BETA VULGARIS 



i6i 



between the vascular systems of the hypocotyl and epicotyl. 

 (Fig. 115, D.) 



The Ontogeny of the Fleshy Axis. — The enlarged fleshy 

 portion of the axis is chiefly root-like, but the upper limits of 

 the hypocotyl are transitional with respect to the arrangement of 

 the primary vascular tissues. In the center of the fleshy portion 

 of the root, there is a small star-shaped region of vascular tissue 

 which consists of the elements of the primary xylem strand and 



Fig. 117. A, cellular drawing of cotyledonary bundle, below level of B, the primary xylem 

 still approximately exarch ; B, transverse section of cotyledon showing protoxylem in a more 

 adaxial position and metaxylem more abaxial than in A. The two phloem groups are still 

 separated from each other by parenchyma ; C, bundle of cotyledon showing further reorien- 

 tation of protoxylem and metaxylem; D, bundle of cotyledon showing endarch primary 

 xylem ; the phloem groups have differentiated in a single unit abaxial to the xylem : co, 

 cortex; ?/;, epidermis ; /><?r, parenchyma; ph, phloem; /ix, protoxylem. (After Lyle.) 



the secondary xylem formed from the primary cambium. Outside 

 this central region is a series of concentric rings of vascular tissue 

 which alternate with bands of storage parenchyma. The number 

 of vascular rings may vary from four to ten or twelve or more, 

 but only four or five of the inner rings contain many mature 

 vascular elements, the outermost ones being very narrow and 

 remaining in a more or less meristematic condition. (Fig. ii8.) 

 A reduction in the number of rings occurs toward the hypocotyle- 

 donary portion of the axis adjacent to the crown stem; and, at this 

 point, many anastomoses of vascular elements occur in connection 



