Observations on the Structure of the Cell Walls of Valonia ventricosa and of Dictyosphaeria favulosa

The dissection of partially macerated piem of the cell wallof Valonia ventricosa is described. Laminae comprising a veryfew, or only one, of the component lamellae of the wall havebeen readily obtained. The occurrence of three directions offibrillar orientation is confirmed. In Dictyosphaeria favulosa the cell walls show three equallywell developed directions of fibrillar orientation, one forminga set of great circle meridians about the cell, so definingtwo diametrically opposite ‘poles’, and the otherstwo series of spirals, right- and left-handed, lying obliquelyto the meridians at approximately equal angles in the regionof 70°–80°. Single lamellae of Valonia walls show only one direction offibril orientation, which is parallel to the major extinctiondirection when viewed between crossed Nicol prisms. When stretchedtransversely to the fibrils these isolated lamellae open outinto networks in a characteristic fashion, indicating the presenceof some system of lateral linkages between the strands. The strands of such networks are shown by electron microscopyto be composed of aggregates of microfibrils of indefinite lengthand of diameter apparently about 100 Å. This is much lessthan the diameter (300 Å.) of similar fundamental microfibrilspreviously reported; the difference may arise from the differentmethode of preparation of the material. Electron-micrographsdo not reveal any structural basis for the lateral linkagesbetween fibrils. The mechanics of the growth of these multi-lamellate walls isbriefly considered.