Roots are found underground. They are negatively phototropic
and positively geotropic i.e. growing away from light and
towards the center of gravity. They absorb water and minerals
from the soil. They are not differentiated into nodes and
internodes. They are non-green. The root tip is protected
by root cap. Roots growing from the main root are called
lateral roots(meaning side roots). The lateral roots are
of two types secondary and tertiary roots.
The main root or primary root is formed from the radical
of the seed. It grows downwards into the soil. This type
of arrangement is tap root system. It is seen only in dicotyledonous
plants. While in monocot plants fibrous roots are seen.
They are equal in length and perform the equal function.
Adventitious roots develop from any other plant except the
radical like roots growing from the stem. In grasses both
adventitious and fibrous roots are present.
The tip region is protected by the root cap which consists
of dead cells. The region above the root cap consists of
highly meristematic region they divide and produce large
number of cells. The region above the meristematic is called
the region of maturation or growth region. This region also
stores food. It does not divide but elongates. From meristematic
new cells are formed which go to maturation region. The
region above maturation is called the region of differentiation.
They modify according to the specific function and position.
Adventitious roots are false roots while fibrous and taproots
are true roots.
Modification In Roots
To perform additional function roots are modified and are
called root modification.
Roots are modified for the storage of food
Conical roots they store food throughout
- e.g. carrot.
Napiform roots store on the tip - e.g.
Fusiform roots store food in their center
- e.g. radish.
Tuberous root is modified fibrous root.
Many single roots are modified to form several similar swollen
roots for the storage of food. They occur in a bunch e.g.
Nodulated roots are fibrous adventitious
roots. They resemble fibers. Some nodule like structures
are present on the root e.g. ginger.
Roots modified for mechanical support
Prop roots - from branches some adventitious
roots develop and give support to the branches. They are
called prop roots as they are pillar like in appearance.
They grow downward and finally reach the ground so they
provide additional support to the plant.
Stilt roots - roots develop from nodes
which are present near to the ground or basal nodes. They
also grow downward and provide additional support. e.g.
Climbing roots - in some weak stemmed plants
roots develop from nodes which are useful to climb on the
Contractile roots - in some underground
stems the roots develop which fix into the ground. They
will contract themselves and the stem will also grow downwards
Floating roots - in some aquatic plants
the roots will float on the surface of the water. With the
help the these roots the plants will also float on the surface
of water. They also help in exchange of gases.
Roots are modified for vital function.
Respiratory roots - these roots are found
in aquatic plants and plants which grow on marshy areas.
In aquatic plants floating roots are acting as respiratory
roots. In marshy area the roots are not getting sufficient
oxygen and hence they grow upwards from the ground. They
have openings called nuematophores which take in oxygen.
Nodulated roots - it has beeds like structures.
Here nutrition is the vital function performed. It contains
nitrates and nitrogen fixing bacteria. Rhizobium is the
bacteria present. Plants coming under the pulse group will
contain rhizobium(leguminous plants).
Changing the crop season after season is called crop rotation.
We are cultivating pulses to increase the nitrogen content
in the soil. In crop rotation pulses are put season after
season. Plants take minerals from the soil which are used
to synthesize its structural components. Plants need proteins
in the absence of nitrates. When plants are grown the soil
decreases in its mineral content. Therefore we need to use
fertilizers to increase the fertility of the soil and regain
its mineral content.
Epiphytic means no nutrition is taken
from the host. The host only provides support. In parasitic
plants nutrition is also taken. Epiphytic roots have only
physical contact. Epiphytic plants have two types of roots
i.e. assimilatory roots and epiphytic roots. Assimilatory
roots synthesize and store food while epiphytic roots fix
the plant. Velamen is the assimilatory root of vanda. So
vanda has both types of roots.
In parasitic plants food sucking roots
are also present called haustoria. They are called so as
they spoil the host plant.
In some plants roots are developed from the leaves and
from that point auxillary buds also originate. These buds
will detach to form separate plant. E.g. bryophyllum.
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