Leafy landscapes under the microscope

By Michael R. Gibson

One simple technique that can be used to obtain a leaf peel involves applying quick-drying, clear nail varnish to a small area of leaf epidermis and, when dry, removing the peel with ordinary Sellotape. Both peel and transparent tape is then transferred to a microscope slide and labelled before observation.

In the March edition of infocus magazine my article “Microscopy in the Third Age”, included passing reference to this method for examining leaf surface features under the microscope, and here I want to go further by illustrating some more of the results obtained with a variety of leaves and lighting techniques.

To begin with, there are many standard slide preparations of stained epidermal sections taken from leaves as illustrated in figures 1, 2 and 3 which show the detailed internal structure of the epidermal cells and, in particular, the stomata. These are characterised by the bean-shaped guard cells that surround each slit-like opening or pore and which play an important part in controlling gas exchange, specifically water vapour during transpiration, and oxygen and carbon dioxide involved in photosynthesis. However, what many of these slides do not show are the actual surface contours that form part of what I have tried to depict in these photographs as the “leafy landscape”.

In looking at acetate leaf peels through the microscope we are in effect obtaining a topographical impression or “print” of the leaf’s actual surface features. As always, it’s important toset up the microscope correctly beforehand and inparticular, one of the most important adjustmentsthat needs to be made is controlling the substagecondenser aperture with the iris diaphragm.Closing the aperture increases contrast but closingthe aperture too much will degrade the image dueto loss of resolution. In most cases, however, asatisfactory image can be obtained by limiting straylight and closing the aperture by no more than athird of the way in. These effects can be checkedvisually by first removing the eyepiece and lookingdirectly down the microscope tube while at thesame time adjusting the aperture lever.

Most of the following images were photographedusing a combination of Rheinberg coloured filtersand oblique (offset) illumination techniquesobtained with a phase condenser on a Swiss WildM20 research microscope coupled to an electronic5 megapixel USB photo eyepiece attached to my computer.

All the images were taken using the Wild M20 microscope with either a x10 or x20 phase objective. The field width (FOV) is approximately 1.8 mm and 0.9mm when using x10 and x20 phase objectives respectively.

Stomata – darkfield image

Tradescantia epidermis

Aloe voigtii epidermis

Bindweed lower epidermal peel

Bindweed peel

Hedera helix (Ivy)

Hedera helix

Hedera helix

Tulip leaf

Laurel leaf

Lily leaf acetate peel

Acetate leaf peel fixed to slide

Michael is a retired teacher and remains an active member of various microscopical clubs and societies including the RMS. He works with schools, museums and libraries in promoting microscopy and other science-related activities. One of his favourite quotes, attributed to Charles Darwin, is “I love fools’ experiments - I am always making them”!