Condenser (heat transfer)
In systems involving heat transfer, a condenser is a device or unit used to condense a substance from its gaseous to its liquid state, by cooling it. In so doing, the latent heat is given up by the substance and transferred to the surrounding environment. Condensers can be made according to numerous designs, come in many sizes ranging from rather small to large. For example, a refrigerator uses a condenser to get rid of heat extracted from the interior of the unit to the outside air. Condensers are used in air conditioning, industrial chemical processes such as distillation, steam power plants and other heat-exchange systems. Use of cooling water or surrounding air as the coolant is common in many condensers. A surface condenser is one in which condensing medium and vapors are physically separated and used when direct contact is not desired, it is a shell and tube heat exchanger installed at the outlet of every steam turbine in thermal power stations. The cooling water flows through the tube side and the steam enters the shell side where the condensation occurs on the outside of the heat transfer tubes.
The condensate drips down and collects at the bottom in a built-in pan called a hotwell. The shell side operates at a vacuum or partial vacuum, produced by the difference in specific volume between the steam and condensate. Conversely, the vapor can be fed through the tubes with the coolant water or air flowing around the outside. In chemistry, a condenser is the apparatus which cools hot vapors, causing them to condense into a liquid. See "Condenser" for laboratory-scale condensers, as opposed to industrial-scale condensers. Examples include the Liebig condenser, Graham condenser, Allihn condenser; this is not to be confused with a condensation reaction which links two fragments into a single molecule by an addition reaction and an elimination reaction. In laboratory distillation and rotary evaporators, several types of condensers are used; the Liebig condenser is a straight tube within a cooling water jacket, is the simplest form of condenser. The Graham condenser is a spiral tube within a water jacket, the Allihn condenser has a series of large and small constrictions on the inside tube, each increasing the surface area upon which the vapor constituents may condense.
Being more complex shapes to manufacture, these latter types are more expensive to purchase. These three types of condensers are laboratory glassware items since they are made of glass. Commercially available condensers are fitted with ground glass joints and come in standard lengths of 100, 200, 400 mm. Air-cooled condensers are unjacketed, while water-cooled condensers contain a jacket for the water. Larger condensers are used in industrial-scale distillation processes to cool distilled vapor into liquid distillate; the coolant flows through the tube side and distilled vapor through the shell side with distillate collecting at or flowing out the bottom. A condenser unit used in central air conditioning systems has a heat exchanger section to cool down and condense incoming refrigerant vapor into liquid, a compressor to raise the pressure of the refrigerant and move it along, a fan for blowing outside air through the heat exchanger section to cool the refrigerant inside. A typical configuration of such a condenser unit is as follows: The heat exchanger section wraps around the sides of the unit with the compressor inside.
In this heat exchanger section, the refrigerant goes through multiple tube passes, which are surrounded by heat transfer fins through which cooling air can circulate from outside to inside the unit. There is a motorized fan inside the condenser unit near the top, covered by some grating to keep any objects from accidentally falling inside on the fan; the fan is used to pull outside cooling air in through the heat exchanger section at the sides and blow it out the top through the grating. These condenser units are located on the outside of the building they are trying to cool, with tubing between the unit and building, one for vapor refrigerant entering and another for liquid refrigerant leaving the unit. Of course, an electric power supply is needed for the fan inside the unit. In a direct-contact condenser, hot vapor and cool liquid are introduced into a vessel and allowed to mix directly, rather than being separated by a barrier such as the wall of a heat exchanger tube; the vapor gives up its latent heat and condenses to a liquid, while the liquid absorbs this heat and undergoes a temperature rise.
The entering vapor and liquid contain a single condensable substance, such as a water spray being used to cool air and adjust its humidity. Other Types of Condensers There are three other condensers used in HVAC systems: Water-cooled Air-cooled EvaporativeApplications: Air cooled – If the condenser is located on the outside of the unit, the air cooled condenser can provide the easiest arrangement; these types of condensers are simple to install. Most common uses for this condenser are domestic refrigerators, upright freezers and in residential packaged air conditioning units. A great feature of the air cooled condenser is they are easy to clean. Since dirt can cause serious issues with the condensers performance, it is recommended that these be kept clear of dirt. Water cooled – Although a little more pricey to install, these condensers are the more efficient type. Used for swimming pools and condensers piped for city water flow, these condensers require regular service and maintenance, they require a cooling tower to conserve water.
