LYCOPERSICUM ESCULENTUM 



571 



phloem lie on the flanks of the primary xylem strand, which con- 

 sists usually of six or eight xylem elements. The primary phloem 

 cells are very small, consisting chiefly of elongated parenchym- 

 atous elements. The pericycle is uniseriate and the protoxylem 

 cells abut it. The narrow cortex is three or four layers in width, 

 the innermost one forming an endodermis with prominent Cas- 

 parian thickenings. 



Vascular Transition. — King (18) and Thiel (33) find that 

 the vascular transition agrees in all respects with that of the 



Fig. X98. A, longisection through mature seed showing portion of embryo and seed coat; 

 B-F, successive stages in development of seedling; G, cotyledons and epicotyl, showing first 

 epicotyledonary leaves ; H, types of first foliage leaves. 



potato and eggplant. The first stage in the reorientation from the 

 exarch, radial protostele of the root to the bicoUateral endarch 

 arrangement is the separation of the diarch xylem strand into two 

 units by parenchymatous cells. At the same time, each group 

 of primary phloem divides into three smaller strands; and, at 

 higher levels, the central one of each group is differentiated pro- 

 gressively toward the center, forming the inner phloem of the 

 hypocotyl. 



The xylem units bifurcate, and the two metaxylem portions of 

 each divided bundle differentiate along two oppositely directed 

 curves. (Fig. 2.^^.') Above this point, the metaxylem is dif- 



