Volume Number: 1  2  3  4  5  6  7  8  9  10  11  12 




When a boy in Massachusetts, I used to observe the great variation among the native American chestnuts in my father's wood lots. Like most boys I was fond of nuts, and in gathering them I soon learned that there were certain trees that bore large, glossy, rich brown nuts with sweet toothsome meats, and that there were other trees that bore only small, flat, ash-colored nuts of insignificant size and inferior quality. I observed that the trees that bore these seemingly quite different nuts differed also in size and in foliage. And I particularly noted that such variations were not seemingly due to any local conditions, inasmuch as the trees bearing fine nuts and those bearing poor ones might stand side by side. I noted similar variations regarding a good many other trees and plants of various kinds. But I recall that the variations among the chestnuts, and also among hickories and shell-barks, made a very vivid impression on my mind. It seemed strange that trees obviously of the same kind should show such diversity as to their fruit. When, at a later period, I began my experiments in California, I recalled the variable chestnuts, and it occurred to me that a plant showing such inherent tendency to vary should afford an unusual opportunity for development-for by this time I had come to appreciate the value of variation as the foundation for the operations of the plant experimenter. But I had conceived the idea also-as our earlier studies have shown-that there would be very great advantage in hybridizing the best native species of plants with plants of foreign origin. And I had the chestnuts in mind among others when I sent to Japan and Italy and the eastern states for new plants with which to operate. So the very first lot of plants that came to me from Japan (in November, 1884), included twenty-five nuts that I find listed in a memorandum as "monster" chestnuts. The same shipment, it may be of interest to recall, included loquats and persimmons with which some interesting experiments were made; pears, peaches, and plums of which the reader has already heard; and climbing blackberries and yellow and red fruited raspberries that had a share in the development of some fruits that presently attained commercial importance. But perhaps there was nothing in the entire consignment that was destined to produce seedlings with more interesting possibilities of development than the 25 "monster" chestnuts. For the hereditary factors that these nuts bore were to have an important influence in developing new races of chestnuts of strange habits of growth-chestnuts dwarfed to the size of bushes, yet bearing mammoth nuts, and of such precocity of habit as sometimes to begin bearing when only six months from the seed. To be sure other chestnut strains were blended with the Japanese before these anomalous results were produced; but it is certain that the oriental parents had a strong influence in determining some at least of the most interesting peculiarities of the new hybrid races.


That the antecedents of the precocious chestnuts may be clearly revealed, let me say at the outset that the Japanese forms were hybridized with the three other species as soon as they were old enough to be mated, and that the hybrids in turn were crossed and recrossed until the strains had been blended of all the different kinds of chestnuts that could be obtained. These included, in addition to the Japanese species just cited, representatives of the European chestnut in several of its varieties-one of which came from China-and of the native American chestnut of the familiar type; and also the little native species known as the Chinquapin. It is interesting to record that the chinquapin, with its almost insignificant nut, crossed readily with the Japanese species, the mammoth nut of which would seem to place it in quite another class. But, in point of fact, there is apparently a very close affinity between all the different chestnuts. All of them have varied and thus perpetuated forms that more or less bridge the gap between the typical representatives of the different species, and, so far as my observations go, all of them may readily be interbred. In a word, the chestnut furnishes most plastic material for the purposes of the plant developer. Just how I have utilized that material will appear as we proceed. At the time when I received the chestnuts from Japan, there were already at hand trees of the European and American species of various sizes. So soon as the Japanese seedlings were of sufficient size, I grafted them on these European and American trees, in this way being able to stimulate development, and to observe the progress of cions from several hundred seedlings on the same tree. This, of course, is precisely the method I used with my plums and other orchard fruits. The advantages already detailed in connection with the orchard fruits were found to apply equally to the chestnut. The engrafted cions were led to fruit much earlier than they would have done on their own roots; there was saving of space; and it was easy to hybridize the many cions that were thus collected on a single tree. Of course, I was carrying forward numerous experiments with the chestnut at the same time-crossing each species with every other species, so that in a single season there would be a large number of hybrid forms of different parentage. So when two of the hybrids were interbred, the strains of four different species or varieties were blended. Thus a hybrid of the second generation might combine the ancestral strains of the Japanese and European and American chestnuts and of the little chinquapin. Moreover I had opportunity for wide selection among hybrids that combined these various strains in different ways. And for the next generation, I could combine different hybrids or inbreed a given strain or introduce the traits of a different variety as I might choose. In point of fact, all these methods were utilized, and in addition, of course, my usual method of rigorous selection was employed, so that I soon had a colony of chestnuts not only of the most complicated ancestry, but also a carefully selected colony in which none that did not show exceptional traits of one kind or another had been permitted to remain.


