Ground tissue
Encyclopedia
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
s develop from ground tissue meristem
Meristem
A meristem is the tissue in most plants consisting of undifferentiated cells , found in zones of the plant where growth can take place....
and consists of three simple tissues:
- Parenchyma (cells with thin primary walls that retain their protoplasmProtoplasmProtoplasm is the living contents of a cell that is surrounded by a plasma membrane. It is a general term of the Cytoplasm . Protoplasm is composed of a mixture of small molecules such as ions, amino acids, monosaccharides and water, and macromolecules such as nucleic acids, proteins, lipids and...
) - Collenchyma (cells with thick primary walls that retain their protoplasm)
- Sclerenchyma (cells with lignified secondary walls that have lost their protoplasm at maturity, i.e. are 'dead')
Parenchyma
Parenchyma is the versatile ground tissue. It forms, for example, the cortexCortex (botany)
In botany, the cortex is the outer layer of the stem or root of a plant, bounded on the outside by the epidermis and on the inside by the endodermis. It is composed mostly of undifferentiated cells, usually large thin-walled parenchyma cells of the ground tissue system. The outer cortical cells...
and pith
Pith
Pith, or medulla, is a tissue in the stems of vascular plants. Pith is composed of soft, spongy parenchyma cells, which store and transport nutrients throughout the plant. In eudicots, pith is located in the center of the stem. In monocots, it extends also into flowering stems and roots...
of stems, the cortex of roots, the mesophyll
Mesophyll
Mesophyll can refer to:* Mesophyll tissue, in plant anatomy, photosynthetic parenchyma cells that lie between the upper and lower epidermis layers of a leaf...
of leaves, the pulp of fruits, and the endosperm
Endosperm
Endosperm is the tissue produced inside the seeds of most flowering plants around the time of fertilization. It surrounds the embryo and provides nutrition in the form of starch, though it can also contain oils and protein. This makes endosperm an important source of nutrition in human diet...
of seeds. Parenchyma cells are living cells and may remain meristematic at maturity, meaning that they are capable of differentiated cell division
Cell division
Cell division is the process by which a parent cell divides into two or more daughter cells . Cell division is usually a small segment of a larger cell cycle. This type of cell division in eukaryotes is known as mitosis, and leaves the daughter cell capable of dividing again. The corresponding sort...
if given the correct hormone stimulus. They have thin but flexible cellulose
Cellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....
cell wall
Cell wall
The cell wall is the tough, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism. A major function of the cell wall is to...
s, and are generally polyhedral when close-packed, but approximately spherical when isolated from their neighbors. They have large central vacuoles, which allows the cells to store and regulate ions, waste products and water.
Parenchyma cells have a variety of functions:
- In leavesLeafA leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....
, they form the mesophyllMesophyllMesophyll can refer to:* Mesophyll tissue, in plant anatomy, photosynthetic parenchyma cells that lie between the upper and lower epidermis layers of a leaf...
and are responsible for photosynthesisPhotosynthesisPhotosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
and the exchange of gases, parenchyma cells in the mesophyllMesophyllMesophyll can refer to:* Mesophyll tissue, in plant anatomy, photosynthetic parenchyma cells that lie between the upper and lower epidermis layers of a leaf...
of leaves are a specialized parenchymatous tissue known as chlorenchyma (parenchyma with chloroplasts). - Storage of starch, protein, fats and oils and water in roots, tubers (e.g. potatoPotatoThe potato is a starchy, tuberous crop from the perennial Solanum tuberosum of the Solanaceae family . The word potato may refer to the plant itself as well as the edible tuber. In the region of the Andes, there are some other closely related cultivated potato species...
), seed endospermEndospermEndosperm is the tissue produced inside the seeds of most flowering plants around the time of fertilization. It surrounds the embryo and provides nutrition in the form of starch, though it can also contain oils and protein. This makes endosperm an important source of nutrition in human diet...
(e.g. cerealCerealCereals are grasses cultivated for the edible components of their grain , composed of the endosperm, germ, and bran...
s) and cotyledonCotyledonA cotyledon , is a significant part of the embryo within the seed of a plant. Upon germination, the cotyledon may become the embryonic first leaves of a seedling. The number of cotyledons present is one characteristic used by botanists to classify the flowering plants...
s (e.g. pulses and groundnutPeanutThe peanut, or groundnut , is a species in the legume or "bean" family , so it is not a nut. The peanut was probably first cultivated in the valleys of Peru. It is an annual herbaceous plant growing tall...
) - SecretionSecretionSecretion is the process of elaborating, releasing, and oozing chemicals, or a secreted chemical substance from a cell or gland. In contrast to excretion, the substance may have a certain function, rather than being a waste product...
