The prothallus is the fern gametophyte. It is a green, photosynthetic structure that is one cell thick, usually heart or kidney shaped, 3–10 mm long and 2–8 mm broad. It is very difficult to find in the bush as it is so tiny. It doesn’t have roots, stems or leaves but it does have rhizoids that anchor it to the soil and help with absorption. The underside of the prothallus is where the gametes are produced from the male and female sex organs. The prothallus has both male and female sex organs.
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