EQUISETACEJE. (HORSETAIL FAMILY.) 619 
rigid, the hard cuticle abounding in grains of silex, hollow, and 
also with an outer circle of smaller air-cavities corresponding with 
the grooves ; the joints closed and solid, each bearing instead of 
leaves a sheath, which surrounds the base of the internode above, 
and is split into teeth corresponding in number and position with 
the principal ridges of the stem : the stomata always occupying 
the principal grooves. Branches, when present, in whorls from 
the base of the sheath, like the stem, but without the central air- 
cavity. (The ancient name, from equus , horse, and seta , bristle.) 
* Stems annual {not surviving the icinter). {Stomata irregularly scat¬ 
ter overed the whole surface of the grooves.) 
Fertile stems different from the sterile ones , earlier , brownish. 
++ Fertile stems never branching , decaying early after fructification : 
the sterile stems hearing simple branches. 
1. E. arvense, L. Sterile stems smoothish, 12- 14furrowed, 
producing ascending sharply 4- (3-5-) angled long branches , with 4 
herbaceous lanceolate pointed teeth; sheaths of the fertile stems {&- 
Xo 1 high) remote , large and loose. — Damp places, common. April. 
2. E. cbtirnemn, Schreber. Sterile stems very smooth, 
ivory-white, about 30 -furrowed, the rough usually 4-angled branches 
again grooved on the angles , and with awl-shaped fragile teeth; sheaths 
of the fertile stems crowded , deeply toothed. (E. fluviatile, Smith.) — 
Shore of the Great Lakes, and northward. April, May. — Fertile 
stems 1° or more high, stout; the sterile, 2P-5P. 
++ ++ Fertile stems producing herbaceous branches after fructification. 
3. E. sylvaticum, L. Sterile and fertile stems about 12-fur- 
rowed, bearing numerous whorls of compound racemed branches; 
sheaths loose, with 8-14 rather blunt membranous teeth which are 
more or less united; those of th^branches bearing 4 or 5, of the 
branchlets 3, lance-pointed divergent teeth.— Wet shady places, 
common northward. May. 
- - Fertile and sterile stems similar and contemporaneous , both herba¬ 
ceous , or all the stems fertile , fruiting in summer , producing mostly 
simple branches from the upper or middle joints , sometimes quite 
naked. 
4. E. lilBlosimi, L. Stems tall (2>-3» high), smoothi, slightly 
14 - 16-furrowed, usually producing upright simple branches after 
fructification ; sheaths appressed, rather short, with dark-brown and 
acute rigid short teeth. (E. uliginbsum, Muhl.) In shallow water, 
&c. - Air-cavities none under the grooves, but small ones under the 
ridges. —Near this is the European E. palustre, with a strongly 
grooved roughish stem, large air-cavities under the grooves, an pa e 
sheaths, also attributed to this country, probably incorrectly, by Fursh. 
