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Der Elm ist ein 25 km langer, 3 bis 8 km breiter, maximal ,3 m ü. NHN hoher und bewaldeter Mittelgebirgszug südöstlich von Braunschweig in den Landkreisen Helmstedt und Wolfenbüttel in Niedersachsen. Der Elm ist ein 25 km langer, 3 bis 8 km breiter, maximal ,3 m ü. NHN hoher und bewaldeter Mittelgebirgszug südöstlich von Braunschweig in den. Der Elm ist ein 25 km langer und km breiter, bewaldeter Bergzug südöstlich von Braunschweig in Niedersachsen. Seine maximale Höhe beträgt ,3 m ü. Geologisch ist der Elm hauptsächlich aus fossilienreichem Muschelkalkgestein aufgebaut, das als Elmkalkstein seit dem Mittelalter ein begehrter Baustoff ist. Den Naturpark im südöstlichen Niedersachsen prägen die bewaldeten Höhenzüge von Elm, Lappwald und Dorm sowie das Gebiet der Helmstedter Mulde, heißt.
Der Elm ist ein bewaldeter Mittelgebirgszug südöstlich von Braunschweig innerhalb der Landkreise Helmstedt und Wolfenbüttel (Niedersachsen). Geologisch ist der Elm hauptsächlich aus fossilienreichem Muschelkalkgestein aufgebaut, das als Elmkalkstein seit dem Mittelalter ein begehrter Baustoff ist. Den Naturpark im südöstlichen Niedersachsen prägen die bewaldeten Höhenzüge von Elm, Lappwald und Dorm sowie das Gebiet der Helmstedter Mulde, heißt.
There are about 30 to 40 species of Ulmus elm ; the ambiguity in number results from difficulty in delineating species, owing to the ease of hybridization between them and the development of local seed-sterile vegetatively propagated microspecies in some areas, mainly in the field elm Ulmus minor group.
Oliver Rackham  describes Ulmus as the most critical genus in the entire British flora, adding that 'species and varieties are a distinction in the human mind rather than a measured degree of genetic variation'.
Eight species are endemic to North America, and a smaller number to Europe;  the greatest diversity is found in Asia.
The classification adopted in the List of elm species, varieties, cultivars and hybrids is largely based on that established by Brummitt.
As part of the sub-order urticalean rosids they are distant cousins of cannabis , hops , and nettles.
The name Ulmus is the Latin name for these trees, while the English "elm" and many other European names are either cognate with or derived from it.
The genus is hermaphroditic , having apetalous perfect flowers which are wind-pollinated. Elm leaves are alternate, with simple, single- or, most commonly, doubly serrate margins, usually asymmetric at the base and acuminate at the apex.
The fruit is a round wind-dispersed samara flushed with chlorophyll , facilitating photosynthesis before the leaves emerge. The elm tree can grow to great height, often with a forked trunk creating a vase profile.
Dutch elm disease DED devastated elms throughout Europe and much of North America in the second half of the 20th century.
It derives its name 'Dutch' from the first description of the disease and its cause in the s by the Dutch botanists Bea Schwarz and Christina Johanna Buisman.
Owing to its geographical isolation and effective quarantine enforcement, Australia, has so far remained unaffected by Dutch Elm Disease, as have the provinces of Alberta and British Columbia in western Canada.
DED is caused by a micro- fungus transmitted by two species of Scolytus elm-bark beetle which act as vectors. The disease affects all species of elm native to North America and Europe, but many Asiatic species have evolved anti-fungal genes and are resistant.
Fungal spores, introduced into wounds in the tree caused by the beetles, invade the xylem or vascular system.
The tree responds by producing tyloses , effectively blocking the flow from roots to leaves. Woodland trees in North America are not quite as susceptible to the disease because they usually lack the root-grafting of the urban elms and are somewhat more isolated from each other.
In France, inoculation with the fungus of over three hundred clones of the European species failed to find a single variety possessed of any significant resistance.
