Some weeks ago, May 10th to be exact, on that other forum, Jane McGary contributed the following in the form of a question, >Can anyone explain the mechanism by which flowers emit fragrance at >particular times of day? I know that many flower scents are detectible only >in warm temperatures, regardless of time of day, but others are detectible >primarily in the late afternoon and night, whether the flowers are open or >not. What actually happens, physiologically, when the fragrance is emitted? > >I was moved to ask this because I have some flowers of Gladiolus tristis in >the house right now. Their beautiful scent is not very strong in the >morning, but in late afternoon it suddenly strengthens, even though they >are on cut stems in a room with artificial light as well as daylight. > >Most night-scented flowers seem to be light-colored (like this pale yellow gladiolus) and are said to attract moths as pollinators. Over 40 years ago I worked a bit on release of fragrance from excised corollas of Cestrum nocturnum (night-blooming jasmine)...it turned out that even the excised corollas were most heavily scented in the evenings as if the circadian control was due to mechanisms localized in the coralla and not the entire plant....but we didn't go further. it turns out that there is marvelous stuff going on. In the June 28th issue of Science (vol. 286 p 2327-2329) there is a review of some recent work on fragrance in Clarkia and Antirhinnum. In Clarkia 8 to 12 major compounds were discovered related to their characteristic aroma and the researchers isolated an enzyme in the petals that catalyzes the synthesis of one of linalool (common to many flowers). Now 3 other enzymes have been characterized and they're mainly in the epidermal layer of the petals. The research offers promise for a) understanding the biochemistry and timing of release of aroma from flowers,and b) through genomic studies, which intend to identify the genes controlling the pertinent enzymes, the hope of re-introducing scent to species where scent has been lost in the course of breeding programs (where the primary goals have been bloom size, color and vase life). --