Comparative data on spermatogenesis spanning a range of pteridophytes will be collected. Emphasis will be placed on elucidating the ultrastructural details of spermiogenesis and the fine structure of the mature sperm cell. The role of three cytoskeletal elements - microtubules, actin and centrin - in the differentiation process will be evaluated by fluorescent labelling and immunogold-localization. These data will be compared with data already available on the bryophytes. Both taxa of spermatophytes that have flagellated sperm and two species of charaphytes will also be examined. The bryophytes, algae, and seed plants will be used as outgroups in a cladistic analysis of the data. The purpose of this study is resolve phylogenetic relationships among early pteridophytes and between them and the algal, bryophyte and seed plant lineages. The major dichotomies in early diversification of archegoniate groups remain as speculative today as they did before the advent of biological electron microscopy. This study should enable the resolution of early lines of diversification from the green algae to the major extant groups of land plants.
