<p>(A) Geometry of a quadrilateral shell element for the finite element method. The thin three-dimensional surface is parametrized by a two-dimensional shell with implicit thickness and set of director vectors <i>D</i> (<a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1003410#pcbi.1003410.s008" target="_blank">Text S1</a>). (B) An element used in the triangular biquadratic spring model. and represent positions and edge lengths in resting and deformed state, respectively. The strain tensor can be expressed in terms of edges of the element in resting and deformed states. (C) The quadrilateral patch used for comparing triangular biquadratic springs and finite element shell models. (D, E) Different templates representing selected plant-like geometries used in tissue pressure simulations.</p