To prevent corrosion and the fo
The longleaf pine is a pine native to the Southeastern United States, found along the coastal plain from East Texas to southern Maryland, extending into northern and central Florida. It reaches a height of 30–35 m and a diameter of 0.7 m. In the past, before extensive logging, they grew to 47 m with a diameter of 1.2 m. The tree is a cultural symbol of the Southern United States, being the official state tree of Alabama and the unofficial state tree of North Carolina; the bark is thick, reddish-brown, scaly. The leaves are dark green and needle-like, occur in bundles of three, they are twisted and 20–45 cm in length. It is one of the two Southeastern U. S. pines with long needles, the other being slash pine. The cones, both female seed cones and male pollen cones, are initiated during the growing season before buds emerge. Pollen cones begin forming in their buds in July, while seed conelets are formed during a short period of time in August. Pollination occurs early the following spring, with the male cones 3–8 cm long.
The female cones mature in about 20 months from pollination. The seeds are 7–9 mm long, with a 25–40 mm wing. Longleaf pine may live to be 500 years old; when young, they grow a long taproot, 2–3 m long. They grow on well-drained sandy soil, characteristically in pure stands. Longleaf pine is known as being one of several species grouped as a southern yellow pine or longleaf yellow pine, in the past as pitch pine; the species epithet palustris is Latin for "of the marsh" and indicates its common habitat. The scientific name meaning "of marshes" is a misunderstanding on the part of Philip Miller, who described the species, after seeing longleaf pine forests with temporary winter flooding. Longleaf pine is pyrophytic. Periodic natural wildfire selects for this species by killing other trees, leading to open longleaf pine forests or savannas. New seedlings do not resemble a dark-green fountain of needles; this form is called the grass stage. During this stage, which lasts for 5–12 years, vertical growth is slow, the tree may take a number of years to grow ankle high.
After that, it makes a growth spurt if no tree canopy is above it. In the grass stage, it is resistant to low intensity fires because the terminal bud is protected from lethal heating by the packed needles. While immune to fire at this stage, the plant is quite appealing to feral pigs. Longleaf pine forests are rich in biodiversity, they are well-documented for their high levels of plant diversity, in groups including sedges, carnivorous plants, orchids. These forests provide habitat for gopher tortoises, which as keystone species, dig burrows that provide habitat for hundreds of other species of animals; the red-cockaded woodpecker is dependent on mature pine forests and is now endangered as a result of this decline. Longleaf pine seeds are large and nutritious, forming a significant food source for birds and other wildlife. Nine salamander species and 26 frog species are characteristic of pine savannas, along with 56 species of reptiles, 13 of which could be considered specialists on this habitat.
The Red Hills Region of Florida and Georgia is home to some of the best-preserved stands of longleaf pines. These forests have been burned for many decades to encourage bobwhite quail habitat in private hunting plantations. Vast forests of longleaf pine once were present along the southeastern Atlantic coast and Gulf Coast of North America, as part of the eastern savannas; these forests were the source of naval stores - resin and timber - needed by merchants and the navy for their ships. They have been cutover since for timber and replaced with faster-growing loblolly pine and slash pine, for agriculture, for urban and suburban development. Due to this deforestation and overharvesting, only about 3% of the original longleaf pine forest remains, little new is planted. Longleaf pine is available, however, at many nurseries within its range; the yellow, resinous wood is used for pulp. Boards cut years ago from virgin timber were wide, up to 1 m, a thriving salvage business obtains these boards from demolition projects to be reused as flooring in upscale homes.
