Cork is a time period variously used for a light-weight, elastic, water resistant, pure materials of economic significance and for the widespread names of two bushes from which it’s primarily harvested: the cork oak tree, Quercus suber (the precept supply of economic cork) and the Chinese language cork oak, Quercus variabilis. Extra technically, the time period is used for the specialised secondary organic tissue that’s produced by and develops exterior the cork cambrium of the stems and roots of many vascular vegetation, which serves as a nonliving, water resistant, protecting outer protecting. Cork is also used because the widespread identify for varied species of the unrelated genus, Phellodendron, which isn’t a business supply of cork.
Business cork—as a result of it’s nearly impervious to liquids and gases and but is buoyant, light-weight, adhesive, chemically inert and elastic—has many makes use of. These embody use as wine bottle stoppers, bulletin boards, coasters, scorching pads to guard tables from scorching pans, insulation, sealing for lids, flooring, gaskets for engines, fishing bobbers, handles for fishing rods and tennis rackets and so forth.
Folks have discovered to reap cork in a method that’s not dangerous to the bushes, permitting these specialised tissues to proceed to supply their protecting worth to the vegetation whereas offering people with a renewable useful resource. By harvesting cork oaks solely each 10 to 12 years, a tree might present a dozen or extra harvests in its lifetime.
Cork, cork cambium, and bark
Cork, generally confused with bark in colloquial speech, is the outermost layer of a woody stem, derived from the cork cambium. Cork is an exterior, secondary tissue impermeable to water and gases. It serves as safety in opposition to harm, parasites, and illnesses, in addition to dehydration and excessive temperatures. Some cork is considerably thicker, offering additional insulation and giving the bark a attribute construction; in some circumstances thick sufficient to be harvestable as cork product with out killing the tree.
Cork is a part of the bark. Bark is the outermost layer of stems and roots of woody vegetation, comparable to bushes and shrubs. The tissues included as a part of bark rely on how broadly the time period is outlined and the age of the plant (whether or not contemplating main tissues or secondary progress). Broadly outlined, bark refers to all these tissues exterior the vascular cambium, or all tissues from the residing phloem outward. Some definitions embody the vascular cambium within the definition. Nonetheless, in common use, the time period bark is commonly utilized in reference to solely the cork or solely to the periderm (cork, cork cambium, and phellederm) in vegetation with secondary progress.
For a lot of vegetation, the dividing level between bark and the remainder of the organism often is taken into account the vascular cambium. The vascular cambium is part of a woody stem the place cell division happens. It incorporates undifferentiated cells that divide quickly to supply secondary xylem to the within and secondary phloem to the skin. The vascular cambium lies between these two layers. Vascular cambium is often discovered on dicots and gymnosperms however not monocots, which lack secondary progress.
In younger stems of woody vegetation (bushes, shrubs, and a few perennial vines), the bark is made up of the next tissues organized from the skin floor to the within:
- Cork – an exterior, secondary tissue impermeable to water and gases.
- Cork cambium – A layer of cells, usually one or two cell layers thick that’s in a persistent meristematic state that produces cork.
- Phelloderm – (not all the time current) A layer of cells fashioned in some vegetation from the inside cells of the cork cambium (cork is produced from the outer layer).
- Cortex – The first tissue of stems and roots. In stems, the cortex is between the dermis layer and the phloem, in roots the inside layer is just not phloem however the pericycle.
- Phloem – nutrient conducting tissue composed of sieve tub or sieve cells blended with parenchym and fibers.
In main tissues, the bark of stems (broadly outlined) consists of the phloem, cortex, and dermis, and the bark of roots can be the cortex and dermis. The cork cambium subsequently is accountable for secondary progress that replaces the dermis in roots and stems. In roots with secondary progress, the cortex and dermis could also be sloughed off as cork is fashioned, and in these circumstances the bark consists of the phloem, cork cambrium, cork, and phelloderm.
In previous stems, the epidermal layer, cortex, and first phloem develop into separated from the inside tissues by thicker formations of cork. As a result of thickening cork layer, these cells die as a result of they don’t obtain water and vitamins. This useless layer is the tough corky bark that varieties round tree trunks and different stems. In smaller stems and on usually non-woody vegetation, generally a secondary protecting kind referred to as the periderm, which is made up of cork cambian, cork, and phelloderm. It replaces the dermal layer and acts as a protecting very like the corky bark—it too is made up of principally useless tissue. The pores and skin on the potato is a periderm.
Cork cambium, a tissue discovered in lots of vascular vegetation as a part of the periderm. is among the plant’s meristems—the collection of tissues consisting of embryonic (incompletely differentiated) cells from which the plant grows. It is among the many layers of bark. The perform of cork cambium is to supply the cork, a tricky protecting materials. Synonyms for cork cambium are bark cambium, pericambium, or phellogen. Phellogen is outlined because the meristematic cell layer accountable for the event of the periderm. Cells that develop inwards from the phellogen are termed phelloderm, and cells that develops outwards are termed phellem or cork.
Cork materials is a subset of generic cork tissue, harvested for business use primarily from the evergreen cork oak tree, Quercus suber or the deciduous Chinese language cork oak, Quercus variabilis. These sources of economic oak primarily comes from the Iberian Peninsula and the western Mediterranean, with a lot of the cork worldwide produced from bushes in Portugal.
Cork consists principally of suberin. Suberin is a waxy substance present in greater vegetation and is known as after the cork oak, Quercus suber. It’s extremely hydrophobic and its major perform is to forestall water from penetrating the tissue. Amongst different areas, suberin is discovered within the phellem (cork) layer of the periderm. That is outermost layer of the bark. The cells on this layer are useless and plentiful in suberin, stopping water loss from the tissues under.
