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{{wiktionary|adventitious}} |
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'''Adventitious''' has various meanings in various disciplines and in general usage. |
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''Adventitious'' is from the Latin root ''advenire'', meaning "to come to" and in English the meanings tend to have connections to "accidental/casual occurrence", "arising from without; supervenient, accidental, casual".<ref name="isbn0-19-861271-0">{{cite book |author =Brown, Lesley |title=The New shorter Oxford English dictionary on historical principles |publisher=Clarendon |location=Oxford |year=1993 |pages= |isbn=0-19-861271-0 |oclc= |doi= |accessdate=}}</ref> |
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{{R from related word}} |
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People sometimes speak of an event or occurrence as being "]", when the word "adventitious", or perhaps "]al", might be more strictly correct. |
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}} |
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== {{anchor|Botany}} Botany == |
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In ], ''adventitious'' refers to structures that develop in an unusual place. This part of the article discusses adventitious ]s, ]s and ]s, which are very common in ]s. |
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===Buds and shoots=== |
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Adventitious ]s develop from places other than a shoot ], which occurs at the tip of a stem, or on a ], at the leaf axil, the bud being left there during the primary growth. They may develop on roots or leaves, or on shoots as a new growth. Shoot apical meristems produce one or more axillary or lateral buds at each node. When stems produce considerable ], the axillary buds may be destroyed. Adventitious buds may then develop on stems with secondary growth. |
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Adventitious buds are often formed after the stem is wounded or ]. The adventitious buds help to replace lost branches. Adventitious buds and shoots also may develop on mature tree trunks when a shaded trunk is exposed to bright sunlight because surrounding trees are cut down. ] (''Sequoia sempervirens'') trees often develop many adventitious buds on their lower trunks. If the main trunk dies, a new one often sprouts from one of the adventitious buds. Small pieces of redwood trunk are sold as souvenirs termed redwood burls. They are placed in a pan of water, and the adventitious buds sprout to form shoots. |
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Some plants normally develop adventitious buds on their roots, which can extend quite a distance from the plant. Shoots that develop from adventitious buds on roots are termed ]. They are a type of natural ] in many ], e.g. many grasses, ] and ]. The ] grew from one trunk to 47,000 trunks via adventitious bud formation on a single root system. |
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Some leaves develop adventitious buds, which then form adventitious roots, as part of ]; e.g. piggyback plant ('']'') and mother-of-thousands ('']''). The adventitious plantlets then drop off the parent plant and develop as separate ]s of the parent. |
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] is the practice of cutting ] stems to the ground to promote rapid growth of adventitious shoots. It is traditionally used to produce poles, fence material or firewood. It is also practiced for ] crops grown for fuel, such as ] or willow. |
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===Roots=== |
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] |
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Adventitious rooting may be a stress-avoidance acclimation for some species, driven by such inputs as ]<ref>), (Visser et al. 1996)</ref> or nutrient deficiency. Another ecologically important function of adventitious rooting is the vegetative propagation of tree species such as ''Salix'' and ''Sequoia'' in ] settings.<ref>. ''Annual Reviews in Ecological Systems''</ref> |
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The ability of plant stems to form adventitious roots is utilised in commercial propagation by ]s. Understanding of the physiological mechanisms behind adventitious rooting has allowed some progress to be made in improving the rooting of cuttings by the application of synthetic auxins as rooting powders and by the use of selective basal wounding.<ref>. In Vitro Cell & Developmental Biology - Plant 35 3;189-199</ref> Further progress can be made in future years by applying research into other regulatory mechanisms to commercial propagation and by the comparative analysis of molecular and ecophysiological control of adventitious rooting in 'hard to root' vs. 'easy to root' species. |
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====Growth==== |
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Adventitious roots and buds usually develop near the existing vascular tissues so they can connect to the ] and ]. However, the exact location varies greatly. In young stems, adventitious roots often form from ] between the ]s. In stems with secondary growth, adventitious roots often originate in phloem parenchyma near the ]. In stem cuttings, adventitious roots sometimes also originate in the ] cells that form at the cut surface. Leaf cuttings of the '']'' form adventitious roots in the epidermis.<ref>McVeigh, I. 1938. Regeneration in ''Crassula multicava''. ''American Journal of Botany'' 25: 7-11. </ref> |
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====Modified forms==== |
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*'''Tuberous roots''' lack a definite shape; example: ]. |
