18 BOTANICAL GAZETTE [july 



main axis of the seedling dying down. At the beginning of the next 

 growing season, the growth of the plant is continued by the 

 rhizomes, the apices of these turning upward as they grow, to form 

 the aerial shoots, each internode of which contains one central and 

 six peripheral bundles, each surrounded by a complete endodermis. 

 The development of these internodal structures is exactly that 

 which has been described for the seedling. 



Passing back from the apex (see diagram, fig. 2), one finds at 

 the second node a vascular ring, which just below the node breaks 

 immediately into six bundles. As in the seedling, there is no differ- 

 entiation of a sheath in this (second) internode. In the next node, 

 however, a sheath appears, surrounding the vascular ring. Below 

 this the sheath sinks in around the six peripheral bundles. An 

 irregular sheath also appears around the central bundle, which 

 first shows in this (third) internode. The internal endodermis 

 passes through the next node in the manner already described in an 

 old node of the seedling (figs. 3-8). 



A cambium develops in the pair of bundles entering the stem 

 from the leaves in the second internode from the apex. It appears 

 in the side bundles in the next lower one. This cambium at first 

 forms an incomplete ring, but in the older internodes it is frequently 

 complete. The concentric structure thus produced, of pith sur- 

 rounded by xylem, phloem, and a stereomatic pericycle, the whole 

 surrounded by a sharply differentiated endodermis, certainly justi- 

 fies Holm's statement (5, p. 309) that "in Dianthera the steles 

 are very distinct and readily to be recognized as such, since they 

 are cylindric and possess all the necessary elements." 



The central bundle in the mature plant is plainly derived from 

 vascular tissue passing downward from the four side bundles (figs. 

 2-7). As in the seedling, it arises first in the third internode, 

 cambium usually showing in the fourth. The mature central 

 bundle, as Holm has described, usually has the appearance of being 

 double, the mestome forming two arches, with parenchyma between, 

 the whole surrounded by a well marked endodermal sheath. 



The mature type of vascular structure seems to be rather 

 constant. Holm mentions that the central bundle may sometimes 

 be lacking, but an examination of several hundred internodes of 



mature plants has failed 



One single 



