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

The pollen wall is consisted of two layers the outer exine and inner intine. The exine is chiefly made up of sporopollenin, which is derived by the oxidative polymerization of carotenoids. Sporopollenin is one of the most resistant biological materials known. Exine is thin in begining but become very thick with maturity. During secondary growth in extrastelar region cork cambium or phellogen cells divide periclinally, cutting off cells towards the outside and inside. The cells cutoff towards outside become suberised and dead and form cork. Cork is impervious to water due to suberin and provides protection to underlying tissues.