人工兴安落叶松次生木质部的解剖学研究

运用木材解剖图像分析系统和显微照相的方法对人工兴安落叶松次生木质部的解剖结构进行研究,结果表明:落叶松具正常树脂道和受伤树脂道两种类型,前者常见于晚材。落叶松生长轮内的早晚材在干和枝内急变,在根内缓变。早材管胞呈六边形至多边形,胞壁常见单列具缘纹孔,偶见对列具缘纹孔;晚材管胞多呈矩形,胞壁鲜见具缘纹孔,通常为单列具缘纹孔。落叶松木射线同时具有单列木射线和纺锤形木射线两种类型,纺锤形木射线中仅含一枚纵行树脂道。纵行管胞与木射线交叉形成的纹孔场为云杉型。从根到干再到枝,管胞逐渐细化,管胞长度逐渐减小,木射线分布由密到疏。     

Cavitation in dehydrating xylem of Picea abies: energy properties of ultrasonic emissions reflect tracheid dimensions

Ultrasonic emission (UE) testing is used to analyse the vulnerability of xylem to embolism, but the number of UEs often does not sufficiently reflect effects on hydraulic conductivity. We monitored the absolute energy of UE signals in dehydrating xylem samples hypothesizing that (i) conduit diameter is correlated with UE energy and (ii) monitoring of UE energy may enhance the utility of this technique for analysis of xylem vulnerability. Split xylem samples were prepared from trunk wood of Picea abies, and four categories of samples, derived from mature (I: earlywood, II: 30-50% latewood, III: >50% latewood) or juvenile wood (IV: earlywood) were used. Ultrasonic emissions during dehydration were registered and anatomical parameters (tracheid lumen area, number per area) were analysed from cross-sections. Attenuation of UE energy was measured on a dehydrating wood beam by repeated lead breaks. Vulnerability to drought-induced embolism was analysed on dehydrating branches by hydraulic, UE number or UE energy measurements. In split samples, the cumulative number of UEs increased linearly with the number of tracheids per cross-section, and UE energy was positively correlated with the mean lumen area. Ultrasonic emission energies of earlywood samples (I and IV), which showed normally distributed tracheid lumen areas, increased during dehydration, whereas samples with latewood (II and III) exhibited a right-skewed distribution of lumina and UE energies. Ultrasonic emission energy was hardly influenced by moisture content until ～40% moisture loss, and decreased exponentially thereafter. Dehydrating branches showed a 50% loss of conductivity at -3.6 MPa in hydraulic measurements and at -3.9 and -3.5 MPa in UE analysis based on cumulative number or energy of signals, respectively. Ultrasonic emission energy emitted by cavitating conduits is determined by the xylem water potential and by the size of element. Energy patterns during dehydration are thus influenced by the vulnerability to cavitation, conduit size distribution as well as attenuation properties. Measurements of UE energy may be used as an alternative to the number of UEs in vulnerability analysis.     

Simulation of effects of wood microstructure on water transport

A tracheid-level model was used to quantify the effects of differences in wood microstructure between coastal and interior Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii and var. glauca) wood on larger scale properties like hydraulic conductivity. The model showed that tracheid length, the ease of flow through a bordered pit and effective tracheid diameter can all limit maximum hydraulic conductivity. Among the model parameters tested, increasing bordered pit conductivity and tracheid length resulted in the greatest increase in maximum conductivity in both the inland and coastal ecotypes. A sensitivity analysis of the uncertainty between parameters governing flow through the bordered pit and air-seeding potential showed that, although decreased pit flow resistance increased maximum hydraulic conductivity, increased cavitation led to lower conductivity over time. The benefits of increasing the number of bordered pits depended on the intensity of the meteorological driving function: in drier environmental conditions, wood with fewer pits was more conductive over time than wood with more pits. Switching the bordered pit characteristics between coastal and interior wood indicated that the conductivity time course of coastal and interior wood was primarily governed by differences in the number of bordered pits and not differences in tracheid dimensions. The rate at which tracheids refilled had little effect on the conductivity time course of either coastal or interior wood during the first two summers when the wood was highly saturated, but had a marked influence in subsequent years once the cavitation profile stabilized. Our work highlights the need for more empirical work on bordered pits to determine whether variation in their number and properties is related to changing environmental conditions. In addition, a detailed simulation model of a bordered pit is needed to understand how variation in pit properties affects the relationship between ease of flow through a bordered pit and its potential for facilitating air-seeding.     

