Popular Science Monthly/Volume 25/August 1884/Hickory-Nuts and Butternuts
THE tall choke-cherry tree in the corner of the meadow, near the hickory clump, is a favorite resort of all the fruit-eating birds in the township for half a mile around in every direction. To the judicious human palate, indeed, the flavor of choke-cherries is not exactly alluring or attractive; they have a disagreeable astringent tinge about their pulp that rather reminds one of alum or borax, and they are not sweet enough or luscious enough to be worth eating by people who have grapes and plums and peaches and apples and a dozen other cultivated fruits at easy command. But to the unsophisticated native birds it is quite clear that choke-cherries are rather a dainty and tooth-some delicacy than otherwise; and one has only to look at the pretty berries in order to see that they deliberately lay themselves out to attract the favorable attention of these winged allies and visitors. The color of the choke-cherry shows at once that it wishes specially to challenge and allure the notice of the passer-by; its sweet pulp and nutritive qualities show that it means them to eat it, and so aid in dispersing its seed. For the actual, final end of the choke-cherry itself, of course, lies in the stone and its inclosed kernel; all the rest is merely the attractive covering which the plant gives in, as it were, to any friendly bird which will be kind enough to assist it in planting out its young seedlings under favorable circumstances for their future welfare. From time immemorial, those choke-cherries which best succeeded in enticing birds to swallow them, and ultimately to scatter their seeds, protected from injury by the hard and horny covering, have left the largest number of offspring to represent them, and so have survived most frequently, in the person of their descendants, through the midst of that perpetual battling competition for the surface of the earth which goes on as fiercely between trees and plants as between men themselves or other animals. To put it briefly in a single phrase, we may say at once that a choke-cherry is one of the kind of fruits which want to be eaten, and sedulously lay themselves out beforehand for that very particular purpose.
But, when we turn from the choke-cherry to the hickory-trees which grow close by, we are brought face to face at once with another and very different state of things. If the choke-cherry wants to be eaten, the hickory-nut clearly wants to avoid that unpleasant and destructive predicament. In the first place, its color, instead of being brilliant and attractive, like that of most edible fruits, is very quiet and unobtrusive, being green while the nut still remains among the fresh foliage upon the branches of the tree, and pale brown when it falls upon the dead leaves and dry grasses that cover the damp and moldering ground beneath. If the hickory-nut were a conscious creature which deliberately wished to escape notice, these are the precise tactics which it would be likely to adopt for the sake of protection. Then, again, even when its disguise is pierced, and the nut, with its outer husk entire, is spied upon the ground by some hungry animal, it is coated with a very nasty, bitter covering, which effectually repels one from tearing it open readily with the teeth. We hand-wearing human beings, however, may perhaps manage to peel off the outer husk with a knife or stone, or, by more popular practice, to put a lot of the nuts together in a wheat-sack and thrash them out by stamping on them with our feet. Even so, however, we still have the actual woody inner nut-shell itself to deal with; and unless we have arrived at that highest stage of civilization where nut-crackers are specially manufactured for us, to aid us in the struggle, we must crack them as best we may with our own precious and too unstable molars. But the native enemies of the hickory-nut—squirrels and the like—can not proceed in any such crunching and radically destructive fashion. They must bore a hole through the shell somewhere, and then extract the kernel little by little with their long, sharp, curved front teeth; and, somehow, the arrangement of the nut inside the shell is of such sort as to render this work of gradual excavation as difficult as possible for the aggressive rodent. The kernel, instead of being all plain and straightforward, as in the acorn or the chestnut, is divided up and frittered away in little troublesome cricks and corners which seem as if they had been invented on purpose to prevent you from getting a single good bite out of the nut in any part whatsoever. Clearly, the hickory-nut is in all these respects the exact antipodes of the choke-cherry: it doesn't want to get eaten if it can by any means possibly help it.
