Conference on Plant Breeding and Hybridization, 1904: 75-78
VARIANT TENDENCY AND INDIVIDUAL PREPOTENCY IN GARDEN VEGETABLES
W. W. Tracy
The examination of a great number of plants will sometimes reveal what would not appear from a more careful study of a few.
I do not claim to be a scientist, or that any investigations I may have made have been conducted in a strictly scientific manner, particularly as to their records, and my only excuse for occupying your time is that I have had exceptional opportunities to observe a vast number of plants of different garden races, both as to their variant tendencies and the influence of conditions of heredity and environment. For the past twenty years I have annually examined, for the purpose of detecting variation and the influence of heredity and environment, some 400 acres of tomatoes, 1,000 acres of cucumbers, 5,000 acres of garden beans, 200 acres of cabbage, and corresponding quantities of other garden vegetables and flowers. These crops have been grown in widely separated fields, under different conditions of soil and climate, and most of them from seed with whose pedigree I have been familiar, in some cases, back for ten or more generations. It seems to me that such extensive observation of an immense number of individuals, developed under varying conditions, might give hints of certain facts which would not be revealed in a more critical study of the comparatively few specimens to which all intensive study is necessarily limited, and the purpose of this paper is the statement of some convictions ill regard to racial variation which have resulted from such observations.
1. The different plants of the same natural order tend to vary along parallel lines. Fruits of the variety of tomatoes known as Early Conqueror, those of the pepper known as Squash or Tomato shaped, and of the Scarlet Fruited egg plant, could be selected, which would be as much alike in form as fruits from a single plant of any one of them; and I have seen a "potato ball" of the same form. I have found fruits of squash, muskmelon, watermelon and cucumber each having the peculiar forms and markings generally confined to one of the others. Thus, last year, I found a plant of watermelon whose fruit was distinctly warted, and in form would pass for a fairly typical one of Summer Crookneck Squash. I have seen muskmelons as flat and deeply scalloped as a fair sample of White Bush Scalloped Squash—squashes as well netted and distinctly ribbed as a Bay View Muskmelon. And it is taste and usefulness rather than limitation of variant tendency which determines the common shapes of each of these vegetables. I believe that hybridization is often credited with variation which is due to this common variant tendency.
2. The natural orders are distinctly, but differently, affected as to the character of their seed product, by conditions of soil and climate. For instance, if sweet corn, from the same ear, be planted where it will be subjected to different conditions of soil and climate, for but a single generation, the seed product will give plants differing materially in both stalk and ear. We think the same thing is true of wheat, oats and other gramineous plants. But we have never been able to detect the least difference in the character of seed grown from the same stock under different conditions in cucurbitaceous plants. We once planted a 10-acre field with Round Icing watermelon, five acres with seed which had been grown for four generations within 100 miles of the Gulf of Mexico, and the balance with seed, originally of the same stock, which had been grown for five generations in Michigan, and the most careful examination could detect no difference in the crop produced, either in earliness or other characteristics. Quite distinct varieties of melon are common at the North and South, and sometimes northern and southern strains of the same variety are quite distinct, but we think that this comes from the selection of the sorts best suited to the climate and to difference of ideals, and consequently in selection of seed stock rather than from influence of climate.
3. Cultural and climatic conditions are cumulative in their influence, and affect the whole species.
Thus, the Lima bean, originally a climbing plant, continued so for many years, during which time several distinct races were developed, but no dwarf form appeared; then, within three years, dwarf forms of all the different racial types appeared, and in several different places simultaneously. The sweet pea, cultivated for many years and closely watched by many enthusiasts, gave only climbing plants until 1892, when the "Cupids," or dwarf forms, appeared in at least three locations and different stocks and five individuals, and since then they have appeared in a great many different stocks and places, and often where there could not have been pollen influence to induce the sport. In most vegetables, if any new form, no matter how distinct from those commonly cultivated, appears in one stock and place, there is almost a certainty that practically identical variations will appear elsewhere. For instance, the Navy Blue Sweet Pea was a very new and distinct shade, and appeared in the fields of two cultivators the same year, the only discernible difference in the two sports being that the seed of one had a greater tendency to skin-crack than that of the other. This tendency to sport into new forms developing in the species rather than in any particular stock is often the cause of much annoyance to seedsmen, two or more of them being accused of sending out a new form under different names, when each supposed that he had the only origination of that type.
