What is Heterospory, pollen, ovule?

Mosses and most ferns are homosporous: one kind of spore, one kind of gametophyte bearing both sexes. Seed plants (and a few ferns and clubmosses) are heterosporous: microspores, small and many, grow into male gametophytes; megaspores, large and few, into female ones. In seed plants both are reduced to almost nothing and neither leaves the sporophyte’s tissues on its own. The male gametophyte is the pollen grain: a microspore that has divided two or three times inside its wall, carried by wind or animals to the female organ, where it grows a pollen tube and delivers its sperm — no water needed. The female gametophyte develops inside the megasporangium, which stays on the parent enclosed in one or two integuments with a pore, the micropyle: the whole structure is the ovule. After fertilisation the ovule becomes the seed: an embryo sporophyte, a store of food, and a coat made from the integuments, dormant until conditions are right.