726 
Journal of Agricultural Research 
Yol. XXI, No. xo 
(3) The direction of the change in reaction of the culture solutions 
produced by the growing wheat plants was determined by the nature 
of the salt constituents comprised in the solutions. 
(4) Ferric phosphate, in the quantities used, was not sufficiently avail¬ 
able in the Tottingham solutions to supply the needs of the plants for 
iron. The low yields produced by these solutions were correlated with 
a high degree of chlorosis and with high P It values. O11 the other hand, 
this form of iron appears to be readily available to the plants in the 
solutions containing ammonium sulphate. The high yields produced by 
these solutions were associated with relatively low P„ values, and the 
plants were entirely free from chlorosis. 
(5) Ferrous sulphate, in the quantities used, was sufficiently available 
in the Tottingham solutions to satisfy the needs of the plants for iron. 
These solutions with the soluble form of iron produced excellent growth 
and high yields, and no chlorotic or toxic effects were apparent. The 
solutions containing ammonium sulphate with this form of iron in quan¬ 
tities of more than 0.01 mgm. of iron per liter of nutrient solution were 
very toxic to the plants, the degree of toxicity increasing with increase in 
the amounts of iron added to the solutions. 
(6) The nature of the nutrient solution with respect to the salt consti¬ 
tuents and hydrogen-ion concentration appears to determine the availa¬ 
bility and the efficiency of a given iron salt for plant growth. 
(7) The highest six yields of wheat tops from the Tottingham series 
axe correlated with relatively wide ranges in the proportions of all four 
salts employed. The maximum yield of tops from these series was pro¬ 
duced by a solution having the following salt proportions: Potassium 
nitrate 0.0060 M.; potassium phosphate 0.0021 M.; calcium nitrate 
0.0044 M.; and magnesium sulphate 0.0071 M„ with ferrous sulphate 
(0.83 mgm. of iron per liter) as the source of iron for the plants. 
(8) The highest six yields of tops from the series of solutions contain¬ 
ing ammonium sulphate are associated with relatively wide ranges in the 
proportions of potassium phosphate, calcium nitrate, and magnesium 
sulphate, but with a narrow range in the proportions of ammonium sul¬ 
phate. The maximum yield of tops from these series was produced by 
a solution having the following salt proportions: Ammonium sulphate 
0.0014 M.; potassium phosphate 0.0021 M.; calcium nitrate, 0.0073 M.; 
and magnesium sulphate 0.0071 M., with ferric phosphate (0.83 mgm. of 
iron per liter) as the source of iron for the plants. 
(9) In the series of solutions containing ammonium sulphate, high 
yields of tops were generally associated with high yields of roots; but 
no such correlation between tops and roots existed in the Tottingham 
series. 
