IAWA Bulletin n.s., Vol. 11 (2), 1990: 195-202

ULTRASTRUCTURE OF WOOD FROM AN ANCIENr POLYNESIAN CANOE

by

L. A. Donaldson and A. P. Singh Ministry ofForestry, Forest Research Institute, Private Bag, Rotorua, New Zealand

Summary A sample of Terminalia wood recovered In this article we describe the structure of from an ancient Polynesian canoe thought to a piece of tropical hardwood buried by a tsu­ be approximately 1000 years old, was exam­ nami (a tidal wave caused by an earthquake ined by light and electron microscopy to de­ on the sea floor) over a thousand years ago. termine the extent and pattern of degradation. The wood was recovered from an archaeo­ A chemical analysis was also carried out. The logical site at Fa'ahia on the island of Hua­ secondary walls of fibres, vessels and paren­ hine in the Society Islands. The site, original­ chyma cells were extensively degraded but ly a village, was covered by ametre of sand the compound middle lamella remained rela­ as the result of inundation by a tsunami in tively intact. Vestures in intervascular pits about 850 AD. The deposition of sand block­ were preserved, presumably by virtue of ed a stream causing the water table to rise, their high lignin concentration. Plasmodes­ creating an environment in which wooden mata were also preserved by infiltration with artefacts became waterlogged. The wood extractives thought to be tannins. sample described in this report was a plank Key words: Terminalia, cell walls, vestured from a canoe. pits, plasmodesmata, extractives, bacterial degration. Materials and Methods Samples of wood originating from planks Introduction forming part of a canoe recovered from Fa'a­ The effects of long term exposure to the hia on the island of Huahine in the Society environment on wood properties have been Islands were examined. The wood sampIes, examined by various approaches ranging which were received in FAA solution, were from chemical analysis to strength measure­ dissected into small blocks of about 1 mm3, ments. Microscopic studies of wood subjec­ dehydrated in an acetone series and embed­ ed to long term exposure to the environment ded in Spurr's embedding medium (Spurr are relatively few (Crook er al. 1965; Sachs 1969). The material was sectioned for light 1965; Wayman er al. 1971; Borgin er al. microscopy at a thickness of 2 ~m on an 1975a, b; Parameswaran & Borgin 1980; LKB ultramicrotome using glass knives. Ul­ Buth & Bisht 1981; Tsoumis 1983). Trans­ trathin sections for transmission electron mi­ mission electron microscopy in particular has croscopy were obtained on the same micro­ had limited application (Sachs 1965; Borgin tome using a diamond knife. Sections were er al. 1975b). Observations from both micro­ stained with potassium permanganate or with scopic and chemical studies have recently uranyl acetate and lead citrate prior to obser­ been summarlsed (Fengel & Wegener 1984). vation in a Philips EM 300 transmission elec­ The loss of structural components of the wood tron microscope. has varied from slight loss of polysaccha­ Refractive index measurements were made rides and near normal appearance of the wood using interference microscopy following the (Wayman er al. 1971; Borgin er al. 1975a, b) technique described by Donaldson (1985a). to almost totalloss of polysaccharides (Sachs All measurements and observations were made 1965; Wayman er al. 1971). using a Zeiss Photomicroscope 11 equipped

