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is apparently random and transmission electron microscopy (TEM) shows
bacteria penetrating through the primary wall and middle lamella into adja-
cent cell walls. In badly attacked regions, the cell wall is riddled with tunnels,
showing bacteria at their distal ends and a series of concave transverse layers
along the tunnels. These transverse layers or cross walls are thought to be
composed of mucopolysaccharide deposited by the advancing bacterium and
have been described as chambered tunnels. These observations suggest that
cell wall lysis is therefore not a continuous process.
Recent studies into the condition of waterlogged archaeological wood from
a range of sources, indicate that attack by tunnelling bacteria and soft rot fungi
is more concentrated in the outer layers and erosion bacteria predominate
deeper into the wood, suggesting the latter are much less oxygen dependent.
2.5 Cavitation Bacteria
Bacterial attack of wood cell walls, which produces cavities can take two forms,
tunnelling – one chambered (see above) and the other non-chambered tun-
nelling or cavitation attack. Cavitation attack was described from preservative-
treated pine posts in horticultural soils and microscopically, the decay pattern
was similar to that described in ancient softwood piling timber in Stockholm.
Decay occurs in the wood cell wall producing angular, often diamond-shaped
Figure 8An SEM of bacterial attack (erosion) of wood