#31 Murder in the Bloom : Palynological Microscopy II
- Aiza Jamil
- Aug 28
- 3 min read
Updated: Oct 4
Hello, and welcome back, folks, to another episode of STEM on the Streets! If you are new here, my name is Aiza, and this is my partner, CAI (crime AI). Together, we stroll through the criminal-ridden streets of STEM!
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Collecting Samples
You might think pollen is just floating about in the air, happily so and ready to be sampled; however, in forensic cases, it is collected intentionally and carefully. Investigators don’t just grab a handful of dirt —or air, if the pollen is happily floating about —they follow strict protocols to ensure the pollen is not contaminated and is of the standard to be used as evidence in court.
There are many ways pollen is sampled. Investigators may use sterile cotton swabs and adhesive tape to lift pollen from clothing, hair, shoes, or any object at the crime scene. They also use vacuum sampling in which they use a small portable vacuum device to collect poed from carpets, soil, or vehicle interiors without damaging the pollen itself.
Investigators also take background samples from the environment, like soils, nearby plants, to see what pollen is naturally present in the area. This is called a controlled sample. Now control samples are crucial because this helps investigators compare the experimental sample (the sample collected from the crime scene) to the control sample (the sample from he environment) and identify whether the pollen collected from the crime scene is transferred or naturally present in the environment.
Then comes preservation. Once the samples are collected, they must be preserved properly in sterile containers or ziploc bags with some alcohol to prevent microbial growth and then frozen..
Finally, the pollen spa, we discussed this in the previous blog as well. Pollen goes through chemical treatments to “purify” it before microscopy. KOH is used to dissolve organic debris such as humic material, and HCL is added, left to sit for 24 hours undisturbed before stirring, and then centrifuged with distilled water to remove carbonates. And acetolysis is used to remove cellulose, leaving the exine (the tough outer shell) intact for microscopy.
This rather long and meticulous process has been used by forensic scientists to trace specific plants and locations for a long time.
What to look for under the microscope
Hey CAI, wanna do the next bit?
(✿◡‿◡) CAI: Yep.
So when pollen is looked at under a microscope, scientists look for specific features.
Exine Texture.
Exine texture would be how the surface is sculptured. I’ll give an example of two different
pollen to compare: Sunflower pollen and Pine pollen.
So sunflower pollen has a spiny (echinate) surface, tiny projections or sponges that help pollen grains stick to insect bodies, aiding in pollination. Pine pollen, in contrast, has a smoother surface; this smoother and streamlined texture helps the pollen stay aloft and drift in the wind.
Sacci
Sacci are air sacs. We’ll continue with the previous example.
Sunflower pollen does not have sacci as it relies on a more sticky texture and insect
transport than airborne dispersal. However, the same can’t be said about pine pollen. In the image, you can see that it is what could be considered a “Micky Mouse head” shape. The two spheres attached on either side are air sacs, which is why pine pollen is called bisaccate. These air sacs increase buoyancy and slow descent, which allows longer wind dispersal distances.
Apertures
Apertures are furrows and/or spores.
Many flowering plants, such as the sunflower, have copulate or tricolpate pollen, meaning
they feature multiple furrows (colpi) or pores through which the pollen tube can emerge. Gymnosperms like pine usually have a single groove called a suculus from where the pollen tube merges.
Well, that is all for today, folks. Next episode, we will be diving further into the world of forensic botany and the founders of the science.
This is Aiza Jamil signing out!
I am a forensics sleuth. What's your mystery to solve?
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