PLATE 20. 

 Vertical sections of a branch of Betula alba Linn. 



(One-third nat. size.) 

 Galled by 



Eriophyes rudis Canest. 



The specimen illustrated on the opposite page is the same 

 as shown on plate 19. 



It has been divided into halves vertically, and reveals the 

 solid and woody nature of the core, the grain of which, it may 

 be observed, is quite different from that of the branch. 



