VEGETATION OF THIBET. 19 
but, especially in the more easterly tracts, little snow falls. In the 
lower parts of the Indus valley the quantity is considerable; and in 
the mountains south of the Indus it is great, and increases rapidly 
as the Indian Himalaya is approached. In summer, though light 
clouds are common and cloudy days occur now and then, very little 
rain is seen. It cannot be said that it never rains; but on the very 
few occasions on which I have observed rain to fall, the quantity has 
not exceeded a few drops,—not nearly sufficient to wet the ground. In 
the midst of these desert tracts, and in spite of the aridity of the 
climate, the industry of man has turned to useful purpose every available 
piece of ground. Wherever a level soil, in the least productive, and 
a sufficiency of water are found together, a village and cultivation are 
sure to be seen. As the heavens afford no rain, an ample supply of 
water is indispensably necessary, so that the existence of cultivated 
tracts may be ascribed to the circumstance that the mountains rise 
above the level of perpetual snow, the gradual melting of which during 
the summer months affords a supply of water for irrigation. The crops 
consist principally of Wheat and Barley, the latter only at high eleva- 
tions. A little Buck-wheat, Sinapis for oil, Peas, and Beans, are 
grown; and at low levels and hot exposures, one or two Paniceous 
species are also to be seen. 
In so desert a country you will not be surprised to hear that the 
natural vegetation is very scanty. Iam not, however, at present able 
to form any estimate of the number of species which I have met with, 
but at a rude guess I do not think they exceed 500; and yet, 
entering the country as I did on the 22nd of June, at which time the 
early E plants Fine Gagea, Lloydia, Orucifere) were in flower, 
Ido not think that many have escaped me. The cultivated tracts 
round es have a pum luxuriant vegetation ; and even on the barren 
tracts for the first fortnight a considerable number of species might 
be found; but lately everything has been dry and burnt up. The 
alpine flora commences about the elevation of 14,000 feet, and is prin- 
cipally confined to the edges of streams and places moistened by melting 
snow. The general features of the vegetation are entirely northern, 
and in the abundance of Asfragali it approaches the Siberian flora. 
Crucifere, Boraginee, Labiate, and Chenopodiacee are predominant 
Orders. In the cultivated fields Vaccaria, Silene conica, or conoidea, a 
