COMPOSITES 



441 



ray flowers all yellow; heads small, numerous, 1-1^ in. broad, corymbed, 

 giving a spicy odor when bruised. Perennial. Weed, common. 



C. lanceolata, Linn. Perennial, native and cultivated: nearly or quite 

 glabrous: leaves oblong or linear, mostly entire, obtuse: heads large, yellow- 

 rayed, on very long stems. 



22. CfRSIUM. THISTLE. 



Perennial or biennial herbs, with pinnatifid, very prickly leaves : florets 

 all tubular and usually all perfect; scales of the involucre prickly; torus 

 bristly ; pappus of soft bristles, by means of which the fruit is carried in the 

 wind. Several species in our territory. 



C. lanceolatum, Hill. Common thistle. Figs. 253-255. Strong, branching 

 biennial: leaves pinnatifid, decurrent, woolly beneath: heads large, purple, 

 with all the involucre-scales prickly. Europe. 



C. arvense, Scop. Canada thistle. Fig. 409. Lower, perennial and a pes- 

 tiferous weed: leaves smooth or nearly so beneath: flowers rose-purple, in 

 small, imperfectly dioecious heads, only the outer scales prickly. Europe. 



23. ARCTIUM. BURDOCK. 



Coarse biennials or perennials, strong-scented, with large dock-like 

 simple leaves: head becoming a bur with hooked bristles, the florets all 

 tubular and perfect; torus bristly; pappus of short, rough, deciduous bristles. 



A. Lappa, Linn. Burdock. Common weed from Europe, with a deep, 

 hard root, and bushy top 2-3 ft. high: leaves broad-ovate, 

 somewhat woolly beneath, entire or angled. 



24. CENTAUREA. STAR-THISTLE. CENTAUREA. 



Alternate-leaved herbs, the following annuals, with single 

 heads terminating the long branches: heads many-flowered, 

 the florets all tubular but the outer ones usually much larger 



659. Centaurea Cyan us. At the left is an outer or ray floret; then follow three 

 details of a disk floret; then follows the fruit. 



