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IAWA Journal, Vol. 15 (3), 1994: 199-227 THE TIIIRD PACIFIC REGIONAL WOOD ANATOMY CONFERENCE 1994 Joint meeting of the IAWA Pacific Regional Committee and IUFRO S 5.01 (Wood Quality) organised by the Forest Research Institute, Rotorua, New Zealand, November 20-24,1994 Conveners: Dr. Brian G. Butterfieid, Mr. Lloyd Donaldson, and Dr. Adya Singh ABSTRACTS OF PAPERS AND POSTERS H. ABE, R. FUNADA, J. OHTANI, K. FUKAZA­ number of naturally and plantation grown wA, Department of Forest Science, Hokkaido trees of Light Red Meranti (Shorea leprosula University, Sapporo, 060, Japan. - The re­ and S. parvifolia) in radii of stern disks taken lationship between the expansion of celIs at various heights in the bole. and the orientation of depositing micro­ In both naturally and plantation grown fibriIs in the tracheids of Abies sachali­ trees variation in specific gravity is most sig­ nensis. - (Poster) nificant within trees, i. e., it increases from To clarify the relationship between the pith to bark. This variation can largely be ex­ change of orientation of the depositing cellu­ plained by an increase in fibre cell wall per­ lose microfibrils (MFs) and the expansion of centage, despite a decrease of total fibre area cells, we observed the arrangements of the percentage. MFs of radial cell walls in tracheids of Abies Longitudinal variation shows a more or sachalinensis Masters during the expansion less consistent pattern in the few trees stud­ of cells, by mainly field-emission scanning ied, with a minimal specific gravity at about electron microscopy (FE-SEM) and polaris­ 5 m in the bole and higher densities towards ing microscopy. the crown and the stern base. The radial diameter of tracheids increased The substantial tree-to-tree variation in all to three to four times that of cambial initial parameters studied of the plantation grown cells. The MFs on the innermost surface of material is within the range found in naturally primary walls of tracheids at early stages grown trees. Along stern radii at breast height were not weIl ordered and most of the MFs the wood of plantation grown trees seems to were oriented longitudinally. As each cell ex­ be slightly less variable than that ofthe 'wild' panded, the MFs in the process of deposition trees. The tree-to-tree variation found invites were still not weH ordered, but their orienta­ studies on the heritability of wood quality tion changed from longitudinal to transverse. parameters (specific gravity, fibre wall per­ When cell expansion ceased, the MFs were centage) so that these can be incorporated in weIl ordered and oriented transversely. breeding programmes of an important tropical Furthermore, we analysed the temporal hardwood, so far only exploited from now relationship between the completion of the strongly endangered virgin rain forests. expansion of cells and the beginning of the deposition of the secondary wall, using a M. BARISKA, University Stellenbosch, Repub­ computer image analysing method. lic of South Mrica. - Fracture mechanies and wood anatomy. PrETER BAAS, MONIQUE T.M. BOSMAN, Rijks­ Fracture mechanics is the study of crack herbarium/Hortus Botanicus, PO Box 9514, development and crack propagation in mate­ 2300 RA Leiden, The Netherlands. - Ra­ rials. For the past 100 years this science un­ dial and longitudinal variation in wood folded independently along many lines such properties of naturally and plantation as engineering and anatomy. In engineering, grown light red meranti (Slwrea, Dip­ three types of crack formation were derived terocarpaceae). for wood: Fracture mode I in which the Cell wall percentage, tissue proportions, structure is opened as in cross grain tension; and basic specific gravity were studied in a Fracture mode II in which wood is sheared, Downloaded from Brill.com10/09/2021 02:15:05PM via free access 200 IAWA Journal, Vol. 15 1994 for instance parallel to the grain; and fracture or glass fibre in fibreglass. The microfibril mode III in which wood is sheared perpen­ angle orientation in each of these layers is dicularly to the grain along a line. Theories, quite different. In the S3 layer the micro­ mostly of a mathematical nature, deal with fibrils lie at a large angle to the cell axis. This the stress/ strain situation at the crack tip that stiffens the cell wall against collapse, and is about to be formed. Anatomists found that hence assists the tree to pull water from the fracture showed characteristic morphology at roots to the foliage by water tension without each organisationallevel such as the macro­ cell collapse. In addition the S3 wall helps to molecular, the ultrastructural and the anatom­ protect the cell walls against crack propaga­ icallevels. Morphology of fractured surfaces tion in the tangential and radial directions. were studied to determine the influence of the The S2 layer is about 40 times thicker than cell structure, the tissue patterns, the moisture all other layers combined and carries the content, the temperature and other factors on weight of the