136 ON INSECTS WHICH INFEST CONIFERS. 



as to admit of a free circulation of air among the young plants, and 

 to prevent overcrowding and other obstructions to the radiation from 

 the earth's surface, and evaporation from the trees themselves in 

 their young state, has likewise a salutary effect in preventing the 

 inroads of insect vermin. This is especially the case with larch 

 plantations, for moss-covered hark, engendered hy damp, close, and 

 confined situations and hahits of the tree, are fruitfid of disease, and 

 harbour innumerahle parasitical foes of the pine tribe. When plan- 

 tations have heen once thinned, and are fairly established in 

 growth, it suits very well to allow the second thinnings and prim- 

 ings to lie in the wood for a year after being cut, and then to 

 remove them suddenly in midsummer and burn them up. By this 

 plan a vast number of those insects which prefer settling upon fresh 

 cut and drying shoots and branches are destroyed ; but as, gene- 

 rally speaking, in & first thinning of any wood, their presence would 

 be rather in the way than otherwise, the plan suggested may be 

 found effectual with a second or third thinning — say when the 

 trees are sufficiently apart, and are probably from 12 to 18 feet high 

 or thereby, so that a free circulation of air can play through them 

 without being interrupted to any extent by the felled branches and 

 other primings during the first season after the thinning process 

 has been effected. To prevent harbours for insects in hard-wooded 

 plantations, the stools should be cut as loiv as possible, so as to prevent 

 sprouting, and the formation of cluster heads and bush-like forms. 



Note. — Coloured illustrations of several of the insects mentioned in 

 the foregoing paper are being executed, and will be given to 

 the Society, by Mr Hutchison, in the next part of the Transac- 

 tions. — Ed. 



