Ultrastructure of the Attack of Eusideroxylon zwageri Wood by Tunnelling Bacteria

The decay of the naturally durable wood species Eusideroxylon zwageri by tunnelling bacteria (TB) was examined by light microscopy and transmission electron microscopy. Observations were made primarily on fibres with parenchyma cells included in some cases. Both fibres and parenchyma are rieh 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 cells, extractives are present in large amounts in the lumen. Inner areas of parenchyma walls are also heavily permeated.The degradation of E. zwageri wood is markedly slower than any wood species we have examined previously. However, in advanced stages of TB attack, all areas of the fibre, except corner middle lamellae and extractive filled lumina, are heavily degraded.The degradation ofE. zwageri wood involves other differences. TB attack of the fibre wall Starts from the St layer moving inwards. The tunnels formed vary greatly in form, ranging from long and relatively straight to "S", "V", hook, folded and convoluted forms. These variations from previously observed tunnel appearances most likely reflect differences in the thickness and chemical composition of the fibre walls of E. zwageri wood.