Movement of Growth Regulators in Plants

S ummary This paper describes the effects on auxin transport of treatments which changed the rate of elongation of the transporting tissues. The inclusion of mannitol in blocks of agar gel applied to each end of segments cut from petioles of Phaseolus vulgaris L. reduced elongation of the segments. This treatment also increased basipetal movement of 2,4‐dichlorophenoxyacetic acid (2,4‐D) from donor blocks through the segments into receiver blocks and decreased net acropetal movement, so that the polarity of 2,4‐D transport was raised, Gibberellic acid applied in the donor blocks promoted elongation but decreased the basipetal movement of 2,4‐D and increased its net acropetal movement, so that the polarity of 2,4‐D transport was lowered. It is concluded that polar transport of this auxin is not dependent on elongation of the transporting tissues.