Ultrastructural changes occurring in beetroot parenchyma were studied from the time of cutting into disks and throughout the following 192 hr of aerated washing. The most marked change was the reduction of the endoplasmic reticulum to small cytoplasmic vesicles immediately after cutting (when leakage of ions is greatest), followed by a reorganization into lamellae (coinciding with the onset of net ion accumulation) and subsequent extension of the lamellar system. The possible relationships between these observations and others on plant cells are discussed.