- The process of development of new organisms through the formation and fusion of gametes is called sexual reproduction.
- In angiosperms, the organs specialised to perform sexual reproduction are flowers.
- Flowers are modified condensed reproductive shoots.
- A typical flower has a broad base called thalamus over which four whorls of floral leaves, i.e., sepals (calyx), petals (corolla),
stamens (androecium) and carpels (gynoecium) are borne. - Stamens and carpels represent male and female reproductive structures of flowers respectively. They are called essential floral organs.
- Sepals and petals are called non-essential floral organs because they have only supportive role.
STAMEN-THE MALE REPRODUCTIVE ORGAN
- Stamen consists of two parts-filament and anther.
- Filament is long and slender stalk attached proximally to thalamus, petal or tepal. It bears an anther distally.
- Anther is bilobed, knob-like fertile part of the stamen. The two anther lobes separated by a deep groove in the anterior side
and attached to each other by a sterile parenchymatous tissue called connective on the posterior side. - Each anther lobe has two chambers which posses pollen sacs or microsporangia.
- A bilobed anther is tetrasporangiate.
- A microsporangium or pollen sac is a cylindrical sac which appears circular in transverse section.
- It consists of two parts : outer wall and central homogeneous sporogenous tissue.
- The outer wall has four types of layers epidermis, endothecium, 1-3 middle layers and tapetum.
- The outer three layers protect the young anther and take part in the mechanism of dehiscence in the ripe anther.
- The endothecium is also called fibrous layer due to the presence of fibrous thickenings.
- The tapetal cells enlarge and become filled with dense protoplasmic content as well as nutrients.
- Two types of tapetum are present amoeboid and secretory.
Functions of Tapetum- It provides nourishment to the developing microspore mother cells and pollen grains either by forming a plasmodium (amoeboid
type) or through diffusion (secretory type). - It produces lipid rich Ubisch granules containing sporopollenin for exine formation.
- It secretes enzymes like callase responsible for degradation of callose wall around pollen tetrad.
Class XII
Sexual Reproduction in Flowering Plants
This article covers high yield facts of the given topic.