The Root
 

Introduction:

• The root is usually an underground part of the plant.
• It is primarily responsible for the fixation and absorption of water.
• The root with its branches is known as the root system.

In this concept we will discuss the following sub-concepts:

• Morphology of root and its types
• Regions of the root
• Modification of Taproots and adventitious roots
  
  
  
   

Morphology of Root:
 

Introduction:

• Generally underground, descending portion of the plant axis and non-green part of the plant.
• Lacks nodes, internodes and buds.

Detailed explanation:
 

A. Characteristic features of the root-

- Generally underground, descending portion of the plant axis and non-green part of the plant.
- It lacks nodes, internodes, and buds.
- Positively Geotropic- grows downward into the soil in the direction of gravity.
- Negatively Phototropic- grows against the direction of light.
- Positively Hydrotropic- grows towards water.
- Endogenous Origin- Lateral branches arise from the pericycle.
- Functions- It provides anchorage to the plants, stores reserve food, absorbs water and minerals from the soil and also synthesizes plant growth regulators.

You may also want to learn plant definition. 

B. On the basis of origin the roots can be classified into the following types:
 

- Tap root: (Example: Dicots- Mustard)

• Thick primary root arises directly from the radicle and grows inside the soil.
• It bears lateral roots of several orders that are referred to as secondary, tertiary roots etc.
• The primary roots and its branches constitute the tap root system.
• Tap root is deep penetrating.
  
  
  
   

- Fibrous root: (Example: Monocots- Wheat)

• The primary root is short-lived and is generally replaced by several fine fibrous roots.
• These roots originate from the base of the stem.
• Fibrous roots are not deep penetrating hence often called surface feeders.
  
  
  
   

- Adventitious root: (Example: Grass, Monstera, Banyan tree)

• Some plants have specialized roots called adventitious roots.
• Adventitious means different in origin.
• These roots develop from any parts of the plant other than the radicle.
  
  
   

Regions of Root
 

Introduction:

• A typical root consists of four main regions from tip towards the base, which are as follows:
  1. Root cap
  2. Region of meristematic activity
  3. Region of elongation
  4. Region of maturation

Detailed explanation:
 

Regions of Root:
 

1. Root cap:

• The apex of the root is covered by a thimble-like structure called root cap.
• It is multicellular and parenchymatous.
• It protects the tender apex of the root as it makes its way through the soil.
• They are rich in Golgi vesicles.
• Due to the presence of the root cap at the apex, the growth of the root is subterminal.
  
  
   

2. Region of meristematic activity:

• This layer is a few millimetres above the root cap.
• It consists of thin-walled meristematic cells having dense protoplasm and a prominent nucleus.
• These cells divide very rapidly to produce new cells.

3. Region of elongation:

• The cells proximal to the meristematic region undergo rapid elongation and enlargement.
• Responsible for the increase in the length of the root.

4. Region of maturation:

• It lies proximal to the region of elongation.
• Here, the elongated cells finally get differentiated and mature.
• Some of the epidermal cells of this region differentiate to form fine, delicate and thread-like structures called the root hairs.
• Root hairs help to increase the surface area of absorption of water and minerals from the soil.

Modification of Taproots and adventitious roots
 

Introduction:

• A root is a positively geotropic and negatively phototropic structure which grows into the soil.
• It provides anchorage to the plants, absorbs water and minerals from the soil and also synthesizes plant growth regulators.
• Apart from these primary functions sometimes the root undergoes some structural modifications for performing special functions such as-
  1. Storage of food: e.g., Carrot, radish, turnip, sweet potato, etc.
  2. Respiration: e.g., Rhizophora
  3. Photosynthesis: e.g., Trapa, Tinospora
  4. Mechanical support: e.g., Ficus, sugarcane
  5. Vegetative propagation: e.g., Dahlia
  6. Haustorial/Parasitic: e.g., Cuscuta
  7. Floating: e.g., Jussiaea

Detailed explanation:
 

A. Modifications of tap roots:

• Taproots can be modified for performing various functions such as food storage, nitrogen fixation and respiration.

