NCERT Textbook - Anatomy of Flowering Plants NEET Notes | EduRev

NCERT Textbooks (Class 6 to Class 12)

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NEET : NCERT Textbook - Anatomy of Flowering Plants NEET Notes | EduRev

 Page 1


84 BIOLOGY
You can very easily see the structural similarities and variations in the
external morphology of the larger living organism, both plants and
animals. Similarly, if we were to study the internal structure, one also
finds several similarities as well as differences. This chapter introduces
you to the internal structure and functional organisation of higher plants.
Study of internal structure of plants is called anatomy. Plants have cells
as the basic unit, cells are organised into tissues and in turn the tissues
are organised into organs. Different organs in a plant show differences in
their internal structure. Within angiosperms, the monocots and dicots
are also seen to be anatomically different. Internal structures also show
adaptations to diverse environments.
6.1 THE TISSUES
A tissue is a group of cells having a common origin and usually performing
a common function. A plant is made up of different kinds of tissues. Tissues
are classified into two main groups, namely, meristematic  and permanent
tissues based on whether the cells being formed are capable of dividing
or not.
6.1.1 Meristematic Tissues
Growth in plants is largely restricted to specialised regions of active cell division
called meristems (Gk. meristos: divided). Plants have different kinds of
meristems. The meristems which occur at the tips of roots and shoots and
produce primary tissues are called apical meristems (Figure 6.1).
ANATOMY OF FLOWERING PLANTS
CHAPTER  6
6.1 The Tissues
6.2 The Tissue
System
6.3 Anatomy of
Dicotyledonous
and
Monocotyledonous
Plants
6.4 Secondary
Growth
2015-16(19/01/2015)
Page 2


84 BIOLOGY
You can very easily see the structural similarities and variations in the
external morphology of the larger living organism, both plants and
animals. Similarly, if we were to study the internal structure, one also
finds several similarities as well as differences. This chapter introduces
you to the internal structure and functional organisation of higher plants.
Study of internal structure of plants is called anatomy. Plants have cells
as the basic unit, cells are organised into tissues and in turn the tissues
are organised into organs. Different organs in a plant show differences in
their internal structure. Within angiosperms, the monocots and dicots
are also seen to be anatomically different. Internal structures also show
adaptations to diverse environments.
6.1 THE TISSUES
A tissue is a group of cells having a common origin and usually performing
a common function. A plant is made up of different kinds of tissues. Tissues
are classified into two main groups, namely, meristematic  and permanent
tissues based on whether the cells being formed are capable of dividing
or not.
6.1.1 Meristematic Tissues
Growth in plants is largely restricted to specialised regions of active cell division
called meristems (Gk. meristos: divided). Plants have different kinds of
meristems. The meristems which occur at the tips of roots and shoots and
produce primary tissues are called apical meristems (Figure 6.1).
ANATOMY OF FLOWERING PLANTS
CHAPTER  6
6.1 The Tissues
6.2 The Tissue
System
6.3 Anatomy of
Dicotyledonous
and
Monocotyledonous
Plants
6.4 Secondary
Growth
2015-16(19/01/2015)
ANATOMY OF F LOWERING PLANTS 85
Root apical meristem occupies the tip of a root while the shoot apical
meristem occupies the distant most region of the stem axis. During the
formation of leaves and elongation of stem, some cells ‘left behind’ from
shoot apical meristem, constitute the axillary bud. Such buds are present
in the axils of leaves and are capable of forming a branch or a flower. The
meristem which occurs between mature tissues is known as intercalary
meristem. They occur in grasses and regenerate parts removed by the
grazing herbivores. Both apical meristems and intercalary meristems are
primary meristems because they appear early in life of a plant and
contribute to the formation of the primary plant body.
The meristem that occurs in the mature regions of roots and shoots of
many plants, particularly those that produce woody axis and appear
later than primary meristem is called the secondary or lateral meristem.
