GENERA OF GRASSES OF THE UNITED STATES. 



Ill 



Stipa, A. elatior to Arrhenatherum, A. pennsylvanica to Trisetum, A. flavescens 

 to Trisetum, A. fra'gilis to Gaudinia, A.,spicata to Danthonia. In the Genera 



FIG. 57. Sphenopholis obtusata. Plant, X i ; spike- 

 let and floret, X 5. 



Plantarum, Linnaeus cites 

 Tournefort's figure 26 f 

 (error for 297), which is 

 Avena sat iva,. Hence 

 this is the type species. 



The most impor- 

 tant species of the 

 genus is Avena sativa, 

 the familiar culti- 

 vated oat. In many 

 of the varieties the 

 awn is straight, often 

 reduced, or even want- 

 ing. The spikelets 

 contain usually two 

 florets that do not 

 easily disarticulate. 

 The lemmas are 

 smooth or slightly 

 hairy at the base, the 

 apical teeth acute but 

 not awned. The grain 

 is permanently in- 

 closed in the lemma 

 and palea. Two other 

 introduced species are 

 known as wild oats, 

 because of their close 

 resemblance to the 

 cultivated oat. Avena 

 fatua L. (fig. 58) dif- 

 fers from A. sativa 

 in the readily disar- 

 ticulating florets, be- 

 set with stiff, usually 

 brown hairs, and in 



he well-developed 



. . J 



geniculate and twisted 

 awn. A variety of this (A. fatua glalrata Peterm.) has glabrous 



