Cork is an impermeable buoyant material, the phellem layer of bark tissue, harvested for commercial use from Quercus suber, endemic to southwest Europe and northwest Africa. Cork is composed of a hydrophobic substance; because of its impermeable, buoyant and fire retardant properties, it is used in a variety of products, the most common of, wine stoppers. The montado landscape of Portugal produces half of cork harvested annually worldwide, with Corticeira Amorim being the leading company in the industry. Cork was examined microscopically by Robert Hooke, which led to his discovery and naming of the cell. There are about 2,200,000 hectares of cork forest worldwide. Annual production is about 200,000 tons. Once the trees are about 25 years old the cork is traditionally stripped from the trunks every nine years, with the first two harvests producing lower quality cork; the trees live for about 300 years. The cork industry is regarded as environmentally friendly. Cork production is considered sustainable because the cork tree is not cut down to obtain cork.
The tree continues to grow. The sustainability of production and the easy recycling of cork products and by-products are two of its most distinctive aspects. Cork oak forests prevent desertification and are a particular habitat in the Iberian Peninsula and the refuge of various endangered species. Carbon footprint studies conducted by Corticeira Amorim, Oeneo Bouchage of France and the Cork Supply Group of Portugal concluded that cork is the most environmentally friendly wine stopper in comparison to other alternatives; the Corticeira Amorim’s study, in particular, was developed by PricewaterhouseCoopers, according to ISO 14040. Results concluded that, concerning the emission of greenhouse gases, each plastic stopper released 10 times more CO2, whilst an aluminium screw cap releases 26 times more CO2 than does a cork stopper; the cork oak is unrelated to the "cork trees", which have corky bark but are not used for cork production. Cork is extracted only from early May to late August, when the cork can be separated from the tree without causing permanent damage.
When the tree reaches 25–30 years of age and about 24 in in circumference, the cork can be removed for the first time. However, this first harvest always produces poor quality or "virgin" cork. Bark from initial harvests can be used to make flooring, shoes and other industrial products. Subsequent extractions occur at intervals of 9 years, though it can take up to 13 for the cork to reach an acceptable size. If the product is of high quality it is known as "gentle" cork, ideally, is used to make stoppers for wine and champagne bottles; the workers who specialize in removing the cork are known as extractors. An extractor uses a sharp axe to make two types of cuts on the tree: one horizontal cut around the plant, called a crown or necklace, at a height of about 2–3 times the circumference of the tree, several vertical cuts called rulers or openings; this is the most delicate phase of the work because though cutting the cork requires significant force, the extractor must not damage the underlying phellogen or the tree will be harmed.
To free the cork from the tree, the extractor pushes the handle of the axe into the rulers. A good extractor needs to use a firm but precise touch in order to free a large amount of cork without damaging the product or tree; these freed portions of the cork are called planks. The planks are carried off by hand since cork forests are accessible to vehicles; the cork is stacked in piles in the forest or in yards at a factory and traditionally left to dry, after which it can be loaded onto a truck and shipped to a processor. Cork's elasticity combined with its near-impermeability makes it suitable as a material for bottle stoppers for wine bottles. Cork stoppers represent about 60% of all cork based production. Cork has an zero Poisson's ratio, which means the radius of a cork does not change when squeezed or pulled. Cork is an excellent gasket material; some carburetor float bowl gaskets are made for example. Cork is an essential element in the production of badminton shuttlecocks. Cork's bubble-form structure and natural fire retardant make it suitable for acoustic and thermal insulation in house walls, floors and facades.
