CH. rr. 



COURSE OF THE SAP. 



57 



Now, in reference to ' the temperate and cold 

 zones/ it appears to me a contradiction to say that the 

 carbon of all our plants is formed from the carbonic 

 acid in the air, and that the superabundance of carbonic 

 acid in the air is formed by the plants. And in 

 reference to ' the tropics and warm climates,' suppose 

 this soldier's * wind to have conveyed the two gases 

 to their opposite destinations, tropical heat generates 

 aridity and sterility, unless where the soil is irrigated 

 by nature or art. What farther proof can we want 

 that the ' immeasurably luxuriant vegetation ' is drawn 

 by the roots from the soil, not by the leaves from the 

 exotic carbonic acid imported on so grand a scale by 

 Liebig from the north and south ? 



Then, the oxygen evolved by plants is essential to 

 the breathing of man and animals. And ' thus, cultiva- 

 tion heightens the healthy state of a country,' and a 

 previously healthy ' country would be rendered quite 

 uninhabitable by the cessation of all cultivation.' It 

 appears here that we poor beasts grow our air from 

 our plants, as well as our plants from our air. But 

 has Nature no plants without cultivation P And in 

 countries where she has no plants, as on sandy deserts, 

 or in regions of eternal snow, is the air impure and 

 unwholesome ? Or does more malaria hang over the 

 wide wide sea than over tropical swamps, which are 



* But perhaps Liebig will lay a down-line to the tropics above 

 his up-line to the poles. And will he dispatch his luggage- trains 

 of heavy carbonic acid gas by that ? Gravity forbid ! ! 



