370 



Oblique Venation. — A study of the oblique venation, or that which is intermediate between the 

 approximately right-angled and parallel venations, and of which E. globulus may be regarded as a type, 

 reveals the fact that the bulk of the Eucalypts fall within this class. It is found that they occur in the 

 dry interior and also well up on the mountain region to elevations in a few cases of 5,000 feet. This form 

 is most strongly represented in the coastal area, but that is largely because species and individuals are more 

 numerous in that division. It is also the dominant form on the Western Slopes and in the interior, in fact, 

 except for the two species with transverse venation mentioned as occurring in those divisions, practically 

 all other species there belong to the oblique venation series. It is fairly common in the mountain region 

 between the altitudes of 2,000 and 4,000 feet, but becomes less plentiful above that elevation, and practically 

 ceases just above 5,000 feet. 



Considering the prevalence of this type of leaf all over Australia, it seems a correct assumption that 

 it is fairly ancient, and was evolved from the transverse venation as a form better suited to make progress 

 amidst the surroundings in which it was placed. 



Parallel Venation. — The type of leaf referred to as having parallel venation, or haying the lateral 

 veins arranged at an angle of less than about 25 degrees with the midrib, belongs chiefly to the mountain 

 region, and secondly to the coastal area; and so far as New South Wales is concerned, is practically 

 confined to those two divisions, the form being absent from the Western Slopes and the interior. E. 

 coriacea and stellulata are very pronounced examples of this class of venation. 



A study of the distribution of this type of leaf in New South Wales, Victoria, and Tasmania, leads 

 to the conclusion that it has been evolved largely, if not wholly, in response to cool and moist conditions, 

 and it is of interest to note that the Eucalypt which ascends higher than any other in Australia, viz., E. 

 coriacea, and which reaches an altitude of 6,500 feet, is one of the most typical of the parallel-veined forms 

 in the genus. Everything seems to point to the conclusion that the parallel-veined leaf is the newest type 

 of Eucalyptus leaf in existence, that it was developed in the south as an offshoot from the oblique venation, 

 and after the Kosciusko uplift, migrated north along the resultant Main Divide throughout the entire length 

 of New Soulh Wales." 



N. R. T. Baker, 1913. In Reft. Aust. Assoc. Adv. Sri., xiv, 309, gives lists of 

 species which yield over 75, 50, 25, 10 per cent, of Cineol and also under 10 per cent, of 

 Cineol respectively. These Groups follow no known affinities of species in other 

 directions. I will reserve my criticisms in this direction until the work of Messrs. 

 Baker and Smith (1920) is brought under review. 



O. Baker and Smith,, 1915. ' The Botanical and Chemical Characters of the 

 Eucalypts and their Correlation." (This is part of a paper contained in the First 

 Report of a Committee, British Association Report, 1915, and deals with essential 

 oils). 



" The essential oils . . . vary in composition in a striking degree, but the variation is of a 

 remarkably uniform character, and apparently has been contemporaneous with distinctive botanical changes ; 

 this is strongly brought out by the progressive alteration in the veins of the mature lanceolate leaves, starting 

 from the featherlike veuation of the members of the Corymbosse group, through the intermediate form 

 representative of the members of the cineol-pinene group, to the looping or butterfly-wing venation of the 

 leaves of the ' Peppermints ' and the ' Ashes,' a form indicative of the presence of the terpene phellan- 

 drene. The varying thicknesses of the midribs ; the disposition of the marginal veins ; the second vein 

 in No. 3, and the varying amount of oil-glands in these pictures should all be noted. 



The first type is represented by the Angophoras and by certain Eucalypts, between which there is 

 general chemical agreement. The terpene in the oils of the species of Eucalyptus characterised by this 

 venation, and also in the Angophoras, is pinene ; phellandrene does not occur in them, and cineol is either 

 absent or only present in small amount, whilst the yield of oil is always small. 



