Figure 8.

Growth-induced longitudinal tissue tension in a stalk of rhubarb. The stalk is modeled as a quarter of a cylindrical tube with elastic volume elements and growing surface elements. With decreasing surface-to-volume growth ratios from $\widehat{\vartheta }=1.000$, to $\widehat{\vartheta }=0.975$, $\widehat{\vartheta }=0.950$, $\widehat{\vartheta }=0.925$, $\widehat{\vartheta }=0.900$, $\widehat{\vartheta }=0.850$, and $\widehat{\vartheta }=0.750$, the surface tension increases and induces a higher curvature when the stalk is cut into quarters. Red colors indicate compression, green and blue colors indicate tension.