There are three main parts of the embryo. These are-

1. Egg apparatus: The three cells near the oviduct of the embryo are collectively called the egg apparatus. Among them, the large cell in the middle is called ovule and the smaller cells on both sides are called companion cells.
2. Antipodal cell: The three cells on the ovule side of the embryo are collectively called antipodal cells.
3. Secondary nucleus: Two nuclei come from the two poles in the middle of the embryo. The two nuclei then fuse to form a secondary nucleus.

An embryo containing four gametes is called Tetrasporic. 7 types of tetrasporic embryos.

(i) Adoxa type: Adoxa embryo has 8 nuclei. For example, Adoxa moschatellina.

(ii) Peperomia: Peperomia is a 16-nucleate embryo sac. For example – Peperomia pellucida.

(iii) Penia type: Penia is a 16-nucleate embryo sac.

(iv) Drusa: Drusa embryo contains 16 nuclei. For example – Drusa amatista.

(v) Fritilliaria type: Fritilliaria embryo has 8 nuclei. For example, Fritilliaria imperialis.

(vi) Plumbagella: Plumbagella is an embryo sac with 8 nuclei. For example – Plumbagella micrantha.

(vii) Plumbaga type: Plumbaga is a 16 nucleated embryo sac. For example – Plumbaga zeylanica.

An embryo containing two spermatozoa is called Bisporic. Bisporic embryos are of two types.

(i) Allium type: Allium is an embryo with 8 nuclei. For example – Allium cepa.

(ii) Endymion type: Endymion is an 8-nucleate embryo sac. For example- Endymion hispanica.

An embryo containing only one zygote is called monosporic. About 75% of the plant kingdom is monosporic. In 1879, Strusberger first described the structure of the monosporic embryo of the plant Polygonum divaricatum. Monosporic embryos are of two types.

(i) Oenothera type: Oenothera is a 4-nucleate embryo sac. eg Oenothera lamarckiana.

(ii) Polygonum type: Polygonum is an 8-nucleate embryo sac. For example, Polygonum hydropiper.

The sac-like part inside the nucellus that carries the egg is called the embryo sac. Amniotic sac is of three types.
1. Monosporic: An embryo containing only one zygote is called monosporic. About 75% of the plant kingdom is monosporic. In 1879, Strusberger first described the structure of the monosporic embryo of the plant Polygonum divaricatum. Monosporic embryos are of two types.
(i) Oenothera type: Oenothera is a 4-nucleate embryo sac. eg Oenothera lamarckiana.
(ii) Polygonum type: Polygonum is an 8-nucleate embryo sac. For example, Polygonum hydropiper.
2. Bisporic: An embryo containing two spermatozoa is called Bisporic. Bisporic embryos are of two types.
(i) Allium type: Allium is an embryo with 8 nuclei. For example – Allium cepa.
(ii) Endymion type: Endymion is an 8-nucleate embryo sac. For example- Endymion hispanica.
3. Tetrasporic: An embryo containing four gametes is called Tetrasporic. 7 types of tetrasporic embryos.
(i) Adoxa type: Adoxa embryo has 8 nuclei. For example, Adoxa moschatellina.
(ii) Peperomia: Peperomia is a 16-nucleate embryo sac. For example – Peperomia pellucida.
(iii) Penia type: Penia is a 16-nucleate embryo sac.
(iv) Drusa: Drusa embryo contains 16 nuclei. For example – Drusa amatista.
(v) Fritilliaria type: Fritilliaria embryo has 8 nuclei. For example, Fritilliaria imperialis.
(vi) Plumbagella: Plumbagella is an embryo sac with 8 nuclei. For example – Plumbagella micrantha.
(vii) Plumbaga type: Plumbaga is a 16 nucleated embryo sac. For example – Plumbaga zeylanica.

A small swollen area is formed in the amara inside the ovary of the female flower. The swollen area gradually turns into an ovule. The endosperm contains one or more archisporial cells. Each archisporial cell is large in size, the cytoplasm is dense and the nucleus is large. It produces two cells by periclinal division. wall cells on the outside and primary reproductive cells or sporogenous cells on the inside. Wall cells divide to form the wall of the zygote. The sporogenous cell develops into the female mother cell either directly or by division. Each female mother cell divides by meiosis to produce four megaspores or gametes. Of the four spermatozoa, three are destroyed and one remains viable.

