Vegetable Histology - SpeedyLook encyclopedia

The vegetable Histologie is the part of the vegetable Biologie which studies the microscopic structure of the vegetable fabrics. This science was constituted at the 19th century, with the improvement of the Microscope. It rests on the Cytologie, which is the study of the alive cell.

The Plante is made up different fabrics with the specific roles.

The fabrics of protection

The skin is a primary education fabric made up of a base of jointed alive cells sometimes covered with Cuticule. The skin has a role of protection.

The Suber is a whole of impermeable dead cells because containing Subérine. The suber or Liege is a secondary fabric of origin; it comes from the differentiation of meristematic cells resulting from the operation of a secondary Méristème, suberophellodermic base or Phellogène. It has a role of protection. Let us note that the cells being impermeable, all the cells located outside the suber are dedicated to die. These scaling dead cells constitute the rhytidome at the woody plants, or more simply the bark of the Arbre S. Suberous base that one finds on the surface of the young people root S is, it, of primary origin.

Fundamental fabrics

The Parenchyma, the fabric often most abundant, consists of cells of globular form. The parenchyma presents specializations in relation to its position. There are thus chlorophyllian parenchymas, seats of the Photosynthèse; parenchymas of reserve which one often finds in the underground bodies. With its alive cells with the rich cellular contents, the parenchyma takes part especially in the functions of Nutrition.

Fabrics of support

The Collenchyme is a primary education fabric made up of alive cells with pectocellulosic Paroi important. The cells of the collenchyme are often lengthened and narrowly coupled the ones with the others. The collenchyme generally occupies of the external positions, and plays especially a part of support.

The Sclérenchyme is a primary education fabric. It is the whole of the died cells with wall thick, impregnated lignin and present in the form of fibers. The sclérenchyme is generally more in-depth than the collenchyme.

These fabrics ensure the support of the plant. One thus finds them primarily in the air parts like the stem and the sheet.

Conducting fabrics

The conducting fabrics of Angiospermes are the xylème and the phloem. The xylème leads the crude sap, the phloem the elaborate sap.

the Xylème is composed:

Of two types of conducting cells of sap: vessels made up of files of dead cells whose walls are impregnated of lignin; according to the degree of lignin impregnation, one distinguishes the punctuated or réticulés vessels. The trachéides, less rich in lignin, known as are ringed or spiral. The trachéides are never transformed into vessels.
Of woody fibers, made up of dead cells.
Of formed woody parenchymas of alive cells which gather the vertical parenchyma and the horizontal parenchyma. The first is especially present in the secondary xylème and plays a part of reserve, the second shape of the woody rays and results from the activity of wood-and-bast cambium (méristème secondary).

The Xylème allows the circulation of the crude sap made up of water and Rock salt drawn from the ground by the roots. In the vessels circulation is done primarily vertically and in the trachéides the presence of transverse wall causes a circulation out of baffle. The xylème has also a role of support.

The primary xylème comes from the differentiation of the primary méristème. In the body in the course of elongation appears procambium, fabric meristematic from which certain cells are different in trachéides capable of elongation (the protoxylème) and others in vessels (the métaxylème).

The differentiation of procambium is not identical in the stem and the root. It is centrifugal in the roots and centripetal in the stems. This difference makes it possible to distinguish a root of a stem.

The secondary xylème, or wood, is characterized by a radial alignment of its cells because of the operating features of wood-and-bast cambium (méristème secondary): it is formed in internal position compared to cambium and leads to the formation of vessels, fibers, vertical and horizontal parenchymas.

the Phloem

Like the xylème, the phloem gathers various fabrics:

sifted tubes, lengthened alive cells, which have longitudinal and transverse walls having pores called screens. These cells do not have a core but particular contents hyaloplasmic with lengthened proteins. The plasmalemme persists allowing exchanges.
the cells partners joined with the sifted tubes.
vertical playing a part of reserve, and horizontal bast Parenchymas forming the ray bast and bast fibers.

The phloem has a conducting role, it allows the vertical conduction of the elaborate sap which is a solution rich in organic matter. It has also a role of reserve with the parenchymas and a role of support with bast fibers. One distinguishes the primary education phloem formed by differentiation from the cells procambiales, the secondary phloem, with aligned cells, formed by differentiation of the cells of the cambium (wood-and-bast generating base)

See too

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