The movement of radioactivity added in the form of indoleacetic acid (as the natural hormone) or as 2,4-dichlorophenoxyacetic acid (as a synthetic growth regulator) was followed in segments cut from petioles of Phaseolus vulgaris.

The movement of 14C added as IAA was strongly basipetally polar, although significant amounts moved acropetally during 24 hours. The velocity of basipetal movement was 6 mm/hour for IAA-[14C], and was the same for donor concentrations of 5 or 50 μM. The flux increased with increasing concentration in the donor blocks, but a progressively smaller percentage of the applied radioactivity was transported.

2,4-D-[14C] was found to have very similar transport properties to those of IAA-[14C], except that its velocity of basipetal movement was much less, namely 1 mm/hour. After correction had been made for the much slower net loss of 2,4-D from its donor blocks, the acropetal movement of the 14C from the two substances was essentially the same.