Beschreibung:
<p>The inner limits of the distribution of three common corticolous lichens are mapped in the west central Scotland area. By employing a modified version of Hawksworth & Rose's (1970) qualitative zone scale for estimating mean winter SO<sub>2</sub> using linches, the patterns of SO<sub>2</sub> air pollution over the survey region is traced. That the lichen data reflect SO<sub>2</sub> levels rather than other factors is supported by (a) field transplant experiments which show that Hypogymnia physodes and Usnea subfloridana accumulate sulphur and exhibit morphological damage in proportion to the mean SO<sub>2</sub> levels, and to a lesser extent by (b) bark pH studies which demonstrate that a good linear relationship pertains between mean pH and SO<sub>2</sub>. A new technique for determining microgram amounts of sulphur in lichen material is briefly outlined.</p>