COMPOSITAE. 375 



none, in which case the flowers are all perfect and tubular; 

 receptacle chaffy; pappus of 2-4 rigid backwardly-barbed awns; 

 ray- and disk-akenes obcompressed. 



Plant aquatic; submerged leaves capillary. B. beckii. 

 Plants terrestrial; none of the leaves capillary. 



Akenes 4-angled; leaves dentate. B. cernua. 



Akenes flat; leaves more or less incised. B. elata. 



Bidens beckii Torr. (Megalodonta remota Greene.) Aquatic, glabrous; 

 stems simple or little branched, 30-100 cm. long; submersed leaves 2-5 cm. 

 long, finely dissected into filiform segments; emersed leaves a few pairs, lan- 

 ceolate, acute, serrate, 1-3 cm. long; heads solitary, short-peduncled ; tegules 

 oblong, obtuse, glabrous; ray-flowers golden-yellow; akenes smooth, the stout 

 awns barbed near the tip. 



Green Lake, Seattle, Washington, Piper; not otherwise known in our limits. 



Bidens cernua L. Annual, glabrous or minutely hispid; stems erect, simple 

 or with few short branches, 30-60 cm. high; leaves linear- lanceolate to lanceo- 

 late, coarsely and unequally serrate, acuminate, sessile and somewhat cuneate 

 at base, 6-12 cm. long; heads short-peduncled, 12-15 mm. broad; outer tegules 

 foliaceous, much longer than the membranous inner ones; ray-flowers 6-12, 

 bright yellow, or sometimes absent; akenes elongate, wedge-shaped, 4-angled 

 and bearing 4 backwardly barbed awns half as long as the body. 



A very variable species growing in wet places, blooming in autumn. 



Bidens elata (T. & G.) Sherff. (B. amplissima Greene.) Glabrous or 

 nearly so; stems stout, 40-100 cm. high; leaves lanceolate, oblanceolate or oval, 

 acute, deeply serrate or incised, 8-18 cm. long; heads 1-3, nearly sessile, 2 cm. 

 broad; outer tegules linear to oblanceolate, larger than the head, often incised; 

 ray-flowers pale yellow; akenes 8 mm. long, glabrous, flat, broadly cuneate, 

 the margins inwardly barbed; awns 4, rarely 2, about half as long as the akene, 

 retrorsely barbed. 



Sauvies Island, Oregon, Nuttall; Vancouver Island, Macoun. 



516. COREOPSIS. 



Annual or perennial herbs usually with opposite leaves; heads 

 many-flowered, radiate; involucre of 2 rows of about 8 tegules 

 each, the outer spreading and foliaceous, the inner appressed and 

 nearly membranaceous ; ray-flowers mostly 8, neutral, yellow or 

 purple, rarely wanting; receptacle flat with deciduous mem- 

 branaceous chaff; akenes obcompressed, often winged, with 2 

 barbless subulate awns. 



Coreopsis atkinsoniana Dougl. Glabrous; stems 30-100 cm. high, erect, 

 usually branched; leaves all opposite, the lowest bipinnately parted into 

 linear lobes, the upper reduced to simple linear bracts; heads cymosely panicu- 

 late; tegules in two series, the outer short, the inner ovate, scarious-margined, 

 6-8 mm. long; ray-flowers yellow, with brown bases; akenes oblong, narrowly 

 winged, bearing two short subulate teeth. 



In wet places on river banks, rare in our limits. 



517. RUDBECKIA. 



Mostly perennial herbs; leaves alternate ; heads many -flowered, 

 mostly with sterile ray-flowers, sometimes rayless; disk-flowers 