The by-product of more lucrative stopper production, corkboard is gaining popularity as a non-allergenic, easy-to-handle and safe alternative to petrochemical-based insulation products. Sheets of cork often the by-product of stopper production, are used to make bulletin boards as well as floor and wall tiles. Cork's low density makes it a suitable material for fishing floats and buoys, as well as handles for fishing rods. Granules of cork can be mixed into concrete; the composites made by mixing cork granules and cement have lower thermal conductivity, lower density and good energy absorption. Some of the property ranges of the composites are density, compressive strength and flexural strength; as late as the mid-17th century, French vintners did not use cork stoppers, using instead oil-soaked rag
Vascular plants known as tracheophytes, form a large group of plants that are defined as those land plants that have lignified tissues for conducting water and minerals throughout the plant. They have a specialized non-lignified tissue to conduct products of photosynthesis. Vascular plants include the clubmosses, ferns and angiosperms. Scientific names for the group include Tracheophyta and Equisetopsida sensu lato; the term higher plants should be avoided as a synonym for vascular plants as it is a remnant of the abandoned concept of the great chain of being. Vascular plants are defined by three primary characteristics: Vascular plants have vascular tissues which distribute resources through the plant; this feature allows vascular plants to evolve to a larger size than non-vascular plants, which lack these specialized conducting tissues and are thereby restricted to small sizes. In vascular plants, the principal generation phase is the sporophyte, which produce spores and is diploid. By contrast, the principal generation phase in non-vascular plants is the gametophyte, which produces gametes and is haploid.
They have true roots and stems if one or more of these traits are secondarily lost in some groups. The formal definition of the division Tracheophyta encompasses both these characteristics in the Latin phrase "facies diploida xylem et phloem instructa". One possible mechanism for the presumed switch from emphasis on the haploid generation to emphasis on the diploid generation is the greater efficiency in spore dispersal with more complex diploid structures. In other words, elaboration of the spore stalk enabled the production of more spores, enabled the development of the ability to release them higher and to broadcast them farther; such developments may include more photosynthetic area for the spore-bearing structure, the ability to grow independent roots, woody structure for support, more branching. A proposed phylogeny of the vascular plants after Kenrick and Crane is as follows, with modification to the gymnosperms from Christenhusz et al. Pteridophyta from Smith et al. and lycophytes and ferns by Christenhusz et al.
This phylogeny is supported by several molecular studies. Other researchers state that taking fossils into account leads to different conclusions, for example that the ferns are not monophyletic. Water and nutrients in the form of inorganic solutes are drawn up from the soil by the roots and transported throughout the plant by the xylem. Organic compounds such as sucrose produced by photosynthesis in leaves are distributed by the phloem sieve tube elements; the xylem consists of vessels in flowering plants and tracheids in other vascular plants, which are dead hard-walled hollow cells arranged to form files of tubes that function in water transport. A tracheid cell wall contains the polymer lignin; the phloem however consists of living cells called sieve-tube members. Between the sieve-tube members are sieve plates, which have pores to allow molecules to pass through. Sieve-tube members lack such organs as nuclei or ribosomes, but cells next to them, the companion cells, function to keep the sieve-tube members alive.
The most abundant compound in all plants, as in all cellular organisms, is water which serves an important structural role and a vital role in plant metabolism. Transpiration is the main process of water movement within plant tissues. Water is transpired from the plant through its stomata to the atmosphere and replaced by soil water taken up by the roots; the movement of water out of the leaf stomata creates a transpiration pull or tension in the water column in the xylem vessels or tracheids. The pull is the result of water surface tension within the cell walls of the mesophyll cells, from the surfaces of which evaporation takes place when the stomata are open. Hydrogen bonds exist between water molecules; the draw of water upwards may be passive and can be assisted by the movement of water into the roots via osmosis. Transpiration requires little energy to be used by the plant. Transpiration assists the plant in absorbing nutrients from the soil as soluble salts. Living root cells passively absorb water in the absence of transpiration pull via osmosis creating root pressure.
