May, 1916] Morphology of the Zoocecidia of Celtis 273 



Fig. 9b shows the detail of the region indicated at Fig. 9a, b. 

 The simple-pitted sclerenchyma cells differ only in the shape 

 they have assumed on either side of the vascular bundle. On 

 their outer side they are bordered by crystal "sacs," a relation 

 which as observed earlier, obtains in the normal stem. More 

 highly magnified sections of these cells are shown in PI. XVII, 

 Fig. 9c. 



10. Phytophaga wellsi Felt. Cecidium nov. 



(PI. XVII, Figs. 10, 10a). 

 On leaf, under side, more or less definitely obconic, resembling 

 the shape of a somewhat flattened top. Generally found in 

 clusters attached to the sides of the principal veins near the 

 point of their divergence from the petiole. 2,}/^-S mm. high, 

 3-4 mm. wide. Distal end shows a more or less definite 

 central prominence. Yellowish tinged, with short pubescence. 

 Walls pithy in texture, yet firm; tissue when old, brown. 

 Chamber sub-cylindric. Protective layer poorly developed, 

 confined to proximal one-third of gall. Nutritive layer very 

 thin. Fibro-vascular bundles traverse galls near the surface. 

 This is the simplest of all the itonid galls studied. 



Description of adult insect b}^ Dr. E. P. Felt, in manuscript. 



11. Cecidomyia sp. (PI. XVII, Figs. 11, 11a). 



On leaf, under side, a small (2-3 mm. long, 1-1^2 mm. wide) 

 sub-cylindric gall with attenuate tip, which is more or less defin- 

 itely constricted from the body of the gall. Base rounded, light 

 green to yellow, smooth. Thin walled, the chamber approxi- 

 mating the shape of the gall. The galls are commonly tilted 

 over at a sharp angle, particularly when they arise from one 

 of the larger veins. The protective and nutritive layers are 

 distributed much as those of No. 7. 



Riley first described this gall (No. 35 in his paper) and called 

 attention to its similarity to C. unguicola Beut. (See No. 8). 

 It differs constantly from that gall, however, in its smaller size 

 and its non-flaring base. 



Riley, 5th Rept. U. S. Ent. Comm. p. 614. 1890. 



12. Cecidomyia sp. (PI. XVII, Figs. 12, 12a). 



"On leaf, under side, stoutly conical and nippled at tip. 

 Succulent, pale green, and covered with fine bloom when young. 

 3x4 mm. Present in great numbers; larva, white." Sears. 



