Cytoplasm views from the Devonian: Observations on cells of Rhynia gwynne-vaughanii

Abstract

A light microscopy study of a vascular plant (Rhynia gwynne-vaughanii) of the Lower Devonian period fossilized in the Rhynie chert (NE Scotland), allowed for observations of uncompressed tissues, with minute cytological features, some of which have not been reported before in the literature. In a few cells of the outer cortical parenchyma a slightly shrunken cytoplasm was observed, stretched in thin strands, on which granules of around 1 μm are visible. The latter could represent mitochondria or lipid droplets. When the surface of the cytoplasm is focussed, granules of about 4 μm are visible, and these may be interpreted as chloroplasts. A dark rounded structure with fading contour, about 20 μm in diameter, was observed in the core of the cell and was interpreted as the nucleus. The cytological details suggest that both physical and chemical factors stopped the decaying process in these cells in a sudden and efficient way, and that a rapid silicification followed fixation. There was intense volcanic activity in the Rhynie region in the Lower Devonian era, and this included lightning and hot gaseous releases, both of which could have caused the death of the entire biological community, later fixed in the chert. The mechanism of preservation of biological structures is discussed in the light of the recently proposed role of lightning in the rapid fixation of plant tissues.

Key words:

• Chloroplast
• cytoplasm
• Devonian
• nucleus
• mitosis
• fern
• fossil plant cells
• Rhynia

Acknowledgements

The author is indebted to Prof N. Trewin (Aberdeen University, Department of Geology and Petroleum Geology) for the kind gift of the chert slabs and to an unknown referee for his precious comments. Thanks are also due to U. Sacchi (Stazione Zoologica A. Dorhn, Naples, Italy) and to Dr S. Fasulo (University of Messina) for help in making the images.