COMPOSITE. 



455 



XIX. BIDENS. BIDETSTS. 



Glabrous herbs, with opposite leaves, and hemispherical heads of 

 yellow flowers. Involucres of 2 or 3 rows of bracts, the outer ones 

 often longer and leafy. Florets either all tubular, or the outer ones 

 ligulate and radiating. Receptacle with chaffy scales between the 

 florets. Achenes flattened, crowned by 2 or 3 (very rarely 4 or 5) short, 

 stiff bristles or awns, which are rough with minute deflexed prickles. 



A genus not very numerous in species, but diffused over the whole 

 surface of the globe, some species being among the commonest tropical 

 weeds, whilst others extend into the Arctic Circle. 



Leaves undivided 1. Nodding JB. 



Leaves deeply cut into 3 or 5 segments 2. Three-cleft B. 



1. Nodding Bidens. Bidens eernua, Linn. (Fig. 544.) 

 (Eng. Bot. t. 1114. Bur-Marigold) 



A rather stout, erect annual^ 1. to 2 

 feet high, with spreading branches. 

 Leaves lanceolate and serrate, but not 

 divided. Flower-heads drooping, on ter- 

 minal peduncles from \ an inch to an 

 inch diameter ; the florets usually all 

 tubular, but occasionally a few of the 

 outer ones become ligulate. Inner bracts 

 of the involucre broad, and often shining, 

 and yellow on their edges ; outer ones 

 more leafy, and often much longer, and 

 spreading. Awns of the achenes usually 

 2 or 3, very rarely 4. 



In wet ditches and marshes, through- 

 out the temperate and northern regions 

 of Europe, Asia, and America. Com- 

 mon in England and southern Scotland. 

 Fl. summer and autumn. 



Fig. 544. 



2. Three-cleft Bidens. Bidens tripartita, Linn. 

 (Fig. 545.) 



(Eng. Bot. t. 1113.) 



Only differs from the Nodding B. in the leaves, which are deeply 



