THE LEAF
The leaf is a lateral, generally flattened structure on
the stem. It develops at the node and bears a bud in its
axil. The bud later develops into a branch. Leaves
originate from shoot apical meristems and are arran
an acropetal order. They are the most important
vegetative organs for photosynthesis.
Parts of a Leaf
A typical leaf has three main parts
i. Leaf Base ( Hypopodium)
The leaf is attached to the stem by the leaf base. In
monocots, the leaf base is said to be sheathing as it
expands and partially and wholly surrounds the stem. In
dicots, the leaf base bears two lateral outgrowths called
stipules.
In some leguminous plants, the leaf base may become
swollen which is called the pulvinus. Leaves with stipules
are called stipulate and those without them are termed as
exstipulate.
ii. Petiole (Mesopodium)
It is the stalk of a leaf. Petiole helps to hold the leaf blade
towards light. Petiole raises the lamina high to the level of
stem so as to provide maximum required exposure to light
and air.
iii. Lamina (Epipodium)
The lamina or leaf blade is the green, expanded part of the
leaf with veins and veinlets. It has a prominent median
vein called the midrib. It produces thinner lateral veins
in turn branch to form veinlets.
The lamina is the seat of photosynthesis, gaseous exchange,
transpiration and other metabolic activities. The shape,
margin, apex, surface and extent of incision of lamina vane
in different leaves.
Venation
The arrangement of veins and veinlets in the lamina of leaf
called venation. The midrib, veins and veinlets contain
vascular tissues, i.e., xylem and phloem for conduction
water, mineral salts and food.
Leaves have mainly two types of venation
i. Reticulate Venation
When the veinlets form a network, the venation is called
reticulate. It is found in dicot leaves. However, some
monocot leaves like Smilax, Dioscorea and Alocasia alq) show
reticulate venation.
ii. Parallel Venation
When the veins run parallel to each other within a lamina,
the venation is termed as parallel, e.g., Calophyllum,
Zingiber officinale, etc. It can be of the following types as
shown in the figure below.
Types of Leaves
Leaves can be of following types
i. Simple Leaves
A leaf having a single or undivided lamina is
called simple leaf. The lamina of a simple leaf
may be incised, but the incisions do not touch
the midrib. An axillary bud is always present in
the axil of leaf petiole and stem.
The lamina can have various types of incisions
which may reach upto half (fid), more than half
(partite) or near the base or midrib (sect).
ii. Compound Leaves
A leaf is called compound when the incision of
the leaf blade goes down to the midrib (rachis)
or to the petiole so that the leaf is broken up
into a number of segments called leaflets.
A bud is present in the axil of petiole in both
simple and compound leaves, but not in the
axil of leaflets of the compound leaf.
A compound leaf can be of following two types
(a) Pinnately Compound Leaves In these
leaves, the incision of lamina is directed
towards the midrib, which is known as
rachis. Leaflets are arranged on both side
on the rachis, e.g., neem, rose, etc.
(b) Palmate Compound Leaves The leaflets are attached at a
common point, i.e., at the tip of petiole as in silk cotton.
Phyllotaxy
The pattern of arrangement of leaves on the stem or branch is called
phyllotaxy. It helps to avoid overcrowding and provides every leaf with
optimum sunshine.
Phyllotaxy is usually of three types
i. Alternate (Spiral) Phyllotaxy
A single leaf arises at each node in alternate manner, e.g.. China rose,
mustard and sunflower plants.
ii. Opposite Phyllotaxy
A pair of leaves arises at each node and opposite to each other, e.g.,
Calotropis and Psidium guajava (guava plants).
iii- Whorled (Verticillate) Phyllotaxy
If more than two leaves arise at a node and form a whorl. it is called
whorled. The leaves of one whorl generally alternate with those of the
adjacent whorls in order to provide maximum exposure, e.g., Nerium
(kaner), Alstonia.