Of the many rather striking peculiarities of the new hybrids, doubtless the one that attracts most general attention is the habit of precocious bearing. From the outset my hybrids were urged to early bearing, by the method of grafting and selection, as already noted; and of course I saved for further purposes of experiment only the individuals that were the most precocious. But, even so, I was not prepared to find my seedlings bearing large nuts in abundance in eighteen months from the time of planting the seed. Yet such extraordinary precocity as this was shown by many of the seedlings in the third and subsequent generations. Moreover, if the grafts are taken from the seedlings and placed on older trees, they would produce, although not so abundantly, within six months after grafting. During the past ten years, seedlings have quite often produced nuts, like annual plants, the first year of planting, while growing on their own roots, and when not over twelve to eighteen inches in height. The value of such habits of early bearing, from the standpoint of the plant developer, will be obvious. Ordinarily one must expect, in dealing with nut-bearing trees, to wait for a long term of years between generations. In the case of the hickory, for example, after one has planted the nut, it cannot be expected that the seedlings will bear flowers and thus give opportunity for a second hybridizing for at least ten years, and no large crop of nuts may be produced till the tree is forty or fifty years old. So even two or three generations of the hickory compass a large part of a century. But with my new hybrid chestnuts, generation may succeed generation at intervals of a single year, just as if we were dealing with an annual plant instead of a tree that may live for a century. And of course to this fact very largely I owe the rapid progress of my experiments in the development of new varieties of chestnuts. Not only do the mixed hybrids show this extra-ordinary precocity, but some of them also develop the propensity to bear perpetually. On the same tree may be found at a given time flowers and ripe nuts. Flowers both staminate and pistillate appear on the same tree from time to time, season after season, and in due course the flowers are replaced by growing nuts, so that there is a regular succession month after month. This habit of perpetual bearing, manifested by a tree that ordinarily produces its flowers and in turn its nuts at fixed seasons, is perhaps scarcely less remarkable than the habit of early bearing. Doubtless the two are genetrically associated.


The care of the chestnut seedlings presents no important complications. My general plan in selecting seedlings for further tests is the same employed in the selection of seedling fruit trees. Prominent buds, large leaves, thick, heavy twigs, almost invariably forecast large, fine nuts. There is, however, an exception to be noted in the case of the Japanese chestnut, which has smaller leaves. It is necessary to bear this in mind in dealing with seedlings that have a Japanese strain. It is needless to say that the capacity to select the right seedlings for preservation is highly important, as an element in saving time and expense in the practical development of improved varieties of chestnuts. I have already referred to the saving of time that may be accomplished through grafting the chestnut seedlings instead of waiting for them to develop on their own roots. Unlike most other trees, the chestnut should not be grafted until just before the bark begins to slip in the spring. If grafted much earlier it is necessary to protect the grafts by tying a paper sack over them until they start growth to prevent evaporation; but in every case it is better to wait till shortly before the bark begins to slip. This is unlike the cherry, which must be grafted very early or success is extremely doubtful. When grafting is performed after the bark begins to slip, it is necessary to tie down the bark against the graft with a string to keep it in place, otherwise it rolls away from the graft and union does not take place. If grafting is done at the right time and with reasonable care, it is usually successful. In the main, very little attention has been paid to the chestnut by cultivators of nuts. Until very recently, such chestnuts as have appeared in the market have been gathered from wild trees, or, imported from Europe. Recently, however, the possibility of cultivating the chestnut has gained a good deal of attention and in a certain number of cases orchards have been started. I have introduced three different varieties of hybrid chestnuts, one of them known as the Hale, another as the Coe, and the third as the McFarland, and these have been grafted