The Ferns of Washington 81 



4. Equisetum fluviatile L. (Plate 4, Fig. 7.) 



Water Horse-tail. 



Rootstocks hollow; stems above ground annual, 2-3 

 ft. high, slightly many-furrowed, smooth, usually pro- 

 ducing upright branches after fructification; air-cavities 

 wanting under grooves, small under ridges; central 

 hollow very large; stem-sheaths appressed, toothed; their 

 teeth about 18, dark brown, short, acute, rigid; branches 

 hollow, slender, smaller but otherwise like stems, short 

 or elongated. 



•— 



Wa 



and Virginia; Europe; Asia. 



5. Equisetum scirpoides Michx. (Plate 4, Fig. 4.) 



Dwarf Scof i ring-rush. 



Stems perennial, evergreen, very slender or filiform, 

 3-6 in. high, somewhat rough, flexuous and curving, 

 tufted, mostly 6-furrowed with the ridges acute, simple 



or branched from near base; central hollow wanting; 

 stem-sheath 3-toothed, the bristle-like tips rather per- 

 sistant. — Alaska to Labrador, south to Washington, 

 Illinois and Pennsylvania. 



6. Equisetum variegatt \i Schl. (Plate 4, Fig. 1.) 



Variegated Seou ring-rush. 



Steins perennial, evergreen, slender, tufted, 5-10- 

 furrowed, 6-20 in. long, simple: central hollow small; 

 stem-sheath green, variegated with black above, edged 

 with white, o-lO-toothed, tipped with deciduous bristles. 

 Spore-leaves very small, tipped with a comparatively 

 large point, — Arctic America, south to Nevada and 



Pennsylvania, 



7. Equisetum laevigatum A. Br. (Plate 4, Figs. 2, 3.) 



Smooth $( >(ring-rush. 



Stems 1-5 ft. high, simple or little branched, pale 



