In recent years, the argument that "plants also have emotions" has appeared more and more frequently in various popular science books. Do plants really have emotions? In the vast plant kingdom, what is the real secret?
Under the mask of "science"
"Plants also have emotions"—if this is just an anthropomorphic technique used in literature, it is understandable; but if it is a dissemination of knowledge, we should ask: Is this true?
"Twitching" cabbage
As early as 1848, Gustav Theodor Fechner, a professor of physics at the university of Leipzig in Germany, put forward a view: "Plants also have emotions, just like people and animals. If you want the plant to grow healthier, you must chat with it often and pay attention and love to it. However, since Professor Fechner's research areas were mainly psychophysics and philosophical psychology, and because he was in the stage of resuming work after the initial recovery of a serious illness, his idea did not attract much attention.
One of the first people to draw attention to This idea of Fischner was the Indian scientist Jagatish Chandra Bose, whose main contribution in the field of biophysics was the use of physical methods to give empirical evidence that various stimuli can trigger electrical conduction in plants, such as injuries and chemical agents that stimulate plants. Since the 18th century, the public has accepted the fact that there are electrical phenomena (potential differences) in animal-specific cells and muscles. However, the theory that electricity is also present in plant tissues is not widely accepted. Bose began experimenting with plants in 1900 when he invented a highly sensitive instrument that could measure the potential of plant tissues. Bose, with the help of the instrument, found that every plant, and even every part of the plant, seems to have a sensitive nervous system, which can undergo subtle shape changes (such as bending, swelling, etc.) under external stimuli. He called this change "twitching," similar to the twitching of animal muscles. Once, the famous British playwright George Bernard Shaw visited Bose's laboratory. It is said that after witnessing the intense "convulsions" of the cabbage in the process of being cooked, the vegetarian's heart was greatly shaken. Bose claims that plants grow faster in pleasant music and slower in noisy, harsh noises. He said that plants understand both feelings and pain, and these conclusions were obtained by analyzing and comparing the cell membrane potential fluctuations of plants in different environments. Bose also said that a plant that grows under the care of care and affection for love exhibits "convulsions" that are completely different from those that endure pain. The remarkable movements of plants such as flycatchers, thatched grasses, and mimosas have long been described, and Bose claims that he has observed similar phenomena in algae and even fungi. He said: "Don't these records tell us the characteristics of some universal and persistent substance?"
"Frightened" Hilin taro
Bose's experiment ended here, but some later researchers took Bose's conclusions out of context, and with the help of some experimental appearances, pushed the theory of "plants also have emotions" to the peak. Since the 1960s, because the use of some science and technology has done more harm than good, which has had a negative impact on the environment and people's lives, the public has developed a hostile attitude towards some scientific and technological achievements, especially those who rely on science and technology wars to turn to new ways to understand our universe. In response to this trend of thought, in 1973, the secret life of plants, co-authored by American journalist Tompkins and Gardener Bird, was published. In the book, the author describes plants as possessing the same mental attributes as higher animals such as humans, including fear, pleasure, communication with other creatures, and so on. One empirical evidence that the book highly recommends is a series of experiments inadvertently initiated by a polygraph expert.
The polygraph expert, Baxter, has a career in teaching lie detectors. One day in February 1966, Baxter had a whim and connected a lie detector to the leaves of the ornamental plant heylin taro in his office, and he wanted to see if the surface resistance of the leaves of the hibiscus was the same as that of human skin, which could change with each watering. For humans, a lie detector can record a subject's uncontrolled autonomic nervous system response (mainly sweating), which is often associated with lying and other emotional disorders, and the method of recording is to measure the change in skin resistance between the two electrodes. Baxter thought to himself that if the evaporation of water from plant leaves increased, the resistance between the upper and lower surfaces of the leaves should decrease and be reflected by changes in the graph recorded by the lie detector. However, when Baxter looked at the graph recorded by the lie detector, he was surprised to find that it was very similar to the graph produced by the emotional changes caused by stress when people were tested.
Driven by curiosity, Baxter began to study other reactions of plants. Once, he intended to burn off one of the leaves of a plant. While he was contemplating the matter in his mind, he was looking for matches, and he did not move the plant at that time, or even touch it. However, a dramatic scene occurred: the graph changed drastically. Surprised, Baxter deduced that the idea of burning the leaves had somehow stirred up the plant's fear. To confirm this idea, Baxter began experimenting repeatedly: drawing a match in front of a plant, thinking "I'm going to burn it" in his heart, or just pretending to burn it... As a result, he got two patterns: reactive and unresponsive. Without further analysing whether water changes the resistance of certain parts of the plant during the delivery process, or whether external factors affect the pointer of the lie detector, Baxter gives his conclusion: the reactive pattern is produced when he "wants to burn the plant", while the unresponsive pattern is produced when he "pretends to burn the plant".
