Prothallal lichen substances in two species of crustose lichens, Fuscidea cyathoides and Rhizocarpon geographicum

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Abstract
Lichen substances in the prothallus of two species of crustose lichens, Fuscidea cyathoides (Ach.)Wirth and Rhizocarpon geographicum (L.)DC., were compared with those in the primary thallus. Quantification was accomplished using thin-layer chromatography and microdensitometry. In both species, at least some of the prothallal tissue, although it consisted only of fungal hyphae, contained the same lichen substances as the main part of the thallus. The quantities present in the prothallus, however, were lower, especially in the case of R. geographicum, where there was no more than about 5% as much psoromic acid per unit dry weight of prothallus as of areoles. In scanning electron micrographs the extrahyphal depositions present in prothalli appeared similar to those in the medullary regions of the primary thallus, but in R. geographicum they were noticeably less copious. The possibility that lichen substances could migrate within the thallus is discussed.