ROSE-GALLS. 305 



the use of the knife. There are about thirty-five of these 

 ^vooden knobs. 



On selecting one of the knobs, and examining it, a few very 

 small circular holes are seen, showing that the insects have 

 made their escape from the cells. Indeed, one or two of the 

 insects were found entangled amid the dry and crisp hairs that 

 surrounded the gall, and thus formed a second barrier, which 

 they could not penetrate. When, however, a sharp knife is 

 carefully used, the woody tubercle can be laid open in several 

 directions, and then proves to be a congeries of cells fused 

 together into one mass, and varying from four to twenty in 

 number, according to the size of the insect. Perhaps, on an 

 average, ten cells may be reckoned in each knob. 



The cells are of difterent sizes, some being more than ten 

 times as large as others. The superior dimensions of the cell 

 seem to be obtained at the expense of the walls, so that the 

 large cells can be broken by the finger and thumb, while the 

 small cells cannot be opened without the knife. 



The insects themselves are equally variable, some being mere 

 dots of shining blue and green, while others are about as large 

 as the common red ant of the garden, but with plumper bodies. 

 In consequence of these two facts, the large, strong-jawed insect 

 can easily make its way through the comparatively thin walls of 

 the large cell in which it was enclosed, while the small and 

 necessarily weak-jawed specimens are utterly unable to pierce 

 the walls of their cells, which are so thick that they must bore 

 a hole equal in length to that of their whole body before they 

 can escape into the air. Consequently, the great mass of the 

 insects that are found in the cells are the small specimens, the 

 larger having made their escape. I find that on an average 

 twenty small insects are thus found in proportion to one of the 

 larger kind. 



There is another gall, very common in England, which is 

 found upon the oak, and which is generally thought, by persons 

 who are unacquainted with botany or entomology, to be the 

 bud which naturally grows upon the tree. 



X 



