A New Look at a Blue-Green Alga

Abstract

Electron microscopy has enabled biologists to take a new look at the blue-green algae. Electron micrographs of cell sections are revealing details of cell structure heretofore unseen. New concepts of the membrane systems and associated organelles are beginning to appear. An electron micrograph of cells in a filament of Phormidium luridum was used as the basis of the diagram accompanying this paper. Phormidium luridum is in the same family as the more familiar Oscillatoria. The cells of the species Phormidiurn luridum are of much smaller dimensions than the cells of most blue-green algae. Such very small cells are of special interest to electron microscopists. For example, one of the cells of the species represented in Fig. 1 is scarcely two microns long. Such a cell is so very small that it is possible to draw an outline of it and draw all of its constituent parts, even its finest organelles, on the same scale. This is not possible in the case of the larger microorganisms such as a euglena, ameba, or paramecium. The nucleus of a euglena has an average diameter of about five microns. It is easy to appreciate the relative smallness of these blue-green alga cells in Fig. 1 when one determines that it would take about three of them, end-to-end, to stretch across a euglena nucleus. These very small blue-green cells are described as procaryotic because of their internal organization.