Elso S. Barghoorn, the Botany professor who dropped out of sight during Panama's anti-American rioting has returned to Cambridge, his co-workers reported yesterday.

Barghoorn, who is curator of the University's Paleobotanical Collection, was in Panama to collect rock-core samples when violence broke out over a flag-raising incident.

Two members of the Harvard expedition--Alan K. Graham, a research fellow in Biology, and his wife--reached Cambridge Jan. 8, but the University could obtain no news of Barghoorn and his assistant, Dorothy Osgood.

Even when the two researchers were found safe, their return was delayed by the cancellation of all flights from the Canal Zone to the U.S. They arrived in New York Monday by ship.

According to newspaper accounts, Barghoorn and Miss Osgood watched from their hotel window while shouting student mobs fired cars and smashed windows. Barghoorn told reporters that he thought the disorders were "rigged" since the stones thrown by the rioters were not native to the area.

"You do not find angular rocks such as the rioters used in that part of the city," Miss Osgood was quoted as saying.

Barghoorn could not be reached yesterday for comment. His brother, Frederick C. Barghoorn, professor of Political Science at Yale, was seized in the Soviet Union last November on spy charges and released only after President Kennedy sent a strong protest to the Kremlin.