170 BOTANICAL GAZETTE [MARCH 
This clearly indicates that the anion as well as the cation plays a 
part in antagonism. A similar antagonism exists between these 
salts as measured in terms of nitrification. 
Furthermore, using the ammonia produced as the criterion, 
an antagonism is seen to exist between sodium sulphate vs. iron 
sulphate, calcium chloride vs. iron sulphate, sodium chloride vs. 
iron chloride, sodium chloride vs. iron sulphate, magnesium chloride 
vs. iron nitrate, sodium chloride vs. iron carbonate, calcium chlo- 
ride vs. iron carbonate, calcium chloride vs. iron nitrate, sodium 
nitrate vs. iron chloride, calcium chloride vs. iron chloride, sodium 
carbonate vs. iron nitrate, sodium carbonate vs..iron carbonate, 
sodium sulphate vs. iron nitrate, sodium chloride vs. iron nitrate,mag- 
nesium sulphate vs. iron nitrate, sodium carbonate vs. iron sulphate, 
sodium nitrate vs. iron nitrate, sodium nitrate vs. iron sulphate, 
magnesium sulphate vs. iron chloride, and magnesium sulphate vs. 
iron carbonate. This was small in the case of the first pair, and 
increased in the order named until the last, which neutralized 75 
per cent of the toxic effect. of magnesium sulphate. 
As measured in terms of nitrification, a true antagonism was 
found to exist between sodium carbonate vs. iron carbonate, 
sodium chloride vs. iron chloride, magnesium sulphate 2s. iron 
nitrate, sodium carbonate vs. iron sulphate, sodium nitrate vs. iron 
sulphate, sodium sulphate vs. iron carbonate, calcium chloride vs. 
iron carbonate, sodium nitrate vs. iron carbonate, sodium chloride 
vs. iron nitrate, magnesium sulphate vs. iron carbonate, sodium 
nitrate vs. iron chloride, sodium sulphate vs. iron nitrate, sodium 
sulphate vs. iron chloride, magnesium chloride vs. iron carbonate, 
calcium chloride vs. iron nitrate, magnesium sulphate vs. iron 
chloride, sodium chloride vs. iron sulphate, magnesium chloride 
vs. iron chloride, sodium carbonate vs. iron chloride, and magnesium 
chloride vs. iron nitrate. This was low in the case of the first pair, 
and increased progressively in the order named up to the last named 
pair, in which the iron nitrate increased the nitrification 420.7 per 
cent over that soil treated with magnesium chloride alone. 
The results, therefore, indicate the toxicity of soluble salts 
toward soil microorganisms to be due to an osmotic effect which 
makes it impossible for the cell to take up its normal nutrients, 
