GALLS CAUSED BY MITES 97 



also said to be the cause of the dense masses of small twigs 

 which almost completely cover the trunks of some Beech 

 trees. A remarkable example is shown in Plate XIV. ; 

 the absence of twigs from the lower part of the trunk is 

 probably due to rubbing by cattle. 



The Sycamore leaf on Plate XIII., Fig. i, is studded with 

 the galls of Eriophyes macvorrhynchus. They are very common 

 in June and July, often occurring in hundreds on a single 

 leaf. The average diameter is 2 mm., the height 3 mm. ; 

 the shape is shown in Fig. 2, which gives a magnified view 

 of two galls. Fig. 3 is a section of the same magnification, 

 showing that the hairs within are more abundant towards 

 the base. Fig. 4 is an enlarged view of the aperture of the 

 gall, with its armature of hairs ; and Fig, 5 a magnified hair, 

 to show its unicellular character. Hairs are often present 

 at the base of the gall on the upper surface of the leaf; a gall 

 may occasionally be found on the lower surface. Mites 

 occur but rarely in galls filled with hairs ; hairs are always 

 present at the orifice, and probably afford some protection 

 to the inmates. 



There is a splendid photograph of these growths in Con- 

 nold's " Vegetable Galls," wherein they are ascribed to Phyl- 

 locoptes acericola, a mite which sometimes occurs in Company 

 with E. macrorrhynchus. The characteristic gall of P. acericola, 

 however, is a very slight swelling on the upper surface of the 

 leaf, with the corresponding depression on the lower one 

 filled with a mass of swollen hairs. It is situated between 

 the larger veins. Fig. 15 is a magnified section through two 

 veins and the gall of P. acericola between them. Fig. 6 

 represents E. macrorrhynchus magnified 250 times. This mite 

 also gives rise to the well-known red pimples often occurring 

 in enormous numbers on Maple leaves. They appear in 

 the latter part of May as minute specks, when they are 

 noticeable only because of their light green tint; at maturity 

 they assume a beautiful reddish-purple tint (Plate XIII., 

 Fig. 7). They are spherical and usually densely gregarious. 

 Fig. 8 shows three mature galls and a young one ; Fig. 9 is 

 7 



