Responses of Pea Roots to Growth Substances.

The responses of pea seedlings roots to various growth substances were studied. The substances were applied in three ways: 1. To the hypocotyl of seedlings growing on moist filter paper in polyethene sacks. 2. To the solution used for moistening the filter paper with the same culture method as in 1. 3. To the culture solution of seedlings growing in test tubes. With this method mainly the effect of growth-regulators on other aspects of growth than root elongation was studied. The method is thought to be suitable as an assay method for phenoxy-type auxins. With all three methods pronounced differences were obtained in the response of the seedlings to phenoxyacetic acids with auxin activity on the one hand and IAA on the other. When the substance were applied to the hypocotyl, the elongation of the roots was inhibited by smaller quantities of the phenoxy auxins than of IAA. Furthermore, the inhibition caused by IAA was followed by rapid growth recovery while phenoxy compounds caused a more permanent inhibition. The effects of NAA and IBA were similar to those of IAA. The root growth of seedlings grown on filter paper moistened with phenoxy auxins in concentrations giving only moderate growth inhibition in the beginning of the experiment decreased progressively with time and most roots stopped growing in a day or two. Also when the seedlings were grown in 10 ml, nutrient solution in test tubes the effects of added phenoxy auxins were enhanced with time. [ABSTRACT FROM AUTHOR]