What is a stem? From the point of view of biology, this is the part of the plant on which the leaves and flowers are located, which is a continuation of the vascular system, which originates in the roots. The main function of the stem is to carry water and essential minerals from the soil to the leaves and other parts of the plant. Green stems are also responsible for nutrition and are involved in photosynthesis.
Stem: its structure and meaning
Tissues at the end of the stem, capable of cell division and causing it to elongate, are called apical meristems. The layers of the stem include the epidermis, an outer layer of cells coated with a special plant wax that provides protection from the external environment. Primary tissues bind the epidermis and internal phloems, which are responsible for the distribution of photosynthesis products throughout the plant. Xylem tissues distribute water and minerals from the roots to the very top, thus providing structural support in plants. The cambium tissues are a layer of dividing tissues, their growth allows the trunk to grow in width. The value of the stem lies, first of all, in providing the vital substances of the whole plant. If it gets damagedor tightly bandaged, then over time, tissues deprived of nutrition begin to slowly dry out. Complete death occurs with the death of the root system. The stem parts also include the pith, which in older woody plants is filled with the tough xylem of woody fibers and is used for plant identification. It can be solid or hollow. Its section can be round, triangular or star-shaped.
External characteristics
What is a stem and what does it look like? The top of the stem is its main point of growth. The receptors located there can be presented in the form of leafy vegetative buds and reproductive buds. In many plants, a special apical hormone, auxin, inhibits the development of lateral buds, thereby orienting the plant upward rather than sideways. If the apical bud is removed during pruning, then the lateral buds growing from the axils of the leaves will develop more actively, and the stem will take on a bushy shape. As a rule, the top is covered with modified sheets - kidney scales, which serve for protection. The bark is the outer protective tissue of woody plants and develops with age.
Vascular system
The vascular system is represented by a network of pipes through which water and nutrients are transported throughout the plant, connecting the roots, stem and leaves. Not all representatives of the flora can boast of this, for example, mosses and algae receive nutrition in a diffuse way. Vascular plants include flowering and cone-bearing plants, andalso ferns. The system consists of two main tissues: phloem and xylem. Xylem is a network of pipes that transports water and minerals throughout the plant. In addition, it also provides a secondary function of structural support, which can be compared to the spine, which helps to maintain an upright position. The texture of the stem often depends on the amount of this tissue, for example, it is very abundant in tree trunks, it is much less in flowers.
Common varieties of stems
- Wood. This includes vertically growing trees with a relatively large core, as well as shrubs (roses, grapes, blackberries, raspberries).
- Changed. For example, tulips, lilies, and onions have thick, underground stems with fleshy leaves. Gladiolus has a short, thickened underground stem with short, scaly leaves. A compressed stem, with leaves growing above and below the roots and flowers have strawberry, dandelion, African violet.
- Horizontal. For example, above-ground shoots of strawberries, iris.
- Climbing stems (hops, honeysuckle, beans).
- Stem types also include tuber, such as potatoes.
- The tuberous trunk, short and flattened, is found in begonias, dahlias. Unlike tubers, which have scattered receptors, tuberous stems only have leaf buds at the top.
Stem functions
1. It supports the leaves, flowers and fruits by binding them to the roots. In trees and shrubs, the main stem or trunk is characterized by a strong columnar structure.
2. It is a conductor of water, nutrients and photosynthesis products. Its transport system is designed in such a way that vertical and lateral movement within the plant organism becomes possible.
3. The ability to conserve water and photosynthetic products is a vital function of the stems of plants such as cacti and palms.
4. The young green stem plays a secondary role in food production through the process of photosynthesis, but in some species (such as cacti) the stem is the main photosynthetic organ.5. It serves as a means of asexual reproduction in many plant species, including cuttings.
Stem parts
All stems of angiosperms, including those that are highly modified, have nodes, internodes, buds and leaves. A node is a point from which leaves or buds grow. The area between them is called an internode. A bud is an embryonic stem that has the potential to grow and develop. It can develop into a leaf or a flower. Such buds are referred to as leaf buds, buds and mixed buds. Many of them remain dormant for a certain period, then grow into separate parts or are embedded naturally in stem tissues and are hardly noticeable. Trees and shrubs, in addition to the main stem, as a rule, also have side branches, to which smaller branches are attached. Exceptleaves and buds, other structures may be present in the form of hairs, which are outgrowths of epidermal cells, spines and stipules.
Stem dimensions
When answering the question about what a stem is, it is also important to consider its size. In all plants, it is most often the aerial part that provides structural support and serves as an intermediary and conduit between the root system and leaves. The stems vary in size, ranging from a small vine to a 15-meter diameter tree!
Meaning
What is a stem? We can say that this is the central axis to which all other parts are attached. In most plants, they are located above the surface, but in some species the stem may be hidden underground. Its structure and meaning are inextricably linked. Due to the unique structure, water and nutrients are delivered to both the leaves and the roots. The importance of the stem cannot be overestimated; the blockage of this vital artery leads to the death of the plant. There are a large number of industrial applications, including woodworking (logs, firewood, lumber). It is also a rich source of cellulose for paper making, and certain types of stems can be a source of nutrition. Its processed fibers are used in medicines, latex, tannins, paints, and more. Some types of stems are used for asexual or vegetative propagation of plants.
A huge number of applications
There are thousands of plant species whose stems are of great importance for agriculture, such as the potato. Sugar cane stalks are the main source of sugar. Maple sugar is obtained from the trunks of maple trees. Vegetables include asparagus stalks, bamboo shoots, kohlrabi, and water chestnuts. Spicy cinnamon is the bark. Gum arabic is a food supplement derived from acacia trees. Chicle is the main ingredient in chewing gum and comes from the chicle tree. Bamboo is used to make paper, furniture, boats, musical instruments, fishing rods, water pipes, and even houses. Cork is obtained from the bark of the cork oak. The rattan used for furniture and baskets is made from tropical palm stalks. The earliest example of the use of this important part of the plant is papyrus, popular in ancient Egypt. Amber is the fossilized sap from tree trunks, used for jewelry and may contain the remains of ancient animals. Softwood resins are used to make turpentine and rosin.
