PAN XUNBIN / SCIENCE PHOTO LIBRARY PAN XUNBIN / SCIENCE PHOTO LIBRARY
Fern prothallus, light micrograph. This structure (also called the prothallium) is the gametophyte stage in the life of a fern or other pteridophyte. It forms part of a life cycle known as alternation of generations and is the haploid stage of life of a sexually reproducing plant. The corresponding stage is the sporophyte, which develops from the prothallus following sexual reproduction. The prothallus in turn develops from spores produced by the sporophyte stage.
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