They are cylindrical meristems. Fascicular vascular cambium,
interfascicular cambium and cork-cambium are examples of lateral
meristems. These are responsible for producing the secondary tissues.
Following divisions of cells in both primary and as well as secondary
meristems, the newly formed cells become structurally and functionally
specialised and lose the ability to divide. Such cells are termed permanent
or mature cells and constitute the permanent tissues. During the
formation of the primary plant body, specific regions of the apical meristem
produce dermal tissues, ground tissues and vascular tissues.
Central cylinder
Cortex
Protoderm
Initials of central
cylinder
and cortex
Initials of
root cap
Root cap
Root apical
meristem
Leaf primordium
Shoot apical
Meristematic zone
Axillary bud
Differentiating
vascular tissue
Figure 6.1  Apical meristem: (a) Root  (b) Shoot
2015-16(19/01/2015)
Page 3


84 BIOLOGY
You can very easily see the structural similarities and variations in the
external morphology of the larger living organism, both plants and
animals. Similarly, if we were to study the internal structure, one also
finds several similarities as well as differences. This chapter introduces
you to the internal structure and functional organisation of higher plants.
Study of internal structure of plants is called anatomy. Plants have cells
as the basic unit, cells are organised into tissues and in turn the tissues
are organised into organs. Different organs in a plant show differences in
their internal structure. Within angiosperms, the monocots and dicots
are also seen to be anatomically different. Internal structures also show
adaptations to diverse environments.
6.1 THE TISSUES
A tissue is a group of cells having a common origin and usually performing
a common function. A plant is made up of different kinds of tissues. Tissues
are classified into two main groups, namely, meristematic  and permanent
tissues based on whether the cells being formed are capable of dividing
or not.
6.1.1 Meristematic Tissues
Growth in plants is largely restricted to specialised regions of active cell division
called meristems (Gk. meristos: divided). Plants have different kinds of
meristems. The meristems which occur at the tips of roots and shoots and
produce primary tissues are called apical meristems (Figure 6.1).
ANATOMY OF FLOWERING PLANTS
CHAPTER  6
6.1 The Tissues
6.2 The Tissue
System
6.3 Anatomy of
Dicotyledonous
and
Monocotyledonous
Plants
6.4 Secondary
Growth
2015-16(19/01/2015)
ANATOMY OF F LOWERING PLANTS 85
Root apical meristem occupies the tip of a root while the shoot apical
meristem occupies the distant most region of the stem axis. During the
formation of leaves and elongation of stem, some cells ‘left behind’ from
shoot apical meristem, constitute the axillary bud. Such buds are present
in the axils of leaves and are capable of forming a branch or a flower. The
meristem which occurs between mature tissues is known as intercalary
meristem. They occur in grasses and regenerate parts removed by the
grazing herbivores. Both apical meristems and intercalary meristems are
primary meristems because they appear early in life of a plant and
contribute to the formation of the primary plant body.
The meristem that occurs in the mature regions of roots and shoots of
many plants, particularly those that produce woody axis and appear
later than primary meristem is called the secondary or lateral meristem.
They are cylindrical meristems. Fascicular vascular cambium,
interfascicular cambium and cork-cambium are examples of lateral
meristems. These are responsible for producing the secondary tissues.
Following divisions of cells in both primary and as well as secondary
meristems, the newly formed cells become structurally and functionally
specialised and lose the ability to divide. Such cells are termed permanent
or mature cells and constitute the permanent tissues. During the
formation of the primary plant body, specific regions of the apical meristem
produce dermal tissues, ground tissues and vascular tissues.
