There may very well have been genuine researchers in the field of physics who explored the possibility of plants feeling pain and came to wrong conclusions applying material laws to the phenomenon of pain that is mental.

Medical researchers have similarly tried to find out how long it takes for consciousness or mind - set in the foetus after conception. They too applied laws of physics with the most advanced techniques to investigate a mental-material phenomenon and have written papers on the subject stating how many months after conception consciousness begins. They still keep writing papers but the time keeps getting shorter and shorter.

The laws governing mental-material phenomena were first enunciated by the Buddha in terms of mind and matter because one cannot exist without the other. All feelings of pain and pleasure result from contact with the external world.

A person under general anesthesia has no contact with the external world but he has not lost his consciousness as is generally believed even by the medical profession.  Consciousness exists in the form of bhavanga (no space to explain that here) for as long as life exists.

The patient has only been unable to establish consciousness with the world external to him. It is important to realize that it is the matter providing support for the mind that is immobilized and not the mind itself.

It is only the physiological functioning of the matter (brain) supporting the mind that can be made to respond to drugs either to completely immobilize the mind temporarily or to affect it in any other way. Drugs have no direct access to the mind and hence to consciousness.

The difference between the mind and consciousness is that the mind by itself is pure but it loses its purity on contact with the objects of the external world when it gets associated with them.

Feelings of pain come under tactile consciousness.  For tactile consciousness to arise there has to be contact and for contact to arise there has to be attention (manasikara).

For attention to arise the plant should have a mind or consciousness. To say that plants have a mind because they bend towards light is misinterpretation of a physical phenomenon.

While there may have been genuine people who may have thought that plants feel pain the main reason why this concept was introduced has been to "prove" that Buddhism is hypocrisy when they say that one should not kill while they kill plants inflicting pain on them and eat. I am grateful to Dr. Athukorale for following up on this.

 If any reader wants to know the Buddhist explanation of how pain arises it will have to be in another letter.