An Electron Microscope Study of the Path of Water Movement in Transpiring Leaves of Cotton (Gossypium hirsulumL.)

Abstract

Precipitation of ferrocyanide by ferric ions in cotton leaves produced electron-opaque crystals visible with othe electron microscope and identifiable as Prussian blue by X-ray and electron diffraction. These crystals were formed within the lumina and exposed primary walls of the tracheary elements but not within their secondary walls. The precipitation pattern indicated that water moved from the tracheary elements into the parenchyma of the bundle sheath and bundle sheath extensions. From these cells water moved into the epidermis or through the mesophyll to the transpirational exits. Prussian blue accumulated in the walls of cells lining the substomatal cavities and to a lesser extent between adjacent covering hairs. Ferrocyanide anions did not follow the water stream through the cuticle. In parenchyma and epidermal cells Prussian blue crystals were found within the primary wall, in the region between the plasma-lemma and the cell wall, and within the protoplast.