1. Self-incompatibility:  A condition wherein the pollen is ineffective in fertilizing the same flower or other flowers on the same plant usually due to inhibition of the growth of the pollen tube in the stigma and style, thereby preventing delivery of male gametes to the ovules.
2. Maturation of pistil before that of stamen (protogyny) or maturation of stamen before that of the pistil (protandry) inhibit self-pollination.

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.

1. Apomixis is a form of asexual reproduction that mimics sexual reproduction and seeds are formed without fertilisation.
2. Apomictic embryos are genetically identical to the female parent.
3. If hybrid seeds can be made apomictic, the desirable characters can be maintained in the progeny.
4. It is often associated with polyembrony.

Advantage
Since cleistogamous flowers are autogamous, there is an assured seed-set.
Disadvantage
Continued self-pollination leads to inbreeding depression.

Advantage
1. Since cleistogamous flowers are autogamous, there is an assured seed-set.
Disadvantage
1. Continued self-pollination leads to inbreeding depression.

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.

1. Male gametophyte - In the Anther (microsporangia) and later on the stigma and style.
2. Female gametophyte - inside the ovule.

Triple fusion:
It is  the process of fusion of three nuclei, two polar nuclei (fuse to form a diploid secondary nucleus) and a male gamete.
It occurs in the central cell of the embryo sac of the ovule of angiosperms.
Then nuclei involved are two polar nuclei and a male gamete.

Vallisneria is pollinated by water.
Water lily is pollinated by insects.
In Vallisneria, the male flowers (later pollen grains) are released on the surface of water and keep floating.
The female flowers reach the surface of water by uncoiling of the long stalk
When the passively carried male flowers/pollen grains meet the female flowers, pollination is effected.
The stalk of the female flower coils and the flower is drawn inside the water column.

(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.

(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.

(i) part that develops into seed coat integuments
(ii) part that develops into an embryo after fertilization-egg
(iii) that develops into endosperm in a albuminous seed-polar nuclei
(iv) through which pollen tube enters into embryo sac-micropyle
(v) that attaches the ovule to the placenta funiculus.

(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.

(i) The zygote starts dividing only after a certain amount of endosperm is formed as an adaptation to provide assured nutrition to the developing embryo; hence we can say it remains dormant for some time.
(ii) In groundnut, the developing embryo utilises the endosperm completely. There is no residual endosperm in the seed and so the seed is exalbuminous. In castor, the endosperm is not completely used up by the developing embryo, there is some amount of endosperm left in the seeds and the seeds are albuminous.
(iii) The micropyle facilitates the entry of water- and oxygen into the seed during germination.
(iv) The loss of water (up to 10-15% of weight) reduces the metabolic activity and seeds can enter a state of dormancy during unfavorable environment.
(v) Since, the thalamus (part other than ovary) contributes to fruit formation, these fruits are called false fruits and not true fruits.

(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.

(a) The sporogenous cells of anther may directly function as microspore mother cells (also called pollen mother cells or PMCs) or they may undergo a few mitosis to add up to their number before entering meiosis. Each PMC, by a meiotic division, gives rise to a group of four haploid microspores. The aggregates of four microspores are referred to as microspore tetrads.

(b) Both assertion and reason are true but reason is not the correct explanation of assertion.