Here's why:
* Pollen Tube: The pollen grain, containing the male gametophyte, lands on the stigma of the flower. It then germinates and produces a pollen tube, a long tubular structure that grows down through the style towards the ovary.
* Sperm Transport: The sperm nuclei, located within the male gametophyte, are transported within the pollen tube to the ovule, where the egg cell is located.
* No Need for Flagella: Since the sperm are passively transported within the pollen tube, they don't require flagella for movement.
This is in contrast to other plant groups like gymnosperms (conifers, cycads, etc.) and ferns, where the sperm are flagellated and must swim through a film of water to reach the egg.
The development of the pollen tube in angiosperms is a key innovation that allowed them to conquer dry environments and become the dominant plant group on Earth.
