Asterionella ( Gr. asterion, a kind of spider) sp. Diatom colony, stained with acridine orange to show the nuclei. Asterionella diatom cells are elongate and joined at the ends by mucilage pads to form star-shaped colonies. The labiate chloroplast, showing red auto fluorescence, is distributed over the whole cell length. Acridine orange is used as a nucleic acid-selective fluorescent dye, showing DNA and RNA in yellow-green color under blue excitation. Culture material of the Culture Collection of Algae at the University of Cologne. Microscopic contrast technique : Incident fluorescence, blue excitation. Magnification 580x when printed 10 centimetres wide.