EQUISETACE^. (lIORSETAlL FAMILY.) 677 



whitish-margined; branches always hollow, 4-7-angled, rather few m a 

 whorl.— Wet places, Niagara River {Clinton), Wise. {Austin), and northward. 

 June, (Eu.) 



5. E. littorale, Klihlewein. Stems (8-18' high) slender, deeplv - IG- 

 grooved, the ruhjrs rounded, the teeth shorter than in the last, narrowlv wliite- 

 margiued; branches often solid, 3 - 4-augled, 2 - 6 in a whorl. —Wet sand v 

 shores, Vt. and N. Y., and northward. — Spores always abortive, whence the 

 plant has been considered a hybrid, perhaps of E. arvense and E. limosum 

 July. (Eu.) 



6. E. limosum, L. (PI. 21, fig. l -5.) ^tem^ [2 -b°\v\gh) slightly many- 

 furroiced, smooth, sometimes continuing unbranched, but usually producing 

 ascending branches after fructification; sheaths appressed, with 10-22 (com- 

 monly about 18) dark-brown and acute rigid sliort teeth. — In shallow water; 

 rather common. — Air-cavities none under the grooves, but small ones under 

 #he ridges. A form in which the branches bear numerous small spikes is var. 

 polystAchyum, Bruckner. June, July. (Eu.) 



§ 2. Stems all alike, evergreen, unbranched, or producing a few slender erect 

 branches ; fruiting in summer. Central air-cavity of the stem very large. 

 Stems tall and stout (1^-4° or even 6° high), simple, or casually branched, 

 evenly many-grooved ; sheaths appressed. 



7. E. hyemale, L. (Scourixg-Rush. Shave-Grass.) Stems H-4° 

 nigh, 8-34 grooved, the ridges roughened by two more or less distinct lines of 

 tubercles ; sheaths elongated, with a black girdle above the base and a black limb ; 

 ridges of the sheaths obscurely 4-carinate, the teeth blackish, membranaceous, 

 soon falling off. — Wet banks; comm.cn northward. Formerly in common 

 use for polishing wood and metal. (Eu.) 



8. E. robustum, Braun Stems tall and stout (sometimes 8-10° high 

 and nearly an inch thick), 20-48-grooved, the ridges roughened with one line 

 of transversely oblong tubercles ; sheaths rather short, with a black girdle at base 

 and a black limb; ridges of the sheaths tricarinate, the blackish teeth soon 

 falling off. — River-banks, Ohio and westward. 



9. E. Isevigatum, Braun . Stems 1 - 4° high, rather slender, pale green, 

 I4-30-grooved, the ridges almost smooth; sheath slightly enlarged upward, 

 with a black girdle at the base of the mostly deciduous white-margined teeth, 

 and rarely also at the base of the sheath ; ridges of the sheath with Oi^e keel, 

 or sometimes obscurely tricarinate. — By streams and in clayey places, Ohio 

 CO Minn., and westward. 



* * Stems slender, in tiifts, 5-10-grooved; sheaths looser. 



10. E. variegatum, Schleicher. Stems ascending (6-18' long), usually 

 simple from a branched base, 5-lO-groored : sheaths green variegated with 

 black above, the 5-10 teeth tipped with a deciduous bristle. — Shores or river- 

 banks, N. H. (Bellows Falls, Carey) and Niagara to Minn, and nortliward; 

 rare. (Eu.) 



11. E. SCirpoideS, Michx. Stems very numerous in a tufi, filiform (3 - 6' 

 high), fexuous and curving, mostly 6-grooved, with acute ridges ; sheaths 3- 

 toothed, the bristle-pointed teeth more persistent ; central air-cavity wanting 

 — Wooded hillsides, X. Eng. to Penn., Minn., and northward. (Eu.) 