The long needles are popular for use in the ancient craft of coiled basket making. The stumps and taproots of old trees become will not rot. Farmers sometimes find old buried stumps in fields in some that were cleared a century ago, these are dug up and sold as fatwood, "fat lighter", or "lighter wood", in demand as kindling for fireplaces, wood stoves, barbecue pits. In old-growth pine, the heartwood of the bole is saturated in the same way; when boards are cut from the fat lighter wood, they are heavy and will not rot, but buildings constructed of them are quite flammable and make hot fires. Th
Terpenes are a large and diverse class of organic compounds, produced by a variety of plants conifers, by some insects. They have a strong odor and may protect the plants that produce them by deterring herbivores and by attracting predators and parasites of herbivores. Although sometimes used interchangeably with "terpenes", terpenoids are modified terpenes as they contain additional functional groups oxygen-containing. Terpenes are hydrocarbons. Terpenes are the major components of turpentine produced from resin; the name "terpene" is derived from the word "terpentine", an obsolete form of the word "turpentine". Terpenes are major biosynthetic building blocks. Steroids, for example, are derivatives of the triterpene squalene. Terpenes and terpenoids are the primary constituents of the essential oils of many types of plants and flowers. Essential oils are used as fragrances in perfumery and traditional medicine, such as aromatherapy. Synthetic variations and derivatives of natural terpenes and terpenoids greatly expand the variety of aromas used in perfumery and flavors used in food additives.
Vitamin A is a terpenoid. The term "terpene" was coined in 1866 by the German chemist August Kekulé. Terpenes are derived biosynthetically from units of isopentenyl pyrophosphate. Although the structures of terpenoids are rationalized as derivatives of isoprene, isoprene is not involved in the biosynthesis; the biogenetic isoprene rule or the C5 rule was described in 1953, by Leopold Ružička, who explained that terpinoids can be visualized as the result of linking isoprene units "head to tail" to form chains, which can be arranged to form rings. There are two metabolic pathways that create terpenoids: Many organisms manufacture terpenoids through the HMG-CoA reductase pathway, known as the Mevalonate pathway, which produces cholesterol. One of the intermediates in this pathway is mevalonic acid; the reactions take place in the cytosol. The pathway was discovered in the 1950s; the 2-C-methyl-D-erythritol 4-phosphate/1-deoxy-D-xylulose 5-phosphate pathway known as non-mevalonate pathway or mevalonic acid-independent pathway, takes place in the plastids of plants and apicomplexan protozoa, as well as in many bacteria.
It was discovered in the late 1980s. Pyruvate and glyceraldehyde 3-phosphate are converted by DOXP synthase to 1-deoxy-D-xylulose 5-phosphate, by DOXP reductase to 2-C-methyl-D-erythritol 4-phosphate; the subsequent three reaction steps catalyzed by 4-diphosphocytidyl-2-C-methyl-D-erythritol synthase, 4-diphosphocytidyl-2-C-methyl-D-erythritol kinase, 2-C-methyl-D-erythritol 2,4-cyclodiphosphate synthase mediate the formation of 2-C-methyl-D-erythritol 2,4-cyclopyrophosphate. MEcPP is converted to -4-hydroxy-3-methyl-but-2-enyl pyrophosphate by HMB-PP synthase, HMB-PP is converted to isopentenyl pyrophosphate and dimethylallyl pyrophosphate by HMB-PP reductase. IPP and DMAPP are the end-products in either pathway, are the precursors of isoprene, diterpenoids, carotenoids and plastoquinone-9. Synthesis of all higher terpenoids proceeds via formation of geranyl pyrophosphate, farnesyl pyrophosphate, geranylgeranyl pyrophosphate; the MVA and MEP are mutually exclusive in most organisms. In both MVA and MEP pathways, IPP is isomerized to DMAPP by the enzyme isopentenyl pyrophosphate isomerase.
