Reproduction in Flowering Plants

Introduction: The Flower Is a Reproductive Workshop

You have probably handled flowers many times — plucking petals, smelling jasmine, watching bees buzz around hibiscus blooms. But behind their scent and colour, flowers are doing serious biological work. The flower is the reproductive organ of a flowering plant, designed to produce gametes, attract pollinators, ensure fertilization, and finally develop seeds and fruits.

In this part we will dissect the flower piece by piece, follow the journey of a pollen grain, and watch how a tiny ovule transforms into a seed inside a juicy fruit.

11.12 Parts of a Typical Flower

A typical flower (such as hibiscus, mustard or rose) has four main whorls arranged on a swollen tip of the stalk called the thalamus. From outside in, these whorls are sepals, petals, stamens and pistil.

(i) Calyx — the green outer whorl

The outermost whorl of small green leaf-like structures is called the calyx. Each member is a sepal. Sepals protect the developing flower bud and may also carry out photosynthesis.

(ii) Corolla — the colourful petals

Inside the calyx is the corolla, made of brightly coloured petals. The petals attract insects, birds or bats that act as pollinators. They are non-essential for reproduction itself but are vital for cross-pollination.

(iii) Androecium — the male part (stamens)

The third whorl is the androecium — the male reproductive whorl made up of stamens. Each stamen has two parts: a slender filament and a swollen anther at its tip. Inside the anther, tiny pollen grains are produced. Each pollen grain contains the male gametes.

(iv) Gynoecium / Pistil — the female part

The innermost whorl is the gynoecium (also called the pistil). It is the female reproductive whorl. A pistil has three parts:

• Stigma — the sticky tip that catches and holds pollen grains.
• Style — the slender stalk connecting the stigma to the ovary; the pollen tube grows down through it.
• Ovary — the swollen base, containing one or more ovules. Each ovule contains a female gamete (egg cell). After fertilization, ovules become seeds and the ovary becomes the fruit.

11.13 Bisexual and Unisexual Flowers

If a flower has both stamens (male) and pistil (female), it is called a bisexual flower. Examples: hibiscus, rose, mustard, tomato. If a flower has only stamens or only the pistil, it is unisexual. Papaya, watermelon and corn are common examples — papaya has separate male and female flowers, often on different trees.

11.14 Pollination — Pollen on the Move

For sexual reproduction in a flowering plant, the pollen produced in the anther of one flower must be transferred to the stigma of (the same or another) flower of the same species. This transfer is called pollination.

Self-pollination vs cross-pollination

• Self-pollination — pollen lands on the stigma of the same flower or another flower of the same plant. The offspring are similar to the parent. Common in pea, wheat, rice.
• Cross-pollination — pollen is transferred to the stigma of a flower on a different plant of the same species. The offspring carry mixed features from two plants — this gives more variation. Common in mustard, papaya, maize.

Agents of pollination

Since flowers cannot move, pollen must be carried by an outside agent. The main agents are:

• Wind — pollen is light, dry, and produced in huge amounts. Stigmas are large and feathery. Examples: grasses, maize, wheat.
• Water — for aquatic plants like Vallisneria. The light pollen floats on water and reaches the stigma.
• Insects (and other animals) — bees, butterflies, moths, beetles, sometimes birds and bats. The flowers are showy, scented, often produce nectar; pollen is sticky and clings to the visitor.

11.15 Fertilization — From Pollen to Zygote

When a pollen grain falls on a compatible stigma, it does not stop there. The grain absorbs water and starts to grow a long thin tube called the pollen tube. The tube grows down through the style, carrying the male gametes inside it. When it reaches an ovule in the ovary, it enters through a tiny pore (the micropyle) and releases the male gametes.

Inside the ovule, one male gamete fuses with the female gamete (egg cell) to form the zygote. Another male gamete fuses with two polar nuclei to form the endosperm, which will store food for the developing embryo. This characteristic process of flowering plants is called double fertilization.

11.16 After Fertilization — Seeds and Fruits

Fertilization is not the end — it is the beginning of seed and fruit development. The transformations are precise:

The fruit performs two important jobs: it protects the developing seeds and helps in their dispersal. Seeds inside fleshy fruits like mango, guava and tomato are often eaten by animals; the seeds pass out unharmed at a distance and germinate there.

Seed germination

A seed waits for water, warmth and air. When conditions are right, the seed coat softens, the embryo absorbs water, and the tiny root (radicle) emerges first to anchor the plant. Next, the shoot (plumule) grows upward toward light. The seedling lives off the food stored in the seed (cotyledons or endosperm) until its first leaves can photosynthesise. A new flowering plant has begun its life.

11.17 Activity — Studying a Hibiscus Flower

Quick Recap