the Organization of fabrics. Stalks

you are: the Organization of fabrics

Processes of cellular division and differentiation in stalks in many respects remind corresponding processes in roots. The top (apeks) a stalk dvudolnogo plants contains meristematicheskuju a zone which consists of quickly sharing cages (fig. 3.7). Behind this zone of sharing cages the area of fast growth by a stretching lies, and it is followed in turn by area of cellular differentiation merging and blocked with it. In a differentiation zone development epidermisa, the central cylinder and a primary bark is traced. Stalks differ from roots mainly core presence, and also other order of an arrangement ksilemy and floemy. At dvudolnyh round a core it is placed ksilema, and around ksilemy - floema; at odnodolnyh containing ksilemu and floemu vascular bunches can be disseminated and in bark, and the central cylinder which are not divided here by a clear boundary.

Though the anatomy of a stalk of any plant is determined genetically, external conditions Are capable in some measure of it to influence; for example, the stalks which have been grown up on light, do not contain usually accurately expressed endodermy whereas in the stalks which have been grown up in the dark, endoderma generally is available.

In a stalk as well as in a root, kambialnyj the layer is put between ksilemoj and floemoj; sharing intensively in both directions, this kamby forms cages which are from the inside differentiated in elements ksilemy, and with external - |в elements floemy. The stalk, as well as a root, grows at thickness at the expense of an internal gain. External layers of a stalk under the pressure of this internal gain are broken off and in due course are dumped. The plant forms thus on the bared sites new protective cages. Here too appears pith kamby, generating cages with the thick walls containing suberin - a water-proof material, characteristic for oprobkovevshih fabrics. as the stalk grows at thickness, consecutive layers of the stopper making now a component of a bark, are broken off, slushchivajutsja and are replaced with new cages which are postponed either old, or again arisen layers pith kambija. The stopper valuable to technical use which are cut off from trunks of a pith oak (Quercus suber), represents a product of such process.

Characteristic for wood trunks year rings arise as consequence of distinctions in weather conditions at various times year. In the spring at plentiful supply by water and other favorable conditions kamby forms it is rather thin-stenye cages with a wide cavity. In the summer and in the autumn when the plant quite often lacks some water, at again formed traheid walls happen more thickly, and a cavity already. vledstvie such regular alternation of spring and summer wood also there is a year ring (fig. 3.8). Usually transition from spring wood to summer in any year appears smooth whereas transition from the summer wood formed in the end of one vegetative period, to the spring wood formed in next year, happens sharp, and the border between them looks like an accurate line; on these lines also define age of a tree.

The Regularity of year rings allows to date remained rests of trees and the escaped wooden subjects, and on them and ancient civilisations. We will admit, we know that in those or other areas the certain climatic cycles including changes in an amount of precipitation and temperature took place. In the years especially favorable for growth, very wide year rings, and in years droughty - very narrow are formed. Having compared, say, wood structure in a fixing rack of any structure concerning nowadays disappeared civilisation, with a material which age to us is known, we can date such way and a civilisation. This method possible to find out, for example that a round table in the Winchester cathedral in England, belonging, as; assumed, to king Arthur, actually has been made much later, in 1538 This method though also very useful, cannot be considered, however, quite reliable, first, because in unusual conditions for a year is formed sometimes not one ring, and two and more, and, secondly, because the next year rings not always happen are accurately differentiated. When additional certificates are required, it is necessary to resort, and to any other ways of dating, for example to a radio carbon method.