BETA VULGARIS 159 



apart although the protoxylem points are approximately in the same 

 position with reference to the diameter of the axis. The metaxylem 

 vessels occupy a more and more lateral position with respect to the 

 protoxylem, and the phloem masses show a slight division into two 

 units, being separated from each other by cells of the fundamental 

 parenchyma. (Fig. 1x4, D.) 



"The metaxylem continues to differentiate more and more tan- 

 gentially with reference to the protoxylem in the upper hypocotyl. 

 With the protoxylem point as the common apex, it forms two sub- 

 triangular groups which occupy a collateral position with respect 

 to the phloem groups. (Fig. 114, E and Fig. 1x5, C.) The vascular 

 system of the hypocotyl in the region of the cotyledonary plate is a 

 dissected siphonostele made up of two cotyledonary bundles and the 

 bundles of the foliage leaves. (Fig. ii6, /4.) The cotyledonary traces 

 diverge from the stele quite abruptly. In the cotyledonary bundle 

 the primary xylem is still approximately exarch, but the metaxylem 

 vessels have differentiated more laterally forming the vascular strands 

 which Thomas (18) designates as 'double bundles.' (Fig. 1x4, F 

 and Fig. ixy, B.) 



"At increasing distances from the cotyledonary node, in the coty- 

 ledonary petiole and blade, the protoxylem occupies a more and more 

 adaxial position and the metaxylem a more abaxial one. (Fig. 114, 

 G, H, I, and Fig. 117, C, D.) Thus, the endarch condition of the 

 primary xylem is finally attained in the blade of the cotyledon. (Fig. 

 1x4, /.) The phloem groups in the 'double bundles' are separated 

 from each other by parenchyma, but at the level at which the primary 

 xylem is endarch they differentiate as one group in an abaxial position 

 to the metaxylem." 



The Epicotyl. — The first two foliage leaves develop from 

 the growing point of the unelongated epicotyledonary axis which 

 is surrounded by the bases of the cotyledons. The pro vascular 

 strands develop early in the leaf primordia, and all the primary 

 bundles of the leaf and epicotyledonary axis are collateral and 

 endarch. The trace of the first foliage leaf above the cotyledons 

 consists of a large central bundle and two smaller lateral ones which 

 pass into the cortex independently, but the laterals anastomose 

 with a vascular strand which continues into the internode above. 

 Fron (8) has designated this combined strand as a "cauline" 

 bundle. The leaf trace is differentiated downward into the 

 nodal region of the cotyledon where the two "cauline bundles" 

 and the central bundle of the trace anastomose. This endarch 

 bundle gradually becomes smaller in the upper hypocotyl and 

 finally ends blindly in the fundamental parenchyma between the 

 cotyledonary bundles. (Fig. 1x5, C.) The maturation of the 



