22 PRELIMINARY INQUIRIES. 



■^ater ; — according to Forbes' theory their jDresence offers no difficulty at all, so long as any 

 portion of the land remained above the water. 



The preponderance of arboreal over herbaceous vegetation again, is a pecidiarity shared by 

 other lands which are not oceanic — North Ajiaerica, Japan, Ilong Kong. But I am ready to acbnit 

 that the dissemination of such plants may have been to a certain extent due to accidental or 

 occasional dispersion, in which, however, man was probably the chief agent. I do not so much 

 disjjute the fact of occasional colonization having taken place (especially among plants), as I object 

 to the attempt to refer everything to that cause. 



If I am correct in holding that the transformation of old species into new is usually (if not 

 always) effected through the medium of large numbers of individuals, chance colonists, being of 

 course solitary or few in number, would not undergo this change until their numbers had suffi- 

 ciently multiplied. I would, therefore, infer wherever individuals belonging to the same identical 

 species occur in different lands (always excepting polar districts and those where the physical 

 condition is uniform), that their presence is probably due to colonization ; and where the species 

 are representative that there is a presimiption that the land in which they occur must at some 

 former period have been connected ^vith that of the typical sjiiecies. 



