Light micrograph of Hydrodictyon reticulatum (Gr. hydro, water & Gr. dictyon, net), showing cells of a younger colony. Hydrodictyon cells are multinucleate, shown here by staining with Acridine Orange causing yellow-green fluorescent response of the nuclei under blue light excitation. The single reticulated chloroplast shows red fluorescence. Culture material of the Culture Collection of Algae at the University of Cologne. Microscopic contrast method: Fluorescence contrast, blue excitation. Magnification 380x when printed at 10 centimetres width.