GALLS AND PARASITES. 281 



trees and shrubs, but ^unfortunately not until after the 

 insects had escaped. Doubtless they were produced 

 by a similar fly. 



OAK-ROOT GALLS. Irregular excrescences, often 

 as large as the fist, at the root of oaks, are a kind of 

 gall produced by another species of Cynips. 1 These 

 may be easily mistaken for mere woody expansions 

 or gouty swellings, without suspicion of insect work, 

 but if they are cut into with a strong knife, their real 

 character will soon be discovered, with the cells, and 

 probably the larvae inclosed within them. These ex- 

 crescences are by no means uncommon, although they 

 are rather difficult to remove, as they grow upon the 

 thick roots, and are almost as hard as the timber 

 itself. Another kind of gall, consisting of single cells, 

 has been once or twice observed at the extremities of 

 the rootlets of oak. 



OAK SPANGLES. Two kinds of flat discoid galls 

 are very commonly produced on the under surface 

 of oak-leaves. One of these, called Oak Spangles, 

 consists of a small lentil-shaped body, thickest in the 

 middle, and attached beneath by a small point like 

 the shank of a button. The upper surface of these 

 galls is sprinkled with tufts of small hairs. It is often 

 supposed that these are fungi by persons who are un- 

 acquainted with those polymorphic plants ; but they 

 are in reality the work of insects. Leaves bearing 

 these galls fall from the tree in autumn, and lie on the 

 ground through the winter, during which time the in- 

 closed insect is being developed. If decaying oak- 



1 Cynips radids. 



