The only genns of the Order is
Fig. 272 is a view of the fertile stem of Equisetum arvense, the Common Horsetail, of about the natural size. It may be observed early in spring almost anywhere in moist sandy or gravelly soil. It is of a pale brown colour, and in place of leaves there is at each joint a sheath split into several teeth. At the summit of the stem is a sort of conical catkin, made up of a large number of six-sided bodies, each attached to the stem by a short pedicel. Each of these six-sided bodies turns out on examination to be made up of six or seven sporangia or spore-cases, which open down their inner margins to discharge their spores. Figs. 273 and 274 are enlarged outer and inner views of one of them. The spores themselves are of a similar nature to those of the Ferns, and reproduction is carried on in the same manner; but each spore of the Horsetail is furnished, with four minute tentacles which closely envelope it when moist, and uncoil themselves when dry. The use of these tentacles is doubtless to assist in the escape and dispersion of the spores.
The fertile stems will have almost withered away by the time the sterile ones appear. The latter are of the same thickness as the fertile ones, but they are very much taller and are green in colour. Observe, also, the grooving of the sterile stem, and the whorls of 4-angled branches produced at the nodes.
* Annual-stemmed, not surviving the winter.
+ Fruiting in spring, the fertile stems pale or brownish, and earlier than the herbaceous sterile stems or branches.
1. E. arven'se, L. (Common Horsetail.) Fertile stems not branching, 4-10 inches high. Sterile stems slender, taller, with many 4-angular green branches. - Moist sandy or gravelly soil, common.
2. E. praten'se, Ehrh. Stems more slender, with 3-sided simple branches shorter than in E. arvense. Stem-sheaths with short, ovate-lanceolate teeth (those of the branches 3-toothed.) The fertile stems produce branches, when older, except at the top, which perishes after fructification. - Low meadows, Atl. Prov. and northward.
3. E. sylvat'icum, L. Fertile stems branching. Branches compound, with loose sheaths, those of the stem having 8-14 somewhat blunt teeth, while those of the branches have 4-5 (of the branchlets 3) lance-pointed diverging teeth. Top withering away after fructification. - Damp shady places, Atl. Prov. and northward. .
+ + Fruiting in summer. Stems all similar, or the fertile contemporaneous with the sterile ones.
4. E. palus'tre, L. Stems 10-18 inches high, slender, very deeply 5-9-grooved, the lance-awl-shaped teeth whitish-margined. - Atl. Prov. and northward.
5. E. limo'sum, L. Stem 2-5 feet high, slightly many-furrouxd. Sheaths appressed. with 10-22 dark-brown acute snort rigid teeth. - In shallow water
* * Stems evergreen, all similar, not branching, or only slightly so.
6. E. hyema'le, L. (Scouring Rush.) Stems stout and tall. Sheaths elongated, with a black girdle above the base, and about 20 narrow linear teeth, 1-keeled at the base, and with awl-shaped deciduous points. - "Wet banks.
7. E. laevigatum, Braun. Stems 1-4 feet 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 white-margined teeth. - N.W.
8. E. variegatum, Schleicher. Stem slender, in tufts, with 5-10 grooves, ascending, 6-18 inches high. Sheaths green, variegated with black above, 5-10 toothed. - Shores and river-banks.
9 E. scirpoi'des, Michx. Stem slender, very numerous in a tuft, filiform, 3-6 inches high, curving, mostly 6-grooved. Sheaths 3-toothed. - Wooded hill-sides.