|
| This contest is fueled by the following news: |
| | Wood - in routine life & technology is the internal part of tree, located under the bark, is called wood. Fabrics or set of fabrics, formed from procambium or cambium are understood as wood or xylem.
Wood formation:
Wood is one of the components of fibro-vascular bundle & is referred to usual other component of bundle, occurring from this procambium or cambium – inner bark or phloem. 2 cases are observed during the formation of fibrovascular bundle from procambium: entire procambium cells transform into elements of wood and inner bark – obtained so-called closed bundles (higher cryptogamous, monocotyledonous & some dicotyledonous plants) or layer of active fabric is left on border between wood & inner bark – cambium & open bundles are obtained (dicotyledonous & gymnospermous).
In first case, quantity of wood remains constant & the plant is incapable of becoming thicker; in the second case, thanks to activity of cambium, with every year the quantity of wood increases & plant trunk grows thicker & thicker gradually. In Russian wood species, wood is concentrated at the center of tree (axis) & inner bark - close to circle (periphery). Other relative positioning of wood and inner bark is observed in some other plants (see fibrovascular bundles). Already dead cell elements with stiffened, basically with thick coats form the composition of wood; inner bark is made, on the contrary, of live elements, with live protoplasm, cell sap and thin un-stiffened coat. Even dead, thick-walled and stiffened are found in inner bark & on the contrary, live elements are found in wood, but from this, however, general rule does not change substantially. Both parts of fibrovascular bundle differ from each other according to physiological function: so-called raw sap, i.e water is present with substances dissolved in it, move upwards from soil to leaves along the wood and formed , in other words, plastic sap, moves downwards along the inner bark (see saps in plants). Stiffening phenomena of cell coats are caused by impregnation of cellulose coat by special substances, compounds usually under general name “lignin”. Availability of lignin & at the same time, stiffening of coat is easily identified by means of some reactions. Thanks to stiffening, plant coats become stronger, firm & elastic; at the same time, at easy water permeability, they lose ability to absorb water & to inflate.
Valuable wood species:
Value of various wood species depends on their strength, durability & originality of pattern. Such wood is used for manufacturing fine furniture, parquet, doors, various interior objects, which are considered elite by taking into consideration the initial high cost & amount of efforts, spent for its treatment. In Russia, following species are extensively found: oak, cherry, beech, pear, rosewood mahogany, walnut, maple (white, sugar, acutifoliate).
Basic operating features:
* Hardness - indicator of service life of top layer of wood. Deterioration is slow if the wood is hard;
* Stability and shrink level - indicates compatibility of various wood species during use in combination (in parquet, incrustations etc.). Also shows suitability of their use in various climatic conditions;
* Degree of oxidation - shows change of color of wood under the influence of light. If the degree of oxidation is more, then the wood becomes more & more darker;
* Expressiveness of texture - influences visual perception of person. At high contrast, high exciting effect is created;
* Durability to loads - ability of wood to withstand any type of loads.
All the properties can be different for each species (sometimes even for various parts of tree) & this depends on various conditions in which the tree grows.
|
|
| | 19 Contest Pictures Page 1 2 - View All
|
|
