The plant world is one of the most amazing and unusual wonders on our planet. Plants differ from each other sometimes as much as they differ in relation to animals. The only thing that unites some of them is the stem. Of course, this is a rather complex and heterogeneous structure, the functions of which are very diverse. Therefore, in the framework of this article, we will consider the structure of the stem.
General information
This is the main stem part of the plant. Leaves are attached to it, which are brought to the light on the stem, through its channels nutrient solutions, water and mineral s alts come to them. It should be remembered that it is in it that the deposition of nutrients "in reserve" can be carried out. In addition, the structure of the stem involves the development of fruits, seeds and flowers on it, which serve to reproduce the plant organism.
The main structural units are the knot and the internode. knotcalled the area directly on which the leaves or buds are located. Thus, an internode is located between two neighboring nodes. The space that forms between the node and the leaf petiole is called the sinus. Accordingly, those kidneys that are located in this area are called axillary. At the very top of the growing stem there is a bud, which is called the apical bud.
If we deviate a little from the main direction of the article, we can tell something interesting. Did you know that the internodes of some plants are large enough to make even small barrels out of them? Some types of bamboo, of course! This giant herb has stems so strong that they make not only dishes, but also excellent rafts. Bamboo stems are hollow, strong, almost do not rot, which determined the choice of many sailors in ancient times.
Lifespan
Everyone knows that the stems of woody and herbaceous plants differ greatly in life expectancy. So, in a variety of herbs that are common in the temperate zone, he lives no more than one season. The stem of woody plants can be preserved for more than one century. The Prometheus bristlecone pine is known all over the world, which grew in the territory of the present United States (index WPN-114). It was cut down in 1964. According to radiocarbon analysis, her age was … 4862 years! This tree even met the Nativity of Christ, being already at a very “venerable” age!
What other features are worth knowingstudying the structure of the stem? The main stem is called the trunk, in shrubs that have several growth points at once, such formations are called stems. Recall that there are several types of them at once. Here is the classification of stem types that is currently accepted.
Main classification
The upright variety is very common. Almost all the trees, a considerable part of the herbs are immediately remembered. At the same time, the structure of the plant stem is distinguished by a well-developed mechanical part, but it is not at all necessary that its tissues be completely stiff. An example is sunflower, corn, in which the trunk is still quite flexible and lively. In cereals, the aerial part of the stem is called the culm. As a rule, it is hollow inside (with the exception of the nodal zones). However, hollow varieties are widespread among melons, umbrella plants, etc.
Some herbs have a creeping stem. Its characteristic feature is the ability of nodal rooting. A perfect example is the wild strawberry.
The climbing and climbing type, which is in many ways a variation of the previous one, is widespread among vines. Among these plants there are also herbaceous and woody species. All of them are distinguished by a huge growth rate, due to which the reinforcing mechanical part simply does not have time to develop, and therefore the vine is in dire need of support.
Curly, according to their name, wrap around the base. It is curious that in some species, the antennae wrap around the base clockwisearrow, and some - in the opposite direction. There are also plants whose stems can equally well bend in all directions. In contrast, the clinging varieties climb the support, clinging to the smallest cracks and irregularities on its surface with their antennae (hops, ivy).
Most common stem shapes
If you take a plant and cut it, then the structure of the stem in this case will most often resemble a circle. Of course, nature doesn't end there:
- Trihedral cut of sedge.
- Tetrahedral nettle.
- Beautiful and incredibly complex cactus polyhedrons.
- Prickly pears have a flattened, almost flat-looking cut.
- In sweet peas, the structure of the plant stem resembles a wing.
But do not assume that this variety can be infinite. Excessively wide asymmetrical stems often arise as a result of some serious anomalies and developmental disorders. Here are the types of stem structure.
How does water and solutions of mineral s alts move along the stem?
As we know, a plant for a normal life must be provided with water and solutions of mineral s alts. One of the most important functions of the stem is their transport. If you cut a birch or maple branch at the very beginning of sap flow, then you can easily verify this, since tree sap will flow abundantly from the cut surface.
Almost the entire body of plants is permeatedconductive tissues. Moreover, all of them are differentiated: water and aqueous solutions rise through one, and organic substances - through other channels. In plants, these structures are often permeated with bundles of mechanical tissues that provide the strength they need.
How does organic matter move along the stem? Where can they stock up?
All organic nutrients are deposited in specialized cells that play a storage role. Actually, it was precisely for the sake of these substances that man tamed plants: he extracts oils and fats from them, the most valuable raw materials for the chemical, processing and food industries.
As a rule, all these compounds are deposited in young shoots, seeds and fruits of plants. We think that everyone knows potatoes, sweet potatoes or peanuts, in the case of which everything happens that way. As for trees, organic matter most often accumulates in the core. So, it is from this part of some types of palms that valuable raw materials for the chemical industry (paraffins, oils) are extracted.
What's inside?
The youngest, most recently grown stems of plants are first covered with a delicate skin. Subsequently, it is completely replaced by a cork. Her cells completely die, leaving only empty "cases" filled with air. Thus, the skin and cork are classified as integumentary tissues, and the cork is a multilayer structure.
Contrary to popular belief, it is formed already in the first year of a plant's life. As its age increases, so does the thickness of the cork layer. All integumentary tissues are designed by nature to protect the plant organism from adverse effects and environmental phenomena.
It must be remembered that all this data is of no small importance in some industries. First of all in woodworking. So, when processing wood, one should always remember that those parts in which young and rapidly dividing cells predominated during the life of the tree should not be used. Actually, the tops are thrown away during woodworking for this very reason. That's how important biology is in everyday life! The structure of the stem is very complex, but it is necessary to know it.
