PHYSICAL INTERACTIONS OF 2 RHIZOMORPH-FORMING LICHENS WITH THEIR ROCKSUBSTRATE

Samples of a calcareous conglomerate rock colonized by Sguamarina cart ilaginea and a siliceous schist colonized by Acarospora scotica were c ut and examined with SEM-backscattered electron imaging. Both species produce extensive rhizomorphs (sensu late), whose component hyphae int erpenetrated, separated, and incorporated substrate particles in the c ourse of development. Rhizomorph expansion and contraction associated with hydration cycles could also detach adherent fragments within the substrate. In S. cartilaginea, rhizomorphs and associated hyphae also directly penetrated the calcareous substrate matrix, probably by chemi cal dissolution. Those of A. scotica appeared to penetrate the schist mainly by forcing their way between the fine, angular, somewhat flatte ned particles which comprises the substrate. The orientation of these particles influenced the form of developing rhizomorphs and the subseq uent pattern of substrate exfoliation. Lichen compounds of potential b iodeteriorative significance occurred within the squamules of both spe cies but were not detectable in their rhizomorphs. Lichenized photobio nts were abundant within the substrate; their developmental relationsh ip to epilithic squamules could be demonstrated in the case of A. scot ica.