A nature walk for the microscopist presents more of a challenge at this time of year, with a few inches to a few feet of snow on the ground with little evidence of Spring yet. But if you look closely there's still plenty of colour and variety in the miniature world around us.
This month is hopefully a bit easier going after the introduction to the structure and identification of mosses last month!
Before you put your boots on, please read the important notes on collecting.
"It has been a bitterly cold night, and as the sun shines on a clear keen morning, and glistens in the hoar frost which covers the trees, it might seem an unpropitious time for visiting ponds, in search of microscopic prey."
So wrote H J Slack in his delightful book 'Marvels of Pond Life' in 1891. He wrote a chapter for each month on what to find in a pond. The present author agrees with Mr Slack so why not investigate your roof gutter instead for water bears! A rather stylised drawing of a water bear from an old textbook is shown on the right.
Finding the bears: What you should look for either in the gutter, shed roof or in damp areas of the garden, is the 'pin-cushion' like clumps of mosses. These often contain a fascinating variety of microscopic life, including water bears.
Transfer some of the moss clumps to a dish containing some rainwater and allow the mosses to soak thoroughly overnight, especially if the moss is dry.
Then hold the moss over a petri dish and squeeze out the water very firmly from the moss. Study the water under a stereo microscope and hopefully you should notice one or more of the following.
- nematodes (roundworms): these are tiny worms
- rotifers: the commonest probably move in a leech-like manner and were described in the January walk.
- water bears (tardigrades): these do in fact look like bears with four pairs of legs and move in a lumbering fashion.
To study under a high power microscope, transfer a water bear to a microscope slide with a little water and cover with a cover glass supported on a little vaseline to avoid crushing. A water bear is illustrated on the left. They are delightful creatures to study under a microscope. Water bears are more accurately referred to as tardigrades, which are a class of organisms containing about 350 species. They are usually 1mm or less in size.
They live in various habitats including damp moss, sand, freshwater and seawater. They have a well-developed head, and four fused body segments each bearing a pair of limbs which often have sharp claws. Most tardigrades eat plants, and feed by piercing plant cells with their stylets (spearlike structures near the mouth).
The most remarkable feature of tardigrades is their ability to withstand drying up and very low temperatures. Hence the reason why you can revive them from the driest piece of moss. When living conditions become unfavourable they go into a state of suspended animation. Specimens have been kept by scientists for over a year in liquid air (-190degC) and they have been successfully revived.
An unassuming but remarkable organism!
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No heavy botany this month! Just a picture gallery to illustrate the shapes, colours and textures that can be found in your garden or surrounding countryside. All the images below can be seen with a 10x hand lens. So get out there with a lens and start looking at the world around you in close-up!
This surreal-looking landscape is simply insect damage to a variegated holly leaf. Wonderful colours and textures are all around us if you look closely enough.
This is the underside of a bramble (Rubus) leaf showing the raised network of leaf veins and attack possibly by a microfungi.
This colourful track is made by a leaf miner, an insect larva of one of a number of insect groups which feed inside the leaf.
Thorns and prickles on leaf edges and ribs are worth studying. This is a prickle on the edge of a holly (Ilex) leaf.
This thorn is on the midrib of a bramble leaf (underside).
The leaf edge of a bramble leaf.
This network of lines is the underside of a dried ornamental grass leaf, with oblique top lighting to show the fine ribbing more clearly.
Dead seed and flower heads are worth studying. This is a sepal-like bract from the seed head of a knapweed (Centaurea).
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Natural History Book Services A comprehensive on-line service with search facilities.
An excellent book with superb illustrations showing every
facet of microscopic life is:
'Microcosmos' by J. Burgess, M. Marten, R. Taylor. Cambridge University Press, UK, 1987. ISBN 0 521 30433 4.
An excellent introduction with further reading can be found in:
'An Introduction to the Study of Tardigrades' by P Greaves. Microscopy, 1989, vol 36, p230-239. Microscopy is the Journal of the Quekett Microscopical Club.
Tardigrade drawing from "Microscopic Freshwater
Life" by FJW Plaskitt, 1926. All other images by the author.
Fractal leaf created using Fractal Vision v2.5 by Dick Oliver, Cedar Software.
Tardigrade image captured from the still frame of a VHS video. Plant images were taken using a CCD camera attached to the eyepiece tube of a stereo microscope using a x1 paired objective with no eyepiece. Camera images were transferred to the PC using a Creative Video Spigot capture card.
Image manipulation using Photostyler v2.0 software.
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