THE GRAMINE^ OF NORTH AMERICA. 667 



North America, as would be expected from its extent and con- 

 figuration, ]ias a greater number and variety of grasses than Eu- 

 rope, and Europe a greater number and variety tlian Australia. 

 Europe lacks many of the species found in tropical and subtropical 

 North America and Australia. North America compares favorably 

 with both Europe and Australia combined. In the north of North 

 America are species of European genera; in the south, species of 

 many of the Australian genera. 



CENTRES OF' CERTAIN LARGE GENERA, SO FAR AS 

 NORTH AMERICA IS CONCERNED. 



Agrostis. Cool west North America. 

 Andropogon. East of Eocky Mountains in warm states. 

 Aristida. East of Rocky Mountains in warm states. 

 BouteJoiia. Arizona and Texas. 

 Bromus. Cool west North America. 

 Eragrostis. Warm east North America. 

 Melica. Pacific coast to Rocky Mountains. 

 Mulilenlergia. Arizona and New Mexico. 

 Panicum. Warm southeastern North America. 

 Paspalum. Warm southeastern Nortli America, especially 

 Elorida. 



Poa. Cool regions of west North America. 

 Sporoholus. Warm regions of west North America. 

 Stipa. Warm regions of west North America. 



The following upon the same subject was taken from a paper 

 read at a meeting of the A. A. A. S. in 1893 by Prof. S. M. Tracy: 



"Agrostis, with its 37 species and great number of varieties, is, 

 as the manuals say, 'common everywhere,' New England having 

 6 species, 'Minnesota 3, Oregon 21, Texas 6, and Florida 3; 14 of 

 the 37 species are confined to the Pacific coast. 



" Agropgron, with its 9 species, is distinctively western, all the 

 species being found in Colorado, the only instance in which so large 

 a genus has representatives of all its forms in a single state. 



