Microscopes and Microscopy: A Guide

MICROSCOPES AND
MICROSCOPY
Chapter 7

The Basics of the Microscope
• A microscope is an optical instrument that
uses a lens or a combination of lenses to
magnify and resolve the fine details of an
object.
• The earliest methods for examining physical
evidence in crime laboratories relied almost
solely on the microscope to study the
structure and composition of matter.

• The microscope is still one of the most used
tools in a crime laboratory for analyzing
evidence, even with the advent of other
modern instrumentation.

• The earliest and simplest microscope was the
single lens commonly referred to as a
magnifying glass. The handheld magnifying
glass makes things appear larger than they are
because of the way light rays are refracted, or
bent, in passing from the air into the glass,
and back to the air.
• The magnified image is observed by looking
through the lens.

• Since the image appears to be on the same side
of the lens as the object, it cannot be projected
onto a screen. Such images are termed virtual
images and they appear upright, not inverted.
Figure 1 presents an illustration of how a simple
magnifying lens operates. The object (in this
case the subject is a rose) is being viewed with a
simple bi-convex lens. Light reflected from the
rose enters the lens in straight lines as
illustrated in Figure 1. This light is refracted and
focused by the lens to produce a virtual image
on the retina. The image of the rose is magnified
because we perceive the actual size of the
object (the rose) to be at infinity because our
eyes trace the light rays back in straight lines to
the virtual image (Figure 1). This is discussed in
greater detail below.
Simple Lenses

• The ordinary magnifying glass can achieve a
magnification of about 5 to 10 times. Higher
magnifying power is obtainable only with a
compound microscope, constructed of two
lenses mounted at each end of a hollow tube.
The object to be magnified is placed under the
lower lens, called the objective lens, and the
magnified image is viewed through the upper
lens, called the eyepiece lens.
History and Anatomy of the
Microscope

• As shown in the figure to the
left, the objective lens forms
a real, inverted, magnified
image of the object. They
eyepiece, acting just like a
magnifying glass, further
magnifies this image into a
virtual image, which is seen
by the eye. The combined
magnifying power of both
lenses can produce an image
magnified up to 1,500 times.
Microscope

• Microscopes are instruments designed to
produce magnified visual or photographic images
of small objects. The microscope must
accomplish three tasks: produce a magnified
image of the specimen, separate the details in
the image, and render the details visible to the
human eye or camera. This group of instruments
includes not only multiple-lens designs with
objectives and condensers, but also very simple
single lens devices that are often hand-held, such
as a magnifying glass.
Microscope

• The microscope illustrated in Figure 1 is a
simple compound microscope invented
by British microscopist Robert Hooke
sometime in the 1660s. This beautifully
crafted microscope has an objective lens
near the specimen and is focused by
turning the body of the microscope to
move the objective closer to or farther
from the specimen. An eyepiece lens is
inserted at the top of the microscope
and, in many cases, there is an internal
"field lens" within the barrel to increase
the size of the viewfield. The microscope
in Figure 1 is illuminated through the oil
lamp and water-filled spherical reservoir,
also illustrated in Figure 1. Light from the
lamp is diffused when it passes through
the reservoir and is then focused onto the
specimen with a lens attached to the
reservoir. This early microscope suffered
from chromatic (and spherical)
aberration, and all images viewed in
white light contained "halos" that were
either blue or red in color.
Microscope

• Since so many microscope users rely upon direct
observation, it is important to understand the
relationship between the microscope and the eye.
Our eyes are capable of distinguishing color in the
visible portion of the spectrum: from violet to blue to
green to yellow to orange to red; the eye cannot
perceive ultraviolet or infrared rays. The eye also is
able to sense differences in brightness or intensity
ranging from black to white and all the gray shades in
between. Thus, for an image to be seen by the
eye, the image must be presented to the eye in colors
of the visible spectrum and/or varying degrees of
light intensity.
Microscope

