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World Cucumber Day

A beginner's guide to plant perception

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Plants can respond in remarkably clever ways to stimuli, but debate rages on whether this can be considered ‘intelligence’. We grasp this hot potato of a subject, and throw it through the hothouse window of normality… hang on, this metaphor is confusing me now – best ignore this introduction and read the bit below. Bye.  (It was lovely to see you by the way, your hair looks great…)

Why do we struggle to comprehend that plants have an intelligence? There are probably two main reasons: plants respond to things on a different timescale to our own, and plants are weird. 

Let’s start with the second point, plants are weird. They don’t look like us (depending on who is reading this, no offence meant to the cucumber community) or behave like us, and they don’t even have a brain. Well, actually it turns out they do have a ‘brain’, of sorts: the root tips or ‘radicles’. Incredibly, scientists have shown that a plant’s radicles transmit the same signals as neurons do in an animal brain (scientists, feel free to stamp your foot if you disagree). OK, they’re not as sophisticated as a brain, but a plant can have hundreds of thousands, or even millions of radicles. And because they’re not located in one place (as in an animal’s skull), the plant has better ‘survivability’ – if it had one central ‘brain’ and a passing hippo trod on it, the plant would be killed. The idea of the radicle as the plant’s ‘brain' is not a new one – Charles Darwin was talking about it in 1880. 

However, a large number of scientists reject the idea of comparing a plant’s sensory system to a brain, seeing the two things as being far too different. Many also say that describing a plant as being intelligent is incorrect. But this depends on how you define intelligence, and there are several definitions that would apply to plants. So there! Ya boo sucks!

So what do plants use their ‘intelligence’ to achieve? To seek sunlight, to catch prey (some can even catch birds), to lure pollinating animals, to poison predators. There is even evidence that plants’ roots will alter course before hitting an obstacle, demonstrating that they can generate a complex ‘sense’ picture of the scene ahead. More remarkable still, plants will send out a chemical signal when being attacked by predators, and nearby plants of the same species will detect this message and prepare their defences. Plants can learn, and may even have memories. They also respond to sound and touch. 

Plants respond to environmental stimuli by changing their form (morphology) and movement. I’m personally only capable of the latter response, though I am trying to develop my biceps for an arm-wrestling competition. 

So slow!
As well as being weird, plants generally move very slowly compared to animals. Though they may be responding in complicated ways to stimuli, they do so in ways so much slower than ours that it’s hard to comprehend their movements and actions. Yet this isn’t true of all plants – a truly astonishing exception is the white mulberry bush, which catapults pollen at 400mph (over half the speed of sound)! Some plants that lure, catch and eat animals also need fast reactions, as well as keen senses. 

Whether we use the word ‘intelligence’ or not when describing plant behaviour, the world of plant perception and response is a fascinating one. Remember this next time you’re on a moonlit picnic with your cucumber plant. 

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