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.
