thuya and libocedrus
thuya and libocedrus defined in 1944 yearthuya and libocedrus - Thuya and Libocedrus;
thuya and libocedrus - The genus Thuya L. (Family Cupressaceae) has flattened foliage closely resemBling that of the Shining Cypresses (Chamacyparis), the scale-like leaves being ranked in groups of four, two of each group being flattened and two bent, the whole encircling the stem of the branchlet, and concealing both stem and terminal buds. On closer observation, however, the edges of the side-leaflets will usually be found to be more curved than those of Chamacyparis, so that the edges of each opposite pair run together to form a Y-shaped line with sinupus arms. (Contrast the straight-armed V of Chamacyparis The branchlets are finely divided, and the smaller ones ultimately fall with the leaves attached; the main ones elongate, bearing the vestiges of their old leaflets in the form of long drawn-out Y's. The leaves bear oil-glands. The name Thuya is derived from an ancient Greek root.
The Thuyas are tall trees of slender habit, with a distinctive thin, fissured, fibrous bark. The male flowers are small, inconspicuous structures borne on the branchlets, and are reddish in colour. The female flowers appear at the tips of branchlets, as numerous green conical bodies, less than 1 inch in length, which are not readily seen until they have ripened into cones in autumn. The cones of Thuya at once distinguish it from the true Cypresses; the oval scales all arise at or near the base, and are infolded together or imbricated. (Contrast the broad scales of Cupressus, each stalked at the centre.) The seeds are minute (70,000 to the lb.), each being surrounded by a thin membranous wing, and resemble those of Cypress. On germination, they form two oblong cotyledons, followed by juvenile needle-like foliage, at first in pairs, later in whorls of 4, which is succeeded by the adult flattened foliage in the second season. Nurserymen's forms in which the juvenile foliage persists are known as " Retinispora ".
Thuya is a small genus found only in China, Japan and the temperate zone of North America. It is cultivated in Britain under the name of Arbor Vitae, or Tree of Life, being a common garden tree and hedge-plant, but is known in America as "Cedar". Seed must be collected as soon as ripe, since it falls quickly and the main difficulty in raising plants in a nursery arises from the minute size of the first-year seedlings, necessitating careful weeding. Only one species has so far been planted on any scale here as a forest tree.
Thuya Plicata, D. Don., the Western Red Cedar or Canoe Cedar of North America (also known as T. gigantea) is an important timber tree from Alaska to California, being found in much the same area as the Douglas Fir. In Britain it is usually planted out as a two- year-one or two-year-two transplant, being used either pure or for under-planting. It likes a fresh or limy soil, thriving well on chalk, but being of recent introduction to our sylviculture, not a great deal is known as to its needs and performance here. It bears deep shade, and is a useful tree for under-planting. Its habit of growth is good, and the poles from thinnings are useful for fencing, containing a high proportion of durable heartwood. Whilst the green foliage is resistant to fire, after it dies and dries the oils and resins within it make it burn furiously; the timber is a good firewood.
The foliage of T. plicata closely resembles that of Lawson Cypress, so much so that only a nurseryman or forester who handles both species daily can be sure of distinguishing them by leaves alone. Both have white resin lines on the undersides of the branchlets. The foliage of Thuya is patterned with Y's, that of Cypress in V's or X's, but this, like other differences that have been suggested, is variable and a matter of degree only. Both have a resinous odour, but in the Thuya it is sharp and acrid, in Lawson Cypress dull and heavy. The tips of the side leaflets are clear-cut and sharp in T. plicata, but incurved against the stem in the typical C. lawsoniana.
The timber of Thuya plicata has a red-brown heart and a narrow zone of grey sapwood. It is strong, and extremely durable. In America it is widely used for roof shingles; it cleaves well and cleft shingles have a long life without preservative treatment; sawn shingles are also used. Other uses are transmission poles, piles, sleepers, boxwood, and building work generally. It is suitable for boat building and whole trees are hollowed out by the Indians for use as light canoes. If it can be grown here in quantity, it will be a valuable addition to our coniferous timbers, being attractive in appearance, light for its strength, durable, and fragrant.
In establishing plantations, close planting is advisable to preserve the tree's pyramidal habit of growth and cause it to develop a strong leader early. The thinnings are clean and readily saleable. There is often a market for the foliage which is much used for evergreen wreaths, and it is advantageous to get brashing material removed, as it is highly inflammable if allowed to dry. Thuya plicata is a splendid hedge plant, standing severe clipping if done in the summer months; it makes a good high hedge or screen and does not spread too broadly - as Lawson Cypress is very prone to do.
A closely allied American Thuya, T. occidentalis L., or White Cedar, is a valued timber tree in Canada and the eastern states and is used for hedges in Britain. A Chinese species, T. orientalis, L. and two Japanese species, T. dolabrata, L. and T.japonica, Maximowicz, are widely cultivated as ornamental trees both in Britain and the far East. Numerous cultivated forms are known, which are propagated by cuttings. Figs. 1a, 2c, 3d.
The Incense Cedars of the genus Libocedrus, Endlicher (Faipüy Cupressaceas) closely resemble the Thuyas, but are distinguished by their cones, which have few scales meeting at their edges; and larger seeds, few in number, with one large obvious wing and a second rudimentary wing, smaller than the seed, set at an angle to the main wing.
The genus has a wider distribution around the Pacific zone, species being recorded from New Zealand, New Guinea, New Caledonia, Chile, California, and China. Only one species is commonly grown in Britain, the Californian Incense Cedar (Libocedrus de currens, Torrey) which is valued for its beautiful columnar habit of growth, the erect trunk being clothed in dense dark green foliage. The leaf spray is finely divided, with pointed leaflets. Cotyledons of seedling two, followed by long spirally ranged juvenile leaves, and intermediate transitional leaves, before the adult foliage is assumed. Like the Thuya, Libocedrus may be propagated by cuttings. The wood resembles that of Thuya. Little or nothing is known of the Incense Cedars as forest trees in Britain; in some localities L. decurrens thrives exceedingly as an ornamental tree, but the genus is unlikely to be commonly planted in our forests. Figs. 4c, 5.
Thuya attains a height of 200 feet in America, 100 feet in Britain (to date). Libocedrus has reached 80 feet tall, 10 feet girth, in Britain in 66 years' growth.
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