What is Wood?
[[File:Ein Raummeter Holz.jpg|250px|right|frameless]] [[File:Gatunki drewna - Brockhaus 1937.jpg |thumb|250px|Different trees make different wood: 1. [[Pine]] 2. Common [[Beech]] 3. [[Sycamore]] 4. [[Oak]] 5. [[Birch]] 6. Sugar [[Maple]] 7. Microberlinia 8. African [[Rosewood]] 9. Okoumé 10. Common [[Walnut]] 11. Brazilian Rosewood 12. [[Ebony]]]] '''Wood''' is the main substance in [[tree]]s. It is mainly formed by the [[xylem]] vessels which carry water up the plant. The two main substances in wood are [[cellulose]] and [[lignin]]. Wood is used to make [[building]]s and [[furniture]], and also for [[art]]. [[Firewood]] is a fuel. [[Paper]] is made from [[wood fibre]]s. Wood is a [[renewable resource]] although it has become scarcer in recent centuries. Its origin is about 425 million years ago.<ref>Labandeira C. 2007. The origin of herbivory on land: Initial patterns of plant tissue consumption by arthropods. ''Insect Science''. '''14''' (4): 259–275. [https://doi.org/10.1111/j.1744-7917.2007.00152.x]</ref> Wood is hard to cut, but it is also strong. A [[lumberjack]] is a person who cuts down trees. After a tree falls, the wood in it can be cut into long, straight pieces called [[lumber]]. Lumber can then be used to make [[wikt:post|posts]], or put together with [[nail]]s, [[screw]]s, or even [[glue]] to make wooden [[frame]]s for other shapes. Wood comes in many different kinds. [[Oak]], [[maple]] (hardwood) and [[pine]] and [[redwood]] (softwood) are widely used types of wood. Woods are usually divided into [[softwood]] (from [[conifers]]) and [[hardwood]] from [[flowering plants]].<ref>Jane F.W. 1970.'' The structure of wood''. 2nd ed, edited by K. Wilson & D.J.B. White. London: Adam & Charles Black. {{ISBN|9780713609127}}</ref> == Housing == For a long time and even today, many [[building]]s, mostly [[house]]s, have been made of wood. To build a house with wood, lumber is put together into frames that are the shape of each wall, floor, and [[roof]] of the house. Then the frames are placed into the shape