VISUALIZATION OF EXTRACELLULAR DEPOSITS IN RECENT AND SUBFOSSIL UMBILICARIA-HYPERBOREA

Field emission scanning electron microscopy was used to characterize m ycobiont wall surfaces in Umbilicaria hyperborea from Greenland. To de termine the precise intrathalline distribution of phenolics, compariso ns were made of hyphal surface features and dimensions before and afte r acetone extraction. Stratification was evident within the medulla, a s extracellular phenolics were observed only on hyphae near or within the algal zone. The outside diameter of hyphae in this region was thus significantly greater than in the remainder of the medulla. Surface d eposits were also examined in 1350-year-old subfossil thalli and hypha l diameters were compared statistically to those in extant thalli. The mean hyphal diameter in the upper medulla was nor significantly less in subfossil specimens than in recent thalli, suggesting that phenolic cover was maintained in spite of glaciation. However, after ice buria l phenolic masses tended to be flatter than in recent specimens and fi nely tuberculate. The appearance of mycobiont hyphae in the cortex of subfossil thalli seemed to be the same as in extant thalli, except tha t there tended to be more compressible, smaller and less conglutinated filaments near the algal layer. (C) 1997 The British Lichen Society.