Reaction wood 4147579 213048315 2008-05-17T14:57:31Z Matthead 50001 /* See also */ '''Reaction wood''' is formed in response to mechanical stress, and helps to position newly formed parts of the [[plant]] in an optimal position. Reaction wood forms when a woody [[plant]] part is subjected to mechanical stress. This stress may be the result of [[wind]] exposure, excess of [[snow]], soil movement, etc. The reaction wood appear as asymmetric growth. The [[cambium]] in the affected part of the trunk is more active on one side, leading to thicker growth rings. Branches practically always have reaction wood, since they need support to maintain their horizontal or nearly horizontal position. There are two different types of reaction wood, which represent two different approaches to the same problem by these groups of [[plant]]s: * In [[angiosperms]] reaction wood is called '''tension wood'''. Tension wood forms above the affected part of the plant, pulling it up. It is composed almost entirely of [[cellulose]]. * In [[conifers]] it is called '''compression wood'''. Compression wood forms below the bent part, pushing it up. Compression wood is rich in [[lignin]]. As a rule, reaction wood is undesirable in any commercial application, primarily as its mechanical properties are different. Reaction wood is hard, brittle and it breaks the uniformity of timber. It also responds differently to changes in moisture. ==See also== * [[Krummholz]] [[Category:Wood]] [[Category:Plant physiology]] [[fi:Lyly (puu)]] [[sv:Tjurved]]