Central cylinder
Cortex
Protoderm
Initials of central
cylinder
and cortex
Initials of
root cap
Root cap
Root apical
meristem
Leaf primordium
Shoot apical
Meristematic zone
Axillary bud
Differentiating
vascular tissue
Figure 6.1  Apical meristem: (a) Root  (b) Shoot
2015-16(19/01/2015)
86 BIOLOGY
6.1.2 Permanent Tissues
The cells of the permanent tissues do not generally
divide further. Permanent tissues having all cells
similar in structure and function are called simple
tissues. Permanent tissues having many different
types of cells are called complex tissues.
6.1.2.1 Simple Tissues
A simple tissue is made of only one type of cells.
The various simple tissues in plants are
parenchyma, collenchyma and sclerenchyma
(Figure 6.2). Parenchyma forms the  major
component within organs. The cells of the
parenchyma  are generally isodiametric. They
may be spherical, oval, round, polygonal or
elongated in shape. Their walls are thin and made
up of cellulose. They may either be closely packed
or have small intercellular spaces. The
parenchyma performs  various functions like
photosynthesis, storage, secretion.
The collenchyma occurs in layers below the
epidermis in dicotyledonous plants. It is found
either as a homogeneous layer or in patches. It
consists of cells which are much thickened at the
corners due to a deposition of cellulose,
hemicellulose and pectin. Collenchymatous cells
may be oval, spherical or polygonal and often
contain chloroplasts. These cells assimilate food
when they contain chloroplasts. Intercellular
spaces are absent. They provide mechanical
support to the growing parts of the plant such as
young stem and petiole of a leaf.
Sclerenchyma consists of long, narrow cells
with thick and lignified cell walls having a few or
numerous pits. They are usually dead and without
protoplasts. On the basis of variation in form,
structure, origin and development, sclerenchyma
may be either fibres or sclereids. The fibres are
thick-walled, elongated and pointed cells,
generally occuring in groups, in various parts of
the plant. The sclereids are spherical, oval or
cylindrical, highly thickened dead cells with very
Intercelluar space
Figure 6.2 Simple tissues :
(a) Parenchyma
(b) Collenchyma
(c) Sclerenchyma
A fibre
A sclereid
(c)
Lumen
Thick
cell wall
Lumen
Pits
Thick
cell wall
(b)
Thickened corners
Protoplasm
Vacuole
Cell wall
(a)
2015-16(19/01/2015)
Page 4


84 BIOLOGY
You can very easily see the structural similarities and variations in the
external morphology of the larger living organism, both plants and
animals. Similarly, if we were to study the internal structure, one also
finds several similarities as well as differences. This chapter introduces
you to the internal structure and functional organisation of higher plants.
Study of internal structure of plants is called anatomy. Plants have cells
as the basic unit, cells are organised into tissues and in turn the tissues
are organised into organs. Different organs in a plant show differences in
their internal structure. Within angiosperms, the monocots and dicots
are also seen to be anatomically different. Internal structures also show
adaptations to diverse environments.
6.1 THE TISSUES
A tissue is a group of cells having a common origin and usually performing
a common function. A plant is made up of different kinds of tissues. Tissues
are classified into two main groups, namely, meristematic  and permanent
tissues based on whether the cells being formed are capable of dividing
or not.
6.1.1 Meristematic Tissues
Growth in plants is largely restricted to specialised regions of active cell division
called meristems (Gk. meristos: divided). Plants have different kinds of
meristems. The meristems which occur at the tips of roots and shoots and
produce primary tissues are called apical meristems (Figure 6.1).
ANATOMY OF FLOWERING PLANTS
CHAPTER  6
6.1 The Tissues
6.2 The Tissue
System
6.3 Anatomy of
Dicotyledonous
and
Monocotyledonous
Plants
6.4 Secondary
Growth
2015-16(19/01/2015)
ANATOMY OF F LOWERING PLANTS 85
Root apical meristem occupies the tip of a root while the shoot apical
meristem occupies the distant most region of the stem axis. During the
formation of leaves and elongation of stem, some cells ‘left behind’ from
shoot apical meristem, constitute the axillary bud. Such buds are present
in the axils of leaves and are capable of forming a branch or a flower. The
meristem which occurs between mature tissues is known as intercalary
meristem. They occur in grasses and regenerate parts removed by the
grazing herbivores. Both apical meristems and intercalary meristems are
primary meristems because they appear early in life of a plant and
contribute to the formation of the primary plant body.
