Page:Popular Science Monthly Volume 13.djvu/626

608 carbon, under the influence of solar energies, show a tendency to assume tints other than green. This tendency would, of course, be checked by natural selection in those seeds which, like nuts, are destroyed by animals, and so endeavor to escape their notice; while it would be increased by natural selection in those seeds which, like fruits proper, derive benefit from the observation of animals, and so endeavor to attract their attention. But it is noticeable that fruits themselves are sour, green, and hard, during their unripe stage—that is to say, before the seeds are ready to be severed from the mother plant; and that they only acquire their sweet taste, brilliant color, and soft pulp, just at the time when their mature seeds become capable of a separate existence.

Perhaps, however, the point which most clearly proves the purely functional origin of fruits is found in the immense variety of their structure, a variety far surpassing that of any other vegetable organ. It does not matter at all what portion of the seed-covering or its adjacent parts happens first to show the tendency toward succulence, sweetness, fragrance, and brilliancy. It serves the attractive purpose equally well whether it be calyx, or stalk, or skin, or receptacle. Just as, in the case of flowers, we found that the colored portion might equally well consist of stamens, petals, sepals, bracts, or spathe—so, but even more conspicuously, in the case of fruits, the attractive pulp may be formed of any organ whatsoever which exhibits the least tendency toward a pulpy habit, and an accumulation of saccharine deposits.

Thus, in the pomegranate, each separate seed is inclosed in a juicy testa or altered shell; in the nutmeg and the spindle-tree, an aril or purely gratuitous colored mass spreads gradually over the whole inner nut; in the plum and cherry, a single part, the pericarp, divides itself into two membranes, whereof the inner or protective coat is hard and stony, while the outer or attractive coat is soft, sweet, and bright colored; in the strawberry, the receptacle, which should naturally be a mere green bed for the various seed-vessels, grows high, round, pulpy, sweet, and ruddy; in the rose, the fruit-stem expands into a scarlet berry, containing the seed-vessels within, which also happens in a slightly different manner with the apple, pear, and quince; while in the fig, a similar stem incloses the innumerable seeds belonging to a whole colony of tiny blossoms, which thus form a compound fruit, just as the daisy-head, with its mass of clustered florets, forms a composite flower. Strangest of all, the common South American cashew-tree produces its nut (which is the true fruit) at the end of a swollen, pulpy, colored stalk, and so preserves its embryo by the vicarious sacrifice of a fallacious substitute. These are only a few out of the many ways in which the selective power of animals has varied the surroundings of different seeds to serve a single ultimate purpose.

Nor is any plan too extravagant for adoption by some aberrant species. What seed-organ could seem less adapted for the attraction