Plants may be very different than us because they are rooted in one place while we can move. However, plants still need to be aware of their surroundings. Plants don’t have brains but they are still able to react to changes in their environment to help them survive. There are many similarities between us and plants in the ways that we sense the word.
Plants are aware of light. We have all witnessed how plants grow towards light. Plants shaded by trees may bend to the side to find a patch of light. Germinating plants must be put under artificial light when they are grown indoors. Plants can detect a broader light spectrum than us and can respond to far red light and ultraviolet light that is invisible to us. Plants are also very aware of the day and night cycle. Some species need certain lengths of dark or light to decide to bloom to make sure it is optimum conditions for pollination.
Plants are aware of being touched. There are time lapse videos of young vines reaching outwards until they touch a fence and then it winds around the fence. Windblown plants grow short and stocky, in response to the constant movement in their upper branches, they put more energy into growing thick trunks and deep roots. Plants can also sense vibrations such as an insect walking on their stem. The leaves of Wild senna will curl up when touched to avoid damage.
Plants can pick up pheromones and they can sense odors in the air and respond to them. Ripening fruit produces ethylene which other plants can sense through the air and begin fruit maturity. Coordinating the time to ripen helps more fruits be distributed by attracting big flocks of birds. A hot item in scientific research right now is how plants will release scents into the air when they are under insect attack. Other plants nearby will pick up the scent and start producing chemical compounds to make their leaves less tasty to insects. It is almost like an air raid siren but with scent instead of sound. Plant roots can also pick up chemical signals through the soil or passed to them through mycorrhizae.
Plants sense gravity. They know to send their roots down and stem up. They do this in a very similar way to what we do. When we get vertigo it is because our crystal otoconia have moved into the wrong part of our ear and need to be moved back into position. Plants use statoliths that are sensitive to being tilted against gravity to tell which way is up.
Plants can sense the temperature. Some seeds need certain lengths of cold winter days in order to germinate. We often mimic the seeds requirement for cold by putting it in the refrigerator for winter stratification. Heat is also sensed by plants. After the heat of a forest fire, pinecones will open to spread their seeds in the nutrient rich soil after the competition has been removed. Some plants need a certain daytime temperature to emerge in spring or need a certain number of cold winter nights before they reach maturity and bloom the next season.
Because plants don’t have brains or eyes, ears, or tongues it is often hard for us humans to think about them as sensing their world. We could say that plants can see because they sense and respond to light even though they don’t have eyes. The biggest difference might be that plants do things so slowly we often don’t hang around long enough to notice.
