May, 1916] Morphology of the Zoocecidia of Celtis 275 



might be interpreted as an immature specimen of the above. 

 Sear's number 34 is a variation of the above with the basal 

 one-third developing low irregular ridges. 



Riley, 5th Rept. U. vS. Ent. Comm. p. 613. 1890. 

 Sears, Ohio Nat. lo:3S4, PL 19, Fig. 34. 1914. 



15. Cecidomyia sp. (PI. XVII, Figs. 15, 15a, 15b.) 



This gall exhibits a remarkable variation from the previously 

 described simpler types. Riley, who first described it, gave 

 a very complete description of it, which will be quoted. 



"31. Galls on the tender twigs, occurring either singly or 

 in groups of two, three or four or more specimens; rarely 

 also singly on the under side or even the upper side of the leaf. 

 The gall bears a close resemblance to the winged seed capsule 

 (achenium) of a Rumex, but the wings vary in number from 

 three to five and are often irregularly developed, while the tip 

 always ends in a curved, long spine. The wings terminate in a 

 sharp ridge which is sometimes double. Gall opaque, not 

 hairy. Color pale-yellowish green, at apical third usually of a 

 more decided green and darker. A longitudinal section reveals 

 a single large regularly ovoid cell surrounded by a thin hard 

 wall. Average height of gall, 4.5 mm., excluding the apical 

 spine; generally as wide as high; length of apical spine variable, 

 but usually a little more than half the height of the gall." 

 Riley. 



The histology presents some points of special interest. The 

 fibro-vascular bundles are found in the edge of the wings 

 (PI. XVII, Fig. 15b), from which branches are distributed 

 inwardly to the protective layer. This is better shown in the 

 longitudinal section. Fig. 15a. The protective layer is found, 

 as in most of the preceding galls, to be confined to the proximal 

 two-thirds or three-fourths of the chamber wall. Trichomes 

 line the apical canal to the point where it opens in the chamber. 



16. Cecidomyia sp. Cecidium nov. (PI. XVIII, Figs. 6, 



pi. XIX; 16, 16a). 

 A gall of the leaves, stem, petiole or fruit occurring generally 

 in an aggregate condition. An isolated specimen on the stem 

 will be described to elucidate the fundamental unit character- 

 istics (PI. XVIII, Figs. 16, 16a). When found singly, the gall 

 is irregularly conic or sub-cylindric, with a very blunt truncate 

 tip. The chief character is involved in the fact that the gall 



