The
plants that we see today are the result of billions of years of evolution.
Today, plants cover almost 30 per cent of the total landmass and account for
the 50 per cent of the plant’s productivity (generation of biomass). Plants
fulfill many roles in the ecosystem.
They are a source of food, nutrition, and shelter,
maintain the integrity of soil (by preventing erosion) and most importantly,
they are the main source for balancing the oxygen level in the atmosphere.
Anatomically, plants are very complex organisms and are classified into various types based on certain defining characteristics. Roots are very important structures that provide a variety of functions, but contrary to popular belief, all plants do not have roots.
Roots are absent in plants like mosses and liverworts.
Read On: Flowering Plants: Structure and Characteristics
Definition of Root
Roots
are the important underground part of all vascular plants. This part of the
plant is mainly responsible for anchoring it down into the ground and absorbing
the essential mineral elements, nutrients,
and water from the soil. It is also used to store food.
Root,
in botany, that part of a vascular plant normally underground.
Its
primary functions are anchorage of the plant, absorption of water and dissolved minerals
and conduction of these to the stem, and storage of reserve foods.
The
root differs from the stem mainly by lacking leaf scars and buds, having a
root cap, and having branches that originate from internal tissue rather
than from buds.
However,
not all plants have their roots underground; some plants have their roots
growing above the ground.
These are called aerial roots. Alike underground roots, these aerial roots are also responsible for absorbing nutrients, anchoring and affixing the plant by supporting them to the structures such as nearby walls, rocks, trellises, etc.
Few examples of plants with the aerial roots are–Bonsai, Banyan
Tree, Mangroves, etc.
What is Root System?
Root System The root system is the part of the plant growing in the soil. This excludes the underground stems which are organs of perennation (survival from year to year by vegetative means).
There
are two kinds of root systems, namely: tap root and fibrous root system. The
root system develops from radicle of embryo which normally stays below the
ground, and because it never bears leaves or flowers is not divisible into
nodes and internodes.
Types of Root Systems
Plants
have three types of root systems:
1. Taproot, with a main taproot that is larger and grows faster
than the branch roots.
2. Fibrous, with all roots about the same size
1. Tap Root System:
This system is characteristic of the dicotyledonous plants. There is just one
main root known as the tap root growing deep down and giving rise to smaller
branches, the lateral roots. Tap roots are firm, if the primary radicle
establishes itself to become a permanent and clearly defined organ, then
together with its lateral branches it forms a tap root system and the primary
radicle become the tap root.
2. The Fibrous Root System: This
is characteristic of monocotyledonous plants. In this system, there is a mass
of roots arising from the base of the stem. The mass consists of several main
roots of approximately the same size. These give off numerous branch roots
which in turn give off other branch roots of smaller size. The roots are
slender in appearance.
Both the main and branch roots bear a root cap at their tips. The root cap protects the soft growing regions of the root tips. Here the cells are actively dividing to add new cells to the root. A little above the root tips are some unicellular root hairs used for absorption of water and mineral salts from the soil into the plant body.
The root hairs are very numerous and tiny
and should not be confused with the very small branch roots seen after an
intact plant has been uprooted from the soil. One may need a microscope to
observe the root hairs if they have not been damaged by uprooting.
The root begins to thicken above the root
hair region. Root produced from parts other than the radicle of a seed is known
as adventitious roots. For example, the prop roots of maize which grows from
the lower nodes of the stem into the soil.
The roots seen in stem tubers, rhizomes,
bulbs and corms are all adventitious roots.
Characteristics of Roots
The
general characteristics of roots are as follows:
1.
Roots grow inside the ground except for some modified aerial roots
2.
Roots lack buds
3.
Roots end in caps (stems end in buds)
4.
Roots do not bear green pigments or chlorophyll
5.
Roots possess unicellular hairs known as root hairs. (Hairs found in some stems
and leaves are multicellular)
6.
Nodes and intermodals are absent in roots.
Read On: Mosses: Characteristics, Reproduction and Economic Importance
Functions of Roots
The
Main Importance Functions of Roots are:
1.
For absorption of water and dissolved mineral salts from the soil into the
plant body through the root hairs.
2.
For anchoring the whole plant firmly to the soil
3.
Certain roots become modified to perform some special functions such as food
storage, vegetative reproduction, climbing, breathing in water-logged soil and
for extra support to the plant.
Modification of Roots
These
will be summarized with reference to the particular function the modification
serves. Both tap and fibrous roots may be modified for support, food storage or
climbing.
