11. Another report states that pollen tubes do not change growth direction under AC electric fields. 12. The growth of the pollen tube is controlled by the vegetative ( or tube ) cytoplasm. 13. Inaperaturate pollen grains often have thin walls, which facilitates pollen tube germination at any position. 14. Lipids at the surface of the stigma may also stimulate pollen tube growth for compatible pollen. 15. From here, a pollen tube seeks out the female gametophyte and if successful, fertilization occurs. 16. Tip growth occurs in algae ( e . g ., root hairs and pollen tubes ). 17. Once the pollen tube successfully attains an ovule, it delivers the two sperm cells with a burst. 18. In chalazogamous plants, the pollen tubes enter the ovule through the chalaza instead of the micropyle opening. 19. The sperm nuclei reach the eggs through fertilization tubes, similar to the pollen tube mechanism in plants. 20. It is an outgrowth of the placenta, important in nourishing and guiding pollen tubes to the micropyle.
