January 6, 1909 97 
“yr, The individual is the taxonomic unit, usually undesig- 
nated.” 
“2. Similar individuals constitute a race.” 
“For general taxonomic purposes races need not be desig- 
nated; the conception and description of the species is broad 
enough to include all races of which it iscomposed. There will 
never be complete uniformity of agreement as. to the distinction 
between races and species, any more than there will ever be 
complete agreement as to the limitation of genera. It is futile 
in science to attempt to lay down principles which interfere 
with individual judgments. For special purposes the races may 
be designated numerically, as Quercus alba, race 2; Oenothera 
biennts, trace 12; Bursa Bursa-pastoris, race 17; Draba verna, 
race 104. There are doubtless many instances when the species 
is composed of only one race, just as we have monotypic genera 
composed of but one species.” 
‘2. Similar races constitute a species, the species designated 
binomially.” 
“4, Similar species constitute a genus, the genus designated 
monomnially.” 
Professor Arthur, in the beginning of his article, brings out 
the fact that we still do not really know what a species is, and 
that even Darwin in his “Origin of Species” did not define it. 
He cites some very interesting examples of experiments made 
by himself. 
‘It is found that by taking rust spores from a single host 
of any particular Carex and sowing them upon an Aster, or a 
Solidago or an Erigeron, they will grow upon one of these gen- 
era, it makes not much difference what the species, but not upon 
the other two. Now if spores are taken from another Carex, the 
spores being so exactly like the former that they can not be dis- 
tinguished by any visible characters, and sown upon plants of 
the same three genera, they may grow upon a different one than 
in the former instance, but not upon the remaining two. Thus 
finally we will get three sets of forms, one growing on Aster, one 
