Growth and Development in Plants

The term meristem originates from the Greek word meristos, meaning "division." Meristems are specialized tissues with cells that divide rapidly by mitosis. These cells give rise to daughter cells, which either:

1. Differentiate to form permanent tissues.
2. Retain meristematic properties for continuous growth.

Characteristics of meristematic cells

1. Thin, extensible cell walls.
2. Small vacuoles and dense cytoplasm.
3. Numerous ribosomes and mitochondria, indicating a high rate of metabolism.
4. Tightly packed living cells undergoing frequent division.

Meristems are classified based on their location in the plant body:

1. Apical meristems:
   • Location: Found at the tips of roots and shoots.
   • Function: Responsible for primary growth, leading to an increase in the length of the plant body.
   • Produces the primary plant body.
2. Lateral meristems:
   • Location: Found in the cylindrical regions of stems and roots.
   • Function: Responsible for secondary growth, which increases the girth or diameter of the plant body.
   • Includes the vascular cambium and cork cambium.
3. Intercalary meristems:
   • Location: Found at nodes and the base of leaves in monocotyledonous plants (e.g., grasses).
   • Function:
     • Enables growth in already differentiated regions, such as stem internodes.
     • Aids in the regrowth of damaged leaves (e.g., in grasses).

Growth in plants can be categorized into two major types:

1. Primary Growth:
   • Occurs due to the activity of apical meristems.
   • Results in an increase in the length of roots and shoots.
   • Responsible for the formation of the primary plant body.
2. Secondary Growth:
   • Occurs due to the activity of lateral meristems.
   • Results in an increase in the girth or thickness of the plant.
   • Contributes to the development of wood and bark in trees.

Plant growth is typically represented by a sigmoid curve, showing:

1. Lag Phase: Slow initial growth.
2. Log Phase: Rapid exponential growth.
3. Plateau Phase: Growth slows as the plant matures.