Part 18

I see no particular reason why that crop cannot be increased ten, twenty or a hundred fold by just a stimulation of interest in the black walnut. I recall back just previous to World War I, or about that time, there was a tremendous demand, as usual, for black walnut for gun stocks. I happened to be free for a month or so at that time so I could give some attention to the purchasing and delivery of both veneer stock and walnut for gun stocks. It was quite interesting to me as I went over a couple of counties in which I made some purchases, to see that someone in the 40, 50 or 60 years back had had a vision of what the walnut tree would be worth to them on their tracts of land and how we were at that time reaping the harvest of the person who had a vision of the value of the walnut tree. A great many of those trees were trees that had been set or walnuts that had been planted years before by some far-seeing person, and it had gone on without any interruption, probably without the slightest bit of protection, until the time that it was needed and desperately needed for economic purposes.

We have some work going on also in connection with the planting of walnuts in pasture fields. The returns _from the pasture_ in the planting of walnut trees have been just practically the same, maybe a little bit better in favor of the walnuts than where we did not have walnuts in the pasture. This work is being conducted down at the Middle Tennessee Agricultural Experiment Station of the University of Tennessee at Columbia. We are using the walnut tree and also the black locust in this experiment. We don't know what the future of it is going to be, but those walnut trees have grown large enough so that they have had to be thinned to keep them from putting too much shade over the ground.

I made a statement several years ago in the presence of quite a distinguished agronomist or horticulturist that I had never seen a walnut tree growing in the open, whether it was in the blue grass region or outside of a blue grass region that did not have blue grass growing under it. He looked at me askance, and I said, "Do you believe it?" "Well, I don't know," he answered.

So we happened to be coming out of Quincy, Florida, up through southern Georgia outside of the blue grass region, and we were both sitting in the back seat of the car. Our driver drove up to a filling station, and I saw this fellow looked up at a walnut tree over in the yard not very far away, in fact, the next yard to the filling station. I somehow or other sensed what he was thinking. He pushed his door open, got out. I pushed my door open, went around the car and followed him. He walked up to that walnut tree, turned around and said, "Well, it's there." He turned around and walked back.

Now, of course, a condition may prevail in dense shade, where that does not happen in young walnut trees, but I just happened to be right. There is a symbiotic relationship between plants--I don't want to get into that subject--but this one thing I am thinking, and that is that the reason why they were able to get this good grazing from under these walnut trees is that there is a relationship there between those two plants that makes it ideal for the production of pasture grass, and blue grass over a great many of our states is our leading grass.

I might say to the gentleman from Virginia that I had a letter from up there a few days ago. I don't know why they wanted to write to me, wanting to know if the walnut tree was _a legume_. So I presume that that was the reason, that the grass grew very nicely under those trees.

I have taken too much of your valuable time. It certainly has been a pleasure and an honor to be here and talk to you these few minutes. Thank you.

* * * * *

President Davidson: Thank you, Mr. Chance. We will take a short recess.

(Recess taken.)

President Davidson: The meeting will now come to order, please. The embryo development of the black walnut will be illustrated and discussed by Dr. L. H. MacDaniels of Cornell University.

(Paper to appear in next volume.)

Dr. Crane: I was very glad Dr. MacDaniels' paper preceded mine, because it does give you a very much better picture of the development of all of our oily nuts, excepting the filbert and, of course, the almond to some extent. But we take in pecans and the hickories and for the walnuts the situation is quite general.

Now, this paper that I am going to read is one that our staff in nut investigations has been working on for the past twenty or more years, and we feel we know a lot about the growing and the development and filling of nuts. And there is a lot in this paper that I think will be of value to all nut growers regardless of the kind of nuts that we are trying to grow.

The Development and Filling of Nuts

H. L. CRANE, Principal Horticulturist, United States Department of Agriculture, Agricultural Research Administration, Bureau of Plant Industry, Soils, and Agricultural Engineering, Division of Fruit and Vegetable Crops and Diseases.

All nut growers are confronted with the problems involved in the production of nuts of large size with well filled kernels that are "bright" or light colored. Unsatisfactory development and filling of the kernels is more often a cause of complaint by growers than any other single factor affecting nut production. This is because all of our commercial nuts now sold in the shell are priced on a basis of size and the degree to which they are filled. The size and degree of filling of the nuts varies not only from year to year, but from district to district, orchard to orchard, and even in the same orchard, because nuts of one variety may fill well and those of another poorly. This is true even though the kind and variety of nut being produced is grown in a locality usually having suitable climatic conditions for normal nut production.

