BETA VULGARIS 



2-57 



at successively higher levels until the endarch condition is attained 

 in the blade of the cotyledon. Since the tissues of the hypocotyl 

 differentiate at varying rates, maturing progressively towards the 

 cotyledonary plate, the lower portion in a young seedling may show 



D 



B protoxylem 

 g metaxylem 

 [g phloem 



Fig. 114. Diagrams showing vascular transition : A, root with diarch xylem strand of 

 proto- and metaxylem; B, lower hypocotyl, lateral differentiation of metaxylem; C, two- 

 thirds distance between root and epicotyl, reorientation of xylem, circumferential extension 

 of phloem; D E, upper third of hypocotyl, primary xylem separated into two groups by 

 parenchyma, lateral orientation of metaxylem; F, cotyledonary node; G-H, cotyledonary 

 petiole; /, base of cotyledonary blade, adaxial differentiation of protoxylem and abaxial 

 development of metaxylem ; /, blade with endarch primary xylem. (After Lyle.) 



primary tissues completely differentiated and the beginning of secondary 

 thickening while in the upper part the primary tissues are just beginning 

 to mature. The meristematic condition of the region near the coty- 

 ledonary plate accounts for the continued elongation of the upper 

 hypocotyl. • 



