimately o1)liged to give up the experiment, because my strain gradually became very much debilitated without, however, producing the desired result. In 1893 I raised about fifty ])lants from bought seed, but difl not make any detailed record of them. Most of them produced combs in every degree of de\'el- opment,^ but usually of small size, 5 — 10 centimeters broad or less. Fig. 117. Celosia cris- tata. Top of a plant about Vz meter high ; the stem was much branched and its in- florescences were ear- shaped l)ut mostly with comb-shaped tops. ^ n. Solms-Laubach, Bof. Zcitung, 1900, p. 42. ^ The plane of the fasciation is the median plane of the cotyle- dons ; and this is also the case in Crcpis biennis. This fact might be used as a starting point for an inquiry into the ontogeny of fas- ciations. The Significance of I he Atavists. 519 Six plants had a terminal spike at the top of the main stem with a small comh ; in six others this comb was ab- sent, althongh small fasciations occurred here and there amongst the lateral branches. These six plants were selected as seed-parents, and from their seeds 1 obtained the second generation (1894), in which about half the individuals bore terminal spikes without a comb. There were 41 of these. The remaining 55 had combs ranging from 1-3 centimeters broad and were thrown away. Of the selected atavists, several produced lateral combs later, and each one of these plants was destroyed as soon as I discovered the anomaly, until at the end of the harvest period there were left only five plants which, though profusely branched, manifested no trace of fasciation. In the following year there were 29 plants wnth small combs and 6 without any at all ; these latter were again isolated as seed-parents. In 1896 I had 38 individuals, all of which, without exception, produced combs, the length of which ranged between 2 and 8.5 cer.timeters with a mean of 4.5. Only one plant had no comb at the apex of the stem ; but had a much flattened lateral branch instead. This, and the plants with the smallest terminal combs, were selected as seed-parents. Again, in the following year (1897), no progress was made, inasmuch as only a single weakly individual failed to produce a comb. Therefore I gave up the experiment and I con- clude that complete atavists are very rare in Celosia crisfafa and that even under repeated selection in the minus direction they will only be obtained in very small quantities. At present at least there seems not to be any prospect of obtaining a pure atavistic strain. The experiments I have described show that, as a rule, there is no sharp limit between the fasciated individuals 520 The Inconstancy of Fasciafed Races. and the atavists. This fact can be illustrated by statistical examination of the material, provided it can be made sufficiently large by cultivation. As an example of this I may again cite my race of Crepis biennis fasciataA In order to obtain a pure curve, I sowed the seeds of a single broadly fasciated individual of the third gene- ration of my race (1890) in March 1894. The plant had flowered together with two other fasciated individ- uals of the same ancestry, but this little group had been completely isolated. The seeds were sown in pans in the greenhouse and afterwards planted out at suitable dis- tances in the bed. Whilst still in the rosette stage many of them produced in the first year a comb-shaped heart. Others did not exhibit fasciation until the stem began to develop in the second year. Still others had not produced a single comb at the time when all their branches were fully developed. The external conditions had been as favorable as possible, so that I obtained a relatively high proportion of fasciated individuals. When I examined the plants in June of the second year, I obtained the fol- lowing result : Stems without fasciation 33 " with slight fasciation at the top . 9 " fasciated along their whole length 108 Total 150 The breadths of the stems of these latter 108 plants were distributed as follows : Cm. 2 3 4 5 6 7 8 9 10 11 12 13 14 19 Ind. 9 9 4 11 11 11 13 15 11 6 3 3 1 1 The numbers are plotted in Fig. 118 in the form of a curve. In this curve 0 indicates the group of 33 ata- Sur les courhes Galtoniennes des monstruosites, Bull. Scientif., public par A. Giard, XXVII, 1896, p. 396. The Significance of the Atavisfs. 521 vists, 1 the nine plants with cyhndrical stems and shght broadening at the top; whilst 2-20 denote the breadth of the stems in centimeters. The curve is seen to have two peaks, one of which is formed by the atavists (a), the other by the fasciations of mean breadth, i. e., of about nine centimeters. Ex- pressed in words, the result is that transitions between 9 10 11 12 13 14 15 16 17 18 19 20 Cm. Fig. ii8. Crepis biennis fasciata. A curve representing the breadth of the main stems of all the individuals of my culture of 1895. The numbers under the base line indi- cate the breadth of the stems in centimeters, o, stem round; i, stems only flattened at the upper end; 2-20, stems flattened along their whole length. The height of the ordinates gives the number of individuals. Total number of individuals 150. a, the peak of the atavists; h, that of the fasciated individuals.^ the fasciated individuals and the atavists do occur, but are relatively rare. The race produces by preference the two pure types, and the same thing is seen to happen in chance fasciations and in many other monstrosities. I call to mind the relative rarity of hemi-tncotyls and hemi- syncotyls, both in the wild state and in the tricotylous 'Bull. Scientif., he. cit., Vol. XXVII, p. 397. 522 The Inconstaiicy of Fasciatcd Races. and syncotylous races described in the first two chapters of this part. Similar resuks mav be obtained with other fasciated Fig. 119. Geranium molle fasciatum. Fasciated branches with broadened and spHt fruits, a, b, c. races. Thus I obtained in the fifth generation of my fas- ciated race of Aster Tripolhim, under biennial culture : WITHOUT FASCIATION WITH FASCIATION Cm. 1 2 3 4 5 6 Individuals 16 2 6 8 11 1 The Significance of the Atavists. 523 The curve representing these 35 plants would have a distinct peak representing the atavists and another cor- responding to the fasciated individuals of the average breadth of 3 centimeters.-^ In Geranium inolle fasciatnm the variation of this character proved, after a statistical examination of the material to l)e represented by a many-peaked curve. This t Fig. 120. Geranium mollc fasciatnm. a, fruit containing 6 single fruits ; b, split into one group of 4 and one of 5 ; c, split into three groups containing 5 — 7 and 5 single fruits ; d, one group has 16 and the other 5 divisions of fruil and stigmas; c, fruit with ^2> divisions and stigmas (1895). race- is remarkable from the fact that tlie stems have, as is v^ell known, a sympodial structure (Fig. 119), Therefore the anomaly affects, as a rule, one member of the sympodium only ; but sometimes it extends to two or more adjacent ones. These are again succeeded bv atavistic members. Each part terminates n^ a flower. ^ Revue gcncralc dc hotaniqiic, 1899, Vol. XT, p. 143. ^ Bntanisch Jaarh. Gent, 1894. p. 81: and 1897. p. 67. 524 TJie Inconstancy of Fasciatcd Races. In the fasciated parts these flowers are broadened and usually more or less divided, the fruit sometimes form- ing a flat structure (Fig. 120^), with or without one or two lateral fruits in the same flower (Fig. \20 c and d). Often these latter are pentamerous. Lastly the whole fruit can be split into two or three nearly equal parts 10 II 15 20 23 Fig. 121. Geranium molle fasciatuin. Curve representing the number of sections of the fruit in the individual flowers of the sixth generation, June 1895 ; a, number of normal flowers far above 100; number of flowers with 6 to 23 stigmas, 120. (Fig 120 b). In these various types of splitting there seems to be a tendency to the production of whorls of five, and the lateral flowers nearly always present this number. My race began with a specimen found wild in 1888 and m the third and fourth generations produced 25 to The Significance of the Ataz'isis. 525 30% individuals with fasciations. In llic two following generations they were much more abundant. In the sixth there were 65% fasciated specimens, in a culture of 220 plants, and these afforded me sufficient material for a statistical examination. For this purpose I collected, shortly before the ripening of the seed, all the aberrant flowers from a certain number of plants, and counted the number of the divisions of the fruit or that of the stig- mas of 120 individual flowers taken at random. The figures which I obtained were as follows : NUMBER OF Stigmas 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 Flowers 13 9 4 5 10 15 2 2 10 15 6 3 7 5 9 3 1 1 I did not count the normal flowers, but their number far exceeded that of the whole group of the fasciated ones. In the curve in Fig. 121, in which the above series of figures is graphically displayed, the apex representing the atavists is therefore only formally indicated. The secondary peaks fall at 11 (10), 15 and 20 pistils, and the normal pentamery of the flowers is thus clearly re- peated in these multiple figures.^ Besides illustrating this curious fact, the curve shows that low grades of fasciation are relatively rare and that atavistic and normal flowers constitute two distinct groups, although connected by intermediate stages. Let us now summarize the conclusions we have come to in regard to fasciated eversporting varieties. 1. The races always consist of fasciated individuals and atavists. 2. The proportion of the former varies greatly, of- ten amounting to only 40% or less, but not infrequently ' A further inquiry into this point is, in my opinion, urgently called for. 526 The InconstLUicy of fasciatcd Races. to more {Geranium and Crcpis with 65% and 85%; Celosia cr is tat a). 3. The fasciated individuals and the atavists are con- nected by transitional forms, which are, however, rare ; and the statistical curves representing them have there- fore two apices. 4. These proportions are to a large extent dependent on external conditions of life, which can transform ata- vists into fasciated plants and vice versa. This trans- formation obviously takes place during the plastic period in youth, before the character in question is actually de- veloped. 5. The atavists, as well as the selected individuals, produce fasciated offspring, and often in proportions very little lower than those in which the selected individuals produce them. They may therefore be used for the per- petuation of the race. 6. Between the broadened s]:)ecimens and the atavists there is no essential or fundamental difference, in spite of the great difference in tlieir external forms. IV. HERITABLE SPIRAL TORSIONS. (Plate VI.) § i8. THE SPIRAL DISPOSITION OF THE LEAVES. In tlie case of spiral torsion the difference between normal and abnormal individuals is far more striking than in that of fasciations. Valeriana officinalis is one of the best known and the most frequently figured instances (Fig. 122). Llere the whole stem, instead of growing to a height of more than a meter, can be reduced to about a decimeter, and becomes more or less funnel-shaped. Low down the leaves are disposed spirally, but higher up, the spiral gradually becomes steeper, until, in the ex- panded upper part of the funnel all the leaves are directed to one side like a fan. The terminal inflorescence sur- passes the highest lateral flowering branches very little or not at all. By no means every stem of the spirally twisted plant manifests the anomaly. On the contrary, very few of them do as a rule. Since 1889, I have had a specimen wliich has graduallv increased by runn.ers and now covers an area of several square meters in the botanical garden of Amsterdam. It produces spiral torsions every year, Imt they are rare, and, as a rule, there are not more than two or three among several hundreds of normal stems. The same rarity is seen in the inheritance of the anomaly, both in Valeriana and other sjiecies ; as a rule. 528 Heritable Spiral Torsions. only a small proportion of the plants repeat the anomaly, even when the seeds have been saved on the most highly modified stems. Races w^hich produce the anomaly abun- dantly have been very rare hitherto. They will be de- scribed in the following section (§ 19). Fig. 122. Valeriana officinalis. xA-ii entire plant the stem of which attained the height of lO centimeters only. Photo- graphed from life in June 1900. Disposition of the leaves spiral below, unilateral above. In consequence of this rarity the belief prevailed, up till about 10 years ago, that these torsions were not heritable. The general view was that they were induced by special external influences which operated immediately upon the individual every time the anomaly arose. At that time the experiments which I had made with a twisted The Spiral Disposition of the Leaves. 529 .> Fig. 123. Dipsaciis sylvestris torsus. Two spirally twisted main stems, zv, root ; r, stem with the scars of the radical leaves and at i — 5 the windings of the spiral; g, stalk of the terminal inflorescence ; A, leaf-spiral left hand, stem riglit hand; B, leaf spiral right hand, stem left. Stems thickened and hollow. 530 Heritable Spiral Torsion. race of Dipsacus sylvestris torsns, during over thirteen years, together with a long series of further observations on the inheritance of this anomaly in other plants, have proved that this character is as heritable as other anomalies are. Plate VI gives a view of a culture of this race, re- produced from a photograph of one of my beds. Real spiral torsion only occurs in those species which normally have a decussate or whorled disposition of the leaves. It consists in the substitution of a spiral arrange- ment for this. The leaves arise from an unbroken spiral, along which they are attached to one another more or less closely to their bases (Fig. 123). This close spiral is sometimes interrupted and normal internodes are inter- calated in the twisted part. Not infrequently the torsion is limited to a greater or a lesser part of the stem (com- pare, e. g., below^ Dianthiis, Fig. 129). Indeed no sin- gle stem is completely abnormal from the very beginning. As might be expected the fusion of the base of tlie peduncles into a continuous band results in an inhibition of the longitudinal growth of the stem. The internodes cannot elongate normally, and as they strive to extend, they partly unwind the leaf spirals. In consequence the spiral becomes steeper and not infrequently unwinds so much in the up])er parts of the stem, i. e., those parts which normally grow in length, as to become a straight line. When this occurs the leaves and their axillary buds arise in a longitudinal series on one side of the stem (Fig. 122). Obviously this can only be reached by the stem twisting itself in the opposite direction to that of the leaf-spiral (Fig. 123). Inside the twisted stem, if it is hollow, the diaphragms which normally occur at the nodes, do not exist as such, but are united together The Spiral Disposition of the Leaves. 531 to a continuous screw-like l)an(l which corresponds ex- actly to the leaf-spiral on the outer side. Twisted stems look as if they were inllated (Figs. 122 and 123), and are much thicker tlian the normal stems of the same species. Longituchnal growth has, so to speak, been changed into a tangential growth, as the course of the otherwise vertical ribs clearly shows in our figures. The longer the particular internodes on the normal individuals are, the broader are the correspond- ing parts on the twisted ones. In this way the funnel shape of the twisted Valerian, as well as other specific and local differences, are easily explained. From this we see that a right-hand torsion of the stem (mounting in the direction of the movement of the hands of a clock) must be associated with a left-hand leaf-spiral and vice versa (Fig. 123). The explanation here given was first suggested by Braun, and later demonstrated by Klebahn, by the microscopical examination of the top of the stem of a twisted Galiiun} It can now easily be confirmed 1)y every one on the material afforded by my heritable races. - In Dipsacits syhesfris torsus the spiral arrangement oi the leaves can be detected towards the end of the first summer in the heart of the rosette of radical leaves, with the naked eye, and without any damage to the plant. After germination and in the earlier stages the leaves are decussate (Fig. 124 A) in all the plants with very rare exceptions; it is not until later that this arrangement ^ Al. Braun, Monatsher. d. k. Akad. d. IViss., Berlin. 1854. p 440- See Bof. Zcitung, 1873, p. 31 ; H. Klebahn, Ber. d. d. hot. Ges., Vol. VI, p. 346. See also Ucher die Erblichkeit dcr Zivangsdrchungcn, same journal, Vol. VII, p. 291. 'For the literature of the subject see Monogvat^hic dcr Zzi'angs- drchuugcn. Jahrh. f. wiss. Bot., Vol. XXIII. 1891. 532 Heritable Spiral Torsions. is changed into the spiral one, and in different individuals this occurs at varying ages. If a transverse section of the plant is then examined under high power, at the level of the growing point, the spiral arrangement of the leaves can easily be seen. Taken later, i. e., during the elongation of the stem, such transverse sections have still more or less the same appearance (Fig. 124 B). The outer leaves of this figure have been cut through their lower parts where they are fused laterally with one another; their left-hand spiral can easily be followed Fig. 124. Dipsacus sylvestris torsus. A, a transverse sec- tion through a seedling a Httle above the growing point showing the normal decussate arrangement of the leaves ; c, c' , the cotyledons ; B, a transverse section through the still young point of the stem of a twisted individual with spiral arrangement of leaves. in the figure. The subsequent leaves were still very young and were therefore cut across their upper free parts, but are nevertheless obviously arranged in a spiral. The three youngest leaves do not seem to form part of the spiral, but a trimerous whorl, such as very often occurs in the upper part of the stem of twisted speci- mens of Dipsacus If the angle of divergence of the leaves is measured it usually corresponds pretty closely The Spiral Disposition of the Leaves. bi^ to one of the ordinary types of leaf arrangement, (e. g., %). In the rosettes of radical leaves, where the internodes do not lenginen, the spiral disposition of the leaves does not involve any further disturbance. The leaves simply grow out and retain their original position. But when, in the second year, the young internodes begin to elon- gate, this cannot happen equally on all sides of the stem, because the line of attachment of the leaves acts as a check. In consequence of this the stem must twist and unwind the leaf-spiral, the angle of divergence between successive leaves becoming gradually smaller. The num- ber of windings decreases, and on the other hand, the numbers of leaves on a single section of the spiral (i. e., from a given point on the stem to another vertically above it) increases, as our Fig. 123 clearly shows. Spiral torsion is, therefore, a mechanical result of the loss of a single character, the decussate arrangement of the leaves. Once this is lost, the ancestral spiral dispo- sition steps In, but now accompanied by peculiarities in the structure of the basal parts of the leaves, which on normal plants never occur Independent of an arrangement in whorls, since they can only, so to speak, agree with the normal structure of plants with this arrangement. There- fore, In my opinion spiral torsion is due to a retrogressive transformation of the decussate arrangement of leaves. That It Is a mechanical result can be proved by ex- periment; all that Is necessary Is to remove the cause of the twisting at an early stage, by cutting through the leaf spiral. If this is done carefully, the general growth of the plant Is not Interfered with, but the torsion will be locally inhibited, or, more strictly speaking, does not appear at the place operated on. Thus a straight inter- 534 Heritable Spiral Torsions. node will become intercalated in the middle of an other- wise twisted stem. This can easily be seen in Fig. 125 at a, in the gaping wonnd and in tlie vertically ascending longitudinal ribs. Sometimes nature itself makes a simi- Fig. 125. Dipsaciis sylvcstris torsiis. The two leaves a and h of the twisted stem have been separated from one another in earliest youth by a cut : between them is seen the gaping spht. The one leaf, b, is situated now about 2 centimeters higher than the other, a. Above a the stem has remained straight for more than 2 centimeters. Some of the lower leaves were removed before photographing in order to show the important parts more clearly. lar experiment, and longitudinal growth tears the leaf- spiral in one or two places, without, however, making so deep a wound as results from an expernnent. The result of such a natural experiment is a straight internode TJic Spiral Disposition of tlic Leaves. 535 of normal length, for instance of a decimeter or more, in the middle of a twisted stem. Like other anomalies spiral torsions are to a very large extent dependent on external conditions. Under unfavorable treatment the anomaly may be almost en- tirely absent, even from culttires from seeds which other- wise would gi\e rise to a third or mcn'e of individuals with fine spiral torsions. The experiments which I have made on this point with Dipsaciis sylvestris tarsus and which have been confirmed by the results of my experi- ments with other species, seem to justify the following- conclusion.-^ The more favorable the conditions of life and the more vigorous therefore the growth, the greater will be the proportion of beautifully twisted plants in a given culture, and the more complete will be the torsions which are produced. The most important of these conditions is the space given to the individual plants. They ought not to be shaded by one another nor touch one anotlier. More than 20-25 plants should never be grown on a square meter. Grown thus they nevertheless stand in close con- tact in autumn, and it is obviously still better that no more than 10-15 plants should occupy a square meter. Fewer torsions are produced on a given area when the plants are crowded than when the distances ])etween them are greater. No useful purpose is therefore served by increasing the number of plants on the same bed. Tf nevertheless this is done the twisted individuals will be found almost exclusively along the edges of the bed. The time of sowing the seed is a point of considerable ^ O;; Biasfrcf>sis ?';; Its Relation to Cultivation. Annals of Botany, Vol. XIII, 1899, p. 395. 536 Heritable Spiral Torsions. importance, inasmuch as it determines the length of the life of the plant up to the moment of the production of the stem. The longer this period continues under favor- able circumstances the greater is the likelihood of the leaves becoming spirally arranged. Sowings, made in summer or early autumn, which gave rise to stems in the next year, reduced the prospect of obtaining- torsions almost to nil. On the other hand, autumn sowings which do not give rise to stems until the summer after the next, contam very large numbers of twisted specimens; so that if the seeds are sown late in the autumn the proportion of plants with a spiral ar- rangement of their leaves is even greater than amongst plants raised from seeds sown in th« spring. Little effect is produced upon the result of a culture by sowing in March or in April or even in the begin- ning of May. Also it does not matter much whether the sowing is carried out in the greenhouse in pans and the seedlings planted out later into the beds, or whether the seeds are sown where they are to grow. For various reasons I have for many years preferred the former method, as it is more convenient and safer, especially in dry springs. A good loose soil with a strong manure rich in nitrates seems to be an essential condition. On unmanured sandy soil even the best seeds do not produce twisted individuals, and on hard or barren soil the proportion is considerably diminished. It is possible to confine the cycle of life of Dipsactis sylvestris tarsus within the limits of a year by sowing the seeds under favorable circumstances immediately after they are ripe. In this way a generation can be grown every year, and an annual twisted race might pos- Rare Spiral Torsions. 537 sibly be raised by selection. At present, however, the annual habit and the torsion are mutually exclusive, the anomaly being represented on the stems of such plants either not at all or as faint indications only. § 19. RARE SPIRAL TORSIONS. From time to time spiral torsions are also found on wild and cultivated plants under conditions which make it impossible to make any other observations on the in- heritance of the anomaly than that they occur relatively frequently on the several branches of the same plant or in more or less numerous examples in the same locality ; or recur during the course of several years. They may be found in dozens in Weigelia amahilis, and are also well known in several species of Galium. In Galiinii venim and G. At>arine I have collected them in this neighborhood. Eqiiisctiim is also a well-known example, which deserves special mention as belonging to the vas- cular cryptograms as well as on account of its j^eculiar leaf-whorls. Our figure 126 is photographed from a stem which Dr. Th. Weevers found near Nymegen in the summer of 1900. Here it grew among several other instances of torsion in the same species. Casuarina also sometimes forms such anomalies on its branches ; for instance, several occurred in 1897 in the botanical garden of Amsterdam (Fig. 127 a). In the first chapter of this part we have seen how, as a result of the correlation between various abnormal types of leaf arrangement, the selection of tricotylous seedlings often leads to the discovery of s])iral torsions in species from wdiich otherwise they can be ol^tained only very rarely. As instances of such species I may 538 Heritable Spiral Torsions. recall Dracoeeplialiiiii inoldavicuin (Fig. 74, p. 369), Aspenila azurca, Centranthus macrosiphon and especially Mercurialis annua. In the latter species these malforma- tions appeared almost every year and often in consider- Fig. 126. Eqiiisetum Tehnatcja. Spiral torsion of an erect stem. able nnmbers, in my tricotylons and syncotylons races (Fig. 96, p. 464). Unless direct experiments in isolation have been made it is impossible in the majority of cases to be certain Rare Spiral Torsiojis. 539 wliether the race we are dealing with is a half or an inter- mediate race. Nevertheless the rarity of the anomaly in repeated sowings strongly indicates the former alter- native. This was certainly the case in Liipiiius Intciis, Fig. 127. Casiiarina quadrivalvis. A branch with a hitcral torsion, a. From the botanical garden in Anisterdani, 1897. Silcne nodi flora and other species which occasionally produced spiral torsions in my cultures. In J^alcriana officinalis (Fig. 122, p. 528), which has already been mentioned, the proportion of anomabms individuals raised 540 Heritable Spiral Torsions. from seeds gathered from twisted stems was very small, and in Rubia tinctorum, of which I have had several beautiful instances of spiral torsions from the fields in Holland, they are never by any means common, although Fig. 128. Agrostemma Githago. The calyx is open at one side and fused with the uppermost pair of leaves and transformed into a spiral. Culture of 1896. they occur nearly every year.^ In Agrostemma Githago I have often observed torsions in a race which I have cultivated during ten generations since 1888, but always "^ Eenige gevaUcn van Klemdraai by de Meehrap (Riibia tinc- torum). Botan. Jaarb. Gent, 1891, p. 74 and Plate IV. Rare Spiral Torsions. 