The sensitive plant is well known for its response to touch, but less known for its sleep movement similar to Albizia and the French bean. It was originally thought that this was a response to an external environmental cue, perhaps light. This nightly leaf folding in Mimosa pudica was the subject of the first-ever experiment in the field of chronobiology, undertaken in 1729 by Jean-Jacques de Mairan, a French astronomer. He put the plant in his cupboard, and found that it would open and close its leaves on a daily cycle even when it was kept in the dark. In 1758, researchers repeated the experiment, placing the plant in a suitcase wrapped in a blanket, inside a wardrobe in a cave, eliminating all light; it still moved, showing that the plant was indeed responding to an internal rhythm. Some were still not convinced, arguing that it could potentially be driven by some subtle and undetected geophysical cue associated with the rotation of the earth on its axis. The role for an internal circadian clock was definitely proven by the field of molecular genetics, which identified the timekeeping components.
