May, 1921] 
HITCHCOCK — THE TYPE CONCEPT 
Leidensis where two species are described, both being included in the Species 
Plantarum. From these two Andropogon virginicus was chosen as the type 
because that species retained the name in its usual significance. The 
other species, A. hirtus, is now by many botanists referred to a different 
genus. 
Poa L. Linnaeus describes 17 species. He first used the genus in his 
Flora Lapponica. From among the species there described Poa pratensis is 
selected as the type because that retains the name of this economic species 
in its usual signification. 
Uniola L. Two species are described. One is referred now to Distichlis. 
The other is selected as the type, thus retaining the name in its current 
usage. 
Hordeum L. Six species are described. The reference in the Genera 
Plantarum is to figure 295 in Tournefort's work, representing Hordeum 
vulgar e, the common barley, which is therefore selected as the type. 
Aira L. Of the 14 species described four are included in the Flora 
Lapponica. To take the first of these as the type would transfer the name 
Aira to what we now call Trisetum. Hence another one of the four, A. 
caespitosa, is selected in order to retain the name in its usual signification. 
Some botanists apply the name Aira to the last two of the 14 original species, 
including A. caryophyllea, and refer Aira caespitosa and its allies to Des- 
champsia. These two species are from southern Europe and were not 
included by Linnaeus in his first use of the term Aira in the Flora Lapponica, 
and hence did not represent Linnaeus's original idea of the genus. 
In general, one should ascertain if possible what species or group of 
species an author had chiefly in mind in establishing a new genus. 
The application of the type concept to species is similar. If more than 
one specimen is cited, one should find which one the author had chiefly in 
mind. This may be shown by comparison with the description, by one 
having been selected for an illustration, by notes on the original sheet, by 
the specific name. Only when other methods fail should the first specimen 
cited be arbitrarily selected. 
The above illustrates what is meant by applying the rule of reason in 
the selection of types. Let us hope that soon all taxonomic botanists will 
accept the concept of types and that they may agree on the types to be 
selected. 
Bureau of Plant Industry, 
Washington, D. C. " 
