COMPOSITE. 67 



* * Pappus not of hair-like bristles, but either altogether wanting or consisting 

 of a few chaffy scales or teeth, or only a minute crown. 



Hh Receptacle naked. 



21. Hele'niutn. Rays yellow, wedge-shaped, 3-5-cleft at the summit. Scales 



of the involucre reflexed, awl-shaped. Pappus of 5-8 chaffy scales, 1- 

 ncrved, the nerve usually extending into a point. Leaves alternate, 

 decurrent on the angled stem. Heads corymbed, showy. 



22. L.eucaii'tliemum. Rays white ; disk yellow. Disk-corollas with a 



flattened tube. Pappus none. Heads single. 



4- 4- Receptacle chaffy. 



23. Maru'ta. Rays white, soon reflexed ; disk yellow. Ray-Jlorets neutral. 



Pappus none. Receptacle conical, more or less chaffy. Herbs with 

 strong odour. 



24. Rudbeck'ia. Rays yellow, usually long; disk dark-purple, or in one 



species greenish-yellow. Scales of the involucre leaf-like. -Receptacle 

 conical. Pappus none, or only a minute crown. Ray-florets neutral. 



25. Heliaii'thus. Rays yellow, neutral. Receptacle flattish or convex. 



Chaff persistent, and embracing the b-sided achenes. Pappus deciduous, 

 of 2 thin scales. Stout coarse herbs. 



26. Bideiis. Rays yellow, few ; but 2 species are without rays. Scales of the 



involucre in 2 rows, the outer large and leaf-like. Ray-florets neutral. 

 Achenes crowned with 2 or more stiff awns which are barbed backward. 



27. Heliop'sis. Rays yellow, 10 or more, pistillate. Scales of the involucre 



in 2 or 3 rows, the outer leaf-like. Receptacle conical ; chaff linear. 

 Achenia smooth, 4-angled. Pappus none. 



28. Achille'a. Rays white (occasionally pinkish), few. Receptacle flattish. 



Pappus none. Achenes margined. Heads small, in flat corymbs. Leaves 

 very finely dissected. 



29. Polym'nia. Rays whitish-yellow, wedge-form, shorter than the involucre, 



few in number. Scales of the involucre in 2 rows, the outer leaf -like, 

 the inner small, and partly clasping the achenes. Pappus none. Coarse 

 clammy herbs with an unpleasant odour. 



30. Sil'phium. Easily known by its stout square stem, and the upper con- 



nate leaves forming a sort of cup. Flowers yellow. Achenos broad and 

 flat. 



SUBORDER II. 



Corolla strap-shaped in all the florets of the head. All the 

 florets perfect. Herbs with milky juice, and alternate leaves. 



31. Cyn'thia. Flowers yellow. Pappus double, the outer short, of many 

 minute chaffy scales, the inner of many long capillary bristles. Low 

 perennials with single showy heads on scapes. 



