KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Content • Macroscopic structure of wood • Cell types and function • Comparative wood structure Wood s structure and variability The microscopic structure of wood 0.0 title ! www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics Wood s structure and variability www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics Macroscopic wood structure • Anisotropic structure – Longitudinal, radial, tangential planes • Various parts of the stem Cell type and function – Cambium, bark, wood • Variable wood types • Various cell types – Arranged longitudinally and radially (rays) tangential Cambium and various wood cells in softwoods and hardwoods longitudinal – Sapwood, heartwood, juvenile and reaction woods radial Wood s structure and variability www.csaw.utas.edu.au 0.0 title ! www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Cambium Cell differentiation • The cambium is a thin delicate layer of tissue between the bark and the wood • During dormancy, the cambium consists of a single cell layer • As the growing season begins, this single cell layer subdivides radially to form the cambial zone eight to ten cells wide • During the growing season, these cells continue to subdivide to produce cells that: • About three weeks after formation, wood cells differentiate • The cells tend to change in shape and a secondary wall is formed • The cell dies and becomes ready to serve for: – conduction, – support or – storage – remain in the cambial zone, – develop into bark – develop into wood Wood s structure and variability www.csaw.utas.edu.au Wood s structure and variability www.csaw.utas.edu.au 1! KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Major cell structure in the wood Cell structure: Wall and pits Hardwood Softwood wo od ray lumen s longitudinal longitudinal al nti ge tan Cell wall in section, showing simple pits (left) and bordered pits (right) SEM photo of bordered pits in softwood Source: http://www.scielo.cl/scielo.php? pid=s0718-221x2005000100001&script=sci_arttext Source: http://www.tutorvista.com/content/biology/biology-iii/cell-organization/cellwall.php • Cell walls are made up of a primary layer and often a secondary layer enclosing a lumen • The secondary layer often has interruptions called pits • Pits occurring in matched pairs in adjacent cells allow fluids and gases to move between adjoining cells Wood s structure and variability www.csaw.utas.edu.au Wood s structure and variability www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Cell structure: Longitudinal and rays cells Major cell types • Rays are bands of tissue running radially from the pith towards the cambium, perpendicular to the longitudinal axis • They mainly store food and are often coupled with resin or gum canals • Rays in different species have different ray heights, widths and composition and are often used for identification Cells Softwood Hardwood Function Parenchyma √ √ Storage Tracheids √ √ Support Conduction Fibers Vessels √ Support √ Conduction Wall thickness Table 1: Functions and wall thickness of the various types of cells found in softwoods and hardwoods (Source: Desch & Dinwoodie 1996) Rays viewed from major wood planes ! Source: http://www.museum-albersdorf.de/BERNSTEN/holzblok.gif Wood s structure and variability www.csaw.utas.edu.au • Parenchyma and tracheid cells can operate longitudinally or radially (as ray cells) Wood s structure and variability www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Parenchyma cells Tracheids http://www.tutornext.com/system/files/u73/Chapter%203.3-8_1.jpg • Parenchyma cells are generally short and thin walled cells responsible for storage in softwoods and hardwoods • They make up: – Less than 10% of the total wood volume in softwoods – On average, 20% of hardwoods but it can be as high as 30% • They can be aligned longitudinally and radially • The shape of parenchyma cells vary but ray parenchyma cells are generally brick-shaped Wood s structure and variability www.csaw.utas.edu.au • Tracheids cells are generally long, slender, hollow needle-shaped cells, with closed and pointed ends • They are rounded or rectangular in shape radially and have a hollow centre: the lumen or cavity Earlywood tracheids are thin-walled with relatively large diameters compared to thick-walled smaller diameters in latewood They conduct fluids through the tree and provide support They can be aligned longitudinally and radially – They are 2.5 -5.0mm (or up 10mm) long, 100 times greater than their diameters • • • – In softwoods, 95% of the cells are vertically aligned, whereas in hardwoods, 80% • They make up about 90-95% of the volume of softwood stem, Wood s structure and variability Conduction cells with pits lining the cell walls: A longitudinal file of tracheids (left) and a single tracheid www.csaw.utas.edu.au 2! KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Fibers Fibers in Australian hardwoods • Fibers or fiber tracheids in hardwoods are usually long, tapered and thick walled – approx to mm in length and 20-30 micrometers in diameters • They are: – shorter than the longitudinal tracheids in softwoods (1-2 mm compared to 3-4mm), – are rounded in shape (compared to the rectangular in softwoods), – have bordered pits like longitudinal tracheids in softwoods but with less developed borders ESEM images of E obliqua & E pilularis at 700x magnification The images have been cropped to show fiber cells only Courtesy of Adam Redman, DEEDI, Qld Wood s structure and variability www.csaw.utas.edu.au Wood s structure and variability KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Vessels Vessels Vessels and fibers in birch Source: http://www.swst.org/teach/set2/struct1.html • Vessels are longitudinal cells found in hardwoods that link end to end and conduct sap along the stem • They differentiate hardwoods from softwoods • Compared to fibers and tracheids, they are shorter, with larger diameter cells and thinner walls This makes them appear like pores • Their walls are heavily pitted These providing lateral movement of water and air between