SPECIES AND VARIETIES Their Origin by Mutation Species and Varieties Their Origin by Mutation Lectures delivered at the University of California by Hugo DeVries Professor of Botany in the University of Amsterdam Edited by Daniel Trembly MacDougal Assistant Director of the New York Botanical Garden CHICAGO The Ooen Court Publishing Company LONDON Kegan Paul, Trench, Triibner & Co., Ltd. /ft ( & COPYRIGHT 1904 BY THE OPEN COURT PUB. Co. CHICAGO THE ORIGIN OF SPECIES The origin of species is a natural phenomenon. LAMARCK. The origin of species is an object of inquiry. DARWIN. The origin of species is an object of experi- mental investigation. PREFACE BY THE AUTHOR THE purpose of these lectures is to point out the means and methods by which the origin of species and varieties may become an object for experimental inquiry, in the interest of agricultural and horticultural practice as well as in that of general biologic science. Comparative studies have contributed all the evidence hitherto adduced for the support of the Darwinian theory of descent and given us some general ideas about the main lines of the pedigree of the. vegetable kingdom, but the way in which one species originates from another has not been ade- quately explained. The current belief assumes that spe- cies are slowly changed into new types. In contradiction to this conception the theory of mutation assumes that new species and varieties are produced from existing forms by sudden leaps. The parent-type itself remains unchanged throughout this process, and may repeatedly give birth to new forms. These may arise simultaneously and in groups or separately at more or less widely dis- tant periods. The principal features of the theory of mutation have been dealt with at length in my book "Die Mutations- theorie" (Vol. I., 1901, Vol. II., 1903. Leipsic, Veit & Co.), in which I have endeavored to present as com- pletely as possible the detailed evidence obtained from trustworthy historical records, and from my own experi- mental researches, upon which the theory is based. The University of California invited me to deliver a series of lectures on this subject, at Berkeley during the vii viii Preface by the Author summer of 1904, and these lectures are offered in this form to a public now thoroughly interested in the pro- •gress of modern ideas on evolution. Some of my experi- ments and pedigree-cultures are described here in a man- ner similar to that used in the " Mutationstheorie," but partly abridged and partly elaborated, in order to give a clear conception of their extent and scope. New experi- ments and observations have been added, and a wider choice of the material afforded by the more recent cur- rent literature has been made in the interest of a clear representation of the leading ideas, leaving the exact and detailed proofs thereof to the students of the larger book. Scientific demonstration is often long and encumbered with difficult points of minor importance. In these lec- tures I have tried to devote attention to the more im- portant phases of the subject and have avoided the de- tails of lesser interest to the general reader. Considerable care has been bestowed upon the indica- tion of the lacunae in our knowledge of the subject and the methods by which they may be filled. Many inter- esting observations bearing upon the little known parts of the subject may be made with limited facilities, either in the garden or upon the wild flora. Accuracy and per- severance, and a warm love for Nature's children are here the chief requirements in such investigations. In his admirable treatise on Evolution and Adaptation (New York, Macmillan & Co., 1903), Thomas Hunt Mor- gan has dealt in a critical manner with many of the speculations upon problems subsidiary to the theory of descent, in so convincing and complete a manner, that I think myself justified in neglecting these questions here. His book gives an accurate survey of them all, and is easily understood by the general reader. In concluding I have to offer my thanks to Dr. D. T. MacDougal and Miss A. M. Vail of the New York Botan- ical Garden for their painstaking work in the prepara- tion of the manuscript for the press. Dr. MacDougal, by Preface by tine Author ix his publications, has introduced my results to his Ameri- can colleagues, and moreover by his cultures of the muta- tive species of the great evening-primrose has con- tributed additional proof of the validity of my views, which will go far to obviate the difficulties, which are still in the way of a more universal acceptation of the theory of mutation. My work claims to be in full ac- cord with the principles laid down by Darwin, and to give a thorough and sharp analysis of some of the ideas of variability, inheritance, selection, and mutation, which were necessarily vague at his time. It is only just to state, that Darwin established so broad a basis for scien- tific research upon these subjects, that after half a century many problems of major interest remain to be taken up. The work now demanding our attention is manifestly that of the experimental observation and control of the origin of species. The principal object of these lectures is to secure a more general appreciation of this kind of work. HUGO DE VRIES. Amsterdam, October, PREFACE BY THE EDITOR PROFESSOR DE VRIES has rendered an additional service to all naturalists by the preparation of the lectures on mutation published in the present volume. A perusal of the lectures will show that the subject-matter of "Die Mutationstheorie " has been presented in a somewhat condensed form, and that the time which has elapsed since the original was prepared has given opportunity for the acquisition of additional facts, and a re-examination of some of the more important conclusions with the re- sult that a notable gain has been made in the treatment of some complicated problems. It is hoped that the appearance of this English version of the theory of mutation will do much to stimulate in- vestigation of the various phases of the subject. This volume, however, is by no means intended to replace, as a work of reference, the larger book with its detailed recital of facts and its comprehensive records, but it may prove a substitute for the use of the general reader. The revision of the lectures has been a task attended with no little pleasure, especially since it has given the editor the opportunity for an advance consideration of some of the more recent results, thus materially facilitat- ing investigations which have been in progress at the New York Botanical Garden for some time. So far as the ground has been covered the researches in question corroborate the conclusions of de Vries in all important particulars. The preparation of the manuscript for the printer has consisted chiefly in the adaptation of oral xii , Preface by the Editor discussions and demonstrations to a form suitable for permanent record, together with certain other alterations which have been duly submitted to the author. The original phraseology has been preserved as far as pos- sible. The editor wishes to acknowledge material as- sistance in this work from Miss A. M. Vail, Librarian of the New York Botanical Garden. D. T. MACDOUGAL. New York Botanical Garden, October, ERRATA FOR DE VRIES SPECIES AND VARIETIES Read " parent-species " for " parent species," line 11 from top of page 35. Read "Babington" for " Babbington," line 6 from bot- tom of p. 36. Read " field-pansy " for " field pansy/' line 3 from bot- tom of p. 39. Read " pubescent variety " for " pubescent- variety," line 4 from top of p. 139. Read " entire " for " white," line 12 from top of p. 147. Read " DC " for " D. C.," line 5 from top of p. 157. Read " occur " for " occcur," line 5 from bottom of page 202. Read " degressive " for " regressive," line 16 from top of p. 221. Read " is " for " it," line 16 from top of p. 264. Read " the character was active and not that of the par- ent in which," after line 5 from top of p. 278. Read " maternal " for " material," line 7 from bottom of p. 297. Read "black berries" for "blackberries," line 3 from bottom of p. 298. Read " 42.2% " for " 52.2%," line 9 from top of p. 304. Read " nutrition " for " mutation," line 6 from top of p. 335. Read " the " before " same," line 11, p. 358. Read " specimens " for " species," line 11 from top of p. 380. Insert period after " carefully," line 3 from bottom of p. 380. Omit line 12 from top of p. 418 and read " -tures. Start- ing points are the stray tricotyls." Read "&onica" for " conioa," line 7 from bottom of p. 419. 1 2 Errata. Read " seedling " for " seedlings," line 18 from top of p. 426. Read "identical" for " indentieal," line 15, p. 439. Read " exposure to " for " exposed," line 6 from bottom of p. 448. Read " constitution " for " constition," line 10 from top of p. 477. Omit hyphens in line 2 from top of p. 485. Read "degressive " for " digressive," line 18 from top of p. 564. Read " decreasing " for " increasing," line 2 from top of p. 639. Read " leaves of the group. All of the rosettes of the whole" instead of line 6 from bottom of page 646. Read " Equisetum " for " Equiseteum," line 7 from top of p. 649. Read " lateral branches " for " lateral-branches," line 13 from top of p. 649. Read " gamopetalism " for " gamepetalism," line 5 from top of p. 661. Read " Rhododendron " for " Rhodondendron," line 9 from top of p. 661. Read "hybrids" for "hyprids," line 12 from top of p. 668. Read " uninjurious " for " injurious," line 8 from bottom of p. 671. Omit line 6 from bottom of p. 674. Omit " are " from beginning of line 5 from top of p. 680. Read " uninjurious " for " injurious," line 7 from top of p. 683. Read "belonging" for "belong," line 1, p. 699. Read " Euoenothera " for " Euonothera," lines 1 and 4 from top of p. 709. Read " bels " for " bles," line 21 from top of p. 717. Read " longest " for " tallest," line 8 from top of p. 722. CONTENTS A. INTRODUCTION. LECTURE PAGE I. Descent : theories of evolution and methods of investigation 1 The theory of descent and of natural se- lection. Evolution and adaptation. Elementary species and varieties. Meth- ods of scientific pedigree-culture. B. ELEMENTARY SPECIES. II. Elementary species in nature ... 32 Viola tricolor, Draba verna, Primula acaulis, and other examples. Euphorbia Ipecacuanha. Prunus maritima. Taraxa- cum and Hieracium. III. Elementary species of cultivated plants. 63 Beets, apples, pears, clover, flax and coco- nut. IV. Selection of elementary species ... 92 Cereals, Le Couteur, running out of varie- ties. Kimpau and Kisler, Avena fatua. Meadows. Old Egyptian cereals. Selec- tion by the Komans. Sheriff. Hays. C. EETROGRADE VARIETIES. V. Characters of retrograde varieties . . 121 Seed varieties of pure, not hybrid origin. Differences from elementary species. Latent characters. Kay-florets of com- xiii XIV Contents LECTURE PAGE poshes. Progressive red varieties. Ap- parent losses. Xanthium Canadense. Correlative variability. Laciniate leaves and petals. Compound characters. VI. Stability and real atavism .... 154 Constancy of retrograde varieties. Atav- ism in Ribes sanguineum albidum, in conifers, in Iris pallida. Seedlings of Acacia. Reversion by buds. VU. Ordinary or false atavism .... 185 Vicinism or variation under the influence of pollination by neighboring individ- uals. Vicinism in nurseries. Purify- ing new and old varieties. A case of running out of corn in Germany. VIII. Latent characters ... *. :• •/. . . 216 Leaves of seedlings, adventitious buds, sys- tematic latency and regressive evolu- tion. Degressive evolution. Latency of specific and varietal characters in Dianthus caryophyllus spicatus, in the green dahlias, in white campanulas and others. Systematic latency of flower colors. IX. Crossing of species and varieties . . 247, Unisexual and bisexual, or species and variety crosses. Constant hybrids of Oenothera muricata and O. biennis. Aegilops, Medicago, brambles and other instances. X. Mendel's law of bisexual crosses . . 276 Pairs of antagonistic characters, one ac- tive and one latent. Papaver somnif- Contents xv LECTURE PAGE erum Mephisto Danebrog. Mendel's laws. Unit-characters. D. EVERSPOBTING VARIETIES. XI. Striped flowers 309 Antirrhinum majus luteum rubro-striatum with pedigree. Striped flowers, fruits and radishes. Double stocks. XII. "Five leaved" clover .340 Origin of this variety. Periodicity of the anomaly. Pedigree-cultures. Ascidia. XTTT. Polycephalic poppies 369 Permanency and high variability. Sensi- tive period of the anomaly. Depend- ency on external conditions. XIV. Monstrosities 400 , Inheritance of monstrosities. Half-races and middle races. Hereditary value of atavists. Twisted stems and fascia- tions. Middle races of triocotyls and syncotyls. Selection by the hereditary percentage among the offspring. XV. Double adaptations ...... 430 Analogy between double adaptations and anomalous middle races. Polygonum amphibium. Alpine plants. Othonna crassifolia. Leaves in sunshine and shadow. Giants and dwarfs. Figs and ivy. Leaves of seedlings. E. MUTATIONS. XVI. Origin of the peloric toad-flax ... 459 Sudden and frequent origin in the wild state. Origin in the experiment-garden. Law of repeated mutations. Probable origin of other pelories. XVI Contents LECTURE PAGE XVII. The production of double flowers . . 488 Sudden appearance of double flowers in horticulture. Historical evidence. Ex- perimental origin of Chrysanthemum segetum plenum. Dependency upon nourishment. Petalody of stamens. XVIII. New species of Oenothera .... 516 Mutations of Oenothera Lamarckiana in the wild state near Hilversum. New varieties of O. laevifolia, O. brevistylis, and O. nanella. New elementary species, O. gigas, O. rubrinervis, albida, and ob- longa. O. lata a pistillate form. In- constancy of O. scintillans. XIX. Experimental pedigree-cultures . . . 547, Pedigree of the mutative products of Oenothera Lamarckiana in the Botan- ical Garden at Amsterdam. Laws of mutability. Sudden and repeated leaps from an unchanging main strain. Con- stancy of the new forms. Mutations in all directions. XX. Origin of wild species and varieties . . 576 < Problems to solve. Capsella Heegeri. Oenothera biennis cruciata. Epilobium hirsutum cruciatum. Hibiscus Mos- cheutos. Purple beech. Monophyllous strawberries. Chances of success with new mutations. XXI. Mutations in horticulture f,^<; ^ . . 604 Chelidonium majus lacinatum. Dwarf and spineless varieties. Laciniate leaves. Monophyllous and broom-like varieties. Contents xvn LECTURE PAGE Purple leaves. Celosia. Italian poplar. Cactus dahlia. Mutative origin of Dah- lia fistulosa, and Geranium pratense *in the experiment-garden. XXII. Systematic atavism 630 Reappearance of ancestral characters. Primula acaulis umbellata. Bracts of crucifers. Zea Mays cryptosperma. Equisetum, Dipsacus sylvestris torsus. Tomatoes. XXIII. Taxonomic anomalies 658 Specific characters occurring in other cases as casual anomalies. Papaver brac- teatum monopetalum. Desmodium gyrans and monophyllous varieties. Pel- tate leaves and ascidia. Flowers on leaves. Leaves. Hordeum trifurcatum. XXIV. Hypothesis of periodical mutations . . 686 Discovering mutable strains. Periods of mutability and constancy. Periods of mutations. Genealogical trees. Limited life-time of the organic kingdom. F. FLUCTUATIONS. XXV. General laws of fluctuations .... 715 Fluctuating variability. Quetelet's law. Individual and partial fluctuations. Linear variability. Influence of nutri- tion. Periodicity-curves. XXVI. Asexual multiplication of extremes . . 742 Selection between species and intra-spe- cific selection. Excluding individual XV111 Contents LECTURE PAGE and embryonic variability. Sugar-canes. Flowering cannas. Double lilacs. Other instances. Burbank's method of selec- tion. XXVII. Inconstancy of improved races . . . 770 Larger variability in the case of propaga- tion by seed. Progression and regres- sion after a single selection, and after repeated selections. Selection experi- ments with corn. Advantages and effect of repeated selection. XXYin. Artificial and natural selection . . . 798 Conclusions. Specific and intra-specific selection. Natural selection in the field. Acclimatization. Improvement-selection of sugar-beets by various methods. Rye. Hereditary percentage and centgener power as marks by which intra-specific selection may be guided. Index 827 A. INTRODUCTION LECTURE I DESCENT : THEORIES OF EVOLUTION, AND METHODS OF INVESTIGATION Newton convinced his contemporaries that natural laws rule the whole universe. Lyell showed, by his principle of slow and gradual evolution, that natural laws have reigned since the beginning of time. To Darwin we owe the almost universal acceptance of the theory of descent. This doctrine is one of the most noted land- marks in the advance of science. It teaches the validity of natural laws of life in its broadest sense, and crowns the philosophy, founded by Newton and Lyell. Lamarck proposed the hypothesis of a com- mon origin of all living beings and this ingenious and thoroughly philosophical conception was warmly welcomed by his partisans, but was not widely accepted owing to lack of supporting evi- dence. To Darwin was reserved the task of 1 2 Descent bringing the theory of common descent to its present high rank in scientific and social phi- losophy. Two main features in his work have contrib- uted to this early and unexpected victory. One of them is the almost unlimited amount of com- parative evidence, the other is his demonstration of the possibility of a physiological explanation of the process of descent itself. The universal belief in the independent crea- tion of living organisms was revised by Linnaeus and was put upon a new foundation. Before him the genera were supposed to be created, the species and minor forms having arisen from them through the agency of ex- ternal conditions. In his first book Linnaeus adhered to this belief, but later changed his mind, and maintained the principle of the sep- arate creation of species. The weight of his authority soon brought this conception to uni- versal acceptance, and up to the present time the prevailing conception of a species has been chiefly based on the definition given by Linnaeus. His species comprised subspecies and varieties, and these were in their turn, supposed to have evolved from species by the common method. Darwin tried to show that the links which bind species to genera are of the same nature as those which determine the relationship of Theories of Evolution 3 subspecies and varieties. If an origin by nat- ural laws is conceded for the latter, it must, on this ground, be granted for the first also. In this discussion he simply returned to the pre- Linnean attitude. But his material was such as to allow him to go one step further, and this step was an important and decisive one. He showed that the relation between the various genera of a family does not exhibit any fea- tures of a nature other than that between the species of a genus. What has been conceded for the one must needs be accepted for the ether. The same holds good for the large groups. The conviction of the common origin of closely allied forms necessarily leads to the conception of a similar descent even in remote relationships. The origin of subspecies and varieties as found in nature was not proved, but only gen- erally recognized as evident. A broader knowledge has brought about the same state of opinion for greater groups of relationships. Systematic affinities find their one possible ex- planation by the aid of this principle; without it, all similarity is only apparent and accidental. Geographic and paleontologic facts, brought to- gether by Darwin and others on a previously unequalled scale, point clearly in the same di- rection. The vast amount of evidence of all 4 . Descent comparative sciences compels us to accept the idea. To deny it, is to give up all oppor- tunity of conceiving Nature in her true form. The general features of the theory of descent are now accepted as the basis of all biological science. Half a century of discussion and in- vestigation has cleared up the minor points and brought out an abundance of facts; but these have not changed the principle. Descent with modification is now universally accepted as the chief law of nature in the organic world. In honor of him, who with unsurpassed genius, and by unlimited labor has made it the basis of modern thought, this law is called the " Dar- winian theory of descent. ' ' Darwin 's second contribution to this attain- ment was his proof of the possibility of a phys- iological explanation of the process of descent itself. Of this possibility he fully convinced his contemporaries, but in indicating the particular means by which the change of species has been brought about, he has not succeeded in securing universal acceptation. Quite on the contrary, objections have been raised from the very out- set, and with such force as to compel Darwin himself to change his views in his later writings. This however, was of no avail, and objections and criticisms have since steadily accumulated. Physiologic facts concerning the origin of Theories of Evolution 5 species in nature were unknown in the time of Darwin. It was a happy idea to choose the ex- perience of the breeders in the production of new varieties, as a base on which to build an explanation of the processes of nature. In my opinion Darwin was quite right, and he has suc- ceeded in giving the desired proof. But the basis was a frail one, and would not stand too close an examination. Of this Darwin was al- ways well aware. He has been prudent to the utmost, leaving many points undecided, and among them especially the range of validity of his several arguments. Unfortunately this prudence has not been adopted by his followers. Without sufficient warrant they have laid stress on one phase of the problem, quite overlooking the others. Wallace has even gone so far in his zeal and ardent veneration for Darwin, as to describe as Darwinism some things, which in my opinion, had never been a part of Darwin's con- ceptions. The experience of the breeders was quite in- adequate to the use which Darwin made of it. It was neither scientific, nor critically accurate. Laws of variation were barely conjectured ; the different types of variability were only imper- fectly distinguished. The breeders' conception was fairly sufficient for practical purposes, but science needed a clear understanding of the 6 Descent factors in the general process of variation. Re- peatedly Darwin tried to formulate these causes, but the evidence available did not meet his re- quirements. Quetelet's law of variation had not yet been published. Mendel's claim of hereditary units for the explanation of certain laws of hybrids discovered by him, was not yet made. The clear distinction between spontaneous and sud- den changes, as compared with the ever-present fluctuating variations, is only of late coming into recognition by agriculturists. Innumerable minor points which go to elucidate the breeders' experience, and with which we are now quite familiar, were unknown in Darwin's time. No wonder, that he made mistakes, and laid stress on modes of descent, which have since been proved to be of minor importance or even of doubtful validity. Notwithstanding all these apparently unsur- mountable difficulties, Darwin discovered the great principle which rules the evolution of or- ganisms. It is the principle of natural selec- tion. It is the sifting out of all organisms of minor worth through the struggle for life. It is only a sieve, and not a force of nature, no di- rect cause of improvement, as many of Dar- win's adversaries, and unfortunately many of his followers also, have so often asserted. It is Theories of Evolution 7 only a sieve, which decides which is to live, and what is to die. But evolutionary lines are of great length, and the evolution of a flower, or of an insectivorous plant is a way with many side- paths. It is the sieve that keeps evolution on the main line, killing all, or nearly all that try to go in other directions. By this means nat- ural selection is the one directing cause of the broad lines of evolution. Of course, with the single steps of evolution it has nothing to do. Only after the step has been taken, the sieve acts, eliminating the unfit. The problem, as to how the individual steps are brought about, is quite another side of the ques- tion. On this point Darwin has recognized two pos- sibilities. ' One means of change lies in the sud- den and spontaneous production of new forms from the old stock. The other method is the gradual accumulation of those always present and ever fluctuating variations which are in- dicated by the common assertion that no two individuals of a given race are exactly alike. The first changes are what we now call muta- tions, the second are designated as * * individual variations," or as this term is often used in an- other sense, as ' ' fluctuations. ' ' Darwin recog- nized both lines of evolution ; Wallace disregard- ed the sudden changes and proposed fluctuations 8 Descent as the exclusive factor. Of late however, this point of view has been abandoned by many in- vestigators, especially in America. The actual occurrence of mutations is now recognized, and the battle rages about the ques- tion, as to whether they are be regarded as the principal means of evolution, or whether slow and gradual changes have not also played a large and important part. The defenders of the theory of evolution by slow accumulation of slight fluctuations are di- vided into two camps. One group is called the Neo-Lamarckians ; they assume a direct modi- fying agency of the environment, producing a corresponding and useful change in the organ- ization. The other group call themselves Dar- winians or selectionists, but to my mind with no other right beyond the arbitrary restriction of the Darwinian principles by Wallace. They assume fluctuating variations in all directions and leave the choice between them to the sieve of natural selection. Of course we are far from a decision between these views, on the sole ground of the facts as known at present. Mutations under observa- tion are as yet very rare; enough to indicate the possible and most probable ways, but no more. On the other hand the accumulation of fluctuations does not transgress relatively nar- Theories of Evolution 9 row limits as far as the present methods of selection go. But the question remains to be solved, whether our methods are truly the right ones, and whether by the use of new princi- ples, new results might cause the balance of opinion to favor the opposite side. Of late, a thorough and detailed discussion of the opposing views has been given by Morgan, in his valuable book on Evolution and Adapta- tion. He has subjected all the proposed theo- ries to a severe criticism, both on the ground of facts, and on that of their innate possibility and logical value. He decides in favor of the mu- tation-theory. His arguments are incisive and complete, and wholly adapted to the compre- hension of all intelligent readers, so that his book relieves me entirely of the necessity of discussing these general questions, as it could not be done in a better or in a clearer way. I intend to give a review of the facts obtained from plants which go to prove the assertion, that species and varieties have originated by mutation, and are, at present, not known to orig- inate in any other way. This review consists of two parts. One is a critical survey of the facts of agricultural and horticultural breed- ing, as they have accumulated since the time of Darwin. This body of evidence is to be com- bined with some corresponding experiments 10 Descent concerning the real nature of species in the wild state. The other part rests on iny own obser- vations and experiments, made in the botanical garden of the University of Amsterdam. For many years past I have tried to elucidate the hereditary conditions of species and varie- ties, and the occasional occurrence of mutations, that suddenly produce new forms. The present discussion has a double purpose. On one side it will give the justification of the theory of mutations, as derived from the facts now at hand. On the other hand it will point out the deficiencies of available evidence, and indicate the ways by which the lacunae may gradually be filled. Experimental work on heredity does not require vast installments or a costly laboratory equipment. It demands chiefly assiduity and exactitude. Any one who boasts these two qualities, and who has a small garden at his disposal, is requested to take part in this line of investigation. In order to directly observe the birth of new forms it is necessary in the first place to be fully clear concerning the question as to what forms are to be expected to arise from others, and before proceeding to a demonstration of the origin of species, it is pertinent to raise the question as to what constitutes a species. Species is a word, which always has had a Theories of Evolution 11 double meaning. One of them is the systematic species, which is the unit of our system. But these units are not at all undivisible. Long ago Linnaeus knew them to be compound ideas in a great number of instances, and increasing knowledge has shown that the same rule pre- vails in other instances. Today the vast ma- jority of the old systematic species are known to consist of minor units. These minor en- tities are called varieties in systematic works. However, there are many objections to this usage. First the term variety is applied in horticulture and agriculture to things so widely divergent as to convey no clear idea at all. Secondly, the subdivisions of species are by no means all of the same nature, and the systematic varieties include units the real value of which, is widely different in different cases. Some of these varieties are in reality as good as species, and have been " elevated, " as it is called, by some writers, to this rank. This conception of the elementary species would be quite justifiable, and would at once get rid of all difficulties, were it not for one practical obstacle. The number of the species in all genera would be doubled and tripled, and as these numbers are already cumbersome in many cases, the distinction of the native species of any given country would lose most of its charm and interest. 12 Descent In order to meet this difficulty we must recog- nize two sorts of species. The systematic spe- cies are the practical units of the systematists and florists, and all friends of wild nature should do their utmost to preserve them as Linnaeus has proposed them. These units, how- ever, are not really existing entities ; they have as little claim to be regarded as such as the genera and families have. The real units are the elementary species; their limits often ap- parently overlap and can only in rare cases be determined on the sole ground of field-obser- vations. Pedigree-culture is the method re- quired and any form which remains constant and distinct from its allies in the garden is to be considered as an elementary species. In the following lectures we shall con- sider this point at length, to show the compound nature of systematic species in wild and in culti- vated plants. In both cases, the principle is becoming of great importance, and sundry pa- pers published recently indicate its almost uni- versal acceptation. Among the systematic subdivisions of species, not all have the same claim to the title of ele- mentary species. In the first place the cases in which the differences may occur between parts of the same individual are to be excluded. Dividing an alpine plant into two halves and Theories of Evolution 13 planting one in a garden, varietal differences at once arise, and are often designated in sys- tematic works under different varietal names. Secondly all individual differences which are of a fluctuating nature are to be combined into a group. But with these we shall deal later. Apart from these minor points the subdi- visions of the systematic species exhibit two widely different features. I will now try to make this clear in a few words, but will return in another lecture to a fuller discussion of this most interesting contrast. Linnaeus himself knew, that in some cases all subdivisions of a species are of equal rank, to- gether constituting the group called species. No one of them outranks the others; it is not a species with varieties, but a group consisting only of varieties. A closer inquiry into the cases treated in this manner by the great master of systematic science, shows that here his varie- ties were exactly what we now call elementary species. In other cases the varieties are of a deriva- tive nature. The species constitutes a type that is pure in a race which ordinarily is still grow- ing somewhere, though in some cases it may have died out. From this type the varieties are derived, and the way of this derivation is usual- ly quite manifest to the botanist. It is ordina- 14 Descent rily by the disappearance of some superficial character that a variety is distinguished from its species, as by the lack of color in the flowers, of hairs on stems and foliage, of the spines and thorns, &c. Such varieties are, strictly speak- ing, not to be treated in the same way as elemen- tary species, though they often are. We shall designate them by the term of " retrograde varieties, ' ' which clearly indicates the nature of their relationship to the species from which they are assumed to have sprung. In order to lay more stress on the contrast between elementary species and retrograde varieties, it should be stated at once, that the first are considered to have originated from their parent-form in a progressive way. They have succeeded in at- taining something quite new for themselves, while retrograde varieties have only thrown off some peculiarity, previously acquired by their ancestors. The whole vegetable kingdom exhibits a con- stant struggle between progression and retro- gression. Of course, the great lines of the gen- eral pedigree are due to progression, many single steps in this direction leading together to the great superiority of the flowering plants over their cryptogamous ancestors. But pro- gression is nearly always accompanied by re- trogression, in the principal lines of evolution, Theories of Evolution 15 as well as in the collateral branches of the gen- ealogical tree. Sometimes it prevails, and the monocotyledons are obviously a reduced branch of the primitive dicotyledons. In or- chids and aroids, in grasses and sedges reduc- tion plays a most important part, leaving its traces on the flowers as well as on the embryo of the seed. Many instances could be given to prove that progression and retrogression are the two main principles of evolution at large. Hence the conclusion that our analysis must dissect the complicated phenomena of evolution so far as to show the separate functions of these two con- trasting principles. Hundreds of steps were needed to evolve the family of the orchids, but the experimenter must take the single steps for the object of his inquiry. He finds that some are progressive and others retrogressive, and so his investigation falls under two heads, the origin of progressive characters, and the subsequent loss of the same. Progressive steps are the marks of elementary species, while re- trograde varieties are distinguished by ap- parent losses. They have equal claim on our interest and our study. As already stated I propose to deal first with the elementary species and afterwards with the retrograde varieties. I shall try to depict them to you in the first place as they are seen in 16 Descent nature and in culture, leaving the question of their origin to a subsequent experimental treat- ment. The question of experimental origin of new species and varieties has to be taken up from two widely diverging starting points. This may be inferred from what we have already seen concerning the two opposing theories, de- rived and isolated from Darwin's original broad conception. One of them considers mutations as the origin of new forms, while the other assumes fluctuations to be the source of all evolution. As mentioned above, my own experience has led me to accept the first view. Therefore I shall have to show that mutations do yield new and constant forms, while fluctuations are not adequate to do so. Eetrograde varieties and elementary species may both be seen to be produced by sudden mutations. Varieties have often been observed to appear at once and quite unexpectedly in horticulture and agriculture, and a survey of these historical facts will be the subject of one of my lectures. In some in- stances I have succeeded in repeating these observations in my garden, under the strict con- ditions of a scientific experiment, and these in- stances teach us the real nature of the process of mutation in all its visible features. New ele- Theories of Evolution 17 mentary species are far more rare, but I have discovered in the great evening-primrose, or Oenothera Lamarckiana a strain which is pro- ducing them yearly in the wild state as well as in my garden. These observations and pedi- gree-experiments will be dealt with at due length in subsequent lectures. Having proved the existence and importance of mutations, it remains to inquire, how far the improvements may go which are due only to fluctuating variability. As the term indicates, this variability is fluctuating to and fro, oscil- lating around an average type. It never fails nor does it, under ordinary circumstances, de- part far from the fixed average. But the deviation may be enlarged by a choice of extremes. In sowing their seed, the aver- age of the strain is seen to be changed, and in repeating the experiment the change may be considerable. It is not clear, whether theo- retically by such an accumulation, deviations might be reached which could not be attained at once, in a single sowing. This question is hard- ly susceptible of an experimental answer, as it would require such an enormous amount of seed from one strain as can scarcely ever be pro- duced. The whole character of the fluctuations shows them to be of an opposite nature, contrasting 18 Descent manifestly with specific and varietal characters. By this method they may be proved to be in- adequate ever to make a single step along the great lines of evolution, in regard to progressive as well as to retrograde development. First of all fluctuations are linear, amplify- ing or lessening the existing qualities, but not really changing their nature. They are not observed to produce anything quite new, and evolution of course, is not restricted to the in- crease of the already existing peculiarities, but depends chiefly on the continuous addition of new characters to the stock. Fluctuations al- ways oscillate around an average, and if re- moved from this for some time, they show a tendency to return to it. This tendency, called retrogression, has never been observed to fail as it should in order to free the new strain from the links with the average, while new species and new varieties are seen to be quite free from their ancestors, and not linked to them by intermediates. The last few lectures will be devoted to ques- tions concerning the great problem of the anal- ogy between natural and artificial selection. As already stated, Darwin made this analogy the foundation stone of his theory of descent, and he met with the severest objections and crit- icisms precisely on this point But I hope to Theories of Evolution 19 show that he was quite right, and that the cause of the divergence of opinions is due simply to the very incomplete state of knowl- edge concerning both processes. If both are critically analyzed they exhibit the same factors and the discussion may be afterwards limited to the appreciation of the part, which each of them has played in nature and among cultivated plants. Both natural and artificial selection are part- ly specific, and partly intr a- specific or individ- ual. Nature of course, and intelligent men first chose the best elementary species from among the swarms. In cultivation this is the process of variety-testing. In nature it is the survival of the fittest species, or, as Morgan designates it the survival of species in the struggle for ex- istence. The species are not changed by this struggle, they are only weighed against each other, the weak being thrown aside. Within the chosen elementary species there is also a struggle. It is obvious, that the fluc- tuating variability adapts some to the given circumstances, while it lessens the chances of others. A choice results, and this choice is, what is often exclusively called selection, either natural or artificial. In cultivation it produces the improved and the local races ; in nature little is known about improvement in this way, but 20 Descent local adaptations with slight changes of the average character in separate localities, seem to be of quite normal occurrence. A new method of individual selection has been used in recent years, in America, especially by W. M. Hays. It consists in judging the hereditary worth of a plant by the average con- dition of its offspring, instead of by its own visible characters. If this determination of the " centgener power, " as Hays calls it, should prove to be the true principle of selection, then indeed the analogy between natural and artifi- cial selection would lose a large part of its im- portance. We will reserve this question for the last lecture, as it pertains more to the future, than to our present stock of knowledge. Something should be said here concerning hybrids and hybridism. This problem has of late reached such large proportions that it can- not be dealt with adequately in a short survey of the phenomena of heredity in general. It requires a separate treatment. For this reason I shall limit myself to a single phase of the prob- lem, which seems to be indispensable for a true and at the same time easy distinction between elementary species and retrograde varieties. According to Macfarlane's terminology, some crosses are to be considered as unisexual while others are bisexual. The first are one-sided, Theories of Evolution 21 some peculiarity being found in one of the parents and lacking in the other. The second are two-sided, as all the characters are pres- ent in both parents but are found in a different condition. Active in one of them, it is con- cealed or inactive in the other. Hence a pair of contrasting units result, while in unisexual crosses no pairing of the peculiar character un- der consideration is possible. This leads to the principal difference between species and varie- ties, and to an experimental method of deciding between them in difficult and doubtful cases. Having thus indicated the general outlines of the subjects I shall deal with, something now may be said as to methods of investigation. There are two points in which scientific in- vestigation differs from ordinary pedigree-cul- ture in practice. First the isolation of the individuals, and the study of individual inheri- tance instead of averages. Next comes the task of keeping records. Every individual must be entered, its ancestry must be known as com- pletely as possible, and all its relations must be noted in such a form, that the most complete reference is always possible. Mutations may come unexpectedly, and when once arisen, their parents and grand-parents should be known. Records must be available which will allow of a most complete knowledge of the whole ances- 22 Descent tral line. This, and approximately this only, is the essential difference between experimental and accidental observation. Mutations are occurring from time to time in the wild state as well as in horticulture and agriculture. A selection of the most interest- ing instances will be given later. But in all such cases the experimental proof is wanting. The observations as a rule, only began when the mutation had made its appearance. A more or less vague remembrance about the previous state of the plants in question might be avail- able, though even this is generally absent. But on doubtful points, concerning possible crosses or possible introduction of foreign strains, mere recollection is insufficient. The fact of the mu- tation may be very probable, but the full proof is, of course, wanting. Such is the case with the mutative origin of Xanthium commune Wootoni from New Mexico and of Oenoihera biennis cruciata from Holland. The same doubt exists as to the origin of the Capsella Heegeri of Solms-Laubach, and of the oldest recorded mutation, that of Chelidonium lacinia- tum in Heidelberg about 1600. First the unavoidable doubt about the fact it- self. This however, gradually loses its impor- tance in the increasing accumulation of evi- dence. Secondly, the impossibility of a closer Theories of Evolution 23 inquiry into the real nature of the change. For experimental purposes a single mutation does not suffice; it must be studied repeatedly, and be produced more or less arbitrarily, according to the nature of the problems to be solved. And in order to do this, it is evidently not enough to have in hand the mutated individual, but it.is indispensable to have also the mutable parents, or the mutable strain from which it sprang. All conditions previous to the mutation are to be considered as of far higher importance than all those subsequent to it. Now mutations come unexpectedly, and if the ancestry of an accidental mutation, must be known, it is of course necessary to keep ac- counts of all the strains cultivated. It is evi- dent that the required knowledge concerning the ancestry of an accidental mutation, must neces- sarily nearly all be acquired from the plants in the experimental garden. Obviously this rule is as simple in theory, as it is difficult to carry out in practice. First of all comes the book-keeping. The parents, grandparents and previous ancestors must be known individually. Accounts of them must be kept under two headings. A full description of their individual character and peculiarities must always be available on the one hand, and on the other all facts concerning their heredi- 24 Descent tary qualities. These are to be deduced from the composition of the progeny, and in order to obtain complete evidence on this point, two successive generations are often required. The investigation must ascertain the average condi- tion of this offspring and the occurrence of any deviating specimens, and for both purposes it is necessary to cultivate them in relatively large numbers. It is obvious, that properly speak- ing, the whole family of a mutated individual, including all its nearer and more remote rela- tives, should be known and recorded. Hence pedigree-book-keeping must become the general rule. Subordinate to this are two further points, which should likewise be stated here. One pertains to the pure or hybrid nature of the original strain, and the other to the life-conditions and all other external in- fluences. It is manifest that a complete under- standing of a mutation depends upon full infor- mation upon these points. All experiments must have a beginning. The starting-point may be a single individual, or a small group of plants, or a lot of seeds. In many cases the whole previous history is ob- scure, but sometimes a little historical evidence is at hand. Often it is evident that the initial material belongs to a pure species, but with re- spect to the question of elementary species it is Theories of Evolution 25 not rarely open to doubt. Large numbers of hybrid plants and hybrid races are in existence, concerning the origin of which it is impossible to decide. It is impossible in many in- stances to ascertain whether they are of hybrid or of pure origin. Often there is only one way of determining the matter; it is to guess at the probable parents in case of a cross and to repeat the cross. This is a point which always requires great care in the interpretation of unusual facts. Three cases are to be distinguished as to heredity. Many plants are so constituted as to be fertilized with their own pollen. In this case the visits of insects have simply to be ex- cluded, which may be done by covering plants with iron gauze or with bags of prepared paper. Sometimes they fertilize themselves without any aid, as for instance, the common evening- primrose; in other cases the pollen has to be placed artificially on the stigma, as with La- marck's evening-primrose and its derivatives. Other plants need cross-fertilization in order to produce a normal yield of seeds. Here two individuals have always to be combined, and the pedigree becomes a more complicated one. Such is the case with the toad-flax, which is nearly sterile with its own pollen. But even in these cases the visits of insects bringing pollen 26 Descent from other plants, must be carefully excluded. A special lecture will be devoted to this very in- teresting source of impurity and of uncertainty in ordinary cultures. Of course, crosses may lie in the proposed line of work, and this is the third point to be alluded to. They must be surrounded with the same careful isolation and protection against bees, as any other fertilizations. And not only the seed-parent, but also the pollen must be kept pure from all possible foreign admixtures. A pure and accurately recorded ancestry is thus to be considered as the most important condition of success in experimental plant- breeding. Next to this comes the gathering of the seeds of each individual separately. Fifty or sixty, and often more, bags of seeds are by no means uncommon for a single experiment, and in ordinary years the harvest of my garden is preserved in over a thousand separate lots. Complying with these conditions, the origin of species may be seen as easily as any other phenomenon. It is only necessary to have a plant in a mutable condition. Not all species are in such a state at present, and therefore I have begun by ascertaining which were stable and which were not. These attempts, of course, had to be made in the experimental garden, and large quantities of seed had to be procured and Theories of Evolution 27 sown. Cultivated plants of course, had only a small chance to exhibit new qualities, as they have been so strictly controlled during so many years. Moreover their purity of origin is in many cases doubtful. Among the wild plants only those could be expected to reward the in- vestigator which were of easy cultivation. For this reason I have limited myself to the trial of wild plants of Holland, and have had the good fortune to find among them at least one species in a state of mutability. It was not really a native plant, but one probably introduced from America or at least belonging to an American genus. It was the great evening-primrose or the primrose of Lamarck. A strain of this beautiful species is growing on an abandoned field in the vicinity of Hilversum, at a short dis- tance from Amsterdam. Here it has escaped from a park, and multiplied. In doing so it has produced, and is still producing quite a number of new types, some of which may be considered as retrograde varieties, while others evidently are of the nature of progressive elementary species. This interesting plant has afforded me the means of observing directly how new species originate, and of studying the laws of these changes. My researches have followed a double line of inquiry. On one side, I have limited 28 Descent myself to direct field observations, and to trials of seed, collected from the wild plants in their native locality. Obviously the mutations are decided within the seed, and the culture of young plants from them had no other aim than that of ascertaining what had occurred in the field. But then the many chances of destruc- tion that threaten young plants in a wild state, could be avoided in the garden where enviro- nmental factors can be controlled. My second line of inquiry was an experi- mental repetition of the phenomena which were only partly discerned at the native locality. It was not my aim to intrude into the process, nor to try to bring out new features. My only ob- ject was to submit to the precepts just given, concerning pure treatment, individual seed- gathering, exclusion of crosses and accurate recording of all the facts. The result has been a pedigree which now permits of stating the re- lation between all the descendants of my orig- inal introduced plant. This pedigree at once exhibits the laws followed by the mutating spe- cies. The main fact is, that it does not change itself gradually, but remains unaffected during all succeeding generations. It only throws off new forms, which are sharply contrasted with the parent, and which are from the very begin- ning as perfect and as constant, as narrowly Theories of Evolution 29 defined, and as pure of type as might be ex- pected of any species. These new species are not produced once or in single individuals, but yearly and in large numbers. The whole phenomenon conveys the idea of a close group of mutations, all belonging to one single condition of mutability. Of course this mutable state must have had a beginning, as it must sometime come to an end. It is to be considered as a period within the life-tune of the species, and probably it is only a small part of it. The detailed description of this experiment, however, I must delay to a subsequent lecture, and I may be allowed to state, that the discov- ery of this period of mutability is of a definite theoretical importance. One of the greatest ob- jections to the Darwinian theory of descent arose from the length of time it would require if all evolution was to be explained on the ground of slow and nearly invisible changes. This difficulty is at once met, and fully sur- mounted by the hypothesis of periodical but sudden and quite noticeable steps. This as- sumption requires only a limited number of mutative periods, which might well occur within the time allowed by physicists and geologists for the existence of animal and vegetable life on the earth. 