I40 The Ohio Naturalist. [Vol. IV, No. 6, 



appendi:k I. 



GALLS AND INSECTS PRODUCING THEM. 



Melville Thurston Cook. 



Part I. Morphology of Leaf Galls. 



I. GALLS OF THE APHIDIDAE. 



The gall of Pemphigus vagabundus Walsh (Fig. 112) is evi- 

 dently formed as a result of the distortiou of a large number of 

 bud leaves. My specimens of these galls were mature, so I was 

 unable to follow its development. Small fibro- vascular bundles 

 were numerous and tannin was formed in great abundance. The 

 structure was so modified that the leaf characters were lost ; the 

 cells were uniform in character, but were slightly smaller near 

 both the exterior and interior surfaces. 



The galls of Pemphigus rhois Fitch (Fig. 113) are large, blad- 

 dery and evidently the pocketing of a single leaflet of the host 

 plant, Rhus glabra or R. typhina. My specimens of these galls 

 were fully mature, and I was therefore unable to follow the line 

 of development. The leaf structure was modified into the char- 

 acteristic Aphididae gall structure. Fibro-vascular bundles were 

 numerous and near the inner surface of the gall. Opposite each 

 bundle was a large cavity filled with some substance which I was 

 unable to determine. 



2. GALLS OF CECIDOMYIDAE. 



The galls of Cecidomyia pellex O. S. (Figs. 1 14a, b) are formed 

 by a thickening of the petiole, giving it the appearance of a long 

 fleshy bean pod with a slit along the upper side. This gall shows 

 three well defined zones ; an inner nutritive zone of small cells, a 

 parenchyma zone of larger cells and the epidermal zone. The 

 fibro-vascular bundles are numerous and are located between the 

 nutritive and protective zones and arranged around the larval 

 cavity and opening, the largest one just below the larval chamber 

 and corresponding to the mid-rib of the leaflet. 



Cecidomyia impatientis O. S. (Fig, 115) is a fleshy gall occur- 

 ring on the leaves of Impatiens fulva. Some of my specimens 

 had the appearance of deformed flower buds, but upon this point 

 I was unable to decide. This gall .showed two well defined 

 zones ; a zone of small cells lining the larval chamber and making 

 up about one half the thickness of the gall, and an outer zone of 

 large cells. Small fibro-vascular bundles were formed between 

 the zones. 



The galls of Cecidomyia liolotricha O. S. on Hicoria ovata 

 (Figs. ii6a, b, c) are small and very firm. My specimens were 



