The leading American botanist of the nineteenth century, Asa Gray helped organize the main generalizations of the science of plant geography. The manual of botany that carries his name is still in use today. Friend and confidant of Charles Darwin, Gray became the most persistent and effective American protagonist of Darwin's views. Yet at the same time, he believed that religion and Darwin's theory of natural selection could coexist. A. Hunter Dupree's authoritative biography offers the first full-length interpretation of one of America's most important men of science.