Science Scoops: War of the Roses

We've all smelled it—that fresh aroma of raw earth rising up from a garden after a summer rain. But as pleasing as that smell is to us, it's the smell of war…to a microbe!

That's right. The smell we love to sniff after a summer shower is really an invisible cloud of some pretty “poisonous” chemicals released by soil-dwelling bacteria fighting for territory. The microbes use the gas as a biological weapon, to keep competitors away. David Bodanis, author of The Secret Family (Simon & Schuster, 1997), says that the smell is always there, but it simply becomes more noticeable to humans in the increased humidity after a rain.

And there's more to that sweet smell of a humid summer day. Shrubs, Bodanis says, “send an odoriferous alcohol upward to spotlight the point where they're being attacked by caterpillars or other gnawing insects.” The odor, however, is not intended to gas out the leaf munchers. No, it's a chemical message aimed at wasps, to attract them to the caterpillars, the wasp's prey.

More of the aroma of summer comes from flowers planted too closely together, Bodanis says. Plants do not take such crowding lightly. To battle their neighbors, plants send hydrogen cyanide from their roots into the soil to annihilate encroachers. Rosebushes, too, are not averse to killing. They send out gases that try to counterattack fungi.

Yes, Bodanis warns us, it's a jungle out there, and we're blind to it. But we can sniff out the danger.


To destroy completely.

Opposed; reluctant; unwilling.

One who advances beyond one's limits.

Dampness of the air.

Having or giving off an odor.

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  1. Why do the physical properties of some flowers make those flowers attractive to people?
  2. How do the plants mentioned in this article use some of their physical properties to protect themselves?
  3. Many plants or animals use color, shape, or texture as protection. Name two plants or animals that use color, shape, or texture as protection. Write a sentence or two about each plant or animal. Describe how they use their color, shape, or texture.