CORN-THE KING OF AMERICA'S CROPS
NOT ONLY BETTER CORN BUT A BETTER STALK-AND WHY
The potato, tobacco, and Indian corn or maize-these are the three great American contributions to the company of cultivated plants. The potato and tobacco and bean have gone everywhere, but corn is still chiefly raised in the country of its nativity. It is extensively cultivated, however, far to the north of its original habitat. The great corn state now is Iowa, and the original home of the ancestors of the corn plant was the region of Southern Mexico and Central America. In a recent year there were 1,144,500 acres of land in the United States given over to the cultivation of tobacco, and the crop raised amounted to 963,000,000 pounds. For potatoes 3,655,000 acres were utilized, raising a crop of 421,000,000 bushels. Wheat was raised on 18,663,000 acres, giving a crop of 330,000,000 bushels. This is an enormous acreage and a colossal output. Yet it seems almost insignificant in comparison with the record of corn. For to that crop 106,884,000 acres were devoted, and the crop harvested aggregated 3,125,000,000 bushels. Nothing that could be added would better show the supremacy of King Corn than this citation of comparative statistics. A crop that tops the three billion bushel mark stands by itself among all the products of the cultivated acres of the world. Not only is it America's greatest crop; there is no crop of any other cereal or any single vegetable product whatever that equals this record anywhere in the world. It is true that the corn crops of other nations are comparatively insignificant in contrast with the crops of small grains. But this is merely because corn demands peculiar conditions, notably a very hot summer, to bring its product to perfection. A goodly quantity of corn is exported; and the beef and pork that corn has produced are sent everywhere.
THE ANCESTOR OF KING CORN
Among the most interesting experiments that I have performed in the development of corn, have been those that had to do with the primitive plants that were the progenitors of the present developed product. The plant from which Indian corn was unquestionably developed, or at all events, a very closely related form that has not been greatly modified from the primeval type, is a gigantic grass that still grows in Mexico and is a valuable forage plant. It is called Reana luxurians, or Euchleana Mexicana. Its familiar name is Teosinte. This is a tall, sturdy plant, resembling corn as to its stem and stalk, but having a rachis like wheat or barley or rice that by comparison with the ear of the cultivated corn is insignificant. In the wild teosinte each grain shells out readily like oats, wheat, or barley, and has an exceedingly hard, polished, chitenous covering, for protection against marauding birds and animals. The grains are arranged in two double opposite rows on a fragile rachis, like that of other grains such as rye, barley and rice; the cob of the developed corn being wholly a product of man, and being required to hold the numerous large, fat, nutritious kernels which it has been induced to produce through centuries of cultivation. Teosinte, when brought under cultivation at the present time, after a few generations in the new and more favorable environment, like all other cultivated plants tends to vary. Like many of the half wild plants, teosinte has an inveterate tendency to sucker from the root. Anyone who has suckered a field of corn on a hot June day will appreciate the importance of eliminating this wild habit of the teosinte, especially when grown for grain rather than for food. It must have taken centuries to eradicate this defect, as it is even yet more or less persistent in nearly all varieties of corn. In kernel the teosinte most resembles, though not by any means very closely, our common varieties of pop corn; but with this great difference: only a pellicle protects the kernel in all our cultivated corn, while the tough, chitenous covering envelops the kernels of teosinte. But the resemblance of the plant itself to the corn plant leaves no question of their affinity, and the head of grain, notwithstanding its insignificant size, has individual kernels that are suggestive of diminutive kernels of corn. If any doubt were entertained as to the relationship of this wild plant to the cultivated corn, this would be dispelled by hybridizing experiments, for the two cross readily. In Mexico it is quite common for the teosinte to hybridize with the Mexican corn, through the agency of the wind, and the product is well-known under the name of "dog corn." In my own extensive experiments with teosinte, no difficulty was experienced in effecting hybridization, after I had succeeded in making the plant flower at the right season. Left to itself, the plant in this part of California does not bloom until after even the latest varieties of corn are through blooming. It will produce seed only in the southern part of Florida, except the new varieties lately sent me from the high mountains of Mexico, where it necessarily had to adapt itself to a shorter season. I was able, however, by starting the teosinte in the greenhouse, and thus securing fine, large plants to set out in May, and by placing these in the hottest possible positions and fertilizing them heavily, to cause the plant to bloom much earlier. This was further facilitated by removing all side shoots, so that the energies of the plant could be centered on the production of pollen. My hybridizing experiments demonstrated clearly enough the affinity of the teosinte with the cultivated corn plant. They also convinced me that this is without question the parent of the cultivated plant.
