2 66 The Ohio Naturalist. [Vol. II, No. 7, 



The Phj'Uoxera galls show considerable variation from each 

 other. P. c. avenae Fitch, P. c. fallax Riley, and P. c. g/obuli 

 Walsh. (Figs. 16-18), of Hicoria ovata may be taken as forming 

 a rather well defined group and as showing greatest resemblance 

 to the preceding galls of this family. When compared with the 

 normal leaf (Fig. 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 especiallj- true of P. c. globuli (Fig. 18). 



P. c spinosa Shimer (Fig. 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 readil}- , the inner zone of small cells stained very 

 readil)' and show great activity. This may, however, have been 

 due to the fact that my specimens of this gall were much younger 

 than of the preceding Phylloxera galls. A long tube for the exit 

 of the insect is formed. 



In P. c. depressa Shimer (Fig. 20 a. b. ) of H. ovata and P. 

 vastatrix Planchon (Fig. 21 a. b.) of V^itis 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. 



