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LUTHER BURBANK-THE SUM OF HIS WORK WITH PLANT LIFE

WHAT IT HAS MEANT TO SCIENCE AND AGRICULTURE

We have seen that the first edition of "New Creations in Fruits and Flowers" was published in June, 1893. Perhaps we can best give an idea of the impression created by the work by quoting a few paragraphs from the introduction to the supplementary brochure that was published the following year. Although this second work was issued independently, it consisted in the main of a fuller account of some of the plant developments referred to in the first work, together with a large number of photographic illustrations. The two brochures, issued respectively in 1893 and 1894, may be considered as constituting the first official publication of the main outlines of the work in plant development which had begun in Massachusetts fully twenty-five years earlier, and which had occupied Mr. Burbank's attention unreservedly since 1885. The impression created by the first brochure is referred to in the introduction to the supplementary one in the following words: "Twelve months have passed since the first number of New Creations in Fruits and Flowers was sent out on its mission among dealers in trees and plants, great care being taken to confine it to the trade only; but before the few hundred first published were all delivered, orders came pouring in with each mail, like the falling of autumn leaves, for more, more; and again more had to be printed, and to this day the requests for New Creations are increasing rapidly, instead of diminishing, as it had been hoped they would. "Probably no horticultural publication ever created more profound surprise or received a more hearty welcome. Almost every mail brings requests for them from colleges, experiment stations, libraries, students, and scientific societies in Europe and America, and it has been translated into other languages for foreign lands, even where it would seem that scientific Horticulture was hardly recognized; some asking for one, others for two or three, or a dozen or two, or more. All these requests have been cheerfully responded to, but from this time on we shall be obliged to make a charge. We cannot attend to the ever increasing avalanche of letters which they occasion, a large portion of which are from amateurs, with long lists of questions, which would require years, perhaps a lifetime, to answer. "Five years ago we sold out a nursery business which had been built up from nothing, and which was paying us fully ten thousand dollars a year, that we might give all our time and thought to the work of producing new fruits and flowers. Do not think because they are raised in sunny California that they are less likely to prove generally hardy. Are those already before the public any less hardy or any less valuable than most of the Russian fruits which have been so extensively advertised for years? Are not the various Plums, Walnuts, Chestnuts, etc., which have been distributed from our establishment, proving to be hardier even than most of the Russian fruits, and more valuable in all other respects? But the best ones are yet to come. "About twelve years ago, when, having by thorough test found them good, we first commenced to introduce these fruits and nuts, sending circulars to most of the nurserymen in the United States, it was like trying to swim up stream in a rapidly flowing river, as very few had faith enough in them to invest in a tree; but those who were enterprising enough to do so, now find themselves fully prepared to supply the great and ever increasing demand which has followed, and are reaping rich rewards for the small investment of enterprise and coin which they then made." It will appear from this quotation that the announcement of the new fruits and flowers created an altogether exceptional interest, and that this interest was not confined to any one class of people. Although the announcement had been made for the benefit of practical horticulturists and nurserymen, the brochure found its way into the hands of the general public and of theoretical biologists, as well, and it would be hard to say which class of people were most exercised over it. If we briefly review the causes that underlay this widespread interest, and, considering one class of the public after another, attempt to explain just what its attitude was toward the new work, we shall at the same time be able to present an outline of the work itself and interpret it in the light of the mental environment of the time at which the work appeared with reference to the broad problems of heredity. Let us then attempt a brief analysis of the attitude of (1) horticulturists in general, (2) the public at large, (3) scientific biologists, and (4) working experimenters in heredity, with reference to the revelations made in New Creations in Fruits and Flowers. In so doing we shall gain an inkling of the bearing of the work done at Santa Rosa on questions of practical horticulture, of public opinion, and of biological theory. It may be added that the word "heredity" had not at this time been introduced.

