VEGETABLES 375 



a fall crop, for winter storage, the seed for which is sown in 

 June. 



83. Sweet potato. This is a root crop that differs in 

 several particulars from those just described. Sweet potatoes 

 are often mistakenly called tubers. The ordinary potato 

 is a tuber, that is, a thickened underground stem ; but a 

 sweet potato is a thickened root, and is not a tuber any 

 more than radishes, and turnips, and beets are tubers. In 

 these three plants just mentioned, the " vegetable " is the 

 thickened tap-root ; while sweet potatoes are thickened root 

 branches. 



The sweet potato is a morning-glory, in which genus 

 (Ipomcea) there are many showy cultivated plants. The 

 family is called the convolvulus family (Convolvulacese). 

 The sweet potato plant is a trailing vine whose branches root 

 at the joints (Fig. 50), or it may be cultivated as a bushy 

 plant. The potatoes are borne close together under the 

 crown of the plant, that is, just below where the stem merges 

 into the root, or where the joints " strike root." Since sweet 

 potato is a morning-glory, there should be no difficulty 

 in recognizing its 

 conspicuous funnel- 

 shaped, purple flow- 

 ers (Fig. 50). The 

 leaves are quite 

 variable, having a 

 general triangular 

 outline, and often 



i FIG. 50. Sweet potato. 



heart-shaped at base. 



Sweet potatoes are more extensively cultivated in the 

 United States than in any other country, the annual yield 

 being about 50 million bushels. They need a warm, sunny 

 climate, a long growing season, loose, warm soil, and plenty 

 of moisture. These conditions are found in our southern 

 states, and therefore sweet potatoes as a commercial crop are 



