Aug. 15, 1921 
Effect of Ammonium Sulphate upon Plants 
717 
Comparing now the graphs of figure 5 with those representing the dry- 
weight yields of tops from the two series of the preceding experiment 
(fig. 2), it will be observed that the relative positions of the graphs rep¬ 
resenting corresponding series of the two experiments are completely 
reversed. Thus, in experiment I (fig. 2) the graphs representing top 
yields from the cultures of the Tottingham series, throughout its entire 
length, lies much below the graph representing these yields from the 
ammonium-sulphate series, while the corresponding graphs in experi¬ 
ment II (fig. 5) occupy exactly opposite positions. A similar compari¬ 
son of the two sets of graphs representing the dry-weight yields of roots 
from the two series in each experiment (fig. 3, 6) shows that these 
graphs have the same sort of arrangement as the graphs representing 
the dry weight of tops. It should be noted, however, that the differ¬ 
ences between the yield values of tops, and especially of roots, from cor¬ 
responding cultures of 
the two series, as indi 
cated by the pairs of 
graphs representing the 
yields in question, are 
always much less pro¬ 
nounced in experiment 
I than they are in ex¬ 
periment II. 
The small amounts 
of iron used here with 
each culture (0.83 mgm. 
per liter of solution) 
appeared to be suffi¬ 
cient to prevent chlo¬ 
rotic effects in the 
plants of the Totting- __ 
ham series and to ^am scries and the ammonium-sulphate series of experimeut II. 
provide them with the necessary supply of this element for normal 
growth; and, as already stated, the plants of this series were in 
excellent condition during the entire growth period and produced very 
high yields. In the solutions of the ammonium-sulphate series, on the 
other hand, the soluble iron in the small quantities used with each 
culture was very toxic to the plants, which were greatly retarded in their 
growth rates and produced very low yields. That this condition of the 
plants was directly related to the form of iron supplied is clear from the 
fact that in the preceding experiment these same culture solutions pro¬ 
vided with iron, in equivalent amounts, in the form of the insoluble 
ferric phosphate, produced healthy, vigorous plants and high yields. 
In order to test the effect of varying amounts of iron in the form of 
the soluble ferrous sulphate upon the growth of wheat plants in the two 
types of culture solutions used here, a special experiment was carried 