Cork’s elasticity mixed with its near-impermeability makes it appropriate as a fabric for bottle stoppers, particularly for wine bottles. Cork stoppers characterize about 60 p.c of all cork-based manufacturing. Cork’s low density makes it an acceptable materials for fishing floats and buoys, in addition to handles for fishing rods (as a substitute for neoprene). Cork is utilized in musical devices, significantly woodwind devices, the place it’s used to lock collectively segments of the instrument, making the seams hermetic. Sheets of cork, usually the byproduct of extra profitable stopper manufacturing, are used to make ground tiles and bulletin boards. Granules of cork will also be blended into concrete. The composites made by mixing cork granules and cement have low thermal conductivity, low density and good vitality absorption.
The cork oak (Quercus suber) is a medium-sized, evergreen oak tree within the part Quercus sect. Cerris. It’s native to southwest Europe and northwest Africa.
The cork oak grows to as much as 20 meters, though it’s usually extra stunted in its native atmosphere. The leaves are 4–7 centimeters lengthy, weakly lobed or coarsely toothed, darkish inexperienced above, paler beneath, with the leaf margins usually downcurved. The acorns are 2–Three centimeters lengthy, in a deep cup fringed with elongated scales.
The tree varieties a thick, rugged, and corky bark. Over time this bark can develop appreciable thickness and this may be harvested each 10–12 years as cork. The harvesting of cork doesn’t hurt the tree and a brand new layer of cork regrows, making it a renewable useful resource. The tree is extensively cultivated in Spain, Portugal, Algeria, Morocco, France, Italy, and Tunisia. Cork oak forests cowl roughly 2.5 million hectares in these international locations. Portugal accounts for 50 p.c of the world cork harvest. Cork oaks can’t legally be lower down in Portugal, apart from forest administration felling of previous, unproductive bushes.
Cork oaks reside about 150–250 years. Virgin cork (or “male” cork) is the primary cork lower from typically 25-year-old bushes. One other 10–12 years is required for the second harvest, and a tree may be harvested a dozen occasions in its lifetime. Cork harvesting is finished totally with out equipment.
The European cork business produces 340,000 metric tons of cork a yr, with a price of €1.5 billion and using 30,000 folks. Wine corks characterize 15 p.c of cork utilization by weight however 66 p.c of revenues.
Cork oaks are generally planted as particular person bushes, offering a minor revenue to their house owners. The tree can also be generally cultivated for decoration. Hybrids with turkey oak (Quercus cerris) are common, each within the wild in southwest Europe and in cultivation; the hybrid is called Lucombe Oak Quercus × hispanica.
Shut-up of the characteristically corky bark
Cork oaks populate the Massif des Maures countryside
Chinese language cork oak
Chinese language cork oak (Quercus variabilis) is a species of oak within the part Quercus sect. Cerris, native to a large space of jap Asia in China, Japan, and Korea.
It’s a medium-sized to giant deciduous tree rising to 25–30 meters tall with a somewhat open crown, and thick corky bark with deep fissures and marked by sinuous ridges. The leaves are easy, acuminate, variable in measurement, 8–20 centimeters lengthy and a pair of–Eight centimeters broad, with a serrated margin with every vein ending in a particular advantageous hair-like tooth. The leaves are inexperienced above and silvery under with dense quick pubescence.
The flowers are wind-pollinated catkins produced in mid-spring, maturing about 18 months after pollination; the fruit is a globose acorn, 1.5-2 centimeters in diameter, two-thirds enclosed within the acorn cup, which is densely lined in smooth 4–Eight millimeters lengthy ‘mossy’ bristles.
The Chinese language cork oak is cultivated in China to a small extent for cork manufacturing, although its yield is decrease than that of the associated cork oak. Additionally it is often grown as a decorative tree.
Chinese language cork oak planted at Tortworth Court docket, England
Trunk and bark of Chinese language cork oak
Phellodendron amurense autumn leaves and fruit
About 10 species, together with:
Phellodendron or cork-tree, is a genus of deciduous bushes within the household Rutaceae, native to east and northeast Asia. It has leathery, pinnate leaves, and yellow, clumped flowers. The identify refers back to the thick and corky bark of some (however not all) species within the genus.
As a decorative plant, Phellodendron is a tree for all seasons. In spring, it has yellow flowers, in summer time it gives foliage and shade, in fall the leaves flip brilliant yellow, and the textured bark and winding branches add curiosity within the winter. The feminine bears black drupes that entice birds and different wildlife by way of the late fall and winter.
The cork-tree is proof against drought and bugs, and it may thrive in a wide range of soils. It’s hardy to zone Four and it’s straightforward to take care of, generally to the purpose of being invasive. One disadvantage is that the drupes fall and scatter, which can be undesirable on a proper garden.
The bark in some species is thick, resembling that of the cork oak, however is just not thick sufficient for business cork manufacturing. It has been used to supply a yellow dye.
One species, Amur cork tree, Phellodendron amurense, is among the 50 elementary herbs utilized in conventional Chinese language drugs. Not too long ago, Phellodendron has additionally attracted the eye of the pharmaceutical group due to the phytochemicals it produces. Historically, the bark is the principal a part of the plant used medicinally, though oil from the fruit can also be used. The species grows in Northern China, and within the Khabarovsk and Primorskiy areas of Russia.
- Junikka, L. 1994. Macroscopic bark terminology. IAWA Journal 15(1): 3–45.
- Niklas, Ok. J. 1999. The mechanical position of bark. American Journal of Botany, 86 (1999): 465-469.
- Trockenbrodt, M. 1990. Survey and dialogue of the terminology utilized in bark anatomy. IAWA Bulletin, New Sequence 11: 141-166.
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