24 THE JOURNAL OF INDIAN BOTANY. 



In other words, the breach in the Sino-Himalayan range is not the 

 passive work of rivers cutting their way back, but is a far more 

 formidable gap resulting from an active uplift of ranges whose axes 

 cut across a possibly older uplift. 



But whether we hold that this Sino-Himalayan flora was once 

 more widely spread over Tibet at a time when that country had a 

 more genial climate, as suggested in the first alternative ; or whether 

 we hold that it merely crept across from Kauru to the Himalaya 

 along a continuous range, prior to the uplift of the N.E. Frontier ran- 

 ges, subsequently surging southwards through the breach they made, 

 as in the second alternative ; we perceive that many species, now quite 

 isolated, have survived unchanged through a long period, since they 

 are now found in places as far apart as the Himalaya, N.E. Frontier 

 and western China, to say nothing of Japan and N. America. 



I say nothing as to the direction taken by the stream of flora, 

 beyond the manifest fact that the alpine flora of the Htawgaw Hills 

 (Lat. 26° N., Long. 98° 30 E.) has come neither from the east, nor from 

 the west, but straight down the ranges from the north. 



No doubt the flora of the great Asiatic divide has swayed back- 

 wards and forwards, but in the main it is generally believed to have 

 originated within the Arctic circle, and to have moved south- 

 westwards into Asia and south-eastwards down the Atlantic coast of 

 N. America, with the glaciation of the North. So much for its intro- 

 duction into Asia ; but its movements after that are another matter, 

 altogether. That hypothesis sufficiently accounts, in a broad way, for 

 the relationship existing between the floras of the Himalaya, Japan 

 and North America ; it by no means accounts for the relationship 

 existing between the floras of the N. E. Frontier, the Himalaya, and 

 Western China. 



The Chinese element in the flora is also conspicuous, but a dis- 

 tinction must here be made between the two sources from which 

 it has been derived. These are : — 



(i) The valleys to the immediate south and east; (ii) the high 

 ranges of far western China, which, thrusting southwards from the 

 main body hold in their grasp much of Yunnan. These sources must 

 be carefully distinguished. 



As regards the first, this flora extends eastwards no further than 

 the Salween valley, and northwards no further than about the 26th 

 parallel ; that is, it embraces the basin of the Shiveli river. It may be 

 called the Burma-Yunnan area, and is characterised by many identi- 

 cal species of 'Rhododendron, by the Candelabra Primulas, many 

 Gelastraceae, Gesneraceae, etc. This flora is highly endemic. The 

 typical Chinese flora is confined to higher altitudes, and includes 



