198 FLORA 1NDICA. 



an interesting collection made by Captain Hay in the little 

 known district of Lahul. 



The botanical provinces of the Western Himalaya may be 

 divided into two principal groups, characterized both by their 

 climate and geographical position. Of these, the first group 

 consists of seven provinces, all bounded on the south by the 

 plains of India, and through which the Himalayan rivers that 

 water them flow in a direction at right angles to the course of 

 the mountains. The second group of provinces consists of 

 five beyond the Satlej, most of which lie to the northward 

 of the first group, and follow a line parallel to them. These 

 are the upper valleys of some of the same rivers as flow 

 through the first group of provinces, and owe their existence 

 as distinct regions in physical geography to the fact elsewhere 

 indicated (page 168), that the courses of the upper parts of 

 the larger rivers of the Western Himalaya are parallel to the 

 axis of the chain. 



The great elevations of the secondary chains (or spurs ot 

 the main chain) that divide the upper group of provinces 

 from the lower, forming the southern boundary of the upper, 

 prevents the access of humid winds to them, which, together 

 with the greater elevation of their valleys, makes their climate 

 very different. 



It is to be borne in mind that the necessity of thus dividing 

 the North-western Himalaya beyond the Satlej into two pa- 

 rallel lines of provinces does not indicate any great difference 

 between this part of the Himalaya and that to the eastward j 

 for, as we have repeatedly remarked, the heads of all the 

 larger Himalayan rivers are in an arid climate. The upper 

 valleys of most of these rivers are too small to constitute pro- 

 vinces, but it cannot be doubted that when the physical fea- 

 tures of such large rivers as the Subansiri, Aran, etc., come to 

 be explored, their upper valleys will be found to constitute 

 provinces with a climate and vegetation intermediate in cha- 

 racter between those of the Himalaya and Tibet. 



