CLIMATE AS INFLUENCED BY THE FOREST. 131 



may cause by an early frost the loss of millions of 

 dollars to an agricultural district. 



Again, it is in the late autumn, at the time of the 

 early frosts which are so feared in the agricultural 

 districts, that a vegetable covering may be able to 

 fling back to the earth sufficient heat thrown out 

 by the cooling ground to prevent the temperature 

 of the air immediately around growing plants 

 from reaching the freezing-point. 



Forests exert a sheltering action at the time of 

 frosts in keeping the land to the leeward warmer 

 than that to the windward. Not only do they 

 act as an actual barrier or screen, sheltering and 

 protecting the land immediately to the leeward 

 side, but this protecting action extends to a much 

 greater distance beyond the immediate neighbor- 

 hood of the forest than might be supposed. 



The leaves of almost any forest tree, when ex- 

 amined under the microscope, show greatly ex- 

 tended surfaces in the shape of irregularities, or 

 spine-like projections. These extended surfaces 

 aid the tree greatly in throwing off from the very 

 slightly heated earth the stores of heat which it 

 possesses, even in the depth of winter, and which, 

 thus passing into the air, tend to prevent a too 

 marked fall of temperature during winter. 



