Table 3.

Summary of the simulation results.

decisive materials	$\mu$	flexural rigidity	torsional rigidity	twist-to-bend ratio
Parenchyma/epidermis	0.4	reference value	reference value	reference value
Parenchyma/periderm	0.04	increase $\approx 14\%$	increase $\approx 46\%$	decrease $\approx 24\%$
Parenchyma/sclerenchyma*	0.00044	increase $\approx 5600\%$	increase $\approx 112\%$	increase $\approx 2536\%$
Parenchyma/collenchyma**	0.008	increase $\approx 315\%$	increase $\approx 34\%$	increase $\approx 198\%$

The mechanical effect of various changes of the structural reinforcement is given as a percentage increase or decrease with reference to the initial configuration (= reference value). Figure 2a shows the initial configuration in terms of a triangular cross-section comprising of parenchyma with embedded vascular bundles surrounded by an epidermis. $\mu$ is the ratio of estimated elastic moduli (E_est) of the decisive materials (see Table 2). The percentage values inherent to the fibre reinforcements are computed with respect to the optimal number of fibre strands. namely, *49 sclerenchyma strands and **24 collenchyma strands (see Figs. 4, 5).