hegner] GALL INSECTS AND INSECT GALLS . 207 



a. Felt galls: simple galls due to the growing out of hairy 

 coverings of various sorts. The majority of these are caused 

 by mites. 



b. Mantle galls : hollow, simple galls with a lining of a 

 portion of the surface of the affected organ, and in many 

 cases an open communication. 



Fig. 8. Cock's Comb Elm Gall. 



Forms a cock's comb, blubber-like growth on the upper 

 side of the elm. (After Beutenmuller). 



Fig. 9. Goldenrod Gall. 



Consists of a small bunch of accumulated aborted leaves, 

 one-half to three-fourths inches long. Caused by the arrest 

 of the side branches. Inside, at the base, is a hollow space 

 in which the larva lives. On stalk of goldenrod. Singly or 

 in numbers. (After Beutenmuller). 



c. Solid galls: simple galls formed by eggs deposited on 

 the surface and not within the tissue. These differ from the 

 mantle galls in that there is no cavity or opening; the adult 

 gall-insect must, therefore, bore its way out. 

 2. Compound galls: those galls in the production of which 

 several plant organs are concerned. 