WHY THE ORCHARDISTS WERE INTERESTED

The supplementary announcement, issued in 1894, gave the names of several important firms of dealers in horticultural supplies, who had purchased the principal new varieties announced in the brochure of the preceding year. The list included the names of prominent nurserymen from California to New England. The interest thus evidenced by the practical orchardists and nurserymen, who measured the value of the new products in terms of dollars and cents may readily enough be accounted for. Upto-date dealers are always on the lookout for novelties; and the fruits and flowers produced at Santa Rosa were novelties in the most comprehensive and exacting sense of the word. They were not merely new varieties that differed by a shade from old varieties. They were new forms produced by the combination of different species, often of species brought together from different hemispheres; and they were so radically different from the forms previously in existence that many of them would, without hesitation be pronounced new species by any competent botanist were they discovered in the wild state, or were their precise manner of origin unknown. But mere novelty by no means fully explained the interest of the orchardist in the new products. In addition to novelty the hybrid fruits and flowers had qualities of excellence that gave them instant appeal. The resources of the now familiar method of half-tone illustration, at that time quite new, had been utilized to show the exact appearance of the new fruits and flowers, and so far as possible the reproductions were made of exact life size, in a good many cases one or both of the parent forms being reproduced beside their hybrid offspring, to point the contrast. It required but a glance at the Pictures of the new hybrid prunes and plums, blackberries and raspberries, roses and gladioli, nicotianas and tomatoes, to convince the skeptical that these were products calculated to appeal to the most practical growers. The full force of this will be evident if we recall that this first announcement pictured and described such fruits as the hybrid prune that was afterward named the Splendor; the hybrid plum named Perfection, afterward famous as the Wickson; the dewberry-raspberry hybrid known everywhere in later years as the Primus; the offspring of the dewberry and Cuthbert raspberry now known as the Phenomenal; the raspberry hybrid called October Giant and the blackberry hybrid known as Paradox; a seedling rose of exquisite quality; and the profuse-bearing double Gladiolus. Interest was further enhanced by the picturing of the hybrid walnuts, the outlines of mammoth new quinces, curiously diversified stalks of hybrid raspberries and blackberries, leaves and stems of the raspberry-strawberry hybrid, and the curiously deformed products of the engrafted potato and tomato vines. The supplementary brochure of 1894 added striking photographic reproductions of the new white blackberry named Iceberg, a number of hybrid liles, the new and beautiful clematis flowers, the miniature calla Snowflake, branches of the new hybrid Wax Myrtles, a score or so of curiously varying fruits of the Japanese quince, and the new rose Peachblow. There were also pictures showing the curious and spectacular diversity among leaves of the hybrid blackberries that could not fail to excite the attention of the least observant. The contrast between the broad solid leaf of one plant, and the fimbriated fern-like foliage of another; the observation that some leaves were arranged in groups of three and others in groups of five-these were matters that caught the eye even of the amateur, and, as a matter of course, excited the interest of the professional student of plants. Equally striking were the full page reproductions of photographs showing various stems of the hybrid raspberries and blackberries, some of them slender and frail, others coarse and rugged; some almost thornless, and others bristling with spicules or studded with threatening spikes. The diversity of color among these stalks was clearly suggested by the half-tones, and the legend beneath one of them stated that "the colors vary from snow white, through lemon yellow, orange, scarlet, crimson, purple, light and dark blue and brown to black." That such diversities of leaf and stem could be brought about by hybridization was a fact that could scarcely fail to command the attention of the practical orchardist, and to raise questions in his mind as to whether there were any limits to the possibilities of the new method of plant development. At all events, it was obvious enough that, quite aside from the interesting questions suggested by the hybrid leaves and vines, here were numerous new varieties of fruits and flowers-more than fifty of them specifically named or numbered-having qualities that patrons of the orchardist might be expected to appreciate-fruits and flowers calculated to enter into competition on something more than equality with those already on the market. Hence, no second call was necessary to challenge the attention of the orchardist, and no second announcement was required for a large proportion of the newly developed hybrids. In a word, the practical orchardists called for the new hybrid fruits and flowers at once, and paid the prices asked for them because of the obvious practicality of the new products themselves. Their confidence has been justified by the sequel, for great communities have been built up-as in the case of Vacaville, California, one of the great shipping centers-by these fruits, and whole communities benefited, and the occupations of the entire population changed.