The implications/importance of plant pungametophyte development in the biosphere are discussed.
1. Pungamete formation: In this process the pungametophyte develops. The main function of pungametophyte is to produce pungametes or sperm. Two spermatozoa are produced in each pungametophyte.
2. Fertilization: The prerequisite for fertilization is the production of sperm and egg. Pungametophytes produce sperm that participate in fertilization.
3. Origin of seeds: The main source of food for the living world is seeds. The sperm produced in the pungametophyte fuse with the secondary nucleus to form the seed.
4. Fertilization: In this process, the sperm unites with the egg to form a zygote. After the zygote is formed, the flower ovule develops into a seed.
5. Fruit formation: After fertilization, the ovary of the flower gradually turns into a fruit.
6. Reproduction: After the union of sperm and egg, the ovule of the flower turns into a seed. Most plants on Earth reproduce by seeds. Because of this, pungametophytes play a major role in plant protection.
7. Formation of new species: Zygote is formed by the union of two different cells sperm and egg. It gives rise to new species with new characteristics.
8. Creation of Biodiversity: The sperm produced in the pungametophyte fertilizes the egg to form a zygote. New species are formed from the zygote. Biodiversity is created through new species.
From the above discussion, pungametophyte is a very important cell in plant life. It maintains the continuity of life by creating sperm.

Pollen, anther, tube nucleus and pungamete of plants are collectively called pungametophyte. The anthers of plant stamens contain pollen mother cells. Each pollen mother cell produces four microspores or pollen grains by meiosis. Pollen is the first cell of the male gametophyte. Its nucleus divides to form two nuclei. The larger one is called the tubular nucleus and the smaller one is called the gonial nucleus. The ductal nucleus is round and the gonial nucleus is slightly curved. In this condition, the anther wall ruptures and binucleate pollen grains come out. Through pollination, it falls into the ovary of the female flower. When the pollen comes in contact with the endosperm, it gets stuck in the sticky sap and swells by absorbing the endosperm sap. Swelling causes pressure inside the pollen tube. The pressure causes the inteins to come out of the tube through the pore. It is called pollen tube. The process of pollen tube formation is called pollen emergence or germination. Cutinase enzyme degrades the cutin of the endosperm and the pollen tube enters the endosperm. The tube nucleus enters the pollen tube first and the generative nucleus later. The pollen tube enlarges and moves towards the ovary. Before the ovum reaches the pore, the germinal nucleus divides to produce two gametes or spermatozoa. The development of the pungametophyte is complete with the production of spermatozoa.

In the process of microsporogenesis, four microspores or pollen grains are produced from each pollen mother cell. Pollen is the first cell of pungametophyte. It can be round, oval, oblong or triangular. Each pollen grain is covered by a two-layered coat. The outer one is called exine and the inner one is called intein. Exine is thick, tough, uneven and composed of lignin. Its main chemical component is sporopollenin. In place of the exine are thin pore-like areas. This is called the reproductive pore (renurandhra or germpore). Pollen has 3-4 germpores (but can have up to 20). On the other hand, intein is thin, soft, smooth, elastic and made of cellulose. The cytoplasm of pollen is dense and the nucleus is in the middle of the cell. When the cell cavity is formed in the transformed state, the nucleus moves towards the periphery of the cell. Each pollen grain is 10-200 µm in diameter (according to many, 0.025-0.25 mm).
[If a pollen grain has one pore it is called monocolpate and if it has many pores it is called polycolpate]

The process by which pollen is formed is called microsporogenesis. The swollen part of the stamen head of a flower is called the anther. Anthers contain one or more archisporial cells. Each archisporial cell is large in size, the cytoplasm is dense and the nucleus is large. It produces two cells by periclinally dividing. wall cells on the outside and primary reproductive cells or sporogenous cells on the inside. Wall cells divide to form the pollen wall. The outermost layer of the wall is called the tapetum. Sporogenous cells transform into pollen mother cells either directly or by division. Each pollen mother cell divides by meiosis to form four microspores or pollen grains. The four pollen grains together are called tetrads. Most of the pollen is yellow in color. The pollinator receives nutrients from the tapetum. Plants belonging to the family Orchidaceae, Asclepiadaceae etc. have pollen grains together. Pollen sticks together in the metamorphosis to form a special structure. This is called a polynomial.
[Anthers with four anthers are dithetic anthers and this condition is called tetrasporangiate. An anther having two anthers is monothecus anther and this condition is called bisporangiate.