TRACING ANCESTRAL FORMS AND HABITS
The experiments that seemed demonstrative as to this were made partly with the aid of a primitive form of corn known as the single-husked corn, Zea lunicata, of which I received specimens from Mexico. This I believe to be the true primitive type of corn-that is to say, the first corn after advancing from the original type of the teosinte. The seed of the half ear of fine yellow corn of this primitive type that was received from Mexico was planted. The plants that grew from this seed showed the widest variation. Every one knows that the cultivated corn bears its pollenate flowers or tassels at the top of the stem, and its pistillate flowers marked by tufts of so-called corn silk-and subsequently, of course, producing the ears-in the axils of the leaves far down on the stalk. Teosinte bears small tassels at the top of each stalk, in competition with the diminutive ones all along down the stalk. But some of the plants of my single-husked corn bore both tassel and silk together at the top of the stalk. Others bore silk and tassel mingled up and down the stalk, like teosinte. The ears of corn that developed sometimes showed clusters of kernels of the size, shape, color, and general appearance of the Kaffir corn. Others bore long tassels with numerous kernels. By selecting among these different types, I have been able to develop races of corn that, I am confident, represent the primitive type, running back to the form of teosinte, and thus clearly enough demonstrating the origin of the plant that occupies so important a place among the present day farm crops, even if the abundant evidence had not already been developed by my own experiments. In the course of a few generations of selective breeding, I had a race of descendants of the single-husked or tunicate corn, three-quarters of the individuals of which produced kernels only at the top of the stalk. By farther selections a race could readily be produced that would bear its kernels exclusively in this location. As a rule the plants that thus produce kernels at the top of the stalk produce no ears in the ordinary location, although a few generations earlier they had produced the grain about equally in the two locations. The chief interest of the experiment lies in the demonstration that our cultivated corn, which now shows the anomalous habit of bearing its pollenate flowers only at the top of the stalk and its fruit on the main stem below, was originally a grass with the characteristic habit of bearing its grain at the top of the stalk, just as other grasses-including wheat and rye and barley, oats, rice, sugar-cane, and Kaffir corn-habitually do to this day. The presumption is that as the corn was developed under cultivation, and evolved a large ear which attained inordinate size and weight, it became expedient to grow this ear on the part of the stalk that was strong enough to support it. Obviously an ear of corn of the modern variety could not be supported on the slender tip of the stalk where the tassels grow. We saw in the case of the potato plant that was grafted on the stem of the tomato, that the tuber-bearing buds might put out from the axils of the leaves under these exceptional circumstances. Just what the circumstances may have been that led to the bearing of its fruit buds exclusively in the leaf axils in the case of the corn, we of course cannot know. But presumably the anomaly first appeared as a "sport", due without doubt to some altered conditions of nutrition, from being placed under unusual environment, and some one had the intelligence to select this sport and breed from it, with the result of developing a race of corn bearing grain on the stalk that gradually supplanted the old form altogether-except, indeed, that the wild teosinte maintained the traditions of its ancestors, unspoiled by cultivation. I may add that the experiment of running the tunicate corn back to the primeval wild type by selective breeding is a much more simple one than would be the attempt to run it forward within a few generations to the plane of the good varieties of cultivated corn, but even this is comparatively easy of accomplishment. To stimulate and accelerate degenerative processes is comparatively easy; to make progress, as civilized man interprets progress, is far more difficult. One reason at least for this is that the qualities that man prizes in a cultivated vegetable are usually not those that adapt the plant to make its way in a state of nature. They are new innovations that to a certain extent run counter to the hereditary tendencies that have been fortified in the wild plant through countless generations of natural selection.
