THE GEOMETRY OF UNFOLDING TREE LEAVES

Leaves of hornbeam (Carpinus betulus) and beech (Fagus sylvaticus) wer e modelled to a first approximation as plane surfaces, with straight p arallel folds, using numerical methods. In both species the lateral ve ins, when the leaves are outstretched, are angled at 30-50 degrees fro m the centre vein. A higher angle allows the leaf to be folded more co mpactly within the bud, but it takes longer to expand. This may allow the plant to optimize the timing of leaf deployment with ecological an d physiological conditions.