CH. XV] ENDEMISM AND DISTRIBUTION: SPECIES 159 



Australia, while the remaining 15 species of the genus cover 

 smaller ranges. In Dilleiiia, D. indica covers practically the 

 range of the genus throughout Indo-Malaya, while there are 

 many other species covering smaller and smaller ranges within 

 this. In Gymnema, G. sylvestre covers almost the whole range of 

 the genus from West Africa to Australia, whilst in Cissampelos, 

 €. Pareira is found from tropical America through Africa and 

 Asia to the Philippines, almost covering the whole range of this 

 cosmotropical genus. In Najas, finally, N. marina is cosmo- 

 politan, Avhile five other species occupy very large areas, nine 

 occupy areas of moderate size, and seventeen areas of small size. 



Another very frequent case in endemic genera of small area, 

 or in genera with a number of endemic species within a small 

 area, is to have one species occupying a "circle" of some size, 

 and another a (usually) smaller circle touching, or near to, the 

 first, thus giving the impression that the plants occupying it 

 have possibly sprung from some unusually isolated members of 

 the first species, in the case of an endemic genus which has no 

 species covering the range of both. In Ceylon, for example, in 

 the endemic genus Horto?ua, which has three species, H. angusti- 

 folia occurs in the moist plains, and to 2000 feet in the moun- 

 tains, while //. florihunda occurs only in the mountains above 

 4000 feet, and H. ovalifolia is confined to Adam's Peak. Or in 

 the Ceylon endemic genus Schumacheria, S. castaneaefoUa is 

 common to a height of 1000 feet, S. alni folia above that level, 

 and S. angustifolia occupies a tiny circle within the area of the 

 first named, but a long way from S. alnifolia. 



This type of distribution, in smaller circles, usually over- 

 lapping one another to a greater or less extent, Avhile there is no 

 single one covering the whole range, is also very common. To 

 take an example at random from the Indian flora, Christisonia 

 (37, IV, p. 323) has three species in Ceylon, one frequent in the 

 hills, two confined each to one spot (cf. p. 151), three in the 

 Dekkan or the Konkan, three in both Ceylon and South India, 

 and one in Sikkim and the Khasias. None has individually a 

 very large range, yet the genus covers much ground, and there 

 is some overlapping of species. One may see the same type of 

 distribution upon a fairly large scale by taking such a genus as 

 Cyrtandra, whose species are distributed as follows (25, v, i): 



