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Sclereids are a reduced form of
sclerenchyma
The ground tissue of plants includes all tissues that are neither Epidermis (botany), dermal nor Vascular tissue, vascular. It can be divided into three types based on the nature of the cell walls.
# Parenchyma cells have thin primary walls and ...
cells with highly thickened, lignified
cellular walls that form small bundles of durable layers of tissue in most
plant
Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclud ...
s.
[Evert, Ray F; Eichhorn, Susan E. Esau's Plant Anatomy: Meristems, Cells, and Tissues of the Plant Body: Their Structure, Function, and Development. Publisher: Wiley-Liss 2006. ] The presence of numerous sclereids form the cores of
apple
An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple fruit tree, trees are agriculture, cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, wh ...
s and produce the gritty texture of
guava
Guava () is a common tropical fruit cultivated in many tropical and subtropical regions. The common guava ''Psidium guajava'' (lemon guava, apple guava) is a small tree in the myrtle family ( Myrtaceae), native to Mexico, Central America, the ...
s.
Although sclereids are variable in shape, the cells are generally isodiametric, prosenchymatic, forked, or elaborately branched. They can be grouped into bundles, can form complete tubes located at the periphery, or can occur as single cells or small groups of cells within
parenchyma
Parenchyma () is the bulk of functional substance in an animal organ or structure such as a tumour. In zoology it is the name for the tissue that fills the interior of flatworms.
Etymology
The term ''parenchyma'' is New Latin from the word π ...
tissues. An isolated sclereid cell is known as an idioblast. Sclereids are typically found in the
epidermis
The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the amount of water rele ...
,
ground tissue, and
vascular tissue.
The term "sclereid" was introduced by
Alexander Tschirch
Alexander Tschirch (17 October 1856 – 2 December 1939) was a German-Swiss pharmacist born in Guben.
He received pharmacy training in Dresden and at the ''Berner Staatsapotheke'' (Bern state apothecary). From 1878 to 1880 he studied at the U ...
in 1885.
Origin
Sclereids are created through belated
sclerosis of
parenchyma
Parenchyma () is the bulk of functional substance in an animal organ or structure such as a tumour. In zoology it is the name for the tissue that fills the interior of flatworms.
Etymology
The term ''parenchyma'' is New Latin from the word π ...
cells or can arise from sclereid primordia that are individualized early in development. Sclerification typically involves thickening of the cell wall, increasing rigidity. In the
phloem, when tissue ceases to function in conduction cells may begin sclerification. In vascular tissue, sclereids will develop from
cambial and procambial cells.
Stem sclereids
In the vascular region of the stem of ''
Hoya carnosa
''Hoya carnosa'', the porcelainflower or wax plant, is an asclepiad species of flowering plant in the dogbane family Apocynaceae. It is one of the many species of ''Hoya'' that are native to Eastern Asia and Australia. It is a common house plant ...
'', a column of sclereids can be found, and in the
pith of stems of ''
Hoya Hoya may refer to:
Places
*Hoya, Germany, a city in Lower Saxony, Germany
*County of Hoya, a former state in present Germany
* Hoya, Tokyo, now incorporated within Nishi-tokyo, Tokyo, Japan
* Hoya, Hpruso, a place in Hpruso Township, Kayah, Myanma ...
'' and ''
Podocarpus'' groups of sclereids can be found. These are sclereids with thick cell walls and numerous
pits, resembling adjacent parenchyma cells. This resemblance suggests that these sclereids are originally
parenchyma
Parenchyma () is the bulk of functional substance in an animal organ or structure such as a tumour. In zoology it is the name for the tissue that fills the interior of flatworms.
Etymology
The term ''parenchyma'' is New Latin from the word π ...
cells, but are so sclerified that they are now sclereid cells rather than parenchyma cells. These sclereids are an example of brachysclereids, or stone cells.
[
]
Leaf sclereids
Leaves contain a variety of types of sclereids. In the mesophyll
A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, ste ...
, two distinct sclereid structures are found. Sclereids in a diffuse pattern are dispersed throughout the leaf tissue, and sclereids in a terminal pattern are concentrated about the tips of leaf veins
A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...
