26 CONTACTS WITH DARWINISM II [ch. m 



This work fully confirmed the author's doubts concerning the 

 efficacy of natural selection, and the weakness of the explanations 

 that were put forward in its name. He also became interested in 

 endemics for their own sake, for it was becoming evident that 

 upon a correct explanation of them depended much of the proper 

 understanding of what had gone on in the course of the evolution 

 and geographical distribution of plants that had occurred in the 

 earth's past history. 



Work upon endemism has been continued ever since the first 

 experience upon Ritigala, and has led to many interesting results, 

 many of which were published in a book upon Age and Area in 

 1922, and others of which it is hoped to publish in another book 

 dealing with Geographical Distribution only. One of the first 

 interesting points to come out was the very great number that 

 were confined each to one (or more rarely to two or more) of the 

 mountain summits of Ceylon (57). It was shown that over a 

 hundred species were confined to one or more hill-tops. Thus the 

 large tropical genus Eugenia showed E. Fergusonii and E. aprica 

 in the mountains north-east of Kandy, E. cyclophylla and a 

 variety of E. Fergusonii upon Adam's Peak, E. phillyraeoides 

 upon Kalupahanakanda, E. pedunculatus in the Rangala moun- 

 tains, and E. rotundifolia and E. sclerophylla upon the peaks 

 above 6000 ft. The mountains, all rising from a plateau, thus had 

 eight peculiar Eugenias, which one could not figure as being 

 refugees from the plains by way of the plateau (an explanation 

 sometimes advanced). They also contained six endemic Hedyotis, 

 ten Strobilanthes, four Atiaphalis, and so on. Plants like this are 

 usually supposed to be relics of previous vegetation and it was of 

 special interest to notice here what in fact is generally the case 

 throughout the warmer parts of the world. The nineteen genera 

 that show more than one mountain endemic are represented in 

 Ceylon by 268 species, or 14 species per genus against an average 

 representation of 2-7 species, and in the world as a whole these 

 genera contain 4095 species, or 215 per genus, against an average 

 of about 13. They are thus not only very large genera but also 

 genera that make up nearly 10 per cent of the whole flora of 

 Ceylon, and 2 per cent of that of the world. And this is the 

 general rule with regard to endemics, wherever they may occur. 



It looked as if there must be some definite reason for the 

 commonness of endemics upon mountain tops, and I suggested 

 cosmic rays, though mere isolation might be sufficient. 



The mountains of Ceylon thus behaved, in regard to endemism, 



