Source, Etc

Caraways are the ripe fruits of Carum Carvi, Linne (N.O. Umbelliferoe), an erect biennial herb distributed over central and northern Europe. The plant is found in Britain, apparently wild, but possibly only naturalised. It is cultivated principally in Holland, but Sweden, Norway, Russia, Germany, and Morocco also produce caraways, whilst a small quantity is grown in England. When the fruit ripens, the plant is cut and the caraways are separated by thrashing.

Description

The ovary of the caraway is inferior and two-celled; as it ripens it develops into a schizocarp, that is, a fruit which separates into its component carpels by their splitting away from the central axis (carpophore), to which, however, they remain attached. Each complete fruit is termed a cremocarp (a variety of schizocarp), and each half-fruit a mericarp, the mutually apposed inner faces of which are the commissures or commissural surfaces.

Fig. 59.   Caraway fruit. A, entire fruit, side view magnified 3 diam. B, longitudinal section, magnified 3 diam. C, transverse section: μ, vittae; k, ridges, magnified 14 diam. D, portion of the same, further enlarged; i, pericarp; T, seedcoat. (Berg.)

Fig. 59. - Caraway fruit. A, entire fruit, side view magnified 3 diam. B, longitudinal section, magnified 3 diam. C, transverse section: μ, vittae; k, ridges, magnified 14 diam. D, portion of the same, further enlarged; i, pericarp; T, seedcoat. (Berg).

Fig. 60   Caraway fruit. Mericarp, magnified. 6 diam.

Fig. 60 - Caraway fruit. Mericarp, magnified. 6 diam.

The cremocarp of the caraway easily separates into its constituent mericarps, and the commercial drug consists almost entirely of separate mericarps, about 4 to 6 mm. long, very narrow, tapering at each end, and slightly curved. They are quite glabrous, brown, and traversed from base to apex by five narrow raised yellow ridges or ' costae ' (fig. 59 C and D, k). Each of these (primary) ridges contains a fibro-vascular bundle, and this distinguishes them from other (secondary) ridges which some Umbelliferous fruits (coriander) possess. In caraway fruits no secondary ridges are present. In the depressions (' intercostal regions ') between these ridges, embedded in the pericarp of the fruit and extending from base to apex, lie elongated oil-glands (vittae, fig. 59 C and D, μ). In the caraway there are four such vittae on the dorsal and two on the commissural surface of each mericarp. Very many Umbelliferous fruits contain six vittae, but some contain more (anise), whilst others contain none at all (hemlock). They are generally best seen in transverse section under a strong lens, when they appear as dark brown minute spots or cavities (compare fennel, in which they are conspicuous).

The transverse section exhibits also a narrow pericarp and a large oily endosperm, the commissural surface of which is not grooved. The small embryo lies near the apex of the fruit. (Compare fig. 59).

Caraways exhale, when crushed, an agreeable aromatic odour, and possess a pleasant aromatic taste.

The student should observe

(a) The glabrous surface of the fruit,

(b) The six vitloe on the transverse section,

(c) The endosperm, which is not grooved.

Constituents

Caraways yield by distillation from 3.5 to 7'0 per cent, of volatile oil, the principal constituent of which is carvone (50 to 60 per cent.). They also contain fixed oil (in the endosperm) and yield about 6 (not over 9) per cent, of ash.

The volatile oil should have a sp. gr. 0.910 to 0.920 and O.R. + 75° to + 82°; at least 50 per cent, should distil at a temperature over 200°. Oil from which part of the carvone has been removed (' decarvolised' oil) has a lower sp. gr. lower optical rotation, and yields less than 50 per cent, boiling above 200°.

Varieties

Dutch: Holland produces and exports far larger quantities of caraways than any other country; they are of medium size, dark colour, and clean appearance, and yield from 40 to 65 per cent, of oil.

English: these are produced in small quantity only; they are similar to the Dutch but brighter in colour.

Adulteration

Caraways and other Umbelliferous fruits used in the production of volatile oil are distilled either ground or entire; in the former case the yield is increased, and the exhausted fruits are used as cattle food; entire fruits yield less oil, and the exhausted drug after drying may be mixed with the genuine fruits. These exhausted fruits may be recognised by their dark colour, deficiency in aroma, and low yield of aqueous extract; they often also sink at once in water (fennel), whereas the genuine float for a considerable time.

Uses

Caraways, or the volatile oil obtained from them, are extensively used as an aromatic carminative.