Dicot and Monocot Root

Dicots and monocots, two major groups of flowering plants, exhibit differences in their root structures:

• Dicot Root:

  • Typically features a taproot system with a primary root that grows deep into the soil.
  • Secondary growth is common, leading to an increase in girth.
  • Vascular cambium forms between the xylem and phloem, contributing to secondary growth.
  • Xylem often forms a star-shaped pattern in cross-section.

• Monocot Root:

  • Usually has a fibrous root system with numerous roots spreading out horizontally.
  • Lacks secondary growth, as vascular cambium is absent.
  • Vascular bundles are arranged in a ring pattern in the cross-section, each bundle being closed (i.e., without cambium).

Steps of Secondary Growth

Secondary growth, typical in dicots and gymnosperms, involves the thickening of stems and roots. It occurs through the following steps:

1. Activation of Vascular Cambium: A ring of vascular cambium, which initially appears between the primary xylem and phloem, becomes active.

2. Lateral Meristem Growth: The cambium, a lateral meristem, starts producing new cells.

3. Formation of Secondary Xylem and Phloem: Cells on the inside of the cambium ring differentiate into secondary xylem (wood), while those on the outside differentiate into secondary phloem.

4. Cork Cambium Formation: As the stem or root widens, the epidermis is replaced by a secondary protective layer formed by the cork cambium.

5. Development of Bark: The cork cambium produces cork cells towards the outside, forming the bark.

Activity of Cambium

The cambium is responsible for the production of secondary vascular tissues:

• Vascular Cambium: Produces secondary xylem (inward) and secondary phloem (outward).
• Cork Cambium (Phellogen): Produces cork (phellem) on the outside and phelloderm on the inside.

Heartwood and Sapwood

In trees, especially during secondary growth, the wood comprises two parts:

• Heartwood:

  • The inner, older layers of secondary xylem.
  • No longer conducts water, often darker due to deposition of resins, oils, and other substances.
  • Provides structural support.

• Sapwood:

  • The outer, younger layers of secondary xylem.
  • Actively involved in the conduction of water and nutrients.
  • Generally lighter in color.