His specialty was the study of diatoms, which are common components of phytoplankton.
He worked with Albert Mann (1853–1935), who was also a diatomist, at Carnegie Institution for Science in Washington, D.C.
He became a member of the Carnegie Institution and worked as Mann's assistant in the lab in 1922.
After Mann died, Conger served as research associate at the CIS from 1935 to 1943.
During the same years, he was named Honorary Custodian of Diatoms at the United States National Museum.