The first, less aggressive strain of the disease fungus, Ophiostoma ulmi , arrived in Europe from Asia in , and was accidentally introduced to North America in It was steadily weakened by viruses in Europe and had all but disappeared by the s.
However, the disease had a much greater and long-lasting impact in North America, owing to the greater susceptibility of the American elm, Ulmus americana , which masked the emergence of the second, far more virulent strain of the disease Ophiostoma novo-ulmi.
It appeared in the United States sometime in the s, and was originally believed to be a mutation of O. Limited gene flow from O.
It was first recognized in Britain in the early s, believed to have been introduced via a cargo of Canadian rock elm destined for the boatbuilding industry, and rapidly eradicated most of the mature elms from western Europe.
A second subspecies, O. It is now believed that it was this subspecies which was introduced to North America and, like O. The two subspecies have now hybridized in Europe where their ranges have overlapped.
There is no sign of the current pandemic waning, and no evidence of a susceptibility of the fungus to a disease of its own caused by d-factors : naturally occurring virus-like agents that severely debilitated the original O.
Elm phloem necrosis elm yellows is a disease of elm trees that is spread by leafhoppers or by root grafts. It is caused by phytoplasmas which infect the phloem inner bark of the tree.
The disease affects both wild-growing and cultivated trees. Occasionally, cutting the infected tree before the disease completely establishes itself and cleanup and prompt disposal of infected matter has resulted in the plant's survival via stump-sprouts.
Most serious of the elm pests is the elm leaf beetle Xanthogaleruca luteola , which can decimate foliage, although rarely with fatal results.
The beetle was accidentally introduced to North America from Europe. Another unwelcome immigrant to North America is the Japanese beetle Popillia japonica.
In both instances the beetles cause far more damage in North America owing to the absence of the predators present in their native lands.
In Australia, introduced elm trees are sometimes used as foodplants by the larvae of hepialid moths of the genus Aenetus.
These burrow horizontally into the trunk then vertically down. Sapsucker woodpeckers have a great love of young elm trees.
Research has followed two paths:. In North America, careful selection has produced a number of trees resistant not only to DED, but also to the droughts and cold winters that occur within the continent.
Research in the United States has concentrated on the American elm Ulnus americana , resulting in the release of DED-resistant clones, notably the cultivars 'Valley Forge' and 'Jefferson'.
Much work has also been done into the selection of disease-resistant Asiatic species and cultivars. In , Mariam B.
Sticklen and James L. Sherald reported the results of experiments funded by the United States National Park Service and conducted at Michigan State University in East Lansing that were designed to apply genetic engineering techniques to the development of DED-resistant strains of American elm trees.
In Europe, the European white elm Ulmus laevis has received much attention. While this elm has little innate resistance to Dutch elm disease, it is not favoured by the vector bark beetles and thus only becomes colonized and infected when there are no other choices, a rare situation in western Europe.
Research in Spain has suggested that it may be the presence of a triterpene , alnulin , which makes the tree bark unattractive to the beetle species that spread the disease.
Owing to their innate resistance to Dutch elm disease, Asiatic species have been crossed with European species, or with other Asiatic elms, to produce trees which are both highly resistant to disease and tolerant of native climates.
After a number of false dawns in the s, this approach has produced a range of reliable hybrid cultivars now commercially available in North America and Europe.
However, some of these cultivars, notably those with the Siberian elm Ulmus pumila in their ancestry, lack the forms for which the iconic American Elm and English Elm were prized.
Moreover, several exported to northwestern Europe have proven unsuited to the maritime climate conditions there, notably because of their intolerance of anoxic conditions resulting from ponding on poorly drained soils in winter.
Dutch hybridizations invariably included the Himalayan elm Ulmus wallichiana as a source of anti-fungal genes and have proven more tolerant of wet ground; they should also ultimately reach a greater size.
However, the susceptibility of the cultivar 'Lobel', used as a control in Italian trials, to elm yellows has now raised a question mark over all the Dutch clones.
