|
Dry rot is wood decay caused by certain species of fungi that digest parts of the wood which give the wood strength and stiffness. It was previously used to describe any decay of cured wood in ships and buildings by a fungus which resulted in a darkly colored deteriorated and cracked condition. The life-cycle of dry rot can be broken down into four main stages. Dry rot begins as a microscopic spore which, in high enough concentrations, can resemble a fine orange dust. If the spores are subjected to sufficient moisture they will begin to grow fine white strands known as hyphae. As the hyphae germinate they will eventually form a large mass known as mycelium. The final stage is a fruiting body which pumps new spores out into the surrounding air. In other fields, the term has been applied to the decay of crop plants by fungi and the deterioration of rubber. == Discussion == ''Dry rot'' is the term given to brown rot decay caused by certain fungi that deteriorate timber in buildings and other wooden construction seemingly without an apparent source of moisture. The term is a misnomer〔Schwartz, Max. ''Basic lumber engineering for builders''. Carlsbad, CA: Craftsman, 1997. 19. Print.〕 because all wood decaying fungi need a minimum amount of moisture before decay begins.〔Schmidt, Olaf, and Dieter Czeschlik. ''Wood and tree fungi biology, damage, protection, and use''. Berlin: Springer, 2006. 211. Print.〕 The decayed wood takes on a dark or browner crumbly appearance, with cubical like cracking or checking, that becomes brittle and can eventually crush the wood into powder. Chemically, wood attacked by dry rot fungi is decayed by the same process as other brown rot fungi. An outbreak of dry rot within a building can be perceived to be an extremely serious infestation that is hard to eradicate, requiring drastic remedies to correct. Eventually the decay can cause instability and cause the structure to collapse. The term ''dry rot'', or ''true dry rot'', refers to the decay of timbers from only certain species of fungi that are thought to provide their own source of moisture and nutrients to cause decay in otherwise relatively dry timber. However, there has been no published experimental evidence to support the phenomena.〔Timber decay in buildings: the conservation approach to treatment. Ridout, B.V. 2000 SPON PRESS,London. p84-85. ((View on Google Books ))〕 In modern texts, the term 'dry rot' is used in reference to damage inflicted by either: ''Serpula lacrymans'' (formerly ''Merulius lacrymans'') predominantly in the United Kingdom and northern Europe; and/or ''Meruliporia incrassata'' (which has a number of synonyms, including ''Poria incrassata'' and ''Serpula incrassata'') in North America. Both species of fungi cause brown rot decay, preferentially removing cellulose and hemicellulose from the timber leaving a brittle matrix of modified lignin. The term ''dry rot'' is somewhat misleading, as both species of fungi ''Serpula lacrymans'' and ''Meruliporia incrassata'' require an elevated moisture content to initiate an attack on timber (28–30%). Once established, the fungi can remain active in timber with a moisture content of more than 20%. At relative humidities below 86 percent, growth of ''Serpula lacrymans'' is inhibited, but it can stay dormant at relative humidities down to 76 percent.〔J.W. Palfreyman, (The Domestic Dry Rot Fungus, Serpula lacrymans, its natural origins and biological control ). Ariadne workshop 2001.〕 These relative humidities correspond to equilibrium moisture contents of wood of 19 and 15 percent, respectively. An explanation of the term "dry rot" circles around boatyards periodically. In the age of wooden ships, boats were sometimes hauled for the winter and placed in sheds or dry dock for repair. The boats already had some amount of rot occurring in the wood members, but the wood cellular structure was full of water making it still function structurally. As the wood dried out, the cell walls would crumble. In other words, the wood was already rotten and as the boat dried, the wood collapsed and crumbled, causing the workers in the yard to determine it was "dry rot", when in fact, the wood had been rotten all along. Schilling & Jellison note the potential efficiency of these 'dry rot' fungi in growing away from direct moisture sources, although there is no reference for how efficient a brown rot fungus has to be at translocating water in order to be classed as 'dry rot'. Some have suggested the importance of these fungi providing their own source of nutrients as being more significant than providing an adequate source of moisture. Schilling suggests efficient nutrient translocation and utilization, notably nitrogen and iron, may be more distinctive in these species than water translocation. Water translocated in this fashion carries nutrients to the extremities of the organism; not, as is sometimes inferred, to simply render dry timber wet enough to attack. Coggins goes into more detail about water movement in ''Serpula lacrymans''. The perpetual saturation of wood with water also inhibits dry rot, as does perpetual dryness.〔Forest Products Laboratory, (Wood Handbook - Wood as an Engineering Material ). U.S. Department of Agriculture, 2010.〕 ''Dry rot'' would appear to be a paradoxical term seemingly indicating decay of a substance by a fungus without the presence of water. However, its historical usage dates back to the distinction between decay of cured wood in construction, i.e. dry wood, versus decay of wood in living or newly felled trees, i.e. wet wood. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「dry rot」の詳細全文を読む スポンサード リンク
|