Methods and materials

A wide range of mechanical properties is relevant to the understanding of the extremely specialized stem structures found in some climbing stems. They include the stiffness in the elastic range of bending, torsion, and tension as well as other properties in the nonelastic range up to failure of the plant stem as well as toughness, extensibility, and critical strain — to mention a few [13,14]. Additional properties of interest and inextricably linked to stem mechanical properties are hydraulic conductance of the stem and the extent of mechanical deformation that can occur before the essential hydraulic supply of the stem is compromised. In the following account, we confine our attention to bending stiffness in the elastic range. We have chosen this single parameter because it can be measured relatively easily under field or laboratory conditions and because it gives a measure of the bending mechanical properties of the stem before irrereversible deformation and damage outside the normal properties of living healthy plant tissues. Our objective is to compare a wide range of tested species with different climbing habits and, where possible, from plants sampled in their natural habitats. The inclusion of a wide range of mechanical parameters is not feasible with this view in mind. Bending mechanical properties can be measured in a number of ways and via a number of types of bending tests. In the following study, we include data from previous and ongoing research projects in which we use similar bending experimental protocols for a wide range of climbing species, in the laboratory, in relatively sophisticated "field laboratories," and in remote field conditions.

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