Question

explain the process of germination of pollens ? explain with help of diagrams

Answer 1

The Pollen Grain-

-> The mature pollen grain is a cell with a double wall- The outer exine and the inner intine. Its nucleus has already divided into a tube nucleus and a generative (male) nucleus. At this stage, the pollen is transferred to stigma (pollination). Further changes in pollen grain occur only if it has fallen on the stigma of a plant of the same species.

☆ Through a point in the exine, a pollen tube grows out of the pollen grain, carrying at its tip the generative nucleus and the tube nucleus.

☆ Generative nucleus divides into two nuclei called sperm nuclei.

☆ The tube nucleus directs the growth of pollen tube. It pushes through the micropyle and reached the embryo sac. It then disintegrates.

☆ One sperm nucleus from the pollen tube unites with the secondary nucleus to form endosperm cell [two polar nuclei+ one sperm nucleus= 3 nuclei]

☆ The other sperm nucleus enters the egg cell through the assistance of the synergids, which then degenerate, and unites with its nucleus. This is double fertilisation.

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