Microfibril angle non-uniformities within normal and compression wood tracheids

The pattern and extent of variation of microfibril angle (MFA) in normal and compression tracheids of softwood were investigated by using confocal laser scanning microscopy technique. All measurements support the idea that the orientation of microfibrils in single wood tracheids is not uniform. MFA of the radial wall of earlywood tracheids was highly non-uniform and had an approximately circular form of arrangement around the bordered pits (inside the border). Between the bordered pits the measured MFAs were less than the other parts of the tracheid. In the latewood tracheids MFA was less variable. The average orientation of simple pits in the crossfield region was consistent with the mean MFA of the tracheids; however some of the measurements showed a highly variable arrangement in the areas between the simple pits. In many cases the local measured MFAs of compression wood tracheids agreed with the orientation of natural helical cavities of compression wood. Comparing the measured results in different growth rings showed that MFAs in juvenile wood are generally larger than in perfect wood.     

Hydraulic and anatomical properties of light bands in Norway spruce compression wood

Compression wood (CW), which is formed on the underside of conifer branches, exhibits a lower specific hydraulic conductivity (k(s)) compared with normal wood. However, the first-formed tracheids of an annual ring on the underside of a conifer branch often share several properties with normal tracheids, e.g., thin cell walls and angular cross sections. These first-formed tracheids appear bright when observed by the naked eye and are therefore called light bands (LB). In this study, hydraulic and related anatomical properties of LBs were characterized and compared with typical CW and opposite wood (OW). Measurements were made on branches of Norway spruce (Picea abies (L.) Karst.). Specific hydraulic conductivity was measured with fine cannulas connected to microlitre syringes. Micro- and ultrastructural analysis were performed on transverse and radial longitudinal sections by light and scanning electron microscopy. Xylem areas containing both typical CW and LBs had a k(s) 51.5% that of OW (7.95 +/- 0.97 m(2) s(-1) MPa(-1) x 10(-4)), whereas k(s) of pure CW was only 26.7% that of OW. The k(s) of LBs (6.38 +/- 0.97 m(2) s(-1) MPa(-1) x 10(-4); 80.3% of OW) was estimated from these k(s) values because the cannulas were too wide to measure the k(s) of LBs directly. Mean lumen area of first-formed tracheids on the underside of branches was 65.7% that of first-formed tracheids in OW and about three times that of CW. Light-band tracheids exhibited a bordered pit frequency of 42.7 +/- 1.3 pits mm(-1), which was three times that in CW and 1.6 times that in OW. Bordered pit apertures in LB tracheids (9.15 +/- 0.60 microm(2)) were 1.7 times wider than those in CW and similar in aperture to those in OW. The high k(s) of LBs was correlated with their wide tracheid lumina, high pit frequency and wide pit apertures. We therefore suggest that LBs have a primarily hydraulic function within the mechanically optimized CW region. This might be important for supplying water to living tissues on the underside of branches, as well as to other distal areas along water transport pathways following the spiral grain of wood.     

Tangential pitting in black spruce tracheids

Tangential pit features were studied in a 55-year old black spruce (Picea mariana (Mill) B.S.P.) tree by means of light and electron microscopy.It was found that tangential pitting is lacking from the greatest part of the growth ring, except for the last four tangential rows of latewood tracheids and the first row of early wood tracheids. The average number of pits per tangential wall of a 3.55-mm-long tracheid is 234, 144, 28, 4 and zero, respectively, in the last 5 tangential rows of latewood tracheids, starting at the growth-ring boundary.On the average, tangential pits measure 5.4 m in diameter, possess oval to elliptical apertures, and are randomly distributed uniformly over the tangential tracheid wall. All tangential intertracheid pits are bordered and in that respect are similar to those in the radial walls. Although most of the pits contain membranes with tori, some at the growth-ring boundary lack tori and exhibit randomly oriented microfibrillar structure.     

