Ar'chego'nium. The female organ of certain groups of plants, namely, the Bryophytes (mosses, etc.), the Pteridophytes (ferns, etc.), and the gymnosperms (pines, etc.). In general it is a flask-shaped structure. In the bulbous part of the flask the solitary egg is developed; while through the open and often elongated neck the sperms pass for fertilization. So characteristic is this organ that the three groups which possess it are often classed together under the name Archegoniates.
