128 Coville — Juncus marr/lnafus and its Varieties. 



been found in sonthern Brazil. The variety selosus occurs in 

 the southern Great Plains region, ranging over western Kansas. 

 Indian Territory, interior Texas, Arizona, and New INIexico. 

 and southward in Mexico to the states of San Luis Potosi and 

 Jalisco. An isolated locality is also known on ballast ground 

 in Louisiana and another in Arkansas. The ranges of the type 

 form and the variety arlstulains. appear to overlap in the Atlantic 

 States over a considerable area. Ijut in reality the}^ are i)retty 

 well distinguished, for the latter charactei'istically inhabits sandy 

 plains, particularly those along the coast, while the type form 

 grows more abundantly in upland moist areas. 



The most widely diffused and probably the mother form of 

 Junciis inarginatus is its variety aristalatii,s, which is character- 

 istic of the coastal plains from New York to Texas, and extends 

 far up the Mississippi valley, occurring among the coast mount- 

 ains of Mexico southward to Guatemala. Jancm marginatum 

 proper is an outlying and probably dei'ivative form, extending 

 farther north and farther inland, and presents a variation in the 

 direction of smaller size, more reduced inflorescence, and larger 

 heads. Jancus marginatas setosus is a second derivative, with 

 acute, more papery perianth parts, and smaller seeds, charac- 

 teristic of moist places in the subarid regions westward from the 

 range of the mother form. 



This test by geographic range has checked and emphasized 

 the results obtained by a merely morphological examination of 

 specimens, and brings our knowledge of these ])lants into a form 

 more clearly expressive of their develo]>mental relations. The 

 same method may without doubt be applied to any group of 

 plants with highly important results. 



