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Pollen

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Pollen

Marfa Public Radio

Broadcast on February 3, 2011

By Cathryn Hoyt

Is your nose streaming? Are your eyes watering? Feeling a little listless? You may have pollen to thank. As all hay-fever sufferers will tell you, this is a bad year for pollen. Allergists consider any amount of pollen above 150 grains per cubic meter to be an extremely high pollen count. This year, juniper pollen is being recorded at densities up to 23,000 grains per cubic meter. Is all that pollen good for anything besides making you miserable?

In terms of evolution, the development of pollen was revolutionary. Prior to pollen, for the first 200 million years of plant history, plant reproduction depended on freestanding water. Sperm had to swim to find and fertilize an ova.

But then some plants began protecting their sperm cells inside airtight capsules, known today as pollen. Instead of swimming, sperm could fly—carried on the wind or by an insect from the pollen-producing anther to the ovary-holding pistil. Having broken free from the need for standing water to reproduce, flowering plants moved inland and diversified.

This free-flying pollen—so important to the evolution of plant life—is what makes allergy sufferers suffer. Wind-pollinated plants are some of the biggest culprits. Oaks, grasses, and pines produce huge clouds of pollen to improve the odds that a gust of wind will carry their sperm cells onto a receptive ovary. For example, all those brown junipers around at this time of year aren’t dying; they’re loaded with pollen. In order to guarantee reproductive success, they release hundreds of thousands of tiny pollen grains into the air in such numbers that the trees look like they’re smoking.

But take heart: you’re not breathing in all that pollen. Much of the pollen picked up by the wind will eventually settle to the ground, becoming part of an area’s “pollen signature.” Because of their tough outer shell and abundance, pollen grains can be preserved for hundreds of thousands of years—and sometimes even longer. The pollen grains of different types of plants are also uniquely shaped. So, like a family crest, they can be used to identify what kind of plant produced them. This allows palynologists—scientists that study pollen—to read pollen signatures to learn more about past environments and past climates.

Archeologists also use pollen as a tool to understand prehistoric domestic life. The presence of different types of pollen can help answer questions, such as when and where was corn domesticated? What was stored in a ceramic vessel? What time of year was a campsite occupied?

Being able to read a pollen signature has other modern applications. Forensic palynology is the study of pollen associated with crime scenes, and it’s becoming more widely accepted in courts of law. Pollen grains collected off clothing can be used to identify and link a suspect to the scene of a crime—and, because plants only bloom at certain times of the year, can often indicate roughly when a crime took place.

By looking at the types of pollen grains trapped in the dirt between a painted canvas and the frame, pollen has been used to determine the origin and authenticity of a piece of art. When a shipment of whiskey was replaced with bags of dirt, the pollen in the bags of dirt led investigators back to where the whiskey was offloaded and ultimately led to the capture of the thieves.

So even though pollen may make you sneeze, wheeze, and feel miserable, it does have its uses—from plant reproduction to solving crimes.

Dr. Cathryn Hoyt is a palynologist and Executive Director of the Chihuahuan Desert Research Institute.

Have a question or comment about this episode? Contact Nature Notes Coordinator Megan Wilde at mwilde [at] cdri [dot] org. Or discuss this episode on Nature Notes’ Facebook page.

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