tree. The most efficient way to the failure process. do this would be by the microfibrils lying In the present study small scale wood sam­ along the axis of the cells. This would en­ pIes were subjected to loading modes gener­ courage transwall cracking in the axial direc­ ating the three fracture types. The fracture tion. A relationship has been derived between process was observed in a scanning electron microfibril angle and transwall and interwall microscope. The specimens were selected so cracking. When a vertical force is applied to a that the influence of broad rays, pore rings double cell wall the two components twist in and other marked tissue features on the fail­ opposite directions, placing the middle lamel­ ure process could be investigated. Video la in shear. The amount of twisting increases recordings were made which revealed that with microfibril angle. The shear causes con­ failure is initiated at the ultrastructurallevel version of mechanical vibration into heat, - or below - and that the anatomical structurc i.e., it is responsible for preventing wind often overrides the effect of notches, brought damage. The twisting of the S2 wall under onto the specimen to initiate cracks. Regular load causes the cell diameter to increase. The structures such as pore rings and tracheid SI layer, with its microfibrils in the same rows often form the front lines of failure. direction as a reinforced plastic garden hose, Splits tend to frequently propagate in jumps acts as a sleeve to protect the cell against at both ultrastructural and anatomicallevels. bursting. Under cross grain compression cell walls The middle lamella consists of a three di­ often crack at the corners, buckle across the mensionally connected network of chain force direction and collapse into the neigh­ molecules that holds the cells together. It has bouring celliumina. This movement gener­ to be pliable and is also an extremely efficient ates a fold front whose angle is solely deter­ vibration absorber. Microfibrils are absent in mined by the size and the configuration of the the ML as they would obstruct these functions. cells. Anatomical structures and their paper Finally the orientation of microfibrils in models fail in comparable manners. tension wood and compression wood is dis­ An attempt is made to classify anatomical cussed. structures in relation to their failure patterns. BRIAN BUTTERFIELD*, ROBERT HANNA**, ROLF BOOKER, NZFRI Ltd, PB 3020, Roto­ *Department of Plant & Microbial Science, rua, New Zealand. - The functions of the University of Canterbury, PB Christchurch, microfibril orientations in the cell walls New Zealand; **Wood Products Engineer­ of trees. ing, College of Environmental Science and The secondary cell walls of trees consist Forestry, State University of New York, of three different layers that are reinforced Syracuse, NY 13210, USA. - The rela­ with cellulose microfibrils. These are very tionship between microfibril angle and strong in their axial direction and have the wood properties in low density radiata same function as reinforcing iron in concrete pine grown in Canterbury, New Zealand. Downloaded from Brill.com10/09/2021 02:15:05PM via free access Third Pacific Regional Wood Anatomy Conference, Rotorua 1994 - Abstracts 201 Sam pies of low density radiata pine from GEOFFREY DANIEL *, ADYA SINGH** , THOMAS sites on the Canterbury plains and foothills NILSSON*, *Department of Forest Products, were compressional and bending strength Swedish University of Agricultural Sciences, load tested in a micro stage, after which the Box 7008, S-750-07 Uppsala, Sweden; same sampies were examined in an X-ray **New Zealand Forest Research Institute diffractometer to determine the mean micro­ Ltd, Private Bag 3030, Rotorua, New Zea­ fibril angle by the Cave T-method. Sampie land. - Ultrastructural and immuno­ dimensions and percent cell wall area were cytochemical studies on the window and determined using computer enhanced image bordered pit membranes of Pinus sylves­ analysis. tris L. Microfibril angle and modulus of elasticity The physical and chemical structure of showed a elose correlation, with the micro­ window (half-bordcred) and bordered pit fibril angle decreasing sharply over the first membranes is of considerable importance 10 growth rings as the MOE increased. Den­ during both microbial colonisation and im­ sity and cell wall area showed the expected pregnation of wood preservatives into soft­ correlation though image analysis tends to woods. These structures not only represent show a higher percentage of wall material important natural barriers to microbial pene­ than should be present. The dimensions of tration and preservative diffusion but also the original sam pie were compared with provide a readily available source of non­ embedded and microtome cut blocks using lignified carbohydrate (i.e., pectin and cellu­ image analysis. lose). In the present work the fine structure of both window and bordered pit membranes N.J. CHAFFEY*, P.W. BARLOW** J.R.

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