In ferns, as well as in mosses, the alternation of sexual and asexual generations is clearly represented.
In summer, small brown tubercles form on the underside of the fern. The tubercles contain bundles of small sacs – sporangia, in which spores mature.
Ripe spores drop out of the sporangia. The wind blows them. If they get into favorable conditions, they germinate, forming an outgrowth (sexual generation – gametophyte). It lives independently, attaching itself to the soil by rhizoids.
On the underside of the outgrowth, male and female gametes (sperm and eggs) develop. Drops of dew or rainwater linger under the overgrowth, in which sperm can swim to the eggs. Fertilization occurs.
An embryo develops from the zygote, which first receives nutrients from the green growth. It grows and gradually develops a root and a very short stem with the first leaf. Over time, an adult plant, which we usually call a fern, develops from the embryo on the shoot. This asexual generation is a sporophyte.
During the life of a fern, two generations change – sporophyte and gametophyte.
An adult spore-forming fern plant is a sporophyte (asexual generation).
The fern germ is a gametophyte (sexual generation).
Many ferns reproduce well vegetatively, for example using rhizomes or brood buds.
Reproduction also occurs in horsetails and lyre.