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the loosening of the protoplast from the cell cover when a cell is immersed in a hypertonic solution. Plasmolysis is characteristic mainly of plant cells, which have a sturdy cellulose cover. Animal cells contract when transferred to a hypertonic solution. Plasmolysis may be convex, concave, convulsive, or mitriform. These variations are determined by the viscosity of the protoplasm, the difference between the osmotic pressure of the cell and that of the external solution, and the speed and degree of water loss by the protoplasm. Sometimes plasmolyzed cells remain alive; when such cells are immersed in water or a hypotonic solution, deplasmolysis occurs.
There are two methods for comparative evaluation of plasmolysis: borderline plasmolysis and the plasmometric method. The first method, developed by H. de Vries in 1884, consists of immersing tissues in solutions with various concentrations of KNO3, sucrose, or other osmotically active substances and establishing the concentration at which 50 percent of the cells are plasmolyzed. With the plasmometric method, the relative volumes of the cell and the protoplast are measured after plasmolysis, and the osmotic pressure of the cell is calculated according to appropriate formulas from the concentration of the solution.
V. V. KABANOV