CH. Ill] ENDEMISM, AGE AND AREA 27 



just like the separate islands of an archipelago, where again the 

 endemic species behave in this manner, belonging to large genera, 

 with a distinct tendency to differ among themselves upon the 

 different islands. It was, therefore, concluded that there was 

 nothing peculiar in the existence of an oceanic island that should 

 give rise to endemics, other than the qualities that it shares with 

 mountain tops, which show like islands in their possession of local 

 species. "Of these the most obvious is isolation, and we may, 

 I think, justly draw the conclusion that has often been put 

 forward, and say that isolation, as isolation, favours the produc- 

 tion of new forms" (57). 



The study of endemism begun in Ceylon was recommenced at 

 Rio de Janeiro early in 1912, and soon led to the hypothesis of 

 age and area about which many papers and a book (66) were 

 published in the following ten years. By the courtesy of the 

 Editor of the Annals of Botany I am allowed to quote, with 

 modification and omission, from a paper of 1921 (65) a short 

 summary then written: 



Examining on many occasions, from 1896 onwards, the... 

 Flora of Ceylon (46),... I gradually found, somewhat to my 

 surprise, that the strictly local species confined to that island, or 

 endemic species, as we usually call them, which are very numerous 

 in Ceylon, showed on the average the smallest areas of distribu- 

 tion there, whether in the grand total or in individual families 

 (cf. 70, p. 12). On the older view of the meaning of endemic 

 species, which I then held, this seemed a very remarkable thing — 

 that species which were generally looked upon as having been 

 specially evolved to suit the local conditions should be so rare in 

 those very conditions. If these species were specially adapted to 

 Ceylon, therefore, it could not be to the general conditions of the 

 island, but must be to strictly local conditions within its area. 

 There was clearly no difference between island endemics and 

 those of the mainland. Accordingly, still more remarkable did it 

 seem when I came to study in detail the local distribution of 

 these endemic species in Ceylon, and found that, as a rule, they 

 were not confined each to one spot or small region characterised 

 by some special local peculiarity in conditions, to suit which they 

 might have been supposed to have evolved. Not only so, but 

 such spots were frequently to be found with no local species upon 

 them. Only about a quarter of the whole number were confined 

 to single spots, and more than half of those were restricted to the 

 tops of single mountains (57). The remaining three-quarters 

 occupied areas of larger and larger size,* and in diminishing 

 numbers as one went up the scale. . . . The very rare species are 

 as a rule well localised, but the rare and rather rare . . . cover areas 



