Coiling of intact or excised cucumber (Cucumis sativus) tendrils can be induced by IAA or ethylene. The velocity of coiling in different regions of the tendrils correlates with the capacity for auxin-stimulated ethylene synthesis. Ethylene (Ethephon) induces an increase in membrane permeability of tendrils, and as a result the efflux of substances previously taken up (glucose) is stimulated. It is assumed that this may contribute to the contraction of the ventral side of the tendril. The excretion of glucose after ethylene treatment can be reduced by Ca(2+), and calcium also inhibits coiling of tendrils following incubation in ethephon solution. Auxin stimulated ethylene synthesis in the ventral half of the tendril is several times higher than in the dorsal half and it is hypothesized that this may be a cause for the different reactions of the two sides of a tendril following a mechanical stimulus.