Ferns are seedless vascular plants. Most of them are terrestrial where as some are epiphytes, xerophytes or hydrophytes. Some of the members are Salvinia, Azolla, Adiantum etc.
There is a regular alternation of generation between the sporophytic phase and gametophytic phase in the life cycle of ferns. The sporophytic generation is the prominent one. Sporophytic phase may produce spores on the spore producing structure called the sporangia on the under surface of the leaves. The spore represents the first cell of gametophytic generation. The spores are dehisced from the sporangia which get dispersed by wind. These spores under favorable conditions germinate and give rise to gametophytic plant body.
The gametophytic phase is represented by a green heart shaped structure called prothallus. Presence of chlorophylls helps to lead an independent life in certain ferns. The mature prothallus reproduces sexually by gametogenesis and syngamy. The ferns prothallus may be homosporous or heterosporous. In homosporous ferns only one type gametes are present where as in heterosporous ferns both the microspores and megaspores are formed. The microspores give rise to male gametophyte and the megaspores give rise to female gametophyte. The male sex organ is the antheridia and female sex organ is the archegonia. Antheridia give rise to a coiled, multiflagellate and free swimming antherozoids or sperm and the archegonia produces the egg. During fertilization the mature antherozoids are attracted towards the egg by certain chemicals secreted by the archegonia. Then the antherozoid fuses with the egg and forms the zygote. These diploid zygotes represent the first phase of sporophytic generations. The zygote on further division and differentiation produces the embryo which then transforms to young sporophytes which is the adult fern plant.
