Some Interesting Failures
A PETUNA WITH THE TOBACCO HABIT-AND OTHERS
A well known and appreciative critic, after a visit to Santa Rosa, commented on my work in a way that seemed to suggest that what most appealed to him was the great variety of experiments constantly being carried on. "Every plant seems to appeal to Luther Burbank," he said. "This appeal is quite unlike the appeal that is made to the botanist or even to the horticulturist; Burbank likes it because it is a plant and because he would like to try to modify it. Therefore he grows everything he can, no matter where it comes from or of what kind. He cultivates with personal care, multiplies the stock to the limit of his capacities, scrutinizes every variation, hybridizes widely, saves the seeds of the forms that most appeal to him, sows again, hybridizes and selects again, uproots by the hundreds and thousands, extracts the delights from every new experience, and now and then saves out a form that he thinks to be worth introducing to the public. "Every part of the work is worth the while of itself; at every stage the satisfaction of it is reaSon enough for making and continuing the effort. Every form is interesting, whether it is new or the reproduction of an old form. He shows you the odd and intermediate and reversionary forms as well as those that promise to be of general use. "All this leads me to say that the value of Mr. Burbank's work lies above all merely economic considerations. He is a master worker in making plants to vary. Plants are plastic material in his hands. He is demonstrating what can be done. He is setting new ideals and novel problems. "Heretofore, gardeners and other horticulturists have grown plants because they are useful or beautiful: Mr. Burbank grows them because he can make them take on new forms. This is a new kind of pleasure to be got from gardening, a new and captivating purpose in plant growing. It is a new reason for associating with plants. Usually I think of him as a plant-lover rather than plant-breeder. It is little consequence to me whether he produces good commercial varieties or not. He has a sphere of his own, and one that should appeal to a universal constituency. In this way, Luther Burbank's work is a contribution to the satisfaction of living, and is beyond all price." Such appreciative notices of one's work are of course agreeable, and I am bound to admit that what is said about my love of experimenting with any and every kind of plant is altogether true. There is one point, however, at which I am forced to part company with the commentator. To me it is a matter of vital consequence as to whether I "produce good commercial varieties or not." It is necessarily so, inasmuch as I have all along made a living by the sale of the products of my experiments. Had I not produced good commercial varieties, my practical success would have been something quite different from what it has been. Nevertheless, it of course is true that the successful commercial varieties of plants and fruits are comparatively few in number as contrasted with the vast numbers of forms with which I have experimented. It could not well be otherwise, for it would be a strange and novel form of experiment that led always to success. But of course the public in general hears of, and in the main cares for, successes only. There is seldom any reason for exploiting a failure. And so my long list of experiments that have led to no practical result has scarcely been heard of by the public in general. Some of these, however, are in themselves highly interesting, and I have thought it worth while to take the reader into my confidence to the extent of telling about three or four series of experiments which produced no permanent new forms of flower or fruit, and which from the commercial standpoint resulted only in loss of time and money. There are certain lessons to be drawn from these that I think will command the reader's attention and interest.
