Radial Diffusion of Free Energy In Stem Phloem: An Experimental Study¹

Abstract

Abstract The rehydration of a water‐stressed cotton ( Gossypium hirsutum L.) stem was studied experimentally. The main objective of the experiments was to ascertain if a proposed diffusion theory can describe the dynamics of the rehydration process. Stem shrinkage was induced by allowing the soil‐root system of potted cotton plants to dry by evapotranspiration. Tension in the xylem was then released suddenly by severing the stem under distilled, degassed water, with the subsequent increase in stem diameter monitored with an LVDT. From the basic data of stem diameter vs time, fractional uptake curves for free energy were computed and compared with predictions derived from theory. The comparisons indicate that the theory is applicable at least to first order. The overall study illustrates the intimate involvement of the xylem and phloem as far as radial water exchange is concerned.