CHAPTER III 



CONTACTS WITH DARWINISM, continued. 

 ENDEMISM, AGE AND AREA 



JtIaving by this time (1902) completely thrown over natural 

 selection as the chief mechanism of evolution, the author's next 

 piece of work was a study of the remarkable flora of Ritigala 

 mountain, lying isolated in the flat "dry" zone of Ce^don, in 

 which little or no rain falls for the almost six months of 

 the southwest monsoon. A note on the flora had already been 

 published by Trimen (45). The mountain, over 2500 ft. high, falls 

 with a steep cliff to face the south-west wind, and the summit, 

 of but a few acres, receives rain during that monsoon, thus 

 forming an outlier of the "wet" zone flora, which otherwise only 

 begins upon the mountains about 40 miles away to the south. 



The flora of Ritigala summit, of over 100 species, contains one 

 or two which are quite local to it, or endemic, in the botanical 

 sense. The rest of the plants are largely to be found in the wet 

 zone, but not in the intermediate country, which is at a much 

 lower elevation, and is shown by geological evidence probably to 

 have been dry since the Tertiary period. 



Endemism, about which the writer has published a good deal of 

 work, is, it is hardly too much to say, a crucial feature upon whose 

 proper explanation largely hangs niuch of the whole matter of 

 evolution and of geographical distribution. The best known 

 endemic of Ritigala is Coleus elongatus Trim. (46, and Plate 74), 

 easily distinguished by having a calyx of five equal sepals instead 

 of one of two lips, and by having a pendulous cymose inflorescence 

 of five stalked flowers, in place of the sessile bunch of five flowers 

 that is the usual thing in Labiatae. There also occurs upon the 

 summit the closely related C. barbatns, widely distributed in 

 tropical Asia and Africa, and upon the natural selection theory 

 the most "successful" of all the Colei, but here growing together 

 with C. elongatus the most "unsuccessful", and in the same way, 

 upon open rocky places. Why was this so, upon the hypothesis of 

 natural selection? No satisfactory answer could be given by its 

 supporters, and they were obliged to bring in two supplementary 

 hypotheses, which were mutually contradictory. Some said that 



