Architecture of the cell wall of a green alga,Oocystis apiculata

Summary The cell wall of a green alga,Oocystis apiculata, was visualized by electron microscopy after preparation of samples by rapid-freezing and deep-etching techniques. The extracellular spaces clearly showed a random network of dense fibrils of approximately 6.4 nm in diameter. The cell wall was composed of three distinct layers: an outer layer with a smooth appearance and many protuberances on its outermost surface; a middle layer with criss-crossed cellulose microfibrils of approximately 15–17 nm in diameter; and an inner layer with many pores between anastomosing fibers of 8–10 nm in diameter. Both the outer and the inner layer seemed to be composed of amorphous material. Cross-bridges of approximately 4.2 nm in diameter were visualized between adjacent microfibrils by the same techniques. The cross-bridges were easily distinguished from cellulose microfibrils by differences in their dimensions.