24 HAND-BOOK OF TREE-PLANTING. 



have been discovered on turning up the soil. 

 Once stripped of their tree-covering, by what- 

 ever cause, the annual and unimpeded fires 

 which have swept over those plains were 

 sufficient to prevent any subsequent growth. 

 But since settlers have come in and checked the 

 course of the fires by their barriers of plowed 

 fields, and by their watchful care, it has been 

 found that trees will grow wherever they are 

 given a chance to grow. They have been suc- 

 cessfully planted far beyond what many have 

 assigned as the natural limit of tree life. The 

 growth of trees, as of all plants, is dependent 

 upon a due supply of moisture. As we go 

 westward from the Mississippi, there are natural 

 causes which diminish the amount of rainfall in 

 proportion as we approach the Rocky Mount- 

 ains, and it has been held that from about the 

 one-hundredth parallel of longitude the amount 

 of rain is so small that trees could not be made 

 to grow, except sparsely just along the margin 

 of streams, unless by the artificial aid of irriga- 

 tion. But, happily, experience has proved that 

 the field of tree-growth reaches farther west 

 than many have been willing to allow. In West- 