THE PUBLIC INTEREST EXPLAINED

To understand why the general public became so much exercised over the announcement of the new hybrids, it is necessary to recall that the broad general questions of evolution were still exercising the public mind at the time when New Creations appeared. Darwin's epoch-making work had indeed appeared more than thirty years before, and the doctrine of evolution had taken its place as an accepted working hypothesis among men of science, but so revolutionary a doctrine could not be expected to make its way with the general public in less than a generation, and it is probable that, if we could accurately gauge what might be called the intellectual atmosphere, we should find that it was as fully charged in the year 1893 with doubts as to the truth of the Darwinian doctrine as it had been thirty years earlier. At the earlier period, indeed, the man in the street had known but little of the character and implications of the doctrines involved. He perhaps had heard that "Darwin thinks men descended from monkeys", and with a few of the conventional and obvious jokes associated with that idea, the matter, so far as he was concerned, for the most part ended. But by the closing decade of the nineteenth century, after the bitter controversies of the men of science and the theologist had been fought out, a fuller recognition of the true implications of the doctrine of evolution began to permeate the lower strata of mental life of the generation, and thoughtful minds everywhere were eagerly questioning as to what might be the full truth and the final status of the evolutionary doctrine. Into this atmosphere of inquiry and doubt and solicitude came the document from Santa Rosa, ostensibly only a nursery catalog, but conveying a message that made itself heard far beyond the province of the nurseryman. Here were presented brief descriptions and photographic illustrations of a large number of new forms of plant life. These new forms were in many cases so strikingly different from the old ones that the least informed man in the street could not fail to note their diversity. Some of them obviously differed as strikingly from their parent forms, to all casual inspection, as recognized species hitherto familiar differed from one another. In a word, here were illustrations of what appeared to be new species of plants, and these apparently new species were of known origin. They had been developed under the hand of the experimnenter through the hybridization of old species, followed by artificial selection of a character having obvious affinity with the operation of natural selection on plants in the state of nature. Otherwise stated, the Santa Rosa catalog appeared to tell of the creation of new species, by artificial selection, in an experiment garden, in a brief term of years. All details aside, the photographic pictures showed offspring that seemed to be conspicuously unlike their parents-not different enough, to be sure, to belie utterly the familiar doctrine that "like begets like", yet different enough to demonstrate, seemingly, that a new species may arise from the loins, so to speak, of the old ones. However vaguely the laws or principles of heredity involved might be understood; however far from understanding the precise method of production of the new forms the general public might be, the tangible fact that widely divergent forms of plant life might spring from the same source-witness, for example, the brier stems of strikingly different forms or the cluster of utterly different leaves grown from the seed of one plant-was made clear beyond misunderstanding. And this constituted, in the minds of many laymen, a clearer and more cogent argument for the truth of the doctrine of evolution than could have been found in any amount of theorizing or in the presentation of any number of illustrations drawn from the records of fossil forms or the theoretical reconstruction of the genealogies of species of past eras. The arguments of the paleontologist and the embryologist; even the arguments of the theoretical botanist and biologist-these lay mostly beyond the ken of the man in the street. But he could readily enough understand the simple descriptions given in New Creations. With his own eyes he could see the striking and even spectacular differences between the plants of the same fraternity therein depicted. In effect, he received an object lesson in plant variation and a convincing argument for the truth-the tangible, demonstrable truth-of the doctrine of evolution which to him had hitherto seemed an academic question, involving the living forms of the remote geological eras rather than the forms of plant and animal life that are all about him in the world of today. And this, it may be supposed, sufficiently explains and interprets the interest in New Creations that was manifested by that great body of intelligent laymen personified under the title of "the man in the street."