Effects of steam explosion on wood appearance and structure of sub-alpine fir

The technology of steam explosion was applied to pre-treat sub-alpine fir (Abies lasiocarpa (Hook.) Nutt.) lumber and to improve its drying characteristics. Effects of steam explosion on the appearance and structure of the lumber are discussed in this paper. The structure of the wood was examined using light microscope (LM) and scanning electron microscope (SEM). The following results were obtained. With increasing temperature, pressure, and explosion cycles the color of the lumber darkened gradually. No significant structural difference between treated and untreated samples was observed using LM when the treatments were carried out at temperatures below 130°C with ten explosion cycles (group A or B). Some fractures were observed in bordered pit pairs between tracheids after 20 explosion cycles at 130°C (group C). More fractures occurred in bordered pit pairs between earlywood tracheids at a temperature of 160°C (group D). More or less fractures in pits between ray parenchyma cells and earlywood tracheids were observed using SEM in all four cases of treatments. Although no change in bordered pits in the tracheid walls between group A and the control group was discovered, groups B, C, and D showed different extents of ruptures in bordered pits, which may lead to break aspirated pits and improve permeability. In these groups, wrinkles and separations in the inner tracheid walls and detachments in middle lamella also occurred and became more serious as temperature or cycles of the treatment increased.     

Ultrastructure of pits inPinus banksiana lamb

Summary The cross-sectional view of pitting between various cell types inPinus banksiana Lamb. was studied at the ultrastructural level. Cell types inPinus banksiana include longitudinal tracheids, ray tracheids, ray parenchyma cells, buffer cells and epithelial cells. Two common characteristic features of bordered pit-pairs between longitudinal tracheids are an initial pit border and a thickened torus at the center of the pit membrane. The shape and size of the pit border and torus of bordered pit-pairs between two compression wood cells, and between the last-formed latewood longitudinal tracheid and first-formed earlywood longitudinal tracheid were different from those in the earlywood and latewood longitudinal tracheids. The pit border on the ray tracheid side varied in size and shape due to wall dentation. No initial pit border was found on the pit border of the ray tracheid side. The shape of bordered pit-pairs between two ray tracheids varied considerably due to irregularity of the dentate cell wall. The size of bordered pit-pairs in longitudinal tracheids was between 16 m to 20 m, which was twice the diameter of bordered pit-pairs in ray tracheids. Bordered pitpairs at the end wall of two ray tracheids appeared to be the smallest at 5 m, Pit aspiration occurred in the bordered pit-pairs with or without a torus. In the heartwood zone, some half-borders pit-pairs between tracheary and ray parenchyma cells showed an additional secondary wall on the ray parenchyma cell side. Plasmodesmata were found in the half-bordered pit-pairs as well in the simple pit-pairs. Blind pits were observed between a ray tracheid and a longitudinal tracheid. Bordered pit-pairs between two buffer cells were also observed. The possible functions of buffer cells were discussed.Use of transmission electron microscope provided by the Science Instrumentation Lab, Lakehead University and the technical assistance provided by Mr. A. MacKenzie, Director of Science Instrumentation Lab are gratefully appreciated     

Morphological changes in sugi (Cryptomeria japonica) wood after treatment with the ionic liquid, 1-ethyl-3-methylimidazolium chloride

We investigated morphological changes in wood tissues of sugi (Cryptomeria japonica) resulting from treatment with the ionic liquid 1-ethyl-3-methylimidazolium chloride ([C2mim][Cl]), which dissolves cellulose. Treatment with [C2mim][Cl] caused dissociation and distortion of tracheids in latewood, but not in earlywood. This difference was due to the difference in swelling behavior of the cell wall between earlywood and latewood. Many pit membranes in bordered pits were broken by treatment with [C2mim][Cl]. In addition, some chemical changes in wood components, such as cellulose and lignin, occurred before significant disruption or destruction of the cell wall. Our results show that the reaction of wood liquefaction by [C2mim][Cl] treatment is not homogeneous, both from chemical and morphological viewpoints.     