30 Descent Summing up the main points of these intro- ductory remarks, I propose to deal with the sub- jects mentioned above at some length, devoting to each of them, if possible at least an entire lecture. The decisive facts and discussions upon which the conclusions are based will be given in every case. Likewise I hope to point out the weak places and the lacunae in our pres- ent knowledge, and to show the way in which each of you may try to contribute his part to- wards the advancement of science in this sub- ject. Lastly I shall try to prove that sudden mutation is the normal way in which nature produces new species and new varieties. These mutations are more readily accessible to ob- servation and experiment than the slow and gradual changes surmised by Wallace and his followers, which are entirely beyond our pres- ent and future experience. The theory of mutations is a starting-point for direct investigation while the general belief in slow changes has held back science from such investigations during half a century. Coming now to the subdivisions and headings under which my material is to be presented, I propose describing first the real nature of the elementary species and retrograde varieties, both in normal form and in hybridizations. A discussion of other types of varieties, includ- Theories of Evolution 31 ing monstrosities will complete the general plan. The second subdivision will deal with the origin of species and varieties as taught by experiment and observation, treating separately the sud- den variations which to my mind do produce new forms, and subsequently the fluctuations which I hold to be not adequate to this purpose. B. ELEMENTARY SPECIES LECTUBE II ELEMENTARY SPECIES IN NATURE What are species? Species are considered as the true units of nature by the vast majority of biologists. They have gained this high rank in our estimation principally through the influence of Linnaeus. They have supplanted the genera which were the accepted units before Linnaeus. They are now to be replaced in their turn, by smaller types, for reasons which do not rest upon comparative studies, but upon direct experimental evidence. Biological studies and practical interests alike make new demands upon systematic bot- any. Species are not only the subject-material of herbaria and collections, but they are living entities, and their life-history and life-condi- tions gain a gradually increasing interest. One phase of the question, is to determine the easiest manner to deal with the collected forms of a country, and another feature is the problem as 32 Elementary Species in Nature 33 to what groups are real units and will remain constant and unchanged through all the years of our observations. Before Linnaeus, the genera were the real units of the system. De. Candolle pointed out that the old vulgar names of plants, such as roses and clover, poplars and oaks, nearly all refer to the genera. The type of the clovers is rich in the colors, and the shapes of the flower- heads and the single flowers escape common ob- servation ; but notwithstanding this, clovers are easily recognized, even if new types come to hand. White and red clovers and many other species are distinguished simply by adjectives, the generic name remaining the same for all. Tournefort, who lived in the second half of the 17th century (1656-1708), is generally con- sidered as the author of genera in systematic botany. He adopted, what was at that time, the general conception and applied it through- out the vegetable kingdom. He grouped the new and the rare, and the previously over- looked forms in the same manner in which the more conspicuous plants were already ar- ranged by universal consent. Species were dis- tinguished by minor marks, and often indicated by short descriptions, but they were consid- ered of secondary importance. Based on the idea of a direct creation of all 34 Elementary Species living beings the genera were then accepted as the created forms. They were therefore re- garded as the real existing types, and it was generally surmised that species and varieties owed their origin to subsequent changes under the influence of external conditions. Even Lin- naeus agreed with this view in his first treatises and in his Philosophic Botany he still kept to the idea that all genera had been created at once with the beginning of life. Afterwards Linnaeus changed his opinion on this important point, and adopted species as the units of the system. He declared them to be the created forms, and by this decree at once re- duced the genera to the rank of artificial groups. Linnaeus was well aware that this conception was wholly arbitrary, and that even the species are not real indivisible entities. But he simply forbade the study of lesser subdivisions. At his time he was quite justified in doing so, be- cause the first task of the systematic botanists was the clearing up of the chaos of forms and the bringing of them in connection with their real allies. Linnaeus himself designated the subdivisions of the species as varieties, but in doing so he followed two clearly distinct principles. In some cases his species were real plants, and the varieties seemed to be derived from them by Elementary Species in Nature 35 some simple changes. They were subordinated to the parent species. In other cases his spe- cies were groups of lesser forms of equal value, and it was not possible to discern which was the primary and which was the derivative. These two methods of subdivision seem in the main, and notwithstanding their relatively im- perfect application in many single examples, to correspond with two really distinct cases. The derivative varieties are distinguished from the parent species by some single but striking mark, and often this attribute manifests itself as the loss of some apparent quality. The loss of spines and of hairs and the loss of blue and red flower-colors are the most notorious, but in rarer cases many single peculiarities may dis- appear, thereby constituting a variety. This relation of varieties to the parent-species is gradually increasing in importance in the esti- mation of botanists, sharply contrasting with those cases, in which such dependency is not to be met with. If among the subdivisions of a species, no single one can be pointed out as playing a pri- mary part, and the others can not be traced back to it, the relation between these lesser units is of course of another character. They are to be considered of equal importance. They are distinguished from each other by more than 36 Elementary Species one character, often by slight differences in nearly all their organs and qualities. Such forms have come to be designated as " elemen- tary species. " They are only varieties in a broad and vague systematic significance of the word, not in the sense accorded to this term in horticultural usage, nor in a sharper and more scientific conception. Genera and species are, at the present time, for a large part artificial, or stated more cor- rectly, conventional groups. Every systematist is free to delimit them in a wider or in a nar- rower sense, according to his judgment. The greater authorities have as a rule preferred larger genera, others of late have elevated in- numerable subgenera to the rank of genera. This would work no real harm, if unfortu- nately, the names of the plants had not to be changed each time, according to current ideas concerning the genera. Quite the same incon- stancy is observed with species. In the Hand- book of the British Flora, Bentham and Hooker describe the forms of brambles under 5 species, while Babbington in his Manual of British Botany makes 45 species out of the same ma- terial. So also in other cases ; for instance, the willows which have 13 species in one and 31 species in the other of these manuals, and the hawkweeds for which the figures are 7 and 32 Elementary Species in Nature 37 respectively. Other authors have made still greater numbers of species in the same groups. It is very difficult to estimate systematic dif- ferences on the ground of comparative studies alone. All sorts of variability occur, and any individual or small group of specimens can hardly be considered as a reliable representa- tive of the supposed type. Many original diag- noses of new species have been founded on di- vergent specimens and of course, the type can afterwards neither be derived from this indi- vidual, nor from the diagnosis given. This chaotic state of things has brought some ""\ botanists to the conviction that even in syste- matic studies only direct experimental evidence can be relied upon. This conception has in- duced them to test the constancy of species and varieties, and to admit as real units only such groups of individuals as prove to be uniform and constant throughout succeeding gener- ations. The late Alexis Jordan of Lyons in France, made extensive cultures in this direc- tion. In doing so, he discovered that syste- matic species, as a rule, comprise some lesser forms, which often cannot easily be distin- guished when grown in different regions, or by comparing dried material. This fact was, of course, most distasteful to the systematists of his time and even for a long period afterwards 38 Elementary Species they attempted to discredit it Milde and many others have opposed these new ideas with some temporary success. Only of late has the school of Jordan received due recognition, after Thuret, de Bary, Bosen and others tested its practices and openly pronounced for them. Of late Wittrock of Sweden has joined them, making extensive experimental studies concern- ing the real units of some of the larger species of his country. From the evidence, given by these eminent authorities, we may conclude that systematic species, as they are accepted nowadays, are as a rule compound groups. Sometimes they con- sist of two or three, or a few, elementary types, but in other cases they comprise twenty, or fifty, or even hundreds of constant and well differen- tiated forms. The inner constitution of these groups is however, not at all the same in all cases. This will be seen by the description of some of the more interesting of them. The European heartsease, from which our garden-pansies have been chiefly derived, will serve as an example. The garden-pansies are a hybrid race, won by crossing the Viola tricolor with the large flow- ered and bright yellow V. lutea. They com- bine, as everyone knows, in their wide range of Elementary Species in Nature 39 varieties, the attributes of the latter with the peculiarities of the former species. Besides the lutea, there are some other spe- cies, nearly allied to tricolor, as for instance, cornuta, calcarata, and altaica, which are com- bined with it under the head of Melanium as a subgenus, and which together constitute a syste- matic unity of undoubted value, but ranging be- tween the common conceptions of genus and species. These forms are so nearly allied to the heartsease that they have of late been made use of in crosses, in order to widen the range of variability of garden-pansies. Viola tricolor is a common European weed. It is widely dispersed and very abundant, grow- ing in many localities in large numbers. It is an annual and ripens its seeds freely, and if op- portunity is afforded, it multiplies rapidly. Viola tricolor has three subspecies, which are elevated to the rank of species by some authors, and which may here be called, for brevity's sake, by their binary names. One is the typical V. tricolor, with broad flowers, vari- ously colored and veined with yellow, purple and white. It occurs in waste places on sandy soil. The second is called V. arvensis or the field pansy ; it has small inconspicuous flowers, with pale yellowish petals which are shorter than the sepals. It pollinates itself without the 40 Elementary Species aid of insects, and is widely dispersed on culti- vated fields. The third form, V. alpestris, grows in the Alps, but is of lesser importance for our present discussion. Anywhere throughout the central part of Europe V. tricolor and V. arvensis may be seen, each occupying its own locality. They may be considered as ranging among the most common native plants of the particular regions they in- habit. They vary in the color of the flowers, branching of the stems, in the foliage and other parts, but not to such an extent as to consti- tute distinct strains. They have been taken into cultivation by Jordan, Wittrock and others, but throughout Europe they constitute separate types. This type must be very old and very constant, fluctuating always within the same distinct and narrow limits. No slow, gradual changes can have taken place. In different countries their various habitats are as old as the historical records, and probably many centuries older. They are quite independent of one another, the distance being in numerous cases far too great for the exchange of pollen or of seeds. If slow and gradual changes were the rule, the types could not have remained so uniform throughout the whole range of these two species. They would necessarily have split up in thousands Elementary Species in Nature 41 and thousands of minor races, which would show their peculiar characteristics if tested by cultures in adjacent beds. This however, is not what happens. As a matter of fact V. tricolor and V. arvensis are widely distributed but wholly constant types. Besides these, there occur distinct types in numerous localities. Some of them evidently have had time and opportunity to spread more or less widely and now occupy larger regions or even whole countries. Others are narrowly lim- ited, being restricted to a single locality. Witt- rock collected seeds or plants from as many localities as possible in different parts of Sweden and neighboring states and sowed them in his garden near Stockholm. He secured seeds from his plants, and grew from them a second, and in many cases a third, generation in order to estimate the amount of variability. As a rule the forms introduced into his garden proved constant, notwithstanding the new and abnormal conditions under which they were propagated. First of all we may mention three perennial forms called by him Viola tricolor ammotropha, V. tricolor coniophila and V. stenochila. The typical V. tricolor is an annual plant, sowing itself in summer and germinating soon after- wards. The young plants thrive throughout 42 Elementary Species the latter part of the summer and during the fall, reaching an advanced stage of development of the branched stems before winter. Early in the spring the flowers begin to open, but after the ripening of the seeds the whole plant dies. The three perennial species just mentioned develop in the same manner in the first year. During their flowering period, however, and afterwards, they produce new shoots from the lower parts of the stem. They prefer dry and sandy soils, often becoming covered with the sand that is blown on them by the winds. They are prepared for such seemingly adverse cir- cumstances by the accumulation of food in the older stems and by the capacity of the new shoots to thrive on this food till they have be- come long enough to reach the light. Once more V. tricolor ammotropha was found near Ystad in Sweden, and the other two forms on Gotland. All three have narrowly limited habi- tats. The typical tricolored heartsease has re- mained annual in all its other subspecies. It may be divided into two types in the first place : F. tricolor genuina and F. tricolor versicolor. Both of them have a wide distribution and seem to be the prototypes from which the rarer forms must have been derived. Among these latter Wittrock describes several local types, which Elementary Species in Nature 43 proved to be constant in his pedigree-cultures. Some of them have produced other forms, re- lated to them in the way of varieties. They all have nearly the same general habit and do not exhibit any marked differences in their growth, in the structure and branching of the stems, or in the character of their foliage. Differentiat- ing points are to be found mainly in the colors and patterns of the flowers. The veins, which radiate from the centre of the corolla are branched in some and undivided in others; in one elementary species they are wholly lack- ing. The purple color may be absent, leav- ing the flowers of a pale or a deep yellow. Or the purple may be reddish or bluish. Of the petals all five may have the purple hue on their tips, or this attribute may be limited to the two upper ones. Contrasting with this wide variability is the stability of the yellow spot in the centre, which is always present, and becomes inconspicuous only, when the whole petals are of the same hue. It is a general conception that colors and color markings are liable to great variability and do not constitute reliable standards. But the cultures of Wittrock have proved the contrary, at least in the case of the violets. No pattern, however quaint, appears changeable, if one elementary species only is considered. Hundreds of plants from seeds 44 Elementary Species from one locality may be grown, and all will ex- hibit exactly the same markings. Most of these forms are of very local occurrence. The most beautiful of all, the ornatissima, is found only in Jemtland, the aurobadia only in Sodermanland, the anopetala in other localities in the same country, the roseola near Stockholm, and the yellow lutescens in Finmarken. The researches of Wittrock included only a small number of elementary species, but every one who has observed the violets in the central parts of Europe must be convinced that many dozens of constant forms of the typical Viola tricolor might easily be found and isolated. We now come to the field pansy, the Viola ar- vensis, a very common weed in the grain fields of central Europe. I have already mentioned its small corolla, surpassed by the lobes of the calyx, and its capacity of self-fertilization. It has still other curious differentiating charac- ters; the pollen grains, which are square in V. tricolor, are five-sided in V. arvensis. Some transgressive fluctuating variability may occur in both cases through the admixture of pollen-grains. Even three-cornered pollen- grains are seen sometimes. Other marks are observed in the form of the anthers and the spur. There seem to be very many local subspecies Elementary Species in Nature 45 of the field-pansy. Jordan has described some from the vicinity of Lyons, and Wittrock and others from the northern parts of Europe. They diverge from their common prototype in nearly all attributes, the flowers not showing the essential differentiating characters as in the V. tricolor. Some have their flower stalks erect, and in others the flowers are held nearly at right angles to the stem. F. palescens is a small, almost unbranched species with small pale flowers. F. segetatis is a stouter species with two dark blue spots on the tips of the upper petals. A. agrestis is a tall and branched, hairy form. F. nemausensis attains a height of only 10 cm., has rounded leaves and long flower-stalks. Even the seeds afford charac- ters which may be made use of in isolating the various species. The above-mentioned elementary forms be- long to the flora of southern France, and Witt- rock has isolated and cultivated a number of others from the fields of Sweden. A species from Stockholm is called Viola patens; V. arven- sis curtisepala occurs in Gotland, and F. arven- sis striolata is a distinct form, which has ap- peared in his cultures without its true origin being ascertained. The alpine violets comprise a more wide- spread type with some derived local elementary 46 Elementary Species species exactly in the same way as the tricolored field-pansies. Summarizing the general result of this de- scription we see that the original species Viola tricolor may be split up into larger and lesser groups of separate forms. These last prove to be constant in pedigree-cultures, and therefore are to be considered as really existent units. They are very numerous, comprising many dozens in each of the two larger subdivisions. All systematic grouping of these forms, and their combination into subspecies and species rests on the comparative study of their charac- ters. The result of such studies must neces- sarily depend on principles which underlie them. According to the choice of these principles, the construction of the groups will be found to be different. Wittrock trusts in the first place to the morphological charac- ters, and considers the development as passing from the more simple to the more complex types. On the other hand the geographic dis- tribution may be considered as an indication of the direction of evolution, the wide-spread forms being regarded as the common parents of the minor local species. However, such considerations are only of sec- ondary importance. It must be borne in mind that an ordinary systematic species may include Elementary Species in Nature 47 many dozens of elementary forms each of which remains constant and unchanged in successive generations, even if cultivated in the same gar- den and under similar external conditions. Leaving the violets, we may take the vernal whitlow-grass or Draba verna for a second illus- tration. This little annual cruciferous plant is common in the fields of many parts of the United States, though originally introduced from Europe. It has small basal rosettes which develop during summer and winter, and pro- duce numerous leafless flowering stems early in the spring. It is a native of central Europe and western Asia, and may be considered as one of the most common plants, occurring anywhere in immense numbers on sandy soils. Jordan was the first to point out that it is not the same throughout its entire range. Although a hasty survey does not reveal differences, they betray themselves on a closer inspection. Be Bary, Thuret, Eosen and many others confirmed this result, and repeated the pedigree-cultures of Jordan. Every type is constant and remains unchanged in successive generations. The an- thers open in the flower-buds and pollinate the stigmas before the expansion of the flowers, thus assuring self-fertilization. Moreover, these inconspicuous little flowers are only spar- ingly visited by insects. Dozens of subspecies 48 Elementary Species may be cultivated in the same garden without any real danger of their intercrossing. They remain as pure as under perfect isolation. It is very interesting to observe the aspect of such types, when growing near each other. Hundreds of rosettes exhibit one type, and are undoubtedly similar. The alternative group is distinguishable at first sight, though the differ- entiating marks are often so slight as to be traceable with difficulty. Two elementary spe- cies occur in Holland, one with narrow leaves in the western provinces, and one with broader foliage in the northern parts. I have cultivated them side by side, and was as much struck with the uniformity within each group, as with the contrast between the two sets. Nearly all organs show differences. The most marked are those of the leaves, which may be small or large, linear or elliptic or oblong and even rhomboidal in shape, more or less hairy with simple or with stellate branched hairs, and finally of a pure green or of a glaucous color. The petals are as a rule obcordate, but this type may be combined with others having more or less broad emarginations at the summit, and with differences in breadth which vary from al- most linear types to others which touch along their margins. The pods are short and broad, or long and narrow, or varying in sundry other Elementary Species in Nature 49 ways. All in all there are constant differences to such an amount that it has been possible to distinguish and to describe large numbers of types. Many of them have been tested as to their constancy from seed. Jordan made numerous cultures, some of which lasted ten or twelve years; Thuret has verified the assertion con- cerning their constancy by cultures extending over seven years in some instances; Villars and de Bary made numerous trials of shorter dura- tion. All agree as to the main points. The local races are uniform and come true from seed ; the variability of the species is not of a fluctuating, but of a polymorphous nature. A given ele- mentary species keeps within its limits and can- not vary beyond them, but the whole group gives the impression of variability by its large range of distinct but nearly allied forms. The geographic distribution of these ele- mentary species of the whitlow-grass is quite distinct from that of the violets. Here predom- inant species are limited to restricted locali- ties. Most of them occupy one or more depart- ments of France, and in Holland two of them are spread over several provinces. An import- ant number are native in the centre of Europe, and from the vicinity of Lyons, Jordan suc- ceeded in establishing about fifty elementary 50 Elementary Species species in his garden. In this region they are crowded together and not rarely two or even more quite distinct forms are observed to grow side by side on the same spot. Farther away from this center they are more widely dispersed, each holding its own in its habitat. In all, Jor- dan has distinguished about two hundred spe- cies of Draba verna from Europe and western Asia. Subsequent authors have added new types to the already existing number from time to time. The constancy of these elementary species is directly proven by the experiments quoted above, and moreover it may be deduced from the uniformity of each type within its own domain. These are so large that most of the localities are practically isolated from one another, and must have been so for centuries. If the types were slowly changing such localities would often, though of course not always, exhibit slighter differences, and on the geographic limits of neighboring species intermediates would be found. Such, however, are not on record. Hence the elementary species must be regarded as old and constant types. The question naturally arises how these groups of nearly allied forms may originally have been produced. Granting a common ori- gin for all of them, the changes may have been Elementary Species in Nature 51 simultaneous or successive. According to the geographic distribution, the place of common origin must probably be sought in the southern part of central Europe, perhaps even in the vicinity of Lyons. Here we may assume that the old Draba verna has produced a host or a swarm of new types. Thence they must have spread over Europe, but whether in doing so they have remained constant, or whether some or many of them have repeatedly undergone specific mutations, is of course unknown. The main fact is, that such a little species as Draba verna is not at all a uniform type, but comprises over two hundred well distinguished and constant forms. It is readily granted that violets and whitlow- grasses are extreme instances of systematic variability. Such great numbers of elementary species are not often included in single species of the system. But the numbers are of second- ary importance, and the fact that systematic species consist of, as a rule, more than one inde- pendent and constant subspecies, retains its al- most universal validity. In some cases the systematic species are man- ifest groups, sharply differentiated from one another. In other instances the groups of ele- mentary forms as they are shown by direct ob- servation, have been adjudged by many authors 52 Elementary Species to be too large to constitute species. Hence the polymorphous genera, concerning the syste- matic subdivisions of which hardly two authors agree. Brambles and roses are widely known instances, but oaks, elms, apples, and pears, Mentha, Prunus, Vitis, Lactuca, Cucumis, Cu- curbita and numerous others are in the same condition. In some instances the existence of elementary species is so obvious, that they have been de- scribed by taxonomists as systematic varieties, or even as good species. The primroses afford a widely known example. Linnaeus called them Primula veris, and recognized three types as pertaining to this species, but Jacquin and others have elevated these subspecies to the full rank of species. They now bear the names of Primula elatior with larger, P. officinalis with smaller flowers, and P. acaulis. In the last named the common flower-stalk is wanting and the flowers of the umbel seem to be borne in the axils of the basal leaves. In other genera such nearly allied species are more or less universally recognized. Galium Mollugo has been divided into G. datum with a long and weak stem, and G. erectum with shorter and erect stems ; Cochlearia danica, an- glica and officinalis are so nearly allied as to be hardly distinguishable. Sagina apetala and pat- Elementary Species in Nature 53 ula, Spergula media and salina and many other pairs of allied species have differentiating char- acters of the same value as those of the element- ary species of Draba verna. Filago, Plantago, Carex, Ficaria and a long series of other genera afford proofs of the same close relation be- tween smaller and larger groups of species. The European frost-weeds or Helianthemum in- clude a group of species which are so closely al- lied, that ordinary botanical descriptions are not adequate to give any idea of their differen- tiating features. It is almost impossible to determine them by means of the common ana- lytical keys. They have to be gathered from their various native localities and cultivated side by side in the garden to bring out their differences. Among the species of France, ac- cording to Jordan, Helianthemum polifolium, H. apenninum, H. pilosum and H. pulverulen- tum are of this character. A species of cinquefoil, Potentilla Tormen- tilla, which is distinguished by its quaternate flowers, occurs in Holland in two distinct types, which have proved constant in cultural experi- ments. One of them has broad petals, meeting together at the edges, and constituting a round- ed saucer without breaks. The other has nar- row petals, which are strikingly separated from one another and show the sepals between them. 54 Elementary Species In the same manner blue-bells vary in the size and shape of the corolla, which may be wide or narrow, bell-shaped or conical, with the tips turned downwards, sidewards or backwards. As a rule all of the more striking elementary types have been described by local botanists under distinct specific names, while they are thrown together into the larger systematic spe- cies by other authors, who study the distribu- tion of plants over larger portions of the world. Everything depends on the point of view taken. Large floras require large species. But the study of local floras yields the best re- sults, if the many forms of the region are distin- guished and described as completely as possible. And the easiest way is to give to each of them a specific name. If two or more elementary spe- cies are united in the same district, they are often treated in this way, but if each region had its own type of some given species, commonly the part is taken for the whole, and the sundry forms are described under the same name, with- out further distinctions. Of course these questions are all of a practical and conventional nature, but involve the differ- ent methods in which different authors deal with the same general fact. The fact is that systematic species are compound groups, ex- actly like the genera and that their real units Elementary Species in Nature 55 can only be recognized by comparative experi- mental studies. Though the evidence already given might be esteemed to be sufficient for our purpose, I should like to introduce a few more examples ; two of them pertain to American plants. The Ipecac spurge or Euphorbia Ipecacu- anha, occurs from Connecticut to Florida, mainly near the coast, preferring dry and sandy soil. It is often found by the roadsides. Ac- cording to Britton and Brown's Illustrated Flora it is glabrous or pubescent, with several or many stems, ascending or nearly erect; with green or red leaves, which are wonderfully variable in outline, from linear to orbicular, mostly opposite, the upper sometimes whorled, the lower often alternate. The glands of the involucres are elliptic or oblong, and even the seeds vary in shape. Such a wide range of variability evidently points to the existence of some minor types. Dr. John Harshberger has made a study of those which occur in the vicinity of Whitings in New Jersey. His types agree with the descrip- tion given above. Others were gathered by him at Brown's Mills in the pinelands, New Jersey, where they grew in almost pure sand in the bright sunlight. He observed still other differentiating characters. The amount of seed 56 Elementary Species produced and the time of flowering were vari- able to a remarkable degree. Dr. Harshberger had the kindness to send me some dried specimens of the most interesting of these types. They show that the peculiarities are individual, and that each specimen has its own characters. It is very probable that a comparative experimental study will prove the existence of a large number of elementary spe- cies, differing in many points; they will prob- ably also show differences in the amount of the active chemical substances, especially of emetine, which is usually recorded as present in about 1$, but which will undoubtedly be found in larger quantities in some and in smaller quantities in other elementary species. In this way the close and careful distinction of the really existing units might perhaps prove of practical importance. Macfarlane has studied the beach plum or Prunus maritima, which is abundant along the coast regions of the Eastern States from Vir- ginia to New Brunswick. It often covers areas from two to two hundred acres in extent, some- times to the exclusion of other plants. It is most prolific on soft drifting sand near the sea or along the shore, where it may at times be washed with ocean spray. The fruits usually become ripe about the middle of August, and show ex- Elementary Species in Nature 57 treme variations in size, shape, color, taste, con- sistency, and maturation period, indicating the existence of separate races or elementary spe- cies, with widely differing qualities. The earlier varieties begin to ripen from August 10 to 20, and a continuous supply can be had till Septem- ber 10, while a few good varieties continue to ripen till September 20. But even late in Octo- ber some other types are still found maturing their fruits. Exact studies were made of fruit and stone variations, and their characteristics as to color, weight, size, shape and consistency were fully described. Similar variations have been ob- served, as is well known, in the cultivated plums. Fine blue-black fruits were seen on some shrubs and purplish or yellow fruits on others. Some exhibit a firmer texture and others a more watery pulp. Even the stones show differences which are suggestive of dis- tinct races. Recently Mr. Luther Burbank of Santa Eosa, California, has made use of the beach-plum to produce useful new varieties. He observed that it is a very hardy species, and never fails to bear, growing under the most trying condi- tions of dry and sandy, or of rocky and even of heavy soil. The fruits of the wild shrubs are utterly worthless for anything but preserving. 58 Elementary Species But by means of crossing with other species and especially with the Japanese plums, the hardy qualities of the beach-plum have been united with the size, flavor and other valuable qualities of the fruit, and a, group of new plums have been produced with bright colors, ovoid and globular forms which are never flattened and have no suture. The experiments are not yet finished, as far as I have been able to ascertain, and still more startling improvements are said to have been produced. I may perhaps be allowed to avail myself of this opportunity to point out a practical side of the study of elementary species. This itself appears whenever wild plants are subjected to cultivation, either in order to reproduce them as pure strains, or to cross them with other al- ready cultivated species. The latter practice is as a rule made use of, whenever a wild spe- cies is found to be in possession of some quality which is considered as desirable for the culti- vated forms. In the case of the beach-plum it is the hardiness and the great abundance of fruits of the wild species which might profit- ably be combined with the recognized qualities of the ordinary plums. Now it is manifest, that in order to make crosses, distinct individual plants are to be chosen, and that the variability of the wild species may be of very great im- Elementary Species in Nature 59 portance. Among the range of elementary spe- cies those should be used which not only pos- sess the desired advantages in the highest de- gree, but which promise the best results in other respects or their earliest attainment. The fuller our knowledge of the elementary species constituting the systematic groups, the easier and the more reliable will be the choice for the breeder. Many Californian wild flowers with bright colors seem to consist of large numbers of constant elementary forms, as for instance, the lilies, godetias, eschscholtias and others. They have been brought into cultivation many times, but the minutest distinction of their ele- mentary forms is required to attain the highest success. In concluding, I will point out a very interest- ing difficulty, which in some cases impedes the clear understanding of elementary species. It is the lack of self-fertilization. It occurs in widely distant families, but has a special inter- est for us in two genera, which are generally known as very polymorphous groups. One of them is the hawkweed or Hieracium, and the other is the dandelion or Taraxacum officinale. Hawkweeds are known as a genus in which the delimitation of the species is al- most impossible. Thousands of forms may be cultivated side by side in botanical gardens, ex- 60 Elementary Species hibit slight but undoubted differentiating fea- tures, and reproduce themselves truly by seed. Descriptions were formerly difficult and so com- plicated that the ablest writers on this genus, Fries and Nageli are said not to have been able to recognize the separate species by the de- scriptions given by each other. Are these types to be considered as elementary species, or only as individual differences? The decis- ion, of course, would depend upon their behav- ior in cultures. Such tests have been made by various experimenters. In the dandelion the bracts of the involucre give the best characters. The inner ones may be linear or linear-lance- olate, with or without appendages below the tip ; the outer ones may be similar and only shorter. or noticeably larger, erect, spreading or even reflexed, and the color of the involucre may be a pure green or glaucous; the leaves may be nearly entire or pinnatifid, or sinuate-dentate, or very deeply runcinate-pinnatifid, or even pinnately divided, the whole plant being more or less glabrous. Raunkiaer, who has studied experimentally a dozen types from Denmark, found them con- stant, but observed that some of them have no pollen at all, while in others the pollen, though present, is impotent It does not germinate on the stigma, cannot produce the ordinary tube, Elementary Species in Nature 61 and hence has no fertilizing power. But the young ovaries do not need such fertilization. They are sufficient unto themselves. One may cut off all the flowers of a head before the open- ing of the anthers, and leave the ovaries untouched, and the head will ripen its seeds quite as well. The same thing occurs in the hawkweeds. Here, therefore, we have no ferti- lization and the extensive widening of the varia- bility, which generally accompanies this pro- cess is, of course, wanting. Only partial or vegetative variability is present. Unfertilized eggs when developing into embryos are equiva- lent to buds, separated from the parent-plant and planted for themselves. They repeat both the specific and the individual characters of the parent. In the case of the hawkweed and the dandelion there is at present no means of distinguishing between these two contrasting causes of variability. But like the garden- varieties which are always propagated in the vegetative way, their constancy and uniformity are only apparent and afford no real indication of the hereditary qualities. In addition to these and other exceptional cases, seed-cultures are henceforth to be con- sidered as the sole means of recognizing the really existing systematic units of nature. All other groups, including systematic species and 62 Elementary Species genera, are equally artificial or conventional. Incidentally it is to be said " that current misconceptions as to the extreme range of fluc- tuating variability of many native species have generally arisen from a failure to recognize the composite nature of the forms in question/' as has been demonstrated by MacDougal in the case of the common evening-primrose, Onagra biennis. " It is evident that to study the be- havior of the characters of plants we must have them in their simplest combinations ; to investi- gate the origin and movements of species we must deal with them singly and uncomplicated/' LECTURE III ELEMENTARY SPECIES OF CULTIVATED PLANTS Eecalling the results of the last lecture, we see that the species of the systematists are not in reality units, though in the ordinary course of floristic studies they may, as a rule, seem to be so. In some cases representatives of the same species from different countries or re- gions, when compared with one another do not exactly agree. Many species of ferns afford instances of this rule, and Lindley and other great systematists have frequently been puz- zled by the wide range of differences between the individuals of a single species. In other cases the differentiating forms are observed to grow near each other, sometimes in neighboring provinces, sometimes in the same locality, growing and flowering in mixtures of two or three or even more elementary types. The violets exhibit widespread ancient types, from which the local species may be taken to have arisen. The common ancestors of the whitlow-grasses are probably not to be found 63 64 Elementary Species among existing forms, but numerous types are crowded together in the southern part of central Europe and more thinly scattered elsewhere, even as far as western Asia. There can be lit- tle doubt that their common origin is to be sought in the center of their geographic dis- tribution. Numerous other cases exhibit smaller num- bers of elementary units within a systematic species; in fact purely uniform species seem to be relatively rare. But with small num- bers there are of course no indications to be expected concerning their common origin or the starting point of their distribution. It is manifest that these experiences with wild species must find a parallel among cultivated plants. Of course cultivated plants were origi- nally wild, and must have come under the gen- eral law. Hence we may conclude that when first observed and taken up by man, they must already have consisted of sundry elementary subspecies. And we may confidently assert that some must have been rich and others poor in such types. Granting this state of things as the only prob- able one, we can easily imagine what must have been the consequences. If a wild species had been taken into cultivation only once, the culti- vated form would have been a single element- Cultivated Elementary Species 65 ary type. But it is not very likely that such partiality would occur often. The conception that different tribes at different tunes and in distant countries would have used the wild plants of their native regions seems far more natural than that all should have obtained plants for cultivation from the same source or locality. If this theory may be relied upon, the origin of many of the more widely cultivated agricultural plants must have been multiple, and the number of the original elementary spe- cies of the cultivated types must have been so much the larger, the more widely distributed and variable the plants under consideration were before the first period of cultivation. Further it would seem only natural to explain the wide variability of many of our larger agri- cultural and horticultural stocks by such an in- cipient multiformity of the species themselves. Through commercial intercourse the various types might have become mixed so as to make it quite impossible to point out the native locali- ties for each of them. Unfortunately historical evidence on this point is almost wholly lacking. The differences in question could not have been appreciated at that remote period, and interest the common ob- server but little even today. The history of most of the cultivated plants is very obscure, 66 Elementary Species and even the most skillful historians, by sifting the evidence afforded by the older writers, and that obtained by comparative linguistic investi- gations have been able to do little more than frame the most general outline of the cultural history of the most common and most widely used plants. Some authors assume that cultivation itself might have been the principal cause of variabil- ity, but it is not proved, nor even probable, that cultivated plants are intrinsically more variable than their wild prototypes. Appearances in this case are very deceptive. Of course widely distributed plants are as a rule richer in subspe- cies than forms with limited distribution, and the former must have had a better chance to be taken into cultivation than the latter. In many cases, especially with the more recent cultivated species, man has deliberately chosen variable forms, because of their greater promise. Thirdly, wide variability is the most efficient means of acclimatization, and only species with many elementary units would have offered the adequate material for introduction into new countries. From this discussion it would seem that it is more reasonable to assert that variability is one of the causes of the success of cultivation, than to assume that cultivation is a cause of variabil- Cultivated Elementary Species 67 ity at large. And this assumption would be equally sufficient to explain the existing condi- tions among cultivated plants. Of course I do not pretend to say that culti- vated plants should be expected to be less vari- able than in the wild state, or that swarms of elementary species might not be produced dur- ing cultivation quite as well as before. How- ever the chance of such an event, as is easily seen, cannot be very great, and we shall have to be content with a few examples of which the coconut is a notable one. Leaving this general discussion of the sub- ject, we may take up the example of the befits. The sugar-beet is only one type from among a horde of others, and though the origin of all the single types is not historically known, the plant is frequently found in the wild state even at the present time, and the native types may be com- pared with the corresponding cultivated varie- ties. The cultivation of beets for sugar is not of very ancient date. The Eomans knew the beets and used them as vegetables, both the roots and the leaves. They distinguished a variety with white and one with red flesh, but whether they cultivated them, or only collected them from where they grew spontaneously, appears to be unknown. 68 Elementary Species Beets are even now found in large quantities along the shores of Italy. They prefer the vicinity of the sea, as do so many other mem- bers of the beet-family, and are not limited to Italy, but are found growing elsewhere on the littoral of the Mediterranean, in the Canary Islands, and through Persia and Babylonia to India, In most of their native localities they occur in great abundance. The color of the foliage and the size of the roots are extremely variable. Some have red leafstalks and veins, others a uniform red or green foliage, some have red or white or yellow roots, or exhibit alternating rings of a red and of a white tinge on cut surfaces. It seems only natural to consider the white and the red, and even the variegated types as distinct varieties, which in nature do not transgress their limits nor change into one another. In a subsequent lecture I will show that this at least is the rule with the corresponding color-varieties in other genera. The fleshiness or pulpiness of the roots is still more variable. Some are as thick as the arm and edible, others are not thicker than a finger and of a woody composition, and the structure of this woody variety is very interesting. The sugar-beet consists, as is generally known, of concentric layers of sugar-tissue and of vascu- Cultivated Elementary Species 69 lar strands; the larger the first and the smaller the latter, the greater is, as a rule, the average amount of sugar of the race. Through the kindness of the late Mr. Eimpau, a well- known German breeder of sugar-beet varieties, I once got specimens from seed of a native wild locality near Bukharest. The plants produced quite woody roots, showing almost no sugar- tissue at all. Woody layers of strongly de- veloped fibrovascular strands were seen to be separated one from another only by very thin layers of parenchymatous cells. Even the number of layers is variable ; it was observed to be five in my plants; but in larger roots the double number and even more may easily be met with. Some authors have distinguished specific types among these wild forms. While the cultivated beets are collected under the head of Beta vulgaris, separate types with more or less woody roots have been described as Beta mari- tima and Beta patula. These show differences in the habit of the stems and the foliage. Some have a strong tendency to become annual, others to become biennial. The first of course do not store a large quantity of food in their roots, and remain thin, even at the time of flow- ering. The biennial types occur in all sizes of roots. In the annuals the stems may vary from 70 Elementary Species erect to ascending, and the name patula indi- cates stems which are densely branching from the base with widely spreading branches throughout. Mr. Em. von Proskowetz of Kwas- sitz, Austria, kindly sent me seeds of this Beta patula, the variability of which was so great in my cultures as to range from nearly typical sugar-beets to the thin woody type of Buk- harest. Broad and narrow leaves are considered to be differentiating marks between Beta vulgaris and Beta patula, but even here a wide range of forms seem to occur. Rimpau, Proskowetz, Schindler and others have made cultures of beets from wild localities in order to discover a hypothetical common an- cestor of all the present cultivated types. These researches point to the B. patula as the probable ancestor, but of course they were not made to decide the question as to whether the origination of the several now existing types had taken place before or during culture. From a general point of view the variability of the wild species is parallel to that of the cultivated forms to such a degree as to suggest the multiple origin of the former. But a close investigation into this highly important prob- lem has still to be made. The varieties of the cultivated beets are com- Cultivated Elementary Species 71 monly included in four subspecies. The two smallest are the salad-beets and the ornamental forms, the first being used as food. The red varieties are cultivated ordinarily, the second being used as ornamental plants during the fall, when they fill the beds left empty by summer flowers, with a bright foliage that is exceedingly rich in form and color. Of the remaining sub- species, one comprises the numerous sorts culti- vated as forage crops and the other the true sugar-beets. Both of them vary widely as to the shape and the size of the roots, the quality of the tissue, the foliage and other characteris- tics. Some of these forms, no doubt, have origi- ' nated during culture. Most of them have been improved by selection, and no beet found in the wild state ever rivals any cultivated variety. But the improvement chiefly affects the size, the amount of sugar and nutrient substances and some other qualities which recur in most of the varieties. The varietal attributes themselves however, are more or less of a specific nature, and are often indicative of the real industrial value of the race in a minor degree. The short- rooted and the horn-shaped varieties might best be cited as examples. The assertion that the sundry varieties of forage-beets are not the result of artificial selec- 72 Elementary Species tion, is supported in a large measure by the his- toric fact that the most of them are far older than the method of conscious selection of plants itself. This method is due to Louis Vilmorin and dates from the middle of the last century. But in the sixteenth century most of our present varieties of beets were already in cultivation. Caspar Bauhin gives a list of the beets of his time and it is not difficult to recognize in it a large series of subspecies and varieties, and even of special forms, which are still cul- tivated. A more complete list was published towards the close of the same century by Olivier de Serres in his world-renowned " Theatre d 'Agriculture " (Paris, 1600). The red forage-beets which are now cultivated on so large a scale, had been introduced from Italy into France only a short time before. From this historic evidence, the period during which the beets were cultivated from the time of the Romans or perhaps much later, up to the time of Bauhin and De Serres, would seem far too short for the production by the unguided se- lection of man of all the now existing types. On the other hand, the parallelism between the characters of some wild and some cultivated varieties goes to make it very probable that other varieties have been found in the same way, some in this country and others in that, Cultivated Elementary Species 73 and have been taken into cultivation separately. Afterwards of course all must have been im- proved in the direction required by the needs of man. Quite the same conclusion is afforded by ap- ples. The facts are to some extent of another character, and the rule of the derivation of the present cultivated varieties from original wild forms can be illustrated in this case in a more direct way. Of course we must limit our- selves to the varieties of pure ancestry and leave aside all those which are of hybrid, or pre- sumably hybrid origin. Before considering their present state of cul- ture, something must be said about the earlier history and the wild state of the apples. The apple-tree is a common shrub in woods throughout all parts of Europe, with the only exception of the extreme north. Its distribu- tion extends from western Asia to Anatolia, the Caucasus and Ghilan in Persia. It is found in nearly all forests of any extent and often in relatively large numbers of individuals. It ex- hibits varietal characters, which have led to the recognition of several spontaneous forms, especially in France and in Germany. The differentiating qualities relate to the shape and indumentum of the leaves. Nothing is known botanically as to differences between 74 Elementary Species the fruits of these varieties, but as a matter of fact the wild apples of different countries are not at all the same. Alphonse De Candolle, who made a profound study of the probable origin of most of our cul- tivated plants, comes to the conclusion that the apple-tree must have had this wide distribution in prehistoric times, and that its cultivation be- gan in ancient times everywhere. This very important conclusion by so high an authority throws considerable light on the rela- tion between cultivated and wild varieties at large. If the historic facts go to prove a mul- tiple origin for the cultivation of some of the more important useful plants, the probability that different varieties or elementary species have been the starting points for different lines of culture, evidently becomes stronger. Unfortunately, this historic evidence is scanty. The most interesting facts are those concerning the use of apples by the Romans and by their contemporaries of the Swiss and middle European lake-dwellings. Oswald Heer has collected large numbers of the relics of this prehistoric period. Apples were found in large quantities, ordinarily cut into halves and with the signs of having been dried. Heer dis- tinguished two varieties, one with large and one with small fruits. The first about 3 and Cultivated Elementary Species 75 the other about 1.5-2 cm. in diameter. Both are therefore very small compared with our present ordinary varieties, but of the same general size as the wild forms of the present day. Like these, they must have been of a more woody and less fleshy tissue. They would scarcely have been tasteful to us, but in ancient times no better varieties were known and therefore no compari- son was possible. There is no evidence concerning the question, as to whether during the periods mentioned ap- ples were cultivated or only collected in the wild state. The very large numbers which are found, have induced some writers to believe in their culture, but then there is no reason why they should not have been collected in quantity from wild shrubs. The main fact is that the apple was not a uniform species in prehistoric times but showed even then at least some amount of variability. At the present day the wild apples are very rich in elementary species. Those of Ver- sailles are not the same as those of Belgium, and still others are growing in England and in Germany. The botanical differences derived from the blossoms and the leaves are slight, but the flavor, size and shape of the fruits diverge widely. Two opinions have been advanced to explain this high degree of variability, but 76 Elementary Species neither of them conveys a real explanation; their aim is chiefly to support different views as to the causes of variability, and the origin of elementary species at large. One opinion, advocated by De Candolle, Dar- win and others, claims that the varieties owe their origin to the direct influence of cultiva- tion, and that the corresponding forms found in the wild state, are not at all original, but have escaped from cultivation and apparently be- come wild. Of course this possibility cannot be denied, at least in any single instance, but it seems too sweeping an assertion to make for the whole range of observed forms. The alternative theory is that of van Mons, the Belgian originator of commercial varieties of apples, who has published his experiments in a large work called " Arbres fruitiers ou Pomo- nomie beige. ' ' Most of the more remarkable ap- ples of the first half of the last century were pro- duced by van Mons, but his greatest merit is not the direct production of a number of good varieties, but the foundation of the method, by which new varieties may be obtained and un- proved. According to van Mons, the production