Plants leafless, simple stems, or with whorled branches. Stems striate-sulcate, jointed, fistular between, and separable at, the joints. Sheaths dentate, crowning each internode. Fructification a dense, oblong-cylindric, terminal and cone-like spike, composed of 6-sided, peltate-scales arranged spirally, bearing beneath 4 to 7 spore-cases which open laterally. Spores globular, each with 4 elaters attached, involving them spirally, or open when discharged. (Sec Figures.)

An Order consisting at present of a single, genus, growing in wet grounds, on river banks, and borders of woods, throughout most countries. The Equisetaceae abound in the fossil remains of coal measures with other Cryptogamia, as Lycopodiaceae and Filices, indicating that these plants were once of gigantic dimensions, and formed a large part of the original flora of our globe. Species about 10.

Properties. - They abound in silex, and hence are used by cabinet-makers, comb-makers, etc, in polishing their work.

EQUISE'TUM, L. Scouring Rush. (Lat. equus, a horse, seta, hair.) Character the same as that of the order. - The sheaths may be regarded as a whorl of united leaves. The ridges of the stem are air-tubes, and the grooves alone are pierced with the sto-mata.

734, Equisetam arvense. 185, E, sylvaticum

734, Equisetam arvense. 185, E, sylvaticum. 785, Section of the spike, enlarged. 737, A peltate scale with 7 sporanses beneath (or one compound spo-range), magnified. 738, A spore with its elators, highly magnified.

§ 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 steins at length, like the sterile, with compound, whorled branches..................

No. 3

§ 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 Stems always simple, very slender, 3 to 9-furrowed...............................................

Nos. 8, 9

1 E. arvense L. Field Hohsetail. 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, 6 - 8' high, with 3 - 5 joints surmounted by large, inflated sheaths cut into long, dark brown teeth. Spike oblong, 1/2 - 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 E. eburneum Schreb. Ivory Horsetail. Fertile, st. simple, its sheath3 numerous, of 3 lvs. with subulate teeth; sterile st. very smooth, ivory-white, about 30-furrowed; branches simple, sheaths 4 or 5-leaved, with erect, subulate teeth. - Shores of the 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, defloxed, angular branches. - Grows in woods and low grounds, N. States and Brit. Am. Stems 9 - 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 slender, with more numerous whorls of branches. The branches are all subdivided and curved downwards. Spike oval-cylindric, pedicellate. May.

4 E. limosum L. Pipes. Sts. somewhat branched, erect, striate-sulcate; 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, slender, 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 arc furrows (15 - 20). This species is greedily devoured by cattle. July.

5 E. laevigatum Braun. Tall, erect, simple or somewhat branched; sheaths elongated, appressed, green, with a black border, of about 22 lvs., 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 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 of 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 lvs. in the sheaths seem to connect this with the next.

7 E. hyemale 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 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 - 21/2' 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 silex in its composition. June.

8 E. variegatum Schleicher. St. branching only at base, 6 to 12', simple, straight and very slender, roughish, 5 to 9-furrowed; sheaths very short, brown, teeth 5 to 9 ovate with broad, scarious margins and tipped with deciduous setaceous points. - Banks of streams, N. Eng. to Wise, and Can., not common. Inter-nodes about 1'. July.

9 E. scorpoides Mx. Stems growing in tufts, thread-like, 4 to 8', fiexuous and recurved, 3 or 4-furrowed; sheaths black, 3 or 4-tootbed, teeth short-ovate, scarious, bristle-pointed. - Hilly woods, Penn. to N. Eng., Wise, and Can. July.