GALLS CAUSED BY MITES 95 



at maturity. They are usually present in great numbers, 

 and project almost equally, from both surfaces of the leaf. 

 The aperture is in the centre of a depression in the con- 

 vexity on the upper surface, I found these galls In great 

 abundance on Berry Head, Brixham, in June, 1909; about 

 the same time they were taken by the late Edward Connold 

 at Hastings, They are not common, and had not, to my 

 knowledge, been observed hitherto in Britain. 



Yew buds are not infrequently attacked by Eriophyes 

 psilaspis. Affected ones become swollen (Plate XXL, 

 Fig. 9), attaining 8 mm. in diameter. They do not unfold, 

 are often tinted with yellow, and minutely granulated. The 

 mites are very numerous, and congregate between the scales. 

 This gall was first noticed in Britain in the spring of 1875, 

 when it occurred in great numbers in Yew hedges near 

 London. It is frequent on trees and bushes that have been 

 clipped. 



Eriophyes vihurni causes small red pustules (about 5 mm. in 

 diameter) to appear on the upper surface of the leaves of the 

 Mealy Guelder Rose (Plate XXL, Fig. 5). The pustules are 

 usually coalescent, often occurring in such numbers as almost 

 completely to cover the leaf, which, however, is never greatly 

 deformed. These galls are covered with tufts of short, stiff 

 hairs. The opening is on the lower surface, and is surrounded 

 by a felt of hairs ; the interior is lined with hairs, amidst 

 which the mites may be found in hundreds. Various aspects 

 of the gall under low magnification are shown in Plate XXL, 

 Figs. 6 and 7. The Mealy Guelder Rose is frequent in the 

 large wood on the hill to the north of Weston-super-Mare. 

 A careful examination in June, 1910, revealed only two bushes 

 afflicted with the mites. These were growing side by side, 

 and the majority of their leaves, excepting the young 

 ones, bore the characteristic galls in enormous numbers 

 (Plate XXL, Fig. 5) ; closely adjacent bushes were quite 

 free. The limitation of the mites to two bushes only, in a 

 large wood containing hundreds of these bushes, is of great 

 interest. The non-infection of the majority cannot be 