of a new variety consists chiefly of two parts. The first is the discovery of a subspecies with new desirable qualities. The second is the trans- Cultivated Elementary Species 77 formation of the original small and woody ap- ple into large, fleshy and palatable variety. Subspecies, or what we now call elementary species were not produced by man ; nature alone creates new forms, as van Mons has it. He ex- amined with great care the wild apples of his country, and especially those of the Ardennes, and found among them a number of species with different flavors. For the flavor is the one great point, which must be found ready in nature, and which may be improved, but can never be created by artificial selection. The numerous differences in flavor are quite orig- inal; all of them may be found in the wild state, and most of them even in so limited a region as the Ardennes Mountains. Of course van Mons preferred not to start from the wild types themselves, when the same flavor could be met with in some cultivated variety. His general method was, to search for a new flavor, and to try to bring the bearer of it up to the desired standard of size and edibility. The latter improvement, though it always makes the impression of an achievement, is only the last stone to be added to the building up of the commercial value of the variety. Without it, the best flavored apple remains a crab ; with it, it becomes a conquest. According to the method of van Mons it may be reached within 78 Elementary Species two or three generations, and a man's life is wholly sufficient to produce in this way many new types of the very best sorts, as van Mons himself has done. It is done in the usual way, sowing on a large scale and selecting the best, which are in their turn brought to an early maturation of their fruit by grafting, because thereby the life from seed to seed may be re- duced to a few years. Form, taste, color, flavor and other valuable marks of new varieties are the products of nature, says van Mons, only texture, fleshiness and size are added by man. And this is done in each new variety by the same method and ac- cording to the same laws. The richness of the cultivated apples of the present day was al- ready present in the large range of original wild elementary species, though unobserved and requiring improvement. An interesting proof of this principle is af- forded by the experience of Mr. Peter M. Gideon, as related by Bailey. Gideon sowed large quantities of apple-seeds, and one seed produced a new and valuable variety called by him the " Wealthy " apple. He first planted a bushel of apple-seeds, and then every year, for nine years, planted enough seeds to produce a thousand trees. At the end of ten years all seedlings had perished except one hardy seed- Cultivated Elementary Species 79 ling crab. This experiment was made in Min- nesota, and failed wholly. Then he bought a small lot of seeds of apples and crab-apples in Maine and from these the " Wealthy " came. There were only about fifty seeds in the lot of crab-apple seed which produced the "Wealthy," but before this variety was obtained, more than a bushel of seed had been sown. Chance af- forded a species with an unknown taste ; but the growing of many thousands of seedlings of known varieties is not the best means to get something really new. Pears are more difficult to improve than ap- ples. They often require six or more genera- tions to be brought from the wild woody state to the ordinary edible condition. But the va- rieties each seem to have a separate origin, as with apples, and the wide range of form and of taste must have been present in the wild state, long before cultivation. Only recently has the improvement of cherries, plums, currants and gooseberries been undertaken with success by Mr. Burbank, and the differences between the wild and cultivated forms has hitherto been very small. All indications point to the exist- ence, before the era of cultivation, of larger or smaller numbers of elementary species. The same holds good with many of the larger forage crops and other plants of great indus- 80 Elementary Species trial value. Clover exhibits many varieties, which have been cultivated indiscriminately, and often in motley mixtures. The flower- heads may be red or white, large or small, cylin- dric or rounded, the leaves are broader or nar- rower, with or without white spots of a curious pattern. They may be more or less hairy and so forth. Even the seeds exhibit differences in size, shape or color, and of late Martinet has shown, that by the simple means of picking out seeds of the same pattern, pure strains of clover may be obtained, which are of varying cultural value. In this way the best subspecies or va- rieties may be sought out for separate cultiva- tion. Even the white spots on the leaflets have proved to be constant characters corresponding with noticeable differences in yield. Flax is another instance. It was already cul- tivated, or at least made use of during the period of the lake-dwellers, but at that time it was a species referred to as Linum angusti- folium, and not the Linum usitatissimum, which is our present day flax. There are now many subspecies, elementary species, and varieties under cultivation. The oldest of them is known as the " springing flax," in opposition to the ordinary " threshing flax." It has capsules which open of themselves, in order to dissemin- ate the seeds, while the ordinary heads of the Cultivated Elementary Species 81 flax remain closed until the seeds are liberated by threshing. It seems probable that the first form or Linum crepitans might thrive in the wild state as well as any other plant, while in the common species those qualities are lacking which are required for a normal dissemination of the seeds. White or blue flowers, high or dwarf stems, more or less branching at the base and sundry other qualities distinguish the va- rieties, aside from the special industrial differ- ence of the fibres. Even the life-history varies from annual and biennial, to perennial. It would take us too long to consider other in- stances. It is well known that corn, though considered as a single botanical species, is rep- resented by different subspecies and varieties in nearly every region in which it is grown. Of course its history is unknown and it is impossi- ble to decide whether all the tall, and dwarf forms, or starchy, and sweet varieties, dented or rounded kernels, and hundreds of others are older than culture or have come into existence during historic times, or as some assume, through the agency of man. But our main point now is not the origin, but only the existence of constant and sharply differentiated forms within botanical species. Nearly every cultivated plant affords instances of such di- versity. Some include a few types only, while 82 Elementary Species others show a large number of forms clearly separated to a greater or lesser degree. In some few instances it is obvious that this variability is of later date than culture. The most conspicuous case is that of the coconut. This valuable palm is found on nearly all tropi- cal coasts, in America, as well as in Asia, but in Africa and Australia there are many hun- dreds of miles of shore line, where it is not found. Its importance is not at all the same everywhere. On the shores and islands of the Indian Ocean and the Malay Archipelago, man is chiefly dependent upon it, but in America it is only of subordinate usefulness. In connection with these facts, it abounds in subspecies and varieties in the East Indian re- gions, but on the continent of America little at- tention has as yet been given to its diverging qualities. In the Malayan region it affords near- ly all that is required by the inhabitants. The value of its fruit as food, and the delicious beverage which it yields, are well known. The fibrous rind is not less useful; it is manufactured into a kind of cordage, mats and floor-cloths. An excellent oil is obtained from the kernel by compression. The hard covering of the stem is converted into drums and used in the construction of huts ; the lower part is so hard as to take on a beautiful polish, Cultivated Elementary Species 83 when it resembles agate. Finally the un- expanded terminal bud is a delicate article of food. Many other uses could be mentioned, but these may suffice to indicate how closely the life of the inhabitants is bound up with the culture of this palm, and how sharply, in consequence, its qualities must have been watched by early man. Any divergence from the ordinary type must have been noted; those which were in- jurious must have been rejected, but the useful ones must have been appreciated and propa- gated. In a word any degree of variability afforded by nature must have been noticed and cultivated. More than fifty different sorts of the coco- nut are described from the Indian shores and islands, with distinct local and botanical names. Miquel, who was one of the best systematists of tropical plants of the last century, described a large number of them, and since, more have been added. Nearly all useful qualities vary in a higher or lesser degree in the different varie- ties. The fibrous strands of the rind of the nut are developed in some forms to such a length and strength as to yield the industrial product known as the coir-fibre. Only three of them are mentioned by Miquel that have this quality, the Cocos nucifera rutila, cupuli- formis and stupposa. Among them the rutila 84 Elementary Species yields the best and most supple fibres, while those of the stupposa are stiff and almost un- bending. The varieties also differ greatly in size, color, shape and quality, and the trees have also pe- culiar characteristics. One variety exhibits leaves which are nearly entire, the divisions be- ing only imperfectly separated, as often occurs in the very first leaves of the seedlings of other varieties. The flavor of the flesh, oil and milk likewise yield many good varietal marks. In short, the coconut-palm comes under the general rule, that botanical species are built up of a number of sharply distinguishable types, which prove their constancy and relative inde- pendence by their wide distribution in culture. In systematic works all these forms are called varieties, and a closer investigation of their real systematic value has not yet been made. But the question as to the origin of the varieties and of the coconut itself has engrossed the at- tention of many botanists, among whom are De Candolle in the middle of the last century, and Cook at its close. Both questions are closely connected. De Candolle claimed an Asiatic origin for the whole species, while Cook's studies go to prove that its original habitat is to be sought in the north- ern countries of South America. Numerous Cultivated Elementary Species 85 varieties are growing in Asia and have as yet not been observed to occur in America, where the coconut is only of subordinate importance, being one of many useful plants, and not the only one relied on by the natives for their sub- sistence. If therefore, De Candolle's opinion is the right one, the question as to whether the varieties are older or younger than the culti- vated forms of the species, must always remain obscure. But if the proofs of an American origin should be forthcoming, the possibility, and even the probability that the varieties are of later date than the begining of their culture, and have originated while in this condition must at once be granted. An important point in the controversy is the manner in which the coco- nuts were disseminated from shore to shore, from island to island. De Candolle, Darwin and most of the European writers claim that the dispersal was by natural agencies, such as ocean-currents. They point out that the fibrous rind or husk would keep the fruits afloat, and uninjured, for many days or even many weeks, while being carried from one country to another in a manner that would explain their geographic distribution. But the probability of the nuts be- ing thrown upon the strands, and far enough from the shore to find suitable conditions for their germination, is a very small one. To in- 86 Elementary Species sure healthy and vigorous seedlings the nuts must be fully ripe, after which planting cannot be safely delayed for more than a few weeks. If kept too moist the nuts rot. If once on the shore, and allowed to lie in the sun, they become overheated and are thereby destroyed; if thrown in the shade of other shrubs and trees, the seedlings do not find the required conditions for a vigorous growth. Some authors have taken the fibrous rind to be especially adapted to transport by sea, but if this were so, this would argue that water is the normal or at least the very frequent medium of dissemination, which of course it is not. We may claim with quite as much right that the thick husk is necessary to enable the heavy fruit to drop from tall trees with safety. But even for this purpose the protection is not suffi- cient, as the nuts often suffer from falling to such a degree as to be badly injured as to their germinating qualities. It is well known that nuts, which are destined for propagation, are as a rule not allowed to fall off, but are taken from the trees with great care. Summing up his arguments, Cook concludes that there is little in the way of known facts to support the poetic theory of the coconut- palm dropping its fruits into the sea to float away to barren islands and prepare them for Cultivated Elementary Species 87 human habitation. Shipwrecks might furnish a successful method of launching viable coco- nuts, and such have no doubt sometimes con- tributed to their distribution. But this as- sumption implies a dissemination of the nuts by man, and if this principal fact is granted, it is far more natural to believe in a conscious in- telligent dissemination. The coconut is a cultivated tree. It may be met with in some spots distant from human dwellings, but whenever such cases have been subjected to a closer scrutiny, it appears that evidently or at least probably huts had formerly existed in their neighborhood, but having been destroyed by some accident, had left the palm trees uninjured. Even in South America, where it may be found in forests at great dis- tances from the sea shore, it is not at all certain that true native localities occur, and it seems to be quite lost in its natural condition. Granting the cultivated state of the palms as the only really important one, and considering the impossibility or at least great improbability of its dissemination by natural means, the dis- tribution by man himself, according to his wants, assumes the rank of an hypothesis fully adequate to the explanation of all the facts con- cerning the life history of the tree. We now have to inquire into the main ques- 88 Elementary Species tion, whether it is probable that the coconut is of American or of Asiatic origin, leaving aside the historic evidence which goes to prove that nothing is known about the period in which its dissemination from one hemisphere to another took place, we will now consider only the bo- tanic and geographic evidence, brought forward by Cook. He states that the whole family of coconut-palms, consisting of about 20 genera and 200 species, are all strictly American with the exception of the rather aberrant African oil- palm, which has, however, an American relative referred to the same genus. The coconut is the sole representative of this group which is connected with Asia and the Malayan region, but there is no manifest reason why other members of the same group could not have established themselves there, and maintained an existence under conditions, which are not at all unfavor- able to them. The only obvious reason is the assumption already made, that the distribution was brought about by man, and thus only af- fected the species, 'chosen by him for cultiva- tion. That the coconut cannot have been im- ported from Asia into America seems to be the most obvious conclusion from the arguments given. It should be briefly noted, that it was known and widely distributed in tropical Amer- ica at the time of the discovery of that continent Cultivated Elementary Species 89 by Columbus, according to accounts of Oviedo and other contemporary Spanish writers. Concluding we may state that according to the whole evidence as it has been discussed by De Candolle and especially by Cook, the coco- nut-palm is of American origin and has been dis- tributed as a cultivated tree by man through the whole of its wide range. This must have hap- pened in a prehistoric era, thus affording time enough for the subsequent development of the fifty and more known varieties. But the pos- sibility that at least some of them have origin- ated before culture and have been deliberately chosen by man for distribution, of course re- mains unsettled. Coconuts are not very well adapted for natural dispersal on land, and this would rather induce us to suppose an origin within the period of cultivation for the whole group. There are a large number of cultivated varieties of differ- ent species which by some peculiarity do not seem adapted for the conditions of life in the wild state. These last have often been used to prove the origin of varietal forms during cul- ture. One of the oldest instances is the variety or rather subspecies of the opium poppy, which lacks the ability to burst open its capsules. The seeds, which are thrown out by the wind, in the common forms, through the apertures under- 90 Elementary Species neath the stigma, remain enclosed. This is manifestly a very useful adaption for a culti- vated plant, as by this means no seeds are lost. It would be quite a disadvantage for a wild species, and is therefore claimed to have been connected from the beginning with the culti- vated form. The large kernels of corn and grain, of beans and peas, and even of the lupines were consid- ered by Darwin and others to be unable to cope with natural conditions of life. Many valuable fruits are quite sterile, or produce extremely few seeds. This is notoriously the ease with some of the best pears and grapes, with the pine-apples, bananas, bread-fruits, pomegran- ate and some members of the orange tribe. It is open to discussion as to what may be the im- mediate cause of this sterility, but it is quite evident, that all such sterile varieties must have originated in a cultivated condition. Otherwise they would surely have been lost. In horticulture and agriculture the fact that new varieties arise from time to time is beyond all doubt, and it is not this question with which we are now concerned. Our arguments were only intended to prove that cultivated species, as a rule, are derived from wild species, which obey the laws discussed in a previous lecture. The botanic units are compound entities, and Cultivated Elementary Species 91 the real systematic units in elementary species play the same part as in ordinary wild species. The inference that the origin of the cultivated plants is multiple, in most cases, and that more than one, often many separate elementary forms of the same species must originally have been taken into cultivation, throws much light upon many highly important problems of culti- vation and selection. This aspect of the ques- tion will therefore be the subject of the next lecture. LECTURE IV SELECTION OF ELEMENTARY SPECIES The improvement of cultivated plants must obviously begin with already existing forms. This is true of old cultivated sorts as well as for recent introductions. In either case the start- ing-point is as important as the improvement, or rather the results depend in a far higher de- gree on the adequate choice of the initial ma- terial than on the methodical and careful treat- ment of the chosen varieties. This, however, has not always been appreciated as it deserves, nor is its importance at present universally recognized. The method of selecting plants for the improvement of the race was discovered by Louis Vilmorin about the middle of the last century. Before his time selection was ap- plied to domestic animals, but Vilmorin was the first to apply this principle to plants. As is well known, he used this method to increase the amount of sugar in beets and thus to raise their value as forage crops, with such success, that his plants have since originated numerous 92 Selection of Elementary Species 93 races. He must have made some choice among th« numerous available sorts of beets, or other- wise, chance must have placed in his hands one of the most appropriate forms. On this point however, no evidence is at hand. Since the work of Vilmorin the selection prin- ciple has increased enormously in importance, for practical purposes as well as for the the- oretical aspect of the subject. It is now being applied on a large scale to nearly all ornamental plants. It is the one great principle now in universal practice as well as one of preeminent scientific value. Of course, the main argu- ments of the evolution theory rest upon mor- phologic, systematic, geographic and pale- ontologic evidence. But the question as to how we can coordinate the relation between existing species and their supposed ancestors is of course one of a physiologic nature. Di- rect observation or experiments were not avail- able for Darwin and so he found himself con- strained to make use of the experience of breed- ers. This he did on a broad scale, and with such success that it was precisely this side of his arguments that played the major part in convincing his contemporaries. The work of the breeders previous to Dar- win's time had not been very critically per- formed. Eecent analyses of the evidence ob- 94 Elementary Species tained from them show that numerous types of variability were usually thrown together. What type in each case afforded the material, which the breeder in reality made use of, has only been inquired into in the last few decades. Among those who have opened the way for thorough and more scientific treatment are to be mentioned, Rimpau and Von Eiimker of Ger- many and W. M. Hays of America. Von Riimker is to be considered as the first writer, who sharply distinguished between two phases of methodical breeding-selection. One side he calls the production of new forms, the other the improvement of the breed. He dealt with both methods extensively. New forms are considered as spontaneous variations occurring or originating without human aid. They have only to be selected and isolated, and their progeny at once yields a constant and pure race. This race retains its character as long as it is protected against the admixture of other minor varieties, either by cross-pollination, or by ac- cidental seeds. Improvement, on the other hand, is the work of man. New varieties of course can only be isolated if chance is given them; the improve- ment is not incumbent on chance. It does not create really anything new, but develops char- acters, which were already existing. It brings Selection of Elementary Species 95 the race above its average, and must guard constantly against the regression towards this average which usually takes place. Hays has repeatedly insisted upon the prin- ciple of the choice of the most favorable varie- ties as the foundation for all experiments in improving races. He asserts that half the bat- tle is won by choosing the variety which is to serve as a foundation stock, while the other half depends upon the selection of parent-plants within the chosen variety. Thus the choice of the variety is the first principle to be applied in every single case; the so-called artificial selec- tion takes only a secondary place. Calling all minor units within the botanic species by the common name of varieties, without regard to the distinction between elementary species and retrograde varieties, the principle is designated by the term of " variety-testing. " This test- ing of varieties is now, as is universally known, one of the most important lines of work of the agricultural experiment stations. Every state and every region, in some instances even the larger farms, requires a separate variety of corn, or wheat, or other crops. They must be segregated from among the hundreds of gen- erally cultivated forms, within each single bo- tanic species. Once found, the type may be ameliorated according to the local conditions 96 Elementary Species and needs, and this is a question of improve- ment. The fact that our cultivated plants are com- monly mixtures of different sorts, has not al- ways been known. The first to recognize it seems to have been the Spanish professor of botany, Mariano Lagasca, who published a number of Spanish papers dealing with useful plants and botanical subjects between 1810 and 1830, among them a catalogue of plants cultivated in the Madrid Botanical Garden. Once when he was on a visit to Colonel Le Couteur on his farm in Jersey, one of the Channel Islands off the coast of France, in discussing the value of the fields of wheat, he pointed out to his host, that they were not really pure and uniform, as was thought at that time, and suggested the idea that some of the constituents might form a larger part in the harvest than others. In a single field he succeeded in distinguishing no less than 23 varieties, all growing together. Colonel Le Couteur took the hint, and saved the seeds of a single plant of each supposed va- riety separately. These he cultivated and mul- tiplied till he got large lots of each and could compare their value. From among them he then chose the variety producing the greatest amount of the finest, whitest and most nu- tritious flour. This he eventually placed in the Selection of Elementary Species 97 market under the name of " Talavera de Bellevue." It is a tall white variety, with long and slender white heads, almost without awns, and with fine white pointed kernels. It was in- troduced into commerce about 1830, and is still one of the most generally cultivated French wheats. It was highly prized in the magnifi- cent collection of drawings and descriptions of wheats, published by Vilmorin under the title 1 i Les meilleurs bles ' ' and is said to have quite a number of valuable qualities, stocking freely and producing an abundance of good grain and straw. It is however, sensitive to cold win- ters in some degree and thereby limited in its distribution. Hallet, the celebrated English wheat-breeder, tried in vain to improve the peculiar qualities of this valuable production of Le Couteur 's. Le Couteur worked during many years along this line, long before the time when Vilmorin conceived the idea of improvement by race- selections, and he used only the simple principle of distinguishing and isolating the members of his different fields. Later he pub- lished his results in a work on the varieties, peculiarities and classification of wheat (1843), which though now very rare, has been the basis and origin of the principle of variety-testing. The discovery of Lagasca and Le Couteur was 98 Elementary Species of course not applicable to the wheat of Jersey alone. The common cultivated sorts of wheat and other grains were mixtures then as they are even now. Improved varieties are, or at least should be, in most cases pure and uniform, but ordinary sorts, as a rule, are mixtures. Wheat, barley and oats are self -fertile and do not mix on the field through cross-pollination. Every member of the assemblage propagates it- self, and is only checked by its own greater or lesser adaptation to the given conditions of life. Eimpau has dealt at large with the phenomenon as it occurs in the northern and middle parts of Germany. Even Rivett's " Bearded wheat, " which was introduced from England as a fine improved variety, and has become widely dis- tributed throughout large parts of Germany, has kept itself pure. It is found mingled al- most anywhere with the old local varieties, which it was destined to supplant. Any lot of seed exhibits such impurities, as I have had the opportunity of observing myself in sowings in the experimental -garden. But the impurities are only mixtures, and all the plants of Rivett's " Bearded wheat," which of course constitute the large majority, are of pure blood. This may be confirmed when the seeds are col- lected and sown separately in cultures that can be carefully guarded. Selection of Elementary Species 99 In order to get a closer insight into the causes of this confused condition of ordinary races, Eimpau made some observations on Rivett's wheat. He found that it suffers from frost during winter more than the local Ger- man varieties, and that from various causes, alien seeds may accidentally, and not rarely, become mixed with it. The threshing-machines are not always as clean as they should be and may be the cause of an accidental mixture. The manure comes from stables, where straw and the dust from many varieties are thrown together, and consequently living kernels of all may become mixed with dung. Such stray grains will easily germinate in the fields, where they find more congenial conditions than does the improved variety. If winter arrives and kills quantities of this latter, the accidental local races will find ample space to develop. Once started, they will be able to multiply so rapidly, that in one or two following generations they will constitute a very considerable portion of the whole harvest. In this way the awnless German wheat often prevails over the intro- duced English variety, if the latter is not kept pure by continuous selection. The Swiss wheat-breeder Risler made an ex- periment which goes to prove the certainty of the explanation given by Rimpau. He ob- 100 Elementary Species served on his farm at Saleves near the lake of Geneva that after a lapse of time the " Galland- wheat " deteriorated and assumed, as was gen- erally believed, the characters of the local sorts. In order to ascertain the real cause of this ap- parent change, he sowed in alternate rows in a field, the " Galland " and one of the local va- rieties. The " Galland " is a race with ob- vious characters and was easily distinguished from the other at the time when the heads were ripe. They are bearded when flowering, but afterwards throw off the awns. The kernels are very large and yield an extraordinary good white flour During the first summer all the heads of the " Galland " rows had the deciduous awns but the following year they were only seen on half of the plants, the remainder having smooth heads, and the third year the " Galland " had nearly disappeared being supplanted by the com- peting local race. The cause of this rapid change was found to be twofold. First the " Galland," as an improved variety, suffers from the winter in a far higher degree than the native Swiss sorts, and secondly it ripens its kernels one or two weeks later. At the time of harvest it may not have become fully ripe, while all the mixed varieties had reached maturity. The wild oat, Avena fatua, is very common in Selection of Elementary Species 101 Europe from whence it has been introduced in the United States. In summers which are un- favorable to the development of the cultivated oats it may be observed to multiply with an al- most incredible rapidity. It does not contrib- ute to the harvest, and is quite useless. If no selection were made, or if selection were dis- continued, it would readily supplant the culti- vated varieties. From these several observations and experi- ments, it may be seen, that it is not at all easy to keep the common varieties of cereals pure and that even the best are subject to the en- croachment of impurities. Hence it is only natural that races of cereals, when cultivated without the utmost care, or even when selected without an exact knowledge of their single con- stituents, are always observed to be more or less in a mixed condition. Here, as everywhere with cultivated and wild plants, the systematic species consist of a number of minor types, which pertain to different countries and cli- mates, and are growing together in the same climate and under the same external conditions. They do not mingle, nor are their differentiat- ing characters destroyed by intercrossing. They each remain pure, and may be isolated whenever and wherever the desirability for such a proceeding should arise. The purity of 102 Elementary Species the races is a condition implanted in them by man, and nature always strives against this arbitrary and one-sided improvement. Numer- ous slight differences in characters and numer- ous external influences benefit the minor types and bring them into competition with the better ones. Sometimes they tend to supplant the latter wholly, but ordinarily sooner or later a state of equilibrium is reached, in which hence- forth the different sorts may live together. Some are favored by warm and others by cool summers, some are injured by hard winters, while others thrive then and are therefore rela- tively at an advantage. The mixed condition is the rule, purity is the exception. Different sorts of cereals are not always easily distinguishable by the layman and there- fore I will draw your attention to conditions in meadows, where a corresponding phenomenon can be observed in a much simpler way. Only artificial pasture-grounds are seen to consist of a single species of grass or clover. The natural condition in meadows is the occur- rence of clumps of grasses and some clovers, mixed up with perhaps twenty or more species of other genera and families. The numerical proportion of these constituents is of great in- terest, and has been studied at Eothamstead in England and on a number of other farms. It is Selection of Elementary Species 103 always changing. No two successive years show exactly the same proportions. At one time one species prevails, at another time one or two or more other species. The weather during the spring and summer benefits some and hurts others, the winter may be too cold for some, but again harmless for others, the rainfall may partly drown some species, while others re- main uninjured. Some weeds may be seen flow- ering profusely during some years, while in other summers they are scarcely to be found in the same meadow. The whole population is in a fluctuating state, some thriving and others de- teriorating. It is a continuous response to the ever changing conditions of the weather. Rare- ly a species is wholly annihilated, though it may apparently be so for years ; but either from seeds or from rootstocks, or even from neigh- boring lands, it may sooner or later regain its foothold in the general struggle for life. This phenomenon is a very curious and in- teresting one. The struggle for life, which plays so considerable a part in the modern theories of evolution, may be seen directly at work. It does not alter the species themselves, as is commonly supposed, but it is always changing their numerical proportion. Any lasting change in the external conditions will of course alter the average oscillation and the in- 104 Elementary Species fluence of such alterations will manifest itself in most cases simply in new numerical propor- tions. Only extremes have extreme effects, and the chance for the weaker sorts to be complete- ly overthrown is therefore very small. Any one, who has the opportunity of observ- ing a waste field during a series of years, should make notes concerning the numerical propor- tions of its inhabitants. Exact figures are not at all required; approximate estimates will or- dinarily prove to be sufficient, if only the stand- ard remains the same during the succeeding years. The entire mass of historic evidence goes to prove that the same conditions have always prevailed, from the very beginning of cultiva- tion up to the present time. The origin of the cultivation of cereals is to be sought in cen- tral Asia. The recent researches of Solms- Laubach show it to be highly probable that the historic origin of the wheat cultivated in China, is the same as that of the wheat of Egypt and Europe. Eemains of cereals are found in the graves of Egyptian mummies; in the mounds of waste material of the lake-dwellings of Cen- tral Europe, and figures of cereals are to be seen on old Roman coins. In the sepulchre of King Ea-n-Woser of the Fifth Dynasty of Egypt, who lived about 5200 years B. C., two Selection of Elementary Species 105 tombs have recently been opened by the Ger- man Oriental Society. In them were found quantities of the tares of the Triticum dicoccum, one of the more primitive forms of wheat. In other temples and pyramids and even on the stones of the walls of Dashur and El Kab studied by linger, different species and varie- ties of cereals were discovered in large quan- tities, that showed their identity with the pres- ent prevailing cultivated races of Egypt. The inhabitants of the lake-dwellings in Switzerland possessed some varieties of cereals, which have entirely disappeared. They are distinguished by Heer under special names. The small barley and the small wheat of the lake-dwellers are among them. All in all there were ten well distinguished varieties of cereals, the Panicum and the Setaria or millet being of the number. Oats were evidently introduced only toward the very last of the lake-dwelling period, and rye is of far later introduction into western Europe. Similar results are attained by the examination of the cereals figured by the Romans of the same period. All these are archaeologic facts, and give but slight indications concerning the methods of cultivation or the real condition of the culti- vated races of that time. Vergil has left us some knowledge of the requirements of method- 106 Elementary Species ical culture of cereals of his time. In his poem Georgics (I. 197) the following lines are found : Vidi lecta diu, et multo spectata labore Degenerare tamen, ni vis humana quotannis. Maxima quaeque manu legeret. (The chosen seed, through years and labor improved, Was seen to run back, unless yearly Man selected by hand the largest and fullest of ears.) Elsewhere Vergil and also some lines of Columella and Varro go to prove in the same way that selection was applied by the Romans to their cereals, and that it was absolutely necessary to keep their races pure. There is little doubt but that it was the same principle as that which has led, after many centuries, to the complete isolation and improvement of the very best races of the mixed varieties. It fur- ther proves that the mixed conditions of the cereals was known to man at that time, al- though distinct ideas of specific marks and dif- ferences were of course still wholly lacking. It is proof also that cultivated cereals from the earliest times must have been built up of num- erous elementary forms. Moreover it is very probable, that in the lapse of centuries a good- ly number of such types must have disap- Selection of Elementary Species 107 peared. Among the vanished forms are the special barley and wheat of the lake-dwellings, the remains of which have been accidentally preserved, but most of the forms have disap- peared without leaving any trace. This inference is supported by the researches of Solms-Laubach, who found that in Abyssinia numerous primitive types of cereals are still in culture. They are not adequate to compete with our present varieties, and would no doubt also have disappeared, had they not been pre- served by such quite accidental and almost primitive isolation. Closing this somewhat long digression into history we will now resume our discussion con- cerning the origin of the method of selecting cereals for isolation and segregate-cultivation. Some decades after Le Couteur, this method was taken up by the celebrated breeder Patrick Sheriff, of Haddington, in Scotland. His be- lief, which was general at that time, was " That cultivation has not been found to change well defined kinds, and that improvement can be best attained by selecting new and superior varie- ties, which nature occasionally produces, as if inviting the husbandman to stretch forth his hand and cultivate them." Before going into the details of Sheriff's work it is as well to say something concerning 108 Elementary Species the use of the word " selection." This word was used by Sheriff as seen in the quotation given, and it was obviously designed to convey the same idea as the word * * lecta ' ' in the quo- tation from Vergil. It was a choice of the best plants from among known mixed fields, but the chosen individuals were considered to be repre- sentatives of pure and constant races, which could only be isolated, but not ameliorated. Selection therefore, in the primitive sense of the word, is the choice of elementary species and varieties, with no other purpose than that of keeping them as pure as possible from the admixture of minor sorts. The Romans at- tained this end only imperfectly, simply be- cause the laws governing the struggle for life and the competition of numerous sorts in the fields were unsuspected by them. Le Couteur and Sheriff succeeded in the solu- tion of the problem, because they had discovered the importance of isolation. The combination of a careful choice with subsequent isolation was all they knew about it, and it was one of the great achievements to which modern agri- culture owes much of its success. The other great principle was that of Vil- morin. It was the improvement within the race, or the " amelioration of the race " as it was termed by him. It was introduced into Selection of Elementary Species 109 England by F. F. Hallet of Brighton in Sussex, who at once called it " pedigree-culture, " and produced his first new variety under the very name of " Pedigree-wheat. " This principle, which yields improved strains, that are not con- stant but dependent on the continued and care- ful choice of the best plants in each succeeding generation, is now generally called " selec- tion." But it should always be remembered that according to the historic evolution of the idea, the word has the double significance of the distinction and isolation of constant races from mixtures, and that of the choice of the best rep- resentatives of a race during all the years of its existence. Even sugar-beets, the oldest " se- lected " agricultural plants are far from having freed themselves from the necessity of contin- uous improvement. Without this they would not remain constant, but would retrograde with great rapidity. The double meaning of the word selection still prevailed when Darwin published his " Origin of Species." This was in the year 1859, and at that time Sheriff was the highest authority and the most successful breeder of cereals. Vilmorin's method had been applied only to beets, and Hallet had commenced his pedigree-cultures only a few years before and his first publication of the " Pedigree-wheat " 110 Elementary Species appeared some years later at the International Exhibition of London in 1862. Thence, when- ever Darwin speaks of selection, Sheriff's use of the word may as well be meant as that of Vilmorin. However, before going deeper into such the- oretical questions, we will first consider the facts, as are given by Sheriff himself. During the best part of his life, in fact during the largest part of the first half of the nine- teenth century, Sheriff worked according to a very simple principle. When quite young he had noticed that sometimes single plants having better qualities than the average were seen in the fields. He saved the grains, or some- times the whole heads of such plants separate- ly, and tried to multiply them all in such man- ner as to avoid intermixtures. His first result was the " Mungoswell's wheat," In the spring of 1819 he observed quite accidentally in a field of the farm of that name, a single plant which attracted his atten- tion by a deeper green and by being more heav- ily headed out. Without going into further de- tails, he at once chose this specimen as the start- ing point of a new race. He destroyed the sur- rounding plants so as to give it more space, ap- plied manure to its roots, and tended it with special care. It yielded 63 heads and nearly Selection of Elementary Species 111 2500 grains. All of these were sown the fol- lowing fall, and likewise in the succeeding years, the whole harvest was sown in separate lots. After two years of rapid multiplication it proved to be a good new variety and was brought into commerce. It has become one of the prominent varieties of wheat in East Lothian, that county of Scotland of which Had- dington is the principal borough. The grains of " MungoswelPs wheat " are whiter than those of the allied " Hunter's wheat," more rounded but otherwise of the same size and weight. The straw is taller and stronger, and each plant produces more culms and more heads. Sheriff assumed, that the original plant of this variety was a sport from the race in which he had found it, and that it was the only in- stance of this sport and he gives no details about this most interesting side of the ques- tion, omitting even to tell the name of the parent variety. He only asserts that it was seen to be better, and afterwards proved so by the appre- ciation of other breeders and its success in trade. He observed it to be quite constant from the beginning, no subsequent selection be- ing needed. This important feature was simp- ly assumed by him to be true as a matter of course. 112 Elementary Species Some years afterwards, in the summer of 1824, he observed a large specimen of oats in one of the fields of the same farm. Being at that time occupied in making a standard col- lection of oats for a closer comparison of the varieties, he saved the seeds of that plant and sowed them in a row in his experiment-field. It yielded the largest culms of the whole collec- tion and bore long and heavy kernels with a red streak on the concave side and it excelled all other sorts by the fine qualities of its very white meal. In the unequal length of its stalks it has however a drawback, as the field appears thin- ner and more meager than it is in reality. " Hopetown oats," as it is called, has found its way into culture extensively in Scotland and has even been introduced with success into Eng- land, Denmark and the United States. It has been one of the best Scottish oats for more than half a century. The next eight years no single plant judged worthy of selection on his own farm attracted Sheriff's attention. But in the fall of 1832 he saw a beautiful plant of wheat on a neighboring farm and he secured a head of it with about 100 grains. From this he produced the " Hope- town wheat." After careful separation from the kernels this original ear was preserved, and was afte -wards exhibited at the Stirling Agri- Selection of Elementary Species 113 cultural Museum. The " Hopetown wheat" has proved to be a constant variety, excelling the ordinary " Hunter's wheat " by larger grains and longer heads; it yields likewise a straw of superior quality and has become quite popular in large districts of England and Scot- land, where it is known by the name of ' 1 White Hunter's " from its origin and the brilliant whiteness of its heads. In the same way Sheriff's oats were discov- ered in a single plant in a field where it was isolated in order to be brought into commerce after multiplication. It has won the surname of " Make-him-rich. " Nothing is on record about the details of its origin. Four valuable new varieties of wheat and oats were obtained in this way in less than forty years. Then Sheriff changed his ideas and his method of working. Striking specimens ap- peared to be too rare, and the expectation of a profitable result too small. Therefore he be- gan work on a larger scale. He sought and selected during the summer of 1857 seventy heads of wheat, each from a single plant show- ing some marked and presumably favorable pe- culiarity. These were not gathered on one field, but were brought together from all the fields to which he had access in his vicinity. The grains of each of these selected heads were 114 Elementary Species sown separately, and the lots compared during their whole life-period and chiefly at harvest time. Three of the lots were judged of high excellence, and they alone were propagated, and proving to be constant new varieties from the outset were given to the trade under the names of " Sheriff's bearded white," " Sheriff's bearded red/' and " Pringle's wheat." They have found wide acceptance, and the first two of them are still considered by Vilmorin as belonging to the best wheats of France. This second method of Sheriff's evidently is quite analogous to the principle of Lagasca and Le Couteur. The previous assumption that new varieties with striking features were being produced by nature from time to time, was abandoned, and a systematic inquiry into the worth of all the diverging constituents of the fields was begun. Every single ear at once proved to belong to a constant and pure race, but most of these were only of average value. Some few however, excelled to a degree, which made them worth multiplying, and to be intro- duced into trade as separate varieties. Once started, this new method of comparison, selection and isolated multiplication was of course capable of many improvements. The culture in the experiment-field was improved, so as to insure a fuller and more rapid growth. Selection of Elementary Species 115 The ripe heads had to be measured and counted and compared with respect to their size and the number of their kernels. Qualities of grain and of meal had to be considered, and the in- fluence of climate and soil could not be over- looked. Concerning the real origin of his new types Sheriff seems never to have been very inquisi- tive. He remarks that only the best cultivated varieties have a chance to yield still better types, and that it is useless to select and sow the best heads of minor sorts. He further re- marks that it is not probable that he found a new sport every time; on the con- trary he assumes that his selections were pres- ent on the field beforehand, and during a series of succeeding generations. How many years old they were, was of course impossible to de- termine. But there is no reason to believe that the conditions in the fields of Scotland were different from those observed on the Isle of Jersey by Le Couteur. In the year 1862 Sheriff devoted himself to the selection of oats, searching for the best panicles from the whole country, and compar- ing their offspring in his experimental-garden. " Early Fellow," " Fine Fellow," " Longfel- low " and " Early Angus " are very notable varieties introduced into trade in this way. 116 Elementary Species Some years later Patrick Sheriff described his experiments and results in a paper entitled, " On the improvement of cereals/7 but the de- scriptions are very short, and give few details of systematic value. The leading principle, however, is clearly indicated, and anyone who studies with care his method of working, may confidently attempt to improve the varieties of his own locality in the same way. This great principle of " variety-testing," as it has been founded by Le Couteur and Patrick Sheriff, has increased in importance ever since. Two main features are to be considered here. One is the production of local races, the other the choice of the best starting-point for hybrid- izing experiments, as is shown in California by the work of Luther Burbank in crossing dif- ferent elementary species of Lilium pardali- num and others. Every region and locality has its own condi- tions of climate and soil. Any ordinary mixed race will contain some elementary forms which are better adapted for a given district, while others are more suitable to divergent condi- tions. Hence it can readily be inferred that the choice cannot be the same for different re- gions. Every region should select its own type from among the various forms, and variety- testing therefore becomes a task which every Selection of Elementary Species 117 one must undertake under his own conditions. Some varieties will prove, after isolation, to be profitable for large districts and perhaps for whole states. Others will be found to be of more local value, but in such localities to excel all others. As an example we may take one of the varie- ties of wheat originated by the Minnesota Ex- periment Station. Hays described it as fol- lows: It was originated from a single plant From among 400 plants of " Blue stem " sev- eral of the best were chosen, each growing separately, a foot apart in each way. Each of the selected plants yielded 500 or more grains of wheat, weighing 10 or more grams. The seeds from these selected plants were raised for a few years until sufficient was obtained to plant a field. Then for several years the new strains were grown in a field beside the parent variety. One of them was so much superior that all others were discarded. It was the one named " Minnesota No. 169." For a large area of Minnesota this wheat seems capable of yielding at least 1 or 2 bushels more grain per acre than its parent variety, which is the best kind com- monly and almost universally found on the farms in southern and central Minnesota. It would be quite superfluous for our present purpose to give more instances. The fact of 118 Elementary Species the compound nature of so-called species of cultivated plants seems to be beyond all doubt, and its practical importance is quite obvious. Acclimatization is another process, which is largely dependent on the choice of adequate varieties. This is shown on a large scale by the slow and gradual dispersion of the varieties of corn in this country. The largest types are limited to temperate and subtropical regions, while the varieties capable of cultivation in more northern latitudes are smaller in size and stature and require a smaller number of days to reach their full development from seed to seed. Northern varieties are small and short lived, but the ' ' Forty-day-corn ' ' or * ' Quaran- tine maize " is recorded to already have ex- isted in tropical America at the time of Colum- bus. In preference, or rather with the exclu- sion of taller varieties, it has thriven on the northern boundaries of the corn-growing states of Europe since the very begining of its cultiva- tion. According to Naudin, the same rule prevails with melons, cucumbers and gherkins, and other instances could easily be given. Referring now to the inferences that may be drawn from the experience of the breeders in order to elucidate the natural processes, we will return to the whitlow-grasses and pansies. Selection of Elementary Species 119 Nature has constituted them as groups of slightly different constant forms, quite in the same way as wheat and oats and corn. Assum- ing that this happened ages ago somewhere in central Europe, it is of course probable that the same differences in respect to the influence of climatic conditions will have prevailed as with cereals. Subsequent to the period which has produced the numerous elementary spe- cies of the whitlow-grass came a period of wide- spread distribution. The process must have been wholly comparable with that of acclimati- zation. Some species must have been more adapted to northern climates, others to the soils of western or eastern regions and so on. These qualities must have decided the general lines of the distribution, and the species must have been segregated according to their respective climatic qualities, and their adaptability to soil and weather. A struggle for life and a natural selection must have accompanied and guided the distribution, but there is no reason to as- sume that the various forms were changed by this process, and that we see them now en- dowed with other qualities than they had at the outset Natural selection must have played, in this and in a large number of other cases, quite the same part as the artificial method of variety- 120 Elementary Species testing. Indeed it may be surmised that this has been its chief and prominent function. Taking up again our metaphor of the sieve we can assert that in such cases climate and soil exercise sifting action and in this way the ap- plication of the metaphor becomes more defi- nite. Of course, next to the climate and soil, in importance come ecological conditions, the veg- etable and animal enemies of the plants and other influences of the same nature. In conclusion it is to be pointed out that this side of the problem of natural selection and the struggle for life appears to offer the best pros- pects for experimental, or for continued statis- tical inquiry. Direct observations are possible and any comparison of numerical proportions of species in succeeding years affords clear proof of the part it plays. And