compositje. (composite familt.) 211 



28. PARTHENIUM, L. Paethehium. 



Heads many-flowered, inconspicuously radiate ; the 5 ray-flowers with very 

 short and broad obcordate ligules not projecting beyond the woolly disk, pistil- 

 late and fertile ; the disk-flowers staminate with imperfect styles, sterile. Invo- 

 lucre hemispherical, of 2 ranks of short ovate or roundish scales. Receptacle 

 conical, chaffy. Achenia only in the ray, obcompressed, surrounded by a slen- 

 der callous margin, crowned with the persistent ray-corolla and a pappus of 2 

 small chaffy scales. — Leaves alternate. Heads small, corymbed; the flowers 

 whitish. (An ancient name of some plant, from irapBtvos, virgin.) 



1. P. integrifolium, L. Kough-pubescent (l°-3°high); leaves ob- 

 long or ovate, crenate-toothed, or the lower (3' -6' long) cut-lobed below the 

 middle ; heads many, in a dense flat corymb. \ — Dry soil, Maryland to Wis- 

 consin, and southward. 



29. iTA, L. Marsh Eldee. Highwater-sbrtjb. 



Heads several-flowered, not radiate; the pistillate fertile and the staminate 

 sterile flowers in the same heads, the former few (1-5) and marginal, with a 

 small tubular corolla ; the latter with a funnel-form 5-toothed corolla. Scales 

 of' the involucre few, roundish. Receptacle small, with narrow chaiBf among 

 the flowers. Achenia obovoid or lenticular. Pappus none. — Herbaceous or 

 shrubby coarse plants, with thickish leaves, the lower opposite, and small 

 greenish-white heads on short recurved peduncles in the axils of the leaves or 

 of bracts. (Derivation unknown.) 



1 . I. f rutescens, L. Shrubby at the base, nearly smooth (3° - 8° high) ; 

 leaves oval or lanceolate, coarsely and sharply toothed, rather fleshy, the upper 

 reduced to linear bracts, in the axils of which the heads are disposed, forming 

 leafy panicled racemes ; fertile flowers and scales of the involucre 5. — Salt 

 marshes, coast of Massachusetts to Virginia, and southward. Aug. 



2. I. cili&ta, Willd. Annital {2° -8° high), rough and hairy ; leaves oyate, 

 pointed, coarsely toothed, downy beneath, on slender dliate petioles ; heads in dense 

 panicled spikes, with conspicuous ovate-lanceolate rongh-ciliate bracts ; scales 

 of the involucre and fertile flowers 3-5. — Moist ground, from Illinois south- 

 ward. Aug. - Oct. 



30. AMBROSIA, Toum. Ragweed. 



Sterile and fertile flowers occupying different heads on the same plant ; the 

 fertile 1-3 together and sessile in the axil of leaves or bracts, at the base of the 

 racemes or spikes of sterile heads. Sterile involucres flattish or top-shaped, 

 composed of 7 - 12 scales united into a cup, containing 5-20 funnel-form stami- 

 nate flowers ; with slender chaff intermixed, or none. Fertile involucre (fruit) 

 oblong or top-shaped, closed, pointed, and usually with 4-8 tubercles or horns 

 near the top in one row, enclosing a single flower which is composed of a pistil 

 only ; the elongated branches of the style protruding. Achenia ovoid : pappus 

 none. Chiefly annual coarse weeds, with opposite or alternate lobed or dis- 