A number of highly resistant Ulmus cultivars has been released since by the Institute of Plant Protection in Florence, most commonly featuring crosses of the Dutch cultivar 'Plantijn' with the Siberian Elm to produce resistant trees better adapted to the Mediterranean climate.
Elms take many decades to grow to maturity, and as the introduction of these disease-resistant cultivars is relatively recent, their long-term performance and ultimate size and form cannot be predicted with certainty.
The National Elm Trial in North America, begun in , is a nationwide trial to assess strengths and weaknesses of the 19 leading cultivars raised in the US over a ten-year period; European cultivars have been excluded.
Meanwhile, in Europe, American and European cultivars are being assessed in field trials started in by the UK charity Butterfly Conservation.
One of the earliest of ornamental elms was the ball-headed graft narvan elm , Ulmus minor 'Umbraculifera' , cultivated from time immemorial in Persia as a shade tree and widely planted in cities through much of south-west and central Asia.
From the 18th century to the early 20th century, elms, whether species, hybrids or cultivars , were among the most widely planted ornamental trees in both Europe and North America.
They were particularly popular as a street tree in avenue plantings in towns and cities, creating high-tunnelled effects.
Their quick growth and variety of foliage and forms,  their tolerance of air-pollution and the comparatively rapid decomposition of their leaf-litter in the fall were further advantages.
In North America, the species most commonly planted was the American elm Ulmus americana , which had unique properties that made it ideal for such use: rapid growth, adaptation to a broad range of climates and soils, strong wood, resistance to wind damage, and vase-like growth habit requiring minimal pruning.
In Europe, the wych elm Ulmus glabra and the field elm Ulmus minor were the most widely planted in the countryside, the former in northern areas including Scandinavia and northern Britain , the latter further south.
The hybrid between these two, Dutch elm U. In much of England, it was the English elm which later came to dominate the horticultural landscape.
Most commonly planted in hedgerows, it sometimes occurred in densities of over per square kilometre. In south-eastern Australia and New Zealand, large numbers of English and Dutch elms, as well as other species and cultivars, were planted as ornamentals following their introduction in the 19th century, while in northern Japan Japanese Elm Ulmus davidiana var.
From about to , the most prized small ornamental elm in parks and gardens was the Camperdown elm Ulmus glabra 'Camperdownii' , a contorted weeping cultivar of the Wych Elm grafted on to a non-weeping elm trunk to give a wide, spreading and weeping fountain shape in large garden spaces.
In northern Europe elms were, moreover, among the few trees tolerant of saline deposits from sea spray, which can cause "salt-burning" and die-back.
This tolerance made elms reliable both as shelterbelt trees exposed to sea wind, in particular along the coastlines of southern and western Britain   and in the Low Countries, and as trees for coastal towns and cities.
The devastation caused by the Second World War , and the demise in of the huge Späth nursery in Berlin , only accelerated the process.
The outbreak of the new, three times more virulent, strain of Dutch elm disease Ophiostoma novo-ulmi in the late s brought the tree to its nadir.
Since circa the elm has enjoyed a renaissance through the successful development in North America and Europe of cultivars highly resistant to DED.
Some of the latter, however, were by today's standards inadequately described or illustrated before the pandemic, and it is possible that a number survive, or have regenerated, unrecognised.
Enthusiasm for the newer clones often remains low owing to the poor performance of earlier, supposedly disease-resistant Dutch trees released in the s and s.
In the Netherlands, sales of elm cultivars slumped from over 56, in to just 6, in ,  whilst in the UK , only four of the new American and European releases were commercially available in New York City 's Central Park is home to approximately 1, American elm trees, which constitute over half of all trees in the park.
The oldest of these elms were planted during the s by Frederick Law Olmsted , making them among the oldest stands of American elms in the world.
The trees are particularly noteworthy along the Mall and Literary Walk, where four lines of American elms stretch over the walkway forming a cathedral-like covering.
A part of New York City's urban ecology , the elms improve air and water quality, reduce erosion and flooding, and decrease air temperatures during warm days.
