Rose Growing Complete (1976)
E. B. Le Grice

Chapter XVII - Perfume in Roses

[CybeRose note: I can find no information in Organic Chemistry texts to support the notion that the anthocyanin pigments act as catalysts. For the time being I will assume that linkages between color and fragrance is a matter of the relevant genes being located close together on the same chromosome. The dominant scents in roses are derived from carotenes by oxidative degradation. Rosenoxide, not derived from carotenes, provides the distinctive "old rose" scent. Melissa officinalis L. contains trans-rosenoxide.]
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The rose itself has at least four parts which are perfumed. There is the scent of the leaves, especially in the sweet briers and their hybrids. This perfume is strong and noticeable. [snip]

The strong aromatic perfume of R. primula is emitted from the wood even more than from its leaves. The moss of the moss rose is noteworthy. It is in the blossom that the final and strongest perfume may be found. Generally speaking, evidence shows that the perfume is produced by growth substances, chloroplasts, in the green parts of the plant. Their manufacture is very closely associated with the chlorophyll (the green substance aiding the formation of starch by photosynthesis). It is a baffling fact that in these tiny cells, highly complicated compounds are built up with the carbon dioxide from the air combining with the water in the plant. Thus the same elements which produce the starch, a simple and insoluble material which the plant changes to sugar when it is transferred elsewhere, also produce, possibly by the aid of some agent, a highly complicated chemical substance by way of dehydration (glucosides).The materials formed in the green part of the plant, largely the leaf, are odourless, but they may be readily broken down in any part of the plant, if the reagent producing the change is present. As we have seen this may occur in the wood, leaf, sepal, or in the hairy excrescences of the "moss" rose, although generally speaking, the most noticeable scent-bearing part is the flower. These glucosides may be stored or transported in the sap or the petals. The part of the sepal and petal exposed to the light in the bud form is oxidized longer than the upper side of the petal, and in these more exposed cells tannin is formed. The inner side of the petal where the reaction with light takes place later, and oxidation is delayed, produces essential oil, the basis of perfume. During a warm and sunny day activity is greatly increased, and if there is sufficient moisture to encourage chemical action more glucosides than usual are made in the chloroplast. These are more rapidly transported to the petals where they undergo a swift change. This has an important bearing on the increase of perfume, for the glucosides by reaction with water molecules (hydrolysis) are changed into glucose and alcohols, the first step in the building up of the perfumes. A further change takes place with the alcohols are changed to aldehydes, and in this form the perfume strength is increased enormously, in some cases multiplying the strength up to two hundred times. What causes the glucosides to remain stable and then change? This is probably due to an enzyme or ferment, a medium which makes conditions favourable to further chemical change. The essential oil appears at once and begins to circulate. Sometimes this medium appears in wood, root, stem, or leaf but usually is most commonly found on the upper surface of the petal. The cells or structures where these essential oils are oxidized are known as papillae and are like blunt hairs or slight undulations on the surface of the petal presenting the maximum area on which the sun and air can play. There is some doubt as to the method and place of storage of these substances, but it is suggested that these essential oils are also stored just below the outer skin of the petal and the first row of cells, and are thought to be stored there as glucosides (combinations of the sugar, glucose, with the rose alcohols). Part of the difficulty of identification is the rapidity with which the changes take place and the possible difference between various types of plant families. It does seem that most of this storage takes place just below the "skin" or cuticle of the plant and that at times these spaces may intrude upon cell space. Because of their nearness to the surface of the plant's tissues, the slightest bruising of the plant where this storage is found gives rise to the release of perfume. In the rose, it can occur in the green sepals, and one may confuse the scent from the sepals (especially with moss roses) with the scent from the petals with which it mingles. The reaction of light on the colour of the petal may set up the necessary chemical change to produce a particular type of perfume. Enough has been said to show the extremely complicated processes which go to produce rose perfumes, but we may take it that the original unscented basic substances (glucosides) are produced in the plant cells by action of chlorophyll, transported by way of sap to the petals; and in the petals the glucosides are hydrolized into glucose and rose alcohols. The rose alcohols may then be oxidized into the petals to form aldehydes and oxides. Thus, degree of perfume and variety will depend upon weather conditions, soil conditions and the stage the flower has reached. With this brief and necessarily sketchy review of how scent is manufactured in roses we may now consider how perfume can be assessed. This is beset by difficulties, but should not lead to defeat. Rather is it a challenge to explore another delightful aspect of rose cultivation.

In the first place, smelling can be a trained sense and can be greatly improved by experiment and use. Just as ability to taste, discern colours, feel cloths, or distinguish musical notes is developed by intelligent use, so this sense of smell can be improved by comparison and employment.