Control of tracheid cross-sectional dimensions in Norway spruce and Scots pine wood raw material

Abstract

Wood properties, including tracheid cross-sectional dimensions, show a large degree of variation. To improve the properties of products made from wood, different methods to control variation have been developed. This study aims to determine the theoretical efficiency of three control strategies: the fractionation of pulped tracheids into earlywood and latewood, the separation of juvenile and mature wood, and sorting of logs according to tree size. The efficiency of each method was studied by first constructing virtual trees from measured tracheid cross-sectional dimensions, then simulating the efficiency of above-mentioned methods. The tracheid dimension data include Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.). The simulations show that separation into earlywood and latewood classes has the highest theoretical efficiency and yields the lowest variances in raw material. Classification into juvenile and mature wood groups is the second most efficient method, and the sorting of logs according to the size class of the tree is the least efficient method. It was also concluded that the variation in cell-wall thickness and radial diameter mainly originates from differences between earlywood and latewood, whereas the variation in tangential diameter mainly originates from differences between mature and juvenile wood.     

Xylem cavitation and loss of hydraulic conductance in western hemlock following planting

Following planting, western hemlock (Tsuga heterophylla (Raf.) Sarg.) seedlings experience water stress and declining xylem pressure potential (Psi(x)). Low Psi(x) can result in xylem cavitation and embolism formation, causing a decline in hydraulic conductance. This study focused on the relationship between Psi(x), xylem cavitation and transpiration (E) of newly planted seedlings. Leaf specific hydraulic conductance (k(AB)) declined from 0.56 to 0.09 mmol m(-2) s(-1) MPa(-1) over a 9-day period. Stomatal conductance (g(s)) declined from 143.5 to 39.15 mmol m(-2) s(-1) over the same period without an associated change in environmental conditions. A vulnerability profile indicated a 30% loss in hydraulic conductivity when seedlings experienced a Psi(x) between -2.5 and -3.0 MPa. A Psi(x) of -4.0 MPa led to a complete loss of conductivity. We conclude that following planting, western hemlock seedlings often experience Psi(x) values that are low enough to cause xylem cavitation and a decline in k(AB).     

Tradeoffs between hydraulic and mechanical stress responses of mature Norway spruce trunk wood

We tested the effects of growth characteristics and basic density on hydraulic and mechanical properties of mature Norway spruce (Picea abies (L.) Karst.) wood from six 24-year-old clones, grown on two sites in southern Sweden differing in water availability. Hydraulic parameters assessed were specific hydraulic conductivity at full saturation (ks100) and vulnerability to cavitation (Psi50), mechanical parameters included bending strength (sigma b), modulus of elasticity (MOE), compression strength (sigma a) and Young's modulus (E). Basic density, diameter at breast height, tree height, and hydraulic and mechanical parameters varied considerably among clones. Clonal means of hydraulic and mechanical properties were strongly related to basic density and to growth parameters across sites, especially to diameter at breast height. Compared with stem wood of slower growing clones, stem wood of rapidly growing clones had significantly lower basic density, lower sigma b, MOE, sigma a and E, was more vulnerable to cavitation, but had higher ks100. Basic density was negatively correlated to Psi50 and ks100. We therefore found a tradeoff between Psi50 and ks100. Clones with high basic density had significantly lower hydraulic vulnerability, but also lower hydraulic conductivity at full saturation and thus less rapid growth than clones with low basic density. This tradeoff involved a negative relationship between Psi50 and sigma b as well as MOE, and between ks100 and sigma b, MOE and sigma a. Basic density and Psi50 showed no site-specific differences, but tree height, diameter at breast height, ks100 and mechanical strength and stiffness were significantly lower at the drier site. Basic density had no influence on the site-dependent differences in hydraulic and mechanical properties, but was strongly negatively related to diameter at breast height. Selecting for growth may thus lead not only to a reduction in mechanical strength and stiffness but also to a reduction in hydraulic safety.     

日本落叶松无性系木材性质的遗传变异

对10个10年生日本落叶松无性系的木材基本密度、管胞参数进行了测定.结果表明:木材基本密度,早、晚材管胞宽度和早材长宽比无性系间差异显著;木材基本密度,早、晚材管胞长度,早晚材管胞宽度和早晚材长宽比径向变异模式相似,即从髓心向外以曲线形式不断增加,有时亦有起伏;早材从髓心向外以近似直线的形式缓慢增加,晚材从髓心向外以曲线形式增加,初期增加幅度较大,到一定年龄后趋于水平变化并略有波动;材质性状与树木年轮间的关系以对数方程、幂函数方程、指数方程拟合效果较好;除了晚材壁腔比和早材壁厚外,其它木材性质的重复力均在0.5以上,受中度或中度以上的遗传制约,按照20%的选择率,长宽比和晚材管胞长能获得较高的遗传增益.     

