The functional megaspore is the first cell of the embryo sac or female gametophyte. The megaspore elongates along the micropylar-chalazal axis. The nucleus undergoes a mitotic division. Wall formation does not follow the nuclear division. A large central vacuole now appears between the two daughter nuclei. The vacuole expands and pushes the nuclei towards the opposite poles of the embryo sac. Both the nuclei divide twice mitotically, forming four nuclei at each pole. At this stage, all the eight nuclei are present in a common cytoplasm (free nuclear division). After the last nuclear division, the cell undergoes appreciable elongation, assuming a sac-like appearance. This is followed by the cellular organization of the embryo sac. Of the four nuclei at the micropylar end of the embryo sac, three organize into an egg apparatus, the fourth one is left free in the cytoplasm of the central cell as the upper polar nucleus. Three nuclei of the chalazal end form three antipodal cells whereas the fourth one functions as the lower polar nucleus. Depending on the plant the 2 polar nuclei may remain free or may fuse to form a secondary nucleus (central cell). The egg apparatus is made up of a central egg cell and two synergids, one on each side of the egg cell. Synergids secrete chemotropic substances that help to attract the pollen tube. The special cellular thickening called filiform apparatus of synergids to help in the absorption, conduction of nutrients from the nucellus to embryo sac. It also guides the pollen tube into the egg. Thus, a 7 celled with 8 nucleated embryo sac is formed.

(i) The microspore is the first cell of the male gametophyte and is haploid.
(ii) The development of male gametophyte takes place while they are still in the microsporangium.
(iii) The nucleus of the microspore divides to form a vegetative and a generative nuclei.
(iv)  A wall is laid around the generative nucleus resulting in the formation of two unequal cells, a large irregular nucleus bearing with abundant food reserve called vegetative cell and a small generative cell.
(v) At this two celled stage, the pollens are liberated from the anther.
(vi) In some plants, the generative cell again undergoes a division to form two male gametes.
(vii) In these plants, the pollen is liberated at 3 celled stages.
(viii) In 60% of the angiosperms, pollen is liberated in 2 celled stages.
(ix) The growth of the male gametophyte occurs only if the pollen reaches the right stigma.
(x) The pollen on reaching the stigma of absorbs moisture and swells.
(xi) The intine grows as pollen tube through the germ pore.
(xii) In case the pollen is liberated at 2 celled stages the generative cell divides in the pollen into 2 male cells (sperms) after reaching the stigma.
(xiii) The stages in the development of male gametophyte occurs in gynoecium of the plant.

(i) A mature ovule (megasporangium) consist of a stalk and a body
(ii) Funicle - The stalk of the ovule by which it attaches the ovule to the placenta.
(iii) Integuments - one or two protective covering around the nucellus
(iv) Micropyle - Pore present at the tip of the ovule where the integument is absent
(v) Chalaza - The basal region of the body of the ovule where the nucellus, the integument and funicle meet or merge
(vi) Embryosac- The female gametophyte oval sac like structure in the nucellus, toward the micropylar end.

 

(i) The primary sporogeneous cells undergoes mitotic divisions to form sporogeneous tissue.
(ii) Each cell of the sporogenous tissue is a potential microspore mother cell.
(iii) The microspore mother cell divides meiotically to form four haploid microspores. Microspore soon separates from one another.
(iv) They remain free in the anther locule. Then they develop into pollen grains.

(i) Some plants produce two or three different forms of flowers the length of stamen and style differ in them pollination will take place only between organs of same length.
(ii) So cross pollination is only possible. Distyly (eg) Primula-produces two forms of flowers. 

(iii) Stigma of thrum eyed anther of the pin lie in same level, Anther of the thrum eyed stigma of the pin lie in same level.
(iv) So effective cross pollination occurs, Tristyly - (eg) Lythrum
(v) The plant produces three kinds of flowers having difference in length of stamen and style.
(vi) Pollen from flowers of one type pollinate only the other two types can but not their, own type.

Advantages of modern methods
(i) Plants with desired characteristics can be multiplied rapidly in a short duration.
(ii) Plants produced are genetically identical.
(iii) Tissue culture can be carried out in any season.
(iv) Plants which do not produce viable seeds and seeds that are difficult to germinate can be propagated. 
(v) Rare and endangered plants can be propagated. Disease-free plants can be produced cells can be genetically modified and transformed.

In monocot seeds, the embryo is small and consists of single shield-shaped cotyledon known as scutellum present towards the lateral side of the embryonal axis.

The product of triple fusion is Primary Endosperm Nucleus (PEN). It is triploid (3n) in condition.

When the stamens and stigma of a flower mature at the same time it is said to be homogamy. It favours self-pollination to occur. Example: Mirabilis jalapa.

In Asteraceae species, the inner layer of integument get specialized for nourishing the embryosac and this is called integumentary tapetum or endothelium.

(a) Epidermis
(b) Endothecium
(c) Middle layers
(d) Tapetum

In Grafting, parts of two different plants are joined so that they continue to grow as one plant. Of the two plants, the plant which is in contact with the soil is called stock and the plant used for grafting is called Scion.

(a) Allium cepa - Bulb
(b) Zingiber officinal is - Rhizome
(c) Agave - Bulbils
(d) Colocasia - Corm

(a) Budding - Hydra
(b) Fragmentation - Spirogyra
(c) Regeneration - Planaria
(d) Gemma cup formation - Marchantia

Pollination carried out by beetle is called cantharophily.

The fluid part of the coconut represents free-nuclear endosperm and the white kernel represents cellular endosperm.

Gametogenesis ⟶ Syngamy ⟶ Zygote formation ⟶ Embryogenesis

Helobial endosperm: Primary Endosperm Nucleus moves towards the base of embryo sac and divides into two nuclei. Cell wall formation takes place leading to the formation of a large micropylar and small chalazal chamber. The nucleus of the micropylar chamber undergoes several free nuclear division whereas that of chalazal chamber may or may not divide. Examples: Hydril/a and Vallisneria.

The two male gametes released from a male gametophyte are involved in the fertilization. They fertilize two different components of the embryo sac. Since both the male gametes are involved in fertilization, the phenomenon is called double fertilization and is unique to angiosperms. One of the male gametes fuses with the egg nucleus (syngamy) to form Zygote.
The second gamete migrates to the central cell where it fuses with the polar nuclei or their fusion product, the secondary nucleus and forms the primary endosperm nucleus (PEN). Since this involves the fusion of three nuclei, this phenomenon is called triple fusion. This act results in endosperm formation which forms the nutritive tissue for the embryo.

When the pollen deposits on another flower of the same individual plant, it is said to be geitonogamy. It usually occurs in plants which show monoecious condition. It is functionally cross-pollination but is similar to autogamy because the pollen comes from the same plant

(i) Bee pollen is a natural substance with high proteins, carbohydrate, and a trace amount of vitamins and minerals.
(ii) It is used as a dietary supplement as tablets.
(iii) It increases the performance of athletes, racehorses and also heals burn wounds.

In a mature anther, the cells along with junction or the two sporangia of an anther lobe lack cellulose and lignin thickening. This region is called stomium. Stomium along with hygroscopic nature of Endothecium helps in the dehiscence of anther at maturity.

ovule is divided into two types based on the position of the sporogenous cell

The primary endosperm nucleus divides immediately after fertilization. It develops into an endosperm which is a nutritive tissue and a regulatory structure. The zygote divides only after that to form an embryo so that it can get nourishment from the endosperm that has formed earlier.