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The fact that more than 13,000 tons of walnuts are now raised annually in California, chiefly for shipment to the Eastern markets, as against 2300 tons raised in the year 1895, suggests, better than any amount of commentary, the growth of this new industry. Part, at least, of the increased popularity of the walnut may be ascribed to the introduction of varieties having thin shells. All Persian, or so-called English, walnuts have relatively thin shells as compared with the American walnuts, but the production of the "paper-shell" varieties puts these nuts in a class quite by themselves. And this matter of the shell is one of real significance from the standpoint of the consumer. A nut like the American walnut, which can be cracked with difficulty, requiring the use of a hammer, can never gain great popularity. The difficulties encountered in extracting the meat of the nut are too great. Contrariwise, a nut that has a shell so thin that it can easily be crushed in the fingers is sure to make its way and to be found more and more generally on the dinner-table. The terms "paper-shell" and "soft-shell" as applied to the walnut are interchangeable. There are now several varieties of walnuts on the market that are generally classified under one head or the other. 'Their name merely refers to the ease with which the nut can be cracked. As to this there is great variation among ordinary walnuts, and the soft-shell varieties also show a good deal of diversity. But the best varieties are so friable that they can readily be crushed in the fingers. In point of fact, the walnut is so variable that it is possible for the plant developer to consult his own wishes in the matter of modifying its shell. I have developed a variety in which the shell became so soft that it could readily be penetrated by the bills of birds; in fact a nut that had a mere rim of shell, being thus comparable to the stoneless plum. There would be no difficulty in maintaining this variety of shell-less walnuts, but its thinness of shell was a disadvantage, and I found it desirable to breed the variety back to a somewhat thicker shell covering, by striking a compromise between the old hard-shell varieties and a nut that was practically without a protecting shell. One of the thin-shelled new walnuts was introduced under the name of the Santa Rosa Soft-Shell. It was produced by the usual method of selective breeding, and in producing it of course other qualities were in mind besides the thinness of shell. In particular, selection was made for early and abundant bearing, whiteness and palatability of meat, and absence of tannin it being tannin which gives the brown color and bitter taste to the older or ordinary walnuts. The perfected Santa Rosa may be depended upon to give more than twice as large a crop as the best specimens of the France variety of walnuts, known as the Franquette. It should be explained, however, that there are two varieties of the Santa Rosa Soft-Shell. One blooms with the ordinary walnut trees, while the other, like the Franquette, blooms two weeks later, generally escaping the frosts that sometimes affect the early bloomer. In producing the new soft-shell, I inspected nuts of the ordinary walnut from many sources. There is great variation among these nuts, and I found some that were almost entirely without shells. One seedling had nuts with the meats half exposed; that is, with shell covering a portion of its surface, suggesting the abortive stone of the little French plum from which my race of stoneless plums was developed. By selection among the seedlings of this almost shell-less walnut, I discovered that a walnut without any shell, bearing simply a husk, could readily be produced. But, as I have just related, the birds were soon aware of my secret, and they taught me that, except for its scientific interest, the shell-less walnut had no value. After that the experiment in walnut breeding was carried on in a different direction, a shell being obviously desirable. In due time I developed two varieties that had the shell of just the right consistency; combining this trait with the habit of early and abundant bearing and excellent quality of the nuts themselves. Cions from these trees, grafted and regrafted, make up the race of true Santa Rosa Soft-Shells. I am informed, however, that trees grown from the seed have been extensively sold as Santa Rosa Soft-Shells, although they may depart very widely from the characteristics of the parent form. In point of fact, the name cannot be applied with propriety to any trees except those that are grown from cuttings, for the walnut is a variable tree and cannot be depended upon to come true from the seed. The original Santa Rosa Soft-Shell, however, was grown from seed, and of course it was necessary in perfecting the varieties to grow successive generations in the same way. The parent tree was a walnut growing in San Francisco. It bore the most valuable nuts of the kind that had even been seen in California. Mr. Alfred Wright first called my attention to this tree about twenty years ago. I found that it bore not only abundantly but regularly, and that the nuts were of exceedingly fine quality, and of relatively thin shell, their chief fault being that the two halves would sometimes separate slightly, leaving the meat exposed to the air, so that the meat did not keep as well as if in a thoroughly sealed shell. The original tree was destroyed soon after my attention was called to it, to make room for a street, but I had secured nuts and had a colony of seedlings under inspection. Among these there was a great variation, giving me good opportunity for selection. Selection being made with reference to all the desirable qualities of the walnut, in addition to thinness of shell, I presently developed a variety that seemed worthy of introduction, and cions and trees from this were sent out under the name of the Santa Rosa Soft-Shell. The nuts of this variety are of medium size, and they ripen about three weeks earlier than any other walnuts grown in the state. The meat is white and most delicious of flavor. The thin shell is also white. The tree bears enormous crops, and about its only defect is that it may, on occasion, be caught by the late spring frosts. But even with this defect, it produces a larger crop of nuts than any other tree that I have seen.


