STUDIES ON THE BIOCHEMISTRY AND FINE STRUCTURE OF SILICA SHELL FORMATION IN DIATOMS. II. THE STRUCTURE OF THE CELL WALL OF NAVICULA PELLICULOSA (BRÉB.) HILSE

Abstract

The cell wall of the freshwater diatom Navicula pelliculosa (Breb.) Hilse is composed of the silica shell and an organic skin which surrounds it. Isolated skins can be prepared by first removing the contents of the cell by mechanical shaking, followed by a post-treatment of these isolated cell walls with HF vapor to remove the silica shell. The skins can also be seen in sections, particularly well after the silica shell has been removed by HF vapor. The origin and morphological composition of the skin in N. pelliculosa are not yet completely ascertained. As parts of the cell wall, both the silica shell and the skin are extracellularly located. The growth of the silica shell, however, occurs extracellularly inside a vesicle delimited by a triple-layered membrane, the silicalemma. This membrane of secondary excreted organic material or both in various proportions may compose the skin.