174 INSECTS. 



for instance, the tops of nearly all the twigs in a quick- 

 set hedge may sometimes be observed to be thickened, 

 rough, and apparently pierced with small holes, present- 

 ing an appearance very like that of old and deserted 

 woody galls, but arising in reality from a fungous growth. 

 So also an accidental injury to part of a tree will often 

 produce a gall-like excrescence either on the wood or 

 in the leaf-buds. 



These galls are amongst the most puzzling of natural 

 phenomena. All that is actually known is that the 

 parent insect punctures stem, leaf, bud, or stalk, and 

 there deposits an egg and (it is supposed) a drop o; 

 irritating fluid. It is not difficult to imagine that this 3 

 by arresting the circulation, might result in the forma- 

 tion of a shapeless or perhaps globular tumour ; 

 and in plants having a tendency to produce hairs, 

 prickles, &c., that the tumour might be hairy or prickly ; 

 nor even might we see much difficulty in a modification 

 of form or character depending upon the part of the tree 

 affected. But what are the facts ? On the leaf of the 

 oak we find a small globular, smooth, clear gall, closelj 

 resembling that which is found growing on the flower- 

 stalk of the same tree, and that which is found on 

 the rose-leaf; and on the very same leaf we find a 

 number of flat or slightly conical scale-like galls, 

 covered with tufts of hair, and attached to the leaf by a 

 short footstalk. It is clear that the oak-leaf has not 

 insisted upon one mode of developing its little tumour. 

 The rose-tree, upon the leaf or leaf- stalk of which we find 

 the little smooth gall like that of the oak, examined 

 farther, presents us with a ball of moss produced by the 

 puncture of another Gallfly, proving that no necessity- 

 exists in the rose forcing it to develope this mossy cover- 



