Root and its modifications

ideal for higher secondary students as well as for students who are related to plant science or Botany.

1. Ms. Arohi patel Root and its modifications AROHI PATEL

2. What is root? The root is the descending portion of the plant axis. As opposed to the stem, it is positively geotropic, negatively phototropic and positively hydrotropic. The root sur­face is non-green and it is not divided into nodes and internodes.

3. Functions of the root T he root performs the functions of anchorage, absorption and conduction . Anchorage of the plant to the Soil is a mechanical function while absorption of solutes and their conduction upwards are physiological functions. Besides these normal functions, roots may sometimes carry on some special functions according to which even the structure of a root gets modified.

4. Regions of the root The following regions may be distinguished in a root from the APEX upwards. Root cap Region of cell division Region of elongation Region of maturation

5. Types of roots Tap root system A root system which develops from the radicle is called tap root system Adventitious root system The root developing from any portion of the plant other than the radicle is known as adventitious root. It may develop from the base of the stem or from any node or inter node of the branch, or even from the leaf.

6. Modification of roots Roots may be modified to different shapes in order to perform special functions besides their normal functions. Root modification is found both in tap root and adventitious root .

7. Tap root modifications Tap root system is modified into different forms to carry out special function. It is differentiated into following types:   Fusiform : Napiform Conical Tuberous or tubercular Pneumatophores

8. FUSIFORM: It is a modified tap root. The primary root is swollen in the middle while both the ends gradually taper forming a spindle shaped structure . e.g. Radish

9. Napiform The hypocotyls region is considerably swollen, becoming almost spherical and then abruptly tapering towards the lower end, e.g., Turnip ( Brassica campestris var. rapa ) and beet (Beta vulgaris ).

10.   Conical The roots swell, becoming broad at the base and gradually taper towards apex forming a cone like structure, e.g . Carrot

11. Tuberous or tubercular In this case, the root is thick and fleshy but does not form any definite shape, e.g., Mirabilis jalapa .

12. Pneumatophores These roots grow vertically up and come out of the water or marshy soil like conical spikes. They occur in large numbers around the tree trunk. Such roots are provided with numerous pores (breathing pores) through which air is taken for respiration, e.g., Rhizophora .

13. B. Adventitious root modification Roots produced from any portion of the plant other than the radicle is called adventitious roots. It may be changed to different forms for special functions such as storage, mechanical support and vital functions. (a) For storage of food: (b) For mechanical support : (c) For vital functions:

14.  For storage of food In this case, adventitious roots grow from the nodes of the running stem. These roots swell and get modified to irregular forms, known as tuberous. These are produced singly, e.g., Sweet potato (Ipomoea batatas ). Tuberous root

15. Fasciculate root   In Dahlia, Asparagus the tuberous roots are developed from base of the stem! in clusters.

16. Nodulated root Plants belonging to laguminosa family develops nodules. These are produced by nitrogen fixing bacteria and they get carbohydrates from plants This swelling developed by roots is known as nodulated root E.g. plants of laguminosae family

17.   Moniliform or Beaded root:   Swellings are found in the root at frequent intervals. It gives rise to a beaded or moniliform appearance e.g.Momordica , Vitis , Dioscorea and many grasses.

18. Annulated roots In this type, the root has a series of ring-like swellings appearing as if formed by number of discs placed one above another, e.g., Cephalis ipecacuanha .

19. For Mechanical Functions These roots are developed from the horizontal branches of some trees in vertically downward direction. On reaching the soil each root grows into thick and woody pillar-like struc­ture which gives support to the branch from where it developed. These are found in Indian rubber and banyan. Prop Roots

20. These are stout roots developed obliquely from the lower part of the trunk; grows on soft soil. On reaching the soil they help the mother plant to keep erect and also give an additional anchorage support to prevent from being uprooted. These are found in screw pine, maize, sugar­cane etc. Stilt root Stilt Roots

21. Root-Buttresses These are plank-like structures deve­loped with the contribution of both stem and root, come out as erect pro­jections from the basal region of the trunk. Eg . Bitter almond

22. Climbing Roots These are the roots developed from the node of some weak plants and help to climb the host plant. The apices of these roots produce a viscous substance which is dried in the air and so the roots get themselves attached to the host plant. These are found in betel vine (Piper betel)

23. Clinging Roots These are the short roots which, after developing from the stem, penetrate into the cracks and crevices of the supporting trees and help to fix the plant with the host plant. In addition to anchorage, they also absorb some food from the accumulating debris on the host plant. These are found in Vanda

24. For vital functions For Absorbing Moisture from Air Epiphytic Roots These are hanging aerial roots of epiphytic plants. The roots are covered by a thin greyish layer (4 -5 cell-layer in thickness) known as velamen . The velamen can absorb moisture from the atmosphere. It is found in orchid root (Vanda)

25. Parasitic Roots These are also called sucking roots or haustoria . The small root like structure, after developing from the stem of the parasite, penetrates the tissue of the host plant and absorbs food. These roots are found in dodder

26. Assimilatory or Photosynthetic Roots Roots of some plants develop chlorophyll and become green. These roots are able to prepare carbohydrate foods through photosynthesis. E.g. Tinospora cordifolia ( Galo )

27. THANK YOU