Fluorescent staining of a cell of Euglena gracilis. With the dyes used, the nucleus appears red because of the fluorescence of large amounts of nuclear DNA. The mitochondria fluoresce green, and, within mitochondria, the concentrations of mitochondrial DNA (nucleoids) fluoresce yellow.
[From Y. Hayashi and K. Ueda, “The shape of mitochondria and the number of mitochondrial nucleoids during the cell cycle of Euglena gracilis,” J. Cell Sci. 93, 1989, 565. Photo by The Company of Biologists Ltd..