Inter-Plant Communication

After hearing about the plot of "The Happening", I wondered how much evidence there is for inter-plant communication. Surprisingly there is quite a bit. The most interesting of which is the use of chemicals to attract carnivorous predators of herbivores. Check out a summary of the evidence for inter-plant communication.
From the Figure Legend of the picture:
Plants respond to herbivory with the emission of chemical cues above and below ground, which can elicit responses in (1) carnivorous enemies of the herbivores, (2) herbivores and (3) neighbouring plants. The plant–plant interactions comprise interactions among conspecifics and heterospecifics. The red broken arrow represents herbivore attack on a plant; the blue arrows represent the emission of chemical cues that affect other organisms. The thickness of the blue arrows indicates the relative knowledge of the interactions.