on ordinary chestnut stocks to form the basis of many chestnut orchards of the southern states. In some cases the roots of the chinquapin have been used as the foundation for grafting, in regions where the ordinary chestnut does not occur. Chestnut orchards have also been started by planting the seed. Reasonable success attends this method, but of course it lacks the certainty of grafting. Now-a-days no one attempts to start an orchard except by grafting. Unfortunately there has developed within very recent years a disease that attacks the chestnut tree and invariably destroys it. The disease at first appeared in the neighborhood of New York City about the year 1904, and it has spread in all directions each year reaching out a little farther, until in 1914 there were very few chestnut trees unscathed within fifty or sixty miles of the original center of contagion. The cause of the disease is a fungus that is perpetuated by minute spores that are presumably carried through the air and that, when they find lodgment, develop in such a way as to destroy the cambium layer of the bark, presently causing the death of the tree. The small twigs of a single branch will often first show the influence of the fungus and the leaves may die and become brown and shriveled on one or two large limbs of the tree when no other part of it is affected. But in the ensuing season the disease is sure to spread, and the tree seldom survives beyond the third year. As yet no way of combatting the pest has been suggested, except the heroic measure of cutting down trees immediately they are attacked, and burning every portion of their bark. In this way it is hoped to limit somewhat the spread of the disease but it is by no means sure that the method will be effective. There appears to be danger that the pest will spread until it has decimated the ranks of the chestnut throughout the eastern United States; and of course there is no certainty that it may not find its way to the Pacific Coast, although the lack of chestnut trees in the desert and plateau regions of the middle west may serve as a barrier. The precise origin of the fungus that causes the disease was not known until the summer of 1913, when it was discovered by Mr. Frank N. Meyer, of the United States Department of Agriculture, that the fungus (which bears the name Endothia parasitica) is indigenous to China. The Oriental chestnut trees have become practically immune to it, however, and it does not destroy them, but merely blemishes their bark here and there with canker spots. No one knows just how the disease found its way to the United States, but it presumably came on lumber brought from the Orient. The appearance of this pest came as a very discouraging factor just at a time when interest in the chestnut as a commercial proposition was being thoroughly aroused. Government bulletins had called attention to the value of its nut and its possibility as a paying crop. But, of course, all expectations were nullified in the regions where the ravages of the chestnut fungus are felt. Fortunately, it appears that some of the hybrid races that bear the Oriental strain are immune to the disease. Observations as to this have been made very recently by Dr. Robert T. Morris, of New York. Reports show that hybrids between the Japanese chestnut and the American Chinquapin are peculiarly resistant. The chinquapin itself is at least partially immune to the disease, but of course this plant bears a nut that is too small to have commercial value. The hybrids, however, in some cases are said to retain the good qualities of the chestnut tree combined with the capacity to bear large nuts acquired from their Oriental ancestor. It is obvious, then, that here is another case in which the introduction of new blood from the Orient may be of inestimable value. The loss of our native chestnuts is indeed a calamity, but it is a calamity that is not irreparable. We may have full assurance that new chestnut groves will spring up in the wake of the pest. It is obvious that the quick growing chestnut offers great advantages for such reforestration. The probability that these will prove immune to the pest gives them added attractiveness. If, however, the existing varieties should prove not to be immune, it will be necessary to develop resistant varieties. For it is obvious that the cultivation of the chestnut will not be abandoned merely because it has met with an unexpected setback. It has already been pointed out that the chestnut has exceptional food value on account of its high percentage of starchy matter. It therefore occupies a place in the dietary that is not held by any other nut. So there is an exceptional incentive to reintroduce the trees in devastated regions.


