What makes plant tick?
What
eventually converted me to the plant (and algal) world – as I’m fond of saying
– was the image of a plant cell projected onto a wall in the Old Botany
Theatre, at the University of Melbourne. Within the cellulose impregnated
cell-wall there were sacks of DNA, to run the show, and others crammed with
photoreceptors and the apparatus needed for the solar-powered conversion of
carbon dioxide into oxygen and sugar. Along with other bibs and bobs. Who would
have known?
A
teacher friend took me aside once after I told this story and answered this
question for me. Well, she said, ‘You, for a start’. Despite me having not
studied biology at secondary school, it was apparently inconceivable I hadn’t
been told in junior science that plants were made up of cells containing things
like nuclei and chloroplasts.
In
any case, the image did the trick. I dropped maths and physics and headed full
throttle into botany, seasoned with a little organic chemistry and genetics to
help me better understand what went on inside those cells.
By
inclination, then, I seem to be a reductionist. To understand, I first break
something down into its constituent parts, then reassemble as each part becomes
knowable. Add to that my acquired trade as a taxonomist, where I look for
characters – shared and unique – to make sense of the world created by those
plant cells, and you begin to understand why detail matters to me.
To
honest, though, an encounter with an unknown plant or alga typically begins
with its gestalt, and then moves on to a more considered assessment
through reducing it to a collection of traits. I apply the same approach in
this first selection of essays, starting I’m sure with a preformed views of
some kind and then picked away at the question until I confirm my bias or – and
yes it does happen, good scientist that I am – I persuade myself to change my
mind.
Some
of these phenomena are well understood but often misconceived. That includes
why we don’t water our gardens in the middle of day, why some hydrangeas are
pink, and why (almost) no amount of plant and flower material in your bedroom
will suffocate you.
Others present me with that inconvenient or uncomfortable truth – that we just don’t know. An observation that cannot be easily explained, or one that is no better understood through reductionism. This includes plants that seem intelligent, plants that ‘talk’ and why patting a plant might be good for it. In time I expect these extraordinary ideas to be proved or disapproved, but for now, they mock me like the smile of Lewis Carroll’s Cheshire Cat who, it must be said, was often right.
Just when you thought it was safe to return to the garden, scientists warn us of plants screaming, complaining or, on a quiet day, chattering amongst themselves. Not singing, says one commentator helpfully, but another believes they are ‘literally crying out for help’.
Perhaps
I was too hasty in my previous essay to dismiss sentience in the vegetable
kingdom. The idea of a sensitive plant may be more than a poetic
allegory. If they can communicate with each other, and with animals, then it’s
not a big stretch to say they have feelings.
Things are certainly getting curiouser and curiouser. Or perhaps just
dumber and dumber.
First
up, plants do make sounds. A few years ago, I interviewed Melbourne
scientist turned music composer, the late Martin Friedel, about how he
converted the sound of clicking sap, burrowing insects, singing birds, swaying
branches and even base notes from water moving through roots into music for human
ears. Friedel took his highly sensitive microphones into forests and botanic
gardens, capturing every utterance he could associate with a tree.
That
made sense to me. You can hear most of these noises if you listen carefully. On
the other hand, the plaintive cries and complaints captured in recent
experiments are what we call ultrasonic, which means the frequency of the sound
is above what most humans can detect. A good microphone will pick them up, but
it doesn’t make for very interesting listening given we still can’t hear
anything.
If we could, we would hear a an occasional (ultrasonic) blip – maybe one per hour – from a healthy, and apparently relaxed, plant. If you drop the pitch and slow these noises down, they sound like popcorn popping or a knuckle cracking. Add some stress to the life of a tomato, tobacco, wheat, maize, cactus or grape vine (just some of the plants tested) and they become decidedly chatty.
[...]
* * *
Another teaser from my new book of 50 essays, The Sceptical Botanist: Separating Fact from Fiction (CSIRO Publishing, 2025), available from 1 August 2025 at CSIRO Publishing and all good bookstores.
Today, the introduction to a chapter of 10 essays about the way plants work. The short extract from the second essay in this chapter was first published earlier this year, in the February issue of Gardening Australia magazine.
Jerome Entwisle provided the cartoon for this essay, here and in the book.
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