THE FACTORS OF DISTRIBUTION 



pine Region { ^PP* drier ; de ? ert . * snow-line. 

 I Lower, grassland with drizzle. 

 Upper limit of trees. 



Montane Region { M -- ng *" 



f Moister, but not markedly colder than 

 Basal Region the plain, resembling moist lowland 



stations. 



The two lower regions will be wooded, even more so 

 than the plains below them. The cloud-belt extends 

 over the Alpine grassland; but the wind is inimical to 

 trees. Above the cloud-belt the dry cold air and soil 

 produce the xerophytic conditions which, on lofty 

 mountains, prevail immediately below the snow-line. 



Obviously, mountains having their bases in higher, 

 non-equatorial latitudes will not present the lower zones 

 of vegetation of the tropics, but various local condi- 

 tions will also modify their characteristics. An isolated 

 volcanic peak, such as Teneriffe, surrounded by the 

 equalising influence of the ocean, differs from con- 

 tinental mountains, such as the Alps; and the east and 

 west extension of the Pyrenees or Himalayas gives them 

 a very different relation to the vegetation at their feet 

 from that of a meridional chain, such as the American 

 Cordilleras. Thus, while the Himalayas divide the 

 Central Asian xerophytic flora from the hygrophilous 

 Indo-Malayan vegetation, there is said to be a recognisable 

 " American " character in the flora of all latitudes of the 

 New World, from Alaska to Fuegia. The genus Befaria, 

 for instance, represents the Rhododendrons of the Old 

 World from North America to Chile. At the same time, 

 Rhododendron, represented by dwarf forms in Europe 

 from Lapland to Gibraltar, but absent in Africa, is abun- 

 dantly represented in the Himalayas and eastward in 

 Yunnan, and takes advantage of a discontinuous 

 meridional extension of mountainous habitats to appear 

 under the form of R. malayanum Jack, in Sumatra, and 

 even as R. Locha F. v. M. at 5000 feet on Mount 

 Bellenden Ker, far down the line of the Australian chain. 



Raised in isolation above the surrounding vegetation, 

 mountains have been compared to islands. All moun- 

 tains over 5000 feet in altitude, between 55 N. and 

 50 S., are, like islands, rich in endemic plants, both genera 



