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(a) (transparent surface) Mirror image of two cones; (green surface) a leaf blade; φ, folding angle; R0, radius of curvature of the vein situated between the two blades when the leaf is completely folded; ρR0, radius of curvature of the vein situated between the two blades while the leaf unfolds. (b) Successive isometric deformations on the leaf supported by different cones. (Online version in colour.)
