HITCHCOCK AND CHASE NORTH AMERICAN PANICUM. 



89 



Fig. 79.— P. virgatum. From type specimen 

 in Gronovius Herbarium. 



villous at the throat; ligules dense, 2 to 4 mm. long; blades ascending, 10 to 60 cm. 

 long, 3 to 15 mm. wide, slightly narrowed toward the base, and gradually long-acu- 

 minate, flat, sometimes pilose on the upper 

 surface toward the base, rarely to the apex, 

 margins scabrous; panicles long-exserted, 15 to 

 50 cm. long, mostly one-third to half as wide, 

 but sometimes contracted, or very loose and 

 nearly as wide as long, usually many-flowered, 

 the slender, scabrous, usually fascicled branches 

 ascending or spreading, naked at base, repeat- 

 edly branching along the upper half or two- 

 thirds; spikelets rather short-pediceled, 3.5 to 

 5 mm., rarely but 3 or as much as 6 mm. long, 

 1.2 to 1.5 mm. wide, elliptic-ovate, acuminate, 

 strongly nerved ; first glume clasping, two-thirds 

 to three-fourths the length of the spikelet, rarely 

 equaling the sterile, lemma, acuminate to cus- 

 pidate, 5-nerved; second glume longer than the 

 sterile lemma, both much exceeding the fruit, 5 to 7-nerved; fruit narrowly ovate, the 

 margins of the lemma inrolled only at base. 



This species is well marked but variable. The blades are usually glabrous or 

 pilose above near the base only. Sometimes, however, the entire upper surface or 

 even both surfaces are pilose. Examples of this are: Minnesota: Mearns 743; 

 South Dakota: Thornber; Nebraska: Rydberg 1561 ; Kansas: Smyth 92; Georgia: 

 Tracy 3604, Harper 631; Florida: Combs 597; Alabama: Carver 72; Mississippi: 

 Chase 4459. 



The form named by Vasey P. virgatum confertum, with more or less compact panicles, 

 is represented by: New Jersey: Scribner in 1895, Vasey in 1884, Ward in 1884; Vir- 

 ginia: Knowlton in 1897; North Carolina: McCarthy in 1885; Florida: Kearney 158. 

 The size of the panicle is variable, in northern specimens being often much dwarfed. 

 The branches may be stiffly ascending or laxly spreading or drooping, these characters 

 not being coordinate with others. The glaucous character also appears to be without 

 significance in separating forms, glaucous and green individuals growing under the 

 same conditions. All these variations are connected by all shades of intergradation 

 with the typical form. 



Throughout the western portion of the range of the species there is found, chiefly 

 on sandy soil, a form with mostly single or loosely cespitose culms, often decumbent 

 at base, pale green or glaucous foliage, and small panicles with ascending branches. 

 We have been unable to separate this form as a subspecies because of the numerous 

 intergrading specimens. The following, which are not cited under the distribution 

 of the species, are representative of this form: South Dakota: Huron, Williams in 

 1892; Bellefourche, Griffiths 395; White River, Wallace 3, 4, 5; Iowa: Cherokee 

 County, Crozier in 1888; Nebraska: Sidney, Plank 13; Mullen, Rydberg 1597; Kan- 

 sas: Morton County, Hitchcock PI. Kans. 570a; Texas: Tascora, Reverchon 2844; 

 Channing, Williams 3061; Colorado: Raton Mountains, Griffiths 5463; Arizona: 

 Flagstaff, MacDougal 265; without locality, Lemmon 3154. 



The spikelets are frequently affected by a smut, this sometimes resulting in abnor- 

 mal forms with spikelets in glomerules or with two to several staminate or abortive 

 florets to a spikelet, as in Sandberg from Minnesota in 1891 and Brandegee from 

 Colorado in 1878. 



DISTRIBUTION. 



• Prairies, moist open ground, open woods and salt marshes, Maine to Wyoming and 

 south to Florida and Arizona, southwest through Mexico to Costa Rica; also in the 

 Bermudas and Trinidad. 



Maine: Scarboro, Chamberlain 552. 



New Hampshire: Walpole, Fernald 271 (N. E. Bot. Club Herb.). 



