Wood (v. althochdt.: wood = knocking off) marks the solid and/or hard substance of the trunk, the branches and branches of trees and bushes. It is formed in the plants by the cells of the Meristems.

As more versatile, in particular however regenerating raw material is wood one of the most important plant products and wood belongs to the oldest useful plants.

In the forest one does not call wood present and living also Totholz.

Wood

Wood consists of:

• Cellulose (40 50%)
• Lignin (20 30%)
• Hemicellulose (Polyosen) (20 30%)
• Accessory components (also Begleit, contents or extra materials) (1 3%, tropical wood until 15%!): Fats, strength, sugar, protein, phenol, waxes, Pektine, Gerbstoffe (only with hardwood), Sterine, resin, Terpene
• Ash (0,1 0.5%, tropical wood to 5%)

Resinous wood

Evolutionary resinous woods are older than hardwood, have therefore a simpler anatomical cell structure and to possess only two cell kinds.

1. Tracheiden: Elongated (prosenchymatische) cells pointedly approaching at the ends, which are filled with air or water only. They have a portion of 90-100 % of the Holzsubstanz. Over and/or so mentioned takes place the water exchange between the cells. In radial direction the wood jets (Quertracheiden) for the water transportation ensure. They have a portion of 4-12 % of the entire Holzsubstanz.
2. Parenchymzellen: Usually rectangular cells, which take over the line of feeding and stature materials as well as the storage of strength and fats. In radial direction they form for wood jets likewise and surround the resin channels, here speak one then also of epithelium cells. These epithelium cells produce the resin, which they separate into the resin channel. Also coniferous trees, which possess no resin channels (e.g. fir), can in case of a Verwundung of trauma tables of resin channels form in such a way.

The coniferous trees spruce, larch, Kiefer and douglas fir do not possess resin channels, Eibe, fir and Wacholder.

Hardwood

The cells of hardwood are substantially more differentiated than from resinous wood. One can divide it in three functional groups.

1. Guidance fabric: Containers (tracheae), vasizentrische Tracheiden. The two latters are intermediate stages in the development of the Tracheide to the container.
2. Strengthening fabric: Libroformfasern, Fasertracheiden
3. Memory fabric: Holzstrahlenparenchymzellen, epithelium cells

Of hardwood are not characteristic in resinous woods existing containers. They are to be recognized often with the naked eye as small holes in the wood cross section and as grooves in the tangential cut. One differentiates here, depending upon arrangement of these tracheae, ring-porous woods (e.g. Oak, Edelkastanie, ash, Robinie, elm tree"Â…), half ring-porous woods (e.g. Nut tree, cherry"Â…) and absent-minded-porous woods (e.g. Birke, Erle, lime tree, Pappel, red beech, pasture"Â…).

Tropical wood

The term tropical wood is to be understood rather imprecise and not alternatively to leaves or resinous wood. It designates the wood growing in the tropical or subtropical regions of the earth from Central European view. Many tropical woods are characterised by favourable mechanical characteristics and higher stability against weathering, insect or fungal attack, also the color or grain than responding are often felt. The consumption of tropical wood was discussed critically in the industrialized countries for the 1970er years, since the existence of the tropical rain forests is endangered by predatory exploitation among other things. On the other hand wood represents an important restaurant factor for many tropical countries and is (as also in the moderate zones) an important source of income for the rural population.

Examples: Mahagoni, Teak, Balsaholz, Bangkirai, Bongossi, Abachi, Framiere

Emergence of wood

The emergence of Holzsubstanz takes place in divisionable cells of the plant. One differentiates here two different kinds from education fabrics (Meristeme):

• The Scheitelmeristem (vegetation cone) provides for length growth (primary growth) at the sprouting, branch and root points.
• The Kambium, which is between wood and crust, provides for thickness growth (secondary growth). During the division of a Kambiumzelle two equal cells develop, from which however only their division ability keeps and grows up to a new initial cell. From the other one a continuous cell becomes still in or several times divides. Finally a phloem cell (Phloem) develops, from which the interior crust and the bark developing later from it exists, or a wood cell depending upon situation (Xylem). Here it is to be noted that the cell division takes place substantially more frequently inward, thus the formation of wood cells and amounts to so the crust portion of the entire trunk only about 5 15%. After the continuous cell the latter divided times, a differentiation of the wood cell takes place to a line, a strengthening or a memory cell.