While the stand is still vulnerable to DED, in the s the Central Park Conservancy undertook aggressive countermeasures such as heavy pruning and removal of extensively diseased trees.
These efforts have largely been successful in saving the majority of the trees, although several are still lost each year.
DED first appeared on the trees during the s and reached a peak in the s. The NPS used a number of methods to control the epidemic , including sanitation , pruning , injecting trees with fungicide and replanting with DED-resistant cultivars.
The NPS combated the disease's local insect vector , the smaller European elm bark beetle Scolytus multistriatus , by trapping and by spraying with insecticides.
As a result, the population of American elms planted on the Mall and its surrounding areas has remained intact for more than 80 years.
Elm wood is valued for its interlocking grain, and consequent resistance to splitting, with significant uses in wagon wheel hubs, chair seats and coffins.
The bodies of Japanese Taiko drums are often cut from the wood of old elm trees, as the wood's resistance to splitting is highly desired for nailing the skins to them, and a set of three or more is often cut from the same tree.
The elm's wood bends well and distorts easily making it quite pliant. The often long, straight, trunks were favoured as a source of timber for keels in ship construction.
Elm is also prized by bowyers ; of the ancient bows found in Europe, a large portion are elm. During the Middle Ages elm was also used to make longbows if yew was unavailable.
The first written references to elm occur in the Linear B lists of military equipment at Knossos in the Mycenaean Period.
Elm wood is also resistant to decay when permanently wet, and hollowed trunks were widely used as water pipes during the medieval period in Europe.
Elm was also used as piers in the construction of the original London Bridge. However this resistance to decay in water does not extend to ground contact.
The Romans, and more recently the Italians, used to plant elms in vineyards as supports for vines. Lopped at three metres, the elms' quick growth, twiggy lateral branches, light shade and root-suckering made them ideal trees for this purpose.
The lopped branches were used for fodder and firewood. The mucilaginous inner bark of the Slippery Elm Ulmus rubra has long been used as a demulcent , and is still produced commercially for this purpose in the United States with approval for sale as a nutritional supplement by the U.
Food and Drug Administration. Elms also have a long history of cultivation for fodder , with the leafy branches cut to feed livestock.
The practice continues today in the Himalaya , where it contributes to serious deforestation. As fossil fuel resources diminish, increasing attention is being paid to trees as sources of energy.
Elm bark , cut into strips and boiled, sustained much of the rural population of Norway during the great famine of Elm has been listed as one of the 38 substances that are used to prepare Bach flower remedies ,  a kind of alternative medicine.
Chinese elm Ulmus parvifolia is a popular choice for bonsai owing to its tolerance of severe pruning. In , a European Union elm project was initiated, its aim to coordinate the conservation of all the elm genetic resources of the member states and, among other things, to assess their resistance to Dutch elm disease.
Accordingly, over clones were selected and propagated for testing. Many elm Ulmus trees of various kinds have attained great size or otherwise become particularly noteworthy.
Many artists have admired elms for the ease and grace of their branching and foliage, and have painted them with sensitivity.
The first reference in literature to elms occurs in the Iliad. These elms grew to be the tallest in the known world; but when their topmost branches saw far off the ruins of Troy, they immediately withered, so great still was the bitterness of the hero buried below, who had been loved by Laodamia and slain by Hector.
Elms occur often in pastoral poetry , where they symbolise the idyllic life, their shade being mentioned as a place of special coolness and peace.
Aside from references literal and metaphorical to the elm and vine theme, the tree occurs in Latin literature in the Elm of Dreams in the Aeneid.
Virgil refers to a Roman superstition vulgo that elms were trees of ill-omen because their fruit seemed to be of no value. Many references to elm in European literature from the Renaissance onwards fit into one or other of these categories.
There are two examples of pteleogenesis :birth from elms in world myths. In Germanic and Scandinavian mythology the first woman, Embla , was fashioned from an elm,  while in Japanese mythology Kamuy Fuchi , the chief goddess of the Ainu people , "was born from an elm impregnated by the Possessor of the Heavens".