+Climatic Conditions+

Prevailing climatic conditions in any locality determine how well a particular kind of nut will fill. For example, the pecan is native to the southern part of the United States and a small area in northern Mexico. In its native habitat the summers are long and the day and night temperatures are uniformly high, with little difference between maximum and minimum daily temperatures. When the pecan is grown under conditions of shorter summers, or where there is a marked difference between night and day temperatures, the nuts do not grow to proper size and the kernels fill poorly, if at all. Although pecan trees are quite hardy and may be grown successfully well north of their native limits, the normal development of the nuts and the filling of them cannot be expected there.

Good examples of the climactic effects can be cited. At Davis, California, the pecan tree grows, flowers, and sets fruit satisfactorily, but the nuts fail to grow to proper size, fill poorly, and may not mature before frost. At Davis there is an average length of growing season of 242 days; the day temperatures are high, but the night temperatures are comparatively low. Pecan trees are hardy even in Connecticut, but the trees fail to bear because of the short growing season and the great difference between day and night temperatures. The pecan is truly a hot weather crop and is not suited for culture under mountainous conditions. On the other hand it cannot be grown under subtropical conditions because of insufficient cold during the winter to meet the chilling requirement of the trees. Under such conditions, tree growth starts very late in the spring, and, although the trees may flower, few nuts may set and those that stick may be very poorly filled at harvest if they mature.

The pecan is probably more exacting in regard to its climactic requirements than are our other kinds of nuts, but the filbert or hazlenut is probably a close second in this respect. The filbert, however, represents the opposite extreme in that it does best under conditions of mild winter and moderate summer temperatures. These differences are pointed out for the reason that many amateur nut growers want to grow certain nuts outside of their native range in places where unsuitable climatic conditions prevail, and they cannot understand why success is not possible.

+Growth and Fruiting Habit of Nut Trees+

Since the growth and fruiting habits of our different kinds of nut trees are closely related, it is desirable to point out some of these relationships. All of our different species of walnuts, the pecan and all hickory nuts, as well as hazelnuts and filberts, are borne terminally on shoots of the current season. In other words all walnut species, pecan, and all hickory species bear the pistillate flowers that develop into nuts at the terminal end of the shoots produced the same year that the nuts mature. The staminate or pollen-producing flowers of all these species arise from lateral buds on shoots that grew the previous year. In the case of hazelnut and filbert the pistillate flowers are borne in lateral buds on shoots of the previous season, as are also the staminate flowers or catkins. In this case, however, the pistillate flowers are formed and pollinated before the current year's shoot growth is made. Almonds are borne laterally on shoots produced the previous season. All chestnuts are borne laterally on shoots produced the same season as the nuts.

The chestnut bears most of the staminate flowers separately in staminate catkins whereas the pistillate flowers are in mixed catkins, but all are formed laterally on shoots of the current season. The almond, which has perfect flowers, produces these in lateral buds on shoots of the previous year. Both the hazelnut and the almond flower before any current-season growth is made, whereas all of the other kinds of nut trees mentioned produce almost all normal shoot growth before flowering occurs. These differences in growth, flowering, and fruiting habits provide a basis for the explanation of why growth of almond trees, for example, is harder to maintain than is that of walnut or pecan. Flowering and early development of the fruit before shoot growth is made tend to check such growth, so that flowering and fruiting trees will not make as much new growth as they would have made had flowering and fruiting been prevented.

In general, it can be stated that, in the case of bearing trees, the longer the shoot growth and the greater its diameter in proportion to length, the greater is the number of pistillate flowers that may be formed at its terminal. Furthermore, the set of nuts and the size that they attain are in proportion to the length and diameter of the shoots bearing them. In other words, the number of flowers formed, the nuts set, and the size that they attain are directly correlated with the vigor and growth of the trees. As trees attain age, fewer long, strong shoots and more short, weak shoots are formed. Hence the average size of the nuts produced decreases because of the reduction in average shoot growth. Furthermore, under normal conditions, the degree to which the nuts are filled is related to the vigor as it is measured by the length and diameter of the shoots bearing them. Strong, vigorous shoots usually produce the best filled and earliest maturing nuts.

