IAWA Bulletin n.s., Vol. 11 (2), 1990: 195-202 ULTRASTRUCTURE OF TERMINALIA 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 Samoa, 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. (Combretaceae) 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.) Downloaded from Brill.com09/24/2021 04:15:49PM via free access 198 IAWA Bulletin n.s., Vol. 11 (2), 1990 3 __ 180nm For legends, see page 200. Downloaded from Brill.com09/24/2021 04:15:49PM via free access Donaldson & Singh - Ultrastructure of Tenninalia wood from an ancient canoe 199 ',- .... ~..... ' ...... I ••~:..., ., ~ ...... .: ,~J"'" ~ - .... ,. " • ..h', t I ,. 0 --O.81lm ~ y J.. l For legends, see page 200. Downloaded from Brill.com09/24/2021 04:15:49PM via free access 200 IAWA Bulletin n.s., Vol. 11 (2), 1990 .,, _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.