Robert T. Morris, M. D.
So far as we know, the hickories, belonging to the Juglandaceae, are indigenous to the North American continent only. Representatives of the group occur naturally from southern Canada to the central latitude of Mexico, in a curved band upon the map, which would be bounded upon the east by the Atlantic Ocean and the Gulf of Mexico, and on the west roughly by the Missouri River, until that river bends east from the eastern boundary of Kansas. From the angle of that bend the hickory runs approximately southwest into Mexico.
The exact number of species has not been determined as yet, because of the open question of specific or varietal differences in some members of the family. Sargent's classification at present includes eleven species: Hicoria pecan, H. Texana, H. minima, H. myristicaeformis, H. aquatica, H. ovata, H. Carolinae-septentrionalis, H. laciniosa, H. alba. H. glabra, and H. villosa. To this list may be added H. Mexicana (Palmer), which so far seems to have been found only in the high mountains of Alvarez, near San Louis Potosi in Mexico; and H. Buckleyi from Texas, which was described once by Durand, and since that time overlooked by writers, excepting by Mrs. M. J. Young in 1873, who included the species in her "Lessons in Botany." Professor Sargent tells me that the Buckley hickory will be included in the next edition of Sargent's "Manual of the Trees of North America." This brings the number of species up to thirteen. In addition we have well marked varieties: H. glabra odorata, H. glabra pallida, and H. glabra microcarpa, making sixteen well defined hickories that have been described.
Nuts of all of these hickories are in the collection of "Edible Nuts of the World" at Cornell University, with the exception of nuts of the varieties H. glabra odorata and H. glabra pallida.
In addition to the sixteen described varieties and species of hickories in America, we have an endless variety of hybrid forms, because cross-pollenization seems to take place readily between hickories of synchronous flowering time.
Five of the hickories: H. pecan, H. Texana, H. minima, H. myristicaeformis, and H. aquatica belong to the open-bud group, while the rest belong to the scale-bud group. The winter buds of the open-bud group resemble the winter buds of the walnuts in a general way, and in artificial hybridization experiments I seem to note a close relationship between the open-bud hickories and the walnuts.
There is no more promising work for the horticulturist than crossing hickories with walnuts, and crossing hickories with each other. Five hundred years from now we shall probably find extensive orchards of such hybrids occupying thousands of acres of land which is now practically worthless. The hickories are to furnish a substantial part of the food supply of the world in the years to come. At the present time wild hickories held most highly in esteem are: H. pecan, H. ovata, H. Carolinae-septentrionalis, and H. laciniosa. Several other kinds have edible kernels, sometimes of excellent character, but not readily obtained except by boys and squirrels, whose time is not valuable. In this group we have H. alba, H. glabra, H. villosa, H. glabra pallida, H. glabra odorata, H. glabra microcarpa, H. Mexicana, H. Buckleyi, and H. myristicaeformis. In another group of hickories with temptingly thin shells and plump kernels, we have a bitter or astringent pellicle of the kernel. This group contains H. Texana, H. minima, and H. aquatica. Sometimes in the bitter group we find individual trees with edible nuts, and it is not unlikely that some of them represent hybrids in which the bitter and astringent qualities have been recessive.
Among the desirable species of wild hickories there is much variation in character, and selection of trees for propagation is in its infancy. One reason for this has been the difficulty of transplanting hickories. Another reason is the fact that hickories do not come true to parent type from seed. A third reason is the length of time required for seedling hickories to come into bearing.
Concerning the first reason, the enormous taproot of young hickories requires so much pabulum for maintenance that when the trees are transplanted, with destruction of root-hairs along with the feeding roots, transplanted stocks may remain a year or two years in the ground before they are ready to send out buds from the top. On this account, the Stringfellow method has in my locality proven of value. This consists in extreme cutting back of root and top, leaving little more than a short club for transplantation. The short club does not require much pabulum for maintenance, and new feeding roots with their root-hairs get the club under way quickly, because there is little useless load for them to carry. The Stringfellow method further includes the idea that stock should be planted in very hard ground, and seems to be practicable with the hickories. The root-hairs which take up nourishment from the soil find it difficult to carry on osmosis in loose soil. The close contact obtained by forcing a way through compact soil facilitates feeding. On this account, autumn is perhaps a better time for transplantation of hickories, in the northern latitudes, at least. Callus forms over the ends of cut roots at all times when the ground is not frozen, and the more complete the callus formation the more readily are feeding roots sent out.
One of the main obstacles to propagation of hickories has depended upon the fact that nuts did not come true to parent type from seed. This is overcome by budding or grafting, and we can now multiply the progeny from any one desirable plant indefinitely. In the South grafting is nearly as successful as budding, but in the North budding seems to be the better method for propagation. The chief difficulty in grafting or budding the hickories is due to slow formation of callus and of granulation processes which carry on repair of wounds.
