Sexual Reproduction in Flowering Plants

Sexual Organs in Plants and Animals

In large animals, including humans, the sexual organs can be easily identified. Even before adulthood, humans can understand the purpose and importance of these organs in their bodies. However, in the case of plants, many people often feel unsure or do not know when asked about the sexual organs of plant.

This concept may be familiar to science students, but for others, it might be new information. So, without any more suspense, let us learn and explore some interesting facts about the sexual reproductive structures of plants.

Flower and Its Reproductive Organs

A flower is the sexual organ of a plant. In flowering plants, the flower is the main structure where reproduction takes place. It contains two important reproductive parts — androecium and gynoecium.

• Androecium is the male reproductive organ.

• Gynoecium is the female reproductive organ.

The androecium consists of units called stamens.
Each stamen has a long stalk called the filament, and at its tip, there is an anther.
The anther produces pollen grains, which are the male spores of the plant.

The gynoecium is made up of one or more carpels.
Each carpel contains an ovary, and the ovary bears ovules, which are the female spores.
Each ovule contains a single egg cell and some other supporting cells.

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Stamen

The number of stamens are always fixed in a species. The flower may be possess different numbers of stamens. Based on number stamens, stamens are called as-

• Monandrous- when number stamen is one
• Diandrous- when number of stamens are two
• Triandrous- when number of stamens are three
• Tetrandrous - when number of stamens are four
• Pentandrous- when number of stamens are five
• Polyandrous- when number of stamens are more than five 

On the basis of arrangement of sepals, petals with stamens, following terms are used-

• Antisepalous - When the stamens alternate with sepals
• Antipetalous -  When the stamens alternate with petals

A stamen has two main parts:

1. Anther

2. Filament

Anther

• The anther is located at the tip of the stamen.

• It is connected to the filament by a small group of cells called connective tissue.

• Most anthers are bilobed (two-lobed).

• They can vary in shape — some are elongated, some oval, and some globular.

• When you cut an anther transversely, you can see four sac-like structures called pollen sacs or microsporangia.

• Inside each sporangium, many pollen grains (male spores) are formed.

Tapetum: 

The inner cavity of the pollen sac is lined by cells with dense cytoplasm. This layer is called the tapetum. This is a nourishing layer that nourishes developing pollen grains.

Pollen Grain: 

Pollen grains of different species are of different shapes and sizes. They are very minute (10-200 μm) and are dust-like. Each pollen grain consists of a single cell and possesses two coats. The tough, cutinized and often spinous outer coat is called the exine and the thin, delicate inner coat is called intine. A young anther possess compact tissues having homogenous cells at the center called the sporogenous tissue. 

Filament 

• Each stamen consists of a long slender structure called filament.
• The length of the stamens varies considerably in the same flower.
• When all the stamens in a flower are different length, the phenomemen is called heterstemony. 
• Tetradynamous is called when out six stamens inner four are long and outer two are short. Example: Cruciferae
• Dydynamous is called where out four stamens, two are shorter and two are longer.