I20 The Ohio Naturalist [Vol. IV, No. 6, 



zone are bridged by long unicellular threads, but no fibro-vascular 

 bundles (Fig. Si) 



Dr3'ophanta palustris O. S. galls show the four zones well 

 defined (Figs. 29, 65). When mature the contents of the cells 

 of the nutritive zone has been entirel}- used b}' the insect. The 

 protective zone consists of onl}- two or three layers of sclerenchyma 

 cells, to which are attached a few cells of the parenchyma zone 

 (Fig. 82). 



Andricus petiolicola Bassett (Fig. 124) produce a very hard 

 petiole or mid-rib gall which shows the four zones well defined. 

 There is no separation between the second and third zones. The 

 nutritive zone is at first very prominent, but it is reduced as the 

 gall approaches maturity. The protective zone developes its 

 sclerenchyma character rather late (Fig. 83) and gradually merges 

 into the two adjacent zones. 



B. Epidenual Stnictitres. 



The epidermal cells vary in the size and in the thickness of the 

 cell walls. The galls may be smooth, pubescent or covered with 

 spiny structures. The amount of pubescence depends somewhat 

 on the natural pubesence of the host plant. Galls on such smooth 

 plants as Populus deltoides Marsh show ver}- few and very small 

 trichomes, while galls on plants that are naturall}- pubescent are 

 likely to be pubescent. These trichomes vary in shape and gen- 

 eral character and are very prominent when the gall is young. 

 As the gall approaches maturity the trichomes usually disappear. 

 When these trichomes drop off their place of former attachment 

 is marked by a small mass of small cells, usually containing 

 tannin and from which imperfect rows of cells seem to radiate 

 (Figs. 84-90). 



I. GALLS OF CYNIPIDAE. 



Dryophanta palustris O. S. is very pubescent when young 

 (Fig. S4a). In the mature gall the cells are much larger, the 

 trichomes have disappeared and their point of attachment is made 

 visible by the accumulation of tannin (Fig. S4b). 



All my .specimens of Amphibolips inanis O. S. were fully 

 developed, but the points where the trichomes had evidently been 

 attached were very prominent (Fig. 85 ). These points are the 

 large, black spots so prominent on these large bladder}^ galls. 



In Diastrophus siniinis Bassett the trichomes are very large 

 (Fig. 86) and drop off very readily. 



In Diastrophus potentillae Bas.sett the trichomes are very 

 numerous and each is at the apex of a \-cry small elevation (Fig. 

 87). Examination of the epidermis of Acraspis crinacei Walsh 

 show that its spines were due to similar but much more prominent 

 elevations. 



