February 1999, National Geographic, Plants with a Touch of Glass

This comes from the February 1999, National Geographic Magazine, Pgs 114-121, "Diatoms, Plants with a Touch of Glass"

(Pleurosigma is featured on the front cover.)

"Single celled algae, tens of thousands of diatom species, including delicate Pleurosigma, inhabit fresh water or ocean. All build glass shells of fantastic form and practical use."

Article and Photo credits by Darlyne A. Murawski

There's no disputing Charles Darwin on this point: "Few objects are more beautiful than the minute siliceous cases of the diatomacaea, were these created that they might be examined and admired under the higher powers of the microscope?" So Darwin wrote in 1872, sounding as much the Victorian connoisseur as the peerless field scientist. The symmetry and grace of diatoms are now even more evident when seen under the extreme magnification of a scanning electron microscope or in the polarized light of Nomarski interference microscopy, as in the colored images here.

And the living algae that once inhabited these silica shells? About 70,000 species, both fossil and recent have been described and that may only the half of it. As small as they are diverse (some 25 million would fit in a teaspoon), diatoms are both abundant and essential. They make up about a quarter of plant life by weight and produce at least a quarter of the oxygen we breathe. In life they provide high quality nutrition to animals as small as protozoans and as large as baleen whales. In death they rain down on ocean floors, where their oil-rich plasma is eventually buried and transformed into petroleum. Their skeletons are mined for use as filters and abrasives.
Diatoms enable biologists to prinpoint sources of water pollution and monitor the health of ecosystems. They help geologists reconstruct the history of ancient climates. As for me? I stand with Darwin.

The article concludes on this note,

"Optical magic of prisms and polarized light transforms a collection of freshwater diatoms into a bauble factory. Biologist Edward Theriot points out that diatoms have been used as tracers in military intelligence, to connect criminals to crime scenes, to locate the sites of drownings, and in archaeology to find the sources of clay in ancient pots. Almost all diatoms are benign, and that's good. Because they're everywhere."