7 i8 
Journal of Agricultural Research 
Vol. XXI, No. io 
out. This comprised two series of io cultures each. Throughout each 
series the same solutions were used for all the cultures, these solutions 
differing only in the amounts of iron contained. For one of these series 
Tottingham’s solution number T3R1C5 was chosen, and for the other this 
solution was modified by substituting ammonium sulphate for the potas¬ 
sium nitrate, as previously explained, in equivalent osmotic concentra¬ 
tion (solution number T3R1C5 of the ammonium-sulphate series in experi¬ 
ments I and II). These two series will be designated series C and series 
D. Iron was supplied to the solutions of each series in amounts vary¬ 
ing from 0.01 mgm. to 5.0 mgm. The culture methods pursued with 
these two supplementary series were precisely the same as those de¬ 
scribed and used in 
carrying out the main 
experiments of this 
study. The cultures 
were conducted during 
a growth period of 35 
days. 
During the third 
week of the growth 
period evidences of 
toxicity began to ap¬ 
pear in the plants 
growing in the solu¬ 
tions containing am¬ 
monium sulphate. The 
plants assumed an un¬ 
healthy, slightly yel¬ 
lowish, dull color, 
which was entirely 
different from the 
characteristic chlorotic 
appearance of plants 
suffering from the in¬ 
sufficient supply of iron. A weakened condition of the plants was evi¬ 
dent from the manner in whieh the leaves drooped and the growth rates 
were retarded. The plants in the solutions containing the highest 
amounts of iron were the first to be affected, and the toxicity increased 
in severity as the plants grew older and spread to include all of the 
cultures except the one containing the smallest amount of iron (0.01 
mgm. per liter of solution). The plants in this culture were at all times 
green and healthy, grew rapidly, and produced relatively high yields. 
The plants in the Tottingham solutions were green and healthy through¬ 
out the growth period, with the exception of those in the two solutions 
containing 0.01 mgm. and 0.10 mgm. of iron per liter of solution. The 
plants in the first of these two solutions were chlorotic, while those in 
Mfon. per .01 10 .25 50 .75 1.0 1 5 2 0 3.0 5 0 f 
liter 
Fig. 7.—Graphs of actual yield values of wheat tops and roots for 
culture solutions of two types (solution T3R1C5 of the Tottingham 
series and solution T3R1C5 of the ammonium-sulphate series) sup¬ 
plied with varying amounts of iron in the form of ferrous sulphate. 
Series C and D of experiment II. 
