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AMERICAN JOURNAL OF BOTANY 
[Vol. io. 
which the groups of plants and animals as we find them today have de¬ 
scended from those of prehistoric or geologic times? Will it ever be possible 
even to agree upon the delimitations of the groups as they exist today? 
Will not generic delimitations always be, as is commonly said, matters of 
opinion? Even if this be the whole story, be it noted that in the long run 
we may hope to discriminate between the opinions of the biological genius 
and those of the biological dullard. 
The currency of this statement about generic limitations indicates not 
only the difficulty of such discriminations, but from one angle their evolu¬ 
tionary unimportance. So far as we know at present, it is a relatively 
unimportant matter how large or how much subdivided a branch of the 
evolutionary tree is taken for the genus unit, providing only you do not 
put with its twigs those from other branches. But, it may be asked, will 
it ever be possible to get the geneticists to agree on how many these are 
and how to delimit the mutants or segregants of the Oenothera species? 
We may best leave this specific question to the future, but that there is 
coming to be a fair degree of agreement as to the identity and delimitation 
of many Linnaean species will hardly be questioned. We are demonstrating 
in some cases that certain groups long suspected of free interspecific hybrid¬ 
ization are really guilty. The difficulties of the systematists with such 
groups are more than compensated by the joys of the geneticists and 
cytologists with each such new discovery. In fact, the cytologists are even 
now coming to the rescue in the case of the roses, the Jamestown weeds, 
and the cereal grains, not to mention minor cases, with a brand new set of 
earmarks for the identification, characterization, and classification of the 
systematically difficult members of these groups. But discussion of the 
proper treatment in an evolutionary system of classification of hybrids and 
their progeny would certainly carry me beyond the limits of my allotted 
twenty minutes. In my opinion the systematists have been too much in 
haste to tie up their specific names with so-called historic type specimens. 
It is not impossible that we may be able to recognize and characterize in 
its description the actual biologic type form for a species. As you may be 
aware, my studies on the morphogenesis of such simple forms as the Pedi- 
astrums have led me to believe that specific types are very definite and 
concrete entities capable of being recognized and adequately described both 
quantitatively and qualitatively. This attempt to recognize and describe 
what is biologically typical is certainly the aim with present-day system¬ 
atists who know their material in the field as well as in the herbarium, and 
there is little reason to doubt that characterizations so based do in general 
give a picture of the biologic type of the species in its relations to its sub¬ 
species, varieties, etc., and to the other related species of the genus. 
It seems to me safe to assume that the work of classification will never 
be finished till the units large and small are brought as nearly as available 
evidence permits into their evolutionary sequence. 