above all, such observations can be made quite independently of doubtful theoretical considerations about presumed changes of character. The fact of natural selection is plain and it should be studied in its most simple condi- tions. C. RETROGRADE VARIETIES LECTURE V CHAEACTEES OF EETEOGEADE VAEIETIES Every one admires the luxuriance of gar- den-flowers, and their diversity of color and form. All parts of the world have contributed to their number and every taste can find its preference among them. New forms produced by the skill of the breeder are introduced every year. This has been done mostly by crossing and intermingling the characters of introduced species of the same genus. In some of the cases the history of our flowers is so old that their hybrid origin is forgotten, as in the case of the pansies. Hybridizations are still going on in other groups on a large scale, and new forms are openly claimed to be of hybrid origin. Breeders and amateurs generally have more interest in the results than in the way in which it has been brought about. Excel- lent flowers and fruit recommend them- selves and there seems to be no reason for in- 121 122 Retrograde Varieties quiring about their origin. In some cases the name of the originator may be so widely known that it adds weight to the value of the new form, and therefore may advantageously be coupled with it. The origin and history of the greater part of our garden-flowers, fruits and vege- tables are obscure; we see them as they are, and do not know from whence they came. The original habitat for a whole genus or for a species at large, may be known, but questions as to the origin of the single forms, of which it is built up, ordinarily remain unanswered. For these reasons we are restricted in most cases to the comparison of the forms before us. This comparison has led to the general use of the term " variety " in opposition to " species. " The larger groups of forms, which are known to have been introduced as such are called species. All forms which by their characters belong to such a species are designated as varieties, irrespective of their systematic relation to the form, considered as the ancestor of the group. Hence, we distinguish between " hybrid va- rieties " and " pure varieties " according to their origin from different parents or from a single line of ancestors. Moreover, in both groups the forms may be propagated by seeds, or in the vegetative way by buds, by grafting or Retrograde Varieties 123 by cutting, and this leads to the distinction of "" seed- varieties " and " vegetative varieties." In the first case the inheritance of the special characters through the seeds decides the status of the variety, in the latter case this point is left wholly out of consideration. Leaving aside all these different types, we are concerned here only with the " seed- varie- ties " of pure origin, or at least with those, that are supposed to be so. Hybridization and vegetative multiplication of the hybrid no doubt occur in nature, but they are very rare, when compared with the ordinary method of propagation by seed. " Seed-varieties " may further be divided into constant and inconstant ones. The difference is very essential, but the test is not always easy to apply. Constant varieties are as sharply defined and as narrowly limited as are the best wild species, while in- constant types are cultivated chiefly on account of their wide range of form and color. This diversity is repeated yearly, even from the purest seed. We will now discuss the constant seed- varieties, leaving the inconstant and ever- sporting types to a subsequent lecture. In this way we may make an exact inquiry into the departures from the species which are ordinarily considered to constitute the essential character of such a constant and pure seed- 124 Retrograde Varieties variety and need only compare these differ- ences with those that distinguish the elementary species of one and the same group from each other. Two points are very striking. By far the greatest part of the ordinary garden-varieties differ from their species by a single sharp char- acter only. In derivative cases two, three or even more such characters may be combined in one variety, for instance, a dwarfed variety of the larkspur may at the same time bear white flowers, or even double white flowers, but the individuality of the single characters is not in the least obscured by such combinations. The second point is the almost general oc- currence of the same variety in extended series of species. White and double flowers, varie- gated leaves, dwarfs and many other instances may be cited. It is precisely this universal repetition of the same character that strikes us as the essential feature of a variety. And again these two characteristics may now be considered separately. Let us begin with the sharpness of the varietal characters. In this respect varieties differ most obviously from elementary species. They are distin- guished from their nearest allies in almost all organs. There is no prominent distinctive feature between the single forms of Drab a Retrograde Varieties 125 verna, Helianthemum or of Taraxacum; all characters are almost equally concerned. The elementary species of Drab a are characterized, as we have seen, by the forms and the hairiness of the leaves, the number and height of the flower-stalks, the breadth and incision of the petals, the forms of the fruits, and so on. Every one of the two hundred forms included in this collective species has its own type, which it is impossible to express by a single term. Their names are chosen arbitrarily. Quite the contrary is the case with most of the varieties, for which one word ordinarily suffices to ex- press the whole difference. White varieties of species with red or blue flowers are the most common instances. If the species has a compound color and if only one of the constituents is lost, partially colored types arise as inAgrostemmaCoronariabicolor. Or the spots may disappear and the color be- come uniform as in Gentiana punctata concolor and the spotless Arum or Arum maculatum im- maculatum. Absence of hairs produces forms as Biscutella Icevigata glabra; lack of prickles gives the varieties known as inermis, as for in- stance, Ranunculus arvensis inermis. Cytisus prostratus has a variety ciliata, and Solanum Dulcamara, or the bitter-sweet, has a va- riety called tomentosum. The curious mon- 126 Retrograde Varieties ophyllous variety of the strawberry and many other forms will be discussed later. To enlarge this list it would only be necessary to extract from a flora, or from a catalogue of horticultural plants, the names of the varieties enumerated therein. In nearly every instance, where true varieties and not elementary species are concerned, a single term expresses the whole character. Such a list would also serve to illustrate the second point since the same names would recur frequently. Long lists of varieties are called alba, or inermis, or canescens or lutea, and many genera contain the same appellations. In some instances the systematists use a diversity of names to convey exactly the same idea, as if to conceal the monotony of the character, as for instance in the case of the lack of hairs, which is expressed by the varietal names of Papaver dubium glabrum, Arabis ciliata gla- brata, Arabis hirsuta glaberrima, Veronica spicata nit ens, Amygdalus persica laevis, Paeonia corallina leiocarpa, &c. On the contrary we find elementary species in different genera based on the greatest possible diversity of features. The forms of Taraxacum or Helianthemum do not repeat those of Draba or Viola. In roses and brambles the distinguish- ing features are characteristic of the type, as Retrograde Varieties 127 they are evidently derived from it and limited to it. And this is so true that nobody claims the grade of elementary species for white roses or white brambles, but everyone recognizes that forms diverging from the nearest species by a single character only, are to be regarded as varieties. This general conviction is the basis on which we may build up a more sharply defined distinc- tion between elementary species and varieties. It is an old rule in systematic botany, that no form is to be constituted a species upon the basis of a single character. All authors agree on this point; specific differences are derived from the totality of the attributes, not from one organ or one quality. This rule is intimately connected with the idea that varieties are de- rived from species. The species is the typical, really existing, form from which the variety has originated by a definite change. In enumer- ating the different forms the species is distin- guished by the term of genuine or typical, often only indicated as a or the first; then fol- low the varieties sometimes in order of their degree of difference, sometimes simply in alpha- betical order. In the case of elementary species there is no real type; no one of them predom- inates because all are considered to be equal in rank, and the systematic species to which they 128 Retrograde Varieties are referred is not a really existing form, but is the abstraction of the common type of all, just as it is in the case of a genus or of a family. Summarizing the main points of this discus- sion, we find that elementary species are of equal rank and together build up the collective or systematic ideal species. Varieties on the other hand are derived from a real, and com- monly, still existing type. I hope that I have succeeded in showing that the difference between elementary species, or, as they are often called, smaller or subspecies, on the one hand, and varieties on the other is quite a marked one. However, in order to recognize this principle it is necessary to limit the term variety to those propagating themselves by seed and are of pure and not of hybrid origin. But the principle as stated here, does not in- volve an absolute contrast between two groups of characters. It is more a difference in our knowledge and appreciation of them than a dif- ference in the things themselves. The characters of elementary species are, as a rule, new to us, while those of varieties are old and familiar. It seems to me that this is the essential point. And what is it that makes us familiar with them? Obviously the continuous recurrence of the same changes, because by a constant repeti- tion they must of course lose their novelty. Retrograde Varieties 129 Presently we shall look into these characters more in detail and then we shall find that they are not so simple as might be supposed at first sight ; but precisely because we are so familiar with them, we readily see that their different features really belong to a single character; while in elementary species everything is so new that it is impossible for us to discern the unities of the new attributes. If we bear in mind all these difficulties we cannot wonder at the confusion on this ques- tion that seems to prevail everywhere. Some authors following Linnaeus simply call all the subdivisions of species and varieties, others fol- low Jordan and avoid the difficulty by desig- nating all smaller forms directly as species. The ablest systematists prefer to consider the ordinary species as collective groups, calling their constituents " The elements of the spe- cies," as was done by A. P. De Candolle, Alph. De Candolle and Lindley. By this method they clearly point out the dif- ference between the subdivisions of wild spe- cies as they ordinarily occur, and the varieties in our gardens, which would be very rare, were they not singled out and preserved. Our familiarity with a character and our grounds for calling it an old acquaintance may result from two causes, which in judging a new 130 Retrograde Varieties variety are essentially different. The charac- ter in question may be present in the given spe- cies or it may be lacking, but present in the other group. In the first case a variety can only be formed by the loss of the character, in the sec- ond case it arises by the addition of a new one. The first mode may be called a negative pro- cess, while the second is then to be designated as positive. And as it is more easy to lose what one has than to obtain something new, negative varieties are much more common than are posi- tive ones. Let us now take an instance of a character that is apt to vary in both ways, for this is ob- viously the best way of making clear what is meant by a negative and a positive change. In the family of the composites we find a group of genera with two forms of florets on each flower-head. The hermaphrodite ones are tubular with 5, or rarely 4, equal teeth, and oc- cupy the center of the head. These are often called the flosculous florets or disk-florets. Those of the circumference are ligulate and ordinarily uni-sexual, without stamens. In many cases they are sterile, having only an imperfect ovary. They are large and brightly colored and are generally designated as ray-florets. As in- stances we may cite the camomile (Anthemis nobilis), the wild camomile (Matricaria Cham- Retrograde Varieties 131 omilla), the yarrow (Achillea Millefolium), the daisies, the Dahlia and many others. Species occur in this group of plants from time to time that lack the ray-florets, as in the tansy (Tanacetum vulgar e) and some artemisias. And the genus of the marigolds or Bidens is noted for containing both of these types. The smaller and the three-toothed marigold (B. cernua and B. tripartita) are very common plants of wet soil and swamps, ordinarily lack- ing the ray-florets, and in some countries they are very abundant and wholly constant in this respect, never forming radiate flower-heads. On the other hand the white-flowered and the purple marigold (B. leucantha and B. atropur- purea) are cultivated species of our gardens, prized for their showy flower-heads with large white or deeply colored, nearly black-purple florets. Here we have opportunity to observe positive and negative varieties of the same character. The smaller, and the three-toothed marigold occur from time to time, provided with ray- florets, showing a positive variation. And the white marigold has produced in our gardens a variety without rays. Such varieties are quite constant, never returning to the old species. Positive and negative varieties of this kind are by no means rare among the compositae. 132 Retrograde Varieties In systematic works the positive ones are as a rule called " radiate," and the negative ones " discoid." Discoid forms of the ordinary camomile, of the daisy, of some asters (Aster Tripolium), and of some centauries have been described. Eadiate forms have been observed in the tansy (Tanacetum vulgar e)^ the common horse-weed or Canada fleabane (Erigeron cana- densis) and the common groundsel (Senecio vulgaris). Taken broadly the negative varie- ties seem to be somewhat more numerous than the positive ones but it is very difficult to come to a definite conclusion on this point. Quite the contrary is the case with regard to the color-varieties of red and blue flowers. Here the loss of color is so common that every one could give long lists of examples of it. Lin- naeus himself supposed that no blue or red-col- ored wild species would be without a white va- riety. It is well known that he founded his often criticized prescript never to trust to color in recognizing or describing a species, on this belief. On the other hand there are some red varie- ties of white-flowered species. But they are very rare, and little is known about their charac- ters or constancy. Blue varieties of white spe- cies are not found. The yarrow (Achillea Mil- le folium) has a red-flowered form, which occurs Retrograde Varieties 133 from time to time in sunny and sandy localities. I have isolated it and cultivated it during a series of years and during many generations. It is quite true to its character, but the degree of its coloring fluctuates between pink and white and is extremely variable. Perhaps it can be considered as an inconstant variety. A red- flowered form of the common Begonia semper- fiorens is cultivated under the name of " Ver- non," the white hawthorn (Crataegus Oxya- cantha) is often seen with red flowers, and a pink-flowered variety of the " Silverchain " or " Bastard- Acacia " (Robinia Pseud-Acacia) is not rarely cultivated. The " Crown " variety of rice, oats and barley are also to be considered as positive color- variations, the black being due in the latter cases to a very great amount of the red pigment. Among fruits there are also some positive red varieties of greenish or yellowish species, as for instance the red gooseberry (Ribes Grossu- laria) and the red oranges. The red hue is far more common in leaves, as seen among herbs, in cultivated varieties of Coleus and in the brown- leaved form of the ordinary white clover, among trees and shrubs in the hazelnut (Corylus), the beach (Fagus), the birch (Betula), the barberry (Berberis) and many others. But though most of these forms are very ornamental and abun- 134 Retrograde Varieties dant in parks and gardens, little is as yet known concerning the origin of their varietal attributes and their constancy, when propagated by seeds. Besides the ray-florets and the colors, there are of course a great many other characters in which varieties may differ from their species. In most of the cases it is easy to discern whether the new character is a positive or a negative one. And it is not at all necessary to scrutinize very narrowly the list of forms to be- come convinced that the negative form is the one which prevails nearly everywhere, and that positive aberrations are in a general sense so rare that they might even be taken for excep- tions to the rule. Many organs and many qualities may be lost in the origination of a variety. In some in- stances the petals may disappear, as in Nigella, or the stamens, as in the Guelder-rose (Vibur- num Opulus) and the Hortensia and in some bulbs even the whole flowers may be wanting, as in the beautiful " Plumosa " form of the cultivated grape-hyacinth or Muscari comosum. Fruits of the pineapples and bananas without seeds are on record as well as some varieties of apples and pears, of raisins and oranges. And some years ago Mr. Riviere of Algeria de- scribed a date growing in his garden that forms fruit without pits. The stoneless plum of Mr. Retrograde Varieties 135 Burbank of Santa-Rosa, California, is also a very curious variety, the kernel of which is fully developed but naked, no hard substance inter- vening between it and the pulp. More curious still are the unbranched varie- ties consisting of a single stem, as may be seen sometimes in the corn or maize and in the fir. Fir-trees of some three or four meters in height without a single branch, wholly naked and bear- ing leaves only on the shoots of the last year's growth at the apex of the tree may be seen. Of course they cannot bear seed, and so it is with the sterile maize, which never produces any seed-spikes or staminate flowers. Other seed- less varieties can be propagated by buds ; their origin is in most cases unknown, and we are not sure as to whether they should be classified with the constant or with the inconstant varieties. A very curious loss is that of starch in the grains of the sugar-corn and the sugar-peas. It is replaced by sugar or some allied substance (dextrine). Equally remarkable is the loss of the runners in the so-called strawberries of the " Gaillon." Among trees the pendulous or weeping, and the broomlike or fastigiate forms are very marked varieties, which occur in species belong- ing to quite different orders. The ash, the beach, some willows, many other trees and some 136 Retrograde Varieties finer species of garden-plants, as Sophora jap- onica, have given rise to weeping varieties, and the yew-tree or Taxus has a fastigiate form which is much valued because of its ascending branches and pyramidal habit. So it is with the pyramidal varieties of oaks, elms, the bas- tard-acacia and some others. It is generally acknowledged that these forms are to be considered as varieties on the ground of their occurrence in so wide a range of species, and because they always bear the same attrib- utes. The pendulous forms owe their peculiar- ity to a lengthening of the branches and a loss of their habit of growing upwards ; they are too weak to retain a vertical position and the re- sponse to gravity, which is ordinarily the cause of the upright growth, is lacking in them. As far as we know, the cause of this weeping habit is the same in all instances. The fastigiate trees and shrubs are a counterpart of the weep- ing forms. Here the tendency to grow in a horizontal direction is lacking, and with it the bilateral and symmetric structure of the branches has disappeared. In the ordinary yew-tree the upright stem bears its needles equally distributed around its circumference, but on the branches the needles are inserted in two rows, one to the left and one to the right. All the needles turn their upper surfaces up- Retrograde Varieties 137 wards, and their lower surfaces downwards, and all of them are by this means placed in a single horizontal plane, and branching takes place in the same plane. Evidently this general ar- rangement is another response to gravity, and it is the failure of this reaction which induces the branches to grow upwards and to behave like stems. Both weeping and fastigiate characters are therefore to be regarded as steps in a negative direction, and it is highly important that even such marked differences occur without transi- tions or intermediate forms. If these should occur, though ever so rarely, they would proba- bly have been brought to notice, on account of the great prospect the numerous instances would offer. The fact that they are lacking, proves that the steps, though apparently great, are in reality to be considered as covering single units, that cannot be divided into smaller parts. Unfortunately we are still in the dark as to the question of the inheritance of these forms, since in most cases it is difficult to isolate them, when flowering, and to obtain pure seed. We now come to some cases of the loss of superfi- cial organs, of which the nectarines are exam- ple. These are smooth peaches, lacking the soft hairy down, that is such a marked pecul- iarity of the true peaches. They occur in differ- 138 Retrograde Varieties ent races of the peach. As early as the begin- ning of the past century, Gallesio described no less than eight subvarieties of nectarines, each related to a definite race of peach. Most of them reproduce themselves truly from seed, as is well known in this country regarding the clingstones, freestones and some other types. Nectarines have often varied, giving rise to new sorts as in the case of the white nectarine and many others differing greatly in appearance and flavor. On the other hand it is to be re- marked, that the trees do not differ in other re- spects and cannot be distinguished while young, the varietal mark being limited to the loss of the down on the fruit. Peaches have been known to produce nectarines, and nectarines to yield true peaches. Here we have another in- stance of positive and negative steps with refer- ence to the same character, but I cannot with- hold an expression of some doubt as to the possi- bility of crossing and subsequently splitting up of the hybrids as a more probable explanation of at least some of the cases quoted by various writers. Smooth or glabrous varieties often occur, and some of them have already been cited as in- stances of the multiplication of varietal names. Positive aberrations are rather rare, and are mostly restricted to a greater density of the Retrograde Varieties 139 pubescence in some hairy species, as in Galeop- sis Ladanum canescens, Lotus corniculatus hirsutus and so on. But Veronica scutellata is smooth and has a pubescent-variety, and Cyti- sus prostratus and C. spinescens are each re- corded to have a ciliate form. Comparable with the occurrence and the lack of hairs, is the existence or deficiency of the glaucous effect in leaves, as is well known in the common Ricinus. Here the glaucous appear- ance is due to wax distributed in fine particles over the surface of the leaves, and in the green variety this wax is lacking. Other instances could be given as in the green varieties of Pap- aver alpinum and Rumex scutatus. No positive instances are recorded in this case. Spines and prickles may often disappear and give rise to unarmed and defenceless types. Of the thorn-apples both species, the white- flowered Daturar Stramonium and the purple D. Tatula have such varieties. The spiny form has a variety called the " Dutch," which lacks the prickles of the fruit ; it is a very old form and absolutely constant, as are also the thornless thorn-apples. Last year a very curious instance of a partial loss of prickles was discovered by Mr. Cockerell of East Las Vegas in New Mexico. It is a variety of the American cocklebur, often called sea-burdock, or the 140 Retrograde Varieties hedgehog burweed, a stout and common weed of the western States. Its latin name is Xan- thium canadense or X. commune and the form referred to is named by Mr. Cockerell X. Woo- toni, in honor of Professor E. 0. Wooton who described the first collected specimens. The burs of the common species are densely covered with long prickles, which are slightly hooked at the apex. In the new form, which is similar in all other respects to the common cocklebur, the burs are more slender and the prickles much less numerous, about 25 to the bur and mostly stouter at the base. It occurs abundantly in New Mexico, always growing with the common species, and seems to be quite constant from seed. Mr. Cockerell kindly sent me some burs of both forms, and from these I raised in my garden last year a nice lot of the common, as well as of the Wootoni plants. Spineless varieties are recorded for the bas- tard-acacia, the holly and the garden goose- berry (Ribes Grossularia, or R. Uva-crispa). A spineless sport of the prickly Broom (Ulex eu- ropceus) has been seen from time to time, but it has not been propagated. Summarizing the foregoing facts, we have ex- cellent evidence of varieties being produced either by the loss of some marked peculiarity or by the acquisition of others that are already Retrograde Varieties 141 present in allied species. There are a great many cases however, in which the morpholog- ical cause of the dissimilarity is not so easily discerned. But there is no reason to doubt that most of them will be found to conform to the rule on closer investigation. Therefore we can consider the following as the principal differ- ence between elementary species and varieties ; that the first arise by the acquisition of entirely new characters, and the latter by the loss of existing qualities or by the gain of such pecul- iarities as may already be seen in closely allied species. If we suppose elementary species and varie- ties originated by sudden leaps or mutations, then the elementary species have mutated in the line of progression, some varieties have mutated in the line of progression, while others have diverged from their parental types on a line of retrogression, or in the way of repetition. This conception agrees quite well with the cur- rent idea that in the building up of the vegeta- ble kingdom according to the theory of descent, it is species that form the links of the chain from the lower forms to the more highly organ- ized later derivatives: or otherwise expressed, the system is built up of species, and varieties are only local and lateral, but never of real importance for the whole structure. 142 Retrograde Varieties Heretofore we have generally assumed, that varieties differ from the parent species in a sin- gle character only, or at least that only one need be considered. We now come to the study of those varieties, which differ in more than one character. Of these there are two types. In the first the points of dissimilarity are inti- mately connected with one another, in the second they are more or less independent. The mutually related peculiarities may be termed correlative, and we therefore speak, in such cases, of correlative variability. This phenomenon is of the highest importance and is of general occurrence. But before describing some examples, it is as well to note that in the lecture on fluctuating variability, cases of a totally different nature will be dealt with, which unfortunately are designated by the same term. Such merely fluctuating variations are therefore to be left out of the present dis- cussion. The purple thorn-apple, which is considered by some writers as a variety of the white-flow- ered species or Datura Stramonium, and by others as a separate species, D. Tatula, will serve as an illustration. But as its distinguish- ing attributes, as far as we are concerned with them here, are of the nature described above as characteristic of varietal peculiarities no ob- Retrograde Varieties 143 jection can be made to our using them as a case of correlative variability. The essential character of the purple thorn- apple lies in the color of the flowers, which are of a very beautiful pale blue. But this color is not limited to the corolla. It is also to be seen in the stems and in the stalks and veins of the leaves, which are stained with a deep purple, the blue color being added to the original green. Even on the surface of the leaves it may spread into a purplish hue. On the stems it is to be met with everywhere, and even the young seed- lings show it. This is of some importance, as the young plants when unfolding their cotyle- dons and primary leaves, may be distinguished by this means from the seedlings of the white- flowered species. In crossing experiments it is also possible to distinguish the whites and the blues, and experience shows that the correlation of the flowers is quite constant. The color can always be relied upon; if lacking in the seed- lings, it will be lacking in the stems and flowers also ; but if the axis of the young plant is ever so slightly tinged, the color will show itself in its beauty in the later stages of the life of the plant. This is what we term correlation. The colors of the different organs are always in agreement. It is true that they require the concurrence of 144 Retrograde Varieties light for development, and that in the dark or in a faint light the seedlings are apt to remain green, when they should become purple, but aside from such consideration all organs always come true to their color, whether pure green and white, or whether these are combined with the blue tinge. This constancy is so absolute that the colors of the different organs convey the suggestion, that they are only separate marks of a single character. It is on this suggestion that we must work, as it indicates the cause of the correlation. Once present, the faculty of producing the anthocyan, the color in question, will come into activity wherever and whenever opportunity presents itself. It is the cell-sap of the ordinary cell- tissue or parenchyma, which is colored by the anthocyan, and for this reason all organs pos- sessing this tissue, will exhibit the color in ques- tion. Thus the color is not a character belonging to any single organ or cell, nor is it bound to a morphologic unit ; it is a free, physiologic qual- ity. It is not localized, but belongs to the en- tire plant. If we wish to assume for its basis material representative particles, these parti- cles must be supposed to be diffused throughout the whole body of the plant. This conception of a physiologic unit as the Retrograde Varieties 145 cause of colors and other qualities is evidently opposed to the current idea of the cells and tis- sues as the morphologic units of the plants. But I do not doubt, that in the long run it will recommend itself as much to the scientist as to the breeder. For the breeder, when desiring to keep his varieties up to their standard, or when breeding to a definite idea, obviously keeps his standard and his ideal for the whole plant, even if he breeds only for flowers or for fruit. I have chosen the color of the purple thorn- apple as a first example, but the colors of other plants show so many diverging aspects, all pointing so clearly to the same conclusion, that it would be well to take a more extensive view of this interesting subject. First we must consider the correlation in the colors of flowers and fruits. If both are colored in the species, whether red or brown or purple or nearly black, and a variety lacking this hue, is known, it will be lacking in both organs. If the color is pure, the flowers and berries will be- come white, but such cases are rare. Ordinar- ily a yellowish or greenish tinge underlies the ornamental color, and if this latter disappears, the yellowish ground will become manifest. So for instance in the Belladonna, a beautiful per- ennial herb with great shiny black, but very poisonous, fruits. Its flowers are brown, but in 146 Retrograde Varieties some woods a variety with greenish flowers and bright yellow berries occurs, which is also fre- quently seen in botanic gardens. The anthocyan dye is lacking in both organs, and the same is the case with the stems and the leaves. The lady's laurel or Daphne Mezereum has red co- rollas, purple leaves and red fruits; its white- flowered variety may be distinguished by lack of the red hue in the stems and leaves, and by their beautiful yellow berries. Many other instances could be given, since the loss of color in berries is a very common occurrence, so common that for instance, in the heath family or Ericaceae, with only a few exceptions, all berry-bearing species have white-fruited varieties. The same correlation is observed in the seeds. The white-flowered flax may be seen to yield yellow and not brown seeds as in the blue spe- cies. Many varieties of flowers may be recog- nized by the color of their seeds, as in the pop- pies, stocks and others. Other white-flowered varieties may be distinguished when germinat- ing, their young axes being of a pure instead of a purplish green. It is a test ordinarily used by gardeners, to purify their flower beds long before the blooming time, when thinning or weeding them. Even in wild plants, as in Erodium, Calluna, Brunella and others, a bot- anist may recognize the rare white-flowered Retrograde Varieties 147 variety by the pure green color of the leaves, at times when it is not in flower. Some sorts of pears bear colored flowers and a red mark on the stipules of their leaves. Among bulbous plants many varieties may be recognized even in winter by the different tinges of the outer scales. Leaving the colors, we come now to another instance of correlation, which is still more as- tonishing. For it is as rare, as color-varieties are common. It is afforded by some plants the leaves of which, instead of being white or only divided into large parts, are cleft to a greater extent by repeated fissures of the mar- ginal lobes. Such foliar variations are often seen in gardens, where they are cultivated for their beauty or singularity, as with the lacin- iated alders, fern-leaved beeches and limes, oak- leaved laburnums, etc. Many -of them are de- scribed under the varietal name of laciniata. In some cases this fissure extends to the petals of the flowers, and changes them in a way quite analogous to the aberrancy of the leaves. This is known to occur with a variety of brambles, and is often seen in botanic gardens in one of the oldest and most interesting of all anomalies, the laciniated variety of the greater celandine or Chelidonium majus. Many other instances could be given. Most of them belong to the 148 Retrograde Varieties group of negative variations, as we have defined them. But the same thing occurs also with positive varieties, though of course, such cases are very rare. The best known instance is that of the ever-flowering begonia, Begonia semper- florens, which has green leaves and white flow- ers, but which has produced garden varieties with a brown foliage and pink flowers. Here also the new quality manifests itself in different organs. Enough has now been said on correlative changes, to convince us that they are as a rule to be considered as the expression of some gen- eral internal or physiologic quality, which is not limited to a single organ, but affects all parts of the organism, provided they are capable of undergoing the change. Such characters are therefore to be considered as units, and should be referred to the group of single characters. Opposed to these are the true compound char- acters, which consist of different units. These may be segregated by the production of varie- ties, and thereby betray the separate factors of the complex group. The most beautiful instances of such complex characters are offered by the colors of some of the most prized garden-flowers. Earely these are of a single hue, often two or three shades contribute to the effect, and in some cases spe- Retrograde Varieties 149 cial spots or lines or tracings are to be seen on a white or on a colored background. That such spots and lines are separate units is obvious and is demonstrated by the fact that some- times spotless varieties occur, which in all other respects have kept the colors of the species. The complexity of the color is equally evident, whenever it is built up of constituents of the anthocyan and of the yellow group. The an- thocyan dye is limited to the sap-cavity of the cells, while the yellow and pure orange colors are fixed in special organs of the protoplasm. The observation under the microscope shows at once the different units, which though lying in the same cell and in almost immediate vicinity of each other are always wholly separated from one another by the wall of the vacuole or sap- filled cell-cavity. The combination of red and yellow gives a brown tinge, as in the cultivated flower, or those bright hues of a dark orange-red, which are so much sought in tulips. By putting such flowers for a short time in boiling water, the cells die and release the red pigment, which becomes dif- fused in the surrounding fluids and the petals are left behind with their yellow tinge. In this way it is easy to separate the constituents, and demonstrate the compound nature of the orig- inal colors. 150 Retrograde Varieties But the diversity of the color patterns is far from being exhausted with these simple in- stances. Apart from them, or joined to them, other complications are frequently seen, which it is impossible to analyze in such an artificial way. Here we have to return to our former principle, the comparison of different varieties. Assuming that single units may be lost, ir- respective of the others, we may expect to find them segregated by variation, wherever a suffi- ciently wide range of color-varieties is in culti- vation. In fact, in most cases a high degree of dissimilarity may be reached in the simplest way by such a separation of the components, and by their combination into most diverse smaller groups. A very nice instance of such an analysis of flower-colors is afforded by the ordinary snapdragon. The beautiful brown- red color of this common garden-plant is com- posed on one side of yellow elements, on the other out of red units. Of the yellow there are two, one staining the whole corolla with a light hue, as is to be seen in the pure yellow variety called luteum. This form has been produced by the loss of the whole group of the red con- stituents. If the yellow tinge is also lost, there arises a white variety, but this is not absolutely colorless, but shows the other yellow constit- uent. This last stains only some small parts Retrograde Varieties 151 of the lips of the flower around the throat, brightening, as it seems, the entrance for the visiting insects. In many of the red or reddish varieties this one yellow patch remains, while the general yellow hue fails. In the variety called " Brilliant " the yellow ground makes the red color more shiny, and if it is absent the pure carmine tinge predominates. It is readily seen, that in the ordinary form the lips are of a darker red than the tube. This evident dissimilarity indicates some complexity. And in fact we have two varieties which exhibit the two causes of this attribute separately. One of them is called " Delila," and has the red color limited to the lips, whilst the tube is pure white. The other is called i ' Fleshy, ' ' and is of a pale pink throughout the whole corolla. Ad- ding these two units to one another, we get the original dark red of the wild type, and it may be briefly stated here, that the way of effecting such an addition is given us in the crossing of the " Fleshy " and of the " Delila " variety, the hybrid showing the both colors and return- ing thereby to the old prototype. Other cases of compound flower colors or of color patterns might be given as in the Mimulus and the poppy, and in most of these cases some varieties are to be seen in our gardens which show only the single constituents of the group. 152 Retrograde Varieties Many dark flowers have an intermediate bright hued form besides the white variety, as in the case of roses, asters, Nicandra and so on. Intermediate forms with respect to stature may also be seen. The opium-poppy, the snap- dragon, peas, the Nicandra, and many other garden-plants have not only dwarf varieties, but also some of intermediate height. These, though they are intermediate between the tall and dwarf types, cannot be considered as transi- tions, as between them and the extremes, inter- mediates are, as a rule wholly lacking. In- stances of the same occurrence of three types may be seen in the seeds of maize (" Cuzco," " Horse-dent " and "Gracillima") of beans and some other plants. The Xanthium Wootoni, above referred to, with only part of the prickles of Xanthium commune is also a very curious in- stance of the demonstration of the compound nature of a character. Summarizing the conclusions that may be drawn from the evidence given in this lecture, we have seen that varieties differ from elemen- tary species in that they do not possess anything really new. They originate for the greater part in a negative way, by the apparent loss of some quality, and rarely in a positive manner by ac- qrdring a character, already seen in allied spe- cies. These characters are not of the nature of Retrograde Varieties 153 morphologic entities, but are to be considered as physiologic units, present in all parts of the organisms, and manifesting themselves where- ever occasion is afforded. They are units in the sense that they may appear and disappear singly. But very often they are combined to yield compound characters, which are capable of analysis. Opportunities for such an analysis are afforded by the groups of cultivated varie- ties, showing a single distinguishing quality, or a small group of them. LECTURE VI STABILITY AND REAL ATAVISM It is generally believed that varieties are principally distinguished from species by their inconstancy. This conception is derived from some special cases and transferred to others, and in its common form this belief must have originated from the confusion which exists as to the meaning of the term variety. It is true that vegetative varieties as a rule run back, when propagated by seeds ; they are an obvious instance of inconstancy. In the second place we have considered the group of inconstant or sporting varieties, which of course we must ex- clude when studying the stability of other types. However, even these sporting varieties are un- stable only to a certain degree, and in a broader sense will prove to be as true to their character as the most constant types. Having separated these two groups, which include also the wide range of hybrid forms, we may next consider only those varieties of pure origin, and ordinarily propagated by seeds, 154 Stability and Real Atavism 155 which have been discussed in former chapters. Their general character lies in their fidelity to type, and in the fact that this is single, and not double, as in the sporting varieties. But the current belief is, that they are only true to their peculiarities to a certain degree, and that from time to time, and not rarely, they revert to the type from which they have arisen. Such reversion is supposed to prove that they are mere varieties, and at the same time to indicate empirically the species from which they have sprung. In the next lecture we shall examine critically the evidence on which this assumption rests. Before doing so however, it will be necessary to collate the cases in which there is no re- version at all, or in which the reversion is ab- sent at least in experimental and pure sowings. In the present state of our knowledge it is very difficult to decide, whether or not true re- version occurs in constant varieties. If it does occur, it surely does so very rarely and only under unusual circumstances, or in particular individuals. However when such individuals are multiplied by buds and especially when they are the only representatives of their variety, the reversion, though theoretically rare, will be shown by nearly every individual of the prog- eny. Examples of this will be given below. 156 Retrograde Varieties They are generally called atavists or rever- sionists, but even these terms are sometimes used in a different sense. Lastly it is to be said that the empirical and experimental evidence as to the question of con- stancy is not as extensive as it should be. The experimental conditions are seldom described, and it is only recently that an interest in the matter has been awakened. Much remains to be done. Among other things the innumerable varieties of trees, shrubs and perennial herbs should be tested as to their constancy when grown from purely fertilized seeds. Many of them may be included among the number that sport constantly. Leaving aside the doubtful or insufficiently studied cases, we may now turn our attention to the facts that prove the absolute stability of a large number of varieties, at least as far as such completeness can be attained by experi- ment or observation. The best proof is afforded by the varieties which grow wild in localities where they are quite isolated from the species, and where for this reason, no possibility of crossing disturbs the significance of the proof. As one 'instance the rayless form of the wild camomile, or the Matricaria Chamomilla discoidea may be men- tioned. Many systematists have been so strong- Stability and Real Atavism 157 ly impressed with its absolute constancy and its behavior as an ordinary species, that they have elevated it, as it is called, to the rank of a spe- cies. As such it is described under the name of Matricaria discoidea D. C. It is remarkable for its rapid and widespread distribution, as of late years it has become naturalized in different parts of America and of Europe, where it is to be seen especially in France and in Norway. Experimentally I raised in succeeding years be- tween 1000 and 2000 seedlings, but observed no trace of reversion, either in the strongest or in the numerous very small and weak individuals which appeared in the cultures. The tansy ragwort or Senecio Jacob aea may be chosen as a second instance. It is a per- ennial herb with short rootstocks and stout stems bearing numerous short-peduncled heads in a large compact corymb; it multiplies itself abundantly by seeds and is very common on the sandy dunes of Holland. It has two forms, differing only in the occurrence, or the lack of the ray florets. But these two varieties occupy different localities, and are even limited to dif- ferent provinces. As far as I have been able to ascertain on numerous excursions during a series of years, they never sport, and are only intermingled on the outskirts of their habitats. The rayless form is generally considered as the 158 Retrograde Varieties variety but it is quite as stable as the radiate species. The radiate varieties of marigold, quoted in a former lecture, seem to be equally constant, when growing far away from their prototypes. I sowed the seeds of a single plant of the radiate form of Bidens cernua, and found all of the young plants true, and in the next year I had from their seed between 2000 and 3000 flower- ing individuals, all equally radiate. Many species of composites have been tried, and they are all constant. On the other hand rare sports of this kind have been observed by Murr and other authors. Many kinds of vegetables and of fruits give instances of stability. White strawberries, green grapes, white currants, crisped lettuce, crisped parsley and some other crisped forms may be cited. The spinage without prickles is a widely known instance. White-flowered flax never reverts to the blue prototype, if kept pure. Sugar-peas and sugar-corn afford further in- stances. Strawberries without runners have come true from seed ever since their first ap- pearance, over a hundred years ago. Many garden-varieties, the stability of which under ordinary circumstances is doubtful, be- cause of their being sown too close to other va- rieties of the same species, have been tested in Stability and Real Atavism 159 respect to their stability by different writers and at different times. In doing this it is plain that it is very essential to be sure of the purity of the seed. Specimens must be grown in posi- tions isolated from their allies, and if possible be pollinated artificially with the exclusion of the visits of insects. This may be done in differ- ent ways. If it is a rare species, not cultivated in the environment, it is often sufficient to make sure of this fact. Pollen may be conveyed by bees from distances of some ten or twenty meters, or in rare cases from some hundred meters and more, but a greater distance is or- dinarily sufficient for isolation. If the flowers fertilize themselves, as is more often the case than is generally supposed, or if it is easy to pollinate them artificially, with their own pollen or in small groups of similar individuals, the best way is to isolate them by means of close coverings. When flowering, the plants are as a rule too large to be put under bell-glasses, and moreover such coverings would keep the air moist, and cause the flower buds to be thrown off. The best 'coverings are of netting, or of canvas of sufficiently wide mesh, although after a long experience I greatly prefer screens of fine iron-wire, which are put around and over the whole plant or group of plants, and fastened securely in the ground. 