Lichen. Coloured scanning electron micrograph (SEM) of a Cladonia floerkeana lichen. Lichens are symbiotic organisms formed of a fungus and an alga that mutually benefit one another. The red structures are the fruiting bodies of of the fungus, which contain the spores (reproductive cells). The alga is contained within the hyphae (filaments) of the fungus. They are therefore protected from harsh conditions, and in particular from dessication. The alga supplies the fungus with nutrients that it makes by photosynthesis. Magnification: x25 when printed at 10 centimetres wide.