STRUCTURAL ASPECTS OF THE LICHEN-ROCK INTERFACE USING BACKSCATTERED ELECTRON IMAGING

The profound knowledge of the structural and chemical characteristics of the interface between lichen thallus and rock, seems to be indispen sable for the process of understanding the lichen symbiosis as well as the significance of the weathering action of lichens. One of the most promising techniques to be used in this investigation is the Scanning Electron Microscopy (SEM) in the back-scattered electron (BSE) emissi on mode. In the present work thalli of Parmelia conspersa, Aspicilia i ntermutans and Lecidea auriculata growing in granitic rock were examin ed by SEM in BSE mode with (Energy Dispersive Spectroscopy) EDS. In th e case of the foliose thalli the observation of the interface permits detection of the rhizine/hyphae adherence and determination of the ori gin of the minerals which adhere to the rhizine/hyphae. In the case of the crustose thalli BSE permits investigation within the ultrastructu re of the crustose thallus and crustose lichen-rock contact zone and a lso allows observations of the penetration and filling of the fissures and cracks of the underlying rock by components of the thallus and ot her living organisms. The BSE images could contribute to a better know ledge of the cytological state of the rock-inhabiting organisms and al so to the understanding of the action of the chemical treatments used in the removal of lichen from building materials.