IAWA Journal, Vol. 14 (3), 1993: 315-323

AGGREGATE RAYS OF THUJOPSIS DOLABRATA VAK. HONDAI (CUPR.m3SACEAE)

by

Toyonobu Sugawa and Tomoyuki Fujü Wood Anatomy Laboratory, Forestry and Forest Products Research Institute, Tsukuba Norin, P.O. Box 16, Ibaraki 305, Japan

Summary Aggregate rays of Thujopsis dolabrata virens (D. Don) End!. (Bailey & FauII 1934), Sieb. et Zucc. var. hondai are described in and occasional occurrence of biseriate rays for detail. These rays occur sporadically in Thu­ Fitzroya , Thujopsis and Libocedrus (Peirce jopsis stemwood and are composed mainly 1937), and for Sequoia and Metasequoia of muItiseriate rays, with thin-walled ray (Greguss 1955). Also they were reported in parenchyma cells, and ray tracheids of irreg­ association with inden ted growth rings in ular shape and widely varying size. Ray tra­ Cryptomeria japonica D. Don (Imamura & cheids have Iignified three-Iayered secondary Okazaki 1990). To the authors' knowledge, walls, but their S3 layer is very thin, as in the aggregate rays have never been reported for secondary walls ofaxial tracheids. any conifer species. Key words: Thujopsis, aggregate ray, multi­ In this paper, we describe in detail the seriate ray, ray tracheid. anatomical features of the aggregate rays which occur sporadically in the wood of Introduction Thujopsis dolabrata var. hondai. The timber of Thujopsis dolabrata var. hondai is one of the important commercial Materials Wld Methods softwoods in Japan and is used as ground sill One board, with aggregate rays on the sur­ timbers in wooden houses because of its high face as dark coloured blots, obtained from a durability. Timber of old trees is also used commercial market. Two more disk sampies for furniture because of its beautiful appear­ (about 5 cm thick) were obtained from the ance. It has regular, narrow growth rings, butt end of butt logs of 100-120-year-old very smooth surfaces, and a uniform cream­ trees of Thujopsis dolabrata Sieb. et Zucc. yellow colour. var. hondai (Cupressaceae) grown in Noto Obvious marks ('blots') were found on peninsula, Ishikawa prefecture, northern cen­ the relatively uniform surfaces of a commer­ tral Japan. cial timber used in a book shelf and these Aggregate rays were easily observed with blots were subsequently deterrnined to be a hand lens on planed surfaces. In cross sec­ aggregate rays. Interviews in the market of tions they appear as bright coloured streaks Ishikawa prefecture, an important plantation (Fig. 1). Blocks containing aggregate rays forest district of Thujopsis dolabrata var. hon­ were dissected from sampies, sectioned with dai, revealed that the sPQradic occurrence of a sliding rnicrotome. Some sections were these blots in poles and beams in wooden stained with gentian-violet and safranin, oth­ houses is well-known and they are not con­ ers were used for scanning electron rnicro­ sidered to be a serious defect in the district. scopy (SEM: Jeol JXA-840AP) after ion­ Xylem rays in conifers are mostly uniseri­ sputter-coating with Pt-Pd. ate, except for fusiform rays containing radial Some blocks were delignified with acidic resin canals. Although the sporadic occunence NaCI02 and solvent-exchange dried. Xylem of partly biseriate rays is common, frequent elements in the original arrangement were occurrence of biseriate 10 multiseriate rays stripped from the delignified blocks using has been reported only for Sequoia semper- sticky tape and observed with SEM.

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Some other small blocks containing aggre­ Pt-Pd, and then viewed in a transmission gate ray were embedded in epoxy resin and electron microscope (Jeol JEM 2000EX, at tangential and radial-oblique sections of dif­ 80 kV). ferent thickness were obtained with a rotary microtome and an ultramicrotome (LKB ul­ Results and Discussion trotome IV). Part of the sections were used for ultraviolet microscopy (UV: at 280 nm Macroscopic features with wave1ength width of 10 nm). Some Dark-coloured dots on the surface of the others were stained with safranin and gen­ board were aggregates of multiseriate rays tian-violet, and investigated under anormal (Fig. 2). The width and the height of aggre­ and polarised light microscope. Using a pol­ gate rays reached 3.0 mm and 15 mm, re­ arised light microscope, microfibrillar angles spectively, in tangential section. Aggregate were measured on thin radial and tangential rays showed up as bright radiallines in cross sections (0.1-0.2 11m thick) obtained from section and were distinct in wood 30 or more epoxy-embedded sampies. Ultrathin sections rings distant from the pith (Fig. 1). They are (0.1 11m thick) were used for the investiga­ not common, and only four and eleven aggre­ tion of microfibrillar orientation in cell wall gate rays were seen in the two entire disks, layers. They were treated with acidic NaCl02 respectively. to remove lignin after the removal of epoxy resin with NaOCH3 solution, shadowed with (text continued on page 322)

