COMPOSITES. 109 



Unequal length. Achenes with long thread-form beaks, and a 

 pappus of very soft white bristles. Heads numerous, panicled. 

 Tall smooth herbs with runcinate leaves. 



57. Mulge'dium. Flowers chiefly blue. Structure of the heads and 



general aspect of the plant as in Lactuca, but the beak of the 

 achenes short and thick, aud, the pappus tawny. Heads in a 

 dense panicle. 



58. Sou Vims. Flowers pale yellow. Heads many-flowered, enlarg- 



ing at the base. Achenes without beaks. Pappus very soft 

 and white. Tall glaucous herbs with spiny-toothed leaves. 



59. Tragopo'goii. Flowers yellow or purple. Heads large. Involucre 



of about 12 lanceolate rather fleshy scales in one row, somewhat 

 united at the base, Achenes with long tapering beaks. Pappus 

 of plumose bristles, 5 of these longer and naked at the summit. 

 Leaves entire, straight-veined, clasping. 



1. NI'CUS, Tourn. COMMON THISTLE. 



1. C, laneeola'tus, Hoff. (Cirsium lanceolatum, Scop.) 

 (COMMON THISTLE.) All the scales of the involucre prickly- 

 pointed. Leaves decurrent, pinnatifid, the lobes prickly- 

 pointed, rough above, woolly with webby hairs beneath. 

 Fields and roadsides everywhere. 



2. C. undula'tus, Gray. {Cirsium undidatum, Spreng.) 

 White-woolly throughout. Low and stout, leafy. Scales 

 tipped with short prickles. Leaves undulate-pinnatifid, 

 N.W. prairies. 



4. C. pu'milus, Torr. Differs from the last in being 

 pubescent but not woolly. The leaves, also, are not pin- 

 natifid. Stem 1-flowered. Lake Huron. 



5. C. altiSS'imus, Willd., var. dis'eolOP, Gray. (Cirsium 

 discolor, Spreng.) The inner scales of the involucre not 

 prickly. Stem grooved. Leaves prickly, green above, 

 white-woolly beneath. Flowers pale purple. Whole plant 

 with a whitish aspect. Dry thickets. 



3. C. mu'tieus, Pursh. (Cirsium muticum, Michx.) 

 (SWAMP THISTLE.) Scales of the webby involucre hardly prickly, 