THE INTEREST OF THEORETICAL EVOLUTIONISTS AND BOTANISTS

To understand the interest of a smaller but highly important coterie of people who may be broadly classified as students of evolution-including college professors on one hand and a few practical breeders of plants and animals on the other-we must consider yet another aspect of the intellectual atmosphere of the closing decade of the nineteenth century. We must understand that in this period, whereas the general doctrine of evolution had been accepted, there was wide diversity of opinion as to many of its important details. It could scarcely be said that there was any prevalent doctrine as to what forces in nature caused the observed variation between wild forms of plant and animal life upon which the operation of natural selection is based. The "survival of the fittest" was an accepted doctrine, but the origin of the fittest was an unsolved enigma. A suggestion that new forms might arise by hybridizing existing species had occurred, doubtless, to many minds. But this idea was combated or annulled by the prevalent notion that the offspring of true species are necessarily infertile. It is true that a few plant breeders, notably Dean Herbert and Andrew Knight, had advocated the idea that hybrids between true species may be fertile, and, indeed, had even seemed to demonstrate the truth of this view some three generations earlier. But the influence of the celebrated experimenter, Carl Friedrich von Gaertner, had served to give vogue to the opposite opinion. Darwin had argued for the fertility of some natural hybrids, but he had not been able to make out a case that by any means carried conviction to the generality of biologists and botanists; and the current opinion was that the comparatively few cases of the fertility of seeming hybrids might best be explained either on the supposition that the observed forms were not really of the parentage ascribed to them; or else that the parent forms, even though classified as different, were not really entitled to rank as independent species. In a word, the doctrine of Kolreuter and his followers, which would make the sterility of the hybrid offspring a test of the specific diversity of the parent forms, was perhaps the stock doctrine of the biological world. The implications of such an argument are obvious. If we are to answer the question, "What is the test as to whether two forms are entitled to recognition as different species?" by saying, "They are different if their hybrid offspring are sterile, and they are only varieties if their offspring are fertile" -we should obviously supply a definition that takes the matter beyond the range of argument. And, inasmuch as the minds of the biologists were now adjusted to the new Darwinian idea that there is a wide range of variation in natural forms, and that natural species are after all only varieties that have separated a little farther, the idea that the classifier might be mistaken in ascribing specific difference to any pair of forms, and that the physiological test of the production of sterile hybrids might afford a final guide, was not without its practical value, and made perhaps not unnatural appeal to the more or less befuddled classifiers themselves. And so long as cross-fertilization was effected solely between forms of animal or plant life that were fcund growing wild in the same region, and were obviously not very distantly related, it was hardly possible to present evidence of the fertility of hybrids between true species that would be convincing. The more fully the biologist grasped the philosophical idea that the word "species" is after all only a convenient formula to apply to a given form rather for convenience of nomenclature than as representing true and permanent distinctions, the more logically might he grasp the dictum that any two forms that can interbreed and produce fertile offspring are not entitled to rank as species, even in the modified view of the meaning of the word species that the evolutionary doctrine has introduced. Yet after all there is a certain tangibility about the idea connoted by the word species that the practical classifier cannot ignore. The blackberry and the raspberry, for example, are so obviously different in many really essential parts of their structure that to deny them specific individuality would be to introduce an element of iconoclasm that would shake the entire structure of systematic botany. So when evidence is presented that a blackberry and a raspberry have been hybridized, and that the offspring is a plant quite as fertile as either of its parents, though markedly different from both, the case seems to give evidence that the offspring of true species are not necessarily sterile. And the fact that the new hybrid differs so widely from either parent that it would be named by the classifier as constituting a new species according to ordinary standards, and that it breeds true to its new form, seems to furnish further evidence that new species of plant life may conceivably arise by the hybridization of old species. In a word, a single case like that of the hybrid Blackberry-raspberry, described and depicted in New Creations under the name of the Primus Berry, would seem by itself fairly to establish the doctrine that new species of plants may arise by the hybridization of old species. Stated otherwise, the case of the Primus berry would seem to furnish unequivocal evidence as to at least one way in which the problem of the origin of new species might be answered. The survival of the fittest had been explained as an essential part of the Darwinian doctrine. The origin of the fittest (or at least one possible origin) appeared to be explained by the existence of such a hybrid as the Primus Berry. The parents of the Primus berry, it will be recalled, were the California dewberry (Rubus uirsinuis) and the Siberian raspberry (Rubus crataegifolius). Not only are these forms so different in appearance that no botanist would ever think of denying that they belong to totally different species, but the fact that one of them is indigenous to California and the other to Siberia gives what might be