The Measurement of Permeability to water in Disks of Storage Tissues4

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Abstract
1. Experiments have been performed to examine methods to determine hydraulic conductivity and diffusional permeability in disks of red beet (Beta vulgaris) and Jerusalem artichoke (Helianthus tuberosus). 2. The half-time for the weight change caused by transferring disks between pure water and a sucrose solution, or vice-versa, has been shown to be linearly dependent on the square of the disk thickness. 3. The efflux kinetics of sucrose from these disks are also characterized by a half-time linearly dependent on the square of the disk thickness. 4. It is concluded that extracellular solute diffusion, and not hydraulic conductivity, is the principal rate-controlling factor in experiments of this type. 5. Efflux studies with tritiated water also show a characteristic half-time which is linearly dependent on the square of the disk thickness. The cell membrane does not constitute a sufficient barrier to diffusion fot its diffusional permeability to be determined.