MEANS OF DISPERSAL. 3g3 



facts are opposed to the admission of sncli prodigious geo- 

 grapiiical revolutious within the recent period, as are 

 necessary on the view advanced by Forbes and admitted by 

 his followers. The nature and relative proportions of the 

 inhabitants of oceanic islands are likewise opposed to the 

 belief of their former continuity of continents. Nor does 

 the almost universally volcanic composition of such islands 

 favor 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 havo 

 been formed, like other mountain summits, of granite, 

 metamorphic schists, old fossiliferous and other rocks, in- 

 stead 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 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 facilities 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 in- 

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

 that out of eighty-seven kinds, sixty-four germinated 

 after an immersion of twenty-eight days, and a few 

 survived an immersion of 137 days. It deserves notice 

 that certain orders were far more injured than others: nine 

 LeguminosaB were tried, and, wdth one exception, they 

 resisted the salt-water badly; seven species of the allied 

 orders, Hydrophyllaceae and Polemoniacea;, were all killed 

 by a month's immersion. For convenience sake I chiefly 

 tried small seeds without the capsules or fruit; and as all 

 of these sunk in a few days, they could not have been 

 floated across wide spaces of the sea, whether or not they 

 were injured by salt water. Afterward 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 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 branches of 

 ninety-four plants with ripe fruit, and to place them on 



