g!4 ORDER 159. EQUISETACEJB. 



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



a Fertile stems never brandling, the sterilo with simple, whorled branches.... Nos. 1, 2 

 a Fertile stems at length, like the sterile, with compound, whorled branches No. 3 



5 Species fruiting in summer and lasting through the following winter. 



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



1 E. arvense 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, 

 w it,h 3 5 joints surmounted by large, inflated sheaths cut into long, dark brown 

 teeth. Spiko oblong, \ 2' long. Sterilo stems rather taller than the fertile, 

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

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

 sheathed. April. 



2 E. eburneum Schreb. IVORY HORSETAIL. Fertile, st. simple, its sheaths 

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

 3Q-furrowed; branches simple, sheaths 4 or 5-leaved, with erect, subulate teeth. 

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



3 E. sylvaticum 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 9 1G' high; the fertile with 4 5 

 whorls of branches from tho 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 moro numerous whorls of branches. The branches are all subdivided 

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



4 E. limosuni L. PIPES. Sts. somewhat branched, erect, striate-sulcato ; 

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

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

 3f high, sbnder, rarely simple, generally with 2 G 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 arc fur- 

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



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

 elongated, appressed, green, with a Hack border, of about 22 Ivs., sheaths of tho 

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

 South, along tho Miss. River. Stems 18' to 2 or 3f. 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 cf the Western rivers, Terro 

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

 connect this with tho next 



7 E. hyeinalo L. SCOURING RUSH. Sts. all simple, erect, very rough, each 

 bearing a terminal, ovoid spike ; sheath cinereous white, black at the base and sum- 

 mit, short, with about 20 subulate, awned and deciduous teeth. Very noticeablo 

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

 united at base from the same root. Sheaths 2 3" long, 1 2 % apart, tho whito 

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

 The roughness of tho cuticle is owing to the silex in its composition. June. 



8 E. variegattim Schleicher. St. branching only at base, G to 12', simple, 

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

 teeth 5 to 9 ovate with broad, scnrious margins and lipped with deciduous seta- 

 ceous points. Banks of streams, N. EC;;, to Wise, and Can., not common. Inter- 

 nodes about 1'. July. 



9 E. scorpoides MX. Steins growing in tufts, thread-like, 4 to 8', flexuous and 

 recurved, 3 or 4-furrowed ; sheaths black, 3 cr 4-tootbed, teeth Ehort-ovate, sca- 

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