called geographical support to the opinions of the classifiers. Few indeed are the forms of animal or plant life inhabiting the Eastern and the Western Hemispheres that are recognized as specifically identical. The same genera are represented on both continents, because the remote progenitors of all races of animals and plants of the Northern Hemisphere were once inhabitants of a common territory in the region of the North Pole. But there has been no opportunity for the mingling of Asiatic and American forms of plant life since the separation of the continents, until civilized man in very recent time began to transport forms of animal and plant life across the oceans. There had been no communication since a remote geological era-probably not since the last ice age; so on mere geographical grounds the specific difference between the Siberian raspberry and the California dewberry might be accepted without further argument. But, quite aside from this, differences between the two forms are sufficient to give them independent specific rank in the mind of any botanist. The fact that one is classified as a blackberry and the other as a raspberry will sufficiently establish their diversity in the mind of the layman. Yet the report from Santa Rosa told of the hybridizing of these diverse forms, and of the production of a new fruit differing very markedly from either parent, although retaining some of the characteristics of each; and told further that this new hybrid, far from being sterile, has such fertility that it ripens its main crop of berries long before most kinds of raspberries and blackberries commence to bloom, and continues to bear more or less berries all summer. So the evidence that hybrid offspring of two species may be fertile and may thus offer material for the action of natural selection in the creation of new species appeared doubly demonstrative. It is probable, then, that the announcement of the development of the Primus Berry would have aroused no small measure of interest among practical plant breeders and theoretical students of evolution, even had it been made by itself as a single and isolated experiment in hybridization. But, in point of fact, the record of the Primus Berry was accompanied by similar records of an entire company of new hybrid blackberries and raspberries. In the same section of New Creations that told of the Primus Berry, there was the record of an equally remarkable blackberry-raspberry hybrid of an entirely different character, the parents this time being the California dewberry and the well-known Cuthbert raspberry, the latter a native of England. Three hybrids of this cross were offered for introduction, one of them being the extraordinary berry that was afterward named the Humboldt, and then renamed the Phenomenal. There were two other hybrid dewberries of only lesser interest. There was also the hybrid between the Crystal White Blackberry and Shaffer's Colossal Raspberry, which produced the berry famous afterward as the Paradox, and from which new races of raspberries and blackberries of almost every conceivable combination can be produced, as the photograph showing varied leaves, to which reference has already been made, amply demonstrated. Then, too, there was the hybrid between the Japanese Golden Mayberry and the Cuthbert Raspberry; and there were no fewer than ten other raspberry hybrids that were listed specifically each under a definitive name or number, and offered for sale as new varieties at a specified price. Moreover, a list was given of no fewer than thirty-seven named species of Rubus (the generic name of the tribe of raspberries and blackberries) that had been utilized in the hybridizing experiments through which the new varieties have been produced; and the statement was made with reference to the list that "the combinations are endless; the results are startling and as surprising to myself as they will be to others when known." An inkling of the work involved in the production of these unique results is given in an explanatory paragraph: "Everybody appreciates delicious berries, but probably not one person in each million has the faintest idea of the labor and expense of crossing, raising and testing a million new kinds of berries as the writer has done, and selecting with untiring diligence those which are to become standards of excellence as the years roll by. The reader of earlier chapters of this work will fully comprehend the sense in which the phrase "a million new kinds of berries" is used. We have learned that each variant type of cultivated fruit is regarded by the orchardist as an independent variety, owing to the fact that it may be propagated indefinitely by division or by grafting. "A million new kinds" refers to the endless diversity of individual forms among hybrid blackberries and raspberries, from among which a score or so had been selected as worthy of introduction. It should be added, however, that certain of these, including the Primus berry and the Phenomenal, were fixed varieties or new species that would breed true from the seed. In another clause reference is made to "fourteen years" of experiment, revealing the fact that the blackberries and raspberries were among the plants that Mr. Burbank had found time to experiment with extensively during the ten year period of the nursery experience that preceded the establishment of his experiment gardens. It was partly because these fruits had been experimented with for this long period that so large a section of New Creations was devoted to new races of hybrid berries. It should not be understood, however, that the work with the blackberries and raspberries stood at all by itself in presenting evidence of the fertility of hybrids, and in thus throwing new light on the problems of evolution. On the contrary, evidence of precisely the same character was presented by one after another of the different records that made up the total of more than fifty new hybrid varieties of nuts and orchard fruits and flowers offered for introduction in the pages of New Creations. The hybrid walnut, known as the Royal, one parent of which was the black walnut of the East and