Stem.

the body shaft part of the tube plant (ferns and seed plants) developed by the germ. The lower part is connected to the root, and the upper part is made of leaves, flowers and fruit. The main functions of stems are the transmission of nutrients and moisture, the support of leaves, flowers and fruits to a certain space, some stems have the role of storing nutrients, some have reproductive function, the young stems in childhood and the stems of certain plants (such as cacti), and the function of photodexual. Stems have between sections and sections, and leaves are born on the sections. The top of the stem and the leaves are sprouted. When the leaves fall off, leave marks on the section. Most seed plant stems are cylindrical in shape, while a few plant stems have other shapes, such as the stems of salsa plants are triangular, lip-shaped plant stems are square columns, and some cactus plants have flat round or multi-angled columns. The stems of different plants adapt to the external environment, have their own way of growing, so that the leaves can be carried out in space, get enough sunlight, make nutrients, and complete the role of reproduction. According to its different mode of growth, can be divided into erect stems, winding stems, climbing stems, stalks and so on. General plants rarely have only one stem, usually by the development of buds and the formation of branches, a variety of branches have certain laws. The height of stems varies widely, from several centimeters in length to
150 meters. According to the composition of woody cells contained in the stems, they are divided into two main categories: woody stems and grassy stems. Wood stems have a tube formation layer that forms a hard woody part that increases the robustness of the stems, which are trees and shrubs. There are many types of grass stems, some born in
and can only live
one growing season; Wood stems are mostly solid (bamboo-like sections are hollow), grass stems in addition to solids, there are hollow, such asvegetables. Some of the plants of the undergraduate are hollow in the place between the festivals, while the places in the festival are solid. The structure of stems varies greatly according to plant species. Herb stems are similar to the larvae of woody plants, but most one- or two-year-old herbs do not have or have only a small number of secondary structures. Single leaf plant stems generally do not have a tube formation layer, so there is no secondary structure, some single leaf plant stems can be thickened, by the stem end of the base of the initial thickening
organic
cells to divide the results. In addition to the primary structure, the stems of the naked and gemal plants also have the secondary ligament and secondary woody part formed by the tube formation layer, as well as the periths formed by the wood hydrant formation layer; The stem of a plant, which changes in morphological structure due to the adaptation of the change of environment, forms the pervert of the stem, which can be divided into the pervert of the above-ground stem and the pervert of the underground stem. Plant stems have a variety of economic uses, perennary wood stem, secondary wood accounted for the largest volume, that is, wood, in construction, mining, transportation, furniture widely used;

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