A MISGUIDED PETUNIA
One of the most curious hybridizing experiments that I ever performed consisted of crossing the common garden petunia with a variety of tobacco, known as Nicotiana Wigandioides rubra. In this cross the petunia pollen was used to fertilize the pistil of the tobacco plant. The seed thus produced was planted in the summer, as soon as it ripened, and possibly two hundred plants were raised. When about a foot high the plants were placed in boxes in the greenhouse to keep over winter. They revealed no inclination to bloom, nor did they vary greatly from the parent tobacco plant, except in the matter of growth, which was very uneven, some of the hybrids being two or three times as large as others. The foliage was somewhat unusual; yet its resemblance to the tobacco was so great that a casual observer would have doubted whether the cross had really been made. In a word, the characteristics of the tobacco plant seemed to preponderate. But towards spring, when the plants were set again out of doors, they soon began to show the influence of their mixed heritage. Some of them turned crimson, and others pink; yet others remaining green. Moreover, the plants themselves developed a great diversity of habit. Even during the winter some of them had begun to fall over and show a tendency to trail like vines. As the second season advanced, some of these became genuine trailers like the petunia, and produced blossoms altogether different in color from the red flowers of the tobacco plant. These plants did not bloom very abundantly, but their great diversity of form and peculiarity of foliage and flower made them a very striking lot of plants. Some of them grew four or more feet in height with large tobacco-like leaves, and others were trailing dwarfs that to all appearances might have belonged to an entirely distinct race. The plants that closely resembled the tobacco parent were, for the most part, weeded out. The ones that gave evidence of their hybrid origin were carefully nurtured. But it was noticed towards fall that although the tops grew splendidly, there seemed to be an unusual lack of roots. The plants would come to a certain size, and then take on what could perhaps be best described as a "pinched" appearance, from lack of vitality incident to their defective roots. There was, however, a great difference among the individual plants, some of them remaining strong throughout the season. When the plants were taken up, it appeared that the sickly ones had produced only a few long, frail, wiry roots. It appeared to have been impossible for them to develop a thoroughly good root system. Evidently most of the new plants had inherited the rank-growing tops of the giant tobacco and the smaller, less efficient roots of the petunia. A visitor whose attention was called to this peculiarity remarked facetiously that my petunias had obviously been stunted in growth and vitality through acquiring the tobacco habit, just as boys are stunted when they make the same mistake. It is only fair to recall, however, that the petunias had no choice in the matter. Their association with the tobacco had been thrust upon them. Owing to the lack of vitality of the hybrids, and the fact that they seemed unlikely to develop additional characteristics of exceptional interest, the plants were not especially sheltered, and they perished from freezing during the ensuing winter. Thus the experiment of hybridizing the petunia and the tobacco came to an end; not, however, without illustrating one or two suggestive points of plant breeding to which further reference will be made in due course.
SOME MONGREL POTATOES
Inasmuch as my first experiments in plant breeding had to do with the potato, it is not strange that the tribe of plants to which this vegetable belongs have always had for me a rather exceptional interest. Early in the course of my California work I secured specimens of a remote cousin of the cultilvated potato which grows in our southwestern States and which is known to the Indians as the Squaw potato (Solanum Jainesii). It is a wild rambling potato, spreading in all directions by tubers that seem to be connected by long strings. Although used for food by the Indians, this potato is hardly worth the notice of the gardener, except for its hardiness. This trait suggested that it might possibly be crossed to advantage with other species. But although several crosses were effected with other species of the potato, nothing of value came of them. An allied species, however, namely the Solanum Commersoni, a worthless form introduced from Europe, gave more interesting results. This plant, although recommended as a valuable commercial product, really had very little value. Like most wild potatoes, it scattered its tubers widely from the hill; moreover it had a bitter taste that made it unpalatable. The blossoms, however, were handsome, and, unlike the blossoms of the ordinary potato, they were quite fragrant. Moreover, the blossoms were produced in astounding profusion. But they did not ordinarily produce seed. When I crossed the plant with other tuberous Solanums, however, I produced a number of seed balls. By cross-fertilization the plants had acquired a virility that they otherwise lacked. These hybrid seeds produced many strange forms of potato plants. Some had extremely large blossoms in great quantities, others extremely small ones; the blossoms varied in all shades from deep blue through sky blue to red and white. Some of the blossoms might have been thought not unworthy to be introduced as garden ornaments. But they offered no advantage over numerous flowers already in existence, and as the tuber proved worthless, these experiments also were discontinued. But by far the most interesting experiments that I have made with the wild potatoes were made by combining the form known as the Darwin potato (Solaium maglia), a yellow fleshy tuber with big seed balls, with the common potato, and with various other tuberous Solanums. Thus I produced a plant which yielded balls of fruit at least three or four times as large as those ever produced by the ordinary potato. In one case, the fruit of this hybrid proved to have an excellent flavor, in some respects superior in quality to the tomato. It was white when ripe, and had also a highly pleasing aroma. The flesh of this fruit resembled that of a firm tomato. To the taste it suggested a delightful commingling of acids and sugars. As the fruit grew on a hybrid potato vine, and in itself had much the appearance of a tomato, it was christened the "Pomato." The name itself was appropriate enough, but was unfortunate in that it led to the unauthorized assumption that the fruit was really a cross between the tomato and the potato. In point of fact, I have never been able to cross these two plants, and there was no strain of the tomato in the ancestry of the new fruit. The pomato plant produced fruit abundantly, but very few tubers, and when the latter were planted, the vines seemed to run out, giving their entire attention to the production of seed balls. But the seed when planted never reproduced itself exactly true to form, showing its hybrid quality by the production of unique and abnormal forms. Thus there was no practical method of propagating the pomato, the tubers being wholly absent or merely rudimentary, and the seed not producing a satisfactory product. It is probable that if I could have found time to continue the experiments, I should have been able to fix the race through selection, and thus have added a fruit of an altogether new variety to the list of garden products. But to have done this would have necessitated experiments on a large scale, and this would have required more time than I could give at the moment. I think it not unlikely, however, that some one will take up the experiment in future and develop a fruit comparable to my pomato that will have commercial value.
