Fertilization

The pollen tube grows through the style toward the embryo sac. The tube nucleus is at the tip of the pollen tube. The pollen tube enters the ovule through a small hole called the micropyle. Upon reaching the ovule, the pollen tube bursts, releasing male gametes into the embryo sac.

• Double Fertilization: One male gamete fuses with the nucleus of the functional egg cell to form a diploid zygote, while the other male gamete fuses with two polar nuclei to form a triploid nucleus, known as the endosperm. This process, known as double fertilization, is unique to flowering plants.

Other nuclei, such as the antipodal and synergids, degenerate after fertilization. The zygote undergoes rapid cell division, forming a multicellular embryo. This embryo differentiates into a young shoot called the plumule, a young root called the radicle, and simple leaves called cotyledons.

After fertilization, the embryo remains enclosed in the ovule for protection. As the ovule matures, it transforms into a seed, and the endosperm becomes a nutritive tissue.

The mature ovary becomes the fruit, and its wall differentiates into the pericarp. The pericarp is further differentiated into three layers:

• Exocarp (outermost layer)
• Mesocarp (middle layer)
• Endocarp (innermost layer)

Meanwhile, other parts of the flower, such as the stamen, petals, and sepals, wither and fall off.

• Self-Fertilization occurs when gametes from the same plant are involved.
• Cross-Fertilization happens when gametes from different plants of the same species are involved.