38 Bulletin VII. 1. 



papillate-pilose. Spikelets obovate. Panicle nearly sim- 

 ple, few-flowered i8. P. scoparium. 



20. Culms branching only near the base; leaves erect, one to 

 two lines wide or less; panicle nearly simple, few-flow- 

 ered; spikelets ovate, acutish, smooth; fourth glume 

 rounded-obtuse, smooth . . . . 20. P. depauperatum. 



20. Culms branching throughout; leaves of the primary stem 



2-3 lines wide, erect or spreading, those of the wiry 

 branches involute filiform. Spikelets oblong elliptical, 

 finely pubescent; fourth glume barbulate at the apex . . 



19. P. ANGUSTIFOLIUM. 



2 1. Culms stout, 3-4 feet high, very densely and softly pubes- 

 cent throughout and viscid when fresh. Leaves of the 

 primary culm 5-10 inches long. Spikelets one line long, 

 rounded-obovate ]6. P. viscidum. 



21. Culms more slender, not viscid 22 



22. Ligule entirely wanting 23 



22. Ligule present 24 



23. Sheaths shorter than the internodes; leaves erect, 2-4 inches 



long, the uppermost 1-3 inches, firm in texture .... 



22. P. SPH.^ROCARPON. 



23. Sheaths longer than the internodes; leaves widely spread- 



ing, 4-10 inches long, the uppermost on the primary stem 

 usually 5 or 6 inches long and one-half to one inch wide 



23 P. MICROCARPON. 



24. Note. — Those who have attempted the study of the following species 



will understand and appreciate the difRciilty of preparing any key 

 which will be satisfactory, and I only now venture the following as 

 a possible aid to their determination : 



Spikelets more or less pubescent. Sheaths and leaves densely 

 pubescent. 



Leaves firm, nearly erect, spikelets i line long 



26. P. PUBESCENS. 



Leaves rather thin, more spreading, spikelets | line long . 



27. P. LANUGINOSUM. 



Sheaths pilose with long deflexed hairs. 24. P. laxiflorum. 



Sheaths and leaves ciliate on the margins. 25. P. ciliatum. 



Sheaths and leaves glabrous 29. P. nitidum. 



Spikelets smooth. 



Sheaths and leaves pilose . . 28. P. longepedunculatum. 

 Sheaths and leaves glabrous. 



Nodes smooth 30- P- dichotomum. 



Nodes bearded with reflexed hairs . 31. P. barbulatum. 



I. Panicum sanguinale Linn. Crab-grass. 



Plate VII. Figure 26. 

 A much-branched leafy annual, more or less decumbent at the 

 base, and often rooting at the lower joints. Culms smooth, one to 

 three or four feet long, ascending; nodes smooth or sometimes 

 bearded with deflexed hairs. Sheaths loose, smooth, or pilose- 

 hairy, usually ciliate on the margins; ligule membranaceous, about 