(e.g. hydathodeHydathodeA hydathode is a type of secretory tissue in leaves, usually of Angiosperms, that secretes water through pores in the epidermis or margin of leaves, typically at the tip of a marginal tooth or serration. They probably evolved from modified stomata...
s, nectaries and cells lining the inside of resin ducts) - Wound repair and the potential for renewed meristematic activity
- Other specialized functions such as aeration (aerenchymaAerenchymaAerenchyma is an air channel in the roots of some plants, which allows exchange of gases between the shoot and the root. The channel of large air-filled cavities provides a low-resistance internal pathway for the exchange of gases such as oxygen and ethylene between the plant above the water and...
) and support
The form of parenchyma cells varies with their function. The epidermal parenchyma cells of a leaf are barrel shaped in cross section, but have a variety of outline shapes ranging from simple polygons to strongly branched and interlocked shapes resembling the pieces of a jigsaw puzzle
Jigsaw puzzle
A jigsaw puzzle is a tiling puzzle that requires the assembly of numerous small, often oddly shaped, interlocking and tessellating pieces.Each piece usually has a small part of a picture on it; when complete, a jigsaw puzzle produces a complete picture...
, as in the leaves of Arabidopsis thaliana
Arabidopsis thaliana
Arabidopsis thaliana is a small flowering plant native to Europe, Asia, and northwestern Africa. A spring annual with a relatively short life cycle, arabidopsis is popular as a model organism in plant biology and genetics...
. In the epidermis of higher plants, only the guard cells have chloroplast
Chloroplast
Chloroplasts are organelles found in plant cells and other eukaryotic organisms that conduct photosynthesis. Chloroplasts capture light energy to conserve free energy in the form of ATP and reduce NADP to NADPH through a complex set of processes called photosynthesis.Chloroplasts are green...
s. This tissue serves as a barrier wall and protects the internal tissues from injury. In the spongy mesophyll
Mesophyll
Mesophyll can refer to:* Mesophyll tissue, in plant anatomy, photosynthetic parenchyma cells that lie between the upper and lower epidermis layers of a leaf...
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 the arms to form a three-dimensional network, as in the red kidney bean Phaseolus vulgaris and other mesophyte
Mesophyte
Mesophytes are terrestrial plants which are adapted to neither a particularly dry nor particularly wet environment. An example of a mesophytic habitat would be a rural temperate meadow, which might contain Goldenrod, Clover, Oxeye Daisy, and Rosa multiflora.Mesophytes make up the largest ecological...
s. These cells, with the epidermal
Epidermis (botany)
The epidermis is a single-layered group of cells that covers plants' leaves, flowers, roots and stems. It forms a boundary between the plant and the external environment. The epidermis serves several functions, it protects against water loss, regulates gas exchange, secretes metabolic compounds,...
guard cell
Guard cell
Guard cells are specialized cells located in the Leaf epidermis of plants. Pairs of guard cells surround tiny stomatal airway pores . These tiny holes in the surface of leaves are necessary for gas exchange into and out of the plant; carbon dioxide enters the plant allowing the carbon fixation...
s of the stoma
Stoma
In botany, a stoma is a pore, found in the leaf and stem epidermis that is used forgas exchange. The pore is bordered by a pair of specialized parenchyma cells known as guard cells that are responsible for regulating the size of the opening...
, form a system of air spaces and chambers that regulate the exchange of gases. They usually contain plastids.
Collenchyma
The name 'collenchyma' derives from the Greek word κολλα ("kól-la"), meaning "glue", which refers to the thick, glistening appearance of the walls in fresh tissues. Collenchyma tissue is composed of elongated cells with unevenly thickened wallsCell wall
The cell wall is the tough, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism. A major function of the cell wall is to...
. They provide structural support, particularly in growing shoot
Shoot
Shoots are new plant growth, they can include stems, flowering stems with flower buds, and leaves. The new growth from seed germination that grows upward is a shoot where leaves will develop...
s and leaves
Leaf
A leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....
. Collenchyma tissue composes, for example, the resilient strands in stalks of celery
Celery
Apium graveolens is a plant species in the family Apiaceae commonly known as celery or celeriac , depending on whether the petioles or roots are eaten: celery refers to the former and celeriac to the latter. Apium graveolens grows to 1 m tall...
. Its growth 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. The wall is made up of cellulose and pectin.
There are three principal 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)
- Lacunar collenchyma (have intercellular space and thickening proximal to the intercellular space)
Collenchyma cells are most often found adjacent to outer growing tissues, the vascular cambium
Vascular cambium
The vascular cambium is a part of the morphology of plants. It consists of cells that are partly specialized, for the tissues that transport water solutions, but have not reached any of the final forms that occur in their branch of the specialization graph...
and are known for increasing structural support and integrity.
Sclerenchyma
Sclerenchyma is a supporting tissue in plants. Two groups of sclerenchyma cells exist: fibres and sclereids. Their walls consist of celluloseCellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....
