PHAXTOM FLOWERS. 



75 



acid pervades the atmosphere, from wliieli the leaves 

 are constamly separatmg it from tlie oxygen, and ap- 

 propriating its carbon as a continuous contribution to 

 the gTOwth of the plant. The roots, by a process of 

 their ot^'u. in like manner extract the same substance 

 from the carbonic acid of the water around and below 

 them, and convey it upward into the body of the plant. 

 But much the largest portion of the carbonic acid 

 which forms the food of plants, is absorbed by the 

 leaves. 



As carbon, and not carbonic acid, is the food of 

 plants, the power of decomposing the latter, so as to 

 leave them in possession of the former, and of expel- 

 ling the supertiuous oxygen, is therefore indispensable 

 to their growth. In reality, the leaves are the lungs, 

 as their fimctions are strikingly analogous to those 

 performed by the lungs of animals. The green leaves 

 of a gi-owing plant absorb carbonic acid : they expose 

 it to the action of the sun's light ; the oxygen is 

 separated from the carbonic acid, and is given out 

 by the leaves : the carbon remains, and, entering 

 into the system of the plant, immediately increases 

 its bidk. 



The growth and vigor of the tree depend on the 

 rapidity with which this decomposition, or digestion of 



