reproduction in flowering plants introduction
All flowering plants show sexual reproduction. A look at the diversity of structures of the inflorescences, flowers and floral parts, shows an amazing range of adaptations to ensure formation of the end products of sexual reproduction, the fruits and seeds.
FLOWER – A FASCINATING ORGAN OF ANGIOSPERMS :
- Human beings have had an intimate relationship with flowers since time immemorial.
- Flowers are objects of aesthetic, ornamental, social, religious and cultural value– they have always been used as symbols for conveying important human feelings such as love, affection, happiness, grief, mourning, etc.
PRE-FERTILISATION: STRUCTURES AND EVENTS :
Much before the actual flower is seen on a plant, the decision that the plant is going to flower has taken place.
Several hormonal and structural changes are initiated which lead to the differentiation and further development of the floral primordium.
Inflorescences are formed which bear the floral buds and then the flowers.
In the flower the male and female reproductive structures, the androecium and the gynoecium differentiate and develop.
You would recollect that the androecium consists of a whorl of stamens representing the male reproductive organ and the gynoecium represents the female reproductive organ.
Stamen, Microsporangium and Pollen Grain
The two parts of a typical stamen – the long and slender stalk called the filament, and the terminal generally bilobed structure called the anther.
The proximal end of the filament is attached to the thalamus or the petal of the flower.
The number and length of stamens are variable in flowers of different species.
If you were to collect a stamen each from ten flowers (each from different species) and arrange them on a slide, you would be able to appreciate the large variation in size seen in nature.
Careful observation of each stamen under a dissecting microscope and making neat diagrams would elucidate the range in shape and attachment of anthers in different flowers.
A typical angiosperm anther is bilobed with each lobe having two theca, i.e., they are dithecous.
Often a longitudinal groove runs lengthwise separating the theca.
Let us understand the various types of tissues and their organisation in the transverse section of an anther. The bilobed nature of an anther is very distinct in the transverse section of the anther. The anther is a four-sided (tetragonal) structure consisting of four microsporangia located at the corners, two in each lobe. The microsporangia develop further and become pollen sacs. They extend longitudinally all through the length of an anther and are packed with pollen grains.