THE AMERICAN NATURALIST [Vol. XLII 



any to search out and describe all groups that are dif- 

 ferent, regardless of the degree of difference. He must, 

 however, know the relationship of these groups, i. e., 

 whether they are coordinate species, forms or what not. 

 To publish them all as binomials regardless of their rank 

 completely hides their relationship to species already in 

 existence. It is easy to understand that this has resulted 

 partly from the fact that a trinomial is longer and hence 

 less convenient than a binomial. Convenience is much 

 less essential than accuracy and clearness, and must 

 eventually yield to permit the regular use of the trinomial 

 to designate the various differentiations of a species. 

 The treatment of all groups below the genus as essen- 

 tially coordinate is due even more to the fact that ques- 

 tions of ancestry and of origin enter all too rarely into 

 the making of new species. These are questions that 

 can be settled only by the most extensive and intensive 

 field work, followed by thorough experiment. For such 

 work there has as yet been almost no time or sympathy, 

 as is shown by the all but hopeless melange of so-called 



II. Bases for DisTrxorismxo Species 

 The universal basis for distinguishing species has been 

 the degree of morphologic difference. Physiologic and 

 ecologic differences have but rarely been taken into ac- 

 count, except in such groups as the bacteria. The mor- 

 phologic treatment is based upon the fundamental fact 

 that stable structures are'ancestral, and plastic ones de- 

 rived. This has led to the basic principle that repro- 

 ductive characters are of greater worth than vegetative 

 ones. With this the ecologist is in full accord theoret- 

 ically, but he would wish to have experimental evidence 

 before accepting it as universally true. In fact some of 

 the little evidence at present available indicates that this 

 rule must permit some exceptions. It must constantly 

 be borne in mind, especially by those who believe that 

 evolution is always a question of the germ-plasm, that 



