142 RELATIONS OF TKEES TO THE ATMOSPHERE. 



We see a double system of operations carried on in- 

 visibly by trees and other plants. By them the moist- 

 ure of the earth is distilled into the air, where it is con- 

 verted into clouds, and returned to the earth again in 

 the form of dews and rain. Every fall of rain purifies 

 the air through which it descends, and carries down with 

 it into the soil a fresh supply of azote and oxygenated 

 air, which is needful to the roots of the plants. This 

 constant exhalation and absorption resembles the breath- 

 ing of animals, except that with plants inspiration and 

 expiration are simultaneous, and not alternate. I would 

 venture to say that when the sciences of vital chemistry 

 and vegetable meteorology are carried to perfection, the 

 fruitfulness of any region below the Arctic Circle may be 

 established and preserved by the systematic operations 

 of man upon the forest. 



In all temperate latitudes where man has not counter- 

 acted the efforts of Nature by his own works, she has 

 covered the land with forest as the most effectual means 

 of preserving a constant circulation of moisture between 

 the earth, the atmosphere, and the ocean. But this primi- 

 tive condition of the earth is not the one most favorable 

 to the wants of civilized man. There is a certain rela- 

 tive disposition, as >well as proportion of wood, pasture, 

 and tillage, that would improve the climate for man's pur- 

 poses, and another that would injure it. Nature clothes 

 all parts with trees, and leaves it to man to improve or to 

 ruin the climate, according as he is wise or stupid. Nations 

 in most cases have ruined it, and then sunk into barbar- 

 ism ; for civilization has never, in any country, long sur- 

 vived the destruction of its forests. 



