X-Irradiation of the Giant Amoeba, Pelomyxa illinoisensis: III. Electron Microscopy of Centrifuged Organisms

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Abstract
Electron microscope studies of centrifuged Pelomyxa illinoisensis amoebae were made. At 7000 times gravity (g) the Golgi structures were stratified immediately centripetal to the mitochondria. Nuclei stratified at 1000 x g in a narrow band in the centripetal portion of the centrifugal third of the amoeba. The a-granules (0.1-03 [mu] par-ticulates) were found to be small vesicles of different types which migrated centrifugally after the bulk of the mitochondria. The stratum of mitochondria extended throughout most of the centrifugal half of the cell. Some mitochondria remain in the centripetal half of the amoeba until some 5000 x g force is used for 10 minutes. This and previous micrurgi-cal work is interpreted to mean that supralethally irradiated amoebae which receive nonirradiated protoplasm recover and produce mass cultures primarily because of the substitution of nonirradiated mitochondria for irradiated mitochondria.