• The eye receptors of the
retina used for sensing color
are the cone cells; the cells
for distinguishing levels of
intensity, not in color, are
the rod cells. These cells are
located on the retina at the
back of the inside of the eye.
The front of the eye (see
Figure 2), including the iris,
the curved cornea, and the
lens are respectively the
mechanisms for admitting
light and focusing it on the
retina.
Microscope

• More than five hundred
years ago, simple glass
magnifiers were developed.
These were convex lenses
(thicker in the center than
the periphery). The
specimen or object could
then be focused by use of
the magnifier placed
between the object and the
eye. These "simple
microscopes" could spread
the image on the retina by
magnification through
increasing the visual angle
on the retina.
Microscope

Microscope
• The "simple microscope" or
magnifying glass reached its
highest state of perfection, in the
1600's, in the work of Anton von
Leeuwenhoek who was able to
see single-celled animals (which
he called "animalcules") and even
some larger bacteria with a
simple microscope similar to the
one illustrated in Figure 3. The
image produced by such a
magnifier, held close to the
observer's eye, appears as if it
were on the same side of the lens
as the object itself. Such an
image, seen as if it were ten
inches from the eye, is known as a
virtual image and cannot be
captured on film.
Anton Von Leeuwenhoek (1632-1723)
Father of Microbiology

• Around the beginning of the 1600's,
through work attributed to the
Janssen brothers (see the
microscope in Figure 4) in the
Netherlands and Galileo in Italy, the
compound microscope was
developed. In its simplest form, it
consisted of two convex lenses
aligned in series: an object glass
(objective) closer to the object or
specimen; and an eyepiece (ocular)
closer to the observer's eye (with
means of adjusting the position of
the specimen and the microscope
lenses). The compound microscope
achieves a two-stage magnification.
The objective projects a magnified
image into the body tube of the
microscope and the eyepiece
further magnifies the image
projected by the objective.
Microscope
Zacharias Janssen
Microscope
Galileo’s Microscope by
Zacharias Janssen
(circa 1590)

• The eighteenth and nineteenth centuries
witnessed a great improvement in the
mechanical and optical quality of
compound microscopes. Advances in
machine tools allowed more
sophisticated parts to be fabricated
and, by the mid 1800's, brass was the
alloy of choice for the production of high-
quality microscopes. A number of British
and German microscope manufacturers
flourished during this time period. Their
microscopes varied widely in design and
production quality, but the overall
principles defining their optical properties
remained relatively constant. The
microscope illustrated in Figure 5 was
manufactured by Hugh Powell and Peter
Lealand about 1850. The tripod base
provided a sturdy support for the
microscope, which many people consider
the most advanced of its period.
Microscope

• During the first quarter of the twentieth
century, many microscope manufacturers
had begun substituting cast iron for brass
in microscope frames and stages. Iron
was much cheaper and could be not be
distinguished from brass when painted
black. They also started to electroplate
many of the critical brass components
such as knobs, objective
barrels, nosepieces, eyepieces, and
mechanical stage assemblies (illustrated
in Figure 6). These early twentieth
century microscopes still subscribed to a
common design motif. They were
monocular with a substage mirror that
was used with an external lamp to
illuminate the specimen. A typical
microscope of the period is the Zeiss
Laboratory microscope pictured in Figure
6. This type of microscope is very
functional and many are still in use today.
Microscope

• Modern microscopes far exceed the design specifications of
those made prior to the mid 1900's. Glass formulations are
vastly improved allowing greater correction for optical
aberration than ever before, and synthetic anti-glare lens
coatings are now very advanced. Integrated circuit
technology has allowed manufacturers to produce "smart"
microscopes that incorporate microprocessors into the
microscope stand. Photomicrography in the late twentieth
century is easier than ever before with auxiliary
attachments that monitor light intensity, calculate exposure
based on film speed, and automatically perform
complicated tasks such as bracketing, multiple exposure,
and time-lapse photography.
Microscope

