Secondary function : In some plants roots perform additional functions. These are called secondary functions. To perform additional functions, these roots are modified in their structure.
I. Tap root modification
a. Conical Root : These are cone like, broad at the base and gradually tapering towards the apex.
2. Fusiform root : These roots are swollen in the middle and tapering towards both ends.
3. Napiform root : It is very broad and suddenly tapers like a tail at the apex.
b. Breathing root :
Some mangrove plants like Avicennia , Rhizophora , Bruguiera develop special kinds of roots ( Negatively geotropic) for respiration because the soil becomes saturated with water and aeration is very poor. They have a large number of breathing pores or pneumatophores for exchange of gases.
II. Adventitious root modification
a. Storage roots :
1. Tuberous root : These roots are swollen without any defininte shape. Tuberous roots are produced singly and not in clusters.
2. Fasciculated root : These roots are in cluster from the base of the stem.
3. Nodulose root : In this type of roots swelling occurs only near the tips.
4. Moniliform or Beaded root : These roots swell at frequent intervals giving them a beaded appearance.
5. Annulated root : These roots have a series of ring-like swelling on their surface at regular intervals.
b.Mechanical support :
1. Prop (Pillar ) root : These roots grow vertically downward from the lateral branches into the soil.
2. Stilt (Brace ) root : These are thick roots growing obliquely from the basal nodes of the main stem. These provide mechanical support.
3. Chimbing ( clasping or clinging ) roots : These roots are produced from the nodes of the stem which attch themselves to the support and help in climbing.
4. Buttress root : In certain trees broad plank like outgrowths develop towards the base all around the trunk They grow obliquely downwards and give support to huge trunks of trees.
c. Vital functions :
1. Epiphytic or velamen root : Some epiphytic orchids develop a special kind of aerial roots which hang freely in the air.These roots develop a spongy tissue called velamen which helps in absorption of moisture from the surrounding air .
2. Foliar root : Roots are produced from the veins or lamina of the leaf for the formation of new plant.
3. Sucking or Haustorial roots : found in parasitic plants.
4. Photosyntheitic or assimilatory roots : Roots of some climbing or epiphytic plants develop chlorophyll and turn green which help in photosynthesis.
