If you’ve ever had the pleasure of watching a sunflower slowly turn its head to track the sun, you’ll know that plants are quite good at scanning their environment to get what they need. But in The Light Eaters, US climate journalist Zoë Schlanger invites readers to ponder the idea that plants deploy many, and much more sophisticated, smarts, most of which remain invisible to us.
Plants can talk, they can hear, they can count – they decode myriad signals from their surrounds and act in their own best interest.
Talking trees are not new. Some early writing about the wood wide web – the vast underground communication network in forests – has been criticised for exaggerating somewhat, but we now have plenty of research evidence that shows plants use chemical signalling, above and under ground, to warn their neighbours of an insect attack. They “talk” among each other and also directly to the insects that eat them. Making their leaves taste bitter and unpalatable is an unmistakable chemical signal to buzz off.
But plants tuning into soundscapes and completing simple maths?
Schlanger writes with the passion of someone who has become obsessed with their topic, and chapter after chapter is stacked with delightful examples of recently discovered plant skills, including the use of hairlike structures on leaves to detect vibrations that are imperceptible to us. These plants can indeed sense the munching sound of a caterpillar or the footsteps of a moth.
And the Venus flytrap you may have seen catching prey? It will snap shut only if two spiky hairs inside the gaping trap are touched within 20 seconds of each other and, remarkably, it injects digestive juices only if the hairs are triggered five times in quick succession within the closed trap.
Even more intriguing are examples of plants using sound to aid their reproduction. Schlanger joins botanists studying a plant in the Central American rainforest whose ruby flowers can be pollinated only by a bat. Its leaves are shaped like satellite dishes so when a bat comes along, echo-sounding to navigate in the dark, they amplify the echo, guiding the bat straight to the source of nectar.
In an even more sophisticated version of this acoustic trick, another bat-pollinated plant has special sound reflectors on each flower. Once a bat has opened the flower, picking up pollen along the way, these small leaves bend away to leave only unopened flowers still signalling.
Schlanger has turned her attention to botany to ward off disillusionment from reporting on climate change. It worked. Her metaphors are refreshingly original, her enthusiasm contagious, her seemingly boundless curiosity and open-mindedness uplifting.
As engaging as her botanical writing is, it gets even better when she describes the human characters involved in the quest to understand plants. Timing is on her side. She enters the field of botanical research as new technologies are opening possibilities to measure and visualise molecular processes like never before. In the chapter on electrical signals, she watches as an anaesthetised mimosa stops shrinking away from touch and shares in the joy as botanists succeed, with the help of fluorescent dyes, in tracking an electrical pulse travel along a plant’s vascular system.
Botany has also finally recovered from the reputational damage (which Schlanger chronicles) caused by the publication of the 1973 bestseller The Secret Life of Plants, which perpetuated myths of houseplants as sentient beings with a preference for classical music over rock.
The idea of plant intelligence remains a touchy and controversial subject among botanists, but they now have the tools to explore its underlying capabilities, such as memory. Consider the humble garlic, which won’t sprout without a memory of winter. As gardeners know, some fruit trees and flower bulbs do the same.
And there is a colourful, star-shaped flower that can remember the time intervals between bumblebee visits and anticipate the next pollinator visit. It will parcel out dollops of pollen and present them only when it expects a bee to show up – making the most of each chance it gets at reproduction.
“Without memory, very little can be done intelligently,” Schlanger writes. As she joins scientists on far-flung field trips and in some of the world’s best botanical gardens, she works up to the essential question. How does something without nerves and a brain detect signals from its environment, triage multiple stimuli by importance and translate it all into action that benefits itself?
The answer may be surprisingly simple. What if the whole plant acts like a brain – a cellular network in which the whole adds up to more than the sum of its parts?
We tend to take plants for granted and regard them as lesser than our fellow animals. It’s called plant blindness. Schlanger has come up with an enlightening and entertaining cure.
