Unbranched tendrils arising from the fifth node of light grown Alaska pea plants were found to reach maturity at the age of 10 days. Such tendrils, when stroked, coiled rapidly. They remained maximally irritable for at least 3 days.Coiling was separable into 2 components, curvature (measured in degrees) and elongation. Coiling reached a maximum from one-half to 3 hours after tactile stimulation. This maximum is followed by a decrease, then by a further increase up to 48 hours.The optimum temperature range for curvature was 16 to 30 degrees after 2 hours and 16 to 20 degrees after 20 hours. Curvature was minimal and elongation optimal at a pH of 6.6. Both curvature and elongation were greater in white light than in darkness.Severing the dorsal vascular bundles decreased coiling, whereas severing the ventral bundles had no effect. Amputation of the tip of an excised tendril increased curvature but decreased elongation. In some cases, coiling of tendrils in situ was followed by curvature of the subjacent stem.Various growth substances produce effects on elongation and curvature of tendrils in vitro, in light and dark. CCC and GA decrease curvature in the light and increase curvature in the dark and elongation in the light and in the dark. Kinetin decreases curvature in the light, increases it slightly in the dark and has no effect on elongation. IAA increases elongation in the light and in the dark at concentrations above 10(-6)m. At lower concentrations, curvature was increased in the light and decreased in the dark.These data are discussed with a view towards explaining the coiling event.