Additional Notes for Lecture 3
Tap Root Modifications
Tap roots are modified in to different structures, these modified structures carry out specific functions like food storage. Such roots are referred to as modified tap roots. They are different types of modified tap roots like Fusiform, Napiform, Conical, Tuberous or tubercular roots, pneumatophores.
Adventitious Root Modifications
Adventitious roots are the roots that are produced from any portion of the plant other than the radicle. The root system may be changed to different forms for special functions like storage, mechanical support and vital functions.
- For Storage of Food
Tuberous root: The adventitious roots in this are grown from the nodes of the running stem. These roots are modified are swollen into irregular forms and are known as tuberous roots. They are produced in single number. Example: Sweet Potato.
Fasciculate root: The tuberous roots are developed from the base of the stem in cluster.
Nodulose root: The adventitious roots in this case arise from the underground stem. Some roots that are
slender become swollen near the apex and they form nodule like structures. Example: mango-ginger.
Moniliform or Beaded roots: In this case, the roots are swollen at frequent intervals. This formation gives a beaded or moniliform type of appearance. This form of root formations is seen in many grasses, Basella, etc.
Annulated roots: This type of roots has ring-like swellings in a series and appears in the form of a number of discs placed one above the other.
B. For Mechanical Support
Prop roots: Here the plants have tap roots system. The horizontal branches of the stem of the plant gives rise to aerial roots. These aerial roots hang vertically downwards. These roots on reaching the ground, they grow and act like pillars. They provide mechanical support to the plant. Example Ficus bengalensis.
Stilt Roots: These plants have their own roots system like in screw pine. They are not strongly anchored to the soil. Hence, these plants develop adventitious roots from near the base of the stem. These roots grow obliquely downwards. They act like stilt and they provide mechanical support to the plant. Example – the maize plant produces adventitious roots form the lower nodes which also act in a similar way.
Climbing roots: This type of root system is found in climbers. Adventitious roots are developed from the nodes and are aerial roots. These aerial roots twist and clasp the support and help in climbing. Example Betel, Pothos, etc.
Clinging roots: This type of roots is seen in orchids. These roots arise from the stem base of the plant. They enter crevices of the support to fix the epiphyte. They provide the plant with mechanical support.
Root buttresses: Some trees have great plant-like roots that radiate from the base of the stem of the tree. It consists of partly root and partly stem. Example is Bombax.
- For Vital Functions
Sucking roots or Haustoria: Cuscuta is a leafless, parasitic plant, it always grows in association with other plants. The parasatic plant at the point of attachment with the host plant produces some knob like roots known as haustoria which penetrate into the host plant and draws nourishment.
Epiphytic roots: are the plants like orchids that grow perched on tree branches. They attach themselves firmly to the trunk of the tree by the aid of social roots known as climbing roots.
They also have aerial roots for absorption. These roots are fleshy and remain along with the clinging roots. These roots have spongy tissues which absorb moisture from the atmosphere. They also have chlorophyll pigment and photosynthesis takes place.
Floating roots: are found in aquatic plants. These roots develop from the nodes of the floating branches. The roots are spongy and are colorless. These roots are present above the level of water. As these roots are spongy and soft, they store air in them which help the plant in floating. They also help in respiration process.
Assimilatory roots: are normally non-green in color. The adventitious roots are developed from the branches of the plant Tinospora cord folia. These branches are green in color and carry out photosynthesis, the roots developed from this are known as assimilatory roots. The assimilatory roots are slender, long and in hanging state.