364 Jones and Skive.—Influence of Ammonium Sulphate 
ammonium sulphate when supplied with iron in the form of ferrous sulphate, 
may be indirectly related to the H-ion concentration of the solutions. As 
has been shown, the H-ion concentration, of the solutions containing 
ammonium sulphate is usually increased and maintained at a relatively high 
level during contact with the roots of growing plants, while the H-ion con¬ 
centration of the Tottingham solutions under similar conditions is rapidly 
decreased. Thus the solubility and therefore the availability of iron is high 
in the former and relatively low in the latter. This, together with the 
possible influence of the ammonium salt on the permeability of the plant 
Fig. 2. Graphs of actual yield values of soy bean tops and roots grown in Tottingham’s 
solution T 1 R 1 C 5 (series C), and in the ammonium-sulphate modification of this solution (series D), 
supplied with the varying amounts of iron in the form of ferrous sulphate. 
cells for iron, may readily account for the difference in the behaviour of the 
plants towards iron in the two types of solutions, and for the toxic effects 
produced when ferrous sulphate in any but exceedingly low concentrations 
is used as the source of iron for plants in solutions containing ammonium 
sulphate. 
From a consideration of the data presented in the above experiments it 
is evident that the form and quantity of iron in a medium for plant growth 
is a very important factor to be considered in connexion with the growth of 
plants in solution cultures. 
Influence of Salt Proportions on the Yields of Tops and Roots. 
This experiment was carried out for the purpose of determining the 
effect of salt proportions on the growth of soy bean plants in the Tottingham 
