1 912] Morphology and Biology of Insect Galls 341 



Holcaspis bassetti Gillette. 

 Host Quercus macrocarpa Michx. 



A monothalamous gall occurring singly or in clusters around the 

 stems of the host. When grouped the galls often cover completely 4 to 5 

 inches of the stem. 



When the gall is not deformed by crowding, it is irregularly circular 

 in outline at the base, gradually tapering to a distinct point chat is re- 

 curved in most cases. The gall is attached to the host by a small stalk 

 at the centre of the base. Colour green, often tinged with pink when 

 young; becoming brown when more mature. The larval chamber re- 

 sembles closely that found in the former species in being oval and free 

 at maturity, but it differs in being placed nearer the base of the gall and 

 in tapering to a point at the end nearer the twig. 



Dimensions: — Diameter at base, average, 16 mm. 



Except in a few details the anatomical structure of this gall is the 

 same as that found in the species just described. In this species the 

 outer part of the parenchyma zone is composed of cells almost square 

 in outline, but towards the larval chamber the cells become more elongated 

 and arranged in distinctly radial lines. Rays of from one to three cells 

 in width pass in radial lines throughout this zone. The cells composing 

 them are much smaller than the ordinary cells of the zone. The cells of 

 the nutritive layer are much more elongated radially than those of H. 

 globulus Fitch (Figs. 58, 65). The cambial layers and the crystal-beanng 

 tissue hold the same relative positions as in the preceding species. The 

 relation of the crystal layer to the nutritive zone is shown in Fig. 58. 

 The protective sheath in the mature gall extends out almost to the epi- 

 dermis. Except in its distribution it cannot be distinguished from the 

 corresponding zone in H. globulus Fitch. 



Philonix erinacei Beut. 

 Host Quercus alba L. 



A polythalamous gall springing usually from the midrib but rarely 

 from a principal vein of the leaf. It originates from the under or occa- 

 sionally the upper surface of the leaf. 



The gall is spherical or ellipsoidal and slightly flattened on the sur- 

 face in contact with the leaf. The point of attachment is narrow and 

 elongated in the direction of the vein. The epidermis of the gall is divided 

 up into numerous facets, each of which is drawn out at the centre into a 

 trichome structure that becomes more spiny as the gall approaches 

 maturity. The colour of the surface of the gall is yellowish with occasional 

 red tints. The trichomes vary in shade from pink to red. 



Dimensions: — Longer diameter 10-15 rnm. ; shorter diameter 

 5-10 mm. 



