No. 543] BIOTYPES AND PHYLOGENY 



143 



ing of characters which make the resulting forms most 

 confusing. 



Jennings has shown that there are inherent difficulties, 

 which have so far been prohibitive, in securing crosses 

 between biotypes of Paramecium under experimental 

 conditions, yet it is obvious that such crossing must 

 occur constantly in nature; otherwise the whole geno- 

 plast theory becomes reduced to an absurdity. Granting 

 then the natural crossing of biotypes, let us consider the 

 case of a species, which for simplicity's sake we will 

 suppose is made up of three biotypes (1, 2 and 3), each 

 of which is distinguished by certain character-combina- 

 tions, designated a, b and c, respectively. If the union 

 of 1 and 2 is readily effected, while that of 1 and 3 or 

 that of 2 and 3 rarely occurs, it is evident that ab will 

 far more commonly characterize the species than ac or 

 be which will indeed seldom appear. The species will 

 therefore approach identity with one of its biotypes, 

 which may thus be considered the dominant strain. The 

 inequipotency of the biotypes and the resulting definite- 

 ness of character in the species are obvious. If, however, 

 the union of 1 and 3, and of 2 and 3 are as readily effected 

 as that of 1 and 2, ac and be will occur as frequently in 

 the species as ab. In such a case the biotypes are equi- 

 potent and the resulting species may be correspondingly 

 ill-defined. 



The hypothesis here suggested of the "inequipotency 

 of biotypes" may thus be the explanation of the existence 

 of the well-defined species so generally known, while the 

 occurrence of large heterogeneous assemblages of either 

 species or varieties may be interpreted as due to an un- 

 usual equipotency. The experimental determination of 

 the existence of this hypothetical difference in the po- 

 tency of the biotypes within a species would well be worth 

 while, if it should ever prove to be possible. The study 

 of large heterogeneous groups may suggest some other 

 lines of investigation into the nature and even the origin 

 of biotypes. For example, such groups occur chiefly, if 



