72 BRITISH GALLS 



nized by the brown tint around the orifice. The change 

 of colour is perceptible -within a few hours of the departure 

 of the larva. Connold received these galls from Worksop 

 in igog, the first British record ; his photograph is here 

 reproduced. 



The galls caused by Rhopalomyia milUfolii on the Common 

 Milfoil are probably not so uncommon as was at one time 

 supposed. They are usually situated at the top of the root 

 on a level with the earth, a position which makes them very 

 inconspicuous (Plate XXXI.) ; sometimes the leaves are 

 attacked, and even the flowers. They are usually coales- 

 cent when growing at the base of the stem. This gall is an 

 elegant structure about the size and shape of a hemp-seed, 

 green at first, becoming reddish -purple, and finally black. 

 The opening is stellate, with four or five lobes ; the interior 

 contains a single yellow larva. To breed the flies, old galls 

 should be obtained in May, and kept in test-tubes or glass, 

 topped boxes. 



Galls caused by Cystipkora sonchi on the radical leaves of the 

 Common Sow Thistle are shown in Plate XXXII. Sonchus 

 arvensis is of wide distribution in Britain, but its gall is rare, 

 being recorded only from the south of England. The 

 pustules are evident on both surfaces of the leaf, but less so 

 on the lower one. They are purple above, greenish below, 

 and average about 4 mm. in diameter. Usually each gall 

 contains a white larva, but Connold describes it as contain- 

 ing two. The right-hand figure in the plate is the lower 

 surface of a leaf with numerous galls ; some of them show 

 plainly the orifice from which the insect has emerged. 



Two species of Macrodiplosis attack Oak leaves, causing 

 localized folding of the margin. The galls are very different, 

 though not infrequently confused. They appear in June. 

 Those depicted on Plate VIII., Figs. 9 and 10, are caused by 

 M. dryohia. Some of the lobes are folded downwards until 

 they touch the inferior surface ; between the folds one to six 

 whitish larvae may be found. The surface above the fold is 

 tinted red; thus, the gall is easily recognizable (Fig. 10). 



