346 Limits of Plants in North-West Yunnan. 
Pei-ma-shan (see map, p. 334), a mountain on the crest of the 
watershed rising some thousands of feet above the snow-line to the 
S.E. of A-tun-tsi, possesses several glaciers which are clearly 
retreating; their bottle nosed snouts, their lateral moraines ex¬ 
tending for some distance beyond the present limit of the ice, 
and the isolation of their terminal moraines, leave no doubt on the 
point. 
Other evidence is afforded by small mountain lakes which con¬ 
stantly occur between 16,000 and 18,000 feet, occupying depressions 
in the screes, or rock-basins, sometimes of great depth ; by the fact 
that many of the valleys immediately descending from the watershed 
are “ hanging” valleys, and present further a peculiar step-like or 
“tread and riser” ascent at their upper extremities; and finally by 
the immense piles of angular scree material, bearing a strong 
resemblance to morainic material, which occupy the valley heads; 
indeed, the scree shewn in the photograph (PI. 7, Fig. 7) might well be 
a lateral moraine. If this is actually the case, the flora is an ascending 
one, and it is to the circumstance that new ground has probably for 
long periods been gradually opened up for colonisation that I 
attribute the large number of species of certain successful genera, 
such as Saxifraga and Gentiana, found towards the limit of plants 
in N.W. Yunnan; it seems to indicate a changing climate on that 
curious geological freak, the Mekong-Yangtze watershed. 
Description of Plates VII and VIII, Illustrating Mr. F. Kingdon 
Ward’s Paper “ On the Altitudinal Limits of Plants in 
North West Yunnan.” 
Plate VII. 
Fig. 1. Mekong-Yangtze watershed, screes at 16,000 feet. These screes 
face south and are clear of snow in the middle of May. The dark patches are 
Juniper and dwarf Rhododendron. Just over the ridge on the extreme left (not 
shown) and facing north, is a thick carpet of undershrubs with patches of 
melting snow. 
Fig. 2. Mekong valley, arid region at 7,000—8,000 feet. Cultivation is 
only possible where a mountain torrent offers facilities for irrigation. Barley 
on the terraces, with walnut trees. In the foreground Sclaginella involvens. 
Fig. 3. South-facing slope at 15,000 feet showing scrub-oak and bare 
scree. Higher up the limit of Abies is seen. It has been driven out of the 
valley by the concentration of the winds at high altitudes, and obtains pro¬ 
tection just over the ridge. 
Plate VIII. 
Fig. 1. Taken from the same point as the Plate VII, Fig. 3, but looking 
the other way. North-facing slope showing Rhododendron in place of scrub-oak, 
and no screes. Abies at the Limit of Trees, here able to withstand conditions 
in the valley-bottom, giving place to shrub-belt. 
Fig. 2. Mekong-Salween watershed below the Sie-la, 13,000 feet. Alpine 
meadow in the foreground. Higher up is Abies, which cannot survive in the 
valley-bottoms near the passes, owing to concentration of wind. 
