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Tendrils of some species of plants freely coil between their bases and tips to drag up the shoot and ensure no waste of shoot growth. In this study, the drag force generated by tendrils of the luffa plant (Luffa cylindrica) during free coiling was evaluated using a force measurement system that consisted of cantilever wire apparatus, CCD camera and finite element analysis software. How the stiffness of an object to which is attached the tip of tendrils affects the development of drag force because of free coiling was investigated. Experimental results showed that the tendril attached to a stiffer support could take longer to develop drag force and generate stronger drag force than one attached to a less stiff support. The drag force developed by free coiling of the luffa tendril could be on the order of 0.17 N. This force is sufficient to pull up more than eight times the internodal weight of the luffa shoot without other support. The relation between the magnitude of drag force generated by free coiling and the contraction ratio of the tendril was elucidated. The drag force–time curves show that the rate of increase in drag force resulting from free coiling of luffa tendrils in the first 20 h is higher than that after 20 h.

In this study, the mechanical properties of Caladium (Caladium × hortulanun Birdsey) petiole were investigated. The petiole was considered as a composite beam which consists of rind and core parts. To classify the mechanical properties of rind and core part of petioles, two-phase three-point bending tests were conducted on the specimens cut from petioles. Linear beam theory was used to convert the time-dependent bending forces, during the three-point bending tests, to relaxation moduli. The result shows that the mechanical properties of rind and core parts of Caladium are very different. The relaxation modulus of rind is approximate 40 times higher than relaxation modulus of core at time = 600 s after applying bending load, and the relaxation time distribution of core is wider than the relaxation time distribution of core. The three- and seven-parameter linear viscoelastic constitutive models were used to describe the time-dependent relaxation moduli of rind and core of caladium petiole. The fitted results show that the seven-parameter Wiechert model can describe the viscoelastic behaviour of Caladium petiole very well. The finite element analysis was used to assess the error of this test methodology. The reaction force error because of the tapered diameter of specimens is about 12%.