![Stem-histology-cross-section-tag](https://upload.wikimedia.org/wikipedia/commons/9/92/Stem-histology-cross-section-tag.svg)
The ground tissue of plants includes all tissues that are neither
dermal
The dermis or corium is a layer of skin between the epidermis (with which it makes up the cutis) and subcutaneous tissues, that primarily consists of dense irregular connective tissue and cushions the body from stress and strain. It is divided ...
nor
vascular
The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away f ...
. It can be divided into three types based on the nature of the cell walls.
# Parenchyma cells have thin
primary walls and usually remain alive after they become mature. Parenchyma forms the "filler" tissue in the soft parts of plants, and is usually present in
cortex
Cortex or cortical may refer to:
Biology
* Cortex (anatomy), the outermost layer of an organ
** Cerebral cortex, the outer layer of the vertebrate cerebrum, part of which is the ''forebrain''
*** Motor cortex, the regions of the cerebral cortex i ...
,
pericycle
The pericycle is a cylinder of parenchyma or sclerenchyma cells that lies just inside the endodermis and is the outer most part of the stele of plants.
Although it is composed of non-vascular parenchyma cells, it's still considered part of the va ...
,
pith
Pith, or medulla, is a tissue in the stems of vascular plants. Pith is composed of soft, spongy parenchyma cells, which in some cases can store starch. In eudicotyledons, pith is located in the center of the stem. In monocotyledons, it ext ...
, and
medullary rays in primary
stem and
root
In vascular plants, the roots are the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often below the su ...
.
# Collenchyma cells have thin primary walls with some areas of secondary thickening. Collenchyma provides extra mechanical and structural support, particularly in regions of new growth.
# Sclerenchyma cells have thick
lignified secondary walls and often die when mature. Sclerenchyma provides the main structural support to a plant.
Parenchyma
Parenchyma is a versatile ground tissue that generally constitutes the "filler" tissue in soft parts of plants. It forms, among other things, the
cortex
Cortex or cortical may refer to:
Biology
* Cortex (anatomy), the outermost layer of an organ
** Cerebral cortex, the outer layer of the vertebrate cerebrum, part of which is the ''forebrain''
*** Motor cortex, the regions of the cerebral cortex i ...
(outer region) and
pith
Pith, or medulla, is a tissue in the stems of vascular plants. Pith is composed of soft, spongy parenchyma cells, which in some cases can store starch. In eudicotyledons, pith is located in the center of the stem. In monocotyledons, it ext ...
(central region) of stems, the cortex of roots, 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, s ...
of leaves, the pulp of fruits, and the
endosperm of
seeds. Parenchyma cells are often living cells and may remain
meristematic
The meristem is a type of tissue found in plants. It consists of undifferentiated cells (meristematic cells) capable of cell division. Cells in the meristem can develop into all the other tissues and organs that occur in plants. These cells conti ...
, meaning that they are capable of
cell division
Cell division is the process by which a parent cell divides into two daughter cells. Cell division usually occurs as part of a larger cell cycle in which the cell grows and replicates its chromosome(s) before dividing. In eukaryotes, there ar ...
if stimulated. They have thin and flexible
cellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell w ...
cell walls and are generally
polyhedral when close-packed, but can be roughly spherical when isolated from their neighbors. Parenchyma cells are generally large. They have large
central vacuole
A vacuole () is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic mo ...
s, which allow the cells to store and regulate
ions
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...
, waste products, and
water
Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...
. Tissue specialised for food storage is commonly formed of parenchyma cells.
Parenchyma cells have a variety of functions:
* In
leaves, they form two layers of
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, s ...
cells immediately beneath the epidermis of the leaf, that are responsible for
photosynthesis
Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...
and the exchange of gases.
These layers are called the palisade parenchyma and spongy mesophyll. Palisade parenchyma cells can be either cuboidal or elongated. Parenchyma cells 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, s ...
of leaves are specialised parenchyma cells called chlorenchyma cells (parenchyma cells with chloroplasts). Parenchyma cells are also found in other parts of the plant.
