isnard sandrine
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The Beautiful Dance of Circumnutation (Hop - Humulus lupulus, Cannabinaceae) The apex of twining plants exhibit a large revolving movement. This movement was named circumnutation by Darwin who described it as “a continuous self-bowing of the whole shoot, successively directed to all points of the compass”. Circumnutation is a common phenomenon in plants but is exaggerated in twining plant, increasing the probability of encountering a support on which the stem would twine. This beautiful dance accomplishes here by two shoots has been proposed to result from a geotropic feedback loop and/or produced by an endogenous oscillator.
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Winding movement (Hop - Humulus lupulus, Cannabinaceae) Once the stem encounter a support, circumnutation change to a winding movement. The growing stem executes a complex dance, moving rhythmically as it appears to undulate upward around its supporting pole. A coil surrounds the pole, soon tightening basally into a helix that wraps snugly around the pole and leaves a corkscrew-shaped stem. The geometry of the helix, formed by the stem around the support, has been found to change in a predictable way with the diameter of the supporting structure : on thicker supports the vine makes longer wavelengths with smaller angle of ascent. The handedness of the helix is often a characteristic of the species. The majority of species make right-handed helices (viewed from above they wind counter-clockwise) but a substantial minority of species are left-handed (like Hop). |
