Extensive ridge-like structures lining the outer walls of cells at the surface of cell aggregates and less elaborate thickenings on the walls between adjacent cells are reported and compared with the wall thickenings observed in ‘transfer cells’. Mitochondria with an atypical crista are described. Plastids in cells cultured in the standard synthetic medium contain poorly developed internal lamellae and function as amyloplasts during the growth cycle. Their differentiation into chloroplasts is induced by replacing the 2,4-D by NAA in the medium. A structure is proposed for the crystalloid core of the microbodies, which are a prominent feature of stationary phase cells.