1. For food storage:

a. Conical roots: They have a broader and thicker upper end which gradually tapers down at the lower end, e.g., Carrot
b. Fusiform roots: They have a thicker middle portion that tapers down at both ends, e.g., Radish
c. Napiform roots: They have a spherical swollen upper end and a tapering lower end, e.g., Turnip, Beetroot
d. Tuberous roots: They do not have a definite shape, any part of the root may become thick and fleshy storing food, e.g., Mirabilis
 

2. For nitrogen fixation: Nodulated roots-

• Root nodules (small swellings) are present on the roots and their branches which possess nitrogen fixing bacteria that helps to perform biological nitrogen fixation,e.g., leguminous plants.
  
  
   

3. For respiration: Pneumatophores-

• These are the negatively geotropic roots found in the swampy or marshy areas.
• Such areas have an extreme scarcity of oxygen so to compensate for this the tap roots modify and grow vertically upward above the ground.
• They have minute pores called pneumathodes or lenticels through which gaseous exchange occurs, e.g., Rhizophora.
  
  
   

B. Modifications of adventitious roots:
 

1. For storage of food:
 

a. Fasciculated roots - These are the swollen roots that occur in bunches, e.g., Dahlia and Asparagus.
 

b. Moniliform roots - The roots swell up at regular intervals giving it the appearance of beads on a string, e.g., Bitter gourd (Momordica), Portulac
c. Tuberous roots - These are indefinite in shape. They become swollen up to store food, e.g., Sweet potato (Ipomoea batatas)
 

d. Nodulose roots: - These roots are swollen at tips, e.g., Curcuma amada (Mango ginger).
 

2. For mechanical support:

a. Stilt roots - The roots develop obliquely from basal nodes of stem, e.g., maize, sugarcane, screw pine.
 

b. Prop or pillar roots - These are thick pillar like roots which grow vertically downwards from horizontal stem branches, e.g., Banyan tree (Ficus benghalensis)
 

c. Climbing or Clinging roots : These are non-absorptive roots found in climbers. They arise from nodes and help the plant in climbing e.g., Betel, Pothos (Money plant)
 

3. For other vital functions

a. Parasitic roots - These roots are parasitic and obtain nutrition from the host plant. These are also called haustorial roots, e.g., Cuscuta (Total stem parasite)
 

b. Floating roots: These roots store air, become inflated and help the plant to float on the water surface, e.g., Jussiaea.
 

c. Assimilatory/Photosynthetic roots : Green photosynthetic roots, e.g., Tinospora, Trapa.
 

d. Reproductive roots : Adventitious roots develop buds that grow into new plants under favourable conditions, e.g., Dahlia.
 

e. Epiphytic or Hygroscopic roots: Epiphytes bear three: Clinging roots (for fixation); absorbing roots ( for absorbing mineral salts and moisture from dust collected on the bark) and aerial, hygroscopic or epiphytic roots. Hygroscopic or epiphytic roots are thick, irregular and hang down in air and absorb moisture from the air by the help of velamen tissue, e.g., Orchid(Vanda).
 

f. Epiphyllous roots: Roots arising from the leaf are epiphyllous(phyllous means leaf). They have the ability to develop into new plants from leaves that fall to the ground, e.g., Bryophyllum.
 

Frequently Asked Questions: FAQs

Question 1 What are the characteristics of the root?
Answer:
Characteristic features of the root are as follows:

- Generally underground, descending portion of the plant axis and non-green part of the plant.
- It lacks nodes, internodes, and buds.
- Positively Geotropic- grows downward into the soil in the direction of gravity.
- Negatively Phototropic- grows against the direction of light.
- Positively Hydrotropic- grows towards water.
- Endogenous Origin- Lateral branches arise from the pericycle.

Question 2 What are adventitous roots? Give two examples.
Answer:

• Roots developing from parts other than radicle are called adventitious roots.
• Adventitious roots are found in Banyan trees and sugarcane.
• The Banyan tree has huge pillar-like roots that grow downwards and provide support to the tree. These roots are known as prop roots.
• There are small roots coming out from the basal nodes of sugarcane stems that provide support to the plant. These roots are called stilt roots.
• Both the types of roots are adventitious roots that arise from parts other than radicle.

Question 3 Define Pneumatophores.
Answer: In marshlands or swamps, pneumatophores or respiratory roots are the negatively geotropic roots that come up the soil surface and grow vertically upwards to respire through small pores or pneumatophores. Example: Rhizophora

Question 4 Explain the regions of root in a sequence from tip towards the base.
Answer: Regions of Root:

1. Root cap:

• The apex of the root is covered by a thimble-like structure called root cap.
• It is multicellular and parenchymatous.
• It protects the tender apex of the root as it makes its way through the soil.
• They are rich in Golgi vesicles.
• Due to the presence of the root cap at the apex, the growth of the root is subterminal.

