676 EQUISETACE^. (hORSETAIL FAMILY.) 



1. EQXJISETUM, L. Horsetail. Scouring Rush. (Pi. 21.) 



Spore-cases (sporangia, thecal) 6 or 7, adhering to the uuder 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-shaped elastic filaments, Avhich roll up closely 

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

 wide-creeping, hard and blackish, jointed, often branched and sometimes bear- 

 ing small tubers. Stems erect, cylindi-ical, 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 furrows and a set of still smaller ones beneath the ridges ; the nodes closed 

 and solid, each bearing 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 the base of the sheath, like the stem, but without the central air- 

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

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

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



* Frtiiting in spring from soft and rather succulent pale or hrownish fertile stems, 



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

 •^Fertile stems unhranched, destitute of chlorophijll and soon perishing; the 

 sterile branching copiously. 

 1- E. arvense, L. (Commox H.) Fertile stems (4 -lO' high) with loose 

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

 1-2° high), 10 - 14-furrowed, producing long and simple or sparingly branched 

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

 gravelly soil ; very common. March -May. Rootstocks 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 producing herbaceous 3-sided branches, and lasting 

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



2. E. pratense, 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 

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



3. E. sylvaticum, L. Sterile and fertile stems (about 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 sometimes nearly naked. 



4. E. pallistre, L. Stems (10-18' high) slender, very deeply 5-9- 

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



