280 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



13. POACEAE. Grass Family. 



Annual or perennial herbs, with round or flattened, jointed stems (culms), closed 

 at the nodes and hollow between them; leaves parallel-veined, 2-ranked, consisting 

 of a sheath, enveloping the culm like a split tube, and a blade, usually linear; flowers 

 minute, arranged in spikelets, these consisting of a series of 2-ranked bracts, the 

 lower pair {glumes) empty, the others (lemmas) bearing the minute flowers surrounded 

 by a second 2-nerved bract (palca) in their axils (lemma, palea, and flower termed 

 the floret); spikelets with 1 to many florets, borne in spikes or panicles. — The lemmas 

 are variously modified. They may contain no flower (lieing ster'ile) or may be greatly 

 reduced. The palea, also, is sometimes reduced or obsolete. The cultivated grains — 

 wheat, rye, barley, oats, and corn, as well as bluegrass and timothy^ — belong to this 

 family. 



Spikelets ovate, blunt, nearly sessile, subtended by bristles, borne in a compact 



epikelike panicle 1. CHAETOCHLOA. 



Spikelets more or less compressed, not subtended by bristles. (In the barlej^-grasses 



the bristles are the glumes, that is, part of the spikelet itself.) 



Spikelets absolutely sessile on the axis, forming spikes (the rudimentary spikelets 



in Hordeum pedicellate, but the central fertile spikelet sessile). 



Spikes several, racemose on a main axis and appressed to it; spikelets small, flat, 



somewliat heart-shaped, bome on one side of the axis; sheaths not auricled. 



17. BECKMANNIA. 



Spikes solitary; spikelets bome on opposite sides of the axis, they, or their parts, 



pointed or awned; sheaths with a pair of spreading auricles at the summit. 



Axis disjointing with the spikelets attached; spikelets bome 3 together, the 



central one 1-flowered, fertile, the lateral ones reduced to awns, pedicellate. 



28. HORDETJM. 

 Axis not disjointing; spikelets 3 to 8-flowered, all sessile. 



Spikelets bome 2 or 3 together (or the upper and lower ones of the spike 



sometimes solitary) 29. ELYMUS. 



Spikelets borne singly. 



Plants annual; glumes ovate 27. TEITICUM. 



Plants perennial; glumes narrowly lanceolate or subulate. 



26. AGROPYRON. 

 Spikelets on long or short pedicels, often in spikelike panicles but never in one- 

 sided spikes or on opposite sides of the main axis. 

 Fertile floret with a pair of sterile or rudimentary florets below and falling with it. 

 Panicle contracted, dense; sterile florets reduced to minute obscure lemmas; 



plant odorless 2. PHALARIS. 



Panicle open; sterile florets as large as the fertile one; plant strongly fragrant. 



3. TORRESIA. 

 Fertile florets with no sterile florets below them, sometimes with sterile florets 

 above. 

 Spikelets 1-flowered. 

 Lemma indurate, the nerves obscure, awned from the tip, the awn much 

 longer than the body. 

 Awn twisted; base of floret sharp-pointed; flowering culms erect, leafy. 



4. STIPA. 

 Awn not twisted; base of floret blunt; flowering culms decumbent, naked, 

 the sheaths bladeless, the sterile shoots erect, with long blades. 



5. ORYZOPSIS. 

 Lemma membranaceous, awnleas or minutely awn-tipped or awned from the 

 back. 