Downloaded from Brill.com09/24/2021 04:15:49PM via free access 196 IAWA Bulletin n.s., Vol. 11 (2), 1990 for Jamin-Lebedeff interference. To provide Within the residual cell wall material bac­ a comparison with undegraded wood, sam­ teria were present in large numbers in some pIes of Terminalia richii A. Gray, native in areas. Some bacteria had denatured dense , were examined in the same way. cytoplasm but for the majority cytoplasm had Sampies of wood were also analysed to disappeared leaving only the membranes determine their Klason lignin content and car­ (Fig. 4). Fungal mycelium was also observed bohydrate content (Somogyi-Nelson) accord­ in the celliumen (Fig. 5). ing to standard procedures. As indicated earlier, in some cases the sec­ ondary wall appeared to be intact in cells oc­ Results and Discussion curring in isolation amongst those showing The canoe wood was soft and crumbled degradation. In addition, the secondary wall easily presenting problems in handling for associated with vestures in intervascular pits microscopical examination. Judging from the and on the lumen surface of the vessels (Van appearance of the wood an altered fine struc­ Vliet 1978), appeared to be weil preserved. A ture was predictable. One of us (DonaIdson) thin layer of dense material was seen closely was able to identify the wood as T erminalia applied to these structures which may have sp. () on the basis of its anat­ contributed to their preservation (Fig. 6). This omy. material had the appearance of extractives and Figures 1-6 illustrate structural aspects of the wood gave a positive ferric chloride test wall degradation. The appearance of the cells suggesting the presence of tannins which are varied from complete loss of the secondary known to act as preservatives (Rudman 1961; wall where only a few aggregates of granular Hart & Hillis 1974; Chaudhuri & Purkayas­ material remained, to a porous appearance of tha 1979). Vestures (synonym: warts) were the secondary wall. Cells with apparently in­ also preserved in 200-year-old Fagus sylva­ tact walls were seen only very rarely. All of tica wood (Sachs 1965: fig. 2). The preser­ the cell types examined showed similar de­ vation of middle lamella and vestures may gradation patterns. The compound middle la­ have been related to their high lignin con­ mella appeared relatively unaffected except centration (Donaldson 1985b, 1987; Mori er for a few cases where breakdown was evi­ al.1980; Ohtani er al. 1984; Scurfield & Silva dent (Fig. 2). Areas of the cell corner middle 1970). Compound middle lamella and S3 wall lamella showed evidence of fibrillar material areas are known to be more resistant to cavi­ as did some parts of the residual secondary tation (Nilsson & Singh 1984) and erosion wall suggesting the presence of polysaccha­ bacteria (Daniel & Nilsson 1986; Singh & rides (Fig. 3). The altered appearance of the Butcher 1985) than to tunnelling bacteria Terminalia wood is remarkably similar to that (Daniel er al. 1987; Singh et al. 1987). The described for Fagus sylvatica L. wood which S3 layer was also preserved in our material was obtained from a Viking ship exposed to (Fig. 4). Little is known about microbial 2000 years of natural degradation (Sachs action on vestures. Engels & Brice (1985) 1965). showed the warty layer covering the lignified

Table 1. Refractive index measurements on the cell walls of canoe wood and Terminalia richii.

Canoewood Terminalia richii Secondary wall Middle lamella Secondary wall Middle larnella 1.598 1.584 1.550 1.580 1.602 1.581 1.553 1.582 1.600 1.583 1.554 1.588

Downloaded from Brill.com09/24/2021 04:15:49PM via free access Donaldson & Singh - Ultrastructure ofTerminalia wood from an ancient canoe 197

Fig. 1. A low magnification view of canoe wood showing degraded fibres (F), axial parenchyma cells (AP) and ray parenchyma cells (RP). Although the secondary walls are heavily degraded, the middle lamella appears to be intact. (TEM.)

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3 __ 180nm

For legends, see page 200.

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For legends, see page 200.

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.,,

_310nm

Fig. 6. Intervascular pits containing vestures are shown in oblique section. Note the thin layer of extractives (arrow) lining the inner surface of these structures which may have contributed to their preservation. (TEM).

cell walls in barley straw to be resistant to canoe wood and Terminalia richU is shown in rumen microorganisms. Singh et al. (1987) Table 1. These values indicate almost com­ have recently reported that although tunnel­ plete loss of carbohydrates from the second­ ling bacteria can degrade all areas of Aistonia ary wall of the canoe wood cells where the scholaris (L.) R. Br. wood cell walls, inter­ refractive index is similar to that of lignin vascular pit vestures remained intact. (1.604, Donaldson 1985a). The refractive Chemical analysis of canoe wood indicated index of the middle lamella is comparable in a Klason lignin content of 83.7% and a car­ both specimens indicating little loss of mate­ bohydrate content of 8.6% indicating consid­ rial although chemical changes may have erable loss of carbohydrates. Some of this taken place. carbohydrate may be of bacterial or fungal Long term storage under conditions where origin. A comparison of refractive index for biological degradation is absent, appears to the secondary wall and middle lamella of do little damage to wood structure. Wood

