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phloem
phloem (bast) A tissue that conducts food materials in vascular plants from regions where they are produced (notably the leaves) to regions, such as growing points, where they are needed. It consists of hollow tubes (sieve tubes) that run parallel to the long axis of the plant organ and are formed from elongated cells (sieve elements) joined end to end and closely associated with companion cells. The end walls of these cells are broken down to a greater or lesser extent to allow passage of materials. In young plants and in newly formed tissues of mature plants primary phloem is formed by the activity of the apical meristem (see protophloem; metaphloem). In most plants secondary phloem is later differentiated by the vascular cambium and this replaces the earlier formed phloem in older regions. See also mass flow. Compare xylem.
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"phloem." A Dictionary of Biology. 2004. Encyclopedia.com. 11 Feb. 2012 <http://www.encyclopedia.com>. "phloem." A Dictionary of Biology. 2004. Encyclopedia.com. (February 11, 2012). http://www.encyclopedia.com/doc/1O6-phloem.html "phloem." A Dictionary of Biology. 2004. Retrieved February 11, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O6-phloem.html |
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phloem
phloem Vascular tissue for distributing dissolved food materials in plants. Phloem tissue contains several types of cells. The most important are long, hollow cells called sieve-tube cells. Columns of sieve tubes are joined end to end, allowing passage of materials from cell to cell. The sieve tubes are closely associated with ‘companion cells’, which have dense cytoplasm and many mitochondria, and are thought to produce the energy needed to transport the food substances (see active transport). Phloem may also contain fibres that help to support the tissue. See also mitochondrion; xylem
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"phloem." World Encyclopedia. 2005. Encyclopedia.com. 11 Feb. 2012 <http://www.encyclopedia.com>. "phloem." World Encyclopedia. 2005. Encyclopedia.com. (February 11, 2012). http://www.encyclopedia.com/doc/1O142-phloem.html "phloem." World Encyclopedia. 2005. Retrieved February 11, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O142-phloem.html |
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phloem
phloem A tissue comprising various types of cell, which transports dissolved organic and inorganic materials over long distances within vascular plants, by mechanisms that are still not understood fully. It can be distinguished from xylem by the general absence of thickened cells and by the presence of cells containing areas resembling a sieve.
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MICHAEL ALLABY. "phloem." A Dictionary of Plant Sciences. 1998. Encyclopedia.com. 11 Feb. 2012 <http://www.encyclopedia.com>. MICHAEL ALLABY. "phloem." A Dictionary of Plant Sciences. 1998. Encyclopedia.com. (February 11, 2012). http://www.encyclopedia.com/doc/1O7-phloem.html MICHAEL ALLABY. "phloem." A Dictionary of Plant Sciences. 1998. Retrieved February 11, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O7-phloem.html |
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phloem
phlo·em / ˈflōˌem/ • n. Bot. the vascular tissue in plants that conducts sugars and other metabolic products downward from the leaves. |
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"phloem." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. 11 Feb. 2012 <http://www.encyclopedia.com>. "phloem." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. (February 11, 2012). http://www.encyclopedia.com/doc/1O999-phloem.html "phloem." The Oxford Pocket Dictionary of Current English. 2009. Retrieved February 11, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O999-phloem.html |
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phloem
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"phloem." The Columbia Encyclopedia, 6th ed.. 2008. Encyclopedia.com. 11 Feb. 2012 <http://www.encyclopedia.com>. "phloem." The Columbia Encyclopedia, 6th ed.. 2008. Encyclopedia.com. (February 11, 2012). http://www.encyclopedia.com/doc/1E1-X-phloem.html "phloem." The Columbia Encyclopedia, 6th ed.. 2008. Retrieved February 11, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1E1-X-phloem.html |
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