Actually there have been tests into plant volition- but that isn't the point. And just because we lack the senses to to understand plant cognition does not mean that it could'nt exist. 200 years ago, science did not believe in bacteria. 400 years ago, science believed in "spontaneous creation". But that isn't the point either. Many cultures and belief systems did not differientiate between plant life and animal life in the fact they were living, and had some type of cognition. And in doing so understood that life lives to nourish life. But that isn't the point either. If someone is going to go on about the pros and cons of killing something to eat, then why do THEY stop there. I once knew a "fruitarian' who would go out in her garden to "graze" because she was convinced that the lettuce had a right to live. No root veggies, no harvested plants. It sounds a little crazy, but at least she was trying to live by her tenants of the non-murdered foodstuffs and I respect that. She also believed that it was HER personal choice. People like PETA want it on THEIR terms- while telling the rest of us what they consider is "moral" and "ethical". They go on about "what does the animal think?" I believe if it were up to the animal, they would not let themselves' be captured and eaten. If it were left up to the plant, I don't believe that the plant would be aiming for its' own self-destruction, either...The dandelions in my lawn seem to have a pretty tough attitude about staying alive.
BTW- I had a book published in 1890 that was a collection of childrens' stories called "365 daily stories for children". It was aimed for kids 3-10 by the way it was written. One of the stories was called "The five gifts of the Cow", and told of the five things that cows were raised for- milk, meat, leather, glue and something else I can't remember. The book told the children about the sanctity of life- that animals sacrificed THEIR lives for people, and that peoples' lives depended on the life of the animals around them. For most of the world, that is still true today.