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Encyclopedia > Xylem
Multiple cross sections of a stem showing xylem and companion cells
Multiple cross sections of a stem showing xylem and companion cells[1]

In vascular plants, xylem is one of the two types of transport tissue, phloem being the other. The word "xylem" is derived from classical Greek ξυλον (xylon), "wood", and indeed the best known xylem tissue is wood, though it is found throughout the plant. Its basic function is to transport water. Divisions Non-seed-bearing plants †Rhyniophyta †Zosterophyllophyta Lycopodiophyta †Trimerophytophyta Pteridophyta Superdivision Spermatophyta †Pteridospermatophyta Pinophyta Cycadophyta Ginkgophyta Gnetophyta Magnoliophyta Vascular plants (also known as tracheophytes or higher plants) are those plants that have lignified tissues for conducting water, minerals, and photosynthetic products through the plant. ... In vascular plants, phloem is the living tissue that carries organic nutrients, particularly sucrose, a sugar, to all parts of the plant where needed. ... For other uses, see Wood (disambiguation). ...

Contents

Physiology of xylem

The xylem is responsible for the transport of water and mineral nutrients from the roots throughout the plant. Xylem sap consists mainly of water and inorganic ions, although it can contain a number of organic chemicals as well. This transport is not powered by energy spent by the tracheary elements themselves, which are dead at maturity and no longer have living contents. Two phenomena cause xylem sap to flow: Leafhoppers and many other insects feed off plant sap Sap is the fluid transported in xylem cells (tracheids or vessel elements) or phloem sieve tube elements of a plant. ...

  • Transpirational pull: the most important cause of xylem sap flow, is the evaporation of water from the surfaces mesophyll cells to the atmosphere. This transpiration causes millions of minute menisci to form in the mesophyll cell wall. The resulting surface tension causes a negative pressure or tension in the xylem that pulls the water from the roots and soil.
  • Root pressure: If the water potential of the root cells is more negative than the soil, usually due to high concentrations of solute, water can move by osmosis into the root. This causes a positive pressure that forces sap up the xylem towards the leaves. In some circumstances the sap will be forced from the leaf through a hydathode in a phenomenon known as guttation. Root pressure is highest in the morning before the stomata open and allow transpiration to begin. Different plant species can have different root pressures even in a similar environment; examples include up to 145 kPa in Vitis riparia but around zero in Celastrus orbiculatus[2].

Transpirational pull is the main phenomenon driving the flow of water in the xylem tissues of large plants. ... Vaporization redirects here. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... This article is about the leaf, a plant organ. ... Transpiration is the evaporation of excess water from aerial parts and of plants, especially leaves but also stems, flowers and fruits. ... A: Read the bottom of a concave meniscus. ... This box:      Surface tension is a property of the surface of a liquid that causes it to behave as an elastic sheet. ... Tension is a reaction force applied by a stretched string (rope or a similar object) on the objects which stretch it. ... Root pressure is one of the phenomena used by vascular plants to move water into the leaves. ... This does not cite any references or sources. ... Loess field in Germany Surface-water-gley developed in glacial till, Northern Ireland For other uses, see Soil (disambiguation). ... A substance is soluble in a fluid if it dissolves in the fluid. ... Osmosis is the spontaneous net movement of water across a semipermeable membrane from a region of low solute concentration to a solution with a high solute concentration, down a solute concentration gradient. ... A hydathode is a type of tissue in leaves, usually more advanced plant species, that permits the release of water through pores in the epidermis or margin of leaves. ... Guttation is the appearance of drops of water on the leaves of some vascular plants, such as grasses. ... Binomial name Vitis riparia Vitis riparia Michx, also commonly known as River Bank Grape or Frost Grape, is a native American climbing or trailing vine, widely distributed from Quebec to Texas, and Montana to New England. ...

