46 OUTLINES OF FORESTRY. 



It is in the temperate regions of the earth and 

 in some parts of the tropics that the great forest 

 areas are to be found, since it is in these regions 

 that the rain may fall at almost any time of day, 

 and on almost any day of the year. 



There are, however, certain regions in the tropics 

 where forests exist, although there are compara- 

 tively extended periods during the growth of the 

 trees when rain does not fall. Here, however, the 

 air is very moist, and heavy dews take the place 

 of rain, or the rich vegetable humus absorbs the 

 vapor directly from the air; or, in some cases, 

 though growth is not actually suspended, it is at 

 least so markedly retarded that the decreased 

 nourishment of the trees is less injurious. 



It is especially on the sides of mountains, where 

 rain may fall in no matter from what direction the 

 wind comes, or on the side of an island or conti- 

 nent that receives the prevalent wind, that forests 

 are to be found in nearly all portions of the earth's 

 surface, provided the heat is sufficiently great and 

 a suitable soil is present. These conditions of soil 

 and temperature exist on nearly all mountain 

 slopes outside the polar regions. 



The mountains may, therefore, be regarded as 

 the natural home of the forests. The mountains 



