Corn is authentically American. A member of the grass family, it was first domesticated from a wild grain several thousand years ago by Aztec and Mayan Indians in Mexico and Central America. The first corn was a loose-podded variety that looked like the seed head at the top of wheat stalks. The kernels were small and each covered by a hull. Central and South American peoples came to depend so heavily on corn — or maize — that they devised some of the earliest calendars just to keep track of their corn planting and harvesting schedules.
Eventually, corn’s popularity spread to North America. By the time the first European settlers arrived on this continent, corn was the chief food crop of the native Indians. The colonists quickly learned how to grow corn and enthusiastically adopted the new staple. In fact, much of the early fighting that took place between the settlers and the Indians was over cornfields. Today, the cornfields of Nebraska and elsewhere in the world actually make sounds of growing.
In 1620, Sir Matthew Lister introduced the rhubarb plant (native to Mongolia) to England for the first time, where it was praised for its medicinal qualities. It wasn’t until the 1780s that rhubarb was used in pies as a substitute for other fruits.
In the early 1800s, the growers of the Rhubarb Triangle developed “forcing,” which enabled them to produce rhubarb in much greater quantities than ever before. Basically, they allow the rhubarb to grow naturally in a field without harvesting for two years. During this time, the plants are storing energy from the sun in their roots in the form of carbohydrates. After this period, usually in the winter months, the rhubarb is moved into a heated shed which is kept in complete darkness. The supplied heat means they no longer need to use any of their stored energy to make leaves (which turn a sickly yellow-green color), so all of it goes into making the stalk larger (and sweeter).
Hearing Plants Grow
This “forcing” is so successful that you can actually hear the rhubarb growing if you go into the sheds. The buds cracking open is what makes the sound, and there is said to be a constant creaking during growing season. In addition, the rhubarb has to be gathered in very low light, usually candlelight, because the plants are so sensitive to light that the “forcing” would stop.
Of course trees have been around since the beginning of time. In Germany, using Ulmus glabra (elm tree), Lashimke et al (2004) revealed that acoustic emissions from plants do not necessarily occur in conjunction with water stress. The waveforms in the various signals show that acoustic emissions may possibly be generated by still unknown hydraulic events, more complex than cavitation. According to Maeder (2017) plant physiologists have known for several decades that plants emit sounds. He feels that bigger part of these ‘crackling’ or ‘whispering’ sounds emitted by trees [you can listen to the sounds of a Scots Pine tree at this web site] are of transpiratory/hydraulic origin and are therefore related to the circulation of water and air within the plant as part of the transpiration process [the sonogram to the right is of these scots pine emissions]. The frequencies of the loudest acoustic emissions (the so-called cavitation pulses) lie mostly in the ultrasonic range, depending on the species-specific characteristics of plant tissues.
There is something about those Nebraska cornfields, the fields of the Rhubarb triangle of Leeds, England, the elm trees of Germany , or the Scots pines that make eerie noises. Farmers worldwide have long told the story that “on a quiet night you can hear the corn [or rhubarb, or even trees] growing”. Likely there needs to be special equipment to really hear plants and trees, but they do make an acoustic signature through their emissions.
While may seem a bit like something out of a Stephen King movie where children, animals or others are lurking in the fields or talking through these plants, there is now evidence that supports their is quite an emittance of noise by plants while growing.
Plants Make Sounds When Under Stress
Researchers at Tel Aviv University in Israel have discovered that plants emit high-frequency clicking sounds when they are under stress, such as being cut or experiencing dehydration. While these sounds are inaudible to human ears, they could be heard by insects or mammals.
The researchers used microphones to record the sounds emitted by various plants, including tomatoes, tobacco, wheat, corn, grapevines, and cacti, in a controlled acoustic environment. By training a machine-learning algorithm to differentiate between different stress levels, the scientists aim to understand the purpose and potential communication aspect of these plant sounds, which could play a role in attracting pollinators or deterring predators.
Researchers recordings found that the plants in the experiment emitted sounds at frequencies of 40-80 kilohertz. Unstressed plants emitted less than one sound per hour, on average, while the stressed plants – both dehydrated and injured – emitted dozens of sounds every hour.
Although we may not hear them, plants communicate through ultrasonic vibrations, and their ability to emit sounds suggests a previously unknown aspect of their interaction with the environment. The study raises questions about the purpose and function of these sounds. It is still unclear whether the sounds are intentional communication signals or byproducts of physiological processes. Researchers are exploring whether the sound-emitting plants may use their sounds to attract certain insects for pollination or to deter predators. Further investigation is needed to unravel the complex relationship between plants, their sounds, and their ecological interactions.
Understanding the acoustic communication of plants opens up new avenues for research and sheds light on the hidden world of plant behavior. While we may not perceive these sounds directly, they have the potential to influence the interactions between plants and other organisms in their ecosystem. By studying these ultrasonic vibrations, scientists hope to uncover more about how plants communicate, adapt to their surroundings, and respond to stress.
References:
Cook, D., (2016). Acoustic Emissions Techniques to Explore Corn Stalk Growth and Breakage. Presentation to the 172nd Acoustical Society of America Meeting, Honolulu, Hawaii, November 28,
December 1, 2016. Retrieved July 4, 2017.
Laschimke, R., Sigmaringen, F., Burger, M. & Vallen, H. (2004). Acoustic emissions from transpiring plants – new results and conclusions. NDT Net. Retrieved July 4, 2017.
Van Duisen, M., (2013). Rhubarb grows so fast you can hear it. Knowledge Nuts. Retrieved July 4, 2017.