541 in small numbers. Sometimes these were confined to the vegetative parts, but sometimes the calyx, together with the upper pair of leaves, was transformed into an open spiral (Fig. 128). In order to determine the intensity of inheritance of this anomaly in such cases, I have conducted an experi- ment with Dipsacus laciniatus. This plant was of pecu- liar interest to me because it belonged to a genus which has been known for a long time to produce fine spiral torsions and to which also the Dipsacus syk'cstris be- longs, from which I have been able to isolate an ever- sporting variety which produces this anomaly in abun- dance. In Dipsacus laciniatus, on the other hand, the attempt to effect a similar isolation was unsuccessful. In this case an intermediate race was not present, but only a half race; for in spite of extensive cultures for two generations no more than slight local torsions were ob- tained. A plant of Dipsacus laciniatus which I had seen in full bloom in the botanical garden at Groningen formed the starting point of this experiment. It was over two meters high with a perfectly straight stem which, how- ever, had a little group of spirally arranged leaves at one of the upper nodes and here exhibited local twisting. Prof. J. W. Moll kindly sent me seeds of this plant. From these I grew in the two following years 400 plants on a bed of about 16 square meters, that is about 25 per square meter, which may be regarded as giving am])le room. The sowing took place in the beginning of April. In the summer of 1897 all the stems became straight; not a single one was twisted, as in Dipsacus syh'cstris (Fig. 123, p. 529). Moreover, the arrangement of the leaves was decussate in all of them. Slight abnormal- 542 Heritable Spiral Torsions. ities in this arrangement certainly occurred, such as split leaves, trifoliate upi)er whorls, fusion of two pairs of leaves by a so-called line of tearing extending over the internode, a phenomenon which shows that the leaves in their early stages were fused in a spiral manner instead of in whorls. Besides these, there were eight plants, i. e., about 2%, which had a distinct local torsion at one of the upper nodes of the same development as in the parent plant. Their leaf spiral involved from 3-6 leaves. Only these plants were allowed to flower, and there was no other Dipsaens laeiniatus in the garden. Five of them produced a sufficient quantity of seed. The second generation of this culture occupied the vears 1888 and 1889 and consisted of 435 plants which produced stems and were allowed considerably more space than their predecessors, 12 specimens being grown to each square meter. Nevertheless the result was the same as in the foregoing generation. All the plants formed erect and tall but straight stems, from 2-2Yi meters high. Amongst them there were five specimens which had a somewhat larger local twisted part than occurred in the preceding generation, inasmuch as in these cases from 7-12 leaves were combined into an un- interrupted spiral. They arose from three of the five parents. Less pronounced torsions (at the nodes) which affected from 2-3 or rarely from 4-6 leaves, occurred fairly commonly in this year. I counted the percentages of 5, 5, 13, 13, and 28% of such individuals per parent. A general advance had therefore taken place, brought about parti}' b}- selection and partly by the ample room given to the plants ; but whilst the isolation of twisted specimens of Dipsaens sylvestris torsiis resulted imme- diately in a proportion of 34% of fine, almost complete spirally Tivistcd Races. 543 malformations, as soon as the culture was given sufficient room, nothing hut small local tvvistings occurred in this case, in spite of highly favorahle conditions of growth. From this I concluded that an eversporting variety anal- ogous to my Dipsacus sylvcstvis torsiis cannot be raised from these seeds. § 20. SPIRALLY TWISTED RACES. The often mentioned race of Dipsacus sylirstris tar- sus (iM'gs. 123-125, pp. 529-534, and Plate VI) has now completed its ninth generation. It consists of about 40'/r of individuals with fine torsions and about 60% of ata- vists with, as a rule, decussate, bu^, occasionally ternary, arrangement of the leaves. The atavists and the twisted plants with incomplete or interrupted spirals have alwavs been destroyed before flowering. The completely twisted individuals, however, were left to be fertilized bv one another through the agency of insects. This very stringent process of selection has had the result of maintaining the race at a fairly constant level. During the first two generations I did not know the proper conditions and sowed the seed much too thick, and con- sequently only obtained twisted individuals at the edges of the beds, and even here in small numbers. Rut with the improvement of these conditions the proportit^n of twisted stems at once mounted to 34%, and the heredi- tary value has since remained about the same, althougli subject to fluctuation due to the greater or less favorable climatic conditions obtaining in successive years. But no advance could be discovered. In order to exhibit graphically the result of this cul- 544 Heritable Spiral Torsions. tnre, which extended over 18 years, I shall give here a brief summary of the nine successive generations. GENERATION NUMBER OF PLANTS PER PROPORTION OF PLANTS SQUARE METER TWISTED MAIN STEMS 1st. 1884-1885 2d. 1886-1887 1643 50 0.1 3cl. 1888-1889 1616 35 4 4th. 1891-1892 107 25 34 5th. 1893-1894 45 22 10 20^ 6th. 1895-1896 33 8 42 7th. 1897-1898 70 16 46 8th. 1899-4900 1295 22 32 9th. 1901-1902 492 22 41 The mean of the six generations was therefore about 35%. We see from this table that the continued isolation and selection of the finest torsions maintained the race at its level, but did not improve it to any considerable extent. Two points about this result should be noted. In the first place the percentage figures given do not denote the proportion of twisted individuals, but relate solely to those with torsions on the main stem. In some experi- ments, however, instead of pulling up the atavists, I only removed all their inflorescences before the flowers opened, and by this means I found that several, and often many of them, had the power of developing more or less fine local torsions on their lateral branches. In 1902 I made as accurate an account of these as possible, and found 71 of them or 14%. Of twisted i..dividuals there w^ere, therefore, 41-]- 14=55% altogether, i. e., somewhat more than half the individuals produced torsions. It seems of some interest to note that this percentage is the same ^ The percentage figures for the 5th, 6th and 7th generations are hardly decisive on account of the small size of the cultures. spirally Twisted Races. 545 as has been observed elsewhere in intermediate races, and especially in the tricotyls (see page 439). Secondly, I call the attention of the reader to the remark which I made hi the previous chapter (j^ 16, p. 511) with regard to selection. Even as hi the case of fasciation, a double selection, by the visible characters of the seed-parents and by their hereditary value, cannot here be carried out under the ordinary conditions of the experiments. The most valuable character to select by, the hereditary coefficient, fails, and in consequence of this the improvement of the race, wdiich in the case of the tricotyls so soon resulted in a proportion of from 70- 90%, obviously cannot be carried to its full height here. Nothing less than a lucky chance or the conducting of the experiment on a much larger scale can bring this about. In the eighth generation I compared the heredi- tary coefficients of ten parents. They ranged between 10 and 55% ; but as only from 100-140 offspring of each parent could be compared, the percentage numbers did not seem to me to be of much importance from the point of view of selection. In the 9th generation I saved the seeds from over 100 very finely twisted individuals, in the hope of still being able to carry out an experiment in selection by hereditary coefficients. I shall now give a detailed description of the whole experiment.^ The starting point of my race was formed bv two individuals with a twisted main stem which flow- ered in 1885 in a culture sown in 1884 in mv o-arden. All the remaining plants were destroyed before they flowered. In 1886 I obtained a second generation from their seeds. As I have already mentioned, I w^as not at that * Annals of Botany, Vol. XIII, No. LI. Sept. 1899. p. 40T. 546 Heritable Spiral Torsions. time familiar with the most favorable conditions of this culture, and obtained only two twisted individuals amongst nearly 1650, probably for this reason alone. These two flowered in isolation and set an abundance of seed. The third generation (1888-1889) raised from seeds of the second, produced 67 twisted stems in a culture of about the same extent, i. e., about 4%. Here again the seed- parents flowered in isolation. The fourth generation was sown partly in 1890, and produced as many as 10% twisted individuals which however could not be used for the continuation of the race. The rest of the seed was sown in 1891 with a better knowledge of the conditions, whereby the propor- tion of twisted individnals rose to 34%, a value which the later generations on the average maintained, without surpassing it to any considerable extent. The improvement in the method of culture consisted essentially in providing the young plants from their very earliest stages with more room. In the two previous generations about 50 specimens were grown per square meter In this generation, however, the number was reduced to about 25 by the removal of the superfluous ones in June, as soon as the ]:)lants began to touch one another. The seed had been sown in May in the beds. At the beginning of October I noticed, amongst about 100 indi- viduals, 6 with a s])iral arrangement of leaves in the heart of a rosette. In the beginning of November I was able to remove more than half of the plants as undoubted atavists, and when, towards the end of May 1892, the stems grew up vigorously, they were finally examined and recorded. The result, together with that obtained in November, i. e., for the whole culture, is as follows: spirally Tzvistcd Races. 547 Twisted stems 37 =34% Stems with ternary whorls J2 =11% Atavists with decussate arrangement of weaves 58 =55% Total 107 It is very important to notice that the number of twisted stems increased as the result of tlie greater (hs- tances between the plants, not only relatively (i e., per 100 individuals), but absolutely (i. e., per square meter). In the third generation there were 50 plants per square meter, of which 4% (1-7%, from 1-4 specimens) were spirally twisted. In the fourth generation, however, there were 37 twisted individuals on 4 square meters or 9 per square meter. I selected the seven plants with the finest torsions on this bed as seed-parents. They all, moreover, pre- sented local torsions on several branches. I isolated them before they flowered. The fifth generation (1893-1894) was not so success- ful. Only 25% with twisted stems were produced. The seed to produce this generation had not as hitherto been sown on the beds but in seed-pans in tlie greenhouse attached to my laboratory. This method has since proved more convenient and safer, and has been employed in the two generations which follow. The seed saved in September 1892 was sown in the middle of March 1893. In the middle of ]\Iay the best seedlings were planted separately in 10 centimeter pots with good, richly manured garden soil, and planted in tlie bed in the middle of Alay, at the same distance a]")art as were the ]')lants in the preceding generation {22 i)]ants ])er square meter). In tlie following year (18^4). all the stems develoi)ed and were recorded. The result was as follows : 548 Heritable Spiral Torsions. A B %A %B Twisted main stems . . 5 2 20 10 Ternary main stems . 1 1 4 5 Decussate mam stems . , 19 17 76 85 Total 25 20 A and B are two groups which had been produced from seeds separately harvested from two seed-parents of 1892. The extent of the culture is, as we see, too small to allow of an exact determination of percentage values. Seed was saved in the autumn of 1894 from the four best plants which had been isolated from the rest before they flowered. The sixth generation (1895-1896) again produced a better result, viz., 42% twisted mani stems, a result due in part at least to the increase in the distance between the plants in the culture, which was in other respects the same as in the previous year. The seed of 1894 was sown in the middle of March in pans in the greenhouse. The seedlings were transplanted to pots in April and into the bed in May Altogether there were only ZZ plants on 4 scfuare meters, that is about 8 per square meter. In October I found 14 rosettes with a spiral arrangement of their inner leaves, whilst seven were ternary and 12 decussate, that is 42% spiral, 21% ternary, and Z6% decussate. This result was confirmed in May and the decussate and ternary individuals were thrown away. The six individuals with the finest torsions were selected as seed-parents and isolated before flowering. The seventh generation (1897-1898) was grown in practically the same way. Seeds of 1896 were sown in the greenhouse in May 1897, were transferred to pots later, and to the beds at the beginning of July at the rate spirally Tzvistcd Races. 549 of 16 individuals per square meter. Altogether there were 70 plants. A record made at the end of May 1898 gave the fol- lowing result: Twisted stems . . . . 32 =46% Ternary stems . . . . 21 =30% Decussate stems . . . . 17 =24% Total 70 In the eighth generation the plants were treated in exactly the same way as in the preceding one. As already mentioned, the offspring of 10 distinct parents were compared. Moreover for each parent the seeds of the terminal inflorescence were compared with those of the inflorescences on the main branches. For the latter de- termination I selected from each parent 4-8 of the strong- est branches which arose from that part of the middle of the stem which had undergone most torsion. They corresponded, therefore, with the period of maximum activity of the stem,^ and confirmed this by the fact that small local torsions appeared on them. From the seed of the primary inflorescences I raised 645 plants with 31%, from those of the secondary inflorescences 650 individ- uals with 34% cwisted main stems. There was therefore no difference of any significance. The ninth generation was composed partly of off- spring of twisted individuals and partly of those of ata- vists. The method of culture employed was the same as before; but I shall revert to the result of it in the next section. Besides Dipsacns sylvcstris I have grown two (^ther con- stant races with an abundance of fine torsions which must *See T. Tammes, Die rcnodicitat morphologischcr lirschci- nungcn hci den P fiance n, Kon. Akad. v. Wet., Amsterdam, 1903. 550 Heritable Spiral Torsions. be regarded as intermediate races. The first is Dianthns barhatus tarsus. I obtained a fine twisted branch of this form in the autumn of 1894 from Mr. J. Ensink in Ruurlo. The torsion was simihu* to that represented in Fig. 129, but the fruits were ripe and fuU of seed. I coidd not, howex'er, sow the seed until the spring of 1897. This species does not flower till the second year, 10-20 shoots being prodticed on each individual. I made a culture of about 300 indi- viduals, which were planted out at distances of 20 centi- meters apart. Plants began to flower in June of the sec- ond year (1898) ; the great majority of their stems were normall}' decussate ; wdiilst several had ternary whorls along the whole length, or in other cases, only in the up- per parts of the stems. Oth- ers again were twisted and manifested a spiral arrange- ment of the leaves. The twisting, too, seemed to pre- fer the upper half of the stem, just underneath the inflorescence. Sometimes how- ever the whole stem, or a great part of it, w^as twisted or the torsion extended into the inflorescence. The maxi- mum development of tlie anomaly largely corresponded, so far as I could determine, with the period of maximum Fig 129. Diatithus barbafus torsus. Twisted Sweet Wil- liam The stem has a de- cussate arrangement of leayes below and spiral above. June 1900. spirally T-i^'is/ctl Races, 551 growth, as in Dipsaciis. Altogether I counted amongst somewliat over 4600 normal stems, 53 more or less dis- tinctly twisted ones in all degrees of dexelopment, 33 torsions extending over a greater part of the shoot and Fig. 130. The dark-ej-ed Viscaria (Viscaria oculala) with spiral torsion of the main stem, a, the terminal flower of this main stem ; the flowerstalk, first bent downwards by the torsion, has subsequently turned upwards again. /'. c, the normal straight portion below the twi^t ; (/. a local interruption of the torsion ( igoo). 552 Heritable Spiral Torsions. 20 over smaller portions. This means a proportion of about 1% of the total number of the stems. The 33 best torsions occurred on ten plants of which five had 12, 6, 5, 3 and 2 twisted shoots, and the remaining live, one such anomaly each. The 20 smaller abnormalities were distributed at random over the plants in such a way that about 10% of the individuals had developed the anomaly. It is worth remarking that the most abnormal individuals occurred chiefly on the most sunny edge of the bed. The selected individuals mentioned were not allowed to flow^er before all the remaining plants had been re- moved. In the spring of 1899 I only sowed the seeds of the plant w^ith 12 torsions. I planted out 180 individ- uals, at the same distances apart and also in other respects under exactly similar conditions as those wdiich obtained in the preceding generation. They flowered in the sum- mer of 1900. At the beginning of the flowering period I had 2246 stems, in 1246 of which the arrangement of the leaves was decussate, whilst in 414 it was ternary. Further, there were 227 stems which were twisted over more than half their length and 359 which were twisted in the upper part only, i. e., 26% twisted shoots as against 1 % in the preceding generation, on the average 3 torsions per plant. According to a rough estimate well over half the individuals had produced one or more twisted stems. Two generations, therefore, had sufficed for the iso- lation of a genuine intermediate race from an original insect-fertilized sample of seed. The other race referred to above occurred in Viscaria ocidata {Lychnis Coeli-rosa), a favorite garden plant. The plant is annual and its culture easy. In twisting, its stems become much shortened, and the plants become low, but they flowered freely (Fig. 130). In 1897 in a spirally Tzvisfed Races. 553 culture grown for another purpose, I found a twisted plant like the one figured and saved its seed separately; its iiowers had not been protected. From this seed I raised in 1898 a culture of 300 plants of which 259 were normal, whilst 40 exhibited torsions in the main stem and 28 others in one or several of the lateral branches, i. e., a proportion of 21% twisted indi- viduals. I only allowed the 21 finest specimens of these to flower and set seed ; and of these I only sowed the seeds of the one finest twisted plant. In the following year, 1899, I raised from it 385 individuals of which 137 or about 35% showed torsions. Here also, as in the case of Dipsacns and Dianthns, many individuals exhibited a ternary arrangement in the whorls. I counted about 100 of these, which therefore constituted about one-quarter of the whole culture. In 1900 I grew the fourth generation, but on a smaller scale. Torsions were as abundant as before, and amongst their number was the plant represented in Fig. 130. There is little doubt that similar intermediate races could be raised by an isolation of the spirally twisted individuals of several other species. And the best chance would obviously be given by those which frequently give rise to this anomaly without selection. Thus, for in- stance, Gypsopliila paniculata, Urfica nrcns (of which I have already cultivated two generations with success), and perhaps also Scahiosa atropurpiirca. On the other hand, as stated in the previous section, my sowings of the seeds of spirally twisted examples of Valeriana officinalis, Saponaria officinalis, Galium Aparine^ and others, have offered no such prospects. ^Bvdragcn tot dc leer van den klenidraat. Botanisch Jaarboek, Gent, IV, 1892, p. 154, PI. XV. 554 Heritable Spiral Torsions. The existence of constant intermediate races or ever- sporting varieties exhibiting spiral torsion seems to me to be conchisively demonstrated by the experiments de- scribed. They were found by chance and then easily extracted by isolation, and induced to produce a pro- portion of 30-40% twisted individuals. This result could be made permanent by subsequent cultivation, but could not be increased by a continuation of the selection. § 21. THE SIGx\IFICANCE OF THE ATAVISTS. In spite of every attention and in spite of repeated and careful selection spirally twisted races will continue to produce numerotis atavists. These are either decussate individuals of the normal structure of the species, or they have ternary leaf whorls, as is also often seen in twisted individuals above the torsions. I propose now to examine more closely the nature of, and especially the mode of, inheritance in these ata- vists, as I have done in the case of the fasciations. The essential point about them is that the atavists do not, as we may express it, depart from the twisted race ; but can be used almost as safely for its continuation, as the twisted individuals.^ A fact of the highest importance is that there is no sharp limit between the atavists and the twisted individ- uals. Of course the difference between the tall erect stems and the short stunted anomalous ones is most striking, as our Plate VI shows. It is quite clear that this is not a case of the fluctuating variation of a single ^ In Stocks the double specimens are sterile, as is well known, and the variety has to be propagated by means of the seeds of the single ones. Under cultivation in the field as a rule about 50% of "single" atavists are produced. The Significance of the Atavists. 555 character, but that two antagonistic factors are at work, the one excluding the other, ahhough never completely. Even the stems with the most pronounced torsions pro- duce branches, most of which revert to the decussate arrangement of leaves. It never occurs that this char- acter is completely excluded from the whole plant. Con- versely, as we have already seen, atavistic individuals with perfectly erect main stems and with a decussate or ternary arrangement of the leaves frequently exhibit torsions in their lateral branches. In 1887 I cut half the atavists of my culture of Dipsacus syhestris torsiis close down to the ground; they shot out from the base of the stem. In this way I obtained about 2000 branches of the second and third order. Amongst them 235 had a slight but quite definite torsion and 26 had a small many-leaved spiral. In the third generation I repeated the experiment with the same result; and moreover observed torsions on the lateral branches of some atavists which had been allowed to remain on the l)e(ls until they were just about to flower. Other abnormalities in the arrangement of leaves also betray the real nature of the atavists. First, there are the individuals with ternary whorls. Sucli whorls do not occur in the early stages of the plant, and tricotylous seedlings are even very rare. At first the arrangement of the leaves is always decussate, and it is not until late summer or autumn, at the time when other specimens begin to produce their leaves in a spiral, that the decussate arrangement gives place to a ternary one. But when this has once appeared it usually remains on the stem up to the terminal flowerhead. Such plants look quite normal, ai^l especially their leaves do not ])ro(luce those forkings of the mid-rib which are so common in the 556 Heritable Spiral Torsions. C D Fig. 131. Dipsacus syhestris tarsus. Split leaves from the decussate atavists of the eighth generation. A-D, in- creasing degrees of splitting. The Siynificojice of the Atavists. 557 decussate individuals. On the lateral branches of these whorled stems, on the other liand, these splittings, as well as local torsions and other anomalies are by no means rare. The relation of the ternary whorl to the spiral ar- rangement demands closer investigation. Perhaps the former is to be regarded as a lower stage of the anomaly ; arid this view is supported by the fact that highly twisted individuals which have one or more straight internodes above the torsion, usually exhibit ternary whorls between them. The decussate individuals often produce leaves with split midribs (Fig. 131 AB), and in all degrees of split- ting from leaves with two tips to leaves split down to the base.-^ Sometimes they even produce one or two ternary wdiorls in the upper parts of the plant. The range of variation in these splittings has been dealt with by Delpino^^ and material for a complete demonstration of these forms may be furnished by every generation of my race. In the third generation I left three atavists on the bed until shortly before they flowered. They all bore some split leaves in the upper part of their stem; in the ninth generation I observed the same anomaly on the main stems of 172 of the 200 decussate atavists, that is to say, in about 80% of the whole group. Several of the re- mainder exhibited the anomaly on the lateral branches. From the axil of a split leaf tliere usually arises, ac- cording to my observations, a single sh(^ot ; but sometimes two of them, or a single broad flattened one witli two ' Bcr. d. d. hot. Grs., Vol. VTI. iSSg. p. 296. " F. Delptno. Tcon'a (^enrralr dcUa Fillolassi. Atti della R. Uni- versita di Geneva, IV, Parte IT, 1883. 558 Heritable Spiral Torsions. inflorescences at the top. In this respect also, my results confirm those of Delpino. External conditions exert a great influence on these secondary anomalies just as they do on the main torsions. The more favorable the conditions, the rarer are the in- dividuals, all of whose branches and leaves are normal. Obviously this fact suggests that the factor for the iiial- foruiation must be present iu all of them. Brief mention should also be made of the so-called local torsions. They occur occasionally in all twisted races. Fig. 132 represents an instance of them in Wile- riana ojficinaHs. It flowered in the same year and on the same l)ed as the completely twisted stem shown in Fig. 122 (p. 528). In Dipsacus laciniatus the malformation was confined to these, and in Dipsacus sylvestris torsus I observed them, under very special conditions of culture, on erect and otherwise dectissate stems ; but on the lateral branches of twisted individuals, especially on the strongest ones, such as those which arise from the axils of the radical leaves or from the middle of the twisted stems, they are always seen to be most profusely produced. As in the case of fasciations, forms intermediate be- tween these local torsions and the normal arran element of the leaves, are relatively rare. This is not true, how- ever, if the ternary whorls, split leaves, and the local toi-sions on the lateral branches are included, but onlv if we confinp our attention to the torsions on the main stems. Unfortunately the exact measurement of tlie part bearing leaves in a spiral is a matter of considerable difficult}' : inasmuch as the s]:)iral begins inside the ro- sette at a time when the oldest leaves have alreadv rotted off and disappeared. Nevertheless I have recorded tlie l)e- The Significance of llic .Atai'isls. 559 ginning of the spiral accurately in sonic cases In mark- ing and counting the pairs of leaves, as they made their appearance, from the moment of germination. But T have not yet plotted a curve from data collected in this extremelv lahorious wav. On the other hand the numher of straight internodes ahove the torsion can easih' he O r Fig 132. ]^a\criana ofhc'maWs. A stem witli a local tor- sion, from the same culUire as Fig. 122. (June 1900.) counted; and their numher ojjviously varies inversely with the extent of the twisted part. Tn 1900, when my eighth generation consisted of 1295 flowering plants, T recorded tlie numher of straight internodes ahove the torsion in everv twisted stem. Omit- 560 Heritable Spiral Torsions. ting tlie long stalk of the terminal inflorescence, which is always i)resent, I obtained the following series. PLANTS WITHOUT WITH 0-6 STRAIGHT INTER- TORSION NODES ABOVE THE TORSION Straight internodes 6 5 4 3 2 1 0 Individuals 900 2 3 1 2 40 200 148 The curve constructed from these figures is obviously one with two peaks, and essentially the same as the cor- responding curve for fasciations seen in Fig. 118 (p.521). Torsions with two, with one, and without any straight internodes above the torsions are far the commonest. Smaller torsions only occurred in nine cases among 1295, that is less than 1% of all the individuals, or in about 2% of the twisted individuals. I repeated the same ex- aminations in 1902; the intermediate forms wxre some- what more numerous and reached a proportion of about 7% in 492 individuals. The form of the curve, was, how^ever, not essentially modified. In order to determine the hereditary coefficients of the atavists I instituted an experiment in the eighth and ninth generation of my race. In July 1900, I had some highly twisted plants, some completely decussate ones, and some with ternarv wdiorls only, on the same bed. Before the flowering period I reduced the inflorescences to the required number and afterwards insured pure fer- tilization in the following w^ay. All the inflorescences were enclosed in parchment bags, and the bags were taken off the individuals falling into one group, for sev- eral hours one day out of three for each group. The humble bees flying about could thus fertilize only twisted individuals on some days, on others only decussate, and on still others only ternarv ones. This practice was continued until all the flowers Avere gone. The seeds The Sigiiificaucc of the Ataz'isls. 561 were saved separately from each plant. In the spring ij\ 1901 I sowed the seeds of two decussate, three ternary and four twisted seed-parents and recorded the main stems produced by each parent in 1902, just before the flowering period ; but since the numbers from the indi- vidual seed-parents of each group did not differ to any considerable extent amongst themselves, I shall give the total result only. OFFSPRESTG, IN PERCENTAGES. SEED-PARENTS Nl'MBER DECUSSATE TERNARY TWISTED Decussate 48 8 44 201 Ternary 39 24 37 136 Twisted 45 14 41 155 Total 492 We see that the offspring of the afaz'isfs produced just as large a proportion of twisted steins as the offspring of the tzvisted individuals. On the other hand the choice of decussate or of ternary atavists seems to have exerted some inHuence in the direction of ternary offspring. The twisted stems of Dipsacus are partly right-hand and partly left-hand spirals; and about equal numbers of the two sorts are always found. -^ A very curious question thus presents Itself, viz., whether this equilibrium can be disturbed by selection and whether the balance can be upset in a given direc- tion.