INJUKIKS To TKKKS. 



107 



forests, and when abundant may do much damage, though mi 

 account of their comparatively small number they do but slight 

 injury. 



Severe Winters. These may injure many kinds of young 

 seedlings, which when two or three years old will be perfectly 

 hardy. Seedlings of such kinds should be dug at the end of the 

 first season's growth, and be heeled in over winter, or protected 

 by a mulch or earth covering in winter. 



Alternate Freezing and Thawing. Seedlings are often 

 thrown out of the ground by alternate freezing and thawing, and 



\1 



Figure 24. HEAVING OUT BY FROST, (a) Tree in 

 natural position, (b) Drawn up by alternate freezing 

 and thawing. 



in this way have their roots broken. This is most likely to hap- 

 pen where the ground is bare; if covered with leaves or grass, 

 or shaded in other ways, this seldom happens. The best pre- 

 ventive is to mulch the surface soil with leaves or other simi- 

 lar material, but as mice generally like to live in such places poi- 

 son should be used. It should be placed under the mulch, in tin 



