The Rusty Backed Fern

(Ceterach officinarum)

by Brian Darnton, UK

Introduction

Objects for microscopic study are more numerous than we might imagine. It only requires a knowledge of which method of observation we should use, to convert some dull rusty looking object into an optical treasure house. The Rusty Backed Fern is one of those plants!

Collecting

It grows throughout the more sheltered areas of the British Isles and across Europe as far North as Holland. Similar species can also be found in Asia. Older books often list it as Asplenium ceterach. It enjoys the cracks between stones in the ruins of castles and old limestone walls where there is free drainage. Hold a clean sheet of paper under the leaves and scrape some scales from the underside of a leaf.

Mounting

The collecting paper can be folded , labelled and taken home where the scales can be sorted under a good hand lens or low power microscope. A rosette of 7 scales can be assembled on a blank slide in a weak dilution of Gum Tragacanth. Under a warm lamp the rosette can be dried out, a drop of Canada Balsam applied and a cover slip laid.

Observation

Under a X10 objective lens and a microscope equipped with two crossed polarising filters the reason for all the preparations will be revealed. The delicate framework of the scale glows as a reticulate pattern. When dried out and ringed, it should be labelled; including such information as where it was found and how it was prepared. A variety of ferns have interesting scales, but it is mostly those that are adapted for life in dry places that are the most fascinating. In the southern parts of the United States and in Mexico the Cloak fern (Astrolena sinuata) has fine scales and in the West Indies, Niphobolus has stalked whorls of minute scales like a microscopic moss.

Comments to the author Brian Darnton welcomed.

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Published in September 1998 Micscape Magazine.

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