Unit-II: Morphology of Reproductive Parts

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1. Structure and Functions of Floral Parts

The flower is the reproductive unit in angiosperms. It typically consists of four whorls arranged on a fleshy base called the thalamus or receptacle.

• Calyx (Sepals): The outermost whorl, usually green; protects the flower in the bud stage and performs photosynthesis.
• Corolla (Petals): Often brightly colored to attract pollinators like insects and birds.
• Androecium (Stamens): The male reproductive part; produces pollen grains.
• Gynoecium (Carpels/Pistils): The female reproductive part; contains ovules that develop into seeds.

2. Flower as a Modified Shoot

Morphologically, a flower is considered a modified determinate shoot. This concept is supported by several anatomical and developmental evidences:

• The thalamus represents a condensed axis with highly reduced internodes.
• Floral organs (sepals, petals, etc.) are homologous to leaves but modified for reproduction.
• Occasionally, the thalamus may continue to grow, showing a "proliferous" habit, which proves its shoot-like nature.

3. Floral Formula and Diagram

These are symbolic and graphical representations used to describe the characteristics of a flower.

Floral Formula: A shorthand notation representing the symmetry, sex, and number of floral parts.
Floral Diagram: A cross-sectional ground plan showing the arrangement and cohesion/adhesion of floral parts.

4. Morphology and Evolution of Stamen and Carpel

The evolution of reproductive organs marks a transition from leaf-like structures to highly specialized filaments and ovaries.

A. Stamen Evolution

• Primitive: Broad, leaf-like structures with embedded microsporangia (e.g., Degeneria).
• Advanced: Differentiation into a slender filament, a distal anther, and a connective.

B. Carpel Evolution

• Primitive: Open, leaf-like structures (megasporophylls) that folded to protect ovules (Conduplicate carpels).
• Advanced: Complete closure forming a distinct ovary, style, and stigma.

5. Placentation: Types and Evolution

Placentation is the arrangement of ovules within the ovary.

6. Fruit and Seed Evolution and Types

Fruits develop from the mature ovary, while seeds develop from fertilized ovules.

Evolutionary Trends:

• Evolution from simple follicles to complex fleshy fruits to aid animal-mediated dispersal.
• Development of wings or hairs for wind dispersal.

Types of Fruits:

• Simple: Develop from a single ovary (e.g., Mango, Pea).
• Aggregate: Develop from a multicarpellary, apocarpous gynoecium (e.g., Raspberry).
• Multiple: Develop from an entire inflorescence (e.g., Pineapple, Jackfruit).

7. Seed Germination and its Types

Germination is the process where the embryo within the seed grows into a seedling.

• Epigeal Germination: The hypocotyl elongates, pushing the cotyledons above the soil (e.g., Bean, Castor).
• Hypogeal Germination: The epicotyl elongates, and cotyledons remain underground (e.g., Pea, Maize).
• Viviparous Germination: Seeds germinate while still attached to the parent plant (common in Mangroves).