One of the most influential research and teaching programs to emerge in the new science of ecology in the early twentieth century was that which developed at the University of Chicago under the direction of botanist Henry Chandler Cowles. Not a prolific writer, Cowles was nevertheless author of two of the seminal papers in American plant ecology. On the basis of those early contributions, as well as his considerable abilities as field guide, he was able to draw numerous students into Chicago’s new plant ecology program for both introductory and advanced work. No small part of the attraction of the program was Cowles’s ability to interpret successional changes in vegetation in terms that fitted in well with the forward-looking, reform-minded mood of the educated elite of the nation and the city of Chicago during the early decades of the century. Cowles’s favorite outdoor laboratory, the region of sand dunes along the Indiana shore of Lake Michigan, provided the ideal setting for his vivid telling and retelling of the story of the struggles and transformations of plant communities toward the establishment of the inevitable climax community. Both this dramatic tale of progressive change and the unusual diversity of species and communities at the dunes reflected qualities of Chicago itself, and Cowles interpreted these ecological phenomena in a manner that bore a striking resemblance to the frontier hypothesis of Frederick Jackson Turner.