SOME HYBRID BERRIES
One of the most curious hybridizing experiments that I have ever conducted was made in an effort to test the limitations of affinity between the various members of the rose family. I had on my place a bush of the California dewberry, a plant that differs from most other members of the family in that its staminate and pistillate flowers are borne separately. The particular bush in question had only pistillate flowers, and as it grew in isolation, it ordinarily bore no fruit, as its flowers were seldom fertilized. At most it occasionally developed single drupelets, a result no doubt of partial fertilization from grains of pollen accidentally brought from a distance by wind or insect. The isolation of the plant, and the fact that it bore unisexual flowers, seemed to offer a favorable opportunity for experiment. Upon this plant I applied the pollen of various species of plants of the same family. The list is a striking one, for it included the apple, the mountain-ash, the hawthorn, the quince, the pear, and various kinds of roses. I worked at these hybridizations attentively during the blooming season of the dewberry in the summer of 1886. The pistils thus fertilized developed an abundant crop of fruit, and in the ensuing season I raised from these berries between five and six thousand seedlings. Never on earth, perhaps, was there seen a more widely varying lot of seedlings that were the immediate offspring of a single plant. The hybrids took almost every possible form that could be suggested as combining the traits of the various parent plants. Most of them were absolutely thornless. Many grew upright like the apple tree, showing nothing of the drooping tendency even of the raspberry, much less the trailing habit of the dewberry. The leaves were generally quite smooth, some resembling those of the pear, others being partially trifoliate, and most of them assuming strange and unusual forms. When this motley company came to the time of blooming, there was still another surprise, for the flowers were as varied as the foliage. Some of the blossoms were crimson in color, and half as large as an apple blossom; some were pink and quite small; others were white. A large number of plants, however, did not bloom at all, although they were attentively cared for, and were otherwise normal. From these strange hybrids I not unnaturally expected to raise a remarkable variety of fruits. I had hopes even of being able to produce something of real value, at any rate from the second generation. But when it came time for the fruits to ripen, another surprise awaited me; only two plants out of the five thousand produced a single fruit. One of these was a plant somewhat resembling a raspberry bush, and this produced a number of ill-tasting berries of a yellowish-brown. The other bush produced insignificant fruits of an orange-yellow color. Though unpromising in themselves, these fruits were carefully watched and guarded, for I felt convinced that possibilities of strange variation were contained in them, if only I could get from them a few seedlings. But when the fruits were fully matured, I examined the seeds and found all of them hollow. They were nothing but shells, containing no kernel. So by no possibility could I get a single seedling of a succeeding generation. Some of the most curious of the plants were preserved for another season, but they proved as unproductive as before; and as I needed the ground for other purposes I felt constrained to destroy the entire company of curious hybrids. In all my experience I never destroyed a lot of plants with more sincere regret. An experiment perhaps even bolder was made at about the time of my experience with the hybrid dewberries. This was the hybridization of the strawberry and the raspberry. The attempt to cross plants of such unlike appearance would seem to most experimenters absurd. Yet the cross was successfully effected. The raspberry was selected as the pistillate plant, and pollen was applied from whatever strawberry was at hand. It was impossible to choose as to the latter point, for the strawberry is for the most part out of season when the raspberry blossoms. I had to use such material as I could find. The pollenation proved effective, and the raspberry plant produced a full crop of fruit. There is no very marked immediate effect observable from such a hybridization. The pulp of the berry seems not to be affected; but the essential seeds within the berry are enormously modified, as the sequel showed. For when the raspberry seeds were planted in the greenhouse, the young hybrid plants that came up in profusion had all the appearance of ordinary strawberry plants. No one who inspected them casually would suspect their hybrid origin. The raspberry, the pistillate parent on which the seeds had grown, has leaves with five leaflets. But there was no leaf of this character among all the hybrids; without exception their leaves were trifoliate like the leaf of the strawberry. In other words, in the matter of foliage, the strawberry plant was entirely prepotent or dominant, and the characteristics of the other parent were latent or recessive. When the hybrids were old enough, they were carefully set out in rows in the open field. For a month or more after transplanting they showed no inclination to depart from the habit of the