The Ohio £JS£aturalist, 
PUBLISHED BY 
The Biological Club of the Ohio State University. 
Volume II, MAY, 1902. No. 7. 
GALLS AND INSECTS PRODUCING THEM. 
Melville Thurston Cook. 
Part i. The Morphology of Leaf Galls. 
The purpose of this study was to contribute to the knowledge 
of cellular activity of the plant under peculiar animal stimulus ; 
to compare the effects of the two sets of insect organs, mouth 
parts and ovipositors, and to throw additional light on the classi- 
fication. The statements made in this paper are based on a large 
number of collections. The collection of stem galls was too 
incomplete to draw conclusions and is therefore reserved for a 
future paper. No attempt was made to follow the development 
of the galls but rather to make a comparison of the structure of 
the various forms of galls. 
My paper was practically complete before I received the papers 
of H. Fockeu. After receiving his paper I reviewed my own to 
determine wherein my results agreed with or varied from his 
conclusions. Experiments such as are described by H. Fockeu 
to ascertain the cause of the gall formation were not attempted. 
Fockeu’ s studies were grouped according to the plants affected ; 
my own studies were grouped with reference to the insect pro- 
ducing the galls. 
METHODS. 
For the killing and fixing, several fluids were used, but the 
most successful were Chromo-acetic and Picric-alcohol. A num- 
ber of different stains were used, but Delafields-Haemotoxylou 
proved very satisfactory for most work. 
P'or the drawings a Bausch & Lomb microscope and camera 
lucida were used ; for the normal leaf, a i-inch ocular and a 
i-inch objective, and for the galls a i-inch ocular and a ^i-inch 
objective. Since it was unnecessary to make drawings of the 
entire galls, drawings were made from one or more parts to show 
the characteristic structure, and this part is indicated on the small 
diagrammatic drawings. Since the galls were so variable in size, 
it was practically impossible to make the diagrammatic drawings 
on a definite scale. 
GENERAL CLASSIFICATION. 
As a matter of convenience the following temporary classifica- 
tion, based on location of the galls was adopted for this and other 
