the Organization of fabrics. Roots

you are: the Organization of fabrics

Cages of an external layer {proepidermisa) a young root turn in due course or in uploshchennye epidermalnye cages, or to root hairs (fig. 3.6 see). At some kinds of plants the destiny of these cages is defined already during the moment of their occurrence - at cellular division because though the nuclear material of a parent cage proepidermisa shares between daughter cells fifty-fifty, its cytoplasm (at formation of a cellular plate) is distributed between them non-uniformly. As a result of such non-uniform division there are two unequal cages: big from them turns eventually in epidermalnuju a cage, and smaller - to a root hair. root hairs are separate cages epidermisa, supplied long threadlike vyrostami (on these vyrostam they and are named ' by hairs '); the big surface allows them to absorb very effectively water and the mineral substances dissolved in it. During fast growth of these cages the kernel almost always is in the tip of a hair and serves, apparently, as the centre of high metabolic activity. Root hairs are rather short-lived, they sit on roots very densely and are quickly formed again as the tip korija moves ahead in soil. Was, for example, it is counted up that the total length of roots at the one and only plant of the rye growing within four months in a box filled by the earth (30X30X55 sm), has made about 717 km. At this calculation summarised length of all 13 million basic and lateral roots, and also 15 billion root hairs. From this data it is easy to see, presence of root hairs is how much strong increases the area of a surface of the root, being in direct contact to an environment.

The Core in roots usually is absent, and the central fabric, being differentiated, turns to spending elements (fig. 3.5 see). This type of changes can be observed even in culture of fabrics. Here seldom it is possible to see traheidy or the vessels differentiated on a surface kallusnoj of weight, but in the heart of such quickly growing weight of not differentiated fabric congestions nonfunctional traheid, reminding on the morphology traheidy functional ksilemy are found out small, in a kind mutovok. It is possible to assume therefore what exactly in fabric weight is something favouring ksilemnomu to differentiation type. It ' something ', probably, consists in a lack of oxygen or of special conditions of a food in weight of cages or, at last, in absence of contact to an environment.

Ksilema - the main way on which in a plant water and mineral substances are transported. This fabric includes some different types of the dead spending cages extended at length which are in close contact with live parenhimnymi with cages. One group form, it is strong odrevesnevshie traheidy, vessels and fibres, in a mature condition deprived of live contents. In vessels and traheidah inside there is extensive enough cavity on which water is transported. Sometimes this cavity is tightly hammered vyrostami next parenhimnyh cages, so-called tilami and then such vessel loses ability to spend water. Fibres are similar with traheidami and differ from them only that their walls more thickly, and a cavity already; they carry out basically mechanical, or basic, function - support the given body. All mentioned cages have the bordered time; large apertures in cross-section walls are available only in vessels. Basic function carries out also kollenhima, which covers of cages utolshcheny only on corners.

Round cages ksilemy in a root bunches floemy, meristematichesky a pericycle in which lateral roots, and endoderma, surrounding all central cylinder, or stelu are put settle down. While lateral runaways of a stalk develop from the kidneys put on a surface, in stalk knots, lateral roots are formed of internal parts of the main root, namely from a pericycle, and, to leave on a surface, they should break through the fabrics lying outside from stely, i.e. A bark and epidermis. Floema serves in a plant as the main way for transport of carbohydrates - photosynthesis products. As well as ksilema, this fabric consists of cages of different types. Sitovidnye tubes (the main spending element floemy) represent longitudinal numbers of the extended cages (chlenikov) with the punched partitions through which pass cytoplasmatic tjazhi, making a single whole with contents chlenikov. CHleniki sitovidnyh tubes in a mature condition do not contain kernels, but small cages-companions lying with them nearby have large kernels. To sitovidnym to tubes adjoin as well numerous cages floemnoj parenhimy.

Cages endodermy are characterised by presence of a corbel of Kaspara - a special thickening from the water-proof material covering in the form of a strip radial walls of a cage, Pojasok Kaspari serves as a barrier interfering diffusion of substances between a bark and steloj on cellular walls; it directs movement of all substances from apoplasta (a spatial continuum out of plasmatic.membran) through selectively nontight membrane of cages endodermy in simplast (a spatial continuum in plasmatic membranes and plazmodesm).

Between the central cylinder and epidermisom a root there is its bark consisting from large, thin-walled, ryhlo of packed cages (fig. 3.5 see). These parenhimatoznye cages with a large kernel, central vakuolju and numerous lejkoplastami serve mainly as storehouse for such spare substances, as starch. With occurrence kambija, put between ksilemoj and floemoj the central cylinder and sharing in a tangential plane, the thickening of a root representing result kambialnoj of activity begins. The bark under the pressure of this gain bursts and on periphery slushchivaetsja, and wounds are tightened thanks to activity of numerous separate sites pith kambija. Finally at older root and epidermis, and a bark are dumped entirely, and from already continuous secondary meristemy - pith kambija - the new integumentary fabric - periderma which essential component is the stopper is formed.