Studies on opposite wood in conifers part II: Histology and ultrastructure

Summary A study has been made of the histology and ultrastructure of opposite wood in Larix laricina, Picea rubens, and Pinus resinosa. The width of the growth rings varied considerably, in one case from 0.1–1.0 mm, with the wide rings containing a much higher proportion of latewood than the narrow ones. The earlywood tracheids were square in outline and more regularly arranged than in normal wood. In the latewood they were sometimes irregular and distorted. The S₃ layer in the tracheids was 0.2 m thick in the earlywood and 0.4–0.8 m in the latewood, as compared to a thickness in normal wood of 0.1–0.2 m in both zones. The S₃ was often buckled in the latewood and was terminated towards the lumen by a spiral thickening. The cell wall structure of the tracheid pit border was described. Normal coniferous wood might be regarded as an intermediate between opposite wood and compression wood.This paper is dedicated to Dean Edwin C. Jahn in honor of his 70th birthday.     

Elevated temperature and CO(2) concentration effects on xylem anatomy of Scots pine

We studied the effects of elevated temperature and carbon dioxide concentration ([CO(2)]) alone and together on wood anatomy of 20-year-old Scots pine (Pinus sylvestris L.) trees. The study was conducted in 16 closed chambers, providing a factorial combination of two temperature regimes and two CO(2) concentrations (ambient and elevated), with four trees in each treatment. The climate scenario included a doubling of [CO(2)] and a corresponding increase of 2-6 degrees C in temperature at the site depending on the season. Anatomical characteristics analyzed were annual earlywood, latewood and ring widths, intra-ring wood densities (earlywood, latewood and mean wood density), tracheid width, length, wall thickness, lumen diameter, wall thickness:lumen diameter ratio and mass per unit length (coarseness), and numbers of rays, resin canals and tracheids per xylem cross-sectional area. Elevated [CO(2)] increased ring width in four of six treatment years; earlywood width increased in the first two years and latewood width in the third year. Tracheid walls in both the earlywood and latewood tended to become thicker over the 6-year treatment period when temperature or [CO(2)] was elevated alone, whereas in the combined treatment they tended to become thinner relative to the tracheids of trees grown under ambient conditions. Latewood tracheid lumen diameters were larger in all the treatments relative to ambient conditions over the 6-year period, whereas lumen diameters in earlywood increased only in response to elevated [CO(2)] and were 3-6% smaller in the treatments with elevated temperature than in ambient conditions. Tracheid width, length and coarseness were greater in trees grown in elevated than in ambient temperature. The number of resin canals per mm(2) decreased in the elevated [CO(2)] treatment and increased in the elevated temperature treatments relative to ambient conditions. The treatments decreased the number of rays and tracheids per mm(2) of cross-sectional area, the greatest decrease occurring in the elevated [CO(2)] treatment. It seemed that xylem anatomy was affected more by elevated temperature than by elevated [CO(2)] and that the effects of temperature were confined to the earlywood.     

Distribution of lignin in normal and compression wood of Pinus taeda L.

Summary The distribution of lignin in normal and compression wood of loblolly pine (Pinus taeda L.) has been studied by the technique of lignin skeletonizing. Hydrolysis of the wood carbohydrates with hydrofluoric acid left normal wood tracheids with a uniform distribution of lignin in the S1 and S2 cell wall layers. However, the S3 region of both earlywood and latewood tracheids consistently retained a dense network of unhydrolyzable material throughout, perhaps lignin.Lignin content in compression wood averaged about 7% more than in normal wood and appears to be concentrated in the outer zone of the S2 layer. The inner S2 region, despite helical checking, is also heavily lignified. The S1 layer, although thicker than normal in compression wood tracheids, contains relatively little lignin.Ray cells, at least in normal wood, appear to be lignified to the same extent, if not more so in certain cases, than the longitudinal tracheids. Other locations where lignin may be concentrated include initial pit border regions and the membranes of bordered pits.This report is a detailed excerpt from the Ph. D. dissertation of R. A. P. Financial support provided by the College of Forestry at Syracuse University and the National Defense Education Act is hereby gratefully acknowledged.     

