258 



ISLAND LIFE 



PART II 



Beta, oats, Capsicum, and the potato, grew after 100 days' 

 immersion, while a large number survived fifty days. But 

 he also found that most of them sink after a few days' im- 

 mersion, and this would certainly prevent them being 

 floated to very great distances. It is very possible, how- 

 ever, that dried branches or flower-heads containing seeds 

 would float longer, while it is quite certain that many 

 tropical seeds do float for enormous distances, as witness 

 the double cocoa-nuts which cross the Indian ocean from 

 the Seychelle Islands to the coast of Sumatra, and the 

 West Indian beans which frequently reach the west coast 

 of Scotland. There is therefore ample evidence of the 

 possibility of seeds being conveyed across the sea for great 

 distances by winds and surface currents.^ 



Birds as Seed-carriers. — The great variety of fruits that 

 are eaten by birds afford a means of plant-dispersal in the 

 fact that seeds often pass through the bodies of birds in a 

 state well-fitted for germination ; and such seeds may 

 occasionally be carried long distances by this means. Of 

 the twenty-two land-birds found in the Azores, half are, 

 more or less, fruit-eaters, and these may have been the 

 means of introducing many plants into the islands. 



Birds also frequently have small portions of earth on 

 their feet ; and Mr. Darwin has shown by actual experi- 

 ment that almost all such earth contains seeds. Thus in 



^ Some of Mr. Darwin's experiments are very interesting and suggestive. 

 Ripe hazel-nuts sank immediately, but when dried they floated for ninety 

 days, and afterwards germinated. An asparagus-plant with ripe berries, 

 when dried, floated for eighty-five days, and the seeds afterwards germi- 

 nated. Out of ninety-four dried plants experimented with, eighteen floated 

 for more than a month, and some for three months, and their powers of 

 germination seem never to have been wholly destroyed. Now, as oceanic 

 currents vary from thirty to sixty miles a day, such plants under the most 

 favourable conditions might be carried 90x 60 — 5, 400 miles ! But even half 

 of this is ample to enable them to reach any oceanic island, and we must re- 

 member that till completely water-logged they might be driven along at a 

 much greater rate by the wind. Mr. Darwin calculates the distance by the 

 average time of flotation to be 924 miles ; but in such a case as this we 

 are entitled to take the extreme cases, because such countless thousands of 

 plants and seeds must be carried out to sea annually that the extreme eases 

 in a single experiment with only ninety-four plants, must happen hundreds 

 or thousands of times and with hundreds or thousands of species, naturally, 

 and thus aff'ord ample opportunities for successful migration. (See Origin 

 of Species, 6th Edition, p. 325.) 



