- Downward growing part of the vascular plant is called root.
- Root can also be aerial or aerating, that is, growing up above the ground or especially above water.
- Therefore, the root is best defined as the non-leaf, non-nodes bearing parts of the plant’s body.
- On the germination of seed the first root arises from the radicle of the embryo. This is called the primary root.
- There are various types of root. But, generally it is of two types. They are: Tap root and adventitious root.
- Root has various functions. Some of them are:
a)Absorption of water and inorganic nutrients.
b)Anchoring of the plant body to the ground, and supporting it.
c)Storage of food and nutrients.
d)Translocating water and minerals to the stem.
e)In response to the concentration of nutrients, roots also synthesize cytokinin, which acts as a signal as to how fast the shoots can grow.
Modification of roots:
- The normal type of root is modified variously to perform many functions.
- This helps the plant to survive in surrounding environment which is known as the modification of root.
A)Modification of Tap root
- It is the normal tap root modified to store the food material.
- It changes its shape and size due to accumulation of food materials.
- According to their shape, they are classified into following types:
- It is spindle shaped root with middle part swollen and gradually tapering towards the both ends.
- e.g., Radish.
- The upper part of the root becomes almost globular due to maximum swelling.
- It tapers sharply towards the lower ends.
- e.g., Turnip, Beet root.
- Broad at the base and gradually tapers towards the apex like a cone.
- Thick and fleshy root with adefinite shape.
- e.g., 4 O’ clock plant.
B)Modifications of Adventitious root
- They are modified to perform various functions such as storage of food, support, assimilation and other important functions.
1)For storage of food
- This is a swollen root without any definite shape.
- It appears singly.
- e.g., Ipomoea.
- Root modified to form a series of ring-like swelling or annuli on its body.
- e.g., Ipecacuanha.
- Root becomes suddenly swollen at or near the apex.
- g., mango, ginger.
- Several roots appear in cluster at the base of the stem.
- e.g., Dahlia, Asparagus, etc.
e)Moniliform or Beaded
- Roots swell at regular intervals giving a beaded appearance.
- e.g., Momordica, Portulaca, Indian Spinach, etc.
2)For mechanical support
- These are the roots arising from the main stem and branches of a tree.
- They grow vertically or obliquely downwards to the soil.
- They provide support to the plant body.
- Look like pillars and allow tree to grow in large area.
- e.g., Banyan tree.
- The lower nodes above the ground level give rise to a ring of stout and slender roots; stilt roots.
- They grow obliquely downwards into the soil and give support to the stem.
- e.g., Maize, Sugarcane, Pandanus.
- Roots developing from the nodes and internodes of the many tropical climbers is known as climbing roots.
- They attach themselves to any support and help in climbing.
- e.g., Piper betel, P. longum, etc.
3)For vital functions
a)Haustorium or sucking root
- Parasitic plants develop a peg-like structure known as haustoria.
- The haustoria penetrate the living host tissue and absorb food by sucking.
- They have no root cap.
- e.g., Cuscuta.
- Epiphytic plant develops a special kind of aerial roots.
- These roots contain spongy tissue called velamen.
- The cells of velamen are dead and empty, which help in absorption of moisture from the air.
- e.g., Orchid.
c)Respiratory root or Pneumatophores
- Some plants growing in marshy places and salt lakes produce special roots which grow vertically upward from the underground roots.
- They usually develop above the level of water around the trunk of the tree.
- They have numerous aerating pores that help in respiration.
- e.g., Jussiaea, Rhizophora, etc.
- Long slender hanging root develop from the branches in some plants.
- They contain chlorophyll and carry out photosynthesis.
- e.g., Trapa, Tinospora, etc.
- Spongy roots of some hydrophytic plants are known as floating roots.
- They store air and help in buoyancy.
- e.g., Pistea, Jussiaea, etc.
- It is found in gymnosperms.
- The younger portions of the tap root become closely invested by the hyphae of a fungus.
- They lead symbiotic life, as the fungus helps in absorbing minerals and water and in turn the plant root provides the organic food.
- e.g., roots of Pinus, Cycas, etc.
floating roots mycorrhizal roots