CHAP. XII.] 
THE AZOEES. 
249 
carried enormous distances. An immense number are specially 
adapted to be cafried by the wind, through the possession of 
down or hairs, or membranous wings or processes ; while others 
are so minute, and produced in such profusion, that it is difficult 
to place a limit to the distance they might be carried by gales 
of wind or hurricanes. Another class of somewhat heavier 
seeds or dry fruits are capable of being exposed for a long 
time to sea-water without injury. Mr. Darwin made many 
experiments on this point, and he found that many seeds, 
especially of Atriplex, 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’ immersion, and this would certainly prevent them being 
floated to very great distances. It is very possible, however, 
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. 1 
1 Some of Mr. Darwin’s experiments are very interesting and suggestive. 
Eipe 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 90 x 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 ; hut 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 cases 
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 afford ample opportunities for successful migration. (See Origin 
of Species, 6th Edition, p. 325.) 
