I don't have an absolute scientific answer. However, the ethylene gas to which you make reference comes from the decay of certain fruits. As an example, placing sliced apples in a plastic bag with a bromiliad will force it to bloom. I believe this works with some other plants also. I don't think ripening tomatoes would do this.....now if they fall off and begin to rot, that may be a different story.....I'd like to hear from others because this is interesting, since I have used sliced apples on my chids to attract snails in the past and this definitly works to catch those little critters and I saw no ill effects on the chids or their flowers.