247 



Reputed constancy of characters in Eucalyptus. 

 The following statements have been made : — 



1. " Comparative constancy of specific characters of Eucalyptus species ..... 

 but it is individual species that we maintain show a comparative constancy of specific characters throughout 

 their known geographical distribution." (Messrs. Baker and Smith.) 



And a°:ain : — 



o 



2. " The reputed or supposed great variation of individual Eucalyptus species has probably arisen 

 by the attempts of botanists to found species on morphological characters alone." (The italics are not mine.) 



Two points are involved in this statement : 



(a) The reputed invariability (or in other Avords, the " comparative constancy ") 



of species of Eucalyptus ; 



(b) The founding of species on morphological characters alone. 



Meal genetic relationships take cognisance of all the characters. 



Some of the items in regard to which I always endeavour to obtain informa- 

 tion as regards any particular species of Eucalyptus are as follows : — 



Shape of juvenile leaves ; venation and mature leaves ; principal constituents 

 of oil ; anthers ; fruit ; bark ; timber ; kino ; habit ; any other character. 



I attach great importance to studying the trees in the field. In this way 

 habitat, habit, size, bark, timber, can best be studied. 



In these researches I may be pardoned for saying that I have travelled more 

 or less in every State of tbe Commonwealtb, covering thousands of miles on foot in 

 pursuit of this study alone, in contradistinction to mere herbarium work. 



This is one way of learning what are "natural" species, and affinities and 

 dissimilarities can be largely learned iu this way. I have, indeed, inaugurated on a 

 comprehensive scale the study of genetic relationships in Eucalypts, and have always 

 deprecated the study of this genus from herbarium specimens or " morphological 

 characters alone." 



The extracts from the writings of eminent botanists are pertinent in this 

 connection : — 



1. It is clear that at present the question (relation of plants to one another) is very far from 

 settled ; indeed, hardly more than a beginning has been made in the establishment of a system which can 

 be said to represent real genetic relationships.* 



2. Rather there is an increasing tendency to the view that the solution of plant-affinities, as 

 Linna?us long ago affirmed, must be sought in a comparative study of all the characters, t 



3. The idea that morphology has nothing to do with the function of organs has been acquired 

 entirely because the fact has been overlooked that the transformations seen in organs are conditioned by a 

 change of function. Their functions, therefore, have been treated as subordinate in determining the 

 characters of organs ; external relations alone have been taken as the chief points for consideration. But 

 the relationships of mere form are by no means the permanent ones in ' the tide of phenomena.' They also 

 change. The determination of this change, that is to say, of the alterations which have taken place, and 

 are believed to take place in the formation of organs of a natural group, is one of the weightiest tasks of 

 organography. If we separate function from form we are at once led into altogether unfruitful speculations.^ 



* D. H. Campbell, Evolution of Plants, p. 13- 



+ A. B. Rendle, The Classification of Flowering Plants, i, p. 28. 



J. Organography of Plants. Goebel. Part i, p. 12. 



