202 Our Field and Forest Trees 



when we breathe out, we send into the air carbonic 

 acid gas. 



So we and the trees suit one another like Jack 

 Spratt and his wife. Each takes from the air what 

 the other cannot use. Each puts into it what the 

 other needs. Sunbeams fall into a clear, warm 

 pool, where pond weeds are growing; little bub- 

 bles rise in a steady stream from the leaves which 

 are covered by the water. These bubbles are filled 

 with oxygen — and when we see how much of it 

 is made by one pond herb, we can imagine the 

 quantity which is given forth by a forest under a 

 bright July sun. 



Thus leaves purify the air, and help men and 

 animals to live. 



" Air in which lungs can no longer breathe, nor 

 candles burn, can be restored to its original con- 

 dition by the presence in it for a time of vigorous 

 plants." (Priestly.) 



An acre of forest, with its many boughs one 

 above another like the floors of a house, gives out 

 much more oxygen than could come from an acre 

 of truck farm, or of pasture, and it has tier above 

 tier of green leaves to devour the carbonic acid 

 gas, so harmful to animal life. 



Hence, the forests, which fill the air with sweet 

 odors, also rob it of poison and put into it the 

 essence of life. 



