Observations on the Growth of Certain Plants in Nutrient Solutions Containing Synthetic Growth-Regulating Substances III. The Relative Toxicity of Isopropylphenylcarbamate and Some Phenoxyacetic Acid Derivatives to Some Cereals.

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Abstract
Wheat and rice plants were grown from 2 to 4 weeks in soln. cultures containing ammonium 2,4-dichlorophenoxyacetate, ammonium 2-methyl-4-chlorophenoxyacetate, 2,4-dichlorophenoxyacetic acid, isopropylphenylcarbamate, or mixtures of the latter 2 substances. The vegetative growth of young wheat plants was much inhibited by these substances. Isopropylphenylcarbamate and 2,4-dichlorophenoxyacetic acid were approx. equally active in reducing the growth of 3-weeks-old wheat plants. Two-weeks-old wheat was less sensitive to ammonium 2,4-dichlorophenoxyacetate than to either the acid or ammonium 2-methyl-4-chlorophenoxyacetate. Some treatments with low conc. of the latter resulted in significantly less inhibition of growth than equivalent treatments with 2,4-dichlorophenoxyacetic acid. Growth of 10-weeks-old rice was less inhibited by isopropylphenylcarbamate than by 2,4-dichlorophenoxyacetic acid. Compared to the activity of the latter, significant supplemental inhibition of growth did not result from treatments with mixtures of these 2 substances. A series of morphological changes of the root of wheat plants treated with phenoxyacetic acid derivatives, particularly 2,4-dichlorophenoxyacetic acid, was qualitatively and quantitatively descr. in relation to conc. of regulator.

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