The Flower

Parts of a Flower (4 Whorls)

A typical bisexual flower consists of four main whorls, arranged concentrically on the receptacle (the part of the flower stalk to which the parts of the flower are attached).

1. Calyx (Sepals):

   • Structure: The outermost whorl, typically green, leaf-like structures called sepals.
   • Function: Protects the flower in its bud stage.

2. Corolla (Petals):

   • Structure: The whorl inside the calyx, consisting of brightly colored and often fragrant petals.
   • Function: Attracts pollinators (like insects and birds) due to their color, scent, and nectar guides.

3. Androecium (Stamens):

   • Structure: The male reproductive part, consisting of one or more stamens. Each stamen has two parts:
     • Anther: A sac-like structure that produces and contains pollen grains.
     • Filament: A stalk that supports the anther.
   • Function: Produces pollen grains, which contain the male gametes.

4. Gynoecium (Pistil/Carpel):

   • Structure: The female reproductive part, located at the center of the flower, consisting of one or more carpels. Each carpel has three parts:
     • Stigma: The receptive tip that receives pollen.
     • Style: A stalk that connects the stigma to the ovary.
     • Ovary: A swollen base that contains ovules (which contain the female gametes).
   • Function: Contains the ovules, which develop into seeds after fertilization.

Pollination

Pollination is the transfer of pollen grains from the anther to the stigma of a flower.

• Self-Pollination: The transfer of pollen from the anther to the stigma of the same flower or another flower on the same plant.
• Cross-Pollination: The transfer of pollen from the anther of a flower on one plant to the stigma of a flower on another plant of the same species.

Agents of Cross-Pollination

Cross-pollination requires external agents to transfer pollen. Here's an idea about them:

1. Wind (Anemophily):

   • Characteristics of Wind-Pollinated Flowers: Small, inconspicuous, dull-colored, lack scent and nectar. Produce large amounts of light, dry pollen. Stigmas are large and feathery to catch pollen.
   • Examples: Grasses, Maize, Wheat, Pine.

2. Water (Hydrophily):

   • Characteristics of Water-Pollinated Flowers: Small, inconspicuous, often submerged. Pollen is light and unwettable.
   • Examples: Vallisneria, Hydrilla.

3. Insects (Entomophily):

   • Characteristics of Insect-Pollinated Flowers: Large, brightly colored, often fragrant, produce nectar. Pollen is sticky or spiny to adhere to insect bodies. Stigmas are often sticky.
   • Examples: Rose, Sunflower, Hibiscus, Pea.

Fertilization

Fertilization is the fusion of the male gamete (from the pollen grain) with the female gamete (present in the ovule) to form a zygote.

Process in Simple Terms:

1. A pollen grain lands on the stigma (pollination).
2. The pollen grain germinates and grows a pollen tube down through the style to the ovary.
3. The male gametes travel down the pollen tube to the ovule.
4. One male gamete fuses with the egg cell inside the ovule.
5. This fusion forms the zygote, which will develop into the embryo.

Formation of Fruit

After fertilization, significant changes occur in the flower parts:

• Ovary: Develops into the fruit.
• Ovules: Develop into the seeds.
• Sepals, Petals, Stamens, Style, Stigma: Usually wither and fall off.

Parts of Fruits

Fruits protect the seeds and aid in their dispersal.

• Dry Fruits: Fruits where the pericarp (fruit wall) is dry at maturity.
  • Examples: Pea pod, Groundnut, Rice, Wheat.
• Fleshy Fruits: Fruits where the pericarp is fleshy and juicy at maturity.
  • Examples: Mango, Apple, Tomato, Orange.

Parts of the Pericarp of Fleshy Fruits

The pericarp (fruit wall) of fleshy fruits is typically differentiated into three layers:

1. Epicarp:
   • Structure: The outermost layer, forming the skin or peel of the fruit.
   • Function: Provides protection to the inner parts of the fruit.
2. Mesocarp:
   • Structure: The middle, fleshy, and often edible part of the fruit.
   • Function: Stores food and water, making the fruit palatable.
3. Endocarp:
   • Structure: The innermost layer, which can be hard and stony (e.g., in mango, peach) or membranous (e.g., in orange).
   • Function: Encloses and protects the seed(s).

Seed

A seed is a fertilized ovule that contains an embryo and stored food, enclosed within a protective seed coat.

Parts of a Seed

• Seed Coat: The outer protective layer of the seed.
• Embryo: The miniature plant within the seed, consisting of:
  • Radicle: The embryonic root, which develops into the root system.
  • Plumule: The embryonic shoot, which develops into the shoot system (stem and leaves).
• Cotyledon(s): Seed leaves that store food for the developing embryo or help in transferring food from the endosperm.

Types of Seeds

• Monocotyledonous (Monocot) Seed: Contains a single cotyledon.
  • Examples: Maize, Rice, Wheat.
• Dicotyledonous (Dicot) Seed: Contains two cotyledons.
  • Examples: Bean, Pea, Gram.

Germination

Germination is the process by which a seed sprouts and grows into a new plant.

Conditions Required for Germination

1. Moisture (Water): Seeds need water to swell up, soften the seed coat, and activate enzymes that break down stored food.
2. Warmth (Suitable Temperature): Each seed has an optimal temperature range for germination. Enzymes involved in germination function best at these temperatures.
3. Air (Oxygen): Oxygen is required for the respiration of the embryo to release energy for growth.

Seed Germination of Different Seeds

• Bean Seed (Dicot - Epigeal Germination): The cotyledons are pushed above the soil surface by the elongation of the hypocotyl (the part of the stem below the cotyledons).
• Maize Seed (Monocot - Hypogeal Germination): The cotyledon remains below the soil surface, and the plumule emerges above ground.