Fertilization in Plants
· Pollen grains reach the right stigma and begin to germinate.
· Pollen grain forms a small tube-like structure called pollen tube which emerges through the germ pore. The contents of the pollen grain move into the tube.
· Pollen tube grows through the tissues of the stigma and style and finally reaches the ovule through the micropyle.
· Vegetative cell degenerates and the generative cell divides to form two sperms (or male gametes).
· Tip of pollen tube bursts and the two sperms enter the embryo sac.
· One sperm fuses with the egg (syngamy) and forms a diploid zygote. The other sperm fuses with the secondary nucleus (Triple fusion) to form the primary endosperm nucleus which is triploid in nature. Since two types of fusion syngamy and triple fusion take place in an embryo sac the process is termed as double fertilization.
· After triple fusion, primary endosperm nucleus develops into an endosperm.
· Endosperm provides food to the developing embryo.
· Later the synergids and antipodal cells degenerate.
(i) It stimulates the ovary to develop into fruit.
(ii) It helps in development of new characters from two different individuals.
1. The ovule develops into a seed.
2. The integuments of the ovule develop into the seed coat.
3. The ovary enlarges and develops into a fruit.
The seed contains the future plant or embryo which develops into a seedling under appropriate conditions.