* Storage of starch, protein, fats, oils and water in roots, tubers (e.g.
potatoes), seed
endosperm (e.g.
cereals) and
cotyledon
A cotyledon (; ; ; , gen. (), ) is a significant part of the embryo within the seed of a plant, and is defined as "the embryonic leaf in seed-bearing plants, one or more of which are the first to appear from a germinating seed." The num ...
s (e.g.
pulses
In medicine, a pulse represents the tactile arterial palpation of the cardiac cycle (heartbeat) by trained fingertips. The pulse may be palpated in any place that allows an artery to be compressed near the surface of the body, such as at the nec ...
and
peanut
The peanut (''Arachis hypogaea''), also known as the groundnut, goober (US), pindar (US) or monkey nut (UK), is a legume crop grown mainly for its edible seeds. It is widely grown in the tropics and subtropics, important to both small and ...
s)
*
Secretion (e.g. the parenchyma cells lining the inside of
resin ducts)
* Wound repair and the potential for renewed
meristematic
The meristem is a type of tissue found in plants. It consists of undifferentiated cells (meristematic cells) capable of cell division. Cells in the meristem can develop into all the other tissues and organs that occur in plants. These cells conti ...
activity
* Other specialised functions such as
aeration
Aeration (also called aerification or aeriation) is the process by which air is circulated through, mixed with or dissolved in a liquid or other substances that act as a fluid (such as soil). Aeration processes create additional surface area in ...
(
aerenchyma
Aerenchyma or aeriferous parenchyma or lacunae, is a modification of the parenchyma to form a spongy tissue that creates spaces or air channels in the leaves, stems and roots of some plants, which allows exchange of gases between the shoot and th ...
) provides buoyancy and helps aquatic plants float.
* Chlorenchyma cells carry out photosynthesis and manufacture food.
The shape of parenchyma cells varies with their function. In the spongy
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, s ...
of a leaf, parenchyma cells range from near-spherical and loosely arranged with large intercellular spaces,
to branched or
stellate, mutually interconnected with their neighbours at the ends of their arms to form a three-dimensional network, like in the red kidney bean ''
Phaseolus vulgaris'' and other
mesophyte Mesophytes are terrestrial plants which are neither adapted to particularly dry nor particularly wet environments. An example of a mesophytic habitat would be a rural temperate meadow, which might contain goldenrod, clover, oxeye daisy, and ''Rosa ...
s.
[Jeffree CE, Read N, Smith JAC and Dale JE (1987). Water droplets and ice deposits in leaf intercellular spaces: redistribution of water during cryofixation for scanning electron microscopy. Planta 172, 20-37] These cells, along with the
epidermal
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 relea ...
guard cell
Guard cells are specialized plant cells in the epidermis of leaves, stems and other organs that are used to control gas exchange. They are produced in pairs with a gap between them that forms a stomatal pore. The stomatal pores are largest when ...
s of the
stoma, form a system of air spaces and chambers that regulate the exchange of gases. In some works, the cells of the leaf epidermis are regarded as specialised parenchymal cells,
[Hill, J. Ben; Overholts, Lee O; Popp, Henry W. Grove Jr., Alvin R. Botany. A textbook for colleges. Publisher: MacGraw-Hill 1960] but the modern preference has long been to classify the epidermis as
plant dermal tissue, and parenchyma as ground tissue.
[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. ]
Shapes of parenchyma:
* Polyhedral (found in pallisade tissue of the leaf)
* Spherical
* Stellate (found in stem of plants and have well developed air spaces between them)
* Elongated (also found in pallisade tissue of leaf)
* Lobed (found in spongy and pallisade mesophyll tissue of some plants)
Collenchyma
![Plant cell type collenchyma](https://upload.wikimedia.org/wikipedia/commons/9/97/Plant_cell_type_collenchyma.png)
Collenchyma tissue is composed of elongated cells with irregularly thickened
walls
Walls may refer to:
*The plural of wall, a structure
*Walls (surname), a list of notable people with the surname
Places
* Walls, Louisiana, United States
* Walls, Mississippi, United States
* Walls, Ontario, neighborhood in Perry, Ontario, C ...
