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 clove tree, Eugenia caryophyllata, Thunberg (N.O. Myrtaceœ), is a handsome evergreen tree and a native of the Molucca Islands, where, as well as on the neighbouring islands, it was formerly extensively cultivated.
Although the spice was known in China about 220 B.C. and in Europe in the fourth century, the Clove Islands were not discovered till 1504. They passed into the hands of the Portuguese and then into those of the Dutch, who unsuccessfully attempted to monopolise the trade in cloves and confine the tree to the Moluccas. The French succeeded in introducing the plant into Mauritius and Reunion, whence it was brought to Cayenne and to Zanzibar. On the latter-island and its neighbour, Pemba, the clove tree is now extensively cultivated, and these two islands furnish the bulk of the world's supply, the remainder being obtained from Penang, Amboyna, Madagascar, etc.
The inflorescence of the plant is a compound raceme, on the ultimate ramifications of which the flowers are borne. When quite young the buds are white; as they develop the lower portion assumes a green and finally a crimson colour. The buds are then collected, before the white corolla expands, and dried in the sun, during which the crimson colour changes to a dark reddish brown. Sometimes the whole inflorescence is collected, or sometimes the buds are knocked off with bamboos. The buds are finally separated from peduncles, which are exported separately under the name of ' clove stalks.' The ripe fruits are also occasionally collected; they are known in commerce as 'mother cloves" (anthophylli).
The cloves of commerce are therefore the dried flower-buds of the tree. Each of them consists of a nearly cylindrical, dark reddish-brown portion, slightly tapering at the base, which is sometimes regarded as a gynophore, sometimes as a fleshy calyxtube, but is perhaps most correctly interpreted as the solid lower portion of the ovary (Tschirch), crowned by four, thick, divergent calyx-teeth of a similar colour, from the centre of which arise four, paler, brown, unexpanded, imbricated petals. After soaking in water for twenty-four hours the petals can be removed, and they will be found to enclose a large number of stamens bending over a stiff erect style arising from a depression in the centre of a small disc. Just below the disc is the two-celled ovary with its numerous ovules; it can be found by cutting the clove either longitudinally or transversely.
The lower part of the ovary is solid and fleshy, spongy near the centre. It contains, especially near the periphery, a large number of oil-glands, visible, when the transverse section is examined under the lens, as dark shining points or small cavities. Similar glands can be seen both in the calyx-teeth and petals; in the latter they appear as translucent dots by transmitted light.
Cloves are strongly aromatic and have a pungent aromatic taste. Good cloves should be plump and heavy, have a bright, reddish-brown colour, sink in water, and exude oil when indented with the finger-nail.
Peabody, 1895) of tannin, which has been identified as gallotannic acid, and a colourless, odourless, crystalline substance, caiyophyllin. They yield from 5 to 7 per cent, of ash.
The most important of these constituents is the volatile oil, and the value of the drug is determined chiefly by the amount of oil that it contains, good cloves yielding from 15 to 20 per cent.
The chief constituent of the oil (not less than 85 per cent.) is eugenol, C10H12O2, a colourless liquid with an odour of cloves, boiling at 253°; a terpene (caryo-phyllene), aceteugenol, a-methylfurfural, dimethylfurfural, methyl salicylate and other bodies are also present. The amount of eugenol present can be approximately determined by shaking a measured quantity of the oil with
Fig. 38. - Clove (Eugenia caryophyllata).
A, clove cut vertically, showing calyx, corolla, stamens, pistil, and ovules; near the margin oil-glands; magnified.
B, fruit (mother clove), natural size.
C, the same, cut vertically and magnified.
D, embryo, natural size. (Luerssen).
5 per cent, solution of potassium hydroxide with which the eugenol forms a water-soluble compound; the caryophyllene which floats on the surface can be measured by suitable means and deducted from the volume of oil used, the difference being eugenol. Specific gravity 1.047 to 1.065. The oil is largely used for the production of vanillin.
Cloves are used as an agreeable aromatic stimulant, antispasmodic, and carminative, properties that are due to the volatile oil they contain.
Although Zanzibar supplies the bulk of the cloves imported, those from Penang, Amboyna and Madagascar are considered the best and realise the highest prices. Smaller quantities are imported from Java, the Seychelles, Ceylon, etc.
Penang cloves are large, plump, and of a bright, reddish-brown colour; Amboyna cloves are similar but rather smaller; Zanzibar cloves are darker in colour, leaner, and smaller still.
' Blown' cloves are the expanded flowers from which both corolla and stamens have usually been broken off (forming clove dust).
These do not often exceed 3-5 cm. in length or 3 mm. in thickness; they branch usually twice or thrice trichotomously, the ultimate branchlets which support the flowers being about 3 mm. long. They are brownish, dry and woody; they break with a short fracture, and exhibit in transverse section but few oil-glands. They have, however, when crushed, an aromatic odour and a pungent clove-like taste. They yield much less volatile oil than cloves (about 5 to 7 per cent.), and that which they do yield is less aromatic. They are said to be used for adulterating powdered cloves, a sophistication easily determined by microscopical examination (they contain iso-diametric sclerenchymatous cells1 which do not occur in cloves) and by the amount of ash yielded by the drug, good cloves affording not more than 7 per cent.
Of the numerous ovules contained in the ovary of the clove, only one arrives at maturity. After fertilisation it rapidly increases in size, pushes the other ovules and surrounding tissue aside, and forces its way into the lower part of the ovary (compare fig. 38, C). The ripe fruits are ovoid brown berries and about 12 mm. long. They contain much less oil than cloves, and are said to be used for adulterating powdered cloves; their presence can easily be detected, as they contain starch, from which cloves are free.
Exhausted cloves, i.e. cloves which have been deprived of their volatile oil by distillation, are darker, yield no oil when indented with the nail and float in water.
1 Compare Greenish and Collin, Anatomical Atlas, p. 96.