DESCRIPTIONS OF OAK-GALLS. 



207 



cell. The galls occurring on Q. puhescens are covered with 

 short, scattered, both simple and branched, hairs, of about 

 0'3 millimetre in length, so that they greatly resemble the 

 following species. In the second fortnight of May, sometimes 



Fig. 70. SPATHEOASTEn BACCARUM. 



the beginning of June, the flies bite through the gails, where- 

 upon they become completely shrivelled in a few days ; only 

 such galls as are inhabited by inquilines retain their shape ; 

 and often dry, brownish yellow, but still perfectly spherical, 

 galls may be found in autumn, which always contain a 

 Pteromaloicl larva or pupa. From Herr Forel I obtained the 

 galls of this species from the Vosges and from the Lake of 

 Geneva. — G. L. Mayr. 



It is this species which is the cause of the well-known 

 currant galls of the oak ; and here we have a slight departure 

 from the general uniformity of gall species : those of S. 

 baccarwn differ somewhat from the circumstance of their 

 situation, and become divisible into two varieties, though 

 both are structurally constant: these are (1) the true currant 

 gall, Linne's Quercus pedunculi, occurring on the stamini- 

 ferous flowers ; and (2) the berry gall, Linne's Quercus 

 baccarum, occurring on the leaf. Both varieties occur 

 together; they are very common, generally distributed, and 

 conspicuous either on the young leaves or catkins in the first 

 fortinght of May in the South of England, June, in North 

 Britain. Like other abundant galls its increase is much 



