“The first time I heard anyone speak of the “wood wide web,” more than a decade ago now, I was trying not to cry. A beloved friend was dying too young and too quickly. I had gone to see him for what I took to be the last time. He was tired by pain and drugs. We sat together, talked. My friend was a woodsman. Trees grew through his life and thought. His grandfather’s surname was Wood, he lived in a timber-framed house that he had built himself, and he had planted thousands of trees by hand over the years. “I have sap in my veins,” he wrote once.” Excerpted from his recently published book, Underland: A Deep Time Journey, “The Understory” is an examination of the life beneath the forest floor. Encountering the depth and complexity of communication that happens underground, Robert Macfarlane returns to the entangled mutualism at the root of language.