• The microscope illustrated in Figure
7 is an Olympus Provis AX70
research microscope. This
microscope represents the latest
state-of-the-art design that
incorporates multiple illuminators
(episcopic and diascopic), analyzers
and polarizers, DIC
prisms, fluorescence
attachments, and phase contrast
capabilities. The photomicrography
system is the ultimate in
sophistication and performance
featuring spot
measurement, automatic exposure
control, and zoom magnification for
flexible, easy framing. The Y-shaped
frame is designed to be user-
friendly by offering the maximum in
operator comfort and ease of use.
Microscope

• The optical principles of the compound
microscope are incorporated into the basic design
of different types of light microscopes. The
microscopes most applicable for examining
forensic specimens are as follows:
– The compound microscope
– The comparison microscope
– The stereoscopic microscope
– The polarizing microscope
– The microspectrophotometer
Microscope

• The parts of the compound microscope are
illustrated at the left. This microscope consists of a
mechanical system, which supports the
microscope, and an optical system.
• The mechanical system of the compound
microscope is composed of six main parts:
– BASE: the support on which the instrument rests
– ARM: a C-shaped upright structure, hinged to the
base, that supports the microscope and acts as a handle
for carrying
– STAGE: The horizontal plate on which the specimens are
placed for study. The specimens are normally mounted
on glass slides that are held firmly in place on the stage
by stage clips.
– BODY TUBE: A cylindrical hollow tube on which the
objective and eyepiece lenses are mounted at opposite
ends. This tube is merely a corridor through which light
passes from one lens to another.
– COARSE ADJUSTMENT: This knob focuses the microscope
lenses on the specimen by raising and lowering the stage.
– FINE ADJUSTMENT: The movements effected by this
knob are similar to those of the coarse adjustment but
are of a much smaller magnitude.
The Compound Microscope

• The optical system is made up of
four parts:
– ILLUMINATOR: Most modern
microscopes use artificial light
supplied by a lightbulb to illuminate
the specimen being examined. If the
specimen is transparent, the light is
directed up toward and through the
specimen stage from an illuminator
built into the base of the microscope.
This is known as transmitted
illumination. When the object is
opaque – that is, not transparent – the
light source must be placed above the
specimen so that it can reflect off the
specimen’s surface and into the lens
system of the microscope. This type of
illumination is known as vertical or
reflected illumination.

– CONDENSER: The condenser is a lens system
under the microscope stage that collects light
rays from the base illuminator and focuses
them on the specimen. The simplest
condenser is known as the Abbé condenser.
It consists of two lenses held together in a
metal mount. The condenser also includes an
iris diaphragm that can be opened or closed
to control the amount of light passing into
the condenser.
– OBJECTIVE LENS: This is the lens positioned
closest to the specimen. To facilitate
changing from one objective lens to
another, several objectives are mounted on a
revolving nosepiece or turret located about
the specimen. Most microscopes are
parfocal, meaning that when the microscope
is focused with one objective in position, the
other objective can be rotated into place by
revolving the nosepiece while the specimen
remains very nearly in correct focus.
– EYEPIECE or OCULAR LENS: This is the lens
closest to the eye. A microscope with only
one eyepiece is monocular; one constructed
with two eyepieces is binocular.

Each microscope lens is inscribed with a number
signifying its magnifying power. The image viewed by
the microscopist will have a total magnification equal
to the product of the magnifying power of the
objective and eyepiece lenses. For example, an
eyepiece lens with a magnification of 10 times (10x)
used in combination with an objective lens of 10x has a
total magnification power of 100x. Most forensic work
requires a 10x eyepiece in combination with either a
4x, 10x, 20x, or 45x objective. The respective
magnifications will be 400x, 100x, 200x, and 450x.
Magnification and Resolution

• In addition, each objective lens is inscribed with its
numerical aperture. (N.A.). The ability of an objective lens
to resolve details into separate images instead of one
blurred image is directly proportional to the numerical
aperture value of the objective lens. For example, an
objective lens of N.A. 1.30 can separate details at half the
distance of a lens with an N.A. of 0.65. The maximum
useful magnification of a compound microscope is
approximately 1,000 times the N.A. of the objective being
used. This magnification is sufficient to permit the eye to
see all the detail that can be resolved. Any effort to
increase the total magnification beyond this figure will yield
no additional detail and is referred to as empty
magnification.

