Electron microscopic examinations of decaying Pinus radiata horticultural posts which had been treated with CCA preservative prior to being placed in service about nine years ago showed the presence of soft rot fungi and tunnelling bacteria. Some novel observations on the micromorphology of the soft-rotted areas of tracheid walls are described here. The micromorphology of soft-rotted areas was highly variable. In some areas soft rot cavities were associated with little or no dense residues, whereas in other areas a considerable amount of dense residues was seen around cavities. The dense soft-rotted regions appeared regular in some cases but irregular in others, depending upon the extent to which the tracheid wall around soft rot cavities had been modified. The observed morphological appearance of soft-rotted zones suggests that the initial fungal activities during soft rot attacks of wood cell walls may involve production of molecules small enough to diffuse through the microcapillaries of lignified walls, and in this respect some types of soft rot attack appears to be similar to brown rot attack.

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