In 1997, at age 19, Toby Kiers talked her way into the Smithsonian's renowned tropical research institute on Barro Colorado, an island in the middle of the Panama Canal. The scientists studied the many species of local bats, the monkeys they outfitted with radio or GPS collars, and the towering rainforest canopy.

There, during a year-long fellowship, Kiers learned about a type of fungi known as mycorrhizae that formed intimate associations with the tropical trees and grew in sprawling, underground networks. Found all over the world, mycorrhizae are microscopic. But if you stretched out all the mycorrhizae present in a hectare of grassland, end to end, they would be the length of many, many Amazon Rivers.

"It seemed like the most sort of frontier world at that time," she says, "because yo

See Full Page