Plant wilting. Two Japanese aralia, or castor oil, plants (Fatsia japonica); one healthy (turgid), the other wilting (flaccid). Wilting occurs because the plants' stems and leaves are partially supported by the pressure of water within them. This water is gradually lost through holes (stomata) in the leaves and replaced by water obtained from the soil by the roots. In dry conditions the roots cannot take up enough water to replace losses through the stomata. The plant's only defence is to close or narrow the stomata.