GRASSES OF IOWA. 405 



The Zizania aquatica is common in British America, northern Mis- 

 sissippi Valley, along the Atlantic coast from Newfoundland to Penn- 

 svlvania and Florida, Arkansas, eastern Texas to Missouri and central 

 Nebraska. It is also found in central Siberia and Japan. The genus 

 Zizaniopsis, with one species and two varieties, occurs from southern 

 United States to Brazil. 



The Large genus of Paspalum, with one hundred and sixty species, is 

 p »orly represented in northern United States; Iowa having a single 

 species and a doubtful second, the P. mucronatum. In southern United 

 States the genus is a large and important one. The genus Panicum in 

 number of species outranks the former. Three hundred are recognized. 

 It is generally found in warm countries with a few in the temperate re- 

 gions. The genus is conspicuous in the savannas of South America. 

 Panicum is the largest genus of grasses in Iowa. The genus Andropogon 

 occurs in warmer regions of North America, Asia and temperate Europe. 

 The latter with eight or nine species. Fifty species of the Arthrolophis 

 (subgenus) like A. provincialis are largely American. The subgenus Sor- 

 ghum, belongs to the torrid and warm temperate countries (Africa, etc.). 

 Hackel in concluding his paragraph on the distribution of grasses says: 



"Not less than 90 genera are common to both continents; among 

 these are many that are exclusively tropical, and besides ten single types. 

 No one tribe is confined to one hemisphere, and no genus of numerous 

 species to any one floral region. All this goes to prove that grasses are a 

 family distributed very uniformly, and that the separation of their tribes 

 _ r oes back to very ancient times. To be sure., the single tribes have varied 

 under the influence of the later divisions into zones; while the) Paniceae 

 and Andrupogoneae preponderate in the tropics, they are put in the back- 

 ground by the Festuccae Aveneae, and Hordeae in the temperate and 

 frigid zones. The eastern North American forest region has preserved 

 man) - more of them (and in general of tropic types) than has the Old 

 World." 



Dr. W. J. Beal in an admirable article summarizes the distribution 

 ot grasses as follows: 



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

 uration, has a greater number and variety of grasses than Europe, and 

 Europe a greater number and variety than Australia. Europe lacks main 

 of the species found in tropical and subtropical North America and Aus- 

 tralia. North America compares favorably with Europe and Aus- 

 tralia combined. In the north of North America are species of European 

 genera; in the south, species of many of the Australian genera." 



