TUBEBOnS PABTS 363 



poses of maintaining life during unpropitious sea- 

 sons and of multiplying the number of individ- 

 uals. 



456. What is a sweet potato? One is shown 

 in Fig. 381. It has no "eyes" or scales. It pro- 

 duces roots. It is a thickened root. 



Fig. 381. 

 Sweet potato. 



456a. In botanical writings, a muoh-thiekened and shortened 

 stem is called a tuber; a mueli thickened root is called a tuberous 

 root. It would probably be better if both were called tubers, one 

 being designated as stem-tuber and the other as root-tuber. Stem- 

 tubers may produce roots from their surface, but they usually do 

 not. 



4566. A tuber, then, may be defined as a prominently thickened 

 and homogeneous portipn of a root or stem, usually subterranean, 

 and which does not increase or perpetuate itself (as bulbs and 

 corms do) by direct offshoots or accessions. 



457. There is a third class of tubers which 

 partakes of the nature of both root and stem. 

 These are sometimes called tubercles, although the 

 name is unfortunate. Dahlia roots, turnip, beet, 



