• Sexual reproduction in flowering plants involves transformation of diploid sporophytic cells into haploid gametophytic cells by meiosis and subsequent fusion of haploid gametes of opposite sex to form diploid zygote. The zygote then develops into an embryo which ultimately forms a diploid plant body. In fl owering plants, all these steps of sexual reproduction occur within specialized reproductive organs, called the fl owers.
• Sexual reproduction in plants includes microsporogenesis, megasporogenesis, pollination, fertilization, embryogenesis and seed formation.
FLOWER
• Flowers are the most fascinating organs in plants found only in angiosperms i.e., plants in which seeds are enclosed within fruit.
• Flowers and their parts are responsible for sexual reproduction in angiosperms and all flower bearing plants reproduce sexually.
• The colour, fragrance, modifi cation in shape of fl ower ensure its sexual reproduction.
• Fruits and seeds are the end products of sexual reproduction.
• Flowers are highly modifi ed shoots, bearing nodes and modifi ed fl oral leaves, which are meant essentially for sexual reproduction in plant. The fl ower is commonly borne on short or long stalk called the pedicel, it has upper swollen region known as receptacle or thalamus or torus.
• Flowers, usually have four different kinds of fl oral members arranged in four whorls (i.e., calyx, corolla, androecium and gynoecium). attached on the receptacle. Of these, the two lower whorls (i.e., calyx and corolla) are sterile and considered as non-essential, accessory or helping whorls. The two upper whorls (i.e., androecium and gynoecium) are fertile and considered as essential or reproductive whorls.
(i) Callyx – It consists of number of green leafy sepals. It is the outermost whorl.
Calyx protects all the inner fl oral whorls in the bud condition and it synthesizes the food of the plant body when green in colour.
(ii) Corrolllla – It consists of a number of usually bright coloured petals and is the second whorl in the flower.
(iii) Androecium – This is the male whorl and consists of stamens and each stamen can be regarded as modifi ed leaf (microsporophyll) that consists of fi lament and anther.The anther may contains two-four microsporangia that produce a large number of pollen grains.
(iv) Gynoecium or Pistil – It is present in the centre of the fl ower and is the female reproductive whorl. Its unit is called carpel. Each carpel is made up of ‘3’ parts — ovary, style and stigma. Ovary is the swollen basal part of the carpel that encloses ovules and each ovule encloses embryo sac containing egg. Stigma is the receptive part of carpel whereas style is the tubular structure that joins stigma & ovary.
Thus, androecium & gynoecium are the two innermost whorl of fl ower in which sexual reproduction take place. Anther bears spores in sporangia and ovary contains ovules which bear embryo-sac with egg.
