Plants cry for help.

Don't read this if you're prone to depression. From LiveScience:

When injured, plants can cry for help via a chemical phone call to the roots.

If under attack by a pathogen, such as disease-causing bacteria, a plant's leaf can send out an S.O.S. to the roots for help, and the roots will then secrete an acid that brings beneficial bacteria to the rescue, scientists announced today. The finding builds on research earlier this year showing that parasitic plants can tap into a host plant's communication system.

"Plants are a lot smarter than we give them credit for," said Harsh Bais, assistant professor of plant and soil sciences at the University of Delaware. "People think that plants, rooted in the ground, are just sitting ducks when it comes to attack by harmful fungi or bacteria, but we've found that plants have ways of seeking external help," he notes.