Born in the state of New York, Asa Gray (1810–88) abandoned a medical career to pursue his true interest in botany. He sought the mentorship of the influential American botanist John Torrey, and their collaborative efforts in classifying North American flora according to biological similarities paved the way for Gray's professorship at Harvard University after years of research. Gray was also one of the few scientists to whom Charles Darwin revealed his early ideas of evolutionary theory. After Gray's death, his fellow botanist Charles Sprague Sargent (1841–1927) compiled the lesser-known writings of a prolific author whose user-friendly Manual of the Botany of the Northern United States and other works inspired generations of botany enthusiasts. The two-volume collection appeared in 1889. Covering the period from 1841 to 1886, Volume 2 contains essays on botanical topics and biographical sketches of influential naturalists.