Anatomy of xylem

Xylem can be found:

Note that, in transitional stages of plants with secondary growth, the first two categories are not mutually exclusive, although usually a vascular bundle will contain primary xylem only. Cross section of celery stalk, showing vascular bundles, which include both phloem and xylem A vascular bundle is a part of the transport system in vascular plants. ... Tunica-Corpus model of the apical meristem. ... The vascular cambium is a lateral meristem: The vascular cambium is the source of both the secondary xylem (inwards) and the secondary phloem (outwards), and hence is located between these tissues in the stem. ... In a vascular plant, the stele is the central part of the root or stem containing the vascular tissue and occasionally a pith. ... This article is about the group of pteridophyte plants. ...


The most distinctive cells found in xylem are the tracheary elements: tracheids and vessel elements. However, the xylem is a complex tissue of plants, which means that it includes more than one type of cell. In fact, xylem contains other kinds of cells, such as parenchyma, in addition to those that serve to transport water. Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell being used to describe the smallest unit of a living organism Cells in culture, stained for keratin (red) and DNA (green) The cell is the... Tracheids are elongated cells in the xylem of vascular plants, serving in the transport of water. ... A vessel element is an important part of the wood (Xylem) of hardwood plants and is found in all Angiosperms. ... Parenchyma is a term used to describe a bulk of a substance. ...


Primary and Secondary xylem

Primary xylem is the xylem that is formed during primary growth from procambium. It includes protoxylem and metaxylem. Metaxylem develops after the protoxylem but before secondary xylem. It is distinguished by wider vessels and tracheids. The procambium, in plants, is a primary meristem of roots and shoots that forms the vascular tissue (primary xylem and primary phloem. ...


Secondary xylem is the xylem that is formed during secondary growth from vascular cambium. Although secondary xylem is also found in members of the "gymnosperm" groups Gnetophyta and Ginkgophyta and to a lesser extent in members of the Cycadophyta, the two main groups in which secondary xylem can be found are: The vascular cambium is a lateral meristem: The vascular cambium is the source of both the secondary xylem (inwards) and the secondary phloem (outwards), and hence is located between these tissues in the stem. ... Divisions Pinophyta (or Coniferophyta) - Conifers Ginkgophyta - Ginkgo Cycadophyta - Cycads Gnetophyta - Gnetum, Ephedra, Welwitschia Gymnosperm (Gymnospermae) are a group of spermatophyte seed-bearing plants with ovules on the edge or blade of an open sporophyll, which are usually arranged in cone-like structures. ... taxa: Gnetales Welwitschiales Ephedrales The plant division Gnetophyta or gnetophytes comprise three related families of woody plants grouped in the gymnosperms, a paraphyletic group of seed plant divisions. ... Binomial name Ginkgo biloba L. The Ginkgo (Ginkgo biloba), sometimes also known as the Maidenhair tree, is a unique tree with no living relatives. ... Families Cycadaceae cycas family Stangeriaceae stangeria family Zamiaceae zamia family Cycads are an ancient group of seed plants which are characterized by a large crown of compound leaves and a stout trunk. ...

  1. conifers (Coniferae): there are some six hundred species of conifers. All species have secondary xylem, which is relatively uniform in structure throughout this group. Many conifers become tall trees: the secondary xylem of such trees is marketed as softwood.
  2. angiosperms (Angiospermae): there are some quarter of a million to four hundred thousand species of angiosperms. Within this group secondary xylem has not been found in the monocots. In the remainder of the angiosperms this secondary xylem may or may not be present, this may vary even within a species, depending on growing circumstances. In view of the size of this group it will be no surprise that no absolutes apply to the structure of secondary xylem within the angiosperms. Many non-monocot angiosperms become trees, and the secondary xylem of these is marketed as hardwood.

