326 J. H. MAIDEN. 



Other characters of Eucalyptus leaves we require to 

 know more about, are their size, texture and prominence 

 of venation. They are minor characters, and some species 

 present much variation in this respect. 



(c) Venation — Messrs. Baker and Smith 1 have grouped 

 certain Eucalyptus leaves into sections in regard to the 

 disposition of their veins, pointing out that the oil-content 

 of the leaves can in a measure be gauged from the venation. 

 The suggestion is ingenious but as the venation is, like 

 other characters, variable within such large limits, (e.g., in 

 the same twig the lower leaves may have spreading veins, 

 while the upper ones may have a nearly pinnate venation), 

 the method will only be practically useful in the hands 

 of experts. 



(d) Young stems — Some Eucalypts have marked quad- 

 rangular stems. E.g., globulus, Maideni, goniocalyx, 

 quadrangulatd, tetragona, and many others, but, as a rule 

 this quadrangular appearance, often well marked at an 

 early stage of growth, passes away as growth proceeds. 



(e) Essential oil — The perfume of Eucalyptus leaves is 

 owing to the presence of an oil. It varies in different 

 species in regard to both character or amount. In young 

 it is commonly more abundant than in mature foliage, the 

 high proportion of resinous matter in the young foliage 

 being, however, a drawback to distillation. In some cases 

 the perfume is not easy to define, but the crushing of the 

 fresh or even dried leaves in the warm hand has been used 

 as a diagnostic character for many years. It affords a 

 rough but ready test, which is always available, and really 

 valuable in skilled hands. Incidentally it may be mentioned 

 that some few leaves, e.g., corymbosa, contain a substance 

 allied to caoutchouc in their tissues especially in their 

 young state. 



1 This Journal, xxxv., p. 116. 



