It is absolutely obvious that being able to survive on this planet without having the abilities to think, feel, remember, and communicate is highly impossible. Moreover, with the immobility factor that characterizes plants and distinguishes them from other living beings, being sentient becomes all the more necessary for them.
Sentience or the state of being conscious enables plants to respond to different stimuli in appropriate ways. Being sentient also signifies that plants, like humans, can also feel pain and fear. However, this hypothesis is highly debated.
Can Plants Feel?
Laboratory experiments along these lines have shown that this is indeed true. Plants' senses of touch, smell, taste, hearing, and vision are highly active, rather more active than those of us humans, albeit in a different form.
Scientist Daniel Chamovitz conducted a research to analyze how plants distinguish between light and the dark. He found that a unique group of genes present in plants, enable them to do so. Interestingly, the same group of genes is also found in the human DNA, helping them respond appropriately to light and darkness.
This, in a way, also shows that there are some, if not many, genetic similarities in plants and humans. Here's how plants may display their senses from time to time.
This is one of the most important senses that plants possess, and it is indeed fascinating that they have various defense mechanisms built around this very ability. For instance, if a tree is attacked by pests, it discharges a kind of signal in the form of some special chemical components, which can be 'smelled' by the surrounding vegetation.
It warns the surrounding flora of a possible pest attack. In response to this signal, the surrounding plants produce some chemical substances that discourage the pests from attacking them.
What is remarkable about these signals is the fact that they are extremely sophisticated in nature, and the chemical deterrents that are produced by the plants are essentially different for different kinds of pests.
According to scientific research, there are more than 1000 varieties of touch-sensitive plants, which respond to stimuli by means of very small electrical impulses. Most plants that possess a sense of touch are predatory by nature.
The most common example of a touch-sensitive predatory plant is the Venus flytrap (Dionaea muscipula), that closes its leaves and traps any insect that crawls on its surface.
Though the tactile senses in the mimosa and the Venus flytrap plants are pretty visual in the form of quick responses to stimuli, it should be noted that all plants respond to touch. However, these responses may not be visible enough because they are either very slow or too fast for the human eye to notice them.
A study carried out in North Carolina by Professor Mordecai Jaffe indicates that even if a stem of a given plant is stroked for a few seconds each day, it results in activating its tactile senses. The result is obviously not seen immediately. However, as the plant grows, its stem tends to become thicker and thicker as a sort of defense against the stimulus.
For one, there have been a large number of experiments done with respect to the effect of music on plant growth. But, a study also tells us that if plants are exposed to certain sounds, which are outside the human range, say 70 to 80 decibels, for a given period of time, their growth is enhanced to a large extent; actually the growth rate may even double.
Inside the plant cells, there are certain proteins called the cryptochromes and the phytochromes. These two are very sensitive to light; they can even 'see' things, which are far beyond the human range of vision.
Various hypotheses have been postulated in this regard, wherein it has been said that the presence of certain colors in the vicinity help to enhance plant growth, while certain others curb the same.
A certain kind of gene in plants enables their roots to 'taste' the surrounding soil. By doing so, the roots automatically turn towards the place that is nutritionally rich, thus aiding in their smooth growth.
The sense of taste that the plants have, also functions as their defense mechanism, in that whenever an approaching pest secretes a chemical substance, the roots taste it and the plant immediately reacts by producing chemical deterrents.
On the Intelligence of Plants...
A large variety of studies have revealed that plants are, in actuality, very intelligent. They can not only think but also react in a suitable manner, depending on the circumstances. A classic example of this is the lima bean (Phaseolus lunatus).
These plants, when attacked by parasites, discharge a particular chemical that attracts other types of parasites, which feed on those which have attacked. This is indeed very intelligent; since the plant cannot do anything much by itself, to combat the attacker, because it cannot move, it attracts and provokes another organism that does the job for it.
Even more intriguing is the fact that plants seem to know the exact time when certain predators are most active. It has been observed that they release certain chemicals exactly at that time, in order to either attract or repel them. This shows that plants actually have a power to think and decide on the plan of action, accordingly.
Unlike humans, plants do not have brains. In spite of this, they can not only think, as mentioned, but can also remember things. According to Daniel Chamovitz, plants have various kinds of memories, ranging from short-term memory to immune memory to the transgenerational one, and they can form, retain as well as recall memories.
Though this may seem a little difficult to accept, experiments suggest that the shorter memories are based on electric stimuli, whereas those which last long are based on epigenetic inheritance.
With respect to the capacity of the plants to think and memorize, Charles Darwin had postulated a "root-brain" hypothesis. He said that the tip of the plant's root functions like its brain. It receives the various sensory signals and directs the plant to "act" in a certain manner. Several modern researches are being done on Darwin's hypothesis.
Though there are not many proven facts with respect to whether the plants can feel and think, there is no doubt that they can definitely sense a lot of things just as we humans do, but in a different way.
Certainly, plants are very well-equipped with various defense mechanisms, which they use from time to time in order to survive and adapt to a particular environment that they inhabit. Their apt responses to stimuli, and their ways of protecting themselves from dangers, definitely make them winners in the race for survival.