112. Quercus Suber, Linn.—The Cork Tree.
Φελλος, Theophrast., Hist. Plant, lib. iii. cap. 16; Suber, Pliny, Hist. Nat. lib. xvi. cap. 13, and lib xxiv. cap. 8.—This species of Quercus has a cracked fungous bark, and ovate-oblong, bluntish, coriaceous, entire or sharply serrated leaves, which are downy beneath. It is a native of northern parts of Africa and of the southern parts of Europe, especially of Spain, Portugal, and France. It grows to the height of twenty or thirty feet. According to Mohl, [Lond. and Edinb. Phil. Mag. vol. xii. p. 53, 1838.] the bark of a young branch of Quercus Suber consists of four distinct parts: 1st, an exterior layer or epidermis; 2dly, colourless cellular tissue, the cpiphlaeum of Link, the phlaeum (φλοιος, the bark of trees) or peridermis of Mohl, the suberous envelop of some writers; 3dly, green parenchyma, the mesophlaeum of Link, the herbaceous or cellular integument of others; 4thly, a fibrous layer called endophlaeum or liber. Of these four layers, two (namely the 2d and 4th) are useful in pharmacy and medicine.
1. Suber; Cork; Cortex exterior Quercus Suberis; Exterior Bark of the Cork-Tree.—The substance known in commerce as cork is the epiphlaeum or suberous envelop, above mentioned. When the branches are from three to five years old, the epidermis cracks by distension, and the second layer enlarges on the inner side by the deposition of new layers. These constitute cork. [See also Dutrochet, Comptes Rendus, t. iv. p. 48, Paris, 1838.] It falls naturally every eight or nine years, but for commercial purposes is usually removed one or two years before this period. That season of the year is selected when the bark adheres the most firmly to the wood, in order that the cork may be raised without endangering the separation of the liber from the alburnum. By this precaution, the trees are not at all injured by the corking process; nay, they are said to be more healthy and vigorous than when the cork is allowed to accumulate on their stems. The trees yield these crops from the age of fifteen to one hundred and fifty years.
To remove the cork, an incision is made from the top to the bottom of the tree, and a transverse circular incision at each extremity; the cork is then stripped off. To flatten it, a number of layers are piled up in a pit of water, and loaded with weights to keep them down. Subsequently they are dried, and in that state exported. Our supply is principally derived from Spain and Portugal. To close the transverse pores, cork is charred.
The physical properties of cork are too well known to need description. Its leading character is elasticity. In this respect it is similar to the wood of Anona palustris, called cork wood, and which is used in Jamaica by the country people, instead of corks, to stop up their jugs and calabashes. [The Civil and Natural History of Jamaica, by P. Brown, M.D. p. 256, Lond. 1789.] When thin slices of cork are examined by the microscope, they present a cellular appearance, the cells being four-cornered and tabular.
The most important chemical examinations of cork are those of Chevreul [Ann. Chimie, t. xcvi. p. 155.] and Doepping. [Annalen d. Chem. u. Pharm. Bd. xiv. S. 286, 1843; also The Chemical Gazette, July 1, 1843.] According to Chevreul, cork contains traces of a volatile oil, wax (cerin), soft resin, red and yellow colouring principles, tannin, a nitrogenous brown substance, gallic acid, acetic acid, calcareous salts, and suberin.
The substance to which the name of suberin has been given is the body which remains after cork has been successively treated with alcohol, ether, water, and diluted hydrochloric acid. In its form and physical characters it differs but little from ordinary cork. According to Doepping, it cannot be obtained pure, but always contains cork cellulose (C24H5O20), some cork wax (C25H5O3), and a small quantity of a nitrogenous body. He found it to consist of carbon 67.8, hydrogen 8.7, nitrogen 2.3, and oxygen 21.12. When cork is treated with nitric acid, the suberin yields suberic acid (C8H6O3), which imparts a peculiar character to cork, and to all barks containing cork. [Mulder, The Chemistry of Vegetable and Animal Physiology, p. 478, 1849.]
