(68) 



3. Evax. — Scales of the involucre 1-2 ser- 

 iate. Pappus 0. 



4. Filago. — Scales of the involucre imbri- 

 cate. Pappus pilose. 



III. Frustranea. 



1. Corethrogjne. — Eeceptacle naked. 



2. Centaurea. — Eeceptacle bristly. 



3. Bidens. — Palese of the receptacle decidu- 

 ous. 



4. Helianthus. — Palese of the receptacle per- 

 sistent. Pappus paleaceous, caducous. 



5. Helianthella. Palese of the receptacle 

 persistent. Pappus 2 persistent awns, 

 besides the caducous palese. 



IV. Necessaria. 



A. Receptacle naked. 



a. Anthers obtuse at the base, at least not 

 calcarate. 



aa. Branches of the style of the ? foioers 

 flat and tipped with an appendix. 



1 Erigeron. 



bb. Branches of the style not flat, hut 

 tapering, sometimes with an appendix. 



1. Hemizonia. — Involucre 1-seriate, each 

 scale with its base half embracing a ray 

 akene. Pappus of ray 0. 



