Many Modes of Movement

The interesting array of articles for the special issue "Movement: Molecular to Robotic" (7 Apr., pp. 79-106) examines the biology of movement for animals with endoskeletons, animals with exoskeletons, robots, and molecules, but movement in an entire kingdom—the plant kingdom—is overlooked. Movement in plants is based on physical mechanisms that are very different from most animal movements, and movements have been a central factor in the evolution of many plant adaptations. Mechanisms include hydraulic shifts operating by means of osmotic engines, differential growth, fracturing of structures due to localized desiccation, and cell separations or dissolution leading to projectile actions.