"The odour strength of a compound depends to some extent on its volatility, but even more on the irritating properties on the nerves of the inner nose membranes which are above the roof of the mouth and between the eye sockets." This fact points to the necessity for taking a deep sniff. To get the best results one should hold the severed bloom in cupped, warmed hands, expelling warm breath into the flower and then inhaling through the nose. Make sure hands are clean and soap free. Even so, experience shows that there is a very wide divergence in the power to smell and more, that individuals are highly selective in the odours which they can smell. The majority can smell the strong damask perfume, but other types of perfume appeal to a very varied selection of human beings. We are highly selective in what we notice when we inhale. Judging perfume has always been a controversial issue, and the method used by the Royal National Rose Society of taking a majority vote of all judges assembled, gives a fair cross-section, and is probably as accurate as any. The difficulty is heightened by the fact that different roses have their optimum diffusion period for perfume. One half-open bloom in one variety will have more scent at that time than at any other stage, while another variety may have more perfume at full expansion.

I am told that one branch of the rose, the Synstylae, where the stigmas are fused together, have their perfume in the anthers and not in the petals. This I have not proved but I do know that certain roses of this type lose their perfume as soon as the anthers begin to die and long before the petals show signs of degeneration.

A further important point is that the perfume of a rose can be seriously affected and diminished in a room, for there are too many background odours. Outside, the perfume is less seriously affected by surroundings, and ability to discern scent is stronger. "In all things charity" should be the rule when judging for perfume and final judgment can only be accurate when it has been accumulated over a number of tests carried out at different times with differing stages of flower. Climatic conditions greatly affect the production and dissemination of perfume, so that all assessments can only be comparative. [snip] Before we consider the differing types of perfume some further explanation of the behaviour of this factor of scent is advisable. The availability of a perfume at any time depends on various circumstances. One of these is the vapour pressure. The more volatile the essence, the more readily it disperses; the less volatile the more slowly does it become discernible. Thus the variety Crimson Glory passes from rose to clove scent. The damask rose perfume, being more volatile and so appearing first, diminishes with age, when the less volatile clove takes over. As we have seen odours depend upon when the glucosides are changed, and this process may be delayed until the flower has fully developed.

The most powerful perfume is produced when the alcohols of the original processes are oxidized into aldehydes which are very much stronger in degree of scent. Another factor with perfume is that on dilution, the vapour as it loses intensity appears to change its character. The strong orris becomes violet with greater dilution.
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The following have been chosen as possible guides to their identification: "damask", "orris-violet", "apple", "lemon", and "clove".

Damask This is the strong, sweet, heady perfume which has been associated with roses as a whole. It is largely confined to reds and pinks with a magenta base. While the standard basis for this perfume may be considered to be R. damascena Kazanlik it is at times difficult to flower this cultivar in our cooler climate. Transferring the character to present-day roses we would think of older roses such as Étoile de Holland, Crimson Glory (both obtainable in their climbing forms), with Ellen Mary, Maturity, Ernest H. Morse and Alec's Red in descending order of strength.

For a long while it seemed certain that there was a special rose oil constituent having a rose odour which had not been isolated. Mr. Neville F. Miller tells me that this has now been done. This has been named "rosenoxide" [rose oxide] by its discoverers. This powerful rose constituent helps to explain why a single flower R. damascena Kazanlik can be identified by its odour when the observer is twenty feet or more away from the plant. Mr. Miller continues, "This new compound has sufficient volatility and the right kind of odour to account for this fact. It is my theory that this newly discovered compound is manufactured in the petals by action of the sunlight and by the catalytic action of the red or pink pigment in the petals. This would account for the damask or true rose odor being confined to red or pink roses." It is possible that one may be more precise and suggest that the important colour factor is magenta found in both red and pink types, e.g. Crimson Glory.

In my last edition the next type of perfume was called "nasturtium". We do not feel this to be an accurate description for present-day roses such as Pink Favorite. While the scent is sweet one would prefer to call it lingering rather than intense, and with it is linked the green growing smell with a slight spiciness like peppercorns — a strange combination but recognizable once one has smelled it. A more recent and stronger perfume of the same type may be found in Peer Gynt.

Orris-violet is a perfume obtained from the dried rhizomes of some iris. Diluted by air, this gives an odour of violet and is present in a number of roses both as a predominant factor and in combination with the type called "nasturtium". Among those possessing an orris perfume it appears that the salmon colour in the petal acts as the catalyst. Because of the vast increase in the orange-salmon roses this has become a more usual although recent addition. It is a sharp lingering perfume often in combination. The strongest perfume may be found in Orange Sensation, while Salmon Sprite and Elizabeth of Glamis are good examples of this strong and penetrating perfume. Examples of damask-orris are My Choice and Dearest, while the very fragrant Blue Moon maybe described as lemon-orris.

Apple. Many perfumes are described as "fruity" which I feel is conducive to sloppy thinking, but it does provide for the multitude of roses which are perfumed but not comparable with known existing scents. Apple is probably a fair description for New Dawn and Ellinor Le Grice.

Lemon is a common perfume mostly in combination. I would prefer to think of it as lemon-scented verbena (Lippia citriodora). A rose with this perfume is Sutter's Gold, while City of Hereford, Harriny and Ophelia are a mixture of damask and lemon, the former being more evident in the younger flower. [CybeRose note: to my nose the scent of Harriny is distinctly grapefruit.]

Clove. There are some with a honey-like sweetness which is cloying. Of these Amberlight is quite distinct reminding one of exotic honeys imported from Australia. The clove perfume is also alleged to be present in a number of roses such as Rosa paulii.

