Nectar is a sugar-rich liquid produced by plants. It is produced in glands called nectaries, either within the flowers, in which it attracts pollinating animals, or by extrafloral nectaries, which provide a nutrient source to animal mutualists, which in turn provide anti-herbivore protection. Common nectar-consuming pollinators include bees, butterflies and moths, hummingbirds and bats.
Nectar is an ecologically important item, the sugar source for honey. It is also useful in agriculture and horticulture because the adult stages of some predatory insects feed on nectar.
Nectar secretion increases as the flower is visited by pollinators. After pollination, the nectar is frequently reabsorbed into the plant.
An essential oil is a concentrated hydrophobic liquid containing volatile aroma compounds from plants. Essential oils are also known as volatile oils, ethereal oils or aetherolea, or simply as the “oil of” the plant from which they were extracted, such as oil of clove. An oil is “essential” in the sense that it carries a distinctive scent, or essence, of the plant. Essential oils do not form a distinctive category for any medical, pharmacological, or culinary purpose.
Essential oils are generally extracted by distillation. Other processes include expression, or solvent extraction. They are used in perfumes, cosmetics, soaps and other products, for flavoring food and drink, and for adding scents to incense and household cleaning products.
Various essential oils have been used medicinally at different periods in history. Medical applications proposed by those who sell medicinal oils range from skin treatments to remedies for cancer, and often are based solely on historical accounts of use of essential oils for these purposes. Claims for the efficacy of medical treatments and treatment of cancers in particular, are now subject to regulation in most countries.
As the use of essential oils has declined in evidence-based medicine, one must consult older textbooks for much information on their use. Modern works are less inclined to generalize; rather than refer to “essential oils” as a class at all, they prefer to discuss specific compounds, such as methyl salicylate, rather than “oil of wintergreen”.
Interest in essential oils has revived in recent decades with the popularity of aromatherapy, a branch of alternative medicine that claims that essential oils and other aromatic compounds have curative effects. Oils are volatilized or diluted in a carrier oil and used in massage, diffused in the air by a nebulizer, heated over a candle flame, or burned as incense.