2. Region of meristematic activity:

• This layer is a few millimetres above the root cap.
• It consists of thin-walled meristematic cells having dense protoplasm and a prominent nucleus.
• These cells divide very rapidly to produce new cells.

3. Region of elongation:

• The cells proximal to the meristematic region undergo rapid elongation and enlargement.
• Responsible for the increase in the length of the root.

4. Region of maturation:

• It lies proximal to the region of elongation.
• Here, the elongated cells finally get differentiated and mature.
• Some of the epidermal cells of this region differentiate to form fine, delicate and thread-like structures called the root hairs.
• Root hairs help to increase the surface area of absorption of water and minerals from the soil.

Question 5 In which region are the root hairs present ?
Answer: Region of maturation lies proximal to the region of elongation.Here, the elongated cells finally get differentiated and mature. Some of the epidermal cells of this region differentiate to form fine, delicate and thread-like structures called the root hairs. Root hairs help to increase the surface area of absorption of water and minerals from the soil.

Question 6 What are the different modifications of taproot for storage of food?
Answer:

• Conical roots: They have a broader and thicker upper end which gradually tapers down at the lower end, e.g., Carrot
• Fusiform roots: They have a thicker middle portion that tapers down at both ends, e.g., Radish
• Napiform roots: They have a spherical swollen upper end and a tapering lower end, e.g., Turnip, Beetroot
• Tuberous roots: They do not have a definite shape, any part of the root may become thick and fleshy storing food, e.g., Mirabilis

Question 7 Discuss any three modifications of adventitious roots for storage of food
Answer:

• Three modifications of adventitious roots for food storage are as follows:
  a. Fasciculated roots - These are the swollen roots that occur in bunches, e.g., Dahlia and Asparagus.
  b. Moniliform roots - The roots swell up at regular intervals giving it the appearance of beads on a string, e.g., Bitter gourd (Momordica), Portulaca
  c. Tuberous roots - These are indefinite in shape. They become swollen up to store food, e.g., Sweet potato (Ipomoea batatas)

Question 8 What is the difference between taproot and adventitious root?
Answer:
Tap root is thick primary root arises directly from the radicle and grows inside the soil.It bears lateral roots of several orders that are referred to as secondary, tertiary roots etc. However,the roots develop from any parts of the plant other than the radicle is known as adventitious roots .

Question 10 How Roots are used in the vegetative propagation in Sweet potatoes?
Answer:

• The reproduction in which the vegetative part of the plant gives rise to a new plant is known as vegetative reproduction.
• Roots are used in vegetative propagation of sweet potato.
• The roots bear adventitious buds from which new plants can develop when it is buried in the moist soil. Such roots are called reproductive roots.

Question 11. What are the different types of roots?
Answer:
- Tap root: (Example: Dicots- Mustard)

• Thick primary root arises directly from the radicle and grows inside the soil.
• It bears lateral roots of several orders that are referred to as secondary, tertiary roots etc.
• The primary roots and its branches constitute the tap root system.
• Tap root is deep penetrating.

- Fibrous root: (Example: Monocots- Wheat)

• The primary root is short-lived and is generally replaced by several fine fibrous roots.
• These roots originate from the base of the stem.
• Fibrous roots are not deep penetrating hence often called surface feeders.

- Adventitious root: (Example: Grass, Monstera, Banyan tree)

• Some plants have specialized roots called adventitious roots.
• Adventitious means different in origin.
• These roots develop from any parts of the plant other than the radicle.

Question 12. What are epiphyllous roots?
Answer: Roots arising from the leaf are epiphyllous(phyllous means leaf). They have the ability to develop into new plants from leaves that fall to the ground, e.g., Bryophyllum

Question 13. What are epiphytic or hygroscopic roots?
Answer: Epiphytes bear three: Clinging roots (for fixation); absorbing roots ( for absorbing mineral salts and moisture from dust collected on the bark) and aerial, hygroscopic or epiphytic roots. Hygroscopic or epiphytic roots are thick, irregular and hang down in air and absorb moisture from the air by the help of velamen tissue, e.g., Orchid (Vanda).