12 MISC. PUBLICATION 200, U. S. DEPT. OF AGRICULTURE 



The arrangement of the genera in this manual is, in general, from 

 the simple to the complex. It is, of course, impossible to arrange all 

 the genera in linear sequence and at the same time represents gradual 

 increase in complexity because plants have not developed in a single 

 line, but have diverged in all directions, their relationships being a 

 complex network. The highest genus of one tribe may be much more 

 complex than the lowest genus of the next tribe above. On the 

 average the Bambuseae seem to be the most primitive and the 

 Tripsaceae the most complex. A grass with a spikelet consisting of 

 glumes and several florets, the lemmas and glumes being similar and 

 resembling bracts, is a primitive form. Grasses with spikelets in 

 which the parts are reduced, enlarged, or much differentiated, are 

 derived or complex forms. Derived forms may be simple from the 

 reduction of parts and yet not be primitive. In the main the genera 

 of grasses fall readily into a few large groups or tribes, but several 

 genera of uncertain affinities are, for convenience, placed in the recog- 

 nized tribes on artificial characters, with the hope that further study 

 and exploration will bring to light their true relationships. 



The grasses of the world (about 510 genera) have been grouped into 

 14 tribes, all of which are represented in the United States. 



The sequence of tribes and genera in the manual with a few minor 

 changes, is that found in The Genera of Grasses of the United States. 



NOMENCLATURE 



The cooperative study of botany depends for progress and success on 

 definiteness in the application of the names of plants. Research 

 workers in all branches of botany must use the names of plants in the 

 same sense or serious misunderstandings will result. One of the 

 functions of systematic botany is to determine the correct names of 

 plants. The study of the application of plant names is nomenclature. 

 By common consent of the botanists of the world Latin has been 

 accepted as the language for technical plant names. _ 



Modern nomenclature commences with the publication in 1753 of 

 Linnaeus' Species Plantarum in which the binomial system of naming 

 plants was first proposed. During the nearly 200 years following that 

 date many thousands of plants have been described. During this 

 time there has been a lack of uniformity in the use of names, causing 

 much confusion, and resulting in frequent changes. The same 

 species has been described under different names at different times, 

 and the same name has been given to different plants. This con- 

 fusion has been especially embarrassing to the agriculturist, ranger, 

 seedsman, pathologist, entomologist, and to all others interested in 

 plants, but not familiar with nomenclature and the history of the 

 names used. 



The difference in the Latin names applied in different books to the 

 same kind of grass is due to several causes. 



(1) A species is described as new by one author without knowing that the same 

 species had been previously described by another author. The second name is 

 known as a synonym. _ 



(2) An author applies a new name to a variant of a species already described. 

 The author recognizes the variant as a distinct species. Other botanists may 

 consider it to be only a variety of the older species or may consider it as a variant 

 not sufficiently distinct to be worthy of varietal rank. 



- Hitchcock A S the genera of grasses of the united states, with special reference to the 

 economic species. U.S. Dept. Agr. Bull. 772, 307 pp., illus. 1920. 



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