1. Emasculation is the process of removal of stamens from a bisexual flower before they shed pollen in order to prevent self-pollination and permit cross-pollination of stigma with desired pollen. During breeding, the breeder wants to make sure that the desired pollen grains are used for pollination and the stigma is protected from contamination (from unwanted pollen).
2. A plant breeder employs this technique to select and incorporate specific traits in the progeny.

Self-incompatibility
It is the third device to prevent inbreeding. It is a genetic phenomenon of preventing the pollen from fertilising ovules of the same flower by inhibiting pollen germination or pollen tube growth in the pistil.

An embryo sac is called monosporic because it develops from one of the four megaspores formed from the division of megaspore mother cell.

There are six haploid cells. They are:  three antipodal cells, two synergids and one female gamete.

Cross pollination or xenogamy.

Parthenocarpy.

There is an adaptation in angiospermic plants to provide assured nutrition to the developing embryo. Most zygotes divide only after certain amount of endosperm is formed. Therefore, zygote remains dormant for sometime in a fertilised ovule.

Tapetum is the innermost layer of the microsporangium. It produces the exine layer of the pollen grains, which is composed of the sporopollenin, the most resistant organic material. During microsporogenesis, the cells of tapetum produce various enzymes, hormones, amino acids and other nutritious materials required for the development of pollen grains.

In wind pollinated flowers,
(i) The stamens are well-exposed, so that pollen grains are easily dispersed in wind currents.
(ii) The stigma is large and often feathery, to easily trap the air-borne pollen grains.
(iii) The pollen grains are light and non-sticky, to be transported in wind currents.
(iv) Pollen grains are produced in enormous quantity.
(v) Numerous small flowers are packed into an inflorescence.
(vi) There is a single ovule in the ovary of these flowers.

(i) Emasculation refers to the practice of removal of anthers/stamens from a bisexual flower before the pollen grains mature.
(ii) It is necessary to prevent the self-pollen from contaminating the stigma.
(iii) Bagging refers to the covering of the emasculated flowers with a suitable bag made of butter paper; it is essential to prevent contamination of the stigma of the emasculated flower with unwanted pollen grains.
(iv) When the stigma becomes receptive, the pollen grains from the selected flowers are dusted on it and the flower is rebagged for the development of fruits and seeds.
(v) If female parent bears unisexual flowers, there is no need for emasculation.
(vi) The female flower buds are bagged before they open.
(vi) When the stigma becomes receptive, pollination is carried out with the desired pollen the flowers are rebagged.

(a) (i) In the mature embryo sac of an angiosperm, two polar nuclei in the central cell fuse to form a diploid secondary nucleus.
(ii) During fertilisation, one of the male gametes fuses with the secondary nucleus to form a triploid primary endosperm nucleus (PEN); the central cell is now called primary endosperm cell (PEC).
(iii) Since, three nuclei triple fusion.
(b)(i) The primary endosperm nucleus of the primary endosperm cell undergoes repeated mitotic divisions, to give rise to a number of free nuclei; at this stage, the endosperm is called free nuclear endosperm.
(ii) Subsequently, cell wall formation starts from the periphery and the endosperm becomes cellular.
(iii) The water in the tender coconut represents the nuclear endosperm, while the white kernel represents the cellular endosperm.

1. The ovule is attached to the placenta by a short stalk called funiculus.
2. The junction between the funiculus and the ovule, is called hilum.
3. The primordium of the ovule grows into a mass of cells, forming the nucellus, the main body of the ovule.
4. It becomes surrounded by two protective envelopes called integuments, which leave a small opening called micropyle, at the tip of the ovule.
5. The basal part of the ovule (opposite to the micropyle) is called chalaza. Cells of the nucellus are rich in reserve food materials.
6. There is a single embryo sac/female gametophyte in the nucellus; it has developed from a megaspore.
7. The embryo sac contains the following cells:
(i) Three antipodal cells at the chalazal end.
(ii) Three cells at the micropylar end, forming egg apparatus, which consists of two synergids and a female gamete.
(iii) Two nuclei in the central cell, called polar nuclei, which fuse to form a diploid secondary nucleus.

