The underside of a fern leaf. The numerous brown structures are sori each of which consists of many sporangia. Mother cells within the sporangia undergo meiosis to produce spores which are released when the sporangia dry out and split open. In conditions of continuous dampness a spore will germinate on the ground and form a haploid gametophyte. This structure develops archegonia containing ova and antheridia which produce motile spermatozoids. Although the gametophyte possesses organs of both sexes, cross-fertilisation often occurs resulting in a new fern plant, the sporophyte.