ON THE MODES OF DISTRIBUTION OF PLANTS. 369 



identical with some from the banks of the lower Congo, can be ac- 

 counted for on the supposition that the seeds were carried from one 

 place to the other by an ocean-current. This becomes still more rea- 

 sonable 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. Alto- 

 gether, out of ninety-four plants, eighteen floated for above twenty- 

 eight days, and some of the eighteen for a much longer period. f Es- 

 timating 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 con- 

 veyed 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 alga?," 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 co- 

 tyledons, roots, and terminal bud, quite fresh.' " || Even if, as is sug- 



* Darwin, " Origin of Species," chapter xii , p. 324. f Ibid., p. 325. 



% Ibid., p. 326. Ibid., p. 326. 



|| Address by Mr. Bentham before the Linntean Society. " Nature," vol. vi., p. 131.. 

 vol. xvii. 24 



