Antagonistic Effect of the lons.—The classic investigations by Loeb (1906) have shown that certain salts such as sodium chloride, when alone, have a poisonous effect upon plants but that with the addition of magnesium or calcium the poisonous nature of the sodium chloride solution may be decreased or entirely neutralized. [Nota de rodapé 1: Instructive examples of the antagonistic action of different ions are also cited by Iljin (1925).] In this antagonistic action the concentration of the solutions doubtless plays an important role (see also p. 186). (Braun-Blanquet 1932:180)
The sulphates occur mostly as sodium sulphate, Na2SO4, or as magnesium sulphate, MgSO4; calcium sulphate, CaSO4, occurs more rarely, and sometimes the chlorides predominate. (Braun-Blanquet 1932:201)
BRAUN-BLANQUET, Josias. 1932. Plant sociology: the study of plant communities. (Trans.: George D. Fuller; Henry S. Conard) New York: McGraw-Hill Book Company.