356 COMPOSITE. 



4. C. Calcitrapa (Common Star-Thistle). Scales of 

 the involucre ending each in a long and stiff thorn. Gra- 

 velly and sandy places in the South of England. Well 

 marked by its purplish flowers, which are armed below 

 with spreading thorns, and resemble in figure the cruel 

 iron instrument, named a Caltrops, which is used in war 

 to lame horses, being thrown on the ground where it is 

 expected that cavalry will pass. The instrument is so 

 constructed, that, in whatever position it lies, one point 

 sticks upwards. Fl. July, August. Annual. 



* C. Jdcea (Brown Radiant Knap-weed) is a very 

 rare species, with purple flowers, the outer scales of the 

 involucre being pinnatifid, the inner regularly jagged. 



III. TUBIFLOIUE. Tansy Group. 



22. BIDENS (Bur-Marigold). 



1. B. cernua (Nodding Bur-Marigold). Heads of 

 flowers drooping ; leaves serrated, undivided ; bristles of 

 the fruit 3 4. Watery places; frequent. A somewhat 

 succulent plant, 1 2 feet high, with narrow, serrated, 

 smooth leaves, and button-like, drooping heads of brown- 

 ish yellow flowers, at the base of which are several leafy 

 bracts. The fruit is oblong, and terminates in several 

 stiff bristles, each of which is thickly set with minute 

 points, which are turned back like the barbs of an arrow, 

 so as to take a firm hold on the coat of any animal 

 which comes in contact with them. Fl. July Sep- 

 tember. Annual. 



2. B. tripartita (Trifid Bur-Marigold). Heads of 

 flowers nearly erect ; leaves 3-parted. Watery places ; 

 common. Distinguished from the last by its somewhat 



