COLOR OF SKIN 



259 



spends to an underground branch of the stem that has become 

 thickened (Fig. 100). 



The eyes of the potato correspond to latent buds on the stem, 

 while the inner portion corresponds to the structural parts of the 

 stem. The sweet potato differs from the Irish potato in being an 

 enlarged root, not a stem. 



Classification of Potatoes. At least 400 to 500 varieties of 

 potatoes are known in America, while the total in the world is of 

 course much larger. New varie- 

 ties are each year put on the 

 market. However, many varie- 

 ties are so similar that for all 

 practical purposes there is no 

 difference, and in many cases 

 old established varieties have 

 simply been given new names. 



The classification of Ameri- 

 can potatoes has been studied by 

 Mr. William Stuart, of the 

 United States Department of 

 Agriculture. He divides them 

 into eleven natural groups which 

 can be fairly easily distinguished. 

 The principal features he uses in 

 classifying are the shape and 

 color of tuber, the color of 

 sprouts, and color of flowers. 



Shape of Tuber. Many descriptive terms are necessary to de- 

 scribe potato tubers, as they are so variable. 



Round, oblong, and long refer to relative length. Any of the 

 types may be flattened or round. Flat types are also described as 

 broad or narrow. Spindle shape refers to tubers tapering at one 

 end, as contrasted with uniform. 



Color of Skin. Color of tuber is described as white, cream- 

 white, flesh color, pink, rose, red and bluish, mottled, and russet 

 brown. 



FIG. 99. Drawing in diagram of potato 

 flower, and mature seed balls (flower enlarged). 

 They are almost identical with the flowers 

 and fruits of the tomato, showing the close 

 relation of the two plants. 



