An Unusual Organelle in the Peripheral Cytoplasm of Chara Cells

Abstract

DURING the course of an investigation of the fine structure of the development of laterals of limited growth of Chara, unusual structures were observed at the surface of some of the cells (Fig. 1). They consisted of an invagination of the plasmalemma, approximately ovoid in shape, containing a knot of anastomosing tubules. Each tubule, when cut transversely, showed a circular outline, 200–500 Å in diameter, bounded by a single unit membrane the same thickness as the plasmalemma. The organelles were present in the cylindrical cells of well-developed laterals, being confined to the cytoplasm adjacent to the outer walls, where they lay next to the layer of chloroplasts found in this region. Mitochondria also occurred in this position but, while superficially resembling the organelles, they could be distinguished because of their double outer membrane. The organelles were not observed in meristematic cells of young lateral branches.