January 27, 1909 TOS 
“In the main it may be said that there are two opposing 
conceptions of species that are to-day struggling for mastery in 
the realm of biologic thought. The more prevalent idea, dat- 
ing in its essence from the time of Darwin, has been that spe- 
cies are artificial creations, mere matters of convenience in the 
classification of the organic world, arbitrary concepts that have 
no great and enduring reality. Partisans of this view hold to 
the doctrine of continuity, maintaining that all species have 
been connected with other species by a series of intergrades, and 
that there is no vital distinction between variation and muta- 
tion. . . In somewhat striking contrast to this concept of 
species stands the idea that species are entities, which arise by 
discontinuous variation or mutation, and which have their full 
specific value from the start. Nor does time change specific 
form by any slow gradations; the species at its death shows.no 
essential difference from the species at its birth.” 
“There are, then, two radically different conceptions of spe- 
cies now current, one of a rank as much higher than the other 
as the genus is above the Linnaean species, or the family above 
the genus. Ecological observations support both views, but it 
is especially the experimental method that has made things 
clear. Whether or not one calls them species, it is evident that 
the genus Oenothera contains a number of entities, sharply de- 
fined from one another. In such genera as Salix and Aster 
there is reason ts believe that species do not thus differ sharply, 
but that they are connected with one another by all but imper- 
ceptible gradations. . . It appears that the method of evolu- 
tion in various groups of plants and animals is radically differ- 
ent, and it follows as a corollary that what are called species in 
these various groups are necessarily not homologous.” 
“In the future it must be recognized that the final test of 
the validity of species is experimental, and taxonomists must 
work no less in the herbarium, but more in the field and in the 
garden. If the taxonomists of the future fail in these respects, 
a hard but certain fate awaits them. The world of morpholo- 
