April, 1904.] Galls and Insects Producing Them. 143 



by the separation of the cells in this zone is bridged bj^ numerous 

 unicellular threads as in C, papillatus (Figs. 30a, b, c). In the 

 outer part of the parenchyma zone, but near the cavity, are 

 formed the fibro-vascular bundles. The epidermal zone is well 

 defined and the trichomes on the surface are uni-cellular (Fig. 

 126CJ. 



4. GALLS OF TENTHREDINIDAE. 



The galls of Nematus pomum Walsh were the only leaf galls of 

 this family that I secured and they were mature. There was no 

 indication of a zonal structure, but the cells were very uniform in 

 size and structure throughout the entire gall (Fig. 127). Many 

 of the cells contained tannin and intercellular spaces were large 

 and evenly distributed. 



Part II. Lateral Bud Galls. 



Mature specimens of Holcaspis globulus Fitch show the four 

 well defined zones (Fig. 128). The inner nutritive zone is thick, 

 composed of small cells and well supplied with nutriment for the 

 larva. The protective zone is thin and composed of very small 

 cells with thin walls. It gradually merges into the nutritive zone 

 on the one side and the parenchyma zone on the other side. The 

 parenchyma zone is very thick, the cell walls medium in size and 

 the fibro-vascular bundles small and numerous. Further obser- 

 vations upon this gall emphasize the statement previously made 

 that it is the enlargement of an incipient stem. 



Further observations upon the gall of Andricus seminator 

 Harris confirm the statement previously made that it is a com- 

 pound gall produced by the insect depositing an o^^g in each 

 element of the bud. 



Part III. Stem Galls. 



The gall of Diastrophus nebulosus O. S. (Fig. i2ga, b) is a 

 very large swelling on the canes of Rubus villosus and is about 

 two or three inches in length. It contains a large number of 

 larval chambers each containing a single larva (Fig. 129a). The 

 four zones are especiallj^ well defined. The nutritive and protec- 

 tive zones are composed of a few laj-ers of cells while the paren- 

 chyma zone is very thick, composed of smaller cells and more 

 dense than the corresponding zone in most galls of this family. 



Andricus cornigerus O. S. (Fig. 130) produces one of the 

 hardest of the stem galls. My specimens of this were gathered 

 in the winter and were fully mature. The horn-like protuber- 

 ance is a closed tube extending to near the center of the gall. 

 This tube is composed of sclerenchyma tissue and evidently cor- 

 responds to the protective zone. Near the base of the tube is a 

 thin partition forming the larval chamber. When mature the 