the other the black walnut of California, was represented by its gigantic nut, depicted on the same page with the smaller nuts of the ancestral forms. And it was particularly noted that the new hybrid had borne nuts in abundance, although the other hybrid walnut, due to the union of the California and Persian walnut, had not then borne fruit. It may be added that the relative infertility of hybrids between forms distantly related is recognized in the course of the description of this second hybrid walnut, in the statement that in its failure to bear fruit it is like many true hybrids; the writer having doubtless in mind such examples as those furnished by the new plant called the Nicotunia, a combination of the tobacco and the petunia, which is described on another page of New Creations; and the equally interesting hybrid between the raspberry and the strawberry, also described and depicted. These sterile hybrids, with which the reader of the present work is already familiar, illustrate another aspect of heredity no less interesting; but at the moment we are concerned with the fertile hybrids. And these, it may be added, include all the fifty-odd plants described in the catalog, with the three exceptions just noted. Without entering into specific details, we may briefly note that the new hybrid plums here listed, and for the most part pictorially shown, were ten in number, involving the racial strains of species from Japan and China, from Europe, and from various regions of America. The hybrids among flowers were also given full representation, ten pages of the catalog being devoted to them, and the new varieties named and described including roses, callas, lilies, gladioli, a number of forms of clematis, and a new poppy. New types of hybrid seedling potatoes were also listed, and a new form of crossbred tomato, called the Combination. The extraordinary Aerial potatoes grown on potato vines grafted on the roots of the tomato; and the no less extraordinary potatoes grown on a stock having an engrafted tomato top are also shown, although merely as curiosities and not as commercial products. To complete the summary of the evidence that was presented for the possibility of producing new varieties through hybridizing old species, it should be added that mention was made in a separate section of numerous experiments with seedlings of the ampelopsis, a new type of wax myrtle, and "some charming, crossbred seedling tigridias, new cannas, arums, amaryllis, brodiaeas, aquiligias, asters, and a multitude of other things not yet near enough to perfection to merit a special description; yet some of the hybrids of which are worthy of much study." A list of other species that had been mutually hybridized begins with the peach and almond, and names more than twenty crosses between the various types of orchard fruits-apricot, plum, quince, and apple, as well as peach-in various combinations. Without detailing further examples, it may be said that this body of evidence was overwhelming. It could be supplemented indefinitely, of course, by examples from other plants in my experiment gardens. But without further elaboration, the examples cited in my first two catalogs sufficiently establish the fertility of hybrids of many species of widely different families. Thenceforth there could never be any doubt in the minds of practical plant developers that true species, within certain limits of affinity, may be interbred and produce fertile offspring. On the other hand, the examples of the strawberry-raspberry, and the petunia-tobacco might be cited in proof that species too widely removed from each other produce sterile hybrids. Thus the experiments as a whole show on one hand the method through which material is supplied for the operation of natural selection; while, on the other hand, they show how barriers are ultimately erected that prevent crossbreeding from being carried to an extent that would introduce a chaotic element in the scheme of evolution. The importance of such a demonstration as this, made for the first time on a really comprehensive scale in the experiment gardens at Santa Rosa and Sebastopol, soon came to be generally recognized.

THE NEW EXPERIMENTS AND MENDELISM

Perhaps it may be of interest, in extension of the present theme, briefly to trace the relation of the new experiments to the particular aspect of the theory of heredity that has most actively claimed the attention of the biological world in very recent years. He refers, of course, to the doctrine of Mendelism, which was to take the biological world by storm in the first decade of the twentieth century. Of course the results of the hybridizing experiments performed in my experimental gardens and recorded in the catalog of 1893 could not be at once interpreted in what are now spoken of as Mendelian terms, because at that time no one knew anything of Mendelism as such. The experiments of Mendel had indeed been made just thirty years before, and Mendel himself, as it chanced, had died in the very year-namely 1884-in which my first importation of plants from the Orient, to furnish material for experiments, was made. But, as the reader is aware, the publication of Mendel was altogether ignored, and nothing was heard of his experiments until his paper was rediscovered by Professor de Vries and by two others about the year 1900. But it is elsewhere pointed out that whereas the Mendelian formula was not then in vogue, yet the essentials of the aspect of heredity that Mendel espoused were abundantly illustrated in the hybridizing experiments, the results of which were published in New Creations (1893) and its successive supplements. It is scarcely necessary to remind the reader that the essentials of the aspect of heredity in question had to do, as stated by Mendel, not so much with the great mass of heritable characters, as with some of the minor points of difference that mark varieties within a species. Mendel himself did not hybridize different species, or, if he did, the records of such hybridizing have been lost. His essential experiments had to do with garden peas and with the manner of transmission of the minor difference between