Page:Popular Science Monthly Volume 17.djvu/383

Rh identical with some from the banks of the lower Congo, can be accounted for on the supposition that the seeds were carried from one place to the other by an ocean-current. This becomes still more reasonable when we find that the equatorial current of the Atlantic sweeps up the west coast of Africa until after it has passed the mouth of the Congo, and then crosses the Atlantic to the coast of Brazil. We find, also, that the seeds of all these plants, common to both coasts, are incased in hard coverings, and are the ones of all others capable of resisting the action of the sea-water.

The many islands of the Pacific Ocean have undoubtedly been planted with the cocoanut-palm by ocean-currents. Growing as it does in close proximity to the shore, and thriving on salt and salt water, the nuts could be easily carried out on the ocean by the tide, and then be drifted miles away from the place of growth.

Mr. Darwin found that, out of eighty-seven kinds of seeds, sixty-four germinated after an immersion of twenty-eight days, and a few survived an immersion in salt water of one hundred and thirty-seven days. He found that ripe hazel-nuts sank immediately, but that when dried they floated for ninety days and then germinated; an asparagus plant with ripe berries floated for twenty-three days, and when dry for eighty-five days, and the seeds when planted germinated. Altogether, out of ninety-four plants, eighteen floated for above twenty-eight days, and some of the eighteen for a much longer period. Estimating the average rate of the several Atlantic currents at thirty-three miles a day, Darwin came to the conclusion that seeds of one tenth of the plants of a flora, after being dried, could be floated across a space of sea nine hundred miles wide, and would then, if driven to a favorable locality, be capable of germination. Seeds have sometimes been found lodged in trees completely protected from contact with the atmosphere. Rocks are known to be lodged in roots of trees, and these, floating on the ocean, are often drifted to islands, and the rocks taken out by the natives. Mr. Darwin thinks that seeds could often effect a lodgment in the crevices with these stones and thus be conveyed long distances.

Captain Mitchell says he passed through a mass of sea-weed, etc., twelve to fourteen miles across, when three hundred miles from the mouth of the Gambia, which, as Dr. Dickie, who noticed the fact, believed, had come from some part of America within the influence of the Gulf Stream. "Besides algæ," says Mr. Bentham, whom we quote, "the portions of this mass picked up by Captain Mitchell and examined by Dr. Dickie contained, among other substances, fruits, seeds, and 'seedling plants several inches long, all with a pair of cotyledons, roots, and terminal bud, quite fresh.'" Even if, as is