During the extensive period tlms represented, the species have materially 

 differentiated from the parent stock, and have so well established their 

 individuality that the evidences here published show but a few species under- 

 going varietal evolution at the present time. That there are variations cannot be 

 denied, but they are comparatively few when the extensive range of the genus 

 is considered. With the exception of about half a dozen, all the Eucalypts 

 enumerated in this work will be found to possess comparatively constant 

 characters throughout their geographical distribution. On the whole, therefore, 

 we think the Eucalypts may be regarded as fairly invariable. It must, of 

 course, be admitted that herbarium material of Eucalyptus species can be so 

 arranged as to show perfect gradations ; but then all other physical characters 

 are ignored. 



Further, it is found that the constituents occurring in the oils of all those 

 species about which there is no difference of opinion are always in agreement, 

 and only differ in amount within the limits experienced with the oils of all the 

 species at varying times of the year ; it may also be that this rule applies to all 

 those species about which little has been previously known. Several instances 

 of this constancy of constituents will be found under the respective species in this 

 work. 



The late Baron von Mueller, who had a most extensive knowledge of the 

 Eucalypts of Australia, recognised the assistance that might be rendered to the 

 botanist in the discrimination of the different species by the chemical investi- 

 gation of their several products. The following reference is from his " Eucalypto- 

 graphia," Decade III, article Eucalyptus piperita, published in 1879 : " E. oblu/ua 



is distinguished it cm E. pi per if a by and perhaps by anatomic, 



histologic, and chemical peculiarities of the bark and wood, which characteristics 

 remain yet more comprehensively to be studied." 



Since the time the above was written much has been done in determining 

 the chemical characteristics of many of the species, and the results are of so 

 satisfactory a naiure in this connection, that it must be apparent that no investi- 

 gation of the Eucalypts over any one portion of the continent can be considered 

 complete or conclusive, without it embraces also the chemical investigation of 

 their several products, and other physical characters. This is well illustrated 

 by the several species that have previously been classified under the name of 

 E. amygdalinn. 



In a paper by Dr. Gladstone on Essential Oils (Journ. Chem. Soc., 1864, 

 p. 3), the oil of Eucalyptus amygdalina is stated to have a specific gravity of 

 0-8812 at 15-5 C., a rotation for a column having a length of 10 inches, of- 

 136, or corrected for optical rotation a D -- 53-54, 'and refractive index for 

 D= 1-4788. From what is shown in this work under E. phellandra, there seems 

 little doubt but that this particular sample of oil was obtained from E. dives. If 

 these figures are compared with those for this species distilled recently, it will 

 be seen how closely they agree, so that the constancy of the products obtainable 

 from this species of Eucalyptus is thus indicated. 



The specific rotations given by Mr. \V. Percy Wilkinson (Proc. Roy. Soc., 

 Victoria, Vol. VI, p. 197), for various samples of supposed E. amygdalina oils, 

 varying from 88-9 to 16-3, show, when compared with our results, 

 that these samples of oil had been obtained from more than one species. 

 The specific gravities given in the paper also suggest the same conclusion. This 

 grouping of the species on a morphological basis illustrates the difficulties under 

 which Mr. Wilkinson laboured in his commendable attempt at that time to 

 extend our knowledge of Eucalyptus oils. 



