GALLS 



399 



formed by dipterous insects the nutritive layers are often sharply sepa- 

 rated from the mechanical tissue adjoining. The epidermis of the gall 

 may represent the nutritive tissue when it develops as an inner hairy 

 lining to the larval chamber. Albuminous substances are found in such 

 papilla, or hairs, as well as drops of fat and small grains of starch, so 

 that the larvae are surrounded by abundant supplies of a rich pabulum. 

 Nutritive parenchyma may be formed within the mechanic mantel and 

 here it is available to the larval occupant of the cell (Fig. 162). In 



Fig. 162. — Cross-section of an un- 

 known gall on Quercus Wlslizeni. Ep, 

 pidermis; Mi, outer mechanic mantle; 

 St, starch-filled outer nutritive layer; 

 Ms, inner mechanic mantle. (After 

 Kiister, p. 252.) 



Fig. 163. — Insect gall on scrub oak, 

 Quercus nana, due to gall insect, Amphi- 

 bolips ilici folia with interior of gall. 

 Pine Barrens near Chatsworth, N. J., 

 May 27, 1916. 



Other cases, the food materials are stored outside the mechanic mantel, 

 and they become available only by the larvae breaking through the 

 stereid layer. The cells of the nutritive parenchyma are usually iso- 

 diametric, elongated and sac-like forms, or as delicate cell threads. In 

 the highly organized galls of the Cynipidae, the cells of the innermost 

 layers on which the larvae feed contain a cloudy dense cytoplasm in 

 which small fat globules are seen and this layer may be termed appro- 

 priately the protein layer. A starch layer lies outside of the protein 

 layer. Here the cells contain starch. Besides the nutritive bodies 



