1915-16.] BOTANICAL SOCIETY OF EDINBURGH 19 



in the forest belt, is very considerable — but in the plant 

 formations, showing clearly enough the effects of climate, 

 especially rainfall. But the Mekong-Salween divide, being 

 on the edge of the monsoon area, its flora might be supposed 

 to have originated in the west, while the flora of the Mekong- 

 Yangtze divide might be supposed to have originated in 

 China, thus accounting for any differences observed. I 

 will only remark here that the most typical plants of the 

 monsoon jungles, west of the 'Nmai-hka (or eastern branch 

 of the Irrawaddy), e.g. Fandanus, rattans and other palms, 

 tree ferns, many species of Ficus, climbing ferns (LygodiuTn), 

 etc., are entirely absent from the Mekong-Salween divide, 

 and will prove in the sequel that this range and the Mekong- 

 Yangtze divide, whatever their differences now, must once 

 have had the same flora ; further, that the Mekong-Salween 

 divide has still — but may not long retain — the same flora 

 as the Salween-Irrawaddy divide. The obvious inference 

 is that these three parallel ranges were peopled from a 

 common source, and that a change of climate, amountino- 

 to a pushing back or limiting of the south-west monsoon,^ 

 has been, and probably still is, taking place in this area. 



During two seasons spent at Atuntsu I have climbed a 

 good deal on the Mekong- Yangtze divide between latitudes 

 27° and 30°, crossing the range by six passes in all, and 

 one result has been to establish the fact that the glaciers 

 there have retreated some distance and are still retreating. 

 This is proved by (i) an examination of existing glaciers on 

 the range, now little more than shrivelled ice-caps moulded 

 like myxomycetes to the rocks over which they flow, and 

 thrusting out blunt icy pseudopodia as it were into the 

 valley : their bottle snouts and distant terminal moraines, 

 the material of which is alread}^ almost wholly rearranged 

 by flowing water, complete the picture of exhaustion ; (ii) 

 an examination of other parts of the range, where the deeply 

 eroded U-shaped main valley into which open numerous 

 hanging valleys, the rock basins, mostly occupied by lakes, 

 but sometimes silted up, roches moutonnees, occasional 

 moraines, and peculiar cirques at the valley heads, prove 

 that glaciers were once present. In the absence of two 

 familiar indications of past glacial action, namely, striae 

 and perched or erratic blocks, I pictured as M^ell as I could 