. They provide structural support, particularly in growing
shoot
In botany, a plant shoot consists of any plant stem together with its appendages, leaves and lateral buds, flowering stems, and flower buds. The new growth from seed germination that grows upward is a shoot where leaves will develop. In the sp ...
s and
leaves. Collenchyma tissue makes up things such as the resilient strands in stalks of
celery
Celery (''Apium graveolens'') is a marshland plant in the family Apiaceae that has been cultivated as a vegetable since antiquity. Celery has a long fibrous stalk tapering into leaves. Depending on location and cultivar, either its stalks, ...
. Collenchyma cells are usually living, and have only a thick
primary cell wall made up of cellulose and pectin. Cell wall thickness is strongly affected by mechanical stress upon the plant. The walls of collenchyma in shaken plants (to mimic the effects of wind etc.), may be 40–100% thicker than those not shaken.
There are four main types of collenchyma:
* Angular collenchyma (thickened at intercellular contact points)
* Tangential collenchyma (cells arranged into ordered rows and thickened at the tangential face of the cell wall)
* Annular collenchyma (uniformly thickened cell walls)
* Lacunar collenchyma (collenchyma with intercellular spaces)
Collenchyma cells are most often found adjacent to outer growing tissues such as the
vascular cambium
The vascular cambium is the main growth tissue in the stems and roots of many plants, specifically in dicots such as buttercups and oak trees, gymnosperms such as pine trees, as well as in certain other vascular plants. It produces secondary xy ...
and are known for increasing structural support and integrity.
The first use of "collenchyma" () was by
Link (1837) who used it to describe the sticky substance on ''
Bletia'' (Orchidaceae) pollen. Complaining about Link's excessive nomenclature,
Schleiden
Schleiden is a town in North Rhine-Westphalia, Germany. It lies in the Eifel hills, in the district of Euskirchen, and has 12,998 inhabitants as of 30 June 2017. Schleiden is connected by a tourist railway to Kall, on the Eifel Railway between ...
(1839) stated mockingly that the term "collenchyma" could have more easily been used to describe elongated sub-epidermal cells with unevenly thickened cell walls.
Sclerenchyma
Sclerenchyma is the tissue which makes the plant hard and stiff. Sclerenchyma is the supporting tissue in
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 exclu ...
s. Two types of sclerenchyma cells exist: fibers cellular and
sclereid
Sclereids are a reduced form of sclerenchyma cells with highly thickened, lignified cellular walls that form small bundles of durable layers of tissue in most plants.Evert, Ray F; Eichhorn, Susan E. Esau's Plant Anatomy: Meristems, Cells, and T ...
s. Their
cell walls consist of
cellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell w ...
,
hemicellulose
A hemicellulose (also known as polyose) is one of a number of heteropolymers (matrix polysaccharides), such as arabinoxylans, present along with cellulose in almost all terrestrial plant cell walls.Scheller HV, Ulvskov Hemicelluloses.// Annu Rev ...
, and
lignin. Sclerenchyma cells are the principal supporting cells in plant tissues that have ceased elongation. Sclerenchyma fibers are of great economic importance, since they constitute the source material for many fabrics (e.g.
flax,
hemp,
jute, and
ramie
Ramie (pronounced: , ; from Malay ) is a flowering plant in the nettle family Urticaceae, native to eastern Asia. It is a herbaceous perennial growing to tall; ).
Unlike the collenchyma, mature sclerenchyma is composed of dead cells with extremely thick cell walls (
secondary walls) that make up to 90% of the whole cell volume. The term ''sclerenchyma'' is derived from the Greek σκληρός (''sklērós''), meaning "hard." It is the hard, thick walls that make sclerenchyma cells important strengthening and supporting elements in plant parts that have ceased elongation. The difference between sclereids is not always clear: transitions do exist, sometimes even within the same plant.
