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xylem
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{{Short description|Water transport tissue in vascular plants}}{{For|the company|Xylem Inc.}}(File:Xylem and phloem diagram.svg|thumb|323x323px|Xylem (blue) transports water and minerals from the roots upwards.|alt=)Xylem is one of the two types of transport tissue in vascular plants, the other being phloem. The basic function of the xylem is to transport water from roots to stems and leaves, but it also transports nutrients.WEB, Purcell, Adam, Xylem and phloem,weblink Basic Biology, live,weblink 2016-05-04, BOOK, Handbook of Plant Science, 1, Keith Roberts, Illustrated, Wiley (publisher), John Wiley & Sons, 2007, 9780470057230, 185, The word xylem is derived from the Ancient Greek word (xylon), meaning "wood"; the best-known xylem tissue is wood, though it is found throughout a plant.BOOK, Providing for Energy: Report of the Twentieth Century Fund Task Force on United States Energy Policy,weblink registration, Richard B. Mancke, illustrated, Tata McGraw-Hill Education, 1977, 9780070656178, 42, The term was introduced by Carl Nägeli in 1858.JOURNAL, Nägeli, Carl, Das Wachstum des Stammes und der Wurzel bei den GefäÃpflanzen und die Anordnung der GefäÃstränge im Stengel, Beiträge zur Wissenschaftlichen Botanik (Contributions to Scientific Botany), 1858, 1, 1â156,weblink The growth of the stem and of the root among vascular plants and the arrangement of the vascular strands in the stalk, de, From p. 9: "Ich will die beiden welche von dem Cambium nach aussen und nach innen gebildet werden, Phloëm und Xylem nennen." (I will call the two parts of the permanent tissue, which are formed by the cambium outwardly and inwardly, "phloëm" and "xylem".)BOOK, 10.1007/978-3-642-73635-3_10, Phloem, Ontogeny, Cell Differentiation, and Structure of Vascular Plants, 287â368, 1989, Buvat, Roger, 978-3-642-73637-7, - the content below is remote from Wikipedia
- it has been imported raw for GetWiki
Structure
{{plain image with caption|Xylem cells.svg|Diagrammatic structure of xylem cells|400px|right}}The most distinctive xylem cells are the long tracheary elements that transport water. Tracheids and vessel elements are distinguished by their shape; vessel elements are shorter, and are connected together into long tubes that are called vessels.BOOK, Raven, Peter A., Evert, Ray F., Eichhorn, Susan E., 1999, Biology of Plants, W.H. Freeman and Company, 576â577, 978-1-57259-611-5, Xylem also contains two other type of cells: parenchyma and fibers.Xylem {{webarchive |url=https://web.archive.org/web/20110916145301weblink |date=2011-09-16 }}. Encyclopædia BritannicaXylem can be found:- in vascular bundles, present in non-woody plants and non-woody parts of woody plants
- in secondary xylem, laid down by a meristem called the vascular cambium in woody plants
- as part of a stelar arrangement not divided into bundles, as in many ferns.
Primary and secondary xylem
Primary xylem is formed during primary growth from procambium. It includes protoxylem and metaxylem. Metaxylem develops after the protoxylem but before secondary xylem. Metaxylem has wider vessels and tracheids than protoxylem.Secondary xylem 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:- conifers (Coniferae): there are approximately 600 known species of conifers.BOOK, Walter S. Judd, Plant systematics: A phylogenetic approach, 2002, W.H. Freeman, 0-87893-403-0, Walter S. Judd, 2, registration,weblink 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 used and marketed as softwood.
- angiosperms (Angiospermae): there are approximately 250,000 known species of angiosperms. Within this group secondary xylem is rare in the monocots.BOOK, Dickison, W.C., 2000, Integrative Plant Anatomy (page 196), Elsevier Science, 9780080508917,weblink live,weblink 2017-11-06, Many non-monocot angiosperms become trees, and the secondary xylem of these is used and marketed as hardwood.