The propagation of trees from a desirable individual plant can be accomplished also by transplanting roots. A hickory root dug from the ground, divested of small rootlets, cut into segments a foot or more in length, and set perpendicularly in sand with half an inch protruding, will throw out shoots from adventitious buds. In my experimental work with hickory roots, in covered jars, surrounded by wet moss, but with the entire root reached by light, adventitious buds have started along the entire length of the root, and we may find this an economical way for root propagation, dividing up sprouting roots into small segments. The chief objection to this method of propagation as compared with budding is the length of time required for seedling trees to come into bearing, propagation from roots probably requiring the same length of time as propagation from seed, whereas by budding or grafting the bearing period begins very much earlier. Forty-six years ago Mr. J. W. Kerr of Denton, Maryland, planted three pecks of large shagbark hickory nuts, but of the progeny only about twenty were satisfactory, most of the trees bearing inferior nuts. These trees required from thirteen to eighteen years to come into bearing, and young trees that Mr. Kerr purchased from nurseries and planted were twenty-five years old before they began to bear. Others who have planted shagbark hickories and pecans state that nearly twenty years are required for the trees to come into bearing on an average. When budded or grafted the pecan sometimes comes into bearing in two years, and frequently in four years. We may anticipate that other hickories will act analogously.
The hickories prefer rich, well drained soil for best development of nuts, and an abundance of moisture, provided the land is well drained. Many of the hickories, however, are so adaptable to various soils that they often thrive in lands that are sandy, and dry, and almost barren. In the latter case, they have to maintain an enormous root system for feeding purposes, and this is detrimental to good bearing qualities. The mocker-nut, pignut, and hairy hickory, perhaps adapt themselves best to sandy soils. This feature may make them valuable species for planting when one has no other soil, because the stocks can be used for grafting better kinds.
While the hickories prefer neutral or alkaline soil, most of them will grow fairly well even in acid glacial tills. Their preference, however, for neutral or alkaline soils would suggest the use of a good deal of lime in acid soils, when hickories are to be grown in orchard form.
All of the trees in the hickory group are intolerant of shade and of competition with other trees. The more sunlight they can have the better. Most of us are familiar with the hickory tree standing alone in the cultivated field, which bears a heavy annual crop, when the neighbors at the edge of the forest bear sparingly. Hickories in forest growth put their energies into the formation of wood chiefly, and in the struggle for food and light devote very little energy to fruiting.
The best method for cultivation of hickories has been worked out only with the pecan up to the present time. With this species, it has been determined that clean cultivation with plenty of fertilization gives best results, as with apples. It is probable that Stringfellow's sod culture method will come next in order, and will perhaps be most generally used by nut orchardists, because it is less expensive and requires less labor. The sod culture method includes the idea of cutting all grass and weeds beneath the trees, in order to take away competition, allowing these vegetable substances to decompose beneath the trees and furnish food. There is no objection to adding artificial fertilizer, or a still greater amount of vegetable matter.
The enemies of the hickories are not many in the forest, where the balance of nature is maintained, but when man disturbs the balance of nature by planting hickories in large numbers in orchard form certain enemies increase, and must be met by our resources. Fungous and bacterial enemies are beginning to menace some varieties of the pecan in the South, and both in the North and in the South certain insect enemies are becoming important in relation to all valuable hickories.
The bark boring beetle (Scolytus) has been reported as destructive to hickories in some sections, the trees dying as a result of depredations of the larvae of this beetle.
I find a large borer at work on some of my hickories, but have not as yet determined its species. It may be the painted hickory borer (Cylene), or the locust borer. It makes a hole as large as a small lead pencil, directly into the trunk or limbs, and excavates long tunnels into the heart wood. The painted hickory borer is supposed to occur chiefly on dead and dying hickories, but the borer of which I speak is found in the vigorous young hickories in the vicinity of my locusts, which are riddled with locust borers.
In some localities involucre borers make tunnels between the nut and the involucre, interfering with the development of the kernel.
The hickory twig girdler (Oncideres) is abundant in some localities, but not as yet very destructive.
Hickory nut weevils destroy many nuts in some localities, and their colonies increase about individual trees markedly. In such cases, it is important to collect the entire crop each year from a given tree, taking pains to destroy all nuts which contain weevil larvae. These may be selected in a general way by dumping the freshly gathered nuts into a tub of water. Nuts containing weevil larvae will float for the most part, and in order to make sure of the destruction of larvae in the remaining nuts they may be placed in a closed receptacle, and carbon bisulphide poured over them.
One of the bud worms is sometimes very destructive to individual hickory trees which have developed colonies, the larvae destroying the axillary buds, and burrowing into the base of the petioles of leaves.
A new enemy which I found this year for the first time is the Conotrachelus juglandis. This beetle ordinarily lays its eggs in the involucre of the butternut. With the introduction of exotic walnuts, the beetle has changed its habits, and lays its eggs in the herbaceous shoots of walnuts and hickories. The larvae tunnel into the center of a shoot, and destroy it, or seriously interfere with its nutrition.
Among the enemies of the hickory we must not forget the common field mouse, and the pine mouse, which burrow beneath the surface of the ground, and in winter feed freely upon the bark of the roots of the hickories. They have destroyed many thousands of young hickories of various kinds in my nursery, and in digging up roots of old hickories for experimental root grafting I find that mice have been living freely for years upon the bark of some roots.