Fibers
![Plant cell type sclerenchyma fibers](https://upload.wikimedia.org/wikipedia/commons/0/07/Plant_cell_type_sclerenchyma_fibers.png)
Fibers or
bast are generally long, slender, so-called prosenchymatous cells, usually occurring in strands or bundles. Such bundles or the totality of a stem's bundles are colloquially called fibers. Their high load-bearing capacity and the ease with which they can be processed has since antiquity made them the source material for a number of things, like
rope
A rope is a group of yarns, plies, fibres, or strands that are twisted or braided together into a larger and stronger form. Ropes have tensile strength and so can be used for dragging and lifting. Rope is thicker and stronger than similar ...
s,
fabrics
Textile is an umbrella term that includes various fiber-based materials, including fibers, yarns, filaments, threads, different fabric types, etc. At first, the word "textiles" only referred to woven fabrics. However, weaving is not the ...
and
mattresses. The fibers of
flax (''Linum usitatissimum'') have been known in
Europe
Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located entirel ...
and
Egypt
Egypt ( ar, مصر , ), officially the Arab Republic of Egypt, is a transcontinental country spanning the northeast corner of Africa and southwest corner of Asia via a land bridge formed by the Sinai Peninsula. It is bordered by the Medit ...
for more than 3,000 years, those of
hemp (''Cannabis sativa'') in
China for just as long. These fibers, and those of
jute (''Corchorus capsularis'') and
ramie
Ramie (pronounced: , ; from Malay ) is a flowering plant in the nettle family Urticaceae, native to eastern Asia. It is a herbaceous perennial growing to tall; (''Boehmeria nivea'', a
nettle
{{redirect, Nettle
Nettle refers to plants with stinging hairs, particularly those of the genus '' Urtica''. It can also refer to plants which resemble ''Urtica'' species in appearance but do not have stinging hairs. Plants called "nettle" includ ...
), are extremely soft and elastic and are especially well suited for the processing to
textile
Textile is an umbrella term that includes various fiber-based materials, including fibers, yarns, filaments, threads, different fabric types, etc. At first, the word "textiles" only referred to woven fabrics. However, weaving is not the ...
s. Their principal cell wall material is
cellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell w ...
.
Contrasting are hard fibers that are mostly found in
monocot
Monocotyledons (), commonly referred to as monocots, (Lilianae ''sensu'' Chase & Reveal) are grass and grass-like flowering plants (angiosperms), the seeds of which typically contain only one Embryo#Plant embryos, embryonic leaf, or cotyledon. Th ...
s. Typical examples are the fiber of many
grasses
Poaceae () or Gramineae () is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in lawns ...
, ''Agave sisalana'' (
sisal
Sisal (, ) (''Agave sisalana'') is a species of flowering plant native to southern Mexico, but widely cultivated and naturalized in many other countries. It yields a stiff fibre used in making rope and various other products. The term sisal may ...
), ''
Yucca
''Yucca'' is a genus of perennial plant, perennial shrubs and trees in the family (biology), family Asparagaceae, subfamily Agavoideae. Its 40–50 species are notable for their Rosette (botany), rosettes of evergreen, tough, sword-shaped Leaf, ...
'' or ''
Phormium tenax
''Phormium tenax'' (called flax in New Zealand English; in Māori; New Zealand flax outside New Zealand; and New Zealand hemp in historical nautical contexts) is an evergreen perennial plant native to New Zealand and Norfolk Island that is an i ...
'', ''
Musa textilis
Musa may refer to:
Places
*Mūša, a river in Lithuania and Latvia
*Musa, Azerbaijan, a village in Yardymli Rayon
*Musa, Iran, a village in Ilam Province
*Musa, Chaharmahal and Bakhtiari, Iran
*Musa, Kerman, Iran
*Musa, Bukan, West Azerbaijan Pro ...
'' and others. Their cell walls contain, besides cellulose, a high proportion of
lignin. The load-bearing capacity of ''Phormium tenax'' is as high as 20–25 kg/mm², the same as that of good
steel wire (25 kg/ mm²), but the fibre tears as soon as too great a strain is placed upon it, while the wire distorts and does not tear before a strain of 80 kg/mm². The thickening of a cell wall has been studied in ''
Linum
''Linum'' (flax) is a genus of approximately 200 species[''Linum''.]