This glimpse at the habits and manners of the hickory enables us to give a brief and intelligible answer to the question. What is a nut? The reply is, a fruit that tries by inconspicuous coloring and hard coverings to escape being observed and eaten. The reason for such a disposition on the part of the nut is easy enough to understand. In the true or succulent fruits—fruits, that is to say, according to the popular and strictly practical sense of the word—the part we eat is not the actual seed itself, the cherry-stone or plum-stone or raspberry-kernels (which even if we swallow we do not digest), but a soft, pulpy covering which has nothing essential to do with the young embryo or future plantlet. In nuts, on the other hand, the part we eat is the actual kernel or embryo itself, with all the starches, oils, and other food-stuffs laid up for its use by the mother-plant. In the simplest and earliest form of seeds, like those of mustard and cress, for example, there is hardly any store of nutriment put away by the mother for the benefit of its struggling seedling. These poorly endowed plantlets have to open their green leaves to the sunlight the moment they begin to sprout, and, unless they can assimilate fresh food from the air immediately under that genial influence, they must die forthwith of pure inanition. But at a very early period in the evolutionary history of plants, some seeds began to be stored at the outset with small quantities of starch or oil, which enabled their budding embryos to push their heads higher above the surrounding vegetation without depending entirely for support on the mere hand-to-mouth system of daily gains. They had, so to speak, a small reserve of capital to live upon. Of course, this gave all such plants a great advantage over their neighbors in the struggle for existence: they could live under conditions where poorer seedlings would starve and die; and so, from generation to generation, those kinds which laid by most material survived the best on the average, till at last in many cases the embryo came to be very richly endowed indeed with starches, oils, gluten, and other valuable collected food-stuffs. This is especially the case with such seeds as wheat, barley, rye, oats, Indian corn, rice, peas, beans, lentils, and buck-wheat.
Unfortunately for the plants, however, what will feed a seedling will feed an animal just as well: and so, exactly in proportion as the plants began to lay by food-stuffs for their own purposes in their embryos, did the animals begin to prey feloniously upon these convenient reservoirs of nutritious gums and starches. Not only does man eat the cereals and pulses, which are the richest in nutriment of almost all seeds, but many earlier and lower animals, such as harvest-mice, rats, chipmunks, deer, antelopes, horses, cow-kind, and even prairie-dogs commit great depredations upon them, both in the wild and cultivated states. Still more particularly have large numbers of animals, such as the squirrels, dormice, monkeys, parrots, nut-hatches, and even many grubs, taken to feeding off the fruits and seeds of forest-trees or woodland bushes. As a consequence, only those richly-stored seeds have for the most part survived which possessed some natural means of defense against their aggressive enemies; and in many instances these means of defense have been multiplied over and over again for still greater precaution, so that the final outcome is a seed almost absolutely fortified against the onslaught of every possible aggressor.
In England, where there are only three native nut-eaters of any importance—the squirrel, the dormouse, and the nut-hatch—most of our indigenous trees have not found it necessary to arm themselves to any large extent against this class of depredators; and consequently there are only three kinds of nuts in the truly aboriginal English flora, namely, the beechnut, the acorn, and the filbert. Chestnuts, walnuts, and horse-chestnuts are cultivated in the British Isles to some slight extent, but they do not thrive, and the two former seldom produce fertile nuts. These three native English kinds, therefore, may be taken as good examples of very simple and undeveloped forms of nuts, far inferior to the most advanced American specimens. The acorn, in all countries, is comparatively little armed with protective coverings: it has only a thin shell, and is guarded from depredations mainly by its slightly bitter taste, as well as by its cup, or saucer, which acts as a barrier against the attacks of insects who try to lay their eggs at its tender base. Beechnuts have a rather more leathery shell, and are externally protected by their prickly husk, which makes them difficult for the delicate noses of squirrels to tackle as they grow upon their native boughs. Filberts, specially exposed to the attacks of the cunning dormouse and the persistent nut-hatch, are far more effectually guarded by a double coat-of-mail: their shell is solid and woody in texture, while their outer husk, which completely envelops them from stem to tip, is thickly sprinkled with stiff and annoying hairs, very painful to our human fingers, and still more so, no doubt, to the tender skin on the naked noses of the inquiring rodents.
