Food is very complicated, which is why it is so difficult to be sure what you are eating. And it will vary according to environment in which it is grown, trace elements in the soil and variety I suspect.
He certainly seems to have written a lot. I will look through the herbal books I inherited from my parents and see if any are by him. They were interested in herbs in the 1980s, not as herbalists, but in establishing a herb garden to demonstrate their uses, but did do a lot of reading on the subject.