^ According to the view laid down in this book, that it is not true that with selection all things are pos- sible, we might expect that this would not be a fixablo character and that selection would have no influence on "^Annals of Botany, he. cit., p. 404. 'R. M. Yerkes, Variation in the Fiddler Crab, GeJasimus pup- lator, Proceed. Amer. Ac. of Arts and Sciences, 1901. Vol. XXX\'I. No. 24, p. 417. On page z^4T this autlior states tliat rigiit- and left- handed animals occur in approximately equal numbers. 562 Heritable Spiral Torsions. it. For this reason I allowed ])lants with a right-hand spiral only to flower in the seventh generation ; and in the following one also, the spiral of all the chosen seed- parents was right-handed. The result was as follows : LEAF-SPIRAL RIGHT-HAND LEFT-HAND 8th generation 205 215 individuals 9th generation 40 24 individuals These constant but eversporting twisted varieties offer fa\orable material for attempting to transfer the mal- formation to related species by means of hybridization. At present, however, only a single attempt of this kind lias been made, viz., one which was communicated to me by Prof. Le Monnier of Nancy. ^. He sent me two twisted stems of Dipsacus ftiUonuni which exhibited a torsion as pronounced and as complete as the best instances of my race (Fig. 123 a and h, p. 529) ; and which owed this malformation to a cross be- t^veen the species in question and my Dipsacus syh'csfris tarsus, which Mr. Le Monnier had cultivated on a large scale for many years. In 1896 my race flowered at the same time as the normal D. fuUonnui in the botanical garden at Nancy, at a distance of 100 meters apart but in great quantities of individuals. Pollen could easily be transferred by insects from one bed to the other. From the seeds of these Dipsacus fuUonuui there arose besides numerous normal plants three with twisted stems; one of them had upwardly directed bracts in the involucre, a char- acter of D. syh'csfris which distinguishes it from D. ful- louuui. The investigation of this important question has, however, not been continued. ' Jniini. Roy. JJorfic. Soc, 1900, Vol. XXIV, p. 69. TJic SiijiiifiCiUicc of the Atai'ists. 563 The facts described in this and the preceding section^ seem to me to furnish sufficient proof that the twisted eversporting varieties behave in exactly the same wax- as the corresponchng fasciated races; and that, in both cases, atavism is merely a morphological phenomenon and not a real deviation from the race. PART III. THE RELATIONS OF THE MUTATION THEORY TO OTHER BRANCHES OF INQUIRY. 1. Till-: CO^XEPTIOX OF SPECIES ACCORDlX(; TO THE THEORY OF MUTATlOX. § I. SYSTEMATIC BIOLOGY AND THE THEORY OF MUTATION. In every case in wliicli we were al)le to obtain a deeper insight into the nature of the hereditary character of an organism by direct observation or experiment we ha\e found this character to be of a compound nature. Xo plant transmits its pecuharities to its offspring as an in- separable whole, as has been the general view until n()w. On the contrary we have described a long series of phe- nomena in which a single character or a smaller or larger group of them can be separated from the rest and behave in an entirely different way. When new species or vari- eties originate, it Is not the whole nature of the organism that is changed; on the contrary everything remains in a state of rest except at one or two points, and it is only to the changes of these points that all the improvement is due. In hybridization the two types which se.xually unite are always alike in the vast majority of their char- acters, and the differences between them are limited to a few definite units, which, in the simplest cases, can be dealt with numerically. The analysis of organisms, therefore, leads us to the hypothesis of units, which are in many respects analogous to the molecules of the chemist. Thev are, however, of 568 Species According to the Theory of Mutation. a much more complicated structure and have arisen in a historical way. They cannot be isolated and then sub- jected to experiment like chemical bodies; we can only investigate them by studying the relation of closely allied species and varieties, i. e., forms in which a definite unit, or several of them, are present in one plant and absent in the other. For this reason our investigations are, for the present at any rate, confined to the units which have arisen most recently. But even as it is the business of comparative science in general, first, to apply the conclusions derived directly from the facts, to cases that have not been themselves observed and then to extend them gradually further and further, it is our duty and our riglit to test the applica- bility of our conclusions as thoroughly and as widely as possible. Therefore we have now to face the question whether the theory of the origin of species by mutation and the theory that hereditary characters are composed of ele- mentary units are in harmony with the theoretical concep- tions to which systematic science on the one hand and embryology on the other have given rise. If it can be shown that the mutation theory satisfies the demands of these sciences better than the present form of the theory of selection, its justification as a theory of the nature of inheritance will, in my opinion, be placed on a sure foundation. For this reason I shall devote the last part of tin's work to general considerations of this kind. In doing so I leave the safe ground of facts and venture into a region in which I can no longer mainly depend on my own experience. But experimental inquiry must derive its problems from tin's more general aspect of the ques- Progressive, Retrogressive, Degressive Mutations. 569 tions; and it does not by any means seem snpeiiluous to ask ourselves from time to time what has ah-eady been achieved and what is to be done in the immediate future. In doing so I shall have to keep a close rein on myself and, whenever possible, conform to the opinions of rec- ognized authorities, limiting my own views to such points as may throw light on the relation between those opinions and the theory of mutation. I shall try to avoid ques- tions of minor importance or concerning uncertain or subordinate points; the literature of the subject has long since grown so prodigiously that it is no longer possible to keep pace with it. My only object is to demonstrate the applicability of the theory of mutation to the main conclusions of the doctrine of evolution ; and only to do this briefly and sometimes no more than in outline. New theories and new hypotheses I shall not have to introduce, the more so, as I am convinced that the doctrine of mutation will lead everywhere to a simplification and a clearer concep- tion of the problems. The prospect of recognition of a theory rests on the one hand on its empirical foundation, and on the other on its suggestiveness and the number of facts which it explains. Therefore the consideration of this latter point will now be my task. I shall devote the several chapters of this part to the various problems involved. § 2. PROGRESSIVE, RETROGRESSIVE AND DEGRESSIVE MUTATIONS. Progress in organic nature consists essentially in in- crease of differentiation. The peculiarities which go to make up the individual character of the species become 570 Species According to the Theory of Mutation. more nunieroiis. Every more highly organized being has, as a rule, more of them than its ancestors of long ago had. In applying this principle to the doctrine of elementary characters we see at once that the number of these units must increase with increasing differentiation ; or, con- versely, that the degree of differentiation is ultimately determined by the number of elementary characters. Whenever a new unit is added to those already existing, dift'erentiation advances a step forward. If it were pos- sible to count the units we should have a measure of the degree of differentiation of all organisms. Obviously the individual steps are only small ones, at the present time at least ; and any single one of them can hardlv eft'ect a noticeable increase in dift'erentiation. At any rate we have at present no means of so exactly measuring the degree of differentiation, since we cannot estimate the possible influence of a single unit on a com- plex built up of thousands of them. Only groups of units produce clear and obvious differences in the degree of organization; but within the limits of a small genus or of a multiform collective species the several types seem to us to be almost always equivalent. The individual steps into which, according to tliis view, the process of gradual diff'erentiation can l^e ana- lyzed, we propose to call mutations ; and since they con- stitute an advance, progressive mutations. Each of them contributes a new character to the complex of hereditary qualities already present. Such a new character need not, however, become vis- ible as soon as it arises, since we are not dealing solely with external qualities but with the internal factors to which they owe their appearance. Even as the germ contains large numbers of qualities awaiting development, Progrcssk'c, Retrogressive, Degressive M ufufioiis. 571 so we can imagine that a new character remains hitenl for some time after its first origin, its phylogenelic birth, if I may so express it, and does not become active until after the lapse of a lesser or greater period of time. According to this view, every progressive mutation is fundamentally a double process, and consists in the production of a new internal factor and in its activation. Both may sometimes happen at the same time, but this is not necessary. It is therefore desirable to apply sepa- rate names to the two processes : the internal one I have called premutation, the externally visible one a mutation seusu strieto. The premutation is therefore of a hypothetical, the mutation, however, of an empirical nature. It further follows from this that an niternal factor does not of itself lead to the origin of an external change. As in ontogeny so also in phylogeny an elementary char- acter can be sometimes active, but at other times latent or inactive. If a new character emerges from its original latent conditions and becomes active, we call the process a progressive mutation ; conversely we can denote its return from the active to the latent condition as a retro- gressive mutation. The experience of gardeners and of the systematists with the smaller species and varieties teaches that retn^- gressive mutations of this kind are common phenomena. Almost any character may disappear. This applies not nnlv to the sunerficial characters, such as col(^r. hairs, or thorns, but also to those deeper ones which affect the inner organization of the plant, such as the decussate ar- ran element of leaves, and even the svmmetrv of the origan- ism. Spiral torsion and peloria show how i)rofound an alteration in the appearance of a i^lant (-»r in the structure z^72 Species According to the Theory of Mutation, of a flower may be brought about even by only one of these elementary characters becoming inactive. Retrogressive mutations give the impression of some- thing being lost ; some character or other disappears from the picture. But everything seems to point to the con- Fig. 133. Castanea vesca. Ab- normally leaved catkins. A, with two leaves ; B and C, with one leaf each. C has also a lateral twig, a male, h female flowers; c normal leaf. Apel- doorn, 1896. Collected by Dr. P. F. Abbink-Spaink. Fig 134. MercuriaUs annua. A sprig of the male plant with stray fruits on the long thin ears. On the female plants the fruits are inserted on short stalks in the axils of the leaves. elusion that, in the vast majority of cases at least, this loss is only an external one ; and that the factor remains in the inner organization of the plant, in an inactive state. This view is especially supported by tliose cases in wliich a systematic character which has become latent is occa- Progressive, Retrogressive, Degressive Mutations. 573 sionally manifested as an anomaly; as for instance the appearance of female flowers on male specimens of cli(L"- cions species (Fig. 134), or of leaves on normally leaf- less inflorescences (Fig. 133). Two races, which only differ in the latency or activity of a single factor, therefore possess the same number of elementary units in their internal organization. Ob- viously the relation between them is different from that between two races, of which one has arisen from the other bv the formation of a new factor; in which case there is a difference of one, in the number of units, be- tween the two. But before we examine this relation more closely we must face the Cjuestion whether the active and the in- active states are the only ones in which an internal factor can occur. Theoretically this is obviously not necessarily the case, for we can easily imagine various degrees of activity between the two extremes, and as a matter of fact, experience shows that these intermediate stages do actually occur. We have described them above (p. 20) as semi-latent ; and have given the name of middle races to those which possess such semi-latent characters. Of these there are two types, which we frequently meet both in nature and in our cultures, half races and intermediate races, or eversporting varieties. In both of them the semi-latent quality is associated in such a way with some active character that the two cannot be manifested at the same time. They exclude one another, if we may so ex- press it, and so constitute a mutually vicarious pair. Tri- foliate and quinciuefoliate leaves of clover, tricotylous seedlings or split cotyledons and dicotylous ones, normal and peloric flowers, cylindrical and fasciated stems, ordi- nary and petaloid stamens, constitute such pairs. The 574 Species Accord iug to the Theory of Mutation. same leaf cannot be at once trifoliate and quinquefoliate and so on ; in a word, an organ cannot be both normal and abnormal. These vicarious pairs of characters are the sources of a great varialjility inasmuch as the anomaly can ap- pear in all degrees of development. In such cases the individuals of a group are not ranged round a mean in respect of their external qualities, as with ordinary fluc- tuating or oscillating variability, but l)etween two t}pes which are often widely separated and more or less anti- thetic to one another. They have the appearance of being inconstant ; and races and varieties of this kind are usuallv so described, but this is only true in the sen.se that the range of forms which they present is a very wide one ; and, moreover, is ditypic or dimorphic. But it would not be true in the sense that any individual could transgress the boundaries of this range and found a new race. In this sense the so-called inconstant races are just as stable as the best constant species and varieties. The difference between half and middle races lies solelv in the difference between the mutual relation of the members of the vicarious pair in the two cases. If, under ordinary conditions, and in the absence of selection, one of them predominates over the other to a very large extent, the race is, so to speak, unilateral and is called a half race (e. g.. Fig. 135). But if, under similar cir- cumstances, neither of them predominates but an equilib- rium is maintained, we have an intermediate race fe. g.. Fig. 27 of the first volume, page 138). In the case of tricotyls and syncotyls the half race rarely contains more than a verv few anomalous individuals, in the absence of selection : whilst the intermediate race consists as a rule about half of normal, and the other half of tricotvl- Progressive, Retrogressive, Degressive Mutations. 375 oiis or syncotylous individuals. The seeds, lif the peloric Linaria. Sudden transitions of this kind arc exactly what we call mutations; and to distinguish thcni from the progressi\'e and retrogressive t}-pes. we may refer to them as degressive nuitations. Every mutation therefore consists fundamentally \n ^ig. 135. Papavcr coin- iiiutattmi polycct^lialum. The same anomaly wliicli occurs in P. soninifcntm as a middle race (Vol. 1, Fig. 27, p. 138) occurs here as a half race, mani- festing the character very rarely and only to a small extent. 576 Species According to the Theory of Miitation. the transposition of an internal character; from being latent it becomes active; from semi-latent, semi-active; and so on. If new factors are becoming active for the first time after having been latent through a shorter or longer series of ancestors, we speak of progressive muta- tions. If the active characters again become latent, the process is a retrogressive one. In all other cases it is degressive. The phenomena of hybridization find a ready ex- planation in the principles derived, in the first part of this volume, from our consideration of the origin of species and varieties. There are tw^o main types of crosses, the bi-sexual or ]\Iendelian and the uni-sexual. The former conform to the laws of segregation, they lead to various combinations of elementary characters, and thus can lead to the origin of as many new races as the number of pos- sible combinations indicates. These races are constant; the hybrids, however, always exhibit segregation in the formation of their sexual cells and sometimes even in the formation of buds. The hybrids of uni-sexual crosses on the other hand are constant ; so far as my experience goes, they do not segregate. If they are fertile they are, as a rule, as true from seed as their parents ; but they may inherit the inconstancy of these (if, for instance, one of these belonged to an eversporting variety) and transmit it to their posterity. A strong body of facts, which have been given else- ■\vhere lead to the conclusion that crosses follow Mendel's laws if one of the two parents stands in the relation to the other of having arisen from it by retrogressive or de- gressive mutation. This means that the two parents of the cross possess exactly the same internal elementary characters; but that one or more of these occur in dif- Progressive, Retrogressive, Degressive Mutations. z>17 ferent conditions in the two parents; as for instance in the union of latent characters with active, of semi-latent with semi-active, and so forth. The opposite visible qual- ities, determined by the two different conditions of the same internal factor, constitute a so-called pair of char- acters. Therefore, racial forms which differ from one another by such qualities only, constitute a group for themselves, in the theory both of hybridization and of the origin of species. Uni-sexual crosses are of an entirely different nature and lead to the direct production of constant hybrid races. They occur when at least one character is present in one parent, but is absent from the other. Hence Mac- farlane's name uni-sexual. In more complicated cases one form may have a larger excess of factors; or again, each of the parents may possess factors which are absent from the other. The excess will be unilateral, if one of the forms has arisen directly from the other, but bi-lateral if both have arisen in diverging directions from the same ancestor. In tliese cases vicarious pairs of characters do not exist in the two forms crossed, although externally they may seem to do so. Therefore uni-sexual crosses correspond to progres- sive mutations; the Mendelian law, however, to the retro- gressive and degressive forms of differentiation. Con- versely we may infer that characters which, when crossed, behave in a Mendelian way, are in a latent or semi-latent condition, and that in the uni-sexual crosses an internal factor is entirely absent on one side. I willingly achnit that the main purpose of this discussion is t(^ make my principles clear, and to show how the two great branches of the theory of mutation mav. in s]')ite of the \ast differ- ence in their points of departure, ultimately lead t(^ the 578 Species According to the Theory of Mutation. same theoretical conception of the nature of elementary characters. This conception may in the present state of our knowledge be most conveniently formulated as fol- lows : Forms which have arisen by retrogressive and de- gressive mutation follow Mendel's law, when crossed with their ancestors; whilst forms which have arisen by- progressive mutation behave uni-sexually. § 3. THE THEORETICAL DISTINCTION BETWEEN SPE- CIES AND VARIETIES. The idea of a fundamental difference between ancient and recent characters runs like a scarlet thread through ihe whole history of systematic biology. The nature and limits of this assumed difference have often furnished problems which the greatest investigators in this field have attempted to solve; and the answer has been a different one according to the information available at the time when it was attempted. From the transmuta- tionists up to Nageli's well-known distinction ]:>etween organic and adaptive characters there has been a long series of attempts to deal with these questions. In ancient times the matter was easily settled by in- voking supernatural causes. The higher systematic cliar- acters were assumed to have arisen by creation ; the later ones by natural means ; but in practice even this view led to confusion, because some authors regarded the genera, others the collective species, and yet others the constant elementary forms as the units which had been created. Our discussions have led us also along several differ- ent lines, to the conviction that, as a matter of fact, there Distinction Bctzvecn Species and I 'arictics. 579 is a fundamental antithesis between ancient and reeeni characters, which hnds its expression both in the ])lic- noniena of specific differentiation, and in those of arti- ficial hybridization; for on the one hand forms can arise from others without the production of new factors, simjjl)- by the transference of factors already present into another condition, as from latent to active ; and on the other hand, by the genuine appearance of new elementary characters. Progress in organization is due to the latter process, whilst the former is to a large extent the cause of the di- versity of organic life. If we compare this experimental result with the abu\e theoretical considerations, we mav assume that the 'lis- tinction between older and younger characters consists in the difference between the formation of a new factor and the transposition of factors already present. On the basis of the doctrine of creation the origin of new units must be explained as being due to a supernatural cause, but no one has as yet applied this theory to the change in position of factors already present. Moreover in the light of the idea of evolution also the antithesis mentioned has its real and full significance. It would lead me too far to analyze here the concep- tions of other authors on these points, but such an anal- ysis has led me to the conviction that the difference be- tween the formation and the transposition of factors cor- responds closely to the difference which the best systeni- atists consider to exist between species and varieties.^ A form which owes its origin to the producti(^n of a new internal factor is to be regarded as a si-)ecies : a lornj which owes its peculiarity merely to the change in con- dition of a factor already present is to be regarded as a * See also Vol. T, p. 185. and Vol. IT. pp. Ji-/^- 580 Species According to the Theory of Mutation. variety ;^ or, as we have already expressed it in the first part of this volume (pp. 64, 71, etc.), the origin of new characters leads to specific differentiation, whereas the true derivative varieties arise by so-called retrogressive and degressive mutations without the formation of new characters. In my opinion this is, at any rate, the sim- plest view of the matter. This, however, is purely theoretical, for in practice our definition can, at present, only rarely be applied. Here however the principles of hybridization come to our aid ; for, expressed in hybridological terminology, our gen- eralization runs : Forms, all of the characters of which follow Mendel's laws in crosses, are to be regarded as varieties of the same species. This form of our generali- zation obviously admits of an immediate application in every case where the material can be dealt with experi- mentally. Obviously this generalization is at present too sweep- ing; nevertheless the best investigators^ have regarded the study of hybridization as an empirical foundation on which this distinction may be based. Moreover the diffi- culties are not really so great as they seem to be at first sight ; for as soon as the body of evidence will have at- tained a certain extent, definite laws will be detected which will fit the majority of cases by judging from anal- ogy. The species, however, which I am here distinguishing from varieties are the smaller or elementary species ; the delimitation of the larger or collective species is, from the very nature of the case, a question not for the experi- ^ It should not be forgotten that varieties have been called In- cipient species and that from seed they are just as constant as species. ^See Nagelt, loc. cit., p. 396; Focke. loc. cit., pp. 488, 502; Nau- DiN, loc. cit., p. 164 ; Abbado^ loc. cit., p. 9, etc. Distinction Between Species and Varieties. 581 mental but for the comparative biologist.^ The elemen- tary species are demonstrably the existing units ul the system; whilst the larger species are only aggregations of these. They will therefore be discussed in dealing with the question of the practical differences between spe- cies and varieties. But, before I proceed to this, reference must be made to the more complicated but more common case in which two closely related forms differ from one another, i)artly by progressive and partly by retrogressive or degressive characters. To judge by the former they should be re- garded as elementary species, by the latter however, as derivative varieties; and as they are hardly allowed to be in our system both at the same time, we must make a decision one way or the other With a view to clearing up these difficulties let me deal with a particular instance, and select Lychnis vcspcr- tina and L. diiirna, which are regarded by several sys- tematists as belonging to one species, Lychnis dioica. If we regard these two forms as having been derived from a common original ancestor, and consider their individual characters, the difference in the color of the flowers stands out as the most striking distmguishing feature. The flowers of the original species must obviously have been red, and those of L. vespertina must have become white in the same way as those of other white-flnwercd varieties of red species. This view is suj^ported by the fact that the colors of the flowers in these two species behave in exactlv the same way in crosses as they do in many varieties, inasmuch as they conform to Mexdki/s laws. Other differences between the two campic^ns are ^ T do not propose to enter here into the question of the desirabil- ity of a ternary nomenclature (see p. 65) ; it is entirely a question of convention. 582 Species According to the Theory of Mutation. the breadth of the leaves and the length of the lluwer stalks. But these characters do not segregate in the offspring of the hybrids. They are presumably to be regarded as results of progressive specific dift'erentiation.^ L. vespcrtina is, perhaps, a white-flowered variety of a red-flowered species which has disappeared. At any rate I do not think we shall go far wrong if we conclude that L. vespcrtina and L. diurna differ from one another partly by typical specific, and partly by varietal char- acters. Gartner has repeatedly expressed exactly the same view and has illustrated it by the same instance.- He says that any doubt as to the specific difference between closely related species, as for instance between Lychnis diurna and L. vespcrtina, can be most easily removed by crossing; for if such species give exactly similar hybrids with some other, i. e., with a third species, the difference between the two is of a varietal nature only. But if this does not occur we have proof that the essential nature of the species crossed, although they appear closely related with regard to their external features, is specifically dis- tinct. For instance the two species of Lychnis just men- tioned give wholly different hybrids with Cnciibalus vis- cosus. On the other hand Gartner lavs stress on the fact that these species behave as varieties in regard to the color of their flowers when they are mutually crossed. Moreo\'er Lychnis vespcrtina behaves as a variety with regard to the bending over of the teeth of the capsule, that is to say as a retrogressive variety of a species with the character of L. diurna. ^ For a historical and critical treatment of the point, see a paper by R. Allen Rolfe, Hybridisation Viewed from the Standpoint of Systematic Botany, Journ. Roy. Hort. Soc, April 1900, p. 197. ' Gartner, he. cif., pp. 581-582. Distinctioi BcIikjccii Spi'cics and I ariclics. 