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 of 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 

 which bore something like roses ; he talks of it, as 



