676 EQUISETACEvE. (HORSETAIL FAMILY.) 



1. EQUISETUM, L. Horsetail. Scouring Rush. (H. 21.) 

 Spore-cases [sporangia, thecce) 6 or 7, adhering to the under side of the an- 

 gled shield-shaped scales of the spike, 1 -celled, opening down the inner side 

 and discharging the numerous loose spores. To the base of each spore are 

 attached 4 thread-like and club-sliaped elastic filaments, which roll up closely 

 around the spore when moist, and uncoil when dry. — Eootstocks perennial, 

 wide-creeping, hard and blackish, joint sd, often branched and sometimes bear- 

 ing small tubers. Stems erect, cylindiical, hollow, jointed ; the surface striated 

 or grooved with alternate ridges and furrows, the cuticle in most species con- 

 taining silica in the form of minute granules, rosettes, or tubercles ; the joints 

 containing besides the central air-cavity a circle of smaller hollows beneath 

 the furroAvs and a set of still smaller ones beneath the ridges ; the nodes closed 

 and solid, each liearins: instead of leaves a sheath which is divided into teeth 

 corresponding in number and position to the principal ridges of the stem; 

 stomata in the furrows, each with two pairs of guard-cells, of which the outer 

 pair is marked with radiating lines of silica. Branches, when present, in 

 whorls from (he base of the sheath, like the stem, but without the central air- 

 cavity. Prolhallus green, formed upon the ground, often variously lobed, 

 usually dioecious. (The ancient name, from eguus, horse, and seta, bristle.) 

 § 1. Annual-stemmed, not surviving the winter. 



* Fruiting in spring from soft and rather succulent pale or hroicnish fertile stems, 



the sterile stems or branches appearing later, herbaceous and very different. 

 -*- Fertile sterns unbranched, destitute of chlorophyll and soon perishing; the 



sterile branrhing copiously. 

 1- E. arvense, L. (Common H.) Fertile stems (4-10' high) with loos* 

 and usually distant about 8- 12-toothed sheaths; the sterile slender (at lengfn 

 1-2° high), 10 - l4-furrowed, producing long and simple or sparingly branched 

 4-angular branches, their teeth 4, herbaceous, lanceolate. — Moist, especially 

 gravelly soil; very common. March -May. Eootstocks often bearing little 

 tubers. — Var. campestre, Milde, is a not uncommon state, in which the ster- 

 ile stem bears a small fruiting spike at the summit. (Eu.) 



•«- H- Fertile stems when older lyroducing herbaceous Z-sided branches, and lasting 

 through the summer, except the naked top which perishes afier fructification. 



2. E. prat6nse, Ehrh. Sterile and finally also the fertile stems producing 

 simple straight branches; sheaths of the stem with ovate-lanceolate short teeth, 

 those of the branches 3-toothed ; stems more slender and the branches shorter 

 Shan in the last. — Mich, to Minn., and northward. April, May. (Eu.) 



3. E. sylvaticum, L. Sterile and fertile stems (al)out 12-furrowed) pro- 

 ducing compound racemed branches; sheaths loose, with 8-14 rather blunt 

 teeth, those of the branches bearing 4 or 5, of the branchlets 3, lance-pointed 

 divergent teeth. — Wet shady places ; common northward. May. (Eu.) 



* * Fruiting in summer ; stems all of one kind, or the fertile contemporaneous 



with and like the sterile, equally herbaceous, producing mostly simple branches, 

 or sorrietimes nearly naked. 



4. E. pallistre, L. Stems (lO-lS' high) slender, very deeply 5-9- 

 grooved, the ridges narrow and acute, roughish, the lance-awl-shaped teetl» 



