74 THE SWEET POTATO. 



leaves, usually those wliicli happen to be supported 

 by darker petioles than the rest, have a faint streak 

 of pink running part-way up the midrib only. 

 Other varieties have a small purplish area on the 

 lower surface of the base of the midrib, i. e., just 

 before the petiole divides into the primary veins. 

 Still others have the lower surface of the veins 

 green. 



The leaves offer another distinguishing feature in 

 the arrangement of the hairs on the upper surface. 

 Some varieties have the leaves entirely covered with 

 hairs. Others have the hairs only along the veins 

 and perhaps over a more or less extended area on 

 the tip of the central lobe. Still others have no 

 hairs on the upper surface of the leaf. 



Although the root, or "tuber," is the most impor- 

 tant part of the plant, it offers few characters of 

 stability which might be used in a practical key. 



The outside color of the tuber, however, is as 

 easily determined as it is important. Some varie- 

 ties have grayish-white or popularly called "white" 

 tubers. Others have yellowish, golden, or bronze- 

 colored tubers. Still others have them colored a 

 yellowish-red, or a pinkish-yellow, and some have 

 dark red or purple ones. 



Although not quite so constant as might be desired, 

 the coloration of the cut surface of a freshly cut 

 normal-sized tuber is characteristic enough to be 

 used as a distingniishing character. On cutting some 

 varieties one finds that the flesh is colored pure 

 white. In others the flesh is cream-colored or yel- 

 lowish-white. Still others show a pinkish hue dif- 

 fused through a white or yellowish mass color. A 

 few have the flesh colored a deep pinkish-orange, 



