435 



Then Alphonse de Candolle says — 



" But as the materials increase, so do the difficulties. Forms which appeared totally distinct, 

 approach or blend through intermediate gradations; characters, stable in a limited number of instances 

 or in a limited district, prove unstable occasionally, or when observed over a wider area ; and the practical 

 question is forced upon the investigator : What here is probably fixed and specific, and what is variant, 

 pertaining to individual, variety or race ? " (" On the Variation and Distribution of Species," by Asa Gray, 

 Collected Works (Sargent), i, 132). 



A brief discussion on the really insoluble question as to the amount of difference 

 from an existing species to constitute a new one, will be found at Part XXVIII. p. 159 

 (under E. vernicosa), and at pp. 161, 162 (under E. Muelleri). 



The intermediate forms can be indicated by curves. In a Presidential Address 

 (Proc. Linn. Soc, N.S.W., xxvi, 799, 1901), before the Society, I tried to emphasise 

 the variation of species in Eucalyptus, and the way in which the forms belonging to 

 allied species overlap, by suggesting the use of concentric circles, and offered a figure. 

 "Where these intersect, a form may be said to be referable to one species or the other. 

 So variable, however, is Eucalyptus, that someone has perpetrated the joke that all 

 forms are varieties of one species — E. australis. 



The reviewer (Joum. Bot., xxxii, 315) of the " Letters of Asa Gray," quotes him 

 as " half dead with Aster," which large genus he was revising. " Never was there so 

 rascally a genus ! I know at length what the types of the old species are ; but how 

 to settle the limits of species I think I shall never know." And so on. 



In the same volume (p. 225) we turn to Hanbury's " Notes on British Hieracia." 

 which also shows that botanists in older countries have difficulties in regard to the 

 demarcation of species similar to those which confront us in Australia in Eucalyptus. 

 And when we also dip into such genera as Salix and Rubus, we see that their difficulties 

 are most formidable, in spite of the fact that they have wider experience than we. 



As one example out of many, let us consider the relations of E. bofryoides and 

 E. saligna, whose puzzling overlapping I have tried to work out (quoted in Part XXIII, 

 p. 52). 



Until such time as every plant on the earth has been collected, and every species 

 appraised (and while this is being done other species are in the making), it must be the 

 case that there are inequalities of value between species, some being termed " strong," 

 probably because we have not stumbled upon their close relations. I say " stumbled 

 upon " advisedly, because, except over small areas, collecting in Australia has been 

 done unequally, and even spasmodically. There is little of the drag-net about it. The 

 element of luck comes in, for, in a continent, a careful man may easily miss an interesting 

 species, while a careless and even ignorant one may stumble upon it. Many species of 

 Eucalyptus were first collected fortuitously. 



