Functions and structure of the plant stem

The vegetable world is one of the most amazing and unusual miracles on our planet. Plants differ from each other at times 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, within the framework of this article, we will consider the structure of the stem.

General information

This is the main core part of the plant. On it, the leaves are attached, which are carried to the light on the stem, nutrient solutions , water and mineral salts are fed through its channels. It should be remembered that it is in it can be postponed the nutrients "in reserve." In addition, the structure of the stem implies the development on it of fruits, seeds and flowers, which serve to multiply the plant organism.

The main structural units are the node and internodes. The node is the one on which the leaves or kidneys are located. Thus, an interstice is located between two neighboring nodes. The space that is formed in the gap 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, which is called apical.

If you digress a little from the main direction of the article, you can tell something interesting. Did you know that the internodes of which plants are large enough to make even small kegs of them? Some types of bamboo, of course! This giant grass has such strong stems that not only dishes, but also excellent rafts are made from them. The stems of the bamboo are hollow, strong, almost decaying, which caused the choice of many seafarers 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, which 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. Around the world is known for the pine flecked Prometheus, which grew on the territory of the current United States (index WPN-114). It was felled in 1964. According to the data of radiocarbon analysis, her age was ... 4862 years! Even the Nativity of Christ, this tree met, already at a very "venerable" age!

What other features are worth knowing while studying the structure of the stem? The trunk is called the main stem, in shrubs that have several growth points at once, such formations are called trunks. Recall that there are several types of them. Let us cite the classification of the species of stems that has been adopted to date.

Main classification

Extremely widespread is a variety. Just remember almost all the trees, a large part of the grass. In this case, the structure of the stem of the plant is distinguished by a perfectly developed mechanical part, but it is not necessary that its tissues are completely stiffened. Example - sunflower, corn, in which the trunk is still quite flexible and alive. In cereals, the above-ground 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 melons, umbellate plants, etc.

Some herbs have a creeping stem. Its characteristic feature is the ability of nodal rooting. A perfect example is wild strawberry.

Climbing and curling type, which in many ways is a variety of the previous one, is widely distributed among lianas. Among these plants 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 liana is in great need of support.

Curly, according to its name, twist the base. It is curious that in some types of antennae wrap around the base clockwise, and in some - in the opposite direction. There are also such plants, the stems of which with equal success can curve in all directions. Unlike them, clinging species climb up the support, catching in the smallest cracks and irregularities on its surface with its 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:

• Three-sided cut in sedge.
• Quadrilateral at the nettle.
• Beautiful and incredibly complex polyhedra of cacti.
• Opuntia have a flattened, almost flat-looking cut.
• In fragrant peas, the structure of the stem of the plant resembles a wing.

But do not assume that this diversity can be infinite. Unusually wide asymmetric stems are often due to some serious anomalies and developmental disorders. Here are some types of stalk structure.

How does water move through the stalk and solutions of mineral salts?

As we know, the plant for normal life must necessarily 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 off a birch or maple branch at the very beginning of the sap movement, then this can be easily verified, since the woody juice will drip off the surface of the cut.

Virtually the whole body of plants is permeated with conducting tissues. And they are all differentiated: water and aqueous solutions are raised one by one, and organic substances by other channels. In plants, these structures are often permeated with bundles of mechanical tissues, which provide the strength they need.

How does the organic matter move along the stem? Where can they store?

All organic nutrients are deposited in specialized cells that play a crucial role. Actually, it is for these substances that man tamed plants: he extracts from them oils and fats, 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 which case everything happens just like that. As for trees, organic substances often accumulate in the core. Thus, it is from this part of some species of palm trees that valuable raw materials for the chemical industry are extracted (paraffins, oils).

What is inside?

The youngest, newly grown stem cells are first covered with a delicate skin. Subsequently, it is completely replaced by a stopper. Her cells completely die, only empty "cases" filled with air remain. Thus, the skin and cork are classified as cover fabrics, and the plug is a multi-layered structure.

Contrary to popular belief, it is formed already in the first year of plant life. With increasing age, the thickness of the cork layer also increases. All coverslips 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. Thus, when processing wood, it should always be remembered that it is better not to use those parts in which young and rapidly dividing cells predominate during the life of the tree. Actually, the tops in the woodworking are thrown out precisely for this reason. Here's how biology is important in everyday life! The structure of the stem is very difficult, but you need to know it.

So, these fabrics prevent excessive evaporation, which is especially important in areas with a harsh and hot climate, protect the plant from penetrating into its thickness dust and harmful microorganisms that can cause illness and body death. For gas exchange on the surface of the integumentary tissues there are tiny stomata through which the plant "breathes".

On the cork, you can see tiny bumps with holes, which are called lenticles. They are formed from especially large cells of the main tissue, which differ in the impressive size of the intercellular space.

Under the cover shell (and not on the surface) is the crust, the inner layer of which is called the bast. In addition, the internal structure of the stem includes sieve-like structures and companion cells. In addition to them, there are also special cells in which nutrients are stored.

Structure of the crust

Bast fibers are extended in length, with the contents and stiff walls that have died out in the process of development, perform a supporting, mechanical role. On them depends the strength of the stem, its resistance to fracture. Sitovid structures are vertically arranged rows of living cells, with destroyed nuclei and cytoplasm, which fits snugly against the inner shell. Their walls are perforated through holes. Sitovid cells belong to the conductive system of the plant, through which water flows and solutions of nutrients.

In the internal structure of the stem also includes cambium, which is distinguished by long, elongated and flat cells. They actively share in the spring and summer periods. The main part of the stem is the wood itself. It is very similar in structure to the forehead, it is also formed by cells of various shapes and functions, which form several tissues (many conducting structures, mechanical and basic tissues). The annual rings of trees are formed by all these cells and tissues.

So studying the structure of the stalk of the 6th grade in a regular general education 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 are loosely adhered to each other, as they play an accumulating and accumulative role. If you have ever seen the core of a tree trunk, then for certain you remember the "antennae" that diverge from it in different directions.

But they play a very important role! It is for these strands, which are large clusters of conductive structures, that nutrients go to the bast and other parts of the plant body. In order to better represent the structure of the stem (dicotyledonous plants in particular), we give the main data in the form of a table.

This table "The structure of the stem of the plant" will help you remember the basic components, understand their functional significance. Strangely enough, but the information from it can be useful in everyday life.

Common features of the anatomical structure of the stem

And now we will analyze the anatomical structure of the stem. Strangely enough, but this topic is extremely often causes difficulties 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, you can also figure out the structure without any special efforts. Simply put, the structure and functions of the stem are inextricably linked, so they should be studied together.

Conductive tissues develop conductive structures (sieve cells), through 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, which are responsible for the strength characteristics. Young shoots contain a developed system of meristems.

Using a conventional light microscope, it can be seen that 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. Cambium, which is a secondary structure, forms a secondary structure of the stem.

Features of the primary system

Consider the features of the structure of the stem. More precisely, its primary structure. It is necessary to distinguish the central core (stela), as well as the cortex of the primary order. Outside this crust is covered with a cover cloth (periderum), and under it there is an assimilation tissue (chlorenchyme). It has a very important role, since it 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 confluence of the conducting and mechanical tissues, of which we have just spoken. The core consists of an almost unspecialized parenchyma. Due to the fact that its cells do not fit well together (as has been repeatedly mentioned above), air cavities often form in it, the volume of which can be quite significant.

Cambium forms secondary xylem and phloem. This is due to the fact that the primary cortex dies constantly, and therefore needs replacement, which is provided by 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. That's how to study the structure of the stalk of the 6th grade.