Baxter's "discovery" also did not initially attract the attention of the scientific community. So Baxter did another experiment, and then said that if the shrimp were boiled in boiling water in front of the taro, it would cause the electrophysiological reaction of the taro. In other words, there is communication between plants and other organisms, and plants can respond to changes in other organisms.
In 1974, with the bestseller of the book The Secret Life of Plants, Baxter's theory became widely known. In 1975, Horowitz and three other scientists published an article in the prestigious scientific journal Science, describing their repeated Baxter experiment on boiling a harvest shrimp in front of a taro and its results. The three scientists made some improvements to the experimental conditions, such as placing the plants in an opaque room and grounding them to reduce resistance; washing the plants clean to reduce leaf dust; only three of the five water-filled containers contained shrimp and the other two filled only with water; throwing the shrimp into boiling water through a spiral pipe; monitoring the process of cooking shrimp with video; measuring with high-sensitivity instruments; and so on. A total of 60 shrimp were used in this experiment, compared to 13 shrimp in Baxter's previous experiment. From the traditional experimental example, the experimental conditions designed by the three scientists are more standardized than Baxter's. However, their experiments did not achieve the same results as Baxter's experiments. Afterwards, Baxter accused the three scientists of making mistakes in setting the basic conditions for the experiment, such as rinsing plant leaves before the experiment, which he thought would affect their relationship with the scientists.
MythBusters
The Discovery Channel's "MythBusters" program aired a program designed to experimentally confirm or refute Baxter's views. The researchers attached a lie detector to the plant and then inflicted actual or imaginary injuries on the plant and objects around it, and 1/3 of the data showed that the plant responded. This surprised the researchers, but they soon discovered that the vibrations generated by their own activities in the lab affected the polygraph's pointers, so they left the lab and repeated the experiment, still showing that 1/3 of the data showed that the plants were responding. So, is the reaction of the plant produced by the experiment itself, or is it produced by external influences? Researchers cannot make accurate judgments. So they used an EEG tracer to improve the accuracy of the recording, and the result was that no response from the plants could be observed. Next, the researchers used a machine to push the eggs into boiling water, and did not observe any reaction from the eggs (of course, some people think that this is because the eggs do not yet have the ability to communicate). This experiment at least proves that Baxter's theory cannot stand up to scrutiny. If an experiment cannot be repeated, it is not a science.
To prove that there are indeed sensory behaviors in an organism (plant or animal), it must first be shown that all or part of the organism can respond systematically to a stimulus in the outside world. The question is, how can this reaction be identified? In the case of large stimuli, the shape, size, and time interval between stimuli and responses of the signal are easy to identify; for small stimuli, what is important is how to distinguish the signal itself from the "noise", which in biological systems is similar to the electrostatic interference of a radio. The noise of biological systems is sometimes really strong, like the receptive organs of most animals that emit electrical impulses like real signals. However, these noises tend to be irregular, and it is difficult to distinguish their response to weak stimuli. To distinguish between signal and noise, it is common to either find out if a pulse with a fixed delay time occurs after the stimulus begins, or use computer technology to determine whether the average of the signal frequency during the stimulus process is higher than when there is no stimulus.
The evidence used in the book "The Secret Life of Plants" to support the theory that "plants also have emotions" can neither distinguish between real reaction signals and noise, nor can it find out the parts and structures of plants that receive signals and respond, so they cannot stand up to scientific principles. Brain nerves and sensory organs are necessary conditions for perceptual ability, people and other advanced animals have brain nerves and sensory organs, so they can experience a variety of emotions such as pain and pleasure, while plants are made of cellulose, they do not have brain nerves and sensory organs. While plants also respond to physical and chemical stimuli, there is no reason to think that plants consciously make these responses, and thus that they are cognitively capable organisms. Plants evolve as a result of natural and artificial selection, and some plants are adaptable and appear to be intelligent, and scientists call them "plant intelligence," but this is just a metaphor. In fact, there is no anatomy in the plant kingdom that is close to the nervous system of insects or even worms, much less anatomical structures comparable to the cerebral cortex of higher primates that can cope with intricacies.
"Wise" plants
The "movement" of mimosa
A pot of lush mimosa is brought to the lab, and the anesthesiologist gently touches the mimosa leaf, which quickly closes and hangs down. At this point, the anesthesiologist placed the mimosa in a plate filled with water and injected a small amount of ether into the water. Ether penetrates into the soil at the root of mimosa through water seepage holes under the pot and is "drunk" into the body by mimosa. An hour later, the anesthesiologist touched the mimosa leaf again, and even cut off a small blade, and the mimosa did not move this time. Could it be that, like animals, it was anesthetized by ether? Ether is an anesthetic that acts primarily on the central nervous system and causes general anesthesia, which causes impaired consciousness associated with inhibition of the ascending activation system of the brainstem reticular structure, while decreased muscle tone is caused by inhibition of the spinal cord. As a plant, mimosa does not have a brainstem and spinal cord, how is it anesthetized?
