Parmelia sulcata a common lichen in woods and rural places, on trees with an acid bark. (foto J. Nascimbene)

     Panel III The main information is briefly given about the lichen’s symbiosis: lichens result, in fact, from the union of two very different partners, an algae and a fungus.
     The growth forms of thallus (leafy, scabby and shrublike) and the internal structure of a lichen is shown in section. This way the double nature of these organisms can be seen by the illustration where the cells of the fungus are different from those of the algae. There is a description of the symbiosis through vegetative reproduction and the structures by which the fungus carries out sexual reproduction. Information is also offered on how lichens are used in monitoring the condition of the environment.
     The photographs show some alpine lichens which develop on different surfaces and in various environments: the anthropic, the forest and at high altitudes.