330 



IXSECT ARCHITECTURE. 



is composed of concentric leaves diverging from the base, 

 and expanding upwards, somewhat like an artichoke. 

 Whether this leafy structure is caused bv a superinduced 

 disease, as the French think, or by the form of the pores in 



'j<ri #'^ 



Artichoke Gall of the Oak-bud, with Gall-fly (_Ci/nips quercus gemmcr), natural size, and 

 its ovipositor "(a) magnified. 



the pellicle of gluten suiTounding the eggs, or rather by 

 the tendency of the exuding sap of the oak to form leaves, 

 has not been ascertained ; but that it is intended, as in the 

 case of the bedeguar, to afford an efficient protection against 

 the weather to the included eggs or grubs, there can be no 

 doubt. 



From the ver}" nature of the process of forming willow- 

 galls, bedeguar, and the artichoke of the oak, whatever 

 theory be adopted, it will be obvious that their growth 

 must be rapid ; for the thickening of the exuded sap, which 

 is quickty effected b}^ evaporation, will soon obstruct and 

 finally- close the orifice of the puncture made by the parent 

 insect. It is accordingly asserted by Reaumur and other 

 observers, that all the species of galls soon I'each their full 

 growth. 



