316 BRITISH FOREST TREES 



root-system, amply sufficient to protect them from being 

 easily thrown. 



Cattle and deer browse on the succulent and nutritious 

 shoots, without doing much practical injury. With the excep- 

 tion of red-rot in the stem, due to Polyporus sidphnreus, it 

 is almost free from fungoid diseases, although the leaves of 

 young shoots suffer from the willow-rust caused by Melamp- 

 sora (which has a change of generation with Caeoma on 

 Scots Pine). Many insects feed on its foliage, but no 

 great amount of damage is thereby occasioned, the principal 

 species being grubs of Lina populi and L. tremula, the 

 caterpillars of Gastropacha neustria, Porthesia chrysorrhxa, 

 and Vanessa polychloros, the larvae of two species of Rhyn- 

 chites, and the full-grown insects, Lytta vesicatoria, Poly- 

 phyllafullo, and Rhynchites; Agrilus viridis as larva destroys 

 the cambium and sap-wood ; the larval- forms of Cossus 

 ligniperda, species of Saperda (S. carcharias especially), and 

 Zeuzera aesculizxz apt to attack the mature wood of the stems 

 growing on unsuitable soil and situation, and, in itsjiursuit 

 of these, woodpeckers often increase the damage done. 



Sylvicultural Treatment of Poplars. Aspen is naturally 

 even less qualified than birch to form pure forests or groups 

 of large size, and a preference is given to the latter wherever 

 there is a conflict between the two species, as the timber of 

 the former is poorer in quality and less marketable, the 

 trees complete their normal development at an earlier date, 

 and are even less able than birch to do anything for the 

 protection of the soil. Wherever it occurs, therefore, it is 

 usually only as an adventitious subordinate species, almost 

 certain to be removed in the course of thinnings, long 

 before the ruling species has attained its maturity. Though 

 neither partial to dry sandy soil nor to marshy ground, it 

 has a distinct preference for situations with moist atmosphere ; 

 and as it is comparatively insensitive to frost, it is apt to 



