EQUISETACE^. (lIORSETAIL FAMILY.) 677 



whitisli-niargined ; branches always liollow, 4-7-an^lc(l, rather few in a 

 whorl. — Wet places, ISiagara Kiver {Clintuti), Wise. (Austin), aiid northward. 

 June. (Kn.) 



5. E. littorkle, KUhlewein. Stems (H -18' high) slender, deeply 6 -16- 

 grooved, (/t«' ridyes rounded, the teeth shorter than in the last, narrowly white- 

 margined; branches often solid, 3-4-angled, 2-G in a whorl. —Wet sandy- 

 shores, Vt. and N. Y., and northward. — Spores always aI)ortivc, whence the 

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

 July. (Eu.) 



6- E. limbsum, L. (PI. 21, fig. 1 -5.) Stems (2-5° high) slightly mnny- 

 furr owed, smooth, sometimes continuing unbranched, l)ut usually producing 

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

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

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

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

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

 § 2. Stems all alike, evergreen, unbranched, or producing a few dander 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. hyem^le, L. (Scourixg-Rush. Shave-Grass.) Stems H-4° 

 high, 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, tlie teeth blackish, membranaceous, 

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

 use for polishing wood and metal. (Eu.) 



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

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

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

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

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



9. E. Isevig^tum, Braun. Stems 1 - 4° high, ratlier slouder, pale green, 

 14-30-groovod, the ridges almost smooth ; sheath slightly enlaj-ged upward, 

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

 and rarely also at the base of the siieatli ; ridges of tlie shcatii with one keel, 

 or sometimes obscurely tricarinate. — By streams and in clayey ^jlacjcs. Ohio 

 to Minn., and westward. 



* * Stems slender, iji tufts, !j-l0-grooved; sheaths looser. 



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

 simple from a branched base, 5-1 0-vroorer/; sheaths greicn variegated with 

 black ahove, the 5 - 10 teeth tij)ped with a deciduous bristk>. — Shorep or river- 

 banks, N. II. (Bellows Falls, Carey) and Niagara to Minn , and northward ; 

 rare. (Eu.) 



11. E. SCirpoides, Michx. Stems I'ery numerous in a tuf, filiform (3- 6' 

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

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

 — Wooded hillsides, N. Eng. to Penn., Minn., and norUiward. (Ko.) 



