When turgor is lost, the walls of the filaments in the medulla swell and the lumina are constricted to a fraction of their original diameter. The sieve plates of the filaments resist the constriction, giving rise to the double “trumpet" form with a plate in the middle. The original situation was deduced from: a. calculation of cell wall and lumen volume, based on K and Na analysis and examination of sections; b. perspex replicas from deep-frozen tissue and sections from tissue frozen before fixation; c. subsequent loss of volume and recovery of medullary tissue after being cut through; d. plasmolysis experiments.