The cell walls of Gonium, Pediastrum, and Oedogonium were studied, using the techniques of staining, electron microscopy, X-ray diffraction, and chromatographic analysis, with major attention given to the α-cellulose fraction. Gonium was found to lack an α-cellulose wall component. Pediastrum cell wall contains a crystalline polysaccharide composed of D-glucose and D-mannose which forms a non-microfibrillar network of interwoven chains of rings. This cell wall polysaccharide is either a gluco-mannan or a glucan intimately associated with a mannan. The cell wall of Oedogonium consists of countless lamellae of parallel microfibrils of cellulose alternating approximately at right angles with each other. These lamellae are encrusted by a spongy substance.