Like bryophytes, pteridophytes reproduce in a cycle that has one sexual and one asexual phase. To describe breeding in pteridophytes, let us take as an example a commonly cultivated fern (Polypodium vulgare).
The fern is an asexual spore-producing plant. Therefore, it represents the phase called sporophyte.
At certain times, on the underside of the fern leaves dark spots called serums. The emergence of sera indicates that ferns are in breeding season - in each serum numerous spores are produced. When the spores mature, the serums open. Then the spores fall into the damp soil; each spore can germinate and give rise to a protalo, that little heart-shaped plant shown in the diagram. Protalo is a sexual plant that produces gametes; therefore, it represents the phase called gametophyte.
Ferns Reproductive Cycle
The fern prototal contains structures where anterozoids and oospheres form. Inside the protalo there is enough water for the anterozoid to move in liquid and "swim" toward the oosphere, fertilizing it. Then appears the zygote, which develops and forms the embryo. The embryo, in turn, develops and forms a new fern, that is, a new sporophyte. As adults, ferns form serums, starting a new breeding cycle.
As you can see, both bryophytes and pteridophytes depend on water for fertilization. But in the bryophytes, the gametophyte is the lasting phase and the sporophyte is the passing phase. In pteridophytes the opposite is true: the gametophyte is transient - it dies after gamete production and fertilization occurs - and the sporophyte is long lasting, as it remains alive after spore production.