Legends of Figures 1-15:

Fig. 1. Aggregate rays show up as bright coloured radiallines (arrows) on the transverse sur­ face of the disko - Fig. 2. Dark coloured blots on the radial surface of the board (arrows). - Fig. 3. Growth ring indented in the area crossing the aggregate rays (arrows). - Figs. 4 & 5. Aggregate ray composed of multiseriate and uniseriate rays. - 4: Whole tangential view of ag­ gregate ray. - 5: Apart of Fig. 4. Aggregate ray is composed of multiseriate and uniseriate rays.

Figs. 6 & 7. Aggregate ray in the tangential section (SEM). The square in Fig. 6 is enlarged in Fig. 7. -7: Multiseriate ray is composed ofray tracheids (RT) and ray parenchyma cells (RP). Ray tracheids have bordered pit pairs (arrows) between each other and also to axial tracheids (T). - Fig. 8. Short and tall ray tracheids (RT) and a ray parenchyma cell (RP) in a marginal row. T = axial tracheid.

Figs. 9 & 10. SEM micrographs of a maceration. - 9: Multiseriate ray in radial split surface. Ray tracheids (RT) and ray parenchyma cells (RP) composing multiseriate ray. The square in Fig. 9a is enlarged in 9b. - 10: Ray tracheids in some rows are upright and have slender tips.

Fig. 11. Ray cell walls in normal (a) and polarised light (b). Ray tracheids have thick secondary walls, which are bright in polarised light. Note differences in wall thickness. Ray parenchyma cells have thin cell walls, which are stained with safranin and gentian violet, and are dark in polarised light. - Fig. 12. UV micrograph ofray cell walls. Ray tracheids (RT) have lignified secondary walls. Ray parenchyma cells (RP) have thin well-lignified walls. Arrows indicated bordered and half-bordered pit pairs.

Figs. 13-15. Ultrathin sections treated with acidic NaCl02 after the removal of embedding resin. - 13: Ray tracheids have secondary walls of three-layered structure. - 14: Secondary wall ofaxial tracheid shows typical three-layered structure, but S3 layer is very thin. - 15: Ray pa­ renchyma has secondary walls of crossed-polylamellate structure.

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The multiseriate rays in indented parts of dai, Kobayashi (1957) reported the rare oc­ growth rings of Cryptomeria japonica are currence of ray tracheids. In our samples ray 3-4-seriate in the maximum and the cells are tracheids were mostly restricted to aggregate mostly large and irregular in shape (Imamura rays and were sporadic in normal wood rays. & Okazaki 1990). The association of multi­ In macerations for SEM observation seriate rays with inden ted growth rings was (Figs. 9 & 10), ray tracheids kept their shape observed also in Thujopsis dolabrata var. and showed bordered pits with tori and mar­ hondai, but the frequency was much more gos of radial strings of microfibrils (Fig. 9). sporadic and they usually occurred within ag­ Ray parenchyma cells collapsed or shrank gregate rays. during solvent exchange drying because of their thin primary walls (Fig. 9). The shape Anatomy of ray tracheids was variable, they occasion­ Aggregate rays were composed mainly of ally showed slender tips at both ends sug­ multiseriate rays of 2 to 15 cells wide and some gesting intrusive growth (Fig. 10). uniseriates (Figs. 3-6). Aggregate rays were compose~ of more or less narrower rays in Cell wall structure the younger wood, and wider multiseriate Ray tracheids had secondary walls ofvar­ rays in older mature wood. Individual multi­ iable thicknesses (Fig. 11a). The relationship seriate and uniseriate rays comprised usually between the wall thickness and the diameter both of ray tracheids and ray parenchyma in tangential section was not obvious. Sec­ cells. Rays composed only of ray parenchy­ ondary walls were birefringent indicating a ma cells were uniseriate, but were very rare layered structure without any relation to the in aggregate complexes. Ray tracheids were thickness variation (Fig. llb) and were ligni­ only sporadically observed in the uniseriate fied (Fig. 12). Three layers were obvious in rays outside of aggregate rays. Multiseriate ultrathin sections, but the S 3 layer was very rays in redwood (Sequoia sempervirens) may thin (Fig. 13). The microfibrillar angles (rel­ be up to five cells wide but their cell structure ative to the radial axis) of the SI. S2 and S3 is similar to narrow rays (Gray 1973), and layers were 60-70, 40-60 and 70-80 de­ ray tracheids are extremely rare (Bailey & grees, respectively. The layered wall struc­ Faull 1934). Although extremely wide rays ture resembles that ofaxial tracheids, but dif­ were found in Chamaecyparis species (Ban­ fers in the microfibrillar angle of S2layer nan 1950), their occurrence was erratic and (Figs. 13 & 14). For axial tracheids, the mi­ restricted to young (juvenile) wood. crofibrillar angles to the longitudinal axis of There was obvious variation in the size of SI, S2 and S3 layers were 60-70, 25-30 ray tracheids in tangential sections. Some tra­ and 60-80 degrees, respectively. Secondary cheids were two to three times wider than ray walls of ray tracheids were lignified, but the parenchyma cells of normal uniseriate rays optical density varied to some extent at 280 (25-50 ~m wide and 45-85 ~m high). They nm regardless of the wall thickness and the have bordered pits in smooth lateral walls diameter (Fig. 12). connecting to other ray tracheids or axial tra­ Ray parenchyma cells in aggregate and cheids (Figs. 7 & 8). Marginal ray tracheids normal rays had thin walls, and together with were short and tall (Fig. 8), resembling square the compound middle lamellae stained with and upright ray cells in hardwoods, and un­ safranin and gentian violet (Fig. l1a). The like the normal ray tracheids in Pinaceae. As cell walls did not show any obvious birefrin­ reviewed by Peirce (1937), although ray tra­ gence in tangential section indicating their cheids generally occur in almost all genera of primary wall nature (Fig. 11 b). The wall struc­ Cupressaceae, they are common only in the ture of ray parenchyma cells in Thujopsis wood of Chamaecyparis nootkatensis. Phil­ dolabrata var. hondai is classified as the Cryp­ lips (1948) described that Chamaecyparis tomeria type, characterised by a thick and nootkatensis has ray tracheids which are well-lignified primary wall (Fujikawa & Ish­ quite large and frequently comprise the entire ida 1975). Chafe (1974a, 1974b) described wood ray. For Thujopsis dolabrata var. hon- the crossed polylamellate structure of the ray