None of these nuts belong to the same family as the hickory; they are all independent modifications of totally different forms, which have simultaneously hit on somewhat the same protective method. But on the Continent of Europe, where a larger number of nut-devouring animals are to be found, the hickory tribe is represented by the common walnut. Everybody must have noticed (in conducting his biological studies at dessert) that the distribution of the two lobes which make up the kernel in the walnut is extremely like that of the hickory; and the resemblance is equally close in all other important structural matters. The walnut shows decidedly more protective care in its coverings than any of the few and simple English nuts. Its outer husk is very bitter and nasty—so nasty that even a little of the flavoring matter off fresh walnuts clinging to one's fingers is enough to give a very unpleasant taste to any food one may touch afterward; and the inner shell, though evidently rendered easier to open for the lazy human consumers by being previously kiln-dried to preserve the kernel from decomposing, is in its native state extremely hard to crack, and still harder to bore a hole through with teeth or hill, as any one may easily convince himself by trying to perform the feat with his own canines, or even with the point of his sharp pocket-knife. The walnut, in fact, is one of the hickory tribe, left behind in Europe and Western Asia; it ranges through Greece and Asia Minor, Lebanon and Persia, as far east as Cashmere; and never compelled by circumstances to acquire the very hard and stony coats of some among its American cousins.
In the New World, however, the walnut family has been driven by its pressing animal foes to adopt far more vigorous and active defensive tactics. The great American forests are the very paradise of endless hungry nut-eaters, from the common gray squirrel, the flying-squirrels, and the numerous other greedy rodents of the Northern plains, to the screaming parrots and powerful-billed monkeys of the tropical South American jungles. Where enemies are so numerous and so persistent, only the very hardest and best-protected nuts of all can survive; and so the nearest American representative of the European walnut is the butternut of Canada and the Northern States—a far more formidable and uncompromising mouthful to tackle than its easy-going Old World cousin. The outer husk of the butternut resembles pretty well that of the walnut; but its very stony shell is extremely difficult either to pierce or crack; the sharp ridges on its surface are naturally very baffling to the teeth of squirrels; and even when you have at last made a good hole in it, the inside can hardly be extracted in pieces of any bigness, because of the horny intervening ridges. This American walnut, in fact, is a far 'cuter and smarter form of seed-vessel than its effete European relative. There is every reason to believe, indeed, that the butternut is an advanced and improved descendant of the same primitive geological ancestor as the Greek walnut. Only, while the walnut has been standing still in peninsular Greece and Anatolia for innumerable generations, the butternut has been going ahead with true American impetuosity, inventing one new improvement or modification after another, till it has now attained to almost absolute perfection in its adaptation to its own peculiar walk in life.
Most of the American walnut kind, however, it must be candidly confessed, have not proceeded along the path of progress quite so quickly or so fully as the go-ahead and truly Yankee butternut. The majority of the best-known forms, such as the hickory, the bitter-nut, and pecan-nut, belong to the specially American group known as Caryas with fruits usually smaller and less rich than the regular European walnuts. Even among this restricted group, however, there are some very instructive and interesting differences. For example, the true hickory-nut has a sweet and pleasant kernel, which makes it a great favorite with squirrels and boys. To protect itself against aggression, therefore, on the part of its four-footed foes—as to the boys, it probably despairs—it has acquired a comparatively hard and woody shell, surrounded by a bitter and acrid husk. But its ally, the bitter-nut, has hit accidentally upon a still more excellent and cunning device: it has made the actual seed itself, the menaced kernel, a reservoir for its disagreeable bitter juice. Consequently, it needs much less external protection than the hickory, and every American boy knows well that its shell can be much more readily and easily broken than that of its sweeter relations. Why hickory-nuts should be less protected than butternuts, on the other hand, is a more difficult question; I incline to believe it is because of the greater number produced by each tree annually, so that, in spite of all the havoc wrought by squirrels and other depredators, enough must always have remained and sprouted to keep up the full normal number of the species from one generation to another.