The elm occurs frequently in English literature, one of the best known instances being in Shakespeare's A Midsummer Night's Dream , where Titania, Queen of the Fairies, addresses her beloved Nick Bottom using an elm-simile.
Here, as often in the elm-and-vine motif, the elm is a masculine symbol:. Another of the most famous kisses in English literature, that of Paul and Helen at the start of Forster's Howards End , is stolen beneath a great wych elm.
The elm tree is also referenced in children's literature. An Elm Tree and Three Sisters by Norma Sommerdorf is a children's book about three young sisters that plant a small elm tree in their backyard.
The cutting of the elm was a diplomatic altercation between the Kings of France and England in , during which an elm tree near Gisors in Normandy was felled.
In politics the elm is associated with revolutions. In England after the Glorious Revolution of , the final victory of parliamentarians over monarchists, and the arrival from Holland, with William III and Mary II , of the 'Dutch Elm' hybrid, planting of this cultivar became a fashion among enthusiasts of the new political order.
In the American Revolution 'The Liberty Tree ' was an American white elm in Boston , Massachusetts, in front of which, from , the first resistance meetings were held against British attempts to tax the American colonists without democratic representation.
When the British, knowing that the tree was a symbol of rebellion, felled it in , the Americans took to widespread 'Liberty Elm' planting, and sewed elm symbols on to their revolutionary flags.
In a chance event linking elms and revolution, on the morning of his execution 30 January , walking to the scaffold at the Palace of Whitehall , King Charles I turned to his guards and pointed out, with evident emotion, an elm near the entrance to Spring Gardens that had been planted by his brother in happier days.
The tree was said to be still standing in the s. Jean-Baptiste Lesueur, President George W. The name of what is now the London neighborhood of Seven Sisters is derived from seven elms which stood there at the time when it was a rural area, planted a circle with a walnut tree at their centre, and traceable on maps back to Elm propagation methods vary according to elm type and location, and the plantsman's needs.
Native species may be propagated by seed. Optimal conditions occur after a late warm spring. They are planted in sandy potting-soil at a depth of one centimetre, and germinate in three weeks.
Slow-germinating American Elm will remain dormant until the second season. Elm uses a single colon to mean "has type".
Types include primitives like integers and strings, and basic data structures such as lists, tuples, and records.
Custom types allow the programmer to create custom types to represent data in a way that matches the problem domain.
Types can refer to other types, for example a List Int. Types are always capitalized; lowercase names are type variables.
For example, a List a is a list of values of unknown type. It is the type of the empty list and of the argument to List.
Code that produces or handles an optional value does so explicitly using this type, and all other code is guaranteed a value of the claimed type is actually present.
Elm has a module system that allows users to break their code into smaller parts called modules. Modules can hide implementation details such as helper functions, and group related code together.
Modules serve as a namespace for imported code, such as Bitwise. Third party libraries or packages consist of one or more modules, and are available from the Elm Public Library.
All libraries are versioned according to semver , which is enforced by the compiler and other tools. That is, removing a function or changing its type can only be done in a major release.
The core development team does not consider it as their primary goal and prefers to focus development on the enhancement of front-end development experience.
Nevertheless, there are several independent projects, which attempt to explore possibilities to use Elm for the back-end.
The projects are mainly stuck on Elm version 0. One of the projects executes Elm directly on the environment  while another one compiles it to Elixir.
Elm does not support higher-kinded polymorphism ,  , which related languages Haskell and PureScript offer in the form of type classes.
This means that, for example, Elm does not have a generic map function which works across multiple data structures such as List and Set.
In Elm, such functions are typically invoked qualified by their module name, for example calling List.
In Haskell or PureScript, there would be only one function map. This is a known feature request that is on Czaplicki's rough roadmap since at least Another outcome is a large amount of boilerplate code in medium to large size projects as illustrated by the author of "Elm in Action" in their single page application example  with almost identical fragments being repeated in update, view, subscriptions, route parsing and building functions.
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