Scher J L, Holbrook N M, Silk W K
Department of Land, Air, and Water Resources, University of California, Davis 95616-8627, USA.
Planta. 2001 Jun;213(2):192-8. doi: 10.1007/s004250000503.
Using the TWIFOR, an electronic device for continuous, in vivo measurement of the forces exerted by twining vines, we examined the forces generated by vines growing on cylindrical poles of slender (6.35 mm) and thicker (19.05 mm) diameter. In stems of Ipomoea purpurea (L.) Roth. magnitudes of twining force (axial tensions) were, on average, less at a particular time and location on the more slender poles; while twining loads (normal force per unit length of vine) were much greater on the slender poles because of the greater curvature of the vines. Thus, the geometry of the helix formed by the vine on the pole affects the ability of the vine to maintain a frictional interaction with its support. In addition, the plant-to-plant variation in twining force was twice as great on the thicker support poles. Metaxylem and fibers developed closer to the plant apex in vines on the slender poles. On the thicker poles, a significant fraction of the maximum twining force developed during the establishment of the first gyre, before fibers were lignified, indicating that primary growth can be sufficient to establish high twining forces. On the slender poles, however, twining force increased with developmental stage until the gyre was at least 1.5 m from the apex. Thus, twining force can increase after cessation of primary growth. No simple relationship was found between the site of fiber differentiation and twining force.
我们使用TWIFOR（一种用于连续、活体测量缠绕藤蔓所施加力的电子设备），研究了生长在直径较细（6.35毫米）和较粗（19.05毫米）圆柱形杆上的藤蔓所产生的力。在紫牵牛（Ipomoea purpurea (L.) Roth.）的茎中，在较细杆上特定时间和位置处的缠绕力（轴向张力）平均较小；而由于藤蔓曲率更大，较细杆上的缠绕负荷（藤蔓每单位长度的法向力）要大得多。因此，藤蔓在杆上形成的螺旋几何形状会影响藤蔓与支撑物保持摩擦相互作用的能力。此外，在较粗的支撑杆上，植株间缠绕力的变化是原来的两倍。在较细杆上的藤蔓中，后生木质部和纤维在更靠近植株顶端的位置发育。在较粗的杆上，在第一个螺旋圈形成期间，在纤维木质化之前，最大缠绕力的很大一部分就已形成，这表明初生生长足以产生较高的缠绕力。然而，在较细的杆上，缠绕力随着发育阶段增加，直到螺旋圈距离顶端至少1.5米。因此，缠绕力在初生生长停止后仍会增加。在纤维分化部位和缠绕力之间未发现简单的关系。
