(WITH FIVE FIGURES)The hypothesis developed to explain the quantitative aspects of selenatesulphate antagonism was based on the assumption of unselective absorption and utilization of the two ions by virtue of their chemical similarity (18,19). The idea subsequently received support from plant analyses showing that the amount of selenium taken into the tissues of certain plants parallels that of sulphur, as though selenium absorption were determined by the sulphur requirement of the species (20). Reasoning by analogy to other pairs of chemically related elements, one of which is toxic and the other essential in nutrition, has led to the discovery that arsenate toxicity is a function of phosphate availability, rubidium toxicity of potassium availability, and strontium toxicity of calcium availability. In view of the small number of pairs that can be selected on such a basis, positive results with all three are highly suggestive of the validity of the basic assumption. The present paper presents the experimental evidence on which the previous brief reports of these relationships were based (22,23 The most obvious effect of arsenic on wheat was killing of the roots with withering and stunting of the tops, apparently as a result of root injury ( fig. 1, D). The severely damaged leaves were narrow and stiff, and sometimes pale green in color.The effect of phosphates on these symptoms was studied first in water cultures and then in several kinds of soil.WATER CULTURES.-Seedlings of Hard Federation wheat were grown for several weeks in low-, medium-, and high-phosphate solutions containing disodium arsenate (Na2HAsO4 7 H20). The three nutrient solutions, with 10, 60 and 120 parts per million of phosphorus, contained, in 19 liters, 31, 184, and 367 cc. M,/10 CaH4(PO4)2 -H20, respectively; plus 95 cc. M/5 MgSO4,

No abstract

No abstract

No abstract

No abstract