68 BRITISH GALLS 



and pupate in the earth. The Yellow Bedstraw occurs 

 throughout Britain, but Perrisia galU is by no means widely 

 distributed, apparently occurring chiefly in the south and 

 east. It attacks various species of Bedstraw on the Con- 

 tinent, but I am not acquainted with British records. 



The inflorescence and the young shoots of the Common 

 Lime are frequently attacked by Contarinia tiliarum. The 

 gall takes the form of an elongated or rounded tumour, 

 sometimes lo mm. in diameter, green at first, becoming 

 reddish (Plate VIII., Fig. 7). It contains numerous larvae 

 of a sulphur-yellow hue (see magnified section, Fig. 8). 

 Other members of the genus attack various plants. There 

 are fifteen recorded British species of gall-causing Contarinia, 

 exactly one-quarter of the number known in Europe. 



A much higher percentage of the members of the genus 

 OUgotrophus are gall-causers in this country. Houard 

 records nineteen Continental species. Eleven occur in 

 Britain, causing galls of very attractive appearance and of 

 great interest. Perhaps the commonest of all is the 

 hypertrophied bud of the Yew, resulting firom the presence 

 of the orange-coloured larvae of OUgotrophus taxi. The gall 

 consists of a mass of adpressed leaves surrounding a whitish, 

 fleshy central part. It is usually terminal. Late in May 

 many of the galls contain pupae ; these are orange- 

 coloured at first, but gradually become darker. The leaves 

 are then erect and nearly straight. Early in June the fly 

 emerges. (It is an orange-coloured creature, 5 mm. 

 long, and not more than 9 mm. in expanse of wing.) 

 The apical leaves then curve and twist, so perceptibly 

 altering the appearance of the gall that it is then quite 

 easy to distinguish those containing pupae from the empty 

 ones. It is doubtful if this change is always delayed until 

 the fly has emerged, for I have found flies crushed between 

 the leaves at the mouth of the gall. They are so minute 

 and delicate that it is not to be marvelled at that many 

 meet an untimely death in their compulsory journey to the 

 outsr world through this dangerous channel of moving leaves. 