IPP and DMAPP condense to give geranyl pyrophosphate, the precursor to monoterpenes and monoterpenoids. Geranyl pyrophosphate is converted to farnesyl pyrophosphate and geranylgeranyl pyrophosphate C15 and C20 precursors to sesquiterpenes and diterpenes. Biosynthesis is mediated by terpene synthase. Selected terpenes Terpenes may be classified by the number of isoprene units in the molecule. Hemiterpenes consist of a single isoprene unit. Isoprene itself is considered the only hemiterpene, but oxygen-containing derivatives such as prenol and isovaleric acid are hemiterpenoids. Monoterpenes consist of two isoprene units and have the molecular formula C10H16. Examples of monoterpenes and monoterpenoids include geraniol, limonene, linalool or pinene. Iridoids derive from monoterpenes. Sesquiterpenes consist of three isoprene units and have the molecular formula C15H24. Examples of sesquiterpenes and sesquiterpenoids include humulene, farnesol. Diterpenes are composed of four isoprene units and have the molecular formula C20H32.
They derive from geranylgeranyl pyrophosphate. Examples of diterpenes and diterpenoids are cafestol, kahweol and taxadiene. Diterpenes form the basis for biologically important compounds such as retinol and phytol. Sesterterpenes, terpenes having 25 carbons and five isoprene units, are rare relative to the other sizes. An example of a sesterterpenoid is geranylfarnesol. Triterpenes consist of six isoprene units and have the molecular formula C30H48; the linear triterpene squalene, the major constituent of shark liver oil, is derived from the reductive coupling of two molecules of farnesyl pyrophosphate. Squalene is processed biosynthetically to generate either lanosterol or cycloartenol, the structural precursors to all the steroids. Sesquarterpenes are composed of s
Pinus halepensis known as the Aleppo pine known as Jerusalem's oren, is a pine native to the Mediterranean region. Its range extends from Morocco and Spain north to southern France, Croatia, Montenegro and east to Greece, all over Malta and northern Tunisia, with an outlying population in Syria, southern Turkey, Jordan and Palestinian territories. Pinus halepensis is found at low altitudes from sea level to 200 m, but can grow up to 1,000 m in southern Spain, well over 1,200 m on Crete, up to 1,700 m in the south, in Morocco and Tunisia; the tree is able to colonize open and disturbed areas. It can grow on all substrates and in all bioclimates in the Mediterranean. Pinus halepensis is a small to medium-sized tree, 15–25 m tall, with a trunk diameter up to 60 cm, exceptionally up to 1 m; the bark is orange-red and fissured at the base of the trunk, thin and flaky in the upper crown. The leaves are slender, 6–12 cm long, distinctly yellowish green, produced in pairs; the cones are narrow conic, 5–12 cm long and 2–3 cm broad at the base when closed, green at first, ripening glossy red-brown when 24 months old.
They open over the next few years, a process quickened if they are exposed to heat such as in forest fires. The cones open 5–8 cm wide to allow the seeds to disperse; the seeds are 5–6 mm long, with a 20-mm wing, are wind-dispersed. The Aleppo pine is related to the Turkish pine, Canary Island pine, maritime pine, which all share many of its characteristics; some authors include the Turkish pine as a subspecies of the Aleppo pine. Brutia Holmboe, but it is regarded as a distinct species, it is a nonvariable species, in that its morphological characteristics stay constant over the entire range. The resin of the Aleppo pine is used to flavor the Greek wine retsina. From the pine nuts of the Aleppo pine is made a pudding called asidet zgougou in the Tunisian dialect. Aleppo pine are used for bonsai. In its native area, P. halepensis is planted for its fine timber, making it one of the most important forestry trees in Algeria and Morocco. In Israel, the Aleppo pine, along with Pinus brutia, has been planted extensively by the JNF.
It proved successful in Yatir Forest in the northern Negev, where foresters had not expected it to survive. Many Aleppo pine forests are used for recreational purposes. Although it is a local species, some argue that the historical replacement of natural oak maquis shrubland and garrigue with tall stands of pine has created "ecological deserts" and has changed the species assemblage of these regions. In Israel natural patches of Aleppo pine forests can be found in the Galilee regions; the species produces timber, valued for its hardness and unproblematic seasoning. Seasoned timber is inclined to tear out with planing, but this can be avoided by using sharp blades or adjusting the sharpening angle of tools; the Aleppo pine is considered an invasive species though useful in South Africa. Pinus halepensis is a popular ornamental tree, extensively planted in gardens and private and agency landscapes in hot dry areas such as Southern California and the Karoo in South Africa, where the Aleppo pine's considerable heat and drought tolerance, fast growth, aesthetic qualities, are valued.
