Spore Germination and Early Gametophyte Development in Anemia mexicana Klotzsch

Abstract

Spore germination and early gametophyte development in the fern Anemia mexicana Klotzsch are described, using scanning electron microscopy of intact plants and light microscopy (LM) of sectioned germinating spores and young gametophytes. The combination of these techniques gives a clearer interpretation of fern spore germination and development than either used alone. Germinating spores rupture along the triradiate mark, and the rhizoid and protonemal cells protrude. The LM observations of serial sections of germinating spores show that the spore cell undergoes two successive asymmetric cell divisions: the first cell differentiates into a rhizoid; the second cell division yields the protonemal cell, which divides again to form the prothallus. As the rhizoid elongates, its nucleus migrates from the base to a central position in the cell at maturity. The spore cell may undergo a third asymmetric cell division, forming a small cell that remains almost entirely within the spore coat. The two-dimensional proth...