Lichens

The work surveys the development of lichen study, then analyzes the thallus and its composite nature, detailing algal gonidia, fungal hyphae, and their physiological interactions. It classifies and describes thallus morphologies—crustaceous, squamulose, foliose, fruticose, radiate, and stratose-radiate—examining cortical, gonidial, and medullary tissues and attachment structures. Special lichen features such as soredia, isidia, cephalodia, cyphellae, and breathing pores are defined and their formation and dispersal discussed. Reproductive structures and life-cycles are treated, including apothecia, perithecia, ascospore development, and asexual propagation. A glossary, bibliography, and numerous figures support identification, cultivation experiments, and taxonomic considerations.