The meristem that occurs in the mature regions of roots and shoots of
many plants, particularly those that produce woody axis and appear
later than primary meristem is called the secondary or lateral meristem.
They are cylindrical meristems. Fascicular vascular cambium,
interfascicular cambium and cork-cambium are examples of lateral
meristems. These are responsible for producing the secondary tissues.
Following divisions of cells in both primary and as well as secondary
meristems, the newly formed cells become structurally and functionally
specialised and lose the ability to divide. Such cells are termed permanent
or mature cells and constitute the permanent tissues. During the
formation of the primary plant body, specific regions of the apical meristem
produce dermal tissues, ground tissues and vascular tissues.
Central cylinder
Cortex
Protoderm
Initials of central
cylinder
and cortex
Initials of
root cap
Root cap
Root apical
meristem
Leaf primordium
Shoot apical
Meristematic zone
Axillary bud
Differentiating
vascular tissue
Figure 6.1  Apical meristem: (a) Root  (b) Shoot
2015-16(19/01/2015)
86 BIOLOGY
6.1.2 Permanent Tissues
The cells of the permanent tissues do not generally
divide further. Permanent tissues having all cells
similar in structure and function are called simple
tissues. Permanent tissues having many different
types of cells are called complex tissues.
6.1.2.1 Simple Tissues
A simple tissue is made of only one type of cells.
The various simple tissues in plants are
parenchyma, collenchyma and sclerenchyma
(Figure 6.2). Parenchyma forms the  major
component within organs. The cells of the
parenchyma  are generally isodiametric. They
may be spherical, oval, round, polygonal or
elongated in shape. Their walls are thin and made
up of cellulose. They may either be closely packed
or have small intercellular spaces. The
parenchyma performs  various functions like
photosynthesis, storage, secretion.
The collenchyma occurs in layers below the
epidermis in dicotyledonous plants. It is found
either as a homogeneous layer or in patches. It
consists of cells which are much thickened at the
corners due to a deposition of cellulose,
hemicellulose and pectin. Collenchymatous cells
may be oval, spherical or polygonal and often
contain chloroplasts. These cells assimilate food
when they contain chloroplasts. Intercellular
spaces are absent. They provide mechanical
support to the growing parts of the plant such as
young stem and petiole of a leaf.
Sclerenchyma consists of long, narrow cells
with thick and lignified cell walls having a few or
numerous pits. They are usually dead and without
protoplasts. On the basis of variation in form,
structure, origin and development, sclerenchyma
may be either fibres or sclereids. The fibres are
thick-walled, elongated and pointed cells,
generally occuring in groups, in various parts of
the plant. The sclereids are spherical, oval or
cylindrical, highly thickened dead cells with very
Intercelluar space
Figure 6.2 Simple tissues :
(a) Parenchyma
(b) Collenchyma
(c) Sclerenchyma
A fibre
A sclereid
(c)
Lumen
Thick
cell wall
Lumen
Pits
Thick
cell wall
(b)
Thickened corners
Protoplasm
Vacuole
Cell wall
(a)
2015-16(19/01/2015)
ANATOMY OF F LOWERING PLANTS 87
narrow cavities (lumen). These are commonly found in the fruit
walls of nuts; pulp of fruits like guava, pear and sapota; seed
coats of legumes and leaves of tea. Sclerenchyma provides
mechanical support to organs.
6.1.2.2 Complex Tissues
The complex tissues are made of more than one type of cells
and these work together as a unit. Xylem and phloem constitute
the complex tissues in plants (Figure 6.3).
