GALLS 185 



leaves, some being so shallow as scarcely to be noticeable, 

 while a few are well-formed pouch-galls. 



Of the Aphides (Green-flies or Plant-lice) a good many 

 produce Mantle - galls, varying from shallow discoloured 

 pouches or curled leaves, as on Currants, to very characteristic 

 pouches or cup-galls of considerable size and depth, and often 

 of peculiar form. Some produce bud-galls of cone-like form, 

 as on the Spruce, or short shoots with broad loose leaf 

 sheaths, between which the insects live. The notorious 

 Phylloxera produces galls on leaves and on roots of the Vine ; 

 and the almost equally notorious American blight, or woolly 

 blight, causes irregular outgrowths or cankers on branches of 



O o n> 



Apple-trees. 



COLEOPTERO-CECIDIA, or the galls of beetles, are com- 

 paratively few. They mostly belong to the closed type of 

 simple galls, and consist of an increase in the cellular tissue, 

 with no clearly defined cavity or complexity of structure. 

 They are found on roots and stems, as swellings of the cortex 

 or of the pith, and are seldom very conspicuous. They do 

 not often occur on leaves. The flowers are more often 

 galled, especially the ovaries. The larger number of gall- 

 making beetles belong to the family of Weevils (Cur- 

 culionidcs). 



DlPTERO-CECIDlA. By far the greater number of the 

 gall- making Diptera belong to the Cecidomyidce or Gall- 

 midges, a group numerous in species but very uniform in 

 appearance. A very large number of genera have of late 

 been put forward by specialists, based frequently on minute 

 distinctions. Many of the Cecidomyidce do not make galls, 

 some feeding on minute fungi, others being carnivorous. 

 From such forms we pass to the gall-makers by gradations 

 from very shallow pouches on the leaf-surface to well-formed 

 closed galls on various parts on the host. They seldom 

 show a complex internal structure. The surface may vary 

 from smooth to very hairy. We find among them, of the 

 simple type, Roll-galls, Pouch-galls, Cup-galls (sometimes 

 with a separable inner gall or lid), and Closed-galls, the 

 latter at times being not very different in appearance from 

 those of Hymenoptera. Bud-galls are very common, both 

 of the leaf type and of the flower type. The larvae live 

 23 E 



