1.2 The Flower

Parts of a Flower (4 Whorls)

1. Calyx (Sepals): Outermost whorl; protects flower in bud stage.
2. Corolla (Petals): Inside calyx; attracts pollinators.
3. Androecium (Stamens): Male reproductive part (anther + filament); produces pollen.
4. Gynoecium (Pistil/Carpel): Female reproductive part (stigma + style + ovary); contains ovules.

Pollination

• Definition: Transfer of pollen grains from anther to stigma.
• Self-Pollination: Pollen transfer within the same flower or same plant.
• Cross-Pollination: Pollen transfer between flowers on different plants of the same species.

Agents of Cross-Pollination

1. Wind (Anemophily): Small, inconspicuous flowers; light, dry pollen (e.g., Grasses, Maize).
2. Water (Hydrophily): Small, inconspicuous flowers; light, unwettable pollen (e.g., Vallisneria, Hydrilla).
3. Insects (Entomophily): Large, bright, scented flowers; sticky pollen (e.g., Rose, Sunflower).

Fertilization

• Definition: Fusion of male gamete (from pollen) with female gamete (in ovule) to form a zygote.
• Process:
  1. Pollen lands on stigma.
  2. Pollen grain germinates, grows pollen tube to ovary.
  3. Male gametes travel down pollen tube to ovule.
  4. Male gamete fuses with egg cell, forming zygote.

Formation of Fruit

• After fertilization:
  • Ovary: Develops into the fruit.
  • Ovules: Develop into the seeds.
  • Other flower parts usually wither and fall off.

Parts of Fruits

• Dry Fruits: Pericarp (fruit wall) is dry at maturity (e.g., Pea pod, Rice).
• Fleshy Fruits: Pericarp is fleshy and juicy at maturity (e.g., Mango, Apple).
• Pericarp Layers (Fleshy Fruits):
  1. Epicarp: Outermost layer (skin/peel).
  2. Mesocarp: Middle, fleshy, edible part.
  3. Endocarp: Innermost layer, encloses seed(s).

Seed

• Definition: Fertilized ovule containing an embryo and stored food, enclosed in a seed coat.
• Parts:
  • Seed Coat: Outer protective layer.
  • Embryo: Miniature plant (radicle - root, plumule - shoot).
  • Cotyledon(s): Seed leaves; store food or transfer food from endosperm.

Types of Seeds

• Monocotyledonous (Monocot) Seed: Single cotyledon (e.g., Maize, Rice).
• Dicotyledonous (Dicot) Seed: Two cotyledons (e.g., Bean, Pea).

Germination

• Definition: Seed sprouts and grows into a new plant.
• Conditions Required:
  1. Moisture (Water): Softens seed coat, activates enzymes.
  2. Warmth (Suitable Temperature): Optimal for enzyme function.
  3. Air (Oxygen): Required for embryo respiration.

Seed Germination of Different Seeds

• Bean Seed (Dicot - Epigeal Germination): Cotyledons pushed above soil by hypocotyl elongation.
• Maize Seed (Monocot - Hypogeal Germination): Cotyledon remains below soil; plumule emerges above ground.