Article: Early Devonian plant fossils from a southern England borehole
Vegetative specimens of the psilopsid Sawdonia ornata and sporangia of Dawsonites arcuatus are described from borehole cores of Emsian age from Oxfordshire. The material has been investigated by hydrofluoric acid maceration, examination by SEM of plant surfaces and latex replicas, and light microscopy of oxidized cuticles and polished rock surfaces. The spines of Sawdonia have become flattened in a vertical plane as a result of compression phenomena; the stomata were sunken. The processes of compression and collapse of plant tissue are evidently a function of the scale of the organs concerned, and so operate differently in axes, spines, and stomata of Sawdonia. The Dawsonites sporangia are in pairs with opposed longitudinal dehiscence slits and spiralized mechanical tissue in the wall. Spores found adhering to sporangial fragments are of Apiculiretusispora type.