BRINGING FORTH AN ENTIRELY NEW COLOR
AND OTHER IMPORTANT WORK WITH THE POPPIES
For some reason blue is not a favorite color among flowers. There are notable and; conspicuous exceptions, of course, but for every species of blue flower in nature there are hundreds of flowers that are yellow, or red, or white. Presumably the color blue does not attract the eye of the insect so strikingly as do the other primary colors. Flowers are not green for the obvious reason that, since leaves in general are green, flowers of that color would blend with the foliage, and thus defeat the primal purpose of the floral envelope. And, no doubt, blue is a color nearer to green in its hue or general aspect than are the reds and yellows. So it is perhaps not surprising that natural selection has weeded out the blue flowers and given us an abundance of red and yellow and white ones. Of course, there may be some underlying reason associated with the chemical character of the different pigments that helps to account for the relative scarcity of blue flowers. But, as to this, no one at present has any definite knowledge, for the chemistry of the pigments, and the underlying differences between the pigments of different colors, in the petals of flowers are very little understood. But, whatever the explanation, the fact of the scarcity of blue flowers is patent enough. Where a flower has adopted the blue pigment, it may hold to it tenaciously. But, on the other hand, there are thousands of blossoms that show great variation in color, ranging through the various tones of scarlet and crimson and pink and orange and yellow, apparently quite without discrimination, yet avoiding blues of every type.
A BLUE POPPY
Conspicuous among the flowers that show this wide range of variation in color, and yet never by any chance have been known to produce a blue flower in the state of nature, is the familiar Poppy. So the production of a blue poppy in my gardens, through a long series of selective experiments, may be considered one of the most striking of the minor plant developments accomplished there. There is no record of a true blue poppy ever having been produced elsewhere. The blue poppies bloom toward the last of May or early in June each year, furnishing a spectacle that never fails to excite the interest of visiting florists. The story of the production of the blue poppy is a comparatively simple one as to its chief outlines. That is to say, the work that was directed exclusively to the production of a flower with this color was carried out without any complications of hybridizing, solely as a problem in selection. A measure of success was attained in the course of five or six years after the problem had definitely presented itself. But, on the other hand, it should be explained that the specific idea of developing a blue poppy came only as a sequel to a long series of very arduous experiments in selective breeding through which the ancestral stock that finally produced the blue poppy had been developed. And it is more than probable that the preliminary experiments, although aimed at quite different purposes, were absolutely essential to the segregation of hereditary factors in the plants of my poppy colony that made possible the final development of the flower with the anomalous color. Therefore, it will be necessary, as preliminary to a specific account of the quest of the blue poppy itself, to give somewhat in detail the story of the development of the ancestral strains of poppies of varied but more usual colors.
ORIGIN OF THE SHIRLEY POPPY
The poppy from which the blue flower was developed is of the variety known as the Shirley poppy. This is one of the most interesting and beautiful varieties of the species Papaver Rhoeas, the corn poppy of Europe. The peculiarity of the Shirley in which it differs from the wild form of field poppy is that it varies in color from the original red to a pale pink and even to a pure white; and that the original black central portion of the flower has been changed to yellow or white. The last-named characters are the distinctive ones. The true Shirleys never have the smallest particle of black about them. They may be scarlet or pink or white or variously flecked. But they have no black about them, and they were never yellow, until pale yellow and pale orange shades have recently arisen. This beautiful variety gains enhanced interest when we learn that it was developed as recently as about the year 1880, in the garden of an English clergyman, the Rev. W. Wilks, through a series of selective experiments of precisely the character so often illustrated in the course of our present studies. It appears that Mr. Wilks discovered in a field of the corn poppy of the usual scarlet color, a solitary flower that had a very narrow edge of white. He marked this flower, saved the seed of it, and the next year carefully watched the seedlings. Out of perhaps two hundred he found four or five on which all the flowers