LEAF VENATION AND CHEMICAL CONSTITUENTS OF EUCALYPTS. 123 



one might expect by environment. Our researches seem to show 

 that the species are only well marked varieties in which the dis- 

 tinctive characters have become permanent. The well defined 

 chemical groups branching off from a centre, which groups in their 

 several members show gradations in which the chain is in places 

 somewhat complete, demonstrates, we think, most strongly the 

 insignificant part that hybridism could have played in the forma- 

 tion of the several species of Eucalyptus. 



We would like to express our thanks to Mr. M. F. Connelly of 

 this Museum, who by his perseverance, has overcome the difficulty 

 of producing the nature photographs of the leaves, and to Messrs. 

 Rumsey and Tremain of the Technical College for the preparation 

 of the excellent lantern slides. 



Explanation of Plate. 



Fig. 1. — Leaf of Eucalyptus corymbosa, Sm. — This venation is indicative 

 of the presence of pinene in the oil. Note the close parallel lateral veins, 

 the thick mid -rib, and the position of the marginal vein close to the edge 

 of the leaf. The yield of oil from leaves showing this venation is small, 

 there not being room between the lateral veins for the formation of 

 many oil glands. 



Fig. 2. — Leaf of Eucalyptus Smithii, E. T. B. — This venation is charac- 

 teristic of species whose oil consists principally of eucalyptol and pinene. 

 Note the more acute lateral veins which are wider apart, thus giving 

 more room for the formation of oil glands ; the yield of oil is thus larger 

 in these species. The marginal vein is further removed from the edge 

 and is slightly bending to meet the lateral veins. 



Fig. 3. — Leaf of Eucalyptus radiala, Sieb. — This venation is character- 

 istic of those species whose oil consists largely of phellandrene and the 

 peppermint ketone. Note the still more acute and fewer lateral veins. 

 The marginal vein has also become so far removed from the edge that 

 a second one occurs, and the slight bending as seen in Fig. 2, has culmin- 

 ated in this group in a series of loops. The spaces for the formation of 

 oil glands are also practically unrestricted and a large yield of oil is 

 thus obtainable. 



