"The dried leaves of Eucalyptus Globulus Labillardiere (Fam. Myrtaceae), collected from the older parts of the tree, without the presence or admixture of more than 3 per cent. of the stems, fruits or other foreign matter." U. S.
Blue Gum-tree Leaves, Australian Fever-tree Leaves, Eucalyptus Leaves; Eucalyptus, Fr. Cod.; Feuilles d'Eucalyptus, Fr.; Eucalyptusblätter, G.; Eucalitto, It.; Eucalipto (Hoja ide). Sp.
The genus Eucalyptus was named by L'Heritier in 1788, from the two Greek words meaning ("I cover well," "in allusion to the operculum or lid which covers the calyx until the stamens are fully formed." The plants, which are known as Gum trees, Woolly butts, Iron barks, etc., by the natives of Australia and Tasmania, are evergreen and vary from shrubs to trees of enormous height, some of them probably being the highest trees known. Kerner gives the height as 140 to 152 meters. They form, it is stated, about three-fourths of the whole vegetation of those countries. At least one hundred and forty species have been described. The leaves frequently vary in shape and in position on both young and mature trees; they are fixed vertically, and not horizontally as the leaves of our trees, the petiole being twisted. The leaves furthermore contain large oil-secreting reservoirs. The flowers are arranged in cymes or axillary umbels and are devoid of petals; the usually whitish stamens are inflexed in the bud and expand when the operculum is removed, giving the name as already stated to the genus. The fruit is a 3- to 6-celled truncated capsule, or pyxis. The seeds are small and very numerous, the sterile ones predominating; this is no doubt one reason why there has been so much difficulty in producing seedlings.
Most of the species do not require excessive heat for their perfecting, and some of them are able to resist moderate frosts. Over forty species are being grown successfully in the United States, and in the neighborhood of Los Angeles and other points in California a pure oil is said to be commercially produced. On account of the rapidity of their growth and the hardness and indestructibility of their timber, many of the species are very valuable for economic purposes. A number of the species are said to be cultivated in the Southwest as a source of honey. (See Bulletin No. 35 of the U. S. Bureau of Forestry.)
With a genus of so many species and numerous varieties it was to be expected that there would be considerable confusion in regard to the accurate determination of its members. Tate and Luehman give prominence to the fruit for purposes of classification. Maiden, however, says that all of its characters display a puzzling amount of variation, and concludes that for herbarium work the best characters are afforded by the anthers and fruits; whereas the scientific forester will be largely guided by the nature of the bark and timber. Baker and Smith, in addition to morphological characters, base their deductions on the chemical properties and physical characters of oils, dyes, kinos, etc. See Bentham, Flora Australiensis; Baron F. von Mueller's Eucalyptographia, 1879 to 1884. Baker and Smith (A Research on the Eucalypts, Sydney, 1902), arrange the species in seven different groups, according to the chemical characteristics of the oils which they produce. It is stated that the leaves of the E. (Eupatorium, not Eucalyptus -Henriette) rebaudianum, of Paraguay, are used in that country in place of sugar, which they exceed in sweetening power.
Eucalyptus globulus is one of the largest known trees, attaining sometimes a height of 300 or even 350 feet, with a smooth, ash-colored bark. The leaves attain a foot in length, and vary, according to age, from a glaucous white to a bluish-green color. The flowers are large, pinkish-white, axillary, occurring singly, or in clusters. Although its wood is very resinous, hard, and durable, the tree is remarkable for the rapidity of its growth, reaching, under favorable circumstances, fifty feet of height in five or six years. It flourishes best in valleys having a rich, moist soil, and has very largely been naturalized in semi-tropical countries, partly on account of its economic value, but chiefly because of the reputation it enjoys as a means of overcoming malaria. Its sanitary powers appear to be established, numerous notoriously miasmatic stations and districts having been rendered healthful by its growth. It is probable that the destruction of the miasma is due not so much to emanations from the tree as to the fact that it evaporates water so rapidly from its innumerable large leaves as to drain the swamps and marshes in which it is planted. It is possible, however, that the large amount of volatile oil which must escape from it has some effect, and it is even affirmed (A. J, P., 1875, p. 423) that the parasitic phylloxera will not attack grape-vines growing near it.
The eucalyptus oil of commerce is, indeed, composed chiefly of the oils of E. amygdalina and E. dumosa, which yield a very much larger product than does the official species. The oils of E. piperita and E. haemastoma have a peppermint odor, and that of E. citriodora a citron-like odor, while the oil of E. staigeriana exactly resembles the oil of verbena; it is probable that these oils will come into commerce for the purposes of the perfumer.