The experiments in which I hybridized the Persian Walnut with the California Black Walnut, producing the tree named the Paradox, have been outlined in an earlier chapter, and will be referred to again in a later one. It will be recalled that this tree has extraordinary qualities of growth, but that it is almost sterile, producing only a few nuts on an entire tree, and these nuts of the poorest quality. Another hybridizing experiment that had great interest was that in which the Persian Walnut was crossed with the Japanese walnut, known as Juglans Sieboldii. The Persian walnut in these crosses was used as the pistillate parent. The first generation hybrids of this cross show a combination of qualities of the two parent species as regards the nuts, which are not borne abundantly. The foliage is much larger, however, than that of either species, the bark is white, and the tree itself is of enormously enhanced growth. It probably makes about twice as much wood in a given period as either of the parent species. The leaves are quite hairy on both sides, even more so than those of the Japanese parent. The branches are inclined to droop. The nuts of the Japanese walnut have an exceedingly hard shell. The meat of the nut, however, is delicious, perhaps equaling that of any other nut, with the exception of some varieties of the pecan. But it is very difficult to get the meats from the shell, as they are usually broken in cracking the nut. There is, however, a form of the Japanese walnut which is so variant that it is sometimes regarded as a distinct species, under the name of Juglans codriformis, but which I think not correctly entitled to this rank, inasmuch as the two forms are closely similar as to general appearance and growth. The chief difference is in the nuts, which in the cordiformis are usually heart-shaped, somewhat similar in appearance to the form of the central chestnut where these nuts grow three in a burr. The nut is exceedingly variable, not only in size but in form and thinness of shell. Some individual trees bear nuts that are six times as large as those borne on other trees in the neighborhood. The shell is much thinner than that of the Japanese walnut, and the meat is of the same excellent quality. I speak thus in detail of this variety of the Japanese walnut, because its qualities are such as to merit fuller recognition than it has hitherto received. The tree is perhaps as hardy as the American black walnut; it is as easily grown, and perhaps even less particular as to soil and climate. The trees are very productive, especially as they grow older. The branches droop under the weight of the nuts. Where other walnut trees bear nuts singly or in clusters of twos or threes, the Japanese walnut tree bears long strings of nuts, sometimes thirty or more in a single cluster. The nuts are thickly set about the axils, the cluster being from six to twelve inches in length.


