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



of range have been found since the maps were engraved. These are 

 included in the text.) Local floras, lists, and records of distribution 

 have been checked and efforts have been made to verify the records 

 that seemed to indicate an extension of range. Other herbaria have 

 been visited or have lent specimens, and many correspondents have 

 submitted specimens for verification. No additions have been made 

 without a study of the specimens. 



The ranges of native species are usually fairly well defined and 

 continuous. A species of the Coastal Plain extends, for example, 

 from New Jersey to North Carolina or from Virginia to Florida and 

 Texas, without a conspicuous break. Mountain plants extend along 

 mountain ranges where similar conditions prevail. Some species have 

 in the main a continuous range but are found also in isolated and 

 distant localities. Bouteloua hirsuta extends over the Great Plains 

 east to Wisconsin and Louisiana, and again occurs abundantly and 

 apparently native on Sanibel Island, Fla. Some Coastal Plain species 

 appear again around the head of Lake Michigan. In these cases it is 

 probable that the species do not occur in the intermediate areas. 



Certain arctic or northern species also show interrupted range, 

 being found within the limits of the United States only on isolated 

 mountain tops. The arctic grass, Phippsia algida, for example, is 

 known within the United States only from alpine summits in Colo- 

 rado. What appear to be interrupted ranges along the northern or 

 southern borders are mostly due to extensions into this country from 

 the main ranges in Canada or Mexico. 



The distribution of recently introduced species is often very erratic. 

 A single introduction may maintain itself or even spread consider- 

 ably for several years before coming to the notice of botanists. In- 

 troduced species often travel rapidly along railroads by means of 

 cattle cars, or they spread as impurities in the seed of crop plants. 

 That seeds may travel great distances through the air has been 

 shown by experiments in which airplanes have collected seeds, 

 insects, and other objects at varying heights in the atmosphere. 

 For example, spikelets of Paspalum dilatatum and P. urvillei were 

 taken at altitudes up to 5,000 feet in Louisiana. 



Grasses introduced into cultivation may spread or " escape" from 

 cultivation and become established over wide areas. Kentucky 

 bluegrass (Poa pratensis) and the ryegrasses (Lolium perenne and L. 

 multiftorum) are familiar examples. Johnson grass is an excellent 

 forage grass, but if it escapes into cultivated fields may become a 

 troublesome weed 



Other cultivated grasses, such as the grains, frequently spread 

 from fields but are unable to maintain themselves for long. Eulalia 

 (Miscanthus sinensis) has been cultivated for ornament in the east- 

 ern part of the United States for many years. Only recently has it 

 shown a tendency to spread by seed. It is now becoming a nuisance 

 in some localities because of its aggressiveness in old fields. 



MORPHOLOGY OF GRASSES 



The organs of grasses undergo many modifications or departures 

 from the usual or typical structure. A knowledge of the structure 

 and modifications of the organs, especially of the parts of the spikelet, 

 is essential for the interpretation of relationships. 



