 In 1884, he graduated with his degree in medicine, and in the following year he embarked on a two-year expedition for Parke, Davis & Co., crossing South America and exploring remote regions of Colombia, Ecuador, Peru, Chile, Bolivia and Brazil.Although trained as a physician, Rusby chose to leave medicine for his interest in plants.In 1889, he became Professor of Botany and Materia Medica at the School of Pharmacy at Columbia University.