IPOMOEA BATATUS 



491 



expansion of the cotyledons, the epicotyl begins to elongate and 

 the first foliage leaves enlarge. In seedlings ii days old there 

 may be three or four foliage leaves which are simple, cordate at 

 the base, and acute or pointed at the tip. (Fig. 151, A-D.^ 



ANATOMY 



The Primary Root. — The primary root has a tetrarch pro- 

 tostele, and four groups of small phloem cells alternate with the 



Fig. 151. Transection of young primary root : co, cortex ; en, endodermis ; mx, meta- 

 xylem; pel, pericycle; pri ph, primary phloem; px, protoxylem. (After Artschwager, 

 Jour. Agr. Res.^ 



primary xylem strands, being separated from them by fundamental 

 parenchyma. (Fig. X52-.) Each point consists of five or six 

 protoxylem elements, the small outer ones abutting the pericycle 

 while the larger inner ones lie adjacent to the centrally located 

 metaxylem vessels. The cortex is limited centripetally by a 



