Describe the structure of pollen grain and explain the development of male gametophyte in it.

The pollen grains represent the male gametophytes that is located in microspores.

By touching the opened anthers of Hibiscus or any other flower, deposition of yellowish powdery pollen grains are found on fingers. Sprinkling these grains on a drop of water taken on a glass slide and observing under a microscopes, variety of architecture sizes, shapes, colours, designs are seen on the pollen grains from different species.

Scanning electron micrographs

of a few pollen grains

Structure of Pollen grains : Pollen grains are generally spherical measuring about $25-50$ micrometers in diameter.

It has a prominent two layered wall. The hard outer layer called the exine is made up of sporopollenin which is one of the most resistant organic material.

It can withstand high temperatures and strong acids and alkali. No enzyme that degrades

- Pollen grain exine has prominent apertures called germ pores. Where sporopollenin is absent. $\Rightarrow$ Pollen grains are well preserved as fossils because of the presence of sporopollenin.