A section taken through any region of a typical plant body
shows the presence of three tissue systems.
Epidermal Tissue System
Origin - It is a derivative
of protoderm.
It is represented by the
epidermis
and
the
associated
structures,
which
are
mainly
involved in providing
protection to the plant
body. The epidermis is
the outermost covering
of the plant body. It is
commonly described
as the skin of the plant
body.
In the stem and the leaf, the epidermal cells are thick-walled
and are meant for protection. In the leaf, there are two
epidermal layers, one on each surface of the leaf.
In the roots, the epidermal
cells are thin-walled, since
they are mainly involved in
the absorption of water and
mineral salts.
In the root, the epidermal
hairs are unicellular and are
called root hairs. The root
hairs penetrate between the
soil particles to absorb
water and minerals
In the stem and the
leaf, the epidermal
hairs are involved in
the secretion of some
compounds
Structure of a leaf
CUTICLE
PALISADE
LAYER
SPONGY
LAYER
VEIN
AIR
SPACES
STOMATA
How are palisade cells specialised?
• Lots of chloroplasts, which contain
chlorophyll to catch light energy.
• Long and thin, so they pack closely
together to collect as much light as
possible.
• They are at the top of the leaves, to get as
much light as possible.
How does the carbon dioxide get
inside the leaf?
The epidermis of the
stem and the leaf is
usually surrounded by a
thin, covering called
cuticle. It is formed by a
waxy substance called
cutin. It’s function is
preventing
excessive
evaporation of water.
Cuticle is absent in the
root epidermis.
stomata
 The epidermis of the leaf and herbaceous stem (green stem) contains
numerous small openings called stomata.
 Each stoma is surrounded by a pair of modified epidermal cells called
the guard cells. The stomata take part in functions such as
transpiration, respiration and photosynthesis.
 Stomata are absent in the epidermis of the root and woody stem.
Leaf Stomata: Allow Gas Exchange
Guard cells with
chloroplasts
Stomata in
Zebrina leaf
epidermis
Stoma
Subsidiary cells
Vascular Tissue System
The vascular tissue system is a derivative of
procambium. It is represented by the conducting
tissues-xylem and phloem.
These vascular tissues occur in the form of
strands extending from one end of the plant body
to another. These strands are known as vascular
bundles or fascicles. In the leaf, the vascular
bundles are known as veins.
Vascular Tissue System
The vascular bundles may
sometimes enclose a piece of
meristematic tissue called
cambium, which brings about
secondary growth in the
bundles.
When cambium is present,
the
vascular bundle
is
described as open and when
the cambium is absent, the
vascular bundle is described as
closed.
Vascular Tissue System
A vascular bundle may contain either only xylem or
only phloem or both.
Xylem tissue is found in the vascular bundle in the stem. It is also found
throughout the plant.
Ground Tissue System
It is a derivative of ground meristem.
It is represented by the different
regions in the plant body that are
mainly involved in storage.
In the cylindrical parts of the plant body such as root and stem,
the ground tissue becomes differentiated into various regions.
In a typical condition, following regions can be recognised in the
ground tissue.
Hypodermis
Cortex
Endodermis
Pericycle
Medullary rays
Pith