Department of Land, Air, and Water Resources, University of California, Davis, California 95616-8627 USA;
Am J Bot. 2005 Nov;92(11):1820-6. doi: 10.3732/ajb.92.11.1820.
The stability of twining vines under gravitational loads suggests an important role for friction. The coefficient of friction, μ, between vine stems and wood is high, often five times greater than between leather and wood, as determined by slip tests on an inclined plane. Stem trichomes function like ratchets to facilitate climbing upward (or to facilitate slipping if the stem is inverted). A mathematical model predicts large masses (kg) must be applied to the base of a twining vine to cause slipping. Vines slip as predicted when μ is low and arc length on the pole is short, and they break before slipping when μ is large or arc length is long. In contrast, twining vines are unstable in compression, collapsing when small masses (<10 g) are hung from the top of the vine. However, if the loads are applied below the uppermost gyre, the stabilizing tensional effect dominates. Therefore, in nature vines twining on a cylindrical support are stable under gravitational loads, unless these loads occur near the apex. A corollary is that a short apical coil can hold up large masses of maturing shoot.
扭绕植物在重力负载下的稳定性表明摩擦力起着重要作用。通过在斜面上进行滑动测试，确定了茎干与木材之间的摩擦系数 μ 较高，通常比皮革与木材之间的摩擦系数大五倍。茎干上的茸毛起到棘轮的作用，有助于向上攀爬（或者如果茎干倒置，有助于滑动）。数学模型预测，必须在扭绕植物的基部施加较大的质量（kg）才能导致滑动。当 μ 较低且杆上的弧长较短时，预测扭绕植物会滑动，而当 μ 较大或弧长较长时，扭绕植物会断裂而不是滑动。相比之下，扭绕植物在压缩下不稳定，当小质量（<10 g）悬挂在植物顶部时，植物会坍塌。然而，如果负载施加在最上部的涡旋下方，张力的稳定作用就会占主导地位。因此，在自然界中，圆柱形支撑上的扭绕植物在重力负载下是稳定的，除非这些负载发生在顶端附近。一个推论是，短的顶端线圈可以支撑大量成熟的嫩枝。
