86 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



40. PHRAGMITES Trin. 



1. Phragmites communis Trin. Heed. 



Marshes; Eastern Branch below the steel plant. Aug. -Sept. Cosmopolitan. (P. 

 phragmites Karst.) 



41. TRIDENS Koem. & Schult. 



1. Tridens flavus (L.) Ilitchc. Purple top. 



Opon woods and dry open grounds; common. Aug. -Sept. Eastern U.S. (Tricuspis 

 seslcrioides Torr.) 



The upper part of the culm and the branches of the panicle become sticky at matu- 

 rity and retain dust and small particles. 



42. ERAGROSTIS Beauv. 



Plants perennial; panicle diffuse, usually purple 1. E. pectinacea. 



Plants annual; panicle opon or contracted but not diffuse (except in E. capillaris). 



Culms creeping; plants dioecious or polygamous 2, E. hypnoides. 



Culms erect or spreading, not creeping; flowers perfect. 

 Spikelets 2- 5-flowered . 

 Plants erect, branched from the base; panicle diffuse, open, pale or green; 



pedicels mostly over 5 mm. long 3. E. capillaris. 



Plants decumbent or spreading, branched above the base; panicle oblong, the 

 branchlets ratber crowded, usually purple; pedicels usually less than 5 mm. 



long 4. E. frankil. 



Spikelets 5-many-flowered. 



Lemmas glandular on the keel; spikelets about 3 mm. wide; panicle somewhat 



contracted 5. E . cilianensis. 



Lemmas not glandular on the keel; spikelets less than 3 mm. wide; panicle more 

 open. 

 Spikelets about 1 mm, wide; panicle branches pilose in the axils. 



6. E. pilosa. 

 Spikelets 1,5-2 mm. wide; panicle branches usually not pilose in the axils. 

 Plant not glandular; spikelets about 1.5 mm. wide, the pedicels appreseed 



along the main branches of the open panicles 7. E. caroliniana. 



Plant glandular on the margins of the blades and sometimes on other por- 

 tions; spikelets about 2 mm. wide, on spreading pedicels; panicle 

 rather compact 8. E. minor. 



1. Eragrostis pectinacea (Michx.) Nees. 



Sandy fields; frequent. Late summer. Eastern U. S. 

 At maturity the panicle breaks away as a tumblcweed. 



2. Eragrostis hypnoides (Lam.) B. S. P. 



Sandy banks of streams, especially parts exposed at low water; frequent along the 

 Potomac and other larger streams. Aug.-Sept. Eastern U. S. (E. reptans Nees.) 



3. Eragrostis capillaris (L.) Nees. 



Open woods; infrequent. Aug.-Sept. Eastern U. S. 

 The plant has a pleasant lemon scent. 



4. Eragrostis frankii (Fisch. Mey. & Lall.) Steud. 



Moist open soil; infrequent; Glen Echo; Cabin John. Eastern U. S. 



5. Eragrostis cilianensis (All.) Link. Stink grass. 

 A common weed in open ground and waste places. Common through the warmer 



parts of the U. S.; naturalized from Eur. (E. major Host; E. megastachya Link; E. 

 poaeoides megastachya A. Gray; E. poaeoides of Ward's Flora.) 



The plants when fresh exude a disagreeable odor, this probably originating in the 

 glands along the keels of the lemmas. 



