S68 



BOTANY OF CROP PLANTS 



The primary root appears first, soon becomes curved, and is 

 followed by the axis of the hypocotyl. The cotyledon leaves 

 are smooth, oval, and more or less elongated, while the first 

 foliage leaves are provided with unbranched hairs. 



Development of the Seed- 

 ling. — From the thirty-sev- 

 enth to the fifty-sixth day 

 after seeding, the stolons 

 arise (Fig. 234); the first 

 pair comes from the axils 

 of the cotyledon leaves. 

 These slender cylindrical 

 stems possess small rudi- 

 mentary leaves. They trail 

 along on the ground and 

 finally penetrate the soil. 

 When their tips strike the 

 ground, they begin to swell 

 and form tubers. Hence the 

 first tubers of the plant, 

 grown from seed, are de- 

 veloped at the tips of slender, 

 stolons coming from the axils 

 of the cotyledon leaves. Roots soon arise from the stolons. 

 Secondary stolons appear in the axils of the first foliage leaves. 

 Tubers from Seedlings. — Tubers produced on seedlings 

 are usually small the first year. However, Frazier reports 

 a tuber weighing over 7 ounces that was formed the first 

 year, and says that the Burbank potato was full-sized the 

 first year from seed. It is reported from Svalof (Sweden) 

 that tubers usually attain normal size and type after about 

 the third year from seed. 

 Tuberization.^ — It has been noted previously that tubers, 



Fig. 234. — Young potato plant- grown 

 from seed. (After Percival.) 



