Studies on the Geotropism of Roots

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Abstract
The auxins contained in 5-mm. tips of horizontal Vicia faba roots have been compared with those in tips of vertical roots after cold ethanol extraction, paper-chromatographic separation, and Avena mesocotyl bioassay. At about the time curvature commences in horizontal roots there is a marked increase in the content of an auxin corresponding to ‘AP(ii)’ of pea roots (Rf 0.35–0.65 in isobutanol/methanol/water). There are indications that this is not due to its release from an inactive bound state but that it is either synthesized de novo or may be converted from another auxin corresponding to ‘AP(iii)’ of pea roots (Rf 0.75–1.0). The literature dealing with the auxins of geotropically stimulated organs is reassessed and it is concluded that, with the exception of the Avena coleoptile, there is very little evidence favouring a simple transport redistribution of auxin under gravity; the majority of the data favour an effect of gravity on auxin metabolism.