Paul Cézanne had an Aleppo pine in his garden at Aix-en-Provence. As of 2005, the tree is still growing in Cézanne's garden. Media related to Pinus halepensis at Wikimedia Commons Data related to Pinus halepensis at Wikispecies Gymnosperm Database: Pinus halepensis Pinus halepensis - distribution map, genetic conservation units and related resources. European Forest Genetic Resources Programme
European Chemicals Agency
The European Chemicals Agency is an agency of the European Union which manages the technical and administrative aspects of the implementation of the European Union regulation called Registration, Evaluation and Restriction of Chemicals. ECHA is the driving force among regulatory authorities in implementing the EU's chemicals legislation. ECHA helps companies to comply with the legislation, advances the safe use of chemicals, provides information on chemicals and addresses chemicals of concern, it is located in Finland. The agency headed by Executive Director Bjorn Hansen, started working on 1 June 2007; the REACH Regulation requires companies to provide information on the hazards and safe use of chemical substances that they manufacture or import. Companies register this information with ECHA and it is freely available on their website. So far, thousands of the most hazardous and the most used substances have been registered; the information is technical but gives detail on the impact of each chemical on people and the environment.
This gives European consumers the right to ask retailers whether the goods they buy contain dangerous substances. The Classification and Packaging Regulation introduces a globally harmonised system for classifying and labelling chemicals into the EU; this worldwide system makes it easier for workers and consumers to know the effects of chemicals and how to use products safely because the labels on products are now the same throughout the world. Companies need to notify ECHA of the labelling of their chemicals. So far, ECHA has received over 5 million notifications for more than 100 000 substances; the information is available on their website. Consumers can check chemicals in the products. Biocidal products include, for example, insect disinfectants used in hospitals; the Biocidal Products Regulation ensures that there is enough information about these products so that consumers can use them safely. ECHA is responsible for implementing the regulation; the law on Prior Informed Consent sets guidelines for the import of hazardous chemicals.
Through this mechanism, countries due to receive hazardous chemicals are informed in advance and have the possibility of rejecting their import. Substances that may have serious effects on human health and the environment are identified as Substances of Very High Concern 1; these are substances which cause cancer, mutation or are toxic to reproduction as well as substances which persist in the body or the environment and do not break down. Other substances considered. Companies manufacturing or importing articles containing these substances in a concentration above 0,1% weight of the article, have legal obligations, they are required to inform users about the presence of the substance and therefore how to use it safely. Consumers have the right to ask the retailer whether these substances are present in the products they buy. Once a substance has been identified in the EU as being of high concern, it will be added to a list; this list is available on ECHA's website and shows consumers and industry which chemicals are identified as SVHCs.
Substances placed on the Candidate List can move to another list. This means that, after a given date, companies will not be allowed to place the substance on the market or to use it, unless they have been given prior authorisation to do so by ECHA. One of the main aims of this listing process is to phase out SVHCs where possible. In its 2018 substance evaluation progress report, ECHA said chemical companies failed to provide “important safety information” in nearly three quarters of cases checked that year. "The numbers show a similar picture to previous years" the report said. The agency noted that member states need to develop risk management measures to control unsafe commercial use of chemicals in 71% of the substances checked. Executive Director Bjorn Hansen called non-compliance with REACH a "worry". Industry group CEFIC acknowledged the problem; the European Environmental Bureau called for faster enforcement to minimise chemical exposure. European Chemicals Bureau Official website
Abies balsamea or balsam fir is a North American fir, native to most of eastern and central Canada and the northeastern United States. It is celebrated for its rich green needles, natural conical shape, needle retention after being cut, it is notably the most fragrant of all Christmas tree varieties. Balsam fir is a small to medium-size evergreen tree 14–20 metres tall reaching a height of 27 metres; the narrow conic crown consists of dark-green leaves. The bark on young trees is smooth and with resin blisters, becoming rough and fissured or scaly on old trees; the leaves are flat and needle-like, 15 to 30 mm long, dark green above with a small patch of stomata near the tip, two white stomatal bands below, a notched tip. They are arranged spirally on the shoot, but with the leaf bases twisted so that the leaves appear to be in two more-or-less horizontal rows on either side of the shoot; the needles become thicker the higher they are on the tree. The seed cones are erect, 40 to 80 mm long, dark purple, ripening brown and disintegrating to release the winged seeds in September.