• The experienced microscopist weighs a number of
important factors before choosing a magnifying power:
– FIELD OF VIEW: A first consideration must be the size of the
specimen area, or the field of view, that the examiner wishes
to study. As magnifying power increases, the field of view
decreases. Thus, it is best to first select a low magnification in
which a good general overall view of the specimen is seen, and
to switch later to a higher power in which a smaller portion of
the specimen can be viewed in more detail.
– DEPTH OF FOCUS: The depth of focus is also a function of
magnifying power. After a focus has been achieved on a
specimen, the depth of focus defines the thickness of that
specimen. Areas above and below this region will be blurred
and can be viewed only when the focus is readjusted. Depth
of focus decreases as magnifying power increases.

• Forensic microscopy often
requires a side-by-side
comparison of specimens. This
kind of examination can be best
performed with a comparison
microscope, such as the one
pictured at left.
• Basically, the comparison
microscope is two compound
microscopes combined into one
unit. The unique feature of its
design is that it uses a bridge
incorporating a series of mirrors
and lenses to join two
independent objective lenses
into a singular binocular unit.
The Comparison Microscope

• A viewer looking through the
eyepiece lenses of the comparison
microscope observes a circular
field, equally divided into two parts
by a fine line. The specimen
mounted under the left-hand
objective appears in the left half of
the field, and the specimen
mounted under the right-hand
objective appears in the left half of
the field.
• Comparison microscopes designed
to compare opaque objects, such
as bullets and cartridge casings, are
equipped with vertical or reflected
illumination.
• Comparison microscopes used to
compare hairs or fibers use
transmitted illumination.
The Comparison Microscope

The Stereoscopic Microscope
• The details that characterize the
structures of many types of physical
evidence do not always require
examination under very high
magnifications. For such specimens, the
stereoscopic microscope has proven quite
adequate, providing magnifying powers
from 10x to 125x. This microscope has the
advantage of presenting a distinctive
three-dimensional image of an object.
Also, whereas the image formed by the
compound microscope is inverted and
reversed, the stereoscopic microscope is
more convenient because prisms in its
light path create a right-side-up image.
• The stereoscopic microscope shown is
actually two monocular compound
microscopes properly spaced and aligned
to present a three dimensional image of a
specimen to the viewer, who looks
through both eyepiece lenses.

• The stereoscopic microscope is undoubtedly the most
frequently used and versatile microscope found in the
crime laboratory. Its wide field of view and great
depth of focus make it an ideal instrument for
locating trace evidence in debris, garments, and tools.
Furthermore, its potentially large working distance
(the distance between the objective lens and the
specimen) makes it ideal for microscopic examination
of big, bulky items. When fitted with vertical
illumination, the stereoscopic microscope becomes
the primary tool for characterizing physical evidence
as diverse as paint, soil, gunpowder residues, and
marijuana.
The Stereoscopic Microscope

• Before we can discuss the polarizing light
microscope, we must first talk about the theory of
light. As with all matter, knowledge of the nature and
behavior of light is fundamental to understanding
physical properties important to the examination of
forensic evidence. Two simple models explain light’s
behavior. The first model describes light as a
continuous wave; the second depicts it as a stream of
discrete energy particles. Together, these two very
different descriptions explain all of the observed
properties of light, but by itself, no one model can
explain all the facets of behavior of light.
The Polarizing Microscope
The Theory of Light

• The wave concept depicts light as having an
up-and-down motion of a continuous
wave, as shown below. Such a wave can be
characterized by two distinct properties:
wavelength and frequency.
Light as a Wave

Wavelength and Wave Motion
• The distance between two consecutive crests (high points)
or troughs (low points) of a wave is called the wavelength;
it is designated by the Greek letter lambda (λ) and is
typically measured in nanometers (nm), or millionths of a
meter. The number of crests (or troughs) passing any one
given point in time is defined as the frequency of the
wave. Frequency is normally designated by the letter ƒ
and is expressed in cycles per second (cps). Frequency
and wavelength are inversely proportional to one
another, as shown in the relationship
F = c/λ
where cequals the speed of light.

