314 ORDER 159. EQUISETACE^E. 



Species fruiting in spring and decaying before the following winter, (a) 



a Fertile steins never branching, the sterile with simple, whorled branches.... Nos. 1, 2 

 a Fertile stems at length, like the sterile, with compound, whorled branches No. 8 



Species fruiting in summer and lasting through the following winter. 



b Steins with whorls of simple branches from the middle joints No. 4 



b Stems mostly simple, large, 20 to 40-furrowed Nos. 5, 6, 7 



b Stems always simple, very slender, 3 to 9-furrowed Nos. 8, 9 



1 E. arv6nae L. FIELD HORSETAIL. Fertile sts. erect, simple ; sterile, 12 to 14- 

 furrowed, with simple, ascending, quadrangular branches, and decumbent at base. 

 Low grounds, Can. to Va. and Ky. Fertile stems first appearing, G 8' high, 

 with 3 5 joints surmounted by large, inflated sheaths cut into long, dark brown 

 teeth. Spike oblong, $ 2' long. Sterile stems rather taller than the fertile, 

 remaining through the season, after these have decayed. At each joint is a whorl 

 of simple, rough branches, issuing from the base of the sheaths, their joints also 

 sheathed. April. 



2 B. ebiirneum Schreb. IVORY HORSETAIL. Fertile, st. simple, its sheaths 

 numerous, of 3 Ivs. with subulate teeth ; sterile st. very smooth, ivory-white, about 

 30 -furrowed; branches simple, sheaths 4 or 6 -leaved, with erect, subulate teeth. 

 Shores of the Great Lakes. Barren stems 2 to 5f high. May. 



3 B. sylvciticum L. WOOD HORSETAIL. Sterile and fertile sts. 12 or 13-fur- 

 rowed, with compound, rough, deflexed, angular branches. Grows in woods and 

 low grounds, N. States and Brit. Am. Stems 16' high; the fertile with 4 5 

 whorls of branches from the base of the sheaths which are 2 3' apart, and cleft 

 into several large, tawny red teeth or segments; the sterile taller and more slen- 

 der, with more numerous whorls of branches. The branches are all subdivided 

 and curved downwards. Spike oval-cylindric, pedicellate. May. 



4 B. limdsum L. PIPES. Sts. somewhat branched, erect, striate-sulcato ; 

 branches from the middle joints, simple, short, 5-sided, smooth ; spike oblong- 

 ovoid; sheaths appressed. Borders of ponds and swamps, frequent. Stems 2 

 3f high, slander, rarely simple, generally with 2 6 whorls of branches about the 

 middle. Branches very irregular in length and position. Sheaths 3 4" long, 

 white at the summit, tipped with as many black, subulate teeth as there are fur- 

 rows (15 20). This species is greedily devoured by cattle. July. 



5 E. leevigattun Braun. Tall, erect, simple or somewhat branched; sheaths 

 elongated, appressed, green, with a black border, of about 22 Ivs., sheaths of the 

 branches about 8-leaved, with subulate, persistent points. Dry soils, Wis. and 

 South, along the Miss. River. Stems 18' to 2 or 3 Apparently distinct. 



6 E. robustum Braun. Very tall and stout, simple or somewhat branched 

 above ; sheaths short, appressed, with a black girdle above the base, rarely with a 

 black border, consisting o/40 (in the branches 11) leaves, the ovate-subulate points 

 deciduous, leaving an exact truncate margin. Banks of the "Western rivers, Terre 

 Haute, to St. Louis and South. Forms with fewer Ivs. in the sheaths seem to 

 connect this with the next. 



7 B. hymale L. SCOURING RUSH. Sts. all simple, erect, very rough, each 

 bearing a terminal, ovoid spike ; sheath cinerous white, Hack at the base and sum- 

 'tnit, short, with about 20 subulate, awned and deciduous teeth. Very noticeable 

 in wet, shady grounds, and by brooksides. Stems about 2f high, often 2 or more 

 united at base from the same root. Sheaths 2 3" long, 1 2 ' apart, the white 

 ring much broader than the black, at length entire from the falling off of the teeth. 

 The roughness of the cuticle is owing to the siles hi its composition. June. 



8 B. variegatum Schleicher. St. branching only at base, 6 to 12', simple, 

 straight and very slender, roughish, 5 to Q-furrowed; sheaths very short, brown, 

 teeth 5 to 9 ovate with broad, scarious margins and tipped with deciduous seta- 

 caous points. Banks of streams, N. Eng. to Wise, and Can., not common. Inter- 

 nodes about 1'. July. 



9 B. scOrpoides MX. Stems growing in tufts, thread-like, 4 to 8', flexuous and 

 recwrved, 3 or ^-furrowed ; sheaths black, 3 cr 4-tootbed, teeth short-ovate, sca- 

 rious, bristle- pointed. Hilly woods, Penn. to N. JEng., Wise, and Can. July. 