160 Retrograde Varieties Paper bags also may be made use of. They are slipped over the flowering branches, and bound together around the twigs, thus enclosing the flowers. It is necessary to make use of prepared papers, in order that they exclude rain or wind. The best sort, and the one that I use almost exclusively in my fertilization-ex- periments, is made of parchment paper. This is a wood-pulp preparation, freed artificially from the so-called wood substance or lignin. Having covered the flowers with care, and hav- ing gathered the seeds that are free from other intermixtures and if possible separately for each single individual, it only remains to sow them in quantities that will yield the greatest possible number of individuals. Reversions are supposed to be rare and small groups of seed- lings of course would not suffice to bring them to light. Only sowings of many hundreds or thousands of individuals are decisive. Such sowings can be made in one year, or can be extended over a series of years and of gen- erations. Hildebrand and Hoffman have pre- ferred the last method, and* so did Hof- meister and many others. Hildebrand sowed the white hyacinth, and the white varieties of the larkspur, the stock and the sweet pea. Hoff- man cultivated the white flax and many other varieties and Hofmeister extended his sowings Stability and Real Atavism 161 over thirty years with the white variety of the yellow foxglove (Digitalis parviflora). White-flowered varieties of perennial garden- plants were used in my own experiments. I bought the plants, flowered them under isolation in the way described above, gathered the seeds from each individual separately and sowed them in isolated groups, keeping many hundreds and in some cases above a thousand plants up to the time of flowering. Among them I found only one inconstant variety, the white form of the yellow columbine, Aquilegia chrysantha. It evidently belonged to the group of sporting va- rieties already referred to. All others came ab- solutely true to type without any exception. The species experimented with, were Campanula persicifolia, Hyssopus officinalis, Lobelia syphil- itica, Lychnis chalcedonica, Polemonium dissec- tum, Salvia sylvestris and some others. Tested in the same way I found that the white varieties of the following annual plants quite true; Chrysanthemum coronarium, Godetia amcena, Linum usitatissimum, Phlox Drummondi, and Silene Armeria. To these may be added the white hemlock stork's-bill (Erodium cicutarium album) which grows very abundantly in some parts of my fatherland, and is easily recogniz- able by its pure green leaves and stems, even when not flowering. I cultivated it in large num- 162 Retrograde Varieties bers during five succeeding generations, but was never able to find even the slightest indication of a reversion to the red prototype. The scar- let pimpernel or Anagallis arvensis has a blue variety which is absolutely constant. Even in Britton and Brown's Flora, which rarely enum- erates varieties, it is mentioned as being prob- ably a distinct species. Eight hundred bloom- ing seedlings were obtained from isolated parents, all of the same blue color. The New Zealand spinage (Tetragonia expansa) has a greenish and a brownish variety, the red color extending over the whole foliage, including the stems and the branches. I have tried both of them during several years, and they never sported into each other. More than 5000 seed- lings, from the different seeds of the same fruits, were grown in the succeeding years, but neither those germinating in the first year, nor the others coming into activity after four years of repose, gave any sign of the red color of the original species. It is an old custom to designate intermediate forms as hybrids, especially when both the types are widely known and the intermediates rare. Many persons believe that in doing so, they are giving an explanation of the rarer forms. But since the laws of hybridism are coming to be known we shall have to break with Stability and Real Atavism 163 all such usages. So for instance there are num- erous flowers which are of a dark red or a dark blue color, and which, besides a white variety, have a pink or a pale blue form. Such pale varieties are of exactly the same value as others, and on testing they are found to be equally stable. So for instance the pink variety of the Sweet William (Silene Armeria rosea, the Clarkia pulchella carnea) and the pale variety of the corn-cockle, called usually Agrostemma Githago nicaeensis or even simply A. nicaeensis. The latter variety I found pure during ten suc- ceeding generations. Another notable stable intermediate form is the poppy bearing the Danish flag (Papaver somniferum Danebrog). It is an old variety, and absolutely pure when cultivated separately. A long list of other in- stances might easily be given. Many garden-varieties, that are still univer- sally prized and cultivated are very old. It is curious to note, how often such forms have been introduced as novelties. The common fox- glove is one of the best examples. It has a mon- strous variety, which is very showy because it bears on the summit of its raceme and branches, large erect cup-shaped flowers, which have quite a different aspect from the normal thimble- shaped side-blossoms. These flowers are or- dinarily described as belonging to the anomaly 164 Retrograde Varieties known as " peloria," or regular form of a normally symmetric type ; they are large and ir- regular on the stems and the vigorous branches but slender and quinate on the weaker twigs. Their beauty and highly interesting anomalous character has been the cause of their being de- scribed many times, and nearly always as a novelty; they have recently been re-introduced into horticulture as such, though they were al- ready cultivated before the middle of the last century. About that time very good descrip- tions with plates were published in his Flora by Vrolik of Amsterdam, but afterwards they seem to have been forgotten. The peloric va- riety of the foxglove always comes true from seed, though, in the strict sense of the word which we have chosen for our discussion, it does not seem to be a constant and pure variety. It is very interesting to compare old botani- cal books, or even old drawings and engravings containing figures of anomalous plants. The celebrated Pinacothec of Munich contains an old picture by Holbein (1495-1543) representing St. Sebastian in a flower-garden. Of the plants many are clearly recognizable, and among others there is one of the " one-leaved " variety of the strawberry, which may still be met with in botanical gardens. In the year 1671 a Dutch botanist, Abraham Hunting pub- Stability and Real Atavism 165 lished a large volume on garden-plants, con- taining a great number of very good engrav- ings. Most of them of course show normal plants, but intermixed with these are varieties, that are still in cultivation and therefore must be at least two centuries old. Others, though not figured, are easily recognized by their names and descriptions. The cockscomb is the most widely known, but many white or double flow- ered varieties were already cultivated at that time. The striped Jalappa, the crested Sedum, the fasciated crown-imperial, white strawber- ries, red gooseberries and many others were known to Munting. Some varieties are as old as culture itself, and it is generally known that the Romans cul- tivated the white form of the opium-poppy and used the foliage of the red variety of the sugar- beet as a vegetable. In our time flowers and fruits are changing nearly as rapidly as the fancies and tastes of men. Every year new forms are introduced and usurp the place of older ones. Many are soon forgotten. But if we look at old country gardens, a goodly number of fine and valued old sorts are still to be found. It would be worth while to make special collections of living plants of old varieties, which surely would be a good and interesting work and bring about a convic- 166 Retrograde Varieties tion of the stability of pure strains. Coming now to the other side of the question, we may consider those cases of reversion which have been recorded from time to time, and which al- ways have been considered as direct proofs of the varietal character of the reverting form. Reversion means the falling back or returning to another type, and the word itself expresses the idea that this latter type is the form from which the variety has arisen. Some instances of atavism of this kind are well known, as they are often repeated by in- dividuals that were multiplied by buds or by grafting. Before looking attentively into the different features of the many cases of rare reversions it will be advisable to quote a few examples. The flowering-currant of the Pacific Coast or North American, the scarlet ribes (Ribes sanguineum), a very popular ornamental shrub, will serve as a good example. It is prized be- cause of its brilliant red racemes of flowers which blossom early in the spring, before the ap- pearance of the leaves. From this species a white form has arisen, which is an old and wide- ly cultivated one, but not so highly prized be- cause of its pale flowers. These are not of a pure white, but have retained a faint reddish hue. The young twigs and the stalks of the Stability and Real Atavism 167 leaves afford an instance of correlated variabil- ity since in this species the red color shows it- self clearly mixed with the green, while in the variety this tinge is wholly wanting. Occasionally this white-flowered currant re- verts back to the original red type and the re- version takes place in the bud. One or two buds on a shrub bearing perhaps a thousand bunches of white flowers produce twigs and leaves in which the red pigment is noticeable and the flowers of which become brightly col- ored. If such a twig is left on the shrub, it may grow further, ramify and evolve into a larger group of branches. All of them keep true to the old type. Once reverted, the branches re- main for ever atavastic. It is a very curious sight, these small groups of red branches among the many white ones. And for this reason at- tention is often called to it, and more than once I myself have had the opportunity of noting its peculiarities. It seems quite certain that by planting such shrubs in a garden, we may rely upon seeing sooner or later some new buds re- verting to the prototype. Very little attention seems hitherto to have been given to this curious phenomenon, though in many respects it deserves a closer investiga- tion. The variety is said to have originated from seed in Scotland, many years ago, and 168 Retrograde Varieties seems to be propagated only by cuttings or by grafting. If this is true, all specimens must be considered as constituting together only one individual, notwithstanding their wide distribu- tion in the gardens and parks of so many coun- tries. This induces me to suppose, that the tendency to reversion is not a character of the variety as such, but rather a peculiarity of this one individual. In other words it seems prob- able that when the whitish variety arises a sec- ond time from the red species, it is not at all necessary that it should exhibit this same tend- ency to revert. Or to put it still in another way, I think that we may suppose that a variety, which might be produced repeatedly from the same original stock, would only in rare indi- viduals have a tendency to revert, and in most cases would be as absolutely constant as the species itself. Such a conception would give us a distinct insight into the cause of the rarity of these reversions. Many varieties of shrubs and trees have originated but once or twice. Most of them must therefore, if our supposition is cor- rect, be expected to be stable. Among the conifers many very good cases of reversions by buds are to be found in gardens and glasshouses. They behave exactly like the whitish currant. But as the varietal characters Stability and Real Atavism 169 are chiefly found in the foliage and in the branches, these aberrations are to be seen on the plants during the whole year. Moreover they are in some cases much more numerous than in the first instance. The Cryptomeria of Japan has a variety with twigs resembling ropes. This is not caused by a twisting, but only by a curvature of the needles in such a way that they seem to grow in spiral lines around the twigs. This variety often reverts to the type with widely spread, straight needles. And on many a specimen four, five, or more reverted branches may be seen on different parts of the same shrub. Still more widely cultivated is the shrub called Cephalotaxus pedunculata fasti- giata, and more commonly known under its old name of Podocarpus koraiana. It is the broom- like variety of a species, nearly allied to the common American and European .species of yew, (Taxus minor and T. baccata). It is a low shrub, with broadly linear leaves of a clear green. In the species the leaves are arranged in two rows, one to the left and one to the right of the horizontally growing and widely spread- ing branches. In the variety the branches are erect and the leaves inserted on all sides. When sporting, it returns to the bilateral pro- totype and flat wings of fan-shaped twigs are produced laterally on its dense broom-like tufts. 170 Retrograde Varieties Wherever this variety is cultivated the same re- version may be seen; it is produced abundant- ly, and even under seemingly normal circum- stances. But as in the case of the Ribes all the specimens are derived by buds from a single original plant. The variety was introduced from Japan about the year 1860, but is prob- ably much older. Nothing is known as to its real origin. It never bears flowers or fruits. It is curious to note that the analogous variety of the European yew, Taxus baccata fastigiata, though much more commonly cultivated than the Cephalotaxus, never reverts, at least as far as I have been able to ascertain. This clearly corroborates the explanation given above. After considering these rare instances of more widely known reversions, we may now ex- amine the question of atavism from a broader point of view. But in doing so it should once more be remembered, that all cases of hybrid- ism and also all varieties sporting annually or frequently, are to be wholly excluded. Only the very rare occurrence of instances of atavism in varieties that are for the rest known to be ab- solutely constant, is to be considered. Atavism or reversion is the falling back to a prototype. But what is a prototype ? We may take the word in a physiologic or in a systematic sense. Physiologically the signification is a Stability and Real Atavism 171 very narrowly restricted one, and includes only those ancestors from which a form is known to have been derived. But such a view is of course an historic one. If a variety has been observed to spring from a definite species, and if the cir- cumstances have been sufficiently ascertained not to leave the slightest doubt as to its pure origin, and if moreover all the evidence has been duly recorded, we may say that the origin of the variety is historically known. In most cases we must be content with the testimony, given somewhat later, and recorded after the new variety has had the opportunity of showing its greater merits. If it now happens that such a variety of re- corded origin should occasionally revert to its parent-species, we have all we can wish for, in the way of a thoroughly proved case of atavism. But such instances are very rare, as the birth of most varieties has only been very imper- fectly controlled. Next to this comes the systematic relation of a variety to its species. The historic origin of the variety may be obscure, or may simply be forgotten. But the distinguishing marks are of the order described in our last lecture, either in the positive or in the negative direction, and on this ground the rarer form is considered to be a variety of the more wide-spread one. If 172 Retrograde Varieties now the presumed variety sports and runs over to the presumed type, the probability of the supposed relation is evidently enhanced. But it is manifest that the explanation rests upon the results of comparative studies, and not upon direct observations of the phenomena themselves. The nearer the relations between the two types in question, the less exposed to doubt and criticism are the conclusions. But the domain of atavism is not restricted to the cases de- scribed. Quite on the contrary the facts that strike us most forcibly as being reversions are those that are apt to give us an insight into the systematic affinity of a higher degree. We are disposed to make use of them in our attempts to perfect the natural system and to remould it in such a way as to become a pedigree of the related groups. Such cases of atavism no doubt occur, but the anomalies referred to them must be interpreted merely on the ground of our assumptions as to the relative places in the sys- tem to be assigned to the different forms. Though such instances cannot be considered as belonging strictly to the subject we are deal- ing with, I think it may be as well to give an ex- ample, especially as it affords an occasion of referring to the highly important researches of Heinricher on the variability and atavistic Stability and Real Atavism 173 tendencies of the pale blue flag or Iris pallida. The flowers of the blue flags have a perianth of six segments united below into a tube. The three outer parts are dilated, and spreading, or reflexed, while the three inner usually stand erect, but in most species are broad and colored like the outer ones. Corresponding to the outer perianth-segments are the three stamens and the three petal-like divisions of the style, each bearing a transverse stigma immediately above the anther. They are pollinated by humble-bees, and in some instances by flies of the genus Rhingia, which search for the honey, brush the pollen out of the anthers and afterwards de- posit it on the stigma. According to systematic views of the monocotyledons the original proto- type of the genus Iris must have had a whorl of six equal, or nearly equal, perianth-segments and six stamens, such as are now seen in the more primitive types of the family of the lilies, as for instance in the lilies themselves, the tulips, hyacinths and others. As to the perianth this view is supported by the existence of one species, the Iris falcifolia, the perianth of which consists of six equal parts. But species with six stamens are wholly lacking. Heinricher however, in culti- vating some anomalous forms of Iris pallidaf succeeded in filling out this gap and in produc- 174 Retrograde Varieties ing flowers with a uniform perianth and six stamens, recalling thereby the supposed ances- tral type. The way in which he got these was as follows: he started from some slight devia- tions observed in the flowers of the pale spe- cies, sowed the seeds in large numbers and se- lected from the seedlings only those, which clearly showed anomalies in the expected atavistic direction. By repeating this during several generations he at last reached his goal and was able to give reality to the prototype, which formerly was only a hypothetic one. The Iris Kaempferi, a large-flowered Japanese spe- cies much cultivated in gardens, is very variable in the number of the different parts of its flow- ers, and may in some instances be seen even with six stamens. If studied in the same way as Heinricher's iris, it no doubt will yield highly interesting and confirmatory results. Many other instances of such systematic atav- ism could be given, and every botanist can easily add some from memory. Many anomalies, oc- curring spontaneously, are evidently due to the same principle, but it would take too long to describe them. Eeversion may occur either by buds or by seeds. It is highly probable that it occurs more readily by sexual than by asexual propagation. But if we restrict the discussion to the limits Stability and Real Atavism 175 hitherto observed, seed-reversions must be said to be extremely rare. Or rather, cases which are sufficiently certain to be relied upon, are very rare, and perhaps wholly lacking. Most of the instances, recorded by various writers, are open to question. Doubts exist as to the purity of the seeds and the possibility of some unobserved cross disturbing the results. In the next lecture we shall deal in general with the ordinary causes and results of such crosses. We may then see that they are so common and occur so regularly under ordinary circumstances that we can never rely on the absolute purity of any seeds, if the impossibility of an occasional cross has not been wholly ex- cluded, either by the circumstances themselves, or by experimental precautions taken during the flowering period. For these reasons cases of atavism given without recording the circumstances, or the pre- cautions that guarantee the purity of the fertili- zation, should always be disregarded. And moreover another proof should always be de- manded. The parent which yielded the seeds might be itself a hybrid, and liable to reversions by the ordinary laws of the splitting up of hy- brids. Such cases should likewise be discarded, since they bring in confusing elements. If we review the long list of recorded cases by these 176 Retrograde Varieties strict methods of criticism very few instances will be found that satisfy legitimate demands. On this ground it is by far safer in the present state of our knowledge, to accept bud-variations only as direct proofs of true atavism. And even these may not always be relied on, as some hybrids are liable to split up in a vegetative way, and in doing so to give rise to bud-varia- tions that are in many respects apparently sim- ilar to cases of atavism. But fortunately such instances are as yet very rare. After this discussion it would be bold indeed to give instances of seed-atavism, and I believe that it will be better to refrain wholly from do- ing so. Many instances of so-called atavism are of purely morphologic nature. The most interest- ing cases are those furnished by the forms which some plants bear only while young, and which evidently connect them with allied species, in which the same features may be seen in the adult state. Some species of the genus Acacia bear bipinnate leaves, while others have no leaves at all, but bear broadened and flattened petioles instead. The second type is presumed to be descended from the first by the loss of the leaflets and the modification of the stalks into flat and simple phyllodes. But many of them are liable to recall this primitive form Stability and Real Atavism 177 when very young, in the first two or three, or sometimes in eight or ten primary leaves. These leaves are small because of the weakness of the young plant and therefore often more or less reduced in structure. But they are usually strictly bipinnate and thereby give testimony as to their descent from species which bear such leaves throughout their life. Other similar cases could be given, but these will suffice. They once more show how neces- sary is it to separate the different cases, thrown together until now, under this general name of atavism. It would be far better to give them all special names, and as long as these are not available we must be cautious not to be mis- guided by the name, and especially not to con- fuse different phenomena with one another, be- cause at the present time they bear the same names. Taking into consideration the relatively nu- merous restrictions, resulting from this discus- sion we will now make a hasty survey of some of the more notable and generally acknowledged cases of atavism by bud-propagation. But it should be repeated once more that most of the highly cultivated plants, grown as vegetables or for their fruit or flowers, have so many crosses in their ancestry, that it seems better to exclude them from all considerations, in which purity of 178 Retrograde Varieties descent is a requisite. By so doing, we exclude most of the facts which were until now gener- ally relied upon. For the roses, the hyacinths, the tulips, the chrysanthemums always have furnished the largest contributions to the dem- onstrations of bud-variation. But they have been crossed so often, that doubt as to the purity of the descent of any single form may recur, and may destroy the usefulness of their many recorded cases of bud- variation for the demon- stration of real atavism. The same assertion holds good in many other cases, as with Azalea and Camellia. And the striped varieties of these genera belong to the group of ever-sport- ing forms, and therefore will be considered later on. So it is with carnations and pinks, which occasionally vary by layering, and of which some kinds are so uncertain in char- acter that they are called by floriculturists " catch-flowers." On the other hand there is a larger group of cases of reversion by buds, which is probably not of hybrid nature, nor due to innate inconstancy of the variety, but must be considered as pure atavism. I refer to the bud-variations of so many of our cultivated varieties of shrubs and trees. Many of them are cultivated because of their foliage. They are propagated by grafting, and in most cases it is probable that all the numerous specimens Stability and Real Atavism 179 of the same variety have been derived in this way from one primitive, aberrant individual. We discard the variegated leaves, spotted or marked with white or yellow, because they are too inconstant types. We may next turn our attention to the va- rieties of trees with cut leaves, as the oak- leaved Laburnum, the parsley-leaved vine and the fern-leaved birch. Here the margin of the leaves is deeply cut and divided into many segments, which sometimes change only the outer parts of the blade, but in other cases may go farther and reach or nearly reach, the mid- vein, and change the simple leaf into a seem- ingly compound structure. The anomaly may even lead to the nearly complete loss of all the chorophyll-tissue and the greater part of the lateral veins, as in the case of the cut-leaved beech or Fagus sylvatica pectinata. Such varieties are often apt to revert by buds to the common forms. The cut-leaved beech sometimes reverts partially only, and the branches often display the different forms of cut-leaved, fern-like, oak-leaved and other vari- ously shaped leaves on the same twigs. But this is merely due to the wide variability of the degree of fissure and is to be considered only as a fluctuation between somewhat widely distant extremes, which may even apparently include 180 Retrograde Varieties the form of the common beech leaves. It is not a bud- variation at all, and it is to be met with quite commonly while the true reversions by buds are very rare and are of the nature of sports appearing suddenly and remaining con- stant on the same twig. Analogous phenomena of wide variability with true reversion may be seen in the variety of the European hornbeam called Carpmus Betulus heterophylla. The leaves of this tree generally show the greatest diversity in form. Some other cases have been brought together by Darwin. In the first place a sub-variety of the weeping-willow with leaves rolled up into a spiral coil ; a tree of this kind kept true for twenty-five years, and then threw out a single upright shoot bearing flat leaves. The barberry (Berberis) offers another case; it has a well known variety with seedless fruit, which can be propagated by cuttings or layers, but which are said always to revert to the com- mon form, and to produce ordinary berries with seeds. Most of the cases referred to by Dar- win however, seem to be doubtful and cannot be considered as true proofs of atavism until more is known about the circumstances under which they were produced. Red or brown-leaved varieties of trees and shrubs also occasionally produce green-leaved branches, and in this way revert to the type Stability and Real Atavism 181 from which they must evidently have arisen. Instances are on record of the hazel, Corylus Avellana, of the allied Corylus tubulosa, of the red beech, the brown birch and of some other purple varieties. Even the red bananas, which bear fruits without seeds and therefore have no other way of being propagated than by buds, have produced a green variety with yellow fruits. The Hortensia of our gardens is an- other instance of a sterile form which has been observed to throw out a branch with cymes bearing in their center the usual small starn- inate and pistillate flowers instead of the large radiate, and neutral corollas of the variety, thereby returning to the original wild type. Crisped weeping willows, crisped parsley and others have reverted in a similar manner. All such cases are badly in need of a closer investigation. And as they occur only occasionally, or as it is commonly stated, by ac- cident, the student of nature should be prepared to examine carefully any case which might pre- sent itself to him. Many phases of this difficult problem could no doubt be solved in this way. First of all the question arises as to whether the case is one of real atavism, or is only seemingly so, being due to hybrid or otherwise impure de- scent of the varying individual, and secondly whether it may be only an instance of the regu- 182 Retrograde Varieties larly occurring so-called atavism of the sporting varieties with which we shall deal in a later lecture. If it proves to be real atavism and rare, the case should be accurately described and figured, or photographed if pos- sible; and the exact position of the reverting bud should be ascertained. Very likely the so- called dormant or resting buds are more liable to reversions than the primary ones in the axils of the leaves of young twigs. Then the char- acters of the atavistic branches should be mi- nutely compared with those of the presumed an- cestor ; they may be quite identical with them or slightly divergent, as has been asserted in some instances. The atavism may be complete in one case, but more or less incomplete in others. By far the most interesting point is the ques- tion, as to what is to be expected from the seeds of such an atavistic branch. Will they keep true to the reverted character, or return to the characters of the plant, which bears the retro- grade branch? Will all of them do so, or only part of them, and how large a part 1 It is very astonishing that this question should still be unsolved where so many individual trees bear atavistic branches that remain on them through long series of years. But then many such branches do not flower at all, or if they flower and bear seed, no care is taken to prevent Stability and Real Atavism 183 cross-fertilization with the other flowers of the same plant, and the results have no scientific value. For anyone who cares to work with the precautions prescribed by science, a wide field is here open for investigation, because old reverted branches may be met with much less rarely than new ones. Finally the possibility is always to be con- sidered that the tendency to bud-reversions may be a special feature of some individuals, and may not be met with in others of the same variety. I have spoken of this before. For the practical' student it indicates that a specimen, once observed to produce atavistic buds, may be expected to do the same thing again. And then there is a very good chance that by combining this view with the idea that dormant buds are more apt to revert than young ones, we may get at a method for further investigation, if we re- cur to the practice of pruning. By cutting away the young twigs in the vicinity of dormant buds, we may incite these to action. Evidently we are not to expect that in so doing they will all become atavistic. For this result is not at all assured; on the contrary, all that we might hope to attain would be the possibility of some of them being induced to sport in the desired direction. Many questions in scientific research can only 184 Retrograde Varieties be answered by long and arduous work in well- equipped laboratories; they are not to be at- tempted by every one. But there are other problems which the most complete of institu- tions are not able to study if opportunity is not offered them, and such opportunities are apt to occur more often in fields, gardens, parks, woods and plains, than in the relatively small experimental gardens of even the largest in- stitution. Therefore, whosoever has the good fortune to find such sports, should never allow the occasion to pass without making an investi- gation that may bring results of very great im- portance to himself and to science. LECTUEE VII FALSE ATAVISM OR VICINISM About the middle of the last century Louis De Vilmorin showed that it was possible to subject plants to the methods of ameliora- tion of races then in use for domestic animals, and since that time atavism has played a large part in all breeding-processes. It was consid- ered to be the greatest enemy of the breeder, and was generally spoken of as a definite force, working against and protracting the endeav- ors of the horticulturist. No clear conception as to its true nature had been formulated, and even the propriety of designating the observed phenomena by the term atavism seemed doubtful. Duchesne used this word some decades ago to designate those cases in which species or varieties revert spontaneously, or from unknown internal causes, to some long-lost characters of their an- cestors. Duchesne 's definition was evidently a sharp and useful one, since it developed for the first time the idea of latent or dormant qualities, 185 186 Retrograde Varieties formerly active, and awaiting probably through centuries an occasion to awaken, and to dis- play the lost characters. Cases of apparent reversion were often seen in nurseries, especially in flower culture, which under ordinary circumstances are rarely wholly pure, but always sport more or less into the colors and forms of allied varieties. Such sporting individuals have to be extirpated regularly, otherwise the whole variety would soon lose its type and its uniformity and run over to some other form in cultivation in the vicinity. For this reason atavism in nurseries demands much care and labor, and consequently is to be dealt with as a very important factor. From time to time the idea has suggested itself to some of the best authorities on the amelioration of plants, that this atavism was not due to an innate tendency, but, in many cases at least, was produced by crosses between neighboring varieties. It is especially owing to Verlot that this side of the question was brought forward. But breeders as a rule have not attached much importance to this supposi- tion, chiefly because of the great practical diffi- culties attending any attempt to guard the spe- cies of the larger cultures against intermixture with other varieties. Bees and humble-bees fly from bud to bud, and carry the pollen from one False Atavism 187 sort to another, and separation by great dis- tances would be required to avoid this source of impurity. Unfortunately the arrangements and necessities of large cultures make it impos- sible to isolate the allied varieties from each other. From a theoretical point of view the origin of these impurities is a highly important ques- tion. If the breeders' atavism is due to crosses, and only to this cause, it has no bearing at all on the question of the constancy of varieties. And the general belief, that varieties are dis- tinguished from true species by their repeated reversion and that even such reversibility is the real distinction of a variety, would not hold. For this reason I have taken much trouble in ascertaining the circumstances which attend this form of atavism. I have visited a number of the leading nurseries of Europe, tested their products in various ways, and made some ex- periments on the unavoidable conditions of hybridizing and on their effect on the ensuing generations. These investigations have led me to the conclusion, that atavism, as it is gener- ally described, always or nearly always is due to hybridization, and therefore it is to be con- sidered as untrue or false atavism. True atavism, or reversion caused by an in- nate latent tendency, seems to be very rare, 188 Retrograde Varieties and limited to such cases as we have spoken of under our last heading. And since the defi- nition, given to this term by its author, Du- chesne, is generally accepted in scientific works, it seems better not to use it in another sense, but rather to replace it in such cases by another term. "For this purpose I propose the word vicinism, derived from the Latin vicinus or neighbor, as indicating the sporting of a variety under the influence of others in its vicinity. Used in this way, this term has the same bear- ing as the word atavism of the breeders, but it has the advantage of indicating the true cause thereof. It is well known that the term variability is commonly employed in the broadest possible sense. No single phenomenon can be desig- nated by this name, unless some primary re- striction be given. Atavism and vicinism are both cases of variability, but in wholly different sense. For this reason it may be as well, to insert here a short survey of the general mean- ings to be conveyed by the term variation. It implies in the first place the occurrence of a wide range of forms and types, irrespective of their origin, and in the second place the process of the change in such forms. In the first signifi- cation it is nearly identical with polymorphy, or richness of types, especially so when these False Atavism 189 types are themselves quite stable, or when it is not at all intended to raise the question of their stability. In scientific works it is commonly used to designate the occurrence of subspecies or varieties, and the same is the case in the ordinary use of the term when dealing with cultivated plants. A species may consist of larger or smaller groups of such units, and they may be absolutely constant, never sport- ing if hybridization is precluded, and neverthe- less it may be called highly variable. The opium-poppy affords a good instance. It " varies " in height, in color of foliage and flowers ; the last are often double or laciniated ; it may have white or bluish seeds, the capsules may open themselves or remain closed and so on. But every single variety is absolutely con- stant, and never runs into another, when the flowers are artificially pollinated, and the visits of insects excluded. So it is with many other species. They are at the same time wholly stable and very variable. The terms variation and variety are used frequently when speaking of hybrids. By cross- ing forms, which are already variable in the sense just mentioned, it is easy to multiply the number of the types, and even in crossing pure forms the different characters may be combined in different ways, the resulting combinations 190 Retrograde Varieties yielding new, and very often, valuable varieties. But it is manifest that this form of variation is of quite another nature from the variations of pure races. Many hybrid varieties are quite constant, and remain true to their type if no further crosses are made ; many others are arti- ficially propagated only in a vegetative way, and for this reason are always found true. Hybrid varieties as a rule were formerly con- fused with pure varieties, and in many in- stances our knowledge as to their origin is quite insufficient for sharp distinctions. To every student of nature it is obvious, that crossing and pure variability are wholly distinct groups of phenomena, which should never be treated under the same head, or under the same name. Leaving aside polymorphy, we may now dis- cuss those cases of variability, in which the changes themselves, and not only their final results play a part. Of such changes two types exist. First, the ever-recurring variability, never absent in any large group of individuals, and determining the differences which are al- ways to be seen between parents and their children, or between the children themselves. This type is commonly called " individual variability " and since this term also has still other meanings, it has of late become customary to use instead the term " fluctuating varia- False Atavism 191 bility." And to avoid the repetition of the lat- ter word it is called " fluctuation. " In con- trast to these fluctuations are the so-called sports or single varieties, not rarely denomi- nated spontaneous variations, and for which I propose to use the term " mutations. " They are of very rare occurrence, and are to be con- sidered as sudden and definite steps. Lastly, we have to consider those varieties, which vary in a much wider range than the ordinary ones, and seem to fluctuate between two opposite extremes, as for instance, varie- gated leaves, cultivated varieties with va- riegated or striped flowers, double flowers and some other anomalies. They are ever- sporting and ever-returning from one type to the other. If however, we take the group of these extremes and their intermediates as a whole, this group remains constant during the succeeding generations. Here we find once more an instance of the seemingly contradictory combination of high variability and absolute constancy. It means that the range of varia- bility has quite definite limits, which in the com- mon course of things, are never transgressed. We may infer therefore that the word varia- bility has such a wide range of meanings that it ought never be used without explanation. 192 Retrograde Varieties Nothing indeed, is more variable than the sig- nification of the term variable itself. For this reason, we will furthermore desig- nate all variations under the influence of neigh- bors with the new and special term ' ' vicinism. ' ' It always indicates the effects of crosses. Leaving this somewhat lengthy terminolog- ical discussion, we now come to the description of the phenomenon itself. In visiting the plan- tations of the seedsmen in summer and exam- ining the large fields of garden-flowers from which seed is to be gathered, it is very rare to find a plot quite pure. On the contrary, occa- sional impurities are the rule. Every plot shows anomalous individuals, red or white flowers among a field of blue, normal among laciniated, single among double and so on. The most curious instance is afforded by dwarf varieties, where in the midst of hundreds and thousands of small individuals of the same height, some specimens show twice their size. So for instance, among the dwarfs of the lark- spur, Delphinium Ajacis. Everywhere gardeners are occupied in de- stroying these " atavists," as they call them. When in full bloom the plants are pulled up and thrown aside. Sometimes the degree of impurity is so high, that great piles of dis- carded plants of the same species lie about the False Atavism 193 paths, as I have seen at Erfurt in the case of numerous varieties of the Indian cress or Tro- paeolum. Each variety is purified at the time when it shows its characters most clearly. With vege- tables, this is done long before flowering, but with flowers only when in full bloom, and with fruits, usually after fertilization has been ac- complished. It needs no demonstration to show that this difference in method must result in very diverging degrees of purity. We will confine ourselves to a consideration of the flowers, and ask what degree of purity may be expected as the result of the elimination of the anomalous plants during the period of blooming. Now it is evident that the colors and forms of the flowers can only be clearly distin- guished, when they are fully displayed. Fur- thermore it is impossible to destroy every single aberrant specimen as soon as it is seen. On the contrary, the gardener must wait until all or nearly all the individuals of the same va- riety have displayed their characters, as only in this way can all diverging specimens be eliminated by a single inspection. Un- fortunately the insects do not wait for this selection. They fertilize the flowers from the beginning, and the damage will have been done 194 Retrograde Varieties long before the day of inspection comes around. Crosses are unavoidable and hybrid seeds will unavoidably come into the harvest. Their number may be limited by an early eradication of the vicinists, or by the elimination of the first ripe seeds before the beginning of the regu- lar harvest, or by other devices. But some degree of impurity will remain under ordinary circumstances. It seems quite superfluous to give more de- tails. In any case in which the selection is not done before the blooming period, some impuri- ties must result. Even if it is done before that time, errors may occur, and among hundreds and thousands of individuals a single anomalous one may escape observation. The conclusion is, that flower seeds as they are offered in commerce, are seldom found absolutely pure. Every gardener knows that he will have to weed out aberrant plants, in order to be sure of the purity of his beds. I tested a large number of samples of seeds for purity, bought directly from the best seed- growers. Most of them were found to contain mixtures and wholly pure samples were very rare. I will now give some illustrative examples. From seeds of a yellow snapdragon, I got one red-flowered specimen among half a hundred False Atavism 195 yellow ones, and from the variety " Delila " of the same species two red ones, a single white and two belonging to another variety called " Firefly. " Calliopsis tinctoria has three va- rieties, the ordinary type, a brown-flowered one and one with tubular rays. Seeds of each of these three sorts ordinarily contain a few belonging to the others. Iberis umbellata rosea often gives some white and violet examples. The " Swan " variety of the opium-poppy, a dwarfish double-flowered form of a pure white, contained some single-flowered and some red- flowered plants, that when sown from seed were said to be pure. But these were only occasional admixtures, since after artificial fertilization of the typical specimens the strain at once be- came absolutely pure, and remained so for a series of generations, as long as the experiment was continued. Seeds of trees often contain large quantities of impurities, and the laciniated varieties of birch, elder and walnut have often been observed to come true only in a small number of seedlings. In the case of new or young varieties, seed- merchants often warn their customers as to the probable degree of purity of the seeds offered, in order to avoid complaints. For example the snow-white variety of the double daisy, Bellis perennis plena, was offered at the start as con- 196 Retrograde Varieties taining as much as 20# of red-flowered speci- mens. Many fine varieties are recorded to come true from seed, as in the case of the hollyhock with yellow fruits, tested by Darwin. Others have been found untrue to a relatively high degree, as is notorious in the case of the purple beech. Seeds of the laciniated beech gave only 10# of laciniated plants; in experiments made by Strasburger, seeds of the monophyllous acacia, Robinia Pseud-Acacia monophylla, were found to be true in only 30$ of the seedlings. Weeping ashes often revert to the upright type, red May-thorns (Crataegus) sometimes revert nearly entirely to the white species and the yellow cornel berry is recorded to have reverted in the same way to the red berries of the Cor- nus Mas. Varieties have to be freed by selection from all such impurities, since isolation is a means which is quite impracticable under ordinary circumstances. Isolation is a scientific require- ment that should never be neglected in ex- periments, indeed it may be said to be the first and most important requisite for all exact re- search in questions of variability and inherit- ance. But in cultivating large fields of allied va- rieties for commercial purposes, it is impossible to grow them at such distances from each other False Atavism 197 as to prevent cross-pollination by the visits of bees. This purification must be done in nearly every generation. The oldest varieties are to be sub- jected to it as well as the latest. There is no regular amelioration, no slow progression in the direction of becoming free from these admix- tures. Continuous selection is indispensable to maintain the races in the degree of purity which is required in commerce, but it does not lead to any improvement. Nor does it go so far as to become unnecessary in the future. This shows that there must be a continuous source of im- purities, which in itself is not neutralized by selection, but of which selection can only elim- inate the deteriorating elements. The same selection is usually applied to new varieties, when they occasionally arise. In this case it is called " fixing," as gardeners gener- ally believe that through selection the varieties are brought to the required degree of purity. This belief seems to rest mainly on obser- vations made in practice, whereas we have seen, isolation is of very rare application. Most va- rieties would no doubt be absolutely pure from the first moment of their existence, if it were only possible to have them purely fertilized. But in practice this is seldom to be obtained. Ordinarily the breeder is content with such slow 198 Retrograde Varieties improvement as may be obtained with a mini- mum of cost, and this mostly implies a culture in the same part of the nursery with older varie- ties of the same species. Three, four or five years are required to purify the novelty, and as this same length of time is also required to produce sufficient quantities of seed for commercial purposes, there is no strong desire to shorten the period of selection and fixation. I had occasion to see this process go- ing on with sundry novelties at Erfurt in Germany. Among them a chamois-colored va- riety of the common stock, a bluish Clarkia elegans and a curiously colored opium-poppy may be mentioned. In some cases the cross- fertilization is so overwhelming, that in the next generation the novelty seems entirely to have disappeared. The examples given may suffice to convey a general idea of the phenomenon, ordinarily called atavism by gardeners, and considered mostly to be the effect of some innate tendency to revert to the ancestral form. It is on this conception that the almost universal belief rests, that varieties are distinguished, as such, from species by their inconstancy. Now I do not deny the phenomenon itself. The impurity of seeds and cultures is so general and so mani- fest, and may so easily be tested by every one False Atavism 199 that it cannot reasonably be subjected to any doubt. It must be conceded to be a fact, that varieties as a rule revert to their species under the ordinary circumstances of commercial cul- ture. And I cannot see any reason why this fact should not be considered as stating a prin- cipal difference between varieties and species, since true species never sport into one another. My objection only refers to the explanation of the observed facts. According to my view nearly all these ordinary reversions are due to crosses, and it is for this reason that I proposed to call them by a separate name, that of " vicin- ists." Varieties then, by means of such spon- taneous intercrossing sport into one another, while species either do not cross, or when cross- ing produce hybrids that are otherwise consti- tuted and do not give the impression of atavis- tic reversion. I must not be content with proposing this new conception, but must give the facts on which this assumption rests. These facts are the results of simple experiments, which never- theless are by no means easy to carry out, as they require the utmost care to secure the absolute purity of the seeds that are employed. This can only be guaranteed by previous cul- tures of isolated plants or groups of plants, or by artificial pollination. 200 Retrograde Varieties Once sure of this preliminary condition, the experiment simply consists in growing a variety at a given distance from its species and allow- ing the insects to transfer the pollen. After harvesting the seed thus subjected to the pre- sumed cause of the impurities, it must be sown in quantities, large enough to bring to light any slight anomaly, and to be examined during the period of blooming. The wild seashore aster, Aster Tripolium, will serve as an example. It has pale violet or bluish rays, but has given rise to a white va- riety, which on testing, I have found pure from seed. Four specimens of this white variety were cultivated at a distance of nearly 100 meters from a large lot of plants of the bluish species. I left fertilization to the bees, har- vested the seeds of the four whites separately and had from them the following year more than a thousand flowering plants. All of them were of the purest white, with only one exception, which was a plant with the bluish rays of the species, wholly reverting to its general type. As the variety does not give such reversions when cultivated in isolation, this sport was obviously due to some cross in the former year. In the same way I tried the white Jacob's ladder, Polemonium coeruleum album in the neighbor- hood of the blue-flowered species, the distance False Atavism 201 in this case being only 40 meters. Of two hun- dred seeds one became a blue atavist, or rather vicinist, while all others remained true to the white type. The same was observed in the white creeping thyme, or Thymus Serpyllum album, and the white self-heal, Brunella vul- garis alba, gave even so much as 28# seed- lings with purple corollas out of some 400 specimens, after being cultivated in close prox- imity to its parent-species. I have tried many other species, but always with the same result. Such atavists only arise by cultivation in the proximity of allied varieties, never in isolation. They are not real atavists, but only vicinists. In order to show this yet more clearly, I made another experiment with the white self- heal. I had a lot of the pinnate-leaved variety with purple flowers and somewhat stouter stems, and cultivated single plants of the white- flowering sort at distances that varied from 2-16 meters. The seeds of each plant were collected and sown separately, those of the nearest gave to 5 or 6 hybrids from the seeds of one parent, while those of the farthest gave only one purple-flowered plant for each parent. Evidently the chance of the pollen being carried by bees is much greater on short than on longer distances. True hybrids between species may arise in 202 Retrograde Varieties quite the same way, and since it is obviously impossible to attribute them to an innate ten- dency to reversion, they afford an absolutely irrefutable proof of the assertion, that pollen is often brought by insects from one lot of plants to another. In this way I obtained a hybrid between the common Jacob's ladder and the allied species Polemonium dissectum. With a distance of 100 meters between them I had two hybrid seeds among a hundred of pure ones. At a similar distance pollen was carried over from the wild radish, Raphanus Raphanis- trum, to the allied Raphanus caudatus, and I observed the following year some very nice hy- brids among my seedlings. A hybrid-bean be- tween Phaseolus nanus and P. multiflorus, and some hybrids between the yellow daisy, Chrysanthemum segetum and the allied Chrys- anthemum coronarium or ox-eye daisy which also arose spontaneously in my garden between parents cultivated at recorded distances, might further be noted. Further details of these ex- periments need not be given. Suffice to say, that occasional crosses between species do occcur, and not even rarely, that they are easily recognized as such and cannot be confused with cases of atavism, and that therefore they give proof to the assumption that in the same way crosses ordinarily occur also between varieties False Atavism 203 of the same species, if cultivated at small dis- tances apart, say 40 - 50 meters or even more. Vicinism therefore, may play a part in all such cultures, enough to account for all the impurities observed in the nurseries or in com- mercial seed-samples. Of course this whole discussion is limited to such species as are not only as a rule visited by insects, but are dependent on these visits for their fertilization. Most of our garden-flowers are included in this category. If not then we may expect to find the cultures and seeds pure, irrespective of the distances between allied va- rieties, as for instance with peas, which are known to be self -fertilizing. Another instance is given by the barley, and one of the most curious anomalous varieties of this cereal, the " Nepaul-barley," with its small adventitious flowers on the palets or inner scales. It is a very old, widely cultivated sort, which always comes true from seed, and which has been tested in repeated experiments in my garden. The spikelets of this curious plant are one- flowered and provided with two linear glumes or outer scales. Of the inner scales or palets, the outer one is three-lobed at the summit, hence the varietal name of Hordeum vulgare trifur- catum. The central lobe is oblong and hollow, covering a small supernumerary floret inserted 204 Retrograde Varieties at its base. The two lateral lobes are narrower, sometimes linear, and are often prolonged into an awn, which is generally turned away from the center of the spike. The central lobe some- times bears two florets at its base, although but one is usually present and it may be incomplete. I might give one more instance from my own experience. A variety of the evening primrose with small linear petals was once found by one of my sons growing wild near Amsterdam. It was represented by only one individual, flower- ing among a great many of the ordinary type with broad petals. But the evening-primroses open their anthers in the morning, fertilize themselves during the day, and only display their beautiful flowers in the evening, after the pollination has been accomplished. They then allure evening moths, such as Agrotis and Plusia, by their bright color, their sweet honey- smell and their nectar. Since the fertiliza- tion is accomplished many hours before opening, crosses are effected only in rare instances, and the seeds commonly remain true to the parent- type. The seeds of this one plant, when sown separately in my garden, produced exclusively flowers with the small linear petals of their parent. Although I had a hundred individuals bearing many thousands of flowers, there was not an instance of reversion. And such would False Atavism 205 immediately have been observed, had it oc- curred, because the hybrids between the cruci- ate and the normal flowers are not intermediate, but bear the broad petals of the 0. biennis. We may now take up another phase of the question, that of the running out of new varie- ties, shortly after their introduction into a new country, or later. The most widely known instance of this is that of the American corn in Baden, recorded by Metzger and quoted by Darwin as a remark- able instance of the direct and prompt action of climate on a plant. It has since been con- sidered as a reversion to the old type, in which return to mediocrity invariably occurs, accord- ing to Wallace, in cases of new varieties, which have been produced quickly. But as we now know, such reversions are due to spontan- eous crosses with the old form, and to the rule, that the hybrids of such origin are not inter- mediate, but assume the features of the older of the two parents. In the light of this exper- ience, Metzger 's observation becomes a typical instance of vicinism. It relates to the ' ' Tusca- rora " corn of St. Louis, a variety with broad and flat white seeds. About the year 1840, this corn was introduced into Baden in Germany, and cultivated by Metz- ger. In the first year it came true to type, and 206 Retrograde Varieties attained a height of 12 feet, but the season did not allow its seeds to ripen normally. Only a few kernels were developed before the winter. From this seed plants of a wholly different type came the next year, of smaller stature, and with more brownish and rounded kernels. They also flowered earlier and ripened a large num- ber of seeds. The depression on the outer side of the seed had almost disappeared, and the original white had become darker. Some of the seeds had even become yellow and in their rounded form they approached the common European maize. Obviously they were hybrids, assuming the character of their pollen-parent, which evidently was the ordinary corn, culti- vated all around. The observation of the next year showed this clearly, for in the third gener- ation nearly all resemblance to the original and very distinct American species was lost. If we assume that only those seeds ripened which reverted to the early-ripening European type, and that those that remained true to the very late American variety could not reach maturity, the case seems to be wholly comprehensible, without supposing any other factors to have been at work than those of vicinism, which though unknown at the period of Metzger's and Darwin's writings, seems now to be fully un- derstood. No innate tendency to run out and False Atavism 207 no changing influence to the climate are re- quired for an adequate explanation of the facts. In the observation quoted, what astonishes us most, is the great rapidity of the change, and the short time necessary for the offspring of the accidental crosses to completely supplant the in- troduced type. In the lecture on the selection of elementary species, closely analogous cases were described. One of them was the wild oat or Avena fatua which rapidly supplants the cultivated oats in bad years in parts of the fields. Other instances were the experiments of Eisler with the " Galland " wheat and the ob- servation of Eimpau on " Rivett's bearded " wheat. Before leaving the question of vicinism and its bearing on the general belief of the insta- bility of varieties, which when tested with due care, prove to be quite stable, it may be as well to consider the phenomena from another point of view. Our present knowledge of the effects of crosses between varieties ena- bles us to formulate some general rules, which may be used to calculate, and in some way to predict, the nature of the impurities which nec- essarily attend the cultivation of allied species in close vicinity. And this mode of cultivation being in almost universal use in the larger nur- 208 Retrograde Varieties series, we may, by this discussion, arrive at a more scientific estimation of the phenomena of vicinism, hitherto described. The