Wave length Peak
Amplitude
Trough

• Many of us have held a glass prism up toward that
sunlight and watched it transform light into the colors
of the rainbow. The process of separating light into its
component colors is called dispersion. Visible light
usually travels at a constant velocity of nearly 300
million meters per second. However, on passing
through a prism, each color component of light is
slowed to a speed slightly different from those of the
others, causing each component to bend at a different
angle as it emerges from the prism. The bending of
light waves because of the change in velocity if called
refraction.

The observation that a substance has a color
is consistent with this description of white
light. For example, when light passes through
a red glass, the glass absorbs all the
component colors of light except red, which
passes through or is transmitted by the glass.
Like wise, one can determine the color of an
opaque object by observing its ability to
absorb some of the component colors of light
while reflecting others back to the eye. Color
is thus a visual indication that objects absorb
certain portions of visible light and transmit
or reflect others. Scientists have long
recognized this phenomenon and have
learned to characterize different chemical
substances by the type and quantity of light
they absorb. This has important applications
for the identification and classification of
forensic evidence.

The Multispectral Sun
This animation shows views of the Sun at various
frequencies across the electromagnetic spectrum. Note
how different features and regions of the Sun are visible
in the different views. The visible light view shows the
photosphere, including several sunspots. The infrared
view shows the lower chromosphere immediately above
the photosphere, where temperatures are still relatively
cool. Most of the high energy photons that produce the
UV and X-ray views come from higher up in the Sun's hot
atmosphere. Notice how the areas of the atmosphere
above sunspots tend to be especially bright in the X-ray
and UV views. Sunspots are visible indicators of magnetic
disturbances on the Sun that high energy phenomena
such as solar flares and coronal mass ejections.
Most of the individual views portray the Sun as seen
through a very narrow range of wavelengths; for
example, the IR view is just a narrow band of infrared
"light" with a wavelength around 1,083 nanometers (as
opposed to the entire IR portion of the spectrum, which
ranges across wavelengths from 750 nm to 1 mm), while
the first UV image is centered around a wavelength of
30.4 nanometers. These narrow wavelength "windows"
in the EM spectrum are actually the "fingerprints" of
specific elements at specific temperatures.

• The observation that a substance or object
has color is consistent with the description of
white light. For example, when light passes
through red glass, the glass absorbs all the
component colors of light except red, which
passes through or is transmitted by the glass.
Likewise, one can determine the color of an
opaque object by observing its ability to
absorb some of the component colors of light
while reflecting others back to the eye.

• Color is thus a visual indication
that objects absorb certain
portions of visible light and
transmit or reflect others.
Scientists have long recognized
this phenomenon and have
learned to characterize
different chemical substances
by the type and quantity of
light they absorb. This has
important applications for the
identification and classification
of forensic evidence.
Perception of COLOR

The Electromagnetic Spectrum
• Similarly, the range of colors that make up the
visible spectrum can be correlated with
frequency. For instance, the lowest frequencies
of visible light are red; waves with a lower
frequency fall into the invisible infrared (IR)
region. The highest frequencies of visible light
are violet, waves with a higher frequency extend
into the invisible, ultraviolet (UV) region. No
definite boundaries exist between any colors or
regions of the electromagnetic spectrum; instead,
each region is composed of a continuous range of
frequencies, each blending into the other.

