EQ VISE TA CEM. 1 29 



in a single series. Southern California in open canons {Mc- 

 Clatchie). 



tt Branches rare except when the main stem is broken. 

 \ Stems rough, tiiberculate. 



10. E. robustum A. Br. Stems 3° — 11° high, sometimes 

 nearly 1' thick, 20 — 48 furrowed ; ridges roughened with a 

 single series of tubercles ; sheaths short, marked with black 

 girdles at base and at base of the caducous teeth ; ridges of 

 sheaths tricarinate. Ohio to California and northward. 



11. E. hiemale L. (ScouRlNG-RUSH.) Stems i°— 4° high, 

 8 — 34 furrowed ; ridges rough, with two indistinct lines of tu- 

 bercles ; sheaths rather long, marked with one or two black 

 girdles; ridges of the sheath obscurely quadricarinate. North 

 America generally. 



\\ Stems smoothish, scarcely tuberculate. 



12. E. laevig-atum A. Br. Stems i" — 5° high, pale green, 

 14 — 30 furrowed ; ridges almost smooth ; sheaths elongate, en- 

 larged upward, marked with a black girdle at the base of the 

 mostly deciduous white-margined teeth, rarely with a second ; 

 ridges of sheath with central keel and rarely faint lateral ones. 

 North Carolina to California and Oregon. 



** Stems slender, tufted, 5 — 10 grooved. 



13. E. variegatum Schleich. Stems ascending, 6' — 18' 

 long, usually simple from a branched base, 5—10 furrowed ; 

 sheaths green, variegated with black above, the teeth 5 — 10, 

 tipped with a deciduous bristle ; central air-cavity small. Bel- 

 lows Falls, New Hampshire {Carey), Niagara Falls to Illinois 

 and northward to Greenland and Alaska. 



14. E. scirpoides Michx. Stems filiform, very numerous, 

 3'_6' high, flexuous and curving, mostly 6-furrowed, with acute 

 ridges; sheaths 3-toothed, the bristle tips more persistent ; cen- 

 tral" air-cavity wanting. New England to Pennsylvania, Illinois 

 and northward. 



