MEANS OF DISPERSAL 405 



ocean, — these and other such facts are opposed to the admis- 

 sion of such prodigious geographical revolutions within the 

 recent period, as arc necessary on the view advanced by 

 Forbes and admitted by his followers. The nature and rela- 

 tive proportions of the inhabitants of oceanic islands are 

 likewise opposed to the belief of their former continuity with 

 continents. Nor does the almost universally volcanic com- 

 position of such islands favour the admission that they are 

 the wrecks of sunken continents; — if they had originally 

 existed as continental mountain ranges, some at least of the 

 islands would have been formed, like other mountain sum- 

 mits, of granite, mctamorphic schists, old fossiliferous and 

 other rocks, instead of consisting of mere piles of volcanic 

 matter. 



I must now say a few words on what are called accidental 

 means, but which more properly should be called occasional 

 means of distribution. I shall here confine myself to plants. 

 In botanical works, this or that plant is often stated to be ill 

 adapted for wide dissemination ; but the greater or less facili- 

 ties for transport across the sea may be said to be almost 

 wholly unknown. Until I tried, with Mr. Berkeley's aid. a 

 few experiments, it was not even known how far seeds 

 could resist the injurious action of sea-water. To my sur- 

 prise I found that out of 87 kinds, 64 germinated after an 

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

 137 davs. It deserves notice that certain orders were far 

 more injured than others: nine Leguminosae were tried, and, 

 with one exception, they resisted the salt-water badly ; seven 

 species of the allied orders, Hydrophyllacede and Polemo- 

 niacere, were all killed by a month's immersion. For con- 

 venience' sake I chiefly tried small seeds without the cap- 

 sule or fruit; and as all of these sank in a few days they 

 could not have been floated across wide spaces of the sea, 

 whether or not they were injured by the salt-water. After- 

 wards I tried some larger fruits, capsules, &c., and some of 

 these floated for a long time. It is well known what a dif- 

 ference there is in the buoyancy of green and seasoned tim- 

 ber ; and it occurred to me that floods would often wash into 

 the sea dried plants or branches with seed-capsules or fruit 

 attached to them. Hence I was led to dry the stems and 



