In 1973, a book claiming that plants were sentient beings that feel emotions, prefer classical music to rock and roll, and can respond to the unspoken thoughts of humans hundreds of miles away landed on the New York Times best-seller list. The Secret Life of Plants," ... described the experiments of a former C.I.A. polygraph expert named Cleve Backster, who ... found that simply by imagining [a houseplant] being set on fire he could make it rouse the needle of the polygraph machine. Much of the research on plant intelligence has been inspired by ... the ways in which remarkably brainy behavior can emerge in the absence of actual brains. "If you are a plant, having a brain is not an advantage," Stefano Mancuso points out. Mancuso is perhaps the field's most impassioned spokesman for the plant point of view. His somewhat grandly named International Laboratory of Plant Neurobiology, a few miles outside Florence, occupies a modest suite of labs and offices. Giving a tour of the labs, he showed me maize plants, grown under lights, that were being taught to ignore shadows; a poplar sapling hooked up to a galvanometer to measure its response to air pollution; and a chamber in which ... an advanced kind of mass spectrometer continuously read all the volatiles emitted by a succession of plants. "We are making a dictionary of each species' entire chemical vocabulary," he explained. He estimates that a plant has three thousand chemicals in its vocabulary, while, he said with a smile, "the average student has only seven hundred words."