Gall-Flies. 407 



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. 



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-willow, more pro- 

 bably from this circumstance than from the red colour of 

 its twigs. The older botanists, not being aware of the cause 

 of such excrescences, considered the plants so aifected as 

 distinct species; and old Gerard accordingly figures and 

 describes the rose-willow as " not only making a gallant 

 show, but also yielding a most cooling air in the heat of 

 summer, being set up in houses for decking the same." 

 The production in question, however, is nothing more than 

 the effect produced by a species of gall-fly (Cynips solids) 

 depositing its eggs in the terminal shoot of a twig, and, like 

 the bedeguar and the oak artichoke, causing leaves to spring 

 out, of a shape totally different from the other leaves of the 

 tree, and arranged very much like the petals of a rose. 

 Decandolle says it is found chiefly on the Salix helix, S. alba, 

 and S. riparia.* 



A production very like that of the rose-willow may be 

 commonly met with on the young shoots of the hawthorn, 

 the growth of the shoot affected being stopped, and a crowded 

 bunch of leaves formed at the termination. These leaves, 

 besides being smaller than natural, are studded with short 

 bristly prickles, from the sap (we may suppose) of the haw- 

 thorn being prevented from rising into a fresh shoot, and 

 thrown out of its usual course in the formation of the arms. 

 These bristles appear indiscriminately on both sides of the 

 leaves, some of which are bent inwards, while others diverge 

 in their natural manner. 



This is not caused by the egg or grub of a true gall-fly, 

 but by the small white tapering grub of some dipterous 

 insect, of which we have not ascertained the species, but 

 * Flore Fran9. Disc. Preliminaire. 