+What Is a Nut and of What Does It Consist?+

Webster gives a general definition of a nut as "a fruit consisting of a kernel or seed enclosed in a hard woody or leathery shell that does not open when ripe, as in the hazel, beech, oak, chestnut." Technically speaking, it is a hard, indehiscent, one-seeded dry fruit resulting from a compound ovary. In horticultural language the fruit consists of the hard or leathery nut containing a kernel, together with the husk, hull, or bur that surrounds the nut shell. This kernel consists of the embryo plus the endosperm or its remains. In all of our important nuts, such as walnuts, pecans, hickory nuts, almonds, and filberts, the kernel is essentially the embryo with its thickened cotyledons or seed leaves, as the endosperm has been absorbed except for a thin membrane.

At the beginning of its development, growth of the embryo is slow, and in very early stages it is merely a rounded mass of cells. Later, the meristems of the epicotyl (stem or top) and root axis develop, but the whole embryo is still microscopic in size. Still later the cotyledons (seed leaves) start development from the apical meristem and their growth in length is rapid, but they are very thin and follow the contours of the seed coat. Growth in length of the cotyledons may be arrested by unfavorable nutritional conditions during the time of elongation. In such case, the lobes of the cotyledons may not attain the full length of the seed coat, or pellicle, which surrounds them. After the cotyledons have attained full length, growth in thickness begins in the area nearest the epicotyl and proceeds toward the margins. This growth in thickness results from cambium-like meristem with the formation of new cells. The formation of well developed or solid kernels that completely fill the cavity within the shell is dependent upon meristematic activity continuing almost to maturity. The weather conditions, the nutrition of the tree, or other factors that affect the synthesis and translocation of elaborated food materials from the leaves and shoots to the kernels at this time determine the degree to which the cotyledons are thickened, or in other words how well the nuts are filled.

+Periods of Development+

In the development of the nuts there are three periods or stages: (1) The period of growth in size; (2) the period of nut filling or development of the kernel; (3) the period of maturing.

What takes place during these periods of development determines the size the nuts attain, the degree to which they are filled, and finally the quality at harvest. These three developmental stages are interdependent, because the size of the nuts may affect the degree of filling, and that, in turn, the time and nature of their maturity. They are not entirely separate and distinct but overlap in that there is more or less development of the kernel, varying with the species, while the nuts are growing in size. In general, however, there is not appreciable kernel development until after the nuts have attained approximately full size, except in the chestnut.

The outstanding example of this situation is the pecan. There is practically no growth of the kernel until after the shell of the nut has started to become hard. At that time growth of the embryo, which constitutes the kernel, become rapid. The major portion of the kernel is formed during a period of approximately one month, starting at Beltsville, Maryland about the middle of September. The final stages of filling occur just before the nuts mature, and the first nuts to fall usually have the best filled kernels. Later maturing nuts are generally poorly filled; their shells and kernels are often discolored, and the shucks fail to open properly, if at all.

The development of walnuts, hickory nuts, and filberts, so far as is known, is in all essentials the same as that described for the pecan nut except that the kernel or embryo begins to grow somewhat earlier in the season. However, the major portion of the filling, which consists in the thickening of the cotyledons, takes place late in the season, and only a month or a little more before the nuts mature.

The period of the maturing of the nuts generally closely follows the completion of the filling of the kernels. During this period in the pecan, certain other species of hickory, the Persian walnut, chestnut, and others, food reserves are transferred from shucks, hulls, or burs to the nuts. Abscission layers are formed and shucks, hulls, or burs split open on drying out, thus partially or wholly releasing the nuts. There is a very direct relationship between the degree to which the nuts are filled and their time of and normality of maturing; well filled nuts mature early and normally, whereas poorly filled nuts mature late, if at all, and shucks, hulls, or burs fail to open properly.

+Growth in Size+

The size of the nuts produced by a tree is determined by a number of factors, one or all of which may operate during the course of the season. These are: (1) Age of tree; (2) position of the nuts on the tree; (3) fertility of the soil and moisture supply, or the nutritional status of the tree; (4) size of the crop borne.

