EUCALYPTUS OIL GLANDS. 213 



a cover of a single pair of cells with the outer and inner 

 walls very thin, and the septum between them S shaped 

 and irregularly thickened and pitted. The double celled lid 

 of the gland may perhaps be characteristic of the Eucalypts, 

 but the most striking feature is its want of definition, in 

 this respect differing from the Rutacese. In most cases it 

 is not an easy matter to decide which are the "lid cells" 

 and which are typical epidermal structures, an example 

 being E. piperita. So far there has been no occasion to 

 consider an S shaped septum as typical, the division 

 between the indefinite "lid cells" being usually straight 

 or slightly curved. 



Turning now to the oil in the gland, it would seem that 

 the idea of the oil being present as a single drop, as usually 

 shown in text books, was not altogether justified. The 

 contents as seen are usually contracted in places from the 

 side of the gland, and in some cases the contents are so 

 sparse as to merely form a fringe round the interior of the 

 cavity. 



In a number of leaves examined the gland contents 

 appeared to have a fine granular appearance, though in 

 some cases small droplets were also seen. These granules 

 on treatment with alcohol of various strengths coalesced, 

 finally disappearing when the alcohol became sufficiently 

 strong to cause solution of the oil ; apparently indicating 

 the presence of an emulsion. As one would expect the 

 percentage of alcohol necessary for complete solution varies 

 in the different species, from 50% in the case of E. austra- 

 liana, E. Luehmanniana, etc., to 95% in E. aggregata, E. 

 oleosa and others. 



No matter what metabolic changes give rise to the oil, 

 it is evident that in the first place it must be in an extremely 

 fine state of division, analogous to the formation of a 

 chemical precipitate. The presence of a protective colloid 



