CYPEEACEAE. 41 



flowered, the lower reflexed, the middle ones spreading, all separating from the 

 axis at maturity: scales green, several-nerved: achenes linear, 2.5-3 mm. long, 

 apiculate, 2-3 times as long as thick, § as long as the scale. — Susquehanna 

 valley. Common, on the dry river shores and islands. — Schists. — Sum. 

 11. C. filiculmis Vahl. Perennial. Leaf -blades 2-4 mm. wide: scape smooth, 

 slender, often wiry, ascending or reclined, 1.5 dm. long: spikelets densely 

 clustered in a sessile head, or in 1-7 peduneled heads, linear, acute, 5-11- 

 flowered, subterete or compressed, 5-12 mm. long, 2 mm. wide or less: scales 

 pale-green, 7-11-nerved, appressed: achenes oblong or obovoid, fully 2 mm. 

 long, 3-angled, dull gray, about twice as long as thick. — S. Occasional, in 

 sand near Peach Bottom. 



3. EE.IOPHORUM L. Bog herbs, perennial by rootstocks. Stems erect, 

 triangular or nearly terete. Leaves with linear blades, or 1 or 2 of the upper 

 mere bladeless sheaths. Spikelets terminal, solitary^ capitate, or in umbels, 

 subtended by an involucre of 1-several bracts, or naked. Scales spirally imbri- 

 cate, usually all flower-bearing. Perianth of 6 or many^ filiform smooth soft 

 bristles, white or brown, the bristles straight or crisped, much exserted. Sta- 

 mens 1-3. Style deciduous. Stigmas 3. Achene 3-angled, often broad. 



1. E. virglnicum L. Stems stiff, smooth, 4-12 dm. tall: leaf-blades narrowly 

 elongate-linear, flat: bracts of the involucre spreading or deflexed: spikelets 

 several or numerous in a dense terminal cluster, erect, or the outer spreading: 

 scales acute, brown with a green center: perianth-bristles numerous, dingy- 

 brown or copper-colored, about 3 times as long as the scale: achenes linear- 

 oblong, acute, apiculate, brown. — E. S. Common in swamps. — Quartzite, 

 schists. — Sum. — Cotton-grass. 



4. SCIRPUS [Tourn.] L. Annual or perennial small or large caulescent 

 or scapose herbs, the leaves sometimes reduced to basal sheaths. Spikelets few- 

 many-flowered, terete or flattened, solitary, capitate, spieate, or umbellate, often 

 subtended by an involucre. Scales spirally imbricate or nearly 2-ranked, the 

 1-3 lower sometimes empty. Perianth of 1-6 slender or rigid bristles or rarely 

 wanting. Stamens 2 or 3. Style not swollen at the base, wholly deciduous 

 from the achene, or its base persistent. Stigmas 2 or 3. Achene triangular, 

 lenticular or plano-convex. — Bulrush. Club-rush. 



Involucre of a single bract, or wanting. 



Spikelets solitary, terminal. 1. 8. planifolius. 



Spikelets typically several or numerous, often apparently 

 lateral. 

 Spikelets few, 1-12, appearing lateral. 



Scapes bluntly .3-angled : plants annual. 2. S. debilis. 



Scapes acutely 3-angled : plants perennial. 3. 8. americanus 



Spikelets several or numerous, In umbels or umbel- 

 like clusters. 4. 8. validus. 

 Involucre of 2 or more bracts with flat blades. 



Spikelets relatively large, few-several, capitate or umbel- 

 late. 5. 8. flin-iatiUs. 

 Spikelets relatively small, very numerous, umbellate. 



Perianthl-bristles downwardly barbed, or wanting : 

 spikelets in umbellate heads. 

 Perianth-bristles equalling the achene or slightly 

 exceeding it : leaf-blades 6-16 mm. wide. 

 Spikelet-scales obtuse : perianth-bristles barbed 



throughout. 6. S. siilvaticus. 



Spikelet-scales acute : perianth-bristles barbed 

 above. 

 Perianth-bristles twice as long as the achene : 

 leaf-blades 4-6 mm. wide. 

 Pei-ianth-bristles smooth or merely pubescent : umbel 

 decompovmd. 

 Spikelets sessile, borne in small heads. 

 Spikelets, or some of them, distinctly peduneled. 



