Cell Structure and Cell Division in the Cyanophyceae

Abstract

1. The cell of the Cyanophyceae possesses no differentiated central organ of the nature of a "central body" or a nucleus. Undifferentiated protoplasm is uniformly distributed throughout the entire cell, the peripheral portion differing from the central portion merely in the presence of pigment. 2. A deeply staining granular substance is present in the central region, which forms stringlike masses somewhat resembling chromosomes. The central substance is homogeneous and shows no differentiation into chromatic and achromatic portions, and no resemblance to a nuclear reticulum. 3. Cell division is accomplished by a centripetally growing cell wall. As this develops, the central substance becomes constricted into two approximately equal masses. The division of the central substance is strictly amitotic. The central granules have no individuality. 4. The central substance resembles chromatin in several ways and it may have similar functions, but it is not organized as a nucleus. 5. The ground substance, or undifferentiated protoplasm, is minutely granular and highly vacuolated. It does not exhibit a reticulate structure. 6. The pigments are held in solution in the peripheral protoplasm, probably in the cell sap of the vacuoles. There is no organized peripheral chromatophore. 7. The peripheral protoplasm contains cyanophycin granules representing reserve food. These may be absent or present in varying degrees of abundance, even among cells of the same filament. They accumulate in resting cells. 8. The Cyanophycean cell is organized without the differentiation seen in the cells of the higher plants. A slight functional differentiation is displayed in the restriction of photosynthetic activity to the peripheral region of the cell, and in the presence of a substance in the center of the cell which is transmitted through successive generations.