Geotropic Responses in Helianthus and their Dependence on the Auxin Ratio. – With a Refined Mathematical Description of the Course of Geotropic Movements

The paper describes a refinement of a previously published theory for geotropic movements of Helianthus annuus hypocotyls. The introduction of a logarithmic relation between growth rate and auxin concentration means an extension compared with the previously published approach. It is theoretically and experimentally shown that the refined theory can successfully be linked with reported measurements on lateral auxin transport in geotropically stimulated plant stems. The non‐linear character of the theory is discussed in connexion with theoretical descriptions on circumnutations of the hypocotyls. The refined theory is shown to predict the amplitude of the circumnutations reasonably well.