Abstract
A diagram is described which is based on the ideal relationship between osmotic potential and volume as defined by Boyle's and Van't Hoff's laws. The new graphical presentation differs from the related earlier one by Hammel and co-workers in the choice of relative water content (RWC), a term depending on the volume changes of the vacuole, as the reciprocally plotted variable. The diagram is well suited for didactic purposes and may have advantages for the analysis of experimental data.