482 OCCURRENCE OF OIL DUCTS IX CERTAIN EUCALYPTS ANB ANGOPHORAS. 



contents of the duct or surrounding cells, and is also found in the oil glands in 

 the leaf. When material is sectioned fresh and transferred direct to 95% alcohol, 

 the ducts and oil glands are found to be free from this residue. 



There are certain resemblances or atiinities between the species of Eucalyptus 

 possessing central ducts. Perliaps tlie most obvious of these are the "Blood- 

 wood" fruits, more or less urceolate in shape, though the presence of urceolate 

 fruits does not necessarily signify ducts, e.g., E. Pluiickoniana, a "Striugybark" 

 from northern N.S.W., has a very similar fruit to that of E. calophyUa, the 

 Red Gum of Wiestern Australia, but there is no e\'idence of ducts in the former 

 species. Another exception is the Tasmanian E. urnigera, * with particularly 

 urceolate fruits. Other exceptions are also found. The leaf venation is 

 characteristic; in all species witii ducts, the lateral veins are very transverse, in 

 some cases almost at right angles to the midrib, close and numerous, while the 

 intramarginal vein is- very near to the edge. Angophora lanceolata is also in 

 this class. The eonver.se however does not hold, e.g. E. saligim, E. robusta, and 

 E. resinifera, possess lateral veins wliich are i]uite transverse, but no ducts 

 occur. The barks of these species show great variation. The great majority 

 fall into the "'fjloodwood" group, the bark being, in some cases, short tibred, 

 friable, and broken, e.g. E. corymbosa. Others such as E. exirma and E. ter- 

 minalis are more flaky. The greatest exceptions are however E. maculata, E. 

 citriodora and Angophora lanceolata, all possessing typical smooth "Gum" barks. 

 The majority of Eucuhipts have isobilateral leaves, in which the palisade 

 mesophyll either extends right across or forms two distinct zones on either 

 side with a narrow zone of spongy mesophyll between, altliough numerous ex- 

 ceptions occur. Among these species with ducts E. Abergiaiia, E. calophyllu, E. 

 corymbosa, E. dichromophloia, E. ficifolia, E. haematojyhni. E. intermedia, to- 

 gether with Angopliora lanceolata, have a distinctly dorsiventral leaf with the 

 palisade mesophyll developed towards the upper surface only, and stomata pre- 

 sent on the lower surface. All the other species mentioned have isobilateral 

 leaves with palisade tissue extending across the leaf and stomata present on 

 either surface. Here again the dorsiventral type of leaf is not peculiar to 

 tliose specimens with ducts, e.g. E. resinifera. E. robusta, and E. saligiia have 

 dorsiventral leaves, but no ducts. 



All the species of Angopliora which have been examined, namely, A. cordi- 

 folia, A. intermedia, A. subvchUina, A. Baleri and A. lanceolata. also possess 

 the palisade tissue developed only towards the upper surface, but only one 

 species has central ducts. 



In those species of Eucalyptus with ducts, of which the oils have been in- 

 vestigated by Baker and Smith (1920), the majority fall in their Group 1, i.e. 

 oils consisting largely of pincne without phellandrcne. E. caloplvylla, E. corym- 

 bosa, JS. e.rimia. E. intermedia and E. trachypliloia are nieuibei-s of this group 

 and possess oils with only a trace of cineol. E. maculata yields an oil without 

 phellandrcne and with tlie cineol percentage increased to 20. In the oil of E. 

 citriodora there is no cineol or phellandrene, the chief constituent being citro- 

 nellal. These authors state that the oil of E. terminalis was not investigated as 

 the number of glands in the leaf was so small. Smith (1914), in a paper on 

 the essential oils of Hie Angophoras. points out the great similarity between the 

 oil of .1. lanceolata and those ol)tained from the "Bloodwood" group of Eucalypts. 

 Cuthl)ert Hall (1914), on flie evidence of cotyledons, places in the Blood- 

 wood or Corymbosa group the following species: E. calophylla. E. perfoliata. E. 

 e.rimia, E. corymbosa. E. trachypliloia. E. citriodora. E. maculata. and E. 

 int,erm.edia. With one excepticm, E. perfoliata, in which ducts have not yet 



• E. tesselaris is also an exception. 