There are two varieties: Abies balsamea var. balsamea – bracts subtending seed scales short, not visible on the closed cones. Most of the species' range. Abies balsamea var. phanerolepis – bracts subtending seed scales longer, visible on the closed cone. The southeast of the species' range, from southernmost Quebec to West Virginia; the name Canaan fir derives from one of the Canaan Valley in West Virginia. Some botanists regard this variety as a natural hybrid between balsam fir and Fraser fir, which occurs further south in the Appalachian mountains. Balsam fir tends to grow in cool climates, ideally with a mean annual temperature of 40 °F, with consistent moisture at its roots, they grow in the following four forest types: Swamp – swamp forest types never dry out, so balsam firs have constant access to water. The ground is covered in sphagnum and other mosses. In swamps, balsam firs grow densely and and are slender. Flat – sometimes referred to as "dry swamps," these areas are better drained than swamps but still retain moisture well.
Fern moss covers the ground and there is a possibility of ground rot. In flat areas balsam fir grows fast and large, mixed with red spruce. Hardwood slope – ground rot is common in this well drained area and leaf litter covers the forest floor. Balsam firs grow fast and large along with big hardwood trees such as yellow birch, sugar maple and beech. Mountain top – On mountain tops, stands of balsam fir develop fir waves, they grow at an elevation of 760 to 910 m in pure strands, or in association with black spruce, white spruce, trembling aspen. The development is similar to that in swamps with slow growth resulting in short trees; some of the low branches touch the ground, may grow roots to produce an independent tree. This tree provides food for moose, American red squirrels and chickadees, as well as shelter for moose, snowshoe hares, white-tailed deer, ruffed grouse, other small mammals and songbirds; the needles are eaten for example the Io moth. The male reproductive organs develop more and appear sooner than the female organs.
The male organs contain microsporangia which divide to form sporogenous tissue, composed of cells which become archesporial cells. These develop into microspores, or pollen-mother cells, once they are rounded and filled with starch grains; when the microspores undergo meiosis in the spring, four haploid microspores are produced which become pollen grains. Once the male strobilus has matured the microsporangia are exposed at which point the pollen is released; the female megasporangiate is larger than the male. It contains megasporophylls, each of which contains two ovules, arranged in a spiral; these develop a nucellus in which a mother cell is formed. Meiosis occurs and a megaspore is produced as the first cell of the megagametophyte; as cell division takes place the nucleus of the megaspore thickens, cell differentiation occurs to produce prothallial tissue containing an ovum. The remaining undifferentiated cells form the endosperm; when the male structure releases its pollen grains, some fall onto the female strobilus and reach the ovule.
At this point the pollen tube begins to generate, the sperm and egg meet at which point fertilization occurs. Both varieties of the species are popular as Christmas trees in the northeastern United States. Contrary to popular belief the balsam firs cut for Christmas are not taken from the forest, but are grown on large plantations; the balsam fir is one of the greatest exports of New England. Many of these plantations are family farms handed down from generation to generation; the techniques of shearing and other cultivation secretly passed down from grandparents to grandchildren. Families like the Rousseau's of Quebec, Rose of New Brunswick, Kessler's of New Hampshire have kept family traditions for a century; the resin is used to produce Canada balsam, was traditionally used as a cold remedy and as a glue for glasses, optical instrument components, for preparing permanent mounts of microscope specimens. Given its use as a traditional remedy and the high ascorbic acid content of its needles, historian Jacques Mathi
A pine is any conifer in the genus Pinus of the family Pinaceae. Pinus is the sole genus in the subfamily Pinoideae; the Plant List compiled by the Royal Botanic Gardens and Missouri Botanical Garden accepts 126 species names of pines as current, together with 35 unresolved species and many more synonyms. The modern English name "pine" derives from Latin pinus, which some have traced to the Indo-European base *pīt- ‘resin’. Before the 19th century, pines were referred to as firs. In some European languages, Germanic cognates of the Old Norse name are still in use for pines—in Danish fyr, in Norwegian fura/fure/furu, Swedish fura/furu, Dutch vuren, German Föhre—but in modern English, fir is now restricted to fir and Douglas fir. Pine trees are evergreen, coniferous resinous trees growing 3–80 m tall, with the majority of species reaching 15–45 m tall; the smallest are Siberian dwarf pine and Potosi pinyon, the tallest is an 81.79 m tall ponderosa pine located in southern Oregon's Rogue River-Siskiyou National Forest.