Thus, these fabrics prevent excessive evaporation, which is especially important in areas with a harsh and hot climate, protect the plant from dust and harmful microorganisms that can cause disease and death of the body. For gas exchange, there are tiny stomata on the surface of the integumentary tissues, through which the plant "breathes".
On the cork, you can see tiny tubercles with holes called lenticels. They are formed from especially large cells of the underlying tissue, which differ in the impressive size of the intercellular space.
Under the integument (and not on the surface) is the bark, the inner layer of which is called the bast. In addition, the internal structure of the stem includes sieve structures and satellite cells. In addition to them, there are also special cells in which nutrients are stored.
Structure of the crust
Bastthe fibers are elongated in length, with contents that have died in the process of development and stiffened walls, perform a bearing, mechanical role. The strength of the stem, its resistance to fracture depends on them. Sieve structures are vertically arranged rows of living cells, with destroyed nuclei and cytoplasm that adheres tightly to the inner membrane. Their walls are pierced with through holes. Sieve cells are part of the plant's conducting system, which carries water and nutrient solutions.
The internal structure of the stem also includes the cambium, which is distinguished by long, elongated and flat cells. They are actively divided in the spring and summer periods. The main part of the stem is the wood itself. Very similar in structure to the bast, it is also formed by cells of various shapes and functional purposes, which form several tissues (many conductive structures, mechanical and basic tissues). Tree rings are formed by all these cells and tissues.
This is how the 6th grade studies the structure of the stem in an ordinary secondary school. Unfortunately, the educational program does not often pay attention to the core. But it is formed by large cells with a thin wall. They do not fit tightly to each other, as they play a storage and accumulative role. If you have ever seen the core of a tree trunk, then you probably remember the "antennae" that diverge from it in different directions.
But they play the most important role! It is along these strands, which are large clustersconducting structures, nutrients go to the bast and other parts of the plant body. In order for you to better imagine the structure of the stem (including dicotyledonous plants), we will present the main data in the form of a table.
| Name of structural unit | Characteristic |
| Peel | Young shoots of the plant are covered on the outside. Performs a protective function, prepares a place for the formation of a cork, which consists of dead cells filled with air. Is an integumentary tissue. |
| Stoma for gas exchange | They are present in the skin, through the openings of the stomata there is an active gas exchange of the plant with the environment. In the cork layer, the same function is performed by lenticels, small tubercles with holes. They are formed from large cells of the underlying tissue. |
| Cork layer | The main integumentary structure that appears already in the first year of a tree's life. The older the plant, the thicker the cork layer becomes. It is formed by a layer of dead cells, the inner space of which is completely filled with air. Protects the stem of the plant from adverse environmental influences. |
| Kora | Located under the protection of the integumentary layer, its inner part is called the bast. It consists of sieve structures, companion cells, as well as storage cells in which a supply of nutrients is deposited. |
| Cambial layer | Educational tissue, cells are long and narrow. In spring and summer, there is a period of intensive division. Actually, due to the cambium, the stem of the plant grows. |
| Core | Centrally located functional structure. Its cells are large and thin-walled. They perform storage and nutritional functions. |
| Antennae (rays) of the core | They diverge from the core in the radial direction, passing through all layers of the tree to the bast. Their main cells are the cells of the main tissue, they serve as transport routes for nutrients. |
This table "The structure of the plant stem" will help you remember the main components, understand their functional significance. Oddly enough, but the information from it can be useful in everyday life.
General features of the anatomical structure of the stem
And now we will analyze the anatomical structure of the stem. Oddly enough, but this topic is extremely often difficult for those students who study the course of botany. In general, if you at least in general terms know the functional purpose of the various structures of the stem, then you can deal with the structure without any special effort. Simply put, the structure and function of the stem are inextricably linked, so they should be studied together.
Conducting structures (sieve cells) are developed in conducting tissues, with the help of whichNutrients are delivered to all parts of the plant. In the main part of the barrel there is a large number of mechanical tissues that are responsible for the strength characteristics. Young shoots contain a developed system of meristems.
With a conventional light microscope, you can see that the apical meristems give rise to procambium, as well as intercalated meristems. It is due to them that the primary structure of the stem begins to form. In some plants, it persists for a long time. The cambium, which is a secondary structure, forms the secondary structure of the stem.
Features of the primary system
Let's consider the structural features of the stem. More precisely, its primary structure. It is necessary to distinguish between the central core (stele), as well as the bark of the primary order. Outside, this bark is covered with an integumentary tissue (periderm), and under it there is an assimilation tissue (chlorenchyma). She has a very important role, as she plays the role of a kind of bridge between the cortex and mechanical tissues (collenchyma and sclerenchyma).
The central rod is protected from all sides by a layer of endoderm. Most of it is occupied by conductive strands, formed as a result of the fusion of conductive and mechanical tissues, which we have just talked about. The core consists of almost non-specialized parenchyma. Due to the fact that its cells do not adhere well to each other (which has been repeatedly written above), air cavities are often formed in it, the volume of which can be quite significant.
Cambiumforms secondary xylem and phloem. This is due to the fact that the primary cortex is constantly dying, and therefore needs to be replaced, which is provided by the cambial tissue. Finally, it is worth mentioning that the structure of the stems largely depends not only on the type of plants, but also on the conditions in which they grow. This is how grade 6 should study the structure of the stem.