. Sclereid formations in leaves include the branched sclereids of '' Trochodendron'', the columnar sclereids of ''Hakea
''Hakea'' ( ) is a genus of about 150 species of plants in the Family ''Proteaceae'', endemic to Australia. They are shrubs or small trees with leaves that are sometimes flat, otherwise circular in cross section in which case they are sometimes d ...
'', and the hair-like trichosclereids that branch into air chambers within the leaves of the water lily
Water lily or water lilies may refer to:
Plants
* Members of family Nymphaeaceae
* Formerly, members of the genus ''Nelumbo'' (the genus to which lotus belongs)
* Some members of the genus ''Nymphoides''
Other uses
* ''Water Lilies'' (Monet ...
and yellow pond lily
''Nuphar advena'' (spatterdock or cow lily or yellow pond-lily) is a species of ''Nuphar'' native throughout the eastern United States and in some parts of Canada, such as Nova Scotia.Flora of North America''Nuphar advena''/ref> It is similar to ...
. Sclereids can also form part of or the entire epidermis of foliar
A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, ste ...
structures such as the clove scales of ''Allium sativum
Garlic (''Allium sativum'') is a species of bulbous flowering plant in the genus ''Allium''. Its close relatives include the onion, shallot, leek, chive, Welsh onion and Chinese onion. It is native to South Asia, Central Asia and northeastern ...
''.[
Especially interesting are the sclereids in ]olive
The olive, botanical name ''Olea europaea'', meaning 'European olive' in Latin, is a species of small tree or shrub in the family Oleaceae, found traditionally in the Mediterranean Basin. When in shrub form, it is known as ''Olea europaea'' ...
leaves. They are typically in length and are thus named fiberlike sclereids. These sclereids permeate the mesophyll as a dense mat. During sclerification these fiberlike sclereid cells can increase by several hundred times their original size, compared to other parenchyma cells that only increase by two or three times.[
]
Fruit sclereids
Sclereids in fruits vary in form and use. In pear
Pears are fruits produced and consumed around the world, growing on a tree and harvested in the Northern Hemisphere in late summer into October. The pear tree and shrub are a species of genus ''Pyrus'' , in the family Rosaceae, bearing the p ...
s, sclereids from concentric clusters that grow about earlier formed sclereids. These pear sclereids, as well as sclereids within quince
The quince (; ''Cydonia oblonga'') is the sole member of the genus ''Cydonia'' in the Malinae subtribe (which also contains apples and pears, among other fruits) of the Rosaceae family (biology), family. It is a deciduous tree that bears hard ...
fruit, often form bordered pits when the cell wall increases in thickness during sclerification. In apple
An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple fruit tree, trees are agriculture, cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, wh ...
s, layers of elongated sclereids form the endocarp that encloses the seeds.[
]
Seed sclereids
The hardening of seed coats during ripening often occurs through sclerification, when the secondary cell walls are thickened in the epidermis and below the epidermis. Leguminous seeds are examples of such sclerification. Larger sclereids form columns in the epidermis of pea
The pea is most commonly the small spherical seed or the seed-pod of the flowering plant species ''Pisum sativum''. Each pod contains several peas, which can be green or yellow. Botanically, pea pods are fruit, since they contain seeds and d ...
, bean
A bean is the seed of several plants in the family Fabaceae, which are used as vegetables for human or animal food. They can be cooked in many different ways, including boiling, frying, and baking, and are used in many traditional dishes th ...
, and soybean
The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean, which has numerous uses.
Traditional unfermented food uses of soybeans include soy milk, from which tofu an ...
seeds, and bone-shaped osteosclereids occur beneath the epidermis. In the seedcoats of coconut
The coconut tree (''Cocos nucifera'') is a member of the palm tree family ( Arecaceae) and the only living species of the genus ''Cocos''. The term "coconut" (or the archaic "cocoanut") can refer to the whole coconut palm, the seed, or the ...
s, sclereids possess numerous bordered pits.[ These larger macrosclereids found in seedcoats are of protodermal origin.][
]
References
Further reading
*
* Moore, Randy; Clark, W. Dennis; and Vodopich, Darrell S. (1998). ''Botany'' (3rd ed.). McGraw-Hill. .
* Chrispeels MJ, Sadava DE. (2002) Plants, Genes and Crop Biotechnology. Jones and Bartlett Inc.,
{{DEFAULTSORT:Sclereid
Plant anatomy
Plant cells
Tissues (biology)