Walter Stiles 
136 
Similar results were obtained by Osterhout (1907) with a number 
of freshwater and terrestrial species including Spirogyra, Vaucheria, 
Lunularia gemmae and Equisetum spores, as well as wheat seedlings 
and other flowering plants. In this and subsequent investigations, 
Osterhout (1907, 1908 c) introduced a second method of investigating 
antagonism, namely, by determination of differences in growth rate. 
Wheat seedlings, for example, were grown with their roots in the 
experimental solutions, and the amount of growth determined by 
measuring the increase in length of the roots in the various solutions 
after a definite time. Various chlorides and nitrates were employed. 
In this way it was shown that root development proceeded more 
rapidly in solutions containing both salts of sodium and potassium, 
sodium and ammonium, sodium and calcium, and sodium and 
magnesium, than in pure solutions of the same concentration (0-12 M). 
For each pair of salts there is a definite ratio of the two constituents 
in which the rate of growth is a maximum. 
In a separate investigation (1908 a) Osterhout showed that the 
toxicity of magnesium salts (chloride, sulphate and nitrate) was 
reduced by the addition of the corresponding potassium salt. Not 
only is the toxicity of the magnesium reduced by the potassium, but 
the toxicity of potassium is reduced by the presence of a magnesium 
salt, for a solution containing both the potassium and magnesium 
salt is less toxic than a pure solution of either salt in the same 
concentration. 
Much the same method was used by Hansteen (1910) who em¬ 
ployed a Norwegian variety of wheat, seedlings of which were 
maintained for 14 days with their roots in the experimental solutions 
and the root development then estimated by determining the dry 
weights of the roots. Nitrates were used in concentrations consider¬ 
ably lower than those employed by Osterhout. By this method a 
definite antagonism was observed between potassium and calcium, 
a rather slight antagonism between potassium and magnesium, and 
a very little, scarcely noticeable, antagonism between potassium and 
sodium. Antagonism was observed in solutions having a concen¬ 
tration as low as 0-00125 N. 
Further work on these lines was carried out by McCool (1913) 
who worked with wheat and Canadian field peas allowed to grow 
in the experimental solutions for 21 to 30 days. Growth was estimated 
by measurement of length and determination of dry weights of roots 
and shoots. Antagonism between calcium and the following metallic 
ions was found: magnesium, potassium, sodium, ammonium, barium 
