LEAF VENATION AND CHEMICAL CONSTITUENTS OF EUCALYPTS. 11D 



veins branching from the mid-rib become more acute or inclining 

 towards the venation which characterises those species, the oils of 

 which consist largely of the terpene phellandrene. But besides this 

 portion which connects directly with the phellandrene-peppermint 

 group there is a branching off from the eucalyptol pinene bearing 

 species in another direction, the oils of which species all contain 

 the aldehyde aromadendral and in which phellandrene is absent, 

 this sub-group includes that portion of the mallees which embraces 

 such species as E. dumosa, E. polybractea, E. viridis, E, cneortfolia 

 etc., and which culminates in those species containing a maximum 

 of aromadendral; these may be considered the typical "boxes" as 

 E. albens, E. hemiphloia and E. Woollsiana. Those species 

 belonging to the eucalyptol-pinene group which branch off into 

 the phellandrene-peppermint group are continued through that 

 group, the peppermint constituent increasing in amount in the 

 oil of the various Eucalypts, until species like E. dives or E. 

 radiata are reached. It will be observed from the photograph 

 that in the venation of the leaves of these species, the lateral 

 veins are more inclined to run parallel to the mid-rib and that the 

 principal marginal vein is far removed from the outer edge of the 

 leaf. Now, the marginal vein of the leaf of E. melliodora is some- 

 what far removed from the edge, and the value of this evidence 

 is seen in the fact that we discovered phellandrene in the oil of 

 this species long before the importance of the leaf venation in this 

 connection had been demonstrated, and it appears probable that 

 in this species we can detect the road through which the eucalyptol- 

 pinene oils branch off into those consisting largely of phellandrene. 

 This constituent is only present in small amount in this species 

 at any time, and is often difficult to detect, but the solubility in 

 alcohol of the oil, although rich in eucalyptol, indicates that we 

 are probably dealing with an oil in which phellandrene may be 

 present. 



The next group of the Eucalypts which shows a well marked 

 agreement between a characteristic venation of their leaves and 

 the constituents of their oils is that which includes all those species 



