2 66 
The Ohio Naturalist. 
[Vol. II, No. 7 , 
The Phylloxera galls show considerable variation from each 
other. P. c. avenae Fitch, P. c. fallax Riley, and P. c. globuli 
Walsh. (Figs. 16-18), of Hicoria ovata may be taken as forming 
a rather well defined gronp and as showing greatest resemblance 
to the preceding galls of this family. When compared with the 
normal leaf (P'ig. i) of the host, H. ovata, they show a reduc- 
tion in size of the epidermal cells, the palisade cells losing their 
identity', and the mesophyll becoming very' compact. Very little 
of the dark cell contents characteristic of the preceding galls of 
this family was present, the greatest amount being formed in 
P. c. avenae (Fig. 16) where it is restricted to the epidermis and 
to the cells just below it. The cells are even less elongated and 
more irregular than in the preceding galls. In general it may be 
said that in this group the largest cells are midway between the 
two layers of the epidermis and gradually decrease as we approach 
the surfaces. This is especially true of P. c. globuli (Fig. 1 8 ) . 
P. c. spinosci Shinier (P'ig. 19 a. b. ) is a very' large gall occur- 
ring on leaf, petiole, or young, green twigs of Hicoria ovata and 
shows considerable variation from the preceding. Two zones are 
very distinct ; the outer is composed of large cells which do not 
take the stain readily, the inner zone of small cells stained very 
readily' and show great activity'. This may, however, have been 
due to the fact that my specimens of this gall were much y'ounger 
than of the preceding Phylloxera galls. A long tube for the exit 
of the insect is formed. 
In P. c. depressa Shinier (Fig. 20 a. b. ) of H. ovata and P. 
vastatrix Planclion (Fig. 21 a. b. ) of Vitis vulpina we have still 
other and more marked variation. The cavity is much smaller, 
the walls much thicker than in the preceding, and a long tube, 
especially in P. c. depressa is formed for the exit of the insect. 
In both cases the size of the epidermal cells is much reduced when 
compared with the normal (Fig. 1,3), the palisade cells have not 
so completely lost their identity as in the preceding and there 
appears to be a general elongation of the cells with their long 
axis perpendicular and not parallel to the surface of the gall. 
A small but definite, deeply staining zone of cells surrounds the 
cavity in P. c. depressa. Many cells show dark contents similar 
to that found in the galls on Ulmus and Hamamelis (Fig. 12-15). 
P. vastatrix shows a comparatively large number of trichomes, 
especially near the opening, but this is probably a characteristic 
of the host plant rather than of the gall. 
The presence of the two well defined zones, which may be con- 
sidered protective and nutritive in P. c. spinosa and P. c. de- 
pressa, show a very marked resemblance to the Cynipidae galls 
(Figs. 25-30). 
It may be that all young galls show this arrangement into two 
or three zones. 