were edged with white. The best of these were marked, and their seedlings were selected from in turn. In successive years a large proportion of the flowers gained an increasing proportion of white to tone down the red, until they arrived at a quite pale pink, and finally one plant was found that was pure white. The attempt was then made by similar selection to change the black central portion of the flower to yellow or white, and in due course this also was accomplished. The new strain being fixed by selection, the Shirley poppy, which has come to be one of the most popular of flowers, was given to the world. It appears, then, that the Shirley poppy is a variety that has been specially selected within comparatively recent years, with an eye to the one problem of color modification. It therefore represents a strain of plants in which there is a curious mingling of hereditary factors for color. It is a fixed variety, at once recognizable, yet the different flowers that resemble each other to the point of approximate identity as to form and botanical features may be scarlet or pink or white or variegated, and all these colors may be represented in the plants grown from a single lot of seed, and sometimes in a single individual flower. Even as to the matter of the black center which characterizes the original corn poppy, the Shirley shows a tendency to reversion. Now and again flowers appear that have black spots at the base of the petals. These, however, are rigidly excluded by the florists in selecting seed. Other marks of tendency to variation in the Shirley are the uncertain length of the stem, which may be very short or very long, and a propensity to doubling of the petals, which is regarded as a defect. Moreover, there is sometimes manifested a tendency to a crimson hue that is regarded as reversional, and has to be eliminated by the careful flower grower.
PERFECTING THE SHIRLEY POPPY
All these marks of a tendency to variation, together with a history of the development of the flower, marked the Shirley as a plant suitable for further experimentation. So about twenty years ago, at a time when the Shirley was a comparatively new flower, I commenced a series of experiments with this variety, securing seed from every available source. I was somewhat astonished and disappointed to find that, in spite of the diversified color scheme of this flower, there was a very striking uniformity among the plants produced from various lots of seed. Everywhere there was a strong tendency to revert to the original scarlet color, but otherwise the colors were relatively fixed. Attention was chiefly attracted to the form of the petals, however, which seemed rather lacking in gracefulness, being too flat and without character. With the thought of modifying the petal and thus beautifying the flower, I commenced the most rigid selection, choosing the first year only four or five plants out of many thousands, and from the progeny of these reselecting from season to season. I chose the flowers that showed the lighter shades of scarlet, crimson, and pink, and those that were altogether white. Attention was given also to the selection of large flowers, and in particular to those that had the most delicate petals, but firmness of texture and any suggestion of waviness was joyfully welcomed. For many years I kept up this selection, raising large quantities of poppies, and having the aid of four or five men in scrutinizing all the flowers in the field for an hour or two each morning during the blooming time, that no specimens showing favorable variation should be overlooked. At first the progress was very slow. It was easy to find specimens that were semi-double and those that showed the black spots. But there was very slight tendency to crimping of the petals. As usual in such cases, however, there came a time when progress seemed much more rapid. Thenceforward the work was encouraging and full of interest, and in a few years more a most beautiful strain of poppies had been produced which presented almost in ideal combination the various qualities for which I had been selecting. Those that were not pure white showed an astonishing variety and a beautiful blending of the more delicate shades of red and pink. The plants were graceful in form and of uniform height, and, most important of all, the petals of the flowers were of the thinness and almost of the texture of tissue paper, yet of firm texture, and artistically waved and crinkled, in strong contrast with the smooth petals of the original varieties. This plant was introduced through a prominent seedsman as an "Improved Strain of Shirley Poppy," and later when still further improved as the "Santa Rosa Strain of the Shirley Poppy." The modifications are so striking that various horticulturists have suggested that the plant is entitled to rank as a new variety. But I preferred to recognize the variety from which the new plant had been developed by retaining its name.