Modifications of Leaves
Leaves of plants are modified to perform different additional functions
in addition to their main function, i.e., photosynthesis.
i. Leaf Tendrils
These are thread-like sensitive structures, which can coil
around a support to help the plant in climbing, e.g., wild pea
(Lathyrus aphaca), Pisum sativum (sweet pea) and Gloriosa
superba (glory lily).
ii. Phyllode
It is a green, short-lived and flattened petiole or rachis of a
leaf, which performs the function of photosynthesis,
e.g., Australian Acacia. Phyllodes develop usually vertically
and possess fewer stomata hence, reduce transpiration.
iii. Bladder
The segments of the leaf modify into bladder-like structures,
which trap small insects present in the water, e.g.,
bladderwort ( Utricularia).
iv. Pitcher
It is a petiole modified into a tendril to hold the pitcher
upright. The leaf base is expanded to carry out
photosynthesis. The leaf apex is modified into a lid,
e.g., Nepenthes, Dischidia and Sarracenia.
v. Leaf Spines
The entire leaf or a part of a leaf may be modified into a
pointed structure called a spine, as in Opuntia.
vi. Scale Leaves
These are thin, membranous leaves found at the nodal
region. Each scale leaf contains an axillary bud in its axil,
e.g., Zingiber officinale (ginger).

THE ROOT
In plants, root is the non-green (due to the absence of
chlorophyll), cylindrical and descending part that normally
grows downwards into the soil. It does not bear leaves, buds
and is not distinguished into nodes and internodes.
Regions of the Root
A typical root contains following five regions. However,
there is no clear line of distinction between these regions.
i. Root Cap (Calyptra)
The root is covered at the apex by a thimble or cap-like
structure called the root cap. It protects the root meristem
from friction of the soil particles and also protect tender apex
which allow the passage of root through the soil, e.g., Lemna,
Eichhornia. Roots of parasitic plants lack root caps.
ii. Growing Point (Meristematic) Zone
It is a small (about 1 mm in length) thin-walled region
having dense protoplasm. It lies partly within and partly
beyond the root cap. Its cells divide regularly and repeatedly
for elongation. It is responsible for the growth of the root.
iii. Zone of Elongation
It is situated behind the meristematic region (growing
point). The cells elongate speedily and increases the length
of the root. The cells of this region can absorb water and
minerals from the soil.
iv. Root Hair Zone
It is the region where primary tissues differentiate into the
The vascular tissues like xylem and phloem are
formed.
Root hair zone is the most important part of the root for
absorption of water (most of the water) from the soil. The
root hairs increase the exposed surface of the root for
absorption. In aquatic plants, root hairs are usually absent
and the roots are not well-developed.
v. Zone of Maturation
This zone contains mature cells. It forms the permanent
zone of the root and also gives out lateral roots from the
interior part of this region, e.g., In dicots and
gymnosperms.
Types of Root System
The root system can be of two types on the basis of place
of origin
i. Tap Root System
The tap root develops from the radicle of embryo of
seed. In most of the plants. primary root persists
becomes stronger to form tap root. ‘the first root formed
by the elongation of radicle, is called primary root. l,
continuously grows and produces lateral roots called
secondary roots.
The further branches of the secondary roots are calla:
tertiary roots and so on. These types of roots are present
dicots. e.g.. pea. gram. groundnut. etc.
ii. Adventitious Root System
The roots developing from any part of the plant other than
the radicle are known as adventitious
(L.adventitious-extraordinary). These are usually found tr.
monocots.
e adventitious roots can further classified
following on the basis of nature of development
(a) Fibrous Roots The primary root soon gets replaced
by a cluster of slender. thread-like roots originating
from the base of the stem in monocotyledonous
plants, e.g., Triticum vulgare (wheat), Oryza sat;:•
(rice), Allium cepa (onion).
(b) Foliar Roots These roots develop from the
i.e.. from the petiole of the leaf, e.g., Pogostemon,
rubber plant.
(c) True Adventitious Roots These roots develop from
the nodes and internodes of the stem, e.g.,
roots of banyan (Ficus). climbing roots of money plant
(PothoS), roots from the stem when partially immersed in
water (Coleus), roots from nodes (Oxalis repens), etc.
Modification of Roots
The modifications are the changes in shape, form or structure
In an organ to carry out special functions such as support,
storage of food and respiration other than or in addition to the
normal functions. Modification of roots are found in both tap
roots and adventitious roots.
