The emergence of novelty, especially of new categories of people and organizations, is undertheorized in the social sciences. Some social worlds are more hospitable to novel introductions or exogenous perturbations than others. Explaining this relative “poisedness” is essential to understanding when and why new organizational forms appear, persist, and expand, both cognitively and geographically. We offer a comparative analysis of two cases of emergence in 19th-century New York City that examines the conditions under which a new organizational form—a research-intensive botanical garden—developed and took root. We show that social worlds are highly poised when environmental, intellectual, and civic factors have reinforcing consequences. Poisedness is amplified when the social character of the individuals produced by specific historical milieux attunes these innovators to the larger social and material processes that favor the creation of new modes of organization. Although our analysis of poisedness is fixed on a specific time and place, New York City over the course of the 19th century, our arguments about the emergence of new organizational forms apply readily to other settings and time periods.