It is possible for there to be no evapotranspiration and therefore no pull of water towards the shoots and leaves. This is due to high temperatures, high humidity, darkness or drought. Xylem and phloem tissues are involved in the conduction processes within plants. Sugars are conducted throughout the plant in the phloem and other nutrients through the xylem. Conduction occurs from a source to a sink for each separate nutrient. Sugars are produced in the leaves by photosynthesis and transported to the growing shoots and roots for use in growth, cellular respiration or storage. Minerals are transported to the shoots to allow cell division and growth. Fern allies Non-vascular plant “Higher plants” or “vascular plants”
A vessel element or vessel member is one of the cell types found in xylem, the water conducting tissue of plants. Vessel elements are found in flowering plants but absent from most gymnosperms such as conifers. Vessel elements are the main feature distinguishing the "hardwood" of angiosperms from the "softwood" of conifers. Xylem is the tissue in vascular plants. There are two kinds of cell which are involved in the actual transport: tracheids and vessel elements. 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 from the root to the leaves and other parts of the plant. In secondary xylem – the xylem, produced as a stem thickens rather than when it first appears – a vessel element originates from the vascular cambium. 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 "lignified", i.e. it develops reinforcing material made of lignin. The side walls of a vessel element have pits: more or less circular regions in contact with neighbouring cells. Tracheids 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 and the scalariform perforation. Other types include the reticulate perforation plate. At maturity the protoplast – the living material of the cell – dies and disappears, but the lignified cell walls persist. A vessel element is a dead cell, but one that still has a function, is still being protected by surrounding living cells; 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 and their presence in some members of the Gnetales suggest that this hypothesis must be re-examined.
Cronquist considered the vessels of Gnetum to be convergent with those of angiosperms. Vessel-like cells have been found in the xylem of Equisetum, Pteridium aquilinum and Regnellidium, the enigmatic fossil group Gigantopteridales. In these cases, it is agreed that the vessels evolved independently, it is possible. Tracheid Niklas, Karl J; the Evolutionary Biology of Plants. Chicago and London: The University of Chicago Press. ISBN 0-226-58082-2. Schweingruber, F. H. Anatomie europäischer Hölzer - Anatomy of European woods. Eidgenössische Forschungsanstalt für Wald, Schnee und Landscaft, Birmensdorf. Haupt, Bern und Stuttgart. Timonen, Tuuli. Introduction to Microscopic Wood Identification. Finnish Museum of Natural History, University of Helsinki. Wilson, K.. B.. The Anatomy of Wood: Its Diversity and Variability. London: Stobart & Son Ltd. ISBN 0-85442-033-9
In vascular plants, phloem is the living tissue that transports the soluble organic compounds made during photosynthesis and known as photosynthates, in particular the sugar sucrose, to parts of the plant where needed. This transport process is called translocation. In trees, the phloem is the innermost layer of the bark, hence the name, derived from the Greek word φλοιός meaning "bark"; the term was introduced by Nägeli in 1858. Phloem tissue consists of conducting cells called sieve elements, parenchyma cells, including both specialized companion cells or albuminous cells and unspecialized cells and supportive cells, such as fibres and sclereids. Sieve elements are the type of cell that are responsible for transporting sugars throughout the plant. At maturity they lack a nucleus and have few organelles, so they rely on companion cells or albuminous cells for most of their metabolic needs. Sieve tube cells do contain vacuoles and other organelles, such as ribosomes, before they mature, but these migrate to the cell wall and dissolve at maturity.
One of the few organelles they do contain at maturity is the rough endoplasmic reticulum, which can be found at the plasma membrane nearby the plasmodesmata that connect them to their companion or albuminous cells. All sieve cells have groups of pores at their ends that grow from modified and enlarged plasmodesmata, called sieve areas; the pores are reinforced by platelets of a polysaccharide called callose. They are of two types and chlorenchyma. Other parenchyma cells within the phloem are undifferentiated and used for food storage; the metabolic functioning of sieve-tube members depends on a close association with the companion cells, a specialized form of parenchyma cell. All of the cellular functions of a sieve-tube element are carried out by the companion cell, a typical nucleate plant cell except the companion cell has a larger number of ribosomes and mitochondria; the dense cytoplasm of a companion cell is connected to the sieve-tube element by plasmodesmata. The common sidewall shared by a sieve tube element and a companion cell has large numbers of plasmodesmata.
