A typical root can be differentiated into five regions. From apex to base they are:
(a) Root Cap (Calyptra):
- It is a cap like protective structure of the growing root tip.
- In Pandanus (screwpine) multiple root caps present while in aquatic plants (Pistia, Eichhomia, Lemna) root pockets present instead of root cap.
Function:
- Protects root meristem,
- Secrete mucilage that help tender root to penetrate the hard soil,
- Helps in perception of gravity,
- Root packets functions as balances.
(b) Growing point or Meristematic Zone:
- It is about 0.25 – 1.0 mm long, lies just behind the root cap and thus sub-terminal in position.
- Its shape is like an inverted concave dome of cells.
- The central rarely dividing cells are called quiescent centre.
Function:
- Root meristem adds cells to root cap and the basal region of the root.
(c) Zone of elongation:
- It is about 1 -10 mm long and lies just behind the meristematic zone.
- As the name implies, it is the site of rapid and extensive cell elongation.
- This zone increases length of the root.
- The external cells can absorb water and minerals from the soil.
(d) Root hair Zone or Zone of differentiation:
- It is about 1 – 6 cm long.
- It is the zone where cell differentiate to form epiblema, cortex, endodermis, pericycle, xylem and phloem.
- Many cells of epiblema elongate to form unicellular root hairs.
- As the root grows, new root hairs develop and older one shrivel and sloughed off.
Function:
- Root hairs increase the absorptive surface area of root.
(e) Zone of maturation:
- It constitute the major portion of the root.
- The cells attain maturity when they reach this zone.
Function
- Lateral roots may emerge from pericycle.
- Radial differentiation of tissues causes secondary growth in dicots.