Vegetation of the Himalaya. 811 



the other, divides the basin of the Sutloj from that of the Jumna 

 and Ganges. 



From the great depth of the valleys which separate the different 

 mountain-chains, it but seldom happens that any road crosses from 

 one valley to another ; a traveller has therefore, in general, excellent 

 opportunities of studying the direction and ramifications of the dif- 

 ferent chains, either in following the course of the valleys, or by tra- 

 velling along the top of the ridges. In both cases he will find that 

 his course is an undulating one, each chain and each branch of a 

 chain being a curve, which bends first to one side and afterwards to 

 the other, giving off generally a spur on the convex side, while the 

 head of a valley insinuates itself into the concavity. 



After these few words on the physical structure of the mountains, 

 the vegetation of which it is my wish briefly to describe, it will still 

 be necessary to devote a ^qss minutes to the subject of climate and 

 humidity, before I can proceed to my proper subject. 



Situated in the most southern part of the temperate zone, and 

 bounding on the north a great peninsula, which extends far into the 

 torrid zone, the base of the Himalaya to the south possesses an almost 

 tropical climate, tempered, however, when the sun is on the tropiq 

 of Capricorn by a moderately cool winter, and variously modified in 

 different parts of the chain by the degree of humidity, a most io?- 

 portant matter to be taken into consideration in every question con- 

 nected with the phenomena of vegetable life. 



The source of humidity in the Himalaya is almost entirely the 

 Bay of Bengal, which is situated about 5 degrees to the south of the 

 eastern extremity of the chain ; and the wind which carries the humid 

 atmosphere along the chain, is that which is known to nautical me- 

 teorologists as the south-west monsoon, a wind which begins to blow 

 in the open sea about the month of April, but whose effects are not 

 felt in the far interior before the month of June. This wind, though 

 constant in its direction at sea, is not so in its inland course ; at the 

 head of the Bay of Bengal it is almost a south wind ; it blows from 

 the sea nearly due north towards the Himalaya, striking in its course 

 upon the low chain of the Khasya hills, whose maximum elevation 

 is scarcely 7000 feet. 



Upon this range the first force of the monsoon is expended, and 

 the annual fall of rain at Churra Poonjee, elevated 4000 feet on its 

 southern slope, amounts to. about 500 inches. This range, which has 

 its origin among the mountain ranges of the south of China and north 

 of Burmah, lies to the south of the Burrampooter, and following the 

 coui'se of that river, terminates in the concavity of its great bend, 

 where it turns down toward the sea. The Khasya mountains do not, 

 therefore, entirely run across the Bay of Bengal, so as to intercept 

 the force of the monsoon from the whole of the Himalaya, a part of 

 which wind, laden to saturation with moisture at a temperature of 

 nearly 90" F., blows due north from the Bay of Bengal upon the 



