358 
HARRY R. ROSEN 
layers of mesophyll cells in the portion of the gall below the insect, 
show peculiar thickening and dissolution of their cell walls. 
3. Gall development depends upon leaf development; when the 
leaf reaches its maximum size, after twelve to fifteen days of develop- 
ment, the gall becomes mature. 
4. A mature gall shows but slight cuticular development and very 
few stomata. The mesophyll is a huge mass of compact, thin-walled, 
partly empty cells, some of which are undersized, and others enor- 
mously elongated, the vascular elements are scattered by wedges of 
parenchyma cells. Many unicellular and multicellular hairs grow 
out from the gall. 
5. Chemical work on this gall shows it to be a structure in which 
anabolic processes are lacking, and in which large amounts of simple 
sugars and simple proteins are present. 
6. The development of this gall does not seem to support the 
theory that the insect injects some chemical into the leaf which causes 
gall formation. 
7. Intumescences produced by chemical sprays result from en- 
tirely different kinds of hyperplastic responses than hyperplastic 
gall growth. 
8. The investigation establishes the fact that the proboscis may 
pass through the entire thickness of the leaf. 
9. The insect remains fixed, and that portion of the leaf in which 
the proboscis is fixed is marked by lack of growth as compared with 
the huge outgrowths which surround it. 
10. The continuous sucking action by the insect at one fixed point 
for fifteen days is believed to be the initial stimulus for gall develop- 
ment. 
The work on this paper was done in the Botanical Laboratory of 
the University of Wisconsin. My appreciation is due to Professor 
J. B. Overton, under whose direction the work was done, and to 
Professor W. S. Marshall for helpful suggestions and for the use of 
his private library. 
U. S. National Museum 
BIBLIOGRAPHY 
1. Beyerinck, M. W. Ueber die ersten Entwicldungsstadien einiger Cynipiden- 
gallen. Verh. Nederl. Akad. Wetensch. 1882. (Amsterdam.) 
2. Barber, M. A. A Technique for the Inoculation of Bacteria and Other Sub- 
stances into Living Cells. Journ. Infect. Dis. 8: 348. 191 1. 