583 We will now discuss the principle illustrated Ijy this instance from a more general jjoint of \ iew. In the literature of the subject we frecjuently iind the o])iniun that forms which are nuitually fertile and i)r(j(luce a normal harvest of seed, giving fertile hybrids, are to be regarded as varieties of one and the same species. F(jrms, howe\er, the union of which is followed by a diminutitjn in fertility and the hybrids of wdiich are less fertile than tlie species crossed, are regarded by the maj(jrity ui the investigators as specifically distinct. These generaliza- tions have ser\-ed as criteria of relationshi]) from the time of KoLREL'TER and Gartner up to the present; and Darwin himself relies on them in considerations of this kind.^ Based as they were on extensive experience and on a profound systematic knowledge, they constitute prin- ciples which bid fair to become universally recognized. For these reasons they deserve to be placed in the fore- ground as a convenient point of departure for our dis- cussion ; and our object will be not to find out their weak points or to replace them by others, but rather to give them the more definite forms reqtiired Iw' our i)resent knowledge of hybridization. Therefore wq will start from the oft-cited proposi- tion that varieties are only small species.- This means that the difference betw^een species and \'arieties is not of a fundamental nature but rather of a gradual or e\en a conventional knid. Moreover we will start from the conception enunciated in the first part of this volume, according to which the forms wdiich compose the collec- tive species are mainly of tw^o kinds (p. 64) : Honioiwni- See FocKE. Die Pflanzcnmiscldingc , pp. 436, 446-502, etc. "Sec Vol. T. ]). 171 and above p. 5R0. 584 Species According to the Theory of Mutation. ous forms or elementary species and derived forms or trne varieties. As we concluded in § 7, Part I, p. 65, the origin of elementary species is due to the formation of new ele- mentary characters, i. e., to their actual numerical in- crease. True varieties differ from the species to which they belong by the latency of certain characters, which may either be active as in the type of the species, or latent as in the variety, or which may occur in a latent or semi- latent condition in the former, and become active or semi- active in the production of the variety. In other w^ords, we may say that elementary species arise by progressive mutations, but derivative varieties by retrogressive and degressive ones (p. 71). If we now compare the principles derived from the study of hybrids with these conclusions, we see that the two main types of hybrids are in essential agreement with these two systematic groups. Mendelian hybrids correspond to retrogressive and degressive specific dif- ferentiation, and consequently to true varieties ; uni- sexual hybridizations correspond to progressive specific differentiation and consequently to elementary species. There can hardly be any misconception as to the sig- nification of this important conclusion. But it only indi- cates the principle and not its application to particular cases; and, as a matter of fact, it is only another form of the generalization enunciated above relating to the fertility of crosses and hybrids. For Mendelian crosses have as a rule the same fertility as the pure parent forms, and fertility does not diminish in the subsequent hvbrid generations. In uni-sexual crosses, however, fertility di- minishes and it does so in pronortion as the relation be- tween the two forms crossed becomes more remote. Distinction Between Species and Varieties. 585 The truth of this conclusion has become more obvious owing to the attention which has been paid to the subject since the re-discovery of AIendel's work. The paral- lehsni between the two groups of hybridization and tlie two types of systematic subdivisions has been most ex- haustively dealt with by Tschermak, who attempted to base upon it a principle of distinction between the spe- cific hybrids and varietal mongrels.^ We w'ill, then, regard the principle in its new f(jrni as demonstrated, and examine the question why the cri- teria which it supplies are not sufficient for universal application. In doing so I shall, for various reasons, leave the mutation crosses, which Tschermak also re- gards as specific hybrids, out of consideration ; and shall denote the Mendelian hybrids as bi-sexual in accordance with AIacfarlane's terminology, employing also the term uni-sexual in the sense in which it is used by that author. Expressed very briefly, therefore, bi-sexual crosses produce varietal hybrids, unisexual ones spe- cific hybrids. But some limitation is necessary ; and herein lies the difficulty of the question, which is felt by every one who endeavors to apply the conclusions drawn from the study of hybrids to taxinomic problems. This limitation is, that the criterion really applies only to monohybrids ; for di- polyhybrids, however, only in so far as they can be com- pared with these. We have given the name of monohybrids to those mongrels whose parents differ from one another in a single elementary character only. Obviously they occur both in uni-sexual and in bi-sexual crosses. But, of ^E. Tschermak. in the third appendix to his edition of ^Ies- Del's VersHche iibcr PflanzcnJiybridcti. p. 58. 586 Species According to the Theory of Mutation. course, any given monohybridic cross can only l)elong to one of these two groups. If it is bi-sexual and be- haves in a Mendehan fashion we may immediately infer that tlie two parents are to be considered as varieties.^ If it is uni-sexual they are elementary species, of which the one must have been derived from the other. The di-polyhybrids are mongrels whose parents differ from one another in respect of two or more elementary characters. Two cases must be distinguished. Let us confine ourselves first to the dihybrids. In some cases the two points of difference may belong to the same category and therefore follow the same laws in the crosses and their products. If each of them, considered by itself, would lead to the conclusion that the parents were related as varieties, the same conclusion will obviously hold good for the combination. So, for instance, is Pa paver sonini- fernm polycephahun Danehrog to be regarded as a vari- ety ; so also, if it is allowed to judge by analogy, Calliopsis tinctoria piimila purpurea (Vol. I, p. 197). For the same reason the compound colors, which may be split into their components by means of crossing and can be recon- structed out of these, fall within the category of varietal characters. Similarly forms, of wdiich one has arisen from the other by two successive mutations in the progressive di- rection, and whose crosses, therefore, conform to the laws of uni-sexual unions, would most certainly have to be re- garded as elementary species. ^ And this independently of the nomenclature chosen. For in- stance according to the principles enunciated above, Chelidonium laciniatiim Mill, will have to be regarded as a variety of C. majus, even when this more convenient name is retained. See Part I, p. 65. And from a practical point of view it would be very desirable to drop the attempt to correlate the nomenclature with the ever-changing systematic conceptions. Distinction Between Species and Varieties. 587 It may, however, also happen that in forms whicli differ from one another in two points only, one (^f these would give a bi-sexual union, whilst the other would lead to a uni-sexual cross. Such is the often cited instance of Lychnis zrspertina X diurna. One of the characters '>vould follow Mendel's law in crosses, whilst the other would tend to produce a constant intermediate f(^rm.^ In this case, according to the former character, one parent would be related to the other as a derivate variety, but ac- cording to the latter as a homonomous elementary species. Exactly the same, though to a greater extent, must be true of tri-polyhybrids. The points of difference be- tween their parents can be all uni-sexual or all bi-sexual, or some of them uni-sexual and others bi-sexual. In the first case the parents are to be considered as ele- mentary species, in the second as varieties; in the third, however, the principle affords no decision. It is just this case which appears to be the commonest in nature. In experiments in hybridization, we must, if we wish at all to elucidate the laws to which the results conform, confine our attention to certain points of differ- ence and leave all the rest out of consideration as of subordinate importance. Mendel did this in his experi- ments with peas, and the same has to be done in crossing Maize, the races of which do not differ from one another exclusively in varietal characters; so also in Lychnis vcs- pcrtina and diurna and in many other cases. It would take us too long to continue tin's discussion further, and to accumulate examples; my meaning will. I believe, be sufficiently clear. It may be expressed in ^T call to mind the Ociiofhcra Pohliaiia (O. lataXhrcristylis) . one of my crosses, the /a/a-character of which hchavcs as a iMiitatiitnal character in a cross ; whilst the shortness of the stamen behaves as a MendeHan character. 588 Species Accordijig to flic Theory of Mutation. its sim])lest terms, if we call those qualities whicli in cross- ing conform to Mendel's law, varietal characters, and those which give uni-sexual unions, specific characters. This would conduce to a more general form of the thesis based on the experiments with Lychnis (p. 582), viz., that two related forms can differ from one another simul- taneously in varietal and in specific characters. Are they therefore to be regarded as varieties or as species ? Here we arrive at the boundary which separates facts from conventional terminology. Here lies the point to which GoETiiE refers in his well-known lines : ''Dich im Unendlichen zn finden, Musst unterscheiden und dann verbinden." The process of distinguishing is an objective one, that of combining subjective. The former is the imme- diate result of inquiry; in our case, of systematic studies on the one hand, and of experiments in hybridization on the other. The combination is partly a question of taste ; it has to serve special aims ; and above all it must facilitate general conceptions and mutual understanding. It is not my task to go more deeply into the question of systematic subdivisions or to make any definite pro- posals.^ My sole object is to place the actual facts in as clear a light as possible. This attempt, however, again leads to the conclusion that here also this insight can only be obtained on the basis of the theory of mutation. It is only by attempting to analyze the species into its component factors, the elementary characters, that we * If two forms were found to differ from one another exclusively in varietal characters, but the number of these were very large, they would probably have to be separated as species. Here also the dis- tinction between species and variety is an arbitrary one, and as a matter of fact, many of the larger groups and sometimes even whole families have among their distinguishing marks some which do not reallv differ from "varietal character^." The Practical Conception of Species. 589 can hope to arrive at a conception of species wliich shall be both in accord with the facts, and justified by experi- ment. Of course, I am well aware that the experiments which have been carried on up to the present are by no means sufficient and that much remains to be done. Nu- merous experiments in hybridization are necessary before they can serve as a foundation for systematic distinctions. But the leading principle in these researches must always be the attempt to determine the elementary characters. § 4. THE PRACTICAL CONCEPTION OP SPECIES. Both collective and elementary species are called spe- cies ; and this twofold significance of the word has thrust its roots so deeply into the history of descriptive biology, tliat it will probably never be wholly eradicated Lix- NAEUS himself confused the two ideas; and whilst some readers derive from the study of his works the conviction that in his mind the collective forms were the true spe- cies,^ others come to a different view of his attitude, and believe that in formulating the conception of species, he was considering the real units of the system. - The fundamental conception from which almost all investigators start, is that species are the only real enti- ties.-'^ As to what these entities are, opinions dilkT. ''On ne pent pas douter," says De Caxdolee. "que Ic groupe appele espece par Tillustre Suedois ne fut. dan^ ' Sec Vol. I, p. 20. " S. Bet.t.t. Observations critiques sur la rcalite des esf>eees eti iialurc an point dc vuc de la systeniatique des z-egetaux. 1901. ' C Nagelt. Entstehung und Begriff der naturhistonsehen Art. 1865. p. 31. 590 Species According to the TJicory of Mutation. sa maniere de voir, line association de formes voisines."^ On the other hand Jordan, as is well known, based his conception of the smaller or elementary species as the real species on the same fundamental proposition. The wish to see in the s])ecies something real, has always played a prominent part ; but the reality as it appeared to the descriptive biologist has been very different from that in the mind of the experimental investigator. It would certainlv 1)e desirable to aq:ree to call onlv one of the two groups species ; it is only the question which. The older view and the popular idea limit this term to the larger groups, and give the name of sub- species to the smaller ones.- But the term subspecies, as it is now in use does not signify a unit, but a group of units which is also compound and merely differs from the species itself in being smaller (Part I, p. 60). The modern tendency is to regard the smaller types as spe- cies, and wherever the criterion is of an exi^erimental kind, like that employed by Jordan, this view will ])re- dominate. Its importance to descriptive biology has re- centlv been demonstrated in a most clear and convincinsf manner by Belli :^' and there seems every pros]~)ect of its being recognized by the best systematists. It has been proposed to denote collective species by a special name, and the word ''stirp" has been suggested. This term has been applied in this sense by several svs- tematists,"^ and Belli has adduced a long series of histor- ' Alph. de Caxdoi.le. Archiv. dcs sc. dc la hlhJ. uuhcvscUc, Ge- neva, Febr. 1878, Vol. LXI, p. 4. " hi what follows, I shall leave varieties, in the sense in which this term has been used in the foregoing sections, out of account. '' S. Belli, toe. cit. "For instance, H. Leveille. Monographic du genre Oenothera, 1902, T. pp. '/2, 106, etc. The Practical Conception of Species. 391 ical and critical arguments for this ])racticc. 11ic word stirp would perhaps correspond most closely to the ( ier- man word Sippc,^ although this word has been empl(jyed by various authors in a different sense.^ At any rate it is most desirable to make some distinction of this kind, and Belli's suggestion might well form the foundation of such. Rut questions of nomenclature have little interest in this discussion and I prefer to leave the task to others. Wt may now proceed to the practical delimitation of the conception of species. Descriptive biology wants a definition, independent of the results of hybridization ; in its commonest form it is based on the absence or presence of transitional forms, as was explained in the first part of this volume. Groups of individuals which are connected together bv transitions are considered to belong to the same species. The limits between species correspond to gaps in the series.'' \\'ith- out some such convention the description of species oc- curring in collected material would be impossible ; and this method has been emplo3^ed by the best systematists since tlic time of DeCandolle. It is only when direct exj^eri- nients can be carried out that the prol)lcm can be dealt witli in a different wa}^ 1^wo difficulties, however, present themselves, wliich I shall now briefly deal with. In the first place, exactly ^ Die Mutationcn tiiid die Mufafiouspcn'odcu hri drr Ruisfchuui: dcr Artcn. Leipsic, Veit & Co., 1901, p. 14. " C. CoRRENs, Schcinhare Ausnalimen von dcr McndrVschcu Spal- hin^^srcgrl fiir Basfardc, Bcr. d. d. bot. Ges.. ]()02, \'«)l. XX. Part V p. 170. See also the same author in Bcr. d. d. bot. (ics.. 1901. Vol. XTX, p. 77, note i. and his Monograpliic dcr Maisbastordc. p i. and Von Wett.steix, Cnmdciigc dcr gcograf^hisch-niorf^hologischcn Mr- tliodc dcr PHauzcnsystcmatik. 1898. p. .v "Sec, for instance, Anncc hiologiquc. TV. 1898. p. 470: V. 1800. p. T,77 and elsewhere. Also Borrad.mlle. On Crustacians. lyoi, p. iQ^: rrKiSEnACH, Dic J'cgcfafioii dcr Erdc nach Hirer klinmlisclicn Auord- niiiig. 1872. p. 9. and so forth. 592 Species According to the Theory of Mutation. tlie l)est varieties are, as a rule, not united by transitional forms with the parent species ; in the second place, trans- gressive varialjility tends to obscure boundaries where they really exist. These limits are often overlooked in the descriptive method, and the search for them can only be carried out on experimental and statistical lines. With good right De Candolle speaks in such cases of provi- sional species.-^ § 5. THE PARALLEL BETWEEN SYSTEMATIC AND SEXUAL RELATIONSHIP. Since the doctrine of descent now commands general recognition, it is desirable that the systematic divisions should be an expression of the various degrees of rela- tionship. Even before the appearance of Darwin's works it was recognized that the task of systematic biol- og\' as a descriptive and classificatory science was differ- ent from the mere question of actual relationship. To in- vestigate this and, where possible, to bring the divisions of the natural system into harmony with it, these were the ends which the pioneers in the study of hybridization had continually in view. The result did not, however, correspond to tliis ex- pectation. We have not, as yet, succeeded in bringing into harmony the study of hybridization with that of systematic biology. Nageli expressed this incompati- bility most clearly by introducing his conception of sex- ual affinity. The degree of this affinity between two types was judged first by the degree of their fertility when crossed with one another, and, then, by that of the fertility of the hybrids thus produced. * Alph. de Caxdoi.le, La PhyfogropJiic, pp. 98, 167. Systematic and Sexual Relationship. 593 The simplest form to wliicli it lias hceii ])r»)])()Se(l to rediKse the parallel hetween systematic and sexual rela- tionship, is the following: (1) Plants which i)n)(luce offspring when crossed with one anc^ther, always belong to the same genus; (2) Plants whose fertility is not diminished in crossing belong to the same systematic species (or collective species). Both generalizations are in great favor and are defended by ])rominent investi- gators. They have, however, a weak side, viz.. that they cannot be reversed. Let us first examine the former proposition. It de- nies the existence of hybrids between distinct genera, or so-called generic hybrids. It originated amongst those philosophers who regarded the genera as having been created, the species, however, as having arisen from them by natural means. We have already dealt with the his- torical significance of these transmutationists in the fir.st vohime (p. 17). To them the view, stated above, is also due, that not only do species arise within the genera by a normal process of evolution, but that new forms may arise from these species by crossings. W. Herbert is the most famous representative of this view.-^ which was later defended by Godron. The latter investigator de- scribes all genera, the species of which are fertile with those of related genera as artificial, and has collected a mass of evidence in support of this view.^ No fundamental objection can be brought against this view, and its adoption would lead in relatively few cases ^W. Herbert, AmaryUidaccac, With a Treatise Upon Cross-bred Vegetables, London 1837". pp. 337 et seq. See also Gartner, loc. cit . p. 152, and Nageli, Sitcungsber. d. k. bayr. Akad. d. Wiss., Dec. 15. 1865, P- 400- "" A. Godron, Dc Vespcee et des raees dans les ctres organises. 1850. Vol. I, pp. 225-236. and ^fe}n. Acad. Stanislas a Nancy, 1S62. pp. 2<>6- 29R. 594 Species According to the Theory of Mutation. to an enlargement of genera. On the other hand it would put a check on the splitting up of genera which has been so much in vogue of recent years, and not less to the elevation of subgenera to the rank of genera. In practice, however, the application of Herbert's suggestion has proved impossible. At that time there were only a few generic hybrids, but their number has undergone a con- siderable increase ; partly no doubt through the arbitrary splitting up of genera mentioned above, but partly also through the rapid accumulation of experimental data. Berhcris and Mahonia (e. g. B. Nenherti) could well be united into one genus. The suggested union of rye and wlieat, a hybrid between which has been raised by Rim- PAu,-^ into a single genus Fnnncntum, is not likely to win much favor; and the fact that Burbank, in Cali- fornia, has raised a hvbrid ho-iw^tn Nicotiana d.nd Petunia which he calls Nicotunia^ will hardly be regarded as a sufficient ground for a systematic union of these two genera. There are now about 150 bi-generic hybrids amongst the Orchids, especially between the genera Lae- Ha, Cattleya, Epidcndruni and Sophronitis, as also be- tween Zygopctahim, Colax and Batemannia.^ The practical difficulties which stand in the way of Herbert's proposal are, on the one hand, the fact that the limits to possible hybrid combinations are by no means definite, and on the other hand, the objection, which has so often been raised, that crosses are exceptional phe- nomena and that it would therefore be impossible to ^ W. RiMPAU, Kreusungslirodnktc Jandzvirthschaftlichcr Cnlfur- pfianzen. Landwirthsch. Jahrb., 1891, p. 20, and PI. VI, Fig. 58. ^Luther Burbank, New Creations in Fruits and Flowers (Bur- l)ank\s Experiment Grounds, Santa Rosa, California), 1893, with a figure of the Nicotunia. ' C. C. Hurst, Jotirn. Roy. Hort. Soc., Vol. XXTV, pp. 102, 125. SystciiuUic and Sc.vual Relationship. 595 apply the principle in those numerous cases in whicli they fail. W'kh regard to the former point, it should he noted that there are numerotis natural hybrids which cannot as yet be made artificially, as for instance Kibes Cordunia- nuni ; in other words that many possible hybridizations do not succeed within the narrow limits of an experiment. The impossibility of a successful cross can therefore hardly ever be proved experimentally. W'itli regard t<> the second point it suffices to cite the fact that in the great majority of genera no specific hybrids exist at all ; and that therefore here the delimitation of genera accor- ding to this principle, would fail entirely. We come now to the species. Kolreuter expressed the view that crosses wdthin the limits of these are fertile and give fertile offspring; wdiereas crosses between si)e- cies would either show a lessened fertility or at least would prodtice infertile hybrids. Gartner and most of the more recent investigators have subscribed to this view, except that they regard diminished fertility, ratlier than the actual absence of it, as the index of the bound- aries of the species.^ But even to these generalizations the exceptions are so numerous that unanimity in their ap])lication has not yet been reached. The parallel between sexual affinity and systematic relationship holds good in general, but fails only too often in particular cases.- Naudix re- garded these deviations from the rule as exceptions,-' and Abbado and several other investigators have claimed the determining cause of these exceptions in individual cases to be the task of hybridological researches.-* 'Gartner, loc. cit., pp. 163-164, 578-579. etc. "See MuRBECK, Botaniska Noiiscr, 1901. p. 214- 'Ch. Naudin. UHyhridite dans les z'c^rtaux. 1869, p. MS- * Abbado, L'ihridismo nei vegctaVi, 1898, p. 48. 596 Spcxics According to the Theory of Mutation. These causes may fall into two entirely different cat- egories ; on the one hand, they may consist in insufficient systematic knowledge, on the other, in the insufficient num- ber of experimental crosses. With regard to the former point it should be remembered that, although the sys- tematist frequently takes latent characters into considera- tion, it is obviously by no means always possible to de- cide on systematic grounds whether a character which we do not see is really absent or exists only in a latent condition. Nevertheless, latency is often regarded as a retrogressive metamorphosis and therefore as the mark of a variety: whereas absence is considered as a phylo- genetically older step and therefore as a specific character (see above p. 71). From this discussion we see that we may cross a plant in which any given character is active either with one in which the internal factor for this character is absent, or with a species or variety in v/hich it is present but in a latent or inactive state. Externally there is no difference between two such crosses, but fundamentallv thev are exactly opposite, and therefore it is to be expected that their results will differ. The cross, active X absent is a uni-sexual union and will presumably lead to a halving of the external characters of the parents in the hybrid, whereas the cross active X latent is a bi-sexual one, and follows Mendel^'s laws, at least in ordinary cases. ]\Iany paradoxes, which at present seem to negative the parallel between systematic and sexual affinity may perhaps be explained by more exact investigation on these lines. FocKE gives the following cases as instances:^ "Silene vulgaris, and S. luaritinia, Capsella ruhella and C. bursa pastoris, Phaseolus vulgaris and Ph. inultiflorus, or the * FocKE, loc. cif., p. 448. Systcjiiafic and Sexual Relationship. 597 species of Diplaciis {Miumlns) do not seem to l)c luur- phologically more remote from one anotlier than Tro- paeolwn uiajiis and Tr. inimis, Nicotiaiia latissima and A^. Marylandica, N. nistica and iV. Texana or Pisinn sa- tiviiiii and P. arvcnsc. Nevertheless the results iA cross- ing" in the former cases exhibit all the characters of hy- brids, but in the latter those of mongrels." Focke sum- marizes his conclusions on this subject in the thesis that ''systematically probable" crosses often miscarry, whilst improbable ones sometimes succeed {loe. cit., p. 457). Even regarded from this point of view the difference betw^een IMendelian and uni-sexual crosses offers itself as a criterion for distinguishing betw^een species and varieties. But sexual afifinitv does not ahvavs irive reliable in- dications. In the first place Gartner frecjuently found that fertility, as measured by the number of seeds ripen- ing in a capsule, is different in reciprocal crosses. This shows that it is not merely determined by the degree of relationship, but obviously by some other causes besides. The best known of these is the length of the style; and the recent investigations of Burck on the concentration and stimulating properties of the fluid secreted by the stigma have thrown much valuable light on this subject.^ In extreme cases one of the crosses succeeds well, whilst the other does not at all, as for instance Mirabilis Jala pa X longiflova, Geuin urhanum X nrale, Sophronitis X Cattleya, and so forth. In the second place some crosses do not succeed in spite of a very close apparent relation- ship, as for instance betw^een Anagallis arreiisis and eoe- rulea (Gartner). ^W. Burck. Over de bezve^iu^ der sfempcis by M'unulus en To- renia. Sitzunp^sber. d. Kon. Xkad. d. Wet., Amsterdam. 1901, and in previous articles. 598 Species According to tJie Theory of Mutation. I du not propose to elaborate tliis theme further ; it has often been dealt with and especially in great detail b\' FocKE, who has presented it in a masterly way in his textbook on plant hybrids. The main conclusion, how- ever, is that the majority of authors agree that systematic and sexual affinity, if properly understood, are essentially j^arallel ; indeed, that they are really no more than two manifestations of one and the same thing, but that we have not yet succeeded in explaining the apparent ex- ceptions to this parallel. For our purpose, however, the important question is, whether the diagnoses of species and varieties w^ill grad- ually come to be based on elementary characters as units, and whether sexual relationship will come to be judged by the number of differentiating units. Gartner has already pointed out that those genera in which the largest numbers of hybrids have been produced are exactly those in which the number of very closely related species is the greatest (loc. cit., p. 168). Nageli has elaborated this idea and Sachs has followed him in his Lclirbuch (ler Botanik. Abbado, Hurst, Gillot and many others have also subscribed to this view. The opinion expressed by these writers on the paral- lel between systematic and sexual affinity, may be sum- marized in the following thesis, viz., that the fertility of crosses and of the hybrids resulting from them, di- minishes, on the average, as the number of points of difference (that is to say, that of the elementary char- acters, which constitute the differences) increases. But many more experiments are necessary before this sug- gestion can be examined critically or be regarded as resting on a sure foundation of experimental facts. II. THE RANGE OE VALIDITY OE TIIF. DOC- TRINE OE MUTATION. § 6. THE SIGNIFICANCE OF THE AVAILABLE EVIDENCE. Unlike the prevailing form of the theory of selection, the doctrine of mutation lays stress on sudden or dis- continuous changes, and regards only these as active in the formation of species. The Darwinian form of the theory of selection regards both these and Huctuating \'ariations as oi)erati\'e in the origin of new forms, whilst Wallace favors the other extreme, according to which all formation of species goes by a slow and gradual process of change. The two schools of thought naturally adopt dilterent attitudes tow^ards tlie doctrine of mutation. It is at (Mice rejected by Wallace's adherents, whilst those who in- cline to Darwin's own form of the theory are less un- reservedly inimical ; many of them have even greeted it with open arms. Inasmuch as these two lines of thouglit liaxe been clearly manifested in the critiques which have been ])ub- lished of the first volume of this work. I ])ropose t«t dis- cuss them briefly here, in order to ])()int out the funda- mental questions which are involved in this controxersy. The extreme opponents of my thcorx- maintain tliat there are no mutations at all : Xafura uou facif siilfns. thev sav. What I have described as discontinuous changes. 