COMING OF THE BLUE POPPY
It has repeatedly been observed that no flower or fruit is or can be developed beyond possibility of further improvement. However closely a new form may approximate the ideal at which the plant developer aimed there are always variations that suggest new possibilities that perhaps were not contemplated at the outset of the experiment. And the improved Shirley poppy was no exception to this rule. As work continued with the new flower, the form of its petals modified until they were exquisitely delicate, and its colors blended until the most artistic and delicate shades were predominant, attention was attracted one day to a specimen growing among the thousands that revealed a color a shade different from any other previously seen. On inspecting this flower I seemed to detect, underlying the normal color, a smokiness suggestive of a half-concealed blue pigmentation. Naturally this was carefully guarded and the seeds of this plant preserved and sowed by themselves the following season to make the basis of a quite different series of selective experiments. The history of this new colony duplicated that of other groups of plants undergoing selection. Year by year I found an increasing proportion of flowers with the smoky hue, and always among these a few that revealed the obscure blue pigment a little more clearly. Finally, after several years of selection, I had a strain in which about one-third of the plants bore flowers of various shades of blue, some smoky or seemingly mixed with black pigment, and others with fairly clear, if not very bright, blue color. The few flowers that were pure blues were naturally selected to continue the experiment. But their seedlings for the most part failed to reproduce the color. Selecting year by year, however, among the individuals that produced flowers of the purest blue, the strain was gradually fixed until each year a plot of poppies appeared that, seen from a little distance, presented the aspect of uniform blueness. This, of course, is the patch referred to as exciting the astonished comment of florists that visit my grounds at Santa Rosa about the first of June each season. On closer inspection of the plot of blue flowers, it will be found that there are still a good many specimens that tend to revert to the more familiar colors. But the effort to establish the blue variety as a fixed type through inbreeding and selection is still under way, and success is assured. Were the poppy a plant that is propagated by root cuttings or any other of the common modes of division, the blue variety would long since have been given to the world. But as it is necessary with this plant to develop the variety until it will breed true from seed, I have been obliged to continue the experiment at least ten years longer than would otherwise have been necessary. Now, however, it may fairly be said that the experiment has approached completion. The blue poppy is an accomplished fact. Its production constitutes one of the most striking color modifications hitherto made through artificial selection.
CREATION OR REVERSION?
So far as is known, there was never an ancestor of the Shirley poppy that was blue. So here we have an illustration of an experiment that is radically different from any that we hitherto have had occasion to examine. We may suppose, to be sure, that the condition of blue pigment is one that occurred in some very remote ancestor of the new poppy. Otherwise we could not account for the presence of the hereditary factors of blue pigmentation; and obviously it is not to be supposed that our experiment in selection resulted in the creation of new hereditary factors. But the time at which any ancestor of the poppies bore blue flowers must have been very remote indeed, because no poppy either of the species directly in question or any other species has ever been found anywhere in the world that has a flower of blue color. So, as just suggested, the bringing out of this color constitutes a development of radically different character from the mere modification of color of a flower within the range of the color scheme of a species, or of allied species, or even of allied genera. The development of a Shirley poppy that is yellow, for example, which was a second task that a German experimenter set himself, would be comparatively easy, because yellow is a more common color with members of the poppy family, and a tinge of yellow is not unusual. I have myself developed and introduced strains of Shirley poppies of salmon or deep yellowish pink color. These include various shades of salmon and light scarlet, but with no trace of crimson or of darker colors of any kind. This flower, which had been selected also for size and crimping of petals and gracefulness, as well as for color, was introduced under the name of "Burbank's Sunset Shades of Shirley Poppies." But I mention this new variety only to point the contrast. No such amount of work was involved in its production as that which attended the production of the blue poppy, because yellow pigments are in the heredity of the poppies in general, and must have been manifested among the ancestors of any given strain of poppy within relatively recent times. The affinity between the yellow and red, for example, in the case of the poppy, is clearly enough demonstrated in the experiment, outlined in an earlier chapter, in which I developed a race of crimson