The New Student's Reference Work/Prothallium

Prothallium (prō̇-thăl′lĭ-ŭm), among plants, is a name applied in a general way to the gametophytes of Pteridophytes and Spermatophytes. It specially belongs, however, to the ferns, in which the prothallium, often written prothallus, is a quite distinct but very small green and notched thallus. Upon the under side of this small body the antheridia and archegonia occur. From the fertilized egg within the archegonium the ordinary leafy fern-plant arises. When in other plant-groups the prothallium ceases to be independent, as in seed-plants, it often retains the name. For example, many would speak of the female gametophyte (endosperm) found in seeds as a female prothallium. See Gametophyte.