GALLS CAUSED BY GALL- WASPS 35 



582 eggs." The " fly " often attacks the buds so fiercely 

 that the tissues are destroyed and no gall results ; but 

 where her zeal has been tempered with discretion the bud 

 begins to swell about the beginning of May. Gall forma- 

 tion proceeds rapidly, and by the end of the month the 

 " Oak-apple" has arrived at maturity (Plate IV., Fig. i). It 

 is usually solitary, but sometimes three or four may be 

 found together. It is greenish-yellow at first, and soft and 

 sappy, becoming harder and tinted rose colour at maturity. 

 The larval cavities are numerous, and many of them contain 

 parasites, this gall being exceptionally prone to attack by 

 many species. The wasps {Bioyrhiza pallida, also known as 

 Teras terminalis) emerge in July. Both sexes are present ; 

 the male is winged (Fig. 3), the female wingless (Fig. 4), or 

 provided with rudimentary wings. She much resembles 

 her mother, but is smaller. Adler proved by experiment 

 that she crawls down the trunk and pierces the roots. The 

 presence of the larvae therein gives rise to the root-galls 

 already described, and so the generations are repeated. 

 Some females appear to inherit the instincts of the mother 

 instead of the grandmother, pricking leaves and buds instead 

 of roots ; the galls that result are, however, always abortive. 

 The root-gall, it may be observed, yields no inquilines, and 

 but one parasite. 



An Oak sprig bearing an " apple " was worn on May 29 

 to commemorate the return of Charles II. to England on 

 that date (his birthday), and his escape after the Battle of 

 Worcester. The custom still survives in some parts of the 

 kingdom. Excepting in minor details, the life-history of 

 the " Oak-apple " gall-wasp is the same as that of all in 

 which the regular alternation of generations occurs. The 

 larvae of the parthenogenetic winter brood develop in more 

 or less hard galls of slow growth (subterranean in two 

 species) ; the larvae of the sexual summer generation develop 

 in soft sappy galls of rapid growth. The soft galls are 

 produced in spring, when the supply of sap is abundant; 

 the harder galls arise in autumn, when there is diminished 



