322 ON THE ORIGIN OF SPECIES 



period, as are necessitated on the view advanced by 

 Forbes and admitted by his many followers. The 

 nature and relative proportions of the inhabitants of 

 oceanic islands likewise seem to me opposed to the 

 belief of their former continuity with continents. Nor 

 does their almost universally volcanic composition 

 favour the admission that they are the wrecks of 

 sunken continents ; — if they had originally existed as 

 mountain -ranges on the land, some at least of the 

 islands would have been formed, like other mountain- 

 summits, of granite, metamorphic schists, old fossil- 

 iferous or other such rocks, instead of consisting of 

 mere piles of volcanic matter. 



I must now say a few words on what are called acci- 

 dental means, but which more properly might be called 

 occasional means of distribution. I shall here confine 

 myself to plants. In botanical works, this or that plant 

 is stated to be ill adapted for wide dissemination ; but 

 for transport across the sea, the greater or less facilities 

 may be said to be almost wholly unknown. Until 1 

 tried, with Mr. Berkeley's aid, a few experiments, it 

 was not even known how far seeds could resist the in- 

 jurious action of sea-water. To my surprise I found that 

 out, of 87 kinds, 64 germinated after an immersion of 

 28 days, and a few survived an immersion of 137 days. 

 For convenience' sake I chiefly tried small seeds, 

 without the capsule or fruit ; and as all of these sank 

 in a few days, they could not be floated across wide 

 spaces of the sea, whether or not they were injured by 

 the salt-water. Afterwards I tried some larger fruits, 

 capsules, etc., and some of these floated for a long 

 time. It is well known what a difference there is in the 

 buoyancy of green and seasoned timber ; and it occurred 

 to me that floods might wash down plants or branches, 

 and that these might be dried on the banks, and then 

 by a fresh rise in the stream be washed into the sea. 

 Hence I was led to dry stems and branches of 94 plants 

 with ripe fruit, and to place them on sea-water. The 

 majority sank quickly, but some which whilst green 

 floated for a very short time, when dried floated much 



