Some Unique Examples of Dispersion of Seeds and Fruits

IN the driftwood stranded here and there along streams may often be found dry, three-celled fruits of the bladdernut an inch and a half in diameter, brown and light, tough and water-tight. The seeds are very hard and smooth, enabling them, if kept in the water, to remain uninjured for a long time. But the ability to float on the water is not its only means of dispersion. Many of the dry pods hang on until winter, rattling in the wind. On falling, a portion remain near the parent bush and are liable to be carried away the next time the creek overflows its banks; others are moved by the wind, and perhaps again by the water, and still others may be drifted for long distances, even on an up grade, if there chances to be snow on the ground. Here, among the rubbish in spring, are some shriveled wild grapes, which missed a golden opportunity of being eaten by certain birds which could not digest their bony seeds; but they have in reserve another mode of transportation, not by wing of bird, but by floating on water. Clean grape seeds will sink at once, but when covered by the dry skin and pulp they float. In a similar manner the dry seeds of several dogwoods are often eaten by birds for the pulps, but if not eaten they behave after the manner of grapes with dry, wrinkled skins. Narrow-leaved dock is a prominent weed, and is especially at home along ditches and river bottoms. On the back of each dry persistent sepal is an ovoid, pithy or spongy tubercle, all of which are not exactly life-preservers, but they are the next thing to it. The naked achene sinks at once when free from everything else, but when encased in its dry calyx it floats on the water.