Do plants, like human beings feel pain?
Like animals plants do not have any coordinating system namely nervous system to feel the pain when it is injured or disturbed. But they can respond to any stimuli when they receive externally either through wound or by changes in the normal environmental factors.
It is obvious that a plant organ, which reacts to a stimulus, must be able to perceive that stimulus. This perception is known as tone or tonus of the reacting protoplast.
The response shown by an organ depends upon the condition of the protoplast of the cell. It sometimes happens that when a plants is submitted to a particular stimulus no response is shown.
The response of an organ is said to be dependent upon its condition of tone, and this in turn is dependent upon the previous condition to which the organ has been submitted and also upon its stage of development.
It has been found that after a plant organ has been stimulated a number of times, no further response is shown. The plant is aid to have passed into a state of rigour.
The cells of the perceptive organ have lost tone and are no longer in a condition to respond to a stimulus of wounding, and it is only after an interval of time is again recovered and a reaction shown.
It was thought that a difference in intensity of the stimulus over and above a threshold value led to a greater physiological disturbance of the irritable member and that the after effects were also greater.
Recent investigations, however, have shown that there is no relationship between the applied stimulus and response made by the stimulated plant.
The stimulus appears merely to release a certain chain of reactions.
In many cases the response of an organ does not take place until some time after the stimulus has been removed. Thus the perception of the stimulus and the resulting response are separated by a time interval.
Such terms as reaction-time, perception-time and relaxation-time have been used to express the time-relations of plat response to stimulus.