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Do Plants Have Feelings?
Plants behave in all sorts of ways and react to many different types of stimuli. Some people believe that plants grow better when spoken to or when music is played nearby. Anyone who has witnessed the instantaneous wilting of the sensitive plant, Mimosa pudica, when touched has wondered if plants really DO have feelings.
In 1970 Peter Tompkins and Christopher Bird, authors of the best-selling book, The Secret Life of Plants, claimed that plants did indeed have emotions and intuitive capabilities. Although the book is a fascinating read, its unsubstantiated claims have had a negative impact on plant study credibility. It has taken years of serious study and experimentation for plant behavior hypotheses to hold water under scientific scrutiny.
The first step should be to define "intelligence." Plants don't have brains or central nervous systems like humans; therefore, they can't have emotions or reasoning capabilities . They are, however, sentient life forms and they do have "tropic" and "nastic" responses to stimuli. Plants can't vocalize or flee from danger, so they must rely on other ways to thrive and to protect themselves when threatened. They can make decisions per se as to which direction to grow for example and can defend themselves and warn other plants by producing pheromones much like insects.
From scientific study, we have known plants to have responses to light, gravity, and water. We call these reactions phototropic, geotropic, and hydrotropic. They are hormonally driven by the plant chemical auxin which is responsible for changing turgor, the water pressure within the cell walls. This explains why plants grow up toward the light and away from the earth and why roots grow into the earth toward water.
Responses to these things are categorized as tropic: response to directional stimuli such as light and gravity, and nastic: sensory reaction to non-directional stimuli. Nastic responses are usually temporary and do not alter growth. In a sense they can be compared to voluntary or involuntary actions in human physiology.
Tropic Response To Stimuli
Both the sensitivity to touch and the change of "turgor" within the stems when they come into contact with resistance are responsible for the twining of tendrils in climbing and vining plants. These tendencies are called thigmotropic because they are influenced by the tactile response to directional stimuli such as bean poles. posts, etc.
Most tropic responses are very slow such as the bending of a plant toward light and the opening of flowers. Nastic responses, however, are often faster and can readily be seen with the naked eye. Two great examples are the defensive response of the Sensitive Plant and the aggressive response of the Venus Fly trap.
Nastic Response for Defense : Sensitive Plant, Mimosa Pudica
A plant's reaction to touch is referred to as thigmonasty, and it is just one of several natural defenses that botanical specimens use to survive in their threatening or competing environments. In Mimosa pudica, touch causes a reaction in the potassium ions within the plant's cells. This affects the water movement within the vascular structure, causing wilt and recovery. If the stimulus is slight as in the tickle of an insect , the reaction will be the closing of a leaf or its sections. With more overt stimulation, the whole plant will droop. These responses are intended to scare off leaf-eating insects or larger intruders to protect the plant from harm.
In some cases, thigmonasty is used for aggression rather than defense as a means of survival in areas where harsh elements make soil devoid of nutrients. This is the case for carnivorous plants like the Venus Fly Trap, Dionaea muscipula, which thrives in the peat bogs of both North and South Carolina. These insect eating specimens grow from a bulb structure and attract their prey through scent, nectar, and color. The lack of both nitrogen and phosphorus in their growing environments make them dependent upon the protein from insects. Although thought to subsist on flying insects, the mainstay of their nutrients comes from ants, spiders, beetles, and leaf hoppers. The true leaves of these plants are tipped with colorful convex lobes, each edged with hair-like cilia which interlock when triggered to imprison unsuspecting prey. An insect when making contact with two or more prominent hairs on the lobe's surface will trigger a 20 second timer. If it doesn't move on, it will find itself a victim of the quickly snapping trap. Clever in its design, this stimulus detection mechanism allows the plant to distinguish between water droplets and true prey so it doesn't expend unnecessary energy. Brilliant!
Nastic Response for Aggression: Venus Fly Trap
In the botanical world, just as in our human one, living things are equipped to avoid danger and seek optimal conditions for survival. We rely on our basic instincts to sustain us and to reproduce, relying on the "fight or flight" reaction to protect ourselves from harm. Plants use "nastic" and "tropic" responses.
Do plants have feelings? No, not in the same sense that we do. They have stimuli-response. Plants, like all other living things, share the trait of adaptation. It is our common bond.
© 2012 Catherine Tally