260 



If the flora of Transcaspia originated thus from species 

 which at the end of the tertiary period or the beginning of 

 the quaternary period immigrated from the neighbouring 

 mountains, it is natural to expect that many endemic species 

 have developed. For all the factors of the lowlands, cosmic 

 as well as terrestrial, differ from those of the highlands; 

 besides, for many plants Transcaspia has been a closed basin 

 enclosed towards the South and East almost everywhere by 

 mountains the Balchash basin being included and 

 barred towards the West by the Caspian, and towards the 

 North by the cold. 



A third condition favourable for the evolution of endemic 

 species is the dryiiess of the climate, and consequently a very 

 scattered plant-covering. There is no internecine struggle 

 among the plants themselves, but always sufficient open 

 ground available; they have only the conditions of the 

 environment to contend with (comp. ENGLER 1882, pp. 48, 

 324; VAHL p. 154). 



Moreover it is natural that there should be a close flor- 

 istic relationship between Transcaspia and the surrounding 

 mountainous parts. This relationship must be closest towards 

 the South, since the country towards the East rises to a far 

 greater height than towards the South where the natural 

 conditions must resemble those of Transcaspia more closely. 



Utilising the records of distribution given in the plant- 

 list, in chap. 12, we shall endeavour to formulate some con- 

 clusions which may be of interest with regard to these 

 questions. 



The 768 Transcaspian species enumerated in the plant- 

 list (chap. 12) may be assigned with respect to their distri- 

 bution outside Transcaspia to the following eight groups 

 (comp. p. 138): 



1. Endemic species, 169 or 22 p. cent. 



2. Species distributed only towards the South (Western 

 Asia), denoted in the list by V: 142 or 18 p. cent. 



3. Species distributed only towards the North (Russia) 

 denoted in the list by R: 29 or 4 p. cent. 



4. Species distributed towards the East (High-Asia) denoted 

 in the list by H: 83 or 11 p. cent. 