Main function â upwards water transport
The xylem, vessels and tracheids of the roots, stems and leaves are interconnected to form a continuous system of water-conducting channels reaching all parts of the plants. The system transports water and soluble mineral nutrients from the roots throughout the plant. It is also used to replace water lost during transpiration and photosynthesis. Xylem sap consists mainly of water and inorganic ions, although it can also contain a number of organic chemicals as well. The transport is passive, not powered by energy spent by the tracheary elements themselves, which are dead by maturity and no longer have living contents. Transporting sap upwards becomes more difficult as the height of a plant increases and upwards transport of water by xylem is considered to limit the maximum height of trees.JOURNAL, Koch, George W., Sillett, Stephen C., Jennings, Gregory M., Davis, Stephen D., The limits to tree height, Nature, 2004, 428, 6985, 851â854, 10.1038/nature02417, 15103376, 2004Natur.428..851K, 11846291, Three phenomena cause xylem sap to flow:- Pressure flow hypothesis: Sugars produced in the leaves and other green tissues are kept in the phloem system, creating a solute pressure differential versus the xylem system carrying a far lower load of solutes- water and minerals. The phloem pressure can rise to several MPa,JOURNAL, Knoblauch, Michael, Knoblauch, Jan, Mullendore, Daniel L., Savage, Jessica A., Babst, Benjamin A., Beecher, Sierra D., Dodgen, Adam C., Jensen, Kaare H., Holbrook, N. Michele, 2016-06-02, Testing the Münch hypothesis of long distance phloem transport in plants, eLife, en, 5, e15341, 10.7554/eLife.15341, 2050-084X, 4946904, 27253062, free, far higher than atmospheric pressure. Selective inter-connection between these systems allows this high solute concentration in the phloem to draw xylem fluid upwards by negative pressure.
- {{anchor|Transpirational pull}}Transpirational pull: Similarly, the evaporation of water from the surfaces of mesophyll cells to the atmosphere also creates a negative pressure at the top of a plant. This 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 that of the soil, usually due to high concentrations of solute, water can move by osmosis into the root from the soil. 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 opening of stomata 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.JOURNAL, American Journal of Botany, 2000, 87, 1272â78, Root pressure and specific conductivity in temperate lianas: exotic Celastrus orbiculatus (Celastraceae) vs. Native Vitis riparia (Vitaceae), Tim J. Tibbetts, Frank W. Ewers, 10.2307/2656720, 10991898, 9, 2656720, free,
Cohesion-tension theory
The cohesion-tension theory is a theory of intermolecular attraction that explains the process of water flow upwards (against the force of gravity) through the xylem of plants. It was proposed in 1894 by John Joly and Henry Horatio Dixon.JOURNAL, Dixon, Henry H., Joly, J., On the ascent of sap, Annals of Botany, 1894, 8, 468â470,weblink JOURNAL, Dixon, Henry H., Joly, J., On the ascent of sap, Philosophical Transactions of the Royal Society of London, Series B, 1895, 186, 563â576,weblink 10.1098/rstb.1895.0012, free, Despite numerous objections,JOURNAL, Tyree, M.T., 1997, The Cohesion-Tension theory of sap ascent: current controversies, Journal of Experimental Botany, 48, 10, 1753â1765, 10.1093/jxb/48.10.1753, free, JOURNAL, Wang, Z., Chang, C.-C., Hong, S.-J., Sheng, Y.-J., Tsao, H.-K., 2012, Capillary Rise in a Microchannel of Arbitrary Shape and Wettability: Hysteresis Loop, Langmuir, 28, 49, 16917â16926, 10.1021/la3036242, 23171321, this is the most widely accepted theory for the transport of water through a plant's vascular system based on the classical research of Dixon-Joly (1894), Eugen Askenasy (1845â1903) (1895),JOURNAL, Askenasy, E., Ueber das Saftsteigen, On the ascent of sap, Botanisches Centralblatt, 1895, 62, 237â238, de,weblink JOURNAL, Askenasy, E., Ueber das Saftsteigen, Verhandlungen des Naturhistorisch-medizinischen Vereins zu Heidelberg (Proceedings of the Natural History-Medical Society at Heidelberg), 1895, 5, 325â345,weblink 2nd series, On the ascent of sap, de, and Dixon (1914,1924).BOOK, Dixon, H, Transpiration and the ascent of sap in plants, 1914, Macmillan and Co., London, England, UK,weblink BOOK, Dixon, H, The transpiration stream, 1924, University of London Press, Ltd, London, 80, Water is a polar molecule. When two water molecules approach one another, the slightly negatively charged oxygen atom of one forms a hydrogen bond with a slightly positively charged hydrogen atom in the other. This attractive force, along with other