The plant world is one of the most amazing and unusual miracles on our planet. Plants differ from each other sometimes as much as they are different 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 pivotal part of the plant. Leaves are attached to it, which are carried to the light on the stem; through its channels, solutions of nutrients, water and mineral salts come to them. It should be remembered that it is in it that nutrients can be stored “in reserve”. In addition, the structure of the stem involves the development of fruits, seeds and flowers on it, which serve to multiply the plant body.
The main structural units are the node and the internode. A node is the area directly on which 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 kidney called the apical.
If you step back a little from the main direction of the article, you can tell something interesting. Do you know which internodes of which plants are large enough to make even small barrels of them? Some types of bamboo, of course! This giant grass has such strong stems that they make not only dishes, but also excellent rafts. The stalks of bamboo are hollow, strong, almost do not rot, which led to the choice of many sailors in ancient times.
Life span
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 last for more than one century. The spinous pine Prometheus, which grew in the territory of the present United States (WPN-114 index), is known all over the world. It was cut down in 1964. According to radiocarbon analysis, her age was ... 4862 years! Even the Nativity of Christ this tree met, being already in a very "venerable" age!
What other features should you know when studying the structure of the stem? The trunk is called the main stem, in shrubs that have several points of growth at once, such formations are called trunks. Recall that there are several types of them. Here is the classification of the types of stems that is accepted to date.
Main classification
An upright variety is very common. Immediately I recall almost all the trees, a considerable part of the herbs. At the same time, the structure of the plant stem is characterized by a well-developed mechanical part, but it is not necessary that its tissues are completely woody. An example is sunflower, corn, in which the trunk is still quite flexible and vibrant. In cereals, the aerial part of the stem is called a straw. As a rule, inside it is hollow (with the exception of nodal zones). However, hollow varieties are widespread among gourds, umbrella plants, etc.
Some herbs have a creeping stalk. Its characteristic feature is the ability of nodal rooting. A perfect example is wild strawberries.
The climbing and climbing type, which is largely a variation of the previous one, is widespread among vines. Among these plants, there are also grassy and woody species. All of them are characterized by a tremendous growth rate, due to which the reinforcing mechanical part simply does not have time to develop, and therefore the liana is in dire need of support.
Curly, according to its name, wrap around the base. It is curious that in some species, the antennae wrap around the base in a clockwise direction, and in some, in the opposite direction. There are also plants whose stems can equally bend in all directions. In contrast, clinging varieties rise along the support, clinging to the smallest cracks and bumps on its surface with their antennae (hops, ivy).
The most common forms of stems
If you take a plant and cut it, then in appearance the structure of the stem in this case will most often resemble a circle. Of course, nature is not limited to this:
- Trihedral slice in sedge.
- Quadrangular in nettle.
- Beautiful and incredibly complex polyhedra of cacti.
- 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 asymmetric stems often arise due to some serious anomalies and developmental disorders. These are the types of stalk structure.
How does water and solutions of mineral salts move along the stem?
As we know, a plant for normal life must be provided with water and solutions of mineral salts. One of the most important functions of the stem is precisely their transport. If you cut a branch of birch or maple at the very beginning of sap flow, then this can be easily seen, since wood juice will abundantly drain from the surface of the cut.
Almost the entire body of plants is penetrated by conductive tissues. Moreover, they are differentiated: water and aqueous solutions rise in one, and organic substances in other channels. In plants, these structures are often penetrated by bundles of mechanical tissues that provide the strength they need.
How do 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 for the sake of these substances that man tamed plants: he extracts oils and fats from them, the most valuable raw material 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 which case 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 palm trees that valuable raw materials for the chemical industry (paraffins, oils) are extracted.
What is inside?
The youngest, recently grown plant trunks are first covered with delicate skin. Subsequently, it is completely replaced by a cork. Its cells completely die off, only empty “cases” filled with air remain from them. Thus, the skin and cork belong to the category of integumentary tissues, the cork being a multilayer structure.
Contrary to popular belief, it is formed in the first year of the plant's life. With increasing age, the thickness of the cork layer also increases. All integumentary tissues are designed by nature to protect the plant organism from adverse effects and environmental phenomena.
