Fertilization is the fusion of haploid male gamete in the pollen grain with the haploid female gamete in the ovule. To bring about fertilization, the pollen grain which get deposited on the stigma of the carpel must penetrate the style and reach the ovule. Hence it produces a projection called pollen tube which grow through the length of the style and finally reaches the ovule.
The pollen tube contains male gamete inside the ovule, there is a structure called embryo sac which encloses the female gamete, the pollen tube reaches the embryo sac. Then male gamete in pollen tube and female gamete in embryo sac unite, thus fertilization takes place resulting in the formation of a diploid cell called zygote.
