Reviews’ review: botanical semiotics

Plants are organisms that process vital information from their environment and from other plants. Folk biology sees vegetal life as basically passive, “vegetative”. The circadian motion of sun flowers is perceived as an oddity. But all plants behave like other organisms. They simply do so at a slower pace which we tend to confuse with inaction. Immobility and silence are in the eyes and ears of the beholders. Natural selection has fine-tuned our brains to process smell, movements, and sounds that are relevant to our immediate survival. Plants are mostly beyond this pale. They don’t escape when we want to destroy them or collect them. We know when a fruit is ripe and we learn which mushrooms are poisonous. However, we do not perceive the myriad chemical and physical interactions which sustain the growth of weeds and trees in their nutritious but potentially hostile environment. For survival and reproduction plants need to process information from many sources, both proximal and distal. Scientific observation and artificial sensors are needed for us to become aware of their rich sensorial organs and adaptive motions and transformations. What the plants know and what they do about it has now surfaced in human scientific consciousness. But we should not forget that the investigation of plant behaviour was the focus of Charles Darwin’s book, The Power of Movement in Plants (1880). Other researchers between the 18th and the 20th centuries dealt with phenomena that imply astoundingly evolved complexity in the sensorial and behavioral abilities of plants, thus questioning the fallacious divide between zoology and botany.

In 2013 (SemiotiX-XN-11), I reviewed an extraordinary book entitled What a Plant Knows: A Field Guide to the Senses by Daniel Chamovitz. This work was based on robust experiments and measurements which established the reliability of the counter- intuitive conclusions presented by the author. This book both substantiated and vindicated the much debated speculations of German psychologist and semiotician Martin Krampen who, some four decades earlier, had coined the term phytosemiotics (from the Greek word phuton: plant) to stake out a new domain of research for the science of signs within the purview of biosemiotics. This was controversial at the time because the evidence for some form of plant communication was not yet well established. Things have now changed drastically.

Nature recently published a review article by Ian T. Baldwin, in which three new books on plants’ biosemiotics are discussed (Vol. 522, p. 282-283). Baldwin is the founding director of the Max Planck Institute for Chemical Ecology in Jena, Germany. Wittingly entitled “Rediscovering the bush telegraph”, this article addresses the issue of plant behaviour from sensing to communication. 

Leaf Defense by Edward Farmer (Oxford University Press 2014) focuses on leaves as chemical factories in the service of plant survival. Their monitoring of the environment leads to appropriate responses to predatory attacks. Farmer details the multi-tasking of leaves in plants which have evolved these sophisticated organs. In Plant Behaviour and Intelligence (Oxford University Press 2014), Anthony Trewavas leads the readers on a “wild ride” (Baldwin’s metaphor) grounded on his five-decade research into plants’ molecular biology and physiology, covering a wide range of topics from “the origin of life to intelligent nutrient-foraging behaviour in the roots of higher plants.” The reviewer goes as far as celebrating the author’s capacity for empathizing with plants to the point of becoming “phytomorphized”, so to speak. Finally, in Plant Sensing and Communication (University of Chicago Press 2015), Richard Karban pointedly clarifies working concepts such as “communication”, “eavesdropping”, “learning”, “cues”, “signal”, and “memory” when they are applied to plant behaviour. His panoramic review of the field includes precious epistemological discussions.

Based on my earlier reading of Chamovitz’s book and the recent review article of the current literature on plants’ sensorial apparatus and behaviour by Baldwin, this brief report is meant to call the attention of semioticians to an expanding field of research which should not leave them indifferent. Indeed, new research keeps cropping up to shed light on the inner world of plants and their proactive and reactive behaviour. Check, for instance, http://www.abc.net.au/science/articles/2015/07/02/4265302.htm  which documents the reaction of plants to the sound of being eaten alive, a common occurrence in an environment “infested” with herbivores.