562 BOTANY OF CROP PLANTS 



Kerry enclosed by calyx, 5. roslraliim (sand bur, buffalo bur). 

 Tuber-bearing.* 



* Note.— Berthault in his monograph on the tuber-bearing Solanums, has a 

 key to 37 species. A portion of this key is here included (modified) to show 

 the relation of common potato to some wild tuber-bearing species. 

 Corolla rotate. 

 Points of sepals long and tapering. 

 Leaves oval, 5. tuberosum (common potato). 

 Leaves elongated, 5. intmite. 

 Points of sepals long, not tapering much; leaves oval, 5. chiloense. 

 Points of sepals short. 



Anthers straight, smooth, somewhat elongated, 5. tUile. 

 Anthers swollen, roughened, 5. maglia. 

 Corolla star-shaped, 5. jamesii, S. commersonii, etc. 



SOLANUM TUBEROSUM (Potato) 



This species includes all the varieties that are of value for 

 food. They are usually called Irish or common potato, but 

 also white, English, and round potato. 



Habit. — The potato is a branched, more or less spreading 

 herb, growing to a height of 2 to 5 feet or more. It has 

 annual aerial stems, but is practically perennial by means of 

 its tubers or underground stems. 



Roots. — Upon the whole, the development of the root 

 system is less pronounced than in most other crops. The 

 roots are fibrous and fine. They penetrate the soil to a 

 depth of 2 to 4 feet and frequently extend horizontally 2 

 feet or more from the plant. 



Stems. — Potato stems are of two general kinds as to 

 medium in which they grow: Underground and aerial. The 

 underground stems (Fig. 12) are slender rhizomes, or are 

 swollen to form tubers ("potatoes"). The aerial stems are 

 the ordinary fohage-bearing stems. The discussion of 

 rhizomes and tubers is given on pages 29 and 31. 



Stem {aerial). — The aerial or foliage stem of the potato 

 is herbaceous and generally erect when young, but usually 



