THE ULTRASTRUCTURE OF PALEOZOIC FERN SPORES: I. BOTRYOPTERIS

The spores of four species of the Paleozoic filicalean fern Botryopteris are examined at the ultrastructural level. Spores of B. cratis, B. forensis, B. globosa, and an unnamed species from the Lower Pennsylvanian, are compared on the basis of sporoderm stratification and the presence or absence of a sculptine layer. The species examined differ widely as to the type of reproductive unit in which they are borne and include forms that range throughout the Pennsylvanian. In all species the exine is homogeneous, lacking cavities and lamellae. A thin nexine is present in the Middle and Upper Pennsylvanian taxa, but is absent in the Lower Pennsylvanian spores. Only one spore type (B. cratis) possesses a clearly defined sculptine layer. Features of the sporoderm are compared with those of extant, homosporous pteridophyte spores.