600 Validity of the Doctrine of Mutation. are, in their opinion, merely the extreme deviations brought about by ordinary variabihty ; for the further these are from the mean, the rarer they are, and the greater are the intervals by which they are separated. The number of petals in Ranunculus hulbosus semiplcniis oscillates around 9 or 10, frequently reaching 14, very seldom 20-23. Only in one case did I observe a larger number, which happened to be 31 (see p. 252). The gap between 22> and 31 is, however, not a discontinuous variation. It is perfectly normal, and quite a common occurrence in this part of Quetelet's curves. In a general way, gaps of this kind in the curves of variation may be thus explained, and according to my opponents the so-called springs and jumps have to be explained in the same manner. They are assumed to be no more than the extreme variants of series which when investigated further, would prove to be continuous ones. This view is chiefly maintained against my opinion by morpholgists^ and statisticians.^ It is, as KoR- SCHINSKY has lately shown, directly contradicted by horti- cultural experience ;'^ and the absence of transitions and the stability of my new species of Oenothera prove that, in this case at any rate, true mutations do occur. The greatest obstacle in the way of agreement on this point, however, lies in the phenomena of transgressive varia- bility, which to the morphological observer so often give ' Among- my numerous critics T mention here Ch. Schroder, Die J'ariahilitat dcr Adalia hif^uuctata L., Allgeni. Zeitschrift fiir Entomologie, Vols. VT-VIT, 1901-1902. The view taken by Schroder has since been proved to be erroneous by the experiments of A. G. Mayer on the colors of Initterflies. See Effects of Ahifural Scleciion and Race-Tendency Upon the Color-Patterns of Lcpidoptera, Museum Brooklyn Inst, of Arts nnd Sc, 1902, Vol. I, No. 2, p. 31. ^ See the journal Biometrika and especially the articles in it by Weldon. ^ S. KoRSCHiNSKV, Mem. Acad. Imp. Petershourg, 1899, TX. Significance of the Available Evidence. 601 the appearance of transitional forms and only reveal their true nature when tested by breeding- experiments. Several of the critics who have expressed themselves more or less favorably on my theory, have pointed out that the greatest danger for it lies in this very point. In a very clear and concise summary of the doctrine of muta- tion Mac Dougal has expressed himself as follows : "The greatest misunderstanding which may likely arise in the consideration of these results will be that founded on the error of confusing fluctuating variability and mutabil- ity/'i The distinction between species-forming and fluctu- ating variability was first derived by Darwin from his theory of pangenesis, and this may perhaps explain the antipathy which so many investigators bear towards it.- The great majority of writers assume that fluctuating as well as discontinuous variability play a part in the formation of species.^ This view of Darwin, which under Wallace's influence gradually shifted into the background, has in latter years come again prominently to the front ; and the various investigators concede here a less or there a greater share to discontinuous variations or mutations, according to their preconceptions and their experience in investigation. This long series of shades of opinion would seem to indicate that we are not con- cerned here with an independent principle, but with a gradual change of opinion from the prevaih'ng theory ^ D. T. MacDougal, The Origin of Species by Mutation. Torreya. 1902, Vol. II, p. 99. '^ See IntraccUular Pangenesis, e.g., p. 214 (English cmI.I. ami Ber. d. d. Ges., 1900, XVIIi; p. 83. 'Von Wettstein has published a useful summary of his vi-w-^ in the form of a lecture dehvered to tlio Scicntilk and Medical .\ ciation at Karlsbad, and entitled Der Nco-Lamarckismus und scittc Bcsiehungen zum Danvinismus, 1903. 602 Validity of the Doctrine of Mutation. to some other one; and especially amongst American in- vestigators the tendency has been in recent years to pro- ceed as far as possible in this direction. If we look for a fixed point among these oscillating opinions we may well choose the view repeatedly ex- pressed by Darwin himself, that it is possible to imagine that characters may originate by a slow process, but may disappear all of a sudden.^ In combining this with the distinction made in the first part of this volume between progressive, retrogressive and degressive formation of species, the proposition would run : Progressive forma- tion of species may occur slowly and gradually, whilst retrogressive and degressive specific differentiation is due to mutations. Progressive differentiation consists in the formation of a new character which was not previously ])resent; whilst retrogressive and degressive differentia- tion consists in the transference of internal factors, al- ready present, from one condition to another. In the for- mer case the active unit becomes latent ; in the latter the latent becomes active, or the semi-latent semi-active ; but the material vehicles of these characters remain funda- mentally the same throughout ; nothing new arises in the idioplasma.^ In horticulture, as we have seen, mutations are largely of the retrogressive or degressive kind. Discontinuous formation of species on the progressive line is much rarer. Nevertheless I believe that my researches with Oenothera have contributed instances Avhich may demon- strate the occurrence of progressive mutations in this species at any rate. Obviously there is a great need of ^ With reference to this point see the valuable critique by L. Plate, Uebcr Bcdcutung unci Tragzceitc des Dan^'iu'schcii Sclcclions- p rill dps, 1900. p. ^7 and elsewhere. ' See below, §§ 9-1 1. Significance of the Available Evidence. 603 further investigations on this point, and these should not merely be concerned with new i)henoniena, but with ihe testing of results already obtained ; for many instances of discontinuous origin stand in need of more convincing ])roof, and in other cases the progressive nature of a process which is interpreted as a mutation is often subject to doubt. In such investigations attention should be ])aid to the question whether the hypothetical i)remuta- tions may perhaps be prepared gradually, whilst tlie new- character which has been so developed in secret, might unfold suddenly. But it will take many years to decide these points. Starting from general arguments Kolliker^ was the first to insist on the importance of mutations against Darwin^ indicating the process, which was then a purely hypothetical one, by the name heterogenic development. Others have expressed themselves favoral)ly with regard to this view ; especially K. E. von Baer and Bronn, and also Haacke, G. Pfeffer, Delage, Cunningham, Wolff, Dreyer, Driesch, Emery- and many others. This doctrine has of recent years found its strongest cham])ion in Bateson, wdiose view^s I have already dealt with above. Those authors too, wdio have made mono- graphic studies of special genera and species have wel- comed it; for instance Wittrock. in his study of Jlola, inclined to the view that species have originated discon- tinuously. Further, this doctrine is defended on purely speculative grounds by many prominent biologists, amoni;- whom I need only mention Von Hartm axx and also Hamann and Ker.sten." On the zool(\gical side Ilr- ^KoLUKER. Abhandl. Scnchcuh. GcscUsch., 1864. pp- 22y22(). ^ Emery, Biolog. Centralblalt, 1893, No, 13. V- 7^3- ^ See the careful and critical exposition in IT. Kkksten's Die 604 Validity of the Doctrine of Mutation. BRECHT and ]\IoRGAN havc expressed themselves in favor of the new view,^ the latter on the ground of his studies in the regeneration of injured organs.^ Amongst practical agriculturists my views have heen well received by Em. von Proskowetz and Hjalmar NiLSSON. The former has conducted a long series of in- vestigations on the transformation of the wild Beta patula into the sugar beet; and it was found that the changes do not by any means take place by imperceptil^le tran- sitions but suddenly.^ Each new character is brought to light at one stroke ; it is not the product of selection but of internal processes, the nature of which w^e do not as yet know. Even such secondary characters as color, change in the same way. Hjalmar Nilsson, the direc- tor of the practical and experimental station for the im- provement of seed at Svalof in Sweden, has for many years been collecting a valuable mass of evidence, which promises to throw great light on the doctrine of muta- tion, but has not as yet, been grouped for that purpose. Judging from tlie oral and other communications which I have received from time to time from this investigator, I may state here that his results are in perfect harmony with the doctrine of mutation.'* tdcalisfischc Richfting in dcr modcrnen Enfzvichelungslehrc, Zeitschr. f. Naturvv., 1901, Vol. 73, p. 321. ^ A. A. W. HuBRECHT^ De evolutie in niciiwe hancn, Utrecht, 1902. *Th. Hunt Morgan, Danvinism in the Light of Modern Criti- cism, Harpers IMonthly Magazine, Feb. 1903, and in many other papers. ^ Em. v. Proskowetz Jr.. Culturrersuche mit Beta, 1892-1901 in Oesterr.-Ungar. Zeitschrift f. Zuckerindustrie und Landwirthschaft des Centralvereins f. Riibenzuckerindustrie in d. Oest.-Ung. ]\Io- narchie, 1892- 1902. The experiments of a given year will be found in the number for the following year, and in the number for 1892 will be found an account of the earlier experiments and the literature of the subject. For the mutations which occurred see especially the number for 1902. * See the various numbers of the journal issued by the experi- Significance of the Available Evidence. 605 To the important observations already mentioned, made by Heinricher on Iris pallida abavia, by Solms- Laubach on Capsella, by Wittrock on Viola, by Bailey and White on Tomatoes, and by many others, 1 have here to add the follov^ing. Noll has described the sud- den origin of a regular tendril in Tropaeolum, and draws conclusions from this in favor of the possibility of dis- continuous changes and their significance for the theory of descent.^ Tracy has observed the sudden origin of a dwarf variety of Phaseolus lunatiis,^ Macfarlane has investigated the variability in the genus Primus,^ Caruel has collected a number of cases in which direct transitions can be demonstrated and calls them ''Euthymorphoses.""* Carlson has investigated the mutations of the forms of Succisa occurring in Sweden,'"^ and Laurent expresses himself in the same way with regard to several species of fruit trees. ^ Dr. J. W. Harshberger sent me mate- rial of Hibiscus moscheutos and Euphorbia ipecacuanha from Pennsylvania, the extraordinary abundance of forms in which seems to indicate the occurrence of a period of mutation in these species ; and Mr. L. Cockayne has given me information on some transformations of Saro- thammis scoparius and Lupinus arboreus observed by him in New Zealand. It may further be mentioned that mental station at Svalof, Sverigcs Utsddcfdrcnint^s Tidskrift, and particularly the Arsberdttelse under ar 1901. in Vol. XII. 1902, No. i, page 3. ^ F. Noll, Das Auftrctcn cincr typischcn Ranhc an ciucr sottst rankcnlosen PHanzenart, Sitzungsber. d. Niederrhcin. Ges. f. Naturk., Bonn, Jan. 14, 1895. ^ W. W. Tracy, American Naturalist, 1895, XXTX. p. 4S5. ' J. M. Macfarlane, Publications of the University of Pennsyl- vania, 1901, p. 216. ' T. Caruel, Bull Soc. Bot. Ital, Florence, 1896, p. 84. ^ Bot. Not., 1901, p. 224. "E. Laurent, De I' experimentation en horticulture, 1902, p. 12. 606 / 'aliclify of the Pocfrinc of Mutation. BoRRADAiLLE^ Working with decapods, came to the con- chision that great difficulty stands in the way of the ex- ])lanati<)n of si)ecitic (hffercntiation \)\ means of or(hnar\' natural selection.^ ]Mr. R. Lauterborx was so kind as to draw my attention to the appearance of the yellow Atrofya Belladonna lufca, and to the evidence given on this variety hy Dr. SciiiJz.- Dr. Raatz was also kind enough to send me some seeds of a most remarkahle shiny hrown variety of the sugar-heet which suddenly arose in the cultures of Klein-A\'anzlehen, and from which I obtained fine instances of the new character in my garden. I have only given a selection from the long list at my disposal. i\Iy object vras simply to show that the doctrine of mutation already finds adherents everywhere and is supported by a l)r(^ad foundation of facts. This justifies the expectation that the difficulties which still stand in its way will ultimately be overcome. § 7- THE EXPLANATION OE ADAPTATIONS. Ever since the belief in tlic common origin of organ- isms has been recoe'nized as a basis for investigation and speculation, one as])ect of the problem has aroused the special interest both of the author and of the student, viz., the explanation of adaptations. As a matter of fact this problem lies outside the scope of the present book, which is only concerned with tlie empirical foundations of the theory of descent. Nevertheless it seems to me that it M.. A. P)ORRADATLLE, Marine Crustaceans. The Fauna and Gc- ograpliy of tlic Mnldivc and Laccadivc Archipelagoes. Vol. T. Pt. 2. page 197. ' Anifl. BcriclU i'lhcr die 33. J^ersaninil. d. Nattirf. iind Acrzte, Bonn. Sept., 1854 ( r>onn, 1859), p. 139. A single specimen of the plant had been found a few j^ears previously in the Black Forest. The ExpUuialioii of Adaptations. hOl may be of interest to show that the prevailing view, ac- cording to which A\'allace's form of the theory of selec- tion is the only one which will account for adaptations, is erroneous. The \iew that all the characters of organisms varv in everv desired direction, and tliat tlie sliHitest deviation may be subjected to the struggle for existence, and can be accentuated to, and finally fixed at, the necessary de- gree of development, is certainly an extremelv convenient one. I willinHv adnn"t that almost anvthin^- can he squared with this theory in a very plausible wav, and that explanations of this kind are very attractive to the student ; but this is not science. The contradictions in such a system must be satisfactorily explained before it is accepted ; and if we attempt to do this, we soon come to the conclusion that the hypothesis itself is not in harmonv with the available evidence. The limits of the a])])licability of the theory of selec- tion, as applierl to this question, are known to evervbody ; and without doubt they are extremely wide. How mucli the theory of mutation has to offer in this respect we do not know, because no attempt to estimate this has as yet been made, but everything points to the conclusion that this theory will explain adaptations just as com- pletely, or rather just as incompletely, as the present view. It will, however, always have the special feature of emphasizing the hypothetical ])arts (^f the argument, rather tlian of dismissing" them into the backciround. At the present time the theory of selection has still the larger number of adherents ; but amongst the ycMinger investigators a train of th(^ught is dex'eloping whicli. as we have seen above, ascribes a greater importance to discontinuous changes. For them fluctuating variability 608 Validity of the Doctrine of Mutation. consists merely in an oscillation around a given point of equilibrium ; whilst the formation of new species necessi- tates the attainment of a new equilibrium. Especially in America has this view made great progress, as has been described by Conn in an admirable exposition in his new work on evolution.-^ Of the numerous writings which we owe to Wal- lace's school, I shall only mention here that on Natural Selection and Tropical Nature, of this author (1895), and Plate's critical exposition of Wallace's theory.- Although Plate, at the conclusion of his clear and per- ceptive critique of the questions which pertain to this point, declares in favor of the theory of selection, his work, of all those of which I have made use, gives me the impression of the greatest objectivity; and I am con- vinced that the gulf between his views and those I hold will surely be bridged over some day. Therefore I refer the reader to his book for a closer study of these ques- tions, and shall confine myself here to a few points which stand in the closest relation to those discussed above. 1. The significance of fluctuating variability is very limited, whereas the explanation of adaptations demands almost unlimited variability. In earlier days when the law of Quetelet was only known to apply to anthro- pology, almost all the changes of plants and animals were considered to be the consequences of ordinary varia- bility, but now this is shown lO be governed by laws which largely curtail its importance. In the first part of the first volume this theme has been discussed in detail, and I may here simply refer the reader to those chapters. ^ H. W. Conn, The Method of Evolution, New York, 1900, p. 132. ^L. Plate, Ucher Bcdcutung and Tragzvcitc des Darivin'schcn Selectionsprincips, Leipsic, 1900. A very complete bibliographical list will be found on pp. 145-153 of this book. The Explanation of . Uiapfatiotis. 609 A strong argument for my view was \)u{ forward by Rosa and Cattaneo.^ According to these authors the extinction of large groups of species proves that the varial)ihty resident in them was powerless to ada])t them to the clianging conditions of life; and fnjm this cun- clusion they infer that the ordinary variability, as it is alicays manifested, is not sufficient for this ])urpose. Ob- viously some other process is necessary. ][. Fluctuating variability is linear; it oscillates only in a plus and 2.niinns direction, whilst adaptations demand a variability which will produce variations in all direc- tions.- On this point also I have expressed my opinion in the first volume (p. 118). It constitutes, in my opin- ion, one of the strongest objections to the prevailing view ; and it also shows more clearly than anything else how far Darwin's adherents have departed from the views actually expressed by him. To Darwin's mind the essential point was that the struggle for existence should have to select from material supplied by an in- determinate variability. Natural selection is a sieve. It creates nothing, as is so often assumed; it only sifts. It retains only what variability puts into the sieve. Whence the material comes that is put into it, should l:>e kept separate from the theory of its selection. How the struggle for existence sifts is one question; how that which is sifted arose is another. In both respects, Dar- win's original view is still the best, but the point at issue has been often obscured by later writers. The meshes of the sieve are not such as to separate only the very best ; on the contrary natural selection only throws out some part of the individuals, and amongst them the worst, i. c.. ^ See below in § 12. ^GusTAV Wolff. 7^(V" gcgcnwaytigc Sland dcs Darwtnisinus, i.v/). (dlO I'alidity of tiw Doctrine of Mutation. tliose the least adapted to the immediate external condi- tions. Selection is the elimination of the inferior, whilst the choice of the superior individuals should be called ''election, " and this leads to the stock-races {elite races) as in the selection of beets and cereals (Vol. I, pp. 99- 118); or, as an admirable critic, A. Kuyper^ says, "se- lection aims at the maintenance of species ; election is the choice of persons."^ The doctrine of the direct influence of the environment on organisms, as entertained b\- La- marck, is that against which Darwin directed his hy- i:)Othesis of indeterminate variability as being more in harmony with the demands of pure science. This old doctrine is repeatedly met with in modern times,- and this shows at least, in my opinion, that the prevailing form of the theory of selection does not find favor in those quarters.'" Thus the sieve of natural selection perpetually elim- inates numerous individuals of inferior value; but how the differences between the individuals arise is another question. Linear variability provides differences only in two directions, by means of which selection can eitlier increase or diminish, strengthen or weaken the various characters. It cannot eft'ect more, unless material of an- other kind is provided by variation. The hypothesis of mutation meets this demand ; for it necessarily assumes a variability in almost all directions, as I have shown L\. KuYPER, Evohitic, Amsterdam 1899, p. 11. ^G. Henslow, Docs Natural Selection Play any Part in the Ori- gin of Species, Nat. Sc, XT. 1897, p. t66. Warming, Lehrhucli d. Oekologie, p. 382. Von Wettstein, Ber. d. d. hot. Ges., 1900, Vol. XVIIT. GeneralversammUinofsber. p. 184. Strasburger, Ccratophyl- Uim suhmersiim, Jahrb. f. wiss. Bot., Vol. XXXVII. p. 518. where a list of references to papers, dealing with the direct effect of the en- vironment, will be found. ^ R. V. Wettstein, Handhiicli der systcmatischen Botanik. 1901, P- 32. The Explanation of Adaptations. 611 in the first part of the first volume (p. 198). and our consideration of those species which, are rich in suhonh- nate forms, as well as the results ohtained with Oenothera Laniarckiana have justified this claim. Thus we see that the current form of the theory of selection cannot sui)i)lv the kind of variability which the theory demands, whil^1L the doctrine of mutation can supply it, as we know from actual observation. III. The first insignificant beginnings of nezv charac- ters do not come under the operation of natural selection since they are of no significance in the struggle for ex- istence. This is the best known objection against the prevailing form of the theory of selection. It has been elaborated by many authors and admirably expressed by Conn in his w^ork cited above, so that we need not deal with it further here. It ultimately leads every th;low tran- sitions and these slight advantages have no place. Spe- cies-forming variability sim])ly omits these, both in rx- pcrimcnt and in liorticultural experience, so that they constitute no obstacle to the theorv." ' CoxN, toe. cit., p. 134. 'Tt IS ill tlic explanation of instinct tliat tlic current form of tlic 612 Validity of the Doctrine of Mutation. IV. TJie theory of selection explains the existence of useful characters, but does not explain that of useless or actually harmful ones.^ Whereas the doctrine of muta- tion assumes that specific differentiation does not take place in any definite direction, that mutations are pro- duced independently of their adaptive value, and that they may survive, provided that they do not prejudice the existence or annul the fertility of the individual, the theory of selection cannot account for the origin of sterile forms of wdiich, nevertheless, there are many. I have already mentioned instances of these in the first part of this volume, and will here only add a reference to a most remarkable sterile form of oats, recently described and figured by Noll ;- to the dates'^ and grapes'* without pips, and to the highly branched and absolutely sterile variety of our gardens, called Muscari comosur.i pluniosuni, wdiich belongs to a species characterized by a tuft of sterile flowers at the tip of the normal spike (Fig. 136). Instead of giving a further discussion I shall content myself with referring to the curious case of Mimidiis and Torenia, which Burck has described, and which this theory of selection is most evidently insufficient. See Wasmann. Biol. Centralhlatt, Vol. XXI, Nos. 22, 23; also Emery, Gedankcn zur Desccndeua- iind V ererhiingstheovic , Biol. Centralhlatt, 1893. Vol. XIII, Nos. 13 and 14, p. 397; further W. Wagner, Vindusfric dcs Arancina, Mem. Acad. Imp. St. Petershourg, Vllth Ser., Vol. XLII, No. II, 1894; and N. Cholodkovsky^ Die Coniferenldiise, Hor. Soc. Ent. Ross., XXXI, p. 43. ' For a list of these T refer the reader to Demoor, Massart and Van der Velde, L'cvohition regressive, Paris, 1897, especially pp. 286-289. ^F. Noel, Sifaungsber. d. Niederrhein. Gcs. f. Nafiirk., Bonn, March 4, 1901. ^ Ch. Riviere, Societe nat. d'accUmatation, Paris, La Nature, 1901, No. 1477, p. 247. The tree in question grow^s near Hamma in Algeria. *H. Muller-Thurgau has given an exhaustive list of wholly or partially sterile varieties of grapes in Experiment Station Record, XT, p. 16, 1902. The EfVplanation of Adaptations. 613 investigator claims to be of itself siifficiciit to disprove the doctrine of selection. ^ These i)lants contain four stamens in each flower, two large normal ones, and t\v(j Fig. 136. Miiscavi comosum phimosiim. small abnormal ones. The latter contain fertile jxillcn, but never dehisce. The pollen is therefore absolutely *W. BuRCK. Kun. Akad. v. Wet., Amsterdam. 1901 : Allmm d Natiuir, 1902. See also the earlier writings of this author on tacts which cannot be explained by the theory of selection. 614 Validity of the Doctrine of Mutation. useless, although if applied to the pistil, it is capable of producing an abundance of good seed. It is evident that this condition cannot have arisen either by gradual modifications or under the inliuence of the ordinary se- lection of useful characters. All the difficulties which we have mentioned as be- setting the current view, disappear if we substitute muta- bility for fluctuating variability, as the source of the origin of species ; and there is no doubt that adaptations can be explained by mutability just as satisfactorily as by fluctuating variability. § 8. VEGETATIVE MUTATIONS. In order to conduct an experimental investigation into the manner in which mutations arise, it is necessary to know when they occur. According to the prevailing- opinion this moment is assumed to be that of fertilization. Gallesio clearly expressed this view at the beginning of the last century, and advocated it against the belief in the direct influence of the environment wliich was common amongst breeders at that time.^ Some associa- tion of species-forming ^•ariability with fertilization is generally regarded as being clearly demonstrated both in the animal and vegetable kingdoms, and especially for annual plants and those which are ordinarily multi])lied by seed. On the other hand we have the bud variations, or vegetative mutations as they should rather be called. They were well known to the older scientists, but Darwix was the first to insist on their iniportance by collecting all ' G. Gallesto, Tralfr du Citrus: Teoria delta rif^mduciouc vcge- iahile, Pisa. i) I drew attention to the stamens with red stripes in strijK^d flowers and dealt with the question whether the pollen grains themselves might not difl"er with regard to this mark, some of them possessing this character and others not. Obviously this question may be applied just as well to those characters which can not be seen in the stamens. 618 Validity of the Doctrine of Mutation. I shall not pursue this train of thought further ; l:>ut this much seems to be clear, that germinal variations may be the results of changes which have already taken place Fig. 137. Green Dahlia. A branch whose terminal inflores- cence b as well as the lateral one b' have become green, as in the remaining parts of the plant, whilst a branch has arisen at a from an axillary bud, bearing double red inflorescences of normal structure and without a trace of virescence. a', flowering and a", a bud. See above, p. 92, Fig. 14 (1902). See also pp. 628-629. in the pollen- and egg-cells ; and that these changes them- selves may have had their origin before the development Vegetative Mutations. 