The evolution of the animal and plant world gradually led to the complication of their organization. Therefore, the modern diversity of species is so great that it is simply amazing. The complication of the internal structure was reflected in each evolutionary branch.
This especially affected the plants, which managed to transform from lower underwater species to higher representatives settled throughout the globe, having a complex internal and external structure. A major role in this was played by the development of special structures - tissues, which make up the bulk of the individuals of this kingdom.
Meristems: definition and concept
In total, there are five main types of tissues of plant organisms. Among them are the following:
- meristems, or educational tissues;
- reserves;
- conductive;
- mechanical;
- basic.
Each of them has a special structure, different types of cells, and performs a certain important function in the life of a plant. The educational fabric deserves special attention, because it is it that gives rise to almost all the rest and provides the mainA distinctive feature of plants from other living organisms is unlimited growth throughout life.
If we give a more precise biological definition of this type of tissue, then it will sound like this: educational tissue, or meristem is the general name for a special type of tissue that consists of cells that are active throughout life, constantly dividing and development of the plant as a whole.
In addition, it is the meristems that give rise to many other types of tissues in the body. For example, mechanical, conductive, integumentary and others. Due to them, the wounded areas on the body of the plant are healed, the lost structures (leaves, parts of the stem, root) are quickly restored. It is safe to say that the educational tissue is one of the most important that allows plants to exist. Therefore, we will consider its structure and functions in more detail.
Educational tissue cells. General information
There are two main types of cells that make up meristems:
- Polygonal or isodiametric. They contain a very large core, which occupies almost the entire internal space. They have ribosomes, mitochondria, small vacuoles scattered throughout the cytoplasm. The shell is quite thin. Between themselves are located quite loosely. These cells form eumeristems. They give rise to all types of tissue except conductive.
- Prosenchymal cells. On the contrary, they have very large vacuoles filled with cell sap. Connected to each other more tightly, formelongated, cubic or prismatic. The educational tissue built from them gives rise to the conducting systems, the cambium and procambium of plants.
Thus, depending on the type of cells that form the tissue, the function it performs is also determined.
You can also distinguish two more types of meristem cells:
- Initial - actively dividing throughout life cells, providing the accumulation of the total mass of educational tissue. They also give rise to another group.
- Derived cells - may differ from the previous ones in shape, size, number of vacuoles and other parameters.
These types of structures in some plant species may not be distinguishable at all, at least morphologically.
In general, the structure of the educational fabric allows us to distinguish several types that make up its classification.
Classification of meristems
Several different features can be used as the basis. The first of these is the morphology of the cells that make up the tissue. According to this feature, they distinguish:
- lamellar meristems - cells of a cubic shape with a single-layer membrane, forming integumentary tissue;
- columnar educational tissues - form the core of stems and tree trunks, prismatic cells with a dense shell;
- massive meristems - give rise to an increase in thickness, represented by polygonal cells.
The next feature for classification is the ability to differentiate into other structures. SoOn the basis of all meristems can be divided into six groups:
- Fetal educational tissue. Its name speaks for itself. Forms the primary tissues of the embryo.
- Apical meristems, also called apical. They form: procambium, epidermis, conductive tissues, parenchyma.
- Wound educational tissues. Formed at the site of injury and provide a quick recovery of the lost organ or wound healing.
- Intercalary - provide intercalary plant growth in height and width.
- Lateral, or lateral - provide thickening of the axial structures of the body due to the deposition of cambium or phellogen.
- The marginal meristem - it is she who forms the sheet of the leaf.
The last classification by which all meristems can be divided into two groups is genetic. According to it, they are divided into:
- primary - associated with germinal and apical tissues;
- secondary - cambium, procambium and others.
Obviously, various signs of classification confirm the importance of the structures under consideration, especially their role in plant life.
Lamellar meristem
This is an educational tissue, the functions of which are to form the epidermis of the plant. It is lamellar meristems that create integumentary tissues that protect the body from external influences, maintain a certain shape and structure.
The cells of the lamellar educational tissue are arranged in one row, they divide very intensively, andperpendicular to the working body. As a result, the outer epidermis of the plant is formed.
Column fabrics
Another name for these fabrics is core. They got it for the elongated prismatic shape of the cells that make up the structure, which are closely packed with each other and have a fairly thick shell.
Columnar tissue gives rise to and completely forms the core of stems and stems of plants. The cells of this tissue also divide perpendicular to the axial organs.
Massive meristems. Brief description
Features of the educational tissue, which is called massive, is that it allows the plant to accumulate a mass of undifferentiated cells, which lead to thickening and growth of mass. At the same time, this happens quite evenly.
In the future, each part of the cell mass will be transformed into one or another tissue, that is, it will specialize and perform its function. This is how, for example, sporangium tissues and others are formed.
Functions of the educational tissue of plants
The role that meristems play is enormous. It is possible to identify several main most important functions that the tissues in question perform:
- Provides the plant with unlimited growth throughout its life.
- Give rise to the differentiation and specialization of all other tissue types in the body.
- Ensure the normal development of plants.
- Repair damage and restore lost structures.
However, the main function of the educational tissue is the repeated division of cells and their accumulation in a large mass for the possibility of constant use by parts of the plant, which means maintaining its growth and activity throughout life. It is for this reason that there are no such tissues in the body of animals and humans. After all, they grow only to genetically determined (initially laid down in the genome) sizes.
Apical meristem
This educational tissue, the functions and structure of which we will consider, is one of the most important of all types of meristems. There are a number of reasons for this.
- It is the apical tissue that is also called apical, since after the development of the embryo it remains in the cone of growth (the tip of the shoot).
- The apical meristem allows the stem and roots to grow in length.
- Over time, it is the apical tissue that transforms into the floral and meristem of the inflorescence, allowing flowers to form with all its parts.
- Gives rise to all other types of educational fabrics.
That is why we are talking about the high degree of importance of apical meristems in plant life.
This type of tissue has several derivatives that it forms in the body of the plant. They are as follows:
- cover fabric;
- protoderma;
- procambium;
- conductive fabrics;
- basic;
- massive.
Along with the apical ones, the lateral, or lateralmeristems. They give rise to cambium and phellogen, form the so-called growth rings, which are clearly visible on the cross sections of stems and trunks.
Primary Educational Fabrics
These include those that are first laid in the body of the embryo. First of all, these are the embryonic and apical (apical) meristems. Some of them persist throughout life, while others die off, forming the primary body of the plant.
Since we have already considered the apical meristems in more detail above, there is no point in repeating everything again. Primary tissues are the apical educational structures.
Secondary meristems
This group includes a massive meristem, which allows the plant to grow in mass at later stages of development. This is an educational tissue, the functions of which are mainly to form thickenings of the axial organs of plants.
Cambium and phellogen play a special role in this. Most often, secondary meristems come into action after the end of the apical growth of the plant, but there are exceptions. As, for example, in the case of the cambium.
Also important is the value of wound meristems, which lead to the formation of callus - a mass of cells. They tighten the place of injury or damage on the plant.