Xylem functions as a conducting tissue for water and
minerals from roots to the stem and leaves. It also provides
mechanical strength to the plant parts. It is composed of four
different kinds of elements, namely, tracheids, vessels, xylem
fibres and xylem parenchyma. Gymnosperms lack vessels in
their xylem. Tracheids are elongated or tube like cells with
thick and lignified walls and tapering ends. These are dead and
are without protoplasm. The inner layers of the cell walls have
thickenings which vary in form.  In flowering plants, tracheids
and vessels are the main water transporting elements. Vessel is
a long cylindrical tube-like structure made up of many cells
called vessel members, each with lignified walls and a large
central cavity. The vessel cells are also devoid of protoplasm.
Vessel members are interconnected through perforations in their
common walls. The presence of vessels is a characteristic feature
of angiosperms. Xylem fibres have highly thickened walls and
obliterated central lumens. These may either be septate or
aseptate. Xylem parenchyma cells are living and thin-walled,
and their cell walls are made up of cellulose. They store food
materials in the form of starch or fat, and other substances like
tannins. The radial conduction of water takes place by the ray
parenchymatous cells.
Primary xylem is of two types – protoxylem and metaxylem.
The first formed primary xylem elements are called protoxylem
and the later formed primary xylem is called metaxylem. In
stems, the protoxylem lies towards the centre (pith) and the
metaxylem lies towards the periphery of the organ. This type
of primary xylem is called endarch. In roots, the protoxylem
lies towards periphery and metaxylem lies towards the centre.
Such arrangement of primary xylem is called exarch.
Phloem transports food materials, usually from leaves to
other parts of the plant. Phloem in angiosperms is composed
of sieve tube elements, companion cells, phloem parenchyma
Phloem
parenchyma
Companion
cell
(b)
Sieve pore
Sieve tube
element
Figure 6.3 (a) Xylem
      (b) Phloem
(a)
Tracheid
Vessels
2015-16(19/01/2015)
Page 5


84 BIOLOGY
You can very easily see the structural similarities and variations in the
external morphology of the larger living organism, both plants and
animals. Similarly, if we were to study the internal structure, one also
finds several similarities as well as differences. This chapter introduces
you to the internal structure and functional organisation of higher plants.
Study of internal structure of plants is called anatomy. Plants have cells
as the basic unit, cells are organised into tissues and in turn the tissues
are organised into organs. Different organs in a plant show differences in
their internal structure. Within angiosperms, the monocots and dicots
are also seen to be anatomically different. Internal structures also show
adaptations to diverse environments.
6.1 THE TISSUES
A tissue is a group of cells having a common origin and usually performing
a common function. A plant is made up of different kinds of tissues. Tissues
are classified into two main groups, namely, meristematic  and permanent
tissues based on whether the cells being formed are capable of dividing
or not.
6.1.1 Meristematic Tissues
Growth in plants is largely restricted to specialised regions of active cell division
called meristems (Gk. meristos: divided). Plants have different kinds of
meristems. The meristems which occur at the tips of roots and shoots and
produce primary tissues are called apical meristems (Figure 6.1).
ANATOMY OF FLOWERING PLANTS
CHAPTER  6
6.1 The Tissues
6.2 The Tissue
System
6.3 Anatomy of
Dicotyledonous
and
Monocotyledonous
Plants
6.4 Secondary
Growth
2015-16(19/01/2015)
ANATOMY OF F LOWERING PLANTS 85
Root apical meristem occupies the tip of a root while the shoot apical
meristem occupies the distant most region of the stem axis. During the
formation of leaves and elongation of stem, some cells ‘left behind’ from
shoot apical meristem, constitute the axillary bud. Such buds are present
in the axils of leaves and are capable of forming a branch or a flower. The
meristem which occurs between mature tissues is known as intercalary
meristem. They occur in grasses and regenerate parts removed by the
grazing herbivores. Both apical meristems and intercalary meristems are
primary meristems because they appear early in life of a plant and
contribute to the formation of the primary plant body.
