JOURNAL OF AfiRKULTDRAL RESEARCH 
Vol. VIII Washington, D. C., January 29, 1917 No. 5 
MECHANISM OF TUMOR GROWTH IN CROWNGAEL 
By Erwin F. Smith, 
Pathologist in Charge, Laboratory of Plant Pathology , Bureau of Plant Industry *, 
United States Department of Agriculture 
The ultimate cause of cell proliferation in crowngall is the Schizomycete 
Bacterium tumefaciens Sm. and T., as set forth elsewhere (1,2,3); 1 but 
the mere mechanical irritation due to the presence of a few rod-shaped 
bacteria in the tissues can not be the direct cause of the proliferation, 
since other species of bacteria either have no specific action when inocu¬ 
lated into plants or some quite different action, such as a wilt of the foliage 
following an excessive multiplication of bacteria in the vascular system, 
as, for example, in the disease of cucurbits due to Bacillus tracheiphilus > 
or a soft rot of shoots and tubers following an excessive multiplication 
of bacteria in the intercellular spaces with solvent action on the middle 
layers of the cell wall, as, for example, in the potato rot due to Bacillus 
phytophthorus. In each of these types of plant disease (tumor, wilt, 
and softrot), the ultimate cause is a bacterial infection; but the immedi¬ 
ate or proximate cause of the phenomena, except perhaps in case of 
vascular embolisms, must be the chemical or physical action of enzyms 
or other substances produced or activated by the bacteria as a result 
of their metabolism, with a corresponding reaction on the part of the 
plant. 
For a long time I have tried to think out the rationale of what goes 
on in the cell following the introduction of the crowngall organism. 
What we see is excessive and abnormal multiplication of the tissues 
resulting in a tumor, a hyperplasia. What we would wish to know is 
the mechanism of the growth—that is, the chemical or physical stimulus, 
behind the observed phenomena—since, if we can comprehend it in the 
plant, we may be able to apply our knowledge to the understanding of 
similar phenomena in man and animals. 
In this paper, therefore, I have ventured to offer some suggestions 
(supported by experiments) as to the proximate cause of the abnormal 
1 Reference is made by number to “ Literature cited/’ pp. 185-187. 
(165) 
Journal of Agricultural Research, 
Washington, D. C. 
ha 
Vol. VIII, No. s 
Jan. 29, 1917 
Key No. G —104. 
