May, 1916] Morphology of the Zoocecidia of Celtis 25& 



early. Affected stems either smooth or pubescent. The larva 

 finishes feeding on the central part of the galled twig and leaves 

 the structure during the early part of May. It always eats out 

 a circular hole near the base to make its exit. (PI. XIII, Fig. 2 a). 

 The gall soon after turns brown and drops from the parent branch. 



Patton (26) has described a "hollow, elongate, twig swelling" 

 from which he states cecidomyidous flies emerged "about the 

 middle of June." From his brief description it is impossible 

 to state whether his gall is the same as the one here described. 

 The flies noted might have been parasitic on the lepidopteron. 



Riley reports a tortricid, Proteoteras sesculana Riley, 

 occurring on the hackberry. No mention of any gall is made, 

 however, in connection with this tree, other than that the larvae 

 were found "on short twigs." On the buckeye and maple it 

 "bores in the terminal green twigs, producing a swelling or 

 pseudo-gall." (See Am. Nat. cit. below). This may be the 

 insect concerned in the production of the lepidopterous gall 

 herewith described, but from this mere suggestion of its gall 

 forming habit, it is impossible to be certain. 



Riley, Trans. St. Louis Acad. 4:321-322. 1882. 



Rilev, Am. Nat. 16:913-914. 1882. 



Riley, oth Report U. S. Ent. Comm. p. 609. 1890. 



When studied histologically this gall is seen to be an 

 excellent type of kataplasma (PI. XIII, Fig. 2d). Sections of 

 the normal and galled twigs are contrasted in 2b and 2c. The 

 normal stem has suffered serious inhibition of its differentiation 

 associated with marked hyperplasia. The xylem consists of 

 but few primary and secondary vessels. The cambium is 

 practically obliterated in the general mass of parenchyma 

 formed. The bast elements never attain their ordinary heavy 

 walls. The layer of stone cells with its accompanying crystal 

 bearing elements does not appear at all. This study was made 

 from material which had already begun to die back at the distal 

 end, so that the condition found is not any stage of incomplete 

 normal differentiation. 



Fam. PsYLLiD.^. (Ord. Hemiptera). 

 The psyllidse among hemipterous gall makers take third 

 place, the aphididge and coccidce surpassing them in number of 

 genera and species. Kiister (17) reports seven genera from 

 Europe. There are three known in America, the genera 

 Livia, Trioza and Pachypsylla, which latter is confined in its- 

 gall forming habits altogether to the hackberry. 



