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elms
Значение термина elms в knolik
elms - Elms
elms - G. Ulme,. Rüster; F. Orme; W. Llwyfen; E. Leamân.
The elms form a distinct genus of trees widely distributed across the northern hemisphere, occurring in the eastern states of North America, throughout Europe and Central Asia, in China and in Japan. They are, within limits, highly variable in vegetative characteristics, local forms being common, and this has caused great confusion in nomenclature.
The British elms fall into two main types, the Wych Elm, and the Field Elms. The type trees are distinct, but intermediate forms and hybrids are common.
The Wych Elm (Ulmus montana With.) (syn. U. glabra Huds.), known also as the Mountain or Scots Elm, is seen at its best in the Lowlands of Scotland, where on good sites it forms a large tree with fan-like branches terminating in robust twigs with pointed, alternate, slightly downy buds. Its bark is distinctive, being beautifully patterned with vertical fissures. The leaf is large, 3 to 4 inches long, simple, entire, with a serrated edge, and often uneven at the base; the upper surface is very rough to the touch, and the colour is usually a dull green. The seed is borne in the centre of the wing. There is a Weeping variety, propagated by grafting. The Wych Elm does not produce suckers. Figs. 1k, 5,6e.
The various forms of the field elms are seen at their best in the English Midlands, and are typified by erect trunks, with irregularly-disposed lateral branches and a huge circular crown. The towering bulk of their foliage is built up of small leaves about 1 inch in length, borne on smooth, slender twigs. These leaves are alternate, entire, often asymmetrical at the base, with serrated edges. They are amongst the first to appear in March and the last to fall in November, after turning a pale yellow.
The bark of the Field Elms is rough, the vertical fissures having no distinct pattern. The seed is placed above the centre of the wing. Figs. 1h, 2, 3; 4.
To the species Ulmus nitens Moench. may be referred most of the Field" Elms with a smooth or shining upper leaf surface, including the Cornish and Jersey Elms, varieties noted for their tall and slender habit of growth. Ulmus procera Salis, includes most forms with a rough or harsh upper leaf surface. Both species are notable for their production of sucker-shoots from the roots, often in dense masses, which may grow up to replace the parent trees.
"Dutch Elms", which may be of English or imported origin, are hybrids between the Wych Elm and one or other of the many forms of Field Elm. Their characteristics are generally intermediate, but are variable and unstable.
Elms flower very early in the year, about February, before the leaves have opened. The flowers are borne in dense clusters, individually minute, but so numerous as to form distinct crimson tassels on the bare stems/ This colour is due to the anther heads of the stamens; the flowers are hermaphrodite, but there are no petals and the calyx is inconspicuous. Pollination is by wind.
The winged fruits develop early from the flower clusters, and may fall as soon as June. The light circular seed lies in or near the centre of a thin membranous wing, about a third of an inch in diameter. The seeds are spread by wind, and being very light (50,000 go to the lb.), speedily lose germinative power and in some seasons appear to be completely infertile. They make up in numbers for what they lack in quality, and there is little doubt that elms will regenerate themselves naturally wherever protection is afforded against rabbits and grazing animals. Being highly selective as regards soil, the elms are erratic in distribution. Avoiding the poorer soils of the hills, they must have been concentrated through most of the rich alluvial valleys which have now been cleared for agriculture, areas in which natural woodland is now almost unknown. They survive, therefore, mainly as relics of the old woodland in hedgerows and along stream sides - wherever their young growth secures a measure of protection from grazing animals. The theory that the Field Elms were introduced from Europe has no solid foundation; certain forms occur only in Britain.
The seed of the elms must be gathered as soon as ripe, and sown at once. Germinative power is never good, and hence the Field Elms are often grown from sucker shoots. The cotyledons of the seedlings appear above ground, being followed by a pair of opposite primary leaves which are symmetrical in outline; subsequent leaves are alternate and often asymmetrical. After one year in the seedbeds, the seedlings should be transplanted to stand for another two years in the nursery lines, after which they are ready for forest use. Suckers should spend a year in the nursery to develop their root systems before being planted out.
The Field Elms require a deep rich soil, neither acid nor alkaline, both well-drained and well-watered. They are frequently preserved by the hedger, and grow up in the hedgerows to immense size at a rapid rate under ideal conditions, with roots reaching far into the cultivated land on either side. They are wind-firm, stand moderate shade, and need a warm climate, though they do not suffer greatly from frost.
They cannot thrive in a smoky atmosphere, though old trees, which grew up when the air was still clear, may hang on for many years. As their large side branches are liable to fall without warning, the commoner forms are unsuited for public parks, and if growing close to footpaths, it is advisable to lop off these side branches.
The Wych Elm is less exacting in its soil requirements, extends into colder areas, and stands more shade. It will endure a greater degree of smoke, and its branches are less prone to fall. On the other hand, its growth is less rapid and the form of its stem less useful to the timber merchant. It is a tree of the glens and occurs wild in many parts of southern Scotland.
All the elms have suffered severely during recent years from the attacks of a fungus causing the Dutch Elm Disease. This spread with alarming rapidity from a centre in or near Holland, and at first killed out all trees infected. Latterly, its virulence has apparently diminished - more trees resist its attack, and more attacked trees recover; but it Is still a factor to be reckoned with, and restricts any extensive planting of the species.
Whilst elms will coppice, they are not cultivated in this way; but it is quite usual for felled Field Elms to be replaced by their own sucker shoots.
Field Elms may attain a height of over 130 feet in little more than 100 years; and their timber is available in large sizes, owing to their long, straight bole. Wych Elm tends to spread wider, reaching a lesser height, so that its timber is usually found in lesser dimensions. Certain forms of Field Elm are naturally of erect growth even in the open. Girths up to 24 feet are attained.
Red Elm is the timber of the Field Elm tree, and White Elm, that of the Wych Elm, being lighter in colour. " Dutch Elm " is obtained from a variety of intermediate forms, the term " Dutch " being in general use by countrymen to distinguish anything of unusual appearance or suspected foreign origin.
The wood of the Field Elm is rosy-brown in colour, with darker heartwood, tough and difficult to split, and resistant to decay if kept dry or continuously wet; in alternate wet and dry conditions it is not so durable. It has a really beautiful figure, but being of common occurrence is little valued for appearance, and is put to rougher uses such as waggon boarding and the seats of cheap kitchen chairs. In larger sizes it is used as structural timber for under-water works at docks and harbours.
White Elm and Dutch Elm are even tougher, combining the pliancy of ash with resistance to decay under water, They are of great value in the construction of wooden vessels, for keels, boarding, and exposed under-water work generally.
The sapwood of elms is nearly as durable as the heartwood. All the varieties yield excellent firewood.
In the past the cultivation of elm has been the care of the farmer rather than of the forester, but it is unlikely that the agriculture of the future will have much place for the hedgerow elm. Wherever the soil suits it, it might profitably be introduced into new woodlands on a small scale, in mixture with other trees, as its growth is rapid and its timber may be in demand when the present giants of the hedgerows have disappeared.
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