In 1997, a PhD student named Suzanne Simard claimed to have discovered something that challenges everything that we think about plants and whether they ‘think’ like us.

Simard, a self-styled ‘forest detective’ and the daughter of a long line of foresters, was fascinated by the ability of a forest to heal itself if left alone after too aggressive logging practices. In her thesis she set out to find out why.

What she discovered was extraordinary. Forest trees share food and nutrients via a complex network of fungi that form a web between the roots of different trees and have specific roles in locating nutrients, water and carbon and spreading them around.

In this ‘wood wide web,’ as she termed it, trees can ‘broadcast’ to other trees throughout the forest. ‘Mother trees,’ as she calls them, actually recognize their offspring and will nurture them.

By tracing the carbon transferred between trees, Simard and Susan Dudley at McMaster University in Canada discovered that these mother trees would transmit the carbon to an offspring or kin seedling.

‘I don’t know how they recognize their kin,’ Simard remarked in an interview in New Scientist, ‘but I assume it’s by chemicals because when we allow seedlings to connect with the mother trees or with their siblings, through these [fungal] networks, we get responses much more dramatically than if they connect with non-kin. It changes the rooting behavior. It changes their chemistry, the nutrition of the plants and the response to disease.’

These mother trees also act as hubs of information to help other trees in the forest survive.

All of Simard’s work demolishes the Darwinian view of plants and trees as solitary organisms competing for survival over scarce resources. As Simard said: ‘The key finding is that trees are in a connected society, and that it’s a physical network and that they trade and collaborate and interact in a really sophisticated way as a cohesive, holistic society.’

But the idea that trees are caring and sharing also suggests something a little unsettling to scientists: that they are sentient organisms. Simard is convinced that they are, as we know they register biochemical responses to injuries or disturbances, like having their leaves eaten by a herbivore. ‘If I injure trees so much that they start to die they start sending their carbon through their roots to their neighbors,’ said Simard.

Her work is redolent of the work of the late Cleve Backster, at the time America’s leading lie-detector expert, who hooked up a Dracaena plant in his office to some of his lie-detector equipment one evening in 1966 as a late-night diversion.

A lie detector is sensitive to the slightest change in the electrical conductivity of skin, but also monitors changes in blood pressure, respiration, and the strength and rate of the pulse. Low levels of electrical conductivity indicate little stress and a state of calm. Higher electrodermal activity (EDA) readings indicate that the sympathetic nervous system, which is sensitive to stress or certain emotional states, is in overdrive – as would be the case when someone is lying.

In order to elicit the equivalent of alarm in a plant, Backster knew he needed somehow to threaten its well-being. It was obvious to him that he needed to pose an immediate and genuine threat: he would get a match and burn the electroded leaf.

At the very moment he had that thought, the recording pen swung to the top of the polygraph chart and nearly jumped off. He had not burned the plant; he had only thought about doing so. According to his polygraph, the plant had perceived the thought as a direct threat and registered extreme alarm.

He ran to his secretary’s desk in a neighboring office for some matches. When he returned, the plant was still registering alarm on the polygraph; the pen continued on its wild, zigzag course. Backster then returned the matches to his secretary’s desk. The tracing calmed down and began to flat-line.

He hadn’t known what to make of it.

This plant, it seemed, had read his thoughts. The plant somehow must be attuned to its environment, able to receive far more than pure sensory information from water or light.

He and his partner, Bob Henson, set about replicating the initial experiment after modifying the polygraph equipment to amplify electrical signals so that they would be highly sensitive to the slightest electrical change in the plants.

They discovered a number of characteristics: the plants grew attuned to the comings and goings of their main caretaker; they also maintained some sort of ‘territoriality’ and so did not react to events in the other offices near Backster’s lab. They even seemed to tune in to Pete, his Doberman Pinscher, who spent his days at the office.

Most intriguing of all, there seemed to be a continuous two-way flow of information between the plants and other living things in their environment.

Backster enlisted an impressive array of chemists, biologists, psychiatrists, psychologists and physicists to help him design airtight experiments.

Despite near universal ridicule in the mainstream media about his ‘preposterous’ idea that plants can pick up human intentions, Backster stubbornly carried on with his research for some 40 years, eventually amassing file drawers full of studies of what he referred to as ‘primary perception.’

A variety of plants that had been hooked up to his polygraph equipment showed evidence of a reaction to human emotional highs and lows, especially threats and other forms of negative intention.

Largely because he lacked scientific credentials, Backster was never recognized for his contributions. But he had stumbled across the first evidence that living things like plants engage in a constant two-way flow of information with their environment, enabling them to register even the nuances of human thought. The more advanced scientific knowledge of physicists Fritz-Albert Popp of Germany and Konstantin Korotkov of Russia was needed to uncover the actual mechanism of that communication.

Their research into the nature of quantum light emissions from living organisms suddenly makes sense of Backster’s findings. If thoughts are another stream of photons, it is perfectly plausible that a plant could pick up the signals and be affected by them.

Backster’s work suggests something profound about the true sentience of plants and trees only hinted at by Simard’s work. Plants not only are aware of each other; they’re aware of us. And not only what we do but what we think. And every last thought we have may just possibly augment or diminish their light.