In general, old trees bear smaller nuts than do younger trees. Hence size of nut for a particular variety is only relative. The first few crops produced by a tree usually consist of nuts large in size for the variety; and then, as the tree attains age, nuts become smaller in size. Young trees make longer and thicker shoot growth than do older trees. There is, then, under normal conditions, a direct relationship between the growth made by a tree and the size that the nuts attain. The more vigorous trees not only produce larger nuts than those produced by less vigorous trees, but the hulls and shells of such nuts are thicker and constitute a higher total percentage of the total weight of the fruit.

The position of the nuts on a tree has an important effect on the size that they ultimately attain. In general, the nuts in the top are larger than those nearer the ground; and those on the strongest and most vigorous shoots of the top or lateral branches will attain a larger size under normal conditions than those located on weaker and shorter shoots or on the inside of the tree. Here again there is a direct relationship between growth of the tree and growth in size of nuts. All normal trees make longer and stronger shoot growth in the top than they do on the terminals of lateral branches, and the shortest and weaker shoots as well as the smallest nuts are generally on the lateral branches inside of the tree top.

Fertility of soil and moisture supply determine in large measure both the growth made by the tree and the size of nuts. The nuts borne on trees growing on fertile soils adequately supplied with moisture are generally much larger in size than those borne by trees on infertile soil or soil poorly supplied with soil moisture. Deficiency of either nitrogen, or moisture, or both is particularly effective in limiting the size of nuts produced. Pecans grown under soil conditions in which both nitrogen and moisture were deficient have been known to attain only about one-fourth the size of nuts of the same varieties grown in the same orchard but under conditions of clean cultivation and supplementary nitrogen applications. A prolonged drought during the time that the nuts are increasing in size very frequently causes them to be much smaller than they would have been had the moisture supply been adequate.

The size of the crop borne by a tree determines in a very large measure the size that the nuts attain at maturity. There is generally an inverse relationship also between the number of nuts borne in a cluster on a shoot and the size they attain. In this respect nut crops are little different from apples and peaches, which, too, are sold on the basis of size. In order to produce fruits of large size having a high market value, the crops are thinned in years of a heavy set of fruit. In the case of pecans, for example, thinning the crop at the time the nuts are growing in size on heavily producing trees is a very effective method of increasing the average size of the nuts allowed to remain on the trees. The earlier the thinning is done the more effective it is; however, it will increase the size of the nuts even when done as late as when the shells have started to become hard. No practical and economical method of thinning the crop of nuts has as yet been found; nevertheless it is well to bear in mind that a large crop borne by a tree generally means reduced average size of the nuts at harvest.

+Filling or Development of the Kernels+

In general, the fruits (nuts) of a nut-bearing tree are what might be termed storage organs. In them are stored mineral elements and such elaborated food materials as carbohydrates (sugars and starch), oil, amino acids, and proteins that have been removed from the leaves and wood of the tree. These materials are stored for future use of the embryo in the nut to sustain respiration, to permit germination, and to maintain the seedling until it has produced enough leaf area to become self-sufficient.

The question may be asked, why is it so important that nuts be well filled? The answer is very simple, because the quality of the oily nuts is determined by how well the kernels are filled. All but one of our most important nuts--almonds, filberts, hickory nuts, pecans, and walnuts--are oily nuts; and well filled kernels contain from 50 to 75 percent or more of oil, depending upon the species. Chestnuts are starchy nuts and contain less than one percent of oil. The relationship between the degree of filling and the composition of the kernel in oily nuts is outstanding, in that the better filled nuts have a higher content of oil and a lower content of protein, carbohydrates, water, and undetermined constituents than do poorly filled nuts. Highest quality of the kernels is directly associated with highest oil content and highest degree of filling. Nut kernels that are poorly filled are often hollow, shrunken, shriveled, and chaffy. When eaten they may taste sweet, but are lacking in the oily flavor characteristic of the particular species of nut eaten. It is only in the best filled nuts that highest quality, flavor, and oil content are found.

The degree to which nuts are filled or how well the kernels are developed at harvest is determined by a rather large number of interrelated factors: (1) Size of crop, or ratio of number of leaves per nut; (2) average size of nuts; (3) condition of leaves; (4) amount of second growth of the trees; (5) size of preceding crop and how well the nuts produced were filled; (6) disease and insect injury to the nuts; (7) weather conditions; (8) heterosis or effect of cross-pollination on embryo size.