Dec. x, x 9*3 
Morphology of Crowrtgall 
429 
large numbers, were not so easy to locate as in the younger galls. Con¬ 
siderable increase was noticed in the normal xylem near the gall area. 
It appeared that the xylem near the puncture was several times broader 
at this point than it was in a normal region on the same stem. Similar 
observations were reported by Smith (, 8 , />. 2). 
TWENTY-DAY-OnD INOCULATION 
By this time the young gall had developed until it had the character¬ 
istics of a mature tumor. Vascular tissue appeared abundantly in the 
gall tissue, no matter what its original source. The earlier structure of 
a group of cylindrical strands surrounding the position of the bacteria 
was entirely obscured by the confusion of intermingled types of gall 
tissue. The growth of the different tumor tissues had separated the 
original centers of infection until here, as in still older galls, they were 
comparatively inconspicuous. 
A comparison of these observations was made with others on tomato 
stems which were punctured but not inoculated. It appeared that only 
a very small part of the swelling was a response to the wound. This has 
never been found to exceed that which appeared on the four-day-old 
inoculation. No yellowing of the walls had developed around the 
intercellular spaces that were flooded by liquid, either in the subepi- 
dermal region or in the pith. However, a yellowing was noticed in the 
dead cell walls and, on either side of the puncture, in the region of the 
endodermis. In the latter case the color persisted for a number of 
days, but finally disappeared. The nature of this colored substance 
was not determined. A few cell divisions were found to occur next to the 
puncture so that the cavity in the pith was completely filled up. In 
some cases, after two weeks’ time, the hole through the cortex became 
partially filled. 
The stimulus for the development of tumor tissue seems to be some pro¬ 
duct of the bacteria (Smith 6, p. 184 ). This appears to diffuse more or less 
equally in all directions through the surrounding tissue. When the 
stimulus is strong there seems to be a tendency toward the formation of 
hyperplasia; when it is weak a hypertrophy results. However, con¬ 
tinued action of the weaker stimulus may induce the enlarged cells to 
divide up into smaller ones. When the stimulus is very weak it tends to 
serve merely to stimulate the normal processes of the plant to greater 
activity. This may be seen in the unusual development of xylem at the 
edge of the gall. It seems quite plausible as Smith has suggested 
(7, p . 179) that after the gall is once started, the disturbed metabolism 
of the gall tissue may furnish a sufficient stimulus to incite the con¬ 
tinued development of tumor cells. 
As yet the writer has made no intensive study of nuclear phenomena 
in the activities of the cells immediately adjacent to the intercellular 
spaces containing bacteria. However, it was noted, especially in the pith, 
that the nuclei seemed to divide most frequently in the portion of the cell 
that was nearest the bacteria (pi. 1, C). What the nature of this attract¬ 
ing influence may be, or the means by which it attracts the nuclei, is not 
understood. However, this phenomenon appears to be intimately 
associated with the loss of polarity in the cells and the consequent 
development of the tumor tissue. It appears that the stimulus from the 
bacteria attracts the nuclei to the adjacent portion of the cell, and then 
influences them to divide. The result is that the new wall is formed 
