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Root Cortex
The view of a root cortex

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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 like-

Conical roots they store food throughout - e.g. carrot.
Napiform roots store on the tip - e.g. turnip.
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. dahalia.
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. sugarcane.
Climbing roots - in some weak stemmed plants roots develop from nodes which are useful to climb on the hard object.
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 e.g. colocassia.
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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