Several unique patterns of degradation occurring in wood cell walls have been observed in wooden stakes inserted in unsterile soil in the laboratory. Some of the patterns have also been observed in coniferous wood taken from forest floors. All the observed attack types occur within wood cell walls, mainly within the S2 layer. Attack is characterised by channels of varying diameter or small fusiform cavities arranged in the form of a rosette. Some channels are narrow, 0.5-1.0 µm, and form a highly branched network. Other channels are wider, up to approx. 2-3 µm and less branched. All channels are produced by hyphae growing within the wood cell walls. Attack has been observed to arise from the branching of thin hyphae growing longitudinally in the fibre lumina. The small diameter of the hyphae and the fact that these decay patterns have not been described for wood degrading fungi indicate that actinomycetes may be responsible.

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