~-+- Fig. 2. A pit field negatively contrasted by extractives (E) showing an intact pit membrane containing plasmodesmata (arrowheads) which have been infiltrated by the extractives. The primary wall and middle lamella show evidence of degradation adjacent to the pit (arrows). The secondary wall is represented by only a few granular rernnants. (TEM.) - Fig. 3. An area of cell corner showing a fibrillar texture which may indicate the presence of residual poly­ sacharides. In two of the three fibres shown, the S2 layer of the secondary wall has been com­ pletely degraded leaving only the SI layer and the compound middle lamella while in the third cell, a granular rernnant of the S2 layer remains. (TEM.) f- Fig. 4. Numerous bacterial rernnants (short arrows) were observed, both in cell lumens and within areas of degraded wall. This pattern of degradation is characteristic of erosion bacterial attack. (TEM.) - Fig. 5. Fungal hyphae (arrows) were only observed in the celliumen. Such hyphae rnay represent scavengers feeding on debris left by bacterial attack. (TEM.)

Downloaded from Brill.com09/24/2021 04:15:49PM via free access Donaldson & Singh - Ultrastructure ofTenninalia wood from an ancient canoe 201 materials kept under constant storage condi­ Referenoes tions for up to 4400 years, appeared normal Borgin, K. & K. Corbett. 1974. Holzwis­ macroscopically (Borgin & Corbett 1974; senschafdiche Forschung mit dem Raster Borgin et al. 1975b), although some loss of Elektronmikroskop. Leitz Mitt. Wiss. Tech­ wall material was found at the fine structural nik, Supp!. 1: 169-176. level (Borgin et al. 1975b). Certain regions Borgin, K., O. Faix & W. Schweers. 1975a. of wood cell walls developed cracks, the The effect of aging on lignins of wood. most susceptible region being the compound Wood Sei. Technol. 9: 207-211. middle lamella (Borgin et al. 1975b). Borgin, K., N. Parameswaran & W. Liese. Wayman et al. (1971) exarnined wood ma­ 1975b. The effect of aging on the ultra­ terials of 10 and 100 million years old and structure ofwood. Wood Sei. Techno!. 9: found good preservation of wood structure. 87-98. According to these workers, pits were weIl Buth, G.M. & R.S. Bisht. 1981. SEM preserved but intact pit membranes were not study of aneient remains from Kashmir. seen. The structure of the 100 million-year­ Curr. Sei. 50: 728. old sampIe was more affected than the 10 Chaudhuri, A.K. & R.P. Purkayastha. 1979. million-year-old sampIe. Oxidation, thermal The cause of differential resistance of Pte­ degradation and bacterial attack were consid­ rocarpus wood to some polypores. Holz­ ered to be the possible causes of degradation forschung 19: 153-156. (Wayman et al. 1971). Crook, F.M., P.F. Nelson & D.W. Sharp. 1965. An exarnination of ancient Victorian Conclusions woods. Holzforschung 19: 153-156. In the canoe wood which we examined it Daniel, G.F. & T. Nilsson. 1986. Ultra­ seems likely that biological decay in the form structural observations on wood-degrad­ of bacterial attack is responsible for the con­ ing erosion bacteria. Document Intern. dition of the wood and that physical effects Research Group/Wood Preservation, No related to the age of the wood played a minor 1283. role. From our chemie al analysis it appears Daniel, G.F., T. Nilsson & A.P. Singh. that there was litde or no loss of lignin al­ 1987. Degradation of lignocellulosics by though its rnicrobial transformation cannot be unique tunnel-forming bacteria. Can. J. ruled out. Elements of wood structure that Microbiol. 33: 943-948. were retained were either protected by infil­ Donaldson, L.A. 1985a. Critical assessment tration with extractives or contained a high of interference microscopy as a technique proportion oflignin. It is unclear whether bac­ for determining lignin distribution in terial attack occurred prior to burial or during wood cell walls. New Zeal. J. For. Sei. the duration of burial although the presence 15: 349-360. of bacteria with cytoplasmic contents indi­ Donaldson, L. A. 1985b. Within and between­ cates recent activity. Because of the extensive variation in lignin concentration in the decay present and the usually slow nature of tracheid cell wall of Pinus radiata. New bacterial attack, the decay must have taken Zeal. J. For. Sei. 15: 361-369. place over an extended period of time. Donaidson, L.A. 1987. S3 lignin concentra­ tion in radiata pine tracheids. Wood Sei. Acknowledgements Techno!. 21: 227-234. The authors gratefully acknowledge the as­ Engels, E.M. & R.E. Brice. 1985. A barrier sistance of Dr. Y. Sinoto, B.P. Bishop Mu­ covering lignified cell walls of barley straw seum, Hawaii, and Mr. R.R. Cater, Depart­ that restriets access by rumen micro­ ment of Internal Affairs, Wellington, New organisms. Curr. Microbio!. 12: 217-224. Zealand, for providing the wood sampies ex­ Fengel, D. & G. Wegener. 1984. Inhibition of amined and for background information on wood rotting fungi by stilbenes and other these sampies. They also thank Mrs. S. An­ polyphenols in Eucalyptus sideroxylon. derson for performing the chemical analyses. Phytopath. 64: 939-948.

