PLASMOL'YSIS (Neo-Lat., from Gk. plasma, formation, molded figure + X6o-ts, lysis, resolution, from Mew, lyein, to loose), The shrinkage of the protoplasm, due to the extrac tion of water from the cell sap by a solution of higher osmotic pressure in contact with the cell. The mature plant cell consists of a mass of proto plasm, inelosing one or more droplets of cell sap (vacuoles) and surromuled by a membrane called the cell wall. 'Under certain conditions, which are also those of activity. the layer of protoplasm is held so firmly against the cell wall by the osmotic pressure of the substances solved in the water occupying the vacuoles that it is usually stretched until its resilience equals the osmotic pressure within ( Fig. 1 I. if such a cell he surrounded by a solution having an motic pressure greater than that of the cell sap, water will be withdrawn from the III t ter. the pru tOplit-G1 will shrink. the Cell wall, by its elasticit‘, will follow the shrinking protoplasm unt i it has reached its mist retched dimensions.
the IA ithdran al of water still continues, the plasm eontinue to shrink, but the cell wall ma? he strong enough to maintain its form. Thus the protoplasm will be withdrawn from contact with the wall, a condition ordinarily taken to indicate the beginning of plasmolysis. but in reality a later stage ( Fig. 2). If the cell wall be very thin it may collapse upon the shrinking protoplasm. folding and wrinkling irregularly. Should withdrawal of water continue, the plasm may shrink up into a small mass. the vacuole disappearing completely. When the amount of protoplasm in the plasmolyzed cell is relatively small, the protoplasm may happen to divide into two or more parts, a which is taken advantage of for experimentation upon the functions of the nucleus. See OsNtosts;