THE 8WEET POTATO 419 



ties of two varieties crossed are as likely to predominate 

 in the progeny as the good ones. Good results, however, are 

 sometimes obtained from inteUigent crossing and subsequent 

 selection, some of our leading varieties of potatoes having 

 been produced in this way. 



571. Selection. Breeding by selection is by far the most 

 common method of improving varieties of potatoes, and one 

 which may be practiced with profit by any careful grower. 

 It is based on the fact that the productivity of individual 

 tubers in a variety differs. By selecting those tubers which 

 appear to be best and then comparing their productivity by 

 planting them in a uniform field and harvesting the product 

 from each tuber separately, those which produce large yields 

 of good quality may be preserved and propagated. 



The method of selection most practical on the average 

 farm is to observe a large number of hills as they are dug and 

 save for seed the tubers from hills that produced the largest 

 number of desirable potatoes. Many experiments have 

 shown marked improvement from such methods of selection. 



Large potatoes are preferable as seed. 



THE SWEET POTATO 



572. Origin and Description. The sweet potato is a 

 native of the New World and quite probably also of eastern 

 Asia, as it was cultivated in China in early times. It was 

 not known in Europe till after the discovery of America. 

 The edible portion is a true root, one of the few roots 

 used as food. The plant is a member of the Convulvulaceae, 

 or morning-gloiy family; the species is Ipomea batatas. The 

 plant produces numerous running vines several feet in length, 

 with smooth, shining leaves about the shape and size of those 

 of a morning-glory. .The edible roots are produced in a 

 cluster just beneath the surface of the ground. Sweet pota- 

 toes are reproduced from sprouts from the roots or from cut- 

 tings of the vines, and not from seed. 



