Page:Popular Science Monthly Volume 17.djvu/382

368 convoluta, one of the Lycopodiacecæ, and a native of South America, has the same strange habit; for, when the ground where it grows becomes parched and dried up, it curls itself up in a ball, loosens itself from the earth, and is then whirled along over the ground by the wind. When it reaches a place suitable for its growth it uncurls itself, takes root, and flourishes till its new home dries up, when it betakes itself in the same manner to a new locality.

The brief but violent hurricanes of the tropics, which sweep over the land, uprooting trees, overturning houses, and leaving death and desolation behind them, would contribute greatly to a wide dispersion of seeds which would otherwise be but slightly distributed. The tornadoes and cyclones which not infrequently visit the temperate parts of North America would also act a part in this work. An account given by Humboldt shows a possible means of transport over high hills or even mountains. He says "M. Boussingault and Don Mariano de Rivero saw in the middle of the day, about noon, whitish, shining bodies rise from the valley of Caracas, to the summit of the Scilla, five thousand seven hundred and fifty-five feet high, and then sink down toward the neighboring seacoast. The movements continued uninterruptedly for the space of an hour, and the objects, which were at first taken for a flock of small birds, proved to be small agglomerations of straw or blades of grass. Boussingault sent me some of the straws, which were immediately recognized by Professor Kunth for a species of Vilfa (V. tenacissima), a grass which, together with Agrostis, is very abundant in the provinces of Caracas and Cumana."

Let us now turn to another method of transport. As we have seen that, as a general thing, only light seeds, or those with a feathery appendage, are capable of being distributed by the wind, so we shall find that the ones dispersed by means of ocean-currents are of an entirely different character. This must necessarily be the case; for those capable of resisting the action of sea-water for a long time must be inclosed in hard shells. The Gulf Stream, that river of the ocean, is of great use in this work. By its means, seeds of Entada scandens, and other plants of the West Indies and tropical America, are annually thrown upon the shores of Ireland, Scotland, Norway, and even as far north as Spitzbergen. That many of these seeds would be capable of germinating, and of continuing to thrive if the climate were suitable, there can be no doubt. A plant of Guilandina bondue, one of the Leguminosæ, was raised from a seed cast on the west coast of Ireland. Logs of wood and bodies of Indians, which had been conveyed by ocean-currents from the West Indies, have been cast on the shores of the Azores and Madeira Islands. A Sapindus saponaria, the common soap-berry tree of the West Indies, was raised from a seed found on the south shore of one of the Bermuda Islands. The fact already noticed, of some of the plants on the coast of Brazil and British Guiana being