Stamen is the male reproductive part, which produces pollen grains (yellowish substance). Carpel, which is present in the center of a flower, is the female reproductive part. Carpel is made up of three parts. The bottom part, which is swollen, is the ovary; the middle part, which is elongated, is known as the style; and the terminal part, which may be sticky, is known as the stigma.
The ovary contains ovules and each ovule has an egg cell. When pollen grains fall on the stigma of carpel, it burst open and grows a pollen tube downwards through the style towards female gamete in ovary.
A male gamete moves down the pollen tube. The pollen tube enters the ovule in ovary. The tip of pollen tube bursts open and male gamete comes out of pollen tube. In ovary, male gamete of pollen combines with nucleus of female gamete or egg present in ovule to form a fertilised egg (Zygote).