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.