In summer, water rises through the xylem and disperses out of the million tiny mouths on the undersides of leaves, a hundred gallons a day evaporating from the tree’s airy crown into the humid Iowa air. In fall, the yellowing leaves fill Frank Jr. with nostalgia. In winter, bare branches click and hum above the drifts, their blunt resting buds almost sinister with waiting. But for a moment each spring, the pale green catkins and cream-colored flowers put thoughts into Frank Jr.’s head, thoughts he doesn’t know how to have.