Botany - Sexual Reproduction in Flowering Plants Question with Solution | TestHub

Pollen grains are generally spherical, measuring about 25–50 micrometers in diameter. They have 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 known. It can withstand high temperatures and strong acids and alkali. No enzyme that degrades sporopollenin is known to date.