LM of a section through the lobe of Peltigera aphtosa, through a Cephalodium. The thallus is dotted with cephalodia, which contain one of the two symbionts, a cyanobakterium, species Nostoc. Nostoc is located inside the Cephalodia in small clusters. The other symbiont, a green alga genus Coccomyxa, is located under the surface of the lobe in a thin, continuous layer, seen at the bottom of the image. In this fluorescence image, the algae show a bright, red autofluorescent color of the chlorophyll. Microscopic contrast method : Incident fluorescence, UV Excitation. Magnification 380x when printed at 10 centimetres wide.