Thames & Kosmos TK2 Scope, Experiment Manual

When You Have Itchy Fingers…

Preparing a nettle hair for viewing is not difficult. You will need: 

• a slide and a cover slip
• the pipette and water
• a razor blade (see page 11)
• the tweezers
• garden gloves or thin leather gloves
• a piece of the stalk of a stinging nettle

In order to avoid getting stung by the hairs while you’re trying to observe 
them under the microscope, it’s best that you wear garden gloves at first. The 
stinging hairs of the nettle can be seen readily with the naked eye on the 
stalk. Carefully cut off a few hairs from the base and transfer them to a drop 
of water on the slide. During preparation, a few hairs may break off on the 
base or at the tip. So use this tried-and-true method: Place several hairs under 
the cover slip at the same time, so you are more likely to have a perfect speci-
men in the bunch. Now observe your preparation at different magnifications 
and compare them with the image on the next page.

You can also make a quiz with your friends or family. Prepare lots of different 
objects ranging from cat hair to human hair, from artificial fibers to a couple 
of fibers from a cotton bag to plant hairs from leaves or fruits. Now, it’s up to 
the others to try to match the microscopic images of the hairs to the objects of 
their origin. If you’d like, you can even think up a mystery story involving your 
objects that the participants have to solve.

Plant Hairs

Even the invention of innumerable synthetic fibers for the clothing industry has 
not been able to replace cotton to this day. It currently comprises about 44% of 
the entire textile consumption in the world. Almost everyone wears this pure plant 
product every day. But have you ever given any thought to why the cotton plant 
forms its 6 inch-long fibers?

Plants have a wealth of strategies for distributing their descendants. The more 
widely the fruits and seeds can be spread, the higher the chance of populating a 
place that’s not already overgrown. The hairs of the cotton plant are seed hairs 
that serve as flight organs. So it’s the wind that ensures that the descendants of 
a cotton plant are scattered to the four winds — literally. Many plants propagate 
their seeds using the wind.

But plant hairs are capable of lots more. Many plants with white leaves have a 
thick fuzz on their surface made of dead hairs which reflect the light of the sun. In 
this way, those plants prevent their leaves from heating up too much.

Also, flesh-eating plants, such as the venus flytrap, have tactile hairs. When an 
insect touches one of these hairs, the trap falls shut.

Stinging nettles have especially ingeniously constructed hairs. The stinging hairs 
operate on a simple but clever principle. The hair is shaped like a pipette — and 
works like one too. On the lower part, the hair thickens to a bubble, gets thinner 
and thinner toward the top, and is finally topped off with a round little head at 
the tip. Directly underneath this head, the cell wall is particularly thin and, due to 
the deposition of certain substances, quite fragile. This location serves as a break-
ing point. When you come into contact with a nettle hair, the tip breaks off imme-
diately. Left behind is a sharp, hollow needle that can easily bore through the skin. 
What’s more, there is slight overpressure in the nettle hair before the tip is broken 
off, so the stinging and itchy contents are injected under the skin. So the stinging 
nettle has a great weapon against predators and others who would trample it.

Human hairs

Cotton fibers

Fruit capsule of a cotton plant with fringe hairs

Fruits of the dandelion

Venus flytrap — an insect-catching plant

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