385 



Differences in chemical constituents may indicate different species. 



The above fact has not been disputed by responsible botanists for very many 

 years, but it is quaint to see Sir J. E. Smith (1797) and Sir W. J. Hooker (1841) 

 brought in to confirm such a position. In an article in the " New South Wales 

 Educational Gazette " for 1st February, 1905, p. 207, Mr. Baker naively states, in- 

 speaking of E. maculata Hook : — 



This botanist (Hooker), however, was not always guided by morphological characters in his system- 

 atic woriC, but took a wider view of science., and so, in order to give prominence to the chemical constituent 

 of the oil of the leaves, named this Queensland tree E. citriodora. which was the subject of article 18 of this 

 series (December. 190.3). He was not the first to name Eucalypts from their chemical products, for Sir 

 J- E. Smith, another illustrious botanist, named the Sydney Peppermint E. piperita in reference to its oil 

 constituents. This naming of species after chemical properties is not advocated by some botanists, but 

 our researches have led us to support Sir Joseph Hooker and others of his school, and these two species 

 afford a case upon which to discuss the advisability or likewise of this nomenclature." 



In Part LXVII, p. 328, of my " Forest Flora of New South Wales," I give a 

 ' Tentative Bibliography of Eucalyptus Oil." Sir James Smith briefly refers to the 

 aroma of the leaves of three species, while First Assistant Surgeon D. Considen wrote 

 to Sir Joseph Banks on 18th November, 1788, referring to Eucalyptus oil :— " If there 

 is any merit in applying these and many other simples to the benefit of the poor 

 wretches here, I certainly claim it, being the first who discovered and recommended 

 them/'" 



In 1793 Smith described a plant producing oil under the name of a species we 

 now know as E. piperita, and his only two other references to oil, or absence of it, are 

 under E. capitellata and E. obliqua. Thus, under E. obliqua L'Herit, he says : 

 Leaves .... aromatic, but without the flavour of peppermint." 



It is on such slender bases as these that Messrs. Baker and Smith, " Research, 

 &c," 2nd Edition, p. 18, say : " . . . The introduction of the utilisation of 

 chemical constituents in aiding the diagnosis of Eucalyptus trees dates as far back 

 as the foundation of Australia." 



We arrive at modern times, and let us consider the lesson in two instructive 

 papers on Rhus : — 



1. " The Poisonous Principle of Poison Oak."— Poison Oak {Rhus diversiloba) and Poison Ivy {Rhus 

 toxicodendron) are so much alike from the botanical viewpoint that .the slight difference in the shape of the 

 leaflets is the only reason for two species. The conservative botanists, Greene and Engler, consider R. 

 diversiloba to be " type " or sub-species of R. toxicodendron. 



The fact that the pharmacological action of the two species is identical has given the widespread 

 belief that the poisons were identical. W. A. Syme claims to have found upon hydrolysis of the poison of 

 R. toxicodendron, rhamnose, gallic acid, and fisetin. The author was unable to secure these same con- 

 stituents in R. diversiloba. and thinks it strange that such closely-related plants should have such widely- 

 different poisonous principles. The two species have a slightly different range, but " such a difference 

 in the chemical nature of the poisons could hardly be laid to a difference in climate or soil." 



Fisetin, gallic acid, and rhamnose, the constituents of Syme's glucoside, are found in large quantities 

 in Rh> oonHnus and Rhus rhodanfhema. It might be supposed from Syme's observations that these species 

 would be poisonous. As a matter of fact, however, neither of these species is poisonous, 



