270 COMPOSITE. (COMPOSITE FAMILY.) 



2. P. Uvedalia, L. Ronr/h/sh-ha/r//, stout (4-10 high); leaves broadly 

 ovate, angled and toothed, nearly sessile; the lower palmately lobed, abruptly 

 narrowed into a winged petiole ; outer involucral scales very large ; rays 10-15, 

 linear-oblong, much longer than the Inner scales of the involucre, yellow; achenes 

 strongly striate. Rich soil, W. New York and X. J. to Mo., and southward. 



37. SILPHIUM, L. ROSIN-WEED. 



Heads many-flowered, radiate; rays numerous, pistillate and fertile, their 

 broad flat ovaries imbricated in 2 or 3 rows ; disk-flowers apparently perfect, 

 but with entire style and sterile. Scales of the broad and flatfish involucre 

 imbricated in several rows, thickish, broad aud with loose leaf-like summits, 

 except the innermost, which resemble the linear chaff of the flat receptacle. 

 Achenes broad and flat, dorsally compressed, surrounded by a wing notched 

 at the top, without pappus, or with 2 teeth confluent with the winged margin, 

 the achene and its subtending chaff usually falling together ; those of the disk 

 sterile and stalk-like. Coarse and tall rough perennial herbs, with copious 

 resinous juice, and large corymbose-panicled yellow-flowered heads. (2.ix<piov, 

 the ancient name of some resinous plant, transferred by Liuuasus to this 

 American genus.) 



* Ste.m terete, alternate-leaved (root very large and thick). 



1. S. laciniatum, L. (ROSIN-WEED. COMPASS-PLANT.) Rough-bristly 

 throughout, stem stout (3-12 high), leafy; leaves pinnate! i/ parted, petioled 

 but dilated and clasping at the base ; their divisions lanceolate or linear, acute, 

 cut-lobed or pinnatifid, rarely entire; heads few (1 -2' broad), sessile or short- 

 peduncled along the naked summit ; scales orate, taperiny into long and spread- 

 ing rii/id points ; achenes broadly winged and deeply notched, 6" long. 

 Prairies, Mich, to Dak., and southward. July. Lower and root-leaves ver- 

 tical, 12-30' long, ovate in outline; on the wide open prairies disposed to 

 present their edges north aud south ; hence called Compass-Plant. 



2. S. terebinthinaceum, L. (PRAIRIE DOCK.) Stem smooth, slender 

 (4-10 high), panicled at the summit and bearing several or many, large 

 heady,, leafless except toward the base; leaves ovate and ovate-oblong, some- 

 what heart-shaped, serrate-toothed, thick, rough, especially beneath (1 -2 long, 

 on slender petioles) ; xra/cs roundish, obtuse, smooth; achenes narrowly winged, 

 slightly notched and 2-toothed. Var. piNNATfFiDUM, Gray, has the leaves 

 deeply cut or pinnatifid, but varies into the ordinary form. Prairies and oak- 

 openings, Ohio and Mich, to Minn., and southward. July -Sept. 



* * Stem terete or slightly 4-angled, leafy; leaves undivided (not large), some 



opposite. 



3. S. trifoliatum, L. Stem smooth, often glaucous, rather slender (4-7 

 high), branched above ; stem-/eares lanceolate, pointed, entire or scarcely serrate, 

 rough, short-petioled , in whorls of 3 or 4, the uppermost opposite; heads loosely 

 panicled ; achenes rather broadly winged, and sharply 2-toothed at the top. 

 Dry plains and banks, Pe.nn. to Ohio, and southward. Aug. 



4. S. AsteriSCUS, L. Stem hispid (2 - 4 high) ; leaves opposite, or the 

 hirer ran /i/ in irhor/s of:], the upper alternate, oblong or oval-lanceolate, coarsely 

 toothed, rarely entire, rough-hair >j, the lower short-petioled ; heads nearly soli- 



