The following main functions of plant stems can be mentioned:
movement of water and dissolved minerals from roots to leaves;
movement of organic substances from leaves to all other plant organs (roots, flowers, fruits, buds and shoots);
removal of leaves to sunlight and support function.
In connection with the functions performed, the stems higher plants, especially angiosperms, acquired their characteristic internal structure.
As you know, plants have woody and herbaceous stems. In terms of internal structure, they differ from each other more strong development some tissues and underdevelopment of others. The clearest picture of the internal structure of the stem can be seen in the cross section of the tree.
The stem of a woody plant usually consists of four layers: bark,cambium,wood and core. Moreover, each layer can include cells of different tissues. Thus, the bark contains peel, cork, bast fibers, sieve tubes and other tissues.
In young stems of woody plants, the surface remains skin. Like the skin of leaves, it has stomata through which gas exchange occurs. Under the skin or, if there is none, on the surface is cork. In a number of trees, the cork forms a fairly thick layer. There is a plug for gas exchange lentils, which are tubercles with holes. Skin cells and cork cells belong to cover tissue. They protect the internal parts of the stem from damage, penetration of pathogens, and drying out.
Under the plug there may be a so-called primary cortex, and already under it is bast, which consists mainly of sieve tubes And bast fibers. Sieve tubes are bundles of living cells. They move along them organic matter, which were synthesized in leaves during photosynthesis. The cells of bast fibers have thick walls. Bast fibers are quite strong; they perform a mechanical support function.
Under the bark there is a thin layer cambium, which represents educational fabric. Its small cells actively divide during the growing season of the tree (from spring to autumn) and provide thickening of the stem. The resulting cambium cells, which are located closer to the cortex, differentiate into phloem cells. Those cambium cells that are closer to the wood become wood. Over the summer, more wood cells are formed than bast cells. On a tree cut, each year's wood cells are separated from each other by darker, smaller autumn wood cells. Thus, the growth rings are visible.
Under the cambium is wood, which usually makes up the bulk of the stem of a woody plant. Wood contains vessels. Moves along them from the roots water solution. Vascular cells are dead. In addition to vessels, wood contains other types of tissues. So there are cells with thickened, strong walls.
core usually consists of loose storage tissue, consisting of large cells with thin walls.
Stem (caulis)
axial organ of higher plants, together with leaves making up the shoot ,
serves to move water and substances between roots and leaves, to increase the assimilating surface of the plant by branching (See branching)
and orderly arrangement of leaves, as well as flowers and fruits; may participate in the accumulation of water and reserves nutrients, in Photosynthesis e. S. areas from which they depart lateral organs(branches, leaves, etc.) are called nodes, the areas between the nodes are called internodes. S. are herbaceous and woody; The main S. of woody plants is called the trunk. The shape of the plant is varied: cylindrical (the most common), triangular (sedges), tetrahedral (Labiaceae), multifaceted, flattened (cacti), etc. Based on its position in space, plants are classified into erect, recumbent, creeping, climbing, etc.; aboveground and underground (see Fig. 2). Length S. from 1-1.5 mm(freshwater wolffia) up to 200-300 m(tropical rattan palms), diameter from lobes mm(mosses) until 10-11 m(baobab, sequoia). S. grows in length due to the activity of the shoot apical meristem, which makes up the growth cone. In addition to apical growth, in some plants intercalary (intercalary) growth also occurs at the base of internodes (for example, in cereals). In S., anatomical and topographic zones are distinguished: the outer one is the epidermis, the inner one is the central cylinder, or stele, and the zone of the primary cortex located between them (See Primary cortex). ,
the inner parenchymal layer of which is transformed into endoderm. The latter borders the peripheral zone of the stele (represented by parenchymal or mechanical tissues) - Pericycle om
