Spirogyra sp. (Gr. speira, coil & Gr. gyros, twisted) zygnematalean green alga filaments, stained with acridine orange, showing three filaments, focused to the middle of one filament, showing the nucleus in yellow fluorescence. Spirogyra forms filaments composed of cells having spiral, ribbon-shaped chloroplasts. The chloroplasts show res auto fluorescence, the cell walls show green fluorescence. Culture material of the Culture Collection of Algae at the University of Cologne. Microscopic contrast technique : Differential interference contrast. Magnification 370x when printed 10 centimetres wide.