2 °8 Journal of Agricultural Research voi. xxvn, No. 4 
buckwheat during the same period increased the “total apparent 
acidity” of the soils used. 
Breazeale and Le Clerc (3) found that growing wheat seedlings made 
a sodium nitrate solution alkaline, while solutions of potassium chlorid 
and potassium sulphate became acid under the same conditions. 
Of the investigators using the more recent methods for determining 
active acidity and alkalinity, Jones and Shive (7) studied the effect of 
wheat seedlings on the hydrogen-ion concentration of a number of 
nutrient solutions. Wheat seedlings, after having been grown for five 
weeks in “Shive’s Best” solution, were transferred to the nutrient 
solutions. The initial hydrogen-ion values of these solutions were 
recorded, as well as the changes resulting after the seedlings had been in 
contact with the nutrient for 24 and 52 hours. Invariably the changes 
were in the direction of decreased acidity. The initial reactions of most 
of the solutions ranged from P H 4 to P H 4.8. At the end of the experi¬ 
ment the reactions ranged from 5.3 to 6.1. Two of the solutions the 
initial reaction of which had been almost neutral remained practically 
unchanged under the same conditions. 
Hoagland (6), working with barley and several varieties of beans, 
found that “in every instance, without an exception, nutrient solutions 
with an initial acid reaction reached approximately neutral reactions, 
varying from 6.1 to 7.2, after contact with the plant roots for varying 
periods of time.” 
Conner and Sears (4), while studying the effect of aluminum salts on 
plant growth, also found that nutrient solutions with an initial acid 
reaction tend to become less acid in contact with growing rye, barley, 
and popcorn seedlings. 
Arrhenius (i, p. 81) reported that plant roots change the reaction of 
the medium, but that the direction of the change depends on the plant 
used. Rye brought nutrient solutions of original P H values 3 and 9 to 
P H 5.8; peas brought nutrient solutions of original P H values 3 and 8 
to 4.5; and com brought nutrient solutions of original P H values 3 and 
7.5 to 6.5. 
Later the same author ( 2) studied rice in like manner. Acid reac¬ 
tions in the nutrient solution used were obtained by adding hydrochloric 
acid and alkaline reactions by adding sodium hydroxide. In all cases 
the growth of the rice plant brought the reaction to P H 6.2. 
On the other hand, Olsen (8) reports that the kind of plant used does 
not affect the direction in which change of reaction takes place. He 
concluded that the direction depends primarily on the source of nitrogen 
in the nutrient solutions. When ammonium chlorid or nitrate is used, 
all 12 plant species tried caused the solutions to become more acid, 
although some plants produced the change more rapidly than others. 
When sodium nitrate was used, however, the solutions uniformly became 
more alkaline. 
Results obtained in the Bureau of Chemistry (Table I) show that 
factors pther than those given by Arrhenius and Olsen (the kind of 
plants and source of nitrogen) affect the direction of the change in 
reactions produced in nutrient solutions under the influence of growing 
seedlings. 