Downloaded from Brill.com10/03/2021 08:50:38PM via free access Sugawa & Fujii - Aggregate rays of Thujopsis dolabrata var. hondai 323 parenchyma cell walls of Cryptomeria and Chafe, S.C. 1974a. Cell wall structure in the Chamecyparis nootkatensis. The cell wall xylem parenchyma of Cryptomeria. Proto­ structure of ray parenchyma cells in the ag­ plasma 81: 63-76. gregate rays (Fig. 15), which did not differ Chafe, S.c. 1974b. Cell wall thickenings in from that of the ordinary ray parenchyma the ray parenchyma of yellow cypress. cells, agrees well with the classification of IAWA Bull. 1974/2: 3-8. Fujikawa and Ishida (1975). The extent of Fujikawa, K. & S. Ishida. 1975. Ultrastruc­ lignification of cell walls is shown in an UV ture of ray parenchyma cell wall of soft­ micrograph (Fig. 12). Cell walls of ray pa­ wood. Mokuzai Gakkaishi 21: 445-456. renchyma cells were much more lignified Gray, R.L. 1973. Multiseriate rays in red­ than the secondary walls of ray tracheids. wood (Sequoia sempervirens (D. Don) Endl.) IAWA Bull. 1973/1: 7. Greguss, P. 1955. Identification of living Acknowledgements gymnosperms on the basis of xylotomy. Thanks are due to Tatsuo Nakano for pro­ Akademiai Kiado, Budapest. viding sampies and to Pieter Baas, Sadaaki Imamura, Y. & A Okazaki. 1990. Structural Ohta, E.A Wheeler, and an anonymous ref­ aspects on xylem formation in excrescence­ eree for their helpful advice and careful read­ featured varieties of sugi (Cryptomeria ja­ ing of the manuscript. ponica). Wood Research Review 26: 201- 211. References Kobayashi, Y. 1957. A card sorting system Bailey, I.W. & AN. Faull. 1934. The cam­ for the identification of softwood in Japan. bium and its derivative tissues. IX. Struc­ Bull. Gov. For. Exp. St. 98: 1-84. tural variability in the redwood, Sequoia Peirce, A S. 1937. Systematic anatomy of sempervirens, and its significance in the the woods of the Cupressaceae. Tropical identification of fossil woods. J. Arnold Woods 49: 5-21. ArOOr. 15: 233-254. Phillips, E.W.J. 1948. Identification of soft­ Bannan, M.W. 1950. Abnormal xylem rays woods by their microseopie structure. For. in Chamaecyparis. Amer. J. Bot. 37: 232- Prod. Res. Bull. NO.22. Her Majesty's 237. Stationery Office, London.

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