112 PROTECTION OF WOODLANDS. 



greater degree liable to be damaged by them than broad-leaved 

 species ; and woodlands formed of large, contiguous, pure crops of 

 one or the other species, but particularly of Spruce or Scots Pine, 

 are especially exposed to the frequent and serious attacks of insect 

 enemies. 



So far as the species of trees are concerned, insects are either 

 monophagous, when the damage done is practically confined to one 

 kind of tree, as is the case with many insects feeding on conifers, 

 or else they are polyphagous when feeding more or less indis- 

 criminately on a variety of trees, as with a large number of insects 

 infecting broad-leaved species. But every kind of insect usually 

 attacks certain definite portions of trees, whilst every part of a 

 tree has its particular enemies, as we shall see in classifying the 

 injurious insects. And in a similar manner, it will also be found 

 that one insect principally attacks older crops, another poles 

 chiefly, and a third for the most part young crops formed either 

 by natural regeneration, or by sowing or planting (vide par. 63). 



So far as the damage done is concerned, it may be said that in 

 general, coniferous woods suffer far more than those of broad-leaved 

 species, not only because the most numerous and the most 

 destructive kinds of insects are to be found there, but also owing 

 to the latter trees having a much greater recuperative power. 

 The other factors of influence, however, include : 



The age of the crop ; as, for obvious reasons, young seedlings 

 and transplants suffer more than stems of older growth. 



The Part of the Plant attacked ; for destruction of the cambium, 

 or of the roots, is most injurious, and usually leads to the death 

 of the plant when the injury is at all extensive. Where the 

 damage is confined to the foliage, it may pass away merely with 

 the loss of a certain amount of increment, although in the case of 

 conifers 1 even this may lead to death. 



The Season at which the damage is done ; for if the attacks on 

 leaves and needles take place late in summer or in autumn, after 

 the buds have been formed for the following year, the duinn^e 

 always causes less loss of increment than if it take place in 

 spring. 



The Nature of the damage ; as for instance if, particularly in the 

 case of the Pine, the needles are totally devoured along with the 

 sheath encircling them, or if there be any possibility of tl 



1 Especially in the case of Spruce. Trans. 



