Discover what causes Christmas cactus to turn red and how to fix it before the damage gets worse.

This is the time of year when Nicole Hughes gets constantly distracted by the fall foliage as she drives around North Carolina. "I'm always looking," says Hughes, a biologist at High Point University.

Leaves often turn brilliant colors in autumn. One of those colors has generated a lot of heated debate among scientists in recent years. Autumn is a big time for trees. Many shed their leaves, and of ...