28 VASCULAR PLANTS. 



Tribk III. Ambrosiae. 



£ or $ flowers : anthers distinct, not syngen- 

 eic ; style abortive, truncate. $ flowers: co- 

 rolla rudimentary, or wanting ; pappus 0. 



22 Iva. L. 



Necessaria. Superflua. Head co-flowered. 



£ or 6 : flowers cc, tubular, 5-lobed ; style 



truncate ; anthers distinct. $ : flowers few, 



5-dentate ; scales of the involucre 3 — 4, ovate ; 



paleaB of the receptacle, linear ; pappus 0. 2£ . 



23. Ambrosia, DC 



Monoecious. S head co-flowered ; scales of 

 the involucre united into a cup ; anthers dis- 

 tinct ; style truncate ; receptacle flat, naked. 

 9 head 1-flowered ; scales of the involucre uni- 

 ted into a cup ; corolla ; akene enclosed in 

 the persistent involucre. . % . 



24. Franseria, Cav. 



Monoecious. & head co-flowered ; scales of 

 the involucre united into a cup ; anthers dis- 

 tinct ; style truncate ; paleae of the flat recepta- 

 cle filiform. ? head 1, sometimes, 4-flowered; 

 scales of the involucre united into a cup ; if the 

 head be more than 1 -flowered, the cup forming 

 as many cells as there are flowers ; involucre 

 armed with go rows of spines ; akenes inclosed 

 in the persistent involucre. 71. 



