The structure of the wall of the green alga Valonia ventricosa

Abstract

The sets of striations visible in the wall of Valonia with the polarizing microscope parallel the direction of the cellulose chains. The wall consists of several lamellae, of 2 alternating types, the cellulose chains of one layer making an angle of about 80[degree] with those of adjacent layers. The cell was orientated in the x-ray apparatus, using lines drawn on its surface with india ink. As the direction of the cellulose chains was traced, their course was also drawn to map their direction. One set of layers has cellulose chains in the meridian direction, the other in a spiral, with the extinction directions between, their positions determined by the relative directions and proportions of the 2 sets of chains. The path of the spirally arranged chains corresponds roughly to that of a logarithmic equiangular spiral described on the surface of a prolate spheroid. At the poles of the cell, the spiral becomes closer, and the x-ray photographs resemble the series of rings given by a crystalline powder. The plane of spacing 6.1 A of the cellulose crystallites is confined within an angle of about 60[degree] to the wall surface; the spacing is the expected result of unidirectional constriction by drying. The series of layers with alternating directions of cellulose chains distinguishes the wall of the polynuclear Valonia cell from the simpler walls of higher plant fibres, but the structure is fundamentally similar to that of these smaller uninucleate cells.