586 EQUISETACE.E. (HORSETAIL FAMILY.) 



* Stems annual (not surviving the winter) : fructification in spring (April and May). 

 (Stomata irregularly scattered over the whole surface of tlie grooves.) 



*- Fertile stems different from the sterile ones, earlier, brownish. 



*+ Fertile stems never branching, decaying early after fructification : the sterile stems 



bearing simple branches. 



1. E. arvense, L. Sterile stems smoothish, 12- I ^-furrowed, and produc- 

 ing ascending sharply 4- (or 3 - 5-) ungled long branches, with 4 herbaceous lanceolate 

 pointed teeth; sheaths of the fertile stems (8' -15' high) remote, large and loose. 

 Damp places ; common. (Eu.) 



2. E. eburneum, 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 tie Great Lakes, and northward. 

 Fertile stems 1 or more high, stout; the sterile 2 -5. (Eu.) 



** *-* Fertile stems remaining and producing herbaceous branches after fructification. 



3. E. pratense, Ehrh. Sterile and finally also the fertile stems bearing 

 whorls of simple straight branches ; sheaths of the stem split into separate ovate- 

 lanceolate short teeth, those of the branches 3-toothed : otherwise much like the 

 next; in its simple branches resembling No. 1, but narrower in general outline, 

 and blunt. (E. umbrosum, Willd. E. Drummondii, Hook.) Michigan ( Cooley, 

 Sfc.) and northward. (Eu.) 



4. E. sylvsiticuiii, L. Sterile and fertile stems about 12-furrowed, 

 bearing whorls of compound racemed branches ; sheaths loose, with 8-14 rather 

 blunt membranous more or less united teeth ; those of the branches bearing 4 or 5, 

 of the branchlets 3, lance-pointed divergent teeth. Wet shady places ; common 

 northward. (Eu.) 



i- - Fertile and sterile stems similar and contemporaneous, both herbaceous, or all the 

 stems fertile, fruiting in summer, producing mostly simple branches from the upper 

 or middle joints, or sometimes quite naked. 



5. E. limdsuin, L. Stems tall (2 -3 high), smooth, slightly many- 

 furrowed, usually producing upright simple branches after fructification ; sheaths 

 appressed, with 10-22 (commonly about 18) dark-brown and acute rigid short 

 teeth. (E. uliginosum, Muhl.) In shallow water; rather common. Air- 

 cavities none under the grooves, but small ones under the ridges. (Near this is 

 the European E. PALtJSTRE, with a strongly grooved roughish stem, large air- 

 cavities under the grooves, and pale 6 - 9-toothed sheaths ; also attributed to 

 tliis country by Pursh, probably incorrectly.) (Eu.) 



* * Stems perennial, bearing fructification in summer, lasting over the next winter 

 and longer, mostly rough (the cuticle abounding in silex), simple or rarely branched. 

 (Stomata in regular rows, in our species l-rowed on each side of the groove.) 

 Stems large, mostly single : sheaths appressed. (Probably all forms of No. 8.) 



6. E. Irevigiitum, Braun. Stems l-4 high; the ridges convex, ob- 

 tuse, smooth or minutely rough with minute tubercles ; sheatJis elongated, with a 

 narrow black limb and about 22 linear-aid-shaped caducous teeth, l-keeled below. 

 Dryish clay soil, Illinois and southward. 



