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 touched the sensitive plant and witnessed its instantaneous wilting has surely 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 choose which direction to grow, for example, and can defend themselves and aid pollination by moving their leaves, petals, and stamens. Plants also produce both attractive and defensive messenger chemicals called pheromones, much like humans, animals, and insects.
Responses are categorized as either tropic: a movement in response to a specific directional stimuli such as light and gravity, or nastic: a movement in response to non-directional or multiple stimuli such as touch or vibration. Nastic responses are usually temporary and do not alter growth.
From scientific study, we have learned that plants respond to light, gravity, and water. We call these reactions phototropic, geotropic, and hydrotropic, respectively. They are 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 why roots grow into the earth toward water.
Tropic Response To Stimuli
The change of turgor within the stems of some plants when they come into contact with resistance are responsible for the twining of tendrils in climbing and vining plants. These tendencies are called thigmotropic responses 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
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 insure reproduction and to survive in their threatening or competing environments. In Mimosa pudica,the sensitive plant, 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, to reproduce, and to to protect ourselves from harm. Plants use "nastic" and "tropic" responses for these same purposes.
Do plants have feelings? No, not in the same sense that we do. They have stimuli-responses. Plants, like all other living things, share the trait of adaptation for survival. It is our common bond.
© 2012 Catherine Tally