BOTANICAL AND CHEMICAL CHARACTERS OF EUCALYPTS, 103 



cinal purposes thus becomes of some importance and it might be worthy 

 of consideration whether mechanical or chemical means might not be 

 more advantageously used than the ordinary method of distillation. 

 The two largest groups will always supply the Eucalyptus oils to be 

 used for phaiTnaceutical purposes ; as the botanical and chemical 

 peculiarities of individual species are uniform to a remarkable degree, 

 constancy in results can be assured. 



The data that have been collected in Australia regarding oils of 

 undoubted species show that the product of a pai'ticular species, grow- 

 ing under natural confUtions, is remarkably uniform in character and 

 even when commercially distilled should show physical and chemical 

 results within a stipulated range. 



The herbarium material of the two species E. Maculata and E. citrio- 

 dora show close morphological resemblances, j^et the oils differ entii'ely, 

 that from the latter species consisting almost -whoriy of the aldehyde 

 citronellal, which is not present in that from the former. This is not an 

 accidental circumstance due to location, because the uniformity in con- 

 stituents with both is well shown. The causes responsible for this 

 result are not evident from a morphological study but lie deeper and 

 may eventually be traced to chemical influences acting along special 

 lines. This is one o£ the few instances met with among the Eucalypts 

 in which close botanical resemblances are not associated with a corre- 

 sponding similarity in the chemical composition of their oils. 



The oil from E. Macarthmi consists vei'y largely of geranylacetate 

 and geraniiol (12), the ester content often exceeding 70 per cent., so 

 that this species also appears to 'be a departure. The ester geranyl- 

 acetate had its origin apparently in the Angophoras (13) or even perhaps 

 in an older genus ; it is found in small emount in the oils of many 

 Eucalyptus species having general botanical features allied to those of 

 Angophora but the passage forms to E. MaOa/rthuri appear to be 

 wanting. 



Another instance is the citral-limonene bearing oil of E. Staigeriana, 

 in which case again the connecting species haive not been found. These 

 instances ai'e, however, few in a genus so rich in the number of species. 



The rule appears to be that each chemical constituent in the 

 Eucalypts increases in amount through a range of species until it reaches 

 a maximum in one of them, so that in the case of these apparently 

 anomalous species an explanation is forthcoming; they certainly show 

 a maximum in the characteristic constituents their oils contain. The 

 pinenes, cineol, phellandrene, particular esters, oxalic acid, Eudesmin, 

 Armadendrin, the various tannins, as well as other chemical consti- 

 tuents, all appear to follow this rule ; as corresponding botanical features 

 are also shown, an evolutionary theory for the formation of the species 

 of the whole genus is strongly suppoi-ted both by 'botanical and by 

 chemical evidence. 



Kinos or Aslrinqent Exudaiions. — It has been stated already that 

 the essential oils of particular species of Eucalyptus show a remark- 

 able uniformity in constituents as well as in general physical characters ; 

 advantage has been taken of this chemical constancy in the dii'ection of 

 assisting botanical studies in the- genus, so that more correct values 



