304 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS (2) Melaleuca bracteata F. Muell., one of the "Tea Trees" indigenous to northern New South Wales, and southern Queensland, has also been shown to display physiological forms (121). The normal form or Type produces an oil containing 70 to 90 per cent of methyl eugenol, but indi- vidual trees, indistinguishable morphologically from the Type, and grow- ing in the same district, were found to yield oils containing either methyl isoeugenol or elemicin as major constituents. (3) Backhousia myrtifolia Hooker et Harvey is another plant that ex- ists in physiological forms (116) analogous to those of Melaleuca bracteata, in that major components of similar nature are involved. Backhousia myrtifolia Type yields an oil consisting largely of elemicin, but recent work on Queensland trees has shown the occurrence of forms whose oils may consist largely of either methyl isoeugenol or isoelemicin. In addition, Hellyer and McKern (71) have recently found a third variant, the oc- currence of which was predicted on theoretical grounds here the major component of the oil is methyl eugenol. (4) B•ckhousia citriodora F. Muell. is still another Backhousia species in which a physiological form has been observed (124). Previously it had been thought that the leaf oil of this southern Queensland tree contains from 90 to 95 per cent of citral, but lately trees have been discovered that yielded oils consisting chiefly of (-)-citronellal and (+)-isopulegol, to- gether with small quantities of citronellol and esters. It is of interest that the optical activity (- 14.21ø) of this citronellal is the highest yet recorded for the laevo isomer. The isopulegol is an original component of the freshly distilled oil. (5) Leptospermum citratum Chalk Physiological forms of this plant have been further investigated by Penfold, etal. (122). The study of prog- eny from open-pollinated trees has shown that whereas the Type (70 to 85 per cent of aidehyde) and the vat. "A" (terpenic form) bred true, the offspring of the var. "B" showed segregation into various groups. Forty per cent gave oils of a terpenic nature resembling var. "A", 30 per cent showed aldehyde inheritance (30 to 50 per cent of the oil, i.e., intermediate between Type and var. "B"), 23 per cent resembled the original var. "B" parent and 5 per cent gave oils free from aidehyde, but rich in geraniol and geranyl acetate (alcohol-ester form). Field work has shown that all these classes exist in nature. (6) Melaleuca viridiflora Gaertn. Recently Hellyer and McKern (unpublished data, 1955) examined the essential oils derived from single trees of this "Broad-leafed Tea Tree" occurring on the New South Wales coast. In addition to the trees that contain oils of the linalooLnerolidol form, trees were observed which yield oils consisting of almost pure nero- lidol (about 90 per cent), no linalool being present. Other trees growing side by side with these were found to produce oils rich in the crystalline

RECENT DEVELOPMENTS IN ESSENTIAL OILS 305 sesquiterpene alcohol viridiflorol, m.p. 73-75 ø, together with cineole, terpenes, terpineol and sesquiterpenes. In some cases these latter oils contained so much viridiflorol that the crude oils solidified after distillation only a small percentage of cineole was present. An inverse ratio appeared to exist in the quantities of viridiflorol and cineole in such oils a low viridiflorol content seems to be associated with a higher cineole content, these oils approaching cajuput oil in general characteristics. (7) Zieria smithii Andrews. Examining the essential oils of the shrub Zieria smithii (faro. Rutaceae) Morrison, Penfold and Simonsen (103) noted that considerable variation in oil composition may be expected. The following compounds have so far been identified in these oils: safrole, methyl eugenol, elemicin, (+)-o•-pinene, (-)-zX•-carene-5,6-epoxide, lina- lool and eugenol. The phenol ethers occur alone or in admixture, in some cases all three occurring together. In some oils, one of these particular phe- nol ethers--safrole, elemicin or methyl eugenol--may occur to the extent of 80 to 90 per cent. II. Biosynthesis Studies Fascinated by the success obtained in tracing the biosynthesis of ter- penoid compounds by means of radioactive isotopes, Penfold and Willis (126) recently published a review of current experiments which attempt to trace, with the aid of radioactive acetate, the natural synthesis of citro- nellal by Eucalyptus citriodora. The potential value for biosynthesis stud- ies of such a series of physiological (orms as those of Melaleuca bracteata appears obvious, and an outline of proposed experiments is given. McKern, Spies and Willis (94) reveal another line of attack in their critical studies on variations in essential oil yield, and composition within and between indi- vidual trees of various eucalypt species. By applying standard techniques of sampling and distillation, it has been shown that the piperitone content of Eucalyptus dives oil rises as the leaves mature, apparently at the expense of the hydrocarbons. IlL General Research on/lustralian Essential Oils The essential oil of Baeckea crenulata De Candolle has been investigated by Penfold and Morrison (118) it consists principally of (d-)-o•-pinene, (d-)- and (+)-limonene, 3,-terpinene, p-cymene, linalool, sesquiterpenes and baeckeol. The oil was obtained in yields ranging from 0.2 to 0.36 per cent terpenic constituents accounted for about 85 per cent of the oil. Myoporum crassifolium Forst. ("Anyme") is a small tree endemic to New Caledonia, the wood oil of which was shown to consist chiefly of a sesquiterpene alcohol identical or isomeric with bisabolol (113). Later investigations (112) confirmed this sesquiterpene alcohol as a stereoisomer of bisabolol.