Modification of Tap Roots
e tap roots are modified for the function like storage, i
nitrogen-fixation and respiration.
Modification of Tap Roots
The tap roots are modified for the function like storage,
nitrogen-fixation and respiration.
(a) Conical Roots These are fleshy tap roots that resemble
a cone (broad at the base and gradually tapering
towards the apex), e.g., carrot (Daucus carom).
(b) Fusiform Roots The primary root is spindle-shaped. It
is swollen in the middle and gradually tapers at both
the ends, e.g., Radish (Raphanus sativus).
(c) Napiform Roots The primary root is almost spherical
(pitcher-shaped) at the base and tapers abruptly at the
lower end, e.g., beetroot (Beta vulgaris), turnip
(Brassica rapa), etc.
(d ) Tuberous Roots The primary root becomes thick and
fleshy, but do not attain any definite shape
(irregularly-shaped), e.g. 4 0’clock plant (Mirabilis
jalapa), Echinocystis lobata.
(e ) Nodulated Tap Roots In this the secondary,
tertiary and sometimes primary roots bear many
small irregular swellings called root nodules which
contain countless, minute nitrogen-fixing bacteria
of the genus Rhizobium, e.g.,
groundnut
(Arachis hypogea), clover (Medicago falcata), pea
(Pisum sativum), etc.
(f) Pneumatophores These are special roots that
develop in mangrove plants (grow in marshy
areas). The pneumatophores or aerophores or
respiratory roots grow vertically upward and are
negatively geotropic.
They have minute breathing pores called
pneumatophores or lenticels present on the tips of
vertical roots that help in getting oxygen for
respiration.
Modification of Adventitious Roots
The adventitious roots are modified to perform several
additional functions like food storage, mechanical
support and other vital functions.
(a) Fasiculated Roots These arise in clusters from the
base of the stem, e.g., Dahlia, Asparagus.
(b) Nodulous Roots These roots have swellings occur
only near the tips, e.g., arrow root (Maranta), amia
haldi (Curcuma amada).
(c) Tuberous Roots (Single Root Tubers) These are
swollen without any definite shape, e.g., Ipomoea
batatas (sweet potato).
(d) Prop (Pillar) Roots The prop roots grow as the
horizontal branches of the stem and grow
vertically downward.
They become thick pillar-like and provide
mechanical support to the giant trees, e.g., banyan
tree (Ficus benghalensis).
(e) Stilt Roots These are small, thick supporting
roots growing obliquely from the basal nodes of
the main stem. These provide mechanical
support, e.g., Saccharum offcinarum (sugarcane),
Zea mays (maize).
(f) Climbing (Clinging) Roots These roots are found in
climbers. They may arise from the nodes, e.g., Ivy
Pothos (money plant).
(g) Assimilatory (Photosynthetic) Roots These roots
have chlorophyll and can synthesise food, e.g., aerial
or hanging roots of some orchids.
(h) Parasitic (Sucking) Roots These roots occur in
parasitic plant for absorbing nourishment from their
host. These roots function as haustoria, e.g., Cuscuta
(dodder plant or amarbel).
Functions of Roots
The major functions of roots are as follows
(i) Fixation Root provides fixation to the plants with
soil.
(ii) Absorption Roots absorb water and minerals from
the soil and provide it to all parts of the body.
(iii) Storage of many plants store food for the use
of other plant parts and for animals.
(iv) Aeration Plants growing in waterlogged soil or marshy
areas have special roots, i.e., pneumatophores for
respiration.
(v) Conduction Roots transport water and minerals in
upward direction for the uses of stems and leaves.

(i) They are mostly marine called poikilothermic
animals (i.e., they have the capacity to regulate
their body temperature).
(ii) The body is laterally compressed and
spindle-shaped.
(iii) Notochord is persistent throughout the life.
(iv) Mouth is ventral in position, skin is tough containing
minute placoid scales and teeth are
modified placoid scales. They have strong jaw
are predaceous by nature.
(v) Gill slits are generally five pairs and gill cover
(operculum) are absent.
(vi) Heart is two-chambered with one auricle and
ventricle.