LEADING FAMILIES OF FLOWERING PLANTS 369 



represented in the United States, and some genera, such as 

 the ironweed, the golden-rod and aster, the rosinweed, the 

 sunflower, coreopsis, and Helenium, are either exclusively 

 American or at any rate very characteristic of our flora. The 

 prairies and the Great Plains especially abound in composites. 



FIG. 303. Flower cluster and flowers of yarrow 



A, flower cluster ; B, section of flower cluster ; C, a ray flower ; D, a disk flower. 



a, anthers ; ch, chaff of disk ; d, disk flowers ; o, ovary ; re, corollas of ray flowers ; 



s, stigmas ; tc, corolla of tubular flower. A, B, C, seven times natural size ; D, 



eighteen times natural size 



Food plants are rather rare among Compositce. Lettuce is 

 the most generally cultivated, but chicory and endive, dande- 

 lion, oyster plant, the globe artichoke, and the Jerusalem arti- 

 choke are of some value as food. 



Medicinal Compositce are not uncommon. A few of the most 

 familiar are arnica, boneset, camomile, coltsfoot, dandelion, 

 tansy, and wormwood. 



Ornamental plants of this family are so numerous that only 

 a small proportion of them can here be mentioned. Among 



