Abstract
Sensitive plant (Mimosa pudica) is one of the most unique plants, because the petioles moves downward and leaflets unfolds rapidly as response to any mechanical, thermal or electrical stimulus. The folding motion of the leaflet looks like very complicated including twisting motion to overlap each other as making one line for compact spacing. For a design of man-made actuator, therefore, it is quite interesting and useful to understand the mechanism of sensitive plant leaflet motion. In this study, the manner of leaflet connecting to the midrib, the location of pulvinus and the cross-sectional shape of midrib etc. were observed by using various optical microscopes. From the observation, it was found that the leaflets accomplish the complex closing motion by their one-way rotation with the ingenious combination of three installation angles relating to the leaflet, midrib and pulvinus. These are a, /3 and ywhere a is the apex angle of the midrib cross-section, /3 is the angle connecting the pulvinus with the midrib, and y is the angle between the axis of pulvinus and the rachis of leaflet.
