A Root in Cross-Section
You will need:
• bean seeds (e.g. broad beans or scarlet runners)
• an empty margarine tub or the like
• cotton wool or paper towels
• a slide and a cover slip
• the pipette and water
• a razor blade (see page 11)
• the tweezers
Place a layer of cotton wool (paper towels work fine if none is available) into
the empty margarine tub or another plant container and wet it well with
water. Lay a few bean seeds on top with some spacing. Then place the tub in
a windowsill. You should make sure that the cotton is always sufficiently wet,
but the beans should not be swimming in water. After a few days, a few of
the beans will begin to germinate. Give the young plants another two or three
days’ time to develop and then take the roots of the several-days-old seedlings
to study.
Cut the root down the middle using the razor blade. Use the thicker upper
portion of the root to make thin sections for the microscope. Since the young
root is still very soft, it may be quite difficult to place into your cutting aid (see
page 38). In that case, you can also simply use the “cutting board method.” To
do this, place the piece of root onto a slide, hold it in place using the tweezers,
and cut as thin pieces as possible from the root — just like cutting a cucum-
ber. Add a drop of water to the cuttings, and the root cross-section is ready.
In cross-section, you see a thick layer made of large, thin-walled cells on the
outside of the root. In the center of the root, you will find the other types of
cells composing the vascular tissue.
Anchorage in the Ground
Even the greatest of bending strength won’t do the blade of grass any good if its
anchorage in the ground doesn’t hold. Whether the base of a tower or the roots
of a plant, extreme reliability is a must. It’s apparently most favorable to change
the construction principle in comparison to the stem, since the stabilization tissue
of a root, which also serves as a vascular duct, is not wrapped around the rest of
the root as a sheath, but rather as a central strand in the middle of the root — like
a steel cable with a sheath!
Crazy Surfaces
How does a surface have to look so that as little fine dust and other contaminants
stick to it as little as possible? If you think about highly polished car bodies shining
and glistening in the sun, you’d probably say that the surfaces would have to be
especially smooth. Not so! Surely you’ve seen how cars are dustier after a down-
pour than they were before — and without moving an inch. This is because the
rain washes the fine dust out of the air and leaves it behind on the cars. Whereas
the rain water flows off of the car, the dirt sticks. It’s no coincidence that car
washes are equipped with all sorts of brushes.
Just imagine the surprise of the people who discovered of the now-famous “lotus
effect” when they found that the self-cleaning leaves of the lotus plant have an
extremely rough surface. Like the leaves of almost all plants, the rough surface
is covered with a layer of wax. So water drops are not able to wet the surface of
a leaf any more than your skin right after you’ve rubbed sun-tanning oil onto it.
As they roll down the leaf, the water drops take the dirt that has collected on the
leaf along with them.
Cross-section through a bean root
Cross-section through a sunflower
The lotus flower, which originated in Asia, looks
similar to a water lily.
On the surface of the lotus plant, water drops
bead and roll off, taking all of the particles of
dust and dirt with them (the lotus effect). This is
similar to a water lily.
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