The localisation of lignin and phenolic extractives in woody tissue was determined using scanning UV microspectrophotometry. This improved cellular analytical technique enabled direct imaging of the topochemical lignin distribution within individual cell wall layers with a resolution of 0.25 µm 2 . Selected softwood (Picea abies), hardwood (Fagus sylvatica, Entandrophragma cylindricum, Prunus serotina) and monocotyledon (Phyllostachys edulis) sections of 1 µm thickness were scanned at a fixed wavelength and evaluated with the "APAMOS" software. This approach allowed the distribution pattern of lignins and aromatic extractives within the cell wall to be visualised simultaneously. The method was found to be ideally suited to the study of their subcellular distribution in plant cell walls.

The multilayered structure of fibre cell walls was formed mainly during the first year of growth by the deposition of new wall layers of variable thickness, resulting in a high degree of heterogeneity in the layering patterns amongst individual fibres. A degree of 'order' in the distribution of multilayered fibres within the caps does exist, however, with multilayered cell walls common in fibres adjacent to phloem elements and around the edge of the fibre cap. These findings confirm the observations, primarily in Phyllostachys viridi-glaucescens. The layering structure was not found to be specifically related to the thickness of the cell wall.

Summary The decay patterns of brown and soft rot fungi in Sapelli wood (Entandrophragma cylindricum Sprague), with respect to natural durability, were examined by light and transmission electron microscopy as well as UV spectroscopy. Analyses revealed that the typical brown rot fungus Coniophora puteana can cause a soft rot-like decay in the sapwood of Sapelli at high moisture contents of approx. 100%. In accordance with the decay pattern of the typical soft rot fungus Chaetomium globosum, the hyphae of C. puteana penetrated the S2 wall of fibres and formed characteristic rhomboidal cavities orientated parallel to the microfibrillar angle. However, these cavities were larger in diameter (3.9 μm ± 0.9) than those formed by C. globosum (2.1 μm ± 0.5) and with a distinct interspace between the hyphae and surrounding walls. Hyphae of C. globosum were directly attached to the undecayed secondary wall. No lignin degradation for both fungi in close vicinity to the cavities was observed, as evidenced by UV spectroscopy. The inclusion of microscopy for definitive decay type identification is recommended.

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Summary The colour of Sapelli heartwood (Entandrophragma cylindricum Sprague) is variable depending on habitat. In recent years an unusual pinkish-brown colour has been observed in commercial sawn timber of this species from Central Africa. Initial studies of Sapelli heartwood samples from various provenances have furthermore demonstrated pronounced differences in its decay resistance. Heartwood extractive composition varies considerably between provenances. Samples of Sapelli heartwood from the Central African Republic (RCA) contained 6.4% by weight of extractives compared with 12.5% for those from Cameroon and four other provenances investigated. UV microspectrophotometric analysis of heartwood extractives was used to localise phenolic extractives within wood cell walls and to identify their distribution at tissue level. The S2 and S3 wall layers of vessels and fibres in the heartwood were discriminated from sapwood by their high concentration of non-lignin phenolic extractives. These extractives in the cell walls were also found to be variable. As UV absorption properties show, the vessel and fibre secondary walls of Cameroon heartwood had a considerably higher concentration of extractives in comparison with samples from the RCA. In sapwood, the UV absorption levels for the fibre S2 layer and the vessel S3 layer were independent of the extraction procedure, suggesting the phenolic extractives in this part of the trunk were in low concentrations. Furthermore it is suggested that polyphenols constitute part of the cell wall matrix. The non-extractable phenolic content was found to be independent of provenances as demonstrated by wood from Cameroon and the RCA. The natural durability of Sapelli heartwood against fungal decay appears to be dependent on the extractive composition and on their concentration in the fibre tissue.

A timber handrail made from the hardwood Keruing (Dipterocarpus spp.) and exposed in European Hazard Class 3 on railings at the Southbank, London was investigated to (i) determine the visual damage on the hardwood railing cappings quantitatively and to (ii) identify the causal organisms, and (iii) to characterise their decay patterns in the wood. The service life of this handrail of at least 25 years so far shows impressively that Keruing of this quality has exhibited a reasonable resistance to decay for the period. However, the selection of this timber for the construction may not have been ideal due to its large dimensional movement and the effect of this on the aesthetic appearance, in the form of extensive surface cracking, of several of the timber sections, including those rated as free from decay. The two principal decay organisms were identified as the white rot fungus Phellinus contiguus (Fr.) Pat. and the brown rot fungus Dacrymyces stillatus Nees:Fr. Decay patterns observed in the samples of the handrail and in invitro tests demonstrated the ability of P. contiguus and D. stillatus to cause a soft rot -like decay pattern in addition to their typical modes of action, i.e. white and brown rot. These results indicate that "classical" criteria in linking decay features to certain decay types and fungi can be much more complex than expected. Depending on the fungal species, a transition or switch mechanism between brown + soft rot and white + soft rot respectively is probable.

Summary Fresh sapwood blocks of Norway spruce (Picea abies) were exposed to 12‐ and 60‐day attack by Stereum sanguinolentum in pure culture and were examined with respect to structural, topochemical and colour alterations. Final stages of degradation by 5. sanguinolentum were studied on naturally decayed spruce wood after 1 year of fungal growth. The development of discoloration in the main anatomical directions of wood was assessed. Furthermore, microspectrophotometrical studies on the decomposition of cell wall polyphenols were performed. Initial signs of sap streak appeared already 8 days after fungal infection. Within the three‐dimensional decay pattern, mycelial aggregations associ‐ated with the ray tissue proved to be the major cause of discoloration. UV extinction measurements taken at 280 nm of different parts of cell wall transverse sections revealed a specific pattern of lignin distribution and its derivatives during fungal degradation.