The Ferns of Washington 79 



Spores all of the same size and shape, furnished with two 

 narrow appendages (elaters); elaters strap-like, attached 

 at their middle, coiled around the spore, spreading when 

 mature and dry. Thalli on surface of ground, green, 

 usually dioecious. There is onl) r the following genus. 



EQUISETUM. Horse-tail- 



Description the same as for the family. (Latin equus 

 horse; seta = a bristle or hair; because the much- 

 branched ones suggest a horse's tail.) E. arvense and 

 E. telmateia were formerly used for polishing kitchen 

 ware. When very abundant in hay the horse-tails are 

 said to be injurious to cattle. 



A. Aerial stems annual, branched: spike not tipped with a rigid point. 

 B. Steins of two kinds; the sterile one much branched, green; the fertile 

 one unbranehed, short lived, whitish or yellowish, not green. 

 C. Sterile stems slender, less than 2 ft. high, 6-9-f urrowed ; branch- 

 lets sharply 3-4-angled. 1. E. arvense. 

 CC. Sterile stems stout, more than 2 ft. high, 20-40-furrowed ; 



branchlets more than 4-ridged but terete. 



2. E. telmateia. 



BB. Stems all alike, branched, green. 



D. Stems 5-9-furrowed, 10-20 in. high; leaf-sheaths of stem about 



8-toothed. 3. E. palusire. 



DD. Stems many-furrowed, 2-3 ft. high; leaf-sheaths of stem 

 many-toothed. 4. E. fluciatile. 



A A. Aerial stems perennial, little or not at all branched; spike tipped 



with a rigid point. 



E. Stems small, tufted, slender, 3 -10-f urrowed. 

 F. Leaf-sheaths 3-toothed; stem solid, flexible. 



5. E. scirpoides. 



FF. Leaf-sheaths 5-10-toothed; stem hollow, not very flexible. 



6. E. variegalum. 



EE. Stems large, stout, many-furrowed. 



Of* G. Stem smooth; sheath having 1 black girdle at base of 



teeth. 7. E. lavrigatum. 



GG. Stem rough; sheath having 2 black girdles. 



8. E. hyemale. 



1. Equisetum arvense L. (Plate 4, Figs. 8, 9, 10.) 



Field Horse-tail. 

 Stems above ground are annual, of two kinds. Sterile 



