24 OUTLINES OF FORESTRY. 



of the plant. Heat and light are to be found in 

 practically all parts of the earth. They differ, 

 however, in amount, in different regions of the 

 earth, and such differences cause the differences 

 that are noticed in the plants that grow in dif- 

 ferent regions. 



Even in the same region, differences in the light 

 and heat cause differences in the plant's growth, 

 as may be noticed in almost any forest region. 



The plants that form the undergrowth of those 

 portions of the forest where the light is more 

 thoroughly shut out are markedly different from 

 those appearing in the clearings, where the light 

 and heat have full access to the soil. 



The nourishment of the plant comes next in 

 importance. The quantity of carbonic acid found 

 in the air is practically the same in all parts of the 

 earth. The quantity of moisture in the air differs 

 very greatly in different parts of the earth, and 

 on this difference, together with the difference of 

 temperature, depends the differences observed in 

 the plants of various regions. 



The liquid nourishment of the plant in the 

 shape of water is of so great importance to the 

 growth of the plant, that the character of the 

 rain-fall in any country will, to a marked ex- 



