264 The Ohio Joiirual of Science [Vol. XVI, No. 7, 



epidermis. The stone-cell type of sclerenchyma forms an 

 extremely rigid structure. The nutritive tissue does not exhibit 

 the regular cambium-like formation as observed in the preceding 

 gall, its elements assuming an irregular aspect; those on the 

 inner side being tangentionally stretched. The reduced fibro- 

 vascular bundles traverse the outer region of the nutritive layer. 



6. Pachypsylla mamma Riley. (PI. XIX, Fig. 9; PI. XV, 

 Fig. 6, a). 



A short, sub-cylindric gall on the under side of the leaf, 

 5-8 mm. high, 43/^-53/^ mm. wide at base, almost uniformly 

 arising near a principal vein. The distal end varies from a 

 definitely smaller diameter than that at the base, to a noticeably 

 larger diameter, in the first case the galls are sub-conic with 

 rounded ends, in the second, sub-balloon-shape, with the ends 

 more flattened. On the upper side of the leaf is a conspicuous 

 circular depression or basin, in the center of which a minute 

 conic papilla is evident. This papilla is part of the first gall 

 tissue developed, being the cone which grew up around the 

 larva in the process of embedding it in the leaf tissue. In 

 color the galls are light green, varying to violet and purple 

 tints. Most specimens show a definite bluish bloom. The 

 adult galls are smooth, though when very young they are 

 covered with an array of long acicular trichomes. The galls 

 when fully mature show interiorly a dome-shaped cavity, which 

 extends to the very base of the gall. This cavity is developed 

 through the dehiscence of the middle tissue of the nutritive 

 layer. A secondary chamber, variable in size, though much 

 smaller, is found in the region beneath the papilla. It rep- 

 resents the failure of the tissue above the larva to grow com- 

 pletely together. The walls are firm and brittle. The insects 

 leave the gall about the time of the first frost and as imagoes 

 spend the winter concealed in the bark of the tree. The galls 

 are more or less abundant on hackberry trees everywhere. 



Riley, Johnson's Universal Encyclopedia, p. 425. 1877. 

 Riley, oth Rcpt. U. S. Ent. Comm. p. 618-619. 1890. 



This histology of this gall has been previously studied by 

 Cook (2 [v. ;i p. 42()]) and Cosens (3 [p. 308]). The chief 

 difference between those studies and the author's is the fact 

 that the material studied for the present paper, disclosed the 

 presence of a fine canal leading in from the distal end of the 



