But a blade of grass is not the same thing as tree trunk. It has to achieve as much
stability as possible with minimal material. Let’s have a look at a blade of grass
under the microscope.
Hollow Constructions
To study a blade of grass, you will need:
• a slide and a cover slip
• the pipette and water
• the tweezers
• a small piece of styrofoam, or carrot
• a bit of grass blade
Definitely read through the tips on cutting before getting started (see above).
Now, make several cuts cross-wise through the blade of grass and place them
into a drop of water. Observe the object under the microscope after you have
put the cover slip in place. At the lowest magnification (40x), you can first get
an overview of the entire cross-section. It is typical with most grasses for the
stem to be hollow inside. Around this so-called pith cavity are large cells with
thin cell walls. Such cells are often typical storage cells. By virtue of their thin
cell walls, they are quite sensitive. Some are sure to have been crushed by the
cutting. Located in these large cells are usually small agglomerations of smaller
cells: the vascular bundles. Here, you will notice several cells with a large diam-
eter. These are the water ducts that you were able to have a look at with the
watermelon (see “How Does Water Get into a Melon?”). This time, however,
they are cut cross-wise, so you can’t see the ring- or spiral-shaped pattern.
You will find other cross-cut vascular ducts among the smaller cells as well.
These do not transport water from the root to the rest of the plant, but rather
nutrients that are formed with the aid of the sun (see “Living in a Shoebox”).
The other cells in the vascular bundle have the task of stabilizing the ducts and
providing them with goods to transport. Finally, on the very outside, you will
find cells that are responsible for the unbelievable strength of the grass blade.
Directly under the outermost layer of cells — the epidermis — there are small
groups or even a closed ring of small cells with thick cell walls. Just like in the
water ducts, these are mostly dead cells whose sole purpose here is to stabilize
the long blade. So if you take another look at the cross-section as a whole,
you will notice that the blade achieves maximum stability with little effort
and while saving as much material as possible. It’s any engineer’s dream! It can
prove interesting to stain this particular specimen with a blue stain (see page
16). Look at the specimen under the microscope — you will notice that the
various types of cells have absorbed the color to varying degrees.
Cutting, Part 2 — The Styrofoam Trick
Producing a good microscopic preparation is truly an art in and of itself and re-
quires some practice. So here are some more tips and notes on common errors.
Many objects are too thick to look at in their entirety under the microscope.
At the same time, however, they are usually thin enough to yield to the razor
blade when cut. So here’s a tip:
Take a styrofoam cube (or a piece of carrot) and cut a slit into it from the
top. Then stick your object into it (a piece of a blade of grass, a leaf, a root,
etc.). When doing this, make sure that the object is straight in the styrofoam.
Now you can place the razor blade on the styrofoam (or the carrot) and pull
through the styrofoam and object (important: do not simply press the razor
blade through the object, since that will crush sensitive parts of the object and
make it unsightly). Always make several cuts while you’re at it and then place
several of them under the cover slip. By doing this, you will simply increase the
possibility of getting a good cut.
Here’s how to cut thin sections of leaves and
stems using styrofoam.
Although object A in the figure is cut nice and
straight, it is much too thick to be able to see
anything. Here’s the rule of thumb: If the cover
slip is lifted off of the slide, then the cut is too
thick. Make a thin cut and still can’t see any-
thing? That may be because you cut the object
on a slant. The object in example B is cut slanted.
This can be a very useful method for some
objects, especially very hard, lignified branches
or pieces of stem. On one side, the object is
definitely too thick. But on the other side, lots of
things may be visible. Finally, example C is the re-
sult when the object is crooked in the styrofoam.
In this case, even if thin sections are made, there
will generally not be much to see.
Section from the wall of a grass blade. The air-
filled pith cavity is visible on the right side.
40
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