strawberry. To close inspection it might appear that the main stem was unusually thick, and that the leaves were a little more wrinkled than is usual with the strawberry, and their edges slightly more serrated. But aside from this, the hybrid plants were seemingly true strawberries. About the first of June, however, the plants began to throw out underground stolons, whereas strawberry runners are normally on the surface. These stolons suggested roots of the raspberry, yet the new plants that sprang from them here and there were exactly like the strawberry plants. So at this stage it would seem that the influence of the mother parent had been but slight. But along in July came the transformation. Rather suddenly each main plant sent up two, three, or more strong smooth canes, which grew to the height of from two to five feet. These canes were absolutely thornless, as were all other portions of the plant; they were as smooth as strawberry plants in leaf and stem, but their form and manner of growth now departed strangely from the traditions of the trailing parent. Obviously the influence of the raspberry parent had at last made itself potent. Some of the plants were yellowish, indicating that the berries would probably be yellow; others were reddish. There were no blossoms the first season, but the ensuing year panicles of blossoms of great size were put forth, some of the bunches being twelve inches in breadth-far larger than those usually seen on the raspberry. In a single panicle there were sometimes several hundred flowers. The individual blossoms were generally larger than the flowers of the raspberry, but slightly smaller than those of the strawberry. In the center of each blossom was a miniature berry, which might be said to resemble either a strawberry or a raspberry, being so small that its exact characteristics could hardly be distinguished. I was quite sure I had a valuable cross, and that at least one might be found among the many that would produce fruit. But in this I was disappointed; not a plant produced a single berry. The miniature fruit remained unchanged in size until it finally dropped from the bush in the fall. The following season a few of the plants bore one or two fruits having two or three drupelets each, like mere fragments of a normal raspberry. But not a seed was found. The plants were as sterile as mules. So here the experiment ended, and the hybrid strawberry-raspberries followed the hybrid dewberries to the brush heap.
WHY THE EXPERIMENTS FAILED
If now we consider the results of these various experiments, it will be clear that they have certain elements in common. In all cases the hybridizing was effected between species that are botanically related. Some of them (petunia and potato, dewberry and its mates, strawberry and raspberry) belonged to different genera, however, and in no case was the relationship between the mated forms very close. And this fact is of course of salient importance in enabling us to comprehend the results. It is almost axiomatic to say that the hybridizing of plants becomes increasingly difficult in proportion as the attempt is made to cross more and more distantly related species. Even within the same genus it is very often impossible to produce a hybrid that is not sterile. I might cite in further illustration of these difficulties the experiments through which I have hybridized the apple with the pear, and with the quince; the cherry with the plum; and the peach with the almond, with the Japanese plum, and with the apricot, without in any of these cases producing a product of value. These crosses, like the ones just detailed, bring together racial tendencies that are too widely divergent to be harmonized. It would appear that it is essential to the differentiation and perpetuation of species that bounds should be set on the possibility of producing a disturbing influence through hybridization. When plants, even though sprung from the same origin, have diverged so widely and for such periods of time as to produce forms differing from one another so greatly as, for example, the mountainash, the apple, and the rose differ from the dewberry; or the strawberry from the raspberry-it would seemingly not be advantageous in the scheme of evolution to permit the hybridizing of these forms. The mutations that would be produced, were such hybridization to result in virile offspring, would be too divergent, in all probability, to fit into their environment successfully. At all events the possibility of such crosses would constitute a disturbing influence that would rob the scheme of organic nature of a good deal of its orderly character. And so it appears, so far as may be judged from my experiments, that even when hybrids between these divergent forms are produced, the offspring are sterile, and the results of the hybridization are not perpetuated. Such, then, is the barrier that nature erects in the interest of race preservation, between species that have widely diverged. But, on the other hand, we have seen many illustrations of the fact that when species a little more closely related are hybridized, the result may be not to produce sterility but to give added virility to the offspring. We saw this illustrated, for example, when the walnut of the eastern United States was crossed with the black walnut of California. The hybrid