Exine structure of upper cretaceous normapolles grains from anthers (northeastern scania, Sweden)

Abstract

Different forms of Normapolles from four anthers, retrieved from fluvial sediments in southeastern Sweden, have been studied by photomicroscopy, scanning electron microscopy and transmission electron microscopy. The exines are extremely resistant to staining and chemical treatment, probably as a result of increased polymerization, due to heating under oxygen‐deficient conditions in a wildfire (in combination with processes during fossilization and long burial).

Substructurally, short straight or coiling structures and 10 nm wide sites, visible in transmission electron micrographs, are interpreted as fragments of helical strands constituting the bulk of the exine. Similar structures can be seen in scanning electron micrographs of pollen in chemically untreated anthers. Both scanning and transmission electron micrographs indicate that the 10 nm strands are formed by still smaller helical elements and that they may combine to form wider coiling structures.

The exine has two main layers‐tectum and solum‐separated by a thin layer of discrete components, thicker at the protruding apertures. The tectum is penetrated by radial canals of varying width, probably equivalent to the microchannels found in the pollen of extant plants. The solum is massive. An endexine, formed by stain‐resistant elongate constituents embedded in a readily contrasted matrix, has been observed in transmission electron micrographs.