Cleve Backster was a respected operator in the controversial field of polygraphy, the use of lie detectors. But in February 1966 he became known for plant telepathy.

Curious to measure how long it took water to reach the leaves of a dracaena cane plant, Backster attached polygraph electrodes to it. These measure galvanic skin response - electrical conductivity - and should, he thought, have registered a change when water reached the leaf. Unexpectedly, the plant showed readings similar to those of a human.

Backster wondered if the plant would effect the polygraph in other ways. He dipped a leaf into warm coffee. Nothing happened. Then he considered burning the leaf; the polygraph, he claims, "went wild. The pen jumped right off the top of the chart". The plant, it seemed, had registered a stress response to Backster 's thoughts of harming it.

He then dropped brine shrimp into boiling water and the plant appeared to register the shrimps' distress. Was the plant demonstrating some kind of sentient, even telepathic, awareness?

Backster thought so and named it "primary perception". His work appeared in the International Journal of Parapsychology (1968), and in Tomkins and Bird's book The Secret Life of Plants (1973). Soviet scientists invited him to chair a panel at the first Psychotronic Association conference in Prague.

Encouraged, Backster experimented further, wiring up yoghurt bacteria, eggs and human sperm. The results seemed to demonstrate that "primary perception" could be measured in all living things, echoing the beliefs of Hindus, Buddhists and new agers.

Backster's findings are not without their critics. Repeatability is a constant problem - his results, and those of others who tried the experiments, seem to be spontaneous, refusing to comply with approved scientific method. Some have criticized his lack of control experiments, suggesting the polygraphs are merely responding to static electricity build-up in the room, changes in humidity or, according to some parapsychologists, Backster's own telekinetic abilities. That the reliability of the polygraph test itself has come into serious question also doesn't help his argument.

Whatever the case, Backster's idea has blossomed and flourished, and is unlikely to die away.