619 of the sexual cells, and perhaps even before the uri^Mii of the flower itself. In other words : Germinal variations may be regarded as a speeial ease of vegetative mutations; and this possibility always re- mains open where the contrary cannot be proved. Concluding these discussions I propose now to arlduce a series of facts in which mutations have occurred vege- tatively, tliat is to say, such facts as have hitherto been dealt with as bud-variations. It will be necessary to Fig. 138. Cryptomcvia japonica spiralitcr falcafa. with an atavistic branch (sec page 628). consider three groups of phenomena separately : first, vegetative segregation in hybrids; secondly, vegetative atavism in eversporting varieties, especially as cxiu'bited by striped flowers (Part I, Plate I), and thirdly, the true vegetative mutations which are usually of an atavis- tic nature (Figs. 137, 138), but sometimes may happen to be of a progressive kind. Vegetative segregations in hybrids are rare phencnn- ena; but this may perhaps be due to the fact that in many 620 Validity of the Doctrine of Mutation. instances of bud- variations the possibility of the plant in question being- a hybrid has not been considered. A single case has fallen within my own experience ; this is a hybrid between Veronica longifolia and its variety V. I. alba. The flowers of this hybrid are blue, and it may easily be kept in cultivation for many years by means of vegetative propagation. Ever since 1889, when I ob- tained the first specimen, I have had many thousands of stems in flower, arx)ngst which I observed several cases of sectorial and of bud-variation, the last of them in the summer of 1902. The bud-variation sometimes occurred in the rhizome (1902) ; the whole shoot above the earth lacked the red pigment, both in its bark and its flowers, and so was easily recognizable before it bloomed. All the flowers were white, whilst those of the remaining shoots from the same rhizome were blue. Occasionally I found a raceme witli white flowers arising as a lateral 1)ranch from a stem on which the rest of the flowers were blue (1894). The sectorial segregation is manifested in this hybrid in such a way that one side of the raceme had blue flowers, whilst those on the other were white. ^ The breadth of the longitudinal strip bearing white flowers is subject to variation ; it may be either a half of the whole raceme (as in 1891), or a quarter (1898), or even less (1894, 1895). The seeds of flowers which have thus become white by vegetative mutation produce white- flowered offspring, so far as I am able to judge from some preliminary experiments. As is well known, Naudtn has crossed Datura Stra- in oniiwi with D. Jaevis, and found amongst many hybrids with exclusively thorny fruits, three individuals which gave instances of vegetative segregation. These belonged * Bcr. d. d. hot. Gcs., igoo, XVIIT, p. 86. Vegetative Mutations. 621 to the first generation and bore numerous fruits, ilic sur- face of which was partly thorny and partly sniootli as in D. laevis. Sometimes one-half was smooth, but u;>ually only a quarter or a smaller part. The valves without thorns had also reverted to the character of D. laei'is in the fact that they were shorter than the thorned ones, and so did not fit into them properly. Fertilization had been left to insects, so that the results obtained Ijy sowing the seeds would have been of no value. Such vegetative segregations appear, however, to be very rare in Datura. Other investigators do not seem to have obtained them ; and I have myself frequently made extensive cultures of this hybrid in the hope of obtaining some, but as yet without success. The records of instances of hybrid segregation are scattered through the literature of this subject, so that it may be worth while to give the following selection. Sageret obtained a hybrid between Brassiea and Ra- phamis with two types of pods.^ Dounet-Adanson ob- served on an intermediate hybrid between Abies Pinsapo X pectinata a branch with the characters of A. Pitisapor FocKE mentions a case of the cross Anagallis pJioe- nicea X coentlea which had red flowers but exhibited half a petal with the blue color of the latter species.*' Vegetative segregations in the fruits of Citrus hybrids have frequently been described."^ Flowers of dilTerent colors have been found occurring together on the same ^ Sageret, Ann. Sc. Nat., 1826. ^ Bull. Soc. hot. Fr., 1899; Abbado, Uihridlsmo, lor. cit., p. j6. 'W. O. FocKE, Nat. Ver. Bremen, 1887. p. 422. Soc als(> Gart- ner, Die Bastavderzeugung,, p. 309, and I'ocke, J'i1iincentni.s-.h!:iiiH', p. 450. *Verlot, La variahilite, p. 14; Kerner. Pflancenlehen, IT. pp. 559- 560, etc. 622 J'alidify of flic Doctrine of Muiation. stock in hybrids of HcHanfhcininn.^ Hybrid peas may be partly green and partly yellow- and similar segrega- tions have been found by Correns and Webber on grains of hybrid maize. Bnt the best known instance of a vegetative segrega- tion is furnished l)y Cyfisiis Adaiiii {C. Laburnuui X piirpurcns), wliich any one can observe in his garden or in parks. The hybrid is a1)solutely sterile, and all the specimens of it are grown from cuttings from one single individual, ^^dlether the extraordinary tendency to segregate is peculiar to this hybrid as such, or to this particular individual, we cannot knov/.'"^ The fact is, that this hybrid is intermediate between its two parents and besides this produces from time to time buds, of which some l)ecome strong branches of C. Lahuvnuin with its large leaves and long racemes (Fig. 139L), whilst from others the delicate, slender and bushy branches of C. piirpiircus arise, bearing their fruits and flowers either singly or in small groups (Fig. MOP"). The current view is that C. Adami is a graft hybrid. "* There is, however, neither an historical nor a physiolog- ical justification for this view.'" The original raiser of the plant, the Parisian gardener Adam, seems himself to have thought that this form which he put on the ^FocKE. Die PHanacnmischlin^c, p. 473. wliere further instances will be found. See also Br.mjn. Verji'inguiiii, p. 336; Darwin. Ani- mals and Plants Under Doinesfieafion. etc. Similar facts are afforded bv Hieraeiuin. Oxalis, Chamaedorea etc.: see F. Hilderrand, Jen. Zeifsehriff. Vol. XXITT. 1889. Plate XXV. " F. Weldon, Bionictrika, T, 2. 1902. ' See the remarks relating to Datura on the foregoing pages. * Infraeellnlare Pangenesis (Ger. ed.). p. 206. '■ T have given an historical account of Cytisus Adami. in Dutch, in the Album der Natuur, 1894, Part 7. under the title Adam's Gouden Regen. The original source of the historical data is found in Annales de la Societe hortieole de Paris, Vol. VI T, 1830. Vegetative Mutations. 623 market only as a variety of C. piirpiireii.<:. liad arisen as a result of the grafting of C. purpureiis on C. Lahuiinoii ; but his contemporaries did not agree with this, anrj Ca- MUZET maintains that he has seen the tree from which Fig. 139. Cytisiis Adami. A, A', A"; B, a hrancli of C Laburnum, L, L'. L", witli numerous racemes bearing ripe pods. Adam liad taken his hnds for the purpose of making the grafts, and that this tree possessed all the characters of Cytisus Adami. 11ie hypothesis that this form is a graft hybrid, originated with Casi'Akv (1cS()5). Xo case 624 Validity of the Doctrine of Mutation. of an undonbted graft hybrid lias, however, as yet been produced experimentally and, consequently, the charac- Fig. 140. Cytisiis Adami. A, A', bearing at I a bunch of twigs of C. purpureus: P, H, and I. ters which such hybrids would have if they existed are not known and can even hardly be guessed at. Therefore Vegetative Mutaiioiu 625 no conclusion concerning this (juestion can be drawn from the characters of C. Adauii. The view that it is an or(hnary hybrid which waj afterwards grafted on C. Labiirtimn seems to be much more prol^able.-^ In other data relating to graft hybrids this view has long been proved to be incorrect, as in Lin dem urn's ex- Fig. 141. Ulinus canipestris varicgata with atavism by bud variation. A branch with larger green leaves lias arisen at A. periments with potatoes; or the grafts may have been made on hybrid stems, as Laurent suspects to be the case in the Neflier de Bronvaux'r or again, a graft uf ^The same view is adopted by E. Laurent, Dc I'cxpcn'ninilatioii en horticulture, Brussels, 1902, p. 16. The literature dealing with Cytisns Adami has been given so often that 1 need not go into further detail here. " See the papers on this supposed hybrid between Mcspilus and Crataegus in Le Jardin and Jonni. Roy. Hort. Soc., 1900. Vol. 24, 626 Validity of the Doctrine of Mutation. a h\'bricl may have been made on a normal plant, as WiLLE has told me he suspects to be the case in the sup- posed graft hybrid consisting of a pear worked on a white thorn stock. ^ The reader who is interested in the direct influence of the stock on the grafted bud is referred to the recent exhaustive studies by L. Daniel. - By pruning Cytisus Adanii, Beyerinck obtained very important results on the vegetati\'e segregation of hy- brids. He found that buds which, as a rule, are resting, but which can be made to develop by cutting off the higher branches, tend to produce the characters of C. Laburnum or of C. pur pur ens, so that we have it in our power to multiply the number of such segregations at will. More than one hundred instances were obtained by him on some few trees. Sectorial segregations of buds also occurred, sometimes transforming a longitu- dinal half of a shoot into C. Laburnum, whilst the other half remained C. Ad ami. ^ It is to be expected that the application of this principle to other cases will lead to the discovery of important facts. Of the numerous instances of bud-variations de- scribed in the literature of this subject, many are, with- p. 237. Also Laurent, loc. cit., p. 16. For a general review of graft hybrids see Fruwtrth. Zitchtimg landwirthsctiaftJichcr Kultnrpflan- ccii, p. 72 ff. ^ N. WiLLE, Mitfhcihingcn d. hiolog. Gcsellschaft in Chrisfiania, Biol. Centralblatt, 1896, Vol. XVI, No. 3, p. 126. Perhaps this may be Pynis aurictiJaris {P. communis X Sorhiis Aria) or a related hy- brid. See DiPPEL, Handbuch dcr Lauhholzkiinde, III, p. 359. ^LuciEN Daniel, La variation dans la grcffc cf Vhcrcditc des caractercs acquis, Ann. so. nat. bot., 1899, Vlllth scr., Vol. VIII. pp. 1-226 and Plates I-X, and the subsequent publications of the same author. ^ M. W. Beyerinck, Kan. Akad. v. Wctensch., Amsterdam, Nov. 1900. Vegetative Mutations. 627 Dut doubt, cases of such hybrid segregation, and there f«jrc liave no immediate bearing on the question of vegetative mutations. The same is true of the bud-variations of eversporting varieties (see Plate I, Antirrhiiiiiin) which Fig. 142. Rhus typhina. A leaf of an otherwise green blI^h wiiich was almost yellow from a to ^ ; these leaflet^ have grown much smaller (on one side at a). Doom (1880) ; collected bv Mrs. Weber. have already been dealt with at sufficient length. More- over the graded differences between the various branches of a plant belonging to an eversporting variety are not instances of mutations, and, as a rule, do not affect the 628 Validity of the Doctrine of Mutation. hereditary properties of the seeds which they produce; as, for instance, in Chclidoniiun niajiis fiore plcno (p. 336). In the majority of cases a more detailed examina- tion is urgently needed, before the true nature of even the commonest bud-variations can be properly under- stood. This is particularly the case in variegated plants, amongst which every one is familiar with the phenom- enon, on shrubs and trees at anv rate ; but even here the ]>rocess has not yet been exhaustively studied. On the one hand, some of these cases consist of bud-atavism, wh(>le branches of a variegated variet}^ reverting to the normal type of the species in their color as well as in their secondary characters (Fig. 141).^ On the other hand, sometimes halves of leaves become green, or occa- sional branches with usually slightly, but sometimes finely, variegated leaves arise on green individuals (Figs. 142 and 143). On a large tree of Moms nigra in our gar- den the latter phenomenon occurs almost every year. It is not until all these and similar cases have been excluded that bud-variations may be regarded as true cases of vegetative mutations. Even then we should require the proof that the deviating branches will re- produce their type from their seeds, after pure self-fer- tilization. In manv cases, however, this is not possible because the bud-variations in question often bear no seeds, even when they occur regularly, as in Cephalo- fariis pediinculata fasti r/ia fa (p. 109. Fig. 16) and in numerous other conifers, the bud-variations of which have been described by Betssner: as, for instance, in Cryptonicria japonica spiraliter falcata (Fig. 138, p. 619). Even from the i^Teen Dahlia I was, unfortunatelv, unable ^ See above p. in and pp. 272-277. Vegetative Mutatiuns. C)29 to obtain any seed (Fig. 137, p. 61S), l)ccaiise it ilnu- ered too late in the year. I have cultivated this plant, which was descril^ed and figured in the first section of this volume (p. 92), for many years by vegetative meth- ods, because it is perfectly sterile. In the summer of 1902, however, it suddenly began to produce bud-varia- Fig. 143. Carpinus Betulus. At a. a partly variegated leaf on a tree which had otherwise only green leaves, Ililvcr- sum (1887). tions. distributed in considerable numbers over the various main stems; they were apparently independent n{ one another, but seemed to arise in response to the same un- known external influences. The fiowerheads of the ata- vistic branches were of the normal structure of the ordi- nary Dahlias, double, and with carmine red florets, at the tip of each of whicli was a white spot. From this we 630 / \ilidity of the Doctrine of Mutation. may conclude that this f^reen Dahha had arisen from tlie corresponding double-liowered variety. I do not propose to adduce any further instances ; those which I liave given show that varietal characters ma}' chsai)pear in a vegetative way, the original char- acters becoming actixe again. For such a mutation neither the formation of sexual cells nor fertilization is necessary. Therefore the possibility that seed-varia- tions ma}- tiltimately be derived from bud-variations can- not be denied ; 1)ut man}^ more experimental data will have to be collected before a final judgTuent based on a suffi- cient foundation of facts can be given. One of the best methods is that which T have already mentioned, as adopted by Reverixck, of artificially inducing bud-varia- tions by prunuig. III. THE MATERIAL VEHICLES OE Till': HEREDITARY CHARACTERS. § 9. DARWIN'S PANGENESIS. The real meaning of the title of Darwin'.s book. On tJic Origin of Species by Means of Natural Sclecfion, has often been largely misapprehended. In Darwin's mind the emphasis lay on the word "natural." He pleaded a natural origin of species against the accepted super- natural one. The whole object of his work was to show that the genetic relationships of animals and plants may be explained without invoking supernatural causes, and that their explanation by natural means is far more satis- factory and simple. For this conviction lie succeeded in obtaining general credence, and thus laid a broad foun- dation for all future investigation in this spliere. The modern tendency, however, is to sliift the cm- l^hasis on tlie word selection and on the analogy between selection in nature and the artificial production of races in agriculture. In doing so it is often overlooked that half a centurv acio the science of the various forms of varia1)ility, and consequently of selection, was still in its infancy, and that we must not apply our present knowl- edge to the state of opinions which prevailed then. X-i distinction Avas drawn at that time, for instance, between mutability and variability; and il was Darwin who first 632 Vehicles of the Hereditary Characters. attempted in various cases to distinguish between these two types of variation. Even now this contrast does not yet find so clear an expression in the available facts as to insure its immediate recoonition. In Darwin's time manv more obstacles stood in its way, and it is probable that its real signifi- cation did not become manifest to him until after he attempted to deal with the phenomena of heredity in a theoretical way.-^ As is well known, this attempt was made in his pre- liminary hypothesis of "pangenesis" ; it is also known that he attempted to adapt his idea to other theories, prevalent at the time, by a series of subsidiary hypoth- eses which have now become superfluous; and that by doing so he did more harm than good to his theory. For, in combating these secondary hypotheses, most of his critics have overlooked the real value and significance of the main thesis. In my book on Intracellular Pangenesis I liave at- tempted to show how the importance of Darwin's hy- pothesis can only be really appreciated if it is freed of these superfluous adjuncts.^ In this essay I have also endeavored to prove that the germ of the theory reap- pears, in a more or less similar form, in the hypotheses of his successors ; and that in these too, it is usually confused by useless or even erroneous suppositions. My object was to extract this essence and to bring it into as close relation with the available knowledge as was pos- sible without the aid of too many auxiliary hypotheses. It is not now my intention to give a review of tlie \Sce Different Kinds of J'^oriahilify in Darwin and Modern Sci- ence, pp. 66-/4, 1909- ^ IntraceUiilar Pangenesis, translated into English by Prof. C. Stuart Gager, 1910. Darzi'in's Pan(jciicsis. 633 enormous amount of literature which has since accumu- lated on this subject, 1 and with regard to the older the- ories, such as those of Spencer, Nageli and Ukrtwk;. I need do no more than refer to my essay already quoted. My only task is to show that the evidence, brought for- ward in this book for the theory of mutati(jn, affords a strong suport for the principle of pangenesis. All that is necessary to bring the results of observation into line with the doctrine of Pangenesis, is to substitute the idea of internal factors or material vehicles of hereditarv characters for the empirical units of the visible qual- ities.^ This view has been best worked out by Johaxx- sen in the section on the doctrine of pangenesis in his textbook of botany wdiich has recently appeared ; and this fact enables me to deal briefly with the topic.""' • 1 propose to confine myself to a brief exposition of Dak win's conception of pangenesis and to the modification of it which I suggested, without repeating all the obser- vations on the subject which I have recorded in this borik. I shall deal first with the essence of the hypothesis and then with the secondary hypotheses; and shall defer a dis- cussion of the essence of the theory until later. There are two essentially different views relatini,^ to the material vehicles of the hereditary characters of or- ganisms. One view is that of Spencer, according to ^ Full lists of references are given in a large nnmlicr of wnrks of which the following are among the best: C. Keller. I'crcrbun^s- Ichre und Thiercucht. 1895; H. Marliere, Etudes sur riirrcditi'. iS«}5: E. B. Wilson, The Cell in Development and Inheritance. \qoo\ I-ki-- wiRTH, Die Ziichtung der landicirthseliaftlichen Culturf>fianceu, ujoi, etc. ""Ber. d. d. hot. Ges., tqoo. XVTTT. p. S3, -infl ^^tr les unites des caracteres speciftqiics, Revue gcncralc de l)otani(iuc, 1900, XII. p. .257. 'E. Warming and W. Johaknsen. Den alniindeli^e Pofnnik. 4th ed., 1901, pp. 675 fif. It is quite satisfactory to state here that o«lv. We must simply assume that all similar organs or cells are represented hy the same unit. Tlie otherwise hii^hly complex conception of the structure of the idioplasm is thus considerahly simplified. The work of Galton and Brooks has contril)ute(l largely to freeing the theory of pangenesis o\ much use- less hallast, and therefore to exhihitini>' its essence in a much purer light; hut in regard to one important ]hnu\. they still adhere too closely to Darwin's old conception of the theory. This point is the question wliether the organs and the cells themselves are the units which we must think of as being represented in the idioplasm. § 10. INTRACELLULAR PANGENESIS. In contrast to the opinion of the authorities cited in the previous .section, I assume that the units are not the morphological elements, such as the parts of the body and tissues, nor the cells and their visible organs. On the contrary I assume them to be the internrd elementary characters which determine the external feature^ o\ the organism, and which must cooj^erate to build m search for mutations in the field, '"^ because I hoped in tlii-^ way to find facts which would tb.row a more immediate light on the bearers of hereditary characters, and thereby on the theory of heredity in general. The doctrine of pangenesis only touches the kernel of the general theory of heredity and leaves the details to special theories; but experience has taught nie thaf *My belief that tlic transportation of the panpcne;^ is larpjcl\ l)roii.c:ht about by the so-called streaming: of the protoplasm and that this is a normal and general occnrrence has not in the least bee!) shaken by the arguments which have 1ieen urged against it. " Sc the bibliography at the beginning of this volume. ^ T should like to insert here the following little coincideiu-* My IntraccUnlarc Pan (genesis was written during the summer h«'li days, spent near Hilversum in 1888. and the often described localit> of Oenothera Lamarelciaiia was only about ten minute^ walk away. 544 Vehicles of the Hereditary Characters. this kernel is a sufficient basis for experimental investi- cration, and that it is far more likeh^ to lead to the dis- covery of new important facts than the elaborate tissue of hypotheses which have grown up around it. More- over pangenesis is capable of much closer application than the opposite view that each of the units bears the whole of the specific characters. I confidently recommend Dar- win's principle to any one in search of new lines of re- search in this field. In the first place it has led to the proper distinction between the two main types of variability, viz., muta- bility and variability in the restricted sense. ''Finally, we see," says Darwin, ''that on the hypothesis of pan- genesis variability depends on at least two distinct groups of causes."-^ The first group embraces the failure, the over-production and the change in position of particles without their being themselves transformed in the pro- cess. These changes can explain a great deal of fluctu- ating variability. Into the other group fall the changes in the particles themselves producing new types which in multiplying will develop into new characters. Into these categories fall three main types of varia- bility, since tlie first group is obviously a twofold one, embracing in terms of my present view, on the one hand fluctuating variability, and on the other the regressive and degressive mutations. The former may be caused by changes in the number of the pangenes ; the two latter, however, by the "transposition of gemmules and t1ie re- development of those which have long been dormant." Besides these the origin of new forms of pangenes ob- viously corresponds to progressive mutability.- '^Animals and Plants under Domestication, II, 2d cd., 1875, p. 390. ^ See also Intracellular Pangenesis (Engl, ed.), pp. y^, and 214 The Pangcncs. 645 Ninncvical changes of the f^augenes arc therefore the basis of fluctuating variability. Changes in the position of the pangoie in the nucleus lead to retrogressive and degressive mutations, ivhilst to account for progressive mutation zee must assume the for unit ion of new types of pangenes. The facts which have heen descriljcd in iliis work, conform to this hypotliesis so closely that tlicv niav he regarded as proofs of the truth of the princii)le. It seems desirahle to deal further with this point without, however, elahorating" suhsidiary hypotheses. Mendel^s discovery goes far to support the theory of independent bearers of hereditary characters. Their independence stands out more clearly in this case than in any other, Avith the exception of the process of mutation itself. In my first preliminary note on this subject T have pointed out the great importance of his laws in their bearing on the doctrine of pangenesis ; and since that time CoRRENS, Bateson, Cuenot and many other auth(jrs have more or less subscribed to this view. Cu exot. wlio. with Bateson, was the first to demonstrate the applica- l)ility of Mendel's laws to the animal kingdom, calls the units wliich are concerned in these crosses '^particules representatives.^''^ Whether these factors themselves are the pangenes of the nuclear tlu'eads, or whether these factors are composed of groups of similar units, is a highlv important question which, however, can only be decided l)v means of future ex]U'riments. For, as Bateson j^oints out. it is still iic^ssiblc th:it the constant Mendelian Inl^rid races are not absohitely ])ure with regard to their individual characters: that is 'T.. CuKNOT. La In'i dr Mendel cl rin'rciiiti' dc la f^iginnttatiui rhc: Irs soitris. Arch. xool. cxpcrim. ct fjonoralc. T002. No. 2. 040 / 'chicles of the Hereditary Characters. h) say, in the formation of the gcrni-cclls the dominant and the recessive characters ma)' perhaps not separate fully, leaving, either always or only exceptionally, a trace of the dominant character in the germ-cell which has the recessive one, and vice versa. This trace mav then be latent during the course of a number of generations, until at some later moment, and for some unknown reason, atavistic phenomena in such hybrid races awaken the memory of the original cross. Exi)erience does not as yet support this view; it wants a much larger number of generations before a final verdict may l3e expressed. But it is obviotis that an atavism of this kind, if it occurred, would suggest that the IMendelian units were of a com- pound nature. These Mendelian factors maintain their independence during vegetative life and fertilization. According to previous conclusions, such crosses are always concerned with elementary characters which occur in a different condition in the one parent from that in which they occur in the other. There are mainly four distinct conditions : the active and the latent, the semi-active and the semi- latent. Their vehicles do not only separate in the forma- tion of the sexual cells, but occasionallv also in the vepe- tative life of the plant, as is demonstrated by the occur- rence of so-called bud-variations in hybrids.^ They are therefore in such cases only loosely associated and not blended together. Fluctuating variability is due to variation in the num- ber of equix'alent pangenes : this explains wh\' it is onlv linear fVol. I, p. 118) and why it is manifested in two directions only. It goes in the plus direction bv a multi- plication and in the minus direction by a diminution of ' Sec pp. 619-620. The Paiiyciies. 647 their number. Higher nutriticju and favorable e(^n(h- tions of Hfe effect an increase, whereas the opposite cir- cumstances cause a decrease of this number. But the various kinds of pangenes are susceptible to these stimuli, on the one hand in a (hlferent degree, and on the other hand at different periods in the life of tlie ])lant. for ^onie characters are highly variable, others not at all. In the first volume we have pointed out the existence of sus- ceptible periods of variability. They teach us how it is possible that the different characters of organisms may react in different ways to the same external c(^nditions. Correlative variability, in so far as it is not due to a coupling of pangenes by their association in groups, finds its sufficient explanation in this way. The significance of normal fertilization appears in quite a new light when viewed from the standpoint of this conception. The conditions of life aft'ect the several characters in a similar manner thoug^h in a different de- gree ; but they cannot, so far as we can judge at present, combine in the same individual characters, which deviate in opposite directions. The only practical way in which this can be effected is by an exchange of elements, such as happens in fertilization and probably especially at the beginning of the formation of the sexual cells. Tn this way sexual reproduction can unite characters which vary in different degrees and directions, in every possible kind of combination : and it is left to natural selection to de- cide which of these combinations are the best in every individual case. The theory of mutation assumes that the pangenes, or groups of similar pangenes in the idioplasm, mav exist in various conditions and ]^ositions. 1'he normal active condition is that in which they multiply at a definite [K- 648 Vehicles of the Hereditary Characters. riod in the development of the organism and, in part, escape into the protoplasm, there to exercise their func- tions. Diametrically opposite to this is the latent con- dition, for in it this kind of multiplication is possi1)le only to a very limited extent or not at all. In other po- sitions two groups of dissimilar hut homologous pangenes have a mutual effect upon one another which varies ac- cording as the one or the other obtains the mastery. This is seen in the case of the vicariating characters of the half races and eversporting varieties. Here the two ele- ments are affected by external conditions in the same way but in vastly different degrees, the phylogenetically older one being scarcely at all susceptible, while the younger one is highly susceptible. If the latter retires into a latent state, as in the case of half races, the degree of their manifestation, that is of the migration of the material particles, from the nuclei into the protoplasm, is a limited one. If, however, they are in the semi-active condition, as in the case of the eversporting varieties, the result is the extraordinary variability which characterizes these races. The nature of the difference between uni-sexual and Mendelian crosses is now obvious without further dis- cussion. If each element finds its partner during the formation of the sexual cells of a hybrid, exchange takes place as in ordinary fertilization, and the Mendelian crosses become merely a special case of this. But if one or two or several elements do not find partners, the nor- mal process will obviously be disturbed, since the two idioplasms do not fit one another exactly. And on the degree of this disturbance, that is to say on the number of differentiating elements, depend obviously in the first place the fertility of the cross, that is to say the capacity; The Fanycncs. 