i8 



Of course connecting species and sub-groups link up Ihe larger groups 

 above, and such connections are indicated throughout this work by the system 

 of classification adopted. 



The suggestion that the line of sequence is through E. sali^iui and E. 

 botryoides to the " Ironbarks " was indicated, not only by the chemistry of their 

 oils, but also by that of their kinos ; the richer cineol oils also show an association 

 with the "Ironbarks," particularly through that of E. sideroxylon, and they 

 are all grouped in this way to illustrate the sequence. 



The greater number of the Eucalypts yield oils consisting largely of cineol 

 and pinene in varying proportions, with an absence of phellandrenc. It thus 

 appears that phellandrene made its appearance late in the evolutionary arrange- 

 ment of the genus, and if this is so then piperitone is quite a recent formation-, 

 even more so than the other characteristic constituent aromadendral, which 

 is also found in some West Australian species. 



The suggestion that the " Boxes " and associated " Malices " descended 

 through the " Stringybarks " was derived from the oil of E. obliqua, a species 

 with a most extensive range, the oil of which always contains aromadendral, 

 and this characteristic constituent increased in amount as the typical " Boxes " 

 were evolved. 



A good many of the " Mallee " oils do not contain aromadendral, they 

 being evidently more closely associated with the " Gums," and are here arranged 

 in that manner. Such species are E. Morrisii, E. pumila, &c. 



As the genus evolved the venation of the leaves and colour of the 

 timbers changed in agreement with the alteration in the character of their oils. 

 All the species belonging to the " Peppermints," the " Ashes," and associated 

 species have white timbers, while in the earlier members they are usually red. 



The genealogical table we now submit shows, in its general arrangement, 

 the lines of sequence through which the Genus apparently evolved. Of course, 

 it was not possible to depict diagrammatically, the most difficult sub-divisions 

 which, -to any student of the Eucalypts, must become apparent, but if the table 

 is considered broadly, the general grouping will be evident, and this arrangement 

 is supported by botanical as well as chemical evidence. 



Passing onward from E. pilularis a well-defined group of trees is reached, 

 the oils of which contain phellandrene as a pronounced constituent, and instead 

 of aromadendral being present, this constituent has been replaced in these oils 

 by the peppermint ketone, piperitone ; consequently the leaves when crushed 

 give an odour of peppermint, and for this reason the trees are generally known, 

 vernacularly, as " Peppermints " ; the more pronounced of these are E. piperita, 

 E. dives, E. amygdalina, E. vitrea, &c. When the first Eucalyptus oil was distilled 

 in Sydney in 1788 the leaves utilised were those of E. piperita, known 

 locally as " Peppermint," so that the first-named species from New South Wales 

 owes both its vernacular and specific names to the presence of this chemical 

 constituent in the oil; and the introduction of the utilisation of chemical 

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

 foundation of Australia. Results of recent investigations show that the value 

 for determinative purposes of chemical constituents in the tree, as adopted by 

 those early naturalists, was on a sound basis, and in the light of our present 

 knowledge this determination is recognised as being of the greatest value 

 in deciding differences between Eucalyptus trees which are morphologically 

 closely allied. 



It will be seen from plates vi, vn, and vin that the venation of the leaves of 

 trees giving phellandrene-bearing oils has an acute spreading arrangement 

 inclining to run parallel to the mid-rib, which appears to be the completion of 



