162 NATURAL HISTORY. [CH. IX 



under the outward covering of a plant, whence a 

 little mansion springs up which provides its inmate 

 both with shelter and food. Judging- from the great 

 number of plants attacked by them, it would appear 

 that our insects are destined to fill a very important 

 department in the economy of nature. These ex- 

 crescences are found in every part of a plant ; there 

 is scarcely a portion of the oak, for instance, whe- 

 ther it be root, branch, stalk, leaf, or bud, which is 

 not capable of furnishing the gall-insects with a 

 habitation. 



Some of the galls are tenanted by only one em- 

 bryo, others contain many in their larva state, so 

 that these insect-houses consist either of one or 

 many chambers ; they vary in size from the minute- 

 ness 6f a pin's head to the bulk of a walnut ; they 

 sometimes resemble fruit, both in shape and colour: 

 the gall of the oak, for example, is sometimes 

 shaped like an apple, sometimes like a bunch of 

 currants, and sometimes like an artichoke : but it 

 were endless to enumerate the strange and beautiful 

 diversities which are produced by a tiny insect in a 

 space of time varying from a few hours to a few 

 weeks. 



The older botanists mistook the trees in which 

 these vegetable excrescences were produced for 

 distinct species. Thus, Gerard describes a willow 

 ^vhich bore something like roses ; he talks of it, as 