04') of the hybrid to hve, and in the second place the fcriiliiy of the hybrid itself. If, however, they are fertile, the unpaired characters probably sinii)ly divide in the primary hybrids, at the moment of sexual reproduction, in a vej^e- tative way, and this would explain the constancy of such hybrid races. Progressive mutations are due to the formation of new pangenes. Dissimilar entities arise in the idioplasm instead of only similar ones, and this is the process which we have called pre-mutation. The pre-mulalcd pangenes tend to be inactive at first, either because they do not exist in sufficient numbers or for other reasons. Obviously it is very probable that in different si)ecies similar pangenes may lead to the origin of the same new pangenes ; and this might perhaps explain many phencjni- ena of parallel progressive mutability. Lastly we must suppose that the pangenes, or grou])s of them in each of the conditions referred to, may l)e more closely or more loosely associated with the remain- ing ones. If the association is a close one it will remain the same through all generations, and the species or variety is immutable with regard to the character in question. If the equilibrium is an unstable one, the character in question is mutable; and slight external in- fluences may turn it into a stable c(Mi(lition and thus in- duce the visible mutations such as those of the Ocuothcras. Unfortunately, however, the nature of these inlhuMu-i's is still unknown. The stable condition, which in this way arises out of the mutable one, can be either active or latent. It would be easy to extend this discussion further: suffice it, however, to say that the relation of pangen- esis to new discoveries is evervwhere more or less ol>- 650 Vehicles of the Hereditary Characters, vious, if closely examined. This demonstrates, in my opinion, the truth of the two doctrines of pangenesis and mutation ; and opens an ever wider field for the investigation of hereditary phenomena. IV. GEOLOGICAL PERIODS OF MU'l'A'i 1( JX. § 12. THE PERIODICITY OF PROGRESSIVE MUTATIONS. The essence of the theory of mutation he.s within the narrow hmits of the Linnean collective species and agrees equally well with the theory of descent with modification and with the doctrine of creation. Its special province is the question how those smaller species originate which were supposed in pre-Darwinian times to have arisen by natural laws from the created types, i. e., from the collective species. But the light shed by the new theory extends far \k- yond these narrow limits. Its full importance can better be estimated from a general point of view than by a reconsideration of the facts already given, and the final judgment will probably depend in a larger measure on its applicability to the broad questions of descent, than on the significance of the facts upon which it is based. Therefore it seems desirable to show that the muta- tion theory is really in closer accord with present views regarding the phylogeny of plants and animals, in many and indeed in the most important points, than the pre- valent form of the theory of selection.^ Tn doing so I shall confine myself as much as possible to the oj)inions * See my lecture delivered before the association of Gernian nat- uralists and medical men at Hamburg in September igoo. Pi> ^futa- tinncn und die Mutafionsf^cnodrn hci dcr Rntstchuttii dcr Artcn (Leipsic: Veit & Co., tqotV 652 Geological Periods of Mutation. of tlie best authorities; and shall not propose ?ny new hypotheses, but merely point out the agreement between the doctrine of mutation and the theories which have been ])ut forward by others. I shall be treading new ground and shall therefore be as brief as possible, refer- ring the reader to the literature on the subject for in- formation on special points without dealing with these in detail. I will first discuss the conclusions which may be de- rived from a consideration of the mutation period in Oenothera Lamar ckiana, and shall then attempt to show that these are in perfect harmony with geological and paleontological facts. Starting from the fact that our Oenothera is at pres- ent in a condition of mutability, we naturally ask the question whether this condition has had a beginning or not. If it had, the plant must have had, at some pre- vious time, immutable ancestors; if it had not, all its ancestors, back to the most simple organisms, were as mutable as it is now. The former view agrees with that which was held about tlie middle of the previous century, before the spread of Dar wind's ideas. The general conception was, *Vjue les especes varieraient plus a certaines epoques de leur existence qu'a d'autres."^ This obviously leads, in our special instance, to the supposition of a period of mutation ; and this is exactly the view expressed in the first volume of this book. It leads, further, to assume periodic mutations which have alternated with periods of immutability: for if all the various elementary characters whose accumulation has ultimately led to the origin of ^ H. Lecoo. Geographic hotauique, 1854. See also Alph. de Can- DOLLE, Geographic hotauique raisonnee, II, pp. 1100-1102. The Periodicity of Progressiz'c Mi(tatiu)is. 653 our species, have arisen suddenly, these changes must have been distributed more or less regularly over tiie whole line of ancestors of the Oenothera. \h)\\ many steps are combined into a single period of mutation can- not he determined, and the question is obviously of sec- ondary interest only. The available evidence seems to indicate that only one step in the same direction occurs at one time ; but obviously this does not exclude the possi- bility of periods in which more numerous changes occur. In order to apply the results obtained with our prim- roses to earlier hypothetical periods of mutation, I will repeat the empirical pedigree of the first volume (p. 224), but in a somewhat different form. I will indicate the lateral branches which arise from the main stem in suc- cessive years, that is to say the new species, in the form of radiating groups (Fig. 148). Each group denotes the mutations in a single generation. The main stem contin- ues unchanged and successively produces the individual groups. Together, however, they obviously belong to one and the same period, inasmuch as each of them mainly consists of the same species and in approximately ecjual proportions. In order to compare this period with previous ones the whole figure may be compressed to a single group. This has been done in the upper part of Fig. 14^. The lateral branches do not arise here from a single point, and this is intended to indicate the fact that the figure em- braces a series of generations in which the variations were repeated. As stated above, we will now assume that the ances- tors of our Oenothera have not always been mutable. Therefore our group must have a limit below, and nuist, so to speak, be borne by a stem without lateral brandies. 654 Geological Periods of Mutation. Oe^.La rn. Fig. 148. Pedigree of Ocnotlicra Lamarckiana, exhibiting the yearly origin of new species in my experimental garden in the years 1889-1899. g, O. gigas; a, O. albida; It, O. lata; 11, O. nanella; r, O. nihrincrvis; o, O. oblonga; s, O. sciufillans. The numbers preceding the letters are those in which the species in question arose. The num- bers on the main stem show the extent of the yearly cul- tures. TJic Periodicity of Proyrcssii'c Mutations. 655 XylonrCtuxum Kn^iih Fig. 149. Schematic pedigree of progressive formation of species; based on Ocnotlicra LuDiarihi'ana. The upper group is a reduced form of Fig. 148. and contains the same new species. Onagra is the sub-genus to which Ocnottiera Lainarcluana belongs. Euocnothcra, Ktiriffi*! and Xyloptciiniui are other sulvgenera of Orih>tlii'iii. The two small groups of lateral branches which ha\i- been intercalated are intended to rcjirosent the sexrral intermediate periods of mutation. Tlie figure can be continued downwards in a similar manner. 656 Geological Periods of Mutation. If now we follow this stem downwards, we must ob- viously sooner or later arrive at another mutation period, and of course one of which, although direct observation is no longer possible, so many products remain, that we may conclude with a high degree of probability its simi- larity with the period observed by me. I am referring to the differentiation of the sub-genus Onagra, and of its numerous species such as 0. biennis L., O. muricata L., O. cruciata Nntt, etc. I have already dealt at length in the first volume (p. 440) with this hypothetical period, and therefore may now limit myself to representing this 0;/a^;'a-period in Fig. 148 in the same way as the group above it, which relates to the variations now being pro- duced by Oenothera Lamarchiana. Obviously we may now continue our scheme down- wards. We next reach the sub-genus Enoenothera, many of the species of which are very like those of Onagra, and have, indeed, sometimes been confused with them, as, e. g., 0. odorata with 0. snaz'eolens. From these we attain to the genus Oenothera itself, whilst other sub-genera form lateral branches, of which Kneiffia (Fig. 89, p. 458) and Xyloplenrnm have been selected as examples in Fig. 149. I have so often made reference to the vestiges, left by other past, but relatively recent, periods of mutation^ that I may now confine myself to mentioning the follow- ing: Draha verna, according to Jordan and Rosen (Vol. 1, p. 173 and Fig. 3 on page 22) ; Viola tricolor (Vol. I, p. 23, Fig. 4) according to Wittrock''s researches, Hie- racium, Rnhus, Rosa, Helianthemwn and many other genera with their numerous closely related species are ^ It would appear, from Wasmann's beautiful investigations, that certain beetles (of the genus Dinar da) which Hve in association with ants are at present in a mutable state. Biolog. Centralblatt, XXI, Nos. 22 and 23, Dec. 1901. The Periodicity of Progressive Mutations. 657 instances of such groups. In such cases Standkuss, in conducting his well-known experimental investigations into the relations between closely allied species of insects, uses the expression, "changes like successive exphjsiuns."* Every genus rich in species gives him the impression of an explosion. It looks as if an original species burst into hundreds of forms, the smaller species, among which some survived and constitute the present s])ecies. The genus is obviously only this original or collective s\yt- cies. Our Fig. 149 could be continued further downwards. From the elementary species we came to the collective species, and from these to the sub-genera and genera ; in the same way to the more remote explosions would correspond the sub-families and families and the higher grades of the system. If the whole system were per- fectly known to us, and if the pedigree had the form of an ordinary dichotomous table, each point of division would represent a period of mutation, from which, how- ever, only the selected lateral branches, and not all those which had arisen, would be included in tlie ])icture. So much then for the speculations to which an affirma- tive answer to the question proposed above ( p. 6S2) would lead. In the following section we shall see how naturally these fit in with the results of paleontological investiga- tion ; but we must now discuss what are the results which would follow a negative answer t(^ the same question. Such a negative answer would im])ly the assumption that all the ancestors of our Oenothera, back to the first ^ M. Standfuss. Ext^cyimcnlcUc ::oologischc Studicn. Ncne Denkschriften d. allg. sclnvci/c. Ges. f. cl._ pes. Xatiirw.. iS(>^. p. 2.V Further the articles of tlie same author in The Eutomolojiist. May 1.S05, and in BuU. Soc. cntoinolopqnc dc Francr, iQOr. No. 4. .Mso his Handbuch dcr paUuiyktischcn Grosssclunctfrrlini^r. Zurich. iS. 558 Geological Periods of Mutation. forms of life, have been mutal)le. Let us consider this view in relation to two important results of our investi- gation. In the first place it is oljvious that Oenothera is not the only mutable phuit. According to the re- searches of Bailev and White tomatoes are now almost certainly undergoing such a change, and cocoa-palms, since their introduction into the Indian Archipelago, must almost certainly have passed through such a period. Everywhere in the vegetable kingdom we come across vestiges of periods of mutation; and we should be led to the conclusion that the phylogeny of plants is repre- sented by a richly-branched pedigree in which, down- wards from the mutational groups now living, the lines must always be composed of mutable ancestors ; for the assum])tion that mutability is an uninterrupted process is exactly the hypothesis from which we start. But not all plants and animals are mutable at the present time; on the contrary, mutability is a very rare phenomenon. This circumstance can only be brought into harmony with the theory of the ever mutal)le main lines of the i)edigree, by assuming that they have pro- duced lateral branches in which the capacity for mutation has been lost. That such has often been the case we may confidently infer from the available evidence. Accor- ding to the principles enunciated in the previous chapter, all that is necessary to bring this about, is that the repre- sentative elements be transferred from their unstable into a rigid condition. The whole pedigree would then appear as a freel}' branched system of continuous mutable lines without gaps, and which are everywhere clothed, if I may so express it, by numerous immutable lateral branches. These would then stand in the same relation to the stem T/ic Periodicity of Progressive Mutations. 059 as the short fohage-bearing branches ui uur trees clu lu the long branches which form their crowns. Every genus and every sub-genus would then con- tain at least one mutable species, from which the otiiers have arisen, and this one might either still survive in their midst or have perished. In the former cases, pre- sumably rare, these parent species would agree most closely with the supposed generic tyi)es of Gartnkk which he regards as the central or original forms of the genus, on the ground of their behavior in crosses.^ It is easily seen that the contrast between the two pedigrees, to which an affirmative and a negative answer of our question respectively leads, is not of a very funda- mental kind; and that the two can be reconciled if we regard the periodical mutability of the former and the large number of immutable branches of the latter as the two chief features. Let us now consider the conclusions which the i)aleon- tologist Daniele Rosa has drawn from his extremely important studies on the diminution in variability in con- nection with the appearance and extinction of specie^. - A detailed study of the phylogeny of extinct forms led him to conclude that the prospect of the survival of gen- era and families, and indeed of whole orders, was demon- strably correlated with their richness in forms. Cases like Lingnia which have remained the same with very slight changes from Cambrian times up t(^ the present * Gartner, Basfarderccngung im Pitanzcnrclch, pp. 2;.V25V). ■D. Rosa. La riduzionc progrcssha drlln 7'arinhlliti). «• i sunt ro/y/ynrti coll' cstinzionc cf coll' origiuc dcllc stccic. Turin. i8<)Q. (kt- nian iranslation bv H. Rosstiard. Die (progressive Rcduktioti ■' yanobilitcif uud Hire Bczichungeu auin Aussterbeii und :u drr I sfehiiiig der Arten, Jena. TQ03. C Cattaneo. / limiti delli :••• hilita. 'Rivista di Sc. Riolog.. tcx)0. \'o1. TT. Nos. 1-2. Sec al«io I Cope. 'The T.aw of the Unspcciahzcd," Primary Factors of Organ:. Evolution, Chicago, 1896. 660 Geological Periods of Mutation. day, are extremely rare.^ On the contrary we usually see that the smaller groups sooner or later die out, whilst it is only in those cases in which \ariahility, that is to say the production of new forms, has been most active that the groups continue for longer periods of time. Incapac- ity to vaiy dooms a group to death ; only those who can most easily and quickly adapt themselves to changing conditions of life can survive. Species-forming varialjil- ity is therefore not a universal capacity for variation, but only the result of quite special conditions which may often be absent from certain groups. If we assume that the mutability in the main lines of the pedigree is an uninterrupted condition, and that this power, once lost, cannot be regained, it is clear that every branch of the pedigree, i. e., every larger or smaller group, is doomed to extinction as soon as the mutable species in it become extinct from some cause or another. On the other hand it is easy to see that the more numer- ous the mutable types are, the greater is the species- forming capacity of the whole group and, consequently, the greater its prospect of maintenance throughout geo- logical ages. Without giving a definite expression of opinion, it does not seem to me to be likely that mutability has con- tinued throughout geological times without interruption. Therefore I think it more probable that there has been alternation between mutable and immutable periods. This latter view, moreover, is in agreement with the conclu- sions arrived at by Rosa. * Further instances are given by Huxley. Proceed. Roy. Inst., Ill, p. 151 ; and by Poulton, Brit. Assoc., 1896, Zool Section, Presi- dential Address. For the Foraminifcra see Carpenter^ Introduction to the Study of the Foraniinifera, 1862, p. xi, etc. Iterative Formation of Species. 661 § 13. ITERATIVE EORMATION OE SPECIES. There is a great deal of evidence to show that species arise in groups, and that they originate discontinuously in the geological strata.^ For various groups of animals and plants the exhaustive studies of Koken have shown that this mode of the origin of new forms in the gc(j- logical strata is the usual one.- He calls this phenomenon the iterative formation of species. According to him a persistent species produces ''varieties" which appear in swarms at certain periods ; these periods are sej^arated by more or less long phases of rest. He observed this first among the more ancient gastropods; but cases of the iterative formation of species have been described also amongst the Craniadae and Pectinidae. It does not seem to me to be going too far to argue that the conclusions derived, in the foregoing section, from the actual observation of the process of mutation fit in with these results of paleontological investigation in a perfectly simple and satisfactory way, whilst the old theory of selection can only account for this perio- dicity by the help of special hypotheses. White, who has thorougly investigated these phenomena from a paleonto- logical point of view,^ has recently pointed out the agree- ment of my views with his conclusions.'* Our Fig. 140, (p. 655) could be used as a schematic representation of ^ W. 0. FocKE, Die PHanzenmischlingc, 1881, p. 509. ^ E. Koken, Pal'dontoloiiic nnd Dcsccndcnzlchrc, Jena, TQ02. and the literature cited here. See especially pp. 12-13. See als(i W. !'.. Scott. On Variations and Mutations, Am. Journ. Sc, Vol.. XLVIIi, P- 355- ■''Charles A. White. The Relation of Biology to Geological In- vestigation, Report of the U. S. Nat. IMiis.. 1892. p. 245. * The same. The Saltatory Origin of Species. Bull. Torrcy Bot. Club, Aug. 1902. 662 Geological Periods of Miifafioji. Koken's conception. In each of the several periods the new forms appear in a swarm, whilst the periods them- selves are separated by phases of rest. According to the theory of selection the species themselves should be trans- formed into new ones; but according to the theory of mutation the original species does not disappear, whilst the extremes press forward. In the case of Oenothera Laiuarckiana the main stem continually multiplies with undiminished vigor. Its derivate species have the greatest difficulty in maintaining themselves in competition with it in the natural state. Even so, as Koken points out, paleontology recognizes numerous cases in which the type species persists alongside those to which it has given rise, and it may even sometimes persist after these have dis- appeared. The genetic association of the individual types can be demonstrated by experiment ; but in paleontology con- clusions relating to this point must obviously be based on considerations of a comparative nature. Apart from this, everything seems to be exactly the same. *'The swarms of varieties and species succeed one another like the stories of a house. Similar forms recur bv bein"' produced at various times by the conservative guardians of the race, but not by one giving birth to the other."^ Paleontolog}^ has the great advantage of directly demon- strating the stories which follow one another, as such. Comparative biology, on the other hand, has to infer them from classification, whilst experiment will probably always have to confine itself to a single story. According to the jM'ecedent set by Waagen, the sev- eral forms of a group which follow one another in the course of time, and by means of which a type is gradually * E. KoKEN^ Jahrh. d. k. k. gcol. Rcichsaiuts, [896, p. 40. Tlic Biociuuniic lujiiafiiHi. . (>o3 changed, arc usually dcsignalcd, amongst paleontologisis, as mutations.' The name \arictics is ai)|)lic(l bv tlicm t<> those lorms which li\e side by side at the same lime and constitute tlie rays of a fan or the units of a swarm in our diagram in h'ig. 149. In this sense my Ooiotlicras are related to one another as varieties, hut to the parent form as mutations. In experimental science, however, these |)aleontological terms would prove very incon- venient: and the older meaning of the word "mutation." as it was used by botanists long before Waagkn. is greatly to be preferred. W^hat varieties are. will f«jr a long time remain a topic of discussion.^ § T4. THE BTOCTTROXTC EQLWTION. The characters of organisms are not unlimited in number. However complex the structure of a higher plant or animal may seem, and how^ever much the char- acters which compose them may give the impression of being unlimited, no one will deny that, when more closely examined, their organization will appear, although not simple, at least a great deal simpler than it seemed to l)e at first sight. Cope states that for the 28,000 species of vertebrates there are only a few^ hundred organs on which their \aria- tion and diversity rests. ^ If we examine the dichotomou>^ tables for the identification of species in the most variou*^ groups of animals and plants, we are astounded at the ^ See H. K. Ziegler. Uchcr den drrccififioi Shmd drr Drsi'mdi'iic- Ichre ill dcr Zooloi^ir. Jena, 1Q02: and tlie same in Zool. Cciitralblatt, 1902, Nos. 14-15. "See above § .^. p. ^jS. .^acerkt flefincfl mntations a>; "I'an'i'ti's qui sc fonncnt sous nos ycux." Ann. Sc. nat., 1826. p. 299 ' T. I). Cope, The Priinary luulors of Organic F.voUttion. 1806. 664 Geological Periods of Mutation. small number of characters necessary for such identi- fication. If, in the case of single forms, we look at a diag- nosis of species, genus, family or order, we find only a small series of characters referred to. If we attempt to describe a higher plant as completely as possible, it be- comes difficult to prolong the list for over more than a few hundred characters; and even if we have regard to internal structure,-^ latent characters, and so forth, it is very difficult to attain to thousands of characters. The significance of this difficulty is best illustrated by the fact that such a description of a single form would cover over a hundred pages of print. The structure of our eye is infinitely wonderful ; the series of intermediate stages between it and a simple spot of pigment is immeasurably great; and a period of millions of years would be needed on the theory of selec- tion for the attainment of the present high degree of organization from those first beginnings by means of ordinary variability.^ But Murphy^ Brooks and many others have pointed out that these considerations do not necessitate the conclusion that it must have happened in this way.^ On the contrary, the extraordinarily long time which the theory demands, leads us to suspect that there is some weak point in the argument. It is perhaps here that the theory of mutation, re- garded from a general point of view, manifests its great- est advantages over the prevailing form of the theory of selection. In the first part of the first volume I have attempted to show that it agrees with results of experi- ^ A. Gravis. Rcch. anaf. sur les org. veget. de I'Ui'fica dioica, Mem. sav. etr. Acad. Belee. Vol. XLVII. 1884; and the same author, Rech. anat. et phys. stir le Tradescantia virginica, ibid., 1898. ^ Darwin, Origin of Species, p. 143. ^ W. K. Brooks, Heredity, 1883, 2d. ed., p. 283. The Biochronic liquation. 665 ment far better than tliat theory. We now sec that when appHed to the great problems of hfe it is free from those insuperable difhcnlties, which so many investigators have found to stand in the way of the theory of selec- tion. The theory of selection demands almost unlimited time for the evolution of organisms; for the mutation theory, on the other hand, the time which the physical geologists grant to life, is amply sufficient. Idiis view was first clearly expressed by Brooks, in accordance with Huxley, when he showed that all the difficulties which beset the theory of selection and which, according to many investigators, needed 2,500,000,000 years for the whole process of evolution, would disappear if we assume relatively sudden and discontinuous changes to take place from time to time.-^ The most distinguished investigators demand a period of about 24 million years, to cover the duration of life on the earth. If the ancestors of our Oenothera La- inarcklana have produced, once in ever}^ 4000 years, a mu- tation which made them richer by a single character, our plant would now be composed of 6000 such characters, a number far higher than comparative and systematic science can by any means accumulate in its description. This rough calculation shows at any rate that the demands made by the theory of mutation are not so exor- bitant as those made by that of selection. Neither the number of mutation periods passed through, nor that of the characters acquired in them, is beyond our powers of comprehension. On the contrary the phenomena viewed from this standpoint are such that they indicate the possibility of a much closer investigation. ^W. K. Brooks, loc. at., p. 286. 666 Geological Periods of Mutafioii. Let us now proceed to consider the relation between the degree of organization and the speed of the evohition from a more general point of view. For this purpose I shall deal with the several factors as briefly as possible, and propose to begin with biological time. Many investigators have attempted to reach an ap- proximate estimation of biological time, i. e., the dura- tion of life on the earth. Proceeding on entirely different lines, the best of them have arrived at results which aii'ree in a most remarkable wav. From this fact we may infer that the calculations, wdiich from their very nature must be more or less vague, probably represent a fairly close approximation to the truth. I take the following,^ partly from Lord Kelvin's famous researches, and partly from the clear exposition given by W. J. Sollas in his address as President of the geological section of the British Association in the meet- ing of 1900; and further from the recent investigations of Dubois. Lord Kelvin based his first calculations on the in- crease in temperature in the successive depths of a mine.^ This increase, however, has been shown by more recent investigations to vary considerably. The older deter- minations gave from 25 to 37, or sometimes as much as 50 meters for each degree Centigrade. In the neighbor- hood of the North American lakes, however, in a shaft of 1396 meters, an increase of 1° C. per 122 meters has ^ An exhaustive review of the subject can be found in Album der Natuur, Sept. 1901 ; and the -natter is also dealt with by H. Charlton Bastian, Studies on H erogenesis, London, 1901, pp. i-x. See also Nature, Sept. 1900 and Revue scientifique, April 1901. ^ Sir William Thomson (afterwards Lord Kelvin), The Secu- lar Cooling of the Earth, Transact. Roy. Soc. Edinburgh, 1862, Vol. XXIIL TJic Biochronic llquatioi. 