EQ,UISETACE,E. 455 



Moist grounds. Arct. Amer. to Virg. W. to the N. W. Coast. April, May. 

 1J-. Sterile starts 10 15 inches high, with whorls of ascending branches, which 

 are either simple or somewhat divided. Fertile stems 6 8 inches high, with 

 brownish or purple sheaths. Spikes oblong, obtuse ; the scales at first approxi- 

 mated, at length more open. Field Horse-tail. 



** Fertile stems at length branched, bearing the fructification at the same lime 

 with the branches. 



2. E. sylvaticum Linn. : sterile and fertile stems both branched, about 

 12 furrowed; branches compound, curved downwards; sheaths loose, 

 deeply cleft into several broad-lanceolate membranous teeth. 



Moist grounds. Arct. Amer. to Virg. and Ohio. June, July. 7j . Stems 12 18 

 inches high ; the sterile ones usually taller and more slender. Sheaths divided 

 into 8 17 teeth or leaves, whose points are connected in 2 4 or more lobes. 

 Spike oblong. Wood Horse-tail. 



3. E. palustre Linn. : stem deeply grooved, roughish, 7 8-angled ; 

 branches whorled, simple, gradually shorter upwards; sheaths distant, cut 

 at the apex into 6 10 fuscous teeth. 



Swamps. Arct. Amer. to Virg. June. Ij.. Stetns 12 18 inches high, gen- 

 erally with simple erect whorled branches. Sheaths mostly with 7 9 teeth. 

 Spike an inch long, slender and blackish. A variable species. 



Marsh Horse-tail. 



4. E. limosum Linn. : stem smooth, with 16 21 striae, sometimes simple; 

 branches nearly erect, simple, short ; teeth of the sheaths short, rigid, dis- 

 tinct. 



Borders of swamps and ponds. Can. to Virg. W. to Wise. June, July. 1\.. 

 Stems 2 3 feet high, erect, simple, or with a few whorls of branches at the top. 

 Sheaths numerous, appressed, usually with 17 20 brownish or blackish teeth. 

 Spike oblong, scarcely an inch in length. Easily distinguished from the preceding 

 by the structure of its stem and by its teeth. Smooth Swamp Horse-tail. 



*** Stems simple or branclied only at base. 



5. E. hyemak Linn. : stems numerous, simple, naked, erect, very rough ; 

 sheaths short, blackish at the base and apex, with about 14 20 very small 

 obtuse finally deciduous teeth. 



Wet woods and marshes. Can. to Penn. W. to Miss, and Ken. June, July. 

 Ij.. Stems 1 2 feet high, naked, furrowed, pale and somewhat glaucous green. 

 Sheaths 2 4 lines long, the teeth deciduous. Spike ovoid, blackish. The cuti- 

 cle abounds in silica, and the stems are well suited for the polishing of hard 

 woods and the metals. Scouring Rush. Shave-grass. 



6. E. variegatum Schleich. : stems several, usually decumbent or assurgent. 

 simple or only branched at the base, rough, filiform, with 4 8 striae; 

 sheaths with membranaceous lanceolate teeth, blackish at the base. 



Wet sandy places. Arct. Amer. to N. Y. July. 1J.. Stems 612 inches 

 long, several from the same root. Sheaf hs blackish, consisting of about seven 

 4-keeled persistent teeth. Spike ovoid, blackish, smaller than in the preceding. 



Variegated Rough Horse-tail. 



7. E. scirpoides Mich. : stems cespitose, much branched from the root, 

 ascending, naked, filiform, rough ; sheaths blackish, with a few awned 

 teeth. E. variegatum Torr. Comp. E. variegatum var. minus Hook. 



Wet rocky places. Arct. Amer. to N. Y. and N. Eng. 1J-. Stems in dense 

 tufts, 4 8 inches long, very slender. 5 6-angled. Sheaths minute, blackish, 



