I have never forgotten the study done by a gentleman named Cleve Backster reported in the International Journal of Parapsychology in the 1960s.
Mr. Backster who was a polygraph expert got the idea (likely from previous experiments done by the Indian scientist Sir Jagdish Chandra Bose) to attach electrodes to the leaves of plants in order to measure their electrical conductivity to certain stimuli.
He found the plants to be quite sensitive reacting to other cell tissue death, music and apparently even his thoughts. What I found most remarkable was the hypothesis that these plants may have a kind of memory. Backster had several people separately enter a room where the plants were placed, then had one of the participants attack some of the plants with a stick. Sometime later when the perpetrator came back into the room, the electrical resonance was off the scale in comparison to the other participants.
Subsequent tests of this nature have been conducted with varying results and it is obvious that this experiment would not be considered hard science however the idea that plants also have a vibrational life force that allows them to perform complex bio-communication amongst other plant and insect species may not be that far off.
Even on the most basic level, we can observe the intelligent and complex workings of plants from their brilliant colors, germination, adaptations, pollination techniques, and even something as simple as moving towards the sunlight or flowers opening and closing with daylight.