11.2.1 Plant Reproduction—Reproductive Organ: Flower

• Flower as a Modified Shoot:

A flower is a specialized type of modified shoot that serves the purpose of reproduction in higher plants. It is the reproductive organ where sexual reproduction occurs in plants.

• Key Whorls of a Flower:

A flower consists of five main whorls, two of which are directly involved in reproduction:

1. Androecium (male reproductive part)

2. Gynoecium (female reproductive part)

These two whorls are crucial for the plant’s reproductive process. The other three whorls, although not directly involved in reproduction, assist in the process.

• Complete vs. Incomplete Flowers:

• Complete Flower: A flower that has all five whorls (e.g., China rose, datura).

• Incomplete Flower: A flower missing one or more whorls (e.g., bottle gourd, pumpkin).

• Sessile vs. Non-Sessile Flowers:

• Sessile Flower: A flower attached directly to the stem without a pedicel (e.g., China rose, pumpkin).

• Non-Sessile Flower: A flower with a pedicel (e.g., Indian heliotrope).

• Bisexual vs. Unisexual Flowers:

• Bisexual Flower: Contains both androecium and gynoecium (e.g., China rose, datura).

• Unisexual Flower: Contains either androecium or gynoecium, but not both (e.g., bottle gourd, pumpkin).

• Neuter Flower: Lacks both androecium and gynoecium.

Different Parts of a Flower

1. Thalamus:

The thalamus is the floral axis that forms the tip of the flower stalk, from which all other flower parts are arranged.

2. Calyx:

• The outermost whorl of a flower, composed of sepals.

• Sepal Types:

• Gamosepalous/Aposepalous: Sepals that are fused or separate.

• Polysepalous: Sepals that are distinct and separate.

• Function: The calyx protects the inner parts of the flower from harsh conditions such as sunlight, rain, and insects. It also plays a role in attracting pollinators if colored.

3. Corolla:

• The second whorl, composed of petals.

• Petal Types:

• Polypetalous: Separate petals.

• Gamopetalous: Fused petals.

• Function: The corolla protects the inner parts of the flower and attracts pollinators like insects and birds, aiding in the pollination process.

4. Androecium (Male Reproductive Part):

• Located as the third whorl from the outside.

• Composed of stamens, each consisting of a filament (stalk) and anther (sac containing pollen).

• Pollen: The anther produces pollen, which contains male gametes.

• Pollination and Fertilization: Pollen is transferred to the female reproductive parts, where fertilization occurs.

Stamen Types:

• Monadelphous: Stamens fused into a tube (e.g., Chinese hibiscus).

• Diadelphous: Stamens in two groups (e.g., pea plant).

• Polydelphous: Stamens in many groups (e.g., cotton tree).

• Syngenesious: Anthers fused into a single group.

• Epipetalous: Stamens attached to the petals (e.g., Datura).

5. Gynoecium (Female Reproductive Part):

• Located at the center of the flower.

• Composed of one or more carpels. Each carpel has three parts:

• Ovary: Contains ovules (female gametes).

• Style: The stalk connecting the ovary to the stigma.

• Stigma: The part that receives pollen during pollination.

• Types of Gynoecium:

• Syncarpous: Multiple carpels fused together.

• Polycarpous: Carpels are separate.

Function: The gynoecium is involved in the production of ovules and the subsequent fertilization process.

Inflorescence

• Inflorescence: The arrangement of flowers on a stem or branch.

• Peduncle: The main axis or stalk that supports the inflorescence.

• Types of Inflorescence:

• Indefinite Inflorescence (Recemose): The axis grows indefinitely, and the flowers are arranged along the length of the stem.

• Definite Inflorescence (Cymose): The axis grows in a limited manner, and flowers are arranged at the tips of the branches.

Role of Inflorescence: Inflorescences play a significant role in pollination by presenting multiple flowers to pollinators.

Activities

• Observation of Flower Whorls:

• Dissect a flower and observe its different parts (thalamus, calyx, corolla, androecium, and gynoecium) on blotting paper.

• Transverse Section of Ovary:

• Cut and observe the ovary under a microscope to study its structure and the arrangement of ovules.

In conclusion, the flower is the reproductive organ of plants, with its different parts (calyx, corolla, androecium, and gynoecium) playing specific roles in the process of reproduction. The structure of the flower and its reproductive organs ensure successful pollination and fertilization, leading to the formation of seeds and the continuation of the plant species.