Journal of Agricultural Research 
Vol. VIII, No. 5 
166 
cell proliferation in crowngall—a proliferation in opposition to the needs 
and well being of the plant and one following the general law of develop¬ 
ment of animal neoplasms, as I have shown elsewhere (4,18). It is believed 
that the experiments here detailed have important bearings not only on 
the origin of crowngall and of other tumors in plants, including those due 
to nematodes and to gall flies, but also on the origin of various animal 
tumors. For the most part, however, I shall here leave the reader to 
draw his own conclusions respecting remoter applications. 
At first I conceived of the crowngall phenomena as much more com¬ 
plex than it really is. I thought of endotoxins and other complex sub¬ 
stances of unknown chemical structure as probably the cause of the 
excessive cell proliferation, not, however, entirely excluding simpler 
substances, such as ammonia compounds. 1 Absorbed in other features 
of the investigation, I limited myself for a long time to turning over in 
my mind various phases of the problem with what help I could obtain 
from literature, but in June of last year (1916), having reached, theoret¬ 
ically, what seemed to me to be dependable and necessary conclusions, 
I began to make simple experiments, some of which have proved of great 
interest, and the more important of which are here first described, 
though I called attention to them briefly in October (5,6). 
In the beginning I had what I now believe to be a wrong conception of 
growth. I looked upon it as something that an outside substance could 
directly stimulate into development, but probably it is not that (Weigert, 
Ribbert, Loeb). Growth is the normal function of cells.' They are 
always multiplying when they are not inhibited by one thing or another. 
Growth, then, if this view is correct, comes about not by the direct appli¬ 
cation of stimuli, but indirectly by the removal of various inhibitions . 
Under normal conditions the physiological brakes are on at all times, 
more or less, in both plants and animals, and only when they are entirely 
or largely removed in particular areas do we observe an unlimited cell 
proliferation resulting in the hasty and peculiar growths known as neo¬ 
plasms or cancers. What, then, removes the normal growth inhibitions? 
And what are these inhibitions? Cold is one source of inhibition, insuffi¬ 
cient oxygen and drouth are other causes of inhibition, but we have to 
do with none of these inhibitions or their opposites, nor with any others 
in so far as they act on the plant as a whole. The inhibition remover we 
are in search of is one that acts locally, disturbing tissue equilibriums within 
limited areas . 
When all other conditions are favorable, such as abundant food supply, 
water supply, air supply, and right temperature, cell multiplication may 
still be held in check—that is, in unfertilized eggs—as Jacques Loeb has 
1 In a previous paper (i, p. 175), ammonium acetate is especially mentioned as a possible cause of tumor 
stimulus. 