There are two types of companion cells. Ordinary companion cells, which have smooth walls and few or no plasmodesmatal connections to cells other than the sieve tube. Transfer cells, which have much-folded walls that are adjacent to non-sieve cells, allowing for larger areas of transfer, they are specialized in scavenging solutes from those in the cell walls that are pumped requiring energy. Albuminous cells have a similar role to companion cells, but are associated with sieve cells only and are hence found only in seedless vascular plants and gymnosperms. Although its primary function is transport of sugars, phloem may contain cells that have a mechanical support function; these fall into two categories: fibres and sclereids. Both cell types are therefore dead at maturity; the secondary cell wall increases their tensile strength. Bast fibres are the long, narrow supportive cells that provide tension strength without limiting flexibility, they are found in xylem, are the main component of many textiles such as paper and cotton.
Sclereids are irregularly shaped cells that add compression strength but may reduce flexibility to some extent. They serve as anti-herbivory structures, as their irregular shape and hardness will increase wear on teeth as the herbivores chews. For example, they are responsible for the gritty texture in pears, in winter bears Unlike xylem, the phloem is composed of still-living cells that transport sap; the sap is a water-based solution, but rich in sugars made by photosynthesis. These sugars are transported to non-photosynthetic parts of the plant, such as the roots, or into storage structures, such as tubers or bulbs. During the plant's growth period during the spring, storage organs such as the roots are sugar sources, the plant's many growing areas are sugar sinks; the movement in phloem is multidirectional. After the growth period, when the meristems are dormant, the leaves are sources, storage organs are sinks. Developing seed-bearing organs are always sinks; because of this multi-directional flow, coupled with the fact that sap cannot move with ease between adjacent sieve-tubes, it is not unusual for sap in adjacent sieve-tubes to be flowing in opposite directions.
While movement of water and minerals through the xylem is driven by negative pressures most of the time, movement through the phloem is driven by positive hydrostatic pressures. This process is termed translocation, is accomplished by a process called phloem loading and unloading. Phloem sap is thought to play a role in sending informational signals throughout vascular plants. "Loading and unloading patterns are determined by the conductivity and number of plasmodesmata and the position-dependent function of solute-specific, plasma membrane transport proteins. Recent evidence indicates that mobile proteins and RNA are part of the plant's long-distance communication signaling system. Evidence exists for the directed transport and sorting of macromolecules as they pass through plasmodesmata."Organic molecules such as sugars, amino acids, certain hormones, messenger RNAs are transported in the phloem through sieve tube elements. Because phloem tubes are located outside the xylem in most plants, a tree or other plant can be killed by stripping away the bark in a ring on the trunk or stem.
With the phloem destroyed, nutrients cannot reach the
In a vascular plant, the stele is the central part of the root or stem containing the tissues derived from the procambium. These include vascular tissue, in some cases ground tissue and a pericycle, which, if present, defines the outermost boundary of the stele. Outside the stele lies the endodermis, the innermost cell layer of the cortex; the concept of the stele was developed in the late 19th century by French botanists P. E. L. van Tieghem and H. Doultion as a model for understanding the relationship between the shoot and root, for discussing the evolution of vascular plant morphology. Now, at the beginning of the 21st century, plant molecular biologists are coming to understand the genetics and developmental pathways that govern tissue patterns in the stele. Moreover, physiologists are examining how the anatomy of different steles affect the function of organs; the earliest vascular plants had stems with a central core of vascular tissue. This consisted of a cylindrical strand of xylem, surrounded by a region of phloem.
