58 CLIMATE AND EESOUECES OF 



some people think. The fresh verdure of vegetation is a great 

 absorbent of heat ; and moisture, which cools the surrounding 

 air, is largely evaporated from fresh young leaves. These 

 effects are lessened as the leaves lose the freshness of youth, 

 fade, and dry up. Young leaves have a soft, yielding surface, 

 and are filled with sap; as they become older they become 

 harsh and crisp to the touch, and lose their power of absorb- 

 ing and radiating heat ; they also contain less sap, and can 

 give up but a reduced amount by evaporation; hence the 

 effect of forests and vegetation in cooling the air is greater 

 immediately after the trees are fresh clothed with new leaves 

 in spring than when the leaves are drying up and dying. 



Besides the influence of trees in moderating the extremes 

 of heat and cold of the climate of a country, there is the 

 influence they exert on the rainfall. I have stated that the 

 rainfall in the Dooab is small in comparison with that of the 

 Teraee and southern slopes of the Himalayas. Forests and 

 vegetation, by radiation, cool the air, and the cooled air 

 coming into contact with warm air laden with humidity, 

 causes condensation, and the vapour of water in the air is 

 precipitated. The greater rainfall of the Teraee and southern 

 slopes of the Himalayas is due to the greater amount of radia- 

 tion caused by the forests there. The clouds laden with 

 vapour pass over the bare plains without discharging their 

 moisture, because there is a want of absorptive and radiative 

 power, and the air above them not being cooled by radiation, 

 the clouds do not part with their moisture, but retain it till 

 they reach a place where such chilling of the air by radiation 

 occurs, which they find over the Teraee and the southern 

 slopes of the Himalayas. The rank vegetation of the Teraee, 

 and its unhealthiness, are due to the greater precipitation of rain 

 and accumulation of water in the vegetable soil from surface- 

 drainage. By planting the uncultivated lauds of the plains 



