230 



THE FORMATION 



POLYPHYLESIS AND POLYQENESIS 



279. Concept. The idea of polyphylesis, as advanced by Engler, con- 

 tains two distinct concepts: (i) that a species may arise in two different 

 places or at two different times from the same species, and (2) that a genus 

 or higher group may arise at different places or times by the convergence 

 of two or more lines of origin. It is here proposed to restrict polyphylesis, 

 as its meaning would indicate, to the second concept, and to employ for 

 the first the term polygenesis,^ first suggested by Huxley in the sense of 

 polyphylesis. The term polyphylesis is extended, however, to cover the 

 origin of those species which arise at different places or times from the 

 convergence of two or more different species, a logical extension of the 

 idea underlying polyphyletic genera, though it may seem at first thought to 

 be absurd. Polygenesis may be formally defined as the origin of one species 

 from another species at two or more distinct places on the earth's surface, 

 at the same time or at different times, or its origin in the same place at 

 dift'erent times. Polyphylesis, on the contrary, is the origin of one species 

 from two or more different species at different places, at the same time or at 

 different times. It is evident that what is true of species in this connection 

 will hold equally well of genera and higher groups. Opposed to polygenesis 

 is monogenesis, in which a species arises but once from another species ; with 

 polyphylesis is to be contrasted monophylesis, in which the species arises 

 from a single other species. It will be noticed at once that these two concepts 

 are closely related. The following diagrams will serve to make the above 

 distinctions more evident : 



I, Polygenesis 



II. Polyphylesis 



III. Monogenesis 

 (Monophylesis) 



m** 



a 



*When this word was first proposcfl. the author did not know that Briquet had al- 

 ready applied the term polytopism to this concept (Ann. Conserv. Bot. Gen., 5:73. 



