230 THE FORMATION 
POLYPHYLESIS AND POLYGENESIS 
279. Concept. The idea of polyphylesis, as advanced by Engler, con- 
tains two distinct concepts: (1) 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 
different 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) 
a Q B &@ a 
™. mr a an ™m 
UC x \ 
a a c a b c 
1When this word was first proposed, the author did not know that Briquet had al- 
ready applied the term polytopism to this concept (Ann. Conserv. Bot. Gen., 5:73. 
