A typical mature embryo sac of Angiosperms is  a 7-celled and 8-nucleate structure.

(i) At the micropylar end, an egg apparatus is present which consists of an egg cell and 2 synergid cells. Synergids contain filiform apparatus which guides the pollen tube entry into the embryo sac during fertilisation.

(ii) At the chalazal end, three antipodal cells are present.

(iii) In the centre, two polar nuclei are present which get fused prior to fertilisation to form a diploid secondary nucleus.

Hence, 8 nuclei are constituted within 7 cells. Thus, embryo sac is 7-celled and 8-nucleate.

A monocot is a type of flowering plant that is characterized by having a single cotyledon, trimerous flowers, and parallel leaf veins. Monocots are economically important as food sources for both humans and animals, The embryo of each seed plant possesses one or more leaf-like structures called cotyledons, which absorb nutrients and may function as the first leaves in some plants. Monocots have a single such cotyledon, while other flowering plants usually have two. ... The image below at right shows a monocot embryo with cotyledon.

Parts of typical dicot embryo includes- Plumule, cotyledons, hypocotyl, radical and root cap. A typical dicotyledonous embryo, consists of an embryonal axis and two cotyledons. The portion of embryonal axis above the level of cotyledons is the epicotyl, which terminates with the plumule or stem tip. 

Development of a dicot embryo (i) Embryo formation starts after a certain amount of endosperm is formed. (ii) Zygote divides by mitosis to form a proembryo. (iii) Formation of globular and heart-shaped embryo occurs, which finally becomes horse shoe-shaped forms a mature embryo.

Pollen-Pistil interaction

The pollen landing on stigma of pistil might be compatible or incompatible with the stigma. Therefore the acceptance or rejection of the pollen by stigma depends on the compatibility.

If the pollen & pistil are compatible with each other, following events will take place:

• Pistil accepts pollen
• Formation of pollen tube
• Pollen tube reaches ovary
• Pollen grains move into pollen tube
• Pollen tube enters ovule through micropyle
• Pollen tube enters a synergid through filiform apparatus
• Fertilization occurs

On the other hand, If the pollen & pistil are incompatible with each other, following events will take place:

• Pistil rejects pollen
• Prevents pollen tube growth
• Prevents fertilization

Therefore, Pollen-Pistil interaction can be defined as follows:

Pollen-pistil interaction is a dynamic process of pollen recognition followed by promotion or inhibition of the pollen. Chemical components of the pollen interact with those of the pistil.

 Entomophilous flowers: Flowers which are pollinated  by insect are called   entomophilous flowers.
Characters of Entomophilous flowers
(1) The flowers are of large size.
(2) Corolla of flowers is brightly coloured to attract insects. Bracts may become bright coloured
(3) If the flowers are small they are grouped together to form inflorescence which helps attracting insects.
(4) They may produce nectar to lure insects.
(5) The pollen grains are heavy with rough and spiny surface so that they stick to the insects body.

In vallisneria, the female flower reach the surface of water by the long stalk and the male flower or pollen grains are released into the surface of water. They are carried by water currents reaching the female flowers and the stigma. 

In Water lily pollination takes place through wind or insect, female flower imerges above the surface of water and gets pollinated.

• ollination by wind is called anemophily.

# Characteristics of anemophilous flowers -

• Anemophilous flowers dont have colour to attract insects.
• They dont have scent or nectar.
• They have numerous small flowers.
• Stamens have long filaments and are exposed.
• Their pollen grains are dry, light weight and powdery.
• Stigma is sticky & feathery.

Adaptation for pollination In hydrophilous flower: 
(1) Small and inconspicuous flower. 
(2) Flowers without bright colours, fragrance and nectar.
(3) Florid parts and pollen grains are unwettable. 
(4) Plants in which female flowers are submerged, the pollen grains have specific gravity equal to or slightly more than water. In plants with floating female flowers, a specific gravity of pollen grains is less than that of water. 

Adaptation for pollination in anemophilous flower: 
(1) Mowers small, numerous, inconspicuous. 
(2) The absence of nectar. 
(3) Lack bright colours, fragrance. 
(4) Petals small or highly reduced. 
(5) Male flowers more than female flowers and situated at a higher level. 
(6) Anthem versatile and filaments long. 
(7) Pollen pains smooth, dry, light in weight. 
(8) Pollen grains are produced in large numbers to compensate their wastage. 