Possibly the coming of the chestnut plague, even though it has resulted directly in the destruction of the entire chestnut groves throughout wide regions, may be a blessing in disguise, as it may make it necessary to bring the chestnut under cultivation in order to preserve the nut at all, whereas in the past it has grown so abundantly in the wild that little attention has been paid to it. Accounts of the destruction of the trees have doubtless brought the chestnut to the attention of many people who hitherto have never given it a thought. The value of the chestnut as an ornamental tree and its possibilities as a nut producer will perhaps be more fully appreciated than they otherwise would be on the familiar principle that blessings brighten as they take their flight. And it may chance that the tree will be placed under cultivation so generally as to be more abundant twenty-five or thirty years from now in the devastated regions than it would have been if the chestnut blight had not appeared. In any event it seems now at least as desirable as ever before to urge the value of this tree both for ornamental purposes and as a producer of commercial nuts, and the rules for the development of chestnut orchards that have been given by the Department of Agriculture may be reviewed to advantage. Even if people living in the infected district are slow to take up the cultivation of the chestnut, the orchardists of other regions may advantageously do so. For I repeat that it is not supposable that the coming of a fungoid pest will be permitted to exterminate one of our most valuable native trees. In developing a commercial chestnut orchard it is obviously desirable to graft with the improved varieties. Quite aside from the matter of producing trees that are immune to the fungus pest, the orchard may be made far more productive if grafted with foreign stock than if the native species were used. And of course my new hybrid varieties offer attractions that excel those of any other variety of chestnut. Some of my seedlings, for example, produce nuts two inches in diameter, each weighing an ounce or more; and these are borne in clusters of from six to nine nuts to the burr. It is notable, however, that the excessively large nuts are usually lacking in flavor; although the reasonably large ones are of the best quality. These hybrid varieties graft readily on the native stock. They may be counted on to bear abundantly in their second season. It may be well, however, to pick off the burs as soon as formed during the first year or two, in order that the energies of the tree may be given over to the production of branches. Even where the blight has destroyed the chestnut, the sprouts that spring up everywhere about the stumps of the trees may be grafted and trees of more satisfactory shape than the old ones and far more productive may thus be developed in the course of a very few years. Where the chestnut orchard is developed from the seed or by transplanting seedlings, it is recommended that it should be located on a well drained gravelly soil. The trees thrive well on rocky hillsides, and even on rather poor sand, but observation has shown that they are somewhat uncertain of growth on stiff clay soils in the east, although Italian chestnuts in California are said to thrive on heavy clays. In general, the experts consider it more important to have a thoroughly drained soil than soil of a particular character. The authors of the Government Bulletin that has urged the merits of the chestnut as a commercial crop show that the chinquapin chestnuts are practically free from the blights that have hitherto menaced the American species. It will be recalled that my new varieties were developed on the foundation of stocks imported from Japan. It will also be understood, as a matter of course, that my selections with this tree as with all other plants have been made always with an eye to the exclusion of any races that showed susceptibility to fungus pests of any kind. As an illustration of the care with which these selections were made, in the development of the perfected varieties, I may note that in various instances only three or four seedlings were selected out of a company of ten thousand. I may add that orchards made by grafting cions of these improved hybrid chestnuts on ordinary American stock have proved enormously productive. It has been estimated that rocky and otherwise useless hillsides may be made productive, where practically nothing else could be grown that would be of special value.


