[Electron microscopic data on the mesosomelike and myelinlike structures of blue-green algae]

The mesosome-like structures of blue-green algae were studied by freeze-etching without preliminary fixation and, in parallel, by a technique of ultrathin sections. These structures were found mainly in Synechococcus elongatus and Synechocystis aquatilis, less often, in Anacystis nidulans and Anabaena variabilis, and were not detected in Plectonema boryanum. The following types of membrane structures were encountered: (1) formation consisting of three- and five-layered membranes and resembling the lamellar mesosomes of bacteria; (2) complex structures consisting of five-layered membranes and separated from the cytoplasm by an electron-dense substance not found in bacteria; (3) myelin-like structures; (4) formations intermediate between the mesosome-like and myelin-like structures. These structures were not found to be strictly confined to the growth phase of a culture. Possible functions of the mesosome-like and myelin-like structures are discussed ct. those of bacteria.