Fluorescence micrograph of moss (Pogonatum nanum) sporangium. The sporangium is the final stage of moss sporophyte development. Spores are produced as a result of meiotic divisions of archesporial tissue inside the moss capsule. Members of the family Polytrichaceae, including Pogonatum, have capsules equipped with a single ring of U-shaped cells (peristome) that are sensitive to humidity. Peristome cells help in the opening of the sporangium for spore release. Every single haploid spore can germinate into a protonema and start moss gametophyte generation. Observed in ultraviolet (UV) light. Magnification: x200 when printed at 10 x 10 cm.