CONDITIONS FOR THE GROWTH OF TREES. 43 



earth possessing this character of vegetation are 

 called steppe regions. 



"When the rainfall is not very great in amount, 

 but is fairly well distributed throughout the year, 

 so that the rain is never absent for a very long 

 time, regions called meadows or prairies occur. 



If there is an abundance of moisture at nearly all 

 times throughout the year, so that such moisture 

 is absent for no very long time, then the country 

 may be covered by trees. Such areas are called 

 forests. 



Forests cannot exist in the temperate zones of 

 the earth in localities where, during the time of 

 the trees' active growth, a very long interval exists 

 during which no rain falls. "While the active 

 growth of the trees is temporarily suspended, as 

 during the winter, this necessity for liquid nour- 

 ishment, of course, no longer exists. 



The reason forests cannot grow except where 

 moisture is present during nearly all the time the 

 plants are growing, will be easily understood from 

 the following considerations : 



Suppose a soil exists in any section of country, 

 and such soil contains .germs of practically all 

 species of plant life. "When such a soil is sub- 

 mitted to the action of light, heat, and moisture, 



