Jan. 29, 1917 
173 
Mechanism of Tumor Growth in Crowngall 
munis). This strong-growing plant develops crowngall quickly when 
inoculated with Bact. tumefaciens (the hop strain) and is also well 
adapted to the experiments here described not only because the inter¬ 
nodes are hollow and will hold a considerable quantity of fluid, but also 
because in the younger internodes, at least, the cavity is lined by living 
pith cells capable of astonishing proliferation when properly stimulated. 
The older intemodes were also injected, but these generally yielded no 
results other than death of cells immediately in contact with the strong 
alkali. In the younger internodes, on the contrary, striking cell pro¬ 
liferations into the pith cavity were obtained repeatedly. That part of 
the pith which received the brunt of the alkaline action was in every 
case killed for the solution was much too strong; but the remoter tissues, 
especially the inner face of certain xylem bundles, proliferated freely, 
almost furiously, often for long distances, forming raised snow-white 
cushions of delicate cells, which in their morphology strongly suggested 
those cells which are to be seen growing from the margins of gum pockets, 
but were much more abundant and active (PI. 4 and 5). The cell 
proliferations, which in this case arise from the tissues of the vascular 
bundle or its sheath (inner face of the xylem or of the endocycle), are 
apparently much more abundant than one would expect for the repair 
of a simple wound. These cushions have the appearance of tissues 
growing rapidly under an active stimulus of some sort both because of 
the volume of the growths visible within a given short time and because 
of the great number of the cells composing them. 
When these results were obtained with the strong ammonia two ques¬ 
tions arose: 
(1) Whether the growths were simply unusually active wound pro¬ 
liferations—that is, exclusively repair cells, or were really in part pro¬ 
liferations due to the stimulating (inhibition-removing) action of the 
alkali, and not exclusively to its killing (wounding) action; 
(2) Whether the same results could be obtained with the various salts 
of ammonia. 
Respecting the first inquiry we might conceive the growth response 
to be due (1) to the killing effect of the ammonia, the proliferations being 
simply the development of wound-repair tissue, in which case one ought 
to be able tb obtain the same results by use of many other injurious sub¬ 
stances, and killing effects should always be visible, while greatly diluted 
ammonia would then have no visible effect; or (2) to a specific effect of the 
ammonia due to the removal of physiological (or physical) growth inhi¬ 
bitions, in which case it should be excessive as compared with ordinary 
wound-repair tissue, should be obtained with very weak aqua ammonia 
(high dilutions) in the absence of any wounds, and should not be obtained 
from the use of acids or other poisons unless they also have a specific 
effect on the cell membrane; or (3) a nonspecific, water-attractive 
