426 The Systematic Value of the New Species, 



genus Oenothera possess the same systematic value as 

 those which distinguish the species of Linnaeus and 

 later systematists. I shall confine myself to the nearest rel- 

 atives of 0. Lamarckiana, that is to say, to the subgenus 

 Onagra. In this way I shall have the advantage of deal- 

 ing with very well known forms (0. biennis L., 0. muri- 

 cata L., 0. suaveolens Desf., etc.) and of using them 

 as subjects of comparison. The new species differ in 

 some respects as much, in others more, in yet others 

 less from one another and from the parent species than 

 these recognized forms do amongst themselves. 



And first I must emphasize two things which make 

 the treatment of this subject a difficult matter. I mean, 

 our present wholly insufficient knowledge of the units 

 of which the characters of organisms are built up, and 

 secondly the phenomenon of transgressive variability.^ 



I believe that each new mutation is brought about 

 by a single new quality (see page 403). This inner or 

 primary quality then comes in contact with the qualities 

 which are already present in the various organs and it 

 is this interaction to which its particular external mani- 

 festation is due. The nature of the outward and visible 

 form therefore depends only partly on the mutation but 

 partly also on the characters already existing in the 

 organism. Or, in other words, the new species is marked 

 not as a rule by a single new peculiarity but by the trans- 

 formation of many or all of its organs, more or less. 



So long as we do not know the single causes in ques- 

 tion we must compare these visible transformations in 

 new mutations with the visible dififerences between old 

 established species. 



Transgressive variability is one of the main supports 



* See page 56, and the following section. 



