BY M. B. WELCH. 43 ( 



Although affinities do exist between certain species of Eucalyptus in which 

 bark oil-gland-s occur, there is no general feature which is common to all. There 

 is a considerable variation in bark, timber, fruits, leaf -venation and constituents 

 of the essential oil from the leaves, throughout the series. 



They cannot be regarded as primitive types and none of them fall into the 

 Corj'mbosae group. 



Summarij. 



Oil-glands axe typical of the cortical tissues in the young stems of the 

 majority of species of Eucalyptus, but usually there is no subsequent development 

 and they soon cease to function. 



Oil-glands, however, of a secondary nature are developed to a greater or 

 less extent in the secondary phloem of stems and roots of certain species of 

 Eucalyptus, reaching an enormous development in the barks in some types. 



The glands are distributed almost uniformly throughout the outer portion 

 of the secondary phloem in some species; in others they are confined to definite 

 zones separated by broad bands of phloem elements. 



They are never developed in close proximity to the cambium, and in the 

 bark of mature trees seldom approach within 10 mm. of this inner meristem; 

 thus, in stripping bark for oil distillation, it would lie unnecessary to remove 

 the innermost layers. 



Their development is evidently schizo-lysigenous and the glands are always 

 found surrounded by loose thin-walled parenchymatous tissue, either in a broad 

 zone or formed by the spreading out of the medullary ray at that point. 



The contents of the glands in twig-s and those furthest from the outside 

 in mature bark are readily soluble in alcohol; towards the outside, however, the 

 contents become darker in colour and apparently resinous, but are not wholly 

 soluble in any of the ordinary solvents. 



The barks of the various species dealt with show a great variation, from the 

 smooth-barked "Gums," through the loose, .short-fibred "Peppermints" and "Boxes," 

 the long-fibred "Stringybarks," to the rough, deeply-furrowed types approaching 

 the "Ironbarks." 



The occurrence of oil-glands in the roots and bark seems to indicate that 

 they are of a protective nature in the Euealypts rather than a means of reducing 

 transpiration or as food-storage organs. 



In conclusion I should like to express my indebtedness to Mr. J. H. Maiden, 

 I.S.O., F.E.S., for his ciurtesy in allowing me to obtain material of many of the 

 Euealypts from the Botanic Gardens. I am also indebted to Mr. R. T. Baker, 

 Professor Lawson and Dr. McLuekie for kindly advice and criticism throughout 

 the work. 



List of References. 



Baker, R. T., 1898. — On two well known but hitherto undescribed species of 

 Eucalyptus. Proc. Linn. Soc. N.S.W., 23, pp. 162-171. 



Bentham, 1866. — Flora Australiensis. Vol. 3. 



Deane, H. and Maiden, J. H., 1899. — Observations on the Euealypts of New 

 South Wales, part 5. Proc. Linn. Soc. N.S.W., 24, p. 448. 



Maidex, J. H., 1921.— Critical Revision of the Genus Eucalyptus. Vol. 6. 



Muelt,ee, F. v., 1879-84. — Eucalyptogi-aphia. 



Smith, H. G., 1916. — On the Essential oil from the bark of E. Macarthuri. Proc. 

 Roy. Soc. N.S.W., 50, p. 177. 



Solereder, 1908. — Systematic Anatomy of the Dicotyledons. 



