This dissertation studies twentieth-century natural history exhibitions from the Smithsonian Institution and other natural history museums for the source of their authority as scientific and public representations of nature. This study contrasts naturalists' place-specific evolution-based conception of nature to the abstract system-oriented paradigm of ecologists. It renders problematic assumptions about the ease of transferring formalized knowledge from the technical sphere into the public domain. The central case at the Smithsonian Institution's National Museum of Natural History traces the transformation of a tropical rain forest habitat group first planned for a botany hall in the early 1960s into an example of an ecosystem in a projected ecology hall. The representations of nature inside natural history museums are culturally compelling and authoritative, both for scientists and the public, because they retain a concrete physical basis that the products of laboratory science do not.