April 2, 1903] 



NA TURE 



525 



an oil consisting principally of pinene ; this is also the case 

 with about thirteen other species, which together form 

 Group I. in this system of classification. In the succeeding 

 groups, the lateral venation of the leaves becomes gradually 

 more complex, a marginal vein appears, and at the same 

 time the oils produced undergo what may be called a corre- 

 sponding change; thus pinene is partially replaced by cineol, 

 until, as in the Eucalyptus globulus, which the authors 

 appear to regard, probably in deference to its commercial 

 value, as the highest evolutionary product of the genus, 

 this constituent amounts to 60 per cent, of the oil obtained. 

 In the course of this evolution there have appeared several 

 side issues furnishing oils in which cineol is replaced by 

 aromadendral, piperitone, geranyl acetate or citronellal and 

 pinene, wholly or partially by the terpene phellandrene, and 

 in each of these groups, also, there exists a corresponding 

 leaf structure. 



Interesting as is this correlation of morphology and con- 

 stituents in the Eucalyptus species, it may be pointed out 

 that a knowledge of the constituents of a plant is never 

 likely to play such an important part in systematic botany 

 as the authors appear to believe, since there are already 

 known numerous instances of plants which, grown under 

 different climatic conditions, show no morphological change, 

 vet exhibit remarkable variation in constituents, and, on 

 the other hand, plants which are not at all closely related, 

 frequently contain the same colouring matters, alkaloids, 

 &c, so that the necessary specific constancy of constituents, 

 which alone would make such criteria useful, is wanting. 

 The authors lay stress on observations made by them as to 

 the absence of marked variation in the composition of oils 

 yielded by the same Eucalyptus species grown in different 

 districts of Australia, but the evidence of constancy in this 

 respect would be greatly strengthened if it could be shown 

 to hold for the same species grown outside Australia ; for an 

 investigation of this kind ample material now exists in 

 foreign plantations. 



The principal feature of the volume is, however, the pub- 

 lication of results obtained in the examination of the oils 

 yielded by practically all the Eucalyptus species indigenous 

 to Australia. A short description of the oil obtained, with 

 its physical constants and those of its principal fractions, 

 is appended to the botanical description of each species, 

 and in order to render these more readily available, they 

 are tabulated in special appendices. 



The evidence adduced by the authors of the occurrence in 

 the Eucalyptus oils examined of the normal constituents 

 cineol, pinene, phellandrene, &c, is, as a rule, unexception- 

 able, but occasionally there are lapses which perhaps are 

 due more to the magnitude of the authors' task in recording 

 such a mass of facts than to their lack of scientific thorough- 

 ness, e.g. a minute difference in the laevorotation of two 

 fractions seems insufficient evidence for the assumption that 

 aromadendral exists in the oil of E. corymbosa (p. 26) ; 

 similarly, the coincidence of the melting point of the nitroso- 

 chloride of the terpene of E. botryoides with that of pinene 

 nitrosochloride is not conclusive evidence of the presence 

 therein of pinene, and it is usual in such a case to prepare 

 in addition the nitrol-piperide or similar derivative. The 

 evidence given for the occurrence of a valeric acid ester 

 in E. umbra (p. 37) is worthless, whilst the lemon-like 

 odour of a particular fraction of the oil of E. fraxinoides 

 scarcely warn nts the assumption that it is due to citral 

 without characterisation of this aldehyde by the preparation 

 -of at least one of its readily obtained derivatives. The 

 authors also appear to be unaware that the reaction (p. 235) 

 which they employ for the identification of geraniol, viz. its 

 oxidation to citral by chromic acid, is equally well given by 

 the isomeride linalool. The formation of an alcohol 

 (cineol) of the composition C 10 H 18 O (p. 223) by the oxidation 

 of an aldehyde (aromadendral) of the composition C I0 H 14 O 

 is, if it really occurs — and on this point the evidence is 

 slender — a unique reaction, and requires further investi- 

 gation. It seems unfortunate, also, that whilst the specific 

 rotation and solubility of the oils have invariably been deter- 

 mined, the authors did not utilise their unique opportunity 

 to record such useful constants as the refractive index and 

 dispersion. Exception must also be taken to the use of the 

 name eucalyptol in place of'cineol in a scientific publication 

 of this kind. 



