64 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9 
percentage of the ash of the roots than of the tops. They concluded that 
aluminum after absorption is fixed and thus rendered immobile. Stoklasa 
('i8a) has shown that the amount of aluminum in the roots of mesophytic 
plants is determined largely by the amount of soil moisture. An increase 
in the soil moisture increased the percentage of aluminum in the roots, 
but not in the tops in which the percentage was always low. These facts 
probably explain the lessened depression of root growth by the aluminum 
salts in the sand cultures. Rothert's analyses of the corn plants which he 
grew in the cultures containing aluminum showed a large percentage of 
aluminum in the ash of the roots and only a trace in the tops. Hoffer and 
Carr ('20) have shown that most of the aluminum which is carried to the 
stem accumulates in the nodal area. Microchemical tests made with plants 
grown in the present experiment confirm this finding. 
In the present investigation no evidence has been found to confirm 
Rothert's statement that aluminum chloride is more toxic than aluminum 
sulphate. There is some indication of a slightly greater toxicity of the 
aluminum nitrate. 
The H-ion concentrations of solutions "A" and "H" are slightly below 
those which Duggar ('20) has given as the optimum for corn. The slight 
depression of growth caused by 0.0002 N concentration of H2SO4 in solution 
*'H," by 0.0005 ^ in solution ''A," and by 0.001 N in the sand cultures, 
indicates that an initial acidity above pH 3.7 in solution "H," above pH 
3.6 in solution "A," and above pH 3.6 in the sand cultures had little effect 
upon the growth of field corn. When the initial concentration of the acid 
in solution *'H" is increased to 0.0004 ^ (pH 3-5), there is a distinct de- 
pression which is greater than that caused by 0.001 N (pH 3) in the sand 
cultures. A 0.0006 N concentration of nitric, hydrochloric, or sulphuric 
acid is decidedly toxic in the solution cultures. The three acids produced 
a similar depression of the relative weight of tops and roots. The roots 
were much better developed in the sulphuric acid solutions, when compared 
with the effects of the other acids, than is indicated by the relative weights. 
A similar difference was noted in the solutions containing the three ferric 
salts. This feature is clearly shown in Plate IV, figure C. The difference 
in development is in harmony with the favorable effect of sulphates on the 
root development of certain plants which has been noted by Tottingham 
and Hart ('15). In solution ''A," as shown in figure 3, the sulphuric acid 
gave a better yield of the tops than did the other acids. This is most 
marked with a concentration of 0.001 N. The relative yields reported in 
this paper, indicating the effects of the various concentrations of the acids 
in solution "H" on corn, are very similar to those given for wheat, barley, 
and oats by Hartwell and Pember ('07). 
It will be noted from the tables and figures that the solutions in general 
tended to become less acid with the growth of the plants. A similar tend- 
ency has been noted by Duggar ('20), Salter and Mcllvaine ('20), and 
