A few miles outside Sacramento, several large greenhouses sit behind a fence. In the summer the familiar heads of sunflowers are visible through the glass and in the fields surrounding the greenhouses. The plants are tall, straight and healthy, with thick leaves that reach for the California sunlight. They look exactly like sunflower plants grown throughout the United States-except for the plastic cages around each flower.

The flowers are covered by biologists at Pioneer Hi-Bred's research facility in Woodland, Calif., which owns the greenhouses, the fields around them, and the sunflowers in both. The plants are transgenic-that is, genes from other organisms have been inserted into their chromosomes. Caging the sunflower heads helps prevent the breeze from wafting genetically engineered pollen around the area, which would violate federal laws banning release of unapproved transgenic organisms.