On the cross-sectional shape of cellulose crystallites in Valonia ventricosa

The cross-sectional shape of the cellulose crystallites from the Valonia ventricosa cell wall has been investigated by electron microscopy, using negative staining and Bragg contrast in the bright field mode, with emphasis on this latter technique. The appearance of the cellulose crystallites in the electron microscope depends on their orientation. The cross-section of each cellulose crystal is almost square, with an average side of 18 nm. Sub-units corresponding to elementary fibrils were not detectable within the crystals. The differences between these results and those of earlier workers are discussed.