160 USES OF FORESTS AND OTHER 



XIII. 



USES OF FORESTS AND OTHER PLANT COVER'NG 

 OF THE EARTH. 



BY N. S. SHALER. 



THE greater part of the land surface of the 

 earth is thickly covered with growing plants. 

 Where the rainfall is sufficient and where the 

 region is exempt from wide-spread fires, such as 

 sweep over the prairies of the Mississippi Valley, 

 we always find a growth of forest trees. Where 

 the rainfall is scanty, or where these annual confla- 

 grations occur, the forests are replaced by grasses, 

 or other low-growing plants, which may maintain 

 their roots in a living state through the winter, but 

 have no permanent growth above the level of the 

 soil. Generally speaking, only those regions where 

 the rainfall is less than about ten inches a year 

 are without plant covering of any kind, and this 

 area is but a small part of the surface of the 

 earth. 



The influence of this coating of plants on the 

 conditions of the earth is very important in many 



