Dozens of popular courses in psychology, statistics, biology and other fields are also offered primarily online. Students on this scenic campus of stately oaks rarely meet classmates in these courses.

Online education is best known for serving older, nontraditional students who can not travel to colleges because of jobs and family. But the same technologies of “distance learning” are now finding their way onto brick-and-mortar campuses, especially public institutions hit hard by declining state funds. At the University of Florida, for example, resident students are earning 12 percent of their credit hours online this semester, a figure expected to grow to 25 percent in five years.

This may delight undergraduates who do not have to change out of pajamas to “attend” class. But it also raises questions that go to the core of a college’s mission: Is it possible to learn as much when your professor is a mass of pixels whom you never meet? How much of a student’s education and growth  academic and personal  depends on face-to-face contact with instructors and fellow students?

“When I look back, I think it took away from my freshman year,” said Kaitlyn Hartsock, a senior psychology major at Florida who was assigned to two online classes during her first semester in Gainesville. “My mom was really upset about it. She felt like she’s paying for me to go to college and not sit at home and watch through a computer.”

Across the country, online education is exploding: 4.6 million students took a college-level online course during fall 2008, up 17 percent from a year earlier, according to the Sloan Survey of Online Learning. A large majority  about three million  were simultaneously enrolled in face-to-face courses, belying the popular notion that most online students live far from campuses, said Jeff Seaman, co-director of the survey. Many are in community colleges, he said. Very few attend private colleges; families paying $53,000 a year demand low student-faculty ratios.