Light micrograph (fluorescence microscopy) of Spirogyra sp. filamentous green algae. Spirogyra is named for the spiral arrangement of its chloroplasts. Its cylindrical cells connect end to end in long green filaments. In this photograph, the chloroplasts auto-fluoresce in red due to the ultraviolet light used to illuminate the algae. Magnification: x450 when printed at 10 centimetres wide at its longest edge.