4. The variant tendency in a race is common to different stocks and peculiar to each season.
For instance, in 1896, a distinct tendency to neckiness was noticed in Long Green Cucumber; this increased in 1897, when I found several plants, all of the fruit of which more or less closely resembled that of the Summer Crooknecked Squash in shape. This tendency then gradually disappeared, giving place to one toward thicker fruit with white spines.
5. Seed of the same stock and equally well grown, by the same cultivator, in the same location, differ in the variant tendency, and the degree to which their product will be of the desired type in different seasons. The crop of seed of Green Globe Savoy Cabbage produced by a certain grower in 1893 gave much more evenly typical plants and heads than any subsequent crop produced by him of the same strain, though he took the greatest care in selecting stock and growing the plants, even setting them in the same field that gave the superior crop. I have known a practical seedsman, one not likely to waste money on a mere theory, to pay treble the market price for a certain strain of peas produced by him four years before, though he had an abundance of seed of the same strain grown by himself in succeeding years—none of these later crops giving such good results as seed of that particular season.
6. Seeds from individual plants of precisely the same pedigree grown the same season in the same field and equally true to the desired type vary in the degree to which their product will adhere to that type. I have gone into a field of Beauty tomato, of which every plant was from seed of an ideal plant selected the year before from a field similarly grown, and spent hours in picking out five ideal plants, and succeeded in getting those so nearly equally of the desired type that I could not distinguish one from the other; sowed and planted the seed separately and found that the seed of one of these gave fruit quite distinctly inferior to that of the general crop of seed; another gave fruit much superior, while that of the others was intermediate in quality. This is but one of scores of similar experiences which have convinced me that the most certain, if not the only, way to secure a high degree of uniformity and excellence in a race of vegetables is, first, to form a definite and distinct idea of what the race should be; then by selection and testing, find not only an ideal plant, but one of the greatest possible prepotency or ability to reproduce itself, and to multiply the descendants of this plant as rapidly as possible until the entire stock is the lineal descendant of that individual plant—guarding against degeneracy by a never-ceasing search for other individual plants of equal or greater potential excellence, to be in turn increased.
O. F. Cook: I want to say that I speak of coffee as an illustration, not as an argument, and I tried to avoid, as you may say, the use of conflicting instances because of the variety of interpretations that could be put upon them. But I want to claim Mr. Tracy's as an instance of an application of my theories, and, furthermore, that they can be tested by such facts, and that I can accept Mr. Tracy's facts as normal and as actual, and I don't believe that the current theories can accept such facts without violation to the assumptions that are made on them.
The Chair: I am sure we all feel very grateful, indeed, to Mr. Tracy for his paper. It has a special value because of the fact of his connection with seed interests in this country, and his very great opportunities for observation. Probably there are few whose experience is so extended as that of Mr. Tracy, and I am quite sure that when his paper is published we will read it with very great interest, and possibly our scientific friends may, from the account which he gives, be able to reach some conclusions that they might not otherwise have formed.
D. G. Fairchild: Mr. Tracy cites an example of a tomato in which five plants were chosen, and the progeny from those five plants varied greatly. Were those plants self-fertilized, or is it possible that the male parent may have influenced the progeny differently?
W. W. Tracy: The plants were in a single field side by side, and they may have been cross-fertilized, but they were from the same blood line exactly. In this particular case of tomato I know of five generations from the same plants.
W. M. Hays: It has appeared to me that a plant like beet is entirely self-fertilized. There is evidence in a general way, and I think some positive evidence, that wheat does occasionally cross-pollinate, and it may be due to these occasional crosses that wheat is invigorated, and that some one plant among the crosses produced in nature finally dominates, increases more rapidly and becomes the major part of a new variety.
W. Bateson: I heard Mr. Tracy's paper with the greatest possible interest. I have been experimenting with the Cupid sweet pea, and I think the possibility attaches itself at once that it is a pure form, which may possibly explain the reappearance of that form subsequently and simultaneously in different localities. If, for example, the Cupid may once appear in a seed grower's field where it could get crossed on to another sweet pea, then such crossing does occasionally happen. In our country the crossing of sweet peas is occasionally accomplished by the leaf-cutting bee. If the pollen of a Cupid sweet pea were to get on the flowers of a tall growing sweet pea, then the seed might be scattered all over the country by the seed grower, and it would not appear the second year. Then the third year the seed might be distributed, and then the Cupid might appear. Of course, the simultaneous appearance of the Cupid in the third year of its sowing is a strong evidence that once a form has appeared its appearance in three years is explicable.