12 



A PRIMER OF FORESTRY. 



which contain chlorophyll break up the carbonic acid 

 gas with which they come in contact, retain the carbon, 

 one of its elements, and send back the other, oxygen, 



into the air. Then, still 

 under the influence of the 

 sunlight, they combine the 

 carbon with the oxygen 

 and hydrogen of the water 



FIG. 6. Crowns of the Black Hemlock 

 (to the left) and Western Cedar. 

 Washington Forest Reserve. 



from the roots into new 

 chemical compounds, in 

 which nitrogen and the 

 earthy constituents men- 

 tioned above are also pres- 

 ent; that is to say, the food 

 materials which reach the 

 tree through the roots and 

 leaves are first digested in the leaves somewhat as food 

 is digested in the human body, and are then sent 

 to all living parts of tlie roots, stem, and crown, where 

 they pass through another process of digestion, and are 



FIG. 7. Stem and crown of a Long- 

 leaf Pine, the latter covered witli 

 moss swaying in the wind. 



