Page - 405 - in The Origin of Species

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