164 NATURAL HISTORY. [CH. IX 



viviparous. The gall-nut will be, as that unrivalled 

 naturalist has conjectured, a matrix or womb, from 

 which juices are absorbed by the egg, in order to 

 furnish the material of its growth. 



The plant being alive, we can easily imagine that, 

 if any part of it be wounded, the sap would flow from 

 the orifice, and produce a knob, which would grow 

 and harden into an irregular mass. 



The gall-fly, however, has the art of altering the 

 organization of the part : an egg, together with per- 

 haps a most minute drop of fluid, is introduced into 

 a plant ; and a part which, under ordinary circum- 

 stances, would have expanded into a leaf or stalk, is 

 seen to burst out under the form of a fruit or flower, 

 as evidently organized, as if it had been trans- 

 ferred from the plant which it resembles, to that to 

 which it has no natural affinity. 



Why one insect should produce invariably one 

 species of gall, and another insect a different species 

 — why these should resemble the regular forms of 

 parts of other plants, are mysteries extremely diffi- 

 cult, if not utterly incapable, of solution. When the 

 egg is deposited in the young shoot, by a particular 

 kind of gall-fly, instead of pushing forth a sprout, 

 the irritation brings out an abundance of leaves, 

 which gradually assume the figure of an artichoke. 



The first general effect produced by the insertion 

 of the egg is, therefore, to augment the vegetative 

 powers of the part, and the next to alter their action. 

 The hairy gall of the wild rose, formerly employed 

 in medicine, under the name of Bedeguar, has a 

 mossy appearance. Here the liquor of the gall-fly 

 seems to have caused a disjunction of t?iose fibres 

 which, in their ordinary state, would have united and 

 formed a leaf. The difference observable in the 

 consistence of these various galls may possibly arise 

 from the different power of absorbing juices pos- 

 sessed by the different insects inhabiting them ; 

 though it is just as Dossible, in this guess-work, to 