Around the vascular tissue there might have been an endodermis that regulated the flow of water into and out of the vascular system. Such an arrangement is termed a protostele. There are three basic types of protostele: haplostele – consisting of a cylindrical core of xylem surrounded by a ring of phloem. An endodermis surrounds the stele. A centrarch haplostele is prevalent in members such as Rhynia. Actinostele – a variation of the protostele in which the core is lobed or fluted; this stele is found in many species of club moss. Actinosteles are exarch and consist of several to many patches of protoxylem at the tips of the lobes of the metaxylem. Exarch protosteles are a defining characteristic of the lycophyte lineage. Plectostele – a protostele in which plate-like regions of xylem appear in transverse section surrounded by phloem tissue. In fact, these discrete plates are interconnected in longitudinal section; some modern club mosses have plectosteles in their stems. The plectostele may be derived from the actinostele.
Siphonosteles have a region of ground tissue called the pith internal to xylem. The vascular strand comprises a cylinder surrounding the pith. Siphonosteles have interruptions in the vascular strand where leaves originate. Siphonosteles can be ectophloic or they can be amphiphloic. Among living plants, many ferns and some Asterid flowering plants have an amphiphloic stele. An amphiphloic siphonostele can be called a: solenostele – if the cylinder of vascular tissue contains no more than one leaf gap in any transverse section; this type of stele is found in fern stems today. Dictyostele – if multiple gaps in the vascular cylinder exist in any one transverse section; the numerous leaf gaps and leaf traces give a dictyostele the appearance of many isolated islands of xylem surrounded by phloem. Each of the isolated units of a dictyostele can be called a meristele. Among living plants, this type of stele is found only in the stems of ferns. Most seed plant stems possess a vascular arrangement, interpreted as a derived siphonostele, is called a eustele – in this arrangement, the primary vascular tissue consists of vascular bundles in one or two rings around the pith.
In addition to being found in stems, the eustele appears in the roots of monocot flowering plants. The vascular bundles in a eustele can be bicollateral. There is a variant of the eustele found in monocots like maize and rye; the variation is called an atactostele. However, it is just a variant of the eustele. Vascular tissue Vascular bundle
Cellular differentiation is the process where a cell changes from one cell type to another. The cell changes to a more specialized type. Differentiation occurs numerous times during the development of a multicellular organism as it changes from a simple zygote to a complex system of tissues and cell types. Differentiation continues in adulthood as adult stem cells divide and create differentiated daughter cells during tissue repair and during normal cell turnover; some differentiation occurs in response to antigen exposure. Differentiation changes a cell's size, membrane potential, metabolic activity, responsiveness to signals; these changes are due to controlled modifications in gene expression and are the study of epigenetics. With a few exceptions, cellular differentiation never involves a change in the DNA sequence itself. Thus, different cells can have different physical characteristics despite having the same genome. A specialized type of differentiation, known as'terminal differentiation', is of importance in some tissues, for example vertebrate nervous system, striated muscle and gut.
During terminal differentiation, a precursor cell capable of cell division, permanently leaves the cell cycle, dismantles the cell cycle machinery and expresses a range of genes characteristic of the cell's final function. Differentiation may continue to occur after terminal differentiation if the capacity and functions of the cell undergo further changes. Among dividing cells, there are multiple levels of cell potency, the cell's ability to differentiate into other cell types. A greater potency indicates a larger number of cell types. A cell that can differentiate into all cell types, including the placental tissue, is known as totipotent. In mammals, only the zygote and subsequent blastomeres are totipotent, while in plants, many differentiated cells can become totipotent with simple laboratory techniques. A cell that can differentiate into all cell types of the adult organism is known as pluripotent; such cells are called meristematic cells in higher plants and embryonic stem cells in animals, though some groups report the presence of adult pluripotent cells.
Virally induced expression of four transcription factors Oct4, Sox2, c-Myc, KIF4 is sufficient to create pluripotent cells from adult fibroblasts. A multipotent cell is one that can differentiate into multiple different, but related cell types. Oligopotent cells are more restricted than multipotent, but can still differentiate into a few related cell types. Unipotent cells can differentiate into only one cell type, but are capable of self-renewal. In cytopathology, the level of cellular differentiation is used as a measure of cancer progression. "Grade" is a marker of. Three basic categories of cells make up the mammalian body: germ cells, somatic cells, stem cells; each of the 37.2 trillion cells in an adult human has its own copy or copies of the genome except certain cell types, such as red blood cells, that lack nuclei in their differentiated state. Most cells are diploid; such cells, called somatic cells, make up most such as skin and muscle cells. Cells differentiate to specialize for different functions.