• Ordinarily, light in any region of
the ES is a collection of waves
possessing a range of wavelengths.
Under normal circumstances, this
light comprises waves that are all
out of step with each other
(incoherent light).
However, scientists can produce
light that has all its waves
pulsating in unison. This is called a
laser (light amplification by
stimulated emission of radiation).
Light in this form is very intense
and can be focused on a very small
area. Laser beams can be focused
to pinpoints that are so intense
that they can zap microscopic
holes in a diamond.
Lasers

• The light’s wavelike motion in space can be
invoked to explain many facets of its behavior.
The waves that compose a beam of light can be
pictured as vibrating in all directions
perpendicular to the direction in which the light
is traveling. However, when a beam of light
passes through certain types of specially
fabricated crystalline substances, it emerges
vibrating in only one plane. Light that is confined
to a single plane of vibration is said to be plane-
polarized.

• The device that creates polarized light
is called a polarizer.
• Because polarized light appears no
different to the eye from ordinary
light, special means must be devised
for detecting it. This is accomplished
simply placing a second polarizing
crystal, called an analyzer, in the path
of the polarized beam. If the polarizer
and analyzer are aligned parallel to
each other, the polarized light passes
through and is seen by the eye. If, on
the other hand, the polarizer and
analyzer are set perpendicular to one
another, or are “crossed”, no light
penetrates, and the result is total
darkness or extinction.

• Essentially, the polarizer is placed
between the light source and the
sample stage to polarize the light
before it passes through the specimen.
The polarized light penetrating the
specimen must then pass through an
analyzer before it reaches the eyepiece
and finally the eye. Normally the
polarizer and analyzer are “crossed” so
that when no specimen is in place, the
field appears dark. However,
introducing a specimen that polarizes
light reorients the polarized light,
allowing it to pass through the analyzer.
This result produces vivid colors and
intensity contrasts that make the
specimen readily distinguishable.

• Few instruments in a crime laboratory can match the
versatility of the microscope. The microscope’s magnifying
power is indispensable for finding minute traces of
physical evidence. Many items of physical evidence can be
characterized by a microscopic examination of their
morphological features. Likewise, the microscope can be
used to study how light interacts with the material under
investigation, or it can be used to observe the effects that
other chemical substances have on such evidence. Each of
these features allows an examiner to better characterize
and identify physical evidence. Recently, linking the
microscope to a computerized spectrophotometer has
added a new dimension to its capability. This combination
has given rise to a new instrument called the
microspectrophotometer.
The Microspectrophotometer

With the development of the
microspectrophotometer, a forensic
analyst can view a particle under a
microscope while a beam of light is
directed at the particle to obtain its
absorption spectrum. An absorption
spectrum is the characteristic pattern
of dark lines or bands that occurs
when electromagnetic radiation is
passed through an absorbing medium
into a spectroscope. An equivalent
pattern occurs as colored lines or
bands in the emission spectrum of
that medium. The range of
frequencies of electromagnetic
radiation readily absorbed by a
substance by virtue of its chemical
composition is unique to that
substance and creates a “fingerprint”.

• Depending on the type of light employed, an
examiner can acquire either a visible or an IR
spectral pattern of the substance being viewed
under the microscope. The obvious advantage
of this approach is to provide added information
to characterize trace quantities of evidence. A
microspectrophotometer designed to measure
the uptake of visible light by materials is shown
on the previous slide.
Absorption spectrum of the planet Gliese
581g to analyze the possibility of the
presence of life, or the capability of the
planet to support life (similar to ours).

• Visual comparison of color is usually one of the first steps in examining paint, fiber
and ink evidence. Such comparisons are easily obtained using a comparison
microscope. A forensic scientist can use the microspectrophotometer to compare
the color of materials visually while plotting an absorption spectrum for each item
under examination. This displays the
Exact wavelengths at which each item
absorbs light in the visible-light spectrum.
Another emerging technique in forensic
science is the use of the infrared spectro-
photometer to examine fibers and paints.
The “fingerprint” IR spectrum is unique
for each chemical substance.