intermolecular forces, is one of the principal factors responsible for the occurrence of surface tension in liquid water. It also allows plants to draw water from the root through the xylem to the leaf.Water is constantly lost through transpiration from the leaf. When one water molecule is lost another is pulled along by the processes of cohesion and tension. Transpiration pull, utilizing capillary action and the inherent surface tension of water, is the primary mechanism of water movement in plants. However, it is not the only mechanism involved. Any use of water in leaves forces water to move into them.Transpiration in leaves creates tension (differential pressure) in the cell walls of mesophyll cells. Because of this tension, water is being pulled up from the roots into the leaves, helped by cohesion (the pull between individual water molecules, due to hydrogen bonds) and adhesion (the stickiness between water molecules and the hydrophilic cell walls of plants). This mechanism of water flow works because of water potential (water flows from high to low potential), and the rules of simple diffusion.BOOK, Campbell, Neil, Biology, 2002, Pearson Education, Inc., San Francisco, CA, 978-0-8053-6624-2, 759,weblink Over the past century, there has been a great deal of research regarding the mechanism of xylem sap transport; today, most plant scientists continue to agree that the cohesion-tension theory best explains this process, but multiforce theories that hypothesize several alternative mechanisms have been suggested, including longitudinal cellular and xylem osmotic pressure gradients, axial potential gradients in the vessels, and gel- and gas-bubble-supported interfacial gradients.JOURNAL, Zimmerman, Ulrich, What are the driving forces for water lifting in the xylem conduit?, Physiologia Plantarum, 2002, 10.1034/j.1399-3054.2002.1140301.x, 12060254, 114, 3, 327â335, JOURNAL, Tyree, Melvin T., The cohesion-tension theory of sap ascent: current controversies, Journal of Experimental Botany, 48, 10, 1753â1765, 1997, 10.1093/jxb/48.10.1753, free,Measurement of pressure
missing image!
- Pressurebomb.svg|right|thumb|300px|A diagram showing the setup of a pressure bombpressure bombUntil recently, the differential pressure (suction) of transpirational pull could only be measured indirectly, by applying external pressure with a pressure bomb to counteract it.weblink" title="web.archive.org/web/20090918110039weblink">The pressure of the water potential of the xylem in your plant's stem can be determined with the Scholander bomb. bio.usyd.edu.au When the technology to perform direct measurements with a pressure probe was developed, there was initially some doubt about whether the classic theory was correct, because some workers were unable to demonstrate negative pressures. More recent measurements do tend to validate the classic theory, for the most part. Xylem transport is driven by a combinationWEB,weblink Water Uptake and Transport in Vascular Plants, Andrew J. McElrone, Brendan Choat, Greg A. Gambetta, Craig R. Brodersen, 2013, The Nature Education Knowledge Project, of transpirational pull from above and root pressure from below, which makes the interpretation of measurements more complicated.
To photosynthesize, plants must absorb {{co2}} from the atmosphere. However, this comes at a price: while stomata are open to allow {{co2}} to enter, water can evaporate.JOURNAL, Sperry, J. S., Evolution of Water Transport and Xylem Structure, 3691719, International Journal of Plant Sciences, 164, 3, S115âS127, 2003, 10.1086/368398, 15314720, Water is lost much faster than {{co2}} is absorbed, so plants need to replace it, and have developed systems to transport water from the moist soil to the site of photosynthesis. Early plants sucked water between the walls of their cells, then evolved the ability to control water loss (and {{co2}} acquisition) through the use of stomata. Specialized water transport tissues soon evolved in the form of hydroids, tracheids, then secondary xylem, followed by an endodermis and ultimately vessels.The high {{co2}} levels of Silurian-Devonian times, when plants were first colonizing land, meant that the need for water was relatively low. As {{co2}} was withdrawn from the atmosphere by plants, more water was lost in its capture, and more elegant transport mechanisms evolved. As water transport mechanisms, and waterproof cuticles, evolved, plants could survive without being continually covered by a film of water. This transition from poikilohydry to homoiohydry opened up new potential for colonization. Plants then needed a robust internal structure that held long narrow channels for transporting water from