(Hook., Mitch., Trop. Austr., 235.) Citron-scented Gum.

Systematic. - A large tree with a smooth, whitish bark. Leaves lanceolate, up to 6 inches long and 9 lines wide, acuminate, not shining; venation finely marked, lateral veins numerous, oblique, parallel or slightly spreading, intra-marginal vein very slightly removed from the edge, which is more or less irregular. Mowers numerous in axillary panicles. Calyx tube hemispherical to slightly cylindrical, about 2 lines in diameter, pedicel under 2 lines long; operculum hemispherical, umbonate.

Fruit. - Ovoid, truncate, contracted at the edge; rim thin; valves opening downwards; under 4 lines in diameter and 6 lines long.

Only separated with difficulty from E. maculata. Habitat. - North coast district of Queensland.

REMARKS. -The above is the locality as at present known of this species. Sir T. Mitchell collected his specimens far inland, at Beebury Creek, Mantua Downs, and "Sir William Hooker named this Eucalypt (although without flower or fruit) from the deliciously fragrant lemon-like odour, which exists in the dry as well as in the recent state." (Mitch. Trop. Aust. 235.) The term "Citron-scented Gum" is now applied to a Coast tree with a smooth white bark, and is largely cultivated. It is not the only Eucalyptus possessing an aroma of this character in its oil, as this also occurs in the North Queensland "Ironhark." E. Staigeriana, F.v.M. Whether Mitchell's tree is botanically identical with that on the coast and the one to which the name is now applied remains to be proved, for, as stated above, the species was established on the leaves and chemical constituents alone.

ESSENTIAL OIL. - The oil of this species of Eucalyptus consists almost entirely of the aldehyde citronellal, with from 5 to 10 per cent. of other bodies, including a small quantity of ester, a little alcohol, perhaps geraniol or citronellol, and a very small quantity of a terpene. It has no resemblance to that distilled from the leaves of E. maculata.

This Eucalypt is essentially a Queensland one, growing quite extensively in the Gladstone District, but it readily lends itself to cultivation in other parts, and grows quite well in the Sydney District. The species is quite stabilised, so that the oil always shows comparative constancy, no matter where the trees are grown. It also shows considerable vitality, and we have been informed by a gentleman who knows the district well, that on the Herberton Range to the north of Cairns there are many hundreds of acres where E. citriodora grows plentifully. When he was there the trees had been cut down for mining purposes, but a great quantity of "suckers" had come up, and consequently an abundance of leaf was available. He distilled oil from this material and found it of excellent quality.

We were unable to obtain leaves from Queensland for distillation purposes, but have investigated the oil commercially distilled there. It was found to be in agreement with the oil we distilled from a.cultivated tree in Sydney. That the constitution of the oil from cultivated trees is similar to that distilled from material growing in its native habitat, can be seen from the results of the analyses we submit herewith,

The cultivated tree from which the leaves and terminal branchlets were obtained for distillation was growing on land resumed by the Government upon which to erect the new Sydney Railway Station; it was collected in February, 1902. The yield of oil was 0.6 per cent. The oil was but little coloured and had the citronellal odour characteristic of the oil of this species.

The crude oil had specific gravity at 150 C. = 0.864; rotation aD - 1.0°; refractive index at 200 = 1.4594, and was soluble in 1 1/2 volumes 70 per cent. alcohol. The saponification number for the esters and free acid was 7. An aldehyde determination carried out in the ordinary manner showed 91 per cent, absorption; this was assumed to be wholly citronellal.

Only a very small amount of a terpene could have been present, and both cineol and phellandrene were absent.

A sample of the commercially distilled oil was forwarded to the Museum in 1909, by Mr. F. D. Ferguson, who had distilled it at Gladstone, Queensland. It was but little coloured; had specific gravity at 150 C. = 0.8697; rotation aD + 1.7°; refractive index at 200 = 1.4596, and was soluble in 1 1/2 volumes 70 per cent, alcohol. An aldehyde determination gave a result of 92 per cent. of citronellal.

In October, 1919, material was collected for distillation from three-year old plants, grown from seed by Mr. E. Cheel, at Ashfield, near Sydney. The yield of oil was 1 per cent. The product was but little coloured, and was an excellent sample of the oil of this species. It had specific gravity at 150 C. = 0.8657; rotation aD - 1.1°; refractive index at 200 = 1.4515, and was soluble in 1 1/2 volumes 70 per cent. alcohol. An aldehyde determination showed that 95 per cent. was absorbed.

A sample of the oil of this species distilled at the Dunolly Farm in Victoria, was examined by Mr. J. C. Umney (Pharm. Journ. IV. 3, p. 200.). It had specific gravity at 150 C. = 0.8809; rotation aD - 1°; and contained 90 per cent. of aldehyde.

The yield of oil from this species varies somewhat according to the age of the material distilled, but under the most favourable conditions it should be about 1 per cent. In the year 1910, Mr. Ferguson obtained a yield averaging 0.89 per cent. from 80 tons of material.