From 1907 to 1912 Duggar held the chair of plant physiology at Cornell University. In 1912 he became a research professor of plant physiology at Washington University, working with the Missouri Botanical Garden in St. Louis.
Duggar's tenure as head of plant physiology at Cornell University spanned from 1907 to 1912. He then transitioned to a research role at Washington University in 1912, working closely with the Missouri Botanical Garden in St. Louis.