Mimosa leaves quickly close and sag when exposed to external stimuli such as touch, temperature rises, wind blows and shakes, a movement known as "sensory movement", which is based on the principle that the cells of the leaf pillow lose their expansion pressure. The cell vacuoles of mature plants of most plants are very large, and when the vacuoles absorb water and expand, they will push the surrounding cytoplasm to the cell wall, creating a pressure called "expansion" on the cell wall, at which time the leaves of the plant will stretch out under the support of the swollen cells. After being disturbed, the leaf pillows on its stems are stimulated to release chemicals, including potassium ions. Because potassium ions have the effect of prompting water to be rapidly expelled from the vacuole, the cells lose their expansion pressure and shrink, and the leaves quickly close and sag. So, which part of the cell does ether "anesthetize"? Mimosa cells contain a type of actin, which is common in muscle fibers in animals and is involved in the telescopic movement of muscles. The actin of mimosa is a fine mesh structure that supports the cells. The phosphoric acid in actin breaks off when the cell loses its expansion pressure, causing the actin bundle to spread out and the intracellular water to drain. Ether is a compound that can not let the phosphoric acid fall off, mimosa "drink" the ether, its cells will not change, so no matter how to touch, it will not move.
It is worth mentioning that if the mimosa and the instrument measuring the current are connected together, the mimosa emits a weak current signal when it produces a seismic movement, because the liquid in the plant cell will penetrate the cell membrane with the movement of charged ions, forming a potential difference (that is, the membrane potential) on both sides of the cell membrane. If the instrument captures this signal, it feels as if the plant is reacting to the outside world. In fact, the movement of the peduncle when the plant blossoms, the thirsty root system absorbing water in the rain, and the plant's invasion by natural enemies all produce electrical activity, which is very wrong if it is attributed to the consciousness and emotion of the plant.
The "sense of smell" of the silk seed
It is a parasitic plant whose roots and leaves are degraded, containing only a very small amount of chlorophyll, and cannot perform photosynthesis on its own. The slender stem of the silkworm is a climbing vine-like structure used to climb on other plants. When the seed seedling of the seed breaks through the soil and finds a host, it grows a suction device from the stem and pierces into the vascular system of the host plant. At this time, the root of the silk seed completed its mission and quickly withered away. After that, the silkworm depends on the nutrients of the host to grow, if it absorbs enough nutrients, it can grow 12 centimeters per day, and it can even be adsorbed on its own stem, forming a overlapping encirclement of the host. Because the silkworm absorbs a large amount of nutrients from the host and inhibits the growth of the host, once the herbaceous plant encounters the silkworm, it is almost a dead end, and even the perennial woody plants will also have malnutrition symptoms such as leaf fall, fruit fall, top branch death, leaf surface shrinkage, flowering delay or non-flowering under the entanglement of the silkworm seed.
However, the powerful silkworm also has a fatal weakness, that is, it must find a host as soon as possible after the seed is unearthed, otherwise it will not live for a month and die. Although the seeds are scattered in different places, the seeds can find their favorite host. How does it do it? Some scientists believe that it is the light and water around the host that guide the seeds of the seeds to grow in the direction of the host. But some scientists believe that the silk seed relies on the "sense of smell" to find the host. The researchers did the following experiments: they extracted the odor of the tomato plant, injected it into a rubber tube, and then planted the rubber tube with a real tomato into the soil, while also adding a glass cover to the real tomato plant to isolate the odor it emitted. The researchers then planted the seeds of the silkworm between the rubber tube and the tomato plant to see how the seeds were chosen. At first, the silk seemed hesitant, shaking and not knowing which side to choose, but soon it made a decision: reach for the rubber tube overflowing with tomato flavor. How does the seed "smell" the host? It turned out that the volatile chemicals released by the tomato were dispersed through the air, and the seeds received this signal to determine the direction of the host plant. The researchers also did an experiment in which the seeds were asked to choose between their favorite host tomato and non-host wheat, and the "diners" chose the former. Further experiments proved that the attraction to the silkworm seeds came from many compounds released by the host plant, while non-host plants such as wheat released a single compound full of expulsion signals.
Tobacco's "chemical weapons"
The "welcome smell" released by tomatoes provokes parasitic plants to track down, and this kind of troublesome thing is rare in nature, but in the wild without gardeners weeding, most plants do use their own "chemical weapons" to defend themselves against predators.
