What A Plant Knows

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Robert Pavlis

Daniel Chamovitz has written a book called “What a Plant Knows”. An interesting title, but can a plant really know anything?

what a plant knows
What a Plant Knows

 What a Plant Knows

The book is well written and easy to read . The author presents scientific information about the internal workings of a plant in a format that can be understood by most readers even if they don’t know anything about plants. He also provides an historical perspective on some of the experiments that were performed in the early days to better understand how plants function and interact with their environment. The experiments are covered in light detail – just enough to keep it interesting and help you understand the concepts without making it boring.

The book is worth reading, especially if you are a gardener.

Anthropomorphized Plants.

Unfortunately, Chamovitz feels the need to sensationalize the topic. It is not good enough to just talk about the fantastic things plants are able to do. He decides to exaggerate the functionality of plants in order to sell his book. Why is this such a big deal? Because the casual reader will walk away from the book with the wrong understanding of what plants are able to do and not do.

The author understands that he is sensationalizing things. He writes “I ask that you humor me while I use terminology  … that is usually reserved for human experiences. …. I believe this terminology will help challenge us to think in new ways” . It might do that, but I think it will confuse the general public. It will have people thinking plants can do things that they really can’t do.

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Plants See Your shirt Color

Lets look at at a couple of examples from the book.

Chamovitz writes, “Plants see if you are coming near them. They even know if you are wearing a blue or a red shirt”.

These two sentences imply a lot about a plant. Firstly it can ‘see’ which means it has eyes and a brain that takes the signals from the eyes and makes sense of the information. The author quickly points out that plants don’t have eyes and we know they don’t have a brain. They do have sensors that detect light, but that is not the same as ‘seeing’.

What about the ‘you are coming near them’? In order for a plant to know this they would need to have an understanding of the concept of ‘you’, as opposed to ‘me’. You being their gardener are special and they can distinguish between the two of us. They would also need to understand the concept of distance in order to know that you are getting nearer to them. Plants can’t do either of these things.

Can they tell if you have a blue or red shirt? Well sort of. If light reflects off your shirt to the plants, their receptors can distinguish between red and blue light. Is the light reflecting from your shirt strong enough to make a difference to the plant? The book does not indicate that this is the case. I suspect the answer is no, unless you stand very close to the plant. Plants are not going to react to your blue short at 40 paces. And lastly, plants don’t know that you are even wearing a shirt – they have no brain, and cannot comprehend the difference between a shirt and anything else that is red or blue.

If we take the above quote “Plants see if you are coming near them. They even know if you are wearing a blue or a red shirt” and state it correctly, we could say that ‘plants have receptors that can detect blue light, and red light’. I think this is fairly impressive considering the simple structure of plants. I don’t believe it needs to be sensationalized to make it into a good story, unless you want to sell more books.

Plants Smell, Feel and Hear

The book goes on to tell you that plants also smell, feel, hear,remember and know things. None of these are true!

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In fairness to the author, he understands they are not true, and even says so in the book. For smell he gives a definition of ‘smell’ and then says, “smell involves the brain and nervous system … and plants don’t have a nervous system” and he concludes that plants don’t smell. He then goes on to suggest that if we redefine ‘smell’ to include plants then we could say they can smell. So what! If we redefine what a martian is, we would all be martians! What is the point of that.

What Do Plants Really Know?

Plants are able to sense chemicals in the air. They are also able to produce certain chemicals when, for example, an insect chews their leaves. This leads to some fascinating science. Two plants are sitting next to each other – maybe at a bar. Insects land on plant A and start chewing the leaves. The plant produces some chemicals in response to this chewing and one or more of the chemicals are released into the air. Plant B senses these chemicals and in response plant B makes certain other chemicals that will help to ward off an insect attack.

The book interprets these findings in the following way. Plants ‘know’ they are under attack buy the insect. They ‘communicate’ with other plants near them letting them know of the dangers. As a result of this communication Plant B defends itself.

Here is what really happens. Plant A does not ‘know’ insects are eating its leaves – it would need to have a brain to ‘know’ anything. The biology of the plant is such that when a leaf is damaged, a variety of chemical reactions take place in the leaf. These happen automatically and are pre-programmed by the genetics of the plant, and are the result of fairly basic chemical properties and reactions. Some of the chemicals produced may poison insects – they are natural pesticides produced by the plant. Others may be volatile so that they easily evaporate into the air. There is no thought process taking place. There is no grand plan to save its neighbors. Think of it this way. When you through a rock into the water, it makes ripples. The water does not know a rock was thrown. The water does not think about making ripples. It all just happens because of simple chemical and physical properties of water. Plants react the same way, but of course the system is more complex.

Plant A has put a new chemical in the air that was not there before the insect attack. If the neighboring plant is able to sense this chemical, the chemical start a new chain reaction in plant B. This chain reaction is completely automatic. The plant is not aware that it is taking place – it needs a brain to be able to be aware. The chain reaction only happens if plant B is generically programed to react to the specific chemical produced by plant A. This is more likely if plant B is the same species or in the same family, and less likely if the two plants are more different from one another. One of the reactions in plant B might increases the concentration of a natural pesticide in the leaves, and this might just be enough to keep insects away. Plant B has no knowledge of any pending insect attack, nor does it know how to ‘defend’ itself. It simply has an automatic pre-programed reaction to the chemical produced by pant A.

My description is not nearly as exciting as what the book says, but if you understand the complexity of what is going on, it really is fascinating stuff! When this phenomena was first discovered nobody believed that plants were able to do such things. The science is fascinating on it’s own without sensationalizing it with words like ‘know’ and ‘communicate’.

My suggestion is that you read the book. Just smile to yourself at some of the sensational language used in the book, and focus on what plants can really do. That alone is fascinating enough.


1) Photo Source: Daniel Chamovitz

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Robert Pavlis

I have been gardening my whole life and have a science background. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

2 thoughts on “What A Plant Knows”

  1. Thank you for another great post!

    I once had an interesting conversation with someone who read and misunderstood this book and claimed that plants were very intelligent. After explaining some of the concepts you wrote about (that were even mentioned in the book) and explaining some of the science behind it she replied with words to the effect of “we all have different truths, my truth is that plants are intelligent”. Wow, how do you reply to that?

    • That is a very common problem. When people can’t explain their beliefs in logical, reasonable ways, they simply say they believe. If you believe – you can explain and justify just about anything.

      You can not use logical arguments in such a situation. You can simply agree to disagree.


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