“…Opinions on the location of the free space depend on opinions on the place of the membrane, which forms a barrier to the free diffusion of ions into the plant cell. If the tonoplast is considered as the semipermeable membrane, the free space is located in the cell-wall and the cytoplasm, HOPE, 1953;HYLMO, 1953;EPSTEIN, 1956) and the cytoplasm is regarded as the semipermeable membrane, the free space is restricted to the cell-wall (PLOWE, 1931;DAVSON and DANIELLI, 1943 ;WALKER, 1955;LEVITT, 1960).…”