Induction of coiling in tendrils by auxin and carbon dioxide

Symmetric application of indole-3-acetic acid, CO(2), or, to a lesser extent, ethylene can substitute for the contact stimulus in inducing coiling in the tendrils of Marah fabaceus. In the case of auxin, treatment of the apical few millimeters results in strong, permanent coiling throughout the length of the tendril. The speed of the response to CO(2) is comparable to that to tactile stimuli. A possible mechanism for thigmotropism is outlined.