Is there a real "tree demon" hiding in the forest? Not only does it scream, it also gives you information.

All living things, when in danger, will convulse, scream, and seek help. However, this rule seems to apply only to animals that can make sounds, while animals that cannot make sounds will keep a low profile and run away. As for plants, in everyone's impression, facing the lumberjacks with axes and saws approaching step by step, they can only sit in silence and wait for death.

In fact, the world of plants is much more lively than we think, but we just can't hear them. Their liveliness is comparable to the "tree monsters" in Journey to the West.

"Stressful, roaring!"

In fact, British botanists have solved this problem a long time ago. They used a special instrument, a plant detector, to connect the instrument wire to the plant, and people could "hear" the plant "talk" by wearing headphones. Under normal circumstances, the sounds made by plants are mild and harmonious; but when they encounter bad weather or human invasion, they will make low and chaotic sounds to express pain. In order to capture the sounds of plants, Israeli scientists set two dilemmas for tomatoes and tobacco, one is drought and the other is stem cutting. Before the experiment began, they all grew healthily in moist soil. After the experiment began, the fate of the plants was different. Some were not watered, some had their stems cut off, and some continued to live under normal conditions as a control group.

The experiment was conducted in a soundproof box, with the sound receiving equipment placed 10 centimeters away from the plants. The results showed that both drought-stressed plants and plants with severed stems could make a loud noise, with a volume of about 65 decibels (usually the volume of two people talking face to face is about 60 decibels), and a frequency between 20,000 and 100,000 Hz, which is ultrasonic.

These calls are very frequent. Tomato plants under drought stress made an average of 35 calls per hour, and tobacco plants made 11 calls. Tomato plants whose stems had been cut made an average of 25 calls in the next hour, and tobacco plants made 15 calls. In contrast, plants that were not drought-stricken and not cut only made calls occasionally. Scientists believe that these ultrasonic waves are the response of plants to the stress of survival.

Researchers use recording equipment to record the "calls" of plants

How are these sounds formed? It turns out that when there is a lack of water, the air dissolved in the water in the wood of the plant will form bubbles, which will continue to expand and even burst, forming cavitation, which will redistribute the stress in the plant. When stress is concentrated in one part, a large amount of energy may be released quickly - mechanical energy is converted into sound energy, a process called "acoustic emission."

"Tip off"

When danger comes, plants don't just stand there stupidly; they are much more active than we think.

Through experiments, physicist Wagner found evidence that plants communicate, and called the language medium through which they communicate "W waves."

Wagner found that when we cut down a tree, the adjacent trees will emit electric pulses within a few seconds. Through measurement, the speed of this "W wave" is about 10 centimeters per second. When a healthy maple sapling and a maple sapling bitten by an animal are placed together, the healthy sapling will be very "nervous". Scientists speculate that the injured sapling will release some chemical substances to warn the healthy sapling: there may be enemies nearby. Cows and sheep eat grass in one place for a while and then run to other places. Scientists have found that this is because after the leaves of alfalfa are bitten by animals, a chemical substance called protease inhibitor will be produced, which will cause indigestion and diarrhea for cattle and sheep. Moreover, the bitten alfalfa will warn the surrounding companions, "The enemy is coming, I have been bitten, you should quickly prepare for defense!" In this way, the alfalfa in a large area around will no longer be delicious.

“Cross-border communication”

Sound can also help plants and other organisms establish mutualistic relationships. Researchers from the University of Bristol in the UK have confirmed that flowers can send out weak electrical signals to indicate that bees have come to collect nectar, and hearing the buzzing of bees will increase the sugar content in nectar.

In Kalimantan, the carnivorous plant Nepenthes helmsleyi has a pitcher with a back wall that reflects bat sound waves, which attracts bats to rest in the cage and leave their excrement to nourish the plant.

Different species of plants can also form alliances. For example, the "chemical smoke signals" produced by willows can be transmitted across species and received by poplars and sugar maples. Similarly, when lima beans are attacked by insects, they can also transmit danger signals, making the wild green beans and cucumbers growing around them more defensive.

Plants are good at cross-border communication. For example, when corn is attacked by beet armyworms, they can quickly synthesize and release chemicals that attract parasitic wasps, allowing them to lay eggs in the beet armyworms. This is called "killing insects with borrowed knives."