SOME FEA'l'URES OF OAK GALL GEOWTH. 17 



deformities thus produced are well illustrated in 

 Andricus sestivaUs, wliicli normally is cup-sLaped ; B. 

 apterci wlien solitary is globular. Three species of 

 Neurotenis are often much out of shape on account of 

 overcrowding, as may be seen on Plate LX, div. A ; 

 and A. Sieboldi, B. rennm and G. Kollari are at times 

 subject to much distortion from the same cause, 



(b) E iiiHronmPuf.— This also requires little more than 

 a passing notice. Those galls whose normal position is 

 on the under-surface of the leaf do not usually 

 attain their customary dimensions when on the upper 

 surface. A terminal, or nearly terminally situated, 

 specimen of Apldlothrix callicloma is rarely as long as 

 when axillary. (J. Kollari is sometimes badlv pinched 

 in a forked twig (Plate XXXVI, figs. 9-14),^ or when 

 bunched together in clusters (Plate XXXVIII). 



(n) Due to iiitemtd influences. — (a) Parasites are the 

 principal agents in causing these modifications. They 

 destroy the rightful owner of the gall, and in all 

 unilocular galls growth is usually arrested ; the struc- 

 ture either remains a diminutive form of what it would 

 have been, or some peculiarity is accentuated, such as 

 the style on A. solitarius and on C. Kollari (see Plate 

 XXXIX, div. C), or increase in the nund)er of ridges 

 on AjjhilotJirix caliidoma. 



(b) InquUines do not usually destroy the larva, but 

 only live within, and feed upon, tlie tissues of the gall 

 in company with the owner, but not in the same larval 

 cavity. In the majority of galls tenanted hj inquilines 

 no deviation from the normal dimensions are notice- 

 able. This is exceedingly well exemplified in speci- 

 mens of G. Kollari on Plate XXXIX, div. B. It is 

 in every way normal, yet from it there have emerged 

 the rightful owner and thirty- two incjuilines, but their 

 combined depredations have been so great as to leave 

 the exterior a mere shell. 



Of all galls, whether on the oak or any other British 

 plant, none appears to harljour more parasites and 

 inquilines and visitors than that of Teras terminalis, 



2 



