CHAP. XXVII INSECTA : HYMENOPTERA 437 



The Marble or KoUari Gall (formed by Cynips 

 ^alT * T^^llO'i'i) is perhaps the commonest and best 

 known of all ; it appears to be specially plentiful 

 on young " oak scrub " (Plate IV.). The Gall Wasps may be 

 seen emerging from these in September or October, though 

 occasionally they remain within the galls until the following 

 May. After emergence they live for some weeks, and each 

 fly lays about 800 eggs ; so, even allowing for the many 

 accidents which may befall them, it is no wonder that the 

 galls are plentiful. By the following June the new galls 

 are developing rapidly, one or two together, at the 

 end of a branch or in the axil of a leaf. The gall is at 

 first soft, and yellow or green in colour, but as it matures 

 it darkens and hardens, until by September it is dark brown 

 and woody, and by then the majority of the insects are ready 

 to emerge. It is a strange fact that on examination all these 

 insects are found to be females ; no trace of a male has yet 

 been discovered, the generation being, apparently, entirely 

 parthenogenetic. This gall is said to be specially common 

 in the west of England, where, about fifty years ago, it was 

 widely used in the manufacture of a dye for cloth, and it 

 can alsa be used in the manufacture of ink. The galls 

 contain tannin, which, when exposed to the air, produces, by 

 a process of fermentation, gallic acid, a colourless liquid, and 

 this, when extracted and mixed with a solution of iron sul- 

 phate, forms an intense black fluid. The gall, however, which 

 is actually used now in ink-making, is not this British gall, but 

 the Aleppo gall of Turkey and Asia Minor, and also certain 

 Chinese galls. 



The darkening of the liquid in the gall by the action of 

 iron on it can be illustrated by cutting a soft gall with a 

 steel knife, when a dark stain results. 



The Bedeguar Gall, or " Eobin's Cushion " 

 ruar GaU (^o^'^^'i ^J Rhodites rosae), is another common gall, 

 found, in this case, on wild or garden rose-trees 

 (see Plate IV.). It is caused by its special Gall Wasp laying 

 several eggs in a leaf-bud, with the result that, instead of 

 forming a normal shoot with leaves, the bud forms a swelling 

 which finally becomes hard, and from which project many 

 moss-like filaments beautifully tinted green and red. When 

 cut across, the woody centre is found to have several cavities 



