April, 1904 .] Galls and Insects Producing Them. 
143 
by the separation of the cells in this zone is bridged by 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. 
126c). 
4. GALLS OF TENTHREDINIDAE. 
The galls of Nematus pomum Walsh were the only leaf galls of 
this family that I secured and the}^ 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 HolcasjDis 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 verj' small 
cells with thin walls. It graduall}' merges into the nutritive zone 
on the one side and the parenchyma zone on the other side. The 
parenchyma zone is verj’ 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 eidargement of an incipient stem. 
Further observations upon the gall of Andricus seminator 
Harris confirm the statement previou.sly made that it is a com- 
pound gall produced by the insect depositing an egg in each 
element of the I)ud. 
Part III. Stem G.vlls. 
The gall of Diastrophus nebulo.sus O. S. (Fig. 129a, 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 especially well defined. The nutritive and protec- 
tive zones are composed of a few layers 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 famih'. 
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 sclerench^-ina tissue and evidently cor- 
responds to the protective zone. Near the base of the tube is a 
thin partition forming the larv'al chamber. When mature the 