, hemicellulose and lignin
Lignin
Lignin or lignen is a complex chemical compound most commonly derived from wood, and an integral part of the secondary cell walls of plants and some algae. The term was introduced in 1819 by de Candolle and is derived from the Latin word lignum, meaning wood...
. Sclerenchyma cells are the principal, supporting cells in plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
tissues that have ceased elongation. Sclerenchyma fibres are of great economical importance, since they constitute the source material for many fabrics (flax
Flax
Flax is a member of the genus Linum in the family Linaceae. It is native to the region extending from the eastern Mediterranean to India and was probably first domesticated in the Fertile Crescent...
, hemp
Hemp
Hemp is mostly used as a name for low tetrahydrocannabinol strains of the plant Cannabis sativa, of fiber and/or oilseed varieties. In modern times, hemp has been used for industrial purposes including paper, textiles, biodegradable plastics, construction, health food and fuel with modest...
, jute
Jute
Jute is a long, soft, shiny vegetable fibre that can be spun into coarse, strong threads. It is produced from plants in the genus Corchorus, which has been classified in the family Tiliaceae, or more recently in Malvaceae....
, ramie
Ramie
Ramie is a flowering plant in the nettle family Urticaceae, native to eastern Asia. It is a herbaceous perennial growing to 1–2.5 m tall; the leaves are heart-shaped, 7–15 cm long and 6–12 cm broad, and white on the underside with dense small hairs—this gives it a silvery appearance;...
).
Unlike the collenchyma, mature sclerenchyma is composed of dead cells with extremely thick cell wall
Cell wall
The cell wall is the tough, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism. A major function of the cell wall is to...
s (secondary walls) that make up to 90% of the whole cell volume. The term "sclerenchyma" is derived from the Greek σκληρός ("sklē-rós"), 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 fibres and sclereids is not always clear. Transitions do exist, sometimes even within one and the same plant.
Fibres
Fibres 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 fibres. 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 ropeRope
A rope is a length of fibres, twisted or braided together to improve strength for pulling and connecting. It has tensile strength but is too flexible to provide compressive strength...
s, fabric
Textile
A textile or cloth is a flexible woven material consisting of a network of natural or artificial fibres often referred to as thread or yarn. Yarn is produced by spinning raw fibres of wool, flax, cotton, or other material to produce long strands...
s or mattress
Mattress
A mattress is a manufactured product to sleep or lie on, consisting of resilient materials and covered with an outer fabric or ticking. In the developed world it is typically part of a bed set and is placed upon a foundation....
es. The fibres of flax
Flax
Flax is a member of the genus Linum in the family Linaceae. It is native to the region extending from the eastern Mediterranean to India and was probably first domesticated in the Fertile Crescent...
(Linum usitatissimum) have been known in Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
and Egypt
Egypt
Egypt , officially the Arab Republic of Egypt, Arabic: , is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Southwest Asia. Egypt is thus a transcontinental country, and a major power in Africa, the Mediterranean Basin, the Middle East and the Muslim world...
for more than 3000 years, those of hemp
Hemp
Hemp is mostly used as a name for low tetrahydrocannabinol strains of the plant Cannabis sativa, of fiber and/or oilseed varieties. In modern times, hemp has been used for industrial purposes including paper, textiles, biodegradable plastics, construction, health food and fuel with modest...
(Cannabis sativa) in China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
for just as long. These fibres, and those of jute
Jute
Jute is a long, soft, shiny vegetable fibre that can be spun into coarse, strong threads. It is produced from plants in the genus Corchorus, which has been classified in the family Tiliaceae, or more recently in Malvaceae....
(Corchorus capsularis) and ramie
Ramie
Ramie is a flowering plant in the nettle family Urticaceae, native to eastern Asia. It is a herbaceous perennial growing to 1–2.5 m tall; the leaves are heart-shaped, 7–15 cm long and 6–12 cm broad, and white on the underside with dense small hairs—this gives it a silvery appearance;...
(Boehmeria nivea, a nettle
Nettle
Nettles constitute between 24 and 39 species of flowering plants of the genus Urtica in the family Urticaceae, with a cosmopolitan though mainly temperate distribution. They are mostly herbaceous perennial plants, but some are annual and a few are shrubby...
), are extremely soft and elastic and are especially well suited for the processing to textile
Textile
A textile or cloth is a flexible woven material consisting of a network of natural or artificial fibres often referred to as thread or yarn. Yarn is produced by spinning raw fibres of wool, flax, cotton, or other material to produce long strands...
s. Their principal cell wall material is cellulose
Cellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....
.
Contrasting are hard fibres that are mostly found in monocots. Typical examples are the fibres of many Gramineae
Poaceae
The Poaceae is a large and nearly ubiquitous family of flowering plants. Members of this family are commonly called grasses, although the term "grass" is also applied to plants that are not in the Poaceae lineage, including the rushes and sedges...
