AbstractNon‐osmotic moisture stress can be simulated by applying to a plant tissue a solute that cannot penetrate the cell wall. The external reduction in water potential caused by such a non‐penetrating solute is compensated for by a reduction in pressure within the cell. The pressure is ambient throughout a cell that has been plasmolysed by a penetrating osmoticum. A supplementary non‐penetrating osmoticum must also be compensated for by lowering the internal pressure, i.e. a negative turgor pressure must develop. Onion skin cells can withstand a resulting mechanical stress of up to about 10KPa (1/10 Bar) before colla