Pollen form two sperm cells. The sperm cells are carried to their destination in the tip of the pollen tube. Double-strand breaks in DNA that arise during pollen tube growth appear to be efficiently repaired in the generative cell that carries the male genomic information to be passed on to the next plant generation. However, the vegetative cell that is responsible for tube elongation appears to lack this DNA repair capability. Pollen's sporopollenin outer sheath affords it some resistance to the rigours of the fossilisation process that destroy weaker objects; it is also produced in huge quantities. There is an extensive
Hilum (biology) such a mark, and can be used as a distinguishing characteristic of a seed or spore. Hilum (biology) In botany, a hilum (pronounced ) is a scar or mark left on a seed coat by the former attachment to the ovary wall or to the funiculus (which in turn attaches to the ovary wall). On a bean seed, the hilum is called the "eye". For some species of fungus, the hilum is the microscopic indentation left on a spore when it separates from the sterigma of the basidium. A hilum can also be a nucleus of a starch grain; the