In the desert of Utah, drought, heat and lightning often cause fires. After the fire, the chemicals in the smoke awakened sleeping wild tobacco plants— one of the first plant species to grow in ashes. Hungry insects follow, greedily nibbling on the juicy, soft leaves. However, the feast did not take long to stop, and the bugs fled in a hurry. Could it be that the plants counterattacked and won? The researchers examined the composition of the leaves of tobacco plants and found that each leaf contained 5 to 10 mg of nicotine, which is equivalent to the content of nicotine in 8 to 10 cigarettes. When the insects chew on the leaves of tobacco plants, the leaves are quickly filled with nicotine, making the meal a highly toxic meal for the insects, paralyzed, their muscles tightening so that their breathing is almost stopped, and their heartbeat becomes irregular. After regaining consciousness a little, the bugs fled.
However, this war is not over. After the sun sets, the biggest natural enemy of tobacco plants emerges from underground – tobacco moths, which seem to have been born specifically to damage tobacco plants. Tobacco moths dry their wings on the ground, drink some dew, and then begin to lay large numbers of eggs on tobacco plants. Adult tobacco moths are not interested in tobacco leaves, but their larvae feed on them. Within a week, the moth larvae hatch, eating more leaves than they weigh each day. Curiously, instead of being victimized by the nicotine in the tobacco leaves, they enjoyed the meal very much. The attacked tobacco now had to activate a backup distress program— a foul smell worse than a cigarette jar that hadn't been cleaned for a whole week wafted from the leaves of the tobacco plant. Soon, reinforcements—the big-eyed bugs that love the larvae of the moth-eating moth—arrived, and it was the smell of the plants that let them know where to find their prey. The larvae of the moth soon became the belly of the big-eyed bug.
Wild tobacco defends against insects with three weapons: toxins, alarm calls, and bodyguards, and the ability to defend itself or call for help by releasing chemicals can be found in many species of plants. Some plants also release strong chemical information after being harmed by animals to alert their peers around them. The use and reception of chemical information by plants has become an important object of modern phytochemistry research. However, it should be noted that this is not an emotional communication between plants through the nervous system, nor does it carry any characteristics of transmitting information between animals.
The "wisdom" of carnivorous plants
In the plant kingdom, the most "intelligent" plants are carnivorous plants. Carnivorous plants are those that supplement some of the nutrients they need by trapping and digesting small animals or protozoa. The most well-known carnivorous plants are Nepenthes, Bottlegrass, Flycatcher, Sprouts and Tanuki.
The most fascinating part of carnivorous plants is their colorful insect traps, which are actually their characteristic metamorphosis leaves. The pitcher of Nepenthes is a bottle-shaped body with enlarged leaves in the upper part of the elongated tendrils, with a half-open lid at the mouth of the bottle, and honey glands that are used to lure insects near the mouth. Once the insect climbs on the mouth of the bottle, it is easy to step on the smooth wall of the bottle and fall into the bottle containing digestive juices. The trap is spoon-shaped or spherical, with glandular hairs on its surface, the tip of which secretes mucus. When the worm touches the glandular hairs on the leaf, the other glandular hairs curl at the same time, enveloping them in clumps. Flytraps are closed together to catch insects, and their leaves are divided into left and right halves bounded by the midrib, which can be opened and closed at will like a shell. When the insect climbs onto the leaf, the leaf closes rapidly, and the thorny hairs at the leaf edge are staggered and twisted, shutting the insect alive in the middle. The insect traps of Tanuki, which live in water, are also distinctive, with many globular sacs growing at the base of their pinnate compound lobes, usually semi-slurred, with an opening and closing opening and closing, surrounded by tentacles. When the hydra touches these tentacles, the small sac sucks it in like a vacuum cleaner, and the sac mouth closes, cutting off the flea's retreat. Tanuki is the fastest carnivorous plant in the world, and its insect-catching sac only takes 1/15,000 seconds to open and close at a time. Not only there are carnivorous plants in seed plants, but also carnivorous plants in low-level plants such as fungi, such as C. oligosporangia, which form a bacterial network with hyphae, secrete mucus on the surface to stick to the nematodes, and then invade the nematodes with hyphae to suck the nutrients of the nematodes. There are more than 50 species of carnivorous fungi, mainly preying on protozoa such as nematodes, rotifers, ciliates, grasshoppers, and amoeba.
The "intelligence" exhibited by carnivorous plants can easily be mistaken for thinking. In fact, Darwin wrote as early as 75 years to discuss the characteristics of carnivorous plants, clarifying that their rich variation is the result of natural selection.
Science is endless, and in the future we may be able to discover more secrets of plants through more advanced scientific and technological means, but that must go through a rigorous process, after all, as the highest living thing on earth, we cannot desecrate the most precious abilities given by nature.