Feb., 1922] 
ARNDT THE GROWTH OF FIELD CORN 
65 
Hoagland ('19). The acid solutions were more readily shifted toward 
neutrality than the solutions containing the iron and aluminum salts. 
There seems to be a tendency for the sulphuric acid solutions to be shifted 
most readily, particularly in solution "A." The effect of the acid radicle 
of the aluminum salts in determining the shifting of the reaction is shown 
by a comparison of the initial H-ion concentration and the concentration 
after growth. This is well shown by the various graphs. The sulphate 
solutions, with the exception of those containing ferrous sulphate, are 
unique in that in all cases the H-ion concentration was shifted toward 
neutrality. The reverse was true of the solution cultures containing ferrous 
sulphate even at the low concentration of 0.0002 A^. All solutions contain- 
ing nitrates become less acid except 0.0004 N aluminum nitrate. The 
chlorides showed a strong tendency to increase the initial H-ion concentra- 
tion. This tendency was shown by all concentrations of aluminum chloride 
in solution " H," and also by 0.0006 N ferric chloride. In the sand cultures 
the 0.0006 N ferrous sulphate solution was the only one which showed 
after plant growth a H-ion concentration higher than the initial concentra- 
tion of the solution. 
The results of Salter and Mcllvaine show that a H-ion concentration less 
than that necessary to depress growth in solution "H" may produce a 
distinct depression in other nutrient solutions. They found that a reaction 
of pH 4. 1 1 was much less favorable to corn than a reaction of pH 5.16, in 
their strongly buffered solutions. The great changes in the reaction of 
solutions "A" and "H" produced by the growth of corn indicate that 
possibly the initial concentration of the solution is not as important a 
factor in plant growth as is the buffer action of the solution which determines 
the ease with which the plant can shift the reaction. It is very likely that 
the toxicity of the acids in solutions "A" and "H" could have been in- 
creased either by using larger amounts of the solutions, or by renewing 
them more frequently. A survey of the tables will show that the shifting 
of the reaction is roughly proportional to the size of the plant. Thus, the 
pH values given in table 3 and figure 3 show that the change in the reaction 
is greater at the end of the fourth than at the end of the first week; and in 
table 4 it appears that the series (ser. 2) which gave the greatest total 
growth also produced the greatest change in reaction. 
In solutions containing ferrous sulphate, growth shifted the H-ion con- 
centration in the opposite direction. The change was almost negligible 
at the beginning; but as the plants became larger, the H-ion concentration 
was increased. A solution with a similar concentration of the salt was 
kept in the greenhouse in a flask for three days without a change equal to 
pH 0.2. It seems fairly evident that the plant in some manner accelerates 
the hydrolysis and the precipitation of the salt and is the main agency 
which produces the change in acidity. The ferric salts are immediately 
precipitated, giving a high initial acidity to the solution. The ferrous salt 
