Her great-niece Marcia Young confirmed that Ms. Glass died in Montgomery.

Ms. Glass, a professor of geography at Alabama State University, was the secretary of the Women's Political Council, which leapt to action within hours of Ms. Parks's arrest on Dec. 1, 1955. The women's group, realizing that three-quarters of the bus riders in Montgomery were black, called on blacks to boycott the buses to put pressure on the city, the state and the bus company to stop forcing them to ride in the back and surrender their seats to white passengers.

The group urged people to walk or car-pool instead of taking the bus, and Ms. Glass was among those who drove others to work and helped pass out fliers to alert the community to the boycott.

By Monday, Dec. 5, the buses were empty.

"When the first bus came by with nobody on it, I couldn't believe it," Ms. Glass told The Montgomery Advertiser in 2005. As bus after bus rumbled past without a soul on board, she grew more and more delighted. "It's a feeling of such happiness and accomplishment that you just can't quite explain," she said.

The Rev. Dr. Martin Luther King Jr. helped lead the boycott, and thousands participated. For the transit system, it was a swift kick in the pocketbook. Whites retaliated, sometimes with violence, sometimes with arrests and fines for offenses like conspiring to interfere with a business. Dr. King was jailed. The civil rights movement was energized.

"We didn't have time to sit still and be scared," Ms. Glass said.

In November 1956 the Supreme Court ruled that Alabama's laws allowing segregation on the buses were unconstitutional. In December, the boycott ended.

Thelma McWilliams was born in Mobile, Ala., on May 16, 1916. Her father was a hotel cook and her mother a homemaker who sometimes helped her husband. Education was a high priority, and Ms. McWilliams graduated as valedictorian from Dunbar High School in Mobile at age 15. She earned a bachelor's degree from Alabama State University and a master's from Columbia, both in geography. She taught geography at Alabama State for 40 years, and an auditorium there is named for her.

In 1942 she married Arthur Glass, who also taught at Alabama State. Mr. Glass died in 1983.

On July 20, just a few days before her death, Professor Glass attended a black tie gala at the university, clad in an elegant gown.