CiiAP. XI. MEANS OF DISPERSAL. 331 



sceni to me oj^poscd to tlic julinissioii of such jirodigious geo- 

 graphical revolutions -within the recent period, as are necessary 

 on the view advanced b}^ Forbes and admitted by his many- 

 followers. The nature and relative proportions of the inhab- 

 itants of oceanic islands likewise seem to me opposed to the 

 belief of their former continuity with continents. Nor does 

 the almost universall}' volcanic composition of such islands 

 iavor the admission that they are the wrecks of sunken conti- 

 nents; if they had originally existed as continental mountain- 

 ranges, some at least of the islands would ha^-e been formed, 

 like other mountain-sinnmits, of granite, metamorphic schists, 

 old fossiliferous and other rocks, instead of consisting of mere 

 pih.'S of volcanic matter. 



I nmst now say a few words on -what are called accidental 

 means, but which more properly should be called occasional 

 means of distribution. 1 shall here coniine myself to plants. In 

 botanical works, this or tliat 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 I tried, -with JMr. ]5erkeley's aid, a few experiments, it 

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

 action of sea-water. To my surprise, I found that, out of 87 

 kinds, 6-4 germinated after an immersion of 28 days, and a few 

 survived an inmiersion of 137 days. It deserves notice that 

 certain orders Avere far more injured than others : nine Legu- 

 minoste were tried, and, with one exception, they resisted the 

 salt-water badly ; seven species of the allied orders, Hydro- 

 phjdlaccw and Polemoniace:e were all killed by a month's im- 

 mersion. For convenience' sake I chiefly tried small seeds, 

 without the cajisule or fruit ; and, as all of these sank in a few 

 (laj-s, they could not have been floated across wide spaces of 

 th(^ sea, whether or not they were injured by the salt--water. 

 Afterward I tried some larger fruits, capsules, etc., and some 

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

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

 ber; and it occurred to me that floods might wash down plants 

 or branches, and that these might be dried on the banks, and 

 then liy a fresh rise in the stream be washed into the sea. 

 Hence I was led to dry stems and branches of 9-i ])lants with 

 ripe fruit, and to plac(; them on sea-water. The majority sank 

 quickly, but some, which while green floated for a very short 

 time, when drietl floated nmch longer ; for instance, ripe hazel- 

 nuts sank immediately, but when dried they floated for 90 