Germ line cells are any line of cells that give rise to gametes—eggs and sperm—and thus are continuous through the generations. Stem cells, on the other hand, have the ability to divide for indefinite periods and to give rise to specialized cells, they are best described in the context of normal human development. Development begins when a sperm fertilizes an egg and creates a single cell that has the potential to form an entire organism. In the first hours after fertilization, this cell divides into identical cells. In humans four days after fertilization and after several cycles of cell division, these cells begin to specialize, forming a hollow sphere of cells, called a blastocyst; the blastocyst has an outer layer of cells, inside this hollow sphere, there is a cluster of cells called the inner cell mass. The cells of the inner cell mass go on to form all of the tissues of the human body. Although the cells of the inner cell mass can form every type of cell found in the human body, they cannot form an organism.
These cells are referred to as pluripotent. Pluripotent stem cells undergo further specialization into multipotent progenitor cells that give rise to functional cells. Examples of stem and progenitor cells include: Radial glial cells that give rise to excitatory neurons in the fetal brain through the process of neurogenesis. Hematopoietic stem cells from the bone marrow that give rise to red blood cells, white blood cells, platelets Mesenchymal stem cells from the bone marrow that give rise to stromal cells, fat cells, types of bone cells Epithelial stem cells that give rise to the various types of skin cells Muscle satellite cells that contribute to differentiated muscle tissue. A pathway, guided by the cell adhesion molecules consisting of four amino acids, glycine and serine, is created as the cellular blastomere differentiates from the single-layered blastula to the three primary layers of germ cells in mammals, namely the ectoderm and endoderm; the ectoderm ends up forming the skin and the nervous system, the mesoderm forms the bones and muscular tissue, the endoderm forms the internal organ tissues.
Bast fibre is plant fibre collected from the phloem or bast surrounding the stem of certain dicotyledonous plants. It provides strength to the stem; some of the economically important bast fibres are obtained from herbs cultivated in agriculture, as for instance flax, hemp, or ramie, but bast fibres from wild plants, as stinging nettle, trees such as lime or linden and mulberry have been used in the past. Bast fibres are classified as soft fibres, are flexible. Fibres from monocotyledonous plants, called "leaf fibre", are classified as hard fibres and are stiff. Since the valuable fibres are located in the phloem, they must be separated from the xylem material, sometimes from the epidermis; the process for this is called retting, can be performed by micro-organisms either on land or in water, or by chemicals or by pectinolytic enzymes. In the phloem, bast fibres occur in bundles that are glued together by calcium ions. More intense retting separates the fibre bundles into elementary fibres, that can be several centimetres long.
Bast fibres have higher tensile strength than other kinds, are used in high-quality textiles, yarn, composite materials and burlap. An important property of bast fibres is that they contain a special structure, the fibre node, that represents a weak point, gives flexibility. Seed hairs, such as cotton, do not have nodes. Plants that have been used for bast fibre include flax, jute, kudzu, milkweed, okra, paper mulberry and roselle hemp. Bast fibres are processed for use in carpet, rope, traditional carpets, hessian or burlap, sacks, etc. Bast fibres are used in the non-woven and composite technology industries for the manufacturing of non-woven mats and carpets, composite boards as furniture materials, automobile door panels and headliners, etc. From prehistoric times through at least the early 20th century, bast shoes were woven from bast strips in the forest areas of Eastern Europe. Where no other source of tanbark was available, bast has been used for tanning leather. International Jute Study Group Bast Fibre cords in Viking ships Bast fibre production with hemp