Types of Modified Roots
Root-Ilibers:
These are roots which become swollen with food reserves. Hence they are called
storage organs. Examples are seen in the tap roots of carrot, (Boerhaavia
diffusa) and lateral roots of cassava.
Climbing Roots:
They are also known as clasping or adhering roots. These are aerial roots
growing into cracks, walls, or barks of host plants. By clasping the host for
support they are able to climb high.
InFicus
pumila, the aerial roots appear in clusters at the nodes.
In
Scindapus sp., the clasping roots grow downwards and on getting to the soil
they develop lateral roots. In black pepper, the small roots of the plant
produce sticky substance that helps to gum it to the host tree or wall.
Breathing Roots:
These are special roots possessed by some plants in the swamps for breathing in
the air. These breathing roots or pneumatophores, are lateral branches growing
above the soil which is often water logged. Good examples are seen in raphia
and the white mangrove.
Prop Roots:
These are clusters of roots growing from the nodes of a stem straight into the
soil for extra support to the plant. Prop roots occur in maize.
Stilt Roots:
These are branches from the base of certain trees which grow in muddy places
and they help in the support of the plant. In the umbrella tree, for example, the
trunk narrows at the base from where the stilt roots develop to provide the
necessary support. Stilt roots are also seen in the red mangrove.
Buttress Roots:
These are enlarged growths on the upper edges of normal lateral roots of some
huge trees such as silk cotton tree. Buttress roots also act as support to the
plant as well as providing good hiding places for some forest animals.
Ephiphytic Roots:
These are produced by plants growing on another plant with special aerial roots
eg. epiphytic orchid. The plants with such roots are not parasitic.
Sucking Roots:
These are developed by parasitic plants. Such roots are called haustoria e.g.
dodder (cuscuta sp) and mistletoe.
Internal Structure of the Root
Internally,
a root consists of an outer cylinder and an inner central cylinder or stele. A
transverse section of a root shows the following arrangement of tissues from
the circumference to the centre.
Outer Cylinder: Piliferous
layer and Cortex, includes the endodermis
Inner Cylinder or Stele: Pericycle
and Vascular tissuepith
The
outer cylinder consists of a wide zone of loosely packed, thin-walled
parenchyma bound on the outside by a single-cell thick piliferous layer.
Roots
hairs arise from young cells of the piliferous layer. The endodermis is the
innermost layer of the cortex. It is made up of a single-cell thick layer of
barrel-shaped cells. Each cell is encircled by a thick waxy band.
The
stele consists of vascular tissue made up of alternate phloem and xylem bundles
arranged in a ring.
Usually,
there are more vascular bundles in a monocotyledonous root than a
dicotyledonous one. The pericycle which bounds the vascular tissue on the outer
side is a one- or two cell thick layers of thin-walled cells.
The
pith which is large in monocotyledonous roots is composed of thin-walled
parenchyma.
In
most dicotyledonous roots, the xylem fills up the centre of the stele, forming
a centrally supporting column. The main supporting tissues in roots are xylem
and the turgid parenchyma which makes up the cortex Note: Cambium, a
meristematic tissue which gives rise to secondary growth, appears in older
dicotyledonous roots but is completely absent in monocotyledonous roots.
Commonly Question Asked
What are the different types of root systems?
The different types of root systems are:
1. Taproots
2. Fibrous
roots
What are the primary and secondary roots?
Primary
roots are the early roots in young plants that consist of taproots, basal
roots, and lateral roots. Secondary roots are the side branches of the primary
roots.
Mention the plants
with taproots.
1.
The plants with taproots are:
2. Beetroot
3. Carrot
4. Parsley
5. Dandelion
Mention some edible roots
1.
Some edible roots include:
2. Ginger
3. Turnip
4. Yam
tubers
5. Cassava
tubers
What are fibrous roots?
Fibrous
roots are the roots formed by thin, moderately branching roots emerging from
the stem. Wheat, rice and corn are some of the examples of fibrous roots.
What are the functions of roots?
Roots
perform the following functions:
1. Roots
absorb water and nutrients from the soil.
2. They
anchor the plant firmly.
3. They
help in storing food and nutrients.
4. Roots
transport water and minerals to the plant.
What are the
differences between monocot and dicot roots?
The
main difference between monocot and dicot root is that the dicot root contains
xylem in the middle and phloem surrounding the xylem.
Whereas
in monocot root, xylem and phloem are arranged circularly.
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