MANUAL OF THE GRASSES OF THE UNITED STATES 295 



(A. byzantina C. Koch) are derived from A. sterilis. A few varieties 

 adapted to dry countries are derived from A. barbata. The two native 

 species, found in the Rocky Mountain region, are of high palatability, 

 but occur only scatteringly. 



Plants annual. 



Teeth of lemma setaceous; pedicels curved, capillary 3. A. barbata. 



Teeth of lemma acute, not setaceous; pedicels stouter. 



Spikelets mostly 2-flowered, the florets not readily separating; awn usually 



straight or wanting; lemmas glabrous 2. A. sativa. 



Spikelets mostly 3-flowered, the florets readily separating; awn stout, 

 geniculate, twisted; lemmas clothed with stiff brown hairs (hairs 



sometimes white or scant) 1. A. fattja. 



Plants perennial. 



Blades involute; panicle 2 to 5 cm long 6. A. mortoniana. 



Blades flat or folded; panicle 5 to 15 cm long. 



Sheaths, at least the lower, and blades pubescent 4. A. pubescens. 



Sheaths and blades glabrous 5. A. hookeri. 



Section 1. Etjavena Griseb. 



Annuals; spikelets pendulous, mostly more than 2 cm long. Intro- 

 duced from Europe. 



1. Avena fatuaL. Wild oat. (Fig. 585, .4.) Culms 30 to 75 

 cm tall, erect, stout; leaves numerous, the blades flat, usually 4 to 8 

 mm wide, scabrous; panicle loose and open, the slender branches 

 usually horizontally spreading; spikelets usually 3-flowered; glumes 

 about 2.5 cm long; rachilla and lower part of the lemma clothed with 

 long stiff brownish, or sometimes whitish, hairs, these sometimes 

 scant; florets readily falling from the glumes; lemmas nerved above, 

 about 2 cm long, the teeth acuminate, not setaceous; awn stout, 

 geniculate, twisted below, 3 to 4 cm long. © —Cultivated soil 

 and waste places; introduced from Europe; rare in the Eastern 

 States; Maine to Pennsylvania, Missouri and westward, a common 

 weed on the Pacific coast (fig. 586). Seed used for food by the 

 Indians. 



Avena sterilis L. Animated oats. Resembling A. jatua, the 

 spikelets 3.5 to 4.5 cm long, the awns 5 to 7 cm long. © — Some- 

 times cultivated as a curiosity, occasionally spontaneous. When laid 

 on a moist surface the fruits twist and untwist as the awns lose or 

 absorb moisture. 



2. Avena sativa L. Oat. (Fig. 585, B.) Differing from A. jatua 

 in having mostly 2-flowered spikelets, the florets not readily separating 

 from the glumes; lemmas glabrous; awn usually straight, often 

 wanting. © - — Commonly cultivated and occasionally escaped. In 

 A. nuda L., naked oat, the caryopsis readily separates from the lemma 

 and palea. A. brevis Roth is a form with smaller spikelets, the lem- 

 mas plu np, awned. A. strigosa Schreb. has a 1-sided panicle, the 

 lemmas scabrous toward the apex, both florets awned. 



3. Avena barbata Brot. Slender oat. (Fig. 587.) Differing from 

 A. jatua in the somewhat smaller, mostly 2-flowered spikelets on 

 curved capillary pedicels; lemmas clothed with stiff red hairs, the 

 teeth ending in fine points 4 mm long. © — A common weed in 

 fields and waste places, Washington, Oregon, to Arizona and Cali- 

 fornia. 



Cultivated oats fall into three groups according to the number of 

 chromosomes. Group 1, 7 chromosomes, A. brevis, A. strigosa. 

 Group 2, 14 chromosomes, A. barbata. Group 3, 21 chromosomes, A. 