varieties of these peas-tallness versus shortness of stem, purpleness versus whiteness of flower, yellowness versus greenness of pod, and so on. But the peculiar manner in which these antagonistic pairs of qualities are given representation in the offspring of parents having the opposite traits, is precisely duplicated when the cross-fertilization is similarly effected between allied species that show corresponding diversities. In each case, the essential fact is that certain minor characters or groups of characters tend to assume prepotency or dominance in hybrids of the first generation; and that both the dominant and the submerged (or recessive) characters appear in the hybrids of the second generation segregated and variously recombined, so that where several pairs of qualities are under consideration, the offspring of the second generation constitute a most heterogeneous lot, in which the diversified traits of their grandparents are mixed and blended and mosaiced together in every conceivable combination. Not only were these essential facts clearly revealed by my early hybridizing experiments, but they were succinctly expressed in the text of New Creations, and the diversities of forms among second generation hybrids were illustrated by photographs showing many types of hybrid blackberry and raspberry canes and leaves. The diversity of second-generation hybrids was illustrated by such other examples as the Phenomenal Berry and two other hybrids listed in the catalog under separate numbers and announced as of the same origin. But for that matter, the segregation and recombination of characters in the second generation, leading to endless diversity or variation, was illustrated in the case of every new variety named in the entire catalog, with the exception of the Paradox and Royal Walnuts and the Primus Berry, these alone being first-generation hybrids. Quotation has already been made as to the "million kinds" of blackberry hybrids of the second generation. It may be added that in the supplement of 1894, a photograph was reproduced that showed a "sample pile of brush twelve feet wide, fourteen feet in height, and twenty-two feet long, containing sixty-five thousand two-and three-year-old hybrid seedling berry bushes (forty thousand blackberry-raspberry hybrids and twenty-five thousand Shaffer-Gregg hybrids) all dug with their crop of ripening berries. "It was stated in connection with this picture that of the "forty thousand blackberry-raspberry hybrids of this kind, Paradox is the only one now in existence. From the other twenty-five thousand hybrids about two dozen bushes are left for further trial, but from these selected ones, wonderful new berries are appearing whose forces are so fixed in the right direction that they generally produce good and productive seedlings." It may be of interest, as giving farther insight into the work, to quote the concluding sentence which states that: "This pile of brush cost something like $700, and is one of fourteen similar piles which were cremated on one of my places last summer." Of similar import is the account given of the hybrid lilies, which were declared to be so varied in character, thanks to the hybridizing of many species, that "all the earth is not adorned with so many new ones as are growing at my establishment." A description of the varied characteristics of some of these lilies, and two pages of illustrations showing fifteen diversified forms, are introduced by way of substantiation. To the reader of today it may seem a work of supererogation to dwell thus on the fact that experiments, the results of which were published in 1893-1894, demonstrated so obvious a proposition as that hybrids are relatively uniform in the first generation, and highly diversified in the second and a few succeeding generations. But it must be understood that this was the essential discovery that made possible a large part of my successes in producing new varieties by hybridization. And it must further be recalled that the facts in question were ardently contested by large numbers of the leading botanists and the most authoritative students of hereditary theory. It was the demonstration made a thousand times over at the experiment gardens at Santa Rosa and Sebastopol that first showed in a comprehending and convincing way that such is the operation of the principles of heredity in determining the characteristics of hybrid generations. And, as has elsewhere been suggested there is no doubt that it was these demonstrations that prepared some of Mr. Burbank's most eminent critics, including Professor de Vries, to accept the Mendelian statement of this proposition when it came finally to their attention. It may be added that the subsequent history of such aspects of the problem as came to be associated with the name of Mendel has shown curious analogy with the history of the Weissmannian doctrines to which reference has been made in another connection. Just as followers of Weissmann were obliged to shift their ground to meet the evidence brought by new experiments, until finally all that remained of their doctrine had been substantially harmonized with and blended into the broader and earlier theories of Darwinian heredity, only the doctrine of the continuity of the germ plasm remaining as a permanent acquisition; so the attempt to make "Mendelism" comprehend the entire subject of heredity, has necessitated a perpetual modification of the point of view, and an amplification of the terminology to meet the facts of more comprehensive experiments, until Mendelism has come to be harmonized with and blended in the more comprehensive knowledge of heredity, leaving only the formulae associated with dominance and recessiveness to mark the individual contribution of Mendel to the all-comprehending subject of heredity.

-Into an atmosphere of inquiry and doubt and solicitude, came the document from Santa Rosa, ostensibly only a nursery catalog, but conveying a message on heredity that made itself heard far beyond the province of the nurseryman.

This text is from: Luther Burbank: his methods and discoveries and their practical application. Volume 12 Chapter 4