422 Insect Architecture. 



excrescence being rather larger than a walnut. We expected 

 to find this excrescence full of grubs, and were much surprised 

 to discover, upon dissection, that it was only a diseased 



Pseudo-gall of the Bramble, drawn from a specimen. 



growth of the plant, caused (it might be) by the puncture of 

 an insect, but not for the purpose of a nidus or habitation. 

 (J. E.) 



Another sort of excrescence is not uncommon on the 

 terminal shoots of the hawthorn. This is in general irre- 

 gularly oblong, and the bark which covers it is of an iron 

 colour, similar to the scoriae of a blacksmith's forge. When 

 dissected, we find no traces of insects, but a hard, ligneous, 

 and rather porous texture. It is not improbable that this 

 excrescence may originate in the natural growth of a shoot 

 being checked by the punctures of aphides, or of those grubs 

 which we have described. 



Many of these excrescences, however, are probably alto- 

 gether unconnected with insects, and are simply hypertrophic 

 diseases, produced by too much nourishment, like the wens 

 produced on animals. Instances of this may be seen at the 

 roots of the hollyhock (Althea rosea) of three or four years' 

 standing ; on the stems of the elm and other trees, immedi- 

 ately above the root ; and on the upper branches of the birch, 

 where a crowded cluster of twigs sometimes grows, bearing 



