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(a) Left pane: Photograph of the device motivated by liverwort, with R = 5.0 mm and Φ = 110°. Scale bar: 5mm. Right pane: magnified image of the surface of a rib, taken by stereomicroscope (Olympus, Japan). Scale bar: 1mm. (b) Definition of shape parameters Φ, R and a. (c) Photograph of a collection of our plastic models for various radii R and number of ribs N. Scale bar: 10 mm. (Online version in colour.)
