IPOMOEA BATATUS 503 



also calls attention to the abundance of inner phloem in the petiole 

 and hypocotyl. In this instance, he agrees with Scott, stating that 



"in the upper part of the hypocotyl, during the rearrangements in the 

 cotyledonary strand so that the protoxylem becomes external, the 

 internal phloem masses of that bundle fuse, and the fused mass grad- 

 ually passes out between the metaxylem groups (before the latter 

 meet to form the root bundles) and joins on to the external phloem. 

 The same events take place at a lower level in connexion with the inter- 

 cotyledonary bundles, so that finally an ordinary tetrarch root is 

 produced." 



Lamounette (7) investigated several of the Convolvulaceae, 

 including Ipomoea leucantha, and concluded that the inner phloem, 

 when present in the hypocotyl, is differentiated in the medullary 

 parenchyma and is not continuous with the outer phloem of the 

 root. In fact, he rejects the term bkollateral, supporting Herail (4) 

 in this regard. 



In the sweet potato, anastomoses between inner and outer phloem 

 occur at the base of the cotyledonary petiole, but there is no evi- 

 dence to indicate that the inner phloem of the hypocotyl is regu- 

 larly connected with the outer phloem. The inner phloem may be 

 regarded as supplementary to the outer, and its appearance late 

 in the ontogeny of the seedling, at a time when it is beginning to 

 function photosynthetically, suggests a correlation between the 

 function of the phloem and its anatomica development. 



In the upper hypocotyl, the cotyledonary plane may be dis- 

 tinguished from the intercotyledonary by the degree of separation 

 of the two metaxylem groups in each case. Slightly below the 

 cotyledonary node, the metaxylem groups of each intercotyle- 

 donary strand are more widely separated from each other than those 

 of the cotyledonary strand, each group inclining toward one of the 

 latter. At this level, the inner phloem is well developed, so that 

 there are two bicollateral polar bundles of the double bundle type, 

 and four smaller laterally placed bicollateral bundles derived from 

 the intercotyledonary strands. 



At the cotyledonary node, the two lateral bundles of each cotyle- 

 donary trace abut the right and left flanks of the median double 

 bundle of the trace so that it appears to be a single large crescentic 

 unit. Slightly above the level of divergence of the cotyledonary 

 traces from the vascular ring, the lateral bundles of each trace 

 separate from the median bundle which is itself divided to form 



