40 BRITISH GALLS 



shown in Fig. 4. The brown flaps of epidermis that remain 

 after it has fallen away are depicted iii Fig. 5. These are 

 supposed to resemble the valves of an oyster-shell — hence 

 the popular name, which is not very appropriate. The 

 falling of the galls caused a constant pattering noise in the 

 v/Oods throughout August and September, resembling that 

 of rain drops. They fell in such numbers that on a square 

 inch of road beneath an Oak on August 21 I counted 

 thirteen of these galls. The wasp that emerges from the 

 "oyster" gall is the Andricus osfreus. According to Adler, the 

 sexual form is Neurotents Aprilinus, but Mayr holds other 

 views, and Beyerinck claims to have bred N. Aprilinus boia 



2 3 



Fig. 2— Axillary Bod of the Common Oak with Gall CAnsED 



BY THE PRESENCE OF THE Larva OF Andricus fecundatoY. (1/2.) 

 Fig. 3— Staminate Flowers with Galls resulting from the 



PRESENCE OF THE Larvae OF AndricHs pilosus. {3/1.) 



galls caused by the presence of the larvae of Andricus 

 soUtarius, 



In some instances the galls of one generation are rarely 

 seen, whilst those of the alternate one are very common. 

 In the majority the apparently rare galls are the little spring 

 forms on buds and staminate flowers, and it may be con- 

 cluded that they escape observation through their minute- 

 ness, and the fact that they are usually situated on the 

 higher branches. 



The hairy catkin gall and its alternate, the well-known 

 artichoke gall, illustrate this. The former is said to be 

 rare in Britain. It appears on the staminate flowers in 



