I've often said in many of my posts that fragrance in roses is determined by the anatomy of the rose petal. I thought I would share some of the information on the subject from Jack Harkness's book Roses published in 1975. (page 101) Of course, the whole topic is more complicated than presented here:
Fragrance by Jack Harkness
Perfume starts in the green parts of the plant, and its ingredients are light from the sun, carbon dioxide from the air, and the plant’s own water. The energy is supplied by the sun, which causes the tiny granules of green colouring matter within the plant to move. The substance from which the green granules are made is called chlorophyll, which means green leaf. Movement of itself promotes impules and a chain of consequences; as the result of solar energy is to form compounds of water and carbon, known as carbo-hydrates. Of which the most important to the plant are starches and sugars. The process is called photosynthesis, which means making things with light.
The carbo-hydrate needed for perfume is a kind of sugar, which is transported from the leaves and other green parts of the plant, via the inside of the bark, up into the petals, while they are still in the bud. Chiefly on the inner side of the petals, the sugary substance undergoes a series of transformations, so rapidly that the precise sequence has been most difficult to trace. It appears that enzymes are first used to ferment it, and then oxygen and water change it into an oil compound of glucose and alcohol. At this stage there is little scent, until more oxygen is brought to bear to the compound, which magically turns into highly scented substances. These are completed and stored near the petal surface. The manufactories are tiny projections upon the surface of the petals called “papillae’, which means ‘nipples’, and from which droplets of perfumed plant can readily burst out upon the correct stimulus, then float in the air.
The workings of the plant’s perfumery in making sufficient raw materials in its green parts, coveying them to the petals on schedule, and conducting an intricate laboratory process within a swiftly growing and fragile material are marvelous indeed. The perfumery is only one industry within the green skin of a plant, for also in the making of are colours and pollen and ovules, to name but a few, all to be initiated and placed in working order at precise times and places.
From this it will be noted that the petal surface of a fragrant rose is broached by nipples; and the skin of the petal must be elastic to admit the storage of the perfume as it is manufactured. Such petal surfaces are susceptible of damage; they do not travel; they have a fairly high transpiration rate; they are chemically active."
