Tissue, cork

An example of artificial orientation was the orientation attained in cell walls of cork tissue by compression, which gives rise to orientation of the walls in a plane perpendicular to the direction of pressure. Irradiation with the beam in the plane of orientation resulted in a fibre pattern from which the orientation in the walls of the ali-cyclic wax component (friedelin) could be determined ( ). 

The outer bark, which consists mainly of periderm or cork layers, protects the wood tissues against mechanical damage and preserves it from temperature and humidity variations. In most woody plants a periderm replaces the epidermis within the first year of growth. The first periderm in stems usually arises from the cork cambium in the outer surface of bark, either in the subepidermal layer or in the epidermis. The following periderms are then formed in successively deeper layers of the bark or in the bast tissue. Cork tissue is predominantly formed in the outward direction, but some division also occurs inward resulting in so-called phelloderm tissue resembling parenchyma cells. Owing to this sequence the final rhytidome usually occurs as scaly bark and, in addition to the cork cells, contains the same cells as those present in the bast. 

Errera examined the distribution of alkaloids in plant tissues by histochemistry and found that alkaloids were present in active tissues near the vegetative points, ovule, epidermis and the layer just inside of it, hair, peripheral layers of fruits and seeds, vascular bundle, cork cambium, cork tissues, and latex tube (9). Molisch microscopically investigated 15 kinds of alkaloids as distinguishable crystal forms after treatment with acids or alkaloid reagents, and then histochem-ically examined them in plant tissue and cell sections following treatment with acids or alkaloid reagents (9). Tunmann and Rosenthaler observed histochemi-cally the distribution of alkaloids in tissues and cells of 36 families of plants 10). 

Compound Celluloses.—Differing from both of the preceding varieties are the celluloses which are present in the cork tissue and wood of trees, in the stalks of jute and ripe grasses, especially the cereals, and in the parenchymatous tissue of fruits. The celluloses of this type are... 

Adipo-Celluloses.—The third type of compound cellulose has a non-cellulose constituent of a fatty character known as cutin. The compound cellulose is therefore termed an adipo-cellulose, or a cuto-cellulose. Cellulose of this variety is formed in the cork tissue of plants and trees. 

Cork or suberous tissue is composed of cells of tabular shape, whose walls possess suberized layers. Its cells are mostly filled with air containing a yellow or brownish substance. It is derived from the phellogen or cork cambium which cuts off cork cells outwardly. Cork tissue is devoid of intercellular-air-spaces. It forms a protective covering to the roots of secondary growth, stems (after the first season) of Dicotyledons and Gymnosperms, and wounds of stems and branches. Living cork cells contain protoplasm and cell sap while dead cork cells are filled with air. 

Suberization—the process of being converted into cork tissue through the formation of suberin. 

In contrast to the exterior localization of cutin, suberin can be deposited in both external and internal tissues. External deposition occurs in the periderm of secondary roots and stems and on cotton fibers, whereas internal deposition occurs in the root endodermis and the bundle sheath of monocots. The Casparian strip of the root en-dodermis contains suberin, which produces a barrier isolating the apoplast of the root cortex from the central vascular cylinder. Suberin also produces a gas-impermeable barrier between the bundle sheath and mesophyll cells in C4 plants. The bark of trees contains periderm-derived cork cells that have a high suberin content. 

Cork cells Tabular with all walls suberized occur in thick layers on the outer surfaces of older stems and roots Secrete a fatty substance, suberin, into the walls, suberin renders cork cells waterproof and helps protect the tissues beneath... 

Peridermal tissue of stems Cork cells and cork cambium Mechanical protection... 

Yam tubers of Dioscorea alata (Umudike cultivar), D. rotundata (asukwu and obiaturugo cultivars)" and D. cayenensis (water yam and Nkokpu cultivars) were obtained from the National Root Crops Research Institute, Umudike, Nigeria. Some tubers were stored 6 or 12 months at room temperature (25-27 °C), some in vacuum dessicators over a suitable dessicant, and some in paper bags placed in a dark cabinet (absence of circulating air). Fresh tubers were peeled by carefully scraping away the cork layer to minimize loss of outer tissue since much of the protein is concentrated here ( ). They were then cut into 2 cu. cm. pieces, quickly frozen with solid CO2 in 50 9 portions in plastic bags, and stored in a freezer until needed. 

