284 
B. W. WELLS 
boscis is inserted but once, the larva retaining its position through the 
period of gall development, (b) Hypertrophy of the epidermal and adjacent 
mesophyll cells on the lower side of the leaf opposite to that attacked by 
the insect, (c) A slight hyperplasia generally appears in the cells imme- 
diately surrounding the end of the mouth parts, (d) Degeneration of 
chloroplasts in a zone beneath the larva, (e) An increase in the size of the 
nuclei in the same zone. 
3. The above noted changes {b and c) produce a downward evagination 
which lowers the insect into the body of the leaf, after which process a 
"cover-cone" rapidly grows over it, springing from the tissue surrounding 
the larva. 
4. Multinucleate cells appear in the tissue of the floor of the larval 
chamber, most of the nuclei, however, soon disintegrating. The mode of 
origin of these nuclei is believed to be amitotic, though this under the 
condition of high divisional infrequency cannot be definitely proved. 
5. The very early differentiation of a sclerenchyma layer, one cell in 
thickness, is highly characteristic of one of the galls. 
6. The nymph shows practically no increase in size until the gall is about 
half developed. Thus the grand period of growth in the gall is at the 
beginning of its ontogeny while that of the insect is postponed until cecidi- 
ogenesis is well under way. 
7. The morphological facts discovered furnish no assistance whatever in 
the formulation of a theory concerning the nature of the stimulus used by 
the larval insects in initiating and carrying to completion the highly specific 
gall structures characteristic of the two species respectively. 
Department of Botany, 
North Carolina State College 
LITERATURE CITED 
1. Beer, R., and Arber, Agnes. On the occurrence of binucleate and multinucleate cells in 
growing tissues. Annals of Botany 29: 597-598. 19 15. 
2. Kiister, E. Die Gallen der Pflanzen. Leipzig, 191 1. 
3. . Pathologische Pflanzenanatomie. Zweite Auflage. Jena, 191 6. 
4. Petri, L. Uber die Wurzelfaule phylloxierter Weinstocke. Zeitsch. Pflanzenkr. 19: 
18-48. 1909. 
5. Prankerd, T. S. Notes on occurrence of multinucleate cells. Annals of Botany 29: 
599-604. 1915. 
6. Prillieux, E. Etude des alterations produites dans le bois de pommier par le Puceron 
lanigere. Ann. Inst. Nat. Agron. 2: 39-48. 1877. 
7. Rosen, H. R. The development of the Phylloxera vastatrix leaf gall. Amer. Journ. 
Bot. 7: 337-360. 1916. 
8. Wells, B. W. The comparative morphology of the zoocecidia of Celtis occidentalis. 
Ohio Journ. Sci. 16: 249-290. 191 6. 
