336 J. H. MAIDEN. 



The Gum-topped Stringybark has therefore been duly 

 named, and has been given ten synonyms in addition, — not 

 hastily, but by men who have worked on the genus, and 

 who have given reasons for their determinations. The 

 great majority of the determinations can still be defended, 

 and may be looked upon as indicating forms of the species 

 referred to. Study of the Gum-topped Stringybarks presents 

 one of the best instances of variation in the genus that I 

 have met with, and affords a most instructive example of 

 the necessity, in this protean genus, of endeavouring to 

 ascertain what is the type, and of bearing it closely in mind. 



Again, who will have the temerity to define the boun- 

 daries between the Stringybarks, Eucalyptus eugenioicles, 

 c« pit elicit a and meter orrhynclia, and between all of them 

 and E. pllularls ? I could give dozens of specific instances 

 in which species run into each other, showing that we are 

 striving after a wrong ideal when we endeavour to stereo- 

 type them. 



IV. Mannas, Kinos, Oils, etc., are non-essential but 



ACCESSORY OR ADAPTIVE CHARACTERS AND EXAMINATION 

 OF THEM MUST BE SIMPLY LOOKED UPON AS AIDS TO 

 DIAGNOSIS. 



Volatile oils (e.g., of Eucalyptus) are what are termed 

 accessory substances, that is to say, they are not essential 

 to the plant. They probably have various functions, e.g., 1 



1 This is of course following Tyndall, who showed that an envelope of 

 aromatic air around a plant is less pervious to heat rays than is ordinary 

 atmosphere. — Kearney, " Report on a botanical survey of the Dismal 

 Swamp region." — (Contrib. U.S. Nat. Herb., v., 6, p. 392), says, " How 

 effective this may be is yet very doubtful, but it is not to be denied that 

 such aromatic plants are much more abundant in dry soils and climates, 

 where the water supply of the plant needs to be jealously guarded than 

 where other conditions prevail/' He quotes Pfeffer (Pflanzenphys. 2te 

 Auflage, i., 501) who considers that this exhalation is "hardly of high 

 importance" for protection against loss by water. 