As usual there are the Awkward Squad refusing to be dragooned into uniform classifications. There are the so-called hybrid musks which despite their doubtful ancestry have a unique perfume: sweet, but overripe and musty at times. Nevertheless roses like Buff Beauty have an added attraction in their distinct but unidentifiable perfume. A sweeter but less musty perfume is found in the delightful Lavender Lassie. [CybeRose: Pax has the cool scent of clove (or R. moschata) early in the morning, but a Tea rose scent later in the day.]

These basic perfumes may be, and often are, in combination, when the one which vaporizes more easily will appear in the younger flower, and the less volatile will appear later, other factors already mentioned being taken into consideration.

Enough has been said to show what a wide and fascinating study this field of perfumes provides, but it also presents other difficult problems for the hybridist.

It may be said that the British raiser, at least, is showing considerable advance in producing perfumed varieties. This does not mean that raisers of other countries are producing all scentless flowers. It is, however, the popular opinion which creates the demand and it is the aim of the raiser to fulfil it. The Royal National Rose society with its stress on perfume makes it almost impossible to obtain the coveted Gold Medal for a scentless variety of hybrid tea.

While perfume is more common, and is of a much greater variety in new roses than it was twenty years ago, the public have themselves to blame if fewer with damask perfume are appearing. Here we have a baffling linkage of genes. The highly prized red of Ena Harkness is produced by two tones of red: a brilliant currant-red base overlaid by a deep, almost blackish, maroon. This is a most popular colour in red roses and the public demand the characteristic damask perfume with it. But the public also increasingly require a flower which remains upright both when growing and when cut. Unfortunately with this quality of colour goes a weak stem due to length and frailty of the flower stalk, an inherited character, and this linkage so far remains unbroken. [CybeRose: Until Mister Lincoln!] It is possible to breed the perfume of Sutter's Gold (a fruity perfume classed as "lemon") into a red, but this gives a bright red with thin wiry upright stems and sparse foliage, which makes a poor bedding rose. It is possible to cross Ena Harkness with an upright-stemmed pink such as Wellworth, and produce a strongly scented rose such as My Choice or Lively, but crossing into a second generation (F2), always leads to a weak stem if the red damask-scented flower reappears.

The best one can do is to produce a light flower of twenty petals or less, such as Josephine Bruce, whose weight can be supported by a weak stem, so that for most of its life it will appear upright.

While perfume is highly desirable, it is not a necessity, and one should consider it as an extra gift bountifully provided. Test this statement for yourself. The most vociferous exponent of perfume will for get this quality for the moment when face to face with an outstanding colour. Perfume is a gracious asset bestowed more frequently than we are apt to think and by training the faculty of smelling we shall view our roses from a different but very rewarding angle.

Few roses are without some perfume, and the faint fragrance produced by some varieties linger in one's memory long after it has wafted away, leaving a desire to renew the acquaintance whenever possible.

[snip - regarding Attar distillation in France, Morocco and Bulgaria]

The following facts maybe of interest: that thirty-two thousand roses [Kazanlik] weighing about 81 kg (180 lb) yield 28 g (1 oz) of rose oil; five million roses, weighing nearly 4,064 kg (4 tons), would make about 4.5 kg (10 lb) of attar of roses. This would be the daily production of a large distillery and would go on for four or five weeks. Bulgarian "Otto" smells very sweet and quite sharp, but not much like a rose. It is used to add sweetness to many perfumes and is very expensive.

A second area of production is in Southern France in the Grasse area of Provence. This variety is known as the Rose de Mai, from its time of flowering, or Rose de Provence. It has a semi-double flower of rose-pink, with at least two rose of petals. The flowers, which are small, 5 to 7.5 cm (2 to 3 in) across, are carried in trusses with at least ten flowers in a head. This Rose de Mai was a hybrid between R. centifolia (from Asia Minor) and Rose de Provins (R. gallica) which is said to be indigenous, although it is believed that Theobault IV brought back from Damascus to Grasse a type of Rose de Provins with a reddish purple flower. There are two varieties, one with many thorns and one with few. The first is more suited to very dry areas without irrigation. It is more vigorous, with smaller flowers, although these are highly perfumed.
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Since this was written an excellent article has appeared in the 1975 Rose Annual by Dr. A. S. Thomas in which his recent researches have shown that considerable changes have been made both in the varieties used and in the method of production. One great change appears to be that the Rose de Mai has been replaced by more modern roses chief of which are Ulrich Brunner-fils, H.P. (A. Levet 1881), of doubtful origin, Louis van Houtte, H.P. (Lacharme 1869) and Marie van Houtte, T. (Ducher 1871) all of which are less troublesome and are very fragrant and give recurrent bloom.
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The Rose of Provins is a special rose named after the town of Provins and has the peculiar chemical property of retaining its perfume when dried. In 1310 the trade was active, and roses were highly regarded for their medicinal qualities. Its popularity continued throughout six centuries and built up a major industry, including crystallized rose leaves as a confection.

The names Rose de Mai and Rose de Provins appear from recent research to be local names given to forms of R. gallica or closely related hybrids preserved for special purposes.