3^2 
Journal of Agricultural Research 
Vol. XXIII, No. s 
These data show that there is a decrease in the hydrogen-ion concen¬ 
tration of the cell sap between the hours of 9 a. m. and 1 p. m. This 
changed balance in the reactions involved in acid synthesis and decom¬ 
position is not surprising in view of the fact that they have been shown 
to be so dependent on light, temperature, and moisture conditions (24), 
The effect of soil reaction on the hydrogen-ion concentration of the 
cell sap of plants is not always the same, judging from the observations 
reported in the literature. Contrary to what one would expect, Cleven¬ 
ger (7) found that the leaves of oats, soy beans, and cowpeas were more acid 
when there was lime in the soil, although the reverse was true in buck¬ 
wheat. On the other hand, Kappen and Zapfe ( 16 ) state that liming 
the soil had no effect on the hydrogen-ion concentration of the lupine 
or bush bean, measured at the time of blooming; and, likewise, Promsy 
(22) says that the absorption of acids by seedlings did not change the 
acidity of the sap. Truog and Meacham (30) found, however, that in 
12 out of 16 cases, including several different crop plants, lime lowered 
the reaction of the cell sap. Most of the evidence Haas (rr), obtained 
with many different agricultural plants, indicates that plants grown in 
unlimed soil have a higher hydrogen-ion concentration than those from 
limed soil, among these being wheat, although he found a number of 
plants in which file reverse was true. 
All the data bearing on this question of the effect of soil reaction on 
cell-sap reaction obtained in the present investigation, summed up in 
the foregoing figures and in Tables I and II, have been consistent in 
showing a lower hydrogen-ion concentration and lower total acid content of 
the juice of wheat from limed soil as compared to that from unlimed soil. 
However, the acidity of the limed seedlings seems to have increased to 
that of the unlimed seedlings by the time file plants were three months 
old (Table II). The data in these tables show the degree of difference 
in the P H values and indicate the necessity of eliminating the soil vari¬ 
able in any search for heritable varietal differences in cell-sap acidity. 
Whether the greater alkalinity of plants in limed soils is directly due 
to the absorption of neutralizing ions from the soil, or whether it is the 
result of some general effect on the health and vigor of the plants, is an 
open question. In at least one case it was noticed that the limed plants 
were taller and more vigorous than the unlimed ones with lower P H . 
Clevenger (7) suggested that the greater acidity of the leaves of his 
limed plants might be explained by assuming that the plants were 
healthier and metabolism more rapid, but observations on wheat made 
during the present investigation would indicate that the less vigorous 
plants are the more acid. Lack of vigor due to unfavorable conditions 
for growth has been invariably associated with high hydrogen-ion concen¬ 
tration and high total acidity. The most notable examples were wintei 
wheats grown in the greenhouse when the temperature was too high and 
which had the very low P H value of 5.5. Some 14-weeks old Kanred 
and Turkey wheats, stunted and drooping, were 5.48 and 5.50, respec¬ 
tively, while Mindum and Arnautka growing alongside, heading, and in 
erect, vigorous growth, were 5.98 and 6.02. When, in other series, 
these four varieties were equally healthy in appearance, no such differ¬ 
ences were found. It was also found that plantings of any variety on a 
certain shaded bench in the greenhouse resulted in slow-growing plants 
with lower Pg values than those from the other benches. It is very 
interesting to note that Truog and Meacham (30) raise the question as 
to whether the more acid reaction of lupine in limed soil might not be 
