26 THE JOURNAL OF INDIAN BOTANY. 



In the main it clearly separates the Indo-Malayan flora from the 

 Chinese flora. But at the southern end of the belt, there is an inter- 

 polated flora, — endemic to a high degree, but related also to the Indo- 

 Malayan on the one hand, and the Yunnan plateau on the other — 

 occupying the Burma-Yunnan area. 



Striking, however, as is this North East Frontier belt as a barrier, 

 it is even more so as a bridge between the Himalayan ranges to the 

 west and the Chinese ranges to the east. Despite their complete 

 separation, the two former areas possess closely related floras. 



There has been something of a volt face as regards the Himalayan 

 and Chinese floras. Formerly they were believed to be almost iden- 

 tical. Exploration in western China showed that this was not the 

 case, and lately the tendency has been to exaggerate the differences, 

 which after all turn largely on our conception of species. The North 

 East Frontier belt is the link between the two, and their relationship 

 will be better appreciated as the flora of the former is investigated. 



The three areas, Himalaya, North East Frontier and western China 

 form a sort of letter Y, the three limbs of which, each composed of 

 parallel ranges, are separated from one another, but connected 

 independently with the desert plateaux of central Asia ; and it will 

 probably be found that while the easternmost range of the N.E. 

 Frontier belt shows a closer relationship with the western China 

 limb, the westernmost range shows a closer relationship with the 

 Himalayan limb. 



If our conception of a Sino-Himalayan range, subsequently 

 breached, is correct, then clearly a Sino-Himalayan flora reached 

 from Nepal to Sheuri before it appeared on the N.E. Frontier ranges to 

 the South. The subsequent uplift of these ranges, breaching the 

 Sino-Himalayan range, would account for the presence of both 

 Himalayan and north-west China plants so far south, derived from 

 the broken ends of the main range. 



To sum up, the N. E. Frontier belt, and more especially the 

 Mekong-Salween divide, is primarily a barrier, botanical and zoo- 

 logical, marking the eastern limit of the Indo-Malayan, or Oriental 

 region, for at least 750 miles. 



Secondarily it is, or has been, connected in the north with the 

 Himalayan ranges on the one hand, and with the great China divide 

 on the other, serving both to keep them apart and to link them up to 

 a common centre. 



