1. Meristematic Tissues
Types of Tissues :
There are two basic types of tissues:
1- Meristematic Tissues
2- Permanent Tissues
2. 1- Meristematic Tissues : (meristos= divisible)
It is a tissue composed of immature,
not well differentiated cells which has
the capacity of division.
3. 2- Permanent Tissues : It is a tissue
composed of differentiated cells ( in
the growth has ceases) which may be
living or dead and thin or thick walled.
These tissues develop from
meristematic tissue by differentiation.
4. Meristematic Tissues: The term
meristem is derived from a Greek word
Meristos meaning Divisible. It
emphasizes the cell division activity
characteristic of the tissue which bears
this name.
5. • Origin: From early stages of development
some cells remain embryonic in character
and retain the ability to divide in the
mature plant body are called meristems.
• These are formative tissues i.e they add
new cells to the plant body and also
increase their own number.
6. • Some remains meristematic (able to divide)
and are called initiating cells.
• Others develop into various tissue elements
and are known as the Derivatives of the
initiating cells. These cells undergo morpho-
physiological changes and this process is
called differentiation.
7. Structure of Meristematic Cells:
• Thin-walled, isodiametric,spherical,oval or
polygonal in shape.
• Rich in protoplasm.
• Protoplast is without reserve material and crystals.
• Plastids are at proplastid stage.
• Usually vacuoles are small and scattered
throughout the protoplast.
8.
9. Size:
• Size very
• Thick walled meristematic cells are found in
the meristematic are found in the apical
meristems.
• Cells of vascular cambium have thick radial
walls.
10. Classification:
On the basis of origin
1- Promeristem
2- Primary Meristem
3- Secondary Meristem
On the basis of Position
1-Apical Meristem
2- Intercalary Meristem
3- Lateral Meristem
11. On the basis of their function
• 1-Protoderm Meristem
• 2-Procambium Meristem
• 3-Ground Meristem
12. On the basis of origin
• 1- Promeristem or primordial meristem:
• A group of young meristematic cells of a growing
organ. It is the early embryonic meristem from which
other advanced meristems are derived. In a plant, it
occupies a small area at the tip of stem and root. It
further divides to form primary meristem.
13.
14. 2-Primary meristem:
• These are derived from promeristem. They are
present below the promeristem at shoot and
root apices. These cells divide and form
permanent tissues.
15.
16. 3-Secondary meristem: It is derived from
primary permanent tissues which have the
capacity of division e.g. Cork-cambium,
cambium of roots and inter fascicular cambium
of stem.
17.
18. On the basis of Position
1-Apical Meristem: These are found at the apices
or growing points of root and shoot and bring
about increase in length. It includes both pro-
meristem as well as primary meristem.
19. 2- Intercalary Meristem:
• It lies between the region of permanent tissues
and is considered| as a part of primary
meristem which has become detached due to
formation of intermediate permanent tissues. It
is found either at the base of leaf e.g. Pinus or
at the base of internodes e.g. grasses.
20. 3- Lateral Meristem: These are arranged parallel
to the sides of origin and normally divide
periclinally or radially and give rise to secondary
permanent tissues. These increase the thickness
of the plant part.
21.
22. • 1-Protoderm Meristem : A meristem
that is made up of undifferentiated,
actively dividing cells. It is the
outermost meristematic tissue. It
gives rise to epidermis layer.
23. 2-Procambium Meristem: It is
composed of narrow, elongated,
prosenchymatous, meristematic cells
that gives rise to the vascular tissues
system.
24. 3-Ground Meristem: It is composed of
large, thick-walled cells which develop
to form ground tissue system, i.e.
hypodermis, cortex and pith.
