392 MR. M. P. PRICE ON THE VEGETATION OF 
the west of Lake Ubsa, the Larch forest oceurs between 6000 and 7000 feet. 
Some 40 miles to the south of this again, on the Kundelun mountains, the 
ag 
Larch forest occurs between 6300 and 7600 feet, while on the right bank 
of the Upper Kobdo River and round the Kobdo Lakes, the Larch-forest 
zone occurs between 7000 and 8000 feet. Thus the zone gradually rises 
in altitude as the southern latitudes are reached. But in the case of the 
Larch-forest association, latitude and altitade are not the only factors which 
control its distribution, for it appears that shelter from insolation, and 
perhaps wind, is a third factor to be taken into consideration. This is 
suggested from the fact that the Larch-forest association all over the North- 
West Mongolian plateau is found only on that side of the valley which has a 
northern aspect, while it reaches its best development in the shady glens of 
the mountains. Moreover, the complete absence of any Larch forest in the 
country between Achit Nor and the Kobdo River seems to suggest that a 
large area of open down country, even though it may be at a favourable 
altitude and latitude, iftoo exposed to wind and snow, is unfavourable for the 
development of Larch-forest association. In this area, therefore, which is 
drained by the left tributaries of the Kobdo River, namely, the Suok, the 
Taharty, the Olonor, and the Tsagangol Rivers, the Plateau-desert association 
merges into the Alpine association without any intermediate Larch-forest 
association. The following are its most characteristic species :— Larie 
sibirica, Vaccinium Vitis-eldwa, Aconitum sp., Potentilla bifurca. Pinus 
sibirica also occurs in this association in the extreme north, and is found as а 
straggling specimen as far south as the western Tannu-ola mountains, where 
it reaches the summit. It appears that the excess of sun and light is 
responsible for its absence in latitudes further south of this. 
3. The Alpine Association is distributed in North-West Mongolia in the 
following areas :-—In the Kemehik valley of the Upper Yenisei plateau it is 
found on several isolated mountain masses between 6000 and 6500 feet. On 
the Kundelun mountains it begins at an altitude of 7000 feet, and further south 
still, on the right bank of the Kobdo River, it commences at 8000 feet. 
It reaches the snow-line at about 11,000 feet in the last two places, wherever 
there is sufficient soil. Тһе best development of the Alpine association is 
found on the left tributaries of the Upper Kobdo River, namely, on the Suok, 
the Taharty, the Olonor, and Tsagangol Rivers. Here a large area of rolling 
down country between 8000 and 10,090 feet alt. is the geographical feature, 
and is peculiarly favourable for the development of this flora. It is interesting 
to know that it is just here that Ovis ammon, the great mountain sheep of the 
Altai, is found in considerable numbers, and its distribution seems to coincide 
with the widespread distribution of the Alpine association. The charac- 
teristic species of the Alpine meadows of North-West Mongolia are :— G'entiana 
altaica, Gentiana prostrata, балтада Hirculus, Primula nivalis, Trollius 
asiaticus, Papaver nudicaule, Betula nana. 
