DICOTYLEDONOUS PLANTS 185 



those near the base toothed or loberl. Heads in corymbs, with rays half 

 an inch long. Common in southern California, blooming in spring. 

 /. S. triangula'ris Hook. Stems simple, smooth, leafy, 2-5 ft. 

 high. Leaves triangular, sharply toothed, pointed at top. Heads many, 

 in corymbs terminating the stem. Involucre bell-shaped, with a 

 few loose, narrow bracts at base. Rays 6-12, half an inch long. 

 In the Sierra Nevada Mountains to Washington. Summer. 



Tribe 9. CYNAROI'DEJE. Anthers either with tails or 

 arrow-shaped. Style branches without tips or appendages, 

 often united near the apex. Corollas all tubular, with long, 

 narrow, linear divisions. Receptacle densely bristly. 



XXXVIII. CIR'SIUM (CNI'CUS), (CAR'DUUS) Thistle 



Stout herbs, usually biennial, with alternate prickly leaves 

 and large or medium-sized heads of purple, red, white, or 

 yellowish flowers. Scales of the involucre bristle-tipped, 

 arranged in many series, the lower successively shorter. 

 Receptacle flat, densely clothed with bristles. Akenes smooth, 

 obovate or oblong. Pappus of numerous, long, plumose bristles 

 that are deciduous, united in a ring. The style is usually 

 thickened by a knee-like swelling immediately below the stig- 

 matic portion, which consists of two slender divisions united 

 nearly or quite to the top. The species are not easily 

 determined. 



XXXIX. SIL'YBUM, Milk Thistle 



Stout annuals, nearly smooth, with large root leaves 

 blotched with white, and prickly on the margins. Heads 

 many-flowered and often solitary. Involucre with leaf -like 

 closely appressed bracts, tipped with stout spines. Flowers 

 magenta-purple. Pappus of stiff, chaffy bristles in several 

 rows, not spiny. 



S. Maria'num Gaertn. This has been introduced from the Medi- 

 terranean region, and is spreading more and more. 



XL. CENTAURE'A, Star Thistle 



Herbs with small heads of yellow, rose-color, or blue flowers. 

 Involucre globular, the scales spine-tipped or papery at 



