Through the twentieth century, the roles of these organizations on campus expanded to encompass social sororities, professional fraternities and sororities, service fraternities, honor societies, black fraternities and sororities, and multicultural fraternities and sororities. Roughly 30% of the student body are members of social fraternities and sororities, while additional students are involved with service, professional, and honor fraternities. "Rush and pledging" occur in the spring semester for most Greek organizations. Kappa Sigma and the Trigon Engineering Society hold reserved rooms on the Lawn, while Pi Kappa Alpha holds the only undergraduate room on the Range.