NO. 1744, VOL. 67] 



The volume, as a whole, is remarkably well printed, and 

 the plates depicting leaves of the typical groups clearly 

 exhibit the characteristic features to which attention is 

 drawn in the text. 



The mere collection of the material necessary for an 

 elaborate investigation of this kind is a task of considerable 

 magnitude, and when there is added to this the tedious 

 experimental work involved in the investigation of a large 

 number of oils of similar composition, some idea may be 

 obtained of the industry and perseverance the authors have 

 expended on this work. The results should be of inestim- 

 able advantage to the colony far-sighted enough to en- 

 courage the prosecution of such investigations. 



The American volume is intended primarily to enable 

 forest proprietors to identify the Eucalyptus species in their 

 possession, and is therefore largely a compilation of the 

 diagnostic characters of the fifty odd species which have 

 been introduced into the south-western States. The author, 

 however, devotes some space to extolling the ornamental 

 and useful character of these trees, and points out their 

 value, particularly as wind breaks, shade trees, improvers 

 of climate and as sources of timber and essential oil. The 

 virtues of the latter, when of American origin, are described 

 in language somewhat reminiscent of the advertisements 

 of transpontine proprietary medicines. The chemistry of 

 the volume is occasionally at fault, as, for instance, when 

 it is stated that (p. 13) " the exudations from the trees are 

 in most cases not gums, but resins," and " the chief in- 

 gredient of the lemon-scented Eucalypt is citronellon " (p. 

 39). The volume is, like most of the publications of the 

 U.S. Department of Agriculture, well printed and copiously 

 provided with useful and artistic illustrations. 



T. A. Henry. 



OPPOSITION OF MARS. 



A/T ARS is now brightly visible during the whole night, 

 and well placed in the sky for observation. He 

 occupies a position on the equator in Virgo, but the present 

 apparition is not really a favourable one, the distance of Mars 

 from the earth on the date of opposition (March 2S) being 

 nearly sixty millions of miles. The apparent diameter of 

 the planet, as given in the Nautical Almanac, will be I4"'6 ; 

 this is only half the value (2o"'5) which the planet pre- 

 sented in the best circumstances in August, 1892, and 

 September, 1877. At those periods, however, the declin- 

 ation of Mars was more than 24 south of the equator, so 

 that telescopic observations were rendered very difficult at 

 stations in high northern latitudes. A comparison of the 

 last few oppositions of this planet gives the following 

 figures : — 



Opposition. 



Apparent 



[ '1. mi' :< 



Distance. 

 Declination. Millions 

 of iMiles. 



1894, October 20 ... 10 ... 2C,S ... + S'32 ... 40 



1896, December 10 ... 18 ... i6 - 6 ... +2539 ... 52 



1899, January iS ... 12 ... I4'4 ... +2442 ... 61 



1901, February 21 ... 18 ... 13*8 ... + 14 36 ... 63 



1903, March 28 ... 20 ... I4'6 ... -07 ... 60 



Though the conditions under which Mars is now dis- 

 played compare unfavourably with those at a really good 

 opposition, it is quite possible to distinguish a large amount 

 of detail on the disc. The principal features are very dark 

 and well pronounced, and may all be recognised under pretty- 

 high powers. Fortunately, Mars satisfactorily bears more 

 extreme magnification than Jupiter. In studying the latter 

 object with a 10-inch reflecting telescope, the writer has 

 found a power of 252 very efficient and 312 ample for every 

 purpose, but on Mars the most serviceable powers appear 

 to be from 332 to 488. 



The study of Mars is essentially different in character 

 from that of Jupiter. The latter does not exhibit his real 

 disc, but a series of vaporous, longitudinal currents, in 

 which are floating a number of changing spots of various 

 tints. Mars shows real surface markings, which appear 

 subject to certain temporary differences due to atmospheric 

 interference. In fact, the aim of an observer of Mars is to 

 distinguish the outlines of the markings in a comprehensive 



