THE OAK. 17 



the tree itself, or from their fellow-colonists in it, will 

 amount to scarcely less than two thousand. 



To insects must be referred, also, the various species 

 of gall-flies, whose instinct teaches them to originate a 

 local disease in some parts of the Oak, 1 and thus to pro- 

 vide their offspring with food and a dwelling-house. A 

 history of the Oak would he imperfect without a full 

 notice of the curious productions known by the name of 

 Galls ; and as the subject is an interesting one, I do 

 not scruple to dwell upon it, although, strictly speaking, 

 it belongs as much to Entomology as to Botany. 



A small fly alights on a twig, or leaf, or bud, of an Oak, 

 and with an excessively acute instrument, with which it 

 is provided by Nature, for this express purpose, punctures 

 the vegetable fibre, and deposits an egg, or perhaps two or 

 more eggs, so minute as to be almost invisible to the 

 human eye. Why from the puncture of one kind of fly a 

 large irregular excrescence should te produced; \\hy from 

 that of another a smooth spherical gall, or a scaly bud, or 

 a flat circular scale, is all a mystery a mystery so deep 

 that no plausible explanation of it has ever been attempted. 

 To say that an alteration takes place in the character of 

 the juices ; that a disease is produced which arrests them, 

 and causes them to arrange themselves in a certain set 

 form this is not to account for the phenomenon : it is 

 merely an unsatisfactory statement of the result, the real 

 difficulty being left untouched. You must, therefore, be 

 content to read the description of the different kinds of 

 galls which have been observed, and test its accuracy, 

 when you can, by comparing it with the natural objects 

 themselves. 



In the first place, it appears that the different kinds of 

 insects select different parts of the tree in which to deposit 

 their eggs, and that the character of the galls produced 



1 In some parts of the New Forest, the Oaks afford a resting-place 

 to countless white Admirals, of which it is not difficult to capture 

 from twelve to twenty in a single sunny morning. 