simplest case that may be given, is when an ordinary retrograde variety is cultivated with the species to which it belongs. For in- stance, if dwarfs are cultivated next to the taller type, or a white variety next to the red or blue-flowering species, or thornless forms on neighboring beds with the armed species. Bees and humble-bees, butterflies and moths are seen flying from flower to flower, collecting the honey and carrying pollen. I frequently saw them cross the limits of the neighboring beds. Loaded with the pollen of the variety they visit the flowers of the different species and impreg- nate the stigma with it. And returning to the variety they bring about similar crosses in the flowers of the latter. Hybrid seeds will devel- op in both cases and become mixed with the crop. We now have to ask the question, what sort of plants will arise from these crossed seeds. As a general rule we may state, first that the hybrids of either form of cross are practically the same, secondly that they are not intermediate, but that the character of one par- ent prevails to the almost absolute exclusion of the other and in the third place that the older character dominates the younger. False Atavism 209 The hybrid offspring will therefore, in the main, have the character of the species and be ^indistinguishable from it, or show only such differences as escape from ordinary observa- tion. When occurring in the seeds of the va- riety they betray themselves as soon as the dif- ferential characters are displayed. Between the thousands of flowering plants of a white variety the hybrids will instantly catch the eye by their red or blue corollas. Quite the con- trary effect results from the admixture of hy- brids with the seeds of the species itself. Here no difference will show itself, even in the full- est bloom. The effect of the spontaneous crosses will pass unobserved. The strain, if pure in the first year, will seem to be still in the same condition. Or in other terms, the una- voidable spontaneous crosses will disturb the purity of the variety in the second year, while they do not seem to interfere at all with the uni- formity of the species. The direct effect of the visits of the insects is evident in the first case, but passes unobserved in the latter. From this it would seem, that spontaneous crosses are hurtful to varieties, but are in- nocuous to true species. Certainly this would be so, were there no selection. But it is easily seen, that through this operation the effect be- comes quite the opposite. For when the fields 210 Retrograde Varieties are inspected at the time of the fullest display of the varietal characters, the obvious hybrids will be eliminated, but the hidden ones will of ne cessity be spared, as they are concealed amon.o the species, by the similarity of their type. Hence, the harvest of the variety may be ren- dered pure or nearly so, while the harvest of the species will retain the seeds of the hybrids. Moreover it will contain seeds originated by the spontaneous but numerous crosses of the true plants with the sparsely intermingled hybrids. This brings us to the question, as to what will be the visible consequences of the occurrence of such invisible hybrids in the following gener- ation. In opposition to the direct effects just described, we may call them indirect. To judge of their influence, we must know how hybrid seeds of the first generation behave. In one of our lectures we will deal with the laws that show the numerical relations known as the laws of Mendel. But for our present purpose, these numerical relations are only of subordinate importance. What interests us here is the fact that hybrids of varieties do not re- main constant in the next generation but usu- ally split, as it is called, remaining hybrid only in part of their offspring, the other por- tion returning to the parental types. This how- ever, will show itself only in those individuals False Atavism 211 which reassume the character of the varietal parent, all the others apparently remaining true to the type of the species. Now it is easy to foresee what must happen in the second gen- eration if the first generation after the cross is supposed to be kept free from new vicinistic influences, or from crosses with neighboring varieties. We may limit ourselves in the first place to the seeds of the unobserved hybrids. For the greater part they will repeat the character of their parents and remain again concealed. But a small number will assume the varietal marks, as for example showing white flowers in a field of blue ones. Hence, the indirect conse- quence of the spontaneous crosses will be the same in the species, as was the direct effect in the variety. It only appears a year later. It will then be eliminated in the process of selection. Obviously, this elimination conduces only to a partial purification. The conspicuous plants will be destroyed, but a greater number of hy- brids will remain, still concealed by their re- semblance to the general type, and will be spared to repeat the same process next year. So while the variety may be freed every year, from the impurities brought into it in the pre- ceeding summer, the admixtures of the spe- 212 Retrograde Varieties cies will continue during a number of years, and it may not be possible to get rid of them at all. It is an often recurring assertion that white varieties of colored species are the most stable of all horticultural races. They are often said to be at least as constant as the species itself, and even to surpass it in this quality. With our present state of knowledge, the explanation of this general experience is easily given. For se- lection removes the effect of spontaneous cross- es from the variety in each year, and renders it practically pure, while it is wholly inadequate to produce the same effects on the species, be- cause of the concealed hybrids. The explanation given in this simple instance may be applied to the case of different varieties of the same species, when growing together, and crossed naturally by insects. It would take too long to go into all the de- tails that present themselves here to the stu- dent of nature and of gardens. I will only state, that since varieties differ princi- pally from their species by the lack of some sharp character, one variety may be character- ized by the lack of color of the flowers, another by the lack of pubescence, a third by being dwarfed, and so on. Every character must be studied separately in its effects on the offspring False Atavism 213 of the crosses. And it is therefore easily seen, that the hybrids of two varieties may resemble neither of them, but revert to the species itself. This is necessarily and commonly the case, since it is always the older or positive charac- ters that prevail in the hybrids and the younger or negative that lie hidden. So for in- stance, a blue dwarf larkspur, crossed with a tall white variety, must give a tall blue hybrid, reassuming in both characters the essentials of the species. Keeping this rule in view, it will be easy to calculate what may be expected from sponta- neous crosses for a wide range of occurrences, and thus to find an explanation of innumerable cases of apparent variability and reversion in the principle of vicinism. Students have only to recollect that specific-characters prevail over varietal ones, and that every character com- petes only with its own antagonist. Or to give a sharper distinction : whiteness of flowers can- not be expected to be interchanged with pubescence of leaves. In concluding I will point out another danger which in the principle of vicinism may be avoided. If you see a plant in a garden with all the characteristics of its species, how can you be sure that it is truly a representative of the species, and not a hybrid? The prevailing 214 Retrograde Varieties characters are in either case the same. Perhaps in close inspection you may find in some cases a slight difference, some character being not as fully developed in the hybrid as in the spe- cies. But when such is not the case, or where the opportunity for such a closer examination is wanting, a hybrid may easily be taken for a specimen of the pure race. Now take the seeds of your plant and sow them. If you had not supposed it to be hybrid you will be astonished at finding among its progeny some of a wholly different type. You will be led to conclude that you are observing a sudden change in structure such as is usually called a sport. Or in other words you may think that you are assisting at the origination of a new variety. If you are familiar with the principle of vicin- ism, you will refrain from such an inference and consider the supposition of a hybrid origin. But in former times, when this principle was still unknown and not even guessed at, it is evident that many mistakes must have been made, and that many an instance, which until now has been considered reliable proof of a so-called single variation, is in fact only a case of vicinism. In reading the sparse litera- ture on sports, numerous cases will be found, which cannot stand this test. It is evident that crossing must be looked to as an explanation, False Atavism 215 and in other cases the evidence relied upon does not suffice to exclude this assumption. Many a beautiful argument has of late lost its force by this test. Eeturning to our starting point we may now state that regular reversions to a specific type characterize a form as a variety of that species. These reversions, however, are not due to an innate tendency, but to undetected spontaneous crosses. LECTURE VIII LATENT CHARACTERS No organism exhibits all of its qualities at any one time, many of which are generally dor- mant and awaiting a period of activity. For some of them this period comes regularly, while in others the awakening depends upon external influences, and consequently occurs very irreg- ularly. Those of the first group correspond to the differences in age ; the second constitute the responses of the plant to stimuli including wound-injuries. Some illustrative examples may be quoted in order to give a precise idea of this general con- ception of dormant or latent characters. Seed- leaves are only developed in the seed and the seedling; afterwards, during the entire life- time of the plant, the faculty of producing them is not made use of. Every new generation of seeds, however, bears the same kind of seed leaves, and hence it is manifest that it is the same quality, which shows itself from time to time. 216 Latent Characters 217 The primary leaves, following the seed-leaves, are different in many species from the later ones, and the difference is extremely pro- nounced in some cases of reduction. Often, when the leaves of the adult plant are lacking, being replaced by flattened stalks as in the case of the acacias, or by thorns or green stems and twigs as in the prickly broom or Ulex europaeus, the first leaves of the young plant may be more highly differentiated, being pinnate in the first case and bearing three leaflets in the second in- stance. This curious behavior which is very common, brings the plants, when young, nearer to their allies than in the adult state, and mani- festly implies that the more perfect state of the leaves is latent throughout the life of the plant, with the exception of the early juvenile period. Eucalyptus globulus, the Australian gum-tree, has opposite and broadly sessile leaves during the first years of its life. Later these disap- pear and are replaced by long sickle-shaped foliage organs, which seem to be scattered ir- regularly along the branches. The juvenile characters manifestly lie dormant during the adult period, and that this is so, may be shown artificially by cutting off the whole crown of the tree, when the stem responds by producing numerous new branches, which assume the 218 Retrograde Varieties shape proper to the young trees, bearing sessile and opposite leaves. It seerns quite unnecessary to give further instances. They are familiar to every student. It is almost safe to say that every character has its periods of activity and of inactivity, and numbers of flowers and fruits can be mentioned as illustrations. One fact may be added to show that nearly every part of the plant must have the power of producing all or nearly all the characters of the individual to which it belongs. This proof is given by the formation of adventitious buds. These, when once formed, may grow out into twigs, with leaves and flowers and roots. They may even be sep- arated from the plants, and used as cuttings, to reproduce the whole. Hence we may conclude that all tissues, which possess the power of producing adventitious buds, must conceal in a latent state, all the numerous char- acters required for the full development of the whole individual. Adventitious buds may proceed from spe- cialized cells, as on the margin of the leaves of Bryophyllum calycinum; or from the cells of special tissues, as in the epidermis of the be- gonias; or they may be provoked by wounds in nearly every part of the plant provided it be able to heal the wound by swelling tissues or Latent Characters 219 callus. The best instance is afforded by elms and by the horse-chestnut. If the whole tree is hewn down the trunk tries to repair the injury by producing small granulations of tissue be- tween the wood and the bark, which gradually coalesce while becoming larger. From this new ring of living matter innumerable buds arise, expanding into leafy branches and showing clearly that the old trunk possesses, in a latent state, all the qualities of the whole crown. In- deed, such injured stumps may be used for the production of copses and hedges. All the hitherto recorded cases of latency have this in common, that they may become ac- tive during the life-time of any given individual once, or oftener. This may be called the ordi- nary type of latency. Besides this there is another form of latent characters, in which this awakening power is extremely limited, or wholly absent. It is the systematic latency, which may be said to be- long to species and varieties in the same way as the ordinary latency belongs to individuals. As this individual latency may show itself from time to time during the life of a given plant, the first may only become active from time to time during the whole existence of the variety or the species. It has no regular period of activity, nor may it be incited by artificial stimulation. 220 Retrograde Varieties It emerges from concealment only very rarely and only on its own initiative. Such instances of atavism have been described in previous lec- tures, and their existence has been proved be- yond doubt. Systematic latency explains the innumerable instances in which species are seen to lack def- inite characteristics which ordinarily do not fail, either in plants at large, or in the group, or family to which the plant belongs. If we take for instance the broom-rape or Orobanche, or some other pale parasite, we explain their occurrence in families of plants with green leaves, by the loss of the leaves and of the green color. But evidently this loss is not a true one, but only the latency of those characters. And even this latency is not a complete one, as little scales remind us of the leaves, and traces of chlorophyll still exist in the tissues. Nu- merous other cases will present themselves to every practical botanist. Taking for granted, that characters, having once been acquired, may become latent, and that this process is of universal occurrence through- out the whole vegetable and animal kingdom, we may now come to a more precise and clear con- ception of the existing differences between spe- cies and varieties. For this purpose we must take a somewhat Latent Characters 221 broader view of the whole evolution of the vegetable kingdom. It is manifest that highly developed plants have a larger number of characters than the lower groups. These must have been acquired in some way, during preceding times. Such evolution must evident- ly be called a process of improvement, or a progressive evolution. Contrasted to this is the loss, or the latency of characters, and this may be designated retrogressive or retrograde evo- lution. But there is still a third possibility. For a latent character may reassume its ac- tivity, return to the active state, and become once more an important part of the whole or- ganization. This process may be designated as regressive evolution; it obviously completes the series of the general types of evolution. Advancement in general in living nature de- pends on progressive evolution. In different parts of the vegetable kingdom, and even in different families this progression takes place on different lines. By this means it results in an ever increasing divergency between the sev- eral groups. Every step is an advance, and many a step must have been taken to produce flowering plants from the simplest unicellular algae. But related to, and very intimately con- nected with this advancement is the retrogres- 222 Retrograde Varieties sive evolution. It is equally universal, per- haps never failing. No great changes have been attained, without acquiring new qualities on one side, and reducing others to latency. Everywhere such regressions may be seen. The polypetalous genera Pyrola, Ledum, and Monotropa among the sympetalous heaths, are a remarkable instance of this. The whole evo- lution of the monocotyledons from the lowest orders of dicotyledons implies the seeming loss of cambial growth and many other quali- ties. In the order of aroids, from the cala- mus-root or sweet flag, with its small but com- plete flowers, up to the almost wholly reduced duckweeds (Lemna), almost an unbroken line of intermediate steps may be traced showing everywhere the concurrence of progressive and regressive evolution. Degressive evolution is not so common by far, and is not so easy to recognize, but no doubt it occurs very frequently. It is generally called atavism, or better, systematic atavism, and the clearest cases are those in which a quality which is latent in the greater part of a family or group, becomes manifest in one of its members. Bracts in the inflorescence of crucifers are or- dinarily wanting, but may be seen in some genera, Erucastrum Pollichii being perhaps the Latent Characters 223 most widely known instance, although other cases might easily be cited. For our special purpose we may take up only the more simple cases that may be avail- able for experimental work. The great lines of evolution of whole families and even of genera and of many larger species obviously lie outside the limits of experimental observation. They are the outcome of the history of the ancestors of the present types, and a repetition of their history is far beyond human powers. We must limit ourselves to the most recent steps; to the consideration of the smallest differences. But it is obvious that these may be included under the same heads as the larger and older ones. For the larger grades are manifestly to be con- sidered only as groups of smaller steps, going in the same direction. Hence we conclude, that even the smallest steps in the evolution of plants which we are able to observe, may be divided into progres- sive, retrogressive and degressive ones. The acquisition of a single new quality is the most simple step in the progressive line, the becom- ing latent and the reactivating of this same quality are the prototypes of the two other classes. Having taken this theoretical point of view, it remains to inquire, how it concurs with the 224 Retrograde Varieties various facts, given in former lectures and how it may be of use in our further discussions. It is obvious that the differences between ele- mentary species and varieties on the one hand, and between the positive and negative varieties as distinguished above, are quite comparable with our theoretical views. For we have seen that varieties can always be considered as hav- ing originated by an apparent loss of some quality of the species, or by the resumption of a quality, which in allied species is present and visible. In our exposition of the facts we have of course limited ourselves to the observable features of the phenomena without searching for a further explanation. For a more com- petent inquiry however, and for an understand- ing of wider ranges of facts, it is necessary to penetrate deeper into the true nature of the im- plied causes. Therefore we must try to show that elemen- tary species are distinguished from each other by the acquisition of new qualities, and that varieties are derived from their species either by the reduction of one or more characteristics, to the latent state, or by the energizing of dor- mant characters. Here we meet with a great difficulty. Hither- to varieties and subspecies have never been clearly defined, or when they have been, it was Latent Characters 225 not by physiological, but only by morphological research. And the claims of these two great lines of inquiry are obviously very diverging. Morphological or comparative studies need a material standard, by which it may be readily decided, whether certain groups of ani- mals and plants are to be described or de- nominated as species, as subspecies or as varie- ties. To get at the inner nature of the dif- ferences is in most cases impossible, but a de- cision must be made. The physiological line of inquiry has more time at its disposal ; it calls for no haste. Its experiments ordinarily cover years, and a conclusion is only to be reached after long and often weary trials. There is no necessity for opening a discussion until all doubtful points have been cleared up. Of course, large groups of facts remain uncertain, awaiting a closer inquiry, and the teacher is constrained to rely on the few instances only of thoroughly investigated cases. These alone are safe guides, and it seems far better to trust to them and to make use of them for the construc- tion of sharp conceptions, which may help us to point out the lines of inquiry which are still open. Leaving aside all such divisions and defini- tions, as were stamped with the name of pro- visional species and varieties by the great sys- 226 Retrograde Varieties tematist, Alphonse De Candolle, we may now try to give the proofs of our assertion, by using only those instances that have been thoroughly tested in every way. We may at once proceed to the retrogressive or negative varieties. The arguments for the assumption that elementary species owe their origin to the acquisition of new qualities may well be left for later lectures when we shall deal with the experimental proofs in this mat- ter. There are three larger groups of facts, on which the assumption of latent characters in ordinary varieties rests. These are true ata- vism, incomplete loss of characters, and system- atic affinity. Before dealing with each of these separately, it may be as well to recall once more that in former lectures we have treated the apparent losses only as modifications in a negative way, without contemplating the under- lying causes. Let us recall the cases of bud-atavism given by the whitish variety of the scarlet Ribes, by peaches and nectarines, by several conifers, as Cephalotaxus and Cryptomeria. These and many other analogous facts go to prove the re- lation of the variety to the species. Two as- sumptions are allowable. In one the variety differs from the species by the total loss of the Latent Characters 227 distinguishing mark. In the other this mark is only reduced to an inactive or dormant state. The fact of its recurrence from time to time, and of its return with all the secondary charac- teristics of the previous quality, is a manifest proof of the existence of some relation between the lost and the resumed peculiarity. Evident- ly as this relation cannot be accounted for on the assumption of an absolute disappearance, something must remain from which the old fea- tures may be restored. This lengthy discussion may be closed by the citation of the cases, in which plants not only show developmental features of a former state, but also reproduce the special features, they formerly had, but seemingly have lost. Two good illustrative examples may be given. One is afforded by the wheat-ear carnation, the other by some green dahlias, and both have oc- curred of late in my own cultures. A very curious anomaly may from time to time be observed in large beds of carnations. It bears no flowers, but instead of them small green ears, which recall the ears of wheat. Thence the name of " Wheat-ear " carnation. On closer inspection it is easily seen, how they originate. The normal flowers of the carna- tions are preceded by a small group of bracts, 228 Retrograde Varieties which are arranged in opposite pairs and there- fore constitute four rows. In this variety the flower is suppressed and this loss is attended by a corresponding in- crease of the number of the pairs of bracts. This malformation results in square spikes or somewhat elongated heads consisting only of the greenish bracts. As there are no flowers, the variety is quite sterile, and as it is not re- garded by horticulturists as an improvement on the ordinary bright carnations, it is seldom mul- tiplied by layering. Notwithstanding this, it appears from time to time and has been seen in different countries and at different periods, and, what is of great importance for us, in dif- ferent strains of carnations. Though sterile, and obviously dying out as often as it springs into existence, it is nearly two centuries old. It was described in the begining of the 18th cen- tury by Volckamer, and afterwards by Jaeger, De Candolle, Weber, Masters, Magnus and many other botanists. I have had it twice, at different times and from different growers. So far as I have been able to ascertain re- versions of this curious carnation to normal flowers have not yet been recorded. Such a modification occurred last summer in my gar- den on a plant which had not been divided or layered, but on which the slender branches had Latent Characters 229 been left on the stem. Some of them remained true to the varietal type and bore only green spikes. Others reverted wholly or partially to the production of normal flowers. Some branches bore these only, others had spikes and flowers on neighboring twigs, and in still other instances little spikes had been modified in such manner that a more or less well developed flow- er was preceded by some part of an ear. The proof that this retrograde modification was due to the existence of a character in the latent state was given by the color of the flow- ers. If the reverted bud had only lost the power of producing spikes, they would evident- ly simply have returned to the characteristics of the ordinary species, and their color would have been a pale pink. Instead of this, all flowers displayed corollas of a deep brown. They obviously reverted to their special prog- enitor, the chance variety from which they had sprung, and not to the common prototype of the species. Of course it was not possible to as- certain from which variety the plant had really originated, but the reproduction of any one clearly defined varietal mark is in itself proof enough of their origin, and of the latency of the dark brown flower-color in this special case. A still better proof is afforded by a new type of green dahlia. The ordinary green dahlia 230 Retrograde Varieties has large tufts of green bracts instead of flow- ering heads, the scales of the receptacle having assumed the texture and venation of leaves, and being in some measure as fleshy. But the green heads retain the form of the ordinary flower-heads, and as they have no real florets that may fade away, they remain unchanged on the plants, and increase in number through the whole summer. The new types of green dahlia however, with which I have now to deal, are distinguished by the elongation of the axis of the head, which is thereby changed into a long leafy stalk, attaining a length of several inches. These stalks continue growing for a very long time, and for the most part die without produc- ing anything else than green, fleshy scales. This long-headed green dahlia originated at Haarlem some years ago, in the nursery of Messrs. Zocher & Co. It was seen to arise twice, from different varieties. Both of these were double flowered, one a deep carmine with white tips on the rays, the other of a pale orange tint, known by the name of " Sunrise." As they did not bear any florets or seeds, they were quite sterile. The strain arising from the car- mine variety was kindly given to me by Messrs. Zocher & Co., and was propagated in my gar- den, while the other was kept in the nursery. In the earlier cultures both remained true to Latent Characters 231 their types, never producing true florets. No mark of the original difference was to be seen between them. But last summer (1903) both have reverted to their prototypes, bearing rela- tively large numbers of ordinary double flower- heads among the great mass of green stalks. Some intermediate forms also occurred consist- ing of green-scaled stalks ending in small heads with colored florets. Thus far we have an ordinary case of rever- sion. But the important side of the phenome- non was, that each plant exactly " recollected " from which parent it had sprung. All of those in my garden reverted to the carmine florets with white tips, and all of those in the nursery to the pale orange color and the other character- istics of the ' ' Sunrise ' ' variety. It seems absolutely evident, that no simple loss can account for this difference. Something of the character of the parent-varieties must have remained in the plant. And whatever conception we may formulate of these vestigial characters it is clear that the simplest and most obvious idea is their preservation in a dormant or latent state. Assuming that the distinguish- ing marks have only become inactive by vires- cence, it is manifest that on returning each will show its own peculiarities, as recorded above. Our second point was the incomplete loss of 232 Retrograde Varieties the distinguishing quality in some varieties. It is of general occurrence, though often over- looked. Many white varieties of colored flow- ers give striking instances, and so do also many of the most stable and most prized garden-flow- ers. If you look at them separately or in lit- tle bouquets they seem to be of irreproachable purity. But if you examine large beds a pale hue- will become visible. In many cases this tinge is so slight as to be only noticeable in a certain illumination, or by looking in an oblique direction across the bed ; in others it is at once evident as soon as it has been pointed out. It always reminds the observer of the color of the species to which the variety belongs, being bluish in violets and harebells, reddish in godetias and phloxes, in Silene Armeria and many others. It proves that the original color- quality of the species has not wholly, but only partly disappeared. It is dormant, but not en- tirely obliterated; latent, but not totally con- cealed; inactive, but only partially so. Our terminology is an awkward one; it practically assumes, as it so often does in other cases, a conventional understanding, not exactly cor- responding to the simple meaning of the words. But it would be cumbrous to speak always of partial inactivity, incomplete latency or half awakening qualities. Even such words as sub- Latent Characters 233 latent, which would about express the real state of things, would have little chance of coming into general use. Such sub-latent colors are often seen on spe- cial parts in white varieties of flowers. In many cases it is the outer side of the petals which recalls the specific color, as in some white roses. In violets it is often on the spur that the remains of the original pigment are to be seen. In many instances it is on the tips of the petals or of the segments of the corolla, and a large number of white or yellow flowers be- tray their affinity to colored species by becom- ing red or bluish at the edges or on the outer side. The reality of such very slight hues, and their relation to the original pigment of the species may in some cases be proved by direct experi- ment. If it is granted that latency is not an ab- solute quality, then it will be readily accepted, that even latency must be subjected to the laws of gradual variation or fluctuating variability. We will deal with these laws in a later lecture but every one knows that greater de- viations than the ordinary may be attained by sowing very large numbers and by selecting from among them the extreme individuals and sowing anew from their seed. In this way the slightest tinge of any latent color may be 234 Retrograde Varieties strengthened, not indeed to the restoration of the tinge of the species, but at least so far as to leave no doubt as to the identity of the visi- ble color of the species and the latent or sub- latent one of the variety. I made such an experiment with the peach- leaved harebell or Campanula persicifolia. The white variety of this species, which is often met with in our gardens, shows a very pale bluish hue when cultivated in large quantities, which however is subject to individual variations. I selected some plants with a decided tinge, flowered them separately, sowed their seeds, and repeated this during two generations. The result was an increase of the color on the tips of the segments of the corolla in a few in- dividuals, most of them remaining as purely white as the original strain. But in those few plants the color was very manifest, individually variable in degree, but always of the same blue as in the species itself. Many other instances could be given. Smooth varieties are seldom absolutely so, and if scattering hairs are found on the leaves or only on some more or less concealed parts, they correspond in their character to those of the species. So it is with prickles, and even the thornless thorn-apple has fruits with surfaces far from smooth. The thornless horse-chest- Latent Characters 235 nut has in some instances such evident protu- berances on the valves of its fruits, that it may seem doubtful whether it is a pure and stable variety. Systematic latency may betray itself in dif- ferent ways, either by normal systematic marks, or by atavism. With the latter I shall deal at length on another occasion, and there- fore I will give here only one very clear and beautiful example. It is afforded by the com- mon red clover. Obviously the clovers, with their three leaflets on each leaf, stand in the midst of the great family of papilionaceous plants,the leaves of which are generally pinnate. Systematic affinity suggests that the "three- leaved " forms must have been derived from pinnate ancestors, evidently by the reduction of the number of the leaflets. In some species of clover the middle of the three is more or less stalked, as is ordinarily the case in pinnate leaves ; in others it is as sessile as are its neigh- bors. In a subsequent chapter I will describe a very fine variety, which sometimes occurs in the wild state, and may easily be isolated and culti- vated. It is an ordinary red clover with five leaflets instead of three, and with this number varying between three and seven, instead of be- ing nearly wholly stable as in the common form. It produces from time to time pinnate leaves, 236 Retrograde Varieties very few indeed, and only rarely, but then often two or three or even more on the same in- dividual. Intermediate stages are not want- ing, but are of no consequence here. The pin- nate leaves obviously constitute a reversion to some prototype, to some ancestor with ordinary papilionaceous leaves. They give proof of the presence of the common character of the fam- ily, concealed here in a latent state. Any other explanation of this curious anomaly would evidently be artificial. On the other hand nothing is really known about the ances- tors of clover, and the whole conception rests only on prevailing views of the systematic rela- tionships in this family. But, as I have already said, further proof must be left for a subse- quent occasion. Many instances, noted in our former lectures, could be quoted here. The systematic distri- bution of rayed and rayless species and varie- ties among the daisy-group of the composites affords a long series of examples. Accidental variations in both directions occur. The Can- ada fleabane or Erigeron canadensis, the tansy or Tanacetum vulgare and some others may at times be seen with ray florets, and according to Murr, they may sometimes be wanting in Aster Tripolium, Bellis perennis, some species of Anthemis, Arnica montana and in a number Latent Characters 237 of other well-known rayed species. Another in- stance may be quoted; it has been pointed out by Grant Allen, and refers to the dead-nettle or Lamium album. Systematically placed in a genus with red-flowering species, we may re- gard its white color as due to the latency of the general red pigment. But if the flower of this plant is carefully examined, it will be found in most cases not to be purely white, but to have some dusky lines and markings on its lower lip. Similar devices are observed on the lip of the allied Lamium maculatum, and in a less de- gree on the somewhat distant Lamium pur- pur eum. With Lamium maculatum or spotted dead-nettle, the affinity is so close that even Bentham united the two in a single species, con- sidering the ordinary dead-nettle only as a va- riety of the dappled purple type. For the sup- port of this conception of a specific or varietal retrograde change many other facts are af- forded by the distribution of the characteristic color and of the several patterns of the lips of other labiates, and our general understanding of the relationships of the species and genera in this family may in a broad sense be based on the comparison of these seemingly subordinate characteristics. The same holds good in many other cases, and systematists have often become uncertain 238 Retrograde Varieties as to the true value of some form, by its rela- tionship to the allied types in the way of retro- gressive modification. Color-differences are so showy, that they easily overshadow other char- acters. The white and the blue thorn-apple, the white and the red campion (Lychnis ves- pertina and diurna) and many other illustrative cases could be given, in which two forms are specifically separated by some authors, but combined by others on the ground of the retro- grade nature of some differentiating mark. Hitherto we have dealt with negative charac- ters and tried to prove that the conception of latency of the opposite positive characteristics is a more natural explanation of the phenome- non than the idea of a complete loss. We have now to consider the positive varieties, and to show that it is quite improbable that here the species have struck out for themselves a wholly new character. In some instances such may have been the case, but then I should prefer to treat these rather as elementary species. But in the main we will have to assume the latency of the character in the species and its reassump- tion by the variety when originating, as the most probable explanation. Great stress is laid upon this conception by the fact, that positive varieties are so exces- sively rare when compared with the common oc- Latent Characters 239 currence of negative ones. Indeed, if we put aside the radiate and the color-varieties of flowers and foliage, hardly any cases can be cited. We have dealt with this question in a former lecture, and may now limit ourselves to the positive color- varieties. The latency of the faculty of producing the red pigment in leaves must obviously be ac- cepted for nearly the whole vegetable kingdom. Oaks and elms, the beautiful climbing species of Ampelopsis, many conifers, as for instance Cryptomeria japonica, some brambles, the Guelder-rose (Viburnum Opulus) and many other trees and shrubs assume a more or less bright red color in the fall. During summer this tendency must have been dormant, and that this is so, is shown by the young leaves of oaks and others, which, when unfolding in the spring show a similar but paler hue. Moreover, there is a way of awakening the concealed powers at any time. We have only to inflict small wounds on the leaves, or to cut through the nerves or to injure them by a slight bruising, and the leaves frequently respond with an intense reddening of the living tissues around and especially above the wounds. Azolla Caroliniana, a minute moss- like floating plant allied to the ferns, responds to light and cold with a reddish tinge, and to shade or warmth with a pure green. The foli- 240 Retrograde Varieties age of many other plants behaves likewise, as also do apples and peaches on the insolated sides of the fruits. It is quite impossible to state these groups of facts in a more simple way than by the statement that the tendency to be- come red is almost generally present, though latent, in leaves 'and stems, and that it comes into activity whenever a stimulus provokes it. Now it must be granted that the energizing of such a propensity under ordinary circum- stances is quite another thing from the orig- ination of a positive variety by the evolution of the same character. In the variety the ac- tivity has become independent of outer in- fluences or dependent upon them in a far lesser degree. The power of producing the red pig- ments is shown to be latent by the facts given above, and we see that in the variety it is no longer latent but is in perfect and lasting ac- tivity throughout the whole life of the plant. Red varieties of white flowers are much more rare. Here the latency of the red pigment may be deduced partly from general arguments like those just given, partly from the special syste- matic relations in the given cases. Hildebrand has clearly worked out this mode of proof. He showed by the critical examination of a large number of instances that the occurrence of the red flowered varieties is contingent upon the Latent Characters 241 existence of red species in the same genus, or in some rare cases, in nearly allied genera. Colors that are not systematically present in the group to which a white species belongs are only produced in its varieties in extremely rare cases. We may quote some special rules, indicated by Hildebrand. Blue species are in the main very rare, and so are blue varieties of white species also. Carnations, Asiatic or cultivated buttercups (Ranunculus Asiaticus), Mirabilis, poppies, Gladiolus, Dahlia, and some other highly cultivated or very old garden-plants have not been able to produce true blue flowers. But the garden-anemone (Anemone coronaria) has allies with very fine blue flowers. The common stock has bluish varieties and is allied to Aubre- tia and Hesperis, and gooseberries have a red form, recalling the ordinary currant. In nearly all other instances of blue or red varieties every botanist will be able to point out some allied red or blue species, as an indication of the probable source of the varietal character. Dark spots on the lower parts of the petals of some plants afford another instance, as in poppies and in the allied Glaucium, where they sometimes occur as varietal and in other cases as specific marks. The yellow fails in many highly developed 242 Retrograde Varieties flowers, which are not liable to produce yellow variations, as in Salvia, Aster, Centaurea, Vinca, Poly gala and many others. Even the rare pale yellowish species of some of these genera have no tendency in this direction. The hyacinths are the most remarkable, if not the sole known instance of a species having red and blue and white and yellow varieties, but here the yellow is not the bright golden color of the but- tercups. The existence of varietal colors in allied spe- cies obviously points to a common cause, and this cause can be no other than the latency of the pigment in the species that do not show it. The conception of latency of characters as the common source of the origination of varieties, either in the positive or in the negative way, leads to some rules on variability, which are known under the names given to them by Dar- win. They are the rules of repeated, homolog- ous, parallel and analogous variability. Each of them is quite general, and may be recog- nized in instances from the most widely dis- tant families. Each of them is quite evident and easily understood on the principle of latency. By the term of repeated variability is meant the well-known phenomenon, that the same va- riety has sprung at different times and in dif- Latent Characters 243 ferent countries from the same species. The repetition obviously indicated a common inter- nal cause. The white varieties of blue- and red- flowered plants occur in the wild state so often, and in most part of the instances in so few in- dividuals that a common pedigree is absolutely improbable. In horticulture this tendency is widely and vexatiously known, since the repeti- tion of an old variety does not bring any ad- vantage to the breeder. The old name of " conquests, " given by the breeders of hya- cinths, tulips and other flower bulbs to any novelty, in disregard of the common occurrence of repetitions, is an indication of the same ex- perience in the repeated appearance of certain varieties. The rule of parallel variations demands that the same character occasionally makes its ap- pearance in the several varieties or races, de- scended from the same species, and even in widely distinct species. This is a rule, which is very important for the general conception of the meaning of the term variety as contrasted with elementary species. For the recurrence of the same deviation always impresses us as a varietal mark. Laciniated leaves are perhaps the most beautiful instance, since they occur in so many trees and shrubs, as the walnut tree, the beech, the birch, the hazelnut, and even in 244 Retrograde Varieties brambles and some gar den- varieties of the tur- nip (Bras sic a). In such cases of parallel variations the single instances obviously follow the same rules and are therefore to be designated as analogous. Pitchers or ascidia, formed by the union of the margins of a leaf, are perhaps the best proof. They were classified by Morren under two heads, according to their formation from one or more leaves. Monophyllous pitchers obey the same law, viz. : that the upper side of the leaf has be- come the inner side of the pitcher. Only one exception to this rule is known to me. It is af- forded by the pitchers of the banyan or holy fig-tree, Ficus religiosus, but it does not seem to belong to the same class as other pitchers, since as far as it has been possible to ascertain the facts, these pitchers are not formed by a few leaves as in all other cases, but by all the leaves of the tree. In some cases pitchers are only built up of part of the leaf-blade. Such partial malforma- tions obey a rule, that is common to them and to other foliar enations, viz. : that the side of the leaf from which they emerge, is always their outer side. The inner surface of these ena- tions corresponds to the opposite side of the leaf, both in color and in anatomical structure. The last of the four rules above mentioned is Latent Characters 245 that of the homologous variability. It asserts that the same deviation may occur in different, but homologous parts of the same plant. We have already dealt with some instances, as the occurrence of the same pigment in the flowers and foliage, in the fruits and seeds of the same plant, as is also illustrated by the loss of the red or blue tinge by flowers and berries. Other in- stances are afforded by the curious fact that the division of the leaves into numerous and small segments is repeated by the petals, as in the common celandine and some sorts of brambles. It would take too long to make a closer exam- ination of the numerous cases, which afford proof of these statements. Suffice it to say that everywhere the results of close inspection point to the general rule, that the failure of definite qualities both in species and in varieties, must in a great number of cases, be considered as only apparent. Hidden from view, occasionally re- appearing, or only imperfectly concealed, the same character must be assumed to be present though latent. In the case of negative or retrogressive varie- ties it is the transition from the active into a dormant state to which is due the origin of the variety. Positive varieties on the contrary owe their origin to the presence of some character 246 Retrograde Varieties in the species in the latent state, and to the oc- casional re-energizing thereof. Specific or varietal latency is not the same thing as the ordinary latency of characters that only await their period of activity, or the ex- ternal influence which will awake them. They are permanently latent, and could well be des- ignated by the word perlatent. They spring into activity only by some sudden leap, and then at once become independent of ordinary exter- nal stimulation. LECTURE IX CROSSES OF SPECIES AND VARIETIES In the foregoing lectures I have tried to show that there is a real difference between element- ary species and varieties. The first are of equal rank, and together constitute the col- lective or systematic species. The latter are usually derived from real and still existing types. Elementary species are in a sense inde- pendent of each other, while varieties are of a derivative nature. Furthermore I have tried to show that the ways in which elementary or minor species must have originated from their common ancestor must be quite different from the mode of origin of the varieties. We have assumed that the first come into existence by the production of something new, by the acquirement of a char- acter hitherto unnoticed in the line of their an- cestors. On the contrary, varieties, in most cases, evidently owe their origin to the loss of an already existing character, or in other less frequent cases, to the re-assumption of a quality 247 248 Retrograde Varieties formerly lost. Some may originate in a negative way, others in a positive manner, but in both cases nothing really new is acquired. This distinction holds good for all cases in which the relationship between the forms in question is well known. It seems entirely justi- fiable therefore to apply it also to cases in which the systematic affinity is doubtful, as well as to instances in which it is impossible to ar- rive at any taxonornic conclusions. The ex- treme application of the principle would no doubt disturb the limits between many species and varieties as now recognized. It is not to be forgotten however that all taxonomic distinc- tions, which have not been confirmed by physi- ological tests are only provisional, a view ac- knowledged by the best systematists. Of course the description of newly discovered forms can not await the results of physiological inquiries, but it is absolutely impossible to reach definite conclusions on purely morphological evidence. This is well illustrated by the numerous dis- cords of opinion of different authors on the sys- tematic worth of many forms. Assuming the above mentioned principle as established, and disregarding doubtful cases as indicated, the term progressive evolution is used to designate the method in which element- ary species must have originated. It is the Unisexual Crosses 249 manner in which all advance in the animal and vegetable kingdoms must have taken place ; con- tinuously adding new characters to the already existing number. Contrasted with this method of growing differentiation, are the retrogres- sive modifications, which simply retrace a step, and the degressive changes in which the backward step is taken up and old charac- ters revived. No doubt both of these methods have been operative, but they are evidently not in the line of general advancement. In all of these directions we see that the dif- ferentiating marks show more or less clearly that they are built up of units. Allied forms are separated from each other without interme- diates. Transitions are wholly wanting, al- though fallaciously apparent in some instances owing to the wide range of fluctuating variabil- ity of the forms concerned, or to the occurrence of hybrids and subvarieties. These physiological units, which in the end must be the basis for the distinction of the sys- tematic units, may best be designated by the term of " unit-characters. " Their internal na- ture is as yet unknown to us, and we will not now look into the theories, which have been pro- pounded as to the probable material basis un- derlying them. For our present purpose the empirical evidence of the general occurrence of 250 Retrograde Varieties sharp limits between nearly related characters must suffice. As Bateson has put it, species are discontinuous, and we must assume that their characters are discontinuous also. Moreover there is as yet no reason for trying to make a complete analysis of all the charac- ters of a plant. No doubt, if attained, such an analysis would give us a deep insight into the real internal construction of the intricate prop- erties of organisms in general. But taxonomic studies in this direction are only in their in- fancy and do not give us the material required for such an analysis. Quite on the contrary, they compel us to confine our study to the most recently acquired, or youngest characters, which constitute the differentiating marks be- tween nearly allied forms. Obviously this is especially the case in the realm of the hybrids, since only nearly related forms are able to give hybrid offspring. In dealing with this subject we must leave aside all questions concerning more remote relation- ships. It is not my purpose to treat of the doctrine of hybridization at any length. Experience is so rapidly increasing both in a practical and in a purely scientific direction that it would take an entire volume to give only a brief sur- vey of the facts and of all the proposed theories. Unisexual Crosses 251 For our present purposes we are to deal with hybrids only in so far as they afford the means of a still better distinction between elementary species and varieties. I will try to show that these two contrasting groups behave in quite a different manner, when subjected to crossing experiments, and that the hope is justified that some day crosses may become the means of deciding in any given instance, what is to be called species, and what variety on physiolog- ical grounds. It is readily granted that the labor required for such experiments, is perhaps too great for the results to be attained, but then it may be possible to deduce rules from a small series of experiments, which may lead us to a decision in wider ranges of cases. To reach such a point of view it is necessary to compare the evidence given by hybrids, with the conclusions already attained by the com- parison of the differentiating characteristics of allied forms. On this ground we first have to inquire what may be expected respecting the internal nature and the outcome of the process of crossing in the various cases cited in our former discussion. We must always distinguish the qualities, which are the same in both parents, from those that constitute the differentiating marks in every single cross. In respect to the first 252 Retrograde Varieties group the cross is not at all distinguished from a normal fertilization, and ordinarily these characters are simply left out of consideration. But it should never be forgotten that they con- stitute the enormous majority, amounting to hundreds and thousands, whereas the differen- tiating marks in each case are only one or two or a few at most. The whole discussion is to be limited to these last named exceptions. We must consider first what would be the nature of a cross when species are sexually combined, and what must be the case when varieties are sub- jected to the same treatment. In so doing, I in- tend to limit the discussion to the most typical cases. We may take the crosses between ele- mentary species of the same or of very nar- rowly allied systematic species on the one side, and on the other, limit treatment to the crossing of varieties with the species, from which they are supposed to have sprung by a retrograde modification. Crosses of different varieties of the same species with one another obviously constitute a derivative case, and should only be discussed secondarily. And crosses of varie- ties with positive or degressive characters have as yet so rarely been made that we may well disregard them. Elementary species differ from their nearest allies by progressive changes, that is by the ac- Unisexual Crosses 253 quirement of some new character. The deriva- tive species has one unit more than the parent. All other qualities are the same as in the par- ent. Whenever such a derivative is sexually combined with its parent the result will there- fore be exactly as in a normal fertilization. In such ordinary cases it is obvious that each char- acter of the pollen-parent is combined with the same character of the pistil-parent. There may be slight individual differences, but each unit- character will become opposed to, and united with, the same unit-character in the other par- ent. In the offspring the units will thus be paired, each pair consisting of two equivalent units. As to their character the units of each single pair are the same, only they may exhibit slight differences as to the degree of develop- ment of this character. Now we may apply this conception to the sex- ual combination of two different elementary species, assuming one to be the derivative of the other. The differentiating mark is only present in one of the parents and wanting in the other. While all other units are paired in the hybrid, this one is not. It meets with no mate, and must therefore remain unpaired. The hybrid of two such elementary species is in some way incomplete and unnatural. In the ordinary course of things all individuals derive 254 Retrograde Varieties their qualities from both parents ; for each sin- gle mark they possess at least two units. Prac- tically but not absolutely equal, these two op- ponents always work together and give to the offspring a likeness to both parents. No un- paired qualities occur in normal offspring ; these constitute the essential features of the hybrids of species and are at the same time the cause of their wide deviations from the ordinary rules. Turning now to the varieties, we likewise need only to discuss their differentiating marks. In the negative types, these consist of the ap- parent loss of some quality which was active in the species. But it was pointed out in our last lecture that such a change is an apparent loss. On a closer inquiry we are led to the assumption of a latent or dormant state. The presumably lost characters have not absolutely, or at least not permanently disappeared. They show their presence by some slight indication of the quality they represent, or by occasional revers- ions. They are not wanting, but only latent. Basing our discussion concerning the process of crossing on this conception, and still limiting the discussion to one differentiating mark, we come to the inference, that this mark is present and active in the species, and present but dor- mant in the variety. Thus it is present in both, and as all other characters not differentiating Unisexual Crosses 255 find their mates in the cross, so these two will also meet one another. They will unite just as well as though they were both active or both dormant. For essentially they are the same, only differing in their degree of activity. From this we can infer, that in the crossing of varie- ties, no unpaired remainder is left, all units combining in pairs exactly as in ordinary fertil- ization. Setting aside the contrast between activity and latency in this single pair, the procedure in the inter-crossing of varieties is the same as in ordinary normal fertilization. Summarizing this discussion we may con- clude that in normal fertilization and in the inter-crossing of varieties all characters are paired, while in crosses between elementary species the differentiating marks are not mated. In order to distinguish these two great types of fertilization we will use the term bisexual for the one and unisexual for the other. The term bisexual crosses then conveys the idea of com- plete bisexuality, all unit-characters combining in pairs. Unisexual crosses are those in which one or more units do not find their mates and therefore remain unpaired. This clear and useful term was proposed by MacFarlane when studying the minute structure of plant hybrids in comparison with that of their parents (1892). 