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Figure 5
Cross section of a polyporoid layer.
dry the layers of polyporoid under a
press to prevent them from warping.
Experiment 1. As a first step, let,s
find the density of the pores-that
is, the number of pores per unit area
in a layer of a polyporoid. Then we'll
try to measure the diameterD of the
pores. These tasks are rather easy to
do with a microscope, but you can
still do them without one. We'lluse
an ordinary photographic enlarger or
film projector. With a sharp knife or
razorblade cut off a thin section of
the fruit of a polyporoid, which
should be oriented perpendicular to
the pores-that is, parallel to the
bottom surface of the mushroom.
Then place the section in the enlarger
(instead of a negative), focus
the image, and make a magnified
positive photograph of the section.
However, it would be sufficient just
to trace the outline of the pores on
an ordinary sheet of paper. All that,s
left is to calibrate the magnification
of the enlarger/ count the number of
pores in the photograph, and measure
the diameter of the pores. By
way of example, figure 5 shows the
shadow projection of the cross section
of a polyporoid with a 2-mm
scaling bar. Figure 5 is a picture of
the surface layer of a polyporoid obtained
with a more complicated device-the
scanning electron microscope.
The scaiing light bar here
corresponds to 1 mm. These figures
show that the average diameterD of
the pores is about 1/3 mm. The deviation
is not too large, although,
strictly speaking, the pore's shape is
far from being a perfect cylinder.
Try to figure out why we used a thin
section of the mushroom for our measurements
instead of the entire layer,
even though the entire layer also lets
the liglrt through (the pore tubes go all
the way through the mushroom).
Experiment 2. It's interesting to
look at objects through a polyporoid
layer. Turn on
your desk lamp,
place a porous
layer of a polyporoid
in the path
of the light, and
observe the hot
filament through
the pores. To do
this experiment
you need to practice
getting the
right direction and
turning the layer
by small angles.
Thepore-tubes are
narrow/ which results
in a comparatively
small sighting
angle: 0-"* -
DIL ..1. Even for
alayer only3 mm
thic( this is about
Figure 6
Elecfton micrograph of the sudace of a polyporoid.
10o, and for a layer 3 cm thick, it's 1 o.
Figure 7 shows the hot filament of a
tungsten lamp photographed through
the porous layer of a polyporoid.
After you do the second experiment,
you'll probably conclude that
the reflection of visible light from the
walls was very small, as if the walls
were black. Second, you'll observe
some blurring of the {ilament image
connected with the diffraction of light
in narrow openings (which is what
the pores are). For X-ray radiation the
Figure 7
Hot filament of a tungsten lamp photographed tfuough the
porous layer of a polyporoid placed in front of the leis.
Note that the image is somewhat blurred, which is the
result of light diffraetion in the porcs.
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