The stage of plant life cycle in which gametes i.e. sperm and egg are produced is called gametophytic stage. In sporophyte plants, spores are produced inside the sporangium. The spore is the first cell of the gametophyte stage. Spores germinate in favorable environment to form 4-6 celled protonema. Cells on either side of the protonema divide repeatedly in the process of mitosis to form a green heart-shaped prothallus. Pteris is a companion plant. Flax-shaped archegonia below the anterior groove and spherical or ovoid antheridia below the thallus. Each archegonium produces one ovule and 20-50 spermatozoa in the antheridium. Sperm and egg unite to form a zygote. The gametophyte stage ends with the formation of the zygote.