California poppies (Eschscholzia), the parent species being, as is well-known, bright yellow in color. It will be recalled that the new crimson flower was developed by selection through successive generations from a specimen that showed a little line of crimson, like a streak or thread of another color, lengthwise of a single petal. California poppies of various other colors were developed in the same way, but there were no blue ones among them. In the case of these California poppies, then, the relative ease with which the flowers were changed from yellow to crimson would seem to suggest that the latter color lies but slightly submerged, if the expression be permitted, in the hereditary stream, ready to come to the surface if the thin overlaying current of yellow can be removed. Another illustration of the linking of yellow and crimson in the hereditary scheme of the poppies is given by an experiment in which I crossed two distinct species of poppy, one having flowers of pale yellow, the other pure white. The hybrids without exception bore flowers of a clear crimson color. There was not a white one nor a yellow one among them. Another interesting color modification in the case of the poppy was that which produced the so-called silver lining poppy. In this case I discovered a flower in which there was a white line between the black center and the crimson petal. This line was widened by selection until the petal was white with black center, the white extending just over the outer edge of the petal, the rest of the back of the flower being crimson. It may be interesting to recall in this connection a series of experiments in which the only true California poppy (Papaver Californica) was modified by selection, working with a five petaled sport, until a variety was produced that had six petals. The size of the flower was also improved by selection; but the color of the original-a pale orange-refused to budge. Yet another poppy modification of interest was that through which the Iceland poppy was developed until its seed capsules had fifty-six proliferations instead of the original one.
THE VARYING DOMINANCE OF COLORS
The story of the color variation in poppies, as illustrated in the development of the Shirley and its modifications, and in the selective and hybridizing experiments just related, furnishes fairly tangible evidence that the scheme of pigmentation of a flower is of somewhat less fixed or fundamental character than the various characteristics of form and leaf-system and breadth and arrangement of petals and stems and ovules, that are depended upon by the botanist in determining plant relationships. The fact that a certain flower, for example, may vary in color from bright scarlet to pure white, and from salmon to blue, while still retaining the botanical characteristics that would lead any florist to classify it as a Shirley poppy, in itself demonstrates the comparative unimportance of any particular color in the scheme of plant economy. There may be special conditions that make a red flower fit into its environment a little better than a yellow flower, or vice versa; but either red flowers or yellow ones or pink ones or white will attract the insects, and thus fulfill the purpose for which color in the flower has been developed. That, doubtless, explains why it is relatively easy to modify the color of a flower, within certain limits, and-what amounts to saying the same thing-why the same species of flower may so often be found presenting different colors or shades of color in different localities, or under slightly varying conditions of cultivation. But perhaps the chief interest of the entire matter of the coloration of flowers, and specifically the chief interest of such a development as that of the blue poppy, is found in the suggestions given as to the underlying principles of heredity involved in color transformations. It would seem as if we are justified in concluding from the evidence that the hereditary factors for the production of many different pigments are mingled in the germ plasm of any given species of flowering plant. If one color predominates over another in the flower, it is because its pigment is dominant over other pigments, and the study of color dominance furnishes interesting side lights on the question of the hereditary transmission of unit characters. In the animal world, for example, where the study of the heredity of color has been carried out pretty extensively in recent years, there are interesting combinations showing a somewhat more complex character than any that we have hitherto examined. We have seen that in the case of the guinea pigs black pigment is dominant to white, so that when a black guinea pig is mated with a white one the offspring are black, but the recessive trait of whiteness reappears in one in four of the progeny of the second generation. But it appears that in these animals, and similar ones that are subject to wide varation of color, there are curious complexities of heredity, all of which, however, so far as studied, fall within the scheme of "Mendelian" transmission. Thus it is found that in the case of mice, for example, whereas blackness of coat is dominant over whiteness, just as in the case of the guinea pigs' blackness itself may be overlaid, as it were, and entirely obscured by the presence of factors for gray coating, and it further appears that yellow pigment may dominate the