192 BRITISH FOREST TREES 



also by no means a small total. Whatever may be the 

 accurate number of phytophagous insects, the vast majority of 

 them are fortunately not noticeably injurious from a sylvi- 

 cultural point of view, though at the same time the oak has 

 a good many enemies in the insect world. Species of Melo- 

 lontha damage the roots as grubs, and the buds and leaves 

 as complete insects ; trees are sometimes almost completely 

 defoliated over considerable tracts by the caterpillars of 

 Cnethocampa processioned, as also to a less extent by those of 

 Gastropacha neustria, Porthesia chrysorrhaa, Liparis dispar, 

 Chematobia brumata, and Tortrix viridana; young stems are 

 attacked by larvae of Scolytus intricatus, Coraebits bifasciatus, 

 and species of Agrilus, and older stems by those of Xyleborus 

 monographus, dryographus, and dispar. Flowers and buds are 

 often destroyed to a very great extent by the caterpillars of 

 Chematobia brumata, Gastropacha neustria, and Tortrix 

 viridana. The timber is also liable to attacks from 

 Lymexylon navale, the eggs being deposited on unsound boles 

 or barked logs (never, according to Hess, 1 on sound growing 

 stems), and the larvae boring inwards thus ~L and damaging 

 the wood for technical purposes ; this insect is the scourge 

 of dock-yards. Galls on various parts are occasioned by the 

 females of Cynipida depositing their eggs ; the large galls, 

 or wood-apples, often so prominent on the lower sides 

 of leaves, being the nursery beds of the larvae of Cynips 

 quercus folii. 



On cold situations with wet subsoil, the lower portion of 

 the bole is often subject to a disease that renders it useless 

 as timber ; observation and examination have not yet quite 

 determined whether this unhealthy condition is primarily 

 due to the action of frost or of a fungus, but in any case the 

 fungus found in the diseased wood is Nectria ditissima. 

 The roots of one to three-year-old seedlings in nurseries are 

 1 Hess, Der ForstscJmtz, vol. ii. 1890, p. u. 



