Microscopy and Microanalysis

Biological Applications

Scanning Electron Microscopy and Synchrotron Radiation X-Ray Tomographic Microscopy of 330 Million Year Old Charcoalified Seed Fern Fertile Organs

Andrew C. Scotta1 c1, Jean Galtiera2, Neil J. Gostlinga3a7, Selena Y. Smitha1 p1, Margaret E. Collinsona1, Marco Stampanonia4a5, Federica Maronea4, Philip C.J. Donoghuea3 and Stefan Bengtsona6

a1 Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK

a2 CIRAD AMAP TA 40/PS2, Bl. de la Lironde, F-34398 Montpellier cedex 5, France

a3 Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, UK

a4 Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen, Switzerland

a5 Institute for Biomedical Engineering, University and ETH Zurich, 8092 Zurich, Switzerland

a6 Department of Palaeozoology, Swedish Museum of Natural History, Box 50007, SE-104 05 Stockholm, Sweden

a7 Department of Biological Sciences, SUNY, Oswego, NY 13126, USA

Abstract

Abundant charcoalified seed fern (pteridosperm) pollen organs and ovules have been recovered from Late Viséan (Mississippian 330 Ma) limestones from Kingswood, Fife, Scotland. To overcome limitations of data collection from these tiny, sometimes unique, fossils, we have combined low vacuum scanning electron microscopy on uncoated specimens with backscatter detector and synchrotron radiation X-ray tomographic microscopy utilizing the Materials Science and TOMCAT beamlines at the Swiss Light Source of the Paul Scherrer Institut. In combination these techniques improve upon traditional cellulose acetate peel sectioning because they enable study of external morphology and internal anatomy in multiple planes of section on a single specimen that is retained intact. The pollen organ Melissiotheca shows a basal parenchymatous cushion bearing more than 100 sporangia on the distal face. Digital sections show the occurrence of pollen in some sporangia. The described ovule is new and has eight integumentary lobes that are covered in spirally arranged glandular hairs. Virtual longitudinal sections reveal the lobes are free above the pollen chamber. Results are applied in taxonomy and will subsequently contribute to our understanding of the former diversity and evolution of ovules, seeds, and pollen organs in the seed ferns, the first seed-bearing plants to conquer the land.

(Received May 16 2008)

(Accepted December 05 2008)

Correspondence:

c1 Corresponding author. E-mail: a.scott@es.rhul.ac.uk

p1 Current address: Museum of Paleontology, University of Michigan, 1109 Geddes Road, Ann Arbor, MI 48109-1079, USA