Leaves of a maize plant contains 10 chromosomes each, so 2n =10(as leaf is diploid in nature)
Haploid no.; n =5
Gametes will be \(\rightarrow\) 5, each
Chromosome no. in endosperm (3n) = 3 \(\times\) 5 =15 chromosomes
Chromosome no. in zygote (2n) = 2 \(\times\) 5 = 10 chromosomes Maize is an angiosperm and exhibit double fertilisation as its characteristic feature in which two processes called syngamy and triple fusion occurs to form zygote and endosperm, respectively.

The pollen tube releases two male gametes into the synergids in which one male gamete moves towards egg cell and fuses to form a diploid zygote. The other male gametes move towards the central nuclei and fuses with them to form a triploid Primary Endosperm Nucleus (PEN).

Functions of micropyle
(i) It is the passage through which the pollen tube enters the ovule.
(ii) It remains as a small pore in the seed coat and facilitates the entry of water and oxygen during seed germination.

Vivipary is defined as the seed germination, while the fruit is still attached to the mother plant. Plants which grow in marshy places are called mangroves. In these plants when seeds fall on marshy places, they cannot germinate because of high salinity and more water conditions.
So, in those plants, seeds germinate when they are still attached to the mother plant. Litter is the offspring at one birth of animal usually 3-8 in number. Vivipary automatically limits the number of offspring in litter due to the reason that limited number of egg or ovum are produced and fertilised during reproductive cycle of female.

1. After triple fusion the central cell developer to form primary endosperm nucleus.
2. The primary endosperm cell undergoes successive cell divisions to form triploid endosperm which has abundant food reserves.
3. The primary endosperm nucleus undergoes successive nucleus divisions to form many free nuclei this type of endosperm development is called free nuclei endosperm. After which cell walls are laid, and the endosperm becomes cellular endosperm. Ex: coconut water is nuclear endosperm (containing many free nuclei) while white kernel around is cellular endosperm.
4. The endosperm developent preceeds that of zygote to ensure that endosperm containing abundant food reserves is formed earlier and can nourish the developing embryo

(a) Failed to keep pace with demand, failed to provide fast and efficient system of crop improvement.
(b) Large number of plants can be developed in a short duration/production of genetically identical plants/somaclones/healthy plants can be recovered from diseased plants
(c)Tomato/banana/apple.

Exine: It can withstand high temperature/strong acids/alkali. It protects pollens.
Intine: It is a thin and continuous layer made up of cellulose and pectin. The intine produces pollen tube.
Vegetative cell: It is bigger and has abundant food reserve.
Generative cell: It divides mitotically to give rise to two male gametes

(a) Scutellum
(b) Epicotyl
(c) Polyembryony
(d) Patrhenocarpic fruits.

The part responsible for supplying nourishment to the developing embryo is (B) Endosperm because embryo development occurs in the endosperm which is specially meant food to the developing embryo. Cotyledons are the parts of mature embryo which supply food during seed germination.

(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.

Structure of Dicot and Monocot Embryos
A typical dicotyledonous embryo consists of an embryonal axis and two cotyledons. The portion of the embryonal axis above the level of cotyledons is the epicotyl, which terminates in the plumule or stem tip. The cylindrical portion below the level of cotyledons is hypocotyl that terminates in the radicle or root tip, The root tip is covered with a root cap, e.g. mango, apple, radish, rose, etc

Embryo of monocots possesses only one cotyledon at one end (lateral) of the embryonal axis and this cotyledon is called scutellum.
At the lower end, the embryonal axis has radical and root cap enclosed in an undifferentiated sheath called coleorhiza.
The porrion of the embryonal axis above the level of attachment of scutellum is the epicotyl.
The epicotyl has a shoot apex and a few leaf primordia encdosed in a hollow foliar structure called coleoptile, e.g. grass, banana, bamboo, palm, etc.

