THE FOOD OF A TREE. 



11 



and preparing the way for the succeeding genera- 

 tion. As they stand together in the forest, the crowns 

 of the trees form a broken shelter, 

 which is usually spoken of as the 

 leaf canopy, but which may better 

 be called the cover. (See fig. 8.) 



THE FOOD OF A TREE. 



The materials upon which a tree 

 feeds are derived from the soil and 

 the air. The minute root hairs which 

 spring from the rootlets take up 

 water from the ground, and with it 

 various substances which it holds in 

 solution. These are the earthy con- 

 stituents of the tree, which reappear 

 in the form of ashes when any part of 

 it is burned. The water which con- 

 tains these materials goes straight 

 from the roots to the leaves, in which 

 a most important process in thefeed- 

 ingof the tree takes place. This proc- 

 ess is the assimilation or taking up 

 and breaking up, by the leaves, of 

 carbonic acid gas from the air. Jt 

 goes on only in the presence ot light 

 and heat, and through the action of 

 chlorophyll, a substance from which 

 the leaves and the young bark get 

 their green color. 



Plants containing chlorophyll are 

 the chief means by which mineral 

 materials are changed into food, so that nearly all 

 plant and animal life depends upon them. Plant cells 



FIG. 5. Crown and atem 

 of a young Western 

 Larch. Priest River 

 Forest Re serve, 

 Idaho. 



