410 



PRACTICAL BOTANY 



(6) Wood-boring and leaf-eating insects should be killed, 

 if the expense of the process is not too great. It is suggested, 

 for example, that the great damage caused by the spruce- 

 destroying beetle, which kills mature trees by mining the bark 



FIG. 330. Oak trees growing in the open 

 A white oak at the left and red oak at the right 



of the trunk, may be much lessened. This can be accom- 

 plished by cutting and removing most of the infested trees, or 

 by girdling trees early in June to expose them to the attacks of 

 the beetles, then felling and either peeling them or immersing 



