COMPOSITE 



405 



oval, nearly entire, slightly petioled or sessile, sometimes purplish or 

 marked with purple veins: akenes linear, not nar- 

 rowing upward. Dry woods. 



H. aurantiacum, Linn. Oroiige hawktveed. A 

 very bad weed in meadows east, from Europe: 

 hirsute and glandular: leaves narrow: heads deep 

 orange: akenes oblong, blunt. 



7. XANTHIUM. Clotbur. 



Coarse homely annual weeds with large alter- 

 nate leaves, flowers monoecious : in small involucres : 



sterile involucres composed of separate scales, in ,„„ ^ ,, . ,, , 



, 496. Xanthium Canadense. 



short racemes: fertile involucres of united scales 



forming a closed body, clustered in the leaf axils, becoming spiny burs. 



X. Canad6nse, Mill. Common clotbur. Fig. 496. One to 2 ft., branch- 

 ing: leaves broad-ovate, petioled, lobed and toothed: burs oblong-conical, 

 1 in. long, with 2 beaks. Waste places. 



X. spindsum, Linn. Spiny clotbur. Pubescent, with 

 three spines at the base of each leaf: bur 3^ in, long, 

 with 1 beak. Tropical America. 



8. AMBROSIA. Ragweed. 



Homely strong-smelling weeds, monoecious: sterile 

 involucres in racemes on the ends of the branches, the 

 scales united into a cup: fertile involucres clustered in 

 the axils of leaves or bracts, containing 1 pistil, with 

 4-8 horns or projections near the top. Following are 

 annuals: 



A. artemisiaefdlia, Linn. Common ragweed. Fig. 

 497. One to 3 ft., very branchy: leaves opposite or al- 

 ternate, thin, once- or twice-pinnatifid : fruit or but 

 globular, with 6 spines. Roadsides and waste places. 



A. trifida, Linn. Great ragweed. Three to 12 ft., 

 with opposite 3-lobed serrate leaves: fruit or bur ob- 

 ovate, with 5 or 6 tubercles. Swales. 



9. AGERATTTM. Ageratum. 



Small diffuse mostly hairy herbs, with opposite simple leaves: heads 

 small, blue, white or rose, rayless, the involucre cup-shaped and composed 

 of narrow bracts : torus flattish : pappus of a few rough bristles. 



A. conyzoides, Linn. {A Mexicanum of gardens). Annual pubescent 

 herb, with ovate-deltoid serrate leaves: cultivated (from tropical America) 

 for small and numerous clustered soft heads. 



10. DAHLIA. 



Stout familiar garden herbs, tall and branching, from tuberous roots: 

 leaves opposite, pinnately divided: ray flowers in natural state are neutral 

 or pistillate and fertile: disk flowers perfect: involucre double, outer scales 



497. Ambrosia artem 

 isisefolia. 



