422 
The Ohio Naturalist. 
[Vol. Ill, No. 7 , 
contain a large amount of woody, fibrous tissue. Inside the zone 
of fibro-vascular bundles and forming the axis of the stem, is the 
stelar (st) made up of large parenchyma cells. 
In Tiypeta solidaginis (Fig. 40) a solid globular gall on the 
stem of Solidago, we find the walls of the outer parenchymatous 
cells much thickened and numerous large intercellular spaces 
which are not characteristic of the unaffected stem ( Fig. 39). 
The fibro-vascular bundles (f. v. b. ) are spread out and flattened, 
the sclerenchyma tissue and tracheary tissue being reduced and 
the fibrous tissue increased in amount. The parenchyma tissue 
of the stelar (st) part of the gall is increased in amount and the 
size of the cells reduced. This tissue is undoubtedly very active 
and well supplied with nutrition for the larva. Throughout the 
tissue are tubes (tu) lined with cells smaller than the parenchyma 
cells, brown in color, and not affected by haematoxylin stain. 
These tubes are usually associated with small bundles of fibrous 
tissue and are probably important factors in the nutrition of the 
larva. They were not found in sections of normal stem of corre- 
sponding age. 
In Gelechia gallae-solidaginis Fitch (Fig. 41) an elongated, 
hollow gall on Solidago, we find the parenchymatous tissue (pa) 
near the surface increased in amount, the cells larger and the 
walls thicker than in an unaffected stem, but no intercellular 
spaces such as are found in T. solidaginis. The fibro-vascular 
bundles (f. v. b. ) undergo comparatively little change, becoming 
slightly flattened and thinner and with a reduction of the firmer 
fibrous tissue. The larva chamber ( 1 . c.) of the gall is lined with 
a few layers of small parenchymatous cells (st) and is the stelar 
part of the stem. This parenchymatous tissue is udoubtedly 
used for food. 
I11 Cecidomyia rigidae O. S. (Fig. 42) an elongated, hollow gall 
common on Salix discolor, usually near the tips of the twigs, we 
find considerable modification of the normal stem structure. From 
the examination of a number of specimens it is very clear that the 
enlargement of the stem is due to two factors : the formation of 
large intercellular spaces near the surface, similar to those in T. 
solidaginis (Fig. 40), and the formation of the larval chamber 
( 1 . c.) in the stelar part of the stem. The parenchymatous tissue 
lining the chamber is made up of cells very much smaller than 
those in an unaffected stem. 
The Lepidopterous galls on the young stems of Acer negundo 
and Coleopterous galls on Rubus villosus were examined but no 
new points presented. I was unable to secure satisfactory speci- 
mens of stem galls of Cynipidae. 
Although the study of stem galls was in many respects unsat- 
isfactory, I feel justified in giving the following brief conclusions : 
