May, 1916] Morphology of the Zoocecidia of Celtis 271 



The distal one-third of the gall is composed of rows of very 

 thin walled cylindrical cells. Distally the inner superficial 

 layer of these give rise to numerous coarse trichomes, which 

 choke the apical canal leading to the larval chamber. 



The fibro-vascular bundles are not as large in proportion 

 to the rest of the tissues as the principal bundles of the leaf. 

 Their number and distribution are shown in Fig. 8b. Basally 

 they are related directly to the bundles of the leaf or as is often 

 the case they form a "knot" in the median basal region, this 

 "knot" being related to a number of leaf veins. Kiistenmacher 

 (14) finds a similar "knotted" condition of the bundles at the 

 base of certain Rhodites galls. The xylem elements are fine 

 spirally thickened tracheids. The phloem cells are simple 

 elongate cells whose end walls slant at a more or less prominent 

 angle. No bundle sheath tissue is evident; the proximity 

 of the bundles to the rigid protective layer making possible 

 their support without the normal mechanical tissue being 

 present. 



The normal leaf (Fig. 8a) is very little affected where the 

 gall is attached to it. The epidermis with its cystoliths and 

 two palisade layers, exhibits hypertrophy, but this not to a 

 marked degree. It is evident that the primordium of the 

 spongy layer has furnished the basis for the hyperplasia con- 

 stituting the gall. 



In the chamber region is shown the section of the larva. 



9. Phytophaga celtiphyllia Felt. (?) PI. XVIII, Figs. 9, 9a. 



A sub-balloon-shaped gall occurring on the leaves (either 

 side), petioles and stems. 4-8 mm. high, including the apical, 

 variable, attentuate tip, which arises sharply from the distal 

 end of the gall body. 4-53/2 mm. dia. through the broad 

 distal half of the gall. The sides do not taper proximally 

 in the typical balloon fashion, but show a definite constriction 

 below the distal expanded portion. When isolated the galls 

 show a perfect radially symmetric structure, but they are apt 

 to be found in clusters, resulting in more or less loss of symmetry 

 through mutual pressure. When on the leaves they generally 

 are found on the upper side attached close to the principal 

 veins. These galls retain their green color longer than any of 

 the others ; when full size in mid-summer, the content of chloro- 

 plasts in the superficial cell layers is so great as to make them 



