The Secret Life of Plants, a 1973 bestseller by Peter Tompkins and Christopher Bird. The book inaugurated an odd era of people talking to their houseplants and playing them classical music. The CIA and US army funded research into vegetal perception (plants could be deployed in airports to detect the “turbulent emotions” of would-be hijackers, Tompkins and Bird suggested). Research on plant sensation and reaction was hindered. “The twin gatekeepers of science funding boards and peer review boards – always conservative institutions – closed the doors,” Zoë Schlanger writes.
With time-lapse videos, we can see vines sensing and reacting. Most other plants’ behaviour is invisible. Vines aside, plants are pitiful athletes, but they are often quite gifted chemists, exhaling and secreting sophisticated compounds to entice, repel or poison their neighbours. Trees excel here. The woodsy sweetness of balsam trees, the tang of pines: these are not perfumes but chemical weapons deployed in an interspecies war. They are insecticides, and there is something softly psychotic in how much we delight in their smells. Interestingly, trees can smell themselves, or at least detect their own airborne chemical compounds. A leaf, being eaten, can emit gases that prompt other branches – and other nearby trees – to defensively fill their own leaves with toxins. It is well known that acacias secrete sugars and proteins to
recruit ants as foot soldiers in their campaign against vines and caterpillars.
For bolder botanists, such findings reopen the old question of whether plants can think. Plants lack brains – traditionally felt to be a prerequisite for intelligence – but, then again, so do computers. With chatbots showing what can be achieved by neural networks, it might be time to reconsider plants. Perhaps they also have what Stefano Mancuso calls “distributed intelligence”, with the root system acting as “a sort of collective brain”. The ecologist Meg Lowman describes the treetops as a still-unexplored “eighth continent”. The tallest trees, the redwoods of northern California, contain
whole environments in their canopies. There are grasses, ferns, aquatic crustaceans and, indeed, other trees up there, unsullied by the earth, inhabiting the redwoods’ sky worlds.
Old trees, like roots bulging through the pavement, unbalance our sense of time. In Manhattan’s Washington Square Park, surrounded by New York University’s buildings, the Hangman’s Elm protrudes as an eerie relic from the 17th century but as long-lived trees go, that elm is not especially impressive. The UK has yews that are,
literally, ancient, in that they date to antiquity and are thousands of years old. The oldest known tree, a bristlecone pine in California, is about five millennia old, meaning that it was a sapling in the bronze age. (There is a tree in Chile that
might be older. And a few trees can create physically connected, genetically identical copies of themselves; these clonal trees “live,” in the sense of carrying on in replica form, even longer.) Caring for the environment, Farmer believes, will require learning to “think in the fullness of tree time”.