Properties.—The leaves are the official portion of the plant and are officially described as follows: "Laminas lanceolately scythe-shaped, from 8 to 30 cm. in length and from 2 to 7.5 cm. in breadth; summits when present acute or acuminate; bases unequal, obtuse or more or less rounded and connected with a twisted petiole from 5 to 35 mm. in length; margins slightly uneven, revolute; coriaceous; both surfaces varying from pale yellowish-green to grayish-green and more or less glaucous, glabrous, glandular-punctate and with numerous small, circular, brown dots of cork; veins of the first order anastomosing with each other and forming a line nearly parallel with the margin; odor slightly aromatic; taste aromatic, bitter, and cooling. Under the microscope sections of Eucalyptus show the upper and lower surfaces with nearly similar cells, the outer walls being strongly cuticularized; stomata occur on both surfaces, a region of palisade cells made up of from 3 to 4 rows of cells occurring beneath each surface; among the palisade cells occur large oil-secretion reservoirs, with a yellowish or orange colored oily content; calcium oxalate crystals in cells of the loose mesophyll in the form of rosette aggregates or monoclinic prisms varying from 0.015 to 0.025 mm. in diameter. At the periphery of the fibro-vascular bundles of the midrib and petiole occurs a more or less interrupted circle of small groups of slightly lignified bast-fibers." U. S.
Hans Kramer (B. P. G., 1907, p. 319) presents an anatomical study of Eucalyptus with the characteristics of the drug in a powdered form.
In March, 1870, Cloez (J. P. C., 4e ser., xii, 201) reported an elaborate chemical study of the eucalyptus leaves, and his results have been substantially confirmed by Debray (De l'Eucalyptus Globulus, Paris, 1872), Rabuteau (Mem. de l'Academic, Nov., 1872), and Broughton (P. J., 3d ser., iii, 463). Cloez found, besides chlorophyll, resin, tannin, and inert substances, an essential oil, upon which the virtues of the drug appear to depend. Of this oil the fresh leaves afforded 2.75 parts per hundred, the recently dried leaves 6 parts; leaves which had been kept some time yielded a much smaller percentage. In the distillation, the oil for a time comes over freely at from 170° C. (338° F.) to 178° C. (352.4° F.); subsequently another portion of oil distils at 188° C. (370.4° F.) to 190° C. (374° F.), and finally a very minute portion does not volatilize until the temperature reaches 200° C. (392° F.). Cloez believes the oil to be composed of two camphors, differing in their volatility. The bulk of the oil yielded is the portion first distilled; to this Cloez has given the name of eucalyptol, or, as it is now also called, cineol, C10H18O. Gildemeister and Hoffmann (Aetherische Oele, 1899, p. 690) divide the eucalyptus oils into 5 groups according to their constituents, viz.:
- Group 1, Cineol (or Eucalyptol) containing oils, of which group Eucalyptus Globulus is the most important;
- Group 2, Citronellal containing oils, of which group Eucalyptus maculata is the most important;
- Group 3, Citral containing oils, of which E. staigeriana F. von Muell., is the typical example;
- Group 4, Peppermint smelling oils, of which Eucalyptus piperita is an example;
- and Group 5, Less known oils of varying odor.
Schimmel & Co. (Semi-Annual Report, April, 1897) gave a list of some fifteen varieties of eucalyptus oils from the different Eucalyptus species. In their report for October, 1904, they give the sources and state the properties and components of 109 different eucalyptus oils obtained by them from Baker and Smith, Curators of the Technological Museum of Sydney, N. S. W.
According to Duquesnel, the oil of eucalyptus is adulterated with alcohol, to be detected by means of fuchsin, which is insoluble in the pure oil but soluble in that containing even a very small percentage of alcohol; with fixed oil, to be detected by boiling with water, when the fixed oil remains on the surface; with volatile oil of copaiba or turpentine, to be detected by means of the boiling point, that of eucalyptol being 170° C. (338° F.), that of oil of turpentine 155° C. (311° F.), that of oil of copaiba 260° C. (500° F.). (J. P. C., 4e ser., xvi, 45.)
Uses.—Whatever medicinal virtue eucalyptus possesses beyond a slight astringency is due to its volatile oil. Preparations of the crude drug are rarely used in this country. The leaves are occasionally rolled into cigarettes to be smoked for the relief of bronchitis or asthma. For therapeutic properties of the oil of eucalyptus, see page 762.
Dose, of eucalyptus, ten to thirty grains (0.65-2 Gm.); of the oil, five to ten minims (0.3-0.0 mil).
Off. Prep.—Fluidextractum Eucalypti, U. S.
The Dispensatory of the United States of America, 1918, was edited by Joseph P. Remington, Horatio C. Wood and others.