475 



THE OCCURRENCE OF OIL DUCTS IN CERTAIN EUCALYPTS AND 



ANGOPHOKAS. 



By M. B. Welch, B.Sc, A.I.C, Economic Botanist, Techuologieal Museum. 



(Plates xlii.-xlvi., and seven Text-flgures.) 



Tlie presence, in the leaves, of oil glands or secretory cavities in varying 

 number and mode of distribution, is a characteristic feature of the great majority 

 of Eucalypts and Angophoras, though in several species, particularly in the 

 latter genus, tliese glands are practically absent. In section these glands appear 

 as ovate, elliptical, or circular cavities which, though varying in size and shape 

 within small limits, are never elongated sufficiently to approach in any way 

 what are known as "ducts," '"canals" or "passages." Secretory passages differ 

 from the typical secretory cavities only in their elongation; in origin they are 

 schizogenous, lysigenous or schizolysigenous. They are found in a number of 

 Natural Orders, jjarticularly in the Coniferales, and may occur in the pith, 

 xylem, phloem or cortex. In some genera they are confined to the roots, in 

 others they traverse tlie whole plant, or are limited to portions of the stem and 

 leaves. Whatever their mode of distribution may be, they possess, without 

 doul)t. a marked taxonomic importance and value. 



The oil-containing secretory ducts which are described here as being present 

 in certain species of the Eucalypts and Angophoras have apparently not yet 

 been recorded. In fact, Solereder (1908) makes no mention of oil canals oc- 

 euiTing in any of the Myrta-ceae. Macalpine and Remfrey (1891) record, how- 

 ever, the presence of "Central canals," in the petioles of Eucalyptus calnphylla, 



E. ficifolia and E. maculata "with its variety cilriodoraJ' In that paper the 

 presence of oil is discounted and the contents are classed along with those of 

 the cortical cavities of tiie petiole as being probably of a kinoid nature. There 

 is no doubt, however, that oil, apparently similar in character to that in the 

 leaf oil-glands, occurs in these canals, and further that tannin substances have 

 not, so far, been found in them. 



This investigation has shown that ducts occur in the stems and leaves of 

 the following Eucalypts and Angophoras: — E. Aheryiana F. v. M. (PI. xliii., tig. 

 6), E. calophyila r'. Br. (PI. xliii., fig. 4), E. corymhosa Sm. (PI. xlii.; PL xliv., 

 fig. 5: PI. xlvi., tigs. 1, 5-7), E. citriodora Hook. (Fl. xliii., fig. 3), E. dichromo- 

 phlnia F. V. M. (PI. xlv., fig. 1), E. eximia Schau. (PI. xliv., fig. 4), E. ferruginea 

 Schau. (PI. xliv., fig. 1), E. ficifolia F. v. M. (PI. xlvi., fig. 2), E. Eoehcheana 



F. v. M. (PI. xlv., fig. 6), E. haematoxylon J. H. M. (PL xlv., fig-s. 2, 3), E. 

 intermedia R. T. B. (PL xlvi., fig. 4), E. latifolim F. v. M. (PL xlv., fig. 5), 



