1. It is concluded that the tropisms of maize Coleoptiles are mediated by IAA gradients, which are most likely caused by lateral IAA transport as the Cholodny‐Went theory of tropisms describes

2. The dose-response curves for the effects of applied IAA on tropisms and growth of intact Coleoptiles as well as the time courses of tropisms induced in decapitated Coleoptiles could be explained by the three conclusions in the literature: (1) the tip of the coleoptile is the site of auxin production, (2) lateral translocation of auxin in

3. Alteration of growth or tropisms in roots due to localized applications of IAA occurs only if they are applied at a position apical to the elongation zone, suggesting that IAA must reach the elongation zone by Basipetal transport (Davies et al., 1976)