(some plants do not have it). Most of stele consists of conducting tissues (See Conducting tissues), Phloem is located outside the xylem (See Xylem). In deciduous mosses, in the center of the moss there is a “conducting bundle”, the elements of which are only externally similar to the conducting elements of phloem and xylem. In vascular plants, the formation of vascular tissues is preceded by the development of the procambium (See Procambium). In club mosses, the xylem is divided into ribbon-like strands surrounded by phloem; there is no core. Horsetails have closed collateral bundles with the so-called. carinal cavity instead of xylem are located around a central air cavity. In ferns, conductive tissues surround the core in a ring. In S. seed plants There are fascicular and continuous types of structure of the conductive system, intersected by radially diverging parenchymal medullary rays. The outer part of the procambium differentiates into primary phloem, on the periphery of which mechanical fibers often develop, and the inner part - into primary xylem. Between the conducting tissues there remains a layer of cells forming cambium, which deposits elements of secondary phloem - phloem - phloem - bast, and elements of secondary xylem - wood - inside, causing thickening of the stele. Lit.: Serebryakov I.G., Morphology of vegetative organs of higher plants, M., 1952; Meyer K.I., Morphogeny of higher plants, M., 1958; Eames A., Morphology of flowering plants, trans. from English, M., 1964; Botany, ed. L. V. Kudryashova, vol. 1, M., 1966; Esau K., Plant Anatomy, trans. from English, M., 1969. L. I. Lotova. Rice. 1. Anatomical structure of the stem of flowering plants: I - general form conductive system of the stem with an attached three-bundle leaf trail; II - structure of the stem in the area of the three-lacunate node, III - unilacunar, IV - multilacunal; V - palm type of passage of bundles in the stem of monocots; VI - structure of cereal straw; VII - structure of the bignonia stem with areas of bast protruding into the wood; VIII - the structure of the Wistaria stem, the thickening of which is due to several cambia; 1 - core; 2 - stele; 3 - leaf trail; 4 - bunches of leaf trail; 5 - sheet breaks; 6 - phloem fibers; 7 - xylem; 8 - fascicular cambium; 9 - phloem; 10 - stem; 11 - leaf sheath; 12 - closed collateral bundles; 13 - assimilation parenchyma; 14 - air cavity; 15 - xylem vessels; 16 - mechanical fabric; 17 - medullary rays; 18 - periderm; 19 - primary cortex; 20 - wood; 21 - bast
Big Soviet encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .
Synonyms:See what “Stem” is in other dictionaries:
Cycad tree-like plants, differing in the shape and height of the stem, but never reaching such large sizes, which many modern conifers are famous for. Usually, when they talk about cycads, they imagine... ... Biological encyclopedia
STEM, stem, plural. stems, stems, man. 1. The part of a plant, from root to top, that bears branches and leaves. Underground stem (rhizome; bot.). Main stem (trunk; bot.). “The stems of cereals and dandelions, swollen in the spring, in the caressing rays... Dictionary Ushakova
- (caulis), the axial part of a plant shoot, consisting of nodes and internodes. It grows in length due to the apical (in the growth cone) and intercalary, or intercalary, meristems. Bears leaves, buds and sporulation organs, in angiosperms... ... Biological encyclopedic dictionary
Trunk; arrow, actinostele, blade of grass, stalk, shoot, vine, shoot, straw, ataxostema, twig Dictionary of Russian synonyms. stem noun, number of synonyms: 25 actinostele (3) ... Synonym dictionary
- (caulis) an axial organ of plants that grows indefinitely at its apex and produces leaves in acropetal sequence. Top S. for the most part conical or hemispherical and in contrast to the apex of the root, another ... Encyclopedia of Brockhaus and Efron
STEM, an organ of higher plants that bears leaves, buds and flowers. The stems are aboveground and underground, herbaceous and woody. Length from 1 1.5 mm (freshwater wolffia) to 300 m (tropical rattan palms), diameter from fractions of a mm (mosses) to 11 m... ... Modern encyclopedia
A vegetative organ of higher plants, representing the shoot axis and bearing leaves, buds and flowers. The stems are aboveground and underground, herbaceous and woody, erect, climbing, climbing and recumbent. Stem length from 1 1.5 mm... ... Big Encyclopedic Dictionary
Plants, like a tree trunk, symbolize material world, the middle of the three worlds, along with roots as a symbol underworld and branches or flowers as a symbol of the heavenly world... Dictionary of symbols
STALK, fuck, many. bleat, bleat and bleat, husband. 1. Part of a plant (in a herbaceous plant from root to top), having branches, bearing leaves, buds and flowers. S. herbs. Wooden village 2. A thin, small branch shoot. S. leaf. | decrease stalk,... ... Ozhegov's Explanatory Dictionary