10 BRITISH OAK GALLS. 



egg is laid within or upon its tissues no gall formation 

 takes place. Taking this, therefore, as the main 

 feature upon which gall formation depends, it will 

 not be difficult to trace a few leading characteristics 

 relating to the development, environment, aberrations, 

 etc., in British oak gall growth. 



They may be tabulated as shown on page 9. 



DuKATiON OF Growth. 



(a) Bapul ; a few days. 



The periods of duration of growth are either very 

 short or protracted. In point of rapidity probably no 

 other oak gall develops and reaches maturity with 

 such speed as does 8pat]ie(jastev Aprilinus. Under 

 ordinary conditions three or four days are sufficient 

 for it to be completely formed and reach its maximun 

 of size. SjHitJiegaster haccarnm, S. tricolor and Trigoii- 

 asjjt's crusfalis are about equal with each other in the 

 same respect, and either may he mature within seven 

 or eight days. This does not imply that the inhabitant, 

 or inhabitants, have passed through the metamorphoses 

 and the imagines ready to emerge, although in the 

 case of S. Aprillnus only a few days more are required 

 for its 'accomplishment. 



(b) Slow ; several months. 



The gall of Cynvps Kollari doubtless requires a longer 

 time to attain maturity than any other. Beginning- 

 growth early in April, it steadily progresses until 

 September before it ceases. But C. Kollari is a gall 

 by itself. It has been described as neither catkin, 

 leaf, bud, nor stem gall, belonging, indeed, to another 

 and separate category. 



Aphilothrix radicis is the next slowest in growth, 

 five months being occupied in its development. Its 

 persistency and protracted decay are about equal to 

 those of G. Kollari, extending to two or even three 

 years. 



