36 POACEAE 



on both sides; racemes 3-10, linear, 5-18 cm. long; spikelets eUiptic-lanceolate, 

 acute; first glume minute, triangular; lemma apiculate, .elliptic-lanceolate. P. 

 sanguinale L. Crab-grass. Cultivated ground and waste places: Mass. — 

 Fla. — -Calif. — Wash.; Mex.; naturalized from the Old World. Je-S. 



4. S. marginatum (Link) Nash. Stem 5-8 dm. long, prostrate at the base 

 and rooting at the nodes; sheaths densely papillose-hirsute; blades 5-8 cm. long, 

 3-10 mm. wide, flat, glabrous or pubescent; racemes 2-9, variou.sly disposed, 

 2-12 cm. long; spikelets 3-4 mm. long, lance-oblong; first glume minute, triangu- 

 lar, glabrous; second and third glumes long-pubescent; lemma elliptic. Waste 

 places: Md.— Fla.— Mex.— Utah; W. Ind., C. Am., and S. Am. 



9. VALLOTA Chase. 



Perennial grasses, with usually tufted stems, panicles usually densely hairy, 

 narrow or contracted. Spikelets numerous, articulated below the empty glumes, 

 1-flowered, lanceolate, acute or acuminate. Glumes 3, membranous, the second 

 and u.sually also the much shorter first densely silky-pilose or long ciliate on the 

 margins, often acuminate, and sometimes with a short bristle at the apex; the 

 lemma shorter, chartaceous, glabrous and shining, finally indurated, enclosing a 

 shorter palet. Styles distinct; stigmas plumose. 



1. V. saccharata (Buckl.) Chase. Erect perennial; stem 3-9 dm. high, 

 usually much-branched below; sheaths mostly exceeding the internodes, glabrous 

 or papillose-hirsute; leaf-blades 5-15 cm. long, flat, 5 mm. wide or less, more or 

 less pubescent; panicle 1-2 dm. long; spikelets 3-3.5 mm. long, acute; first glume 

 minute, second and third glumes densely silvery-villous. Panicum saccharatuiii. 

 Buckl. P. larhnanthiun Torr. Trichaene saccaratuni Nash. Dry hillsides: Tex. 

 — Colo. — Ariz.; Mex. Son. — Suhmont. My — S. 



10. PANICUM L. Panic-grass, Witch-grass. 



Annuals or perennials. Spikelets in open or contraced panicles, 1-2-flowered, 

 lanceolate, oblong, ovate to obovate or globose, obtuse to acute or acuminate. 

 Glumes 3, membranous, the first and second empty, the first usually much 

 shorter than the spikelet, sometimes minute, the third one empty or enclosing a 

 shorter hyaline palet and often also a staminate flower; lemma shorter and usually 

 more obtuse than the glumes, chartaceous, glabrous and shining, at length in- 

 durated, enclosing a palet. Styles distinct; stigmas plumose. 



Inflorescence truly paniculate. 



Basal leaf-blades long and narrow; spikelets lanceolate or ovate, acute or acuininato. 

 Annuals. 



Branches of the panicle widely spreading, the well developed pulvinus in their 

 axils long-hairy; spikelets lanceolate, acuminate. 1. P. barbipulrirtatum. 

 Branches of the panicle ascending, rarely spreading, the pulvinus glabrou.s or 

 sparingly hairy; spikelets ovate to ellipsoid, acute. 2. P. capillare. 

 Perennials, with long scaly rootstocks and stolons. .3. P. virgatum. 



Basal leaf-blades ovate to lanceolate, obtuse. 

 Spikelets less than 2 mm. long. 



Stem and shcitlis sparingly pubescent, with spreading papillate hairs. 

 Vernal le;ives glabrous or nearly so on the upper side. 



Autumnal stems branching from the lower nodes, forming a spreading 



bunch, 1-1. .5 dm. higli. 4. /'. occidcnlalr. 



Autumnal stems branching from the middle nodes, forming widely 

 spreading mats. 5. P. tenncsseenac. 



Vernal leaves pubescent on the upper side, especially towards the base. 

 Spikelets 1.8-2 mm. long; autumnal form decumbent- spreading. 



(1. P. pacilicum. 

 Spikelets 1.6-1.8 mm. Jong; autumnal form not decumbent-spreading. 



7. /'. HiKichucae. 

 Stem and sheaths densely soft-pubescent: hairs scarcely papillate. 



8. P. Iherrnale. 

 Spikelets more than 2 mm. long. 



Blades of stem-leaves elongated, narrowly linear 



Spikelets glabrous or with a few scattered hairs: stem branching only 



at the base. 9. P. perhnoum. 



Spikelets densely pubescent; stem branching above. 



10. P. Wilroxianum. 



Blades of stem-leaves lanceolate. 11. P. Scribnerianum. 



Inflorescence with racemiform branches. 12. /'. obtiisum. 



