Feb., 1922] ARNDT THE GROWTH OF FIELD CORN 69 
toxic concentrations of aluminum salts. The nitrate usually produced the 
most severe chlorosis. 
The author does not wish to indicate that aluminum or iron salts are 
the only ones which may produce a pathological condition in zone "B." 
These results are to be applied only to the variety of yellow dent field corn 
which was used in this investigation. It has been pointed out by True 
('21) that the metabolism of sweet corn is very different from that of field 
corn. 
The results of the present investigation indicate that from both an 
agricultural and an ecological viewpoint it is important to know both the 
H-ion concentration and the composition of the soil. Field corn is evi- 
dently very tolerant of a fairly high acidity if no aluminum or iron salts 
are present. It is very likely that under field conditions the salts of these 
metals are more toxic than the results of this investigation indicate because 
of their unfavorable effect upon root development. Injury by iron salts 
can be determined readily by the color of the nodes. Microchemical tests 
will be necessary to determine the presence of aluminum. 
Summary 
Yellow dent field corn was grown in two nutrient solutions of a greatly 
different composition to determine the effect of the composition of the 
nutrient solution; first, upon the amount and form of iron necessary for 
optimum growth; second, upon the toxicity of sulphuric, nitric, and hydro- 
chloric acids and their corresponding salts with iron and aluminum. The 
solutions had the following composition: Solution "H," CaH4(P04)2, 
0.00005 Ca(N03)2, 0.0015 M; NH4NO3, 0.001 M; KCl, 0.0008 M; 
MgS04, 0.0008 M; Al2(S04)3, 0.000003 M; MnS04, 0.00001 M; ZnS04, 
0.000005 M; Solution "A," KH2PO4, 0.0024 M; Ca(N03)2, 0.0036 M; 
MgS04, 0.0035 Sand cultures were used to check the results obtained 
in the solution cultures with solution " H." 
The availability of the iron in. ferric phosphate for the growth of corn 
was found to depend largely upon the composition of the nutrient solution. 
A concentration of 7 mg. per liter was sufficient for the optimum growth 
in solution "H." Plants grown in solution ''A" with five times this amount 
were unable to secure sufficient iron. 
The optimum growth in solution "A" was secured with 0.0005 iV ferrous 
sulphate. The addition of ferric nitrate to this solution produced a pre- 
cipitate from which the plant was unable to secure sufficient iron even with 
a 0.001 N concentration. The plants in this concentration as well as in 
one of 0.002 iV, which was strongly toxic, were chlorotic. 
Sulphuric, nitric, and hydrochloric acids were about alike toxic when 
they were added to either solution in low concentration. At the highest 
concentration used, sulphuric acid depressed the growth of the tops less 