• All the microscopes
described thus far use light
coming off the specimen to
produce a magnified
image. The scanning
electron microscope (SEM)
is, however, a special case
in the family of
microscopes . The image is
formed by aiming a beam
of electrons onto the
specimen and studying
electron emissions on a
closed TV circuit.
The Scanning Electron Microscope
(SEM)

• Palynology: The branch of science
concerned with the study of pollen, spores ,
and similar palynomorphs, living and fossil.
• Forensic Palynology: the use of pollen and
spore evidence in legal cases (Mildenhall,
1982). In its broader application, the field of
forensic palynology also includes legal
information derived from the analysis of a
broad range of microscopic organisms--such
as dinoflagellates, acritarchs, and
chitinozoans--that can be found in both
fresh and marine environments (Faegri et
al., 1989). However, in most sampling
situations forensic palynologists rarely
encounter these other types of organisms
because most are restricted to fossil
deposits. Studies of palynomorphs trapped
in materials associated with criminal or civil
investigations are slowly gaining recognition
as valuable forensic techniques.
Introduction to Forensic
Palynology

• Of the many plant species on
earth, more than half a million produce
pollen or spores. The pollen or spores
produced by each species has a unique
type of ornamentation and morphology.
This means that pollen or spores can be
identified and used to provide links
between a crime scene and a person or
object if examined by a trained analyst.
This technique is called forensic
palynology and includes the collection
and examination of pollen and spores
connected with crime scenes, illegal
activities, or terrorism. Microscopy is
the principal tool used in the field of
forensic palynology.
Forensic Palynology: Pollen and
Spores as Evidence

• In nature, pollen grains are the
single-celled male gametophytes of
seed-bearing plants. The pollen
grain wall (exine) is durable because
it protects and carries the sperm
cells needed for plant reproduction.
Spores consist of both male and
female gametes of plants such as
algae, fungi, mosses, and ferns.
Pollen-producing plants are either
anemophilous (their pollen is
dispersed by wind) or
entomophilous (their pollen is
carried and dispersed by insects or
small animals).
Forensic Palynology: Characteristics of
Spores and Pollen

• Fairly precise geographical
locations can often be
identified by the presence
of different mixtures of
airborne pollens produced
by anemophilous plants.
For example, it may be
possible to identify a
geographical origin by a
profile of the pollen
samples retrieved from a
suspect’s clothing simply by
the type and percentages of
airborne pollen grains.
Spores and Pollen

• Entomophilous plants usually
produce a small amount of
pollen that is very sticky in
nature. Therefore, this type of
pollen is very rarely deposited on
clothing or other objects except
by direct contact with the plant.
This information is useful when
reconstructing the events of a
crime because it indicates that
the clothing, a vehicle, or other
objects may have come into
direct contact with plant types
found at a crime scene.
Spores and Pollen

• Both spores and pollen are microscopic in size and are
produced by the adult plants and dispersed by the
millions, and both can be analyzed using similar
methods that use a variety of microscopic techniques.
Using a compound light microscope with magnification
capabilities up to 1,000x, analysts usually can identify
pollen and spores as coming from a specific plant
family or genus, and at times even a unique species.
However, often the pollen or spores of related species
may appear so similar that identification of the species
is possible only with careful analysis using an SEM.
Forensic Palynology: Analysis of
Spores and Pollen

• Unique shapes, aperture type, and surface
ornamentation are typically used to
identify spore samples. Useful features for
characterizing pollen grains include shape,
apertures, and wall and surface
sculpturing. Shapes of pollen grains
include spheres, triangles, ellipses,
hexagons, pentagons, and many other
geometric variations. Apertures are the
openings on pollen grains from which the
pollen tube grows and carries the sperm to
the egg to complete fertilization.
Spores and Pollen

• To avoid destruction or
contamination, early collection of
forensic pollen samples for
analysis is important and should
be completed as soon as possible
at a crime scene by a trained
palynologist. This kind of expert’s
first task is to calculate the
estimated production and
dispersal patterns of spores and
pollen (called the pollen rain) for
the crime scene or area of
interest, and then using that
information to produce a kind of
“pollen fingerprint” of that
location.
Spores and Pollen

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