LATERAL FLOW IN BEECH AND BIRCH AS REVEALED BY THE ELECTRON-MICROSCOPE

Sapwood of beech and birch was impregnated with aqueous salt solutions and suspensions of carbon particles and india ink under a low initial pressure; the pathways marked by the impregnating substances were examined by the electron microscope. The micrographs revealed dark deposits in cell lumina, pit membranes, and other parts of the cell wall. The size of voids occupied by dark deposits ranged from infinitely small to 700 Å in vessels and rays, and from infinitely small to 1,300 Å in fibers. It was concluded that the penetration path of impregnating substances from one cell to the next was through the minute intermicrofibrillar openings in the communicating pit membranes and in the rest of the cell walls. Carbon particles, suspended in plastic monomer, were not observed either in pit membranes or in the rest of the cell wall; they probably represent a nonpolar substance. © 1979 Springer-Verlag.