478 



C0NIFER,E. 



of the tree, from the root to the summit, becomes as it 

 were encased by a mass of living matter, each individual 

 of the countless multitude being engaged in extracting 

 the circulating fluids of the tree by means of a sharp 

 hair-like proboscis which penetrates the exterior bark. In 

 this state the tree appears as if covered or dusted entirely 

 over with a white mealy substance, which, as already 

 observed, exudes from the skin of the insect, and pro- 

 bably answers as a defence against rain and cold, or a 

 protection against its enemies. After an attack such as 

 we have described, and which generally lasts for two 

 or three years, the tree is either left in a dying state, 

 or with a considerable portion of the top destroyed, an 

 unhealthy-looking yellow foliage, and a thickened diseased 

 bark, and these effects, we may observe, are not confined 

 to plants of a small size or tender age, but are equally 

 severe upon full-grown trees of stately dimensions. 



Hitherto no effectual remedy has been discovered, either 

 to prevent the attack or put a stop to the increase and 

 destructive effects of this pernicious insect ; for although 

 there are certain liquids, such as lime-water, infusion of 

 tobacco, &c, which prove fatal when they reach the 

 naked body of the Eriosoma, their application is rendered 

 comparatively unavailing by the nature of the cottony sub- 

 stance that envelopes them, which effectually repels the 

 admission of the liquid to the skin of the insect ; the 

 cost and labour of such applications upon an extensive 

 scale where numbers of trees are affected, as well as the 

 impossibility of reaching every part of an infected tree, 

 also render such remedies almost nugatory, or necessarily 

 confined to a very few cases. 



At Twizell, where the Silver Fir has been liberally 

 introduced, a few trees, which, from their situation it was 



