Sentience and Sensibility: A Selective History of Plant-Human Perceptions

Figure 1. Mandragora, from *Tacuinum Sanitatis* (1474). The image depicts a method for uprooting the plant using a dog rather than a human. Image: Public Domain

Alack, alack, it is not like that I,
So early waking–what with loathsome smells,
And shrieks like mandrakes torn out of the earth,
That living mortals, hearing them, run mad
Romeo and Juliet, IV, iii

It is night-time, and Juliet contemplates taking the drug that will send her into a death-like sleep and subsequent entombment. She is reminded of the mythical mandrake (Mandragora sp.), a plant said to emit a shriek fatal to humans if uprooted. The origins of the myth, which can be traced back at least as far as biblical times, lie not only in the extreme toxicity of the plant, but equally in the zoomorphic form of the mandrake root.

Figure 2. Roots of *Mandragora autumnalis*. Image: EBC 48081 courtesy of the Royal Botanic Gardens, Kew

Such zoomorphism recurs in historical accounts of plant sentience, the notion that plants are organisms capable of feeling and responding to a range of stimuli. Writing almost 300 years after Shakespeare, Charles Darwin returned to the language of zoomorphism in The Power of Movement in Plants. Responding to developments in physiological botany emanating from France and Germany, Darwin’s study of the ‘universally present movement’ in plants is grounded in empirical observation. Animal metaphors abound – plants not only move, they ‘sweep’, ‘bow’, ‘arch’, ‘rise and fall’, ‘loop’, ‘jerk’ and ‘oscillate’. They also ‘sleep’ and ‘rest’, and they are ‘excited’ by light and other stimuli. And yet it is not the use of metaphor which is most striking about this later work of Darwin.

Figure 3. *Averrhoa bilimbi* leaves ‘asleep’ in Charles Darwin, *The power of movement in plants* (London: Macmillan, 1880). Image: Public Domain

At the end of almost 600 pages of evidence, and having argued that ‘light seems to act on plants in nearly the same manner as it does on animals by means of the nervous system’, itself an assertion that strikes the twenty-first-century reader as surprisingly multispecies, he delivers his final salvo: ‘It is hardly an exaggeration to say that the tip of the radicle … having the power of directing the movements of the adjoining parts, acts like the brain of one of the lower animals; the brain being seated within the anterior end of the body, receiving impressions from the sense-organs, and directing the several movements.’ Darwin concludes then that the radicle, or root-tip, is in fact the plant’s brain, directing the actions of the whole organism via a neural network.

Figure 4. Broad bean (*Vicia faba*) radicles moving in response to small squares of card attached by Darwin to the root tip. Image: Public Domain

Issues of plant sentience were something of a nineteenth-century preoccupation. Quite apart from the European scientists cited by Darwin, botanist Richard Spruce (1817-1893) reached his own conclusions, as revealed in a letter to chemist Daniel Hanbury:

I like to look on plants as sentient beings, which live and enjoy their lives—which beautify the earth during life, and after death may adorn my herbarium … if man cannot torture them to his uses or abuses, they are infinitely useful where God has placed them, as I hope to live to show; and they are, at the least, useful to, and beautiful in, themselves—surely the primary motive for every individual existence.

Plants here are so much more than evidence of a divine plan. That they positively derive pleasure from existing, and that they are at the same time capable of being tortured and abused by humans, are notions that take us far away from either Darwin or natural theology. That they have a useful afterlife in herbaria seems only to strengthen Spruce’s conviction, though one suspects that the plants in his own herbarium did not all die of natural causes!

Although Spruce penned these words in 1873, they were not to appear in print until the early twentieth century when his memoirs were published posthumously. By then Indian botanist Jagadish Chandra Bose had been effectively putting Spruce’s argument to the test, conducting experiments to test the hypothesis that plants experienced emotions. By measuring electrical responses, using a range of equipment of his own making, he believed he was recording changing levels of ‘irritability’ or ‘excitation’ in plants.

Figure 5. Jagadish Chandra Bose. Image: Public Domain

Figure 6. Bose’s optical pulse-recorder. A roll of paper, on which reactions are recorded, is fixed to a clockwork-driven twin drum (c). An optical lever (b) attached to the plant leaflet detects any movement and conveys it via a sponge projecting from a sliding inkwell which traces the response-curve onto the paper. Image: Public Domain

Technological advances in film have similarly had interesting consequences for human perceptions of plants and plant sentience. Max Reichmann’s 1926 film The Miracle of Flowers (Blumenwunder) used time-lapse photography to create new understandings of plant growth, mobility and consciousness. ’You do not notice their suffering and struggles because the rhythm of their movements takes place on a different time scale,’ the goddess Flora tells a group of children picking flowers, ’and yet they feel, just like you do, as they bloom and die.’

Figure 7. Plant growth, mobility and sentience conveyed through time-lapse photography in Max Reichmann’s film 1926 *The Miracle of Flowers* (*Blumenwunde*r). Image: Public Domain

Figure 8: Flora in *The Miracle of Flowers.* Image: Public Domain

The issue of what plants might be capable of feeling resurfaced in the 1940s and ‘50s with the work of Soviet scientists Semyon and Valentina Kirlian. By placing photographic paper on a conducting plate, and an object, such as a leaf, on top, and by then applying a high-frequency high-voltage power charge, the Kirlians discovered that they could produce photographs with the object in silhouette, surrounded by an aura of light. The meaning of the aura has been discussed at length; the Kirlians claimed their images showed the plant’s energy field and indicated its physical and emotional state, an idea which, whilst since ‘disproved’ by subsequent scientists*, has proved to be an enduring one nonetheless.

Figure 9. Kirlian photograph of a *Coleus* leaf. Photography by Wikipedia User MrX, CC BY-SA 3.0 via Wikimedia Commons

Beyond Russia the most visible legacy of Kirlian photography is, arguably, The Kirlian Witness which acquired the status of cult film soon after its release. The film takes up the idea of plant emotions and senses when a woman is murdered and her sister, Rilla, communes with plants in the hope of discovering the identity of her sister’s killer.

Figure 10. Cleve Backster 1969. Image: Public Domain

The film draws not only on the trope of Kirlian photography but also on the experiments undertaken by Cleve Backster in the 1960s. Backster, an interrogator for the CIA, used a polygraph or ‘lie-detector’ on plants and came to the conclusion that plants can feel physical and emotional pain. Again, though since ‘disproven’ by scientists, this is an idea with lasting resonance. To understand that, look no further than Harry Potter and the Chamber of Secrets:

Pomona Sprout: We’ll be repotting Mandrakes today. Now, who can tell me the properties of the Mandrake?
Hermione Granger: Mandrake, or Mandragora, is a powerful restorative. It is used to return people who have been transfigured or cursed to their original state.
Pomona Sprout: Excellent. Ten points to Gryffindor. The Mandrake forms an essential part of most antidotes. It is also, however, dangerous. Who can tell me why?
Hermione Granger: The cry of the Mandrake is fatal to anyone who hears it.

Though separated in time by 400 years, Juliet Capulet and Hermione Granger are nonetheless connected through mandrake imaginaries and plant sentience perceptions.