140 



PRINCIPLES OF AMERICAN FORESTRY. 



happens. The best preventive is to mulch the surface 

 soil with leaves or other similar material, but as mice 

 generally like to live in such places, poison should be 

 used. It should be placed under the mulch in tin cans 

 laid on their sides, so they may be readily found in spring 



FIG. 49. Heaving out by frost. A, Tree in natural position. 

 B, Drawn up by alternate freezing and thawing. 



and will not be liable to poison the birds. When seed- 

 lings are thrown out of the ground by frost, they should 

 be pushed back and have the earth pressed against them 

 as soon as the ground is thawed in the spring. 



Late Spring Frosts are common in the low lands of 

 many sections. They injure the trees by killing the new 

 spring growth after it has started several inches. A large 

 number of trees are seriously injured in this way, and are 



