Apr., 1923] 
ADDOMS — HYDROGEN ION AND PROTOPLASM 
217 
The roots, with root hairs, were mounted under the dark-field micro¬ 
scope in aqueous solutions of acid, and were irrigated with the same solution 
from time to time. Figure 2 shows successive stages in the precipitation 
of the protoplasm of one of these hairs that was subjected to the action of 
a 0.45 M solution of hydrochloric acid during a period of five hours. The 
similarities in appearance of this hair and of those previously described 
should be noted, especially since in this hair successive stages in the re¬ 
action between the hydrogen ions in relatively high concentration and the 
protoplasm of a single hair is being followed, whereas the drawings in figure 
1 show different root hairs that were acted upon by hydrogen ions in differ¬ 
ent concentrations. Coagulation appears first at the vacuolar membranes 
and spreads through the protoplasm, enlarging the vacuoles as floccu¬ 
lation proceeds. The process is identical with that in the root hairs that 
were grown in nutrient solutions containing a large amount of phosphate, 
except that the flocculi are larger and the dispersion medium is clearer 
when the precipitation is affected by the hydrochloric-acid solution. Quan¬ 
titative differences are to be expected, for the hydrogen-ion concentration 
is higher. 5 Moreover, in the nutrient solutions two processes may be con¬ 
sidered to be operating—one induced by the nutrient ions, tending to 
maintain the normal structure of the protoplasm, and the other induced 
by the hydrogen ions, tending to coagulate it. In the hydrochloric-acid 
solution there are practically no nutrient ions, so that the coagulation by 
the hydrogen ions is not repaired. This so-called “antagonism” of ions 
is well known, although the processes affected are not always the same. 
In order to determine whether or not coagulation was due to a specific 
effect of the hydrogen ion, the same experiment was performed with a 0.45 M 
solution of sodium chloride instead of hydrochloric acid. The results are 
shown in figure 3. At the end of five hours the protoplasm showed no 
change except that it had become slightly more vacuolated. Since the two 
equivalent solutions differ as to cation but not as to anion, it seems clear 
that the coagulation caused by the hydrochloric acid was induced by the 
hydrogen ion. This inference has led some investigators [McCall and Haag 
(’20), Meier and Halstead (’21)] to seek a direct relation between hydrogen- 
ion concentration and the yield of plants, but they were unable to find such 
a relation, although still convinced that the hydrogen ion does exert an 
influence on plant growth. The nature of this influence forms the subject 
of this paper, and it will emerge that this influence, although it is decidedly 
effective, is of such a kind that there can be no direct relation between the 
hydrogen-ion concentration of nutrient solutions and the yield of plants 
grown in them. 
The conclusion that the coagulation of the protoplasm was induced by 
the hydrogen ion becomes still more probable when the close similarity in 
appearance between this cell and those protoplasts that were coagulated 
5 The pH of a 0.45 M solution of HC 1 is approximately 0.4. 
