PLANT-LICE. 267 



may also be attacked. These plant-lice cause cankered growths 

 to appear on the boughs ; the new wood is their favourite seat 

 of war, where they can easily plunge their beaks into the soft 

 rind. This wound, at first boil-like, usually ends by splitting ; 

 deep cracks and crevices are formed, in which the insects seek 

 shelter. Growth is checked ; the crop does not mature, and 

 often the trees fail under the attack. If we examine this 

 white wool, we shall see that it proceeds from the backs of 

 the lice and females, as tine threads of wax. Amongst this 

 excretion we observe the orange-coloured lice, which get blown 

 from tree to tree with the wool by the wind, and even from 

 orchard to orchard. The adult females are slaty-grey to plum 

 colour, and have no cornicles ; these adults secrete a little wool, 

 but are also well protected by mealy powder and little globules 

 of an oily nature. In July and August there may appear 

 winged females, and in autumn an oviparous female and male 

 sometimes occur. Very few eggs are laid, however ; each 

 oviparous female only laying a single black ovum on the apple- 

 tree, so as to secure the continuity of the species. The majority 

 pass the winter as mother-females in crevices in the bark and 

 at the bottom of the cracks they have produced, more or less 

 protected by their wool from the cold. This species also 

 attacks the roots of the apple-tree. There is a ground form 

 of S. lanigera, like the ground form of the vine phylloxera. 

 The aerial form passes down to the roots in late autumn, and 

 the subterranean form crawls up again in spring. Thus as long 

 as we have the root form present we shall never eradicate this 

 pest on our apple-trees. 



Prevention and Remedies. — We notice this disease chiefly 

 rampant in neglected orchards, where the trees are cramped 

 together, and the trunks and boughs covered with moss and 

 lichens. Keeping the trees properly thinned, with plenty of 

 room for air, and clean, will prevent much damage from this 

 pest. All rough bark should be cleared off, mosses and lichen 

 destroyed by the caustic washes mentioned in the Appendix. 



