Nuclear Migration and Asymmetric Cell Division in Onoclea Sensibilis Spores: An Ultrastructural and Cytochemical Study

A method of preparation for electron microscopy of fern spores in early stages of germination is presented. The cytochemistry and fine structure of Onoclea spores during the early stages of germination are described. The cytoplasm of the hydrated spore is filled with lipid droplets, protein granules and chloroplasts. During the early stages of development ribosomes and mitochondria increase in the area surrounding the central nucleus, and a new peripheral wall forms around the protoplast. Microtubules and large, branching mitochondria are associated with the nucleus during migration from its original central position in the spore to the proximal face and then to one end of the spore. There is no morphological polarization of cytoplasmic organelles of the spore before migration of the nucleus.