An Introduction To The Polariscope and Fern Scales.

Text By B Darnton (UK)


The Introduction.

When the Victorians discovered the aesthetic and scientific potential of the polariscope, there was an even greater flurry of activity in the already hectic world of natural history at that time.

Coloured images eventually reflected the glories to be beholden and Nichol prisms were added to the box of microscopist`s accessories. The Victorian world was soon to become familiar with the beautiful radial crystals of Salicine (ref. A), thin sections of echinoderm spines and the incredible dynamic radulae of the slugs and snails. Their enhancement by slithers of Selenite added to the glitter, and the rotary stage enabled the effect to be compared with, if not surpass, the kaleidoscope itself.

More than a hundred and fifty years on, we are left with the remnants of great collections that have survived the age and several wars. Some years ago it was evident that the more spectacular and showy slides like those mentioned, were still to be found in dingy attics and unused garages but among the treasures were other objects less numerous, no doubt for the more discriminating!

Ferns had been already sectioned and the stages of development conserved, but at a certain time the scales of fronds, rhizomes and stems had been specifically identified for use with the polariscope by a number of mounters and some of these examples still survive. Whole chapters in contemporary books such as Carpenter (ref. B) and Hogg (ref. C) delved into the wonders of the polariscope and suggested suitable methods of viewing and outlined methods of mounting. M.C.Cook (ref. D) in his illustrated "One Thousand Objects for The Microscope" of 1869 illustrates three fern scales of merit: "The Rusty Backed Fern"(Ceterach) from Europe, Nothochlaena laevis from the USA and Niphobolus from the West Indies. When working with Victorian microscopy slides, names become a problem because of the "Synonym syndrome". Just as diatoms collect a little list of alternative generic and even specific names, so the fern family suffers the same problems as progress and better instruments decree that the old names are no longer valid.

Edmund Wheeler`s slide, (illustrated left above) is still as good as new and I have seen at least two excellent examples recently (ref. E). Elaphoglossum squamosum came from the warmth of Central America but the 700 species are fairly ubiquitous in tropical climes.

Wheeler's work was known from 1866 when he was given his first award, until 1885 when he died. During his lifetime large numbers of ferns were being brought into the country for ornamental and decorative purposes by the trading ships and the official expeditions, but only some of these were embellished by delicate scales worthy of mounting.

The rather artificial rosette became the standard and obvious configuration for display (ref. E). Often the empty central area was filled with smaller stellate scales too short to be included in the rosette. The spiny scales appear as florets against the jet black background of the crossed polar field.

The second slide (above right) illustrates the scales from the West Indian Fern Niphobolus hastatus. They were actually strewn by Charles Bailey to good effect. He is known to have been a contributor to "Science Gossip" and published articles on botany, in the journal of the Manchester Literary and Philosophical Society in the late 1860`s.

Practical Notes on mounting.

Leaf scales seem to be far more ornamental than those that protect rhizomes but these must not be ignored. In the United Kingdom the rhizomes of polypody have scales that are quite decorative but rather large. Only the European rustyback fern (Ceterach officinarum) found on limestone walls have leaf scales from the British flora. Amongst the pot plant ferns Cyrtomium taccatum has splendid rhizome scales but they tend to be a little too long. Really and truly the whole field of fern scales is a subject waiting to be explored.

Scales are best scraped from the under sides of the fronds onto a little Petri dish and selected for mounting. They are laid on a 3x1 inch slide with a small sable brush in a weak solution of gum tragacanth and allowed to thoroughly dry out. Two drops of Canada Balsam and a coverslip complete the work which only needs to be dried out, cleaned, ringed and labelled. For photographic work a museum slide of separate scales in rows is a useful asset.

Comments to the author, Brian Darnton, are welcomed.


A# Bracegirdle's "Microscopical Mounts and Mounters" 1998.

ISBN 0-9514441-3-1

B# W.B. Carpenter. "The Microscope and its Revelations" Published by

J Churchill. 1868 4th edition.

C# Jabez Hogg "The Microscope." Published by Routledge 8th edition 1867.

D# M.C.Cook "One Thousand Objects for The Microscope" 1869.

E# New York Botanic Garden have a serious specialism in ferns and in the genus Elaphoglossum in particular. New York Botanic Garden Who
F# The British Pteridological Society not only gives a good introduction to the Fern World but it also hosts a number of links to relevent societies and organisations.
British Pteridological Society Fern World

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