I saw this episode on Mythbusters.

http://en.wikipedia.org/wiki/MythBus...ary_Perception

http://en.wikipedia.org/wiki/Plant_p...on_(paranormal)
More recently, the television show MythBusters performed an experiment aiming to either verify or disprove the concept. The tests were done by connecting plants to a polygraph's galvanometer, and then employing both actual and imagined harm upon the plants, or upon others in the plant's vicinity. The galvanometer showed some readings which surprised the researchers initially (showing some kind of reaction about one third of the time), so a much more accurate EEG machine was used. However, when the presenters used a machine that dropped eggs randomly into boiling water, the plant had no reaction whatsoever, though they were using methods which Backster would not have accepted. The show concluded that the theory was bogus.