The cross between the Persian and Japanese walnuts, like that between the Persian and the California black walnut, did not result in producing a tree that had exceptional value as a nut producer. This cross, like the other, seemingly brings together strains that are too widely separated; and while there is a great accentuation of the tendency to growth, so that trees of tremendous size are produced, there is relative sterility, so that a tree sometimes bears only a few individual nuts in a season. But the results were very strikingly different as regards the matter of bearing when the California black walnut was hybridized with the black walnut from the eastern part of the United States. These two trees are more closely related species, and have diverged relatively little. Doubtless the time when they had a common ancestor is relatively recent as contrasted with the period when that common ancestor branched from the racial stem that bore the Persian and Japanese walnuts. Yet the differences between the walnuts of the eastern and western parts of America are sufficient to introduce a very strong tendency to variation. Indeed, the result of crossing these species was in some respects scarcely less remarkable than that due to the crossing of the Persian walnut with the black walnut of California. In this case, as in the other, the hybrid tree proved to have extraordinary capacity for growth. Indeed, I have never been able to decide as to which of the hybrids is the more rapid grower. But in the matter of nut production, the discrepancy was nothing less than startling. For, whereas the first-generation paradox walnut produced, as we have seen, only occasional nuts, the hybrid between the two black walnuts-it was named the Royal-proved perhaps the most productive nut tree ever seen. I have elsewhere cited a tree, sixteen years of age, that produced twenty large apple boxes full of the nuts in a season-so extensive a crop that I sold more than $500 worth of nuts from this single tree that year. And the following year I sold nuts from another tree to the value of $1,050. The nuts were used for seed to produce trees of the same variety. This extraordinary difference between the two hybrids is doubtless to be explained by the slightly closer affinity between the parents of the Royal. Their relationship chanced to be precisely close enough to introduce the greatest possible vigor and the largest tendency to variation compatible with fertility. The parents of the Paradox, on the other hand, were removed one stage farther from each other, permitting the production of offspring of vigorous growth, but bringing them near to the condition of infecundity. They were not absolutely sterile, but their fecundity was of a very low order. The seedlings of the Royal hybrid vary in the second generation, as might be expected, although the variation in size and foliage is less than in the case of the Paradox. The extraordinary range of size, some of the second generation hybrids being giants and others dwarfs, has been elsewhere referred to. It will be recalled that some of these second generation hybrids grew to the height of four feet in the first year, while beside them were others that grow only six or eight inches. One grew five hundred times as fast as another, the nuts from which they grew having been picked from the same tree, and planted the same day side by side. To make sure of securing trees having the traits of the original Royal, it is necessary to grow the trees from grafts either of the first generation hybrid or a selected second generation hybrid showing rapid growth. The number of the latter, however, is sufficient to ensure a reasonable proportion of good trees from any lot of seed; and the Royal has been in general demand as a tree to furnish stocks on which the Persian walnut may be grafted. It is found that on most soils a Persian walnut grafted on roots of the Royal hybrid will produce several times as large a crop as if on its own roots. Moreover the trees under these conditions are relatively free from the blight. The nuts of the Royal hybrid are similar to those of the parents, except that they are larger in size. The very thick shell is objectionable, as already noted. Doubtless the shell can be made thinner by selective breeding, but no comprehensive efforts in this direction have as yet been carried out. The black walnut, in spite of the really fine quality of its nut, has never become an important article of commerce. But there are great possibilities open to it if the shell could be reduced to a condition comparable to that of the English walnut. The nuts borne by the Paradox are intermediate in form and appearance between the types of nuts of its parents. Exteriorly they resemble the Persian walnut, but the shell partakes of the thickness and solidarity of that of the black walnut. In at least two instances among the thousands of second generation Paradox walnut trees that have been grown, the trees produce extra large fine walnuts in abundance. However, both of these are quite thick-shelled, but from their second generation hybrid, which can be multiplied abundantly, good, hardy, thin-shelled varieties may be produced. It is possible that further hybridizations, in which the Royal and Paradox hybrids were themselves crossed, might result in the development of a variety, properly selected, that would retain the good qualities of the Persian nut, and combine these with the size and prolific bearing of the Royal.


The experiment, at any rate, is well worth trying. But, of course, whoever undertakes it must be content to make haste slowly, for the black walnut has not as yet been made to bear in childhood, so to speak, as the chestnuts and some strains of the English walnut now do. But in this regard also there would doubtless be rapid improvement under selection. The actual method of hand-pollenizing is very simple. Nothing more is necessary than to break off the flower bearing branch, just at the right time, and shake it over the flowers of the pistillate parent. Of course one cannot make sure that some of the flowers will not be self-fertilized, but by planting a large number of the nuts, it will be possible to determine from the appearance of the seedlings which ones are hybrids. Also where the trees grow close together, there are sometimes natural hybrids, though I was not aware of this when I made my first experiments, in years 1875-1880. When I made my first experiments at hybridizing the walnuts, I planted the seeds of the entire tree. In the rows of seedlings, I could at once determine which ones were hybridized, as these grew far more rapidly than the others, besides differing notably in general appearance. My first experiment was made with two black walnuts, and it was the success of this that led me to attempt to hybridize the Persian and California walnuts the following year. The hybridization in which the Japanese walnut was used was made a few seasons later. The results, as regards the production of nuts, have been sufficiently detailed. Up to the present no variety of commercial value as a nut bearer has been produced, although the indirect influence of the hybrids on the Persian walnut industry, through their use as stocks, has been quite notable.


