What stimulus causes the mimosa plant to wilt and droop?

The mimosa plant, specifically Mimosa pudica, wilts and droops in response to touch or mechanical stimulation. This rapid movement is a defensive mechanism triggered by changes in turgor pressure within its cells, caused by the influx and efflux of water. When stimulated, cells in the pulvini (the joints at the base of the leaflets) lose water, leading to a temporary loss of rigidity and causing the leaves to fold and droop. This reaction helps deter herbivores and protects the plant from damage.