COMPOSITE. 103 



A. Ray-flowers entirely absent. 



Scales of the involucre in many rows, bristly-pointed, or fringed. 



*- Florets all perfect. 



1. Cni'cus. Leaves and scales of the involucre prickly. Pappus of 

 long plumose bristles. Receptacle with long soft bristles among 

 the florets. Flowers reddish-purple. 



2. Car'dmis. Resembling Cnicus, but the bristles of the pappus 



are not plumose. Atl. Prov. 



3. Ouopor'don. Leaves and scales of the involucre prickly. 



Heads much as in Cnicus, but the receptacle naked, and deeply 

 honeycombed. Pappus of long bristles, not plumose. Stem 

 winged by the decurrent bases of the leaves. Flowers purple. 



4. Arc'tiniii. Leaves not prickly, but the scales of the globular in- 



volucre tipped with hooked bristles. Pappus of many short 

 rough bristles. Receptacle bristly. Flowers purple. 

 Verno'nla. One species has scales of the involucre somewhat 

 bristly. See No. 15. 



^_^_ Marginal florets often sterile, and much larger than the others, 

 forming a kind of false ray. 



5. Centanre'a. Leaves not prickly. Scales of the involucre 



fringed. Pappus double and bristly, or very short or none. 

 Receptacle bristly. 



+"*-- t~Sterile and fertile florets in separate heads, i.e., monoecious. 

 Fruit a completely closed involucre (usually bristly) containing only 

 ime or two florets, these heads_ sessile in the axus of the bracts or 

 upper leaves. Sterile heads with more numerous florets in fldttish 

 involucres, and forming racemes or spikes. Pappus none. 



6. Xan'tliiiim. Fertile florets only 2 together in burs with hooked 



prickles, clustered in the axils. Sterile heads in short spikes 

 above them, the scales of their involucres in one row only, but 

 not united together. 



7. Ambro'sia. Fertile florets single, in a closed involucre armed 



with a few spines at the top . Sterile heads in racemes or spikes 

 above, the scales of their involucres in a single row and united 

 into a cup. 



8. Franse'ria. Inflorescence much like that of Ambrosia, but the 



fruiting involucre is armed with a number of long flat and thin 

 spines. N.W. 



* * Scales of the involucre without bristles of any kind. 

 + Marginal florets without stamens. 



** Pappus none or minute. Receptacle naked. Very strong -scented 

 herbs. 



