128 Coville Juncus marginatus and its Varieties. 



been found in southern Brazil. The variety setosus occurs in 

 the southern Great Plains region, ranging over western Kansas, 

 Indian Territory, interior Texas, Arizona, and New Mexico, 

 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 aristulatus appear to overlap in the Atlantic 

 States over a considerable area, but in reality they are pretty 

 well distinguished, for the latter characteristically 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 

 Juncus marginatus is its variety aristulatus, 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. Juncus marginatus 

 proper is an outlying and probably derivative form, extending 

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

 direction of smaller size, more reduced inflorescence, and larger 

 heads. Juncus marginatus 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 plants into a form 

 more clearly expressive of their developmental relations. The 

 same method may without doubt be applied to any group of 

 plants with highly important results. 



