Feb., 1922] 
ARNDT THE GROWTH OF FIELD CORN 
67 
states that the toxicity of aluminum nitrate toward field corn is largely due 
to the acidity produced by the hydrolysis of the salt, is no longer tenable. 
It has been previously noted that all soils which show aluminum injury 
are acid. A comparison of the pH values reported at the end of the second 
and at the last renewal (5th week) in the sand cultures shows an increase 
in acidity of the cultures by the continued addition of aluminum salts, 
which fact supports the belief that the hydrolysis of aluminum salts may 
be an important factor in the production of soil acidity through the reac- 
tions noted by Noyes ('19). 
Hartwell and Pember ('08, p. 293), after their investigation of the 
effect of the same normality of sulphuric acid and ferrous sulphate on 
barley and rye, conclude that the injury caused by the salt is largely due 
to the liberation of the acid radicle in hydrolysis. A comparison of the rela- 
tive growth which they report for 0.0004 N ferrous sulphate and the growths 
given here in table 4 shows that this is not the case with corn in solution 
"H." A 0.0002 N ferrous-sulphate concentration depressed the growth 
almost 30 percent, but it did not produce an acidity greater than pH 4.4. 
Since the H-ion concentration of the solution used by Hartwell and Pember 
is not stated, it is somewhat difficult to compare their results with those of 
the present experiment. A still greater difference will be noted in the sand 
cultures where a 0.0006 N concentration of ferrous sulphate produced a 
10 percent greater depression than 0.002 N sulphuric acid. The H-ion 
concentration of both cultures is the same. The score given in table 5 
to indicate the relative root development is very favorable to the acid 
solution. The cultures in solution "A" show most clearly that the toxicity 
of ferrous sulphate is in no way related to an increase in acidity. The 
0.001 N ferrous sulphate culture never showed a H-ion concentration below 
that of the initial solution, but it did produce a 35 percent to 45 percent 
reduction of growth. 
The toxic effects of the ferric salts in the solution cultures were more 
nearly related to the H-ion concentration than was the case with either the 
ferrous or the aluminum salts. This is because they are immediately 
precipitated. Thus, they produce a high initial H-ion concentration. In 
the sand cultures the 0.001 acids gave a far better yield than a 0.0004 ^ 
concentration of the iron salts. A comparison of the acids and the ferric 
salts in these cultures is probably not permissible because the rapid pre- 
cipitation of these salts probably caused a much higher concentration of 
iron in the sand cultures than is indicated by the original solution. If such 
was the case, the increased relative injury as compared with the solution 
cultures must have been due to the precipitated, but probably slightly 
soluble, ferric phosphate and hydroxide. 
The results given in tables 2 and 3 and plotted in figures 2 and 3 seem to 
indicate that in solution "A" the toxicity of iron and aluminum salts is 
largely due to the acidity produced when the salts are precipitated. The 
