This section is from the book "A Text Book Of Materia Medica, Being An Account Of The More Important Crude Drugs Of Vegetable And Animal Origin", by Henry G. Greenish. Also available from Amazon: A Text Book of Materia Medica : Being an Account of the More Important Crude Drugs of Vegetable and Animal Origin.
The common lavender, Lavandula vera, de Candolle (N.O. Labiatoe), is a small under-shrub indigenous to southern France, Italy, and Spain, but cultivated in this country as a garden plant, as well as on a large scale for its aromatic flowers. It is also extensively cultivated in southern France.
The bulk of the flowers produced are used for the distillation of the volatile oil. The spikes are cut with a small hook about 15 to 30 cm. below the flowers. They are then thrown into large stills, water added, and distillation conducted over a naked fire or by steam, the distillate being received in a separating can, 'in which the oil that is carried over is retained.
The inflorescence of the lavender is a terminal spike, on which the flowers are arranged in small verticillasters, each of which arises from the axil of a rhomboidal bract. The calyx is tubular and ribbed, bluish-violet in colour, five-toothed, and hairy, shining oil-glands being visible with a lens amongst the hairs. The bulk of the oil yielded by the flowers is contained in these glands on the calyx. The corolla is bilabiate and of a beautiful bluish violet colour.
The student should observe.
(a) The hairy, ribbed, tubular calyx.
(b) The rhomboidal bracts supporting the flowers.
The principal constituent is the volatile oil, of which the fresh flowers yield about 0.5 per cent.
The chief constituents of the volatile oil are linalool and linalyl acetate; cineol (in English oil), pinene, limonene, and other bodies are also present. The oil should have a sp.
gr. of 0.885 to 0.900 and an optical rotation - 5° to - 10°. English oil contains from 7 to 11 per cent, of esters, foreign oil not less than 30.
Lavandula spica, de Candolle, is distinguished from the true lavender by the linear bracts, spathulate leaves and more compressed inflorescence. The oil (oil of spike) is less fragrant than that of the true lavender, and slightly dextrorotatory.
Fig. 46. - Lavandula vera. A, entire flower, showing bract and hairy calyx, magnified. B, the corolla opened vertically, magnified. (Luerssen).