GALLS CAUSED BY MITES 
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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 macrorvhynchus. 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. macrorvhynchus. 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 
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