The meristem that occurs in the mature regions of roots and shoots of
many plants, particularly those that produce woody axis and appear
later than primary meristem is called the secondary or lateral meristem.
They are cylindrical meristems. Fascicular vascular cambium,
interfascicular cambium and cork-cambium are examples of lateral
meristems. These are responsible for producing the secondary tissues.
Following divisions of cells in both primary and as well as secondary
meristems, the newly formed cells become structurally and functionally
specialised and lose the ability to divide. Such cells are termed permanent
or mature cells and constitute the permanent tissues. During the
formation of the primary plant body, specific regions of the apical meristem
produce dermal tissues, ground tissues and vascular tissues.
Central cylinder
Cortex
Protoderm
Initials of central
cylinder
and cortex
Initials of
root cap
Root cap
Root apical
meristem
Leaf primordium
Shoot apical
Meristematic zone
Axillary bud
Differentiating
vascular tissue
Figure 6.1  Apical meristem: (a) Root  (b) Shoot
2015-16(19/01/2015)
86 BIOLOGY
6.1.2 Permanent Tissues
The cells of the permanent tissues do not generally
divide further. Permanent tissues having all cells
similar in structure and function are called simple
tissues. Permanent tissues having many different
types of cells are called complex tissues.
6.1.2.1 Simple Tissues
A simple tissue is made of only one type of cells.
The various simple tissues in plants are
parenchyma, collenchyma and sclerenchyma
(Figure 6.2). Parenchyma forms the  major
component within organs. The cells of the
parenchyma  are generally isodiametric. They
may be spherical, oval, round, polygonal or
elongated in shape. Their walls are thin and made
up of cellulose. They may either be closely packed
or have small intercellular spaces. The
parenchyma performs  various functions like
photosynthesis, storage, secretion.
The collenchyma occurs in layers below the
epidermis in dicotyledonous plants. It is found
either as a homogeneous layer or in patches. It
consists of cells which are much thickened at the
corners due to a deposition of cellulose,
hemicellulose and pectin. Collenchymatous cells
may be oval, spherical or polygonal and often
contain chloroplasts. These cells assimilate food
when they contain chloroplasts. Intercellular
spaces are absent. They provide mechanical
support to the growing parts of the plant such as
young stem and petiole of a leaf.
Sclerenchyma consists of long, narrow cells
with thick and lignified cell walls having a few or
numerous pits. They are usually dead and without
protoplasts. On the basis of variation in form,
structure, origin and development, sclerenchyma
may be either fibres or sclereids. The fibres are
thick-walled, elongated and pointed cells,
generally occuring in groups, in various parts of
the plant. The sclereids are spherical, oval or
cylindrical, highly thickened dead cells with very
Intercelluar space
Figure 6.2 Simple tissues :
(a) Parenchyma
(b) Collenchyma
(c) Sclerenchyma
A fibre
A sclereid
(c)
Lumen
Thick
cell wall
Lumen
Pits
Thick
cell wall
(b)
Thickened corners
Protoplasm
Vacuole
Cell wall
(a)
2015-16(19/01/2015)
ANATOMY OF F LOWERING PLANTS 87
narrow cavities (lumen). These are commonly found in the fruit
walls of nuts; pulp of fruits like guava, pear and sapota; seed
coats of legumes and leaves of tea. Sclerenchyma provides
mechanical support to organs.
6.1.2.2 Complex Tissues
The complex tissues are made of more than one type of cells
and these work together as a unit. Xylem and phloem constitute
the complex tissues in plants (Figure 6.3).