In our widths it gives climatically causes four growth phases:

• Dwell phase (November February)
• Mobilization phase (March, April)
• Growth phase (May July): Wood cells, those in this season develop are grosslumig, thin-walled and from bright color and form the in such a way specified.
• Deposition phase (August Octobers): Wood cells, those in this season develop are kleinlumig, thick-walled and from dark color and form the in such a way specified (and/or Herbstholz).

From this cyclic growth behavior result Jahresringe, which are clearly in a cross section recognizable by a trunk (see also dendrochronology).

Structure of the cell wall

If one moves from the outside into the inside of a wood cell, one crosses several layers those together the cell wall forms and under an electron microscope is recognizable. Between the cells is the central lamella, which forms the central layer in such a way specified together with the primary wall. Afterwards the secondary wall 1 (S1) and secondary wall 2 (S2) follows, whereby the S2-Schicht is the most powerful and dominierenste. The following Tertiary period wall (S3) is covered by a wart layer and forms Abschluss.Die individual layers or lamellas to consist of Fibrillen (Mikrofibrillen), which are formed again from Elementarfibrillen (Mizellen). Elementarfibrillen are bundles from several cellulose macromolecules, those from 10 - 14,000 glucose components consist and into a matrix of Hemizellulosen and lignin are embedded and form amorphous and crystalline ranges. Pouring and shrinking the wood with water absorption and delivery leave themselves by the orientation of these crystalline ranges, in which the Elementarfibrillen are strictly parallel run, closely packed and a water storage does not take place practically, in which dominaten S2-Schicht explain. Here these ranges are arranged so well parallel to the master axle; amorphous ranges in those more waters to be bound clearly and the volume knows is increased in such a way is in radial and tangential master direction thus more frequently to be found than in master longitudinal direction, in which the wood therefore 10 - 20mal fewer swelling deformations exhibits. In the relatively thin S1 and S3-Schicht run the crystalline ranges orthogonal to those in the thick S2-Schicht.

Verkernung

Splintholz one calls the range of the trunk, which participates actively in the water and nutrient transport. With split pin wood trees (e.g. Sycamore, Birke, Erle, Pappel, pointed maple, white beech"Â…) it is the whole master cross section. It does not exhibit a uniform colour and it takes place Verkernung.

Of the Verkernung of wood one speaks, if the internal water guidance courses of the trunk are interrupted and the cells to die. This takes place with resinous woods with locking the and with hardwood by means of a Verthyllung and filling the cell lumens at an age of approx. 20-40 years. Afterwards core contents materials are formed and stored into the cell walls, which often leads to an increase of the natural durability. If the core range is to be recognized clearly by a dark colouring, one speaks of heartwood trees (e.g. Oak, Walnuss, Kiefer, cherry tree, douglas fir, larch, Robinie"Â…).

If no difference in color is to be recognized, but over the reduced moisture content on it to be closed that that is verkernt internal area, speaks one can of hoar frost wood trees (e.g. Spruces, fir, lime tree, Birnbaum, red beech"Â…).

With core hoar frost wood trees (e.g. Ash, elm tree"Â…) the core is not coloured set off, followed from a hoar frost wood range, just like the core the any more at nutrient transport participates and an outside split pin range.

{|

| align= " centers " | | align= " centers " | | align= " centers " | | - | align= " centers " | fig. 1: Cross section by an oak trunk (heartwood tree). | align= " centers " | fig. 2: Cross section by a Kiefernstamm (heartwood tree). | align= " centers " | fig. 3: Cross section by a spruce trunk (hoar frost wood tree). |} 

Articles in category "Wood"

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