Science Blog

One of the main distinctions between plants and animals is how they respond to stimuli. Humans have brains, where stimuli are understood and responses formed. “Emotional” responses are merely complex responses to complex social stimuli.

Plants lack a central nervous system but are still capable of processing information from external sources and responding to them. While plants don’t have the same “feelings” that we do, they often remember stimuli and communicate with other plants about them.

Plant vs. Animal Feelings

Animals have neurons that transmit sensory feelings to a central nervous system (the brain). In humans, if your brain determines that those feelings are negative and dangerous, it sends a message back to their point of origin, causing you to react to avoid the continuation of that pain.

Animals like us have memories that allow us to avoid future pain. Memories of previous injuries don’t trigger our bodies to produce adrenaline when the memory of that event returns.

Without a central nervous system, plants don’t process sensations that way. But plants do react to negative or unpleasant sensations. Touch the leaves of the aptly named sensitive plant, Mimosa pudica, and it will close them. Prune a shrub, and the shrub will produce a callous around the wound, and likely stimulate new growth below the cut.

Plants retain memories of these events—not in a centralized brain, but distributed throughout the plant, closer to where the memory is needed. This is not merely a biophysical response to stimuli. Touch the leaves of a sensitive plant repeatedly, and the plant will no longer close its leaves. It has learned that the sensation is not a threat, and will retain that knowledge for up to 40 days.

Likewise, perennial flowering plants remember when to begin growing again in spring. Blooming before pollinators have re-emerged from winter will be unproductive. Blooming while it’s still too cold could cause injury, even death. 

So many plants produce proteins that allow them to remember how many days it has been since they were last exposed to the cold, and only begin growing against when they deem it safe.

Interspecies Communication

One of the most important and frequent inter-species relationships on Earth is the mycorrhizal association between fungi and plant roots—a relationship common to some 90% of plant species.

Through these networks, plants communicate with fungi and other plants, transferring nutrients and sending stress signals. Plants share important chemicals like nitrogen, carbon, and phosphorus through fungal networks. Aloe plants, tomatoes, and other plants notify each other with electrical signals as well—the plant equivalent of electronic communication—in order to induce plant growth, improve wound healing, among other reasons. This vast neural network underground puts the Internet to shame.

Plants also signal stress chemically through their leaves. When a herbivore nibbles on a sagebrush plant or an acacia tree, the plant emits toxins not only to ward off the nibbler but to signal to neighbor plants, who also begin emitting toxins.

Plants Listen to Each Other

Like many animals, some plants also communicate using sound. Sound is nothing more than vibrations in airwaves, something plant cells can evolve to produce and plant fibers to detect.

Recent studies of plant communication show that some plants emit high-frequency sound waves.

Article Sources

• Mancuso, Stefano. The Revolutionary Genius of Plants: A New Understanding of Plant Intelligence and Behavior. New York: Atria Books, 2018, 18.
• Fu-Yu Hung, et al. “ WRKY63 transcriptional activation of COOLAIR and COLDAIR regulates vernalization-induced flowering.” Plant Physiology kiac295 (June 16 2022). https://doi.org/10.1093/plphys/kiac295.
• Nguyen, Nhu H. et al. “FUNGuild: An open annotation tool for parsing fungal community datasets by ecological guild” Fungal Ecology 29 (2016), 241–248. https://doi.org/10.1016/j.funeco.2015.06.006.
• Boyno, Gökhan, and Semra Demir. “Plant‑mycorrhiza communication and mycorrhizae in inter‑plant communication.” Symbiosis 86 (2022), 155–168. https://doi.org/10.1007/s13199-022-00837-0.
• Song, Yuan Yuan, et al. “Hijacking common mycorrhizal networks for herbivore-induced defence signal transfer between tomato plants.” Scientific Reports 4:3915 (January 31, 2014) 1–9. DOI: 10.1038/srep03915.
• Volkov, Alexander G., and Yuri B. Shtessel. “Electrotonic signal transduction between Aloe vera plants using underground pathways in soil: Experimental and analytical study.” Biophysics 4:4 (17 October 2017), 576–595. DOI: 10.3934/biophy.2017.4.576; Volkov, Alexander G., and Yuri B. Shtessel. “Electrical signal propagation within and between tomato plants.” Bioelectrochemistry 124 (2018) 195–205. https://doi.org/10.1016/j.bioelechem.2018.08.001.
• Karban, Richard, Patrick Grof-Tisza, and Charline Couchoux. “Consistent individual variation in plant communication: do plants have personalities?” Oecologia 199 (2022),129–137. https://doi.org/10.1007/s00442-022-05173-0; Bonato, Bianca, et al. “Cracking the code: a comparative approach to plant communication.” Communicative & Integrative Biology, 14:1 (2021), 176–185, doi: : 10.1080/19420889.2021.1956719; Wohlleben, Peter. The Hidden Life of Trees: What They Feel, How They Communicate. Berkeley, CA: Greystone Books, 2015, 15.
• Bhandawat, Abhishek, and Kuldip Jayaswall. “Biological relevance of sound in plants.” Environmental and Experimental Botany 200 (August 2022), 104919. https://doi.org/10.1016/j.envexpbot.2022.104919.
• Khait, I., et al. “Plants emit Plants airborne sounds under stress.” BioRxiv 507590 (December 2019), doi: https://doi.org/10.1101/507590.
• Gagliano, Monica, et al. “Tuned in: plant roots use sound to locate water.” Oecologia 184 (2017), 151–160. DOI 10.1007/s00442-017-3862-z.
• Veits, Marine, et al. “Flowers respond to pollinator sound within minutes by increasing nectar sugar concentration.” Ecology Letters 22 (2019), 1483–1492. di: 10.1111/ele.13331.
• Mancuso, op, cit., 56.
• Allmann, Silke, and Ian T. Baldwin. “Insects Betray Themselves in Nature to Predators by Rapid Isomerization of Green Leaf Volatiles” Science 329:5995 (27 August 2010), 1075–1078. doi: 10.1126/science.1191634.