14 HAND-BOOK OF TREE-PLANTING. 



priate remedies for evils when they are made 

 known to us, and warned in part by the experi- 

 ence of those nations, we adopt measures which 

 give promise of relief from the threatening dan- 

 ger, or at least a mitigation of the evils natu- 

 rally consequent upon our previous conduct. 



History shows that the inhabited world has 

 been characteristically a tree-world a world 

 peopled by trees as well as men, and science 

 teaches us that the world is habitable by man 

 only as man and the trees hold it by joint occu- 

 pancy. The trees preceded man on the earth 

 as a prerequisite of his existence here and a 

 preparative for it. It was their office to elimi- 

 nate from the atmosphere of the early world the 

 deleterious gases which made it irrespirable by 

 man, and it is their office now to maintain that 

 balance between its constituent elements upon 

 which man's health and vigor depend. Chem- 

 ists and physiologists show us that plants 

 are continually absorbing carbonic-acid gas and 

 pouring out oxygen, or vital air as it was for- 

 merly called, because it was regarded as having 

 an indispensable connection with life. 



It has been the conclusion of scientific inves- 



