66 BRITISH OAK GALLS. 



other are developing, or have arrived at maturit}^, that 

 the twigs give evidence of their presence. 



SoUtary galls, or several scattered along an ordinary 

 slender twig, are difficult to locate. This may be 

 understood by referring to A, Plate XII. 



The galls are much more abundant in twigs than in 

 leaf petioles. 



This is a most obscure gall, and difficult for the 

 uninitiated gall collector to find. It may usually be 

 found by peeling off the bark of shoots near where 

 galls of Apldlofhrvfi radicis have grown. It occurs 

 only in shoots of the year, or in a leaf petiole. 



Its situation is beneath the bark, more or less 

 embedded in the xjdem, and is therefore completely 

 hidden from view. Its presence in a shoot can only 

 be conjectured by a very slight swelling of the bark 

 immediately above where the gall is situated. 



The gregarious habit does not furnish any additional 

 indication. In a leaf petiole, however, considerable 

 thickening is produced, and the galls are usualh' more 

 numerous there than in a shoot. 



Mayr says : " On Quercns puhescens the swelling 

 occasioned by this gall is still less perceptible on 

 account of the tomentum on the surface, and sometimes 

 it (the swelling) is entirely absent." 



After the imago has emerged the swollen part of the 

 bark subsides, but the minute circular exit-hole betrays 

 the position of the empty gall. 



I have found that this gall occurs more frequently 

 on stub-oaks, young trees, and bushes in hedges than 

 on large trees. 



The gall is widely distributed throughout Britain, 

 and in places very plentiful, a fact accounted for by 

 the vast number of imagines from an average-sized 

 gall of A. radicis. 



