28 FLOEA OF PHILADELPHIA. 



Tribe IV. ORYZEAE. 

 Spikelets monoecious. 14. Zizania. 



Spikelets not monoecious. 15. Homalocenchrus. 



Tribe V. PHALARIDEAE. 



Third and fourth scales 



not awned; stamens 3. 16. Phalaris. 



awned upon the back; stamens 2. 17. Anthoxanthum. 



subtending staminate flowers with 3 stamens; fertile flowers with 2 

 stamens. 18. Savastana. 



Tribe VI. AGEOSTIDEAE. 



Flowering scale indurated at maturity, of firmer texture than the empty, and 

 closely enveloping the grain. 

 RachiUa not prolonged beyond the palet. 



Flowering scale with a three-branched awn; stamens mostly 3. 



19. Aristida. 

 Flowering scale with a simple awn. 



Flowering scale narrow; awn persistent. 



Awn tortuous or twisted, stout; callus evident. 



20. Stipa. 

 Awn straight, very slender; callus minute. 



22. Muhlenhergia. 

 Flowering scale broad; awn slender, straight, deciduous; cal- 

 lus obtuse. 21. Oryzopsis. 



Eachilla with a pedicel-like extension beyond the palet; stamens 2. 



23. Brachyelytrum. 

 Flowering scales hyaline or membranous at maturity; empty scales coarser; 



grain loose. 

 Spikelets in a dense spike-like panicle. (Some species of 27 may be 

 looked for here.) 

 Spikelets 6 mm. or less long. 



Spikelets readily deciduous at maturity. 



Empty scales not awned. 26. Alopecurus. 



Emj)ty scales awned. 28. Polypogoit. 



Spikelets not deciduous; empty scales persistent. 



Flowering scales slightly exceeding the empty ones. 



24. Heleochloa. 

 Flowering scales much shorter than the empty ones. 



25. Phleum. 

 Spikelets 10-12 mm. long; taU seashore grasses. 



32. AmmopMla. 

 Spikelets variously panicled; panicle not spike-like, except in a few 



species of No. 27. 

 Seed loosely enclosed in a pericarp, which opens readily at matur- 

 ity. 27. Sporobolus. 

 Seed adherent to the pericarp. 



Palet one-nerved; stamen 1; flower plainly stalked; scales not 



hairy. 29. Cinna. 



Palet 2-nerved; stamens 3; flower not plainly stalked. 



Flowering scale bifid, with a delicate awn on its back; 

 rachilla prolonged into a short bristle. 



34. Apera. 

 Flowering scale entire ; rachilla not prolonged into a bristle. 

 Callus with a tuft of long hairs at the base (except in 

 some species of No. 31). 

 Rachilla extended beyond the palet. 



31. Calamagrostis. 

 Rachilla not extended beyond the palet. 



33. Calamovilfa. 

 Callus naked or with very short hairs. 



30. Aarostis. 