adjacent cells Wood s structure and variability www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics • Vessels are connected end to end through end walls with holes called perforated plates • Perforations develop near the end of the cell maturation process • Vessels are connected side to side through numerous bordered pit pairs • Just like perforated plates, the shape and arrangement of the vessel-to-vessel pitting is often consistent within a species • Other cell types typically form pits where they contact vessel elements, although tracheids and vessels are sometimes not linked by pitting Wood s structure and variability www.csaw.utas.edu.au Types of vessel perforations: simple, scalariform, foraminate Source http://t2.gstatic.com/images?q=tbn:ANd9GcQHG1569Bj9ignjQrWBwNw85f_Mpw8KFiSUez3mZPio91YxEqxrA&t=1 www.csaw.utas.edu.au KDA503/335 Timber, its origin and characteristics Vessels • Depending on their vessel arrangement , hardwoods are either ring porous or diffuse porous • Ring porous hardwoods have large earlywood vessels, and a distinct latewood zone with small vessels • Diffuse porous hardwoods have vessels with a relatively uniform size, distributed fairly evenly across the growth ring Most hardwood are diffuse porous • When hardwoods are milled into boards, the cut vessels produce distinctive patterns on the radial and tangential surfaces Wood s structure and variability Comparative wood structure Ring porous sassafras Sassafras albidum Source:http://forest.mtu.edu/classes/fw1035/2011/Lab lecture 1-Ring porous hardwoods.pdf ! www.csaw.utas.edu.au 0.0 title ! www.csaw.utas.edu.au 3! KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics softwood and hardwood cells softwood and hardwood cells • Softwoods are basically made up of two cell types, • Hardwoods are made up of at least four cell types: tracheid, vessel element, parenchyma, and fibers – Tracheids constitute about 90-95% of softwoods, the rest are parenchyma – Each hardwood cell type constitutes at least 15% of the total volume of wood Wood s structure and variability www.csaw.utas.edu.au • Softwood cells are aligned in parallel straight radial rows, with straight spoke-like rays • Hardwood elements and rays are seldom aligned in radial rows Distortion from the radial orientation occurs in the vicinity of large vessel elements Wood s structure and variability KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics softwood and hardwood cells Softwood rays Cells Softwood Hardwood Early/spring wood Late/summer wood • Softwood tracheids are generally rectangular whereas hardwood vessels are more rounded • The longitudinal tracheids in softwoods perform both conduction and support • In hardwoods, vessels are largely for conduction, while fiber tracheids are largely for support Wood s structure and variability www.csaw.utas.edu.au • The cells in softwood rays can be either ray parenchyma or ray tracheids • The ray parenchyma cells are brickshaped, about 20 x 25 micromillimeters • Ray tracheids, similar to longitudinal tracheids, are thick walled and have bordered pits • When a ray contains a resin canal, it is called fusiform ray Fusiform rays usually contain both tracheids and parenchyma • Resin canals, consistently found in pines, are intercellular spaces surrounded by parenchyma cells that secrete resin into the canal Resin canal by Dongyang Sun Sample cutting by Stefan Lehneke 3D by • They can be orientated in the Dan Ridley-Ellis, Edinburgh Napier University, August 2010 ! longitudinal or radial direction http://farm5.static.flickr.com/4080/4911220541_c19a716cb9.jpg ! Wood s structure and variability KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics softwood and hardwood rays Summary • • Softwood rays are only a few cells wide • – They usually constitute around 5-7% of the total volume, • • In hardwoods, rays are wider up to 30 cells wide – They constitute on average, 17% but up to 30% of the total volume • In hardwoods, ray cells are very large and these add to the wood's aesthetic appeal Wood s structure and variability www.csaw.utas.edu.au • www.csaw.utas.edu.au During the growing season, cambium cells subdivide to produce cells that remain in the cambial zone, develop into bark or develop into wood About three weeks after formation, wood cells differentiate to serve for conduction, support or storage Cell walls are made up of a primary layer and often a secondary layer enclosing a lumen Liquids and gases can move between them through pits Softwoods are basically made up of two cell types – Tracheids constitute about 90-95% of softwoods, the rest are parenchyma – These are aligned in parallel straight radial rows, with straight spoke-like rays • storied ray cells ! – Each hardwood cell type constitutes at least 15% of the total volume of wood – These are seldom aligned in radial rows Distortion from the radial orientation occurs in the vicinity of large vessel elements Source http://delta-intkey.com/wood/images/brachy-t2.jpg • • www.csaw.utas.edu.au Hardwoods are made up of at least four cell types: tracheid, vessel element, parenchyma, and fibers Rays in different species have different ray heights, widths and composition and are often used for identification Resin canals, consistently found in pines, are intercellular spaces surrounded by parenchyma cells that secrete resin into the canal Wood s structure and variability www.csaw.utas.edu.au 4! KDA503/335 Timber, its origin and characteristics Wood s structure and variability www.csaw.utas.edu.au 5! ... characteristics KDA503/335 Timber, its origin and characteristics softwood and hardwood cells Softwood rays Cells Softwood Hardwood Early/spring wood Late/summer wood • Softwood tracheids are... 20 10 ! longitudinal or radial direction http://farm5.static.flickr.com/4080/491 122 0541_c19a716cb9.jpg ! Wood s structure and variability KDA503/335 Timber, its origin and characteristics KDA503/335...KDA503/335 Timber, its origin and characteristics KDA503/335 Timber, its origin and characteristics Major cell structure in the wood Cell structure: Wall and pits Hardwood Softwood wo od