174 FLORA INDICA. 



differences of vegetation. In the great valleys the tropical 

 flora stretches far into the interior, and is much the same 

 there as in the outer portion of the mountains. In the ex- 

 terior Himalaya there is a well marked rainy season. The 

 width of the belt of the exterior or humid Himalaya is much 

 greater to the eastward than in the extreme west, the rain-fall 

 and humidity being much less to the westward. We there- 

 fore find the plants of the interior zone advancing much 

 nearer to the plains in the western Himalaya than they do in 

 the eastern, where a humid or rainy climate vegetation pene- 

 trates far into the interior. In the outer zone of the eastern 

 Himalaya, indeed, a vegetation characteristic of an equable 

 climate prevails throughout the year, while to the westward 

 those families which delight in humidity only make their ap- 

 pearance with the commencement of the rainy season, before 

 which time no Zingiber acece, terrestrial orchids, especially 

 Malawidea, Cyrtandracea, Acanthacea, or balsams, are to be 

 met with. 



Considered with respect to its longitudinal extent, the Hi- 

 malaya, when regarded solely from a physical point of view, 

 consists of only two divisions, a western and an eastern, cor- 

 responding respectively to the Indus and Brahmaputra. For 

 botanical purposes, however, the chain requires to be divided 

 into western, central, and eastern Himalaya. The kingdom 

 of Nipal, in the middle, constitutes the whole of the central 

 Himalaya. To the eastward lie Sikkim, Bhotan, and Abor, 

 to the westward Kumaon and the Panjab Himalaya. 



We have thus three principal series of divisions of the Hi- 

 malaya, according to length, breadth, and height. Accordingly 



we say 



1 (longitudinally). The eastern, central, and western Hi- 

 malaya. 



2 {latitudinally) . The exterior, interior, and Tibetan Hima- 

 laya. 



3 (altitudinally) . The tropical, temperate, and alpine Hi- 

 malaya. 



