52 THE aWEET POTATO. 



midrib prolonged beyond lamina into a short awn- 

 like tongue, base cordate or truncate, margin entire. 

 The cordate leaves are the first ones to appear in 

 most varieties on the young shoots from tubers as 

 well as on seedlings. They may be retained or be 

 succeeded by hastate, lobed, or cut leaves. Size of 

 leaf varying with age of shoot, variety, and food 

 supply. Normally developed leaves vary in differ- 

 ent varieties from 2i/o to 6 inches or more in their 

 widest diameter. Veins more or less palmately 

 arranged, projecting on both upper and lower. sur- 

 faces, especially on the lower. They are either paler 

 or darker green than the lamina, or faintly or deeply 

 purple on the lower surface or on both surfaces. 



Hairs, consisting of several epidermal cells sup- 

 porting two or three short and one terminal long, 

 pointed cell with thickened walls (Figs. 12 and 13), 

 distributed on entire upper surface, with the excep- 

 tion of a space around the base, or only along veins, 

 or scattered in a few places around edge and apex, 

 or absent, depending on the variety; occasionally 

 occurring on lower surface of veins. 



Color of leaf varies with the age, exposure to sun- 

 light, the variety, and for other reasons unknown, 

 from light green, through dark green, brownish- 

 green, light purple, to dark greenish-purple. 



Young leaves usually shiny on upper surface, old 

 leaves less so or not at all. Young leaves folded 

 along midrib (Fig. 38). In some varieties the sur- 

 face of the lamina has a tendency to pucker towards 

 the upper surface (Norton, etc.). 



Petiole long, varying with size of leaf and habit 

 of plant on normally grown leaves from 21/2 to about 

 9 inches in length, varying in thickness, depending 

 on variety (Figs. 27, 41). The base usually tliick- 



