572 



BOTANY OF CROP PLANTS 



plant (potato) have been found to correspond to these 

 characters. 



Varieties. — There are at the present time over 500 named 

 varieties of potatoes in the United States. Many of these 

 variety names are found to belong to potatoes which are 

 identical in all respects. Usually, new varieties arc the 

 seedlings of established varieties. 



The latest attempt at a classilication of American potatoes 

 is that of Stuart. In his ''proposed system of classilication" 



^^pendertr, 



Fig. 236. — Diagrammatic section of potato tuber. 



he gives the following "groups": Cobbler, Triumph, Early 

 Michigan, Rose, Early Ohio, Hebron, Burbank, Green 

 Mountain, Rural, Pearl, and Peachblow. 'J'uber, sprout 

 and flower characters are made the bases of distinction of 

 the groui)s. The student is referred to Bull. lyO, U. S. 

 Dei^t. Agr. (Professional Paper) for the descriptions of these 

 groups. Fitch has also proposed a classification using about 

 the same characters. 

 Tuber Morphology. — The [)()tato tuber is made up of a 



number of zones or la\ers w 

 follows (Figs. 236 and 237): 



1. Periderm or skin. 



2. Corte.x. 



3. Vascular ring. 



lich are commonly grou[)ed as 



