IPOMOEA BATATUS 



487 



types of sweet potato leaves were rooted and maintained under 

 observation until the plants had formed shoots. The adventitious 

 roots form a fibrous root system and some of them thicken greatly, 

 the fleshy roots varying within wide limits from fusiform to 

 napiform or nearly spherical. (Fig. 149.) Some are smooth and 

 terete, others ribbed and more or less definitely four to six lobed 

 in transection. Laterals arise from the deeply lobed roots in rows 

 along the longitudinal grooves; and, in terete roots, each rootlet 

 lies in a shallow recess sur- 

 rounded by more or less 

 loosened scar tissue. Kamer- 

 ling (6) and Tuyihusa (14) 

 maintained that these fleshy 

 structures were stems rather 

 than roots, but it is clear 

 when the ontogeny of the 

 structure is critically inves- 

 tigated that this concept is 

 unwarranted. 



The Flower. — The pro- 

 duction of flowers is rela- 

 tively rare in continental 

 United States, although 

 Hand and Cockerham (3) 

 report that the small, 

 "morning-glory-shaped 

 bloom, with a purple throat 

 and white margin, may be 

 noticed in commercial 

 fields." In 1914 Stout (12.) 



made a summary of the published records regarding seed pro- 

 duction and concluded that seeds can be obtained from plants 

 which produce flowers if there is proper cross-pollination. 

 Blooming has been reported in all of the southern states where 

 sweet potatoes are grown, but seed is seldom produced and in 

 no instance has seed been matured in any quantity. 



The plants flower profusely in the Virgin Islands, Puerto Rico, 

 Cuba, Santo Domingo, Barbados, St. Vincent, Hawaii, the Philip- 

 pine Islands, Java, and Australia. In many of these localities 

 sufficient seed has been produced either naturally or as a result of 



Fig. 2.49. Yellow Jersey sweet potatoes show- 

 ing variation in shape and size. (Courtesy of the 

 Bur. Plant Industry.) 