the soil to all the different parts of the above-soil plant, especially to the parts where photosynthesis occurred.During the Silurian, {{co2}} was readily available, so little water needed expending to acquire it. By the end of the Carboniferous, when {{co2}} levels had lowered to something approaching today's, around 17 times more water was lost per unit of {{co2}} uptake. However, even in these "easy" early days, water was at a premium, and had to be transported to parts of the plant from the wet soil to avoid desiccation. This early water transport took advantage of the cohesion-tension mechanism inherent in water. Water has a tendency to diffuse to areas that are drier, and this process is accelerated when water can be wicked along a fabric with small spaces. In small passages, such as that between the plant cell walls (or in tracheids), a column of water behaves like rubber â when molecules evaporate from one end, they pull the molecules behind them along the channels. Therefore, transpiration alone provided the driving force for water transport in early plants. However, without dedicated transport vessels, the cohesion-tension mechanism cannot transport water more than about 2 cm, severely limiting the size of the earliest plants. This process demands a steady supply of water from one end, to maintain the chains; to avoid exhausting it, plants developed a waterproof cuticle. Early cuticle may not have had pores but did not cover the entire plant surface, so that gas exchange could continue. However, dehydration at times was inevitable; early plants cope with this by having a lot of water stored between their cell walls, and when it comes to it sticking out the tough times by putting life "on hold" until more water is supplied.- Pressurebomb.svg|right|thumb|300px|A diagram showing the setup of a pressure bombpressure bombUntil recently, the differential pressure (suction) of transpirational pull could only be measured indirectly, by applying external pressure with a pressure bomb to counteract it.weblink" title="web.archive.org/web/20090918110039weblink">The pressure of the water potential of the xylem in your plant's stem can be determined with the Scholander bomb. bio.usyd.edu.au When the technology to perform direct measurements with a pressure probe was developed, there was initially some doubt about whether the classic theory was correct, because some workers were unable to demonstrate negative pressures. More recent measurements do tend to validate the classic theory, for the most part. Xylem transport is driven by a combinationWEB,weblink Water Uptake and Transport in Vascular Plants, Andrew J. McElrone, Brendan Choat, Greg A. Gambetta, Craig R. Brodersen, 2013, The Nature Education Knowledge Project, of transpirational pull from above and root pressure from below, which makes the interpretation of measurements more complicated.
Evolution
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.{{citation needed|date=March 2019}} 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 vascular plants. Several groups of plants later developed pitted tracheid cells independently through convergent evolution. In living plants, pitted tracheids do not appear in development until the maturation of the metaxylem (following the protoxylem).In most plants, pitted tracheids function as the primary transport cells. The other type of vascular element, found in angiosperms, is the vessel element. Vessel elements are joined end to end to form vessels in which water flows unimpeded, as in a pipe. The presence of xylem vessels (also called tracheaWEB, Structure of Plants and Fungi{{!, Digitális Tankönyvtár|url=https://regi.tankonyvtar.hu/hu/tartalom/tamop412A/2011-0073_structure_of_plants_fungi/ch04s04.html|access-date=2021-04-02|website=regi.tankonyvtar.hu|language=hu}}{{Dead link|date=October 2023 |bot=InternetArchiveBot |fix-attempted=yes }}) is considered to be one of the key innovations that led to the success of the angiosperms.JOURNAL, Carlquist, S., E.L. Schneider, 2002, The tracheidâvessel element transition in angiosperms involves multiple independent features: cladistic consequences, American Journal of Botany, 89, 2, 185â195, 10.3732/ajb.89.2.185, 21669726, 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.BOOK, Cronquist, A., August 1988, The Evolution and Classification of Flowering Plants, New York, New York, New York Botanical Garden Press, 978-0-89327-332-3, Whether the absence of vessels in basal angiosperms is a primitive condition is contested, the alternative hypothesis states that vessel elements originated in a precursor to the angiosperms and were subsequently lost.ficusxylem.jpg -missing image!