In continuing my experiments in developing the chestnut, I have endeavored to effect wider hybridizations. In particular I wish to cross the hybrid chestnut with the evergreen golden chestnut (Castanopsis chrysophylls) of California, but the wild trees of this species are so distant from my grounds that I have not found it feasible to gather their pollen, and the ones I have under cultivation, although fifteen years of age, have not yet blossomed. This golden chestnut is a very remarkable species. On the heights of the Sierra Nevada mountains it grows as a shrub only four or five feet tall, much branched. These shrubs produce nuts quite abundantly. Along the coast the same tree grows to a height of 150 feet, with an immense trunk. One can scarcely believe that the little bush and the gigantic tree are of the same species. In point of fact there is a considerable difference in the constitution of the two varieties, the giant from along the coast being rather tender, while the bush-like mountain form is very hardy. Being an unusually ornamental evergreen the mountain variety should be extensively planted in cold climates. I am inclined to believe that the golden evergreen chestnut and the chestnut oak could be combined by crossing. If so, remarkable trees could be produced. As yet, however, I have not been able to attempt this hybridization, nor, indeed, have I as yet hybridized the golden chestnut with the ordinary chestnut, for the reason above stated. I have made tentative efforts, however, to cross my early bearing hybrid chestnuts with the California tanbark or chestnut oak, Quercus densiflorus. Notwithstanding the wide difference between the species, numerous nuts were produced and it seems probable that these were hybrids. As to this, however, I cannot be certain until the seedlings have come to maturity. The object of such wider hybridizing is, in particular, merely to test the possibilities of crossing a plant that shows a high degree of inherent flexibility. But it is also desirable for practical reasons to accentuate the variability and to carry forward further series of experiments in selective breeding. There is a great difference among the different chestnuts as to the amount of their sugar content. In some species the starch is so little transformed that the nuts are scarcely edible unless cooked. In others there is an abundant sugar content the nuts being sweet and palatable. Of course I have had this matter in mind in developing my hybrid varieties. But there is still opportunity for improvement. It is also desirable to reduce the amount of tannin contained in some of the chinquapin varieties. Some of the chinquapin varieties also have the habit of holding the leaves during the winter, giving the trees a very untidy appearance. Seedlings that show this tendency should be avoided in making selection.


Of course it is elementary to say that the nuts should be selected for dark, rich, glossy brown color, for tenderness of flesh, and for productiveness. Of my three introduced varieties, all were early and abundant bearers, but one was particularly notable for its earliness, and another for its combination of good qualities. Doubtless the feature that is next in line of improvement in the development of the chestnut is the bur itself, which should be made spineless. In the wild state, the chestnut needs a spiny bur to protect it from squirrels and birds. It has developed this protective covering through natural selection, just as the walnut has developed its thick coat filled with bitter and astringent juices. But the cultivated chestnut does not require the protective spines, and it will be obviously advantageous from the standpoint of the cultivator to have these removed. I have for some years been working on the hybrid chestnuts with this in mind. I now have one variety that is relatively spineless, its burs not having more than one spicule where the ordinary chestnut bur has ten. There is every reason to expect that in a few generations more I shall develop a chestnut that has a bur as smooth as that of the walnut. The partially spineless variety that I have developed has nuts that are not as large or as good in quality as could be desired. But for the moment I am selecting it solely with reference to the removal of spines; being confident that once this is attained there will be no difficulty in breeding the good qualities of the hybrid nut into the combination. The new partially spineless variety has been developed merely by selection from a hybrid seedling that produced nuts showing a tendency to have fewer spines than ordinarily. Of course the tendency to vary in this regard was accentuated by hybridization just as were other tendencies. Or, stated otherwise and a little more technically, the hybridization has made possible the segregation of hereditary characteristics, bringing to the surface factors for spinelessness that no doubt have been transmitted as recessive traits for a very large number of generations. Doubtless there was a time when the chestnut did not have a spiny bur. So my spineless variety, when perfected, will represent a remote reversion, or the bringing to the surface of a tendency that has long been submerged. No doubt difficulties will be involved in perfecting the race of chestnuts with smooth burs similar to those that attended the development of the thornless blackberry and the spineless cactus. But there is reason to expect that the same measure of success will be attained with the chestnut that was attained with the other spine bearers. A nut that combines all the good qualities of my hybrid early bearing chestnuts and in addition is born in a spineless bur would have a combination of qualities that should appeal to the orchardist, and doubtless will do so when the idea that nuts may form valuable commercial crops gains wider vogue.

This text is from: Luther Burbank: his methods and discoveries and their practical application. Volume 11 Chapter 4