350 ESSENTIALS OF BOTANY 



uses, and the younger trees should not be injured by let- 

 ting those which are felled break them down as they fall. 

 Many kinds of woodland may be kept for centuries in a 

 condition of uninterrupted productiveness by thinning out 

 only the largest trees. 



(2) Forest fires must be prevented, especially in conif- 

 erous forests. This may be done by preventing fires from 

 being kindled for any purpose in large tracts of woodland, 

 and in some cases by cutting up woodlands, by means of 

 roads, into wood lots of moderate size. In dry, hot weather 

 constant inspection is needed to keep from spreading any 

 fires which may occur. 



(3) Parasitic fungi and those -^hich promptly seize upon 

 newly felled wood should be destroyed by^^burning both 

 them and the infected wood, taking suitable precautions to 

 prevent the fire from spreading. 



(4) Destructive insects, such as the various wood-boring 

 and leaf-eating species, should, if possible, be destroyed. 

 In many cases the expense of killing the insect pests of 

 forests would be too great to be undertaken on a large 

 scale. But it is thought that sometimes this may be accom- 

 plished by introducing into the region affected parasitic or 

 other insects which will destroy the species injurious to 

 trees. ^ Attempts are now being made to get rid in this 

 way of the gypsy moth, whose caterpillars strip both conif- 

 erous and deciduous trees until the woods attacked by 

 them look as if swept by fire. The importance of taking 

 prompt action upon the appearance of a new insect-enemy 

 of trees is well illustrated by the case of the gypsy moth 



1 A scale insect once rery destructive in Californian orange orchards wiis 

 SHccessfnlly cDntrolled by tlie introduction of an Australian lady-beetle which 

 fed on the scale insects. 



