COMPOSURE, (composite family.) 251 



inate flowers, -with slender chaff intermixed, or none. Anthers almost sepa- 

 rate. Fertile involucre (fruit) oblong or top-shaped, closed, pointed, resembling 

 an achenium, and usually with 4-8 tubercles or horns near the top in one row, 

 enclosing a single flower which consists of a pistil only ; the elongated branches 

 of the style protruding. Achenia ovoid : pappus none. — Homely and coarse 

 weeds, with opposite or alternate lobed or dissected leaves, and inconspicuous 

 greenish or whitish flowers, produced throughout late summer and autumn : our 

 species are all annuals. ( 'A^(3po(rta, the food of the gods, an ill-chosen name for 

 these miserable weeds. ) 



§ 1. Sterile heads sessile, crowded in a dense cylindrical spike, the top-shaped involucre ■ 

 with its truncate margin extended on one side into a large, lanceolate, hooded, re- 

 curved, bristly-hairy tooth or appendage ; fertile involucre oblong and i-angled. 



1. A. bident^ta, Michx. Hairy (l°-3°high), very leafy; leaves alter- 

 nate, lanceolate, partly clasping, nearly entire, except a short lobe or tooth on 

 each side near the base. — Prairies of Illinois and southward. 



§ 2. Sterile heads in single or panicled racemes or spikes, the involucre regular. 

 « Leaves opposite, only once lobed: sterile involucre 3-ribbed on one side. 



2. A. triflda, L. (Great Eag weed.) Stem stout (4° -12° high), rough- 

 hairy, as are the large deeply 3-lobed leaves, the lobes oval-lanceolate and 

 serrate ; petioles margined ; fruit obovate, 5 - 6-ribbed and tubercled. — Var. 

 integeif6ha is only a smaller form, with the upper leaves, or all of them, un- 

 divided, ovate or oval. — Moist river-banks : common. 



» * Leaves many of them alternate, all once or twice pinnatifd. 



3. A. artemisisefdlia, L. (Roman ■Wormwood. Hog-weed. Bit- 

 TEK-wEED.) Much branched (l°-3° high), hairy or rougliish-pubescent ; 

 leaves thin, tunce-pinnatifd, smoothish above, paler or hoary beneath ; fruit obo- 

 void or globular, armed with about 6 slutrt acute teeth or spines. — Waste places 

 everywhere. — An extremely variable weed, with finely cut leaves ; rarely the 

 spikes bear all fertile heads. 



4. A. psilostichya, DC. Paniculate-branched (2° -5° high), rough and 

 somewhat hoary with short hispid hairs ; leaves once pinnatifid, thickish, the lobes 

 acute, those of the lower leaves often incised ; fruit obovoid, without tubercles or 

 with very small ones, pubescent. (A. coronopifolia, Torr. Sf Gr.) — Prairies and 

 plains, Wisconsin, Illinois, and southwestward. 



31. XANTHIUM, Toum. Cocklebur. Clotbur. 



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

 latter clustered below, the former in short spikes or racemes above. Sterile in- 

 volucres and flowers as in Ambrosia, but the scales separate. Fertile involucre 

 closed, coriaceous, ovoid or oblong, clothed with hooked prickles so as to form 

 a rough bur, 2-celled, 2-flowered ; the flowers consisting of a pistil with a slen- 

 der thread-form corolla, Achenia oblong, flat, destitute of pappus. — Coarse 

 and vile weeds, with annual roots, low and branching stout stems, and alternate 

 toothed or lobed petioled leaves ; flowering in summer and autumn. (Name 

 from ^dvdos, yellow, in allusion to the color the plants are said to yield.) 



