80 THE ORIGIN BY MUTATION OF THE ENDEMIC PLANTS OF CEYLON. 



of this island into groups, are given in numerous tables, the study 

 of which will be of great importance to all scientists interested in 

 the subject. 



One of the main results is that the variation in rarity between 

 the different families or groups of families of Ceylon-endemics is 

 small, and goes to show that no one family has any particular ad- 

 vantage over another. In comparing the genera with one another 

 the same rule prevails, independent of the question which genera 

 are chosen and from which point of view the comparison is made. 



The order of rarity: Ceylon, Ceylon and Peninsular India, Wider 

 Dispersal, holds throughout all comparisons with extraordinary 

 regularity. It is obvious that some general law must be underlying 

 these phenomena. 



If the endemic species had originated by natural selection of 

 infinitesimal steps and in response to the local conditions, which are 

 obviously the only conditions that matter when the species first 

 appears, they must have been, from this very origin, better adapted 

 to these conditions than their parent species. According to the 

 theory of natural selection it would follow that they must surpass 

 their forerunners in the struggle for life and soon spread to a higher 

 degree of commonness. But as the table shows, the reverse is true. 

 Yet they have had ample time even for gaining a comparatively 

 wide dispersal. Several recently introduced species have spread to 

 the stage of very common, often in a few years. Tithonia diversi- 

 folia, one of the Compositae, began to spread about 1866 and in 

 1900 was all over the island in damp enough spots. Mikania scandens 

 began to spread ten years ago and is already common all around 

 Peradeniya. Many other instances could be given, since about 60 

 introduced species have become more or less common in the island. 



Of the 809 endemics of Ceylon only 90 are now common- and only 

 19 very common in the island, the remainder are mostly rare or 

 very rare. If they did not conquer their parents and spread into 

 larger areas, it is obvious that they were not especially adapted to 

 the conditions prevailing in the island, and at least not better adap- 

 ted than the species from which they sprung. Or, in other words, 

 that they did not originate in advantageous response to those 

 local conditions. A large amount of facts and considerations has 

 been brought forward by the author in order to justify this conclu- 

 sion. 



These conclusions provide us with a strong argument against the 

 hypothesis of a slow and gradual evolution by small and almost 



