310 THE COMPOSITE FAMILY. 



edges ; outer ones more leafy, and often much longer, and spreading. Awns 

 of the aehenes usually 2 or 3, very rarely 4. 



In wet ditches and marshes, throughout the temperate and northern 

 regions of Europe, Asia, and America. Common in England and southern 

 Scotland. Fl. summer and autumn. 



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

 (Eng. Bot. t. 1113.) 

 Only diifers from the nodding B. in the leaves, which are deeply cut into 

 3 or 5 lanceolate segments, and in the flower-heads rather less drooping. 



Its geographical range and stations are the same as those of the droop- 

 ing B., but it appears to be rather less common in Britain. Fl. summer 

 and autumn. 



XX. BURTVCSD. XANTHIUM. 



Coarse annuals, with alternate leaves, and unisexual, axillary or terminal 

 heads of green flowers. Involucre of the males of several bracts in a single 

 row, enclosing many tubular florets, separated by the scales of the recep- 

 tacle. Anthers free. Eemale florets 2 together, combined with the invo- 

 lucre into an ovoid or oblong, prickly burr, terminating in 2 beaks, from 

 which the stigmas shortly protrude. 



A genus of two or pe^'haps three species, from the Mediterranean region 

 to the Levant, but spread as weeds of cultivation over a great part of the 

 globe. Its immediate connection with the remamder of Composites can only 

 be traced through several exotic genera forming the small tribe of Ambro- 

 siecB, the general habit and unisexual flowers showuig at first sight some 

 analogy to the Nettle family, and some other Monochlamyds. 



1. Broad Bur^reed. Xanthium Strumarium, Linn.' 

 (Eng. Bot. t. 2544.) 



A coarse, erect annual, 1 to 2 feet high. Leaves on long stalks, rather 

 large, broadly heart-shaped, coarsely toothed or angular, rough on both 

 sides. Elower-heads in axillary or terminal clusters, on short racemes ; the 

 upper ones male ; the lower female heads forming, when in fruit, ovoid 

 burrs, about 6 to 8 hues long, covered with hooked prickles ; the stout, 

 short, conical beaks, erect or tui'ned inwards. 



In cultivated and waste places, tlu-ovighout central and southern Eu- 

 rope and central Asia, extending, as a weed of cultivation, northwards 

 to the Baltic, as well as into many other parts of the globe. Has been 

 occasionally found in some of thj southern counties of England and Ire- 

 land, but is not a truly British pi ■ r.t. Fl. summer. 



XXI. BURDOCK. ARCTIUM. 



A single species, distinguished as a genus from Thistles by the foliage, 

 by the bracts of the mvolucre ending in a long, stiff point hooked at the 

 extremity, and by the short, stifl' pappus. ■* 



1. Comtuon Burdock. Arctium Iiappa, Linn. 

 (Eng. Bot. t. 1228. A. Bardana, Eng. Bot. t. 2478.) 

 A stovit, branching, erect biennial, 3 to 5 feet high, the lower heart* 



