THE STRUCTURE OF THE PRIMARY EPIDERMAL CELL WALL OF AVENA COLEOPTILES

Abstract

Studies with the electron and polarizing microscopes and by low-angle scattering of X-rays show that the outer walls of epidermal cells in Avena coleoptiles ranging in length from 2 to 40 mm are composed of multiple layers of cellulose microfibrils oriented longitudinally. At an earlier age the number of layers is between 10 and 15 but this increases to about 25 in older tissue. Where epidermal cells touch, these multiple layers fuse gradually into a primary wall of the normal type between cells. In these radial walls, the microfibrils are oriented transversely. Growth of the multilayered outer wall, which is not brought about solely by apposition of new layers, provides a severe test of any model of wall growth and is not adequately explained by any single current theory.