Interesting experiments of another type that I have carried out in recent years have resulted in the development of a variety of corn that has the curious distinction of bearing leaves that are striped with various and sundry colors of the rainbow. The parent form from which this new race was developed, I secured in 1908 from Germany. It was called the quadri-colored corn. Among the plants raised in the first season there were two stalks, and two only, that justified the name, their leaves being striped with yellow, white, crimson, and green. The other plants of the lot bore green leaves like those of other corn plants, and the seeds of even the two best ones reverted. I surmised that the corn was really a hybrid between the common green-leaved dwarf corn and the old Japanese variegated corn, sometimes spoken of botanically as Zea mais variegata. The fact that it was a hybrid stock gave the plant additional interest, however, and I determined to experiment farther with it. The ears of corn themselves gave further evidence of their crossbred origin. Some of them were red both as to cob and kernel, and others bore yellow kernels and white cobs. The stalks varied in height from two and a half to six feet. The best plant of the lot was selected, and from the three ears it bore I raised about six hundred plants. About one-third of these hybrids of the second generation resembled their parent plant in having leaves striped in four colors. The rest reverted to the form of their Japanese grand-parent; a plant with variegated leaves that first came from Japan, and which has been known in this country for the past thirty years. From the best of the quadricolor stalks I took suckers, and developed in this way a good-sized patch of corn from cuttings, perhaps the first cornfield ever raised by this method. All of these suckers being from an original quadricolor plant, of course reproduced the qualities of the parent form, just as we have seen to be the rule with all other plants reproduced by root division or cutting, or by grafting of cions. The method of suckering these plants was to pull down the suckers from the old plants when the young were about one foot high. About two-thirds of the foliage was cut back, leaving the stalk with shortened leaves about two to three inches in length. These were placed in pure sand in a moist place away from the wind for a day or two, but in the bright sun, and after a week when they showed signs of making growth they were transplanted into rows in the field. Unfortunately, the suckering was not done early enough in the season to give all the new plants time to ripen a crop of corn. If they had been planted even three or four days earlier, all would have been well. As it was, only about half or two-thirds of the plants ripened their crop. Of course the plants had been hand-pollenized to avoid danger of vitiating the strain with wind-borne pollen from ordinary corn tassels. To guard absolutely against the danger of cross-pollenizing, if there is any other corn in the neighborhood, it is necessary to cover the tassels with a paper bag while they are maturing and before they are pollenized. Pollenizing is effected by dusting a tassel with its load of pollen against the corn silks; these filamentous threads being of course the pistils of the corn flower. Each thread leads to an ovule that becomes a grain of corn in due course, after the nucleus of the pollen grain has made its way down the entire thread to unite with it. I may add that the corn raised from the suckers proved fully as good in all respects as that raised from originally planted seed, when removed early enough in the season and properly treated, the weight of grain per acre being fully as great. But the stalks were much shorter and more compact than those of the other plants. The object of suckering, of course, was to secure a large crop of quadricolor corn in order that the experiments might be carried out more extensively in the next generation. The attempt was altogether successful. Not only did we secure an abundant supply of the quadricolor, but I found also two stalks among many that bore leaves in which the tendency of striping with varied colors had been greatly accentuated, producing a variety that might be called multicolor corn. In addition to the four colors borne by the other plants, these had stripes of bronze and chocolate, and arranged in far more pleasing manner than in any of the former plants. It was by selecting seed from these plants that I grew in the next generation a number of stalks in which this tendency to multiple striping was accentuated, thus producing a race of corn with leaves beautifully striped in six colors, to which the name Rainbow Corn has been given. In perfecting the variety, nothing further was necessary than to select seed from the plants that showed the most even distribution of the stripes, and the most vivid display of color, as well as uniformity of size and early ripening, as this was a very late maturing variety, even for California. In earlier generations there had been a marked tendency to variation, some plants producing only a single stripe of red, some only a stripe or two of yellow or white. But by rigid selection through several years these variants were eliminated, and a variety produced that may be depended on to exhibit rainbow leaves of a pretty uniform type. My further experiments with this variety consisted of crossing the Rainbow Corn with some of the sweet corns, in the hope of giving to this handsome ornamental plant the capacity to bear sweet corn of good quality. These experiments are still under way, but they give no great promise of immediate success, as the stripe seems to be recessive. A rainbow-leaved corn that bears good edible ears would constitute a notable addition to the very small company of habitants of the vegetable garden that are prized equally for their ornamental qualities and their food product.