There is a very near relative of the black walnut, known as the butternut, that was formerly well-known in most forest regions of the eastern United States. The two trees are of closely similar appearance, and the nuts have the same characteristic thick and corrugated shell. The butternut, however, is oval in shape, whereas the walnut is nearly round. The meat of the butternut is also somewhat richer in quality, and it is generally regarded as superior in flavor. The meat itself, indeed, is by many people regarded as superior to that of any other nut. The difficulty is that the shell, like that of the black walnut, is very thick, making it difficult to extract the meat without breaking it. The butternut thrives generally where the black walnut does. It makes a more spreading tree, but the wood is softer and far inferior for cabinet purposes. There is an Asiatic species, known as Juglans Manschurica, that may be regarded as intermediate in form between the butternut and the black walnut. It rather closely resembles the Japanese walnut in general appearance, but it bears a nut with rough surface like the butternut, and the meat is also similar in quality and appearance to that of the butternut, being superior to that of the black walnut. This tree may be said to form a connecting link between the Japanese walnut, the American black walnut, and the butternut. Possibly it could be used advantageously in a hybridizing experiment that would ultimately blend the strains of these different species.


The idea of growing walnuts commercially is one that has scarcely been thought of in the temperate regions of the United States. Even in regions of the middle and eastern states where the English walnut will grow, it has never been cultivated extensively, and of course this tree is too tender to be profitably grown in the northern states. But the black walnut and butternut, on the other hand, are exceedingly hardy trees, thriving even in regions where the winters are excessively cold. All of these trees, however, require a deep, rich, moist, loamy soil, in order to thrive. Trees that produce wood of such extraordinary hardness of texture, and nuts so stocked with fats and proteins, could not be expected to draw adequate nourishment from impoverished soil. In point of fact, the black walnut and the butternut, in the regions of the United States to which they are indigenous, are usually found growing along the rivers, or in rich alluvial valleys. Any idea that they could be raised to advantage on soil that is too poor to produce ordinary crops of cereals or vegetables, is fallacious. At the moment, there is not demand enough for the black walnut or the butternut to justify the raising of these trees on a commercial scale. It will be necessary to produce new varieties by hybridization and selective breeding before these nuts can be made popular. But, as I said before, there is every reason to believe that a series of experiments looking to the production of improved varieties would be more than justified by the results obtained, and I shall point out in another connection the commercial possibilities of producing lumber trees in this way that make the project doubly attractive. It may be well to call attention to one or two peculiarities of the walnut that should be known to anyone that attempts hybridizing experiments. In particular it should be understood that the staminate flowers of the walnut usually bloom and shed their pollen from one to four weeks before the fruit-bearing nutlets appear. One would naturally suppose, under these circumstances, that the pollen would all be lost and that there could be no crop. But, in point of fact, the pollen appears to retain its vitality for a long time, and even where it has been shed some weeks before the ripening of the pistillate flowers, there may be a full crop. The hand-pollenizer must bear in mind this tendency of the two types of walnuts to mature their flowers at different times. Still, as already suggested, the pollen appears to retain its vitality, and ultimately to be able to effect fertilization even though applied some time before the maturation of the pistils. In France the early spring frosts are likely to be very destructive to the ordinary walnuts, and the French nut raisers have come to depend largely on the Franquette, a variety already referred to. While this variety is in some respects inferior, it has the one supreme quality of not blossoming until the season of spring frosts is over. It blooms perhaps four weeks later than ordinary varieties. This ensures a good crop from the Franquette variety, even in years when others have been damaged by the frost, so that the average production of this variety throughout a term of years may be higher than that of others that in any given season may surpass it. There is obvious opportunity to hybridize this variety with the other varieties of the Persian walnut that blossom earlier, but produce a better crop of nuts. Such crossing would doubtless supply material from which races may be developed that will retain the late blossoming habit of the Franquette, combined with the nut producing qualities of the other parent. We have seen that a tendency to fruit late in the season is usually correlative to a tendency to early ripening of fruit so that late bloomers are adapted to growth relatively far to the north. A late blooming strain of the Franquette walnut might furnish material for the development of a variety of walnuts that will be hardy enough to grow in higher altitudes than those to which the English walnut is now limited. But for the production of real hardy races it is probable that hybridizing with the black walnut-the same cross that produced the Paradox-must be looked to, to supply the foundation for a series of experiments in selective breeding. The pioneer work, indeed, has been done in the production of the Paradox walnut itself. It may reasonably be supposed that further experiments in which this hybrid is used as a parent will lead to the development of altogether new races of nuts that will have economic importance. The entire matter of the development of commercial nuts has only recently begun to attract the attention of the orchardists. There is reason to expect that the developments of the next few generations will be comparable to the progress of the past century in the development of orchard fruits.

-The edible nuts are destined to occupy a far more important place in the dietary than they have ever had before, at all events in the temperate zone. And the walnut is in the van of the new movement.

This text is from: Luther Burbank: his methods and discoveries and their practical application. Volume 11 Chapter 2