Page:Popular Science Monthly Volume 30.djvu/625

Rh to innumerable flocks of birds in all parts of the world. But it makes a great difference to the plant species whether a bird prefers a fruit for its flesh or for its kernel. The yellow thrush and cherry-finch are both fond of cherries—one for the sake of their juicy envelope, the other for the piquant meat of the pits. In the latter case harm comes to the plant; in the former case good. The colored, fragrant, sweet-tasting berries are there to be eaten, and that principally by birds, while the seeds pass out undigested and with vitality unharmed, but rid of their coverings, which would have to be consumed by decay if not eaten, and thereby, in some cases, even better adapted for planting and growing than before.

The birds in this way contribute much to the distribution of plants. For the appetizing reward which they enjoy, they afford the species, if not the single tree or plant, the most important service; and when we say that this bird damages the cherries and that one the grapes, we speak from a selfish point of view that which is fundamentally false, for the birds are ultimately useful to the plants. The Smyrneans call the rose-starling the devil's bird when it visits their fruit-trees in July, and forget that they welcomed the same bird as a saint when it cleared away the locusts in May.

Swallowed seeds undergo a superficial change in their passage through the digestive apparatus, which is, however, not detrimental, but rather, like the maceration which the gardener gives to his seeds, only favorable to their vegetation. Acorns which the nut-hatch has macerated in its crop, when dropped, are much surer to grow than those which the forester plants. Some plants are absolutely dependent on birds for their diffusion, and a kind of mutualism exists between the two—one of those remarkable phenomena in which very different kinds of beings are reciprocally advantageous and adapted to one another. A carious example of such adaptation is seen in the case of the mistletoe and the mistle-thrush. The mistletoe, a parasite of trees, is green and evergreen, though few other parasitic plants are so colored; and the color does not perform the same office to the mistletoe as the green of other plants, for this plant derives its nourishment directly from the sap of the tree on which it is growing without the help of chlorophyl. But it has its uses, one of the chief of which is to attract the thrush to itself. Its fruit-bearing time is when the host-tree has shed its leaves, and it, being all upon the trunk that is green, is conspicuous. Its fruit, a berry, inclosing the seeds in a tough, adhesive envelope, is eagerly sought by the thrush, which can recognize it from a distance by means of the sign it throws out. The seeds hang by their sticky gum to the bird's bill after the fruit has been eaten, and the bird, to remove the nuisance, is obliged to rub its bill against the bark of the tree. This enables the seeds to plant themselves in the crevices of the bark, which afford just the soil they need to sprout and grow in.