xii INTRODUCTION 



cent, only are common to the Arctic region, while 25 

 per cent, are common to the Altai range of Northern 

 Asia. The subject is, as Mr. Thiselton-Dyer sa3'S, a 

 complex one; but it can hardly be doubted that '*the 

 alpine flora is a very ancient one, and probably a decay- 

 ing survivor of one of which the extension was at some 

 former time far more considerable." 



The closer resemblance of the flora of the European 

 Alps to that of the Asiatic Alps than to that of Scan- 

 dinavia may be partly accounted for by the fact of the 

 climatic conditions being more nearly alike. In the 

 Arctic Zone the plants which blossom in their brief 

 summer are exposed to almost uninterrupted daylight for 

 many weeks, during which there are no nocturnal dews. 

 In the mountain chains of the Temperate Zone, on the 

 other hand, bright hot days are succeeded by nights of 

 nearly equal duration, during which the temperature is 

 often very low and the dews very heavy. It is obvious, 

 therefore, that the external characters of alpine and of 

 arctic plants may differ considerably, and that a large 

 amount of adaptation may be necessary before an arctic 

 form could become established in the Alps, while no such 

 adaptation need accompany the migration of a species 

 from Central Asia to Central Europe. 



Some of the special characteristics of the alpine flora 

 are familiar to every visitor to the Alps. Either from 

 the large size or the bright colour of the flowers, or from 

 their being grouped together in great masses, they are 

 far more conspicuous, especially in the spring and early 

 summer, than is the case in the lowlands. Although 

 these brilliant masses of flowers often belong to genera 

 which are especially alpine, like the Gentians and the 