A flower is a reproductive part of a plant. It helps in sexual reproduction as it has male parts and female parts. A fully opened flower has the following parts:  Stalk—A flower is attached to the shoot by means of stalk or pedicel stalk. The tip of the stalk is swollen or flattened. This is called torus or thalamus or receptacle. The different parts of a flower are inserted on the thalamus. There are usually four whorls as  Calyx (Sepals)  Corolla (Petals)  Androecium (stamens)  Gynoecium (Carpels) Present on the thalamus  1. Sepals (Calyx): These are the outermost part of the flower. These are leaf like and green in colour. This is the outer covering of the flower and form outer whorl in a flower. The Calyx (sepals) enclose the inner parts of the flower when it is a bud. It is protective in function.  2. Corolla (Petals): Petals form the second whorl inner to the sepals. These are usually coloured, gaudy, or white in colour and scented and give sweet smell. The value of a flower is due to the attractive colour of the petals. These attract the insects for pollination.  3. Stamens (Androecium): The third whorls inner to the petals are stamens. This third whorl is called Androecium. These are the male parts of the flower. Each stamen is formed of a long narrow, hair like structure called filament. On its tip it bears, a rounded broad sac like structure called anther. Each anther has two anther lobes. Each anther lobe has two pollen sacs which have powdery mass called pollen grains.  4. Carpels (Gynoecium): Carpels are the inner most or fourth whorl in a flower. It is lodged on the thalamus and forms the female part of a flower. This whorl of carpels is called gynoecium. Each carpel or pistil has three parts.  (a) The lower most, swollen part is ovary. It is attached to the thalamus.  (b) The middle part is style which is narrow, thread like.  (c) Stigma: The style ends in a knob like, rounded structure which is sticky in nature to receive the pollen grains. The ovaries contain ovules which later turn into seeds after fertilization and the ovary wall forms the fruit sometimes the thalamus also becomes a part of the fruit as in apple.

Apomixis is the mechanism of seed production without involving the process of meiosis and syngamy. It plays an important role in hybrid seed production. The method of producing hybrid seeds by cultivation is very expensive for farmers. Also, by sowing hybrid seeds, it is difficult to maintain hybrid characters as characters segregate during meiosis. Apomixis prevents the loss of specific characters in the hybrid. Also, it is a cost-effective method for producing seeds.

Apomixis is the mechanism of seed production without involving the process of meiosis and syngamy. It plays an important role in hybrid seed production. The method of producing hybrid seeds by cultivation is very expensive for farmers. Also, by sowing hybrid seeds, it is difficult to maintain hybrid characters as characters segregate during meiosis. Apomixis prevents the loss of specific characters in the hybrid. Also, it is a cost-effective method for producing seeds.

Fruits derived from the ovary and other accessory floral parts are called false fruits. On the contrary, true fruits are those fruits which develop from the ovary, but do not consist of the thalamus or any other floral part. In an apple, the fleshy receptacle forms the main edible part. Hence, it is a false fruit.

Embryogenesis is the process of development of an embryo from zygote. In embryogenesis, the zygote undergoes repeated cell division through mitosis. The divisions help in the growth of an embryo. Cells undergo differentiation attaining specific shape, size and function. Cell differentiation occurs at specific location resulting in the production of different tissue, organs and organ system.

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 unwanted 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).

Entomophily is a form of pollination whereby pollen or spores are distributed by insects. Several insects are reported to be responsible for the pollination (potential or effective) of many plant species, particularly bees, Lepidoptera (butterflies and moths), wasps, flies, ants and beetles.

Allogamy the process of cross-fertilizing. It is a terminology utilised in the field of biological reproduction describing the fertilization of an ovum from one individual with the spermatozoa of another. The transfer of pollen grains from the anther of a flower on one plant to the stigma of a flower on another plant of the same species is called allogamy. Allogamy is the common form of out-breeding. It leads to heterozygosity. Such species develop heterozygous balance and exhibit vital inbreeding depression on selfing.

Flowers which are never open to ensure self-pollination is called cleistogamy. They remain closed so that cross-pollination does not occur.
Cleistogamy has the advantage that the plant produces assured seed set even in the absence of pollinators and disadvantage is that self-pollination occur which reduces chances of variation and evolution of genetically superior progen

Opening of flowers only after the completion of pollination is known as chasmogamy. This also promotes self-pollination and is found in crops like wheat, barley, rice and oats. Chasmogamous flowers have exposed anthers and stigmata similar to the flowers of other species.

Geitonogamy

• Transfer of pollen grains from anther to stigma of another flower of same plant
• It is functionally cross-pollination, but genetically self-pollination

Transfer of pollen grains from anther to stigma is termed as Pollination. This transfer of pollen grains occurs with the help of pollinating agents like wind, water, insects, birds etc.