CHAPTER VII 



ISOLATION 



In a paper on the floras of hill-tops in Ceylon, published in 

 1908 (57), the author drew attention to the great proportion of 

 local endemics — one-eighth of the total number of endemic 

 species — that were to be found upon one only, or upon more than 

 one, of the mountain tops of the south-west of Ceylon. The 

 principal massif (the central) is to the south-west, a smaller to 

 the north-east of it, and there are a number of more or less 

 isolated peaks separate from them, the most isolated being Riti- 

 gala in the north of the island (p. 24). The highest summit, 

 Pedurutalagala, attains 8296 ft. ; Adam's Peak, the best known, 

 is 7353 ft., and is rather isolated at the south-western edge of the 

 central mass. There are ninety-seven well-marked Linnean species 

 endemic upon these mountain tops, with eleven varieties of these 

 or other species, some of which are usually reckoned as indepen- 

 dent species. Of the species upon single mountain tops, there are 

 no fewer than twelve upon Adam's Peak, which is so steep that 

 its summit does not present any great area of vegetation for the 

 last 2000 ft. 



Since the widely distributed species, those that were not en- 

 demic to Ceylon, however localised in Ceylon they might be, were 

 never confined to hill-tops, it was clear that there was, quite 

 probably, some definite force or influence acting to cause these 

 local endemics to exist in the places where they occurred. For a 

 long time, opponents of my views maintained that they were 

 relics of previous vegetation, and in fact this view is still popular. 

 As they occur in general at higher levels than other species of their 

 genera that are found in Ceylon, it was suggested that they had, so 

 to speak, fled up the hills from their rivals. But if they could do 

 this, they must have had a good capacity for internal, physio- 

 logical adaptation, and it seems strange that they could not adapt 

 themselves to staying where they were. And as most of the 

 mountains rise from a central plateau, it seems very remarkable 

 that so many of them should each be upon its own mountain. It 

 seemed to me very probable that each was an endemic that had 

 arisen upon the spot where it was found, and at various times, in 

 conversation and elsewhere, I have suggested that the immediate 



