2 BULLETIN 772, U. S. DEPARTMENT OF AGRICULTURE. 



genera should enable- the user to identify the genera of all our grasses^ 

 and the text under each genus should enable him to determine the 

 species of our economic grasses. Under each genus are given the 

 type * and the synonyms based upon American species, or the names 

 that have been used in an American publication. 



The following generic names, of which the types have not been 

 found, are based on American material but are unidentifiable from 

 the descriptions: 



Anthipsimus Raf., Journ. de Phys. 89: 105, 1819. 2 Based on A. gonopodus 

 Raf., " Dry hills of the Ohio." 



Dactylograrama Link, Hort. Berol. 2 : 248. 1833. Based on D. cimwides Link, 

 described from garden specimens grown from seed from western North 

 America. 



Flexularia Raf., Journ. de Phys. 89: 105. 1819. Based on F. comprcssa Raf., 

 "Kentucky and Ohio." 



The tribes have been arranged in a new sequence based on the com- 

 plexity of the flower structure, the most primitive being placed first 

 and the most highly developed last. It is impossible to arrange them 

 in a lineal sequence and at the same time represent their relationships, 

 as the phylogenetic development has not been along a single line. 

 The present arrangement is the closest approximation to natural re- 

 lationships that can be shown in sequence. The highest development 

 in any given tribe may be far more complex than the most primitive 

 example of the tribe placed above it, but the relative development of 

 each tribe is believed to be fairly represented by its position in the 

 sequence. The bamboos are placed lowest, as certain genera, such as 

 Arundinaria, show the least differentiation in the floral structure. 

 The Andropogoneae and Tripsaceae are highly specialized, as is 

 shown by the great diversity and complexity of the floral structures. 

 The tribe Oryzeae of most authors includes two groups of diverse 

 genera, each worthy of tribal rank. The allies of rice (Oryza) are here 



1 The type species of a genus is the species or one of the species the author had chiefly 

 in mind when describing the genus. Most authors of to-day designate the type species, 

 but earlier authors usually did not. To make the application of generic names more cer- 

 tain, old genera are now put on a type basis ; that is, one of the original species is chosen 

 as the type. If, then, a genus as originally established included species belonging in two 

 or more genera the name of the genus goes with the type species and the species related 

 to it. It will be seen that the type species of a genus as here given often bears a differ- 

 ent generic name. (See Miegia, based on Arundinaria macrosperma, p. 22, and Panicu- 

 laria, based on Poa aquatica, p. 34.) This means that the genus was based on a species 

 previously described under a different genus. In this work the type species is given for all 

 generic names, whether valid or synonyms. The reasons for selecting a certain species as 

 the type are given in each case. Among several species, the one most familiar to the au- 

 thor of the genus may be selected as the type. Species described by Linnaeus in his flora 

 of Sweden (Flora Suecica) and in his flora of Lapland (Flora Lapponica) were familiar 

 to him and are often the types of his genera. (For a further discussion of types, see 

 Hitchcock, Generic Types with Special Reference to the Grasses of the United States, Amer. 

 Journ. Bot. 5 : 248-253, May, 1918 ; and Report of the Committee on Generic Types of the 

 Botanical Society of America, Science, n. ser. 49: 333-336, Apr. 4, 1919.) 



2 The form for literature citations throughout this bulletin is in the main that used 

 in publications of the United States National Herbarium. 



