The Nature of Plant essences
Essential oils may be found in different parts of the plant: in the petals (rose), leaves (eucalyptus), roots of grass (vetiver), bark (cinnamon), heartwood (sandalwood), citrus rind (lemon), seeds (caraway), rhizomes (valerian), bulbs (garlic), the aerial or top parts of the plant (marjoram) or resin (frankincense), and sometimes in more than one part of the plant. Lavender, for instance, yields oil from both the flowers and the leaves, while the orange tree produces three different smelling essences with varying medicinal properties; the heady bitter-sweet neroli (flowers), the similar though less refined scent of petitgrain (leaves) and the cheery orange (rind of the fruit).
Although sometimes denigrated as 'waste products' of plant metabolism, studies have shown that plants utilize essential oils for such purposes as attracting pollinating insects, repelling predators and protecting themselves from disease - quite a significant survival mechanism. Yet essential oils are not vital to the life of plants as a whole, as the word 'essential' may suggest. Indeed, while it is true that most plants have an odor to a sensitive nose, not all plants produce volatile oils.
Essential oils accumulate in specialized plant tissues, harboring oil glands. The more oil glands present in the plant, the cheaper the oil, and vice versa. For instance, 100 kilos of lavender yields almost 3 litters of essential oil, whereas 100 kilos of rose petals can yield only a half a liter. Essential oils are highly concentrated substances and therefore rarely used neat, though certain essences, such as lavender and tea tree, are sometimes used undiluted as an antiseptic. For aromatherapy massage, however, they are diluted in a 'carrier' oil such as sweet almond or olive. As well as being soluble in ordinary vegetable oil, essential oils will dissolve in alcohol, egg yolk and waxes (melted beeswax or jojoba for example). However, they are only partially soluble in water - and a little more soluble in vinegar.
Color and consistency
Even though they are technically classified as oils, plant essences are quite different from 'fixed' or fatty oils such as sunflower seed, corn or sweet almond. They are highly volatile, which means they evaporate when left in the open air, and they do not leave a permanent mark on paper. While many essences are virtually colorless (peppermint), yellowish (lavender), greenish (bergamot), amber (patchouli) or dark brown (vetiver), a few are endowed with an idiosyncratic hue. Targets, for example, is dark orange or yellow, whereas German chamomile is a splendid inky-blue. Many essences have the consistency of water or alcohol - lavender, peppermint and rosemary, for example. Others, such as myrrh and vetiver, are viscous, or thick and sticky, whereas rose otto is semi-solid at room temperature, but becomes liquid with the slightest warmth.
The quantity and quality of essential oil produced by a plant is determined by many interrelated factors. As well as climate and altitude, the type of soil and its fertility is significant: German chamomile, for instance, produces a higher yield of oil when grown on soils rich in calcium. There are also special vintage plants whose essential oil quality supercedes that produced in different locations only a few kilometers apart, where soil and climatic conditions are apparently identical. Moreover, the time of year and day has a major influence on the quality and abundance of essential oil, which moves around the plant according to both a daily and a seasonal cycle - individual plant species having their own characteristic rhythm.
While the concentration of essential oil in flowering plants is generally highest at midday during warm dry weather, there are a few exceptions. The oil of jasmine, for instance, is most concentrated in the petals at night, which means the flowers must be picked before dawn. The oil of the damask rose, on the other hand, is most concentrated in the petals after the morning dew and before the greatest heat of the day. And, just like wine, the quality and 'bouquet' of an essential oil will vary from year to year. To the commercial perfumer, who demands a standardized product, such variability is regarded as a distinct disadvantage. But to the aromatherapist and natural perfumer, it simply adds to the charm of using aromatics from the earth rather than from the laboratory.
The fragrances of organic essences are very different from the highly synthetic scents to which many of us have become accustomed. Newcomers to aromatherapy may need to acquirea 'nose' for natural aromatic oils. Similarly, it takes time for a junk-food-laden digestive system to adapt to a whole food diet. But once weaned on to natural essences, synthetic fragrances may even be perceived as a nostril-stinging assault!