46 NATURE'S FOOD-SUPPLY. THE CARBON CYCLE. 



of decomposition, wood is converted into simple chemical com- 

 pounds which join nature's food-supply in the air. 



By the means thus indicated the large part of the carbon ex- 

 tracted from the air by plants is restored again to the air in the form 

 in which it first existed. This carbon cycle is represented graphi- 

 cally in the accompanying diagram (Fig. 13). 