gray coat as well as the black. A further complication occurs in that an animal that is neither yellow nor gray nor black may be chocolate in color. And it is only in case this color also is absent that the mouse will be white. Moreover, if the factors for chocolate are absent, the factors for grayness and blackness may neutralize each other, and exist in what is called a masked condition, neither one being able to make itself manifest on account of the presence of the other, because both are dominant factors; so that the mouse will be white, yet will carry the factors for grayness and for blackness masked in its germ plasm. When the chocolate factors are present, however, in addition to the factors for blackness and grayness, the presence of three dominant color factors has the curious effect of enabling one of them, in this case gray, to make itself manifest. So the chocolate factor is necessary to produce a gray mouse; and the chocolate colored mouse will appear only when the factors for grayness and blackness are absent. This rivalry of dominant color factors, with subordination of one to another, even though both are dominant over whiteness, has previously been briefly referred to, and it has been noted that, for convenience in describing the condition, biologists have come to speak of a factor that thus subordinates another, in the sense in which gray subordinates black in the coat of the mouse, as epistatic; the subordinated color factor (in this case black) being said to be hypostatic. These terms are of obvious convenience, being somewhat parallel in their application to the Mendelian terms dominance and recessiveness, yet being quite distinct, as we have seen, inasmuch as they apply to the relations of factors that are both dominant, yet which refer to the same quality and hence cannot both prevail.
MIXED FACTORS IN THE POPPY
Our studies of inheritance of color in the poppies suggest that closely similar relations exist among the pigments of the flowers. The exact relations of reds and yellows and pinks and blues have not been carefully worked out on a comprehensive scale, as have been the pigment-relations of the coats of mice and rabbits. But the evidence seems to suggest that the relations of red and yellow, for example, in the case of the poppy, are somewhat comparable to the relations of gray and black in the coat of the mouse. That is to say, both of these are dominant to white, but one of them is epistatic to the other. It is probable that red is superior in dominance, or epistatic, to yellow, and hence that a poppy will be yellow in color only when the factor for red pigment is either absent or masked. The experiments that led to the production of the blue poppy suggest the possibility that blue pigment may occupy some such place in the scheme of coloration of the poppy as that occupied by the chocolate color in the scheme of the mouse's coat. In that case, a poppy would be blue only in case the color factors for red and yellow were both absent. And a poppy would be white only in case the color factor for blue was absent, although there might be present color factors for both yellow and red in the condition of equilibrium which we have spoken of as masked. A dingy white flower might contain a trace of blue. This supposition might explain the case of the yellow poppies crossed with the white ones, in which the hybrid offspring were all crimson in color. The hybridizing in this case may be supposed to have brought together latent or masked factors for red (present in the white flower), the mating of which gave that color dominance, and enabled it to assert itself, while the yellow factors were unable to assert themselves, yellow being hypostatic to red. Suppose, for example, that the yellow poppy bore factors for yellow and blue; and the white one, factors for red and yellow. The combination would bring together red, plus yellow, plus blue; and red would be manifest, the other colors being masked. Re-combinations should be expected in the next generation. But the actual conditions are probably a little more complex even than here suggested. The smoky character of the blue poppies, especially in their earlier forms, seemed to suggest the presence of a factor for blackness. And, indeed, the fact that black pigment constantly tends to appear in the poppies shows how potent an influence this is. So, when the entire hereditary color scheme of the poppies is untangled, it will probably be found that there are dominant factors for red and yellow and black and blue corresponding more or less to the yellow and gray and black and chocolate pigments of the coat of the mouse; and that these are mutually dependent on one another in an intricate fashion, the full explication of which would give us a far clearer comprehension of the mysteries of the color transformation in the poppy and in other flowers than anyone can claim to have at present. It is because of the new light they throw on this problem that experiments that led to the production of a blue poppy seem to have unusual interest and importance. But long series of additional experiments involving much expense and many discouragements will be necessary before the exact relations of the different pigments in the poppy, or in any other flower, will be fully understood.
This text is from: Luther Burbank: his methods and discoveries and their practical application. Volume 9 Chapter 4