25O WEEDS OF THE FARM AND GARDEN 



shaped, sessile and deeply divided, the lobes and margins 

 having spiny teeth. Naturalized from Europe. Canada 

 westward and southwest. 



Knapweed (Centurea solstitialis, L.). An erect, 

 branched, annual with cottony winged stem, lower leaves 

 lyrate, upper linear entire, decurrent ; spines of upper 

 bracts long spreading with a few smaller ones at the 

 base ; flowers yellow, pappus soft. 



It is found in fields in the east and south of England, 

 rare; it has been introduced with alfalfa, etc., into the 

 United States. 



Black Knapweed (Centaur ea nigra, L.). It is a scab- 

 rous perennial, with stiff, branched stems, lower leaves 

 spatulate, dentate or lobed, upper leaves oblong or lanceo- 

 late, sessile or partly clasping; the bracts of the involucre 

 are tipped with a fimbriate appendage ; flowers are rose- 

 purple ; achenes four-sided. It is found on the Atlantic 

 coast. The brown knapweed (C. Jacea) is a perennial, 

 much like the preceding, with entire or denticulate leaves, 

 globular involucre, brown bracts with fimbriate append- 

 ages, achenes four-angled. It appears in the East and 

 Northwest on the Pacific coast. Star thistle (C. Calci- 

 trapa) is an annual with pinnatifid leaves, outer bracts 

 of the involucre ovate-oblong, each tipped with a stout 

 spine ; flowers purple ; achenes compound, obscurely four- 

 sided. It appears on the Atlantic coast and in the Pacific 

 northwest, but is native to Europe. 



Blue Bottle, Bachelor's Button (Centaur ea Cyanus, L.). 

 A branched annual from one to one and one-half feet 

 high, woolly, tomentose; leaves linear, entire, the lower 

 dentate or pinnatifid; heads many-flowered on long 

 peduncles, involucre ovoid or globose ; bracts imbricated, 

 greenish yellow; flowers blue or purplish, varying to 

 white; all tubular, the marginal one neutral, achenes 

 compressed or four-angled ; bristles of the pappus un- 



