136 SELECTED WESTERN FLORA 



*** Flowees usually both tubular and eadiate ; receptacle chaffy. 

 t Involucre hard and more or less spiny, ndt-like in fruit, 



21. Ambrosia, heads of two kinds; involucre of the fertile head 1-seeded 

 with a single row of projections about the top. 



22. Xanthium, heads of two kinds, involucre of the fertile head covered 

 with spines, becoming bur-like in fruit. 



tt Involucre not hardened in friHt. 



23. Iva, heads small, drooping; flowers all tubular, the marginal pistillate, 

 the inner perfect. 



24. Heliopsis, heads large ; ray-flowers yellow, fertile, persistent ; achenea 

 4-sided. 



25. Brauneria, heads large, ray-flowers pink or purplish, chaff of 'the 

 receptacle spiny and projecting beyond the achenes. 



26. Rudbeckia, heads large; ray-flowers yellow, neutral, deciduous; 

 receptacle conical. 



27. Lepachys, heads large; ray-flowerS yellow or purple, neutral, decidu- 

 ous; receptacle cylindrical. 



28. Helianthus, heads large; ray-flowers yellow, neutral, deciduous; 

 receptacle flat. 



29. Coreopsis, heads large; ray flowers yellow, neutral; bracts of the 

 involucre in 2 rows. 



30. Bidens, heads large, ray-flowers yellow, bracts of the involucre dis- 

 tinct. 



31. Achillea, heads small, ray-flowers white or pink, bracts of the involucre 

 dry and thin. 



32. Gaillardia, heads large; ray-flowers yellow, 3-toothed. 



33. Helenium, heads large, ray-flowers yellow, bracts of the involucre 

 spreading, leaves entire. 



SERIES B. LIGULIFLOR^. 



Herbs with milky juice and all the flowers in the head perfect, 

 with ligulate corollas. 



* Flowers yello'v^. 

 t Leaves all basal. 



34. Taraxicum, pappus borne on a long beak. 



35. Agoseris, pappus borne on a short beak. 



tt Leaves not all basal. 



36. Crepis, achenes not flattened, tapering towards the top ; pappus white. 



37. Hiracium, achenes neither flattened nor tapering; pappus dark. 



38. Sonchus, achenes flattened. 