Almost all nuts follow more or less one of these two protective types—the type of the hickory and the type of the bitter-nut—or even sometimes both together. In the tropics, where forestine animals are most developed, the nuts often reach a very high stage of evolution. The cocoanut is a familiar example: it has a soft outer husk, stringy and loose, which breaks and deadens its fall from the tall and graceful palm-trees on which it grows; and inside this yielding, protective mat-work, it has a very solid shell, inclosing the large and richly-stored kernel. But the cashew-nut is, perhaps, the most remarkable in some respects of any known example. It has taken most extraordinary pains to preserve its kernel from injury; and it has done so by a curious combination of the tactics peculiar to attractive fruits with those peculiar to repellent nuts. Its stalk swells out into a fleshy edible tuber, something like a pear in shape, and endowed with all the usual allurements of bright color and sweet taste. By this bribe, it entices the South American monkeys to pick and aid in dispersing its seed. But, at the same time, it carefully wraps up the nut itself in an acrid, pungent covering, and places it at the outer end of the pear-like stalk. Woe betide the adventurous monkey who tries to eat the inner kernel of this decidedly well-protected nut! The pungent juice of the rind not only burns his tongue and lips, but even removes the skin from his mischievous fingers as effectually as it could be removed by a cantharides-plaster. Hardly less quaint are the tactics adopted by the familiar pea-nut of our childhood, which is really the underground pod of a bean-like plant. This secretive vegetable has hit upon the device of producing its seeds on subterranean branches, and so escaping the notice of most open-air birds and mammals; though, in thus cunningly avoiding the Scylla of the upper earth, it has merely fallen against the Charybdis of grubbing pigs and burrowing rodents. The little English subterranean clover—I forget just now whether it grows in America, too, and Dr. Asa Gray's magnificent work is not at hand— has an even stranger plan for escaping from the sheep, on whose favorite pastures it grows abundantly. It flowers above-ground, enticing the bees to fertilize its long, white, tubular blossoms by a copious store of pure and fragrant honey; but as soon as its wee pods have been fairly impregnated with pollen from a neighboring head, it screws its stalk down spirally into the ground, by the aid of some queer little corkscrew gimlets developed near the tip, and so buries the precious seeds well out of all danger from the close-nibbling teeth of its dreaded foes upon the sheep-walk.
Last of all, a few words must be said about the structural homologies of the hickory-nut. In principle, most fruits consist of three separate coats or layers, inclosing the seed or seeds. These three layers are very well seen in the peach, which consists, first, of an external skin; next, of a fleshy edible portion; and, finally, a hard inner covering—the stone—which contains the actual seed, or, as we oftener call it in practical language, the kernel. Now, in the hickory-nut, these three layers are still preserved, though in a very different apparent form: the outer surface, or membrane of the rind, answers to the skin of the peach; the bitter and stringy interior of the rind answers to the edible part of the peach; the nut-shell, or inner hard layer, answers to the stone of the peach; and the nut, or actual seed, answers to the kernel of the peach. This example shows very well by what slight changes in the development of various parts a fruit may seem to practical human eyes quite unlike some other one, which is, nevertheless, at bottom, layer for layer, absolutely identical with it. The only important difference, after all, between the peach and the hickory-nut is, that in the fruit the middle layer becomes soft, sweet, and succulent; while in the nut it becomes stringy, bitter, and nauseating. The almond even better enforces this simple evolutionary lesson; for it is, in reality, nothing more or less than a very dry and stringy peach—a very slightly divergent descendant of the same ancestor: its outer- most layer answers exactly to the peach-skin; its tough, fibrous rind is the. altered analogue of the flesh in the peach; and its nut (which part alone, shelled or unshelled, we generally see at table) is the equivalent of the peach-stone. But if you cut open a young walnut, a young hickory-nut, a young almond, a young peach, and a young plum, you will be surprised to find how exactly they answer to one another, part for part, and how entirely the conspicuous adaptive differences in the mature nuts or fruits are due to small varieties of development in the very latest stages of the ripening process. Pour a little sweet juice into the middle coat of the almond, and it would be a peach; add a little woody material to the cell-walls of the flesh in the peach, and it would be a very decent almond indeed.