Michael Pollan, a professor of journalism and a student of food, presents the history of four plants, each of which found a way to make itself essential to humans, thus ensuring widespread propagation. Apples, for sweetness; tulips, for beauty; marijuana, for pleasure; and, potatoes, for sustenance. Each has a story of discovery and adaptation; each has a symbiotic relationship with human civilization. The film tells these stories and examines these relationships.