Orders & Families Cordaitales † Pinales   Pinaceae - Pine family   Araucariaceae - Araucaria family   Podocarpaceae - Yellow-wood family   Sciadopityaceae - Umbrella-pine family   Cupressaceae - Cypress family   Cephalotaxaceae - Plum-yew family   Taxaceae - Yew family Vojnovskyales † Voltziales † The conifers, division Pinophyta, are one of 13 or 14 division level taxa within the Kingdom Plantae. ... Orders & Families Cordaitales † Pinales   Pinaceae - Pine family   Araucariaceae - Araucaria family   Podocarpaceae - Yellow-wood family   Sciadopityaceae - Umbrella-pine family   Cupressaceae - Cypress family   Cephalotaxaceae - Plum-yew family   Taxaceae - Yew family Vojnovskyales † Voltziales † Conifer redirects here. ... Despite being fairly hard, cedar is a softwood Softwood is a generic term used in woodworking and the lumber industries for wood from conifers (needle-bearing trees from the order Pinales). ... Classes Magnoliopsida - Dicots Liliopsida - Monocots The flowering plants (also angiosperms or Magnoliophyta) are one of the major groups of modern plants, comprising those that produce seeds in specialized reproductive organs called flowers, where the ovulary or carpel is enclosed. ... Angiospermae is one of several botanical names allowed (see Art 16 of the ICBN) for the most important group of plants on land, i. ... Orders Base Monocots: Acorus Alismatales Asparagales Dioscoreales Liliales Pandanales Family Petrosaviaceae Commelinids: Arecales Commelinales Poales Zingiberales Family Dasypogonaceae Monocotyledons or monocots are a group of flowering plants usually ranked as a class and once called the Monocotyledoneae. ... Beech is a typical temperate zone hardwood For the record label, see Hardwood Records. ...

Evolution of xylem

Photos showing xylem elements in the shoot of a fig tree (Ficus alba): crushed in hydrochloric acid, between slides and cover slips.
Photos showing xylem elements in the shoot of a fig tree (Ficus alba): crushed in hydrochloric acid, between slides and cover slips.

Xylem appeared early in the history of terrestrial plant life. Fossil plants with anatomically preserved xylem are known from the Silurian (more than 400 million years ago), and trace fossils resembling individual xylem cells may be found in earlier Ordovician rocks. The earliest true and recognizable xylem consists of tracheids with a helical-annular reinforcing layer added to the cell wall. This is the only type of xylem found in the earliest vascular plants, and this type of cell continues to be found in the protoxylem (first-formed xylem) of all living groups of plants. Several groups of plants later developed pitted tracheid cells, apparently through convergent evolution. In living plants, pitted tracheids do not appear in development until the maturation of the metaxylem (following the protoxylem). Download high resolution version (1771x991, 303 KB)Photos of vessels at (Ficus sp). ... Download high resolution version (1771x991, 303 KB)Photos of vessels at (Ficus sp). ... For other uses, see Silurian (disambiguation). ... Artist impression of the Ordovician Sea. ...


In most plants, pitted tracheids function as the primary transport cells. The other type of tracheary element, besides the tracheid, is the vessel element. Vessel elements are joined by perforations into vessels. In vessels, water travels by bulk flow, like in a pipe, rather than by diffusion through cell membranes. The presence of vessels in xylem has been considered to be one of the key innovations that led to the success of the angiosperms[3]. However, the occurrence of vessel elements is not restricted to angiosperms, and they are absent in some archaic or "basal" lineages of the angiosperms: (e.g., Amborellaceae, Tetracentraceae, Trochodendraceae, and Winteraceae), and their secondary xylem is described by Arthur Cronquist as "primitively vesselless". Cronquist considered the vessels of Gnetum to be convergent with those of angiosperms[4]. Whether the absence of vessels in basal angiosperms is a primitive condition is contested, the alternative hypothesis being that vessel elements originated in a precursor to the angiosperms and were subsequently lost. A vessel element is an important part of the wood (Xylem) of hardwood plants and is found in all Angiosperms. ... Binomial name Amborella trichopoda Amborella trichopoda is a rare shrub found only in New Caledonia. ... genera see text Tetracentraceae is the botanical name for a family of flowering plants. ... genera see text Trochodendraceae is the botanical name for a family of flowering plants. ... Genera Belliolum Bubbia Drimys Exospermum Pseudowintera Takhtajania Tasmannia Tetrathalamus Zygogynum The Winteraceae are a family of flowering plants belonging to the Antarctic flora. ... Arthur C. Cronquist (1919–1992) was a North American botanist who wrote An Integrated System of Classification of Flowering Plants (1981) and The Evolution and Classification of Flowering Plants (1988). ... Species see text Gnetum is a genus of about 30-35 species of gymnosperms. ... It has been suggested that Clade be merged into this article or section. ...


