May, 1903 .] Galls and Insects Producing Them. 
4^9 
a development of trichomes, especially the former. In all galls 
the mesophyll is subject to the greatest modification. Many- 
small fibro vascular bundles are formed in this modified mesophyll. 
3. The Acarin may be considered the lowest group of galls, 
the Aphidid the next higher, the Ceciclomyia galls the next 
higher, and the Cynipidous galls the highest. However, many 
of the Cecidomyia galls are lower than the Aphidid galls. 
4. The galls of Acarina and Aphididae show the greatest 
resemblance. In these cases the method of attack is very similar 
and is first directed against the epidermal or adjacent layer of cells. 
5. I11 some of the Cecidomyia galls (e. g. C. verrucola) the 
larva appears to make its entrance into the mesophyll before there 
is any pronounced modification of the cell structure. However, 
the Cecidomyia galls are too varied and the study too incomplete 
to make a positive conclusion. 
6. Both Adler and Fockeu consider that after the first stages 
of formation, the gall becomes an independent organism growing 
upon the host plant. This is probably true in the highly devel- 
oped galls of Aphididae, Cecidomyia and Cynipidae, but the 
writer is very doubtful if this is true of the less complex galls of 
Acarina, Aphididae and Cecidomyia. 
This work was pursued during the year 1902-03, in the Biolog- 
ical Laboratory of DePauw University, but was under the super- 
vision of Professor Herbert Osborn, of the Ohio State University,, 
to whom I am indebted for many valuable suggestions. I am 
also indebted to two of my former students, Miss S. Emma Hick- 
man and Miss Margaretta S. Nutt, for aid in preparing slides and 
making drawings. Drawings made by these two ladies are marked 
with their initials. I also wish to express my thanks to my many 
friends who have called my attention to, or have collected material 
for, these investigations. 
LITERATURE. 
New literature will not be cited at this time, but a more com- 
plete list will be given in connection with later papers upon this 
subject. 
EXPLANATION OF PLATES. 
In making the drawings a Bausch & Lomb microscope, with 
No. 2 ocular and % objective, and a B. & L. camera lucida were 
used. The drawings are, therefore, larger than those used in 
Parts I and II, and the reduction not so great. The diagrams 
are not made upon a definite scale. Drawings 34, a, b, c ; 35, a, 
b ; 37, 38, 55, a, b ; 57, a, b, c, and 58, a, b, c, were made from 
nature, and are very little smaller than the original. The num- 
bering of the drawings is continuous with Parts I and II. 
