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.

Parthenocarpy.

Cross pollination or xenogamy.

1. Embryo developing from synergid is haploid.
2. Embryo developing from nucellus is diploid.

1. Since geitonogamy involves two different flowers of the same plant, it is genetically similar to autogamy; both autogamy and geitonogamy do not result in genetic variation in the progeny.
2. Geitonogamy and cross-pollination involve different flowers and a pollinating agent.

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

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.

The fruits selected to induce parthenocarpy can be watermelon, papaya, etc. It is because these fleshy fruits have a large number of seeds, which interfere with the preparation of jams, jellies, etc.

(i) In coconut, endosperm formation is of nuclear type. The primary endosperm nucleus undergoes repeated nuclear division without cell wall formation.
(ii) Tender coconut is an endosperm. It is rich in nutrients like fats, proteins, carbohydrates, minerals, vitamins, etc. Hence, it is considered as a healthy source of nutrition.
(iii) Pea seeds are non-endospermic, while castor seeds are endospermic.

(a) In plant breeding experiments, pollen from the selected male parent only, are used for pollination.
To prevent contamination of the stigma by any other pollen grain, the pistillate flowers are bagged.
(b) Continued self-pollination leads to inbreeding depression; hence to discourage self-pollination, outbreeding devices have been developed by 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.

(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.

1. Embryo sac develops from a megaspore, which is formed after meiosis in a megaspore mother cell; so it is haploid.
2. Zygote is formed by the fusion of two haploid gametes (a male and a female); hence it is diploid.
3. Endosperm is formed by triple fusion, i.e. fusion of two haploid polar male gamete; hence it if triploid.

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.

(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.

(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.

- 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) A develops into the embryo.
    B develops into the endosperm.
(b) - The endosperm development starts from the primary endosperm cell containing the primary endosperm nucleus.
- In the most common type of endosperm development, the primary endosperm nucleus undergoes successive free nuclear divisions to give rise to a number of free nuclei; at this stage, it is called free nuclear endosperm.
- Subsequently wall formation takes place from the periphery and proceeds towards the centre and the endosperm becomes cellular.
- This type of endosperm development is seen in coconut; the water of the tender coconut represents the free nuclear endosperm with thousands of nuclei in it and the white kernel around it represents the cellular endosperm.
- In albuminous seeds,some amount of endosperm persists in the mature seed, as the developing' embryo does not consume it fully, e.g. wheat/maize.
-In exalbuminous seeds, the endosperm is completely consumed by the developing embryo before seed maturation, e.g. groundnut and pea.
Development of primary endosperm nucleus:
- The PEN undergoes successive nuclear divisions to give rise to free nuclei, this stage of endosperm development is known as free-nuclear endosperm.
- Subsequently cell wall formation occurs and the endosperm becomes cellular .

Meiosis occurs during sporogenesis.
The structure formed at the end are microspores and megaspores respectively.

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.

(a) Megaspore
(b) Haploid
(c) (i) Filiform apparatus refers to the special cellular thickenings in the synergids, towards micropylar tip.
(ii) They play an important role in guiding the pollen tube to enter one of the synergids.

(a) A - Chasmogamous flower
B - Cleistogamous flower
(b) A - Autogamy, geitonogamy and xenogamy
B - Autogamy only.

(a) A - Suspensor
B - Globular embryo
(b) (i) Zygote
(ii) Proembryo

(i) (b): Y is a vascular bundle comprising xylem that transports water and mineral salts to the anther, and phloem that transports sugars to the anther.
(ii) (b): X contains pollen grains. Pollen grain contains two haploid nuclei resulting from mitosis, a generative nucleus and pollen tube/vegetative nucleus.
(iii) (c): Rough surfaces on pollen grains help them to cling onto the surface of insect pollinators.
(iv) (b): Insect-pollinated plants tend to have pollen with rough surfaces to allow them to cling more readily onto the body of insect pollinators. Their stamens are unlikely to be pendulous nor protrude outside the flower, since the pollen is not intended to be released into the air and carried away by the wind.
(v) (b): Entomophily type of pollination takes place through the agency of insects. The entomophilous flowers are brightly coloured and fragmented to attract the insects. Their pollen grains are sticky or spiny to easily get attached with the body of pollinators. When the insects visit the flowers, their body gets dusted with pollen grains, and when they fly and visit other flowers, they brush against the stigma which being sticky, at once receives the pollen grains from their body. Thus, cross-pollination is achieved.

(b) Mostly all the four spores within a tetrad are completely isolated from one another and from the spores in other tetrads of the locule. Usually the microspores separate from one another shortly after meiosis. However, in some plants the spores tend to remain together in tetrads for longer period and develop into compound pollen grains. In many members of Orchidaceae and Asclepiadaceae all the microspores in a sporangium remains together to form what is called a pollinium.

(c) The pollen wall comprises two principal layers, the inner one is called intine and the outer exine. The intine is pecto-cellulosic in nature as is the primary wall of the somatic cells. The exine is composed chiefly of a class of material called sporopollenin.

(c) The body of the ovule consists of a mass of parenchymatous cells named nucellus. The nucellus is mostly consumed by the developing embryo sac or endosperm. But in some plants it persists in the mature seed as a nutritive tissue. The persistent nucellus is called perisperm.

(c) One hypodermal nucellar cell of the micropylar region differentiates into sporogenous cell. It forms a diploid megaspore mother cell or megasporocyte. The megaspore mother cells undergo meiosis and forms a row of four haploid megaspores. Only the chalazal megaspore remains functional while the other three degenerate. The functional megaspore enlarges and gives rise to female gametophyte, also called embryo sac.