Those brown dots are called spore sacks. Ferns use these to spread spores, which if a spore lands in a moist spot it will begin to germinate.
This is in stark contrast to the way most plants, especially the “higher plants,” reproduce. These plants use seeds to reproduce. Commonly seed producing plants are placed into two categories. Angiosperma, meaning a seed in a vessel. ( Greek: angio-vessel, sperma-seed.) Gymnosperm meaning a “naked” seed. (Greek: gymno-naked, sperma-seed.)