progeny not only showed tremendous individual vitality, growing with great rapidity and to enormous size, but they produced an altogether extraordinary abundance of fertile fruit. The hybrid variety thus produced-named, it will be recalled, the "Royal"-constitutes a new race that can more than hold its own against the parent forms. And the reason for this, seemingly, was that the two species of walnut had not become sufficiently divergent to introduce a greater diversity of conflicting tendencies than is consonant with racial progress when the strains are brought together. But it will be recalled that when the California black walnut was hybridized with the English walnut-producing the "Paradox"-the results in this regard were quite different. While the individual offspring showed great vitality, they were almost sterile, producing only a few stray nuts in contrast with the profusion of the Royal hybrids. And we may infer from this result that the California walnut and its remote English cousin have diverged to a point lying just on the border line of the limits of desirable racial mingling. These limits have not quite been crossed as they have been in the case of the dewberry and apple tree, and the strawberry and raspberry, but they are being approximated; and there is no probability that the hybrid offspring of the black walnut and the English walnut could maintain itself through successive generations as a new race in a state of nature. At all events, its fight would be a doubtful one.
THE APPLICATION TO THE HUMAN SPECIES
It is more than likely, then, that the lessons taught by the unsuccessful experiments recorded in this chapter are quite as important as if they had led to seemingly more practical results. For they serve to emphasize a great fundamental truth of heredity, which has a more important bearing on the problems of racial development of all organic beings, including man himself. It has become more and more clear in recent years that the underlying principles of evolution apply in large measure to plants and animals alike, and that much may be learned about the proper breeding of mankind from a direct study of the breeding of the lower organisms. And as regards the particular case under consideration, it is scarcely to be doubted that we may draw important lessons from the obvious results of the hybridizing of plants to apply to the commingling of human races. It is commonly held that the various existing races of man constitute a single species. But this classification was made under the influence of the old idea that sterility of offspring is a valid test of specific difference. No one nowadays holds that view, with regard to plants at any rate, and the view is probably no more valid in its application to a great number of animals, including man himself. But, in any event, the question as to whether mankind constitutes a single species or several species is a matter of definition of no real importance. It is beyond question that the human family comprises widely divergent races, and it is scarcely open to question that the divergencies in many cases are so pronounced as to make hybridization between these races inexpedient, even though it still is possible. The student of history tells us that the great civilized races of the past were all mixed races. This was true of the Egyptians, the Babylonians, the Greeks, and the Romans. It is true of the chief nations of today. But the races that intermingled to produce the great peoples have always been somewhat closely related. No good result has ever been achieved, for example, by the commingling of Mongolian and Aryan blood, or of Aryan with Negro. Such wide crosses must be expected to produce at least a measure of infecundity, and a commingling of racial tendencies too divergent to be advantageously blended. The case is comparable to that of the Paradox walnut, even though it be not quite so extreme as the case of the hybrid strawberries and dewberries. But what chiefly concerns us now is not the past history of mankind, but the present and future history; and in particular the history of mankind here in America. There is taking place in our day what is doubtless the greatest migration in all history. The races of Europe are flooding into America, and there is a more pronounced commingling of racial strains now taking place on our soil, than perhaps ever occurred in any one place, or in any single epoch, in the history of the world. America owes its present greatness in considerable measure to the mingling of moderately divergent strains in the past; but this fact should not blind us to the menace that lies in the mingling of races that are too divergent to blend advantageously. And it is at least an open question whether certain of the Latins, the varied races of Slavs, and the vast hordes of Semites that have come to us in recent years can mingle their racial strains with the Anglo-Saxon stock without disadvantage to the ultimate progeny. It is this thought that I would put forward as the most important suggestion that arises from the study of the hybridizing experiments in which I unsuccessfully attempted to blend the hereditary tendencies of certain races of plants that were too widely divergent.
This text is from: Luther Burbank: his methods and discoveries and their practical application. Volume 2 Chapter 9