The effects of drying on the structure and permeability of the wood of Abies grandis

Summary The effects of air-drying and solvent-drying on the sapwood of Abies grandis have been investigated by a new method for the determination of the size and number of conducting tracheid lumina and pit membrane pores which involves the measurement of gaseous permeability at various mean pressures. Both earlywood and latewood tracheids (83% of the total) were found to be conducting in solvent-dried wood, but in air-dried wood only latewood tracheids (32% of the total) were conducting. In solvent-dried wood there were on average 27,000 pit membrane pores per conducting tracheid compared with only 600 in air-dried wood. In both, the average pit membrane pore radius was about 0.1 m.Liquid permeabilities have been predicted from the calculated radii and numbers. The liquid permeability of solvent-dried wood was 31 times greater than that of air-dried wood in which the lumina were responsible for 13% of the total resistance to flow. The lumina were responsible for 39% of the resistance in solvent-dried wood and it is suggested that in first-formed earlywood the lumina may cause more than half the total resistance.A new method is described for the cleaning of direct carbon replicas of wood. In this the cellulose is removed by cellulase instead of sulphuric acid, and no wax backing is required. This provides much cleaner replicas. Electron micrographs have been obtained of both earlywood and latewood dried by the two methods.The authors wish to thank Mr. A. R. Sayers for preparing the computer programme used in this work, Dr. R. Ph. C. Johnson for his help and advice regarding the electron microscopy and Professors Matthews and Weatherley for their advice and encouragement.     

Longitudinal hardness and Young's modulus of spruce tracheid secondary walls using nanoindentation technique

Summary Using a mechanical properties microprobe, measurements of hardness and elastic modulus of tracheid walls in the longitudinal direction of spruce wood were obtained by continuously measuring force and displacement as a diamond indenter impressed a cell wall. Maximum mechanical properties were found at the edges of the walls of angular shaped tracheids. Both the hardness and elastic modulus of latewood cell walls were higher than cell walls in the earlywood. The high spatial resolution of this new concept of mechanical testing allows a direct comparison with ultrastructural and microchemical parameters of lignified cells which opens a wider area of applications for the understanding of intrinsic wood properties.This work was conducted while the senior author was a Visiting Scientist at the Oak Ridge National Lab, Oak Ridge, TN 37831, USA partly with joint fundings from the Austrian Science Foundation (Schrödinger scholarship J799-BIO)     

Relationships of climate and cell features in stems and roots of black spruce and balsam fir

? The anatomical differences of mature black spruces and balsam firs were examined at stem and root level in order to characterize their wood properties at cellular level and link these differences to climate.

? Anatomical variability of these species was evaluated in relation to climate data gathered from 2001 to 2004 during the cell enlargement (CE) and wall thickening and lignification (WTL) phases. Lumen area, single cell wall thickness and total tracheid radial diameter were analyzed and regrouped into earlywood and latewood.

? Results from a principal component analysis (PCA) indicated that both first eigenvectors account for 82% and 90% of total variance for CE and WTL respectively. These component factors revealed that precipitation, humidity and number of days with precipitation significantly influence the lumen area (p = 0.0168) and radial cell diameter (p = 0.0222) in earlywood. Significant differences were registered between species and tree parts (stem and root) for the lumen area, radial cell diameter and cell wall thickness in both earlywood and latewood.

? In our study, black spruce exhibited smaller tracheid size in both stem and roots compared to balsam fir. Furthermore, the lower amount of tracheids produced during the growing season and higher proportion of latewood ensure a higher wood density of black spruce. The influence of temperature on earlywood formation is significant, whereas no influence was observed on latewood.

     

Fibril angle of loblolly pine wood as related to specific gravity,growth rate,and distance from pith

Summary Fibril angles were greater for earlywood (avg. 33.4°) than for latewood tracheids (avg. 26.9°). For earlywood, fibril angle did not differ between growth rates when the specific gravity was low (avg. 33.3°). When the specific gravity was high, wood of fast growth had a higher fibril angle (avg. 35.1°) than wood of slow growth (avg. 32.0°). No differences were detected between core, middle, and outer wood. In latewood tracheids, fibril angles were greater in corewood (avg. 28.0°) than in middle or outer wood (avg. 26.3°). For whole wood (a weighted average of earlywood and latewood), fibril angle averaged 30.7° and was greater in corewood (avg. 32.2°) than in middle or outer wood (avg. 29.9°).