Why do plants grow straight? – Sara H., 5, New Paltz, New York
Have you ever attended a sporting event or concert and had to move and reposition yourself to get in the right place to see the action? Maybe you had to move left or right to see between two people. Maybe you even had to crouch in your seat to see over the person in front of you.
Well, plants often have to do something similar to be able to “see” as much light as possible. Plants need light to perform photosynthesis – making sugars from water and carbon dioxide in the air for food.
If the sunlight is directly above them, plants will grow directly towards it.
Sometimes, however, it’s not that simple. For example, you may have seen houseplants leaning toward a window rather than growing straight and tall. When light comes from an angle, plants will curve towards it to gain better access to the light they need to grow. Hormones in plant tissues, called auxins, grow the cells on the dark side of the plant, tilting the plant towards the light.
In a forest, plants can branch out so that their leaves are in open areas of sun rather than shade. This often happens if bushes and taller trees tower over them or they grow into a crowd of other plants. It’s kind of like humans seeking out sunny spots or reaching out to a campfire for warmth when they’re cold outside.[More than 140,000 readers get one of The Conversation’s informative newsletters. Join the list today.]
Humans twist or bend by temporarily changing their body position, but when plants twist, bend or lengthen, they are actually growing towards the light. The types of plants that reposition themselves to see the light are species that grow slowly but determinedly.
Other types of plants may not grow directly because they have different strategies. For example, strawberries grow close to the ground and spread laterally sending runners – stems that spread just above the ground to create new plants.
Other plants, like ivy, grow as vines that climb trees, walls, and fences and use them for support. Climbing vines can grow straight, sideways, or at an angle, depending on the types of support structures they grow on. The goal is to expose their leaves to the sun as much as possible.
In my latest book,lessons from plants“I explore how plants typically position themselves to see light. It’s fascinating that we humans often position ourselves to see something interesting.
So the next time you see a plant growing straight, check to see if the light is directly above it. Or if you see a plant that is not straight, notice if it bends towards the light coming from the direction it is facing. Or maybe it’s a vine climbing up a structure and using that support to take a different route to the sun.
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