464 



STRUCTURE AND LIFE HISTORIES 



family. The mustard family contains many valuable 

 economic plants, such as the white and black mustard, 

 radish, cabbage, turnip, kohlrabi, and brussels sprouts. 



413. Rose Family (Rosaceae). — One of the common 

 wild roses (Rosa Carolina) illustrates a type of flower 

 structure more advanced in several ways than that of 

 Rammcuhts. The flowers, with rare exceptions, have 



Fig. 347. — Black mustard {Brassica nigra). 



sepals and petals which are borne on the margin of a 

 well-developed hypanthium, formed by the enlargement 

 of the torus, at the extremity of the peduncle. The 

 numerous stamens are always inserted on the sepals 

 [adnation of parts), and the pistils vary from one to 

 many. In marked contrast to the numerous horticultural 

 varieties of the rose, the wild roses are single; that is, they 

 have one circle of petals (usually five). The "doubling" 

 of the cultivated varieties is caused by the replacement of 



