HOME

TheInfoList




A vessel element or vessel member (also called trachea or xylem vessel) is one of the cell types found in
xylem Xylem is one of the two types of transport tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North Ame ...

xylem
, the water conducting tissue of plants. Vessel elements are typically found in angiosperms (
flowering plant Flowering plants include multiple members of the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greec ...

flowering plant
s) but absent from most
gymnosperm The gymnosperms ( lit. revealed seeds) are a group of seed-producing plants that includes conifers Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also ...
s such as
conifers Conifers are a group of cone-bearing seed plants The spermatophytes (; ), also known as phanerogams (taxon Phanerogamae) or phaenogams (taxon Phaenogamae), comprise those plant Plants are predominantly photosynthetic Photosynthesi ...

conifers
. Vessel elements are the main feature distinguishing the "
hardwood Hardwood is wood Wood is a porous and fibrous structural tissue found in the stems and roots of tree In botany, a tree is a perennial plant with an elongated Plant stem, stem, or trunk (botany), trunk, supporting branches and ...

hardwood
" of angiosperms from the "
softwood Scots Pine, a typical and well-known softwood Softwood is wood Wood is a porous and fibrous structural tissue found in the stems and roots of tree In botany, a tree is a perennial plant with an elongated Plant stem, stem, or t ...
" of conifers.


Morphology

Xylem Xylem is one of the two types of transport tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North Ame ...

Xylem
is the tissue in
vascular plant Vascular plants (from Latin ''vasculum'': duct), also known as Tracheophyta (the tracheophytes , from Greek τραχεῖα ἀρτηρία ''trācheia artēria'' 'windpipe' + φυτά ''phutá'' 'plants'), form a large group of plants ( 300,000 ...
s which conducts water (and substances dissolved in it) upwards in a plant. There are two kinds of cell which are involved in the actual transport:
tracheid A tracheid is a long and tapered lignified cell in the xylem Xylem is one of the two types of transport in s, the other being . The basic function of xylem is to transport from roots to stems and leaves, but it also transports . The word ' ...
s and vessel elements. Tracheids & vessel elements make the tracheary elements of xylem. Vessel elements are the building blocks of vessels, which constitute the major part of the water transporting system in those plants in which they occur. Vessels form an efficient system for transporting water (including necessary minerals) from the root to the leaves and other parts of the plant. In secondary xylem – the xylem which is produced as a stem thickens rather than when it first appears – a vessel element originates from the
vascular cambium The vascular cambium is the main growth tissue Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North America * ...
. A long cell, oriented along the axis of the stem, called a "fusiform initial", divides along its length forming new vessel elements. The cell wall of a vessel element becomes strongly "lignified", i.e. it develops reinforcing material made of
lignin Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and Bark (botany), bark, because they l ...

lignin
. The side walls of a vessel element have pits: more or less circular regions in contact with neighbouring cells. Tracheids also have pits, but only vessel elements have openings at both ends that connect individual vessel elements to form a continuous tubular vessel. These end openings are called perforations or perforation plates. They have a variety of shapes: the most common are the simple perforation (a simple opening) and the scalariform perforation (several elongated openings in a ladder-like design). Other types include the foraminate perforation plate (several round openings) and the reticulate perforation plate (a net-like pattern, with many openings). At maturity, the protoplast – the living material of the cell – dies and disappears, but the lignified cell walls persist. A vessel element is then a dead cell, but one that still has a function, and is still being protected by surrounding living cells.


Evolutionary significance

The presence of vessels in xylem has been considered to be one of the key innovations that led to the success of the flowering plants. It was once thought that vessel elements were an evolutionary innovation of flowering plants, but their absence from some basal
angiosperms Flowering plants include multiple members of the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greec ...
and their presence in some members of the
Gnetales ''Gnetum'' is a genus of gymnosperms, the sole genus in the family Gnetaceae and order Gnetales. They are tropical evergreen trees, shrub A shrub (or bush, but this is more of a gardening term) is a small- to medium-sized perennial woody ...
suggest that this hypothesis must be re-examined; vessel elements in Gnetales may not be homologous with those of angiosperms, or vessel elements that originated in a precursor to the angiosperms may have been subsequently lost in some basal lineages (e.g.,
Amborellaceae ''Amborella'' is a monotypic In biology, a monotypic taxon is a taxonomic group ( taxon) that contains only one immediately subordinate taxon. A monotypic species In biology, a species is the basic unit of biological classification, cla ...
,
Trochodendraceae Trochodendraceae is the only family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families is to maintain the well-being of its members and ...
, and
Winteraceae Winteraceae is a primitive family In human society, family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of families is to main ...
), described by
Arthur Cronquist Arthur John Cronquist (March 19, 1919 – March 22, 1992) was an American biologist, botanist Botany, also called , plant biology or phytology, is the science of plant life and a branch of biology. A botanist, plant scientist or phytol ...
as "primitively vesselless". Cronquist considered the vessels of ''
Gnetum ''Gnetum'' is a genus of gymnosperm The gymnosperms ( Greek language, lit. revealed seeds) are a group of Spermatophyte, seed-producing plants that includes Pinophyta, conifers, cycads, ''Ginkgo'', and gnetophyta, gnetophytes, forming the cla ...
'' to be convergent with those of angiosperms. Vessel-like cells have also been found in the xylem of ''
Equisetum ''Equisetum'' (; horsetail, snake grass, puzzlegrass) is the only living genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study ...

Equisetum
'' (horsetails), ''
Selaginella ''Selaginella'' is the sole genus of vascular plants in the family Selaginellaceae, the spikemosses or lesser clubmosses. This family is distinguished from Lycopodiaceae (the clubmosses) by having scale-leaves bearing a ligule and by having h ...
'' (spike-mosses), ''
Pteridium aquilinum ''Pteridium aquilinum'' (bracken Bracken (''Pteridium'') is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank In biological classification In biology, taxonomy () is the scientific study of nami ...

Pteridium aquilinum
'' (bracken fern), ''
Marsilea ''Marsilea'' is a genus of approximately 65 species of Aquatic plant, aquatic ferns of the family Marsileaceae. The name honours Italian naturalist Luigi Ferdinando Marsili (1656–1730). These small plants are of unusual appearance and do not re ...
'' and ''
Regnellidium Regnellidium is a monotypic genus of ferns of family Marsileaceae. The single living species, ''Regnellidium diphyllum'', the two-leaf water fern, is native to southeastern Brazil and adjacent regions of Argentina. It resembles its relatives fro ...
'' (
aquatic fern The order Salviniales (formerly known as the Hydropteridales and including the former Marsileales) is an order of fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) tha ...
s), and the enigmatic fossil group Gigantopteridales. In these cases, it is generally agreed that the vessels evolved independently. It is possible that vessels may have appeared more than once among the angiosperms as well.


See also

*
Tracheid A tracheid is a long and tapered lignified cell in the xylem Xylem is one of the two types of transport in s, the other being . The basic function of xylem is to transport from roots to stems and leaves, but it also transports . The word ' ...


References


Further references

* Niklas, Karl J. (1997) ''The Evolutionary Biology of Plants''. Chicago and London: The University of Chicago Press. . * Schweingruber, F.H. (1990) ''Anatomie europäischer Hölzer - Anatomy of European woods.'' Eidgenössische Forschungsanstalt für Wald, Schnee und Landscaft, Birmensdorf (Hrsg,). Haupt, Bern und Stuttgart. * Timonen, Tuuli (2002). ''Introduction to Microscopic Wood Identification''. Finnish Museum of Natural History, University of Helsinki. * {{Biological tissue Plant anatomy Wood