Thursday, April 08, 2010

Signs of Spring 6 - pollen

kw: observations, seasons

This morning my car, normally white, looked greenish, even chartreuse. Once I started it, I ran the windshield wipers. The oak and tulip trees at the end of my driveway strike again!

Jostle the right kind of tree, and you'll see a cloud of pollen. When we lived in South Dakota, downwind of the Black Hills, this time of year we could see yellow rivers of pollen in the air, and the black (really dark gray) asphalt streets turned a distinct yellow color, along with everything else.

People who are sensitive to pine pollen just shouldn't be near piney woods in April or May. Trees that depend on the wind (and other wind-pollinated plants such as corn / maize) produce huge amounts of pollen, as much as a kilogram for a large pine tree, or a gram or two from each cornstalk.

This is why so many plants "prefer" to be pollinated by insects. They put less total energy and substance into making flowers to attract pollinators than is used by wind-pollinated plants for their pollen burden.

The greenish color of this morning's pollen tells me it came mostly from the oak tree. Oak pollen is green, as this image shows. Tulip tree pollen is more distinctly yellow, and not quite as abundant. Thus I got a chartreuse mix. This image is from the New York State Department of Environmental Conservation.

Oak pollen follows one strategy that favors wind dispersal: the grains are very small. This image and the one below are at very similar magnifications.

Pine pollen follows another strategy: wings. Each grain has two "air bladders", hollow projections that decrease the average density and make it easier for wind to carry aloft. I found this image at the University of Hamburg Biology Department. The pollen grains have been stained with crystal violet.

This is the last of this year's Signs of Spring series. Yesterday the temperature got up to just below 90°F (32°C), throughout the Philadelphia area. That is the ultimate sign of Spring!

No comments: