When using an apparatus to keep constant the position of the meniscus at the end of a cut petiole of phosphorus-deficient plants, Passioura and Tanner [Aust. J. Plant Physiol.12, 455-61 (1985)] observed oscillations in the applied balancing pressure. They ascribed these to oscillations in the hydraulic con- ductance of the plant. Their results are re-examined using an electric analogue, and it is suggested that oscillations resulted from the combination of hydraulic resistance and capacitance in the plant in conjunction with the apparatus they used. Measurement of the hydraulic resistance and of the period of oscillation makes possible an estimate of the hydraulic capacitance of the plant.