66 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9 
is less readily precipitated, but when conditions are such as to favor its 
precipitation a similar acidity is produced. 
A comparison of the relative yields in solution "H," as shown in figures 
4, 5, and 6, of the acids and the aluminum salts, points to the cation of the 
salt rather than the H-ion concentration produced by the hydrolysis of the 
salts as the toxic factor. The reverse is true in solution "A" (fig. 3). The 
results in solution "H" indicate that corn is affected by soluble aluminum 
salts similarly to rice (Miyake, '16) and barley (Hartwell and Pember, 
'18; Conner, '21). A closer relation seems to exist between t:.e ability of 
the plant to shift the reaction toward neutrality and the relative toxicity 
of the acid and the salt, than exists between the initial H-ion concentration 
and the toxicity of the salt. This inability of the plant to change the 
reaction may be a secondary feature, for, as has been previously pointed 
out, this change is related to the amount of plant growth and it may be 
merely a measure of the toxicity of the solution rather than the cause of 
the toxicity. These results are not in harmony with the conclusions of 
Abbott, Conner, and Smalley ('13). These authors based their conclusions 
largely upon the root development of seven-day-old seedlings. Plate IV, 
figure B, which shows the relative development in 0.0004 TV acid and in 
the same normality of the corresponding aluminum salts, indicates that 
there is a distinct difference between the toxicity of the acid and that of 
the salts as measured by root development when a longer period of growth 
is used. These results agree with those of Miyake. He based his con- 
clusions on the relative elongation of the shoots and states that there is 
little difference in the toxicity of the same strengths of the acid and of the 
salt. His results on root elongation show that the root growth in the acid 
was twice as great as in the corresponding salt solution. The relative 
toxicity of the acid and the salt in solution "H" depends somewhat on the 
concentration used. Except in the case of sulphuric acid, there is little 
difference in the toxicity of the acid and of the corresponding salt in a 
0.0006 TV concentration ; while at 0.0002 N, the acid has practically no effect 
upon growth and the salt produces a considerable reduction of growth. 
A comparison of the relative effects of the acid and of the salt, as shown 
by the results given for the sand cultures in table 5 and in figure 6, is even 
more favorable to the acid. These results are also more dependable when 
considered in relation to the H-ion concentration, as the buffer action of 
the sand kept the concentration more constant; although it is possible 
that the concentration reported does not represent the acidity of the solu- 
tion in contact with the roots. In these cultures a 0.002 N concentration 
of sulphuric acid in the culture was necessary to produce the same depression 
as 0.0006 N aluminum sulphate. The difference in H-ion concentration 
is still greater. In the acid cultures it was approximately four times as 
great, as marked by the difference between pH 3.4 and pH 4.1. This 
indicates that the theory advanced by Abbott, Conner, and Smalley, which 