See also

The cohesion-tension theory is a theory of intermolecular attraction commonly observed in the process of water travelling upwards (against the force of gravity) through the xylem of plants. ... In vascular plants, phloem is the living tissue that carries organic nutrients, particularly sucrose, a sugar, to all parts of the plant where needed. ... In vascular plants, secondary growth or, perhaps more accurately, secondary thickening is the result of the activity of the vascular cambium. ... Transpirational pull is the main phenomenon driving the flow of water in the xylem tissues of large plants. ... Cross section of celery stalk, showing vascular bundles, which include both phloem and xylem. ... Cross section of celery stalk, showing vascular bundles, which include both phloem and xylem A vascular bundle is a part of the transport system in vascular plants. ...

References

  1. ^ Winterborne J, 2005. Hydroponics - Indoor Horticulture [1]
  2. ^ Tim J. Tibbetts; Frank W. Ewers (2000). "Root pressure and specific conductivity in temperate lianas: exotic Celastrus orbiculatus (Celastraceae) vs. native Vitis riparia (Vitaceae)". American Journal of Botany 87: 1272-78. 
  3. ^ Carlquist, S.; E.L. Schneider (2002). "The tracheid–vessel element transition in angiosperms involves multiple independent features: cladistic consequences" 89: 185-195. doi:10.3732/ajb.89.2.185. 
  4. ^ Cronquist, A. (Aug 1988.). The Evolution and Classification of Flowering Plants. New York, New York: New York Botanical Garden Press. ISBN 978-0893273323. 

A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ...

General references

  • Campbell, Neil A.; Jane B. Reece (2002). Biology, 6th ed., Benjamin Cummings. ISBN 978-0805366242. 
  • Kenrick, Paul; Crane, Peter R. (1997). The Origin and Early Diversification of Land Plants: A Cladistic Study. Washington, D. C.: Smithsonian Institution Press. ISBN 1-56098-730-8. 
  • Muhammad, A.F.; R. Sattler (1982). "Vessel Structure of Gnetum and the Origin of Angiosperms". American Journal of Botany 69: 1004-21. doi:10.2307/2442898. 
  • Melvin T. Tyree; Martin H. Zimmermann (2003). Xylem Structure and the Ascent of Sap, 2nd ed., Springer. ISBN 3-540-43354-6.  recent update of the classic book on xylem transport by the late Martin Zimmermann
A digital object identifier (or DOI) is a standard for persistently identifying a piece of intellectual property on a digital network and associating it with related data, the metadata, in a structured extensible way. ...

  Results from FactBites:
 
Xylem - Wikipedia, the free encyclopedia (782 words)
In vascular plants, xylem is one of the two types of transport tissue in plants, phloem being the other one.
The word “xylem” is derived from classical Greek ξυλον, "wood", and indeed the best known xylem tissue is wood, though it is found throughout the plant.
Fossil plants with anatomically preserved xylem are known from the Silurian (more than 400 million years ago), and trace fossils resembling individual xylem cells may be found in earlier Ordovician rocks.
Xylem Tube EP - Wikipedia, the free encyclopedia (200 words)
The Xylem Tube EP is an early EP by electronic music artist Richard D. James, commonly known by his pseudonym of Aphex Twin.
It was his second release under the Aphex Twin alias on RandS Records of Belgium, the alias he used for all of his releases on this label.
Xylem Tube EP was released exclusively on vinyl in June 1992.
  More results at FactBites »

 
 

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