Growth and Germination

Meaning of Growth

Growth is defined as an irreversible increase in the size, dry weight, and complexity of an organism. In plants, growth is typically localized to specific regions called meristems (apical, lateral, and intercalary). Growth involves three main processes: Cell Division (mitosis), Cell Enlargement, and Cell Differentiation.

Germination of Seeds

Germination is the physiological process by which a dormant seed begins to sprout and grow into a seedling. This process involves the activation of the embryo and the mobilization of stored food reserves (starch, proteins, fats) to support early growth until the plant can perform photosynthesis.

Conditions Necessary for Germination

For a seed to germinate, specific environmental factors must be present:

• Water (Moisture): Water is needed to soften the seed coat (testa), activate enzymes (like amylase and protease), and provide a medium for chemical reactions. It also causes the seed to swell and rupture the testa.
• Oxygen: Required for aerobic respiration to produce energy (ATP) for the growing embryo.
• Suitable Temperature: Most seeds germinate within a range of 25°C to 35°C. Enzymes required for growth work optimally within this range.
• Viability: The embryo must be alive and healthy.

Types of Germination

Based on the behavior of the cotyledons during growth, germination is classified into two types:

1. Epigeal Germination

In this type, the hypocotyl (the region below the cotyledons) elongates rapidly, pushing the cotyledons above the soil surface. The cotyledons often turn green and carry out photosynthesis for a short period. Examples include: Cowpea (beans), Melon, Groundnut, and Castor oil seed.

2. Hypogeal Germination

In this type, the epicotyl (the region above the cotyledons) elongates rapidly, while the hypocotyl remains short. As a result, the cotyledons stay underground. Examples include: Maize, Guinea corn, Oil palm, and Coconut.

Growth Patterns and Curves

The growth of an organism typically follows a Sigmoid Curve (S-shaped curve), which consists of the lag phase (slow growth), log/exponential phase (rapid growth), deceleration phase, and stationary phase (plateau).