Xylem functions as a conducting tissue for water and
minerals from roots to the stem and leaves. It also provides
mechanical strength to the plant parts. It is composed of four
different kinds of elements, namely, tracheids, vessels, xylem
fibres and xylem parenchyma. Gymnosperms lack vessels in
their xylem. Tracheids are elongated or tube like cells with
thick and lignified walls and tapering ends. These are dead and
are without protoplasm. The inner layers of the cell walls have
thickenings which vary in form.  In flowering plants, tracheids
and vessels are the main water transporting elements. Vessel is
a long cylindrical tube-like structure made up of many cells
called vessel members, each with lignified walls and a large
central cavity. The vessel cells are also devoid of protoplasm.
Vessel members are interconnected through perforations in their
common walls. The presence of vessels is a characteristic feature
of angiosperms. Xylem fibres have highly thickened walls and
obliterated central lumens. These may either be septate or
aseptate. Xylem parenchyma cells are living and thin-walled,
and their cell walls are made up of cellulose. They store food
materials in the form of starch or fat, and other substances like
tannins. The radial conduction of water takes place by the ray
parenchymatous cells.
Primary xylem is of two types – protoxylem and metaxylem.
The first formed primary xylem elements are called protoxylem
and the later formed primary xylem is called metaxylem. In
stems, the protoxylem lies towards the centre (pith) and the
metaxylem lies towards the periphery of the organ. This type
of primary xylem is called endarch. In roots, the protoxylem
lies towards periphery and metaxylem lies towards the centre.
Such arrangement of primary xylem is called exarch.
Phloem transports food materials, usually from leaves to
other parts of the plant. Phloem in angiosperms is composed
of sieve tube elements, companion cells, phloem parenchyma
Phloem
parenchyma
Companion
cell
(b)
Sieve pore
Sieve tube
element
Figure 6.3 (a) Xylem
      (b) Phloem
(a)
Tracheid
Vessels
2015-16(19/01/2015)
88 BIOLOGY
and phloem fibres. Gymnosperms have albuminous cells and sieve cells.
They lack sieve tubes and companion cells. Sieve tube elements are
also long, tube-like structures, arranged  longitudinally and are
associated with the companion cells. Their end walls are perforated in a
sieve-like manner to form the sieve plates. A mature sieve element
possesses a peripheral cytoplasm and a large vacuole but lacks a nucleus.
The functions of sieve tubes are controlled by the nucleus of companion
cells. The companion cells are specialised parenchymatous cells, which
are closely associated with sieve tube elements. The sieve tube elements
and companion cells are connected by pit fields present between their
common longitudinal walls. The companion cells help in maintaining the
pressure gradient in the sieve tubes. Phloem parenchyma is made up
of elongated, tapering cylindrical cells which have dense cytoplasm and
nucleus. The cell wall is composed of cellulose and has pits through which
plasmodesmatal connections exist between the cells. The phloem
parenchyma stores food material and other substances like resins, latex
and mucilage. Phloem parenchyma is absent in most of the
monocotyledons. Phloem fibres (bast fibres) are made up of
sclerenchymatous cells. These are generally absent in the primary phloem
but are found in the secondary phloem. These are much elongated,
unbranched and have pointed, needle like apices. The cell wall of phloem
fibres is quite thick. At maturity, these fibres lose their protoplasm and
become dead. Phloem fibres of jute, flax and hemp are used commercially.
The first formed primary phloem consists of narrow sieve tubes and is
referred to as protophloem and the later formed phloem has bigger sieve
tubes and is referred to as metaphloem.
6.2 THE TISSUE SYSTEM
We were discussing types of tissues based on the types of cells present.
Let us now consider how tissues vary depending on their location in the
plant body. Their structure and function would also be dependent on
location. On the basis of their structure and location, there are three types
of tissue systems. These are the epidermal tissue system, the ground or
fundamental tissue system and the vascular or conducting tissue system.
6.2.1 Epidermal Tissue System
The epidermal tissue system forms the outer-most covering of the whole
plant body and comprises epidermal cells, stomata and the epidermal
appendages – the trichomes and hairs. The epidermis is the outermost
layer of the primary plant body. It is made up of elongated, compactly
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