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*'''Fasciculated root''' (tuberous root) occur in clusters at the base of the stem; examples: ], ]. |
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*'''Nodulose roots''' become swollen near the tips; example: ]. |
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*'''Stilt roots''' arise from the first few nodes of the stem. These penetrate obliquely down into the soil and give support to the plant; examples: ], ]. |
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*'''Prop roots''' give mechanical support to aerial branches. The lateral branches grow vertically downward into the soil and act as pillars; example: ]. |
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*'''Climbing roots''' arising from nodes attach themselves to some support and climb over it; example: ]. |
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*'''Moniliform or beaded roots''' the fleshy roots give a beaded appearance, e.g.: ], ], ] |
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====Propagation==== |
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Adventitious roots and buds are very important when people propagate plants via cuttings, ], ]. ], termed ]s, are often applied to stem, ] or ] cuttings to promote adventitious root formation, e.g. ] and ] leaves and shoots of ] and ]. Propagation via root cuttings requires adventitious bud formation, e.g. in ] and ]. In layering, adventitious roots are formed on aerial stems before the stem section is removed to make a new plant. Large houseplants are often propagated by ]. Adventitious roots and buds must develop in tissue culture propagation of plants. |
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==Law== |
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In law, ''adventitious'' can mean "falling to a man by mere fortune, or from a stranger..."<ref name="isbn0-19-861271-0"/> |
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==Medicine== |
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In ], ''adventitious'' and related words such as ] refer in various senses to the basic meanings associated with the Latin root ''advenire''. Typically the general intention is to convey something like: ''of the nature of a later addition from without, accidental, casual''.<ref name="isbn0-19-861271-0"/> |
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On similar principles, ''adventitious'' in medical terminology can refer to conditions acquired after birth, particularly if the cause is obscure, casual, or accidental. |
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In ] the term ''adventitious'' refers in general to any diagnostic added sound not normally to be expected in the healthy body and likely to indicate an undesirable condition. The terminology is confused, largely for historical reasons, but roughly speaking one listens for ''crackles'' and ''wheezes'' in the respiratory passages, and ''rubbings'' in pleurisy. |
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A wide variety of other sounds are correspondingly relevant in cardiovascular conditions, fractures, joint problems etc.<ref name="isbn0-19-262140-8">{{cite book |author =Warrell, D. A. |author2=Weatherall, D. J. |author3=Ledingham, J. G. G. |title=Oxford textbook of medicine |publisher=Oxford University Press |location=Oxford |year=1996 |pages= |isbn=0-19-262140-8 |oclc= |doi= |accessdate=}}</ref> |
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== Agriculture == |
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Adventitious presence in agriculture refers to the accidental or unintentional appearance of foreign material in a product. This usually happens in the production, ], ], and marketing of ], ]s, or ]. |
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Grain and seed companies argue that virtually all shipments contain some type, and level, of adventitious material, such as ] material. Generally, buyers recognize that some level of adventitious material is acceptable, and foreign material limits are specified in purchase contracts. |
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Adventitious presence is a key issue in the debate over regulation of ]. As more and more crops, and acres, are devoted to ] (GE) varieties, it becomes increasingly difficult to segregate these from GE-free varieties, which some buyers and countries demand. |
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In 2005, the ] was considering a proposal to require GE labeling of any food or feed product that contains more than 0.5% of material derived from genetically modified organisms.<ref>This section {{CRS|article = Report for Congress: Agriculture: A Glossary of Terms, Programs, and Laws, 2005 Edition|url = http://ncseonline.org/nle/crsreports/05jun/97-905.pdf|author = Jasper Womach}}</ref> |
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==Religion== |
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The Dalai Lama describes the autopilot thoughtstreams as adventitious, in a speech about Rigpa awareness: "However, this primordial quality of buddhahood is obscured by adventitious mental factors, our afflictions and other thought processes." <ref>Dalai Lama, J. Cabezon translator, 2009. Meditation On The Nature Of Mind.</ref> |
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==References== |
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<references/> |
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* Esau, K. 1977. ''Anatomy of Seed Plants''. New York: Wiley. |
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* Hartmann, H.T. and Kester, D.E. 1983. ''Plant Propagation: Principles and Practices''. Englewood Cliffs, NJ: Prentice-Hall. |
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