The uses of cork for making floats for fishermen's nets, anchor-buoys, stoppers to vessels (obturamenta cadorum), and women's winter shoes, are mentioned by Pliny. On account of the astringent matter which it contains, cork is an improper substance for closing vessels containing chalybeate liquids (especially such as are intended for analysis), as the iron is in part absorbed by the cork.
Cork was formerly employed in medicine. Reduced to powder, it was applied as a styptic: hung about the necks of nurses, it was thought to possess the power of stopping the secretion of milk; lastly, burnt cork, mixed with sugar of lead and lard, has been used as an application to piles.
2. Cortex Alcornocae Europaeae; European Alcornoque [Alcornoque is the Spanish name for the cork-oak. It is of Arabic origin, being derived from dorque, signifying "denuded or badly clothed," adding the article al, changing d into c, and introducing the syllable no into the middle of the word. (Diccionario de la Lengua Castellana, compuesto por la Real Academia Espanola, 1726-39.)] Bark; Cork-Tree Bark.—The bark of the cork oak, which I received from Spain under the name of alcornoque bark, bears considerable resemblance to oak bark, and was probably obtained from the younger branches of the corktree. It is ash-gray externally, and wrinkled or grooved internally. The bark imported from Italy, Spain, and Barbary, under the name of corktree bark, and which is used by tanners, appears to be the inner bark of older stems. It consists apparently of the third and fourth layers above mentioned. It is in fibrous or stringy pieces, externally rusty red, internally deeply grooved or furrowed. It has very little odour, and an astringent taste. For tanning purposes the Italian bark is considered inferior to the Spanish and Barbary barks. In its medicinal properties, European alcornoque bark resembles oak bark. It owes its astringency to tannic acid. Its powder, in the dose of a drachm, has been used in hemorrhages and diarrhoea. [Chomel, Abrégé de l'Hist. des Plantes usuelles, t. ii. p. 332, 1761.]
3. Cortex Alcornocae Americanae; American Alcornoque Bark.—This is the genuine alcornoque bark of French and German pharmacologists. The Spanish colonists have applied the name of alcornoque bark to one or more American barks which possess some real or fancied resemblance to the alcornoque bark of their mother-country. Humboldt [Nova Genera et Species Plantarum, t. vi. p. 295.] says that the Bowdichia virgilioides (HBK.) is called by the inhabitants of the districts where it grows, in South America, the alcornoque. In another place, [Personal Narrative, vol. vi. part. i. p. 6.] he states that the same name is given to a Malpighia (Byrsonima) on account of the suberous bark of the trunk. Nees von Esenbech [Geiger's Hand. d. Pharm, 2te Aufl., 2te Abth., 2te Hälfte, S. 1651.] considered Byrsonima crassifolia (Malpighia crassifolia, Auct.) to be the source of the American alcornoque bark. The bark which comes from South America, and is considered to be genuine alcornoque bark, occurs in large, flat, occasionally arched pieces, having some resemblance to coarse, flat Cinchona bark. The epidermis is usually wanting. Externally the bark is reddish, or dark cinnamon brown; internally it is pale. The taste is slightly bitter. It has been repeatedly subjected to analysis. Biliz [Brande's Archiv, xii.; also L. Gmelin's Handb. d. Chemie, Bd. ii. p. 1322.] gives as the constituents—peculiar crystalline matter (alkornin), 1.15; matter soluble in alcohol, not in ether (oxydized tannin?), 1.67; tannin with a lime salt, 14.27; gummy extractive with starch, a nitrogenous substance, and a supersalt of lime, 33.74; woody fibre and loss, 47.71; ashes of the woody fibre, 1.46=100.0.
American alcornoque bark possesses astringent properties. It was introduced into European practice, in 1811, as a remedy for phthisis, but, after a short trial, it soon fell into disuse; and there are no grounds for supposing that it has any curative powers whatever in this disease.—Dose, in powder, ℈j to ℨj. It may also be used in the form of infusion or decoction (prepared with ℥ss of bark and f℥viij of water), in doses of f℥j or f℥ij. the doso of the extract is from gr. x. to ℈j. [For further details respecting alcornoque bark, the reader is referred to a paper by the author in the Pharmaceutical Journal, vol. vi. p. 362, 1847.]