- banded tube.jpg -
A banded tube from the late Silurian/early Devonian. The bands are difficult to see on this specimen, as an opaque carbonaceous coating conceals much of the tube. Bands are just visible in places on the left half of the image â click on the image for a larger view. Scale bar: 20 μm
To be free from the constraints of small size and constant moisture that the parenchymatic transport system inflicted, plants needed a more efficient water transport system. During the early Silurian, they developed specialized cells, which were lignified (or bore similar chemical compounds) to avoid implosion; this process coincided with cell death, allowing their innards to be emptied and water to be passed through them. These wider, dead, empty cells were a million times more conductive than the inter-cell method, giving the potential for transport over longer distances, and higher {{co2}} diffusion rates.The earliest macrofossils to bear water-transport tubes are Silurian plants placed in the genus Cooksonia.JOURNAL, Edwards, D., Davies, K.L., Axe, L., 1992, A vascular conducting strand in the early land plant Cooksonia, Nature, 357, 6380, 683â685, 10.1038/357683a0, 1992Natur.357..683E, 4264332, The early Devonian pretracheophytes Aglaophyton and Horneophyton have structures very similar to the hydroids of modern mosses.Plants continued to innovate new ways of reducing the resistance to flow within their cells, thereby increasing the efficiency of their water transport. Bands on the walls of tubes, in fact apparent from the early Silurian onwards,JOURNAL, Niklas, K. J., Smocovitis, V., Evidence for a Conducting Strand in Early Silurian (Llandoverian) Plants: Implications for the Evolution of the Land Plants, 2400461, Paleobiology, 9, 2, 126â137, 1983, 10.1017/S009483730000751X, 1983Pbio....9..126N, 35550235, are an early improvisation to aid the easy flow of water. Banded tubes, as well as tubes with pitted ornamentation on their walls, were lignified"MEMBERWIDE">- banded tube.jpg -
A banded tube from the late Silurian/early Devonian. The bands are difficult to see on this specimen, as an opaque carbonaceous coating conceals much of the tube. Bands are just visible in places on the left half of the image â click on the image for a larger view. Scale bar: 20 μm
Development
(File:Xylem Development.svg|thumb|upright=0.6|Patterns of xylem development: xylem in brown; arrows show direction of development from protoxylem to metaxylem.)Xylem development can be described by four terms: centrarch, exarch, endarch and mesarch. As it develops in young plants, its nature changes from protoxylem to metaxylem (i.e. from first xylem to after xylem). The patterns in which protoxylem and metaxylem are arranged is important in the study of plant morphology.{{anc|Proto}}Protoxylem and metaxylem
As a young vascular plant grows, one or more strands of primary xylem form in its stems and roots. The first xylem to develop is called 'protoxylem'. In appearance protoxylem is usually distinguished by narrower vessels formed of smaller cells. Some of these cells have walls which contain thickenings in the form of rings or helices. Functionally, protoxylem can extend: the cells are able to grow in size and develop while a stem or root is elongating. Later, 'metaxylem' develops in the strands of xylem. Metaxylem vessels and cells are usually larger; the cells have thickenings which are typically either in the form of ladderlike transverse bars (scalariform) or continuous sheets except for holes or pits (pitted). Functionally, metaxylem completes its development after elongation ceases when the cells no longer need to grow in size.BOOK, Foster, A.S., Gifford, E.M., 1974, Comparative Morphology of Vascular Plants, 2nd, San Francisco, W.H. Freeman, 978-0-7167-0712-7, 55â56,weblink BOOK, Taylor, T.N., Taylor, E.L., Krings, M., 2009, Paleobotany, the Biology and Evolution of Fossil Plants, 2nd, Amsterdam; Boston, Academic Press, 978-0-12-373972-8, 207ff., 212ff,Patterns of protoxylem and metaxylem
There are four main patterns to the arrangement of protoxylem and metaxylem in stems and roots.- Centrarch refers to the case in which the primary xylem forms a single cylinder in the center of the stem and develops from the center outwards. The protoxylem is thus found in the central core and the metaxylem in a cylinder around it.WEB, White, A. Toby, Kazlev, M. Alan, Glossary,weblink palaeos.com, dead,weblink" title="web.archive.org/web/20101220181617weblink">weblink December 20, 2010, This pattern was common in early land plants, such as "rhyniophytes", but is not present in any living plants.{{citation needed|date=February 2015}}
- Exarch is used when there is more than one strand of primary xylem in a stem or root, and the xylem develops from the outside inwards towards the center, i.e. centripetally. The metaxylem is thus closest to the center of the stem or root and the protoxylem closest to the periphery. The roots of vascular plants are normally considered to have exarch development.
