When is a vegetable not a vegetable?

The potato might seem undeniably a vegetable. But Monsanto Corp. has modified the humble tuber to the point where the government no longer classifies some varieties as vegetables.

It all started with the acres of Idaho farmland devoted to potato production – and a form of chemical warfare. Fumigants, herbicides, and insecticides are so frequently used to keep the crop from being eaten alive or suffocated by weeds that the soil looks deathly gray.

So when Monsanto developed the NewLeaf potato, genetically engineered to ward off predators, farmers sighed in relief. The plant's built-in pesticide – a bacterial toxin that fells any beetle that takes a bite – spared farmers time, money, and the spraying of nasty chemicals.

In researching the lifecycle of this GM tuber, however, Michael Pollan, author of the bestselling "The Botany of Desire," discovered how it had slipped through the regulatory cracks.

The Food and Drug Administration didn't officially regard the NewLeaf as a food, but a pesticide because it contains Bt, a naturally occurring pesticide. So the FDA gave no oversight to its introduction into the marketplace, Mr. Pollan writes.

Instead, the potato came under the jurisdiction of the Environmental Protection Agency, which considered it safe. Caveat emptor – no one studied the plant.

"The new plants," Pollan writes in "Botany," "are novel enough to be patented, yet not so novel as to warrant a label telling us what it is we're eating."

In an interview (see story), Pollan raises more unsettling questions when he takes a look at the domination of corn in US agriculture and its impact on our economy, diet, and foreign policy.