The withdrawal of the cytoplasm from the cell wall because of the outward movement of water from the cell vacuole due to *osmosis
. The cytoplasm eventually forms just a small central mass still enclosing a vacuole. Plasmolysis is seen when tissues are placed in solutions of lower water potential than that of the cell. By varying the concentration of external solutions and observing when a solution is just strong enough to induce plasmolysis in 50% of the cells the concentration of solutes in the cell vacuole can be determined. When working with single cells, the concentration that brings about incipient plasmolysis, i.e. the first signs of plasmolysis, is taken as being equal to the concentration of the cell vacuole. Plasmolysis normally only occurs in experimental systems where the external solution can pass through the cell to fill the space between the cell wall and the cytoplasm. Thus the cells of a wilted plant do not undergo plasmolysis.