The attack of the wood of Eusideroxylon zwageri, a naturally durable species, by tunnelling bacteria (TB) was examined by light microscopy and transmission electron microscopy. Observations were made primarily on fibres. Parenchyma were included in some cases. Both fibres and parenchyma are rich in extractives. In fibres, extractives are primarily present in the lumen. The amber colouration of fibre walls under the light microscope suggests that extractives may also permeate fibre walls. In parenchyma, extractives are present in large amounts in the lumen. Inner areas of parenchyma walls are also heavily permeated. The degradation of Eusideroxylon zwageri wood is markedly slower than any wood species we have examined before. However, in advanced stages of TB attack all areas of the fibre, except corner middle lamellae and extractive filled lumen, are heavily degraded. The degradation of Eusideroxylon zwageri wood involves other differences. The TB attack of the fibre wall starts from the S1 layer moving inwards and the tunnels formed vary greatly in their form, ranging from long and relatively straight to "S","V", hook, folded and convoluted forms. These variations from previously observed appearances most likely reflect differences in the thickness and chemical composition of the fibre wall of Eusideroxylon zwageri wood from the woods examined previously.

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