THE ORIGIN BY MUTATION OF THE ENDEMIC 

 PLANTS OF CEYLON. 



In a recent paper Dr. J. C. Willis has made a statistical study 

 of the flora of Ceylon in order to show that the indigenous species 

 of this island must have been developed by mutation and without 

 any kind of advantageous response to local conditions 1 ). 



It is obvious that the mutation theory wants in the first place a 

 study of those facts which may throw a direct light on the evolution 

 of wild species and that only relatively young forms have a sufficient 

 chance of still living under the same or almost the same conditions, 

 under which they originated. The material, afforded by the flora of 

 Ceylon, is exceptionally rich in this respect and thoroughly well 

 prepared by numerous investigators and especially in the great 

 "Flora of Ceylon" by Trimen and Hooker. 



Ceylon is a comparatively small island (25,000 sq. miles) and has 

 a flora of 2,809 species of Angiosperms, of which 809 are endemic 

 to the island. 



Moreover of the 1,027 genera to which those species belong, 

 23 are confined to Ceylon, and among the 149 families, this is the 

 case with six. Among the endemic genera 17 are represented by 

 one species only, four by 2-3 and only two by a large number. 

 These latter are Doona with 11 and Stemonoporus with 15 species, 

 almost all of which are very rare forms, but distinguished from one 

 another by characters of full specific rank. They give the impres- 

 sion that they may have been formed by what Standfuss has called 

 explosive methods, a number of new species being produced almost 

 at the same time. 



As a rule, the endemic species are rare or very rare. More than 

 a hundred of them are confined to one mountain top or to some 

 very small area in the mountains. 



Many of these occur as a very few individuals, say a dozen or 

 little more, and the places where they can thrive are so small that 



i) J. C. Willis, "The Endemic Flora of Ceylon, with Reference to 

 Geographical Distribution and Evolution in General." Phil. Trans. Roy. 

 Soc. London, Series B, Vol. 206, pp. 307 — 342. 



