Aspects of the engineering theory treating the elastic stability of vertical stems and cantilevered leaves supporting their own weight and additional wind-induced forces (drag) are reviewed in light of biomechanical studies of living and fossil terrestrial plant species. The maximum height to which arborescent species can grow before their stems elastically buckle under their own weight is estimated by means of the Euler-Greenhill formula which states that the critical buckling height scales as the 1/3 power of plant tissue-stiffness normalized with respect to tissue bulk density and as the 2/3 power of stem diameter. Data drawn from living plants indicate that progressively taller plant species employ stiffer and lighter-weight plant tissues as the principal stiffening agent in their vertical stems. The elastic stability of plants subjected to high lateral wind-loadings is governed by the drag torque (the product of the drag force and the height above ground at which this force is applied), which cannot exceed the gravitational bending moment (the product of the weight of aerial organs and the lever arm measured at the base of the plant). Data from living plants indicate that the largest arborescent plant species rely on massive trunks and broad, horizontally expansive root crowns to resist drag torques. The drag on the canopies of these plants is also reduced by highly flexible stems and leaves composed of tissues that twist and bend more easily than tissues used to stiffen older, more proximal stems. A brief review of the fossil record suggests that modifications in stem, leaf, and root morphology and anatomy capable of simultaneously coping with self-weight and wind-induced drag forces evolved by Devonian times, suggesting that natural selection acting on the elastic stability of sporophytes occurred early in the history of terrestrial plants.

中文翻译：

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重力和风对陆地植物进化的影响

根据对现存和化石陆生植物物种的生物力学研究，对处理垂直茎和悬臂叶片的弹性稳定性的工程理论方面进行了审查，这些叶片支撑着自身的重量和额外的风致力（阻力）。乔木物种在茎在自身重量作用下弹性屈曲之前可以生长的最大高度是通过欧拉-格林希尔公式估计的，该公式指出，临界屈曲高度按植物组织刚度的 1/3 次方归一化组织体积密度和茎直径的 2/3 次方。从活植物中提取的数据表明，逐渐高大的植物物种采用更硬、重量更轻的植物组织作为其垂直茎中的主要硬化剂。承受高侧向风载荷的植物的弹性稳定性受曳力力矩（曳力与施加该力的地面高度的乘积）控制，不能超过重力弯矩（曳力的乘积）空中器官的重量和在植物底部测量的杠杆臂）。来自活植物的数据表明，最大的树栖植物物种依赖巨大的树干和宽阔、水平扩张的根冠来抵抗阻力扭矩。对这些植物冠层的阻力也被高度灵活的茎和叶所减少，茎和叶由组织组成，这些组织比用于硬化较老的、更近端的茎的组织更容易扭曲和弯曲。对化石记录的简要回顾表明，茎、叶、