EQUISETACE^E. (HORSETAIL FAMILY.) 677 



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

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

 June. (Eu.) 



5. E. littorale, Kiihlewein. Stems (8 -18' high) slender, deeply 6 -16- 

 grooved, the ridges rounded, the teeth shorter than in the last, narrowly white- 

 margined ; branches often solid, 3 - 4-angled, 2-6 in a whorl. Wet sandy 



t 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. limdsum, L. (PI. 21, fig. 1 - 5.) Stems (2 - 5 high) slightly many- 

 furrowed, 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 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. 

 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 (11-4 or even 6 high), simple, or casually branched, 



evenly many-grooved ; sheaths appressed. 



7. E. hyemale, L. (SCOURING-RUSH. SHAVE-GRASS.) Stems 1^-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, the teeth blackish, membranaceous, 

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

 use for polishing wood and metal. (Eu.) 



8. E. robtistum, 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. laevigatum, Braun. Stems 1-4 high, rather slender, pale green, 

 14-30-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 

 to Minn., and westward. 



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



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

 simple from a branched base, 5-W-grooved ; 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 northward ; 

 rare. (Eu.) 



11 . E. SCirpoid.es, Michx. Stems very numerous in a tuft, filiform (3 - 6' 

 high), flexuous and curving, mostly ^-grooved, with acute ridges ; sheaths 3- 

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

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