256 Retrograde Varieties In the first place it shows that a species- hybrid may derive all its distinguishing marks from both parents. In this way it may become intermediate between them, having some char- acters in common with pollen-parent and others with the pistil-parent. As far as these charac- ters do not interfere with each other, they may be fully developed side by side, and in the main this is the way in which hybrid-characters are evolved. But in most cases our existing knowl- edge of the units is far too slender to give a complete analysis, even of these distinguishing marks alone. We recognize the parental marks more or less clearly, but are not prepared for exact delimitations. Leaving these theoretical considerations, we will pass to the description of some illustrative examples. In the first place I will describe a hybrid be- between two American species of Oenothera, which I made some years ago. The parents were the common evening-primrose or Oenothera biennis and its small-flowered congener, Oeno- thera muricata. These two forms were distin- guished by Linnaeus as different species, but have been considered by subsequent writers as elementary species or so-called systematic va- rieties of one species designated with the name of the presumably older type, the 0. biennis. Varietal differences in a physiologic sense they Unisexual Crosses 257 do not possess, and for this reason afford a pure instance of unisexual union, though differ- ing in more than one point, I have made reciprocal crosses, taking at one time the small-flowered and at the other the common species as pistillate parent. These crosses do not lead to the same hybrid as is often supposed in analogous cases ; quite on the contrary, the two types are different in most features, both resembling the pollen-parent far more than the pistil-parent. The same curious result was reached in sundry other re- ciprocal crosses between species of this genus. But I will limit myself here to one of the two hybrids. In the summer of 1895 I castrated some flow- ers of 0. muricata, and pollinated them with 0. ToienniSj surrounding the flowers with paper bags so as to exclude the visits of insects. I sowed the seeds in 1896 and the hybrids were biennial and flowered abundantly the next year and were artificially fertilized with their own pollen, but gave only a very small harvest. Many capsules failed, and the remaining con- tained only some few ripe seeds. From these I had in the following year the second hybrid generation, and in the same way I cultivated also the third and fourth. These were as imperfectly fertile as the first, and in 258 Retrograde Varieties some years did not give any seed at all, so that the operation had to be repeated in order to continue the experiment. Last summer (1903) I had a nice lot of some 25 biennial specimens blooming abundantly. All in all I have grown some 500 hybrids, and of these about 150 speci- mens flowered. These plants were all of the same type, re- sembling in most points the pollen-parent, and in some others the pistil-parent of the original cross. The most obvious characteristic marks are afforded by the flowers, which in 0. muri- cata are not half so large as in biennis, though borne by a calyx-tube of the same length. In* this respect the hybrid is like the biennis bearing the larger flowers. These may at times seem to deviate a little in the direction of the other parent, being somewhat smaller and of a slightly paler color. But it is very difficult to distinguish between them, and if biennis and hybrid-flowers were separated from the plants and thrown together, it is very doubt- ful whether one would succeed in separating them. The next point is offered by the foliage. The leaves of 0. biennis are broad, those of 0. muri- cata narrow. The hybrid has the broad leaves of 0. biennis during most of its life and at the time of flowering. Yet small deviations in the Unisexual Crosses 259 direction of the other parent are not wanting, and in winter the leaves of the hybrid-rosettes are often much narrower than those of 0. bien- nis, and easily distinguishable from both par- ents. A third distinction consists in the den- sity of the spike. The distance between the in- sertion of the flowers of 0. biennis is great when compared with that of 0. muricata. Hence the flowers of the latter species are more crowded and those of 0. biennis more dispersed, the spikes of the first being densely crowned with flowers and flower-buds while those of 0. biennis are more elongated and slender. As a further consequence the 0. biennis opens on the same evening only one, two or three flowers on the same spike, whereas 0. muricata bears often eight or ten or more flowers at a time. In this respect the hybrid is similar to the pistil-parent, and the combination of the larger leaves and broad flowers of 0. biennis, which are crowded at the top of the spikes, cause the hybrids to be much more showy than either of the parent types. Other distinguishing marks are not recorded by the systematists, or are not so sharply sepa- rated as to allow of the corresponding qualities of the hybrids being compared with them. This hybrid remains true to the description given. In some years I cultivated two gener- 260 Retrograde Varieties ations so as to be able to compare them with one another, but did not find any difference. The most interesting point however, is the like- ness between the first generation, which ob- viously must combine in its internal structure the units of both parents, and the second and later generations which are only of a derivative nature. Next to this stands the fact that in each generation all individuals are alike. No reversion to the parental forms either in the whole type or in the single characteristics has ever been observed, though the leaves of some hundreds, and the spikes and flowers of some 150 individual plants have been carefully ex- amined. No segregation or splitting up takes place. Here we have a clear, undoubted and rela- tively simple, case of a true and pure species- hybrid. No occurrence of possible varietal characteristics obscures the result, and in this respect this hybrid stands out much more clearly than all those between garden-plants, where varietal marks nearly always play a most important part. From the breeder's point of view our hybrid Oenothera would be a distinct gain, were it not for the difficulty of its propagation. But to en- large the range of the varieties this simple and stable form would need to be treated anew, by Unisexual Crosses 261 crossing it with the parent-types. Such experi- ments however, have miscarried owing to the too stable nature of the unit-characters. This stability and this absence of the split- ting shown by varietal marks in the offspring of hybrids is one of the best proofs of unisex- ual unions. It is often obscured by the accom- panying varietal marks, or overlooked for this reason. Only in rare cases it is to be met with in a pure state and some examples are given of this below. Before doing so, I must call your attention to another feature of the unisexual unions. This is the diminution of the fertility, a phe- nomenon universally known as occurring in hybridizations. It has two phases. First, the diminished chance of the crosses themselves of giving full crops of seed, as compared with the pure fertilization of either parent. And, sec- ondly, the fertility of the hybrids themselves. Seemingly, all grades of diminished fertility occur and the oldest authors on hybrids have pointed out that a very definite relation exists between the differences of the parents and the degree of sterility, both of the cross and of the hybrid offspring. In a broad sense these two factors are proportionate to each other, the sterility being the greater, the lesser the affin- ity between the parents. Many writers have 262 Retrograde Varieties tried to trace this rule in the single cases, but have met with nearly unsurmountable difficul- ties, owing chiefly to ignorance of the units which form the differences between the parents in the observed cases. In the case of Oenothera muricata x bien- nis the differentiating units reduce the fertility to a low degree, almost threatening the off- spring with complete infertility and extinction. But then we do not know whether these charac- ters are really units, or perhaps only seemingly so and are in reality composed of smaller en- tities which as yet we are not able to segregate. And as long as we are devoid of empirical means of deciding such questions, it seems useless to go farther into the details of the question of the sterility. It should be stated here however, that pure varietal crosses, when not accompan- ied by unisexual characters, have never showed any tendency to diminished fertility. Hence there can be little doubt that the unpaired units are the cause of this decrease in reproductive power. The genus Oenothera is to a large degree de- void of varietal characteristics, especially in the subgenus Onagra, to which biennis, mur- icata, Lamarckiana and some others belong. On the other hand it seems to be rich in elementary species, but an adequate study of Unisexual Crosses 263 them has as yet not been made. Unfortunately many of the better systematists are in the habit of throwing all these interesting forms to- gether, and of omitting their descriptive study. I have performed a large number of crosses between such undescribed types and as a rule got constant hybrid races. Only one or two exceptions could be quoted, as for instance the Oenothera brevistylis, which in its crosses al- ways behaves as a pure retrogressive variety. Instead of giving an exhaustive survey of hybrids, I simply cite my crosses between Lamarckiana and biennis, as having nearly the aspect of the last named species, and remaining true to this in the second generation without any sign of reversion or of splitting. I have crossed another elementary species, the Oeno- thera Mrtella with some of my new and with some older Linnean species, and got several constant hybrid races. Among these the off- spring of a cross between muricata and hirtella is still in cultivation. The cross was made in the summer of 1897 and last year (1903) I grew the fourth generation of the hybrids. These had the characters of the muricata in their nar- row leaves, but the elongated spikes and rela- tively large flowers of the hirtella-pareTLt, and remained true to this type, showing only slight fluctuations and never reverting or segregating 264 Retrograde Varieties the mixed characters. Both parents bear large capsules with an abundance of seed, but in the hybrids the capsules remain narrow and weak, ripening not more than one-tenth the usual quantity of seed. Both parents are easily cultivated in annual generations and the same holds good for the hybrid. But whereas the hybrid of muricata and biennis is a stout plant, this type is weak with a badly developed foliage, and very long strict spikes. Perhaps it was not able to withstand the bad weather of the last few years. A goodly number of constant hybrids are de- scribed in literature, or cultivated in fields and gardens. In such cases the essential question it not whether they are now constant, but whether they have been so from the beginning, or whether they prove to be constant whenever the original cross is repeated. For constant hybrids may also be the issue of incipient split- tings, as we shall soon see. Among other examples we may begin with the hybrid alfalfa or hybrid lucerne (Medicago media). It often originates spontaneously be- tween the common purple lucerne or alfalfa and its wild ally with yellow flowers and pro- cumbent stems, the Medicago falcata. This hybrid is cultivated in some parts of Germany on a large scale, as it is more fertile than Unisexual Crosses 265 the ordinary lucerne. It always comes true from seed and may be seen in a wild state in parks and on lawns. It is one of the oldest hybrids with a pure and known lineage. The original cross has been repeated by Urban, who found the hybrid race to be constant from the beginning. Another very notorious constant hybrid race is the Aegilops speltaeformis. It has been cultivated in botanic gardens for more than half a century, mostly in annual or biennial generations. It is sufficiently fertile and al- ways comes true. Numerous records have been made of it, since formerly it was believed by Fabre and others, to be a spontaneous transi- tion from some wild species of grass to the ordi- nary wheat, not a cross. Godron, however, showed that it can be produced artificially, and how it has probably sprung into existence wherever it is found wild. The hybrid between Aegilops ovata, a small weed, and the common wheat is of itself sterile, producing no good pol- len. But it may be fertilized by the pollen of wheat and then gives rise to a secondary hybrid, which is no other than the Aegilops speltaeformis. This remained constant in God- ron 's experiments during the first few genera- tions, and was at that time identical with its present form. 266 Retrograde Varieties Constant hybrids have been raised by Mil- lardet between several species of strawberries. He combined the old cultivated forms with new types from American localities. They ordi- narily showed only the characteristics of one of their parents and did not exhibit any new combination of qualities, but they have come true to this type in the second and later gener- ations. In the genus Anemone, Janczewski obtained the same results. Some characters of course may split, but others remain constant, and when only such are present, hybrid-races result with new combinations of characters, which are as constant as the best species of the same ge- nus. The hybrids of Janczewski were quite fer- tile, and he points out that there is no other reason why they should not be considered as good new species. If they were not produced artificially, but found in the wild state, their origin would have been unknown, and there can be no doubt that they would have been described by the best systematists as species of the same value as their real parents. Such is especially the case with a hybrid between Anemone magel- lanica and the common Anemone sylvestris. Starting from similar considerations Kerner von Marilaun pointed out the fact long ago that many so-called species, of rare occurrence, Unisexual Crosses 267 standing between two allied types, may be con- sidered to have originated by a cross. Surely a wide field for abuse is opened by such an as- sertion, and it is now a common habit to con- sider intermediate forms as hybrids, on the grounds afforded by their external characters alone, and without any exact knowledge of their real origin and often without knowing anything as to their constancy from seed. All such ap- parent explanations are now slowly becoming antiquated and obsolete, but the cases adduced by Kerner seem to stand this test. Kerner designates a willow, Salix Ehrhart- iana as a constant hybrid between Salix alba and S. pentandra. Rhododendron intermed- ium is an intermediate form between the hairy and the rusty species from the Swiss Alps, R. hirsutum and R. ferrugineum, the former grow- ing on chalky, and the other on silicious soils. Wherever both these types of soil occur in the same valley and these two species approach one another, the hybrid R. intermedium is pro- duced, and is often seen to be propagating itself abundantly. As is indicated by the name, it combines the essential characters of both par- ents. Linaria italic a is a hybrid toad-flax between L. genistifolia and L. vulgaris, a cross which I have repeated in my garden. Drosera obovata 268 Retrograde Varieties is a hybrid sundew between D. anglica and D. rotundifolia. Primula variabilis is a hybrid between the two common primroses, P. offici- nalis and P. grandiflora. The willow-herb (Epilobium), the self-heal (Brunella) and the yellow pond-lilies (Nuphar) afford other in- stances of constant wild hybrids. Macfarlane has discovered a natural hybrid between two species of sundew in the swamps near Atco, N. J. The parents, D. intermedia and D. filiformis, were growing abundantly all around, but of the hybrid only a group of eleven plants was found. A detailed comparison of the hybrid with its parents demonstrated a minute blending of the anatomical peculiarities of the parental species. Luther Burbank of Santa Rosa, California, has produced a great many hybrid brambles, the qualities of which in many respects surpass those of the wild species. Most of them are only propagated by cuttings and layers, not being stable from seed. But some crosses be- tween the blackberry and the raspberry (R. fruticosus and R. Idaeus) which bear good fruit and have become quite popular, are so fixed in their type as to reproduce their com- posite characters from seed with as much regu- larity as the species of Rubus found in nature. Among them are the " Phenomenal " and the Unisexual Crosses 269 « primus." The latter is a cross between the California!! dewberry and the Siberian rasp- berry and is certainly to be regarded as a good stable species, artificially produced. Bell Salter crossed the willow-herbs Epilobium tet- ragonum and E. montanum, and secured inter- mediate hybrids which remained true to their type during four successive generations. Other instances might be given. Many of them are to be found in horticultural journals and in the botanical writings which treat of systematic and anatomical details. The ques- tion of stability is generally dealt with in an incidental manner, and in many cases it is diffi- cult to reach conclusions from the facts given. Especially disturbing is the circumstance that from a horticultural point of view it is quite sufficient that a new type should repeat itself in some of its offspring, to call it stable, and that for this reason the absolute constancy is rarely proved. The range of constant hybrids would be larger by far were it not for two facts. The first is the absolute sterility of so many beauti- ful hybrids, and the second is the common occur- rence of retrogressive characters among culti- vated plants. To describe the importance of both these groups of facts would take too much 270 Retrograde Varieties time, and therefore it seems best to give some illustrative examples instead. Among the species of Ribes or currant, which are cultivated in our gardens, the most beauti- ful are without doubt the Californian and the Missouri currant, or Ribes sanguineum and R. aureum. A third form, often met with, is ' ' Gor- don 's currant," which is considered to be a hybrid between the two. It has some peculiar- ities of both parents. The leaves have the gen- eral form of the Californian parent, but are as smooth as the Missouri species. The racemes or flower-spikes are densely flowered as in the red species, but the flowers themselves are of a yellow tinge, with only a flesh-red hue on the outer side of the calyx. It grows vigorously and is easily multiplied by cuttings, but it never bears any fruit. Whether it would be constant, if fertile, is therefore impossible to decide. Berberis Neuberti is considered as a hybrid between the European barberry (B. vulgaris) and the cultivated shrub Mahonia aquifolia. The latter has pinnate leaves, the former undi- vided ones. The hybrid has undivided leaves which are more spiny than those of the Euro- pean parent, and which are not deciduous like them, but persist during the winter, a peculiar- ity inherited from the Mahonia. As far as I Unisexual Crosses 271 have been able to ascertain, this hybrid never produces seed. Another instance of an absolutely sterile hybrid is the often quoted Cytisus Adami. It is a cross between the common laburnum (Cytisus Laburnum) and another species of the same genus, C. purpureus, and has some traits of both. But since the number of differentiat- ing marks is very great in this case, most of the organs have become intermediate. It is abso- lutely sterile. But it has the curious peculiar- ity of splitting in a vegetative way. It has been multiplied on a large scale by grafting, and was widely found in the parks and gardens of Europe during the last century. Nearly all these specimens reverted from time to time to the presumable parents. Not rarely a bud of Adam's laburnum assumed all the qualities of the common laburnum, its larger leaves, richer flowered racemes, large and brightly yellow flowers and its complete fertility. Other buds on the same tree reverted to the purple parent, with its solitary small flowers, its dense shrub- like branches and very small leaves. These too are fertile, though not producing their seeds as abundantly as the C. Laburnum reversions. Many a botanist has sown the seeds of the latter and obtained only pure common C. Laburnum plants. I had a lot of nearly a hundred seed- 272 Retrograde Varieties lings myself, many of which have already flow- ered, bearing the leaves and flowers of the com- mon species. Seeds of the purple reversions have also been sown, and also yielded the parental type only. Why this most curious hybrid sports so reg- ularly and why others always remain true to their type is as yet an open question. But recalling our former consideration of this subject the supposition seems allowable that the tendency to revert is not connected with the type of the hybrid, but is apt to occur in some rare individuals of every type. But since most of the sterile hybrids are only known to us in a single individual and its vegetative offspring, this surmise offers an explanation of the rare occurrence of sports. Finally, we must consider some of the so- called hybrid races or strains of garden-plants. Dahlia, Gladiolus, Amaryllis, Fuchsia, Pelar- gonium and many other common flowers afford the best known instances. Immeasurable variability seems here to be the result of crossing. But on a closer inspection the range of characters is not so very much wider in these hybrid races, than in all the parent-species which have contributed to the origin of the hybrids. Our tuberous begonias owe their variability to at least seven original parent spe- Unisexual Crosses 273 cies, and to the almost incredible number of combinations which are possible between their characters. The first of these crosses was made in the nursery of Veitch and Sons near London by Seden, and the first hybrid is ac- cordingly known as Begonia Sedeni and is still to be met with. It has been superseded by sub- sequent crosses between the Sedeni itself and the VeitcM and rosiflora, the Davisii, the Clarkii and others. Each of them contributed its advantageous qualities, such as round flow- ers, rosy color, erect flower stalks, elevation of the flowers above the foliage and others. New crosses are being made continuously, partly be- tween the already existing hybrids and partly with newly introduced wild species. Only rarely is it possible to get pure seeds, and I have not yet been able to ascertain whether the hybrids would come true from seed. Specific and varietal characters may occur together in many of the several forms, but nothing is as yet accurately known as to their behavior in pure fertilizations. Constancy and segregation are thrown together in such a manner that ex- treme variability results, and numerous beauti- ful types may be had, and others may be ex- pected from further crosses. For a scientific analysis, however, the large range of recorded facts and the written history, which at first sight 274 Retrograde Varieties seems to have no lacunae, are not sufficient. Most of the questions remain open and need in- vestigation. It would be a capital idea to try to repeat the history of the begonias or any other hybrid race, making all the described crosses and then recording the results in a man- ner requisite for complete and careful scien- tific investigations. Many large genera of hybrid garden-flowers owe their origin to species rich in varieties or in elementary subspecies. Such is the case with the gladiolus and the tulips. In other cases the original types have not been intro- duced from the wild state but from the cultures of other countries. The dahlias were cultivated in Mexico when first discovered by Europeans, and the chrys- anthemums have been introduced from the old gardens of Japan. Both of them consisted of various types, which afterwards have been in- creased chiefly by repeated intercrossing. The history of many hybrid races is obscure, or recorded by different authorities in a differ- ent way. Some have derived their evidence from one nursery, some from another, and the crosses evidently may have been different in different places. The early history of the glad- iolus is an instance. The first crosses are re- corded to have been made between Gladiolus Unisexual Crosses 275 psittacinus and G. cardinalis, and between their hybrid, which is still known under the name of Gandavensis and the purpurea-auratus. But other authors give other lines of descent. So it is with Amaryllis, which is said by De Graaff to owe its stripes to A. vittata, its fine form to A. Brasiliensis, the large petals to A. psittacina, the giant flowers to A. Leopoldi, and the piebald patterns to A. pardina. But here, too, other authors give other derivations. Summarizing the results of our inquiry we see in the first place how very much remains to be done. Many old crosses must be repeated and studied anew, taking care of the purity of the cross as well as of the harvesting of the seeds. Many supposed facts will be shown to be of doubtful validity. New facts have to be gathered, and in doing so the distinction be- tween specific and varietal marks must be taken strictly into account. The first have originated as progressive mutations; they give unisexual crosses with a constant offspring, as far as ex- perience now goes. The second are chiefly due to retrograde modifications, and will be the sub- ject of the next lecture. LECTURE X MENDEL'S LAW OF BISEXUAL CROSSES In the scientific study of the result of crosses, the most essential point is the distinction of the several characters of the parents in their combi- nation in the hybrids and their offspring. From a theoretical point of view it would be best to choose parents which would differ only in a single point. The behavior of the differen- tiating character might then easily be seen. Unfortunately, such simple cases do not read- ily occur. Most species, and even many ele- mentary species are distinguished by more than one quality. Varieties deviating only in one unit-character from the species, are more com- mon. But a closer inspection often reveals some secondary characters which may be over- looked in comparative or descriptive studies, but which reassume their importance in experi- mental crossings. In a former lecture we have dealt with the qualities which must be considered as being due to the acquisition of new characters. If we 276 Bisexual Crosses 277 compare the new form in this case with the type from which it has originated, it may be seen that the new character does not find its mate, or its opposite, and it will be unpaired in the hybrid. In the case of retrogressive changes the vis- ible modification is due, at least in the best known instances, to the reduction of an active quality to a state of inactivity or latency. Now if we make a cross between a species and its variety, the differentiating character will be due to the same internal unit, with no other difference than that it is active in the species and latent in the variety. In the hybrid these two corresponding units will make a pair. But while all other pairs in the same hybrid indi- viduals consist of like antagonists, only this pair consists of slightly unlike opponents. This conception of varietal crosses leads to three assertions, which seem justifiable by actual experience. First, there is no reason for a diminution of the fertility, as all characters are paired in the hybrid, and no disturbance whatever ensues in its internal structure. Secondly, it is quite in- different, how the two types are combined, or which of them is chosen as pistillate and which as staminate parent. The deviating pair will have the same constitution in both cases, being 278 Retrograde Varieties built up of one active and one dormant unit. Thirdly this deviating pair will exhibit the active unit which it contains, and the hybrid will show the character of the parent in which it was dormant. Now the active quality was that of the species, and its latent state was found in the variety. Hence the inference that hybrids between a species and its retrograde variety will bear the aspect of the species. This attribute may be fully developed, and then the hybrid will not be distinguishable from the pure species in its outer appearance. Or the character may be incompletely evolved, owing to the failure of cooperation of the dormant unit. In this case the hybrid will be in some sense intermediate between its parents, but these instances are more rare than the alternate ones, though presumably they may play an im- portant part in the variability of many hybrid garden-flowers. All of these three rules are supported by a large amount of evidence. The complete fertil- ity of varietal hybrids is so universally acknowl- edged that it is not worth while to give special instances. With many prominent systematists it has become a test between species and vari- ety, and from our present point of view this as- sumption is correct. Only the test is of little use in practice, as fertility may be diminished Bisexual Crosses 279 in unisexual unions in all possible degrees, ac- cording to the amount of difference between the parents. If this amount is slight, if for in- stance, only one unit-character causes the dif- ference, the injury to fertility may be so small as to be practically nothing. Hence we see that this test would not enable us to judge of the doubtful cases, although it is quite sufficient as a proof in cases of wider differences. Our second assertion related to the reciprocal crosses. This is the name given to two sexual combinations between the same parents, but with interchanged places as to which furnishes the pollen. In unisexual crosses of the genus Oenothera the hybrids of such reciprocal unions are often different, as we have formerly seen. Sometimes both resemble the pollen-parent more, in other instances the pistil-parent. In varietal crosses no such divergence is as yet known. It would be quite superfluous to ad- duce single cases as proofs for this rule, which was formerly conceived to hold good for hy- brids in general. The work of the older hybrid- ists, such as Koelreuter and Gaertner affords numerous instances. Our third rule is of a wholly different nature. Formerly the distinction between elementary species and varieties was not insisted upon, and the principle which stamps retrograde changes 280 Retrograde Varieties as the true character of varieties is a new one. Therefore it is necessary to cite a considerable amount of evidence in order to prove the asser- tion that a hybrid bears the active character of its species-parent and not the inactive char- acter of the variety chosen for the cross. We may put this assertion in a shorter form, stating that the active character prevails in the hybrid over its dormant antagonist. Or as it is equally often put, the one dominates and the other is recessive. In this terminology the character of the species is dominant in the hybrid while that of the variety is recessive. Hence it follows that in the hybrid the latent or dormant unit is recessive, but it does not follow that these three terms have the same meaning, as we shall see presently. The term recessive only applies to the peculiar state into which the latent character has come in the hybrid by its pairing with the antagonistic active unit. In the first place it is of the highest import- ance to consider crosses between varieties of re- corded origin and the species from which they have sprung. When dealing with mutations of celandine we shall see that the laciniated form originated from the common celandine in a garden at Heidelberg about the year 1590. Among my Oenotheras one of the eldest of the recent productions is the 0. brevistylis or short- Bisexual Crosses 281 styled species which was seen for the first time in the year 1889. The third example offered is a hairless variety of the evening campion, Lychnis vespertina, found the same year, which hitherto had not been observed. For these three cases I have made the crosses of the variety with the parent species, and in each case the hybrid was like the species, and not like the variety. Nor was it intermediate. Here it is proved that the older character dom- inates the younger one. In most cases of wild, and of garden- varieties the relation between them and the parent-spe- cies rests upon comparative evidence. Often the variety is known to be younger, in other cases it may be only of local occurrence, but ordinarily the historic facts about its origin have never been known or have long since been forgotten. The easiest and most widely known varietal crosses are those between varieties with white flowers and the red- or blue-flowered species. Here the color prevails in the hybrid over the lack of pigment, and as a rule the hybrid is as deeply tinted as the species itself, and cannot be distinguished from it, without an investigation of its hereditary qualities. Instances may be cited of the white varieties of the snapdragon, of the red clover, the long-spurred violet (Viola 282 Retrograde Varieties cornuta) the sea-shore aster (Aster Tripolium), corn-rose (Agrostemma Githago), the Sweet William (Silene Armeria), and many garden flowers, as for instance, the Clarkia pulchella, the Polemonium coeruleum, the Veronica longi- folia, the gloxinias and others. If the red hue is combined with a yellow ground-color in the species, the variety will be yellow and the hy- brid will have the red and yellow mixture of the species as for instance, in the genus Geum. The toad-flax has an orange-colored palate, and a variety occurs in which the palate is of the same yellow tinge as the remaining parts of the corolla. The hybrid between them is in all re- spects like the parent species. Other instances could be given. In berries the same rule prevails. The black nightshade has a variety with yellow berries, and the black color returns in the hybrid. Even the foliage of some garden-plants may afford instances, as for instance, the purplish amaranth (Amarantus caudatus). It has a green variety but the hy- brid between the two has the red foliage of the species. Special marks in leaves and in flowers follow the same rule. Some varieties of the opium- poppy have large black patches at the basal end of the petals, while in others this pattern is en- tirely white. In crossing two such varieties, Bisexual Crosses 283 for instance, the dark " Mephisto " with the white hearted " Danebrog," the hybrid shows the active character of the dark pattern. Hairy species crossed with their smooth variety produce hairy hybrids, as in some wheats, in the campion (Lychnis), in Biscutella and others. The same holds good for the crosses between spiny species and their un- armed derivatives, as in the thorn-apple, the corn-crowfoot (Ranunculus arvensis) and others. Lack of starch in seeds is observed in some varieties of corn and of peas. When such de- rivatives are crossed with ordinary starch-pro- ducing types, the starch prevails in the hybrid. It would take too much time to give further examples. But there is still one point which should be insisted upon. It is not the systema- tic relation of the two parents of a cross, that is decisive, but only the occurrence of the same quality, in the one in an active, and in the other in an inactive condition. Hence whenever this relation occurs between the parents of a cross, the active quality prevails in the hybrid, even when the parents differ from each other in other respects so as to be distinguished as sys- tematic species. The white and red campions give a red hybrid, the black and pale henbane (Hyoscyamus niger and H. pallidas) give a hy- 284 Retrograde Varieties brid with the purple veins and center in the corolla of the former, the white and blue thorn- apple produce a blue hybrid, and so on. In- stances of this sort are common in cultivated plants. Having given this long list of examples of the rule of the dominancy of the active character over the opposite dormant unit, the question naturally arises as to how the antagonistic units are combined in the hybrid. This ques- tion is of paramount importance in the consid- eration of the offspring of the hybrids. But before taking it up it is as well to learn the real signification of recessiveness in the hybrids themselves. Recessive characters are shown by those rare cases, in which hybrids revert to the varietal parent in the vegetative way. In other words by bud-variations or sports, analogous to the splitting of Adam's laburnum into its parents, by means of bud-variation already rescribed. But here the wide range of differentiating char- acters of the parents of this most curious hybrid fail. The illustrative examples are extremely simple, and are limited to the active and inactive condition of only one quality. An instance is given by the long-leaved vero- nica (Veronica longifolia), which has bluish flowers in long spikes. The hybrid between Bisexual Crosses 285 this species and its white variety has a blue corolla. But occasionally it produces some purely white flowers, showing parental heri- tages, combined in its internal structures. Such reversions are far from being common, but in lots with thousands of flowering spikes one may expect to find at least one of them. Sometimes it is a whole stem springing from the under- ground system and bearing only white flowers on all its spikes. In other instances it is only a side branch, which reverts and forms white flowers on a stem, the other spikes of which re- main bluish. Sometimes a spike even differen- tiates longitudinally, bearing on one side blue and on the other white corollas, and the white stripe running over the spike may be seen to be long and large, or narrow and short in various degrees. In such cases it is evident that the heritage of the parents remain uninfluenced by each other during the whole life of the hybrid, working side by side, but the active element al- ways prevails over its latent opponent, and is ready to break free whenever an opportunity is offered. It is now generally assumed that this incom- plete mixture of the parental qualities in a hy- brid, this uncertain and limited combination is the true cause of the many deviations, exhibited by varietal hybrids when compared with their 286 Retrograde Varieties parents. Partial departures are rare in the hybrids themselves, but in their offspring the divergence becomes the rule. Segregation seems to be a very difficult pro- cess in the vegetative way, but it must be very easy in sexual reproduction, indeed so easy as to show itself in nearly every single instance. Leaving this first generation, the original hybrids, we now come to a discussion of their offspring. Hybrids should be fertilized either by their own pollen, or by that of other individ- uals born from the same cross. Only in this case can the offspring be considered as a means of arriving at a decision as to the internal na- ture of the hybrids themselves. Breeders gen- erally prefer to fertilize hybrids with the pollen of their parents. But this operation is to be considered as a new cross, and consequently is wholly excluded from our present discussion. Hence it follows that a clear insight into the heredity of hybrids may be expected only from scientific experiments. Furthermore some of the diversity observed as a result of ordinary crosses, may be due to the instability of the par- ents themselves or at least of one of them, since breeders ordinarily choose for their crosses some already very variable strain. Combining such a strain with the desirable qualities of some newly imported species, a new strain may Bisexual Crosses 287 result, having the new attribute in addition to all the variability of the old types. In scientific experiments made for the purpose of investi- gating the general laws of hybridity, such com- plex cases are therefore to be wholly excluded. The hereditary purity of the parents must be considered as one of the first conditions of success. Moreover the progeny must be numerous, since neither constancy, nor the exact propor- tions in the case of instability, can be deter- mined with a small lot of plants. Finally, and in order to come to a definite choice of research material, we should keep in mind that the chief object is to ascertain the relation of the offspring to their parents. Now in nearly all cases the seeds are separated from the fruits and from one another, before it be- comes possible to judge of their qualities. One may open a fruit and count the seeds, but ordi- narily nothing is noted as to their characters. In this respect no other plant equals the corn or maize, as the kernels remain together on the spike, and as it has more than one variety characterized by the color, or constitution, or other qualities of the grains. A corn grain, however, is not a seed, but a fruit containing a seed. Hence the outer parts pertain to the par- ent plant, and only the innermost ones to the 288 Retrograde Varieties seedling and therefore to the following genera- tion. Fruit-characters thus do not offer the qualities we need, only the qualities resulting from fertilizations are characteristic of the new generation. Such attributes are afforded in some cases by the color, in others by the chem- ical constitution. We will choose the latter, and take the sugar- corn in comparison with the ordinary or starch producing forms for our starting point. Both sugar and starch-corns have smooth fruits when ripening. No difference is to be seen in the young ripe spikes. Only the taste, or a direct chemical analysis might reveal the dissimilar- ity. But as soon as the spikes are dried, a diversity is apparent. The starchy grains re- main smooth, but the sugary kernels lose so much water that they become wrinkled. The former becomes opaque, the latter more or less transparent. Every single kernel may in- stantly be recognized as belonging to either of the types in question, even if but a single grain of the opposite quality might be met with on a spike. Kernels can be counted on the spike, and since ordinary spikes may bear from 300- 500 grains and often more, the numerical rela- tion of the different types may be deduced with great accuracy. Coming now to our experiment, both starchy Bisexual Crosses 289 and sugary varieties are in this respect wholly constant, when cultivated separately. No change is to be seen in the spikes. Further- more it is very easy to make the crosses. The best way is to cultivate both types in alternate rows and to cut off the staminate panicles a few days before they open their first flowers. If this operation is done on all the individuals of one variety, sparing all the panicles of the other, it is manifest that all the plants will be- come fertilized by the latter, and hence that the castrated plants will only bear hybrid seeds. The experiment may be made in two ways ; by castrating the sugary or the starchy variety. In both cases the hybrid kernels are the same. As to their composition they repeat the active character of the starchy variety. The sugar is only accumulated as a result of an incapacity of changing it into starch, and the lack of this capacity is to be considered as a retrogressive varietal mark. The starch-producing unit- character, which is active in the ordinary sorts of corns, is therefore latent in sugar-corn. In order to reach the second generation, the hybrid grains are sown under ordinary condi- tions, but sufficiently distant from any other variety of corn to insure pure fertilization. The several individuals may be left to pollinate 290 Retrograde Varieties each other, or they may be artificially pollinated with their own pollen. The outcome of the experiments is shown by the spikes, as soon as they dry. Each spike bears two sorts of kernels irregularly dispersed over its surface. In this point all the spikes are alike. On each of them one may see on the first inspection that the majority of the kernels are starch-containing seeds, while a minor part becomes wrinkled and transparent according to the rule for sugary seeds. This fact shows at once that the hybrid-race is not stable, but has differentiated the parental characters, bringing those of the varietal parent to perfect purity and isolation. Whether the same holds good for the starchy parent, it is impossible to judge from the inspection of the spikes, since it has been seen in the first generation that the hybrid kernels are not externally distinguished from those of the pure starch-producing grains. It is very easy to count the number of both sorts of grains in the spike of such a hybrid. In doing so we find, that the proportion is nearly the same on all the spikes, and only slight varia- tions would be found in the grains on hundreds of them. One-fourth of the seeds are wrinkled and three-fourths are always smooth. The number may vary in single instances and be a little more or a little less than 25#, ranging, for Bisexual Crosses 291 instance, from 20 to 27$ , but as a rule, the aver- age is found nearly equal to 25$. The sugary kernels, when separated, from the hybrid spikes and sown separately, give rise to a pure sugary race, in no degree inferior in purity to the original variety. But the starchy kernels are of different types, some of them being internally like the hybrids of the first generation and others like the original parent. To decide between these two possibilities, it is necessary to examine their progeny. For the study of this third hybrid generation we will now take another example, the opium- poppies. They usually have a dark center in the flowers, the inferior parts of the four petals being stained a deep purple, or often nearly black. Many varieties exhibit this mark as a large black cross in the center of the flower. In other varieties the pigment is wanting, the cross being of a pure white. Obviously it is only re- duced to a latent condition, as in so many other cases of loss of color, since it reappears in a hybrid with the parent species. For my crosses I have taken the dark-centered " Mephisto " and the " Danebrog," or Danish flag, with a white cross on a red field. The sec- ond year the hybrids were all true to the type of " Mephisto. " From the seeds of each artific- cially self -fertilized capsule one-fourth (22.5#) 292 Retrograde Varieties in each instance reverted to the varietal mark of the white cross, and three-fourths (77.5#) retained the dark heart. Once more the flowers were self -pollinated and the visits of insects ex- cluded. The recessives now gave only reces- sives, and hence we may conclude that the varie- tal marks had returned to stability. The dark- hearted or dominants behaved in two different ways. Some of them remained true to their type, all their offspring being dark-hearted. Evidently the latter had returned to the parent with the active mark, and had reassumed this type as purely as the recessives had reached theirs. But others kept true to the hybrid char- acter of the former generation, repeating in their progeny exactly the same mixture as their parents, the hybrids of the first generation, had given. This third generation therefore gives evi- dence, that the second though apparently show- ing only two types, really consists of three dif- ferent groups. Two of them have reassumed the stability of their original grandparents, and the third has retained the instability of the hy- brid parents. The question now arises as to the numerical relation of these groups. Our experiments gave the following results : Bisexual Crosses 293 Cross Mephisto 1. Generation 2. Generation 3. Generation 4- 100% Mephisto Danebrog '77.5% Dom.i All Mephistc 22.5% Recess. 9- all hybrids with 83-68% domi- nants and 17- 32% recessives. 100% Dane- brog. Examining these figures we find one-fourth of constant recessives, as has already been told, further one-fourth of constant dominants, and the rest or one half as unstable hybrids. Both of the pure groups have therefore reappeared in the same numbers. Calling A the specimens with the pure active mark, L those with the la- tent mark, and H the hybrids, these proportions may be expressed as follows : 1A + 2H + 1L. This simple law for the constitution of the sec- ond generation of varietal hybrids with a single differentiating mark in their parents is called the law of Mendel. Mendel published it in 1865, but his paper remained nearly unknown to scientific hybridists. It is only of late years that it has assumed a high place in scientific literature, and attained the first rank as an in- vestigation on fundamental questions of hered- 294 Retrograde Varieties ity. Bead in the light of modern ideas on unit- characters it is now one of the most important works on heredity and has already widespread and abiding influence on the philosophy of hy- bridism in general. But from its very nature and from the choice of the material made by Mendel, it is restricted to bisexual or varietal crosses. It assumes pairs of characters and calls the active unit of the pair dominant, and the latent recessive, without further investigations of the question of latency. It was worked out by Mendel for a large group of varieties of peas, but it holds good, with only apparent exceptions, for a wide range of cases of crosses of varietal characters. Recently many instances have been tested, and even in many cases third and later generations have been counted, and whenever the evidence was complete enough to be trusted, Mendel's prophecy has been found to be right. According to this law of Mendel's the pairs of antagonistic characters in the hybrid split up in their progeny, some individuals reverting to the pure parental types, some crossing with each other anew, and so giving rise to a new generation of hybrids. Mendel has given a very suggestive and simple explanation of his formula. Putting this in the terminology of to-day, and limiting it to the occurrence of only Bisexual Crosses 295 one differential unit in the parents, we may give it in the following manner. In fertiliza- tion, the characters of both parents are not uni- formly mixed, but remain separated though most intimately combined in the hybrid throughout life. They are so combined as to work together nearly always, and to have nearly equal influence on all the processes of the whole individual evolution. But when the tune ar- rives to produce progeny, or rather to produce the sexual cells through the combination of which the offspring arises, the two parental characters leave each other, and enter sepa- rately into the sexual cells. From this it may be seen that one-half of the pollen-cells will have the quality of one parent, and the other the qual- ity of the other. And the same holds good for the egg-cells. Obviously the qualities lie latent in the pollen and in the egg, but ready to be evolved after fertilization has taken place. Granting these premises, we may now ask as to the results of the fertilization of hybrids, when this is brought about by their own pollen. We assume that numerous pollen grains fer- tilize numerous egg cells. This assumption at once allows of applying the law of probability, and to infer that of each kind of pollen grains one-half will reach egg-cells with the same qual- 296 Retrograde Varieties ity and the other half ovules with the opposite latent mark. Calling P pollen and 0 ovules, and represent- ing the active mark by P and 0, the latent qual- ities by P' and 0', they would combine as fol- lows: P + 0 giving uniform pairs with the active mark, P + O' giving unequal pairs, P' + O giving unequal pairs, P' -f- O' giving uniform pairs with the latent mark. In this combination the four groups are ob- viously of the same size, each containing one- fourth of the offspring. Manifestly they corre- spond exactly to the direct results of the experiments, P + 0 representing the indi- viduals which reverted to the specific mark, P'+O' those who reassumed the varietal quality and P+0' and P+0' those who hybrid- ized for the second time. These considerations lead us to the following form of Mendel's formula : P + O = l/4-Active or I A, p, + °' | = 1/2-Hybrid or 2 H, P' + O' =l/4-Latent or IL, Which is evidently the same as Mendel ?s empirical law given above. To give the proof of these assumptions Men- del has devised a very simple crossing experi- Bisexual Crosses 297 ment, which he has effected with his varieties of peas. I have repeated it with the sugar-corn, which gives far better material for demonstra- tion. It starts from the inference that if dissim- ilarity among the pollen grains is excluded, the diversity of the ovules must at once become manifest and vice versa. In other terms, if a hybrid of the first generation is not allowed to fertilize itself, but is pollinated by one of its parents, the outcome will follow Mendel's prin- ciple. In order to see an effect on the spikes, pro- duced in this way, it is of course necessary to fertilize them with the pollen of the variety, and not with that of the specific type. The latter would give partly pure starchy grains and partly hybrid kernels, but these would assume the same type. But if we pollinate the hybrid with pollen of a pure sugar-corn, we may predict the result as follows. If the spike of the hybrid contains dormant paternal marks in one-half of its kernels and in the other half material latent qualities, the sugar-corn pollen will combine with one-half of the ovules to give hybrids, and with the other half so as to give pure sugar-grains. Hence we see that it will be possible to count out direct- ly the two groups of ovules on inspecting the ripe and dry spikes. Experience teaches us 298 Retrograde Varieties that both are present, and in nearly equal num- bers; one-half of the grains remaining smooth, and the other half becoming wrinkled. The corresponding experiment could be made with plants of a pure sugar-race by pollination with hybrid pollen. The spikes would show ex- actly the same mixture as in the above case, and now this may be considered as conclusive proof that half the pollen grains represent the quality of one parent and the other half the quality of the other. Another corollary of Mendel's law is the fol- lowing. In each generation two groups return to purity, and one-half remains hybrid. These last will repeat the same phenomenon of split- ting in their progeny, and it is easily seen that the same rule will hold good for all succeed- ing generations. According to Mendel's prin- ciple, in each year there is a new hybridization, differing in no respect from the first and original one. If the hybrids only are propa- gated, each year will show one-fourth of the offspring returning to the specific character, one-fourth assuming the type of the variety and one-half remaining hybrid. I have tested this with a hybrid between the ordinary nightshade with blackberries, and its variety, Solanum nigrum chlorocarpum, with pale yellow fruits. Eight generations of the hybrids were culti- Bisexual Crosses 299 vated, disregarding always the reverting off- spring. At the end I counted the progeny of the sixth and seventh generations and found figures for their three groups of descendants, which exactly correspond to Mendel's formula. Until now we have limited ourselves to the consideration of single differentiating units. This discussion gives a clear insight into the fundamental phenomena of hybrid fertilization. It at once shows the correctness of the assump- tion of unit-characters, and of their pairing in the sexual combinations. But MendePs law is not at all restricted to these simple cases. Quite on the contrary, it explains the most intricate questions of hybrid- ization, providing they do not transgress the limits of bisexual unions. But in this realm nearly all results may be calculated beforehand, on the ground of the principle of probability. Only one more assumption need be discussed. The several pairs of antagonistic characters must be independent from, and uninfluenced by, one another. This premise seems to hold good in the vast majority of cases, though rare excep- tions seem not wholly to be wanting. Hence the necessity of taking all predictions from Men- dePs law only as probabilities, which will prove true in most, but not necessarily in all cases. 