Rehydration versus Growth-induced Water Uptake in Plant Tissues

Experiments show that the rate of water uptake by living tissues external to mature xylem of cotton stems (Gossypium hirsutum L. Auburn 7-683) is very similar to the corresponding curves for leaf tissue. In both cases one obtains a two-phase curve with phase I corresponding to passive rehydration and phase II pertaining to active growth.A theory of water movement in plant tissue first proposed by Philip allows one to make a more rigorous distinction than made previously between phase I and phase II. This theory is applied explicitly to water uptake by leaf disks and results in a simple expression for the time required for phase I completion. Because the time required varies as the square of the disk radius, it is essential to use a standad disk size in water uptake studies of a particular tissue.Additional analysis indicates that clear temporal distinction cannot be made between phase I and phase II. Different portions of the leaf disk rehydrate at significantly different rates, resulting in a grey zone with phase I and phase II occurring simultaneously in different parts of the disk.