Pollen grains are the male gametes in flowering plants, and they are responsible for the transfer of male gametes to the female gametes in the process of pollination. The male gametes or sperm cells are contained within the pollen grains, which are produced in the anthers of the flower.

The transfer of male gametes from the pollen grain to the female gametes usually occurs through a structure called the pollen tube.

Explanation:
1. Pollen Grain: The pollen grains are produced in the anthers of the flower. They contain the male gametes or sperm cells.
2. Pollination: Pollination is the process by which pollen grains are transferred from the anthers to the stigma of the flower. This can occur through various means such as wind, water, or by the help of animals.
3. Pollen Tube: Once a pollen grain lands on the stigma of a flower, it germinates and produces a structure called the pollen tube. The pollen tube grows down through the style of the flower towards the ovary.
4. Ovule: The ovules are located in the ovary of the flower. They contain the female gametes or egg cells.
5. Fertilization: The pollen tube continues to grow through the ovary and reaches the ovule. The male gametes are released from the pollen grain and travel through the pollen tube to reach the female gametes in the ovule. This process is known as fertilization.
6. Formation of Zygote: The fusion of the male and female gametes results in the formation of a zygote, which eventually develops into an embryo.
7. Seed Formation: After fertilization, the ovule develops into a seed, which contains the embryo and is surrounded by a protective seed coat.
8. Fruit Formation: In some plants, the ovary also develops into a fruit, which protects and helps in the dispersal of the seeds.

In conclusion, the male gametes in pollen grains reach the female gametes through a structure called the pollen tube. The pollen tube grows from the stigma of the flower, through the style, and into the ovary, where it reaches the ovule and allows for the fertilization of the female gametes.

D pollen tube because male have that in pollen grain