GALL-FLIES. 



331 



A very minute reddish-coloured grub feeds upon dyer's 

 broom {Genista), producing a sort of gall, frequently glo- 

 bular, but always studded with bristles, arising from the 

 amorphous leaves. The stem of the shrub passes through 

 this ball, which is composed of a great number of leaves, 

 shorter and broader than natural, and each rolled into the 

 form of a horn, the point of which ends in a bristle. In 

 the interior we find a thick fleshy substance, serving to 

 sustain the leaves, and also for the nourishment of the 

 grubs, some of which are within and some between the 

 leaves. They are in prodigious numbers, — hundreds being 

 assembled in the small gall, and so minute as scarcely to be 

 perceived without the aid of a magnifying glass. The bud 

 of the plant attacked by those grubs, instead of forming a 

 shoot, pushes out nothing but leaves, and these are all 

 rolled and turned round the stem. Some shrubs have 

 several of these galls, which are of various sizes, from that 

 of a filbert to that of a walnut. 



Leafy Gall of Dyer's Broom, produced by Cynips genista ? A, gall, natural size ; B, a 

 leaflet uiagnitied. 



A similar but still more beautiful production is found 

 upon one of the commonest of our indigenous willows {Salix 

 purpurea), which takes the name of rose-willaio, more pro- 



