10 THE PHYLOGENETIC METHOD IN TAXONOMY. 



wholly impracticable, and that genetic analysis can be of value taxonomically only 

 in studying differentiation within the species itself. 



Constancy. — A more generally accepted basis for the species is its constancy, or the 

 ability to "breed true." While it is doubtless true that practically all actual species 

 do this, many of the segregates of to-day do not. More significant still is the fact that 

 the adherents of this definition make no attempt to determine this point before describing 

 a new species. Constancy is undoubtedly a factor to be regularly taken into account 

 in the evolutionary study of species, but it is futile to attempt this without the aid of 

 statistical and experimental methods. On the other hand, the test of constancy alone 

 would require the acceptance of an absurd number of species. For example, Jordan 

 (1873) recognized 200 species of Draba verna, the "Jordanons" of Lotsy (1916), and the 

 United States Department of Agriculture recognizes 250 varieties of wheat, all of which 

 breed true and would thus come to be species. But these are based upon characters 

 that taxonomers regard as slight and non-specific. The case of Draba verna shows that 

 this condition is not confined to cultivated plants, and this is borne out by studies of 

 Cerastium viscosum, Montia perfoliata, and other species at the University of California. 



Extensive field studies in connection with the present monograph have revealed 

 innumerable examples of very similar forms that evidently breed true. The acceptance 

 of this criterion would increase the number of species almost beyond belief, and it would 

 throw taxonomy into inextricable confusion. The idea of constancy is helpful in dis- 

 tinguishing between fixed genetic units and ecads, and is one of the first points to be 

 considered in the experimental analysis of a specific stock. It already appears probable, 

 however, that the prevalent opinion that forms are constant or not constant will have 

 to be modified, and that varying degrees of constancy must be recognized. 



Distinctness. — Regardless of the fetish of constancy, the working definition of the 

 average taxonomist is distinctness, by which he understands the ready recognition of 

 a particular form. It may easily be shown that distinctness or recognizability in itself 

 is no necessary test of a species. Nothing is more readily recognized than the albino 

 mutants of blue and purple flowers, but even the most extreme segregator rarely proposes 

 to call them species. Moreover, recognizability is too often a matter of the herbarium, 

 and completely disappears in the field, or the limits, of the unit fade away. It is pecu- 

 liarly the faculty of the specialist, who sees the finest details in bold relief, and it 

 frequently vanishes with adequate perspective. It ignores the various degrees of 

 differentiation, and emphasizes apparent values at the expense of the real ones. More- 

 over, this working test is applied without any real attempt at consistency, since ecads 

 are not regarded as species when their origin is known, but are called ecologic forms, in 

 spite of the fact that a large number of the specific segregates of to-day are ecads, which 

 are not generally recognized as such because they are known only in the herbarium. 



The idea that recognizability was a test of the species was probably in the mind of 

 Bateson, when he gave systematists the interesting advice to describe all the species 

 that they could induce any reputable journal to print (1913^). This advice is so unsound 

 as to bring its own condemnation, but it is useful in revealing the complete lack of 

 understanding of the foundations of taxonomy. While it must be confessed that too 

 much practice excuses the view that taxonomy is merely a matter of new species and 

 many of them, no one who regards science as organized knowledge can fail to see that 

 taxonomy has no real standing apart from evolution. To follow Bateson's advice would 

 add enormously to the already jmmense accumulation of so-called species, the origin 

 and relationship of which no one understands. What is now needed is not the further 

 increase of such segregates, easy to discover and describe by the thousand, but the 

 organization of this chaotic mass into natural groups. The method of the segregator 

 is to take the scattered and broken twigs of the evolutionary tree and catalogue them 