667 been observed, and near Przil)rani in Bohemia, an in- crease of 1° C. for every 09 meters. Inasmuch as these two latter records have been made in districts which are further removed from local sources of special high temperature than the older mines, we must conclude that the earth has already cooled down much further than was previously thought, and that the pericxl of 20 to 40 million years arrived at by Lord Kelvin, is ])y no means too high an estimate. George Darwin calculates that the moon separated off from the earth at least 56 million years ago, and Geikie put as the maximum for the existence of the earth's crust, a hundred million years. The general view is that the formation of the sea occurred fairly soon, geologically speaking, after the formation of the crust. and that no great period of time was necessary for a cooling of the water, sufficient to render life possible. Further data for similar calculations are furnished by the action of rivers. These carry certain dissolved salts to the sea. From the mean proportion of sodium chloride wdiich they contain and from the total volume of water which is poured into the sea every year by all of them, we can calculate how much the saline contents of the sea must increase from this cause. The total amount of dissolved salts in the ocean can also be cal- culated and we can then estimate the number of years necessary for the accumulation (^f this quantity. From these data Joly calculated the age of rivers to be *^'^ nn'llion years; but it is highly probable that the con- tinents were originally far richer in salt than now. and that the rivers have more or less exhausted them, that is that they carried more salt to the sea in former times than they do now. Applying this qualificatic^n. Som..-\s 668 Geological Periods of Mutation. has reduced Joly's result to fifty million years at the most. ^ Eugene Dubois has made use of the calcareous con- tents of rivers as the starting-point of his calculations.^ He starts from the fact that carbonic acid is the source of plant food, and that the process of assimilation is the only one on this earth by which oxygen arises on a large scale. His arguments led him to conclude that the total amount of oxygen in the atmosphere has become free in this way. Now, carbonic acid is contributed to the at- mosphere by the action of volcanoes. Once arrived here, it is partly decomposed by plants, and partly itself acts on rocks, and especially in combination with lime and magnesia forms salts which are washed out by the rain and carried by the rivers to the sea. Here, however, these salts are again laid down in coral banks, shells, and so forth, and in this way arise the enormous calcare- ous strata wdiich constitute so large a portion of the hard crust of the earth. The volume of these layers can be approximately calculated, and the figure thus obtained, when divided by the annual contribution, gives some idea of the duration of the whole process. In basing his cal- culation on the chalk only, Dubois arrives at an estimate of 45 million years; but if magnesia is included as well, obviously a much smaller figure must be arrived at, viz., 36 million years. I have still to mention briefly two furthc^r methods of arriving at this result. Helmholtz found that the ^ For a further discussion of these calculations see E. Dubois, Kon. Akad. v. Wet. Amsterdam, Jan. 1902, p. 503. ^ E. Dubois, ibid., p. 495, and also loc. cit., June and August, 1900. The same author, Over den Kringloop der stof op aarde. Ley- den. 1899; and Over den ouderdom der aarde. Kon. Ned. Aardryksk. Genootsch., 1900. Tlic Biochroiiic pAiuatioii. 669 snn can have shone fur (jnl\' ahoul 2U niilhon }ears with approximately the same ener^^^y as tliat with whicli it shines now; and since this is the hrst C(jnchtion of hfe on the earth, we must assume that its (hirati(jn has Ijeen about the same as this period. The most authoritative estimate for the total thickness of the geological strata, and of the s])ce(l with which they have been laid down, is that of 80 kilometers, laid down at a rate of 30 centi- meters per century, an.d this leads to an estimate of 26 million years for the whole period. Therefore, about 20 to 40 million years is the j^eriod of the duration of life u])on the earth ; and Lord Kkiain, wdio a few years ago sul)jecte(l the data, on which this estimate is based, to a critical reconsideration, came to the conclusion that the duration (j\ life on the earth may provisionally be put at about 24 million years. ^ We will therefore now ado])t this lioure as a basis for our further arguments. The second question is this: How quickly have the individual periods of mutation followed on one another? We have very few data which enable us to arrive at any conclusion on this point. As is well known, the i)arts of plants which have been preserved in the sepulchers of the pyramids along with the mummies, and in other monuments of the same period, such as flowers, leaves, fruits, cereals, straw and weeds of the fields, prove tlie great antiquity of many species which are still existing. Numerous species are no doubt older than the pyramids, and have therefore remained unchanged for a ])erii»d ^A at least 4000 years. The remains of lake dwelling'^. - ^ See the review in the Phil Mag., Jan. i!^. ^Osw. PTeer. Die Pflanzcn dcr Pfalilbautni. Sdnvciz. Natitrf. Gesellsch.. i866. No. LXVIIT. with one plate: also C Schrotfr and J. Heer, Lchcnshild von Osn'ald Ilccr, Zurich. 18S5. 670 Geological Periods of Mutation. the drawings on Roman coins, and many otlicr facts of the same kind conchice to similar estimates.' On the other hand, the rarity of mutable plants in comparison with immntal)le ones, and also the small number of genera and other groups rich in species, as compared with the ordinary types of the European and American Roras, lead bv an entirely different chain of arqument to con- elusions which mainly support those reached above. We may therefore assume as a provisional conclu- sion that a few thousand }-ears elapse on tlie average between two successive periods of mutation. Of course, it is extremely probable that the speed of the process of evolution has not at all times been the same. On the one hand we must suppose that at first it was more rapid than it is at present.- On the other hand there must have been ])eriods of greater mutability and periods of relative stagnation, ]:)()ssibly m the whole animal and vege- table kingdom, but certainly in special lines of descent owing to which some have reached a high degree of differentiation in the same period of time in which the progress in other lines has been relatively small. 1die Cambrian period divides biological time nito two ap- proximately e(|ual parts, no fossil remains from pre- Cambrian times are known In Cambrian times members of all the more important groups of invertebrates sud- denly a])pear, and among plants the :\lgae are richl\' represented. It almost seems that only th(^se lines of descent which have made their evolution on the cdu- tinents have begun in post-Cambrian times. In a very attractive essay Brooks has shown how ^ Instances of the ages of certain plants are given by De Can- DOLLE, Geographic hotaniquc, II, 1063-1068, 1086 etc. "On this point see my lectnre cited above, pp. 52-57- The Biocliroinc Equation. ()7\ this trnnsformaiion from ilic non-fossiliforons in llie fossiliferous pcritxl nia\- 1)C' inia^incd l<» lia\e taken place' Til the heginnin^" life was chietly conl'inecl to the upper levels of the sea; and extended to only those depths to wliich the rays of the sun penetrated, thus supplyini; the source of energ\' for the nutrition ^^\ the smaller Ali^'ae. These latter were almost the only source of nourishment for the animals which there f(^re had not left this region yet; consequentl\' they were nn^stly small and of delicate structure, and without sucli ])arts as could hecome fossil. Afterwards it was the discoxery, as Brooks call^ it. of the possihility of life on the gloomy hottom of the sea, on the dead remains of the swimming organisms sink- ing there, which extended the distrihutic^n (»f life and furnished a new and most variable abode for living be- ings. Thus was started the rai)id and abundant evolution in the numerous directions which now constitute the main lines of organic descent. Besides this period of rapid evolution. Brooks, to- «'ether with other writers, assumes that there ha\e been other S]:)ecial periods of great variability; for instance at the time when land-animals and aeain when man originated {loc. cif., p. 217). The distribution of fossils also indi- cates the existence of ])eri(^ds in which the forniatiou of species has been esjxx^ially ra])id.- 1die cjuestion arises: Were the individual mutations greater in such ]")eriods, (tr did they onl\' follow more rapidly upon one another?"' This f|uesti(^n is one oi com|)arative anatoni}' and of systematic science. Some MV. K. Brooks, The Foundations of Zoology, i^y). pp. 215-2.^7. 'Die Mulotioncn mid }fi(lationspcn'odrn, jv 5^1; also W . K. Brooks, Foundations of Zoohx^y. \\. jiS; (^11 \> A. Wihtk, 'ihc Rc- lation of Biology, p. 296, etc. ■'' E. KoKEX. Paldontoh^gic und Dcsrcndcn^U-h' <• '"-i' " >o. 672 Geological Periods of Mutation investigators hold one of these views, others the otlier. If we assume that the individual mutations in such pe- riods were changes of a greater amplitude, they might be designated by a special name, for instance by the one suggested by Schneider, the "descenses."^ There is no fundamental difference between these and mutations, and the same changes may, according to Schneider, in some lines attain to the magnitude of descenses, whilst in others they may remain of merely subordinate impor- tance. At present, however, I am concerned merely with an approximate and average estimate, and the knowledge at our disposal suggests that an estimate of a few thousand years fairly closely represents the truth. A third question relates to the number of elementary characters of which one of the higher animals or plants is composed. According to the theory of selection an almost unlimited number of complications would be pos- sible. In my Intracellular Pangenesis I have shown that, quite on the contrary, the number in question cannot be so inordinately great; for we repeatedly see the same characters recurring in different organisms, many of them in systematic groups widely remote from one an- other, as for instance in the higher plants and the higher animals. I need only mention the close similarity be- tween the chemical processes involved in digestion in the stomach and in the leaves of insectivorous plants. Ten- drils and climbing plants, submerged or swimming water- plants, heterostylic and cleistogamous flowers, parasitism and saprophytism and numerous other instances could be adduced. Everywhere nature has built up the whole *K. C. ScHNETPER. Lchrbuch dcr vcrgleichenden Anatomie, Jena 1902, pp. 2-14. 24«. TJie Biochronic Equation. 673 extraordinary richness of its forms, from a relatively small number of elementary units, for almost evcr\' indi- vidual character is found in numerous sj)ecies, and it is to their different grouping and their combination with the rarer factors that the extraordinary diversity of liv- ing forms is due.^ As we can easily see, this view effects a considerable simplification of the problem. ^lany authors have ex- pressed their agreement with it, and only last year Schneider stated his opinion clearly enough, when he said that the number of histological characters is by no means a very large one.^ The question is, however, how many elementary char- acters an angiosperm or a higher animal posses,ses, on the average. In the former case I have attempted to draw up lists of characters. Every such list consists of tw^o parts. The first half embodies the characters which had been acquired up to the time when the sys- tematic group, to which the plant belongs, originated, and this part is therefore the same for every species wnthin the group. The second half contains the later characters, viz., those of the phylum and orders down to the species and varieties. In drawing uj) such lists, it is easy to reach the number of a few hundred characters: but then the task becomes more arduous, and finally in- superable difficulties are encountered. But it is evident that even a complete list would scarcely embrace more than a few^ thousand characters for any single plant. Our conclusions may therefore be summarized in the follown'ng theses : ^ ItifracelluJarc Pangcucsis (Gcr. c(\.) , p. 7: Englisli tratislntion by Prof. C. Stuart Gager, 1910, p. 8. ^ Loc. c'lf.. p. 24^. 674 Geological Periods of Mutation. 1. The number of elementary characters of a higher plant, that is to say, the number of mutations through which its ancestors have passed from the beginning, is probably not more than a few thousand. 2. The a\'erage intervals of time between two suc- cessive periods of mutation are similarly to ])e estimated at a few thousand years. 3. From this we may conclude that a period of some millions of years is sufficient for the whole development of the animal and vegetable kingdom ; or, in other words, 4. The doctrine of mutation does not demand a longer period for the duration of life than that which has been given by Lord Kelvin, viz., 24 million years. These theses may be most simply summarized in the statement that the product of the number of elementary characters of an organism, and of the mean interval of time between two successive mutations of its ancestors, is equal to the extent of biological time.^ If we call the former magnitude M (the number of mutations), the length of the intervals L and biological time BT, we have the expression X L = BT. I have called this the biochronic equation.^ It will, I hope, help to demonstrate the importance of the doc- trine of the elementary units of organisms, and thus bring this doctrine prominently before the eyes of the general reader, as well as of the trained investigator. This is my main object in enunciating it. ' The mutations referred to in these paragraphs are of course progressive mutations. 'Die Mutationcn und die Mutafioiispcrioden, p. 63. INDEX. Abbado, 595. Abbink-Spaink, 572. Abies c.vcclsa, fasciatcd, 492. Abut Hon, 30. Acacia coniigcra, 311; diversi- folia, 23; verticillata, 310. Acer Pscudo-Platanus, tetraco- tyls, 360. Achillea Millefolium, 35; rosea, 321. Adaptations, explanation of, 606. Aesculus Hippocastanum, 201, 225, 370. Affinity, sexual, 592. Agave viz'ipara, 23, Agrosfeinma coronaria bicolor, 62, 85 ; Githago, 15, 501 ; G. nicaeensis, 84; G. pallida, 65. Aloe verrucosa, 70. Alpine plants, 59. Amarantus speciosus, 361 ; trico- tyls, 398; tri-radiate, 497. Amphi-syncotyly, 457. Aiiagallis arvensis coerulca, 84; phoenicea coerulca, 621. Analysis of organisms, 567. Anemone coronaria plena, 13. Anthemis nobilis, 93. Antliyllis Vulneraria, 59. AntirrJiinum majus, 289, 345, 460 ; peloric, 224; striatum, 120; terminal leaves of, 376; trico- tyls, 432. Aquilegia, 30; chrysantlia, 83. Arabis alpina, 274; variegated, 287. Arnica monta)ia, 272. Arum macnlatum inunaculatum, 62. A run do donax, 268. Artemisia Absynthium, fasciatcd, 507. ASCHERSON^ 95. Asperula azurea setosa, tricotyls, 358. _ Aspidistra elatior, 268, Aster Tripolium, 35, 498; annual, 299; fasciatcd, 512. Atavism, 44, 71, 104; by bud- variation, no, 625; mutational, 109 ; phylogenetic, 107 ; physio- logical, 107; vegetative. 619. Atavists, 514; offspring of, 561; significance of, 554. Atropa Belladonna lutca, 63,606. Aurca forms, 2S2. Bailey, 102, 615. Ballota nigra, 284. Bananas, red, 112. Barb area vulgaris variegata, 2S>Z. Batesox, 8, 645. Beet, annual, 291 ; sugar, t,}^x Begonia Scdeni. t>22\ semperHo- rens, 35, 321. Beissner, 106. 676 Index. 1 Belli, 589. Beta patida, 604; vulgaris, 60; vulgaris saccharifera, 636. Bclula alba, 112. Beyerixk, 626. Biastrepsis, 535. Bidcns grandiiiora, 35, 195; ^''^*- partita, 78. Biennial plants, 291. Biochronic equation, 663. Biolog}-, systematic, 567. BiscutcUa laevigata glabra, 62. Blaring HEM J no. Bluebottle. See Centaurea Cya- nus. Bochmeria biloba, 69. Bonnier, 59; and Flot, 636. Borradaille, 591, 606. Boskoop, 91. Brassica Nap us 0 lei f era, 298. Braun, 112, 326, 531. Brien, on beets, 294. Brooks, 670. Bruyning, 335. Buds on leaves, 70. Bud-variation, in, 122, 131, 138, 154, 617; on variegated plants, 273- Burbank, 594. Burck, 612, 597. BURKILL, 330. Cactus Dahlia, 16. Calceolaria, 225 ; peloric, z^Z- Caltha palustris, 22, 28. Camellia japonica, 22. Campanula Persicifolia alba, 83; pyramidalis alba, 83; rotundi- folia, 33, 310. Cannabis sativa, 359; tricotyls, 426. Capsella Bursa Pastoris apetala, 97; Heegeri, 96, 331. Car Una acaulis, 59. Carlson, 605. Carnation, wheat-ear, 92. Carpinus Betulus, 629. Carriere, II, 57, III. Caruel, 605. Caspary, 70, 506. Castanea vesca, 572; variegata, 274. Casuarina quadrivalvis, twisted, 539- Catacorolla, I5- Catananche coerulea alba, 84. Cattaneo, 609. Caulescens, 59. Celakowsky, 28. Cclosia cristata, 33, 337, 489> 497» 517; variegata, 116. Centaurea Cyanus, 117, 330. Ccntranthus macrosiphon, 460, 458. Cephalotaxus pedunculata, 109. Cereals, 335. Characters, antagonistic, 7; be- ginnings of, 611; hereditary, 567; latent, 18, 148; semi- latent, 19; specific, 588; use- less, 588; varietal, 588; vicari- ating, 64S. Chelidonium majiis, double, 324; laciniatuin, 86; latipetalum,S6. Chenopodium album, tricotyls, 386. Chlorotic branches, 281. Chromosomes, 616. Chrysanthemum coronartum, 82, 85. 195; C.album,S4; inodorum, 161, 284; inodorum plcnissi- mum, 184; ostrich-feather, 16; Parthenium, 270; segetum,i()\, 289. Citrus hybrids, 621. Clarkia pulchella, 144, 289; car- nea, 85 ; tricotyls, 429. Index 677 Clover, crimson, 229. Cochlear ia Armovacca variegata, 278. Cockayne, 605. Cockscomb, S^, 517. Coffca arabica, terminal leaf of, ?>77- Combs, 494. Conn, 608. Convolvulus tricolor, 120. Cope, 663. Coreo/^sis tinctoria, 15, 82. Coriandruin sativum with pitcher, 465- Corn marigold, 161. Correlation of anomalies, 234. CoRRENs, 591. Corylus Avcllana, 112. Cotton, 30. Crepis biennis, fasciated, 509. Crosses, fertility of, 648; recip- rocal, 597; types of, 576; uni- sexual, 577. Crossing, 16. Cryptomeria japonica nionstrosa, 495 ; japonica spiralitcr fal- cata, 619. Cucuniis sativus, 70. CuENOT, 645. Curve, dimorphic, 165 ; many- peaked, 523. Cyclamen pcrsicum, 22. Cynips Kollari, 269. Cynoglossum officinale bicolor,62. Cypripedium caudatum, 220. Cytisus Adami, 622; Laburnum, ■225. Dahlia, 116; cactus, 16; green. 91; striata nana, 82; variabilis. 458; variabilis Ustulosa, 100: variabilis viridiflora, 90. Daniel, 626. Daphne Mczcreum album. 63. Darwin, George, 667. Datura Stramonium X D. laevis, (>20. Daucus Carota, annual, 299. Daveni'OKT, 8. De Candolle, Ali'honse, ^2, 61, 589. De Candolle, Casimik, 69. Degressive, 71 ; mutations, 575. Delage, 615. Delphinium, 113. Delpino, 66, 558. Dianthus barbatus, 285; barba- tus torsus, 550; Caryophyllus spicatus, 92. Digitalis lutea, 497; parviAora, 83 ; purpurea monstrosa, 222. Dihybrids, 586. DiNGLER, 495, Dipsacus, fullonum, 562; lacinia- tus,S4i; sylvestris annual, 2gs; sylvestris torsus, 529. Disco idea, 79. Double flowerheads, 194. Dounet-Adanson. 621. Dracoccphalum moldavicum,T,6(), 386; speciosum, 368. Driesch, 642. Dubois, 668. Duration of life, 666. iilection. 610. Elementary species, 65. Llements de I'espccc, 61. Elite races, 610. Enipetrum nigrut)!, 63. Ensink, 550. Epilobium hirsutum, ^2^. Equation, biochronic, 6(»3. lujuisetuin Telmateja. twisted. 538. Ericaceae, 95. 678 Index. Erigcron bcUidiflonis, 498. Ernst, 94. Erodiitin cicutarium album. S4. Eucah'tius Globulus, 311. Euphorbia cxigua, 60; ipecacu- anha, 605. Euthymorphose, 605. Eversportiiig variety, 21. Ez'ouytiius japonica, 504. Explosions, 657. I'agus sylratica, 370; syiicotyls, 462. Fasciated growing point, 493. Fasciation, 463 ; in cvcrsporting varieties, 508: in half races. 502; plane of, 518; radiate, 497 ; ring, 496. Ferns, crested. 337. Fertilization, 616. Picus rcligiosa, 18. Flax, 85. Flecked leaves, 267. r^LOT, 636. Flowers, double. 195. Fluctuating variability, 645. FocKE, 596, 621. Forma alpcslris, 59; gcuuiiut, 60. Formation of species, 661 ; de- gressive, 71. P'orms, derived, 64 ; homononi- ous, 64. I'rumcutum, 594. Galcobdolon lutcum, 226. Galium Aparinc, 537; twisted. 531 ; verum, 537. Gallesio, 614. Galls, variegated, 269. Garjeanne, 31. Gartner, 582. Geikie, 667. Genista Gcnnanicaj 62. Gcntiana punctata concolor, 62. Geological periods, 651. Geranium mollc fasciatnm, 522; pra tense, 119. Gerassimow, 642. Gesnera Geroltiana, 2>77- Geum intermedium, 635 ; urba- num, 280; variegated, 287. GleditscJiia sinensis incrmis, 10 1. Gloxinia superba, 15, 22. Godetia amoena, 84. Goebel, 26, 71, 92, ]o6. Goethe, 588. Gold-green variety, 270. Gooseberry, 63. Gravis, 664. Groombridge, 116. Gymnospernis, 495. Gypsophila paiiiculata, 553. Half race, 21 ; twisted, 541. Hansemann, 642. Harshberger, 605. Hedera Helix variegata, 284. Heeger, 96. Heinricher, 28, 107. Heinsius, 166, 285. Helianthenium, 622. Ilelianthus aiinuus syncotylcus, 466 ; tuberosus, 505 ; variegated, 287. U cliclirysum bracteafum, 115; tricotyls, 430. Helmholtz, 668. Heh^'ingia ruscifiora, 69. Hemi-syncotyly, 457. Hemi-syncotylous race, 476. Hemi-tetracotyl, 346. Hemi-tricotyl, 346, 359. Herbert, 593. Hereditary coefficient, 545. Hesperis matronalis, 136. Heterogenic development, 603. Index 679 Heuze, 298. Hibiscus inosclicutos, 605. Hieracium iimbcUatum, 498. HiLDEBRAND, 83. Hilversum, 643. Hoffmann, 76. hofmeister, i4, 83, 201. HOLMBOE, 81. Hornmeal, 453. Hortcnsia, 112. hubrecht, 604. Huxley, 665. Hyacinthus oriciitalis, 70. Hybridization, 72 ; in twisting, 562. Hybrids, generic, 593. Hyoscyamus pallidus, 85. Hypericum perforatum, 2>Z- Hypocotylous buds, 70. Hyssopus oMcinalis albus, 84. Idioplasma, 634. Impatiens balsami, 115. Inermis,, 62. Instinct, 61 1. Intermediate races. 7, 25. Iris pallida abaria. 107; Pscuda- corus, 82; xiphioides, 115. johannsen, 633. Jordan, 590. Kassowitz, 615. Keller, 633. Kelvin, 666. Kcrria japonica, 112; varicgata, 274. KiCKX on pitchers, z^t,. Klebahn. 531. KOKEN, 661. Kolliker, 603. Korschinskv^ 600. Krasan, 58. Krelage, 198. Kuyper, 610. Lager H EI .M. 498. Lamium album maculalum, 226; variegated, 287. Larkspurs. 1 13. Latency, 66. Latent characters, 19. Laurent, 605. Lauterborn, 606. Lavandula Spica, 60. Leaves, pehate, 69; split. 556; terminal, ^77 ; variegated, 265. Lecoq, 652. Lemoine, 16. Le Monnier, 562. Lenecek, 32. Lconurus Cardiaca, 22^. Lilium candidutn plenum, 8g. Lime-tree, 32. Limosella aquatica, 59. Linaria z'ulgaris, 31, 289; peloria, 201. LiNDEMUTH. 625. LiNDLEV, 61. Linear variability. 609. LiNN.XEUS. 60. Linum usitatissimu)n albutn. 84 Lobelia syphilitica, 84. Lolium perennc ramosum. },2. LuDWiG, 8, 167. Lunaria biennis, variegated. 284 Lupinus arboreus, 605; luteus 22s ; twisted. 322. Lychnis chalcedonica alba. 84. dioica, 581 ; resperlina. «J7. Lynch. S2. Lysimachia -.•ul}:ans. 312. Mac Dougal. 601. Mac Fari.ane. 577. 605, 635. >Liddcr. 493. 680 hidex. Madia clcgans, 85. Magnolia obovata, pitchers, 27, oMakliere, 633. IMaterial vehicles, 631. Matricaria Chaiiioinilla discoidca, 81 ; ilorc plcnissinio, 187. Mayer, 600. Mcdicago hip 11 Una, 232. Mclampynini pratcnsc\, 225; tct- racotyls, 375. Mclilotus cocrulca monophylla, ;Mendel, 576, 645. Mentha aquatica, 220. Mcrcurialis annua, 460, 572; spi- ral torsion, 464; syncotyl, 463; tricotyls, 428. ]Middle race. 21. Mimuhis, 612. ]\IoLL, 541. Monocotyledons. 66. Monohybrids, 585. jMorgax, 604. ]\IORREN, 320. MiJLLER, Fritz, 30. MULLER, H., 82. MUNTING, 187. MURR, 81. Muscari comosuni plumosum,6\^- Mutation, degressive, 569; period, 652; progressive, 569; retro- gressive, 569; vegetative, 619. Myosotis alpcstris, 86; alpcstris conipactaayi', azorica J'ictoria. 330. Myosurus miniinus, 330. Nageli, 578. Naudin, 620. Nf/?/rr dc Bronrau.w 625. Neo-Lamarckism, 601. Nestler, 493. Nicotunia, 594. NiLSSON, 604. Nitclla syncarpa, 94. Nitrates, manuring with, 453. Noll, 605, 612. Nutrition, increased, 307. Oats, sterile, 612. Oenothera Bertcriana, tricotyls, 415; glauca, tricotyls, 454,458; hirtella, 346; hirtella tricotyls, 423 ; Lamarckiana, sectorial variegation, 285 ; Lamarckiana, variegated, 273, 285; rubriner- vis, tricotyls, 384; nibrincrvis, variegated, 285. Oil plants, 298. 6'//(rcr;-(7-period, 656. Origin, polyphyletic, 233. Orobanchc Galii. 255. Pangenesis of Darwin, 631. Pangenes, 641, 643; groups of. 647; new, 649; new types of. 645. Papaver Argeuwne, 30; coai- mutatum, Z3, 243 ; commutahim poJyccphalum, 575; nudicaulc, 115; nudicaule auranfiacum, 200; Rhocas, 289; Rhocas, tri- cotyls, 358, 435; riipifragum, yellow seedlings, 289; somni- fcruni Danebrog, 85; somni- feniin polyccphahun, 14. Paul, William, 12. Pearsox, 8. Pedicularis pahistris, 507. Pedigree, 653. Pelargonium, conale, green. 92. Peloria anectaria, 203. Pelorias, heritable, 220. Penstcmon gentianoides, 359. Pentacotyl, 346, 357. Pexzig, 230. Index. 681 Periodicity, 44, 323. 651. Periods, susceptible, O47. Petaloniania, 92, 243. Petalomanous types, 7. Petunia, 338; double, 200. Peykitsch, 225. PJiaccUa tanacctifolia, tricotyh, 436. Phascolus cocciiicHS, 293 ; luiia- fus, 605; miiUifloyus, 70, 293, 501. Phlox Drummondi alba, 84. Phosphates, manuring with, 453. Phylogeny, 651. Picris hicracioidcs, 458. Pinus Abies aclada, 63, 93. Pnius syk'cstn's, 327. Pitchers, 18, 148, 464. Phmfaf^o lanccolata ramosa, 148; lanccolata, split ears, 506; ma- jor f. bractcata, 32 ; major ro- sea, 33. Plate, 602, 608. Poa alpina vivipara, 23. Podoearpiis Koraiana, 1 10. Polemonium disseetum album, 84. Polygonum Convolvulus, trico- tyls, 389; tri-syncotyls. 461 ; Fagofyyrum, 289. Polyhybrids, 586. Potato seeds, 309. Potent ilia anserina,3iS> ; arena ria. Pkain, 18. Pkehn, 83. Premutation, 571, 649. Primula sinensis, 22. Progressive mutations, 576. Proskowetz. von, 604. Prunus, 605. Pyrethrum Partheniu\n, aureum, 7; roseuni, 199. Quereus sessiliflora albo-varie- gala, (}37. Raatz, 606. Races, balanced, 8; half, 574; in- constant, 574; intermediate, 8. 574: non-isolablc, 227; spirally twisted. 543; thoroughbred, 4JJ. Katiiou'ulus aeonitifolius, 59; ar- ris, 93; acris petalomana. 7; arvensis, 62; arz'ensis tnerniis, 98; aurieomus, 32; bulbosus, fasciated, 490; bulbosus scmi- plenus, 243. Raphanus Raphanistrum, 15; co- tyl-pitcher, 460. Red berries, 63. Reixke, 106. Reseda odorata, 13. Retinospora, 106. Retrogressive, 576: mutatioiT^. 645- Reversions, iii. Rhus typhina. 627. Ribes Gordonianuni. 595. RiMPAU, 94, 292. Robinia Pseud-Aeaeia, 62. Rosa. 609, 659. Rubia tinetorum, 493; spiral, 540 Rubus frutieosus laeiniatus. 640; variegated. 275. Rye, perennial. 294: split cars of, 489: sterile. 94. Saceret, 621, 663. Sagitlaria sagitti folia. 310. .S(i//.r aurita, 323. Salter, 12. Sah-ia syhestris alba. 84. Sand bed culture. 305. SarotlHininus scof>arius. 605. S. WAST a No, 615. 682 Index. Saxifraga dccipicns, 320; um- brosa, 70. Scabiosa alba, 83; atroptirpurea, 2,72, 553- SCHUZ, 606. SCHROTER, 63. Scirpus lacustris, 70. Scrophularia nodosa, 289; trico- tyls, 407. Sectorial plants, 145; variation, 620; variegation, 276. Scdum reiiexum cristatum, 513. Seedlings, yellow, 289. Seeds, choice of, 2>Z^ I of atavists, 516. Segregation, vegetative, 619. Selection, double, 545. Semi-latent characters, 19. Senecio Jacobaea, 81. Sexual relationship, 592. Sieve of natural selection, 610. Silene Armeria alba, 84; Armcria rosea, 85 ; conica, tricotyls, 389 ; conoidea, tricotyls, 390 ; inflata, tricotyls, 437; noctiHora, 390; noctiHora, variegated, 287 ; odontipetala, tricotyls, 357. Si nap is alba, 460. Single variations, 6. Sippe, 591. SOLLAS, 666. Solms-Laubach, 96. Sonchus palustris, 506. Sophora japonica pendula, loi. Species and varieties, 578; col- lective, 61, 589; conception of, 567; elementary, 58; incipient, 9; origin of new, 71; provi- sional, 592 ; sub-progressive formation of, 67. Specularia speculum, 327. Spencer, 6zZ' Spinacia oleracea, tricotyls, 391. Spiraea sorbifolia, 505. Spiral torsion, 368, 463, 527. Spirogyra, 642. Standfuss, 657. Stellaria graminea aurea, 271 ; Holostea apetala, 96. Stirp, 590, 638. Strawberry, "Reus van Zuidwyk," lOI. Striped sorts, 267. Sub- jrogressive formation of species, 67. Subspecies, 60. Succisa, 605. Sugar-beet, brown, 606; fasci- ated, 507. Svalof, 605. Sycios angulota, 458. Syncotylous intermediate races, 466 ; race, isolation of, 469. Syncotyly, 457. Tammes, 502. Taraxacum officinale, 496. Taxus baccata, iii; fastigiata, 98. Teratology, 21. Tetracotyl, 346. Tetragonia expansa, 32, 84, 502, 514; forked, 374. Tetrapoma, 331. Teucrium Folium, 60. Thoroughbred races, 423. Thymus serpyllum, variegated, 271. Time, biological, 666. Tomatoes, 102. Torcnia, 612. Torsions, heritable, 527; local, 558; rare spiral, 537- Tracy, 605. Tradescantia repens, 279. Transgressive variability, 466, 600. Index. 683 Transitional forms, 6oi. Transportation hypothesis, 635. Tricotylous intermediate races. 393- Tricotylous races, isolation of, 422. Tricotyls from bought seed, 3S0. Tricotyly, partial variability <>f, TrifoliiDii incarnatiDn, 289; in- caniatiim quadrifolium, 227; pratcnsc, 289; fratcnsc, pin- nate leaf, 231 ; f^ratcusc quin- quefolium, 36; rcpcns pcrum- bcllatum, 317. Tropaeolum, tendril, 605. Tulips, striped, 115. Twisted plants, 527. Uhnus campestris variegata, 625, 636. Uni-sexual, 577. Units, number of, 598. Uropcdlum Lindcnii. 220. Urtica urcns, 553. Vaccinium, 95. Valeriana alba, 458; officinalis, S27- Variability, fluctuating, 608; in- crease in, 9, 14. Variations, germinal, 619; paral- lel, 67 ; sectorial, 122, 201 ; taxi- nomic, 69. Variegated leaves, 265; plants. 272. 628. Variegation, sectorial, 285. I'arirtas aurca, 7, 270; bicolor, ()2. X'arieties, derived, 60; cvcr.si>«>rt- ing. 8, 18; golden, 7; horticul- tural, 58; sterile, 88; system- atic, 58. \'aricty, 57, 64. 580, 584. ^^\^' DER Vei.de. 635. \''erlot, 57. I'cronica Buxhaumii, no; longt- folia, 494. 496, 620; scutcllata puhcsccns, 63. I'icia Paha, 501. I'lcia lutca hirta, 63. ViLMORiN, on striped flowers, 113- Viola tricolor maxima, 337. Violet, Dames', 136. J'iscaria oculata, twisted, 551. Vroi.ik. 90. Waagen, 662. Wallace. 599. 608. Was MANN, 656. Weevers, 537. IVcigclia amabilis, 28. 537. Weldon, 600. Wettstein, Von, 56, 293. 59'. 601. White. 661. Wille, 626. Willl\mson, 13. Wilson. 633. WiTTROCK. 82. 603. Xauthium catiadrnsc, 336. Zeiner Lassen, 505.