Editing Wood (section)

===Structure===
[[File:BlkWalnut-x-section.jpg|thumb|upright|Magnified cross-section of [[Juglans nigra|black walnut]], showing the vessels, rays (white lines) and annual rings: this is intermediate between diffuse-porous and ring-porous, with vessel size declining gradually]]
Wood is a [[heterogeneous]], [[hygroscopic]], [[cell (biology)|cellular]] and [[anisotropy|anisotropic]] (or more specifically, [[Orthotropic material|orthotropic]]) material. It consists of cells, and the cell walls are composed of micro-fibrils of [[cellulose]] (40–50%) and [[hemicellulose]] (15–25%) impregnated with [[lignin]] (15–30%).<ref>{{cite web|url=http://treetesting.com/wood_properties_growth_and_structure.htm|title=Wood Properties Growth and Structure 2015|work=treetesting.com|url-status=live|archive-url=https://web.archive.org/web/20160313044617/http://treetesting.com/wood_properties_growth_and_structure.htm|archive-date=March 13, 2016|df=mdy-all}}</ref>

In coniferous or [[softwood]] species the wood cells are mostly of one kind, [[tracheid]]s, and as a result the material is much more uniform in structure than that of most [[hardwood]]s. There are no vessels ("pores") in coniferous wood such as one sees so prominently in oak and ash, for example.

The structure of hardwoods is more complex.<ref>{{cite web|url=https://nationalvetcontent.edu.au/alfresco/d/d/workspace/SpacesStore/b2f0fcee-47cb-4650-b248-f533d73d5428/13_05/toolbox13_05/unit9_selecting_timber/section2_characteristics/lesson2_hardwood.htm|title=Timber Plus Toolbox, Selecting timber, Characteristics of timber, Structure of hardwoods|work=nationalvetcontent.edu.au|url-status=dead|archive-url=https://web.archive.org/web/20140810184152/https://nationalvetcontent.edu.au/alfresco/d/d/workspace/SpacesStore/b2f0fcee-47cb-4650-b248-f533d73d5428/13_05/toolbox13_05/unit9_selecting_timber/section2_characteristics/lesson2_hardwood.htm|archive-date=August 10, 2014|df=mdy-all}}</ref> The water conducting capability is mostly taken care of by [[vessel element|vessels]]: in some cases (oak, chestnut, ash) these are quite large and distinct, in others ([[Aesculus|buckeye]], [[Populus|poplar]], [[willow]]) too small to be seen without a hand lens. In discussing such woods it is customary to divide them into two large classes, ''ring-porous'' and ''diffuse-porous''.<ref name="Sperry-1994">{{cite journal |last=Sperry |first=John S. |author2=Nichols, Kirk L. |author3=Sullivan, June E. |author4=Eastlack, Sondra E. |title=Xylem Embolism in ring-porous, diffuse-porous, and coniferous trees of Northern Utah and Interior Alaska |journal=Ecology |date=1994 |volume=75 |issue=6 |pages=1736–1752 |jstor=1939633 |doi=10.2307/1939633 |bibcode=1994Ecol...75.1736S |url=http://bioweb.biology.utah.edu/sperry/publications/Sperry%20et%20al.%201994%20Ecology.pdf |access-date=November 30, 2018 |archive-date=August 10, 2017 |archive-url=https://web.archive.org/web/20170810100919/http://bioweb.biology.utah.edu/sperry/publications/Sperry%20et%20al.%201994%20Ecology.pdf |url-status=dead }}</ref>

In ring-porous species, such as ash, black locust, [[catalpa]], chestnut, [[elm]], hickory, [[mulberry]], and oak,<ref name="Sperry-1994"/> the larger vessels or pores (as cross sections of vessels are called) are localized in the part of the growth ring formed in spring, thus forming a region of more or less open and porous tissue. The rest of the ring, produced in summer, is made up of smaller vessels and a much greater proportion of wood fibers. These fibers are the elements which give strength and toughness to wood, while the vessels are a source of weakness.<ref>{{cite book |last1=Record |first1=Samuel James |title=The Mechanical Properties of Wood, Including a Discussion of the Factors Affecting the Mechanical Properties, and Methods of Timber Testing |date=1914 |publisher=J. Wiley & sons, Incorporated |url=https://books.google.com/books?id=IbjPAAAAMAAJ&pg=PA44 |language=en |access-date=March 20, 2023 |archive-date=September 8, 2023 |archive-url=https://web.archive.org/web/20230908234053/https://books.google.com/books?id=IbjPAAAAMAAJ&pg=PA44 |url-status=live }}</ref>

In diffuse-porous woods the pores are evenly sized so that the water conducting capability is scattered throughout the growth ring instead of being collected in a band or row. Examples of this kind of wood are [[Alnus|alder]],<ref name="Sperry-1994"/> [[Tilia|basswood]],<ref name="SJRecord-1914">{{cite book|author=Samuel James Record|title=The mechanical properties of wood, including a discussion of the factors affecting the mechanical properties, and methods of timber testing|url=https://archive.org/details/mechanicalprope01recogoog|year=1914|publisher=J. Wiley & sons, inc.|pages=[https://archive.org/details/mechanicalprope01recogoog/page/n63 44]–|df=mdy-all}}</ref> [[birch]],<ref name="Sperry-1994"/> buckeye, maple, [[willow]], and the ''[[Populus]]'' species such as aspen, cottonwood and poplar.<ref name="Sperry-1994"/> Some species, such as [[Juglans nigra|walnut]] and [[Prunus pumila|cherry]], are on the border between the two classes, forming an intermediate group.<ref name="SJRecord-1914"/>