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Hart, J.H. & W.E. Hillis. 1974. Inhibition Scurfield, G. & S.R. Silva. 1970. The ves­ of wood rotting fungi by stilbenes and tured pits of Eucalyptus regnans F. Muell.: other polyphenols in Eucalyptus sideroxy­ a study using scanning electron micro­ Ion. Phytopathology 64: 939-948. scopy. J. Linn. Soc. (Bot.) 63: 313-320. Mori, N., M. Fujita, H. Harada & H. Saiki. Singh, A.P. & J.A. Butcher. 1985. Degra­ 1980. An investigation of chemical com­ dation of CCA-treated Pinus radiata posts ponent of vestured pits using uItra-thin by erosion bacteria. J. Inst. Wood Sei. section. Rep. Summary 30th Meeting 10: 140-144. Japan Wood Res. Soc. 55. Singh, A.P., T. Nilsson & G.F. Daniel. Nilsson, T. & A.P. Singh. 1984. Cavitation 1987. Ultrastructure of the attaek of the bacteria. Document Intern. Res. Group / wood of two high lignin tropical speeies, Wood Preservation, No 1235. Aistonia seholaris and Homalium foeti­ Ohtani,J., B.A. Meylan & B.G. Butterfieid. dum, by tunnelling bacteria. J. Inst. W ood 1984. Vestures or warts - proposed ter­ Sci. 11: 26-42. minology. IAWA Bull. n.s. 5: 3-8. Spurr, A.R. 1969. A low-viscosity epoxy Parameswaran, N. & K. Borgin. 1980. Micro­ resin embedding medium for electron mi­ morphological and analytical study of an croseopy. J. Ultrastr. Res. 26: 31-43. ancient pine wood from Cyprus contain­ Tsoumis, G. 1983. SEM observations on ir­ ing metallic copper. Ho1zforschung 34: radiated old wood. IAW A BuH. n. s. 4: 185-190. 41-45. Rudman, P. 1961. The causes of natural dur­ Vliet, G.J.C.M. van. 1978. Vestured pits of ability in timber. VIII. The causes of de­ Combretaceae and allied families. Acta cay resistance in teak, Tectona grandis L. Bot. Neerl. 27: 273-285. Holzforschung 15: 151-156. Wayman, M., M.R. Azhar & Z. Koran. Sachs, LB. 1965. Evidence of lignin in the 1971. Morphology and ehemistry of two Tertiary wall of certain wood cells. In: ancient woods. Wood and Fiber 3: 153- Cellular ultrastructure of woody 165. (ed. W.A. Cöte): 335-339. Syracuse Univ. Press, Syracuse, N. Y.

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