Aug. 15, 1921 
Effect of Ammonium Sulphate upon Plants 
7 2 5 
for the entire series. In the ammonium-sulphate series the ranges in 
the proportions of monopotassiurn phosphate, calcium nitrate, and 
magnesium sulphate are in absolute agreement with the corresponding 
ranges in the proportions of these salts in the Tottingham series, while 
the range in the proportions of ammonium sulphate for high yields of 
tops is relatively low, being only one-third of the total range in the 
proportions of this salt for the entire series. This range includes the 
lowest proportion of this salt used in the series. 
The cultures which produced high root yields in the Tottingham 
series are characterized by relatively wide ranges in the proportions of 
potassium nitrate and magnesium sulphate and relatively narrow ones 
in the proportions of monopotassium phosphate and calcium nitrate, 
while high yields of roots in the ammonium-sulphate series are associ¬ 
ated with a narrow range in the proportions of ammonium sulphate and 
monopotassium phosphate and a wide range in the proportions of the 
other two salts. 
SUMMARY 
The experiments described in this paper were conducted for the purpose 
of studying, in a comparative way, the effects of ammonium sulphate in 
nutrient solutions upon the growth of young wheat plants and to deter¬ 
mine the influence of this salt upon the ability of the plants to utilize 
iron from a soluble ferrous salt and an insoluble ferric salt. A study was 
also made of the change in reaction of the nutrient solutions induced by 
contact with the plant roots. Two series of culture solutions were used. 
The first of these comprised 20 solutions selected from the Tottingham 
series of 84, and the second series consisted of the same solutions modi¬ 
fied by substituting ammonium sulphate for the potassium nitrate in 
equivalent osmotic concentrations. All the solutions had a total os¬ 
motic concentration value of approximately 1 atmosphere. The soluble 
and the insoluble iron in the form of ferrous sulphate and ferric phos¬ 
phate, respectively, was added to the solutions in quantities of 0.83 
mgm. of iron per liter of solution. The culture solutions were renewed 
at regular intervals of 3 yi days throughout a total growth period of 35 
days. 
The main results of the experiments may be summarized as follows: 
(1) The plants grown in the Tottingham solutions invariably produced 
a marked decrease in the hydrogen-ion concentrations of the solutions. 
(2) The plants grown in the solutions containing ammonium sulphate 
invariably increased the hydrogen-ion concentration of these solutions 
during the early stages of growth. During the first five weeks of growth 
the hydrogen-ion concentrations were maintained at a much higher 
level in these solutions than in the unmodified Tottingham solutions, 
although the initial P fI values of corresponding solutions of the two 
types were practically the same. 
