Kach:I remember reading some study from years past, but the subject is well above my pay grade.
I've read that trees will culture their insect protectors (i.e. they will emit sap to attract ants which eat the aphids which eat them).
This could be just a mindless evolutionary trait based on random genetic changes, but there's probably evidence that there exists an altering response mechanism based upon stimuli. Plants have been shown to grown differently in the presence of different sound vibration environments, so they must have some kind of receptor with a response mechanism.
Heck, atoms are just buzzy little consolidations of energy in a predicted space...
Quick search:
Growth and Plant Hormones - Biology Online
Tropisms- A tropism is a plant movement that is determined by the direction of an environmental stimulus.
Thigmotropism- Thigmotropism is a plant growth response to touching a solid object.
The Senses of the Plants
After "tasting" the chemical betraying the presence of an aggressor, a plant is able to unleash a chemical war against it. The most sensitive plants create a strong barrier between the aggressor (virus, bacterium or fungus) and the backward intact cells, killing the attacked cells.