External Responses of Galinsoga Ciliata (Raf.) Blake to Treatment With Low Concentrations of 2,4-Dichlorophenoxyacetic Acid

Soon after the discovery and use of synthetic plant hormones it became apparent that the degree and type of response of plants treated with such hormones depend upon a number of factors. Individual plants of the same species may not react the same, even though subjected to similar environmental conditions. Early investigations were characterized by the use of very low concentrations and minute amounts of hormonal material in an attempt, primarily, to induce root formation (Zimmerman and Hitchcock, 1942). When the economic value of such compounds as herbicides was discovered it caused the investigators to shift attention to quantities and concentrations which were toxic. The responses of a large number of plants to toxic doses of such compounds have been reported. In view of the variable responses exhibited by plants of the same species to different concentrations of growth-regulating substances, it seems desirable to determine the pattern of responses to concentrations below or near the threshold of toxicity