Resistance of fibre regions in wood of Acer pseudoplatanus degraded by Armillaria mellea

The white rotting Armillaria mellea induced a spatially very distinctive pa ttern of degradation in sycamore wood, under both natural and artificial co nditions. Degradation began preferentially within groups of fibres containi ng intercellular spaces, whereas fibre regions lacking such spaces were und egraded and remained largely intact even when decay had become advanced els ewhere. The two types of fibre region differed not only in the presence of intercellular spaces, and hence in the potential for gas exchange, but also in their degree of lignification. This was higher in the more resistant ty pe, as shown by staining of undecayed wood with toluidine blue-O, by micros pectrometry after staining for the Maule colour reaction, and by uv-microsc opy. A spatially similar pattern of cellulose degradation was induced by th e brown rotting Laetiporus sulphureus, which is known to cause preferential degradation of less strongly lignified cell walls. By contrast, the white- rotting Ganoderma pfeifferi showed a tendency to degrade the stronger ligni fied cell walls. Thus, in combination with the application of conventional histological methods, the wood degradation modes observed give additional e vidence for stronger and weaker lignified fibre regions within the wood of sycamore.