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.

A series of tests has been conducted with the object of comparing the effects of selected synthetic growth-regulators on the growth of cereals in nutrient-solution cultures. In earlier tests it had been determined that marked quantitative and morphological eflects were induced when low concentrations of 2,4-dichlorophenoxyacetic acid were supplied in the nutrient solutions (6, 7). Selected for comparison with 2,4-dichlorophenoxyacetic acid were: ammonium 2,4-dichlorophenoxyacetate and ammonium 2methyl-4-chlorophenoxyacetate (both of which are more soluble in water than the respective acids) and isopropylphenylcarbamate (which is much less watersoluble). In other studies (9), the latter two chemicals showed activity differing from that of 2,4-dichlorophenoxyacetic acid. Isopropylphenylcarbamate, particularly, has high inhibitory activity on cereal seedlings (I). Some effects of urethanes on the growth of plants have been reported by other investigators. FRIESEN (4) reported distinct effects of low concentrations of ethyl urethane (ethylcarbamate or C2H500CNH2) on germination and early seedling development of oat and wheat