Unit 4: Pollination and Fertilization

Syllabus Reference: Pollination: Types, Mechanisms and adaptations, Pollen- Pistil Interaction, Contrivances for cross pollination, Double fertilization; Seed-structure appendages and dispersal mechanisms.

1. Pollination: Types & Adaptations

• Autogamy (Self-Pollination): Pollen to stigma of same flower.
• Geitonogamy: Pollen to stigma of another flower on the same plant (Genetically selfing, functionally crossing).
• Xenogamy (Cross-Pollination): Pollen to stigma of a flower on a different plant.

Agents:

• Anemophily (Wind): Flowers small, colorless, nectar-less. Pollen light/dry/winged. Stigma feathery (e.g., Grasses, Maize).
• Entomophily (Insect): Flowers large, colored, fragrant, rich in nectar. Pollen sticky (pollenkitt) (e.g., Rose, Salvia).
• Hydrophily (Water): Pollen covered with mucilage (e.g., Vallisneria).

2. Contrivances for Cross Pollination (Outbreeding Devices)

Mechanisms to prevent self-pollination and encourage crossing:

• Dicliny (Unisexuality): Male and female flowers separate (e.g., Papaya).
• Dichogamy: Anther and Stigma mature at different times.
  Protandry: Anthers mature first (Sunflower).
  Protogyny: Stigma matures first (Mirabilis).
• Herkogamy: Physical barrier between anther and stigma (e.g., Calotropis).
• Self-Incompatibility: Genetic mechanism preventing pollen from germinating on its own stigma (e.g., Tobacco).

3. Double Fertilization

Unique characteristic of Angiosperms (discovered by Nawaschin). Involves two fusion events:

1. Syngamy (Generative Fertilization):
   1st Male Gamete (n) + Egg Cell (n) → Zygote (2n).
2. Triple Fusion (Vegetative Fertilization):
   2nd Male Gamete (n) + Secondary Nucleus (2n) → Primary Endosperm Nucleus (PEN, 3n).

Significance: Ensures endosperm (food) develops only if the egg is fertilized. Zygote becomes Embryo; PEN becomes Endosperm.

[Image of double fertilization diagram]

4. Seed Structure & Dispersal

• Seed: Fertilized Ovule. Integuments become Seed Coats (Testa/Tegmen).
• Dispersal Mechanisms:
  Wind: Wings (Moringa), Hairs (Cotton).
  Water: Fibrous coat (Coconut).
  Animals: Hooks/Barbs (Xanthium), Edible pulp (Guava).