212 
Journal of Agricultural Research 
Vol. XXVII, No. 4 
The changes which occurred in the organic-acid solutions may have been 
due parti)' or wholly to microbiological activity, as it was impracticable 
to keep the solutions sterile. However, oxalic and formic acids, which 
have the highest dissociation constants, were acted upon to a greater 
extent than the other organic acids, especially those in the P H 3 series. 
EFFECT OF NUMBER OF SEEDLINGS ON CHANGE OF REACTION 
In order to bring out more clearly the differences in the behavior of 
the individual acids, the foregoing experiment was repeated, using a 
larger number of seedlings. It was run in duplicate and in two series, 
one with 10 and the other with 20 seedlings per culture, and was confined 
to the inorganic acids. 
The relative behavior of these acids (Table III) was the same as in the 
previous experiment. In a general way the rate of response was pro¬ 
portional to the number of seedlings with both of the initial reactions. 
In the 20-seedling series, with an initial value of P H 4, the difference 
in behavior between nitric acid and the other acids appeared only after 
the solutions had been renewed twice. At this period, however, the 
difference between the decreased acidity of the nitric-acid solution and 
that of the other acids was much more pronounced than in the previous 
experiment. 
In the solutions having an initial P H 3 value, nitric acid was again 
more affected by the action of the seedlings than the other acids. Nu¬ 
merically the changes in total values and the differences are small, but 
quantitatively they are larger than those which took place in the solu¬ 
tions with the initial P H 4 value. Taking the hydrogen-ion concentra¬ 
tion of pure water as a unit, as suggested by Wherry and Adams {i2 } 13 ), 
the decrease in acidity, for example, from P ? 3 to 3.1 would constitute 
a loss of 2,000 units per liter, while the entire decrease in acidity from 
4 to 7 would be only 1,000 units. The fact that losses in acidity desig¬ 
nated by the same P H numerals vary in actual magnitude, depending 
upon the P H range in which they occurred, is not always realized. Thus, 
Conner and Sears (4) believed that greater decreases in acidity were 
produced by growing seedlings in solutions of phosphoric acid with an 
initial hydrogen-ion concentration of P H 3.9 and 4.2, which were re¬ 
duced to 6.3 and 6.4, than in solutions of the same acid with an initial 
•hydrogen-ion concentration of P H 3.2 and 3.6, which came down to 
3.5 and 4.1. Actually, however, the case is just the reverse. Figured 
on the same basis, the first two transformations involve losses of 1,245 
and 625 units, while the last transformations involve losses of 3,150 and 
1,700 units. 
Nevertheless, it is significant that, while in the solutions of the lower 
hydrogen-ion concentrations in these experiments, as well as in those of 
Conner and Sears (4), the acidity originally present was practically 
exhausted, in the case of the higher concentrations the action of the 
seedlings seemed to have stopped while appreciable amounts of acid were 
still left in the solutions. But the seedlings also lost their power to reduce 
acidity in the solutions of the lower initial hydrogen-ion concentrations 
of these experiments when they were renewed several times. Evidently 
there are certain limits to the absolute quantities of acid upon which 
seedlings can act. Within these limits, however, nitric acid was more 
subject than the other acids to that action of the seedlings which is 
responsible for decreasing acidity. 
