A.J. Botha

Iridescent colors on seashells: an optical and structural investigation of Helcion pruinosus

Many animal species display exceptionally bright iridescent coloration caused by interference or diffraction from a periodic surface microstructure. Although many mollusks are colored, only few utilize such a form of structural coloration. We are not referring to the well-known pearly appearance that is due to the nacreous layer found on the inner surfaces of most shells, but to small brightly colored spots on the outer surface. The Helcion pruinosus is one such example. We show by optical measurements and scanning electron microscopy (SEM) that coloration in this shell is indeed of a structural nature based on thin-film interference from a layered quarter-wave stack tilted by approximately 24 degrees with respect to the outer surface. The microstructure is embedded in the transparent top layer of the shell approximately 50 microm below the surface. By comparing the SEM and optical measurements, we were able to establish that the layered structure is made from a birefringent material (crystalline aragonite) giving slightly different spectral peaks for S- and P-type reflections.

Phloeospora irregularis associated with lesions on Rhus pendulina

Phloeospora irregularis is reported as an obligate parasite of Rhus pendulina from the Pretoria region, Transvaal, South Africa. The morphology was studied with light microscopy, SEM and TEM. A Phoma sp. is described as synanamorph. Variations in fungal morphology from that reported previously are described.

A HR-SEM Investigation of the Microstructure of PBMR Test Fuel Particles

There is currently renewed interest in high temperature nuclear fission power reactors. The Pebble Bed Modular Reactor (PBMR) is one of several high temperature gas-cooled reactors being investigated by researchers. The South African design of the PBMR is based on the original German design, with the fuel particles (called TRISO particles) being small multilayer spheres.Copyright

Distinct basidiospore development in Tricholosporum laeteviolaceum

The genus Tricholosporum is characterised by cruciate spores. The formation of these basidiospores and their subsequent growth until release from the sterigmata, is described from a sequence of SEM photographs. The spores on a basidium form either a diad, a triad or a tetrad during their development. The outer cell wall layer of the basidiospore enlarges, resulting in the cruciate shape of the spores and the ultimate calyptrate appearance after release when desiccated. The spores are seceded sequentially.