42 2 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 Tiypcta solidao;i}iis (Fig. 40) a solid globular gall on the 

 stem of Solidago, we find the w'alls 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 Gelcchia gallac-soUdagiuis 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 fiatteued 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. 



In CccidoDiyia rigidac 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 ver}^ 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 unal)le to secure satisfactor}- 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 : 



