INTEODUCTORY ESSAY. 175 



A combination of these three modes of division will be 

 our usual mode of defining the localities of the plants. In 

 the great majority of cases these terms are abimdantly suffi- 

 cient for our purposes, the range of each species being very 

 considerable. There are, however, many instances in which 

 it is desirable to enter into further detail, and in such cases 

 we shall either make use of the river valleys (a very con- 

 venient mode of indicating the regions), or of the political 

 subdivisions usually recognized. To these we shall refer in 

 the following remarks on the great geographical divisions, 

 which correspond to the longitudinal divisions given above, 

 with the addition of a fourth, namely, Tibet, which includes 

 not only the Tibetan slope of the Himalaya, — that is to say, 

 the ramifications which extend from its axis towards the 

 Tibetan Brahmaputra and Indus, — but also the mountainous 

 country to the north of these rivers, as far as the axis of the 

 chain of the Kouenlun. 



Eastern Himalaya. 



In this are included the states of Sikkim and Bhotan, and 

 the districts lying to the eastward of the latter as far as the 

 great bend of the Brahmaputra, which we shall call collec- 

 tively by the name of Abor. 



1. Abor. 



To the eastward of the Subansiri river there is probably 

 only one range of any considerable elevation, and the moun- 

 tains by which the Himalaya terminates in that direction per- 

 haps nowhere attain a greater height than eight or ten thou- 

 sand feet, while the valley of the Dihong or Brahmaputra is 

 probably broad and open. These mountains are inhabited by 

 wild and suspicious tribes, who have hitherto refused all access 

 to the interior of their country. The climate and vegetation 

 are probably identical with those of the Mishmi mountains, 

 to the eastward of the Brahmaputra, which will be noticed in 

 a future page. 



