Permeability of the Cell Membrane of Hydrodictyon reticulatum

1. When a cell of Hydrodictyan was placed in a 1 molar sucrose solution its shrinkage soon occurred and finally it was squeezed flatly to band-like form without causing any separation between the cell membrane and cytoplasm. This may be explained as to be due to the impermeability of the cell membrane to sucrose.2. The impermeability of the cell membrane to sucrose, however, is not absolute, because the shrinkage of the membrane does not continue so long and the normal stretched state recovers again in a long time. The time required for the recovery in solutions of equal osmotic concentration is available as a relative measure of permeability of cell membrane.3. The cell membrane permeability of Hydrodictyon to sucrose is influenced by the hydrogen ion concentration of the medium. It reaches the maximum in the region near pH 7.0 and the minimum between pH 2 and 4. This may probably be explained by the assumption that the hydration degree of the cell membrane depends on the pH-values. The membrane permeability is lower in the younger cell and higher in the adult one.4. The permeability of the cell membrane to organic substances was studied. Small molecular volume and the high surface activity of the solutes are outstanding factors to permit them to pass readily through the cell membrane.