(i) The process of formation of megaspores from Megaspore Mother Cell or MMC (diploid) is called megasporogenesis.
It occurs inside the nucellus of developing ovule of angiosperms. The process begins very early when nucellus is not conmpletely surrounded by the integuments. The MMC (a large cell containing dense cytoplasm and a prominent nucleus) enlarges in size and divides by meiosis. It first divides transversely into two cells called megaspore dyad. 
These two cells apgain divide transversely as a result, a linear row of four haploid cells megaspore tetrad is produced.

Out of the four megaspores one situated at the chalazal end remains functional and the rest three gradually degenerate. Such a development of embryo sac is called monosporic development, e.g. Pobygonum.
(ii)

(b) (i) The egg cell on fertilisation becomes the zygote, which later forms the embryo
(ii) The polar nuclei fuse to form a diploid secondary nucleus; on fertilisation by a male gamete, it forms the primary endosperm nucleus, which later forms the endosperm.

- After entering one of the synergids,the pollen tube discharges the two male gametes into the cytoplasm of that synergid.
- One of the male gametes moves towards the female gamete/egg and fuses with it; this fusion is called syngamy and it results in the formation of a zygote.
- The second male gamete moves towards the two polar nuclei in the central cell.
- The two polar nuclei just fuse to form a secondary nucleus and the second male gamete fuses with the secondary nucleus in the central cell; this fusion is called triple fusion and, it results in the formation of a triploid primary endosperm nucleus.
- Since two fusions, syngamy and triple fusion occur in an ovule, the phenomenon is known as double fertilisation in angiosperms. 
Post-fertilisation events:
- The central cell becomes the primary endosperm cell after triple fusion; the primary endosperm nucleus develops into the endosperm.
- Zygote develops into the embryo.
- Antipodals and synergids degenerate.
- The integuments develop into the seed coat.
- The ovule becomes transformed into a seed.

(a) Differences: 

(b) Pollen-Pistil Interaction.
The stigma/pistil has the ability to recognise the right type of pollen, i.e. the compatible pollen of the same species and rejects the wrong type of pollen grains.
It is the result of interaction between the chemical components of the pollen and those of stigma. - A compatible pollen grain starts its germination on the stigma.
The intine grows out through one of the germ pores as a protuberance.
The contents of the pollen move into this tube, i.e. the tube nucleus (nucleus of the vegetative cell) and the generative cell (or the two male gametes in those species where pollen is liberated in the three-celled stage).
The pollen tube grows through the tissues of stigma and style and enters the ovule through micropyle.
It enters the embryo sac through the filiform apparatus of one of the synergids to liberate the male gametes.
The events from the deposition of pollen on the stigma till the pollen tube enters the ovule, are collectively referred to as pollen-pistil interaction.

(a) Development of Pollen grain:
   - Microsporocytes undergo mitotic divisions to increase the number of functional microspore mother cells.
   - Each microspore mother cell undergoes meiosis to form a microspore tetrad.
   - All the four microspores remain enclosed in a common wall.
   - They start separating from each other.
   - The nucleus undergoes a mitotic division resulting in the formation of a large vegetative cell and a small generative cell.
   - The spore develops a wall of two layers the outer- exine and inner intine.
   - At this stage, the pollen grains are liberated; but in some cereals the generative cell undergoes mitosis and the pollen grain is 3-celled, at the time of liberation.
(b) Mature Pollen Grain:
   - A mature pollen grain has a protective covering of two layers.
   - The outer is thick, sculptured variously and is made of sporopollenin; this layer is called exine.
   - The inner layer, called intine is thin and is made of cellulose.
   - A mature pollen grain is two celled with a large vegetative cell and a small generative cell floating in the cytoplasm of the vegetative cell.
   - The pollen grains of dicot plants have three germ pores while those of monocots have one.