Entry of Pollen Tube into the Ovule
After reaching the ovary, the pollen tube can enter the , ovule either through the micropylar end (porogamy) or through chalaza (chalazogamy) or through funicle or integument (mesogamy). It then enters one of the synergids through the filiform apparatus present at micropylar end. The filiform apparatus directs the growth of pollen tube by secreting some chemical substances.
All these events mentioned above together are referred to as pollen-pistil interaction and the knowledge gained in this area helps plant breeders in manipulating this interaction, even in incompatible pollination, to get desired hybrids.
Double Fertilisation
1. The process was demonstrated for the first time by Nawaschin in 1898 in Lilium and Fritillaria. The most important and unique characteristic feature of angiosperms is the participation of both male gametes in the act of fertilisation. The pollen tube releases the two male gametes into the cytoplasm of one of the synergids, then the penetrated synergid starts degenerating. One male gamete fuses with the egg cell to form a diploid (2n) zygote. This process is called syngamy or generative fertilisation.
2. The diploid zygote finally develops into the embryo. The second male gamete fuses with the two polar nuclei or secondary nucleus in the central cell to form the triploid Primary Endosperm Nucleus (PEN). This process is called triple fusion as three haploid nuclei are involved in the fusion.
3. After triple fusion, the central cell becomes the Primary Endosperm Cell (PEC) which gives rise to the endosperm, while the zygote develops into the embryo. As both the fusions, syngamy and triple fusion, occur in an embryo sac, the phenomenon is termed as double fertilisation.

(i) The major events in post-fertilisation include development of endosperm and embryo, maturation of ovules into seeds and ovary into fruit. They take place soon after the double fertilisation. These are as follows
Development of an Endosperm The development of endosperm precedes embryo development. The primary endosperm cell divides repeatedly to form a triploid endospermn tissue.
In most of the cases, the PEN undergoes successive nuclear divisions without cytokinesis, to give rise to free nuclear endosperm. Subsequently, cell wall formation starts from the periphery and the endosperm becomes completely cellular, e.g. coconut, rice, maize, sunflower, etc.
Development of an Embryo The embryo develops at the micropylar end of the embryo sac where the zygote is situated. Most zygotes divide only after certain amount of endosperm is formed. The nutrition for the development of embryo is provided by the endosperm. The zygote gives rise to proembryo and subsequently to the globular, heart-shaped and mature embryo.
Development of a Seed Double fertilisation in angiosperms triggers the transformation of ovule into a seed. Seeds are formed inside the fruits.
Formation of a Fruit A fruit is formed as a result of cell division and differentiation in the ovary, which is transformed into fruit as a result of stimuli received from pollination as well as from developing seed.
(ii) Pollination can be classified into three different types based on the source of pollen grains. They are:
i) Autogamy: It is defined as the transfer of pollen grains from the anther to the stigma of the same flower in the same plant.
ii) Geitonogamy: It is defined as the transfer of pollen grains from the anther of one flower to the stigma of another flower on the same plant.
iii) Xenogamy: This type of pollination brings genetically different types of pollen grains to the stigma of the flower.

(a) One of the male gametes moves towards the egg cell and fuses with its nucleus thus completing syngamy. This results in the formation of a diploid cell-the zygote, the other male gamete moves
towards the two polar nuclei located in central cell and fuses with them to produce a triploid primary endosperm nucleus Since two types of fusions take place in an embryo sac the phenomenon is known as double fertilization.
(b) There occur two gametic fusions or fertilization in the female gametophyte or embryo sac of angiosperms i.e., one male gamete fuses with the egg to form zygote and the other male gamete fuses with the secondary nucleus to form the primary endosperm nucleus. The former fertilization is called as syngamy and the latter as the triple fusion. Thus, fertilization occurs twice in the same embryo sac, therefore, this is called as the double fertilization. This phenomenon is unique in angiosperms and is not found in any other group of plant kingdom other than angiosperms.

(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.

(i) Insect-pollinated flowers are large, colourful and showy; if flowers are small, they are clustered into inflorescene to make them conspicuous.
(ii) The pollen grains and stigmatic surface are sticky.
(iii) They are highly fragrant; flowers pollinated by flies and beetle have foul odours to attract them.
(iv) To sustain animal visits, the flowers offer certain rewards like nectar, edible pollen and safe place for laying eggs.

(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.