GEOGRAPHICAL VICISSITUDES OF PLANTS. 295 



the Arctic forms would seize on the cleared and 

 thawed ground, always ascending, as the warmth 

 increased and the snow still further disappeared, 

 higher and higher, whilst their brethren were pursu- 

 ing their northern journey. Hence, when the warmth 

 had fully returned, the sames species which had 

 lately lived together on the European and North 

 American lowlands, would again be found in the 

 Arctic regions of the Old and New Worlds, and on 

 many isolated mountain -summits far distant from 

 each other. Thus we can understand the identity 

 of many plants at points so immensely remote as 

 the mountains of the United States and those of 

 Europe. We can thus also understand the fact that 

 the Alpine plants of each mountain range are more 

 especially related to the Arctic forms living due 

 north, or nearly due north of them ; for the first 

 migration when the cold came on, and the re- 

 migration on the returning warmth, would generally 

 have been due south and north. The Alpine plants, 

 for example, of Scotland, as remarked by Mr. H. C. 

 Watson, and those of the Pyrenees, as remarked by 

 Ramond, are more especially allied to the plants of 

 northern Scandinavia ; those of the United States to 

 Labrador ; and those of the mountains of Siberia to 

 the Arctic regions of that country." 



The floras of many countries have been, after the 

 fashion of serial books, " taken in in numbers," and 

 bound afterwards ; but that of Great Britain is of an 



