The fine structure of chloroplasts and pyrenoids in some marine dinoflagellates.

The chloroplasts of some members of the Dinophyceae are bounded by an envelope consisting of three membranes and having a mean thickness of 230 A. Within the chloroplast are arranged, in a more or less parallel manner, many lamellae normally composed of three apposed thylakoids, although the number of thylakoids often varies and may reach 30 in a single stack. By study of disintegrated chloroplasts it was found that the thylakoids are circular in shape with a diameter of 0*15-3-6 /* and a mean thickness of 240 A. Ribosomes, lipid droplets and DNA areas are present in the chloroplast stroma. No connexions were seen between the chloroplasts and any other organelles, nor did the chloroplasts contain girdle lamellae. Stalked pyrenoids, which are found in some dinoflagellates, are shown to arise from the inner face of the chloroplasts, to contain a finely granular material and to be frequently surrounded by an electron-transparent area. These findings are discussed in relation to the fine structure of the chloroplasts and pyrenoids of other algal classes.