McKENZIE BRIDGE, Ore. (AP) - Crews on the ground and in the air searched part of a national forest Wednesday for a University of Oregon professor who went missing days ago after telling friends he was going on a day hike.

A relative said Daming Xu, 63, may be lost without water or a cell phone in the Willamette National Forest in the foothills of the Cascade Range. He was due back Sunday for classes the next day.

The mathematics and statistics professor\'s car was discovered at a trailhead on Tuesday, and the search was centered there.

He is pretty physically fit for 63, said his daughter, Xin Xu. I mean, he hikes every week, but I don\'t think he\'s that savvy when it comes to survival skills because he never has to stay out overnight or anything like that.

Other hikers reported seeing the professor around 1:30 p.m. Sunday on a trail about three hours by foot from the trailhead where his car was found, said Lane County Sheriff Russell Berger. Searchers followed tracks believed to be his but lost them.

A mountain rescue team was flown into the area Wednesday, and 26 searchers, including six on horseback, were looking, Berger said.

The Civil Air Patrol sent up a search plane; an Oregon National Guard helicopter had joined the search Tuesday, and a second arrived Wednesday.

The hiker\'s daughter said Xu did not have a cell phone or a compass, and she did not think he had taken water with him. But deputies said there is ample water in the area, which is rugged but crisscrossed with trails.