Gamete formation in plants

 Pollen formation( Male gametophyte) 

Pollen grain formation occurs in male reproductive part called Anther . An Anther may be unilobed or bilobed . It has pollen chamber (microsporangium )  in which pollen mother cells (PMC or microspore mother cells ) are located . 

Pollen are product of meiotic division which occurs in pollen mother cells (2n or diploid  ) . All four daughter cells if  survive become four pollen grain (n or haploid ) . Each has single nucleus which later on become two by mitotic division . Out of these two cells produced in mitosis one retain more cytoplasm and termed as vegetative cell and other one is generative cell. Both the cells are enclosed by intine( made of pectin + cellulose)  inner coat and outer resistive coat exine (has sporopollenin)  which has gaps or germ pores for emergence of pollen tube . Pollen tube emerges as vegetative cell develops and carry nuclei of generative cell for fertilisation purpose. Initially generative cell has one nucleus but via mitosis it becomes two . Out of these two nuclei one fuses with nucleus of egg cell in embryo sac of ovary and another fuses with polar nuclei of central cell in mid part of embryo sac . Since fertilisation occurs twice it is popularly known as double fertilisation ( term given by Nawaschin) 

Embryo sac formation ( female gametophyte ) 

.Inside pistil ovary is main site where embryo sac is to be formed . Inside ovary ovule or ovules are located . Each ovule has inner and outer wall , nutritive tissue nucellus and two ends or poles : chalazal and micropylar . 

In nucellus tissue megaspore mother cells develop which further divide by meiosis like PMC and form four megaspores.But out of these four only one survive and rest degenerate. Surviving megaspore has three mitosis taking place in sequence inside it giving rise to total eight nuclei . These eight nuclei arranged to form seven celled and eight nucleated embryo sac. Out of these eight nuclei three at chalazal end are antipodals, two polar nuclei in middle , one egg at micropylar end guarded by two synergids.