388 



Real genetic relationships take cognisance of all the characters. 



I have dealt with the matter at some length at p. 247, Part VIII, of the present 

 work, and also in the present Part (p. 383). 



Contemplation of as many characters as possible to form a truly natural 

 s ystem is a very old idea, as the following passage shows : — 



" But the most comprehensive truth with which we are acquainted respecting plants is that which 

 includes the whole of their general structure, and this we learnt from those great Frenchmen who, in the 

 latter half of the eighteenth century, began to study the external world. The first steps were taken after 

 the middle of the century by Adanson, Duhamel de Monceau, and, above all, Desfontaines : three eminent 

 thinkers, who proved the practicability of a natural method hitherto unknown, and of which even Ray 

 himself had only a faint perception. This by weakening the influence of the artificial system of Linneus 

 . ." (Buckle's " History of Civilisation," ii, 397, 1861.) 



The matter is, of course, bound up with the old dogma of " Constancy of 

 Species " dealt with at p. 381. 



Darwin had a strong objection to classification based on a single or few 

 characters. Referring to Owen's paper " On the characters, &c, of the Class 

 Mammalia " (Proc. Linn. Soc. (Zoological), ii, p. 1, 1858), he says (to Hooker) : — 



. . . Though I knew nothing whatever about the brain, I felt a conviction that a classification 

 thus founded on a single character would break down . . ." (" Life and Letters," iii, 10.) 



. . . (to the Marquis de Saporta) ..." I cannot at present give up my belief in the close 

 relationship of man to the higher Simise. I do not put much trust in any single character, even that of 

 dentition, but I put the greatest faith in resemblances in many parts of the whole organisation, for I cannot 

 believe, that such resemblances can be due to any cause except close blood relationship." (lb., p. 162.) 



And again, " When the same organ is rigorously compared in many individuals, I always find some 

 slight variability, and consequently that the diagnosis of species from minute differences is always 

 dangerous . . ." 



" After describing a set of forms as distinct species, tearing up my MS., and making them one species, 

 tearing that up, and making them separate, and then making them one again (which has happened to me), 

 T have gnashed my teeth, cursed species, and asked what sin I had committed to be so punished . . ." 

 (" Life and Letters of Charles Darwin," ii, 37, 40.) 



Sir W. Thistleton-Dyer, F.R.S., the late Director of Kew, says : — 



. . . From what I have myself heard fall from Mr. Darwin, I am led to believe that in the 

 later years of his life he was disposed to think that every detail of plant structure had some adaptive 

 significance, if only the clue could be found to it.* . . . Such a classification, to be perfect, must be 

 the ultimate generalisation of every scrap of knowledge which we can bring to bear upon the study of plant 

 affinity." (British Association Address as Biological President, 1888, p. 690.) 



Mueller early learnt this lesson as regards the genus Eucalyptus, for when on 

 the North Australian Expedition in 1856 he wrote : — 



The Stringy-bark tree of this part of the country (E. tetradonta) differs from the southern species, 

 aud although a Eucahj-ptus it produces, Angophora-like, a four-toothed calyx. Several other species of 

 this genus, all trees, were noticed, of which two are highly ornamental in producing scarlet flowers and 

 lamellar bark; another in having a double operculum. I found it necessary, for the sake of satisfactory 

 distinctions, to describe all the tropical Eucalypti (nearly thirty species), on the spot, and I was never at a, loss 



Many years afterwards, I put the same idea in the following words : — " There is no evidence that we may have two 

 plints, preoisaly similar in morphological characters, which are not specifically identical," 