- Endarch is used when there is more than one strand of primary xylem in a stem or root, and the xylem develops from the inside outwards towards the periphery, i.e. centrifugally. The protoxylem is thus closest to the center of the stem or root and the metaxylem closest to the periphery. The stems of seed plants typically have endarch development.
- Mesarch is used when there is more than one strand of primary xylem in a stem or root, and the xylem develops from the middle of a strand in both directions. The metaxylem is thus on both the peripheral and central sides of the strand with the protoxylem between the metaxylem (possibly surrounded by it). The leaves and stems of many ferns have mesarch development.
History
In his book De plantis libri XVI (On Plants, in 16 books) (1583), the Italian physician and botanist Andrea Cesalpino proposed that plants draw water from soil not by magnetism (ut magnes ferrum trahit, as magnetic iron attracts) nor by suction (vacuum), but by absorption, as occurs in the case of linen, sponges, or powders.See:- BOOK, Cesalpino, Andrea, De Plantis libri XVI, On Plants, in 16 books, 1583, Giorgio Marescotti, Florence, Italy, 4, la,weblink From p. 4: "An quædam sicca secundum naturam humorem trahunt? ut lintea, spongiæ, pulveres: ⦠" (Or [as] dry things attract [i.e., absorb] according to the liquid's nature? [such] as linen, sponges, powders: ⦠)
- BOOK, Bellorini, Cristina, The World of Plants in Renaissance Tuscany: Medicine and Botany, 2016, Routledge, Abingdon-on-Thames, England, 72,weblink 9781317011491,
- BOOK, Kramer, Paul J., Boyer, John S., Water Relations of Plants and Soils, 1995, Elsevier Science, London, England, 2,weblink 9780080924113, The Italian biologist Marcello Malpighi was the first person to describe and illustrate xylem vessels, which he did in his book Anatome plantarum ... (1675).See:
- BOOK, Malpighi, Marcello, Anatome Plantarum â¦, 1675, Royal Society of London, London, England, UK, 8,weblink la,
- JOURNAL, Jansen, Steven, Schenk, H. Jochen, On the ascent of sap in the presence of bubbles, American Journal of Botany, 2015, 102, 10, 1561â1563, 10.3732/ajb.1500305, 26400778, free,
- Lazenby, Elizabeth Mary (1995) "The Historia Plantarum Generalis of John Ray: Book I â a translation and commentary.", doctoral thesis, University of Newcastle upon Tyne, England, UK, vol. 1, p. 160. Available at: University of Newcastle upon Tyne, UK. {{Webarchive|url=https://web.archive.org/web/20180814103423weblink |date=2018-08-14 }}Malpighi first described xylem vessels and named tracheid cells. From p. 8 of (Malpighi, 1675): " ⦠haec tubulosa sunt & subrotunda, identidem tamen angustantur, & perpetuo patent, nullumque, ut observare potui, effundunt humorem: Argentea lamina L, in spiram contorta, componuntur, ut facile laceratione, (velut in bombycinis tracheis expertus sum,) in hanc oblongam & continuatam fasciam resolvantur. Lamina haec, si ulterius microscopio lustretur, particulis squamatim componitur; quod etiam in tracheis insectorum deprehenditur. Spiralibus hisce vasculis, seu ut verius loquar, tracheis, ligneae fibrae M adstant, quae secundum longitudinem productae, ad majorem firmitudinem & robur, transversalium utriculorum ordines N superequitant, ita ut fiat veluti storea." ( ⦠these [vessels] are tubular and somewhat round, yet often become narrow, and they are always open, and none, as [far as] I could perceive, exude a liquid: they are composed of silvery sheets L, twisted into a helix, although they can easily be unbound, by tearing, into this somewhat long and connected strip (just as I have done in silkworm treacheas). This sheet, if it be examined further with a microscope, is composed of scale-like particles; which likewise is observed in the tracheas of insects. On these helical vessels, or as I will more rightly say, "tracheas", there stand woody filaments M, which being extended in length straddle â for greater strength and hardness â lines of transverse cells N, so that it is constructed like a mat.) Although Malpighi believed that xylem contained only air, the British