Leaf hair Photograph by electron microscope

17th November 2000 at 00:00
Would you give house-room to this hideous horned devil? Could you sleep at night knowing that its alien features haunt your conservatory? The chances are that you already do.

For what we have here is nothing more alarming than a leaf from a common pelargonium, as viewed by a scanning electron microscope.

See those vicious horns? They are the tiny thorns that make the surface of the pelargonium rougher to the touch than a cat's tongue.

Those projections with bulbous heads might look like deadly toadstools, but in fact they are microscopic gland hairs that produce the aromatic oil that deters insects but which is part of the plant's attraction to humans who like the zingy fragrance.

As for the beast's dark, staring eyes, they are simply holes - small openings called stomata, which regulate gas exchange between the leaf's interior and the surrounding atmosphere.

And how small is small? How tiny is minuscule? That's easy to demonstrate. Simply take this picture to a photocopier and copy it at 50 per cent of its original size. When you have your half-size copy, run that through the machine at 50 per cent to produce a quarter-size version. Keep doing this until the picture is a mere dot, then do it again and again and again. Before long, the machine will give up and your dot will completely disappear.

Carry on copying, though, for this is a purely theoretical exercise, a way of demonstrating just how small this little devil really is. To get your imaginary dot down to its actual size, you will need to run the picture through the copier 240 times, and use half a pack of paper in the process.

Of course the fact that it's a small world down there in leafland doesn't mean that it's ny less real. Things happen. Creatures live and die. They wander among those thorns. They even go to the toilet.

Or they would if they had mains drainage. Unfortunately they don't, which is why the excreta of the mites that live on the flakes of dead skin that litter our homes always manages to get up our noses, triggering asthma attacks in those with over-sensitive immune systems.

In the tiny world of the invisible dot, even parasites have parasites. The flea that lives on the dog has a mite living in its digestive tract, and it is by way of this mite that disease is transmitted from mammal to mammal.

Are we fortunate in having senses so crude that we cannot peer unaided into this nether region? Quite possibly, for how would we enjoy the pelargonium if we could see the vile forms that erupt from its flesh and witness the popping of bloated gland hairs as we run our finger gently over its surface?

Better, perhaps, not to see. And certainly better not to know what nightmare images would appear should we inadvertently turn the microscope in the direction of the hand that strokes the leaf - and see ourselves through the eyes of a mite.

Web links Dive into the world of the scanning electron microscope at http:www.mos.orgslnsemintro. html, courtesy of the Museum of Science, Boston. This site includes teacher resources, an image gallery and a history of the device.

Nano-organisms are so small that many scientists wonder if they are seeing things. You can decide for yourself at http:www.uq.oz.aunanoworld nanohome.html To find out how your class can have remote access, via the internet, to a real scanning electron microscope, visit http:bugscope.beckman.uiuc.edu

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