Pines are long lived and reach ages of 100–1,000 years, some more. The longest-lived is Pinus longaeva. One individual of this species, dubbed "Methuselah", is one of the world's oldest living organisms at around 4,600 years old; this tree can be found in the White Mountains of California. An older tree, now cut down, was dated at 4,900 years old, it was discovered in a grove beneath Wheeler Peak and it is now known as "Prometheus" after the Greek immortal. The bark of most pines is thick and scaly; the branches are produced in regular "pseudo whorls" a tight spiral but appearing like a ring of branches arising from the same point. Many pines are uninodal, producing just one such whorl of branches each year, from buds at the tip of the year's new shoot, but others are multinodal, producing two or more whorls of branches per year; the spiral growth of branches and cone scales may be arranged in Fibonacci number ratios. The new spring shoots are sometimes called "candles"; these "candles" offer foresters a means to evaluate fertility of the vigour of the trees.
Pines have four types of leaf: Seed leaves on seedlings are borne in a whorl of 4–24. Juvenile leaves, which follow on seedlings and young plants, are 2–6 cm long, green or blue-green, arranged spirally on the shoot; these are produced for six months to five years longer. Scale leaves, similar to bud scales, are small and not photosynthetic, arranged spirally like the juvenile leaves. Needles, the adult leaves, are green and bundled in clusters called fascicles; the needles can number from one to seven per fascicle, but number from two to five. Each fascicle is produced from a small bud on a dwarf shoot in the axil of a scale leaf; these bud scales remain on the fascicle as a basal sheath. The needles persist depending on species. If a shoot is damaged, the needle fascicles just below the damage will generate a bud which can replace the lost leaves. Pines are monoecious, having the male and female cones on the same tree, though a few species are sub-dioecious, with individuals predominantly, but not wholly, single-sex.
The male cones are small 1–5 cm long, only present for a short period, falling as soon as they have shed their pollen. The female cones take 1.5–3 years to mature after pollination, with actual fertilization delayed one year. At maturity the female cones are 3–60 cm long; each cone has numerous spirally. The seeds are small and winged, are anemophilous, but some are larger and have only a vestigial wing, are bird-dispersed. At maturity, the cones open to release the seeds, but in some of the bird-dispersed species, the seeds are only released by the bird breaking the cones open. In others, the seeds are stored in closed cones for many years until an environmental cue triggers the cones to open, releasing the seeds; the most common form of serotiny is pyriscence, in which a resin binds the cones shut until melted by a forest fire. Pines are gymnosperms; the genus is divided into two subgenera, which can be distinguished by cone and leaf characters: Pinus subg. Pinus, the yellow, or hard pine group with harder wood and two or three needles per fascicle Pinus subg.
Strobus, the white, or soft pine group with softer wood and five needles per fascicle Pines are native to the Northern Hemisphere, in a few parts of the tropics in the Southern Hemisphere. Most regions of the Northern Hemisphere host some native species of pines. One species crosses the equator in Sumatra to 2°S. In North America, various species occur in regions at latitudes from as far north as 66°N to as far south as 12°N. Pines may be found in a large variety of environments, ranging from semi-arid desert to rainforests, from sea level up to 5,200 metres, from the coldest to the hottest environments on Earth, they occur in mountainous areas with favorable soils and at least some water. Various species have been introduced to temperate and subtropical regions of both hemisp