PLATE 17. 



A twig of Betula alba Linn. 



(One-fifth nat. size.) 

 Galled by 



Eriophyes rudis Canest. 



The cluster of twigs illustrated on the opposite page 

 furnishes an excellent example of the development in which 

 there is no core, but where, the mites being widely distributed, 

 a bushy tangle of long and slender twigs is the result. 



It was taken to pieces for the purpose of ascertaining how 

 many twigs of not less than six inches long it contained. They 

 were very carefully counted. The number was 329. 



The measure shown in the illustration represents 12 in. 



The illustration is of a specimen from the tree at Guestling, 

 by the author. 