, Agave
Agave
Agave is a genus of monocots. The plants are perennial, but each rosette flowers once and then dies ; they are commonly known as the century plant....
s (sisal
Sisal
Sisal is an agave that yields a stiff fibre traditionally used in making twine, rope and also dartboards. The term may refer either to the plant or the fibre, depending on context...
: Agave sisalana), lilies (Yucca or Phormium tenax), Musa textilis and others. Their cell walls contain, besides cellulose, a high proportion of lignin
Lignin
Lignin or lignen is a complex chemical compound most commonly derived from wood, and an integral part of the secondary cell walls of plants and some algae. The term was introduced in 1819 by de Candolle and is derived from the Latin word lignum, meaning wood...
. The load-bearing capacity of Phormium tenax is as high as 20–25 kg/mm2, the same as that of good steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
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
Linum is a genus of approximately 200 species in the flowering plant family Linaceae, native to temperate and subtropical regions of the world. It includes the Common Flax Linum (flax) is a genus of approximately 200 species in the flowering plant family Linaceae, native to temperate and...
. Starting at the centre of the fibre are the thickening layers of the secondary wall 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 fibres.
Fibres usually originate from meristematic tissues. Cambium
Cambium (botany)
A cambium , in botany, is a tissue layer that provide undifferentiated cells for plant growth. It forms parallel rows of cells, which result in secondary tissues....
and procambium are their main centers of production. They are usually associated with the xylem
Xylem
Xylem is one of the two types of transport tissue in vascular plants. . The word xylem is derived from the Classical Greek word ξυλον , meaning "wood"; the best-known xylem tissue is wood, though it is found throughout the plant...
and phloem
Phloem
In vascular plants, phloem is the living tissue that carries organic nutrients , in particular, glucose, a sugar, to all parts of the plant where needed. In trees, the phloem is the innermost layer of the bark, hence the name, derived from the Greek word "bark"...
of the vascular bundles. The fibres of the xylem are always lignified, while those of the phloem are cellulosic. Reliable evidence for the fibre cells' evolutionary origin from tracheids 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 reduced. Fibres that do not belong to the xylem are bast (outside the ring of cambium) and such fibres that are arranged in characteristic patterns at different sites of the shoot.
Sclereids
Sclereids are a reduced form of scleremchyma cells with highly thickened, lignified walls.They are small bundles of sclerenchyma tissue in plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
s that form durable layers, such as the cores of apple
Apple
The apple is the pomaceous fruit of the apple tree, species Malus domestica in the rose family . It is one of the most widely cultivated tree fruits, and the most widely known of the many members of genus Malus that are used by humans. Apple grow on small, deciduous trees that blossom in the spring...
s and the gritty texture of pear
Pear
The pear is any of several tree species of genus Pyrus and also the name of the pomaceous fruit of these trees. Several species of pear are valued by humans for their edible fruit, but the fruit of other species is small, hard, and astringent....
s. Sclereids are much elongated and flexilble with tapered ends.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
Parenchyma
Parenchyma is a term used to describe a bulk of a substance. It is used in different ways in animals and in plants.The term is New Latin, f. Greek παρέγχυμα - parenkhuma, "visceral flesh", f. παρεγχεῖν - parenkhein, "to pour in" f. para-, "beside" + en-, "in" + khein, "to pour"...
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 pear
Pear
The pear is any of several tree species of genus Pyrus and also the name of the pomaceous fruit of these trees. Several species of pear are valued by humans for their edible fruit, but the fruit of other species is small, hard, and astringent....
s (Pyrus communis) and quince
Quince
The quince , or Cydonia oblonga, is the sole member of the genus Cydonia and native to warm-temperate southwest Asia in the Caucasus region...
s (Cydonia oblonga) and those of the shoot of the wax-plant
Wax-plant
Hoya carnosa, the wax plant, is a species in the family family Apocynaceae , . It is one of the many species of Hoya that are native to Eastern Asia and Australia...
(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 drupe
Drupe
In botany, a drupe is a fruit in which an outer fleshy part surrounds a shell of hardened endocarp with a seed inside. These fruits develop from a single carpel, and mostly from flowers with superior ovaries...
s like cherries
Cherry
The cherry is the fruit of many plants of the genus Prunus, and is a fleshy stone fruit. The cherry fruits of commerce are usually obtained from a limited number of species, including especially cultivars of the wild cherry, Prunus avium....
or plum
Plum
A plum or gage is a stone fruit tree in the genus Prunus, subgenus Prunus. The subgenus is distinguished from other subgenera in the shoots having a terminal bud and solitary side buds , the flowers in groups of one to five together on short stems, and the fruit having a groove running down one...
s are made up from sclereids.
Note: Used to protect other cells!