EXTRA-EARLY SWEET CORN
My earlier experiments with corn date back to the Massachusetts period when I was developing the Burbank potato. I recall a small success that at the time seemed to me quite notable, gained through a trick in the cultivation of sweet corn, that is not without interest. I had learned the value of a very early sweet corn, and I devised a method of forcing the growth so that I was able to put my corn on the market in advance of anyone else in the neighborhood, and therefore to sell it at a fancy price. Many a time I was able to take a buggy load of corn from Lunenberg, where my place was located, to Fitchburg, and return with $50 or $60 as the selling price of what I could load on a common one horse spring wagon. I had a complete monopoly of the early sweet corn market in the manufacturing city for three or four years, and my early corn brought usually 50 cents per dozen ears, although a week or two later any amount of corn could be bought for a fraction of that sum. One of the secrets was in germinating the corn. I obtained fresh stable manure in the proper season, and mixed this with leaf-mould, about half and half. Corn placed in this when it was moist and warm would germinate rapidly. When the young roots were from two to six or eight inches in length, and the tops had made a growth of half an inch or so, I would plant these sprouted grains in ordinary drills, dropping them in just as corn would be dropped, no attention whatever being paid to the way they fall-whether with roots down or up. A half inch covering of dirt being put over the sprouted grain, it was nothing unusual to find shoots coming through the soil the next morning. And this early start would enable the plants to grow marketable ears at least a week earlier than they would have done had the seed been planted in the ordinary way. The growth of the plants could be further stimulated by placing a small quantity of bone meal, or of a good nitrogenous fertilizer containing a certain amount of phosphorus, in the soil about the roots. Preliminary to this method, I had made extremely useful selections of the earliest-ripening ears for a number of seasons.
EARLY HYBRIDIZING EXPERIMENTS
My experiments of this early period were not confined to methods of germinating and forced cultivation, but included also hybridizing tests. My principal work was in crossing the black Mexican corn, the common sweet corn, and the New England yellow field corn. There was, of course, no difficulty in effecting crossing, but I found it very difficult to fix any good variety. These were the first experiments in this special line ever made with corn. They have of course been duplicated a thousand times since. The most important experiments that I made had to do with crossing the yellow field corn with the Early Minnesota and other varieties of sweet corn, my intention being to produce a sweet corn with yellow kernels. There was a demand for such a variety, and none existed at that time. I succeeded in producing hybrids that combined the yellow color of the field corn with the sweetness of the other variety, but had not thoroughly fixed the new variety so that it would uniformly breed true from seed at the time when I removed to California, in 1875; and this interrupted the corn experiments. In the meantime, however, I had gained valuable lessons in heredity from observation of the crossbred corn. In the second generation numerous fine pure yellow ears were obtained without a trace of white, but a part of the kernels were hard and smooth, and not the wrinkled sweet corn that was desired. In the following generation, when the corn was grown in California, I obtained some first-class ears with almost their entire lot of kernels wrinkled, and was confident that in another year I could have obtained the variety desired; namely, one that would bear exclusively wrinkled or sweet corn kernels of a yellow color. But the pressure of other work led me to abandon the experiments at this stage. There is peculiar interest, in the light of more recent knowledge, in noting the results of these early crossbreeding experiments, as just related. It will be observed that I had no difficulty in obtaining crossbred corn with the yellow kernels of one of the parent forms, but that it was difficult to secure a complete ear of wrinkled sweet corn kernels.
STARCH VERSUS SUGAR
To understand the conditions clearly, it should be explained that the kernel of the sweet corn differs from that of field corn in that it contains a large percentage of sugar in solution, and that the wrinkling of the kernel is the outward sign of this condition. The smooth kernel, on the other hand, is one in which the sugar content has been largely transformed into starch, and deposited in this insoluble condition. More recent experiments have shown that whiteness versus yellowness of kernel constitutes a pair of hereditary characters, in which yellowness is dominant. Similarly starchiness versus sweetness of kernel constitutes another pair of characters, in which starchiness is dominant. This being understood, we can predict with some certainty what will occur when such a cross is made as that of my early experiments in hybridizing the field corn and the sweet corn. The crossbreds of the first generation will have ears with yellow kernels, that are all starchy like the field corn kernels, because yellowness and starchiness are dominant qualities. But the offspring of the second generation will show a certain proportion in which the recessive characters of whiteness and of sweetness reappear. Thus in the second generation we shall have yellow kernels that are starchy, and others that are sweet, and white kernels also of both kinds. And the interest of the experiment is enhanced by the fact that the kernels showing these different characteristics are likely to be distributed on the same ear. In many plant breeding experiments we have no tangible feature to guide us as to the quality of the fruit. Some of the seeds of a hybrid blackberry, for example, may bear factors for thornlessness, while others bear factors for thorns. But this can be shown only when the seeds have been planted and have germinated. In the