. The chemistry and mode of action of plant growth substances; proceedings of a symposium held at Wye College, University of London, July 1955. Plant regulators; Auxin; Growth (Plants). Chemical structure and biological activity chemical structure of the substances we found to be active as growth pro- moters and inhibitors. Although we know that the form of a molecule is only one of the different properties which must be taken into consideration if we want to get a complete knowledge of the relation between activity and chemical structure of different substances, nevertheless, we think that th
. The chemistry and mode of action of plant growth substances; proceedings of a symposium held at Wye College, University of London, July 1955. Plant regulators; Auxin; Growth (Plants). Chemical structure and biological activity chemical structure of the substances we found to be active as growth pro- moters and inhibitors. Although we know that the form of a molecule is only one of the different properties which must be taken into consideration if we want to get a complete knowledge of the relation between activity and chemical structure of different substances, nevertheless, we think that this point of view has so far been too much neglected. It will be seen that there are some surprising similarities in the form of substances of similar physiological action which are very different chemically. We cannot believe that the factor 'form' is of no importance when a molecule enters a living system; indeed, we have good reason to assume that the analogy of key and lock is. Figure I. The concentration-action curves of indole-3-acetic acid (lAA) and indole-i- acetonitrile {IAN) in the paste test. log concn. very relevant. We consider that each molecule must be well matched with its corresponding gap by its form, and by its electrical and chemical configuration. In this communication, I will first present some recent results we obtained by investigating the activity of different synthetic substances using our paste method. Secondly, I will give a comparison of some values for the affinities and other significant constants which we evaluated using Kaindl's formula for the concentration-action curves of growth substances and growth inhibitors (Kaindl, 1954). In addition, photographs are included showing similarities of the molecular form and size of different growth substances and growth inhibitors. The first important growth substance examined was indole-3-acetonitrile, a compound first isolated from natural sources by Jones and his co-workers (1952). It was tested in compa
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