In a comment on a Samizdata post about organic food, Pa Annoyed has some interesting things to say about the chemicals that plants produce to defend themselves. Here’s a snippet:
There are an estimated 10,000 such chemicals in use in the plant kingdom (about 10-20 of them typically used by each individual species of plant), virtually none of which have been tested for human safety, but for which roughly half of those that have been tested have been found to be carcinogenic. Many give vegetables their characteristic flavours or odours. A lot of plants are not eaten because they are well-known to be toxic; those that we do eat often have a few nasty surprises. Potatoes and tomatoes are both part of the Belladonna family, containing the neurotoxin alpha-Solanine, which acts in a similar way to nerve gas, and has been associated with Spina Biffida birth defects. Lettuce contains Caffeic acid, at levels which give you an estimated 20 times the carcinogenic effect of DDT before it was banned in 1972.