260 A TEXT-BOOK OF GRASSES 
species was designated, the type is the first binomial species in 
order eligible under the following provisions: [then follow the pro- 
visions]. (Canon 15.) 
A name is rejected when preoccupied (homonym). (Canon 16.) 
A name is rejected when there is an older valid name based on 
another member of the same group (metonym). (Canon 17.) 
285. Comparison of the two recent codes.—The two 
codes agree in taking 1753 as the starting point for priority 
and in using the earliest specific name. They disagree 
chiefly in the following: 
The Vienna Code provides a list of nomina conservanda to 
which the law of priority shall not apply. The American Code 
does not restrict the law of priority, except as indicated in 
principle 2. 
The Vienna Code allows the use of generic and specific names 
although there may be earlier but non-valid homonyms. The Amer- 
ican Code rejects homonyms. (Digitaria and Setaria are accepted 
under the Vienna Code and rejected under the American Code; 
Bromus altissimus Pursh, 1814, not Bromus altissimus Gilib., 
1792, is accepted, under the Vienna Code, because the homonym is 
itself a synonym of another species and is not valid. Pursh’s name 
is rejected under the American Code.) 
The American Code fixes the application of names by reference 
to nomenclatorial types. The Vienna Code does not mention types. 
This, in practice, is a very important difference. Under the Amer- 
ican Code a specific name stands or falls according to the disposition 
of the type specimen, and a genus must always include the type 
species. 
In the present work the nomenclature, with a few 
minor exceptions, follows the American Code. 
COMMON NAMES 
286. The common name is the name by which a plant 
is commonly known in the language of the country. Few 
plants, and these widely and commonly cultivated spe- 
