Seed Plants : Angiosperms 



317 



such an extent that there are now hundreds of forms in culti- 

 vation that bear little resemblance to the wild stock from 

 which they were derived. 



FIG. IQI. Flower clusters of dahlia, sunflower, and thistle, members of the composite 

 family. The small flowers are collected in heads, which are characteristic of the family. 



In the United States the composites bloom chiefly in summer 

 and autumn, and often conspicuously color the landscape. 

 The daisies, goldenrods, and asters of the Eastern states and 

 the sunflowers of the prairie states are well known. The rag- 

 weeds, which are troublesome as weeds, are one of the chief 

 causes of hay fever. Their pollen is highly irritating to the 

 mucous membrane of the nose, and it is advisable that city and 

 village streets be kept clear of them. 



Many other families of the dicots are of interest and im- 

 portance, but descriptions of them must be sought in more 

 specialized botanical texts. 



