580 ORDER CXLII. GRASIINACEjE. 



36. P. Bos'cii, (Poir.) Stem glabrous, simple. Leaves lanceolate, 

 erect, glabrous ; sheaths bearded at the base and on the margin. Pan- 

 icles short, few-flowered, somewhat pubescent. Glumes nerved. Seed 

 naked. — Car. 



37. P. Walte'ri, (Poir.) Leaves oval-lanceolate, amplexicaul, smooth ; 

 sheaths tomentose, bearded at the base. Panicles sessile, branching. 

 Glumes pubescent ; outer valve oval. — Car. to Vir. 



38. P. commuta'tum, (Schal.) Stem erect, glabrous. Leaves lanceo 

 late, slightly cordate, ciliate at the base, distinctly nerved. Panicle 

 diffuse. Pedimclcs pubescent. Glume 2-flowered. — If. May — July. 

 Dry soils. 2 — 3 feet. 



39. P. latifo'lium. Stem procumbent, pubescent. Leaves ovate-lan- 

 ceolate, hairy at the throat. Flowers solitary, scattered. Glumes 2- 

 flowered, perfect and sterile, pubescent. Palece of the perfect flowers 

 larger than those of the sterile ones. — If. Through the summer. 

 Dry, shady soils. Common. 12 — 15 inches. 



Genus XI.— ROTTBCEL'LIA. L. 

 (In honor of C. F. Eottbocll, a Danish botanist.) 



Flowers in one-sided spikes. Glumes 1 — 2-flowered, the 

 flowers sterile and perfect. 



1. R. dimidia'ta, (Mich.) (Stenofaphrnm Americanum, Schra.) 

 Stem creeping, branching, glabrous. Leaves glabrous, sometimes op- 

 posite, perennial ; spikes terminal, flat. Glumes unequal, the exterior 

 shortest. Palece lanceolate, the exterior longest. — If. Through the 

 summer. On the sea-coast. 



Genus XII.— OPLIS'MENUS. Beauv. 



(From the Greek opli-smos, armor.) 



Spikelets 2-flowered or more ; inferior flowers staminate or 

 neutral ; superior flowers perfect. Glumes 2, unequal, concave ; 

 staminate flowers wdth two paleoe, the lower one awned. Sta- 

 mens 3. Perfect flowers ; pale?e 2, the inferior acuminate, 

 mucronate. Styles 2. 



1. 0. seta'rius, (Rcem.) {Panicum hirtellum, Ell.) Stem prociun- 

 beut, creeping, sometimes assurgent, hairy at the joints. Leaves undu- 

 late, scabrous, slightly hairy, contracted at the base, throat, and mar- 

 gin of the sheath; spikes compound; spikelets 5 — 8-flowered ; rachis 

 angled, villous. 6^Z7/?;ies 1 -flowered, with purple awns. — If. Aug — 

 Oct. Rich, dry soils. 



2. O. cbus-gal'li, (Kuuth.) {Panicum crus-galli, L.) Stem erect, 

 terete, glabrous. Leaves long, scabrous. Flowers on spikes, forming a 

 terminal panicle ; rachis angled, hairy. Glumes 2-flowered, one per- 

 fect, the other sterile ; exterior glume with a long awn ; the interior 

 one flat, awned ; the accessory glume very small. Palece pubescent. — 

 0. Aug. — Sept. Cultivated grounds, 2 — 4 feet. 



The glumes of this species are not always awned, and the awns vary very mu«h iu 

 length. 



