— 259 — 



washed by this sea. In this earlier period the climate, which 

 was probably rather moist, had been favourable to the growth 

 of plants and had resulted in a luxuriant and fairly homo- 

 genous flora developing over the immense area between the 

 Himalaya and the Pyrenees. When the sea disappeared the 

 climate became dry. The plants came under the influence 

 of a very different environment so that they were compelled 

 to change. Only in the northern part of the Elburs and the 

 western part of the Caucasus, near two great inland seas, 

 are luxuriant forests still found which are regai-ded as the 

 last, though perhaps somewhat altered, remnants of the old 

 tertiary vegetation of Western Asia. The rest of the plants 

 must either die or adapt themselves to the new conditions. 

 At the same time the Aralocaspian lowlands, left by the sea, 

 were open to immigration from the neighbouring countries. 

 The result of the changes which took place was a new flora, 

 xerophytic and especially adapted to a climate with a short 

 vegetative period, but which was — and is — otherwise 

 closely related to the elements of the flora of the Mediter- 

 ranean lands with which they have a common origin^). 



If the development took place as indicated here ac- 

 cording to Engler, it is evident that the flora of Trans- 

 caspia must for the most part have originated from that of 

 Western Asia, and that the plants must have descended from 

 the mountainous parts towards the South and East (comp. 

 BoRSCZow, above p. 30). Southern Russia cannot come under 

 consideration as a starting point for the species which pop- 

 ulated Transcaspia, because large tracts of it at the beginning 

 of the quaternary period (Sjogren, see also Karpinski) were 

 covered by water (the Aralocaspian Sea) and this "Caspian 

 Transgression" probably originated in ice-water from the 

 margins of the great European ice- sheet, so that the climate 

 must have been cold. With regard to the climate of Western 

 Siberia at that period there is no information, but it must 

 also have been cold, colder than now, therefore the possibility 

 of immigration from there need not be considered. 



') Engler 1879, pp. 57 and following, 184 and following. 



17* 



