They fight for territory, seek out food and evade predators, they just do so at a different speed to us and so it goes unappreciated. As we’ve seen this month, plants move with purpose and are aware of what is going on around them, they have to be because of their static nature.
Up to 80% of the plant lives underground so a lot of activity goes unseen by human eyes. Roots are not the passive things we have assumed, instead they actively seek the nutrients and water they need and as they approach these resources, root growth speeds up. It then slows down so the plant gets to absorb more of them, essentially the plant is foraging. But because this intentional activity goes unseen, humans tend to assume the plant is almost lifeless.
Plants carry out the equivalent of feeling, smelling, hearing etc, they just do so in a plant-centric way, not a human-centric way. Which of course makes a lot of sense, the plant is evolved to care about what plants need. So whilst they aren’t interested in the latest top 40, they are tuned in to the sound of caterpillars munching, that is to say, they have ecologically relevant senses and responses.
“Light for a plant is much more than a signal; light is food.”
– Daniel Chamovitz
Plants use photoreceptors so that they know what time of day and year it is and they respond accordingly. This is how, for example, trees know when it’s time to blossom or let go of their leaves. They can “see” the light and use this to compare the amount of light and the amount of dark. This lets plants identify when it is spring or autumn and hence signals appropriate action.
Experiments have shown that roots are actually sensitive to sound and can communicate, in a plant sort of way, with other plants. They can sense sound and make sense of it, for example they can hear roots of other plants growing and they respond by growing towards that sound.
They can also hear the sound of caterpillars munching away, a very real threat to a plant. If a plant can detect this on nearby plants etc, then they can get their defences up. And as insects use vibration, and sound is vibrations, it makes sense that plants have developed ways of sensing this.
Whilst the realm of plant’s hearing is not one which has been investigated very much, there have long been claims that talking to your plants helps them grow.
Smell is where plants really shine.
Plants can smell themselves, they know when their fruit is ripe, they smell their neighbouring plants, they smell danger and some can even tell between different species of plants based on smell. We can utilise this to use one plant to ripen another, eg bananas being placed near avocados to ripen them quickly. This is actually down to the ethylene which is high in ripening fruits and means that you can also speed up citrus ripening using kerosene. The reason that plants might want to ripen together is to increase the chances of pollination and ensure that the pollination results in reproduction. Very important considering that 99.9% of pollen goes nowhere and fertilises nothing…
We’ve seen the magical ways in which plants defend themselves through use of smell already but plants, obviously, use scent to attract as well as repel. The beautiful fragrance of a rose? That’s there to grab the interest of a pollinator. At the other extreme are plants which smell like rotting meat because they’re interested in attracting dung beetles. Scent is particularly important for night flowering species who can’t use attractive colours to increase their changes of reproduction.
Plants know when they are being touched, they can tell the difference between hot and cold, they know when they are swaying in the breeze. Plants have proprioception which helps them to optimise their positioning.; even as seeds, plants know which way is up and which is down.
And they can also feel themselves, not just sensations acted upon them. If, for example, a tree is hurt, they bloom more heavily to ensure they have more “babies” that year even though this might take everything the tree has. They sacrifice themselves for the species.
There are also plants such as the venus fly trap and the mimosa plant which visibly react to touch.
Whilst it’s easy to think that plants are static, except for external forces, they are always moving. Roots are exploring, shoots are growing. Plants just move in a plant like way. Their leaves curl and unfold, their stems grow and move and twist, their flowers open and close, and they follow the light of the sun across the sky. Tendrils curl and hold on to supports and within the plant, food and water are being transported all the time.
A plant’s view of the world is very different from our own, and it’s easy to get so caught up with being human that we don’t grant agency to species which don’t appear to act as we do. But plants are active beings, they just have plant priorities, not human ones.