physician and botanist Nehemiah Grew, who was Malpighi's contemporary, believed that sap ascended both through the bark and through the xylem.BOOK, Grew, Nehemiah, The Anatomy of Plants â¦, 1682, W. Rawlins, London, England, 124â125,weblink From pp. 124â125: "For the great part of the year, it [i.e., the sap] riseth in the Barque [i.e., bark], sc. in the inner Margin adjacent to the Wood, and in the spring, in or through the Wood it self, and there only." However, according to Grew, capillary action in the xylem would raise the sap by only a few inches; in order to raise the sap to the top of a tree, Grew proposed that the parenchymal cells become turgid and thereby not only squeeze the sap in the tracheids but force some sap from the parenchyma into the tracheids.See:
- (Grew, 1682), p. 126. Grew recognized the limits of capillary action (from p. 126): " ⦠small Glass-Pipes [i.e., capillary tubes] immersed in Water, will give it [i.e., the water] an ascent for some inches; yet there is a certain period, according to the bore of the Pipe, beyond which it will not rise." Grew proposed the following mechanism for the ascent of sap in plants (from p. 126): "But the Bladders [i.e., parenchymal cells] DP, which surround it [i.e., the column of tracheids], being swelled up and turgid with Sap, do hereby press upon it; and so not only a little contract its bore, but also transfuse or strain some Portion of their Sap thereinto: by both which means, the Sap will be forced to rise higher therein."
- BOOK, Arber, Agnes, Oliver, Francis Wall, Makers of British Botany: A Collection of Biographies by Living Botanists, 1913, Cambridge University Press, Cambridge, England, 58,weblink Nehemiah Grew 1641â1712, In 1727, English clergyman and botanist Stephen Hales showed that transpiration by a plant's leaves causes water to move through its xylem.BOOK, Hales, Stephen, Vegetable Staticks: Or, an account of some statical experiments on the sap in vegetables: â¦, 1727, W. & J. Innys and T. Woodward, London, England, 100,weblink 9780356030128, Hales explained that although capillary action might help raise water within the xylem, transpiration caused water to actually move through the xylem.
-
(
- BOOK, Strasburger, Eduard, Histologische Beiträge, Histological Contributions, 1891, Gustav Fischer, Jena, Germany, de, 3: Ueber den Bau und die Verrichtungen der Leitungsbahnen in den Pflanzen [On the structure and the function of vascular bundles in plants], 607â625: Aufsteigen giftiger Flüssigkeiten bis zu bedeutender Höhe in der Pflanze [Ascent of poisonous liquids to considerable heights in plants], pp. 645â671: Die Leitungsfähigkeit getödteter Pflanzentheile [The ability of the killed parts of plants to conduct [water),weblink
- (Jansen & Schenck, 2015), p. 1561.
See also
- Phloem
- Soil plant atmosphere continuum
- Stele
- Suction
- Tylosis
- Vascular bundle
- Vascular tissue
- Xylem sap
Explanatory notes
{{Reflist|group=note}}References
Citations
{{Reflist}}General references
- JOURNAL, C. Wei, E. Steudle, M. T. Tyree, P. M. Lintilhac, The essentials of direct xylem pressure measurement, Plant, Cell and Environment
- JOURNAL, N. Michele Holbrook
, Negative Xylem Pressures in Plants: A Test of the Balancing Pressure Technique
- JOURNAL, Pockman, W.T., J.S. Sperry, J.W. O'Leary, Sustained and significant negative water pressure in xylem
- BOOK, Campbell, Neil A., Jane B. Reece, 2002, Biology, 6th, Benjamin Cummings, 978-0-8053-6624-2,weblink
- BOOK, Kenrick, Paul, Crane, Peter R., 1997, The Origin and Early Diversification of Land Plants: A Cladistic Study, Washington, D. C., Smithsonian Institution Press, 978-1-56098-730-7,
- JOURNAL, Muhammad, A. F., R. Sattler, 1982, Vessel Structure of Gnetum and the Origin of Angiosperms, American Journal of Botany, 69, 1004â21, 10.2307/2442898, 6, 2442898,
- BOOK, Melvin T. Tyree, Martin H. Zimmermann, Xylem Structure and the Ascent of Sap, 2nd, 978-3-540-43354-5, Springer, 2003, recent update of the classic book on xylem transport by the late Martin Zimmermann
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