Scanning electron microscope (SEM) image of the sporangia (spore sacs) of the "male fern". The sporangia are borne on the undersides of the leaf fronds in brown kidney- shaped structures known as sori. Each sporangium is a biconvex capsule in which the mature spores lie freely. As the mature sporangium dries, the tension in the walls of the annulus causes the sporangium to rupture, expelling the spores which are then distributed by the wind. The calibration bar is 20 um and the image was collected at a magnification of 2,280x.
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