What is meant by emasculation? When and why does a plant breeder employ this technique?

(i) In flowers, there are two essential whorls namely androecium and gynoecium.

(ii) Androecium consists of stamens that represent the male reproductive organ and the carpels represent female reproductive organs.

2. Male Reproductive Organ:

(i) Each stamen consists of two parts—a filament and an anther.

(ii) Microspore mother cells undergo meiosis to form microspores which mature into pollen grains.

(iii) Pollen grain has two layered walls—an outer exine and an inner intine.

3. Female Reproductive Organ:

(i) Each carpel has three parts—the stigma, style and ovary.

(ii) Ovules are contained within an ovary.

(iii) Megaspore mother cells (2n) divide by meiosis.

(iv) The development of female gametophyte or embryo sac (normal type) is monosporic and is derived from functional megaspore.

(v) The mature female gametophyte or embryo sac is $7$-celled and $8$-nucleate at the time of fertilisation.

4. Pollination:

(i) Pollination is a mechanism in which pollen grains are transferred from anther to stigma.

(ii) There are two main kinds of pollination, self-pollination (autogamy) and cross-pollination (allogamy).

(iii) Cross pollination is again of two subtypes—geitonogamy and xenogamy.

(iv) Depending on pollinating agents, there are three types of pollination mechanisms—Anemophily, Zoophily, and Hydrophily.

5. Pollen-pistil interaction:

(i) Pollen-pistil interaction involves all events from the landing of pollen grains on the stigma till the pollen tube enters the embryo sac through the ovule.

(ii) In case of compatible pollen, pollen tube is produced by the germination of pollen. Pollen tube grows through the style reaching the ovule.

(iii) When pollen is incompatible, its germination is inhibited and pollen tube is not produced.

6. Fertilisation:

(i) Pollen tube discharges two male gametes.

(ii) One of the male gametes fuses with the egg resulting in a diploid zygote, and it is called syngamy.

(iii) Another male gamete fuses with the secondary nucleus having two polar nuclei to form Primary Endosperm Nucleus (PEN). This fusion is termed triple fusion or vegetative fertilisation.

(iv) Syngamy and triple fusion together are called double fertilisation which is a characteristic of angiosperms.

(v) Zygote develops into an embryo and primary endosperm cell gives rise to endosperm.

7. Post - Fertilisation Events:

(i) An aleurone layer is present around the endosperm in cereals, and it is mostly single-layered.

(ii) After fertilisation, the ovary develops into fruit and ovule develops into a seed. The seeds can be endospermic (in cereals) and non-endospermic (in legumes).

8. Apomixis:

(i) The phenomenon of the formation of asexual embryo is called apomixis.

(ii) Apomixis is of two types: non-recurrent and recurrent. In the former, the embryo develops asexually from haploid cells and in the latter, it develops from diploid cells.

(iii) Recurrent apomixis is classified into adventive embryony, diplospory and apospory and all the three can be included under agamospermy.

(iv) In non-recurrent apomixis, haploid cells of embryo sac give rise to embryo, and it can be referred to apogamy.