The Jepson Manual. ''. Starting at the centre of the fiber, the thickening layers of the secondary wall are deposited one after the other. Growth at both tips of the cell leads to simultaneous elongation. During development the layers of secondary material seem like tubes, of which the outer one is always longer and older than the next. After completion of growth, the missing parts are supplemented, so that the wall is evenly thickened up to the tips of the fibers.
Fibers usually originate from
meristematic
The meristem is a type of tissue found in plants. It consists of undifferentiated cells (meristematic cells) capable of cell division. Cells in the meristem can develop into all the other tissues and organs that occur in plants. These cells conti ...
tissues.
Cambium
A cambium (plural cambia or cambiums), in plants, is a tissue layer that provides partially undifferentiated cells for plant growth. It is found in the area between xylem and phloem. A cambium can also be defined as a cellular plant tissue from w ...
and
procambium
The meristem is a type of tissue found in plants. It consists of undifferentiated cells (meristematic cells) capable of cell division. Cells in the meristem can develop into all the other tissues and organs that occur in plants. These cells conti ...
are their main centers of production. They are usually associated with the
xylem
Xylem is one of the two types of transport tissue in vascular plants, the other being phloem. The basic function of xylem is to transport water from roots to stems and leaves, but it also transports nutrients. The word ''xylem'' is derived from ...
and
phloem
Phloem (, ) is the living tissue in vascular plants that transports the soluble organic compounds made during photosynthesis and known as ''photosynthates'', in particular the sugar sucrose, to the rest of the plant. This transport process is c ...
of the vascular bundles. The fibers of the xylem are always
lignified, while those of the phloem are
cellulosic. Reliable evidence for the fibre cells' evolutionary origin from
tracheid
A tracheid is a long and tapered lignified cell in the xylem of vascular plants. It is a type of conductive cell called a tracheary element. Angiosperms use another type of tracheary element, called vessel elements, to transport water through th ...
s exists. During evolution the strength of the tracheid cell walls was enhanced, the ability to conduct water was lost and the size of the pits was reduced. Fibers that do not belong to the xylem are bast (outside the ring of cambium) and such fibers that are arranged in characteristic patterns at different sites of the shoot.
The term "sclerenchyma" (originally ''Sclerenchyma'') was introduced by
Mettenius in 1865.
[Mettenius, G. 1865. Über die Hymenophyllaceae. ''Abhandlungen der Mathematisch-Physischen Klasse der Königlich-Sächsischen Gesellschaft der Wissenschaften'' 11: 403-504, pl. 1-5]
link
Sclereids
![Plant cell type sclerenchyma sclereid](https://upload.wikimedia.org/wikipedia/commons/1/1a/Plant_cell_type_sclerenchyma_sclereid.png)
Sclereids are the reduced form of sclerenchyma cells with highly thickened, lignified walls.
They are small bundles of sclerenchyma tissue in
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 exclu ...
s that form durable layers, such as the cores of
apple
An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple trees are cultivated worldwide and are the most widely grown species in the genus ''Malus''. The tree originated in Central Asia, where its wild ancestor, ' ...
s and the gritty texture of
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 po ...
s (''Pyrus communis''). Sclereids are variable in shape. The cells can be 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 tissues. But compared with most fibres, sclereids are relatively short. Characteristic examples are
brachysclereids or the stone cells (called stone cells because of their hardness) of pears and
quinces (''Cydonia oblonga'') and those of the shoot of the
wax plant (''Hoya carnosa''). The cell walls fill nearly all the cell's volume. A layering of the walls and the existence of branched pits is clearly visible. Branched pits such as these are called ramiform pits. The shell of many seeds like those of nuts as well as the stones of
drupes like
cherries and
plums are made up from sclereids.
These structures are used to protect other cells.
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.,
{{Biological tissue
Plant anatomy
Plant cells
Tissues (biology)