In 1665, Robert Hooke examined thin slices of cork under his very simple microscope and discovered small, box-like spaces which he named cells. A few years later the Italian anatomist Marcello Malpighi described similar structures in animal tissues, which he called vesicles or utricles and, in 1672, the English botanist Nehemiah Grew published two extensively illustrated volumes greatly extending Hooke s findings. The concept of the cell as a unit of structure in the plant and animal kingdoms was launched, but it was two centuries later before scientists... 

Cork (or Suber). The outer tissues of the stems of the cork oak or the exterior layers of the bark beneath the epidermis. In young stems it consists of epidermis, cortical tissues periderm and in older stems of secondary phloem periderm. Cork is used in some expls mixts described below... 

In Table 1 the chemical composition of the cork used in this work is presented. It shows that the material used contains lignocellulosic tissues, probably from the phloemic remains of the cork bark in the planks used for the production of stoppers The extraction percentages of the cork constituents were calculated based on the amount of constituents initially present in the extractive - free cork... 

The chemical composition of cork is made up by about 43% suberin (composed of fatty acids and alcohols), 28% lignin, 13% cellulose, 6% tannins, 5% waxes, and 5% ash. About 90% of the tissue is gas, resulting in a density of 0.12 to 0.20 kg/L. Cork has a unique capability as a bottle seal because of its excellent resilience after insertion into a bottle. This is due to its structure consisting of polygonal cells (30 to 42 million/cm ) separated by spaces filled with gas (atmospheric air without COj) which slows oxygen diffusion without completely eliminating it. 

Robert Hooke (1635-1703) was the first to publish results on the microscopy of plants and animals. Using a simple two lens compound microscope, he was able to discern the cells in a thin section of cork. The most famous mierobiologist was Antoni van Leeuwenhoek (1632-1723) who, using just a single lens microscope, was able to describe organisms and tissues, such as bacteria and red blood cells, which were previously not known to exist, hi his lifetime, Leeuwenhoek built over 400 microscopes, each one specifically designed for one specimen only. The highest resolution he was able to achieve was about 2 micrometers. 

Dermatogen originates epidermal tissue and derivative structures such as stomata, non-glandular and glandular hairs, glands, and cork cambium. 

Periblem originates cortex tissue, chlorophylloid cells (chlor-enchyma) colloid cells (collenchyma), strengthening cells (scleren-chyma), crystal cells (raphiderchyma) latex cells (lacterchyma), endodermis and cork cambium. 

Epidermis (outer cell walls cutinized) Cork (suberized tissue)... 

Pig. 60.—Cross-section of a young root of Phaseolus muHi-florus. A, pr, cortex m, pith X, stele or central cylinder—all tissue within the pericycle, inclusive g, primary xylem bundles b, primary phloem bundles. B, cross-section of older portion of root lettered as in A b, secondary phloem, k, cork. (Stevens, after Vines.)... 

Sometimes, as in Grape Vines, Honeysuckles, and Asclepias, instead of cork cambium arising from outer cortex cells it may arise at any point in cortex. It is the origin of cork cambium at varying depths that causes extensive sheets of tissue to separate off. That is what gives the stringy appearance to the stems of climbers. 

Fig. 71.—Portion of cross-section of four-year-old stem of Aristolochia sipho, as shown by the rings of growth in the wood. The letters are the same as in Pig. 68 but new tissues have been added by the activity of the cambium and a cork cambium has arisen from the outermost collenchyma cells and given rise to cork. The new tissues are I, cork cambium k, cork g, secondary phloem from the cambium, and just outside this is older crushed phloem , secondary xylem produced by the cambium m, secondary medullary ray made by the cambium (notice that this does not extend to the pith). Half of the pith is shown. Notice how it has been crushed almost out of existence. Compare Figs. 68 and 71, tissue for tissue, to find out what changes the primary tissues undergo with age, and to what extent new tissues are added. Photomicrograph x 20. (From Stevens.)...

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