Abstract
The polar basal transport of the growth substances (auxins, growth hormones) in plants is a well known phenomenon, demonstrated first by Went (81), and studied in detail by van der Weij (78, 80). These investigators used the Avena (oat) coleoptile.1 That the phenomenon is more or less general is indicated by the polar transport of auxin in roots (Cholodny, 19; Nagao GO) ; in hypocotyls of Baphanus (van Overbeek, 62), of Pisum (Skoog, 74) ; in leaves (Avery, 2) ; in the coleoptile of Avena (Went, 81; Laibach and Kornmann, 40; van der Weij, 78, 80; and Skoog, 74) and corn (van Overbeek, 63) ; in Elaeagnus (woody cutting) (van der Weij, 79) ; in stems of Coleus, Vicia, and Phaseolus; and in hypocotyls of Viola, Phaseolus, and Lupinus (Mai, 54) . Other workers have reported non-polar transport of auxin in plants. Hitchcock and Zimmerman (31) and Zimmerman and Wilcoxon (85) have shown an apical transport of heteroauxin (indole-3-acetic acid) and several other active compounds in stems of Helianthus tuberosus, Nicotiana tabacum, and in Lycopersicum esculentum, as indicated by induction of adventitious roots and by epinastic response of leaves. Loehwing and Bauguess (45) have shown that heteroauxin could be absorbed by the root system of potted seedlings of Matthiola incana and be transported apically to increase the stem elongation over that of the controls. Both the BoyceThompson workers and Loehwing and Bauguess have merely shown that auxin applied in high concentrations can be carried in the transpiration stream. This, of course, will not give polar transport. Higher concentrations of auxin may have effects which are not normally encountered. For example, high concentrations applied at the base of Pisum cuttings induce roots there, whereas in the lower, more physiological concentrations roots may be induced at the bases, only by applying auxin at the morphological tips (Went and Thimann, 83). Laibach and Fischnich (41) have shown that the transport of heteroauxin was not strictly polar in leaves of Coleus and in cotyledons of Cucumis sativa, but that transport could occur apically. The apical transport was much smaller than basal transport, however. Avery (2), as mentioned above, found only basal transport. Avery determined this by diffusion of
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