INTRODUCTORY ESSAY. 173 



pal vegetation occurs at the commencement of spring, when 

 the melting snow supplies abundant moisture to small an- 

 nual plants, which run their course with great rapidity, and 

 are speedily shrivelled up by a scorching sun. 



As respects climate, we have therefore two different systems 

 of division of the Himalaya: — 1, into the tropical, temperate, 

 and alpine zones; and 2, into the exterior or rainy, the inte- 

 rior or intermediate, and the Tibetan or arid Himalaya. 



The term tropical is not strictly applicable to any part of 

 the chain, which is nowhere within the tropics, but we find it 

 convenient to adopt it, and, the vegetation being strictly tro- 

 pical, it can, we think, lead to no inconvenience; while the 

 only word which could be substituted, namely subtropical, is 

 required to express the transition from the vegetation of the 

 base to that of the temperate zone. There are of course no 

 strict lines of demarcation between the three zones first enu- 

 merated ; but they are sufficient to express the three promi- 

 nent changes in the vegetation which correspond to those 

 observable in passing from the equator towards the poles, and 

 on the whole are sufficiently distinct to be readily recogniz- 

 able . 



In the extreme west the tropical belt rises to about 4000 

 feet, and as we advance eastward its elevation gradually in- 

 creases. In Kumaon it is 5000 feet, and in Nipal rather 

 higher. In the permanently humid country to the eastward 

 it rises still higher, tropical vegetation being found as high as 

 7000 feet ; but the equable nature of the climate masks the 

 effect, and carries many temperate plants much lower than 

 that level. The alpine zone may be said to commence at the 

 upper limit of trees, which varies from 12,000 feet in the 

 extreme west to nearly 13,000 feet in the eastern Himalaya. 

 A number of trees and shrubs which are peculiar to the 

 higher part of the temperate zone, we shall generally charac- 

 terize as subalpine. 



The division of the Himalaya into exterior, interior, and 



Tibetan, corresponds in the temperate zone to very marked 