It must be remembered that all these data are of no small importance in some industries. First of all, in woodworking. So, when processing wood, it should always be remembered that those parts in which young and rapidly dividing cells prevailed during the life of the tree should not be used. Actually, the tops in woodworking are thrown out precisely for this reason. That's how important biology is in everyday life! The structure of the stem is very difficult, but you need to know it.
So, these tissues 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 illness and death of the body. For gas exchange on the surface of integumentary tissues there are tiny stomata through which the plant “breathes”.
On the cork, you can see tiny tubercles with holes called lentils. They are formed from especially large cells of the main tissue, which are distinguished by 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 special cells in which nutrients are stored.
Bark structure
Bast fibers are elongated in length, with contents that have died out in the process of development and wood walls, play a bearing, mechanical role. The strength of the stem, its fracture resistance, depends on them. Sieve structures are vertically arranged rows of living cells, with destroyed nuclei and cytoplasm, which is tightly adjacent to the inner shell. Their walls are pierced with through holes. Sieve cells belong to the plant's conducting system, through which water and nutrient solutions pass.
The cambium, also characterized by long, elongated and flat cells, also enters the internal structure of the stem. They are actively divided in the spring and summer. The main part of the stem is directly wood. It is very similar in structure to the forehead, it is also formed by cells of various shapes and functional purposes, which form several tissues (many conductive structures, mechanical and basic tissues). Annual rings of trees are formed by all these cells and tissues.
So studies the structure of the stem 6th grade in an ordinary comprehensive school. Unfortunately, the educational program does not pay so much 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 diverges from it in different directions.
But they play a crucial role! It is through these strands, which are large clusters of conducting structures, that nutrients go to the bast and other parts of the plant body. So that you better imagine the structure of the stem (including dicotyledonous plants), we will present the basic data in the form of a table.
Unit name | Characteristic |
Skin | Outside, young shoots of the plant are covered with it. It performs a protective function, prepares a place for the formation of a cork, which consists of dead cells filled with air. It is a cover fabric. |
Gas exchange stomata | 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, lentils, small tubercles with holes perform the same function. They are formed from large cells of the underlying tissue. |
Cork layer | The main integumentary structure that appears already in the first year of the 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 a plant stem from adverse environmental influences. |
Bark | It is located under the protection of the cover 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, a period of intense division begins. Actually, due to the cambium, the stem of the plant grows. |
Core | Centrally located functional structure. Its cells are large, thin-walled. Perform storage and nutritional functions. |
Antennae (rays) of the core | They diverge from the core in the radial direction, pass through all layers of the tree to the bast. Their main cells are the main tissue, serve as transport routes for nutrients. |
This table "Plant stem structure" will help you remember the main components, understand their functional significance. Oddly enough, but 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 extremely often causes difficulties for those students who study the course of botany. In general, if you even at least in general terms know the functional purpose of the various structures of the stem, then you can also understand the structure without any special efforts. Simply put, the structure and functions of the stem are inextricably linked, so they should be studied together.
In conductive tissues, conductive structures (sieve cells) are developed by which nutrients are delivered to all parts of the plant. In the main part of the trunk there is a large number of mechanical tissues that are responsible for the strength characteristics. Young shoots contain a developed system of meristems.
Using a conventional light microscope, you can see that the apical meristems give rise to prokambia, as well as intercalary 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.
Primary System Features
Consider the structural features of the stem. More precisely, its primary structure. It is necessary to distinguish between the central core (stela), as well as the cortex of the primary order. Outside, this cortex is covered with integumentary tissue (periderm), and under it there is assimilation tissue (chlorenchyma). She has a very important role, since she plays the role of a kind of bridge between the cortex and mechanical tissues (collenchyma and sclerenchyma).
The central shaft is protected on 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 just talked about. The core consists of a virtually non-specialized parenchyma. Due to the fact that its cells do not adhere well to each other (as was repeatedly mentioned above), air cavities are often formed in it, the volume of which can be very significant.
Cambium forms secondary xylem and phloem. This is due to the fact that the primary cortex is constantly dying, and therefore needs to be replaced, which the cambial tissue provides. In the end, 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 class 6 should study the structure of the stem.