Plants show indefinite growth. But why does a plant show indefinite growth? Which kind of tissue is present in the root and shoot apices of a plant? The answer to all these questions is meristematic tissue. The plant body is made up of various kinds of tissues that can be broadly classified into two main types, i.e., meristematic tissues and permanent tissues.

The meristematic tissues are undifferentiated cells that undergo rapid cell division to form new cells, which, when differentiated, give rise to permanent tissues. In this article, we will provide detailed information about meristematic tissues, their classification, characteristics, function, types, etc. Continue to read to find out more!

Meristematic Tissues: Definition

The word ‘Meristems’ was derived from the Greek word called ‘Meristos’, which means ‘divisible’. Meristematic tissue is defined as an undifferentiated mass of cells that are totipotent and undergoes continuous cell division. They are mainly responsible for indefinite growth and tissue repair in a plant body. The cells of these tissues retain the power of cell division.

Also, check about Plant Tissues

Meristematic Tissue Characteristics

The characteristics of meristematic tissues are as follows:

1. They are living and contain an undifferentiated mass of rapidly dividing cells.
2. The tissue is made up of cells that show totipotency.
3. The shape of cells is spherical, polygonal or rectangular.
4. Cells remain perpetually embryonic (immature) and totally unspecialised. 
5. The nucleus is large and present either in interphase or in subphases of divisions.
6. The cell wall is thin and made up of a homogeneous substance called cellulose.
7. Cells contain abundant protoplasm and a prominent nucleus.
8. Vacuoles are generally absent, or if present, they are very small.
9. Except for mitochondria, other cell organelles are absent or present in a non-functional state.
10. Do not store reserved food materials or ergastic substances are absent.
11. The tissue occurs in the growing regions of the plant body and contributes to plant growth.
12. The cells do not have intercellular spaces.

Meristematic Tissue Classification

Meristematic tissue is classified on the basis of its position in the plant origin, position, and functions.

Classification Based on Origin

The meristematic tissue is classified on the basis of origin as follows:

I) Promeristems

1. Promeristems are also known as primordial meristems or Precambrian Meristems.
2. These are the earliest and the youngest meristematic cells that originate from the embryo.
3. These meristematic cells form the first meristematic tissues that are found at the tips of root and shoot.
4. They are found in very young plants and are few in numbers and undifferentiated.

II) Primary Meristems

1. These meristems are derived from the Promeristems.
2. They divide rapidly and differentiate into primary permanent tissues, which make the fundamental structure of the plant body.
3. They are mainly found in the growing apical regions of the root and shoot.

III) Secondary Meristems

1. These meristems appear in the later stage of development in the plant body.
2. They lie laterally in position in both the stem and root.
3. Some primary permanent tissues acquire the power of division and become meristematic.
4. These tissues can get differentiated to form secondary meristems as per the need of the plant.
5. Some examples of secondary meristems are cork cambium and interfascicular cambium, which allow secondary growth in tissues.

Classification Based on Position

The meristematic tissue is divided into the following three types based on their position in the plant body:

I) Apical Meristems

1. These meristems are found at the tips of the root and shoot that produce primary tissues.
2. The Root Apical Meristem (RAM) is present at the tip of the root, while the Shoot Apical Meristem (SAM) is present at the tip of the shoot.
3. During the formation of leaves and elongation of the stem, some cells are left behind from the shoot apical meristem that forms the axillary bud.
4. These buds are present in the axil of leaves and are capable of forming a branch or a flower.
5. There are some specific regions of the apical meristem that produce dermal tissues, ground tissues and vascular tissues.

II) Intercalary Meristems

1. This meristem is present between the mature tissues.
2. They are present at the base of internodes or at the base of leaves. It is responsible for the internodal elongation of the stem.
3. They are present in grasses and regenerate their parts which are removed by the grazing herbivores.

Did You Know?

1. Both apical and intercalary meristems are primary meristems as they appear early in the life of a plant. They both contribute to the formation of the primary plant body.
2. Both the meristems are usually responsible for growth in length and present mostly at the base of the node (e.g., mint), the base of internode (e.g., the stem of wheat and grasses) or at the base of the leaf (e.g., Pinus).

III) Lateral Meristems

1. These meristems are found in the mature regions of roots and shoots of many plants that produce the woody axis.
2. Lateral Meristems appear later than primary meristems, so they are also called secondary meristems.
3. They are cylindrical meristems and are present on the lateral sides of the stem.
4. They are responsible for secondary growth in plants.
5. Fascicular vascular cambium, interfascicular cambium and cork cambium, are types of lateral meristems.

Classification Based on Functions

The meristematic tissue is classified into the following three types on the basis of their functions:

1. Protoderm: It forms the outermost portion of the primary meristem found at the apex of the stem and root. It develops into the epidermis.
2. Procambium: It develops into primary vascular tissues. It forms the isolated strands of elongated cells near the central region.
3. Ground Meristem: It develops into the ground tissue. The cells are thin-walled, living and isodiametric. In the later stages of growth, they become differentiated into hypodermis, cortex, endodermis, pericycle, medullary rays and pith.

Meristematic Tissue Functions

The functions of meristematic tissues are as follows:

1. They are the actively and rapidly dividing tissues of the plant, resulting in their indefinite growth.
2. Primary meristems are responsible for the primary growth (elongation) of the plant.
3. The cells of the meristematic tissues undergo differentiation to form permanent tissues.
4. Secondary meristems are also responsible for the secondary growth (thickness and girth) of the plant.
5. They help in the formation and development of new organs.
6. They are responsible for the development of secondary tissues like wood, cork, etc.
7. Buds are formed from meristematic tissues that can further develop into branches or flowers.
8. They help in repairing the tissues which are injured.

Summary

Meristematic tissues are those tissues that are undifferentiated and divide actively and rapidly throughout the whole life of the plant. The meristematic cells can be called the first cells of the plant, which are mainly found at the tips and lateral sides of plants. They can be broadly classified into primary and secondary meristems depending on the type of growth carried out by these tissues. They undergo differentiation to form permanent tissues and are also involved in tissue repair, apart from growth and development.

FAQs on Meristematic Tissues

Let us look at some of the frequently asked questions about Meristematic tissues:

Q.1: What are the 3 types of meristems based on position?
Ans: The three types of meristems based on position are apical meristems, intercalary meristems, and lateral meristems.

Q.2: Where is meristematic tissue found in plants?
Ans: Meristematic tissue is found at the root and shoot tips as well as on the lateral sides of the plant.

Q.3: What are meristematic tissue and its function?
Ans: A meristematic tissue is defined as an undifferentiated mass of cells that are totipotent and undergoes continuous cell division. They are mainly responsible for indefinite growth and tissue repair in a plant body. The cells of these tissues retain the power of cell division.

Q.4: Is meristematic tissue localised or permanent?
Ans: Meristematic tissues are not permanent tissues. They are the actively dividing cells that are present in certain specific regions of the plant, i.e., they are localised.

Q.5: Why is meristematic tissue important in plants?
Ans: a) They are the actively and rapidly dividing tissues of the plant, resulting in their indefinite growth.
b) Primary meristems are responsible for the primary growth (elongation) of the plant.
c) The cells of the meristematic tissues undergo differentiation to form permanent tissues.
d) Secondary meristems are also responsible for the secondary growth (thickness and girth) of the plant.