UPPER INDIA. 11 



same cause. I have since then seen more trees killed by the 

 dry heat, bat 1868 was the first year in which I noticed it, 

 and it was talked of amongst the natives as something pre- 

 viously unknown in Rohilcund. 



The damage done in this way is increased by the wind, 

 which, by bringing fresh particles of dry air continuously 

 into contact with the leaves, causes greater evaporation from 

 them; and we see its effects in the more drooping and 

 withered appearance of the leaves of trees and vegetables in 

 the evening of a windy day than in the evening of a still day. 



The manner in which hot dry air kills trees is plain. 

 When the daily evaporation of moisture from the leaves 

 exceeds the amount of moisture a tree can daily take up by 

 its roots, the tree must wither and die. This is merely a 

 case of daily expenditure exceeding daily income, when the 

 principal has to be encroached on, and bankruptcy occurs, 

 the principal in the case of a tree being its normal amount of 

 sap. It depends, then, on the amount of moisture in the 

 ground within reach of the roots of a tree, and the capability 

 of the roots for pumping it up, whether the tree will suffer or 

 not from evaporation caused by a dry, hot air. In the cases 

 of the trees killed by heat in the Budaon district in 1868 and 

 1869, it is remarkable that the trees so killed were mostly 

 on low-lying lands, and invariably on land with a hardened 

 surface-soil. On the higher land, with a loose, sandy surface- 

 soil, I saw no trees killed by the heat. If we dig into these 

 soils, we soon discover the reason. Beneath the land with the 

 hardened, compacted soil we find next to no moisture, while 

 beneath the loose, sandy surface-soil we meet with a much 

 larger amount of moisture present in the subsoil. 



Heat and moisture are necessary for vegetation ; and we 

 find that the most luxuriant and rank vegetation occurs in 

 those parts of the world where great heat and moisture are 