300 Retrograde Varieties But here we will limit ourselves to normal cases. The first example to be considered is obvious- ly the assumption that the parents of a cross differ from each other in respect to two charac- ters. A good illustrative example is afforded by the thorn-apple. I have crossed the blue- flowered thorny form, usually known as Datura Tatula, with the white thornless type, desig- nated as D. Stramonium inermis. Thorns and blue pigment are obviously active qualities, as they are dominant in the hybrids. In the second generation both pairs of characters are resolved into their constituents and paired anew according to Mendel 's law. After isolating my hybrids during the period of flowering, I counted among their progeny : 128 individuals with blue flowers and thorns 47 " " " " without " 54 « " white " and " 21 " " " " without " 250 The significance of these numbers may easily be seen, when we calculate what was to be ex- pected on the assumption that both characters follow Mendel's law, and that both are inde- pendent from each other. Then we would have three-fourths blue offspring and one-fourth in- dividuals with white flowers. Each of these Bisexual Crosses 301 two groups would consist of thorn-bearing and thornless plants, in the same numerical relation. Thus, we come to the four groups observed in our experiment, and are able to calculate their relative size in the following way : Proportion Blue with thorns 3/4X3/4 = 9/16 = 56.25% 9 Blue, unarmed 3/4 X 1/4 = 3/16 = 18.75% 3 White with thorns 1/4X3/4== 3/16 = 18.75% 3 White, unarmed 1/4 X 1/4 = 1/16 = 6.25% 1 In order to compare this inference from Men- del's law and the assumption of independency, with the results of our experiments, we must cal- culate the figures of the latter in percentages. In this way we find : Found. Calculated. Blue with thorns 128 = 51% 56.25% Blue unarmed 47 = 19% 18.75% White with thorns.... 54 = 22% 18.75% White unarmed 21 = 8% 6.25% The agreement of the experimental and the theoretical figures is as close as might be expected. This experiment is to be considered only as an illustrative example of a rule of wide appli- cation. The rule obviously will hold good in all such cases as comply with the two conditions already premised, viz.: that each character agrees with Mendel's law, and that both are wholly independent of each other. It is clear that our figures show the numerical com- 302 Retrograde Varieties position of the hybrid offspring for any single instance, irrespective of the morphological nature of the qualities involved. Mendel has proved the correctness of these deductions by his experiments with peas, and by combining their color (yellow or green) with the chemical composition (starch or sugar) and other pairs of characters. I will now give two further illustrations afforded by crosses of the ordinary campion. I used the red-flowered or day-campion, which is a perennial herb, and a smooth variety of the white evening-campion, which flowers as a rule in the first summer. The combination of flower-color and pubescence gave the following composition for the second hybrid generation: Number % Calculation Hairy and red 70 44 56.25% Hairy and white 23 14 18.75% Smooth and red 46 23 18.75% Smooth and white 19 12 6.25% For the combination of pubescence and the capacity of flowering in the first year I found : Number % Calculated Hairy, flowering 286 52 56.25% Hairy, without stem . . 128 23 18.75% Smooth, flowering 96 17 18.75% Smooth, without stem 42 8 6.25% Many other cases have been tested by dif- ferent writers and the general result is the Bisexual Crosses 303 applicability of Mendel's formula to all cases complying with the given conditions. Intentionally I have chosen for the last ex- ample two pairs of antagonisms, relating to the same pair of plants, and which may be com- bined into one experiment and into one calcula- tion. For the latter we need only assume the same conditions as mentioned before, but now for three different qualities. It is easily seen that the third quality would split each of our four groups into two smaller ones in the proportion of 3/4:1/4. We would then get eight groups of the follow- ing composition: 9/16 X 3/4 = 27/64 or 42.2% 9/16 X 1/4= 9/84 ' 3/16 X 3/4= 9/64 3/16 X 1/4= 3/64 3/16X3/4= 9/64 3/16 X 1/4= 3/64 1/16 X 3/4= 3/64 14.1% 14.1% 4.7% 14.1% 4.7% 4.7% 1.6% 1/16 X 1/4= 1/64 The characters chosen for our experiment in- clude the absence of stem and flowers in the first year, and therefore would require a second year to determine the flower-color on the per- ennial specimens. Instead of doing so I have taken another character, shown by the teeth of the capsules when opening. These curve out- 304 Retrograde Varieties wards in the red campion, but lack this capacity in the evening-campion, diverging only until an upright position is reached. The combination of hairs, colors and teeth gives eight groups, and the counting of their respective numbers of individuals gave the following result : Teeth Hairs Flowers of capsules Number % Calculated Hairy red curved 91 47 52.2% Hairy red straight 15 7.5 14.1% Hairy white curved 23 12 14.1% Hairy white straight 17 8.5 4.7% Smooth red curved 23 12 14.1% Smooth red straight 9 4.5 4.7% Smooth white curved 5 2.5 4.7% Smooth white straight 12 6 1.6% The agreement is as comprehensive as might be expected from an experiment with about 200 plants, and there can be no doubt that a repeti- tion on a larger scale would give still closer agreement. In the same way we might proceed to crosses with four or more differentiating characters. But each new character will double the number of the groups. Four characters will combine into 16 groups, five into 32, six into 64, seven into 128, etc. Hence it is easily seen that the size of the experiments must be made larger and larger in the same ratio, if we intend to expect numbers equally trustworthy. For Bisexual Crosses 305 seven differentiating marks 16,384 individuals are required for a complete series. And in this set the groups with the seven attributes all in a latent condition would contain only a single individual. Unfortunately the practical value of these calculations is not very great. They indicate the size of the cultures required to get all the possible combinations, and show that in ordi- nary cases many thousands of individuals have to be cultivated, in order to exhaust the whole range of possibilities. They further show that among all these thousands, only very few are constant in all their characters ; in fact, it may easily be seen that with seven differentiating points among the 16,384 named above, only one individual will have all the seven qualities in pure active, and only one will have them all in a purely dormant condition. Then there will be some with some attributes active and others latent, but their numbers will also be very small. All others will split up in the succeeding genera- tion in regard to one or more of their appar- ently active marks. And since only in very rare cases the stable hybrids can be distin- guished by external characters from the un- stable ones, the stability of each individual bearing a desired combination of characters would have to be established by experiment 306 Retrograde Varieties after pure fertilization. Mendel's law teaches us to predict the difficulties, but hardly shows any way to avoid them. It lays great stress on the old prescript, of isolation and pure fertiliza- tion, but it will have to be worked out and ap- plied to a large number of practical cases before it will gain a preeminent influence in horticul- tural practice. Or as Bailey states it, we are only beginning to find a pathway through the bewildering maze of hybridization. This pathway is to be laid out with regard to the following considerations. We are not to cross species or varieties, or even accidental plants. We must cross unit-characters, and consider the plants only as the bearers of these units. We may assume that these units are represented in the hereditary substance of the cell-nucleus by definite bodies of too small a size to be seen, but constituting together the chromo- somes. We may call these innermost repre- sentatives of the unit-characters pangenes, in accordance with Darwin's hypothesis of pan- genesis, or give them any other name, or we may even wholly abstain from such theoretical dis- cussion, and limit ourselves to the conception of the visible character-units. These units then may be present, or lacking and in the first case active, or latent. Bisexual Crosses 307 True elementary species differ from each other by unit-characters. They have arisen by progressive mutation. Such characters are not contrasting. One species has one kind of unit, another species has another kind. On combining these, there can be no inter- change. Mendelism assumes such an inter- change between units of the same character, but in a different condition. Activity and latency are such conditions, and therefore Mendel's law obviously applies to them. They require pairs of antagonistic qualities, and have no connec- tion whatever with those qualities which do not find an opponent in the other parent. Now, only pure varieties afford such pure conditions. When undergoing further modifications, some of them may be in the progressive line and others in the retrogressive. Progressive modi- fications give new units, which are not in con- trast with any other, retrograde changes turn active units into the latent condition and so give rise to pairs. Ordinary species generally originate in this way, and hence differ from each other partly in specific, partly in varietal characters. As to the first, they give in their hybrids stable peculiarities, while as to the latter, they split up according to Mendel's law. Unpaired or unisexual characters lie side by side with paired or bisexual qualities, and they 308 Retrograde Varieties do so in nearly all the crosses made for prac- tical purposes, and in very many scientific ex- periments. Even Mendel's peas were not pure in this respect, much less do the campions noted above differ only in Mendelian characters. Comparative and systematic studies must be made to ascertain the true nature of every unit in every single plant, and crossing experiments must be based on these distinctions in order to decide what laws are applicable in any case. D. EVER-SPORTING VARIETIES LECTURE XI STRIPED FLOWERS Terminology is an awkward thing. It is as equally disagreeable to be compelled to make new names, as to be constrained to use the old faulty ones. Different readers may associate different ideas with the same terms, and unfor- tunately this is the case with much of the terminology of the science of heredity and variability. What are species and what are varieties? How many different conceptions are conveyed by the terms constancy and varia- bility? We are compelled to use them, but we are not at all sure that we are rightly under- stood when we do so. Gradually new terms arise and make their way. They have a more limited applicability than the old ones, and are more narrowly cir- cumscribed. They are not to supplant the older terms, but permit their use in a more general way. 309 310 Ever-sporting Varieties One of these doubtful terms is the word sport, It often means bud-variation, while in other cases it conveys the same idea as the old botan- ical term of mutation. But then all sorts of seemingly sudden variations are occasionally designated by the same term by one writer or another, and even accidental anomalies, such as teratological ascidia, are often said to arise by sports. If we compare all these different conceptions, we will find that their most general feature is the suddenness and the rarity of the phenom- enon. They convey the idea of something un- expected, something not always or not regularly occurring. But even this demarcation is not universal, and there are processes that are reg- ularly repeated and nevertheless are called sports. These at least should be designated by another name. In order to avoid confusion as far as possible, with the least change in existing terminology, I shall use the term " ever-sporting varieties " for such forms as are regularly propagated by seed, and of pure and not hybrid origin, but which sport in nearly every generation. The term is a new one, but the facts are for the most part new, and require to be considered in a new light, Its meaning will become clearer at once when the illustrations afforded by Striped Flowers 311 striped flowers are introduced. In the follow- ing discussion it will be found most convenient to give a summary of what is known concerning them, and follow this by a consideration of th£ detailed evidence obtained experimentally which supports the usage cited. The striped variety of the larkspur of our gardens is known to produce monochromatic flowers, in addition to striped ones. They may be borne by the same racemes, or on different branches, or some seedlings from the same parent-plant may bear monochromatic flow- ers while others may be striped. Such devia- tions are usually called sports. But they occur yearly and regularly and may be observed when the cultures are large enough. Such a variety I shall call " ever-sporting. " The striped larkspur is one of the oldest gar- den varieties. It has kept its capacity of sporting through centuries, and therefore may in some sense be said to be quite stable. Its changes are limited to a rather narrow circle, and this circle is as constant as the peculiari- ties of any other constant species or variety. But within this circle it is always changing, from small stripes to broad streaks, and from them to pure colors. Here the variability is a thing of absolute constancy, while the constancy consists in eternal changes! Such apparent 312 Ever-sporting Varieties contradictions are unavoidable, when we ap- ply the old term to such unusual though not at all new cases. Combining the stability and the qualities of sports in one word, we may evi- dently best express it by the new term of ever- sporting variety. We will now discuss the exact nature of such varieties, and of the laws of heredity which govern them. But before doing so, I might point out, that this new type is a very common one. It embraces most of the so-called variable types in horticulture, and besides these a wide range of anomalies. Every ever-sporting variety has at least two different types, around and between which, it varies in numerous grades, but to which it is absolutely limited. Variegated leaves fluctuate between green and white, or green and yellow, and display these colors in nearly all possible patterns. But their variability ends, and even the patterns are ordinarily narrowly prescribed in the single varieties. Double flowers afford a similar instance. On one side the single type, on the other the nearly wholly double model are the extreme limits, between which the variabil- ity is confined. So it is also with monstrosities. The race consists of anomalous and normal in- dividuals, and displays between them all possi- ble combinations of normal and monstrous Striped Flowers 313 parts. But its variability is restricted to this group. And large as the group may seem on first inspection, it is in reality very narrow. Many monstrosities, such as fasciated branch- es, pitchers, split leaves, peloric flowers, and others constitute such ever-sporting varieties, repeating their anomalies year by year and gen- eration after generation, changing as much as possible within limits, but remaining absolutely true to these limits as long as the variety exists. It must be a very curious combination of the unit-characters which causes such a state of continuous variability. The pure quality of the species must be combined with the peculiarity of the variety in such a way, that the one ex- cludes the other, or modifies it to some extent, although both never fully display themselves in the same part of the same plant. A corolla cannot be at once monochromatic and striped, nor can the same part of stem be twisted and straight. But neighboring organs may show the opposite attributes side by side. In order to look closer into the real mechan- ism of this form of variability, and of this con- stant tendency to occasional reversions, it will be best to limit ourselves first to a single case, and to try to gather all the evidence, which can be obtained by an examination of the he- reditary relations of its sundry constituents. 314 Ever-sporting Varieties This may best be done by determining the de- gree of inheritance for the various constituents of the race during a series of years. It is only necessary to apply the two precautions of ex- cluding all cross-fertilization, and of gathering the seeds of each individual separately. We do not need to ascertain whether the variety as such is permanent; this is already clear from the simple fact of its antiquity in so many cases. We wish to learn what part each in- dividual, or of each group of individuals with similar characters, play in the common line of inheritance. In other words, we must build up a genealogical tree, embracing several generations and a complete set of the single cases occurring within the variety, in order to allow of its being considered as a, part of the genealogy of the whole. It should convey to us an idea of the hereditary relations during the life-time of the variety. It is manifest that the construction of such a genealogical tree requires a number of sepa- rate experiments. These should be extended over a series of years. Each should include a number of individuals large enough to allow the determination of the proportion of the dif- ferent types among the offspring of a single plant. A species which is easily fertilized by its own pollen, and which bears capsules with Striped Flowers 315 large quantities of seeds obviously affords the best opportunities. As such I have chosen the common snapdragon of the gardens, Antirrhi- num majus. It has many striped varieties, some tall, others of middle height, or of dwarfed stature. In some the ground-color of the flow- ers is yellow, in others it is white, the yellow disappearing, with the exception of a large mark in the throat. On these ground-colors the red pigment is seen lying in streaks of pure car- mine, with white intervals where the yellow fails, but combined with yellow to make a fiery red, and with yellow intervals when that color is present. This yellow color is quite constant and does not vary in any marked degree, not- withstanding the fact that it seems to make narrower and broader stripes, according to the parts of the corolla left free by the red pig- ment. But it is easily seen that this appearance is only a fallacious one. The variety of snapdragon chosen was of me- dium height and with the yellow ground-color, and is known by horticulturists as A. majus luteum rubro-stridtum. As the yellow tinge showed itself to be invariable, I may limit my description to the red stripes. Some flowers of this race are striped, others are not. On a hasty survey there seem to be three types, pure yellow, pure red, and stripes 316 Ever-sporting Varieties with all their intermediate links of narrower and broader, fewer and more numerous streaks. But on a close inspection one does not succeed in finding pure yellow racemes. Little lines of red may be found on nearly every flower. They are the extreme type on this side of the range of variability. From them an almost endless range of patterns passes over to the broadest stripes and even to whole sections of a pure red. But then, between these and the wholly red flowers we observe a gap, which may be narrow- er by the choice of numerous broad striped in- dividuals, but which is never wholly filled up. Hence we see that the red flowers are a separate type within the striped variety. This red type springs yearly from the striped form, and yearly reverts to it. This is what in the usual descriptions of this snapdragon is called its sporting. The breadth of the streaks is considered to be an ordinary case of varia- bility, but the red flowers appear suddenly, with- out the expected links. Therefore they are to be considered as sports. Similarly the red forms may suddenly produce striped ones, and this too is to be taken as a sport, according to the usual conception of the word. Such sports may occur in different ways. Either by seeds, or by buds, or even within the single spikes. Both opposite reversions, Striped Flowers 317 from striped to red and from red to stripes, oc- cur by seed, even by the strictest exclusion of cross-fertilization. As far as my experiments go, they are the rule, and parent-plants that do not give such reversions, at least in some of their offspring, are very rare, if not wholly wanting. Bud-variations and variations within the spike I have as yet only observed on the striped individuals, and never on the red ones, though I am confident that they might appear in larger series of experiments. Both cases are more common on individuals with broad stripes than on plants bearing only the narrower red lines, as might be expected, but even on the al- most purely yellow individuals they may be seen from time to time. Bud-variations produce branches with spikes of uniform red flowers. Every bud of the plant seems to have equal chances to be transformed in this way. Some striped racemes bear a few red flowers, which ordinarily are inserted on one side of the spike only. As they often cover a sharply defined section of the raceme, this circumstance has given rise to the term of sectional variability to cover such cases. Sometimes the section is demarcated on the axis of the flower-spike by a brownish or reddish color, sharply contrasting with the green hue of the remaining parts. Sectional variation may be looked at as a 318 Ever-sporting Varieties special type of bud-variation, and from this point of view we may simplify our inquiry and limit ourselves to the inheritance of three types, the striped plants, the red plants and the red asexual variants of the striped individuals. In each case the heredity should be observed not only for one, but at least for two successive generations. Leaving these introductory remarks I now come at once to the genealogical tree, as it may be deduced from my experiments : Year. 1896 95% Str. 84% Red 1895 Striped Indiv. Red Indiv. 1895 98% Str. 71% Red. 1894 Striped branches. Red branches. 1894 98% Str. 76% Red. 1893 90% Striped Indiv. 10% Red Indiv. 1892 Striped Individual. This experiment was begun in the year 1892 with one individual out of a large lot of striped plants grown from seeds which I had purchased from a firm in Erfurt. The capsules were gath- ered separately from this individual, and about 40 flowering plants were obtained from the seeds in the following year. Most of them had neatly striped flowers, some displayed broader stripes and spare flowers were seen with one- Striped Flowers 319 half wholly red. Four individuals were found with only uniform red flowers. These were iso- lated and artificially pollinated, and the same was done with some of the best striped indi- viduals. The seeds from every parent were sown separately, so as to allow the determina- tion of the proportion of uniform red individ- uals in the progeny. Neither group was constant in its off- spring. But as might be expected, the type of the pistil-parent plant prevailed in both groups, and more strongly so in the instances with the striped, than with the red ones. Or in other words seed-reversions were more nu- merous among the already reverted reds than among the striped type itself. I counted 2$ reversion in the latter case, but 24$ from the red pistil-parents. Among the striped plants from the striped pistil-parents I found some that produced bud- variations. I succeeded in isolating these red flowering branches in paper bags and in polli- nating them with their own pollen, and subjected the striped spikes of the same individuals to a similar treatment. Three individuals gave a sufficient harvest from both types, and these six lots of seeds were sown separately. The striped flowers repeated their character in 98$ of their offspring, the red twigs in only 71$, the 320 Ever-sporting Varieties remaining individuals sporting into the oppo- site group. In the following year I continued the experi- ment with the seeds of the offspring of the red bud-variations. The striped individuals gave 95$, but in the red ones only 84$ of the progeny remained true to the parent type. From these figures it is manifest that the red and striped types differ from one another not only in their visible attributes, but also in the degree of their heredity. The striped in- dividuals repeat their peculiarity in 90 - 98$ of their progeny, 2 - 10$ sporting into the uniform red color. On the other hand the red individ- uals are constant in 71 - 84$ of their offspring, while 16 - 29$ go over to the striped type. Or in one word : both types are inherited to a high degree, but the striped type is more strictly inherited than the red one. Moreover the figures show that the degree of inheritance is not contingent upon the question as to how the sport may have arisen. Bud- sports show the same degree of inheritance as seed-sports. Sexual and asexual variability therefore seem to be one and the same process in this instance. But the deeper meaning of this and other special features of our genealog- ical tree are still awaiting further investigation. It seems that much important evidence might Striped Flowers 321 come from an extension of this line of work. Perhaps it might even throw some light on the intimate nature of the bud-variations of ever-sporting varieties in general. Sectional variations remain to be tested as to the degree of inheritance exhibited, and the different occur- rences as to the breadth of the streaks require similar treatment. In ordinary horticultural practice it is desir- able to give some guarantee as to what may be expected to come from the seeds of brightly striped flowers. Neither the pure red type, nor the nearly yellow racemes are the object of the culture, as both of them may be had pure from their own separate varieties. In order to insure proper striping both extremes are usually rejected, and should be rooted out as soon as the flowering period begins. Simi- larly the broad-striped ones should be re- jected, as they give a too large amount of uni- form red flowers. Clearly, but not broadly striped individuals always yield the most reli- able seed. Summing up once more the results of our ped- igree-experiment, we may assert that the striped variety of the snapdragon is wholly permanent, including the two opposite types of uniform color and of stripes. It must have been so since it first originated from the invariable uniform 322 Ever-sporting Varieties varieties, about the middle of the last century, in the nursery of Messrs. Vilmorin, and prob- ably it will remain so as long as popular taste supports its cultivation. It has never been ob- served to transgress its limits to sport into varieties without reversions or sports. It fluc- tuates from one extreme to the other yearly, al- ways recurring in the following year, or even in the same summer, by single buds. Highly va- riable within its limits, it is absolutely constant or permanent, when considered as a definite group. Similar cases occur not rarely among culti- vated plants. In the wild state they seem to be wholly wanting. Neither are they met with as occasional anomalies nor as distinct varie- ties. On the contrary, many garden-flowers that are colored in the species, and besides this have a white or yellow variety, have also striped sorts. The oldest instance is probably the marvel of Peru, Mirdbilis Jalappa, which already had more than one striped variety at the time of its introduction from Peru into the European gardens, about the beginning of the seventeenth century. Stocks, liver-leaf (He- patica), dame's violet (Hesperis), Sweet Wil- liam (Dianthus barbatus), and periwinkles (Vinca minor) seem to be in the same condition, as their striped varieties were already quoted Striped Flowers 323 by the writers of the same century. Tulips, hy- acinths, Cyclamen, Azalea, Camellia, and even such types of garden-plants as the meadow crane's-bill (Geranium pratense) have striped varieties. It is always the red or blue color which occurs in stripes, the underlying ground being white or yellow, according to the presence or absence of the yellow in the original color- mixture. All these varieties are known to be perma- nent, coming true during long series of successive generations. But very little is known concerning the more minute details of their he- reditary qualities. They come from seed, when this is taken from striped individuals, and thence revert from time to time to the corre- sponding monochromatic type. But whether they would do so when self -fertilized, and whether the reversionary individuals are al- ways bound to return towards the center of the group or towards the opposite limit, remains to be investigated. Presumably there is nowhere a real transgression of the limits, and never or only very rarely and at long intervals of time a true production of another race with other he- reditary qualities. In order to satisfy myself on these points, I made some pedigree-cultures with the striped forms of dame's violet (Hesperis matronalis) 324 Ever-sporting Varieties and of Clarkia pulchella. Both of them are ever-sporting varieties. The experiments were conducted during five generations with the vi- olet, and during four with the striped Clarkia, including the progeny of the striped and of the monochromatic red offspring of a primitive striped plant. I need not give the figures here for the numerical relations between the differ- ent types of each group, and shall limit myself to the statement that they behaved in exactly the same manner as the snapdragon. It is worth while to dwell a moment on the capacity of the individuals with red flowers to reproduce the striped type among their off- spring. For it is manifest that this latter qual- ity must have lain dormant in them during their whole life. Darwin has already pointed out that when a character of a grandparent, which is wanting in the progeny, reappears in the sec- ond generation, this quality must always be assumed to have been present though latent in the intermediate generation. To the many in- stances given by him of such alternative inher- itance, the monochromatic reversionists of the striped varieties are to be added as a new type. It is moreover, a very suggestive type, since the latency is manifestly of quite another character than for instance in the case of Mendelian hy- brids, and probably more allied to those in- Striped Flowers 325 stances, where secondary sexual marks, which are as a rule only evolved by one sex, are trans- ferred to the offspring through the other. Stripes are by no means limited to flowers. They may affect the whole foliage, or the fruits and the seeds, and even the roots. But all such cases occur much more rarely than the striped flowers. An interesting instance of striped roots is afforded by radishes. White and red varieties of different shapes are cultivated. Besides them sometimes a curious motley sort may be seen in the markets, which is white with red spots, which are few and narrow in some samples, and more numerous and broader in others. But what is very peculiar and striking is the circumstance, that these stripes do not extend in a longitudinal, but in a transverse direction. Obviously this must be the effect of the very notable growth in thickness. Assum- ing that the colored regions were small in the beginning, they must have been drawn out during the process of thickening of the root, and changed into transverse lines. Rarely a streak may have had its greatest extension in a trans- verse direction from the beginning, in which case it would only be broadened and not defi- nitely changed in its direction. This variety being a very fine one, and more agreeable to the eye than the uniform colors, is 326 Ever-sporting Varieties being more largely cultivated in some countries. It has one great drawback: it never comes wholly true from seed. It may be grown in full isolation, and carefully selected, all red or nearly monochromatic samples being rooted out long before blooming, but nevertheless the seed will always produce some red roots. The most careful selection, pursued through a number of years, has not been sufficient to get rid of this regular occurrence of reversionary individ- uals. Seed-growers receive many complaints from their clients on this account, but they are not able to remove the difficulty. This experi- ence is in full agreement with the experimental evidence given by the snapdragon, and it would certainly be very interesting to make a complete pedigree-culture with the radishes to test definitely their compliance with the rules ob- served for striped flowers. Horticulturists in such cases are in the habit of limiting themselves to the sale of so-called mixed seeds. From these no client expects pu- rity, and the normal and hereditary diversity of types is here in some sense concealed under the impurities included in the mixture from lack of selection. Such cases invite scrutiny, and would, no doubt, with the methods of isola- tion, artificial pollination, and the sowing of the seeds separately from each parent, yield Striped Flowers 327 results of great scientific value. Any one who has a garden, and sufficient perseverance to make pure cultures during a series of years might make important contributions to scien- tific knowledge in this way. Choice might be made from among a wide range of different types. A variety of corn called " Harlequin " shows stripes on its ker- nels, and one ear may offer nearly white and nearly red seeds and all the possible interme- diate steps between them. From these seeds the next generation will repeat the motley ears, but some specimens will produce ears of uniform kernels of a dark purple, showing thus the or- dinary way of reversion. Some varieties of beans have spotted seeds, and among a lot of them one may be sure to find some purely red ones. It remains to be investigated what will be their offspring, and whether they are due to partial or to individual variation. The cockscomb (Celosia cristata) has varie- ties of nearly all colors from white and yellow to red and orange, and besides them some striped varieties occur in our gardens, with the stripes going from the lower parts of the stem up to the very crest of the comb. They are on sale as constant varieties, but nothing has as yet been recorded concerning their peculiar behavior in the inheritance of the stripes. 328 Ever-sporting Varieties Striped grapes, apples and other fruits might be mentioned in this connection. Before leaving the striped varieties, atten- tion is called to an interesting deduction, which probably gives an explanation of one of the most widely known instances of ever-sporting garden plants. Striped races always include two types. Both of them are fertile, and each of them reproduces in its offspring both its own and the alternate type. It is like a game of ball, in which the opposing parties always return the ball. But now suppose that only one of the types were fertile and the other for some reason, wholly sterile, and assuming the reversionary, or primitive monochromatic indi- viduals to be fertile, and the derivative striped specimens to bloom without seed. If this were the case, our knowledge about the hereditary qualities would be greatly limited. In fact the whole pedigree would be reduced to a mono- chromatic strain, which would in each genera- tion sport in some individuals into the striped variety. But, being sterile, they would not be able to propagate themselves. Such seems to be the case with the double flowered stocks. Their double flowers produce neither stamens nor pistils, and as each indi- vidual is either double or single in all its flow- ers, the doubles are wholly destitute of seed. Striped Flowers 329 Nevertheless, they are only reproduced by seed from single flowers, being an annual or bien- nial species. Stocks are a large family, and include a won- derful variety of colors, ranging from white and yellow to purple and red, and with some variations toward blue. They exhibit also di- versity in the habit of growth. Some are an- nuals, including the ten-week and pyramidal forms ; intermediates are ordinarily chosen for pot-culture; and the biennial sorts include the well-known " Brompton " and ' ' Queen " varieties. Some are large and others are small or dwarf. For their brightness, durability and fragrance, they are deservedly popular. There are even some striped varieties. Horticultur- ists and amateurs generally know that seed can be obtained from single stocks only, and that the double flowers never produce any. It is not difficult to choose single plants that will produce a large percentage of double blossoms in the following generation. But only a per- centage, for the experiments of the most skilled growers have never enabled them to save seed, which would result entirely in double flower- ing plants. Each generation in its turn is a motley assembly of singles and doubles. Before looking closer into the hereditary pe- culiarities of this old and interesting ever-sport- 330 Ever-sporting Varieties ing variety, it may be as well to give a short description of the plants with double flowers. From a broad point of view two principal types become double. One is by the conver- sion of stamens into petals, and the other is an anomaly, known under the name of petalomany. The change of stamens into petals is a grad- ual modification. All intermediate steps are easily to be found. In some flowers all sta- mens may be enlarged, in others only part of them. Often the broadened filaments bear one or two fertile anthers. The fertility is no doubt diminished, but not wholly destroyed. Individ- ual specimens may occur, which cannot produce any seed, but then others of the same lot may be as fertile as can be desired. As a whole, such double varieties are regularly propagated by seed. Petalomany is the tendency of the axis of some flowers never to make any stamens or pis- tils, not even in altered or rudimentary form. Instead of these, they simply continue produc- ing petals, going on with this production with- out any other limit than the supply of available food. Numerous petals fill the entire space within the outer rays, and in the heart of the flower innumerable young ones are developed half-way, not obtaining food enough to attain Striped Flowers 331 full size. Absolute sterility is the natural con- sequence of this state of things. Hence it is impossible to have races of petal- omanous types. If the abnormality happens to show itself in a species, which normally prop- agates itself in an asexual way, the type may become a vegetative variety, and be multiplied by bulbs, buds or cuttings, etc. Some cultivated anemones and crowfoots (Ranunculus) are of this character, and even the marsh-marigold (Caltha palustris) has a petalomanous variety. I once found in a meadow such a form of the meadow-buttercup (Ranunculus acris), and suc- ceeded in keeping it in my garden for several years, but it did not make seeds and finally died. Camellias are known to have both types of double flowers; the petalomanous type is highly regular in structure, so much so as to be too uniform in all its parts to be pleasing, while the conversion of stamens into petals in the al- ternative varieties gives to these flowers a more lively diversity of structure. Lilies have a va- riety called Lilium candidum flore plena , in which the flowers seem to be converted into a long spike of bright white narrow bracts, crowded on an axis which never seems to cease their production. It is manifestly impossible to decide how all such sterile double flowers have originated. 332 Ever-sporting Varieties Perhaps each of them originally had a congru- ent single-flowered form, from which it was pro- duced by seed in the same way as the double stocks now are yearly. If this assumption is right, the corresponding fertile line is now lost ; it has perhaps died out, or been masked. But it is not absolutely impossible that such strains might one day be discovered for one or another of these now sterile varieties. Eeturning to the stocks we are led to the con- ception that some varieties are absolutely sin- gle, while others consist of both single-flowered and double-flowered individuals. The single varieties are in respect to this character true to the original wild type. They never give seed which results in doubles, providing all inter- crossing is excluded. The other varieties are ever-sporting, in the sense of this term pre- viously assumed, but with the restriction that the sports are exclusively one-sided, and never return, owing to their absolute sterility. The oldest double varieties of stocks have at- tained an age of a century and more. During all this time we have had a continuous pedi- gree of fertile and single-flowered individuals, throwing off in each generation a definite num- ber of doubles. This ratio is not at all depend- ent on chance or accident, nor is it even variable to a remarkable degree. Quite on the contrary Striped Flowers 333 it is always the same, or nearly the same, and it is to be considered as an inherent quality of the race. If left to themselves, the single indi- viduals always produce singles and doubles in the same quantity ; if cultivated after some spe- cial method, the proportion may be slightly changed, bringing the proportion of doubles up to 60$ or even more. Ordinarily the single and double members of such a race are quite equal in the remainder of their attributes, especially in the color of their flowers. But this is not always the case. The colors of such a race may repeat for themselves the peculiarities of the ever-sporting characters. It often happens that one color is more or less strictly allied to the doubles, and another to the singles. This sometimes makes it difficult to keep the various colors true. There are cer- tain sorts, which invariably exhibit a difference in color between the single and the double flow- ers. The sulphur-yellow varieties may be ad- duced as illustrative examples, because in them the single flowers always come white. Hence in saving seed, it is impossible so to select the plant, that an occasional white does not also appear among the double flowers, agreeing in this deviation too, in accordance with the gen- eral rule of the ever-sporting varieties. I commend all the above instances to those 334 Ever-sporting Varieties who wish to make pedigree-cultures. The co- operation of many is needed to bring about any notable advancement, since the best way to se- cure isolation is to restrict one's self to the culture of one strain, and to avoid the intermix- ture of others. So many facts remain doubtful and open to investigation, that almost any lot of purchased seed may become the starting point for interesting researches. Among these the sulphur-yellow varieties should be consid- ered in the first place. In respect to the great questions of heredity, the stocks offer many points of interest. Some of these features I will now try to describe, in order to show what still remains to be done, and in what manner the stocks may clear the way for the study of the ever-sporting varieties. The first point is the question, which seeds become double-flowered and which single-flow- ered plants? Beyond all doubt, the determi- nation has taken place before the ripening of the seed. But though the color of the seed is often indicative of the color of the flowers, as in some red or purple varieties, and though in balsams and some other instances the most " highly doubled " flowers are to be obtained from the biggest and plumpest seeds ; no such rule seems to exist respecting the double stocks. Yet it is clear that, if one half of the seeds gives doubles. Striped Flowers 335 and the other half singles, the question arises, where are the singles and the doubles to be found on the parent-plant? The answer is partly given by the following experiment. Starting from the general rule of the great influence of mutation on variability, it may be assumed that those seeds will give most doubles, that are best fed. Now it is man- ifest that the stem and larger branches are in a better condition than the smaller twigs, and that likewise the first fruits have better chances than the ones formed later. Even in the same pod the uppermost seeds will be in a compara- tively disadvantageous position. This concep- tion leads to an experiment which is the basis of a practical method much used in France in order to get a higher percentage of seeds of double-flowering plants. This method consists in cutting of, in the first place the upper parts of all the larger spikes, in the second place the upper third part of each pod, and lastly all the small and weak twigs. In doing so the percentage is claimed to go up to 67 - 70$, and in some instances even higher. This operation is to be performed as soon as the required number of flowers have ceased blos- soming. All the nutrient materials, destined for the seeds, are now forced to flow into these relatively few embryos, and it is clear that 336 Ever-sporting Varieties they will be far better nourished, than if no operation were made. In order to control this experiment some breeders have made the operation on the fruits when ripe, instead of on the young pods, and have saved the seeds from the upper parts sep- arately. This seed, produced in abundance, was found to be very poor in double flowers, containing only some 20 -30$. On the con- trary the percentage in the seed of the lower parts was somewhat augmented, and the aver- age of both would have given the normal average of 5(¥. Opposed to the French method is the German practice of cultivating stocks, as I have seen it used on a very large scale at Erfurt and at other places. The stocks are grown in pots on small scaffolds, and not put on or into the earth. The obvious aim of this practice is to keep the earth in the pots dry, and accordingly they are only scantily watered. In consequence they cannot develop as fully as they would have done when planted directly in the beds, and they pro- duce only small racemes and no weak twigs, eliminating thereby without further operation the weaker seeds as by the French method. The effect is increased by planting from 6-10 separate plants in each pot, It would be very interesting to make compar- Striped Flowers 337 ative trials of both methods, in order to discover the true relation between the practice and the results reached. Both should also be compared with cultures on open plots, which is said to give only 50$ of doubles. These methods of culture are practiced wherever it is desired to produce great quantities of seeds at a cheap rate. Such trials would no doubt give an insight into the re- lations of hereditary characters to the distribu- tion of the food of the plant. A second point is the proportional increase of the double-flowering seeds with age. If seed is kept for two or three years, the greater part of the grains will gradually die, and among the remainder there is found on sowing, a higher percentage of double ones. Hence we may in- fer that the single-flowered seeds are shorter- lived than the doubles, and this obviously points to a greater weakness of the first. It is quite evident that there is some common cause for these facts and for the above cited experience, that the first and best pods give more doubles. Much, however, remains to be investigated be- fore a satisfactory answer can be made to these questions. A third point is the curious practice, called by the French " esimpler," and which consists in pulling out the singles when very young. It seems to be done at an age when the flower-buds 338 Ever-sporting Varieties are not yet to be seen, or at least are not far enough developed to show the real distinctive marks. Children may be employed to chose and draw out the singles. There are some slight differences in the fullness and roundness of the buds and the pubescence of the young leaves. Moreover the buds of the doubles are said to be sweeter to the taste than those of the singles. But as yet I have not been able to ascertain, whether any scientific investigation of this proc- ess has ever been made, though according to some communications made to me by the late Mr. Cornu, the practice seems to be very gen- eral in the environs of Paris. In summer large fields may be seen, bearing exclusively double flowers, owing to the weeding out of the singles long before flowering. Bud- variation is the last point to be taken up. It seems to be very rare with stocks, but some instances have been recorded in literature. Darwin mentions a double stock with a branch bearing single flowers, and other cases are known to have occurred. But in no instance does the seed of such a bud-variant seem to have been saved. Occasionally other rever- sions also occur. From time to time speci- mens appear with more luxurious growth and with divergent instead of erect pods. They are called Erfurt " generals " on ac- Striped Flowers 339 count of their stiff and erect appearance, and they are marked by more divergent horns crowning the pods. They are said to produce only a relatively small number of doubles from their seeds, and even this small number might be due to fertilization with pollen of their neighbors. I saw some of these reversionary types, when inspecting the nurseries of Erfurt, but as they are, as a rule, thrown out before ripening their seed, nothing is exactly known about their real hereditary qualities. Much remains to be cleared up, but it seems that one of the best means to find a way through the bewildering maze of the cultures of inherit- ance, is to make groups of related forms and to draw conclusions from a comparison of the members of such groups. Such comparisons must obviously give rise to questions, which in their turn will directly lead to experimental in- vestigation. LECTURE XII FIVE-LEAVED CLOVER Every one knows the " four-leaved " clover. It is occasionally found on lawns, in pastures and by the roadsides. Specimens with five leaf- lets may be found now and then in the same place, or on the same plant, but these are rarer. I have often seen isolated plants with quater- nate leaves, but only rarely have I observed in- dividuals with more than one such leaf. The two cases are essentially dissimilar. They may appear to differ but little morpholog- ically, but from the point of view of heredity they are quite different. Isolated quaternate leaves are of but little interest, while combina- tions of them are of some importance, and may be observed only in cultivated plants, never in wild species. In making experiments upon this point it is necessary to transplant the divergent individuals to a garden in order to furnish them proper cultural conditions and to keep them under constant observation. When a plant bearing a quaternate leaf is thus transplanted, 340 Five-leaved Clover 341 however, it rarely repeats the anomaly. The occurrence of two or more quaternate leaves on the same plant indicates that it belongs to a definite race, which under suitable conditions may prove to be very rich in the anomalies in question. Obviously it is not always easy to decide definitely whether a given individual belongs to such a race or not. Many trials may be neces- sary to secure the special race. I had the good fortune to find two plants of clover, bearing one quinate and several quaternate leaves, on an excursion in the neighborhood of Loosdrecht in Holland. After transplanting them into my garden, I cultivated them during three years and observed a slowly increasing number of anomalous leaves. This number in one summer amounted to 46 quaternate and 16 quinate leaves, and it was evident that I had secured an instance of the rare " five-leaved " race which I am about to describe. Before doing so it seems desirable to look somewhat closer into the morphological fea- tures of the problem. Pinnate and palmate leaves often vary in the number of their parts. This variability is generally of the nature of a common fluctuation, the deviations grouping themselves around an average type in the ordi- nary way. Ash leaves bear five pairs, an