case of the corn, on the other hand, the qualities of the individual kernels are revealed in the outward appearance of the kernels themselves. The kernel that bears the factors for yellowness will be yellow; the kernel that bears the factor for starchiness will be plump and rounded; and the kernel that bears the factor for sweetness will be wrinkled because of its sugary content. So a glance at the crossbred ear of corn reveals at once the story of its ancestry. So striking is the illustration of Mendelian heredity when yellow field corn and white sweet corn are crossed, as in my early experiments, that recent tests, in which actual count of the different types of kernels has been made, have shown results of mathematical exactness. Thus in an experiment recorded by Mr. R. H. Lock, of Cambridge University, in which a smooth yellow type of corn was crossed with a wrinkled white variety, the grains of different colors obtained from a certain number of ears borne by the plants of the second generation were distributed almost as evenly as if the work had been done by hand by a careful human calculator. The precise result was this: (1) Smooth yellow grains 2,869, or 25.3 percent; (2) smooth white grains 2,933, or 25.7 percent.; (3) wrinkled yellow grains 2,798, or 24.5 percent; (4) wrinkled white grains 2,803, or 24.5 percent. We have seen that the condition of whiteness and the wrinkled condition (due to large sugar content) are recessive traits. Therefore if we plant the wrinkled white kernels we may expect sugar corn, the ears of which will be uniformly of that type. But what we wished to secure, it will be recalled, was an ear bearing only yellow wrinkled kernels. There are as many of these as of the others on the ears of the second-generation hybrids. But they will not all breed true, because yellowness is a dominant factor, and so in a certain number of the yellow kernels the quality of whiteness exists as a recessive trait in hiding, that will reappear in the next generation. All the progeny of yellow wrinkled kernels will be wrinkled because the wrinkled condition is recessive; but only about one in four of these kernels will produce yellow progeny with certainty. And no one can tell from mere inspection which of the four is the pure dominant and which the mixed dominant that will have a certain proportion of white offspring. This, of course, accords perfectly with the results of my experiments, as just recorded. But the new tests, which explain the distribution of kernels of different colors, and enables us to predict the manner of their distribution, give added interest to the earlier observations. I should add, however, that whereas it is usual for the crossbred kernels to show this mixed distribution on a single ear, in more recent experiments, in which the Orange sweet corn and a late white variety were crossed, I have secured a product in which there was a pure white ear that exhibited all the qualities of the orange except color, and in another case a pure yellow ear was produced which showed the characteristics of the late white, including the large number of rows of kernels. This is altogether unusual in crossing yellow and white varieties of corn, and the anomaly is not easy to explain.
BREEDING FOR VARIED QUALITIES
My other experiments with corn have been rather numerous, but have largely been concerned with minor details, such as the development through selection of a corn that will produce ears bearing a large number of rows of kernels. I have been able in three years, working with Stowell's Evergreen Corn, to produce a few ears with eighteen to twenty-two rows to the ear, making it clear that by extending the experiments it would be possible to fix a variety growing uniformly twenty-two rows of kernels. Other experiments have shown the feasibility of changing the form of the kernels, making them long, broad, and of uniform size. Attention has also been paid to the production of corn that would fill out all the kernels uniformly, instead of producing a certain number of nubbins as corn is prone to do. The size of the stalk and the number of ears to the stalk are also matters that are subject to easy modification through selection. I have referred in another connection to experiments of others, in which the location of the ear on the stalk was lowered or raised at will in a few generations, and made to droop or stand erect as desired, through selection. I myself have developed a race of corn with gigantic stalks, in which the ears are borne so high that a man of average height can barely reach them from the ground. This was done for experimental purposes, and not because a variety of this kind would have commercial value. I have personally produced and introduced four distinct new varieties of corn, including the two unique ornamental varieties, and two improved extra early sweet corns, besides several strains that have been greatly improved by selection and then turned over to various seedsmen. Reference has been made also to the experiments through which the kernels of corn were made to produce more protein or more starch, as the case might be. These experiments have practical importance because a corn to be used as fodder should have a high protein content, whereas grain to be used for making starch or for purposes of distillation should have a high starch content. The oil content can also be similarly increased or diminished at will. By selection alone it is possible to modify these qualities, and they can be accentuated, modified, combined or separated through the crossing of different varieties. All in all, the great American cereal offers interest for the plant developer somewhat commensurate with the economic importance of the plant itself. Much has been done, but there is still ample opportunity for the improvement of different varieties, and for the development of specialized new varieties differing as to their sugar content, as to time of ripening, and the like. No plant is easier to experiment with for the amateur, and few plants offer better prospects of interesting developments.
This text is from: Luther Burbank: his methods and discoveries and their practical application. Volume 8 Chapter 1