120 
The Ohio Xaturalist. 
[Vol. IV, No. 6, 
zone are bridged by long unicellular threads, but no fibro-vascular 
bundles ( F'ig. 8 1) 
Dryopbanta 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 entirely used by the imsect. The 
protective zone consists of only two or three layers of sclerenchyina 
cells, to which are attached a few cells of the parenchyma zone 
(Fig. 82). 
Andricus petiolicola Bassett (Fig. 124) produce a ver\- 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 maturit}’. The protective zone developes its 
sclerenchyina character rather late ( Fig. 83) and gradually merges 
into the two adjacent zones. 
B. Epidcruial Structures. 
The epidermal cells var}’ in the size and in the thickness of the 
cell walls. The galls may be .smooth, pubescent or covered with 
spin}' structures. The amount of pubescence depends somewhat 
on the natural pube.sence of the host plant. Galls on such smooth 
plants as Populus deltoides Marsh show ver\' few and \'ery small 
trichomes, while galls on plants that are naturalh’ pubescent are 
likel}' to be pube.scent. These trichomes vary in shape and gen- 
eral character and are \-ery prominent when the gall is }’oung. 
As the gall approaches maturity the trichomes usually disapjjear. 
When these trichomes drop off their place of former attachment 
is marked b}^ a small ma.ss 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. 84a). 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. 84b). 
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 bladdery galls. 
In Diastrophus siminis Bassett the trichomes are very large 
(Fig. 86) and drop off very readil}L 
In Diastrophus potentillae Bassett the trichomes are very 
numerous and each is at the apex of a very small elevation (Fig. 
87). Examination of the epidermis of Acraspis erinacei Walsh 
show that its spines were due to .similar but much more prominent 
elevations. 
